Experimental Investigation And Numerical Simulation Of Grain Dust Explosion

The dust explosion hazard continues to represent a constant threat to process industries that manufacture, use and/or handle powders and dusts of combustible materials. Grain industry is a high dust explosion probability industry. With the application of new technology and the expansion of production scale, dust explosion accidents occur frequently and would usually cause heavy casualties and loss of property, and even catastrophic effect. Thus, intensive research work on grain dust explosion has important theoretical significance and engineering value for prevent and control of such hazardous industrial disaster. The features and innovative work product of the thesis are as follwos:A multi-function dust explosion test system was developed based on Ethernet and OPC technique. The data acquisition and control system developed in Lab VIEW has advantages as user-friendly GUI, easy to operate, efficient work, and has functions of experimental process control, automatic data acquiring, curve analysis, database management, etc. The communication between test computer and control box was achieved by OPC technique, which gives the test system good consistency, extensibility and maintainability. The control system of sub-system was connected in LAN, which facilitates comprehensive analysis of experimental data and ensure the integrity and consistency of test data. The 20L spherical explosion test apparatus with certain specific functions was developed, which is by far the only apparatus that support liquid dispersing of similar products and can determine explosion characteristics of combustible dust, gas and vapor. It is also by far the only apparatus that support large energy electrostatic ignition in lOkJ with integrated home-grown large energy electrostatic spark generator of similar products. The developed dust cloud minimum ignition energy test apparatus has a spark generator that integrated several triggering modes and users can select suitable one as needed.The experimental analysis about grain dust explosion in large scale interconnected vessels was conducted to study the fundamental law and influencing factors of grain dust explosion in complex configuration. The test dust is maize and potato starch. Study shows that factors as dust reactivity, ignition location, initial turbulence and dust concentration have important influence on development process of dust explosion. The more explosible a dust tends to be, the more violent is the explosion, and the faster is flame propagating velocity, and the more violent is the secondary explosion. The farther the ignition location is away from vent, the higher is the maximum reduced overpressure Pred,max in primary vessel, and the more violent is the secondary explosion. Initial turbulence has an important influence on dust explosion characteristics and especially on pressure rise rate. With increasing initial turbulence level, the explosion become more violent and propagating velocity of flame and shock wave increase. With suitable dust concentration, the final flame velocity and peak pressure caused by flame propagation are both higher. For interconnected equipments, primary explosion can cause pressure and flame to propagate through pipe. A positive feedback acceleration mechanism can be formed during flame propagating along pipe and lead to a secondary explosion finally. The experimental investigation promote greater understanding of grain dust explosion process and its influencing factors, and provide valuable information for safety protection and optimal design of dust explosion in complex configuration in grain industry, and accumulate valuable experimental data which can be used for validation in further numerical simulation investigation.A comprehensive mathematical model that describes explosion process of starch dust is established. Eulerian-Lagrangian two phase flow model is adopted and the particle phase is modeled by discrete random walk (DRW) model. The DRW model has the following advantages:easy to calculate; the motion of particle can be tracked better when particle undergoing complex change; numerical calculation won’t produce false diffusion; the effect of fluid’s turbulent pulsation on particle can be accounted for. Combustion model of starch particle takes account into detail mechanisms of water vaporization, volatile decomposition, gas phase reaction and surface reaction of carbon. EBU- Arrhenius model is used to simulate the reaction of gas phase which can solve the problem of inaccuracy calculation of turbulent combustion rate and thus improving the precision of numerical simulation. The developed model is a general one for organic dust explosion and is of great theoretical value and practical significance for grain dust explosion investigation.Numerical simulation of different dust explosion case has been carried out by using CFD code FLUENT, and the validity of numerical model has been checked by experimental data. Simulation of dust explosion in 1m3 closed vessel showed that numerical simulation can fully reflect deveploment process of explosion and predict the hazards of dust explosion in closed space. Simulation of dust explosion in 9.63m3 vented vessel showed that numerical simulation is well able to reflect flow and combustion features of explosion venting process. The fluctuation of pressure druing venting can be modelled well. It also shows that igniton location has remarkable effect on explosion development process. Th farther the ignition location is away from vent, the higher is Prcd.max value. Simulation of flame propagation in pipe showed that numerical simulation has reflected main feature of flame propagation in long pipe. In the whole explosion process, flame velocity continued to accelarate, the magnitude of pressure wave ahead flame front increased gradually and pressure rise rate become steeper and steeper. It also indicated that dust concentration has important influence on development of flame propagation. The simulated results have relative good agreement with experimental results and that turns out the applicability and accuracy of the developed model and shows that it can be good in use of numerical simulation and analysis of dust explosion.The study of this thesis fills the gap of domestic investigation on grain dust explosion. The research results have important practical value, and provide certain theoretical foundation and scientific evidence for study, prevent and control of dust explosion hazard in grain industry, and lay a foundation for the further research...