Functional Study Of Dust Explosion Isolation Flap Valves

Dust collector systems are common components where dust explosion occur.If an explosion is generated in one vessel,it is easy to propagate to other areas due to process interconnections,which may cause a more violent secondary explosion.The explosion isolation technology can effectively prevent the propagation of dust explosions in the container-pipeline interconnected system.Recently,protect process enclosures from a dust explosion by venting or suppression is widely recognized,the dust explosion isolation devices,however,is often ignored.Therefore,the functional test and numerical study of dust explosion flap valve can provide reference for understanding the flame propagation in large pipeline during explosion isolation,provide advice for improving the design of explosion isolation flap valve,and will have guiding significance for its application in industry.Set up test arrangement based on the 1m3 standard explosion test vessel,the corn starch as the material,and the DN600 flap valve explosion isolation experiments were conducted to evaluate its function,discuss the basic installation conditions that can be successfully isolated and analyze the reasons for the failure of the device.In addition,the Fluent software was applied to simulate the isolation process of the flap valve,including the two-dimensional corn starch dust explosion model was built and the dynamic process of flap closing was solved by the 6DOF dynamic mesh model.Analyze the pressure development and flame propagation behaviors,further deepen the understanding of the dust explosion isolation process.Moreover,study the factors that may affect the function of the explosion isolation flap valve,and obtain the minimum installation distance.The main conclusions are as follows:(1)The experimental results showed that when the pressure rises to the peak,the explosion venting plate was opened and the pressure dropped continuously with a stepped decay phenomenon.The flap closing time was 55～75ms in the case of isolation success.There are two main reasons for the valve failed the test:one is that the time for the flame to propagate to the flap is less than its closing,lead to the valve fails to prevent the flame in time;the other is that pressure bearing strength of the device is not enough to maintain its mechanical integrity.(2)The numerical results showed that the pressure development,flame propagation behaviors and flap closing process are consistent with the experiment.It is verified that the numerical model used in this paper can be well applied to the research,especially the dynamic simulation,which can be accurately revealed the flame propagation law and the flow velocity distribution variation in the flow field during the dust explosion isolation process.The valve had a negative effect on flame propagation which led to a decrease in flame speed;and as the flap is closed,the formation of backflow behind the valve is occurred due to the negative pressure,the pressure applied to the flap is the difference between the positive pressure before the valve and the negative pressure after the valve consequently.(3)Through simulation of the function test of the explosion isolation flap valve under different installation distances,it is obtained that the minimum installation distance of the DN600 flap valve should longer by a factor 6 to 7 than its diameter.If the installation distance is too short to stop the explosion pressure wave and flame from propagating through pipelines,the pressure and flame are vented through the valve in advance,causing the flow velocity behind the valve to increase significantly,on the other hand,weaken the angular velocity of the valve closing.(4)Furthermore,the speed of the flap movement is affected significantly by the rising rate of dust explosion pressure.The increasing explosion pressure rise rate often leads to the increased closing speed.The greater the mass of the flap,the harder it is to push,the explosion pressure rises more slowly,and the closing time is longer.The initial angle of the flap is smaller,the explosion pressure rises faster,and the closing time is shorter.The quality of the flap and the opening angle of the flap are larger,and the required minimum installation distance will increase to a certain extent.