Analysis of a phosphoric acid fuel cell-based multi-energy hub system for heat, power, and hydrogen generation

Abstract

Natural gas (NG) is delivered to homes and businesses through a complex pipeline network that mainly consists of high-pressure main feed lines and many low-pressure local distribution lines. To date, throttling valves have been employed to reduce the NG pressure between the two types of pipeline, leading to the loss of the work potential generated by the expansion of pressurized NG in the NG supply chain. As a result, research is currently underway to replace throttling valves with turbo expander generators (TEGs) to obtain additional work power. In this study, a multi-energy hub system consisting of phosphoric acid fuel cell (PAFC) and TEG modules is proposed and analyzed using ASPEN-HYSYS® modeling and simulations. The key concept underlying the system configuration is to maximize overall system efficiency through the integration of exothermic PAFC and endothermic TEG operations. When the TEG system is combined with four 460kWe PAFC stacks, the simulation results show that roughly 1.73 MWe of power can be produced in the TEG system via the expansion of a 28,000 kg/h NG stream. However, when the PAFC stack runs under hydrogen production mode (which requires high voltage operation), an additional heating source is required to fully deliver the expansion work generated by the NG flow within the TEG system. This study clearly illustrates the beneficial features of the proposed multi-energy hub system in terms of thermal integration and overall efficiency but also reveals that the system configuration and operation need to be carefully optimized in order to advance the technology.