Professor Dawid Hanak

Delivering net zero transition

Category: Carbon capture and use

  • On viability of power-to-gas for CO2 use

    TL;DR

    • The power-to-gas concept converts surplus renewable energy into methane (CH₄) via the Sabatier reaction:
      4H₂ + CO₂ → CH₄ + 2H₂O.
    • Methane can be injected into existing gas networks for energy storage and distribution.
    • The process shows:
      • Technical feasibility: Energy loss of ~4% for CH₄ production (excluding H₂ and CO₂ generation).
      • Economic challenges: High costs of CO₂ supply and renewable energy limit financial viability.
    • Environmental benefits depend on sourcing CO₂ from biogenic or atmospheric sources rather than fossil fuels.
    • Further research is required to:
      • Optimize efficiency and reduce costs.
      • Explore policy incentives and market opportunities

    What is power-to-gas?

    A power-to-gas concept assumes that we can use the energy from renewables during the period of reduced demand to produce hydrogen via electrolysis. To avoid the need for hydrogen compression and storage, produced hydrogen is then combined with CO2 to produce CH4. This is the so-called Sabatier reaction or CO2 hydrogenation reaction. The produced CH4 can be then injected into the existing gas networks, as shown in Figure 1 below.

    No alt text provided for this image

    Fig. 1: Representation of the power-to-gas network [1]

    This process follows the reaction below:

    4H2 + CO2 → CH4 + 2H2O

    Is the power-to-gas process technically viable?

    As you may know, process design, techno-economics and life-cycle assessments form a substantial part of my consulting and teaching activities. To refresh the curriculum of my modules, I’ve started developing new industrially-inspired case studies – methanation appeals to be an interesting concept from the process design point of view, and that is why I selected it as the very first case study to develop this year (much more to come!).

    power-to-gas process flow diagram dwsim

    Fig. 2: Process flow diagram for methanation process

    You can see the initial process design I developed in DWSIM, assuming both CO2 and H2 need to be compressed to the reaction pressure. Is this process feasible then?

    Well, my initial analysis showed that this process would consume 0.59 kWh (2.12 MJ) of renewable energy to produce 1 kg of CH4 – and this doesn’t account for the energy required for H2 or CO2 production. Considering the heating value of methane of 55 MJ/kg, we are looking at the energy loss of about 4% for this process itself.

    Economics and environmental performance of power-to-gas

    Finally, it’s important to talk about the economics and environmental performance of such a concept. I’m yet to complete the full assessments and optimization of the layout, but my previous work can shed some light on these aspects.

    power-to-gas process flow diagram dwsim techno-economic viability

    Fig. 3. Economic viability of power-to-gas concept [2]

    In my previous collaborative work with the research group led by Prof Luis Romeo [2], we evaluated the techno-economic viability of the power-to-gas process integrated with the oxy-combustion process for CO2 supply.

    The economic analysis (Figure 3), showed that because of the costs associated with CO2 supply, the power-to-gas project may not be viable under the conditions we considered. This would, of course, change considering the recent changes in carbon markets.

    And this brings me to the final point – the environmental implications. Naturally, we would like to use CO2 captured from the power plants so that we could add more value to it. But if that CO2 comes from the combustion of fossil fuels, then we merely shift the emission point. Sure, we could create economic value through this process, but it would not help us solve the global warming challenge.

    So where such CO2 could come from? We would need to consider biogenic and atmospheric sources, but this would definitely have implications on process economics.

    More work is needed – happy to collaborate!

    Conclusions

    In summary, while the power-to-gas process demonstrates technical promise with manageable energy losses, its economic and environmental viability remains contingent upon advancements in CO₂ sourcing and reductions in associated costs. Further research and optimization are necessary to enhance the overall efficiency and economic attractiveness of the system. Collaborative efforts and continued exploration of innovative solutions will be essential to overcome the current barriers and fully harness the potential of power-to-gas technologies in the transition to a sustainable energy future.

