Study On Heat Transfer Characteristcs Of Flue Gas Of Boilter Units

The flue gas in the boiler contains a large amount of water vapor due to WFGD.If the flue gas is directly discharged into the atmosphere from the chimney,severe "gypsum rain" and the phenomenon of white smoke is produced.Even after the GGH heating and then discharged out,there "white smoke" phenomenon still happens in the winter which puts a lot of environmental pressure on power plant.This paper puts forward that the flue gas of the boiler is heated by GGH after condensation of the heat exchanger,so that the water is removed,the dew point temperature is reduced,even if the discharge to the atmosphere is difficult to condense.For flue gas condensation,heat exchanger is an essential equipment.So this paper studies the characteristics of convection condensation heat transfer of flue gas from thermal calculation and experiment.According to the previous research experience,the factors that may affect the heat transfer characteristics of the convective condensation are summarized,including the flue gas flow rate,the volume fraction of flue gas water vapor,cooling water temperature,cooling water flow rate.Taking into account the corrosion of the heat exchanger,the heat transfer characteristics of different heat exchanger materials should be considered.The influence of pipe diameter on the heat transfer characteristics of convective condensation is also considered.The factors that measure the heat transfer characteristics of convective condensation include the temperature of flue gas,condensate,condensation rate,heat transfer coefficient and so on.By thermodynamic calculation,the condensation water amount increases with the increase of the gas flow rate and the volume fraction of the flue gas.With the increase of the flue gas flow rate,the condensate water rate decreases,and the low flue gas velocity and high moisture are more suitable for the recovery of condensed water.Through the study of the cooling water quantity,it is found that the better the cooling water quantity is,the better the effect of convection condensation heat transfer,but the effect is more and more obvious.From the economy to consider,100L/h is the best condensate water.And the convective condensation heat transfer is enhanced with the decrease of the cooling water temperature.The study also found that,for the 0.5mm wall thickness of the PTFE heat exchanger if necessary to achieve the same heat transfer effect and stainless steel heat exchanger,heat transfer area to increase by 33%.And from the angle of strengthening the heat transfer,if the change of the heat transfer area is not changed,the size of the diameter of the convective condensation heat transfer enhancement.Then experiments and theoretical calculation results are compared,a number of differences are found,and then analyzes the reasons.The first is the actual condensation rate is less than the theoretical condensation rate,the main reason is the condensation of droplets can not be recycled,and the stronger the flue gas velocity,the less condensation rate.By comparing the theory with the actual flue gas temperature,it is found that their remains some differences between two temperatures.This is mainly because of inaccuracy of convective heat transfer formula when condensation happens,another reason is the neglect of thermal resistance condensate layer.The third is that the flue gas condensation occurs when flue gas temperature is above the dew point temperature,this is because the temperature of the wall of the heat exchanger is lower than the dew point temperature,so there will be a small amount of condensation occurred.Finally,the experimental results show that the diameter of the pipe is enhanced by convection condensation heat transfer.