隧道式叶丝回潮机排气罩结构的优化设计

Optimization design of exhaust hood in tunnel type tobacco conditioner

为解决隧道式叶丝回潮机在生产过程中存在的因排气罩吸风速度过快、风量过大等原因导致大量叶丝颗粒进入后续生产工序等问题,对排气罩进行了两次优化设计。第一次优化,将罩体底部由敞开式改为封闭式,并将罩体高度增加1 m;第二次优化,在罩体内部增加两块空气挡板,并在罩体壁上开设一条空气条缝。利用流体力学理论和数值模拟方法,建立了罩体内部流场和叶丝颗粒运动数学模型,通过对两次优化方案进行数值模拟,研究了叶丝颗粒运动轨迹与罩体形状、尺寸及内部结构之间的关系。结果表明:1一次优化后进入排气罩内的空气量减少23.5%,在罩体内停留时间大于10 s的叶丝颗粒占68.4%,悬浮的叶丝颗粒容易粘附在罩体内壁上,并发生颗粒沉积和脱落现象。2二次优化后停留时间大于10 s的叶丝颗粒仅占22.8%,粘附内壁现象明显减少;实现了叶丝颗粒的回收利用,回收率达80.67%;出口处颗粒浓度为37.5 mg/m^3,达到工艺排放允许浓度要求。两次优化后减少了排气罩内叶丝沉积现象,提高了叶丝利用率和产品质量。

In order to minimize tobacco particles from being drawn into the exhaust hood in the tunnel type conditioner, the exhaust hood was redesigned. As the first step, the bottom of exhaust hood was changed from open type into close type, and the height of the hood was increased by 1 m. As the second step, two air baffle plates were installed inside the hood, and a slot was created on hood wall. A mathematical model for flow field and tobacco particle movement inside the hood was established based on fluid mechanics theory, and the relationship of tobacco movement trajectory with the shape, size and inside structure of the hood was studied via numerical simulation. The results showed that： 1） After the first step, the volume of air entering into the exhaust hood reduced by 23.5%, 68.4% of the tobacco particles entering into in the hood stayed there for longer than 10 s. The airborne tobacco particles tended to build up on the hood wall, it might drop off occasionally. 2）After the second step, the tobacco that stayed in the hood longer than 10 s only accounted for 22.8%, the amount of tobacco building up on the hood wall reduced obviously. The recovery rate of tobacco particles reached 80.67%, its concentration at the exit was 37.5 mg/m^3, which satisfied the requirement for allowable emission concentration, and the utilization rate of strips and cigarette quality were promoted.