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Lower-temperature fuel cell types such as the proton exchange membrane fuel cell, phosphoric acid fuel cell, and alkaline fuel cell require pure hydrogen as fuel, typically produced from external reforming of natural gas. However, fuels cells operating at high temperature such as the solid oxide fuel cell (SOFC) are not poisoned by carbon monoxide and carbon dioxide, and in fact can accept hydrogen, carbon monoxide, carbon dioxide, steam, and methane mixtures as fuel directly, because of their internal shift and reforming capabilities. This opens up the possibility of efficient fuel cell-based power cycles consuming solid fuels such as coal and biomass, the gasification of which results in syngas containing mostly hydrogen, carbon monoxide and methane which can be cleaned and fed directly to the SOFCs without the added cost and complexity of methane reforming, water gas shifting and hydrogen separation operations which would otherwise be needed to isolate pure hydrogen as fuel. A power cycle based on gasification of solid fuel and SOFCs is called an Integrated Gasification Fuel Cell (IGFC) cycle; the IGFC power plant is analogous to an integrated gasification combined cycle power plant, but with the gas turbine power generation unit replaced with a fuel cell (high temperature type such as SOFC) power generation unit. By taking advantage of intrinsically high energy efficiency of SOFCs and process integration, exceptionally high power plant efficiencies are possible. Furthermore, SOFCs in the IGFC cycle can be operated so as to isolate a carbon dioxide-rich anodic exhaust stream, allowing efficient carbon capture to address greenhouse gas emissions concerns of coal-based power generation. ==Process Configuration== The IGFC system combines use of SOFCs as a topping cycle to the gas turbine or heat recovery steam generator-based bottoming cycle. Typical major components of the IGFC system, this one centered on a SOFC module running at atmospheric pressure, are identified in the simplified cycle diagram. The system fuel as depicted is coal, converted to syngas by the gasifier, which is then supplied to the SOFC module after cleanup and pressure reduction. The syngas pressure reduction step is accomplished in this system concept by an expander/generator, which thereby produces part of the cycle's gross power generation. Oxygen for the coal gasification process is provided by a conventional air separation unit, and steam for the gasifier is raised by power system heat and recycled water. Note that the SOFC module is configured to maintain the anode and cathode off-gas streams separated, and the anode off-gas, which contains some electrochemically-unreacted hydrogen and carbon monoxide, is combusted to completion at the oxy-combustor. Maintaining separation of the off-gas streams restricts the large atmospheric nitrogen content to the cathode side, and simplifies the CO2 capture process to anode off-gas cooling, water-vapor condensation, CO2 drying, and CO2 compression. Compressed CO2 is suitable for carbon utilization or storage (CUS) as appropriate. Heat recovered from the anode-side process can be used by a power-generating bottoming cycle consisting of a heat recovery steam generator and steam turbine. On the cathode side, process air for the SOFC electrochemical process and for module cooling is provided by an air blower; heat can be recovered from the hot cathode off-gas stream to preheat the process air as needed, and for the generation of additional power. Due to the inherently efficient SOFC, and to using recovered SOFC exhaust heat to generate additional electric power, an IGFC system is capable of operating at a high electric efficiency that significantly exceeds those associated with conventional pulverized coal and integrated gasification combined cycle power systems. IGFC efficiency margins considered achievable, based upon the U.S. Department of Energy's National Energy Technology Laboratory comparative studies of advanced power systems, are apparent in the table provided in subsequent discussion. Improvement in the IGFC cycle efficiency is possible by pressurized operation of the SOFCs, as depicted in the diagram of IGFC with pressurized SOFC cycle. The process is basically similar to the atmospheric-pressure cycle, but it would run the SOFC module at elevated pressure, achieving an SOFC voltage boost, and would replace the cathode-side process-air blower with an air compressor. Also, an expander/generator would be installed in the cathode off-gas stream to reduce gas pressures and generate additional power (this tends to drop the temperature of the gases so much that steam generation to run a steam turbine is not a viable option). Optionally, an expander/generator set could also be placed in the anode off-gas stream, just downstream of the oxy-combustor, and ahead of off-gas heat recovery. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Integrated Gasification Fuel Cell Cycle」の詳細全文を読む スポンサード リンク
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