Industrial equipment to complete the absorption operation is collectively referred to as the
Absorption Tower. Commonly, there are two kinds of plate tower,
Packed Tower. Plate tower is mostly used for distillation operations, packed tower is mostly used for absorption operations.
First, the structure of the packed tower
Packed tower is mainly composed of tower, packing and its accessories (defoaming device, liquid distribution device, gas distribution device, packing support device, packing compression device, etc.).
1-foam remover; 2-liquid distributor; 3-packing limiter; 4-shell; 5-packing; 6, 8-unloading packing holes; 7-liquid re Distributor; 9-Packing support plate; 10-Overflow port
Packed tower operation, the gas is fed from the bottom of the tower, distributed by the gas distribution device (small-diameter tower is generally not equipped with gas distribution device) distribution, under the action of differential pressure from the bottom upward and the liquid is countercurrent through the packing layer of the gap continuously, while the liquid from the upper part of the tower into the liquid distribution device evenly sprayed through the liquid redistributor. Into the tower, through the liquid distribution device evenly sprayed on the tower cross-section, under the action of gravity along the packing layer downward flow. On the packing surface, the gas and liquid phases are in close contact for mass and heat transfer.
Packed tower belongs to continuous contact gas-liquid mass transfer equipment, packing layer gas-liquid two-phase countercurrent contact, packing wetting surface for gas-liquid two-phase contact mass transfer surface, gas-liquid two-phase composition along the tower height of the continuous change, under normal operating conditions, the gas phase is continuous phase, liquid phase is dispersed phase.
Under normal operation, the gas phase is continuous and the liquid phase is dispersed.
Second, the characteristics of packed tower
Compared with the plate tower, packed tower has the following characteristics:
1, large production capacity. Packed tower inner pieces of large openings, large void rate, liquid flood point is high.
2, high separation efficiency. Suitable for dealing with difficult to separate the separation of mixed gases, tower height is lower.
3.Small pressure drop, suitable for decompression operation, and low energy consumption.
4.Smaller liquid holding capacity, suitable for dealing with heat-sensitive materials.
5, less flexible operation, more sensitive to changes in liquid load, if the liquid load is small or large, easy to produce dry tower or liquid flooding phenomenon.
6.It is suitable to deal with easy to foam and corrosive materials, can use filler defoaming and anti-corrosive materials made of filler.
7.It is not suitable to deal with solid or easy to polymerize the material, because the cleaning is more trouble.
Third, the role of filler
1, to provide gas-liquid contact area;
2, strengthen the gas turbulence, reduce the gas-phase mass transfer resistance;
3, renew the liquid film surface, reduce the liquid phase mass transfer resistance.
Packing is good or bad to determine the performance of the packing tower is the main factor in the operation of the packing characteristics have a greater impact on the surface area, void rate, packing factor and the number of packing per unit of stacked volume.
Fourth, the performance of the filler
In order to make the packing tower to play a good performance, the filler should meet the following main requirements.
1, to have a large surface area per unit volume of packing layer has a surface area known as the specific surface area of the filler, expressed in δ, the unit is m2/m3. The surface of the filler is only wetted by the liquid phase of the flow, to constitute an effective mass transfer area. Therefore, the packing is also required to have a good surface area.
Therefore, the packing is also required to have good wettability and shape conducive to the uniform distribution of liquid. The same kind of filler, the smaller the size, the larger the surface area.
2, the requirement of a high void rate per unit volume of filler has a void volume called filler void rate, expressed in ε, the unit is m3/m3. Generally speaking, the void rate of filler more in the range of 0.45 ~ 0.95, when ε is higher, the gas-liquid through the ability to large
When ε is higher, the gas-liquid throughput capacity is large and the airflow resistance is small, and the operation elasticity range is wide.
3, the requirements of packing factor is small δ and ε combined into δ / ε3 form that is the dry packing factor, the unit is m-1. packing factor represents the hydrodynamic properties of the packing. When the packing is sprayed liquid wetting, packing surface covered with a layer of liquid film, δ and ε
When the filler is wetted by the spray liquid, the surface of the filler is covered with a liquid film, δ and ε change accordingly, and at this time δ/ε3 is the factor of wet filler, which is expressed as φ. If the value of φ is small, the resistance of filler layer is small, and the gas velocity is increased when liquid flooding occurs, that is to say, it is a good performance of fluid dynamics.
4, the number of fillers per unit stacked volume is appropriate For the same kind of filler, the number of fillers contained in the unit stacked volume is determined by the size of the filler. Packing size decreases, the number of fillers increases, the specific surface area of the packing layer also increases, and the void rate is small, the gas resistance.
Gap rate is small, the gas resistance is also a corresponding increase in packing cost. Conversely, if the size is too large, near the tower wall, the packing layer gap is very large, there will be a large number of liquid through this short circuit. In order to control the uneven distribution of gas-liquid phenomenon, the packing size should not be larger than
In the tower diameter D 1/10 ~ 1/8.
In addition, but also requires packing economic, practical and reliable, requires packing unit volume of light weight, low cost, durable, not easy to block, there is enough institutional strength, for the gas-liquid two-phase media have good chemical stability. Practical application
When the actual application, a variety of filler can not have all of the above requirements, need to be based on specific circumstances to choose.
5. Types of packing
Types of filler according to the shape of the filler, there are mesh filler and solid filler;
According to the material, there are
Metal Filler, plastic filler, ceramic filler and graphite filler;
According to the filling method points, there are bulk (chaotic pile) filler and regular filler. Bulk packing is a class of particles with a certain geometric size, stacked in a bulk manner in the tower.
According to the different structural characteristics, generally divided into ring-shaped packing, saddle-shaped packing, ring saddle-shaped packing and ball packing. Regular packing is a kind of packing which is discharged neatly and regularly in the tower, and it is divided into grid packing, corrugated packing, pulse packing, etc. according to different geometrical structures.
etc.
Commonly used in industrial production of packing: Lacy ring, Bauer ring, ladder ring, arc saddle ring, saddle ring, ball, corrugated packing and pulse packing.
Source: Reprint
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