The principle and structure of the packed tower can be understood at a glance!

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Packing column is a type of tower equipment. The tower is filled with an appropriate height of packing to increase the contact surface between the two fluids. For example, when applied to gas absorption, the liquid enters from the upper part of the tower through the distributor and drops along the packing surface. The gas flows counter-currently from the lower part of the tower through the packing pores, and interacts with the liquid in close contact. The structure is simple and maintenance is convenient. Widely used in gas absorption, distillation, extraction and other operations. 1 Structure of packed tower ◆ Packing layer: Provide a place for gas-liquid contact. ◆liquid distributor: Distribute liquid evenly to avoid channeling. ◆liquid redistributor: Avoid wall flow phenomenon. ◆support plate: Support the packing layer to distribute the gas evenly. ◆Demister: Prevent liquid from being entrained at the gas outlet at the top of the tower. The gas is fed from the bottom of the tower, and after being distributed through the gas distribution device (small diameter towers generally do not have a gas distribution device), it continuously passes through the gaps in the packing layer in countercurrent with the liquid. On the surface of the packing, the gas and liquid phases are in close contact for mass transfer. The packed tower is a continuous contact gas-liquid mass transfer equipment. The two-phase composition changes continuously along the height of the tower. Under normal operating conditions, the gas phase is the continuous phase and the liquid phase is the dispersed phase. 2 Accessories of the packed tower There are five accessories of the packed tower: packing support device, liquid distribution device, liquid redistributor, defoaming device, and packing compression device. ⑴The main purpose of the packing support device is to support the packing in the tower while ensuring the smooth passage of the gas and liquid phases. If not properly designed, flooding of packed towers may first occur on the packing supports. Requirements for packing support devices: ◆For ordinary packing, the free cross-sectional area of ​​the support device should not be less than 50% of the total tower area, and should be greater than the free cross-sectional area of ​​the packing layer ； ◆Has sufficient mechanical strength and stiffness ； ◆The structure must be reasonable, which is conducive to the even distribution of gas and liquid phases, has low resistance, and is easy to disassemble and assemble. ⑵Liquid distribution device distributes liquid evenly in the packed tower, which can increase the wetted surface area of ​​the packing. In order to improve the separation efficiency, the initial distribution of the liquid is very important. Commonly used liquid distribution devices include: Lotus type, disc type, alveolar type and porous ring tube type distributors, etc. The performance of a liquid distributor is mainly determined by the density of liquid distribution points of the distributor (that is, the number of liquid distribution points per unit area), the uniformity of each liquid distribution point, and the uniformity of the liquid phase composition on each liquid distribution point. The design of a liquid distributor mainly determines the structural size of these parameters. General requirements for the selection and design of liquid distributors: Liquid distribution should be even ； The free section ratio should be larger ； Great operational flexibility ； Not easy to block, not easy to cause mist entrainment and foaming, etc. ； It can be made of a variety of materials, and is easy to operate and install, and easy to adjust the level. ⑶Liquid redistribution device The function of the liquid redistribution device is to reduce the wall flow phenomenon. wall flow phenomenon: The liquid existing in the random packing layer gradually flows to the tower wall. Liquid redistribution devices are arranged at certain heights in the packing layer. Commonly used liquid redistribution devices include: Cone shape, trough shape, ascending tube shape, etc. Under normal circumstances, a liquid collector and a liquid distributor are generally used at the same time to form a liquid collection and redistribution device. The function of the liquid collector is to collect the liquid flowing down from the upper packing and then send it to the liquid distributor for liquid redistribution. ⑷De-foaming device When the operating gas velocity in the tower is high or the liquid foam entrainment phenomenon is serious, a defoaming device can be installed above the liquid distributor. Its main purpose is to remove droplets in the outlet air flow. Since the gas leaves the packed tower at the top with a large amount of liquid foam and mist droplets, in order to recover this part of the liquid phase, it is often necessary to install a demister at the top. Commonly used demisters include the following