Performance evaluation, Optimization and exergy analysis of a high temperature co-electrolysis power to gas process using Aspen Plus®-a model based study

In this paper, a high temperature coelectrolysis power to gas (LTE PtG) setup was developed that was fed a stereotypical feed in CO2 one could acquire from carbon capture and sequestration (CCS) retrofit. The electrolyzer was fed an equimolar 10 kmol/s feed in water and CO2 and the electrolyzer product was composed of 38.80 mole% CO2, 30.96 mole% CO, and 30.24 mole% H-2 for a syngas conversion of 43.8%. The product from the methanation unit was only composed of 21.38 mole% CH4, with the rest (76.53 mole%) being predominantly CO2. The methanation unit was composed of only one Sabatier reactor operating at 313 degrees C, which had 90% of its product recycled back to the front end of the unit. The electrolyzer was found to have a LHV efficiency of 31.49%, and the entire HTCE PtG process was found to have an efficiency of 74.31% with methane storage and 76.49% without methane storage. A novel adaptation was developed on previous work on the exergy analysis for flow-sheet simulators which can be used for cyclic and noncyclic processes. The procedure was determined to be accurate, with irreversibilities determined across all the major subunits found to equal the irreversibility around the processes a whole. The electrolyzer was found to be responsible for the majority of the irreversibility within the setup, and this was attributed to the fact that water electrolysis is a very energy intensive process. The exergy efficiency of the electrolyzer was found to be 87.07% and that of the entire LTE PtG processes was found to be 84% with methane storage, and 87% without methane storage. In the end, it was determined that HTCE is unsuitable for the production of methane via retrofit with a methanation unit, and that it would be better suited for the production of liquid hydrocarbon fuels with much higher molecular carbon to hydrogen ratios.

Automated summary

In this paper, a high temperature coelectrolysis process was developed and analyzed. The results show that the system is more suitable for producing liquid hydrocarbon fuels with higher carbon to hydrogen ratios compared to methane production via retrofit.