Design of a Pilot SOFC System for the Combined Production of Hydrogen and Electricity under Refueling Station Requirements

Abstract

The objective of the current work is to support the design of a pilot hydrogen and electricity producing plant that uses natural gas (or biomethane) as raw material, as a transition option towards a 100% renewable transportation system. The plant, with a solid oxide fuel cell (SOFC) as principal technology, is intended to be the main unit of an electric vehicle station. The refueling station has to work at different operation periods characterized by the hydrogen demand and the electricity needed for supply and self‐consumption. The same set of heat exchangers has to satisfy the heating and cooling needs of the different operation periods. In order to optimize the operating variables of the pilot plant and to provide the best heat exchanger network, the applied methodology follows a systematic procedure for multi‐objective, i.e. maximum plant efficiency and minimum number of heat exchanger matches, and multi‐period optimization. The solving strategy combines process flow modeling in steady state, superstructure‐based mathematical programming and the use of an evolutionary‐based algorithm for optimization. The results show that the plant can reach a daily weighted efficiency exceeding 60%, up to 80% when considering heat utilization.

A Cogeneration System Based on Solid Oxide and Proton Exchange Membrane Fuel Cells With Hybrid Storage for Off-Grid Applications

“…It should also be noted that the performance of the polygeneration SOFC unit was based on the optimization results reported in (Pérez-Fortes et al, 2018), in a case where a specific set of operational conditions were used for tailoring the performance on the system to the case under investigation, i.e., a hydrogen refueling station. It can be expected that the system could perform more efficiently, both from an energy and a cost perspective, if its energy integration was optimized for the specific case under study.…”

“…Hemmes et al (2008) simulated these systems in detail, for different types of operational modes, showing that these systems can be operated flexibly, i.e., varying the share of electric and hydrogen power. Pérez-Fortes et al (2018) proposed the design of an SOFCbased co-production system for electricity and hydrogen, based on the multi-stage optimization procedure proposed by Mian et al (2016), thus achieving a combined efficiency above 65% (excluding waste heat) that is maintained over a wide range of combinations of hydrogen and power generation.…”

“…The hybrid SOFC (H-SOFC) is the main unit of the system and is able to generate both electrical power and waste heat for cogeneration purposes. In this paper we assume the use of the system structure proposed by Pérez-Fortes et al (2018), where the composition of the anode off-gas of the SOFC is adapted first by a two-stage water-gas shift (WGS) reactor to enhance the hydrogen content, and then by a pressure swing absorption (PSA) unit for achieving high H 2 purity. The purified hydrogen flow from the PSA is sent to the hydrogen storage tanks.…”

“…The values ofĖ max NG,H−SOFC M ,Q max WGS,H−SOFC M ,Q max EG,H−SOFC M , w H , w WGS , and w EG were calibrated based on the performance of the hybrid SOFC system as described in Pérez-Fortes et al (2018) as to minimize the error between the energy flows reported in the cited source and the ones resulting out of the proposed linear modeling. This results in the total efficiency of the system (based on power and hydrogen production) to range between 64.7 and 66.4% depending on the operational condition, while the corresponding efficiencies for the waste heat in the exhaust gas and the WGS reactor are [0.12-0.14] and [0.17-0.19], respectively.…”

“…It should be noted that in the case of the off-grid dwelling it was assumed to use hydrogen storage tanks at a pressure of 20 bar, which corresponds to the delivery hydrogen pressure of the H-SOFC system used in this study (Pérez-Fortes et al, 2018). Hence, the power demand for the hydrogen compression is already included in the model of the H-SOFC system and the assumption of η H 2 tank,cha = 1 is used.…”