types:: ?Baffle-type demister, which is a device that uses inertia to separate droplets. It is generally used in small towers. ?The cyclone plate demister is composed of several fixed cyclone plates. When the gas passes through, it generates rotational motion, creating a centrifugal force field. Under the action of centrifugal force, the liquid droplets move toward the tower wall to achieve gas-liquid separation. It is suitable for occasions with large tower diameter and high purification requirements. ?Wire mesh demister, which is made of metal wire rolled into a disk shape with a height of 100-150. There are various installation methods. The pressure drop of gas passing through the demister is about 120-250Kp. The diameter of the wire mesh demister is determined by the maximum gas speed of the gas passing through the wire mesh. ⑸The packing compression device is installed on the upper end of the packing layer. Its function is to keep the packing layer as a bed with a fixed height, thereby maintaining a uniform void structure, making the operation normal and stable, and preventing the packing layer from loosening or jumping under conditions such as high pressure drop and instantaneous load fluctuations. divided into: Packing plate: Place it freely on the top of the filler and compress the filler tightly by its own weight. Suitable for bulk fillers made of ceramics and graphite. Its function is to prevent the relative movement of the packing when the gas speed (high pressure drop) and load suddenly fluctuate, thereby preventing the packing from loosening and being damaged. Because the filler is fragile, when debris accumulates in the gaps between the bed fillers and the void ratio of the filler layer decreases, the filler pressing plate can fall along with the filler layer, tightly pressing the filler without loosening the filler and reducing the production capacity and separation efficiency of the packed tower. Bed limiter board: Fixed on top of filler. 3. How to operate the packed tower. The operation of the packed tower is based on several aspects such as material balance, heat balance, phase balance and packed tower performance. The operating conditions of the tower are established and adjusted through the control system to make the packed tower meet the separation requirements. ⑴How packed towers operate: The liquid is sprayed from the top of the tower onto the packing through the liquid distributor and flows down along the surface of the packing. ； The gas is fed from the bottom of the tower, and after being distributed by the gas distribution device, it continuously passes through the gaps in the packing layer in countercurrent with the liquid. ； On the surface of the packing, the gas and liquid phases contact for mass transfer. ⑵Operating characteristics of packed towers: The packed tower is a differential contact gas-liquid mass transfer equipment, and the two-phase composition changes continuously along the height of the tower. ； Under normal operating conditions, the gas phase is the continuous phase and the liquid phase is the dispersed phase. 4 Fluid mechanics properties of gas-liquid two-phase The fluid mechanics properties of packed towers mainly include the liquid holding capacity of the packing layer, the pressure drop of the packing layer, liquid flooding, etc. ⑴The liquid holding capacity of the packing layer. Under certain operating conditions, due to the friction between the liquid film and the packing surface and the friction between the liquid film and the rising gas, some liquid stays on the packing surface and its gaps. ?definition: The volume of liquid accumulated in the packing layer per unit volume is expressed as (m3 liquid)/(m3 packing). ?The influence of liquid holding capacity: Generally speaking, appropriate liquid holding capacity is beneficial to the stability and mass transfer of packed tower operations, and can provide a larger gas-liquid phase contact area. ； However, if the liquid holding capacity is too large, the gaps in the packing layer and the gas phase flow cross-section will be reduced, which will increase the pressure drop and reduce the processing capacity. ?in conclusion: The liquid holding capacity should not be too small or too large. ⑵Pressure drop in the packing layer? Causes: During the operation, the liquid sprayed from the top of the tower flows downward in the form of a film on the surface of the packing by gravity. The frictional resistance between the rising gas and the falling liquid film forms the pressure drop of the packing layer. ?Influencing factors: The pressure drop is related to the liquid spray volume and gas speed: At a certain gas speed, the greater the liquid spray volume, the greater the pressure drop. ； Under a certain amount of liquid spray, the greater the gas velocity, the greater the pressure drop. source: Coal chemical industry knowledge base 20,000 chemical technology technology videos 500 online technology live broadcasts by industry experts 300 industry experts online real-time communication sources: Tianhuayun