Abstract
Due to the increase in energy consumption and energy prices, the reduction in fossil fuel resources, and increasing concerns about global warming and environmental issues, it is necessary to develop more efficient energy conversion systems with low environmental impacts. Utilizing fuel cells in the combined process is a method of refrigeration and electricity simultaneous production with a high efficiency and low pollution. In this study, a combined process for the tri-generation of electricity, medium pressure steam, and liquid carbon dioxide by utilizing a molten carbonate fuel cell, a dual pressure Linde-Hampson liquefaction plant and a heat recovery steam generator is developed. This combined process produces 65.53 MW of electricity, 27.8 kg/s of medium pressure steam, and 142.9 kg/s of liquid carbon dioxide. One of the methods of long-term energy storage involves the use of a carbon dioxide liquefaction system. Some of the generated electricity is used in industrial and residential areas and the rest is used for storage as liquid carbon dioxide. Liquid carbon dioxide can be used for peak shavings in buildings. The waste heat from the Linde-Hampson liquefaction plant is used to produce the fuel cell inlet steam. Moreover, the exhaust heat of the fuel cell and gas turbine would be used to produce the medium pressure steam. The total efficiency of this combined process and the coefficient of performance of the refrigeration plant are 82.21% and 1.866, respectively. The exergy analysis of this combined process reveals that the exergy efficiency and the total exergy destruction are 73.18% and 102.7 MW, respectively. The highest rate of exergy destruction in the hybrid process equipment belongs to the fuel cell (37.72%), the HX6 heat exchanger (8.036%), and the HX7 heat exchanger (6.578%). The results of the sensitivity analysis show that an increase in the exit pressure of the V1 valve by 13.33% would result in an increase in the refrigeration energy by 2.151% and a reduction in the refrigeration cycle performance by 9.654%. Moreover, by increasing the inlet fuel to the fuel cell, the thermal efficiency of the whole combined process rises by 18.09%, and the whole exergy efficiency declines by 12.95%.
Highlights
IntroductionMarefati et al [6] performed an exergy analysis of a hybrid structure for the cogeneration of heat and power which consisted of an Molten carbonate fuel cells (MCFC), a thermoelectric generator, a gas turbine, and solar collectors
Fuel cells are a competitive alternative to conventional power generation technologies from fossil fuels due to their low pollution and high efficiency, especially in small-scale and scattered power generation [28]
Fuel cells do not store energy like a battery; rather, in a fuel cell, a state of energy is converted to another state in a manner that ensures that no material is consumed within the cell
Summary
Marefati et al [6] performed an exergy analysis of a hybrid structure for the cogeneration of heat and power which consisted of an MCFC, a thermoelectric generator, a gas turbine, and solar collectors. Ahmadi et al [7] conducted a multi-objective optimization of a hybrid electricity generation unit employing a MCFC and a Braysson cycle To do so, they investigated several parameters of the integrated structure such as the flow density of the fuel cell, the gas turbine inlet temperature, and the effect of the heating part which transfers heat to the electricity generation cycle. Akrami et al [21] performed exergy and exergoeconomic analyses of three power and CO2 generation integrated structures using a new hybrid cycle of biomass gasification, a gas turbine, a MCFC, an organic Rankine unit, and a CO2 separation and liquefaction unit. CO2 can be used for peak shaving in industrial and residential areas
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