Study On Volatilization And Diffusion Simulations Of Combustible Gas During Anti-corrosion Construction Of Chimney And Their Safety Measures

Chimney anti-corrosion construction involves the operations of high-altitude,limited space,temporary electricity use and hazardous chemical substances use,etc.The anti-corrosion coatings used in chimney anti-corrosion projects often contain volatile flammable and explosive substances such as xylene,acetone,et al.,which lead to large risks of fire and explosion accidents during the practical construction.In this paper,a real chimney anti-corrosion project was taken as the research object.The numerical simulation analysis on the volatile diffusion effect of the anti-corrosion coatings under different working conditions were proceeded by Computational Fluent Dynamic(CFD).The improvement of chimney anti-corrosion process and equipment improvement was achieved by the Inherent Safety Design(ISD)method,and finally some comprehensive risk management and control measures for the fire and explosion accidents were produced with pertinence and rationality.The present study provides some fire and explosion prevention and risks control strategies with regard to the chimney anti-corrosion construction.The research results were summarized as follows:(1)The modelling and verification of the combustible gas volatilization and diffusion model during the construction process.Based on an actual fire accident in the chimney anti-corrosion project,the explosion risk factors of the accident were analyzed.The CFD techniques were used for modelling the combustible gas volatilization and diffusion model during the construction process,which considered two kinds of volatilization sources.The model was simulated under the accident conditions and then the reliability of the model was verified through experiment.The results showed that the average relative error between the experimental and simulation data was within 3%,which demonstrated the numerical model was reliable.(2)The simulation and analysis on the volatilization and diffusion effects of combustible gases in the chimney under different working conditions.The volatilization and diffusion effects of combustible gases in the chimney under different wind speeds from chimney inlet,different wall coating areas and ventilation condition were simulated.Additionally,the variations of combustible gas concentration vs.working time under different conditions were analyzed.The results showed that except for the condition of ventilation,the explosion atmosphere had always been formed in the lower hanging basket,and the concentration of xylene in the hanging baskets could reach explosion limits and maintain rapidly increasing tendency in 0-15 minutes,and the increasing rate decreased over time after 15 minutes.(3)The improvement on chimney anti-corrosion process and equipment safety based on the ISD techniques.Considering the ISD principles,construction efficiency and cost,the linkage system of concentration determination and alarm with the ventilation was produced,which should be installed in the original chimney anti-corrosion process and is capable of controlling the concentration of combustible gas to 1%-5% of the LEL.Subsequently,the Inherent Safety Index(ISI)method was applied to evaluate the inherent safety levels of the process and equipment before and after the improvement.The results showed that the overall intrinsic safety level was improved significantly,increasing about 40%.(4)The establishment of the risk management and control model for fire and explosion accidents in chimney anti-corrosion projects.Based on the theories of Layers of Protection(LOP)and Safety Barriers(SB),the LOP-SBM model for risk management and control of fire and explosion accidents in chimney anti-corrosion projects has been established,with 3 levels of protection layers,under which there were 20 security barriers.Moreover,the risk management and control measures involved in each safety barrier were elaborate.The level of confidence(LC)of all the 3 levels of protection layers were then evaluated,and the results showed that they were all in LC3 or LC4.The reliability of this accidents risk management and control model is good.