Research On Low-grade Waste Heat Recovery And Emission Control Of Coal-fired Power Plant

Under the historical background of carbon peak and carbon neutral strategy,China will surely usher in a profound energy reform,and the dominant position of fossil energy will be gradually shaken by the development of new energy.However,today’s Chinese society is still deeply dependent on fossil energy,and coal-fired power plants still account for the majority of China’s power supply market.The huge consumption of fossil energy by coal-fired power plants and the resulting environmental pollution have stung the public’s nerves.However,such energy patterns are unlikely to change much in the short term.So,in order to achieve China’s carbon peak target by 2030,it is imperative to retrofit coal-fired power plants for energy saving and emission reduction.This paper puts forward its solutions to the problem of effective utilization of low-grade waste heat from flue gas and the emission reduction of sulfur oxides and carbon dioxide in coal-fired power plants,and corresponding studies are conducted.Firstly,by introducing wet sulfuric acid process,sulfur dioxide in flue gas is catalyzed to sulfur trioxide and condensed in special heat exchanger and recovered as sulfuric acid by-product,so as to break the acid dew point limit of low grade waste heat depth utilization of flue gas.Then the waste heat of flue gas is deeply utilized by the waste heat recovery system integrated with organic Rankine cycle and absorption refrigeration.The waste heat recovery system is studied by numerical simulation.After establishing mathematical model,the reliability and accuracy of numerical simulation are ensured by model verification.For the organic Rankine cycle,the working fluid selection is carried out firstly,and the two components which are most suitable for the heat source condition are selected as the non-azeotropic working fluid from several pure working fluids,and the optimal mixing ratio and evaporation pressure are selected by comparison and optimization.For absorption refrigeration system,physical properties were modeled by data fitting,and then a simplified thermodynamic model was established by degree of freedom analysis.The absorption refrigeration parameters and sensitivity of design variables were analyzed.Compared with another advanced waste heat recovery design,the thermodynamic superiority of the system is demonstrated.The economic analysis of waste heat recovery system shows that the system has good economic potential.Carbon capture is an important technical means of carbon dioxide emission reduction in coal-fired power plants.Since several kinds of energy needed in carbon capture process can be provided by waste heat recovery,this paper proposes a carbon capture system for flue gas of coal-fired power plants based on waste heat recovery.The system is divided into energy supply side and energy demand side.On the energy supply side,cold energy,heat energy and electric energy are generated through flue gas waste heat recovery.On the energy demand side,the energy demand information of carbon capture process is obtained through software simulation.Compared with another advanced carbon capture system,the advantages and disadvantages of this system are summarized.The economic analysis shows the economic superiority of the system.The research results show that the waste heat recovery system can generate an electric energy of 8055 k W and a cooling capacity of 25493 k W.The waste heat recovery system improves the power generation efficiency by 0.34%,and the system investment can be recovered in 4.8 years.The carbon capture system based on waste heat recovery proposed in this paper can capture 292,977 tons of CO₂annually under the condition of complete self-sufficiency of energy,accounting for 5%of the annual CO₂emissions of the power plant,and can reduce the CO₂emissions per unit of power generation by 38.4 g/（k Wh）.The initial investment recovery period of the carbon capture system is 4.7 years.The scheme proposed in this paper can realize the deep recovery of low-grade waste heat from flue gas of coal-fired power plants and the emission control of sulfur dioxide and part of carbon dioxide,which has great significance of energy saving and emission reduction.