Performance Of Solar-aided Coal-fired Units With Integrated Carbon Capture And Storage

Coal-fired power generation units using carbon capture and storage（CCS）can reduce CO₂ emissions significantly whereas CCS consumes large amounts of renewable energy,leading to an efficiency penalty.To decrease the steam extraction and promote energy utilization efficiency,this study employs organic Rankine cycle（ORC）to recover the waste heat of reboiler condensate and utilizes the waste heat in CO₂ compressed processes to provide energy for carbon capture system.Three technical scenarios are proposed:1)Coal-fired carbon capture power generation system:the medium-pressure cylinder exhaust is throttled by an auxiliary turbine and exchanges heat with H6 heater to provide energy for a reboiler;2)Coal-fired carbon capture power generation system using ORC to recover the residual heat of reboiler condensate;3)Solar-aided coal-fired power generation system using ORC and CCS:the heat in CO₂ compression processes and the solar collectors is supplied for a reboiler and ORC recovers the residual heat of reboiler condensate.The energy balance and overall performance of different scenarios are investigated with EBSILON,and the parameter sensitivity of scenario III is conducted.Results reveal that all scenarios improve the thermal performance of the system,and the thermo-economics of scenario III is the best at the heat ratio of 0.4.Based on the external fuel exergy matrix model,the influence of the heat ratio of the CO₂ compression process and solar collector to the heat required by the reboiler and the integrated ORC system on the contribution of external fuel exergy,is examined.Results reveal that the thermo-economics of the integrated system is the best and exhibits reasonable irreversibility at the heat ratio of 0.4.After integrating ORC system,the contributions of coal exergy in the boiler,primary and secondary reheat coal exergy to the system products are raised.With increasing heat ratio,the contributions of coal exergy in boiler,primary and secondary reheat coal exergy to carbon capture system products are reduced,whereas the contributions of the exergy of compressed waste heat and solar are raised.Based on the SimaPro 9.0.0.48 software,the ReCiPe Midpoint（H）V1.13 method is used to conduct a complete life cycle assessment of the three scenarios.The influence of the integrated auxiliary equipment on the environmental categories is analyzed in the life cycle of each scenario,and the sensitivity analysis of the impact of some key factors in the life cycle（life span,solar radiation intensity,collectors to replace regenerative heaters,heat ratio and the energy consumption and capture rate of carbon capture system）on the system environment is carried out.The results show that among the impact scores of all selected categories of functional units,the climate change potential（CCP）score is the highest,and the CO₂ emitted during the operation phase of the three scenarios accounts for a considerable part and contributes the most to the CCP.The ozone depletion potential（ODP）has the least impact score.In addition to CCP,due to the addition of carbon capture and storage systems,ORC systems and solar systems,other impact categories are scored as follows:scenario VI>scenario V>scenario IV.Regarding the human toxicity potential（HTP）score,the mining and transportation stages of coal have the largest contribution,and the other impact categories have the largest contribution in the system operation stage.The unit electricity CCP and HTP of the three scenarios gradually decrease with the increase of the life cycle,radiation intensity,heat source ratio and the serial number of the solar collector to replace the heater.For scenario V and VI,as the carbon capture rate of the carbon capture system increases,the CCP per unit of electricity decreases while the HTP increases.With the increase of regenerative energy consumption,the unit power CCP and HTP both show an increasing trend.