Plate column and packed column are two main types of distillation column. Although they are very common in distillation operation, there is a great difference between them. Tower type selection, operation characteristics, equipment performance, applicable occasions have their own characteristics. Today Xiaobian will tell you about this way.

Comparison of packed tower and plate tower
In chemical operation, the distillation column is divided into two main types: plate column and packing tower. For operation requirements, equipment performance, equipment maintenance, trial occasions have their own characteristics.
Type
Plate tower
Packing tower
Operating characteristics
Gas-liquid countercurrent step by step contact
Differential contact can be operated by countercurrent or parallel flow.
Equipment performance
Empty tower speed (that is, production capacity) is high, efficiency is high and stable, pressure drop is large, liquid and gas ratio has a wide range of adaptability, liquid holding capacity is large, and operation flexibility is small.
The gas velocity of large size air tower is larger, the gas velocity of small size air tower is smaller, the separation efficiency is high at low pressure, the separation efficiency is low at high pressure, the traditional packing efficiency is low, the new type of heap and the efficiency of the structured packing are high.
The pressure drop of large size is smaller and the pressure of small size is reduced.
It requires large amount of liquid spray, small liquid holding capacity and large operation flexibility.
Manufacturing and maintenance
The tower with diameter below 600mm is difficult to install, simple installation procedure, easy maintenance and cleaning, and large consumption of metal materials.
The new packing has complex preparation, high cost, difficult maintenance and cleaning, and can be made of non-metallic materials, but the installation process is more difficult.
Structural characteristics
Each laminates are assembled with different types of gas and liquid contact elements or special structures, such as sieve plates, bubble covers, floating valves, and so on. There are multi layers of tray in the tower for gas-liquid contact.
Packing in the tower, such as La west ring, Bauer ring, saddle filler and other bulk packing, grille, corrugated plate, pulse and other regular fillers, and packing are the basic components of gas and liquid contact.
Application
Material with large volume, flexible operation and dirt.
Handling strong corrosion, large liquid to gas ratio, vacuum operation requiring low pressure material.
Type selection of plate tower and tray
The general principle of the plate type tower type selection is:
The factors that should be considered when selecting are: material properties, operating conditions, tower equipment performance and tower fabrication, installation, operation and maintenance.
Plate tower is preferred in the following cases:
The liquid volume in the tower is large, and the range of operation load is wide. It is insensitive to the change of feed concentration, and the operation is easy to be stable.
The load of liquid phase is small.
With solid particles, it is easy to scale and crystallized materials, because the plate tower can choose the larger tray of the liquid flow channel, and the risk of blockage is less.
During the operation, the internal heat exchange components, such as heating coil, need to be set up in the tower with heat release or heating materials. This is because, on the one hand, the structure of the plate column is easy to realize. In addition, there are more stagnant liquid on the tray to carry out effective heat transfer with heating or cooling pipes.
Plate columns are still used in distillation columns operating at higher pressures.
Type and selection of plate tower tray
1. Type of tray
According to the relative flow state of gas-liquid two-phase flow on the tray, the plate column is divided into a through flow type and an overflow type. At present, most plate towers use overflow tower plates. The flow type tray operation is unstable and is rarely used.
2. Comparison of all kinds of tray performance
There are many kinds of materials to be separated from the industry and their operating conditions. In order to meet various operational requirements, there are many types of trays that have been developed and used so far. These trays have their own characteristics and usage systems.
Performance comparison of the main tray
Tray type
Advantage
shortcoming
Application
Blister plate
More mature and stable operation
Complex structure, high cost, large resistance to tray and small processing capacity.
A highly clogged system
Floating valve plate
High efficiency and wide range of operation
Float valve is easy to fall off
High separation requirement and large load change
Sieve plate
The structure is simple, the cost is low, and the efficiency of the tower is high
Easy to block and operate with small elasticity
High separation requirements and large number of tower plates
Tongue plate
Simple structure and small resistance
Narrow operating flexibility and low efficiency
Flashing tower with low separation requirements
Selection of packing tower and filler
1. General principle of packing tower type selection
The tower packing is the core component of the packing tower. It provides an effective phase interface for the two phase heat and mass transfer of gas and liquid. Only the excellent performance of the tower filler and the ideal inner part of the tower can make it possible to form a technical advanced packing tower.
The packing tower is preferred in the following cases:
In the case of high separation requirement, some new fillers haveBecause of the high mass transfer efficiency, a new type of filler can be used to reduce the height of the tower.
For distillation and separation of heat sensitive materials, because the liquid content of the new packing is small and the pressure drop is small, it is preferable to choose the packed tower under vacuum operation.
The packing tower can be used as a corrosive material. Because the packing tower can be made of non-metallic materials, such as ceramics and plastics.
The material which is easy to foam is suitable for packing tower.
2. Selection of packing material for packed tower
The geometric characteristics of fillers include surface area, voidage, packing factor and so on, which are the basic parameters for evaluating the performance of fillers.
Specific surface area
The packing surface area of unit volume packing is called the specific surface area, expressed in a, and its unit is m2/m3. The larger the specific surface area of the packing, the larger the area of gas-liquid mass transfer. Therefore, the specific surface area is an important index to evaluate the performance of the filler.
Voidage
The void volume in unit volume packing is called voidage, &epsilon, indicating that its unit is m3/m3 or expressed in%. The larger the voidage of the filler, the greater the ability of the gas to pass through and the pressure drop. Therefore, voidage is another important index to evaluate the performance of fillers.
Packing factor
The ratio of the specific surface area of the filler to the three power ratio of the voidage is a / ε 3, it is called filler factor, and its unit is 1/m. It indicates the hydrodynamic performance of fillers. The smaller the value, the smaller the flow resistance.
3, the performance of packing is usually measured by three factors: efficiency, flux and pressure drop.
Under the same operating conditions, the larger the specific surface area of the packing, the more homogeneous the gas-liquid distribution and the better the wetting performance of the surface, the higher the mass transfer efficiency.
The larger the voidage of the filler is, the more open the structure is, the greater the flux and the lower the pressure drop.
The performance of nine commonly used fillers is evaluated by fuzzy mathematics in China.
Fillers name
Evaluation value
evaluate
sort
Fillers name
Wire Mesh Corrugated Packing
Zero point eight six
very good
One
Zero point eight six
mellapak
Zero point six one
Quite good
Two
Zero point six one
Metal Intalox
Zero point five nine
Quite good
Three
Zero point five nine
Metal saddle ring
Zero point five seven
Quite good
Four
Zero point five seven
Metal staircase ring
Zero point five three
Generally good
Five
Zero point five three
Pall ring
Zero point five one
Generally good
Six
Zero point five one
Porcelain Intalox
Zero point four one
preferably
Seven
Zero point four one
Porcelain saddle ring
Zero point three eight
Slightly better
Eight
Zero point three eight
Porcelain pull West Ring
Zero point three six
Slightly better
Nine
Zero point three six