Final Report Summary - REFFIBRE (REFFIBRE - Tools for Resource-EFficient use of recycled FIBRE materials)
Executive Summary:
The main aims of the project were to develop tools and knowledge, which are needed for the “eco-design” of the resource efficient paper and paperboard production chains based on Paper for Recycling (PfR).
The modelling related to paper product and production design developed knowledge and tools to model and simulate the influence of paper for recycling (the role of different fibre fractions and fillers) on the properties of produced paper/ paperboard. The tools helped to find pulp combinations and paper compositions which reduce material or energy consumption while safeguarding paper properties. Models and experimental work showed that removing fillers and contaminated fines increased strength properties without any effect on optical properties of the paper products and less energy was needed in paper production to remove water in wire and press sections.
The process models can be used for optimising the quality and purity of the recycled pulps but also for developing indicator based tools for further optimisation of stock preparation systems in the future. Increasing rejects in deinking units removed selectively fines and fillers from the recycled pulp. The deinking sludge or otherwise separated fines and fillers and other rejects from the stock preparation can then be valorised at the mill or by other industrial partners (industrial symbiosis). The side stream plastic composites were successfully produced from rejects, deinking sludge and fly ash (from the power plant when the sludge was incinerated in the mill) in co-operation with two industrial partners. The novel by-products improved resource efficiency, reduced environmental impacts of the mills and the production was in all cases feasible and profitable. As an other option the recovering of fillers with a pyrolysis process looked also feasible and profitable for paper mills with no possibility to incinerate their sludge.
The main work in the value chain assessments was to calculate the value chain level impacts of energy and material savings due to the optimised use of recycled fibre. As an outcome of the Fibre Flow mass balance modelling recycling rates (R), mean fibre ages (MFA), mean number of uses in the future (MNU) for different paper grades were defined within the CEPI region (countries as members in the Confederation of European Paper Industries). These can be used to calculate the allocation factors (Ai and Ao) needed when calculating environmental impacts according to the method ISO/TS 14067 Greenhouse gases - carbon footprint of products requirements and guidelines for qualification and communication. The methodology was developed and it is ready but the research work after this project needs to be continued. The final allocation factors will be re-calculated with corrected mass balances in close co-operation with CEPI and several industrial partners in order to reach consensus about the allocation numbers to be used for the standardisation work. The information from different modelling tools can be used for estimating economic and environmental assessment of the improved paper or paperboard products and potential side stream products. The ways how to use these tools in co-operation with specialists are described in details in a practical guide. These value chain methods and indicators were used for two cases where the amount of fibre rejects were minimised by improvements in the stock preparation systems by installing novel equipment in two paper and paperboard mills during the project. In both cases the amount of waste was reduced and the profitability of the paper and paperboard production improved.
Project Context and Objectives:
Reffibre project was focused on tools, methodologies and modelling to improve resource efficiency in printing paper and paperboard mills using paper for recycling as their main raw-material. The research targets of the methodology and modelling work were focused on three different levels: modelling the paper quality in current printing paper or paperboard production lines, modelling and controlling processes in stock preparation line, where the focus was in the separation of the unwanted fractions and modelling the resource efficiency in the whole value chain. The use of side stream fractions in novel products was first studied in laboratory scale and later the most potential ones were demonstrated in pilot or industrial scale.
The modelling related to paper product and production design developed knowledge and tools to simulate the influence of paper for recycling (the role of different fibre fractions and fillers) on the properties of produced paper and paperboard. Modelling developed knowledge and tools for both basic printing and packaging paper properties and also for layered structures in order to show the potential of layered paper design. The target of the paper product models was to predict changes in paper properties due to the changes in fibre properties. Additionally, one target of this modelling was to use these tools to calculate energy demand for dewatering and drying and provide the data for the whole value chain calculations. The tools can help to find pulp combinations and paper compositions, which reduce material or energy consumption while safeguarding paper properties. The effects of removed side streams on paper properties and energy and steam consumption on the paper machine were also modelled. Models were used to optimise different optical properties and/or functional properties such as bending stiffness and strength properties of printing papers or paperboards produced. These properties can be optimised for single layer products or for multilayered products.
The process models were developed for different separation processes at two paper mills. These models can be used for optimising the pulp quality and purity but also for developing indicator based tools for superordinate optimisation in the future. Increasing rejects in deinking units removed selectively fines and fillers from the recycled pulp. The deinking sludge or otherwise separated fines and fillers and other rejects from the stock preparation can then be valorised at the mill or by other industrial partners (industrial symbiosis). The second target was to identify the most potential valorisation routes of side stream products based on the literature and most potential ones were selected for laboratory and large scale work in order to support the “multi-product mill” approach. The side stream plastic composites were successfully produced from rejects, deinking sludge and fly ash (from the power plant when the sludge was incinerated in the mill) in co-operation with several industrial partners. Fractionation of the rejects and recovering of fillers with the pyrolysis process were studied in pilot scale.
The main work in the value chain assessments was to calculate the value chain level impacts of energy and material savings due to the optimised use of recycled fibre. The objectives were to define the case studies and related value chains and define resource efficiency indicators for paper and paperboard applications. The other target was to use the existing fibre flow model to define parameters to allocate burdens of the virgin fibres in fair way in environmental assessment of paper and paperboard products that are recycled several times building circular economy. As an outcome of the calculations recycling rates (R), mean fibre ages (MFA), mean number of uses in the future (MNU) for different paper grades were defined within the CEPI region (countries as members in the Confederation of European Paper Industries). These are used to calculate the allocation factors (Ai and Ao) needed when calculating environmental impacts according to the method ISO/TS 14067 -Greenhouse gases - carbon footprint of products - requirements and guidelines for qualification and communication. These value chain methods including both economic and environmental indicators were used for several cases including also by-products. In both simple cases where the amount of fibre rejects were minimised by improvements in the stock preparation systems by installing novel equipment in two paper and paperboard mills during the project the amount of waste could be reduced and the profitability of the paper and paperboard production was improved. The information from different modelling tools can be used for estimating economic and environmental impacts of the improved paper or paperboard products and potential side stream products. The ways how to use these tools in co-operation with specialists are described in details in the practical guide.
Project Results:
Paper making product and production models
The developed paper making models are intended to help to correlate pulp characteristics, which are changed by various (dry and wet) stock preparation processes, with the quality parameters of the papers produced. These models together with the process models covering process units in the stock preparation describe basic manufacturing processes in a paper mill.
The most important paper quality parameters for publication papers are optical and structural paper properties. But mechanical properties are also necessary in order to ensure a certain level of paper machine runability and proper behaviour in paper converting. The vector of pulp characteristics is the input for paper property models including the abbreviations and testing procedures used. The content of the vector corresponds to those pulp and fibre characteristics that can be influenced by the selection of paper for recycling grades and can then be varied by various dry sorting and stock preparation processes. The Schopper-Riegler value SR and water retention value WRV characterise the behaviour of suspensions. Both values are closely related to the dewatering and drying behaviour of a paper machine and the amount of energy consumed for these purposes. Some basic rules on how to correlate SR and WRV with the specific energy consumption necessary for dewatering publication papers were already available. These rules, together with the amount of materials, can be used directly by the tools on the value chain level, which help to determine resource efficiency.
Paper properties on a real paper machine depend on many process parameters and can vary between the machine direction and cross direction. In order to make paper quality independent of a real paper machine, a decision was taken to use the paper properties of handsheets. Because handsheet formation is a standardised procedure, paper properties resulting from different pulps can be compared. On the other hand, handsheet properties are directly correlated to machine paper properties and it is common procedure in paper mills to transfer handsheet properties to machine paper properties using simple ratios.
Modelling the influence of in-organics on structural and mechanical paper properties needs to know quantitatively what happens in the fibre network when pigments are incorporated. One of the key structural paper properties is the Relative Bonded Area (RBA) of a paper sheet. A new method is introduced which allows a faster determination of the RBA. The new method uses the density of the sheet but the cross sectional information of the fibres and a simplified fibre network model, so called d-parallel fibre networks, are used to find a relation between density and RBA, which takes the morphology of the fibres into account.
The availability of RBA data allows to study two effects of pigment incorporation into fibre networks in more detail – the network “Expansion” effect (which leads to a decline of RBA) and the “Integration” or “Bond-weakening” effect (where Shear Bond Strength decline can be derived from the decline of the Tensile via RBA). Due to increased pigment inclusion in the paper sheet the network skeleton is widened (the expansion effect). Simultaneously pigments are attached to the fibre-fibre bonds and reduce the bond strength (the bond weakening effect).
For both effects numerical models were developed based on laboratory trials. The models have been validated based on sample data from a graphic paper mill which is using nearly 100% of paper for recycling. For improving resource efficiency and introducing a multi-product-mill concept it is important to know potential benefits that the reduction of in-organics by means of e.g. fractionation brings to the products. The simulation results showed that the reduction of the in-organics from recycled paper did not reduce optical properties especially opacity but increased strength. On the contrary the addition of fresh fillers improved opacity. It looks like that the fillers are getting contaminated in recycling processes and they lose their scattering power. One of the fundamental benefits of the model is the ability to estimate the influence of in-organics reducing measures in stock preparation on final tensile strength. Because tensile is closely related to many strength properties the influence of in-organics on the other strength properties important for packaging materials can also be predicted.
Critical factors affecting strength properties for paperboard were demonstrated with the numerical models in order to improve resource efficiency in a packaging paper mill. One of a potential future scenario is the increase of fillers in paper for recycling. In order to guarantee certain paper strength, multiple scenarios are thinkable: increasing paper grammage, higher amount of strength additives (starch), separation of in-organics (e.g. by flotation) to be used as a by-product or replacement of certain amounts of paper for recycling by virgin fibres. Whereas the two first ones will decline resource efficiency the two latter ones were interesting to evaluate in more details. Based on given pulp vectors the following cases have been calculated: Reference (100% paper for recycling), Case 1: about 4% in-organics are separated from the pulp, Case 2: about 7.5% in-organics are separated from the pulp, Case 3. about 4% of the recycled pulp is substituted by virgin fibres and Case 4: about 7.5% of the recycled pulp is substituted by virgin fibres. According to the models both measures (separating in-organics and substituting paper for recycling by virgin fibres) improve basic packaging paper properties nearly at the same level. Separation of in-organics requires a higher input of paper for recycling and investments for a separation stage (e.g. flotation). If the separated in-organics can be converted into a valuable by-product the higher costs are amortised. Substituting paper for recycling by virgin fibres will increase the raw material costs in a higher degree than it will happen in cases where fillers are removed. Additionally investments for a refining stage are necessary. From a cost perspective point of view this alternative seems to be not attractive at the moment.
For evaluating the quality of recycled fibre material a novel and simple concept, Integrity Value, was introduced. Integrity Value for recycled pulp uses the approach based on the strength based quality potential of the fibre material. Strength potential is seen as a basic requirement of material, and good strength potential give larger window for optimising other quality properties of paper product. If quality potential is quantified by using a simple set of measurements, then the utilisation options for paper making are better understood. If quality potential is already low, then also other than papermaking utilisation options must be considered. The other utilisation options for side streams can vary and this value does not prefer any utilisation option over another.
The measurements show that deinking increases Integrity Values. Integrity is also much greater when using fresh, non-recycled pulps. Different mills have different integrity value levels, which reflects to the day-to-day operations of those mills. Integrity was also shown to correlate well with strength properties measured from handsheets when the bonded area of the sheets was also taken into account and estimated from sheet density. This correlation verifies the connection of the between Integrity Value and the strength potential of the pulps and demonstrates its utilisation potential also in continuous evaluation of the incoming recycled pulp at the mill. The integrity number for recycled pulp is an approach with great potential to evaluate potential of paper for recycling.
