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Partners of Pump and Valve Home, click on the font below to enter the 2019 Wenzhou Golden Eagle Pump and Valve Exhibition, which will be launched on October 25th! ★★Jiangnan Pump and Valve-Professional Chemical Pump-Trustworthy★★ High-quality elbow flange elbow tee and other pipe fittings manufacturer Foreword After long-term development, tower equipment has formed a variety of structures to meet the special needs of all aspects. In order to facilitate research and comparison, people classify tower equipment from different perspectives. For example: According to the operating pressure, it is divided into pressurized tower, normal pressure tower and pressure reducing tower. ； According to unit operations, it is divided into distillation tower, absorption tower, desorption tower, extraction tower, reaction tower and drying tower. ； According to the way the interphase contact interface is formed, it is divided into towers with fixed phase interfaces and towers with phase interfaces formed during the flow process. ； There are also classifications based on the form of tower kettles. However, for a long time, the most commonly used classification is to divide the tower into two categories: plate tower and packed tower according to the internal structure of the tower. There are also several towers equipped with mechanical moving components. 1. When the plate distillation tower is operating, the liquid in the tower relies on gravity to flow from the downcomer of the upper tray to the liquid receiving tray of the lower tray, then flows across the tray laterally, and flows from the downcomer on the other side to the next tray. The function of the overflow weir is to maintain a certain thickness of liquid layer on the tray. Driven by the pressure difference, the gas passes through the gas channels (bubble caps, screen holes or float valves, etc.) of each tray from bottom to top, disperses into small air flows, and bubbles through the liquid layer of each tray. On the tray, the gas and liquid phases are in close contact, exchanging heat and mass. In the plate tower, the gas and liquid phases come into contact step by step, and the composition of the two phases changes in a stepwise manner along the height of the tower. Figure 1 Tray structure Figure 2 Plate tower structure Plate tower is a step-by-step contact gas-liquid mass transfer equipment. It is mainly composed of a cylindrical shell, a tray, an overflow weir, a downcomer, a liquid receiving tray and other components. Performance characteristics: The plate tower has sufficient gas-liquid contact and large processing capacity. It also has small pressure drop, leakage and entrainment. The plate tower has a simple structure, reliable operation, easy installation and low investment. The optimal design of plate towers is very complex. It requires not only theoretical knowledge, but also sufficient practical experience. 2. The bubble cap tower is equipped with bubble cap trays. The rising steam passes through the teeth of the bubble cap and comes into contact with the liquid. Mass transfer and heat transfer are performed between the gas and liquid phases. The tower is equipped with a multi-layer horizontal tray, with several short tubes for steam (or gas) to pass through. Each of them is covered with a bubble cap with tooth slits or small grooves at the bottom edge, and is equipped with an overflow pipe. Figure 3 Bubble cap structure Figure 4 When the bubble cap tower structure is operating, liquid continuously enters from the upper part of the tower, descends plate by plate through the overflow pipe, and accumulates liquid layers on each plate to form a liquid seal. ； Steam (or gas) enters from the bottom of the tower, disperses into small bubbles through the tooth gaps or small grooves on the bottom edge of the bubble cap, fully contacts the liquid, passes through the liquid layer to the liquid level, and then rises to the upper tray. The short tube is installed in the tower, which is called internal overflow type. ； There are also those installed outside the tower, called external overflow type. Performance characteristics: The bubble cap tower has suitable operating flexibility, is not easy to block, has high efficiency, and is easy to operate. However, its structure is complex, the cost is high, and the pressure drop is large. The bubble cap tower is widely used for distillation and gas absorption. The disadvantages are complex structure, high cost, thick liquid layer on the plate, large pressure drop on the tray, low production capacity and plate efficiency. Bubble cap trays have been gradually replaced by sieve trays and float valve trays, and are rarely used in new tower equipment. 