Study On The Heat And Mass Exchange Performances Of The Packed Flue Gas Waste Heat Recovery Unit

The recovery of waste heat resource is an important part of energy saving and emission reduction in China.Flue gas is one of the main forms of waste heat.Aiming at the gas-steam combined cycle system,this paper proposes using the packed flue gas waste heat recovery unit to recover the tail flue gas waste heat and makes a lot of in-depth study.Finally,through the combination of simulation and experiment,the heat and mass exchange performances of the packed flue gas waste heat recovery unit are analyzed,including:（1）On the basis of theory for heat and mass exchange of packing,the mathematical model of the packed flue gas waste heat recovery unit is established.By the method of control volume balance,differential equations of heat balance and mass balance are solved.The refluent heat and mass exchange of the flue gas and cooling water in the unit can be simulated,which provides the theoretical basis for the performance analysis.（2）A system of the performance experiment of the packed flue gas waste heat recovery unit is set up.The inlet temperature of flue gas,the inlet moisture content of flue gas,the mass flow rate of flue gas per unit area,the inlet temperature of cooling water,the spraying density of cooling water and the height of the packing are taken as independent variables.After making the orthogonal design,the performances of the packing and the unit are tested.（3）By combining the mathematical model with genetic algorithm,the heat transfer and mass transfer coefficients of the packing under experimental conditions are given.And the empirical correlations of heat transfer and mass transfer coefficients are obtained through the multiple stepwise regression.Based on these,the sensitivity analysis of the heat transfer and mass transfer coefficients is made.The results show that when the inlet temperature of flue gas increases from 75℃to 95℃,the heat transfer coefficient increases by 28.6%and the mass transfer coefficient increases by11.0%.When the inlet moisture content of flue gas increases from 0.045kg/kg _DA to0.050kg/kg _DA,the heat transfer coefficient increases by 9.4%and the mass transfer coefficient increases by 13.5%.When the mass flow rate of flue gas per unit area increases from 1.14kg/（m²·s）to 1.52kg/（m²·s）,the heat transfer coefficient increases by31.0%and the mass transfer coefficient increases by 15.0%.When the inlet temperature of cooling water increases from 20℃to 26℃,the heat transfer coefficient increases by 13.9%and the mass transfer coefficient increases by 6.5%.When the spraying density of cooling water increases from 1.74kg/（m²·s）to 3.13kg/（m²·s）,the heat transfer coefficient increases by 25.9%and the mass transfer coefficient increases by 31.6%.When the height of the packing increases from 0.2m to 1.0m,the heat transfer coefficient decreases by 55.5%and the mass transfer coefficient decreases by 40.2%.At the same time,the calculation formula of Lewis factor which is suitable for flue gas waste heat recovery is given,and the Lewis number in the calculation formula should be 0.681.The applicability of the calculation formula in different working conditions is also verified.（4）The waste heat recovery efficiency is taken as the performance evaluation index of the packed flue gas waste heat recovery unit,and the variation factors of the waste heat recovery efficiency are analyzed.The results show that the waste heat recovery efficiency is positively correlated with the inlet temperature of flue gas,the inlet moisture content of flue gas,the spraying density of cooling water,the height of packing,and is negatively correlated with the mass flow rate of flue gas per unit area,the inlet temperature of cooling water.