Thermodynamic Assessment of the Conversion of a Typical CCGT Power Plant to a Fully E-Fuel Fired Unit

With the increasing need for flexibility in the electricity grid, combined with longer periods of low electricity prices due to an oversupply of renewable electricity, alternative solutions which include the production of carbon-free fuels in combination with the use of combined cycle power plants, are identified as a possible solution. These so-called power-to-gas-to-power solutions (P2G2P), with hydrogen and ammonia as fuel, require further research to determine their feasibility. Within this scope, the European collaborative project FLEXnCONFU aims at providing an answer toward this feasibility. The specific project idea is to recover excess grid power to produce hydrogen through proton exchange membrane (PEM) water electrolysis. Then, this hydrogen could be stored directly, or it could be fed in an ammonia synthesis process. Finally, the decarbonized fuels (ammonia and/or hydrogen) are burned in the gas turbine to produce electricity with no greenhouse gases (GHG) emission. The aim of this paper is to evaluate the impact of P2G2P system integration in a power plant. Different concepts have been applied to an existing ENGIE plant, based in Belgium, with the idea of installing all the technologies (electrolyzers, compressors, and storage, as well as ammonia fabrication units) on the power plant site. Simulations show that a considerable production time is needed to operate the plant for several hours using these e-fuels. Moreover, hydrogen storage requires an extremely huge footprint, hence it looks more reasonable to operate ammonia synthesis to store large quantities of decarbonized fuel, given the site space constraints. Additionally, Aspen plus models have been realized to evaluate the global efficiency of the P2G2P systems as well as the specific cooling requirements of the added technologies. The global efficiency for the P2H2P (with hydrogen) system is 32%. For the P2A2P (with pure ammonia) and power-to-amonia-to-hydrogen-to power (part of the produced ammonia is cracked to recover hydrogen, feeding the combustion chamber of the combined cycle gas turbine (CCGT) with a blend of 70% NH₃ and 30% H₂) systems, this global efficiency is reduced, respectively, to 24% and 19%. From these results, it is thus apparent that there remain still several challenges that need to be overcome to make P2G2P an efficient way to decarbonize electricity production. These main challenges are: Increase the efficiency of the transformation processes to limit the energy losses; Enhance hydrogen storage technologies to limit the footprint or develop an efficient hydrogen distribution; Reduce the cost of P2G technologies and especially of PEM electrolyzers; Progress on decarbonized fuels combustion and specifically limit NO_x emission for the NH₃ firing configuration.