A theoretical investigation of power-to-green syngas production using low- and high-temperature electrolyzers

This work proposes and evaluates an integrated power-to-green syngas system that couples a natural-gas-fired Allam–Fetvedt cycle with low- and high-temperature CO2–H2O co-electrolysis. Aspen HYSYS is used to model a 795 MW gross/437 MW net AF cycle supplying high-purity CO2 and H2O, which are partially diverted to electrolyzers while the remainder is recycled within the closed CO2 loop. Three syngas production configurations are assessed: parallel PEM+AEM electrolyzers, a single co-AEM electrolyzer, and a co-SOE electrolyzer. These designs enable flexible H2/CO ratios between 0.25 and 2.0 while internally generating O2 that offsets part of the AF cycle's air-separation demand. At 437 MW net power, the integrated system produces approximately 36,000–98,000 kg h−1 of syngas while consuming only 1–3% of the AF cycle's CO2 output and 7–35% of its H2O, maintaining effective resource self-sufficiency. A techno-economic analysis shows that the levelized cost of syngas ranges from about 1.25 to 3.85 $ kg−1 under conservative assumptions and decreases to 1.2–3.2 $ kg−1 under optimistic conditions, with PEM+AEM hybrids offering the lowest costs. Overall, AEM-based and hybrid systems integrated with the AF cycle emerge as promising pathways for flexible, near-zero-emission green syngas production.