Comparative analysis of the Allam cycle and the cycle of compressorless combined cycle gas turbine unit

Abstract

Nowadays, alternative thermodynamic cycles are actively studied. They allow to remove CO2, formed as a result of fuel combustion, from a cycle without significant energy costs. Calculations have shown that such cycles may meet or exceed the most advanced power plants in terms of heat efficiency. The Allam cycle is recognized as one of the best alternative cycles for the production of electricity. Nevertheless, a cycle of compressorless combined cycle gas turbine (CCGT) unit is seemed more promising for cogeneration of electricity and heat. A comparative analysis of the thermal efficiency of these two cycles was performed. Particular attention was paid to ensuring equal conditions for comparison. The cycle of compressorless CCGT unit was as close as possible to the Allam cycle due to the choice of parameters. The processes, in which the difference remained, were analysed. Thereafter, an analysis of how close the parameters, adopted for comparison, to optimal for the compressorless CCGT unit cycle was made. This analysis showed that these two cycles are quite close only for the production of electricity. The Allam cycle has some superiority but not indisputable. However, if cogeneration of electricity and heat is considered, the thermal efficiency of the cycle of compressorless CCGT unit will be significantly higher. Since it allows to independently regulate a number of parameters, on which the electric power, the ratio of electric and thermal power, the temperature of a working fluid at the turbine inlet depend. Thus, the optimal parameters of the thermodynamic cycle can be obtained in a wide range of operating modes of the unit with different ratios of thermal and eclectic powers. Therefore, the compressorless CCGT unit can significantly surpass the best steam turbine and combined cycle gas turbine plants in district heating system in terms of thermal efficiency.

Conceptual methods of starting and controlling operating modes of compressorless combined cycle gas turbine unit

“…1. A detailed description of the CCCGT scheme can be found in [9], [10]. Immediately after the pump, the CO2 enters a CO2 heater, then a CO2 recuperator, and then the combustion chamber.…”

“…Among such cycles, one can distinguish a cycle of a compressorless combined cycle gas turbine (CCCGT) unit [6], [7], [8]. This cycle, while generating electricity and heat together, exceeds the main known cycles in terms of thermal efficiency [9], [10]. However, during a creation process of new energy complexes, it is important to have a concept of a complex operation in non-calculated modes at the very early stages of design.…”

Designing a pilot model of compressorless combined cycle unit

“…Thus, in addition to efficient energy production, it is necessary to pay attention to the impact of the created installations on the environment, especially the emissions of carbon dioxide into the atmosphere. In works [1][2][3][4][5][6], a cycle of a compressorless combined cycle unit (CCCU) is considered, which main distinct feature is its focus on the combined production of heat and electric energy. At the same time, CCCU allows to independently regulate the parameters, affecting the ratio of generated heat and electric power, temperature at the turbine inlet, and also permits to separate CO2 from combustion products in a liquid form, being convenient for further utilization.…”