Retrofitting Russian natural gas thermal power plants for hydrogen production: comparative assessment of steam extraction and return strategies

Retrofitting existing natural gas thermal power plants (TPPs) for integrated hydrogen production requires minimizing the inherent thermodynamic penalty of steam extraction. This study develops a power loss factor (PLF)-based thermo-economic framework to analyze and optimize this trade-off. A validated model of a large-scale Russian TPP (TPP-22) is coupled with a modular high-temperature steam electrolysis (HTSE) system simulated in Aspen HYSYS. 

Two steam-condensate reintegration strategies are rigorously compared: a conventional steam-condenser scheme and a novel steam-heater scheme that redirects flow to the regenerative feedwater system. The steam-water cycle of the host TPP is modeled and validated using United Cycle against real operational data, achieving an error of less than 0.02 % after accounting for water injection for steam temperature control. The HTSE modules are simulated in Aspen HYSYS as an exact replica of the validated Idaho National Laboratory reference design. A comprehensive uncertainty quantification is performed, including sensitivity analysis (tornado diagram), seasonal performance assessment (summer/ winter modes), and SOEC degradation analysis over a 5-year period (0.5-0.75 % per 1,000 hours). Results show that the steam-heater configuration reduces the PLF from 1.7 % to 0.1 % in summer and from 5.6 % to 4.9 % in winter, preserving up to 14 MW of electrical output compared to the steam-condenser scheme. This improvement translates into a consistent reduction of the levelized cost of hydrogen (LCOH₂) by approximately 16-17 % under both 2021 and 2025 Russian economic conditions, yielding average LCOH2 values of 3.56-6.51 $/kg for hydrogen production rates of 0.2 kg/s per module. The specific CO2 emissions of the proposed system are 0.056 kg CO₂/kg H2, which is two orders of magnitude lower than grey hydrogen and significantly below green hydrogen from renewable electrolysis. The results provide a critical thermal design guideline, demonstrating that condensate return strategy is a decisive parameter for the efficiency and economic viability of repurposing thermal power assets for hydrogen co-generation.

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