Thermoeconomic and optimization analyses of direct oxy-combustion supercritical carbon dioxide power cycles with dry and wet cooling

Development of an analytical constituent split method to analyze a semi-closed supercritical carbon dioxide power cycle

Because of the fossil fuels crisis in recent years, increasing fossil fuel consumption and the oil crisis, energy efficiency is becoming a major concern of the twenty-first century. In this research, the combined cycle of steam Rankine and organic Rankine with the primary mover of the Allam generation cycle has been simulated. The hybrid cycle is configured in such a way that the high temperature waste heat first acts as the steam cycle evaporator and the waste heat output from the steam cycle evaporator is used as the low temperature evaporator of the organic cycle. Then, the effect of changing various parameters such as evaporator temperature and steam cycle condenser pressure on output work values, total irreversibility, energy efficiency, exergy efficiency and exergy-economic variables is investigated. The results show that the energy efficiency and exergy efficiency of the combined cycle are 0.57 and 0.66, respectively, and the amount of output work and total irreversibility are 150,125 kW and 91,237 kW, respectively. Also, according to the study results, a lot of exergy destruction takes place in the system, thus it is recommended to increase the initial price in different components in order to improve the performance of the system. Evaporators and steam cycle condensers are components that should be considered from an exergy-economic perspective, as they have the highest rate for the sum of the initial cost rate and the cost of exergy destruction.

Thermoeconomic analysis of combined steam and organic Rankine cycle with primary mover of Allam cycle

Application of trigeneration system power by concentrating photovoltaic-thermal solar collectors for energy demands of an industrial complex

Proposal of multistage mass storage process to approach isothermal heat rejection of semi-closed S–CO2 cycle

The Allam Cycle takes a novel approach to reducing emissions by employing oxy-combustion that utilizes carbon dioxide (CO2) working fluid, highly recuperated cycle. In this research, the main parts of the Allam cycle, including the combustion chamber, air separation unit, heat exchanger and cooling tower, have been simulated in Thermoflow software. This cycle is based on combustion using pure oxygen instead of ambient air and the working fluid of this cycle is carbon dioxide. According to the results of the validation part of the initial simulation, the efficiency of the supercritical carbon dioxide cycle with three cooling stages in the compression part (in non-optimal and initial state) is 54%, which is approximately 4% of the cycle efficiency. By reducing the inlet fluid pressure to the pump from 75.38 to 73.43 bar, the cycle efficiency increases from 53.9 to 54. According to the second part of the results, which shows the effect of combustion chamber temperature (in the range of 800–1300 °C) on cycle performance, by increasing the combustion chamber temperature from 800 to 1200 °C, the cycle efficiency increases from 44.61 to 61.38. Also, the highest efficiency of the Brayton cycle is obtained in the pressure ratio of 20, which is approximately equal to 38% for the cycle with real specifications, while the highest efficiency is obtained in the Allam cycle with a pressure ratio of 10, which is about 55%. Therefore, in addition to being able to absorb 100% of carbon dioxide, the Allam cycle has a much higher efficiency than the Brayton cycle.

Simulation of the Allam cycle with carbon dioxide working fluid and comparison with Brayton cycle

In recent years, the use of Allam cycle based on the closed cycle of carbon dioxide has been considered by researchers due to its high efficiency and reduction of carbon dioxide emissions in the environment. In the present study, the combined system including Allam cycle and absorption cycle has been investigated from the perspective of energy, exergy and exergy–economy. The use of the absorption cycle is to use the waste heat of the power cycle and increase energy efficiency. The simulation results show that the total exergy efficiency of the cogeneration cycle is 0.72. Turbine, compressor and absorption cycle are introduced as primary components that should be considered from the exergy–economic point of view because they account for the highest cost rate of exergy efficiency. Also, the results of parametric analysis indicate that increasing the compressor pressure ratio has a negative effect on the cycle performance, thus reducing the overall work and efficiency of the exergy as well as increasing the cost rate. Similarly, changing the compressor pressure ratio has the greatest impact on the performance of the combined cycle, so that changing the pressure ratio in the range of 2 to 10 resulted in reducing the exergy efficiency by 63%. The key assessment is that the performance of the system increases as the temperature of the cooled water in the evaporator rises. Exergy efficiency works in contrast to the system performance coefficient and the main reason for the return of imperfections in the absorption cooling system is the undesirable heat transfer in the system heat exchangers.

Emad Dokhaee

Papers

Simulation of the Allam cycle with carbon dioxide working fluid and comparison with Brayton cycle

Exergy and thermoeconomic analysis of a combined Allam generation system and absorption cooling system