The properties of a single-layer paper sheet are determined by the pulp characteristics and the performance of the paper machine, whereas a multi-layer paper offers some more variables to improve the paper properties. By designing the sequence of the layers and selecting suitable materials per layer it is possible to achieve higher bending stiffness or brightness levels even if the sum of the materials is the same as in a single-layer sheet. Therefore, layered paper design is a promising way to improve resource efficiency.
There are two different technologies for producing multi-layer sheets – multi-ply sheet forming and stratified sheet forming. Whereas the first technology is a state of the art for producing carton board, the second one is relatively new and allows the layering of lower-grammage papers like graphic papers. In multi-ply sheet forming the individual layers are formed separately in separate forming sections using several headboxes, and couched together after the forming process. During stratified sheet forming several stock layers are brought together in one headbox and only one forming unit is used for dewatering. Because of the technology used, it is not possible to clearly distinguish between the individual layers of a stratified sheet. There are transition areas between the layers. Due to retention effects during stratified sheet forming fines and fillers cannot be introduced exclusively in a certain layer. This should be kept in mind when estimating the potential of layered sheet forming.
All results based solely on numerical modelling calculations show that a fractionation of the pulp and subsequent redistribution of the fractions to the individual layers could improve the paper properties remarkably. Of course the results and trends presented depend on the quality of the paper for recycling used. Basic assumption in the calculations was that the total pulp is fractionated and all fractions are used in the layered paper sheet. Alternatively, only a part of the total pulp could be fractionated. Some fractions could be valorised in side streams whereas the remaining fractions and remaining original pulp are used in a layered sheet. The numerical model introduced was very nonlinear. Solving an optimisation problem for this type of models is non-trivial because there can be various local maximum or minimum. The optimisation problem is solved step-wise by an iterative procedure. Depending on the type of solver and on the starting values, the optimisation results can differ.
Fractionating recycled pulp and redistributing the fractions to the layers of a multi-layered sheet could be an effective method to improve resource efficiency. Even with state of the art fractionation technologies paper properties might be improved or raw material can be saved. The available numerical models can be used to find the best manufacturing conditions depending on the quality of the paper for recycling serving as raw material and on the requirements made on the final paper product. Due to the increasing number of variables (number of pulp fractions, number of layers in the multi-layered sheet) it is crucial to use a special software (a so called solver) to solve the optimisation problem and find optimal solutions.
Process models in stock preparation and routes to make good use of side streams.
Modelling of the processes to separate side streams
For the description of all material flows in deinking plants, a vector has been developed which includes basic information on the volumetric and mass flow rates and the consistencies at the inputs and outputs of units and systems in the stock preparation area.
This information is necessary for balancing the material composition. The suspension is considered to be a composition comprising long fibres (LF), short fibres (SF), fines (FS), minerals (ASH) and stickys (ADH). Additionally, drainage and optical properties were used for the physical description of pulp. Among the optical properties brightness (R457), luminosity (Y), effective residual ink concentration (ERIC) values and dirt specks (SPEC) were in focus of process modelling. The drainage properties were reduced to the modelling of the Schopper-Riegler (SR) and water-retention values (WRV).
The described parameters were selected because they represent the main composition and quality parameters for the production of graphic papers. The fibre composition and the content of stickies are crucial parameters for the prediction of the runability of the paper machine whereas the optical parameters are important for the sale of the produced paper. The drainage parameters play an important role, too, as they provide reference values for the energy consumption needed for the dewatering of the paper web on the paper machine. This data vector is in line and consistent with other approaches for modelling the downstream paper making process.
The developed data vector was filled with current process data of the inputs and outputs of units prior to the modelling of processes and systems in order to compute several key figures for each separation unit. Data was collected from online process control systems to a certain extent. However, not all parameters listed in the data vector were available as time-continuous online measurements. For cost reasons the number of online measurement equipment in deinking plants was usually reduced to a minimum. Therefore, samples must be taken at the inputs and outputs of units in the deinking plants and analysed in the laboratory in order to complete online data. The process conditions and the input paper quality were kept constant during this sample collection.
A separation process was described by means of three mass flows, one input mass flow and two output mass flows respectively. If two mass flows were known for a unit, the missing third mass flow could easily be calculated. If all three mass flows could be calculated using measured volumetric flow rates and the corresponding measured consistencies, the mass conservation law can be infringed due to inaccurate online or laboratory measurements or due to occurring process fluctuations and time-lags during sampling. A similar problem occurs when combining the mass balances of several units but also when combining multiple systems. The calculated output mass flow of coarse screening was for instance greater than the input mass flow to pre flotation. In these cases, an equalisation calculus had to be applied. In the calculus, the inputs and outputs are changed to the same extent, because both have the same absolute uncertainty.
As the models are semi-empirical and data-driven, the time-continuous integration of factory-related data into the models is of high importance. The biggest challenge was missing data due to the lack of instrumentation and measuring equipment in industrial systems. The instrumentation is a reasonable cost factor and is therefore limited to the indispensable minimum in many paper mills. Deinking plant processes are commonly controlled by distributed control systems (DCS). Common control systems can handle thousands of process signals simultaneously and enable a straightforward access to data via easy to use interfaces. Software tools allow users to gain access to both present and previous data. Additionally, a high amount of data is collected and archived discontinuously in external databases. This knowledge on the data access enables the query for online and offline data necessary to run process models and to compute the resource efficiency indicators.
The models can be used as an offline tool for simulating process conditions and operation modes in order to predict changes in efficiency and pulp quality as well as effects on the indicators. Results of the different models have to be combined in order to get a rough overview of the deinking plant’s overall trends. For use as an online tool which follows the real process, the models have to be fed with online data such as volumetric flow rate and consistency of the input. Variations in pulp quality or changes in the characteristics of devices may require an additional manual data input. These changes in the process model framework are implemented with a VBA Macro in MS Excel which is triggered off automatically in the case of any changes to the input data.
Process models for separation processes in deinking plants were established. It was shown that it was possible to integrate resource efficiency parameters in the conventional process models of composition and quality data for deinking plants. The process models for separation processes were in line with other process models predicting paper quality and calculating the impact of changes in the production process over the whole value chain resulting in reduced costs and improved material efficiency.
In contrast to existing process models for deinking plants, which only focus on the material composition and the separation of impurities, the extended data structure facilitates the calculation of the up to now unknown optimum between the use of resources, pulp quality and the amount of residues for disposal. The assessment of side stream applications made from residual materials (e.g. increased amount of sludge from deinking in order to reduce in-organics) is enabled by the implementation of the process models in the deinking plants. Additionally, the time lag between manual inputs by operators or caused by process control systems and the impact on both the product and the process can be overcome. By the introduction of internal transfer prices, it is possible to make process changes measurable on a monetary level. The high amount of data collected in the deinking plants can be aggregated in five essential indicators.
It is important to emphasise that it is feasible to model and simulate deinking plants in terms of both pulp quality and resource efficiency parameters. The development is however connected with a great data collection and interpretation which is often coupled with difficulties. This requires a certain additional effort in recording and analysing additional data. If a higher accuracy of the process models is intended, a higher amount of samplings or more online measuring equipment is essential as the separation indices describing the separation behaviour of partial matter are subject to deviations caused by process fluctuations, changes in the input materials and errors in sampling.
Controlling the separation of side streams
When using some fractions of recycled fibre material for non-paper applications, such as novel fibre-based materials, composites, bioenergy and biorefinery concepts, the amount to be separated has to be controlled in-line. Thus, for paper making and other potential uses of fibre raw material must be evaluated in a new way. A new, simple concept for evaluating the quality and utilisation potential of recycled fibre material from the strength point of view, entitled the “fibre material integrity value”.
In general, strength, or the ability to bear and distribute stresses, is a fundamental property of a solid material. The same applies to fibre-based materials; without strength, the material is useless. Fibre material integrity, a new value associated with fibre material quality, should therefore reflect its strength potential. Although strength is not always the key requirement for products, it is always important. Only when the structure has sufficient strength can other material properties be optimised. Generally speaking, a higher strength potential means more freedom in optimising optical properties or reducing the amount of material and energy used in production. High integrity means that the material has high strength potential and is therefore easier to make into a product of sufficient strength. When such potential changes during recycling or another process, this should be reflected in the fibre material integrity value.
The chemical composition of the pulp must also be considered. For example, the presence of cellulose, holocellulose, or lignin fractions can reveal the origin of recycled material. Pulps (and fines) of mechanical or chemical origin have different potential for later treatments. In addition, the filler amount reduces the recycled material’s ability to bear and distribute stresses around the network because of the lower amount of fibre material and reduced bonding between it. To approximate the key parameters discussed here, the following factors were included as measures of the integrity value of recycled pulp: amount of fibre-based organic versus inorganic material in the pulp or amount of fibre fraction; chemical pulp fibres versus mechanical pulp fibres; cellulose or holocellulose or lignin content (amount of cellulose or ~lignin) of the fibres; strength of fibres; effective fibre length; fibre coarseness; fibre shape; and fines content.
These parameters can illuminate much about the strength potential of recycled pulps. In practice, however, in materials such as paper, strength also depends on the number of interference connections, i.e. bonding, and on the density of the structure. The integrity value should therefore be independent of the bonding degree and density of the pulp. On the other hand, structural density and bonding can be controlled through process parameters, including refining, wet pressing, strength chemicals, press drying, etc. Strength potential can therefore only be realized when process conditions are selected that make use of the material’s strength potential. In current papermaking practices, some key properties, including optical properties (color, light absorption and, to some degree, light scattering coefficients) are almost independent of strength potential.
The challenge with the on-line measurement was that suspension from paper for recycling containing fillers and starch did not give clear results for the material integrity value since signals from filler and from starch interfered with other measurements. So finally during this project the fibre integrity measurement could not be proven yet as valuable for characterising recovered fibre suspensions as expected. Therefore, further work is needed.
Side stream valorisation routes
Reliable statistics regarding side stream generation by the Paper and Board Industries (PBIs) are difficult to come by; in 2005 around 11 million tonnes of solid waste were generated in Europe (including from pulp production) and roughly 70% (7.7 million tonnes) thereof originated from using Paper for Recycling (PfR) as a raw material. The utilisation of PfR results in 50-100 kg of dry solid waste per tonne of packaging paper production, 170-190 kg per tonne of newsprint production, 450-550 kg per tonne of graphic paper production and 500-600 kg per tonne of tissue production. Different paper mills, however, produce different amounts of side streams of varying compositions. The main two outlets for solid side streams have historically been land-filling and incineration, although the significance of the former has greatly decreased owing to bans imposed in several European countries. In any case, both options have entailed significant costs for the sector, with recent information e.g. from Germany and the Netherlands indicating that disposing of rejects and sludges could cost up to 100 € per tonne. Reducing these costs, and even turning them into profits, depends on the ability of the sector to utilise the valuable components in the side streams by reusing them internally or converting them to intermediates or products for other parties.
The side streams generated by paper and board mills that are considered were rejects, deinking sludge and primary wastewater treatment sludge. Rejects (ragger, heavy, coarse, fine) are produced during the utilisation of PfR and they can contain fibre lumps, plastics, metals, sand and glass. The most important types of rejects in terms of their valorisation potential are coarse rejects, produced during early filtration steps in which large non-fibre objects such as plastics are removed, and fine rejects, produced during filtration steps with screens with very small slots so as to remove possible sticky content that may disturb the production process and diminish the quality of the end product; fine rejects contain a considerable amount of fibres. Deinking sludge is produced during the flotation deinking of PfR and it contains mostly short fibres/fines, inorganic fillers, as well as ink particles. Primary wastewater treatment sludge is produced during process water clarification by mechanical means and it contains mostly short fibres/fines and fillers.
