Green ammonia production using current and emerging electrolysis technologies

Abstract

This study investigates utilizing hydrogen produced via water electrolysis to produce green ammonia. Routes are benchmarked based on employing either alkaline electrolysis (AEC) or solid oxide electrolysis (SOEC). Both existing and possible improvements are modeled for the AEC and SOEC technologies coupled with the Haber-Bosch process to synthesize ammonia. The cost of green ammonia is estimated considering the cost of electrolyzers for both today and future projections and are compared with that of "fossil" ammonia synthesized from natural gas. Threshold CO2 taxes required to achieve cost parity between green and "fossil" ammonia are determined based on the price of natural gas and the levelized cost of electricity. It is found that whereas the green ammonia produced from a system based on AEC is cheaper today, SOEC shows to be more cost-effective, when basing the comparison on the projected future cost of the electrolyzers. Green ammonia from an SOEC-based plant is estimated to have accost of 495 €/t by 2050 with an assumed electricity price of 30 €/MWh. In the SOEC-based ammonia plants, approximately 57 % and 31 % of the steam needed for the electrolyzers can be generated through heat integration between the electrolyzer and Haber-Bosch process, for low-pressure and high-pressure electrolyzers, respectively. A good fraction of the heat can also be covered by the intercoolers of the compressors. With the projected cost for SOEC, reducing the levelized cost of electricity from 60 to 10 €/MWh would decrease the cost of green ammonia from 690 to 340 €/t by 2050.