Analysis And Experimental Study On Heat Transfer Mechanism Of Oil-soluble Fouling In Shell And Tube Heat Exchanger

In petrochemical production,heat exchangers account for more than 40% of the total equipment.99% of the shell and tube heat exchangers are plagued to fouling.According to authoritative data analysis,due to the damage caused by fouling,it accounts for 0.3% of the gross national product.Therefore,improving the heat transfer performance of the shell and tube heat exchangers has become a research hotspot.This paper mainly described the effect of heat exchanger fouling deposition on the heat transfer performance of the shell-and-tube heat exchanger,and the research object is ‘Oil-soluble fouling in shell-and-tube heat exchanger of Beijing No.1Yanshan Chemical Plant.’ The fouling characteristics of the oil-soluble fouling of the shell-and-tube heat exchanger were analyzed.Based on the analysis of oil-soluble fouling components,the formation process and main influencing factors of oil-soluble fouling were studied;By constructing an experimental test platform for fouling heat transfer parameters and using the fouling samples of typical shell-and-tube heat exchangers,a unit experimental study was completed,and data samples of thermal conductivity of fouling under different operating conditions were obtained,and oil-soluble fouling was obtained.The change rule of thermal conductivity of oil-soluble fouling at different thicknesses and different temperatures was obtained,so the regularity of the simulation results was verified;The CFD software was used to numerically simulate the heat transfer performance of the shell-and-tube heat exchanger.The influence of the thickness of the fouling layer and the medium temperature on the heat transfer performance of the shell-and-tube heat exchanger was studied.Combined with the simulation results and analysis experiments,the scale dissolution experiment was carried out,and the online cleaning process of the heat exchanger was revised.The following conclusions are obtained:(1)Using the TC-3200 high temperature thermal conductivity meter to obtain the relationship between the fouling thickness of the heat exchanger,the ambient temperature and the heat transfer performance of the heat exchanger.The verification results show that the influence of the polypropylene and asphalt scale thickness on thermal conductivity is coincident approximately;When the thickness of the dirt is constant,the comparison results of the thermal conductivity of polypropylene andasphalt dirt with the ambient temperature show that the higher the ambient temperature,the greater the thermal conductivity,and when the thickness of the dirt reaches 3mm,the effect of the ambient temperature on the thermal conductivity becomes significantly smaller;When the thickness of the two kinds of dirt changes at the same time,The thicker the scale layer,the smaller the thermal conductivity,and the resonance coefficient of the asphalt specimen is greater than that of the polypropylene specimen.(2)The results of numerical simulation analysis show that,as the fouling thickness of the heat exchanger increases,the shell side outlet temperature of the heat exchanger increases,the tube side outlet temperature decreases,the heat exchange becomes smaller,and the heat transfer coefficient of the shell and tube heat exchanger gradually decreases.The thicker of the fouling thickness,the lower the sensitivity of the thickness to the heat transfer coefficient.When the fouling thickness reaches 2mm,the thermal conductivity is close to the critical low value.As the inlet temperature of the tube side increases,the outlet temperature of the shell side of the heat exchanger rises,and the thicker of the fouling,the higher the outlet temperature of the shell side.The heat transfer coefficient of the tube and shell heat exchanger gradually decreases.Compared with the thickness of the fouling,the effect of the inlet temperature of the tube side on the heat transfer coefficient is slightly smaller than the thickness of the fouling.(3)Since the thickness of the scale reaching a critical value would has a great influence on the heat transfer performance,an experimental study of scale dissolution was conducted.The best formula for oil-soluble scale is obtained.The cleaning formula has been effectively verified in the online cleaning of oil-soluble fouling of the shell-and-tube heat exchanger of the No.1 Yanshan Chemical Plant,which provides positive effect for enterprises to improve production efficiency and ensures the efficient operation of the shell-and-tube heat exchanger.