(491c) A SOFC-Based Multi-Energy System for the Efficient Production of Hydrogen and Power from Natural Gas for Hydrogen Refuelling Station Applications
While most hydrogen production from natural gas relies on thermochemical process like steam methane reforming (SMR) , using an electrochemical reactor with internal reformation capabilities like a SOFC allows producing hydrogen in addition to electricity and heating or cooling, resulting in a âmulti-energyâ system. Moreover, in the electrochemically-driven internal reforming process: (i) the amount of high temperature heat produced by the exothermic reactions within the fuel cell stack is typically greater than that heat required for fuel processing, so that the reforming process can be driven by the stack losses instead of requiring the combustion of part of the fuel, as typical for conventional SMR; and (ii) The fuel cell thus generates at the exit of the anode a hydrogen-rich stream that could be subsequently purified and delivered to a compression and storage unit. The SOFC operating condition, in terms of current density and fuel utilization, can be tuned to follow a particular profile of hydrogen and electrical /heating demand, making the system flexible and versatile.
We focus here on a case where the SOFC-system is coupled with a hydrogen refuelling station (200 kg/d) demand of hydrogen (with a storage of compressed hydrogen at 700 bar), electricity (to power all auxiliaries in the refuelling station) and cooling (due to the precooling unit upstream the dispenser). Cooling will be produced via coupling the heat production from the SOFC system to a low temperature absorption refrigeration unit. The synergy with the cooling load of the precooling unit of the hydrogen station is particularly important due to the high impact that the refrigeration section has on the overall hydrogen cost. For a 200 kg/d refuelling station, Elgowainy et al.,  predicts that a 13 kW compression refrigeration system is required, consuming approximately 0.3 kWh/kg at full load. This section adds approximately $0.5/kg to the cost hydrogen.
Hydrogen purification and compression is made with a small Water gas shift + PSA unit followed by and electrochemical compressor to the station buffer tank. When hydrogen is not required, it can be either stored or the SOFC can move to an electricity-only operating condition. Once the separation of hydrogen is complete, the residual flue gases are mainly composed by CO2 and water; so that the system could be also applied to CO2 separation and CCS (carbon capture and ), provided thereâs the possibility to store or sell CO2, as well as to the production of water. The latter possibility is particularly interesting if the plant is installed in dry climates, following the concept of a âmulti-goodâ configuration.
The system is preliminarily designed to cover all or a major part of the hydrogen demand, while supplying part of electricity (the rest being exchanged with the grid) and cooling, based on typical daily and weekly demand profiles. The work compares the proposed system in terms of efficiency and CO2 emissions with respect to a baseline configuration where the loads are covered by: i) a traditional grid connection while grey hydrogen is generated in a conventional SMR and transported to an external dispensing station; ii) onsite hydrogen production and electric connection.
The SOFC system is simulated with the process simulation software âGSâ originally conceived at Princeton University and then developed at Politecnico di Milano. The software is characterized by modular black-box components models, which can be connected to create complex power and chemical systems. The software has already been extensively utilized by some of the authors to simulate fuel cell-based multi-good systems . In this work, we extend the capabilities of the model integrating a 1D SOFC model able to reproduce the performance of a commercial stack operated at low fuel utilization factor. The 1D SOFC model â despite being validated for conventional SOFC operation  â will be compared with newly measured data on a SOFC short stack operated at low fuel utilization factor. The kinetics and electrokinetics models will be re-assessed in order to take into account the reduced yield of the internal reformation reaction when the fuel cell is operated at low fuel utilization and its effect onto the electrochemical cell performance.
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