Acid Corrosion、Ash Deposition And Heat Transfer Characteristics Of External Surface Of Dust Gas Cross-Flow 3-D Finned Tubes

China consumes about 400 million tons of standard coal for coal-fired boilers every year,but the heat loss of exhaust gas of coal-fired boilers is generally high,and the recovery rate of residual heat is low.The traditional smooth tube heat exchanger has the disadvantages of flue gas waste heat recovery in low heat transfer efficiency and large floor area.Due to the severe turbulence of the three-dimensional fin structure on the surface,the three-dimensional finned tube has high heat transfer efficiency and is considered to have great potential in the field of industrial waste heat recovery.However,the presence of acid gas and fly ash particles in the flue gas will cause low temperature corrosion on the surface of the heat exchanger,and viscous ash deposition will affect the heat transfer efficiency.Therefore,in this paper,the simulated flue gas method is used.Firstly,the influence of the change of working conditions on the low-temperature corrosion of the three-dimensional finned tube when the flue gas cross-flow the tube is studied,and the influence of the working conditions on the acid deposition rate of the three-dimensional finned tube surface is obtained;then,the fly ash particles are added into the low-temperature flue gas,the corrosion ash deposition characteristics of the three-dimensional finned tube surface are analyzed from the parameters of different working conditions and fin structures.Finally,the influence of the corrosion ash on the heat transfer performance of the three-dimensional finned tube is studied.The Nu of the three-dimensional finned tube with the corrosion and ash deposition is obtained.At the same time,the heat transfer performance of the smooth tube and several special working conditions are analyzed and compared.,so as to provide some reference for the engineering application of the three-dimensional finned tube.The main results are as follows:Hydrogen evolution corrosion mainly occurs on the windward side and oxygen absorption corrosion mainly occurs on the leeward side in low-temperature corrosion at the cooling water inlet temperature of 30 ℃;with the decrease of cooling water inlet temperature,the acid deposition rate increases first and then decreases,oxygen corrosion is increasing;with the increase of flue gas velocity and acid volume fraction,the acid deposition rate increases continuously.The inlet temperature of cooling water has obvious effect on the morphology of corrosion ash deposition.When the inlet water temperature is reduced,the amount of corrosion ash deposition of three-dimensional finned tube increases;the amount of corrosion ash deposition of three-dimensional finned tube increases gradually with the increase of fly ash concentration and acid volume fraction in flue gas.With the increase of fin height and fin width,the amount of corrosion ash deposition increases first and then decreases,which is the most at the fin height of 4.5 mm and fin width of 4 mm;with the increase of axial spacing,the amount of corrosion ash deposition decreases continuously.In the process of corrosion and ash deposition,the heat exchange performance of the three-dimensional finned tube decreases with the increase of time under different working conditions and fin structures,it is basically stable finally.In the experimental range,the decrease of Nu of the three-dimensional finned tube increases with the decrease of the inlet temperature of the cooling water and the increase of the fly ash concentration and acid volume fraction.With the increase of fin height and fin width,the decrease of Nu first increases and then decreases;the decrease of the Nu decreases with the increase of axial spacing.The heat transfer performance of the three-dimensional finned tube is better than smooth tube,and the outside Nu is about1.6 times that of smooth tube.The Nu of the three-dimensional finned tube under the three working conditions decreases with the increase of time,and the heat transfer performance under the pure ash deposition condition is better than that under the wet ash deposition condition and is more better than that under the corrosion and ash deposition condition.