An Exergetic Analysis of New Thermodynamic Cycles Involving Carbon Dioxide Capture

The article presents the results of an exergetic analysis of two new thermodynamic cycles: the Allam cycle and the cycle of a compressorless combined-cycle plant (the JIHT cycle). Their fundamental feature is that the carbon dioxide produced during fossil-fuel combustion can be removed directly from the power-installation cycle. Owing to this feature, such installations become extremely attractive for performing energy decarbonization. The JIHT cycle based installations are more versatile because they can be used for generating not only electricity but also heat for district heating purposes; in addition, they open the possibility to remove carbon dioxide from the cycle not in gaseous but in liquid form, which is more convenient for transportation to a consumer and/or for storage. It is shown that the electrical efficiency of an installation based on the Allam cycle makes 58.1% and that of the JIHT cycle installation operating in the cogeneration mode makes 45.5% with the total fuel efficiency equal to 92.5%. If there is no heat supply, the JIHT cycle electrical efficiency approaches that of the Allam cycle. The calculations are supported by detailed presentation of the considered cycles on a T, s diagram. The processes in which the main exergy loss occurs are highlighted. A conclusion is drawn that the installations considered can really compete with the conventional power installations with carbon dioxide capturing by means of sorption and membrane methods. To verify the procedure and computation model, an exergetic analysis was preliminarily performed for a conventional GTU-110 simple cycle gas-turbine unit, a 325 MWe combined-cycle plant (CCP) based on this unit, and a Capstone C30 microturbine with regeneration. The key scientific-technical problems that have to be solved for successfully harnessing the considered innovative cycles are highlighted. They include the development of a regenerative heat exchanger with a recovery ratio higher than 95% operating at a temperature of approximately 1000 K, an oxy–fuel combustion chamber for a pressure above 30 MPa, and a combined-cycle turbine with working fluid with an inlet temperature of higher than 1400 K and pressure above 30 MPa. These problems do not seem to be more complex than those that were set forth and successfully solved in the development of modern high-temperature high-capacity gas-turbine units.