A large number of side stream valorisation opportunities, either already on the market or in various stages of development, were studied and disseminated to stakeholders in the sector of ways to utilise the full potential of their raw materials. The valorisation routes presented are organised in four categories, namely application of the side stream in its current form without further processing, application by conversion into a material product, application by conversion into energy, and application by conversion into an energy carrier. These options include the following: land management, absorbent materials production, building materials production, wood-plastic composites production, fractionation, hydrolysis to fermentation feedstock, nanocellulose production, PHAs production, alginates production, incineration, gasification, pyrolysis, anaerobic digestion, secondary fuels production.
The principles of the Biobased Economy and the Circular Economy will increasingly guide business decisions. In order to adapt to such a new reality more needs to be done with regard to extracting value out of side streams in another way, by utilising their potential as raw materials and not as energy sources. An important step towards optimally valorising the content of PBI side streams should be managing to reclaim as much high-quality material from them as possible for the sector’s own operations. It can be said with some certainty that the maximum value of a tonne of reclaimed fibres will be obtained when they are applied in paper making compared to any other valorisation possibility. Developments in the field of side stream fractionation could prove to be very important in this context, allowing the sector to keep the materials that can best serve its own production process, while seeking the optimal valorisation route for the fractions that have less to offer to the PBI. Some paper makers are already trying to implement side stream valorisation by means of recirculating the materials back to their production process without fractionation; this option has shortcomings however. Reintroducing all components of a side stream to paper making can have a negative influence in terms of process parametres such as dewatering, drying, machine speed etc., or product characteristics such as strength; these adverse effects of side stream reuse can be avoided by means of fractionation.
Three valorisation routes: 1. using side streams as fillers or for strength improvement in plastic composites, 2. fractionation and reusing the fibres or other fractions in papermaking and 3. recovering fillers by pyrolysis were further studied in laboratory and/or pilot scale.
Production of plastic composites
Various types of PBI side streams, both sludges and rejects, could be used in the production of wood-plastic composites (WPCs). These are, as the name denotes, composite materials made of wood fibre, usually in the form of wood flour, and thermoplastic materials, such as PE, PP, PVC, etc. Depending on the characteristics of a given side stream, it could be applied either as a low-cost substitute for more expensive raw materials without leading to a deterioration of the end product quality, or as an additive that could improve the characteristics of the end product, for example by reinforcing it. WPCs have a growing market and various existing and potential applications. Each one of these applications sets its own requirements with regard to the characteristics and quality of the end product, which may pose higher, lower or no obstacles for the use of PBI side streams in the production process.
Fractionation
Although fractionation is included here among the identified side stream valorisation opportunities, it is in practice an intermediate step that, when undertaken, makes the pursuit of other valorisation routes possible or, at least, simpler and more efficient. The term “fractionation” denotes the separation of one or more fractions from a side stream, although it can also be applied in the pulp stream, based on the specific characteristics of each fraction’s components. When applied on side streams of the PBI, fractionation can produce fractions that are either suitable for reuse within the same sector or attractive for applications outside the paper industry; the characteristics of the new fractions make them better suited for the proposed application than the untreated side stream would be, which improves the chances of profitable side stream valorisation instead of simply less costly disposal. The extent of side stream fractionation can be determined by the paper mill, depending on its wishes. Fractionation could be as simple as separating the organic (fibres, fines) from the inorganic (fillers) material in a sludge stream or as complex as producing various organic fractions of fibres and fines with different characteristics. Currently applied or proposed examples of side stream fractionation involve technologies that are already widely used within the sector, with their optimal combination appearing to be the key factor for success.
Pyrolysis
Another form of thermal treatment, in the total absence of oxygen, pyrolysis produces a mixture of solid, gaseous and liquid products, depending on the composition of the feedstock and process conditions. Pyrolysis oil and gas can be directly used as fuels, providing the pyrolysis process itself with the energy necessary, and the oil could potentially also be converted into other fuels or chemicals. When PBI sludges are pyrolysed the mineral fraction returns as a clean secondary product, which could be applicable again as a filler for paper making if its quality is sufficiently high, while when mixed rejects are pyrolysed the metal fraction returns as a clean secondary product. Reject pyrolysis has already been commercially applied, while sludge pyrolysis is in the phase of pilot scale development.
Industrial and pilot scale demonstrations of the REFFIBRE cases
Conversion of a variety of side streams from Holmen and Utzenstorf into raw materials for the production of composites, conducted jointly by VTT and a number of different external parties in Finland, Sweden and the Swizerland. These demonstration trials for the production of composite materials have indicated that side streams can be used in injection moulding and profile extrusion. Further product development and regulatory approval for the use the side streams are needed.
Pilot-scale sludge fractionation in cooperation with Kadant-Lamort showed that it is possible to separate different fractions out of paper industry sludge. The purity of these fractions was, however, worse than anticipated. The reuse of organic fractions with paper making potential for the partial substitution of “fresh” pulp produced limited paper strength improvements and led to some dewatering problems that would in a production run appear in both the wire and press sections of the paper machine.
The goal of the trial for the recovering of fibres from fine screen rejects was to focus on the most accessible type of side stream for raw material reclamation, since fine screen rejects contain long fibres with a high brightness. Extensive testing was carried out at the Utzenstorf mill in cooperation with the Finnish SME-company Haarla Oy that has developed this fibre reclamation concept (ZRI concept). This industrial-scale demonstration has shown that stabilising the content of impurities (macro stickies) in the pulp stream after the addition of the reclaimed fibres was possible; this can be for the time being achieved by careful management of the ratios of “fresh” pulp and reclaimed fibres. The installed equipment remains in continuous use in the Utzenstorf mill for longer-term evaluation. This will determine whether reduced waste generation and improved resource efficiency are sufficiently high to justify an investment in the full-scale application of the technology.
The pyrolysis pilot trials by project SME-partner Alucha have demonstrated the separation of fillers from paper mill side streams but the quality of this reclaimed material was not found to currently be high enough for reuse within the papermaking process. The quality of these fillers needs to be further optimised in order to remove char or, alternatively, other end uses for these recovered fillers need to be studied, where their impurities will not be of such high importance as in paper production.
Resource efficiency in paper and paperboard value chains
One of the objectives of the REFFIBRE project was to calculate the value chain level impacts of energy and material savings due to the optimised use of recycled fibre. This was assessed with different case studies defined for each of the industrial companies involved in the project: Utzenstorf, Holmen and Vrancart.
To do so, a list of resource efficiency indicators used at product and process levels that take into account the potential impacts on the value chain was defined. The verification of the applicability of these resource efficiency indicators was done by evaluating the economic and environmental impacts at the value chain level with real industrial data from three paper and paperboard mills.
Methodology development
Supporting the verification of the applicability of the resource efficiency indicators, two methodological approaches for allocation in paper industry have been considered: the first method was based on ISO 14067 in which the allocation factors are defined as the Medium Fibre Age (MFA) and Medium Number of Uses (MNU); and the second method was a new approach based on findings from a fibre flow model.
A material mass flow balance was developed for the region of CEPI member countries based on data collected and provided by CEPI. The most important challenge of modelling is the fact that an increasing portion of fibres are used repeatedly in paper making cycles, i.e. unsold and consumed paper products are used again as raw materials of new paper products. The material mass flow balance allows calculating the average ash content in paper products and paper for recycling grades and the mean number of cycles the fibres in a certain paper product are used from the beginning to date or will be used from now until their end of life. The use of paper for recycling as raw material differs from paper product to paper product. Case materials and newspapers are nearly completely based on paper for recycling in many countries, whereas a certain amount of fresh fibres is necessary for high quality publication papers. Recycled newsprint and publication papers are then used as raw materials for packaging paper grades. As a result, the assumed single cycle must be divided into various connected sub cycles.
The paper production within a region of the CEPI member countries (18 member countries, 17 EU countries and Norway) can be divided into six major segments: Newsprint (NP), Other Graphic Papers (OGP), Case Materials (CM), Cartonboard (CB), Household/Sanitary (HS) and Other Paper and Board (for technical applications) (OPB). Paper products of the first four segments are recycled and used as raw material in all six segments. Paper products from the last two segments are not recycled. They are assumed to be unwanted materials in paper for recycling. Additionally, all four recycling loops are connected with each other, i.e. products from one cycle are used after recycling as raw material in the other cycle and for the production of Household/Sanitary Papers and Other Paper and Board. All six paper segments have separate entries (Virgin fibres and Filler/Pigments) and various exits. Exits of the four recycling loops are the net trade of paper products and paper for recycling and the losses due to disposal and long-time usage. The export and import of these materials not included in statistics are not taken into account in this study. Rejects from paper production are defined as a separate exit for all six paper segments.
Based on the mass flow balance the ash content can be calculated easily at every point of the flow chart. The mass flow consists of two material categories: fibrous (organic fibres and fines) and non-fibrous (pigments, fillers) materials. Calculating the composition of a mixture of multipole mass flows is trivial. If a mass flow is separated into multiple single mass flows, one should consider the way of separation. If the mass flow has been separated as a result of paper collection or sorting, the composition in terms of fibrous and non-fibrous components is assumed to be equal for every single mass flow. The separation process in a paper mill is more selective because it is focused on discharging non-fibrous components from paper for recycling. For simplification it was assumed that all rejects (except for those from tissue production) contain 40% non-fibrous materials. If paper for recycling is used for the production of sanitary or household papers, an average content of 20% non-fibrous materials was assumed in rejects. Fibres, fillers and pigments are taken into account in the mass balance, while additives are ignored.
The key input parameters of the mass flow balance for every individual recycling system are the Recycling Rate R: Percentage of paper for recycling “utilisation + net trade” compared to the total paper & board consumption, the paper for recycling Utilisation Rate U: Percentage of paper for recycling utilisation compared to the total paper production, the Reject Rate L: Percentage of losses compared to paper for recycling utilisation. The key output parameters are the Mean Fibre Age MFA: Mean number of generations a fibre has been used to date within a certain paper product and the Mean Number of Future Uses MNU: Mean number of future repeated uses of a fibre starting from the current paper product until the end of its life.
Based on a data set provided by CEPI it was shown how a mass flow balance could be derived that took the six major paper segments and their recycling-induced connections into account. The ash content in paper for recycling grades influences the quality of paper products, especially their strength properties. Valid information about the future development of ash content in paper for recycling grades will enable paper mills to plan effective countermeasures in order to guarantee a constant product quality. Similar mass flow balances can be calculated if we assume some trends for paper production and consumption in the near future.
High values of MFA (for CM and NP) express high paper for recycling utilisation rates and this will not change remarkably over the next years. The small drop in NP and OGP in the next years is due to the changing composition of paper for recycling grades used for graphic paper production. Less newsprint but a higher share of other graphic papers will become typical. High values of MNU (NP, OGP and CM) reflect the close recycling loop for those paper grades. The other grades are used over longer periods (CM) or are not recycled (HS and OPB). Fibres which have always been used in newsprint will be used about a half generation longer in 2020 than today because of their increased “chance” to be subsequently used as raw material for the growing market of packaging papers instead of for graphic papers. We can be sure that recycled newsprint fibres will be a valuable raw material for packaging papers and their recycling rate R will increase.
The highest total numbers of uses, i.e. MFA+MNU-1, occur when the fibres are used at least one time for Newsprint or Case Material production (about 5.1 to 5.2). This is mainly caused by the high paper for recycling utilisation and recycling rates. With values of 3.2 and 3.6 the total numbers are lower for fibres used for the production of other graphic papers, cartonboard and other packaging papers. Not surprisingly the total numbers are low (1.3 for HS and 1.9 for OPB) when the fibres are used for the production of sanitary and tissue papers or for other technical papers.