3. The light phase (dispersed phase) is introduced at the bottom of the sieve plate extraction tower and dispersed through the sieve holes. It rises in the heavy phase (continuous phase) and gathers at the bottom of the upper sieve plate to form a layer of light liquid, which is then dispersed and then gathered. The process of dispersion is the extraction and mass transfer process. The extraction phase and raffinate phase are obtained at the top and bottom of the tower respectively. Figure 5 Structural and performance characteristics of sieve plate extraction tower: Sieve plate extraction towers are widely used in chemical production processes due to their large processing capacity, simple structure, and low cost. The flow structure of the liquid and liquid phases in the tower has an important influence on the mass transfer efficiency. At the same time, the flow structure of the continuous phase is closely related to the structure of the tower internals. However, its operating flexibility is small and it is easy to get clogged when handling dirty materials. The 4-reciprocating sieve plate extraction tower is equipped with a series of trays and annular baffles that reduce axial mixing on a central rotating shaft. The crankshaft is used to make the sieve plate on the central axis reciprocate up and down, promoting the liquid to be sprayed in the sieve holes to cause dispersion and mixing, and contact mass transfer. Figure 6 Structural and performance characteristics of reciprocating sieve plate extraction tower: The tower is widely used in petroleum, chemical, food and wet alloy industries, such as purifying drugs, removing phenol from wastewater, etc. The tower has the advantages of high flux, low theoretical equivalent height, can handle materials that are easily emulsified or containing solid particles, and has a simple structure. 5 Turntable sieve plate extraction tower The turntable extraction tower is composed of a vertical cylinder with horizontal baffles. The static ring baffle is a flat plate with a hole in the center. The static ring baffle divides the cylinder into a series of extraction chambers. There is a turntable in the center of the extraction chamber, and the diameter of the turntable is slightly smaller than the opening diameter of the static ring baffle. A series of turntables are mounted in parallel on a rotating shaft. In this way, the turntable and shaft can be easily loaded into the tower. Two clarification sections are formed between the top static ring baffle and the bottom static ring baffle and the top of the tower, and the bottom static ring baffle and the bottom of the tower, which are used to clarify the light phase and the heavy phase respectively. During operation, the light phase and heavy phase enter the rotating disk tower from the bottom and top of the tower respectively, and the two phases are in counter-current contact in the extraction tower. Under the action of the turntable, the dispersed phase forms small droplets, which increases the mass transfer area between the two liquids. The light phase and heavy phase that complete the extraction process flow out from the top and bottom of the tower respectively. Performance characteristics: The mechanical rotation of the turntable is used to drive the continuous phase and dispersed phase to rotate together, increasing the contact area between the phases and strengthening the extraction and mass transfer process. Figure 7 Rotary disk sieve plate extraction tower structure 6 Gas cooling tower Hot gas enters from the bottom of the tower and contacts with cold water bubbling in the tower for heat transfer. The top outlet is cooled gas and the bottom outlet is heated water. Figure 8 Structural performance characteristics of gas cooling tower: Waste heat generated during industrial production or refrigeration processes is generally directed away by cooling water. The function of the cooling tower is to exchange heat between the cooling water carrying waste heat and the air in the tower, so that the waste heat is transferred to the air and dispersed into the atmosphere. Cooling tower application range: It is mainly used in air conditioning cooling systems, refrigeration series, injection molding, tanning, foaming, power generation, steam turbines, aluminum profile processing, air compressors, industrial water cooling and other fields. The most common applications are in air conditioning cooling, refrigeration, and plastic chemical industries. 7 Packed Extraction Tower At present, packed tower technology has made great progress in basic research and application. However, due to the complexity of the fluid flow and mass transfer process inside the packed tower, the design of the packed tower still remains at the empirical and semi-empirical level. For example, the determination of the mass transfer coefficient or the height of the equal plate, the estimation of some fluid mechanical properties, etc., all need to be further strengthened in basic research. Figure 9 Structure of extraction packed tower Figure 10 Structural performance characteristics of packed tower: Among extraction equipment, packed extraction tower is one of the most widely used extraction equipment. It not only has the advantages of simple structure and easy manufacturing and installation, but also due to the development of new scraping packing, the processing capacity of the packed extraction tower has been greatly improved, and the mass transfer efficiency has been improved. ； It also shows its unique advantages in low-pressure operation, separation of heat-sensitive substances and energy saving. However, in the sub-liquid-liquid extraction process, the density difference between the two phases is small, the viscosity of the continuous phase is large, the axial back-mixing of the two phases is serious, and the interface phenomena are complex. 