System Evaluations and Life-Cycle Cost Analyses for High-Temperature Electrolysis Hydrogen Production Facilities
This report presents results of system evaluations and lifecycle cost analyses performed for several different commercial-scale high-temperature electrolysis (HTE) hydrogen production concepts. The concepts presented in this report rely on grid electricity and non-nuclear high-temperature process heat sources for the required energy inputs. The HYSYS process analysis software was used to evaluate both central plant designs for large-scale hydrogen production (50,000 kg/day or larger) and forecourt plant designs for distributed production and delivery at about 1,500 kg/day. The HYSYS software inherently ensures mass and energy balances across all components and it includes thermodynamic data for all chemical species. The optimized designs described in this report are based on analyses of process flow diagrams that included realistic representations of fluid conditions and component efficiencies and operating parameters for each of the HTE hydrogen production configurations analyzed. As with previous HTE system analyses performed at the INL, a custom electrolyzer model was incorporated into the overall process flow sheet. This electrolyzer model allows for the determination of the average Nernst potential, cell operating voltage, gas outlet temperatures, and electrolyzer efficiency for any specified inlet steam, hydrogen, and sweep-gas flow rates, current density, cell active area, and external heat loss or gain. The lifecycle cost analyses were performed using the H2A analysis methodology developed by the Department of Energy (DOE) Hydrogen Program. This methodology utilizes spreadsheet analysis tools that require detailed plant performance information (obtained from HYSYS), along with financial and cost information to calculate lifecycle costs. There are standard default sets of assumptions that the methodology uses to ensure consistency when comparing the cost of different production or plant design options. However, these assumptions may also be varied within the spreadsheets when better information is available or to allow the performance of sensitivity studies. The selected reference plant design for this study was a 1500 kg/day forecourt hydrogen production plant operating in the thermal-neutral mode. The plant utilized industrial natural gas-fired heaters to provide process heat, and grid electricity to supply power to the electrolyzer modules and system components. Modifications to the reference design included replacing the gas-fired heaters with electric resistance heaters, changing the operating mode of the electrolyzer (to operate below the thermal-neutral voltage), and considering a larger 50,000 kg/day central hydrogen production plant design. Total H2A-calculated hydrogen production costs for the reference 1,500 kg/day forecourt hydrogen production plant were $\$$3.42/kg. The all-electric plant design using electric resistance heaters for process heat, and the reference design operating below the thermal-neutral voltage had calculated lifecycle hydrogen productions costs of $\$$3.55/kg and $\$$5.29/kg, respectively. Because of its larger size and associated economies of scale, the 50,000 kg/day central hydrogen production plant was able to produce hydrogen at a cost of only $\$$ 2.89/kg.