Exergy/Exergoeconomic Analysis Of Supercritical Carbon Dioxide Cycle Coal-Fired Power Generation System With Carbon Capture Based On Variable Load

At present,thermal power generation is still the main form of power generation in China.The traditional water vapor Rankine cycle is limited by factors such as high-temperature materials,and the efficiency reaches up to 47%,which is extremely difficult to further improve.At the same time,the supercritical carbon dioxide（SCO₂）cycle efficiency above 500°C is higher than the steam cycle efficiency,which can avoid the development of superalloys,and has the advantages of small unit size and low cost,which is one of the key frontier technologies in the field of coal power that needs to be broken through and improved.It is of great significance to study the energy exchange network of the thermodynamic cycle process with carbon dioxide as the working medium.In this paper,a model of SCO₂ cycle ultra-low emission coal-fired power generation system is constructed.Based on the exergy（exergoeconomic）analysis method,the change law of energy transfer process exergy loss in the system is revealed,and the exergoeconomic performance of the system and its components is evaluated.Finally,the influence of carbon capture process on the energy integration of SCO₂ cycle power generation system under different working conditions is explored.The specific research contents are as follows:Aspen Plus process simulation software was used to build a model of SCO₂ cycle coal-fired power generation system that meets ultra-low emission requirements,including SCO₂cycle unit,coal combustion unit and flue gas pollutant control unit.Under the condition of constant heat source and heat exchange of the recuperator,the influence of relevant parameters on system performance was analyzed.It was found that the compression shunt coefficient increases,the power consumption of the recompressor increases greatly,and the net power of the system decreases.The increase in the inlet pressure of the low-pressure turbine increases the pressure drop and significantly increases the work.Reducing the inlet pressure of the main compressor,increasing the outlet pressure and inlet temperature of the main compressor would increase the power consumption of the main compressor and reduce the cycle efficiency.Due to the high density near the critical point of the working fluid itself,the change in cycle efficiency was very small when the inlet temperature of the main compressor changes near the critical temperature.The exergoeconomic model of the SCO₂ cycle ultra-low emission coal-fired power generation system was established,and the exergy loss and exergoeconomic performance of the system and its components were analyzed under the design conditions.It was found that the boiler had the largest exergy loss,followed by precooler,high-temperature reheater,low-temperature reheater,etc.In the flue gas pollution control system,the FGD unit has a greater exergy loss than the SCR unit and the ESP unit.The exergoeconomic coefficient of the whole system is 35.90%,and it is necessary to increase the investment cost and reasonably optimize the parameters to improve the efficiency of the equipment.FGD units have higher exergy loss cost and non-energy cost,the exergoeconomic cost difference per unit power supply is the largest,and the exergoeconomic cost difference per unit of SCR unit is mainly caused by large non-energy cost.The output power of the system is changed by means of flow regulation,and the impact of carbon capture unit under 100%,75%,50%and 30%load on the SCO₂ cycle ultra-low emission coal-fired power generation system is clarified.It is found that with the decrease of system load,the influence of circulating working fluid absorption of CO₂ product gas heat on temperature is more significant,the temperature of boiler inlet and outlet working fluid increases,the turbine work increases,and the boiler heat exchange exergy loss decreases.The vacuum pump and CO₂ product gas compressor have a larger operating energy consumption,resulting in the carbon capture system with 1.21～1.76 percentage points lower exergy efficiency than the ultra-low emission system without carbon capture.The unit power supply of VTSA unit has the largest exergoeconomic cost difference,accounting for 45.21%～54.54%of the total exergoeconomic cost difference of flue gas pollutant control subsystem,which is mainly due to the high desorption energy consumption,expensive adsorbent and high equipment investment cost of the adsorption tower.Through the complete simulation of SCO₂ cycle ultra-low emission coal-fired power generation system,an exergoeconomic model was established to discuss the thermodynamic performance and exergoeconomic performance of the analysis system,and the system characteristics of carbon capture units under different loads were explored,which provides model support and theoretical basis for the optimization design of SCO₂ cycle ultra-low emission coal-fired power generation system.