Exergy Analysis And Optimization Of Flue Gas Ultra-low Emission System In Coal-fired Power Generation

With the increasingly strict emission standards of atmospheric pollutants,at present,China’s coal-fired power plants have fully implemented ultra-low emission technologies,but more attention is paid to controlling the emission concentration of flue gas pollutants,ignoring the substances in the process of ultra-low emission of flue gas.The intrinsic link between consumption,energy use and the technology economy.Therefore,the material consumption analysis and energy utilization analysis of the flue gas pollution control system of coal-fired power plants is an important step to further optimize the technical performance of the system.It is of great significance to carry out this part of the work,but the theory of helium analysis is currently applied to the flue gas.Research on pollution control systems has not been reported in the literature.This paper first simulates the flue gas pollution control unit of a typical 600 MW coal-fired unit in China,including: SCR denitrification unit,electrostatic precipitator unit(ESP)+ wet electric electrostatic precipitator unit(WESP),limestone-gypsum wet desulfurization unit(WFGD).Then,several important parameters are selected for simple influencing factor analysis.When the appropriate parameters are selected,the process simulation of the flue gas pollution control system is established,and the energy consumption simulation results and thermodynamic parameters are obtained,and then the material and energy conservation calculations are carried out..The research results show that the relative error between the simulation result and the actual data is within 5%,and it meets the ultra-low emission standard of flue gas.Therefore,the model of Aspen Plus software applied to the flue gas pollution control system is reliable and smoke.The flow rate and temperature show an increasing trend with increasing load.Secondly,based on the established model and the first and second laws of thermodynamics,the detailed analysis of the flue gas pollution control system under different loads is carried out.Firstly,the exergy utilization status of the flue gas pollution control system under variable load conditions is analyzed.Then,the flue gas pollution control system is decomposed into units,and the exergy values of the input and output streams of each unit under different load operating conditions are analyzed.The formula for exergy analysis calculates the exergy loss,exergy efficiency,and loss of the entire system or each unit,so as to find the location and cause of the exergy loss.The results show that the exergy efficiency of the flue gas pollution control system increases with the increase of load(except 100% load),the highest can reach 53.71%,and the exergy efficiency is the lowest at 50% load,which is 41.01%.ESP under different loads.The exergy loss with WESP does not change much,and the load change has a great influence on SCR unit,GGH unit and FGD unit.The degree of influence is from large to small: FGD>SCR>GGH,and each unit in the system is under the same load.The order of efficiency from high to low is: WESP>ESP>GGH>SCR>FGD,so that the unit with the lowest efficiency of the entire flue gas pollution control system in the FGD unit is known,and the FGD unit is further decomposed to find the SO2 absorption system.It is the link with the lowest efficiency and the largest loss of helium in the whole desulfurization process.Then,the flue gas pollution control system is optimized from the perspective of exergy analysis.The optimization includes two parts:(1)optimization of unit operating parameters: selection of several key operating parameters such as liquid-gas ratio,slurry p H and slurry density,and analysis of this The influence of several factors on the loss and exergy efficiency of the FGD unit;(2)Optimization of the process route: on the basis of the pollutant control process of the traditional coal-fired power plant,through the increase/improvement of the pollutant removal unit to achieve ultra-low emission of pollutants,The heat of the flue gas in the ultra-low emission process is rationally utilized,so as to calculate the exergy efficiency and the exergy loss,and compare the changes before and after,and then propose a technically reasonable ultra-low emission technical route of flue gas.The results show that the influence of liquid-gas ratio,slurry p H and slurry density on the exergy efficiency and exergy loss is from large to small: liquid-gas ratio > slurry p H > slurry density,and after analysis,the best liquid-gas ratio should be Around 18 l/m3,the slurry p H was 5.3,and the slurry density was 1115-1120 kg/m3.Then the technical route was optimized,and it was found that the low-temperature economizer can absorb up to 29.6 MW,the coal consumption can save 1.8 g/(k W·h),and the heat loss is reduced to 48.3 k J/(k W·h).The use of the gas cooler and the flue gas cooler reduced the moisture content of the whole process,and the efficiency of the optimized desulfurization system increased from 91.33% to 95.05%,and the efficiency of the flue gas pollution control system increased from 47.86% to 51.39%,increasing 3.53%.It shows that the optimized technical effect is more significant,providing support and guidance for the optimization of flue gas ultra-low emission technology route.