Study On Characteristics Of Coal-fired Power Generation System Based On Calcium Looping Cycle/Lithium Looping Cycle For CO₂ Adsorption

With the rapid growth of global energy demand,the use of coal is increasing day by day,and coal-fired power generation is the main way of using coal.An important environmental problem caused by coal power generation is high CO₂ emissions.CO₂ is one of the greenhouse gases,which will cause the greenhouse effect,cause global temperatures to rise,and cause serious harm to the ecological environment.Therefore,it is essential to reduce CO₂ emissions from coal-fired power plants and promote low-carbon development.In this paper,a 1000MW ultra supercritical coal-fired power generation system in China was taken as the prototype,which combined the CO₂ adsorption model of calcium-based sorbent Ca O cycle carbonation/calcination reaction and the same model of lithium-based sorbent Li₄Si O₄ cycle carbonation/calcination reaction respectively.At the same time,Aspen Plus software was used to establish a coal-fired power generation system based on calcium looping cycle for CO₂ adsorption and the same one based on lithium looping cycle for CO₂adsorption.The rationality of the former system model was verified,and it was speculated that the latter system model under the same process was also reasonable.The thermal characteristics,CO₂ emission characteristics and economy of sorbent material of these two types of coal-fired power generation systems were compared.And the sensitivity analysis of key system parameters of lithium-based sorbent system was carried out,in order to explore the influence of the values of CO₂ capture rate,average conversion rate of lithium-based sorbent,material emission ratio,gas-solid separation efficiency after carbonator,CO₂ compression power consumption and waste heat utilization rate on the mass flow of circulating materials in front of calciner,the power consumption of calciner,power generation and theoretical thermal efficiency of power generation.At the same time,in order to study the changes in the total CO₂emissions of coal-fired power plants combined with the CO₂ adsorption model of lithium-based sorbent cycle carbonation/calcination reaction,the life cycle assessment method was used to calculate the CO₂ emission of each stage of the life cycle of the coal-fired power generation system based on lithium looping cycle for CO₂ adsorption.The impact of CO₂ emissions on the total emissions at each stage was analyzed,and it was compared with the results of the life cycle assessment of coal-fired power plants combined with calcium looping cycle for CO₂ adsorption.The comparative study of coal-fired power generation system based on lithium looping cycle and calcium looping cycle respectively shows that because the cycle adsorption performance of lithium-based sorbent Li₄Si O₄ is better than calcium-based sorbent Ca O,and the temperature required for the calcination reaction is low,the theoretical thermal efficiency of the former system is 1.92 percentage points higher than that of the latter,but the CO₂emission factor is relatively high due to the low net power generation.The cost of lithium-based sorbents is higher than that of calcium-based sorbents.Under the premise of resource recycling,large-scale recovery of lithium batteries to obtain raw materials Li₂CO₃ is expected to reduce the cost of Li₄Si O₄ synthesis.The sensitivity analysis of the coal-fired power generation system based on lithium looping cycle for CO₂ adsorption shows that the CO₂ capture rate has the largest impact on the theoretical power consumption of the calciner,with a change range of 54.2%,and the largest impact on the net power generation,with a change range of 13.1%.The utilization rate of waste heat and the average conversion rate of lithium-based sorbent have a great influence on the power generation,with a change range of 6.8%and 5.9%respectively.The utilization rate of waste heat has the greatest influence on the theoretical power generation,reaching 6.8%.Increasing the CO₂ capture rate within a certain range will increase the power generation capacity of the system and reduce the CO₂ emission factor,and increase the utilization of waste heat can significantly improve the thermal efficiency of the system power generation.The research on the life cycle assessment of the coal-fired power generation system based on lithium looping cycle for CO₂ adsorption shows that after increasing the cycle process of CO₂ adsorption,the whole life cycle coal consumption increases by 71.1%compared with the original coal-fired power plant,the system gross power generation increases by 72.7%,and the CO₂ emission coefficient reduced by 43.1%,effectively reducing CO₂ emissions.In the whole life cycle,the CO₂ emissions during the sorbent production stage and the adsorption system operation stage accounted for 44.15%and 37.09%of the total CO₂ emissions respectively.The former is due to the high energy consumption in the production of Li₂CO₃,which is the raw material of sorbent.The CO₂ emission in this production stage is much higher than that in the production process of calcium-based sorbent.The latter requires power consumption of electrical equipment to compress and store CO₂,which indirectly causes a large amount of CO₂emission.By optimizing the production process of Li₂CO₃ to reduce energy consumption,finding an alternative source of Li₂CO₃ on the premise of sustainable utilization of resources,and using the coal-fired power generation system’s own power generation to supply equipment as much as possible,the CO₂ emission factor of the coal-fired power generation system can be effectively reduced.The processes of the construction of coal-fired power plants,the construction of CO₂ adsorption systems,the transportation of CO₂ sorbents,the decommissioning of coal-fired power plants and the decommissioning of CO₂ adsorption systems all account for less than 1%of the CO₂ emissions,indicating that these processes have little effect on the total CO₂ emissions.