Research On Optimization Of Flow Field Between Air Preheater And Desulfurization Tower Of Large Coal-fired Power Plant Boiler

The dust collector and the induced draft fan are two indispensable equipment in the flue system of coal-fired units.The uniformity of flow field in the inlet and outlet flue of the abovementioned equipment will directly affect the efficiency of the equipment and the safety of the unit operation.Recently,in order to implement the policy of "energy reduction and emission reduction",most domestic coal-fired units choose to install cryogenic economizer in the inlet flue of dust collector to reduce the energy consumption of the unit.The uneven flow field in the inlet flue of dust collector will aggravate the wear of heat exchange tube bundles in cryogenic economizer.At the same time,the uneven flow field in the inlet and outlet flues of the induced draft fan will seriously affect the safe operation of the induced draft fan.Therefore,it is of great engineering value and practical significance to study the existing problems of flow field between air preheater and desulfurization tower of coal-fired units and put forward pertinent optimization schemes.In order to solve the problems of severe wear of heat exchanger tubes of the lowtemperature economizer,wear of filter bags and abnormal vibration of the casing and outlet flue duct of the induced draft fan in an 660 MW unit boiler after energy saving and emission reduction modification,the flue duct system between the air preheater outlet and the desulfurization tower inlet of the unit was taken as the research object.Firstly,the flue flow field and the performance of the induced draft fan are tested,and the problems existing in the flow field and the reasons causing the abnormal vibration of the induced draft fan are preliminarily analyzed.Secondly,the numerical simulation software was used to simulate the dust collector and its inlet and outlet flue.According to the simulation results,the problems existing in the flow field in the flue were analyzed and the optimization scheme was designed.The results show that the unreasonable design of the inlet manifold of the dust collector is the main reason for the wear of the tube of the low-temperature economizer.The effect of adding the deflector in the flue is limited.By redesigning the flue shunt structure,the uniformity of the flue gas flow field can be effectively improved and the flue flow distribution deviation can be reduced;The uniformity of flow field distribution in front of heat exchanger tube bundles can be improved by adding a uniform plate with a hole ratio of 0.5 in the inlet flue of low temperature economizer.By installing a uniform plate between the electric field and the bag area of the dust collector,the flue gas velocity on the windward side of the bag area can be effectively reduced,and then the problem of bag wear can be solved.When the opening ratio of the uniform plate is between 0.4 and 0.6,the influence on the electric field is minimal.Changing the right-angle elbow of flue duct at the outlet confluence section of dust collector to two arc elbows can significantlyimprove the uniformity of flow field at the inlet of induced draft fan,and also reduce the flow resistance at the operation of the single-side fan.Finally,the flow field of the exit flue of induced draft fan was optimized by numerical simulation.The results show that the main cause of flue vibration is the mutual extrusion interference between the outlet flue gas of two side induced draft fans.Taking reasonable measures to avoid the mutual interference of flue gas can significantly reduce the vibration amplitude of flue.