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板式精馏塔设计

2021-07-20 17:48:22
板式精馏塔设计
详细介绍:


板式精馏塔设计内部原理:液体靠重力作用由顶部逐板流向塔底排出,并在各层塔板的板面上形成流动的液层;气体则在压力差推动下,由塔底向上经过均布在塔板上的开孔依次传播各层塔板由塔顶排出。

塔板上气液两相的接触状态是决定板上两相流流体力学及传质和传热规律的重要因素。当液体流量一定时, 随着气速的增加,可以出现以下几种接触状态:

1. 鼓泡接触状态气速 

较低时,气体以鼓泡形式通过液层。由于气泡的数量不多,形成的气液混合物基本上以液体为主,气液两相接触的表面积不大,传质

效率很低。

2. 蜂窝状接触状态

随着气速增加,气泡数量不断增加。当气泡形成速度大于气泡浮升速度时气泡在液层中累积。气泡间相互碰撞,形成各种多面体的大气

泡。由于气泡不易破裂,表面得不到更新,所以此种状态不利于传热和传质。

3. 泡沫接触状态

当气速 继续增加,气泡数量急剧增加,气泡不断发生碰撞和破裂,此时板上液体大部分以液膜的形式存在于气泡之间,形成一些直径较小,扰动十分剧烈动态泡沫,由于泡沫接触状态表面积大,并不断更新,是一种较好的接触状态。

4. 喷射接触状态

当气速继续增加,把板上液体向上喷成大小不等的液滴,直径较大的液滴受重力作用落回到塔板上,直径较小的液滴被气体带走,形成液沫夹带。液滴回到塔板上又被分散,这种液滴反复形成和聚集,使传质面积增加,表面不断更新,是- -种较好的接触状态。

板式精馏塔设计小编提醒大家,因喷射接触状态的气速高于泡沫接触状态,故喷射接触状态有较大的生产能力,但喷射状态液沫夹带较多,若控制不好,会破坏传质过程,所以多数塔均控制在泡沫接触状态下工作。



The internal principle of the design of the plate rectification tower: the liquid is discharged from the top plate to the bottom of the tower by gravity, and a flowing liquid layer is formed on the plate surface of each layer of the plate; the gas is driven by the pressure difference and passes upward from the bottom The openings evenly distributed on the tower plate spread each layer of the tower plate in turn and are discharged from the tower top.


The contact state of the gas-liquid two-phase on the plate is an important factor that determines the hydrodynamics of the two-phase flow on the plate and the law of mass and heat transfer. When the liquid flow rate is constant, as the gas velocity increases, the following contact states can occur:


1. Air velocity in bubbling contact state

When it is lower, the gas flows through the liquid layer in the form of bubbling. Due to the small number of bubbles, the gas-liquid mixture formed is basically liquid, and the surface area of the gas-liquid contact is not large, and the mass transferlow efficiency.


2. Honeycomb contact state

As the gas velocity increases, the number of bubbles continues to increase. When the bubble formation speed is greater than the bubble rise speed, the bubbles accumulate in the liquid layer. The bubbles collide with each other to form various polyhedral atmospheres bubble. Since the bubbles are not easy to burst and the surface cannot be renewed, this state is not conducive to heat and mass transfer.


3. Foam contact state

When the gas velocity continues to increase, the number of bubbles increases sharply, and the bubbles continue to collide and rupture. At this time, most of the liquid on the plate exists between the bubbles in the form of a liquid film, forming some dynamic bubbles with small diameters and very violent disturbances. The contact state has a large surface area and is constantly updated, which is a good contact state.


4. Spray contact state

When the gas velocity continues to increase, the liquid on the plate is sprayed upward into droplets of varying sizes. The droplets with a larger diameter fall back to the plate by gravity, and the droplets with a smaller diameter are taken away by the gas to form liquid droplets. Entrainment. The droplets return to the tray and are dispersed again. Such droplets are repeatedly formed and aggregated, increasing the mass transfer area and constantly renewing the surface, which is a better contact state.


The design editor of the plate rectification tower reminds everyone that because the gas velocity in the spray contact state is higher than the foam contact state, the spray contact state has a larger production capacity, but the spray state has more liquid foam entrainment, and if it is not well controlled, it will be destroyed During the mass transfer process, most towers are controlled to work in the foam contact state.

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