Study On Ignition Characteristics And Flame Retardancy Of PMMA Dust Layer Accumulation On Hot Surface

In the actual industrial production process,combustible dust may be accumulated on the hot surface of industrial equipment or pipelines due to improper production or management.Due to the high temperature of the equipment surface,it can cause fires and even explosions under certain conditions.Caused heavy casualties and property losses.In order to effectively prevent and reduce the risk of ignition by dust accumulation on hot surfaces and reduce the possibility of accidents from the source,this study is based on investigating the ignition behavior of the PMMA dust layer under different conditions,reveals the influence of dust particle size,dust layer diameter and dust layer thickness on fire sensitivity.The flame retardant effects of KHCO₃ and ABC on PMMA have been investigated,and the flame retardant mechanism has been revealed.The main conclusions are as follows:The pyrolysis of PMMA generates a variety of combustible gases including C₂H₄,CO and MMA.When the concentration reaches the Lower Flammability Limit,it can cause the dust layer to burn under the action of the ignition source.The surface reaction of finer dust particles is more intensive,resulting in lower pyrolysis temperature and shorter ignition delay time.As the heating temperature increases,the ignition delay time of the dust layer gradually decreases.The ignition delay time and critical heating temperature of the PMMA dust layer increase with the increase of the thickness of the dust layer.As the thickness of the dust layer increases,the depth of gas diffusion increases significantly,and the combustible gas cannot diffuse effectively,which eventually leads to an increase in ignition delay time.For a 10 mm thick dust layer,the critical heating temperatures for 100 nm,5μm and 30μm PMMA dust layers are 330℃,300℃ and 320℃,respectively.When the thickness of the dust layer increases to 30 mm,the critical heating temperature of the 100 nm,5μm and 30μm PMMA dust layers increase by 30℃,80℃ and 110℃.The increase in the diameter of the dust layer has a week effect on the heat transfer in the dust layer and the pyrolysis process.When the diameter of the dust layer increases from 50mm to 100 mm,the temperature in the dust layer changes slightly,and the ambient temperature drops slightly,resulting in an increase in the Lower Flammability Limit of combustible gas,and finally the ignition delay time of the dust layer increases by less than7.5%.KHCO₃ and ABC can effectively extend the ignition delay time of the PMMA dust layer and increase the critical heating temperature of the dust layer.Among them,the flame retardant effect of ABC is better than that of KHCO₃.For 10 mm thick 5μm and 30μm PMMA dust layers,when the heating temperature is 400℃,40%KHCO₃ can increase the ignition delay time of 5μm and 30μm PMMA by 288.3%and 750%,respectively.After adding 40%ABC,the ignition delay time of 5μm PMMA is increased by 398.3%,while 30μm PMMA can no longer be ignited.For 10 mm thick 5μm and 30μm PMMA dust layers,adding 10%KHCO₃ can increase the critical heating temperature by 60℃ and 40℃,respectively.Similarly,adding 10%ABC can increase the critical heating temperature of 5μm and 30μm PMMA by 80℃ and 60℃ respectively.The endothermic process of decomposition of KHCO₃ and ABC can inhibit the pyrolysis of PMMA.The decomposition of KHCO₃ to generate a large amount of CO₂ can effectively dilute the combustible gas generate by PMMA pyrolysis,reduce the concentration of combustible gas,thereby prolong the ignition delay time and even prevent the combustion of the dust layer.The P₂O₅ and HPO₃ generated by the thermal decomposition of ABC can cover the surface of dust particles and agglomerates to form a dense spherical shell,which prevents the heat and mass transfer process,thereby inhibiting combustion.