According to the environmental assessment, it is important to explain the different possibilities in terms of the allocation method procedures that can be used for an environmental evaluation based on life cycle assessment. The Mean Fibre Age, MFA, the Mean Number of Future Uses, MNU, and the Recycling Rate, R, can then be used to calculate the allocation factors for all paper grades. The number of cycles that a fibre is used repeatedly can be applied in allocation methods to share the burdens of fibre extraction and end-of-life operations between different life cycles. The MFA and MNU values depend solely on the mass balance that was derived from data reported by the national associations to CEPI. Some additional assumptions had to be made to fill those gaps, where no information was available. However, due to inconsistencies these assumptions need further research and can lead to changes in MFA and MNU values.
In this regard, two main approaches were considered for REFFIBRE: An allocation method that combines ISO 14067 and the Medium Fibre Age (MFA) and Medium Number of Uses (MNU) and a new approach based on findings from the fibre flow model developed in the REFFIBRE project. The main difference between both approaches is whether or not to consider the recycling credit. On the one hand, in the ISO 14067 approach, a recycling credit is discounted in order to consider the future uses of the virgin fibres. On the other hand, in the new approach based on the fibre flow model, instead of a recycling credit, allocation factors were used for the usage of the virgin fibres and recycled fibres due to the multiply usage further on in the fibre circulations.
Resource efficiency indicators
The impact evaluation of economic and environmental consequences of the REFFIBRE cases compared to the baselines scenarios at each company was carried out in co-operation with three paper mills. In the economic assessment, the main focus was to evaluate and measure economic impacts of potential cases built on value chains based on the process owner’s point of view. The evaluation of the economic impacts of the REFFIBRE cases proposed are based on indicators such as variable costs, revenues, profitability, savings and affordable investment. The environmental impacts of the reference cases were modelled using LCA methodology. Based on this, the environmental indicators for both the reference and the REFFIBRE cases were calculated. The environmental assessment was based on the evaluation of the following indicators; Global Warming Potential, Fossil fuel depletion, Freshwater eutrophication, Water footprint, Cumulative Energy Demand and Material efficiency. An eco efficiency indicator was also included as a combination of environmental and economic indicators. The case calculations for the economic and environmental assessments were conducted in cooperation with the industrial partners who provided data for the core processes.
Economic indicators:
The ability of different economic indicators to demonstrate potential impacts that could occur in the REFFIBRE cases compared to the baseline case was tested. Five indicators were in focus: variable cost, revenue, profitability, achievable savings and affordable investment.
All economic indicators were able to show the differences between the case scenarios and against the baseline (reference) scenario. The scale in the comparison was fit to all the cases. For cases with minor changes, e.g. small changes in reject amounts: increased or less rejects, the effects are small, but recognisable.
Profitability and achievable savings indicators give an overall picture of the economic effects. It must be kept in mind that profitability indicators do not account for fixed costs and that an achievable savings indicator takes into account fixed costs, such as labour, overhead and maintenance materials but not capital charges due to, e.g. investments. These indicators can also be used as stand-alone. Affordable investment is the supporting indicator for these. Affordable investment provides absolute value for maximum investment based on achievable savings, thus, giving an insight into investment possibilities.
Additional economic key figures are given for each case, where applicable: investment estimation (if available), annual savings and additional revenues that also take into account the case investment estimation, additional labour estimations for operation of the case line, return on investment (ROI) for the additional investment for each case (in the event of negative savings, ROI cannot be calculated) and possible additional investment, which is calculated based on savings and additional revenues that include case investment if estimated (must be positive, otherwise no figure is given).
Environmental indicators
The ability of six different environmental indicators to demonstrate potential impacts that occur in the REFFIBRE cases compared to a baseline case was tested. Of these indicators, material efficiency highlighted well the differences between the REFFIBRE cases and was regarded as an informative environmental indicator for sustainability screening. This indicator accounts for the total amount of useful products as well as the amount of generated waste, both of which are changing variables in the studied REFFIBRE cases. Material efficiency was the highest for “WPC ash”, where 100% of the ash fraction was utilised, and the largest amount of useful products were produced (paper plus WPC). Also the pyrolysis case showed an increase in material efficiency due to a reduction in the amount of waste and an increase in the amount of products. For one mill, the pyrolysis case was the most material efficient because all sludge components were used for pyrolysis. It must be noted, though, that in this case the sludge that goes to ceramics and to agriculture is treated as waste because no income is gained.
In the case of the global warming potential impact indicator, only minor changes were detected (per tonne paper product): There was either a minor increase in the impact or no impact at all. For example, in the case of “increased rejects”, the reduction in the use of electricity at PM was not enough to outweigh the increase in emissions caused by, e.g. the efforts for sorting more collected PfR. It must also be noted that even though the integrated production of WPC did not have an impact on the paper product global warming potential impact, it increased the absolute global warming potential impact of the production site (gradle-to-gate). Assuming that all of the ash from the power plant is used in WPC production, the total global warming potential impact would be more than doubled, when compared to the baseline case where only paper is produced. Another vital point is that the benefit of producing plastic composites by substituting polypropylene with either ash or DIP was not taken into account by calculating the avoided emissions when the use of ash or DIP reduced the need to produce polypropylene elsewhere. It was, however, estimated that the global warming potential impact of the new side stream plastic composite products was about 60-70% of that of a product composed of 100% polypropylene.
As regards the water scarcity footprint indicator, most of the cases showed no changes or a minor change. Here, the increased use of chemicals and PfR in “increasing rejects” was seen most clearly to have a negative impact on the water scarcity footprint if the side stream was not valorised in the mill.
Eco efficiency indicates the highest benefits of producing WPC, more specifically, WPC by profile extrusion since the revenue is assumed to be the same for both injection moulding and profile extrusion but the environmental impact is higher for the injection moulding due to high energy consumption.
Integration of the models to a practical guide
The research carried out shows clear benefits for engineers and managers in the mills; they can develop the processes that enhance environmental performance and maintain economic feasibility with the help of the defined indicators. The environmental indicators cover the most relevant aspects to be considered in the pulp and paper industry as well as the economic indicators that describe the affordable investment and the ROI of the new technologies tested. This allows mill managers to prioritise different action plans depending on their general strategy. Therefore, the set of indicators selected reveals to paper mill managers the environmental consequences that different changes in processes will have along the whole value chain, and, at the same time, this set of indicators support the decision-making process in the mills from an economic point of view.
In order to support paper mills better a guide was prepared that will help users to understand the models and tools developed in the assessment of economic and environmental impacts throughout the value chain. In this regard, a brief introduction of the process modelling work carried out in REFFIBRE was also presented in order to simulate future changes in paper production and separation processes when optimising materials in the stock preparation phase.
The guide details resource-efficient indicators based on life cycle thinking which were defined to represent the main impacts of the test cases within the scope of the Reffibre project. In this regard, the selected resource efficiency indicators to assess the impacts on the value chains of the different test cases were divided into economic indicators, environmental indicators and technical indicators. The guide presents also the tools which were developed to support the practical implementation of resource-efficient indicators at industry level. These tools include a software tool, based on process models which can calculate the indicator values from the data available in the mill data management systems of the industrial partners, and the methodological approach proposed for open-loop allocation in the Life Cycle Assessment (LCA) of the pulp and paper industry, based on the amount of cycles the fibres have undergone and will undergo in the future. The guide also provides the formulas required for the calculation of the economic indicators and a proposal for visualising the indicators as the practical implementation of resource efficiency indicators at industry level through the definition of the Reffibre Balanced Scorecard including the Balanced Scorecard Map and Dashboard.
Potential Impact:
Project partners have delivered a project website and updated it with six newsletters, numerous presentations in three public workshops and in the final conference, and two videos. Dissemination activities included mostly oral presentations in conferences and workshops, but several peer-reviewed articles, posters, flyers, videos and news and reports on web-sites were also among the activities.
Different allocation methods that are debated issues in LCA standardisation at the moment, were tested in the environmental assessment studies. The new methodology to take into account circular economy as paper grade specific allocation factors based on real circulation paths in the paper and board industry was developed and tested. A technical guide for the practical implementation was formulated and the allocation factors will be proposed to be included in the ISO/TS 14067 as an appendix. ISO/TS 14067 is recommended becuase it takes better into account recycling fibres several times in circular economy than PEF -method that takes into account only one recycling of the material and final recovering of the material as energy. The recycling rates, Mean Fibre Age and Mean Number of Uses can be up-dated based on the newest data reported annually by Confederation of European Paper Industries (CEPI) and allocation factors for ISO/TS 14067 can be up-dated when collection rates and volumes of different paper for recycling are changing in the future. Similar allocation factors can also be calculated for other industries in co-operation with the Industrial Associations. The sustainability assessment results can be calculated for complete value chains of paper and paperboard industry with a standardised way. The method can be used to further develop guidance in the available standards and Product Category Rules (PCRs). This additional guidance will contribute to increased harmonisation and consistency of LCA practice in the pulp and paper sector as well as to the enhanced practical implementation of LCA at industry level.
The results of the REFFIRE project can be widely used across the industry. The adoption of the developed REFFIBRE allocation method has a big impact for executing LCA calculations in cases where paper for recycling is used, if the method is implemented across the industry. The work for expanding the use of the method will be done in cooperation between VTT and ITENE. In addition, the now verified set of economic and environmental indicators will also be used in future research and consultation assignments for assessing value chain impacts of changes in process configurations. The models for fibre flow of recycled fibres, and calculation methods for mean fibre age (MFA) and mean number of future uses (MNU) have a large impact. The algorithms will be up-dated by the original developer PTS based on the data from CEPI. The algorithms from fibre flow model, R, MFA, NMU will be used to create statistical information and communicate environmental impacts to consumers and companies and the improvements in LCA methodology (allocation) will be communicated to LCA practitioners. Paper mills and paper recycling mills will be informed about the possibilities of side stream applications.
All research partners plan to actively exploit the models and tools developed within the project to provide consultation especially to the paper and board industry on sustainable and cost-effective paper and board manufacturing. Experience gathered through the demonstration trials will be used as a reference material on explaining how resource-efficiency can be improved at mills. The academic partner (TUDA) will utilise the developed process models and optimisation tools as a foundation for further research and learning material for students in the field of optimised process control for pulp and paper industry. The work with the fibre integrity number needs further research but may provide a novel software sensor to monitor the quality of pulp containing paper for recycling and the concept will be offered to manufacturers interested in fibre analysers.
The paper product and process modelling work have shown that contaminated fillers and fines are reducing resource efficiency and how the unwanted filler, fines and impurities can be separated from recycled fibre material. These unwanted materials are slowing down dewatering of the fibre furnishes in the wire and press sections and causing breaks in the wet press section. Current typical valorisation routes are incineration in the biomaterial power plant on site and using filler containing side streams in concrete industry.
The use of side streams in plastic composites and recovering fillers with pyrolysis will reduce waste to landfill and at the same time improve competitiveness of the mills. The pyrolysis is a good alternative for mills using natural gas as their energy source and/or for mills without possibility to burn the waste fractions. By taking out fillers and contaminated fines the quality of the paper or board products can be improved and/or maintained when the quality of paper for recycling will reduce in the future due to higher recycling rates and higher amounts of fillers, glues and other materials as impurities in paper for recycling and thus, lowering the raw material quality in the future. The work focused on recovering of fillers with pyrolysis from deinking sludge need to be continued in order to achieve high enough brightness level by removing char from the recovered fillers. Novel composite materials can be produced with side streams from paper industry. VTT and Holmen will continue with their development, aiming at sustainable and cost-effective material solutions and put efforts in finding applications for (bio)composites in building sector. The Utzenstorf and Vrancart mills will continue with their optimisation efforts that were started during the project to further increase the resource efficiency of their paper making process, production capacity and product quality.