8. Packed absorption tower The packed tower body is a vertical cylinder with a packing support plate installed at the bottom. The filler is placed on the support plate in a random pile or in a complete pile. A packing pressure plate is installed above the packing to prevent it from being blown by the rising airflow. Figure 11 Packed absorption tower structure The liquid is sprayed onto the packing from the top of the tower through the liquid distributor, and flows down along the surface of the packing. After the gas passes through the 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 liquid redistribution device consists of two parts: a liquid collector and a liquid redistributor. The liquid flowing down from the upper packing is collected by the liquid collector and sent to the liquid redistributor. After redistribution, it is sprayed onto the lower packing to avoid the wall flow effect. Performance characteristics: The packed tower has the advantages of simple structure, easy manufacturing with corrosion-resistant materials, large production capacity, high separation efficiency, small pressure drop, small liquid holding capacity, and high operating flexibility. When the tower diameter is below φ800mm, the cost is lower than that of the plate tower, and installation and maintenance are easy. 9 Fractionating tower A fractionating tower is a chemical equipment that fractionates mixed volatile liquids (such as petroleum). The essence of fractional distillation is the result of sequential heating and separation based on the different boiling points of liquid mixtures. Fractional distillation requires continuous vaporization and condensation multiple times. The separated substances are still mixtures, but with different boiling point ranges. The fractionation tower is used to vaporize and condensate the mixture multiple times in one operation. Figure 12 Fractionating tower structure The fractionating tower can use the magnetic ring in the tower to increase the heat exchange area of the liquid mixture as much as possible in the limited space. Performance characteristics: The mixture generally used for rectification and fractionation is an organic azeotrope, and the plate fractionation tower is a commonly used separation equipment in petrochemical companies. The azeotrope is first heated from the reaction kettle and rises to the fractionation section, and the one with a lower boiling point continues to rise. Because the temperature of the top of the tower is the same as that of the low-boiling matter after receiving heat transfer from the low-boiling point, the low-boiling point is fractionated out, while the higher boiling point is not. When it reaches the corresponding boiling point, it will be cooled and then refluxed into the reaction kettle or the lower part of the fractionation tower. After the low boiling point substances are completely distilled, the higher boiling point substances will be fractionated one after another, then the high boiling point substances will be distilled out, and finally the residue will be at the bottom of the reaction kettle. 10 Washing tower The washing tower is similar to the distillation tower and consists of a tower body, trays, reboiler and condenser. Since the scrubber is a device for rough separation, the number of trays is generally small, usually no more than ten stages. Figure 12 Scrubber tower structure The scrubber tower is suitable for separation of mixed gases containing a small amount of dust. The components will not react and the product should be easily liquefied. Dust and other impurities (also called high boilers) are not easy to liquefy or solidify. When the mixed gas passes into the scrubber from the middle of the scrubber, due to the presence of product component liquid between the trays, the product component gas liquefies and evaporates part of it at the same time. Since the impurities cannot be liquefied or solidified, they will be fixed by the product component liquid when passing through the trays where liquid exists, resulting in a washing effect. Performance characteristics: Water-washed exhaust gas treatment system, cheap and simple treatment method ； Upright structure is most suitable for economical space installation ； Suitable for gaseous and liquid pollution sources ； Treat a single source of pollution ； Suitable for medium and low air volumes. Merchants recommend acid-resistant pumps, fluorine-lined pumps, desulfurization pumps, and magnetic pumps for technical consultation, please click "Read the original text”