Optimized Flow Sheet for a Reference Commercial-Scale Nuclear-Driven High-Temperature Electrolysis Hydrogen Production Plant

Abstract

This report presents results from the development and optimization of a reference commercialscale high-temperature electrolysis (HTE) plant for hydrogen production. The reference plant design is driven by a high-temperature helium-cooled reactor coupled to a direct Brayton power cycle. The reference design reactor power is 600 MWt, with a primary system pressure of 7.0 MPa, and reactor inlet and outlet fluid temperatures of 540° C and 900°C, respectively. The electrolysis unit used to produce hydrogen consists of 4.176 × 10 6 cells with a per-cell active area of 225 cm 2 . A nominal cell area-specific resistance, ASR, value of 0.4 Ohm·cm 2 with a current density of 0.25 A/cm 2 was used, and isothermal boundary conditions were assumed. The optimized design for the reference hydrogen production plant operates at a system pressure of 5.0 MPa, and utilizes an air-sweep system to remove the excess oxygen that is evolved on the anode side of the electrolyzer. The inlet air for the air-sweep system is compressed to the system operating pressure of 5.0 MPa in a four-stage compressor with intercooling. The overall system thermal-to-hydrogen production efficiency (based on the low heating value of the produced hydrogen) is 49.07% at a hydrogen production rate of 2.45 kg/s with the high-temperature helium-cooled reactor concept. The information presented in this report is intended to establish an optimized design for the reference nuclear-driven HTE hydrogen production plant so that parameters can be compared with other hydrogen production methods and power cycles to evaluate relative performance characteristics and plant economics.iii

Heat exchanger temperature response for duty-cycle transients in the NGNP/HTE

“…The electrolytic cell is operated exothermically compared to a more recent trend where it is operated thermal neutral. [6] In [6], an ASR of 0.4 ohms-cm 2 , current density of 0.25 amp/cm 2 , and cell outlet temperature of 850 C compare with values of 0.7 ohms-cm 2 , 0.45 amps/cm 2 , and 970 C, respectively, used in the present work. The values of the main operating parameters in the Reference Interface plant are summarized in Table I.…”

System Analyses of High and Low-Temperature Interface Designs for a Nuclear-Driven High-Temperature Electrolysis Hydrogen Production Plant

“…The UniSim power-cycle model was initially described in [2]. The reactor power source shown at the bottom left of Figure 1 supplies 600 MW t of energy to the electrolysis process.…”

“…For the integrated INL Reference Design configuration shown in Figure 1, which incorporated the electrolysis model shown in Figure 2, the calculated total number of electrolysis cells required was 4,000,900 assuming a cell area of 225 cm 2 , a cell current density of 0.25 amperes/cm 2 , and a per cell area specific resistance (ASR) of 0.4 ohm-cm 2 . The UniSim calculated power cycle efficiency in this case was 53.2% and the calculated overall hydrogen production efficiency was 47.1%.…”

Economic Analysis of a Nuclear Reactor Powered High-Temperature Electrolysis Hydrogen Production Plant

“…In addition, the availability of high temperature process heat from these advanced reactors can further enhance hydrogen production efficiencies. Based on these results, a high-temperature gas-cooled nuclear reactor coupled to a helium recuperated Brayton power cycle (as shown in Figure 2 with 600 MW t power and a power conversion efficiency of 53.2%) was selected as the reference power source [12]. The primary helium coolant in Figure 2 exiting the reactor at 900°C, is split at T1, with more than 85% of the flow going to the power cycle and the remainder ( 15%) going to the intermediate heat exchanger (IHX) to provide process heat for the HTE loop.…”

“…Based on the results of these parametric studies, an air-sweep system was selected for the reference design. While slightly higher overall hydrogen production efficiencies (an increase of 1.0 -1.5%) can be achieved when no gas sweep system is used, concerns with the handling of the high temperature oxygen product gas led to the decision to use an air-sweep system for oxygen removal from the electrolyzer anode [12].…”