Design of Trough Liquid Distributors for Packed Columns

  Packing tower commonly used regular packing, due to high separation efficiency, large void ratio, small liquid holding capacity and thus small operating pressure drop and other aspects of the characteristics of the application is becoming more and more widely used, and a good packing if there is not a good liquid distributor, can not reach a good vapor-liquid distribution effect.

　　1, liquid distributor design requirements

　　In the design of packing tower, usually assuming that the gas phase and liquid phase along the tower cross-section is uniformly distributed, but a large number of tests show that the liquid in the packing layer is not a uniform plunger flow state, but by the wall flow, ditch flow and other lateral flow, this uneven distribution will reduce the separation performance of the tower. The uneven distribution of liquid caused by many factors, in addition to the packing itself inherent dispersion characteristics of the liquid, the liquid distributor is one of the key factors affecting the distribution of liquid.

　　Liquid distribution points on the tower cross-section cannot be infinite. For the distribution point of small holes, often hope that the more holes the better. This can improve the degree of uniform distribution, but for a certain liquid flow, the more holes, the smaller the pore size. Pore size is too small necessarily sensitive to solid impurities, the hole is easy to be blocked, the number of holes instead of causing uneven distribution, the lower limit of the pore size should depend on the solid particles in the material.

　　Packed tower operating elasticity is often not determined by the performance of the packing, but by the operating elasticity of the liquid distributor. Continuous operation of the packed tower, liquid return flow or spray volume is relatively stable. General-purpose liquid distributor operating elasticity is generally 30%-100%, can fully meet the requirements of the operating tower. For batch distillation columns, the reflux ratio has a large change in 1 operating cycle. For multi-purpose towers, the separated material system changes frequently, and the reflux ratio or spray volume also changes greatly. The operational flexibility of the liquid distributor in this case is very high and requires special design, otherwise the performance of the tower will be sporadic.

　　For most of the material system, the efficiency of the packed tower in addition to the characteristics of the filler itself, and the degree of uniformity of the liquid also has a great relationship. In addition to the use of packing, there are structurally sound tower components, especially good performance of the liquid distributor. Good liquid distributor should have the following characteristics: uniform distribution of liquid, gas phase through the free cross-section, resistance is small, operating flexibility, not easy to clog, not easy to cause foam entrainment and foam, easy to manufacture, installation. In terms of the driving force of liquid distribution, liquid distribution can be divided into pressure and gravity type 2 categories. I will discuss the gravity type trough distributor commonly used in packing tower.

　　2, spray density determination

　　The poor distribution of liquid in the packed tower can be divided into small-scale (natural) and large-scale poor distribution of 2 kinds. Small-scale poor distribution is caused by the liquid in the packing of the channel flow. Foreign research shows that the impact of this bad distribution can be reduced by the mutual mixing of the ditch flow, the efficiency of the packing tower has little impact. Large-scale poor distribution of liquid is mainly due to poor initial distribution of the distributor, it can make the whole packing tower efficiency decline.

　　3、Structure

　　Slot distributor is composed of slots of unequal lengths, there are main and sub-slots, sub-slots have type and connected type. The liquid firstly enters into the main tank, and then distributes to each sub-tank by the main tank, and then sprays the liquid onto the packing surface. In order to prevent liquid splashing and fluctuations in the liquid level in the main tank, the liquid enters the tube in the liquid distribution hole flow rate should not exceed 1.2 m/s. By designing the slot distributor into a split-type, so as to be sent to the tower from the manhole for assembly, usually 2 to 3 slots are connected to one, so that the liquid level in these slots is kept consistent, in order to facilitate uniform distribution of liquid. In order to improve the distribution effect of the slot liquid distributor, in the design of the structure, often set up in the spray hole near the baffle, will be shot by the spray hole of the liquid flow broken into droplet groups, the point of the spray into a line spray, so that the distribution is uniform.

　　4, conclusion

　　Slot liquid distributor is a new type of high-efficiency liquid distributor, the quality of its high and low on the operation of the packing tower has a great impact on the design should be analyzed in detail according to the actual conclusions and theoretical formulas, to give full play to the advantages of its uniformity of liquid distribution, operational flexibility to the advantages of the packing tower.