Leveraging Residual Heat for eFuel Production
Using residual heat from industrial processes is an effective way to improve efficiency and recover thermal energy that would otherwise go to waste. Often repurposed for applications like district heating, this surplus heat can also support eFuel production by preheating raw materials and reducing reliance on additional energy sources, contributing to more sustainable and cost-effective operations.
How Residual Heat Can Be Used in eFuel Production
Residual heat generated within eFuel facilities can be repurposed to improve the energy efficiency of eFuel production as well as supporting district heating networks. This dual use of thermal energy enhances the circularity of the process by ensuring that even the heat produced during eFuel manufacturing contributes to broader energy efficiency goals.
In the case of eMethanol production, residual heat can be integrated at various stages to reduce reliance on additional fuels or electricity, making the overall process more sustainable. Here’s how:
Hydrogen Production: Green hydrogen, essential for eMethanol production, is generated through electrolysis, which splits water into hydrogen and oxygen using electricity. Electrolyzers operate most efficiently within a specific temperature range, generating heat during operation. This residual heat can be harnessed internally to preheat the incoming water, reducing the need for additional energy to reach optimal operating temperatures. By repurposing this thermal energy through internal heat exchange, the overall efficiency of the process is improved while minimizing energy demand.
CO₂ Separation: In CO₂ separation, flue gases are directed into an absorber unit, where a solvent captures the CO₂ molecules while letting other gases pass through. Once the solvent is saturated with CO₂, it is pumped into a desorber unit, where heat is used to release the CO₂. At this stage, residual heat can be used to reduce the energy needed for heating, making the process more efficient. >> Read more about Carbon Capture here
Methanol Synthesis: CO₂ and hydrogen are combined in a catalytic reaction to create methanol. This reaction produces heat which is also required to ensure that the catalyst and other parts of the process work efficiently. Residual heat can be used to preheat the gases before they enter the reactor or maintain the reactor’s temperature during the process.
Distillation: After the methanol synthesis process, the resulting methanol mixture contains approximately 40% water, which must be removed through distillation to achieve a higher concentration of methanol. This stage requires significant energy to separate methanol from water and other hydrocarbons. While most of this energy is provided by an external boiler, residual heat can supplement the process, improving overall energy efficiency.
Preheating Feedstocks and Water: Feedstocks and water used in eFuel production can also benefit from residual heat. By preheating materials like CO₂ and water before they enter the reactors or electrolysers, residual heat reduces the need for additional energy inputs such as electricity.
Supporting District Heating: Waste heat that isn’t reused within the eMethanol production process can instead be redirected to district heating networks, provided it meets the required temperature or is upgraded using heat pumps. This ensures that all available thermal energy is effectively utilised. By supplying district heating, eFuel facilities improve resource efficiency while contributing to sustainable urban energy systems.
Learn more about the different stages in the eMethanol production process:
Environmental Benefits
Although eFuel is considered a sustainable fuel, its production involves energy-intensive processes that contribute to its environmental impact. Using residual heat can significantly reduce the carbon footprint, especially when combined with renewable energy sources and efficient production setups. The key benefits include:
Reduction in CO₂ Emissions: By using waste heat, eFuel facilities can reduce the need for fossil fuels in the production process, significantly lowering CO₂ emissions.
Enhancing Energy Efficiency: Capturing and reusing residual heat makes the entire eFuel production process more efficient, reducing overall energy demand and maximizing the utility of existing resources.
Contribution to a Circular Economy: Using residual heat embraces the concept of a circular economy, where waste from one process becomes a resource for another. This minimizes inefficiencies and maximizes resource efficiency, creating a closed-loop system that is more sustainable over time.
Technological Solutions to Enhance Residual Heat Utilization
Innovations in technology are making it easier to tackle the challenges of integrating residual heat into eFuel production. Advanced heat storage systems allow heat to be stored and used when needed, ensuring a steady supply of thermal energy. Heat pumps are another valuable tool that can raise the temperature of lower-grade waste heat, making them suitable for use in eFuel production processes. These technologies help balance fluctuations in heat supply and improve the overall efficiency of the system, particularly in industries with variable output.
Conclusion: A Circular Energy Solution for eFuel Production
Integrating residual heat into eFuel production processes offers a practical and sustainable solution to improve energy efficiency and reduce overall energy demand.
By repurposing waste heat for critical stages such as hydrogen production, CO₂ separation, methanol synthesis, distillation, and feedstock preheating, eFuel facilities can make better use of available resources while lowering reliance on external energy sources. This not only enhances the economic and environmental performance of eFuel production but also supports broader efforts toward creating a circular and sustainable energy system.
Content contributor
Thomas Stenhede, Senior Technical Adviser, Liquid Wind