| The storage tanks were an important part of volatile organic compounds（VOCs）fugitive emission sources of the petrochemical industry.VOCs fugitive emission of storage tanks in petrochemical industry caused critical problems of environment and oil product loss,which was represented by withdrawal loss of floating roof tanks.First of all,a model instrument was designed for simulating the oil loading process by the hexane,octane,gasoline,diesel oil and crude oil as the research object.The factors affecting withdrawal loss of floating roof tanks were properties of tank wall corrosion,rim seal,liquid and wall material were investigated.Secondly,the corrosion resistance of tank wall coatings was researched with electrochemical method.Thirdly,the oil vapor-air diffusion was numerically simulated by CFD during the loading process of floating roof tank.Finally,floating roof tanks of a petrochemical enterprise is taken as an example to analyze the withdrawal loss and effective measures for decreasing withdrawal loss were proposed.The main conclusions are as follows:（1）The theoretical calculation formula shows that the key parameters influencing withdrawal loss of external floating tanks were shell clingage factor firstly,and then annual turnover volume and organic liquid density.The key parameters influencing withdrawal loss of internal floating tanks were shell clingage factor firstly,and then annual turnover volume and number of columns.（2）According to the model instrument of simulating the oil loading process,it was found that there was a positive correlation between the withdrawal loss and the viscosity,density and the corrosion of the tank wall.The effect of the scraping oil was more obvious with the rim seal enhanced.In addition,the tank surface roughness reduces the compression of rim seal on the tank wall,meanwhile the effect of scraping decreased.Analyzed the sensitivity of factors influencing the withdrawal loss by Analytic Hierachy Process（AHP）and Multivariate Analysis of Variance,it can be seen that the degree of corrosion has the greatest influence on the withdrawal loss,and then liquid viscosity,turnover,rim seal,tank diameter and tank wall material.Therefore,AP-42 withdrawal loss formula for floating roof tank is recommended to take into full account the effect of the rim seal to improve the accuracy in loss evaluation.（3）The study of corrosion resistance of tank wall coating found that in the initial immersion,the impedance of the epoxy resin coating and epoxy-zinc resin coating were larger and the corrosion rate of carbon steel was extremely small because of the solution has not penetrated into the interface of the coating and the carbon steel substrate.The capacitive arc resistance of the coating showed a decreasing trend and the anti-corrosion performance of the coating became gradually reduced with the immersion time.In the middle immersion,as the solution medium continuously penetrated into the interface betweem the coating and carbon steel,more and more corrosion products were generated at the interface.The resistance value of the coating was increased due to the corrosion products increased,so that the corrosion resistance of the coating increased and the corrosion rate of the carbon steel slowed down.In the later part of immersion,the corrosion of carbon steel was severe because the coating resistance was minimized with the appearance of blistering and peeling,and the coating basically failed.In addition,the corrosion resistance of epoxy-zinc resin coating was better than the epoxy resin coating.（4）The oil vapor-air diffusion was numerically simulated during the loading operation for floating roof tank showed that the rate of uniform distribution of oil and gas in the tank vapor space can be increased by increasing the loading speed,and then reduce the evaporation loss.The increase in initial oil-gas mass fraction decreased the gradient of oil-gas mass fraction of the tank,thus reducing the evaporation rate of gasoline.Therefore,it was recommended that the loading speed and the initial oil-gas mass fraction should be considered in AP-42 withdrawal loss formula for floating roof tank by using an appropriate loading speed to reduce the evaporation loss.（5）The total withdrawal loss of floating roof tanks in a petrochemical enterprise was 1.82 t·a-11 or 180.83t·a-1 under light rust or dense rust condition,respectively.Finally,some measures of reducing the withdrawal loss were put forward in all-round from the source,process and end so as to provide some guidance of effectively reducing the evaporation loss of oil and gas in the storage tank. |