    PS: If you need consultancy or training in process design and process economics, green energy transition, industrial decarbonisation, and carbon removal technologies, I am open to discussing how we can collaborate together!

    References

    1. Bailera M, Lisbona P, Llera E et al. Renewable energy sources and power-to-gas aided cogeneration for non-residential buildings. Energy 2019;181:226–38.

    2. Bailera M, Hanak DP, Lisbona P et al. Techno-economic feasibility of power to gas–oxy-fuel boiler hybrid system under uncertainty. International Journal of Hydrogen Energy 2019:9505–

    Frequently Asked Questions:
    Power-to-Gas and Methanation Process

    1. What is the power-to-gas concept?

    The power-to-gas concept uses surplus renewable energy to produce hydrogen (H₂) through electrolysis. The hydrogen is then combined with carbon dioxide (CO₂) in a reaction known as the Sabatier reaction to produce methane (CH₄). This methane can be injected into existing gas networks, providing a way to store and transport renewable energy.

    2. What is the Sabatier reaction?

    The Sabatier reaction is a chemical process where CO₂ reacts with H₂ to produce CH₄ and water (H₂O):
    4H₂ + CO₂ → CH₄ + 2H₂O
    This reaction is exothermic, meaning it releases heat, and it requires specific catalysts and operating conditions to achieve efficient conversion.

    3. How efficient is the power-to-gas process?

    The initial analysis indicates that the process consumes 0.59 kWh (2.12 MJ) of renewable energy to produce 1 kg of CH₄, resulting in an energy loss of approximately 4%. However, this does not include the energy required to produce H₂ and CO₂, which affects overall efficiency.

    4. Is the power-to-gas process economically viable?

    Economic viability depends on several factors, including the cost of renewable electricity, hydrogen production, and CO₂ supply. Current analyses show that high costs associated with CO₂ supply, particularly from fossil fuel combustion, can render the process unfeasible. However, changes in carbon markets and alternative CO₂ sources may improve its economic outlook.

    5. What are the environmental benefits of power-to-gas?

    The environmental benefits depend on the source of CO₂. Using CO₂ from biogenic or atmospheric sources supports a circular carbon economy and helps mitigate climate change. However, using CO₂ from fossil fuel combustion shifts emissions without reducing net greenhouse gas levels.

    6. Where can the CO₂ for this process come from?

    CO₂ can be sourced from power plant flue gases, industrial emissions, or biogenic and atmospheric sources. While fossil-based CO₂ is more readily available, it does not offer net emissions reduction. Biogenic and atmospheric CO₂ sources are more sustainable but often come with higher costs and technological challenges.

    7. How does power-to-gas compare to other energy storage solutions?

    Power-to-gas offers the unique advantage of utilising existing gas networks for energy storage and distribution. Unlike batteries, which are limited in storage capacity and duration, power-to-gas can store large amounts of energy for extended periods. However, its efficiency and cost-effectiveness are lower compared to some battery technologies.

    8. What are the next steps to make power-to-gas more viable?

    Further research is needed to:

    • Improve the efficiency of the Sabatier reaction.
    • Optimize the integration of hydrogen production and CO₂ capture.
    • Reduce the cost of renewable energy and CO₂ supply.
    • Explore policy and market incentives to support deployment.

    9. Can I collaborate on research in this area?

    Yes, collaborations are welcome! If you’re interested in working on process design, optimization, or techno-economic and environmental assessments, feel free to reach out.

    10. Why did you choose methanation as a case study?

    Methanation is an industrially relevant and technically challenging process that showcases key aspects of process design, optimization, and sustainability assessment. It serves as an excellent example for educational purposes and aligns with my expertise in process design and consulting.

