除尘系统管道粉尘爆炸加速机制研究

Tearing damage occurred in the middle of the dust removal pipe in Kunshan accident, and this is the proof of explosion acceleration in the propagation process through the pipeline. With both sides of the pipe was arranged with dust collecting branches which should have explosion venting effect, the damage phenomenon of the dust removal pipe is defying the common sense. The lifting and transporting effect on chosen dust samples such as polishing aluminium dust and corn starch caused by the shock wave from the initial explosion in the dust remover will be investigated under the existed equipment and the one planned to develop experimental system. The critical condition for the secondary explosion caused by the initial explosion in the filter and the mechanism of flame acceleration and pressure transmission will be investigated systematically. Complete explosion propagation model in the dust removal system will be established, and then numerical experiments on dust explosion propagation process will be conducted on more complex conditions. Aiming at different explosion level of combustible dust, the designing criteria for dust removal and venting system will be made. The safety and reasonable designing criteria will provide important theoretical and practical guidance for preventing catastrophic explosion accidents to happen in process industries with the existing of dust.

昆山事故中，除尘主管道在两侧存在多吸尘支管的情况下，中间段仍出现了撕裂性破坏，表明铝粉爆炸在管道内有明显的加速传播，支管开孔未发挥预期的泄爆作用。项目通过部分已有和预搭建的除尘管网爆炸测试系统，以抛光铝粉和玉米淀粉为代表，系统研究除尘器初始爆炸产生的冲击波对管道内粉尘卷扬以及运移作用；得到由除尘器初始爆炸引发除尘管道内二次爆炸的临界条件以及火焰加速和压力传播机理；建立完善的除尘系统管道粉尘爆炸传播模型；对更广泛复杂情况下粉尘爆炸传播过程进行数值实验；针对不同爆炸级别的可燃粉尘，提出安全、合理的通风除尘管道防爆安全设计准则，为防治粉尘涉爆企业发生灾难性粉尘爆炸事故提供实验依据和理论指导。

课题组在Hartman粉尘爆炸实验仪上利用高速摄像和PIV技术观测、分析了粉尘在小型带支管管道中的扩散、运移规律，建立了火焰图像识别模型，表明粉尘可进入支管并发生火焰传播，且火焰具有涡流、逆流等传播特征，支管管径增大对支管内的火焰传播过程的加剧远大于管径增大泄压对火焰传播的削弱。支管存在对主管道粉尘爆炸起压力泄放作用，但当支管内发生粉尘燃烧时该泄压作用减弱。主管道内火焰传播加剧可增强支管内的火焰传播，当主管道爆燃减弱时支管内爆燃也将随之变弱。课题组进一步建立了工业量级的除尘系统爆炸模拟管路，包括直管道、分叉管道、变径管道及弯管4种典型除尘系统异形管道类型，通过物理实验和数值模拟分析，揭示了除尘器内的初始爆炸在各种管道内爆炸超力和爆炸火焰的发展、传播规律，总体上管道的存在对除尘器内部超压的影响较小，主要是泄压引起的抑制超压作用，但分叉构件、变径管及弯头管道对超压的抑制作用小于直管道，原因是异形管道内的反射波阻碍了冲击波的泄放；但各种管道对爆炸火焰的传播速度都有极大的加速作用，火焰速度均随着传播距离的增加而上升，尤其是带有变径比较大的变径管的直管道（如C型管道），即便是在300g/m³较低的粉尘浓度条件下，管道末端的最大火焰速度也达到了550m/s，接近爆轰水平。基于此，除尘系统的设计从控制爆炸超压的角度应增加直管道、减少U型管、降低除尘器内粉尘浓度，从降低火焰传播速度角度应增加弯头数量、减少变径管、避免管道粉尘沉积，以控制管道内爆炸加速导致的严重后果。