A novel direct heat exchange concept helps energy-intensive industries reuse waste heat
Energy-intensive industries are important emitters of greenhouse gases in Europe, with the cement, chemical and steel sectors dominating industrial emissions. Finding solutions to drive down energy consumption and emissions is a top priority. Exploiting waste heat fosters a circular economy and lower fossil fuel-derived-energy consumption and emissions. The EU-funded TASIO project set out to support that effort with a new generation of waste heat recovery technology targeting energy-intensive industrial applications in the cement, glass, steelmaking and petrochemical industries, but equally useful elsewhere.
Eliminating the go-between
Waste heat recovery systems transfer the heat to a gas or liquid whose thermal energy can then be converted to electrical or mechanical energy. The generated energy can be consumed directly by the industrial plant where it is generated or connected to the grid. The organic Rankine cycle (ORC) is ideal for waste heat recovery and reuse. Instead of water as in the ordinary Rankine cycle, it uses an organic fluid that has a much lower boiling point. The vapour powers a turbine that can be directly coupled to a generator to produce electricity or to a compressor to compress air for mechanical work. The ORC is typically implemented with indirect exchange of heat to the organic fluid via a heat transfer fluid. Direct heat exchange is the subject of intensive research within the automotive and transport sectors for exploitation of exhaust heat. However, as project coordinator Pedro Egizabal of Tecnalia explains, “TASIO was the first application of direct heat exchange-based ORC technology to energy-intensive industries. Compared to conventional ORC technology, it eliminates the intermediate heat transfer fluid, makes the process simpler, enhances heat transfer efficiency and reduces maintenance costs.”
Powering a revolution in sustainability
Egizabal continues: “We successfully demonstrated the technical and economic feasibility of the direct heat exchange ORC technology to produce up to 2 Megawatts of electric capacity in an operating cement plant. The system also reduced water consumption; lower operating temperature eliminates the need for a conditioning tower (with a high-pressure pump providing water to cool the waste gas).” Furthermore, the team validated a small-scale demonstrator of a 15 kW ORC module to generate compressed air. Fundamental to project success was the development of new coating/steel substrate combinations for production of components for the higher-temperature conditions relative to a conventional ORC. Finally, researchers conducted feasibility and cost analyses associated with applying ORC technology to a pilot plant for the treatment of petrochemical sludge.
Incentivising a sustainability transition
Although energy-intensive industries account for more than half of the energy consumption of EU industry, they produce goods and materials that enable reduction of emissions in other sectors like transport, construction and power generation. They are also critical to many strategic value chains. Egizabal concludes: “TASIO has successfully used ‘dirty’ industrial processes and waste gases to produce electricity through sustainable ORC technology. Public policies and incentives that increase the use of such technologies will enhance the competitiveness and sustainability of these energy-intensive industries that have direct and indirect impact on job creation and the economy.”
Keywords
TASIO, heat, energy, waste heat, energy-intensive industries, direct heat exchange, waste heat recovery, organic Rankine cycle, cement
