A&nbsp;combined cycle power plant&nbsp;is an assembly of&nbsp;heat engines&nbsp;that work in tandem from the same source of heat, converting it into&nbsp;mechanical energy. Combining two or more thermodynamic cycles improves overall thermal efficiency of the plant, which reduces fuel costs. By generating power from multiple cycles, the overall thermal efficiency of the plant can be increased from 34% (for a simple cycle without regeneration) or 42% (for a simple cycle with regeneration) to as much as 60% (for a combined cycle).&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; In stationary and marine power plants, a widely used combined cycle has a large topping gas turbine&nbsp;(operating by the&nbsp;Brayton cycle). The turbine's hot exhaust powers a&nbsp;bottoming steam power plant&nbsp;(operating by the&nbsp;Rankine cycle). This is a&nbsp;well known combined cycle gas turbine&nbsp;(CCGT) plant achieving a theoretical thermal efficiency&nbsp;of around 60%. But it has to operate on high grade liquid or gaseous fuels as the products of combustion have to be expanded in the gas turbine. With the solid fuels, it is not possible to expand the products of combustion (gases) as it contains a lot of ash.&nbsp;&nbsp; In the present research work, a novel Argon-Steam combined cycle Gas Turbine Engine (ASGTE) with regeneration in the topping argon cycle&nbsp; is proposed for using solid fuels like coal instead of liquid or gaseous fuels. &nbsp;ASGTE consists of a gas turbine engine (operating by the&nbsp;closed Brayton cycle) with the argon as the working fluid and a steam turbine engine (operating by the&nbsp;Rankine cycle) with the steam as the working fluid. The heat energy of the hot products of combustion produced upon burning of the coal in the air is initially transferred at a high temperature &nbsp;to the compressed argon to raise its temperature to a Turbine Inlet Temperature (TIT). A major portion of the remaining energy of exhaust gases and the argon exhaust from the turbine after regeneration is utilized to generate the steam at a high pressure and temperature for running the steam turbine. Argon has been chosen as the working fluid in the topping cycle because of its low specific heat, high density and high specific heat ratio which are desirable characteristics of any working fluid for higher energy conversion.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; The thermodynamic cycle of operation of ASGTE is analyzed based on first and second laws of thermodynamics, and a computer code is developed in MATLAB to simulate the engine performance at different compressor pressure ratios and TITs. For initial thermodynamic calculations, two gas turbine engines called GT8C2 and GT26 made by Alstom Power Corporation are considered. It is found that ASGTE achieves 40 to 50% thermal efficiency as against 30 to 35% of coal based steam turbine plant.

Investigation of the Performance of Air-Steam Combined Cycle for Electric Power Plants Using Low Grade Solid Fuels

Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2021/volume/85109

ASME 2021 Power Conference (POWER2021)

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