List of Websites:
http://reffibre.eu
Ulla Forsström
ulla.forsstrom@vtt.fi
+358 40 8202191
The main aims of the project were to develop tools and knowledge, which are needed for the “eco-design” of the resource efficient paper and paperboard production chains based on Paper for Recycling (PfR).
The modelling related to paper product and production design developed knowledge and tools to model and simulate the influence of paper for recycling (the role of different fibre fractions and fillers) on the properties of produced paper/ paperboard. The tools helped to find pulp combinations and paper compositions which reduce material or energy consumption while safeguarding paper properties. Models and experimental work showed that removing fillers and contaminated fines increased strength properties without any effect on optical properties of the paper products and less energy was needed in paper production to remove water in wire and press sections.
The process models can be used for optimising the quality and purity of the recycled pulps but also for developing indicator based tools for further optimisation of stock preparation systems in the future. Increasing rejects in deinking units removed selectively fines and fillers from the recycled pulp. The deinking sludge or otherwise separated fines and fillers and other rejects from the stock preparation can then be valorised at the mill or by other industrial partners (industrial symbiosis). The side stream plastic composites were successfully produced from rejects, deinking sludge and fly ash (from the power plant when the sludge was incinerated in the mill) in co-operation with two industrial partners. The novel by-products improved resource efficiency, reduced environmental impacts of the mills and the production was in all cases feasible and profitable. As an other option the recovering of fillers with a pyrolysis process looked also feasible and profitable for paper mills with no possibility to incinerate their sludge.
The main work in the value chain assessments was to calculate the value chain level impacts of energy and material savings due to the optimised use of recycled fibre. As an outcome of the Fibre Flow mass balance modelling recycling rates (R), mean fibre ages (MFA), mean number of uses in the future (MNU) for different paper grades were defined within the CEPI region (countries as members in the Confederation of European Paper Industries). These can be used to calculate the allocation factors (Ai and Ao) needed when calculating environmental impacts according to the method ISO/TS 14067 Greenhouse gases - carbon footprint of products requirements and guidelines for qualification and communication. The methodology was developed and it is ready but the research work after this project needs to be continued. The final allocation factors will be re-calculated with corrected mass balances in close co-operation with CEPI and several industrial partners in order to reach consensus about the allocation numbers to be used for the standardisation work. The information from different modelling tools can be used for estimating economic and environmental assessment of the improved paper or paperboard products and potential side stream products. The ways how to use these tools in co-operation with specialists are described in details in a practical guide. These value chain methods and indicators were used for two cases where the amount of fibre rejects were minimised by improvements in the stock preparation systems by installing novel equipment in two paper and paperboard mills during the project. In both cases the amount of waste was reduced and the profitability of the paper and paperboard production improved.
Project Context and Objectives:
Reffibre project was focused on tools, methodologies and modelling to improve resource efficiency in printing paper and paperboard mills using paper for recycling as their main raw-material. The research targets of the methodology and modelling work were focused on three different levels: modelling the paper quality in current printing paper or paperboard production lines, modelling and controlling processes in stock preparation line, where the focus was in the separation of the unwanted fractions and modelling the resource efficiency in the whole value chain. The use of side stream fractions in novel products was first studied in laboratory scale and later the most potential ones were demonstrated in pilot or industrial scale.
The modelling related to paper product and production design developed knowledge and tools to simulate the influence of paper for recycling (the role of different fibre fractions and fillers) on the properties of produced paper and paperboard. Modelling developed knowledge and tools for both basic printing and packaging paper properties and also for layered structures in order to show the potential of layered paper design. The target of the paper product models was to predict changes in paper properties due to the changes in fibre properties. Additionally, one target of this modelling was to use these tools to calculate energy demand for dewatering and drying and provide the data for the whole value chain calculations. The tools can help to find pulp combinations and paper compositions, which reduce material or energy consumption while safeguarding paper properties. The effects of removed side streams on paper properties and energy and steam consumption on the paper machine were also modelled. Models were used to optimise different optical properties and/or functional properties such as bending stiffness and strength properties of printing papers or paperboards produced. These properties can be optimised for single layer products or for multilayered products.
The process models were developed for different separation processes at two paper mills. These models can be used for optimising the pulp quality and purity but also for developing indicator based tools for superordinate optimisation in the future. Increasing rejects in deinking units removed selectively fines and fillers from the recycled pulp. The deinking sludge or otherwise separated fines and fillers and other rejects from the stock preparation can then be valorised at the mill or by other industrial partners (industrial symbiosis). The second target was to identify the most potential valorisation routes of side stream products based on the literature and most potential ones were selected for laboratory and large scale work in order to support the “multi-product mill” approach. The side stream plastic composites were successfully produced from rejects, deinking sludge and fly ash (from the power plant when the sludge was incinerated in the mill) in co-operation with several industrial partners. Fractionation of the rejects and recovering of fillers with the pyrolysis process were studied in pilot scale.
The main work in the value chain assessments was to calculate the value chain level impacts of energy and material savings due to the optimised use of recycled fibre. The objectives were to define the case studies and related value chains and define resource efficiency indicators for paper and paperboard applications. The other target was to use the existing fibre flow model to define parameters to allocate burdens of the virgin fibres in fair way in environmental assessment of paper and paperboard products that are recycled several times building circular economy. As an outcome of the calculations recycling rates (R), mean fibre ages (MFA), mean number of uses in the future (MNU) for different paper grades were defined within the CEPI region (countries as members in the Confederation of European Paper Industries). These are used to calculate the allocation factors (Ai and Ao) needed when calculating environmental impacts according to the method ISO/TS 14067 -Greenhouse gases - carbon footprint of products - requirements and guidelines for qualification and communication. These value chain methods including both economic and environmental indicators were used for several cases including also by-products. In both simple cases where the amount of fibre rejects were minimised by improvements in the stock preparation systems by installing novel equipment in two paper and paperboard mills during the project the amount of waste could be reduced and the profitability of the paper and paperboard production was improved. The information from different modelling tools can be used for estimating economic and environmental impacts of the improved paper or paperboard products and potential side stream products. The ways how to use these tools in co-operation with specialists are described in details in the practical guide.
Project Results:
Paper making product and production models
The developed paper making models are intended to help to correlate pulp characteristics, which are changed by various (dry and wet) stock preparation processes, with the quality parameters of the papers produced. These models together with the process models covering process units in the stock preparation describe basic manufacturing processes in a paper mill.
The most important paper quality parameters for publication papers are optical and structural paper properties. But mechanical properties are also necessary in order to ensure a certain level of paper machine runability and proper behaviour in paper converting. The vector of pulp characteristics is the input for paper property models including the abbreviations and testing procedures used. The content of the vector corresponds to those pulp and fibre characteristics that can be influenced by the selection of paper for recycling grades and can then be varied by various dry sorting and stock preparation processes. The Schopper-Riegler value SR and water retention value WRV characterise the behaviour of suspensions. Both values are closely related to the dewatering and drying behaviour of a paper machine and the amount of energy consumed for these purposes. Some basic rules on how to correlate SR and WRV with the specific energy consumption necessary for dewatering publication papers were already available. These rules, together with the amount of materials, can be used directly by the tools on the value chain level, which help to determine resource efficiency.
Paper properties on a real paper machine depend on many process parameters and can vary between the machine direction and cross direction. In order to make paper quality independent of a real paper machine, a decision was taken to use the paper properties of handsheets. Because handsheet formation is a standardised procedure, paper properties resulting from different pulps can be compared. On the other hand, handsheet properties are directly correlated to machine paper properties and it is common procedure in paper mills to transfer handsheet properties to machine paper properties using simple ratios.
Modelling the influence of in-organics on structural and mechanical paper properties needs to know quantitatively what happens in the fibre network when pigments are incorporated. One of the key structural paper properties is the Relative Bonded Area (RBA) of a paper sheet. A new method is introduced which allows a faster determination of the RBA. The new method uses the density of the sheet but the cross sectional information of the fibres and a simplified fibre network model, so called d-parallel fibre networks, are used to find a relation between density and RBA, which takes the morphology of the fibres into account.
The availability of RBA data allows to study two effects of pigment incorporation into fibre networks in more detail – the network “Expansion” effect (which leads to a decline of RBA) and the “Integration” or “Bond-weakening” effect (where Shear Bond Strength decline can be derived from the decline of the Tensile via RBA). Due to increased pigment inclusion in the paper sheet the network skeleton is widened (the expansion effect). Simultaneously pigments are attached to the fibre-fibre bonds and reduce the bond strength (the bond weakening effect).
For both effects numerical models were developed based on laboratory trials. The models have been validated based on sample data from a graphic paper mill which is using nearly 100% of paper for recycling. For improving resource efficiency and introducing a multi-product-mill concept it is important to know potential benefits that the reduction of in-organics by means of e.g. fractionation brings to the products. The simulation results showed that the reduction of the in-organics from recycled paper did not reduce optical properties especially opacity but increased strength. On the contrary the addition of fresh fillers improved opacity. It looks like that the fillers are getting contaminated in recycling processes and they lose their scattering power. One of the fundamental benefits of the model is the ability to estimate the influence of in-organics reducing measures in stock preparation on final tensile strength. Because tensile is closely related to many strength properties the influence of in-organics on the other strength properties important for packaging materials can also be predicted.
Critical factors affecting strength properties for paperboard were demonstrated with the numerical models in order to improve resource efficiency in a packaging paper mill. One of a potential future scenario is the increase of fillers in paper for recycling. In order to guarantee certain paper strength, multiple scenarios are thinkable: increasing paper grammage, higher amount of strength additives (starch), separation of in-organics (e.g. by flotation) to be used as a by-product or replacement of certain amounts of paper for recycling by virgin fibres. Whereas the two first ones will decline resource efficiency the two latter ones were interesting to evaluate in more details. Based on given pulp vectors the following cases have been calculated: Reference (100% paper for recycling), Case 1: about 4% in-organics are separated from the pulp, Case 2: about 7.5% in-organics are separated from the pulp, Case 3. about 4% of the recycled pulp is substituted by virgin fibres and Case 4: about 7.5% of the recycled pulp is substituted by virgin fibres. According to the models both measures (separating in-organics and substituting paper for recycling by virgin fibres) improve basic packaging paper properties nearly at the same level. Separation of in-organics requires a higher input of paper for recycling and investments for a separation stage (e.g. flotation). If the separated in-organics can be converted into a valuable by-product the higher costs are amortised. Substituting paper for recycling by virgin fibres will increase the raw material costs in a higher degree than it will happen in cases where fillers are removed. Additionally investments for a refining stage are necessary. From a cost perspective point of view this alternative seems to be not attractive at the moment.
For evaluating the quality of recycled fibre material a novel and simple concept, Integrity Value, was introduced. Integrity Value for recycled pulp uses the approach based on the strength based quality potential of the fibre material. Strength potential is seen as a basic requirement of material, and good strength potential give larger window for optimising other quality properties of paper product. If quality potential is quantified by using a simple set of measurements, then the utilisation options for paper making are better understood. If quality potential is already low, then also other than papermaking utilisation options must be considered. The other utilisation options for side streams can vary and this value does not prefer any utilisation option over another.
The measurements show that deinking increases Integrity Values. Integrity is also much greater when using fresh, non-recycled pulps. Different mills have different integrity value levels, which reflects to the day-to-day operations of those mills. Integrity was also shown to correlate well with strength properties measured from handsheets when the bonded area of the sheets was also taken into account and estimated from sheet density. This correlation verifies the connection of the between Integrity Value and the strength potential of the pulps and demonstrates its utilisation potential also in continuous evaluation of the incoming recycled pulp at the mill. The integrity number for recycled pulp is an approach with great potential to evaluate potential of paper for recycling.