  • Unlocking the potential of waste-to-energy and CCUS synergy: Redefining negative emissions in the UK

    TL;DR

    • WtE plants contribute significantly to UK emissions, yet play a vital role in waste management and energy generation.
    • Traditional CCUS methods like amine scrubbing are not ideal for WtE due to high energy demands, negatively impacting WtE’s energy output and economic viability.
    • Our research at the Net Zero Industry Innovation Centre explores CaL as a cost-effective and energy-efficient alternative for CO2 capture in WtE plants.
    • CaL offers significant advantages: Competitive cost of CO2 avoided: Lower than traditional methods, potentially incentivising WtE operators to adopt CCUS. Minimal efficiency penalties: CaL maintains or even increases WtE’s energy generation capacity unlike amine scrubbing. Net negative emissions potential: Captured CO2 exceeds plant emissions, contributing to negative emissions goals.

    Crossroads for WtE and CCUS: Redefining Sustainability in the UK

    The UK’s Ten Point Plan for a Green Industrial Revolution boldly aspirates for a cleaner future. Carbon Capture, Utilisation, and Storage (CCUS) is critical in delivering this aspiration. The East Coast Cluster stands in the vanguard of this ambitious strategy, aiming to remove nearly 50% of the UK’s industrial cluster emissions and support an average of 25,000 green jobs annually between now and 2050. While most of the current CCUS projects focus on low-carbon power generation or hydrogen supply, another promising pairing can contribute to delivering the net zero aspirations. Although not prioritised in the UK Government Track-1 CCUS cluster sequencing exercise, integration of waste-to-energy (WtE) and CCUS can deliver negative CO2 emissions and reduce the amount of landfilled waste.

    Notably, while WtE offers a valuable waste management solution and generates energy, its contribution to the CO2 emissions in the UK is substantial. In the Teesside Cluster alone, which is a part of the East Coast Cluster, WtE accounts for a staggering 18% of total greenhouse gas emissions. The projections are also concerning, as the UK’s WtE has been forecasted to emit up to 20 MtCO2e annually by the mid-2020s. Such a figure is higher than 11 MtCO2e annually reported in 2021 for industrial processes in the UK. The preliminary work on WtE and CCS integration by the Energy Systems Catapult showed that the specific CO2 emissions from WtE are 600 gCO2/kWh (excluding biogenic carbon), and flue gas contains up to 12%vol CO2. As a result, their ESME model demonstrated that unabated WtEs must be phased out by 2040 due to reduced carbon budgets, indicating the need to develop low-carbon alternatives.

    This is where CCUS can play a role. By strategically integrating CCUS into existing WtE plants, the UK can achieve a two-pronged victory: significantly curbing its carbon footprint and transforming WtE into a net negative emitter of greenhouse gases. Yet, unlocking the full potential of WtE-CCUS synergy requires careful consideration. Existing CCUS solutions, while potentially effective in larger-scale applications, pose challenges for WtE due to their high energy demands and potential impact on energy output and profitability. The search for alternative CCUS technologies with lower energy penalties and costs becomes paramount.

    Therefore, the future of WtE in the UK’s decarbonisation strategy hinges on two pillars: embracing innovation in CCUS technologies tailored to WtE applications and forging strategic partnerships to navigate the technological and economic complexities.

    The Challenge: Decarbonising WtE without hindering energy or economic performance

    While amine scrubbing has emerged as the CCUS technology of choice for many industrial applications, such as the Net Zero Teesside Power, its application to WtE presents unique and prohibitive challenges. This mature approach to CO2 capture stumbles on the high demand for steam required for its regeneration. In the UK, WtE plants often play a critical role in supplying heating, electricity, and/or industrial steam. Implementing amine scrubbing can have a detrimental impact on these vital functions, jeopardising both WtE’s energy output and economic viability.

