Cascade Utilization Of Flue Gas Waste Heat In Coal-Fired Power Plant To Reduce The Cost Of Carbon Capture

CO₂ is one of the main greenhouse gases which causethe increase of global greenhouse effect,and it has a great influence on people's life.Therefore,CO₂ emission reduction is imperative.The combustion of fossil fuels leads to a large number of CO₂ emissions,of which coal-fired power plants are suitable for carbon capture because of the largest CO₂ centralized emission point sources.The traditional carbon capture process has high desorption energy consumption and consumes a lot of low pressure steam.CO₂ liquefaction process requires deep dehydration of TSA,complicated process and high energy consumption in refrigeration process.The flue gas emission temperature?160°C?of coal-fired power plantis high,resulting in a large amount of waste heat waste.Therefore,from the perspectives of low-grade flue gas waste heat recovery,reduce the steam consumption of carbon capture process,reduce theenergy consumption of liquefaction process and then reduce the cost of whole process,we propose a cascade utilization of coal-fired power plant flue gas waste heat to reduce the cost of carbon capture-liquefaction technology.First of all,for thedrawbacks of traditional carbon capture-CO₂ liquefaction process of low temperature and flue gas emission temperature?160°C?high,the cascade utilization of low grade waste heat of carbon capture – compression-absorption refrigeration liquefied process is proposed.In this study,the desorption temperature of traditional carbon capture process is 118°Cby simulating and optimizing,matching the emission temperature of flue gas.The top gas temperature of stripper tower is 98°C,and this part of the heat canrecover.The CO₂ liquefactionnew process of compression-absorption refrigerationis by increasing CO₂ condensation temperature,operating pressure to achieve liquefaction.Take the lithium bromide absorption refrigeration as an example,the top gas as the driving heat source for cooling system generates cooling capacity.The CO₂ liquefaction new technology omits the TSA dehydration section,which replacedthe mechanical work of high grade energy consumption in the traditional cryogenic liquefaction processbytop gas heat of low-grade energy consumption.The liquefaction conditions and operation range of the CO₂ liquefaction new process were determined.After simulation and calculation,the total unit energy consumption of the CO₂ liquefaction new process was 24% lower than that of the traditional liquefaction process.Foran annual output of 200 thousand tons of industrial liquid carbon dioxide for enhancing oil recovery,the total energy consumption of new liquefaction process can save 962 kWh of electricity per hour compared with the traditional process.In the new process,flue gas waste heat instead of low pressure saturated steam as desorption heat source to achieve the first utilization,and thetop gas waste heat as low temperature driving heat source of single effect Li-Br absorption refrigeration system to achieve the second utilization,so as to realize the cascade utilization of waste heat of flue gas.By using the energy balance analysis,a total recovery of low grade waste heat is 117.25 GJ/h using flue gas waste heat cascade,and by heat exchanger network analysis of whole the process,confirmed the feasibility of flue gas waste heat cascade utilization.By analysis and evaluation of exergyeffective,carbon capture-liquefaction of the new technique to save exergy consumption rate of 528.83 kJ/kgCO₂ compared with the traditional process,energy consumption can be saved 18.9%.Finally,for the economic benefits of carbon capture-liquefaction,traditional process and new process are compared and analyzed.The traditional and new technique were carried out preliminary equipment cost calculation and annual operation costcalculation.Through the calculation,the new technique can save the operation cost of 167 ×104 CNY/a,which significantly lower than that of the traditional process.The annual profit of the total process was analyzed,and the annual profit of the new process was 197.5 ×104 CNY/ahigher than the traditional process,and the recovery period was 4.5 years.