The properties of a single-layer paper sheet are determined by the pulp characteristics and the performance of the paper machine, whereas a multi-layer paper offers some more variables to improve the paper properties. By designing the sequence of the layers and selecting suitable materials per layer it is possible to achieve higher bending stiffness or brightness levels even if the sum of the materials is the same as in a single-layer sheet. Therefore, layered paper design is a promising way to improve resource efficiency.
There are two different technologies for producing multi-layer sheets – multi-ply sheet forming and stratified sheet forming. Whereas the first technology is a state of the art for producing carton board, the second one is relatively new and allows the layering of lower-grammage papers like graphic papers. In multi-ply sheet forming the individual layers are formed separately in separate forming sections using several headboxes, and couched together after the forming process. During stratified sheet forming several stock layers are brought together in one headbox and only one forming unit is used for dewatering. Because of the technology used, it is not possible to clearly distinguish between the individual layers of a stratified sheet. There are transition areas between the layers. Due to retention effects during stratified sheet forming fines and fillers cannot be introduced exclusively in a certain layer. This should be kept in mind when estimating the potential of layered sheet forming.
All results based solely on numerical modelling calculations show that a fractionation of the pulp and subsequent redistribution of the fractions to the individual layers could improve the paper properties remarkably. Of course the results and trends presented depend on the quality of the paper for recycling used. Basic assumption in the calculations was that the total pulp is fractionated and all fractions are used in the layered paper sheet. Alternatively, only a part of the total pulp could be fractionated. Some fractions could be valorised in side streams whereas the remaining fractions and remaining original pulp are used in a layered sheet. The numerical model introduced was very nonlinear. Solving an optimisation problem for this type of models is non-trivial because there can be various local maximum or minimum. The optimisation problem is solved step-wise by an iterative procedure. Depending on the type of solver and on the starting values, the optimisation results can differ.
Fractionating recycled pulp and redistributing the fractions to the layers of a multi-layered sheet could be an effective method to improve resource efficiency. Even with state of the art fractionation technologies paper properties might be improved or raw material can be saved. The available numerical models can be used to find the best manufacturing conditions depending on the quality of the paper for recycling serving as raw material and on the requirements made on the final paper product. Due to the increasing number of variables (number of pulp fractions, number of layers in the multi-layered sheet) it is crucial to use a special software (a so called solver) to solve the optimisation problem and find optimal solutions.
Process models in stock preparation and routes to make good use of side streams.
Modelling of the processes to separate side streams
For the description of all material flows in deinking plants, a vector has been developed which includes basic information on the volumetric and mass flow rates and the consistencies at the inputs and outputs of units and systems in the stock preparation area.
This information is necessary for balancing the material composition. The suspension is considered to be a composition comprising long fibres (LF), short fibres (SF), fines (FS), minerals (ASH) and stickys (ADH). Additionally, drainage and optical properties were used for the physical description of pulp. Among the optical properties brightness (R457), luminosity (Y), effective residual ink concentration (ERIC) values and dirt specks (SPEC) were in focus of process modelling. The drainage properties were reduced to the modelling of the Schopper-Riegler (SR) and water-retention values (WRV).
The described parameters were selected because they represent the main composition and quality parameters for the production of graphic papers. The fibre composition and the content of stickies are crucial parameters for the prediction of the runability of the paper machine whereas the optical parameters are important for the sale of the produced paper. The drainage parameters play an important role, too, as they provide reference values for the energy consumption needed for the dewatering of the paper web on the paper machine. This data vector is in line and consistent with other approaches for modelling the downstream paper making process.
The developed data vector was filled with current process data of the inputs and outputs of units prior to the modelling of processes and systems in order to compute several key figures for each separation unit. Data was collected from online process control systems to a certain extent. However, not all parameters listed in the data vector were available as time-continuous online measurements. For cost reasons the number of online measurement equipment in deinking plants was usually reduced to a minimum. Therefore, samples must be taken at the inputs and outputs of units in the deinking plants and analysed in the laboratory in order to complete online data. The process conditions and the input paper quality were kept constant during this sample collection.
A separation process was described by means of three mass flows, one input mass flow and two output mass flows respectively. If two mass flows were known for a unit, the missing third mass flow could easily be calculated. If all three mass flows could be calculated using measured volumetric flow rates and the corresponding measured consistencies, the mass conservation law can be infringed due to inaccurate online or laboratory measurements or due to occurring process fluctuations and time-lags during sampling. A similar problem occurs when combining the mass balances of several units but also when combining multiple systems. The calculated output mass flow of coarse screening was for instance greater than the input mass flow to pre flotation. In these cases, an equalisation calculus had to be applied. In the calculus, the inputs and outputs are changed to the same extent, because both have the same absolute uncertainty.
As the models are semi-empirical and data-driven, the time-continuous integration of factory-related data into the models is of high importance. The biggest challenge was missing data due to the lack of instrumentation and measuring equipment in industrial systems. The instrumentation is a reasonable cost factor and is therefore limited to the indispensable minimum in many paper mills. Deinking plant processes are commonly controlled by distributed control systems (DCS). Common control systems can handle thousands of process signals simultaneously and enable a straightforward access to data via easy to use interfaces. Software tools allow users to gain access to both present and previous data. Additionally, a high amount of data is collected and archived discontinuously in external databases. This knowledge on the data access enables the query for online and offline data necessary to run process models and to compute the resource efficiency indicators.
The models can be used as an offline tool for simulating process conditions and operation modes in order to predict changes in efficiency and pulp quality as well as effects on the indicators. Results of the different models have to be combined in order to get a rough overview of the deinking plant’s overall trends. For use as an online tool which follows the real process, the models have to be fed with online data such as volumetric flow rate and consistency of the input. Variations in pulp quality or changes in the characteristics of devices may require an additional manual data input. These changes in the process model framework are implemented with a VBA Macro in MS Excel which is triggered off automatically in the case of any changes to the input data.
Process models for separation processes in deinking plants were established. It was shown that it was possible to integrate resource efficiency parameters in the conventional process models of composition and quality data for deinking plants. The process models for separation processes were in line with other process models predicting paper quality and calculating the impact of changes in the production process over the whole value chain resulting in reduced costs and improved material efficiency.
In contrast to existing process models for deinking plants, which only focus on the material composition and the separation of impurities, the extended data structure facilitates the calculation of the up to now unknown optimum between the use of resources, pulp quality and the amount of residues for disposal. The assessment of side stream applications made from residual materials (e.g. increased amount of sludge from deinking in order to reduce in-organics) is enabled by the implementation of the process models in the deinking plants. Additionally, the time lag between manual inputs by operators or caused by process control systems and the impact on both the product and the process can be overcome. By the introduction of internal transfer prices, it is possible to make process changes measurable on a monetary level. The high amount of data collected in the deinking plants can be aggregated in five essential indicators.
It is important to emphasise that it is feasible to model and simulate deinking plants in terms of both pulp quality and resource efficiency parameters. The development is however connected with a great data collection and interpretation which is often coupled with difficulties. This requires a certain additional effort in recording and analysing additional data. If a higher accuracy of the process models is intended, a higher amount of samplings or more online measuring equipment is essential as the separation indices describing the separation behaviour of partial matter are subject to deviations caused by process fluctuations, changes in the input materials and errors in sampling.
Controlling the separation of side streams
When using some fractions of recycled fibre material for non-paper applications, such as novel fibre-based materials, composites, bioenergy and biorefinery concepts, the amount to be separated has to be controlled in-line. Thus, for paper making and other potential uses of fibre raw material must be evaluated in a new way. A new, simple concept for evaluating the quality and utilisation potential of recycled fibre material from the strength point of view, entitled the “fibre material integrity value”.
In general, strength, or the ability to bear and distribute stresses, is a fundamental property of a solid material. The same applies to fibre-based materials; without strength, the material is useless. Fibre material integrity, a new value associated with fibre material quality, should therefore reflect its strength potential. Although strength is not always the key requirement for products, it is always important. Only when the structure has sufficient strength can other material properties be optimised. Generally speaking, a higher strength potential means more freedom in optimising optical properties or reducing the amount of material and energy used in production. High integrity means that the material has high strength potential and is therefore easier to make into a product of sufficient strength. When such potential changes during recycling or another process, this should be reflected in the fibre material integrity value.
The chemical composition of the pulp must also be considered. For example, the presence of cellulose, holocellulose, or lignin fractions can reveal the origin of recycled material. Pulps (and fines) of mechanical or chemical origin have different potential for later treatments. In addition, the filler amount reduces the recycled material’s ability to bear and distribute stresses around the network because of the lower amount of fibre material and reduced bonding between it. To approximate the key parameters discussed here, the following factors were included as measures of the integrity value of recycled pulp: amount of fibre-based organic versus inorganic material in the pulp or amount of fibre fraction; chemical pulp fibres versus mechanical pulp fibres; cellulose or holocellulose or lignin content (amount of cellulose or ~lignin) of the fibres; strength of fibres; effective fibre length; fibre coarseness; fibre shape; and fines content.
These parameters can illuminate much about the strength potential of recycled pulps. In practice, however, in materials such as paper, strength also depends on the number of interference connections, i.e. bonding, and on the density of the structure. The integrity value should therefore be independent of the bonding degree and density of the pulp. On the other hand, structural density and bonding can be controlled through process parameters, including refining, wet pressing, strength chemicals, press drying, etc. Strength potential can therefore only be realized when process conditions are selected that make use of the material’s strength potential. In current papermaking practices, some key properties, including optical properties (color, light absorption and, to some degree, light scattering coefficients) are almost independent of strength potential.
The challenge with the on-line measurement was that suspension from paper for recycling containing fillers and starch did not give clear results for the material integrity value since signals from filler and from starch interfered with other measurements. So finally during this project the fibre integrity measurement could not be proven yet as valuable for characterising recovered fibre suspensions as expected. Therefore, further work is needed.
Side stream valorisation routes
Reliable statistics regarding side stream generation by the Paper and Board Industries (PBIs) are difficult to come by; in 2005 around 11 million tonnes of solid waste were generated in Europe (including from pulp production) and roughly 70% (7.7 million tonnes) thereof originated from using Paper for Recycling (PfR) as a raw material. The utilisation of PfR results in 50-100 kg of dry solid waste per tonne of packaging paper production, 170-190 kg per tonne of newsprint production, 450-550 kg per tonne of graphic paper production and 500-600 kg per tonne of tissue production. Different paper mills, however, produce different amounts of side streams of varying compositions. The main two outlets for solid side streams have historically been land-filling and incineration, although the significance of the former has greatly decreased owing to bans imposed in several European countries. In any case, both options have entailed significant costs for the sector, with recent information e.g. from Germany and the Netherlands indicating that disposing of rejects and sludges could cost up to 100 € per tonne. Reducing these costs, and even turning them into profits, depends on the ability of the sector to utilise the valuable components in the side streams by reusing them internally or converting them to intermediates or products for other parties.
The side streams generated by paper and board mills that are considered were rejects, deinking sludge and primary wastewater treatment sludge. Rejects (ragger, heavy, coarse, fine) are produced during the utilisation of PfR and they can contain fibre lumps, plastics, metals, sand and glass. The most important types of rejects in terms of their valorisation potential are coarse rejects, produced during early filtration steps in which large non-fibre objects such as plastics are removed, and fine rejects, produced during filtration steps with screens with very small slots so as to remove possible sticky content that may disturb the production process and diminish the quality of the end product; fine rejects contain a considerable amount of fibres. Deinking sludge is produced during the flotation deinking of PfR and it contains mostly short fibres/fines, inorganic fillers, as well as ink particles. Primary wastewater treatment sludge is produced during process water clarification by mechanical means and it contains mostly short fibres/fines and fillers.