    The severity of these challenges is well documented. An AECOM study revealed that amine-based capture units could consume a staggering 66% of the total thermal input to the steam turbine at a combustion-based WtE plant. This translates to a significant reduction in electricity generation, a key revenue stream for WtE facilities. Further research by Magnanelli et al. confirmed this concern, demonstrating that amine scrubbing integration can lead to a 30% reduction in power output and a 12% reduction in heat output from a typical WtE plant. Supplying such an amount of steam will not only be limited by technical considerations but will also substantially impair the economic viability of the WtE plant.

    Adding to the complexity is the lack of readily available information regarding post-combustion CO2 capture for gasification-based WtE plants. These facilities, utilising a different waste processing technology, present additional unknowns regarding CCUS compatibility. This knowledge gap further accentuates the need for alternative CCUS solutions that can overcome the limitations of amine scrubbing and effectively decarbonise WtE without compromising its energy production and economic viability.

    A Promising Solution: Exploring the potential of carbonate looping

    Amidst the challenges of WtE decarbonisation with mature amine scrubbing, our research at the Net Zero Industry Innovation Centre has focused on emerging carbonate looping (CaL) technology. Unlike steam-hungry amine scrubbing, CaL offers a potentially cost-effective and energy-efficient solution for capturing CO2 from WtEs. Our past studies have demonstrated the remarkable cost advantages of CaL. Hanak et al. revealed that post-combustion CaL retrofits to coal-fired power plants could achieve a competitive cost of CO2 avoided (~£40/tCO2), significantly lower than the range reported for amine scrubbing by Wood (ranging from £73 to £173/tCO2). This translates to a potential financial incentive for WtE operators considering CO2 capture.

    However, the benefits of CaL extend beyond cost savings. Compared to amine scrubbing, CaL exhibits a demonstrably lower impact on energy efficiency (<7% points) and can actually increase the power output by 20-50%. This means that WtE facilities adopting CaL can maintain their current energy generation capabilities while simultaneously capturing CO2.

    However, our research pushes the boundaries even further. We have proposed calcium looping combustion (CaLC) as a potential breakthrough technology for WtE decarbonisation. By replacing conventional incinerators with indirect heat transfer in the calciner, CaLC can minimise efficiency penalties to an impressive <3% points. For power generation from coal, our research showed a remarkably low cost of CO2 avoided of <£35/tCO2. Notably, municipal solid waste is a lower-quality fuel than conventional fossil fuels. Therefore, the expected efficiency penalties and cost of CO2 avoided are expected to be higher. Yet we forecast it will still be substantially lower than the mature amine scrubbing retrofits. At NZIIC, we are currently working with the UKCCSRC and the major waste-to-energy organisations in the Teesside Cluster to assess the feasibility of such technology.

    Conclusion

    As the UK embarks on its Green Industrial Revolution, the East Coast Cluster stands as a beacon of ambition, aiming to capture nearly half of the UK’s industrial emissions. While the focus is low-carbon power and hydrogen, an often-overlooked pairing holds immense potential: integrating Waste-to-Energy (WtE) with Carbon Capture, Utilisation, and Storage (CCUS). Such a synergy offers a two-pronged victory, curbing the nation’s carbon footprint and transforming WtE into a net negative emitter.

    However, unlocking this potential requires navigating a complex landscape. While effective in larger applications, traditional amine scrubbing proves problematic for WtE due to its high energy demands and detrimental impact on energy output and profitability. The search for alternative CCUS solutions with lower energy penalties and costs becomes paramount.

    Our research at the Net Zero Industry Innovation Centre focuses on carbonate looping (CaL) as a promising alternative. Unlike amine scrubbing, CaL presents a cost-effective and energy-efficient solution. Studies indicate a competitive cost of CO2 avoided and minimal efficiency penalties. This allows WtE operators to embrace carbon capture without compromising their core functions.

    Acknowledgement

    This publication is based on research conducted within the “Techno-economic and carbon footprint assessment of advanced waste-to-energy with carbon capture and storage for East Coast Cluster” project funded by the UK Carbon Capture and Storage Research Community