Optimization of a flexible technological chaine of CO2/H2O co-electrolysis and CO-hydrogenation into synthetic methane – CHOCHCO

CHOCHCO project deals with the issue of CO2 value chain and with the development of a novel family of solutions for renewable electricity storage through a gas vector, named “Power to gas”. The share of intermittent and renewable sources (wind farms, photovoltaics) in the French and European electricity mix increases. It induces a global geographical and time gap between electricity production and demand, which “Power to gas” and more particularly “Power to Methane” could help filling : by converting the temporary over-production of low cost renewable electricity into an energy vector, e.g. synthetic methane, and by injecting the latter into the local, national or supra-national natural gas grids, one handles both the storage and the long-distance transport of this energy (and thus mitigates the risk of local saturation of the electricity distribution grid). Besides, this solution enables to build a carbon circular economy by enhancing CO2 value. The “Power to Methane” chain is made of:
1) an electrolysis block (H2 production) or here, in the case of CHOCHCO, a high temperature co-electrolysis block (electrochemical conversion of steam and CO2 into a syngas made of H2 and CO)
2) a catalytic methanation block
3) and probably, a methane upgrading block, to reach injection specifications for the natural gas grid.
These blocks are connected both hydraulically (by the gas streams to be converted) and thermally (mainly through the recycling of methanation heat).
Three main statements lead to the approach chosen for CHOCHCO project:
•The technical and economical optimization of such a chain depends on the potential performance range of each block, which varies depending on their respective inlet pressure and composition conditions: inlet conditions impact the mass and energy efficiency of each step, their integration quality, but also the performance upkeeping over time. Yet, for both co-electrolysis and methanation, the best operation conditions (in view of this global optimization) are still to be specified, especially as experimental data are lacking.
•The overall system must be able to adapt with the variation over time of convertible electrical power load, while minimizing the induced efficiency penalty and over-costs
•To answer the need for a wide panel of installed power conversion capacities, it sounds strategically interesting to favor an architecture (for co-electrolyzer but also for méthanation reactor) based on stacks of Repeated Elementary Modules, as it is designed for electrolyzers.
CHOCHCO Project proposal is to work on this chain optimization, with a focus of the experimental and innovation task force on:
• Experimental validation of co-electrolysis performance and lifetime, depending on pressure conditions.
• Its limitations, in particular in terms of outlet gas composition (depending on varying electrical power load or pressure)
• Methanation block, with the building and testing of a novel Repeated Elementary Module, able to maintain its temperature level below 400°C and to reach high methane conversion efficiency.
At the end of the project, the following items shall have been figured out:
• Experimentation knowledge of bottlenecks and constraints for co-electrolysis, in terms of outlet gas composition (depending on varying pressure or power loads)
• Validation of a novel concept of reactor- exchanger for methanation
• Description of the optimized global chain flowsheet, with its mass and energy efficiency
• Cost of converted kWhe or stored and transported kWhPCS
•Assessment of the carbon and resources (rare earth elements) footprint of the process chain
The partners are : GDF SUEZ, from the utilities sector, potential end-user with a strong experience in gas processing and distribution; IrmaTech, for its know-how on catalytic layer deposition ; CEA LITEN, for its expertise on co-electrolysis and reactor-exchanger development ; ICPEES, for its knowledge on catalytic materials (for methane synthesis).