A large number of side stream valorisation opportunities, either already on the market or in various stages of development, were studied and disseminated to stakeholders in the sector of ways to utilise the full potential of their raw materials. The valorisation routes presented are organised in four categories, namely application of the side stream in its current form without further processing, application by conversion into a material product, application by conversion into energy, and application by conversion into an energy carrier. These options include the following: land management, absorbent materials production, building materials production, wood-plastic composites production, fractionation, hydrolysis to fermentation feedstock, nanocellulose production, PHAs production, alginates production, incineration, gasification, pyrolysis, anaerobic digestion, secondary fuels production.
The principles of the Biobased Economy and the Circular Economy will increasingly guide business decisions. In order to adapt to such a new reality more needs to be done with regard to extracting value out of side streams in another way, by utilising their potential as raw materials and not as energy sources. An important step towards optimally valorising the content of PBI side streams should be managing to reclaim as much high-quality material from them as possible for the sector’s own operations. It can be said with some certainty that the maximum value of a tonne of reclaimed fibres will be obtained when they are applied in paper making compared to any other valorisation possibility. Developments in the field of side stream fractionation could prove to be very important in this context, allowing the sector to keep the materials that can best serve its own production process, while seeking the optimal valorisation route for the fractions that have less to offer to the PBI. Some paper makers are already trying to implement side stream valorisation by means of recirculating the materials back to their production process without fractionation; this option has shortcomings however. Reintroducing all components of a side stream to paper making can have a negative influence in terms of process parametres such as dewatering, drying, machine speed etc., or product characteristics such as strength; these adverse effects of side stream reuse can be avoided by means of fractionation.
Three valorisation routes: 1. using side streams as fillers or for strength improvement in plastic composites, 2. fractionation and reusing the fibres or other fractions in papermaking and 3. recovering fillers by pyrolysis were further studied in laboratory and/or pilot scale.
Production of plastic composites
Various types of PBI side streams, both sludges and rejects, could be used in the production of wood-plastic composites (WPCs). These are, as the name denotes, composite materials made of wood fibre, usually in the form of wood flour, and thermoplastic materials, such as PE, PP, PVC, etc. Depending on the characteristics of a given side stream, it could be applied either as a low-cost substitute for more expensive raw materials without leading to a deterioration of the end product quality, or as an additive that could improve the characteristics of the end product, for example by reinforcing it. WPCs have a growing market and various existing and potential applications. Each one of these applications sets its own requirements with regard to the characteristics and quality of the end product, which may pose higher, lower or no obstacles for the use of PBI side streams in the production process.
Fractionation
Although fractionation is included here among the identified side stream valorisation opportunities, it is in practice an intermediate step that, when undertaken, makes the pursuit of other valorisation routes possible or, at least, simpler and more efficient. The term “fractionation” denotes the separation of one or more fractions from a side stream, although it can also be applied in the pulp stream, based on the specific characteristics of each fraction’s components. When applied on side streams of the PBI, fractionation can produce fractions that are either suitable for reuse within the same sector or attractive for applications outside the paper industry; the characteristics of the new fractions make them better suited for the proposed application than the untreated side stream would be, which improves the chances of profitable side stream valorisation instead of simply less costly disposal. The extent of side stream fractionation can be determined by the paper mill, depending on its wishes. Fractionation could be as simple as separating the organic (fibres, fines) from the inorganic (fillers) material in a sludge stream or as complex as producing various organic fractions of fibres and fines with different characteristics. Currently applied or proposed examples of side stream fractionation involve technologies that are already widely used within the sector, with their optimal combination appearing to be the key factor for success.
Pyrolysis
Another form of thermal treatment, in the total absence of oxygen, pyrolysis produces a mixture of solid, gaseous and liquid products, depending on the composition of the feedstock and process conditions. Pyrolysis oil and gas can be directly used as fuels, providing the pyrolysis process itself with the energy necessary, and the oil could potentially also be converted into other fuels or chemicals. When PBI sludges are pyrolysed the mineral fraction returns as a clean secondary product, which could be applicable again as a filler for paper making if its quality is sufficiently high, while when mixed rejects are pyrolysed the metal fraction returns as a clean secondary product. Reject pyrolysis has already been commercially applied, while sludge pyrolysis is in the phase of pilot scale development.
Industrial and pilot scale demonstrations of the REFFIBRE cases
Conversion of a variety of side streams from Holmen and Utzenstorf into raw materials for the production of composites, conducted jointly by VTT and a number of different external parties in Finland, Sweden and the Swizerland. These demonstration trials for the production of composite materials have indicated that side streams can be used in injection moulding and profile extrusion. Further product development and regulatory approval for the use the side streams are needed.
Pilot-scale sludge fractionation in cooperation with Kadant-Lamort showed that it is possible to separate different fractions out of paper industry sludge. The purity of these fractions was, however, worse than anticipated. The reuse of organic fractions with paper making potential for the partial substitution of “fresh” pulp produced limited paper strength improvements and led to some dewatering problems that would in a production run appear in both the wire and press sections of the paper machine.
The goal of the trial for the recovering of fibres from fine screen rejects was to focus on the most accessible type of side stream for raw material reclamation, since fine screen rejects contain long fibres with a high brightness. Extensive testing was carried out at the Utzenstorf mill in cooperation with the Finnish SME-company Haarla Oy that has developed this fibre reclamation concept (ZRI concept). This industrial-scale demonstration has shown that stabilising the content of impurities (macro stickies) in the pulp stream after the addition of the reclaimed fibres was possible; this can be for the time being achieved by careful management of the ratios of “fresh” pulp and reclaimed fibres. The installed equipment remains in continuous use in the Utzenstorf mill for longer-term evaluation. This will determine whether reduced waste generation and improved resource efficiency are sufficiently high to justify an investment in the full-scale application of the technology.
The pyrolysis pilot trials by project SME-partner Alucha have demonstrated the separation of fillers from paper mill side streams but the quality of this reclaimed material was not found to currently be high enough for reuse within the papermaking process. The quality of these fillers needs to be further optimised in order to remove char or, alternatively, other end uses for these recovered fillers need to be studied, where their impurities will not be of such high importance as in paper production.
Resource efficiency in paper and paperboard value chains
One of the objectives of the REFFIBRE project was to calculate the value chain level impacts of energy and material savings due to the optimised use of recycled fibre. This was assessed with different case studies defined for each of the industrial companies involved in the project: Utzenstorf, Holmen and Vrancart.
To do so, a list of resource efficiency indicators used at product and process levels that take into account the potential impacts on the value chain was defined. The verification of the applicability of these resource efficiency indicators was done by evaluating the economic and environmental impacts at the value chain level with real industrial data from three paper and paperboard mills.
Methodology development
Supporting the verification of the applicability of the resource efficiency indicators, two methodological approaches for allocation in paper industry have been considered: the first method was based on ISO 14067 in which the allocation factors are defined as the Medium Fibre Age (MFA) and Medium Number of Uses (MNU); and the second method was a new approach based on findings from a fibre flow model.
A material mass flow balance was developed for the region of CEPI member countries based on data collected and provided by CEPI. The most important challenge of modelling is the fact that an increasing portion of fibres are used repeatedly in paper making cycles, i.e. unsold and consumed paper products are used again as raw materials of new paper products. The material mass flow balance allows calculating the average ash content in paper products and paper for recycling grades and the mean number of cycles the fibres in a certain paper product are used from the beginning to date or will be used from now until their end of life. The use of paper for recycling as raw material differs from paper product to paper product. Case materials and newspapers are nearly completely based on paper for recycling in many countries, whereas a certain amount of fresh fibres is necessary for high quality publication papers. Recycled newsprint and publication papers are then used as raw materials for packaging paper grades. As a result, the assumed single cycle must be divided into various connected sub cycles.
The paper production within a region of the CEPI member countries (18 member countries, 17 EU countries and Norway) can be divided into six major segments: Newsprint (NP), Other Graphic Papers (OGP), Case Materials (CM), Cartonboard (CB), Household/Sanitary (HS) and Other Paper and Board (for technical applications) (OPB). Paper products of the first four segments are recycled and used as raw material in all six segments. Paper products from the last two segments are not recycled. They are assumed to be unwanted materials in paper for recycling. Additionally, all four recycling loops are connected with each other, i.e. products from one cycle are used after recycling as raw material in the other cycle and for the production of Household/Sanitary Papers and Other Paper and Board. All six paper segments have separate entries (Virgin fibres and Filler/Pigments) and various exits. Exits of the four recycling loops are the net trade of paper products and paper for recycling and the losses due to disposal and long-time usage. The export and import of these materials not included in statistics are not taken into account in this study. Rejects from paper production are defined as a separate exit for all six paper segments.
Based on the mass flow balance the ash content can be calculated easily at every point of the flow chart. The mass flow consists of two material categories: fibrous (organic fibres and fines) and non-fibrous (pigments, fillers) materials. Calculating the composition of a mixture of multipole mass flows is trivial. If a mass flow is separated into multiple single mass flows, one should consider the way of separation. If the mass flow has been separated as a result of paper collection or sorting, the composition in terms of fibrous and non-fibrous components is assumed to be equal for every single mass flow. The separation process in a paper mill is more selective because it is focused on discharging non-fibrous components from paper for recycling. For simplification it was assumed that all rejects (except for those from tissue production) contain 40% non-fibrous materials. If paper for recycling is used for the production of sanitary or household papers, an average content of 20% non-fibrous materials was assumed in rejects. Fibres, fillers and pigments are taken into account in the mass balance, while additives are ignored.
The key input parameters of the mass flow balance for every individual recycling system are the Recycling Rate R: Percentage of paper for recycling “utilisation + net trade” compared to the total paper & board consumption, the paper for recycling Utilisation Rate U: Percentage of paper for recycling utilisation compared to the total paper production, the Reject Rate L: Percentage of losses compared to paper for recycling utilisation. The key output parameters are the Mean Fibre Age MFA: Mean number of generations a fibre has been used to date within a certain paper product and the Mean Number of Future Uses MNU: Mean number of future repeated uses of a fibre starting from the current paper product until the end of its life.
Based on a data set provided by CEPI it was shown how a mass flow balance could be derived that took the six major paper segments and their recycling-induced connections into account. The ash content in paper for recycling grades influences the quality of paper products, especially their strength properties. Valid information about the future development of ash content in paper for recycling grades will enable paper mills to plan effective countermeasures in order to guarantee a constant product quality. Similar mass flow balances can be calculated if we assume some trends for paper production and consumption in the near future.
High values of MFA (for CM and NP) express high paper for recycling utilisation rates and this will not change remarkably over the next years. The small drop in NP and OGP in the next years is due to the changing composition of paper for recycling grades used for graphic paper production. Less newsprint but a higher share of other graphic papers will become typical. High values of MNU (NP, OGP and CM) reflect the close recycling loop for those paper grades. The other grades are used over longer periods (CM) or are not recycled (HS and OPB). Fibres which have always been used in newsprint will be used about a half generation longer in 2020 than today because of their increased “chance” to be subsequently used as raw material for the growing market of packaging papers instead of for graphic papers. We can be sure that recycled newsprint fibres will be a valuable raw material for packaging papers and their recycling rate R will increase.
The highest total numbers of uses, i.e. MFA+MNU-1, occur when the fibres are used at least one time for Newsprint or Case Material production (about 5.1 to 5.2). This is mainly caused by the high paper for recycling utilisation and recycling rates. With values of 3.2 and 3.6 the total numbers are lower for fibres used for the production of other graphic papers, cartonboard and other packaging papers. Not surprisingly the total numbers are low (1.3 for HS and 1.9 for OPB) when the fibres are used for the production of sanitary and tissue papers or for other technical papers.
