| In the chemical industry,the prevention and control of environmental pollution and safety in production have always been the focus of attention of enterprises.Accidents in chemical production will cause casualties and environmental pollution.At present,China’s chemical industry is in a highspeed development stage,but also exposed more safety and environmental problems.Many chemical enterprises are surrounded by cities or villages in geographical location.Once there is a production accident in the chemical production process,its consequences may cause casualties,environmental pollution and other serious consequences.In recent two years,"11.28" accidents occurred in 2018 and "4.24" accidents occurred in 2019 in domestic chlor-alkali industry.Both accidents were caused by leakage of vinyl chloride gas tank,which caused serious casualties and environmental pollution.The vinyl chloride wet bell jar gas holder used in the production process of chlor alkali industry has exposed serious safety and environmental problems,which need to be solved urgently.In this paper,the leakage,fire and explosion of vinyl chloride gas holder in domestic chlor-alkali production enterprises are taken as the research object,and the coupling mechanism of accident occurrence,spread and multiple disasters is analyzed by numerical simulation.From the simulation results,we can find the key nodes of multiple disasters coupling and cutting off the accident chain,find the ways of cutting off the chain for disaster reduction,so as to cut off or reduce the casualties and environmental pollution caused by the accident,improve the intrinsic safety of the industry,and reduce the production source of environmental pollution.This study provides technical support for domestic chlor-alkali production enterprises to reduce the occurrence of vinyl chloride gas tank accidents and curb the occurrence of safety and environmental accidents.Through the study of the existing production process parameters of the vinyl chloride wet gas holder in the typical domestic chlor-alkali production enterprises,the connection and mutual influence with the production process before and after,as well as the layout of the equipment and facilities around the vinyl chloride gas holder and the characteristics of the surrounding environment,it is shown that the possible types of accidents caused by the vinyl chloride gas holder are both negative pressure explosion accidents and positive pressure leakage accidents.The harm of negative pressure explosion accident is the harm of surface overpressure caused by explosion to personnel and equipment,and the positive pressure leakage accident will lead to poisoning and explosion accident chain.Most of the two accidents are caused by process control failure or operation error or equipment failure.The severity of the two accidents is mainly affected by the surrounding environment.Based on the hydrodynamics,the leakage accident chain transfer model of VCM gasholder is established by UG,COMSOL and Multiphysics software to simulate the relationship between the spatial distribution of VCM gas and the leakage time after the leakage accident of VCM gasholder.The simulation results show that the leakage rate is 3.47kg/s when the control of vinyl chloride from the vinyl chloride monomer synthesis section to the gas tank fails,When the leakage time reaches 120 s,the "toxic end point concentration-1" of vinyl chloride environment is about to spread to the outside of the plant,while the "toxic end point concentration-2" range has reached the maximum value,and the range is small,and the scope of toxic harm is mainly manifested as "toxic end point concentration-1".When the control of vinyl chloride from the monomer storage tank to the gas tank fails,the leakage amount is 68.74kg/s,the leakage time reaches 120 s,"toxic end point concentration-2" range has spread to the outside of the plant,and the toxic harm range mainly displays as "toxic end point concentration-2".Therefore,under the two failure scenarios,the effective control time of the leakage accident is set within 120 s,which can effectively reduce the safety and environmental hazards caused by the leakage of vinyl chloride gas tank.Based on the leakage accident transfer model,the leakage early warning app is developed to provide early warning technical support for the production enterprises.Based on the simulation results of leakage transfer model,combined with TNT equivalent method and MATLAB software,the combustion and explosion accidents caused by vinyl chloride gas tank are simulated and analyzed.The maximum surface overpressure and death radius of VCM gasholder were 0.49 mpa and 21 m respectively.Based on the simulation results of leakage transfer model,the space range and volume concentration of vinyl chloride gas will not change with the leakage.The maximum surface overpressure is 0.31 mpa and the death radius is 15.1,which will cause harm to acetylene gas tank,compressor room and pipe gallery.In this study,the traditional TNT equivalent method is modified to calculate the energy of combustion and explosion,and the calculation method of "leakage combustion and explosion" is established.This study shows that it is not feasible to prevent and control the risk of combustion and explosion of vinyl chloride gas holder based on the method of increasing the safety distance,increasing the safety distance between vinyl chloride gas holder and acetylene gas holder,increasing the space range of vinyl chloride gas combustion and explosion,while the maximum surface overpressure caused by combustion and explosion is basically the same.Based on the improvement of the existing wet bell jar gas holder,this paper designs a "double hood semi underground wet gas holder with automatic leakage treatment".Through LOPA analysis,the failure probability of the original gas holder is reduced by 10000 times.The improved gas tank is an active defense technology for gas tank accidents,which can be used for the storage of vinyl chloride or other insoluble or slightly soluble gas. |
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