Heat integration and part-load performance of an SOEC-coupled Haber–Bosch process

Integrating the Haber–Bosch (HB) process with high-temperature water electrolysis for hydrogen production, such as using solid oxide electrolysis cells (SOEC), offers a promising opportunity to utilize the heat generated during ammonia synthesis for steam generation to partially cover the steam demand of the SOEC. While heat integration studies are typically conducted for full load conditions, this study explores the synergies between a thermoneutral, low-pressure SOEC system and a large-scale HB process across a load range from 10.7 % to 100 % by considering individual part-load strategies. At full load, optimal heat integration increases the efficiency of the SOEC system from 79.5 % to 93.0 % (LHV, DC). This results in an overall energy consumption of 26.4 GJ t NH 3 − 1 and a Power-to-Ammonia efficiency of 70.9 % (LHV, DC). During part-load operation, the specific energy consumption increases hyperbolically due to heat losses from the SOEC and kickback capacity control of the centrifugal make-up compressors in the HB process. Down to a part load of 32.4 %, the extra waste heat generated by the compressors replaces the electrical heating and hereby the total electricity consumption only increases moderately. At lower loads, however, the adopted part-load strategies lead to an increasingly steep rise in specific energy consumption. At the minimum load of 10.7 %, the specific energy consumption is 46 % higher than at full load. • Simulation of an SOEC-coupled Haber–Bosch process including part-load strategies. • Stepwise energy integration optimization is evaluated along a load trajectory. • Optimal heat integration results in 26.4 GJ t NH 3 − 1 energy consumption at full load. • Make-up compressor waste heat can moderate efficiency decrease in medium load range. • Haber–Bosch compressors and SOEC heat loss severely reduce efficiency at low loads.