According to the environmental assessment, it is important to explain the different possibilities in terms of the allocation method procedures that can be used for an environmental evaluation based on life cycle assessment. The Mean Fibre Age, MFA, the Mean Number of Future Uses, MNU, and the Recycling Rate, R, can then be used to calculate the allocation factors for all paper grades. The number of cycles that a fibre is used repeatedly can be applied in allocation methods to share the burdens of fibre extraction and end-of-life operations between different life cycles. The MFA and MNU values depend solely on the mass balance that was derived from data reported by the national associations to CEPI. Some additional assumptions had to be made to fill those gaps, where no information was available. However, due to inconsistencies these assumptions need further research and can lead to changes in MFA and MNU values.
In this regard, two main approaches were considered for REFFIBRE: An allocation method that combines ISO 14067 and the Medium Fibre Age (MFA) and Medium Number of Uses (MNU) and a new approach based on findings from the fibre flow model developed in the REFFIBRE project. The main difference between both approaches is whether or not to consider the recycling credit. On the one hand, in the ISO 14067 approach, a recycling credit is discounted in order to consider the future uses of the virgin fibres. On the other hand, in the new approach based on the fibre flow model, instead of a recycling credit, allocation factors were used for the usage of the virgin fibres and recycled fibres due to the multiply usage further on in the fibre circulations.
Resource efficiency indicators
The impact evaluation of economic and environmental consequences of the REFFIBRE cases compared to the baselines scenarios at each company was carried out in co-operation with three paper mills. In the economic assessment, the main focus was to evaluate and measure economic impacts of potential cases built on value chains based on the process owner’s point of view. The evaluation of the economic impacts of the REFFIBRE cases proposed are based on indicators such as variable costs, revenues, profitability, savings and affordable investment. The environmental impacts of the reference cases were modelled using LCA methodology. Based on this, the environmental indicators for both the reference and the REFFIBRE cases were calculated. The environmental assessment was based on the evaluation of the following indicators; Global Warming Potential, Fossil fuel depletion, Freshwater eutrophication, Water footprint, Cumulative Energy Demand and Material efficiency. An eco efficiency indicator was also included as a combination of environmental and economic indicators. The case calculations for the economic and environmental assessments were conducted in cooperation with the industrial partners who provided data for the core processes.
Economic indicators:
The ability of different economic indicators to demonstrate potential impacts that could occur in the REFFIBRE cases compared to the baseline case was tested. Five indicators were in focus: variable cost, revenue, profitability, achievable savings and affordable investment.
All economic indicators were able to show the differences between the case scenarios and against the baseline (reference) scenario. The scale in the comparison was fit to all the cases. For cases with minor changes, e.g. small changes in reject amounts: increased or less rejects, the effects are small, but recognisable.
Profitability and achievable savings indicators give an overall picture of the economic effects. It must be kept in mind that profitability indicators do not account for fixed costs and that an achievable savings indicator takes into account fixed costs, such as labour, overhead and maintenance materials but not capital charges due to, e.g. investments. These indicators can also be used as stand-alone. Affordable investment is the supporting indicator for these. Affordable investment provides absolute value for maximum investment based on achievable savings, thus, giving an insight into investment possibilities.
Additional economic key figures are given for each case, where applicable: investment estimation (if available), annual savings and additional revenues that also take into account the case investment estimation, additional labour estimations for operation of the case line, return on investment (ROI) for the additional investment for each case (in the event of negative savings, ROI cannot be calculated) and possible additional investment, which is calculated based on savings and additional revenues that include case investment if estimated (must be positive, otherwise no figure is given).
Environmental indicators
The ability of six different environmental indicators to demonstrate potential impacts that occur in the REFFIBRE cases compared to a baseline case was tested. Of these indicators, material efficiency highlighted well the differences between the REFFIBRE cases and was regarded as an informative environmental indicator for sustainability screening. This indicator accounts for the total amount of useful products as well as the amount of generated waste, both of which are changing variables in the studied REFFIBRE cases. Material efficiency was the highest for “WPC ash”, where 100% of the ash fraction was utilised, and the largest amount of useful products were produced (paper plus WPC). Also the pyrolysis case showed an increase in material efficiency due to a reduction in the amount of waste and an increase in the amount of products. For one mill, the pyrolysis case was the most material efficient because all sludge components were used for pyrolysis. It must be noted, though, that in this case the sludge that goes to ceramics and to agriculture is treated as waste because no income is gained.
In the case of the global warming potential impact indicator, only minor changes were detected (per tonne paper product): There was either a minor increase in the impact or no impact at all. For example, in the case of “increased rejects”, the reduction in the use of electricity at PM was not enough to outweigh the increase in emissions caused by, e.g. the efforts for sorting more collected PfR. It must also be noted that even though the integrated production of WPC did not have an impact on the paper product global warming potential impact, it increased the absolute global warming potential impact of the production site (gradle-to-gate). Assuming that all of the ash from the power plant is used in WPC production, the total global warming potential impact would be more than doubled, when compared to the baseline case where only paper is produced. Another vital point is that the benefit of producing plastic composites by substituting polypropylene with either ash or DIP was not taken into account by calculating the avoided emissions when the use of ash or DIP reduced the need to produce polypropylene elsewhere. It was, however, estimated that the global warming potential impact of the new side stream plastic composite products was about 60-70% of that of a product composed of 100% polypropylene.
As regards the water scarcity footprint indicator, most of the cases showed no changes or a minor change. Here, the increased use of chemicals and PfR in “increasing rejects” was seen most clearly to have a negative impact on the water scarcity footprint if the side stream was not valorised in the mill.
Eco efficiency indicates the highest benefits of producing WPC, more specifically, WPC by profile extrusion since the revenue is assumed to be the same for both injection moulding and profile extrusion but the environmental impact is higher for the injection moulding due to high energy consumption.
Integration of the models to a practical guide
The research carried out shows clear benefits for engineers and managers in the mills; they can develop the processes that enhance environmental performance and maintain economic feasibility with the help of the defined indicators. The environmental indicators cover the most relevant aspects to be considered in the pulp and paper industry as well as the economic indicators that describe the affordable investment and the ROI of the new technologies tested. This allows mill managers to prioritise different action plans depending on their general strategy. Therefore, the set of indicators selected reveals to paper mill managers the environmental consequences that different changes in processes will have along the whole value chain, and, at the same time, this set of indicators support the decision-making process in the mills from an economic point of view.
In order to support paper mills better a guide was prepared that will help users to understand the models and tools developed in the assessment of economic and environmental impacts throughout the value chain. In this regard, a brief introduction of the process modelling work carried out in REFFIBRE was also presented in order to simulate future changes in paper production and separation processes when optimising materials in the stock preparation phase.
The guide details resource-efficient indicators based on life cycle thinking which were defined to represent the main impacts of the test cases within the scope of the Reffibre project. In this regard, the selected resource efficiency indicators to assess the impacts on the value chains of the different test cases were divided into economic indicators, environmental indicators and technical indicators. The guide presents also the tools which were developed to support the practical implementation of resource-efficient indicators at industry level. These tools include a software tool, based on process models which can calculate the indicator values from the data available in the mill data management systems of the industrial partners, and the methodological approach proposed for open-loop allocation in the Life Cycle Assessment (LCA) of the pulp and paper industry, based on the amount of cycles the fibres have undergone and will undergo in the future. The guide also provides the formulas required for the calculation of the economic indicators and a proposal for visualising the indicators as the practical implementation of resource efficiency indicators at industry level through the definition of the Reffibre Balanced Scorecard including the Balanced Scorecard Map and Dashboard.
Potential Impact:
Project partners have delivered a project website and updated it with six newsletters, numerous presentations in three public workshops and in the final conference, and two videos. Dissemination activities included mostly oral presentations in conferences and workshops, but several peer-reviewed articles, posters, flyers, videos and news and reports on web-sites were also among the activities.
Different allocation methods that are debated issues in LCA standardisation at the moment, were tested in the environmental assessment studies. The new methodology to take into account circular economy as paper grade specific allocation factors based on real circulation paths in the paper and board industry was developed and tested. A technical guide for the practical implementation was formulated and the allocation factors will be proposed to be included in the ISO/TS 14067 as an appendix. ISO/TS 14067 is recommended becuase it takes better into account recycling fibres several times in circular economy than PEF -method that takes into account only one recycling of the material and final recovering of the material as energy. The recycling rates, Mean Fibre Age and Mean Number of Uses can be up-dated based on the newest data reported annually by Confederation of European Paper Industries (CEPI) and allocation factors for ISO/TS 14067 can be up-dated when collection rates and volumes of different paper for recycling are changing in the future. Similar allocation factors can also be calculated for other industries in co-operation with the Industrial Associations. The sustainability assessment results can be calculated for complete value chains of paper and paperboard industry with a standardised way. The method can be used to further develop guidance in the available standards and Product Category Rules (PCRs). This additional guidance will contribute to increased harmonisation and consistency of LCA practice in the pulp and paper sector as well as to the enhanced practical implementation of LCA at industry level.
The results of the REFFIRE project can be widely used across the industry. The adoption of the developed REFFIBRE allocation method has a big impact for executing LCA calculations in cases where paper for recycling is used, if the method is implemented across the industry. The work for expanding the use of the method will be done in cooperation between VTT and ITENE. In addition, the now verified set of economic and environmental indicators will also be used in future research and consultation assignments for assessing value chain impacts of changes in process configurations. The models for fibre flow of recycled fibres, and calculation methods for mean fibre age (MFA) and mean number of future uses (MNU) have a large impact. The algorithms will be up-dated by the original developer PTS based on the data from CEPI. The algorithms from fibre flow model, R, MFA, NMU will be used to create statistical information and communicate environmental impacts to consumers and companies and the improvements in LCA methodology (allocation) will be communicated to LCA practitioners. Paper mills and paper recycling mills will be informed about the possibilities of side stream applications.
All research partners plan to actively exploit the models and tools developed within the project to provide consultation especially to the paper and board industry on sustainable and cost-effective paper and board manufacturing. Experience gathered through the demonstration trials will be used as a reference material on explaining how resource-efficiency can be improved at mills. The academic partner (TUDA) will utilise the developed process models and optimisation tools as a foundation for further research and learning material for students in the field of optimised process control for pulp and paper industry. The work with the fibre integrity number needs further research but may provide a novel software sensor to monitor the quality of pulp containing paper for recycling and the concept will be offered to manufacturers interested in fibre analysers.
The paper product and process modelling work have shown that contaminated fillers and fines are reducing resource efficiency and how the unwanted filler, fines and impurities can be separated from recycled fibre material. These unwanted materials are slowing down dewatering of the fibre furnishes in the wire and press sections and causing breaks in the wet press section. Current typical valorisation routes are incineration in the biomaterial power plant on site and using filler containing side streams in concrete industry.
The use of side streams in plastic composites and recovering fillers with pyrolysis will reduce waste to landfill and at the same time improve competitiveness of the mills. The pyrolysis is a good alternative for mills using natural gas as their energy source and/or for mills without possibility to burn the waste fractions. By taking out fillers and contaminated fines the quality of the paper or board products can be improved and/or maintained when the quality of paper for recycling will reduce in the future due to higher recycling rates and higher amounts of fillers, glues and other materials as impurities in paper for recycling and thus, lowering the raw material quality in the future. The work focused on recovering of fillers with pyrolysis from deinking sludge need to be continued in order to achieve high enough brightness level by removing char from the recovered fillers. Novel composite materials can be produced with side streams from paper industry. VTT and Holmen will continue with their development, aiming at sustainable and cost-effective material solutions and put efforts in finding applications for (bio)composites in building sector. The Utzenstorf and Vrancart mills will continue with their optimisation efforts that were started during the project to further increase the resource efficiency of their paper making process, production capacity and product quality.
List of Websites:
http://reffibre.eu
Ulla Forsström
ulla.forsstrom@vtt.fi
+358 40 8202191
