Working principles of various tower equipment

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Tower equipment is the most prominent type of equipment in the petrochemical industry. Within such towers, thorough contact between gas and liquid or between liquids can occur, enabling mass transfer between phases. Therefore, tower equipment is widely used in production processes for unit operations such as distillation, absorption, desorption, gas humidification, and cooling. 1. Introduction to packed absorption towers: A packed tower is a mass transfer device that uses the packing inside the tower as the component for contact between the gas and liquid phases. The tower body of a packed tower is a vertical cylinder, with a packing support plate at its bottom; the packing is placed on this support plate either in a random pile or in an organized manner. A packing pressure plate is installed above the packing to prevent it from being blown by upward air currents. The liquid is sprayed from the top of the tower through a liquid distributor onto the packing, and flows down along the surface of the packing. Gas is fed in from the bottom of the tower; after being distributed by a gas distribution device (which is generally not used in towers with small diameters), it flows counter-currently to the liquid through the gaps in the packing layer. On the surface of the packing, the gas and liquid phases come into close contact, enabling mass transfer to occur. A packed tower is a type of continuous-contact gas-liquid mass transfer device, in which the composition of the two phases changes continuously along the height of the tower. Under normal operating conditions, the gas phase acts as the continuous phase, while the liquid phase is the dispersed phase. Advantages: high production capacity, high separation efficiency, low pressure drop, low liquid holdup, and great operational flexibility. Disadvantages: The packing is expensive; it cannot effectively wet the surface of the packing when the liquid load is low, which reduces the mass transfer efficiency; it cannot be used directly with materials that contain suspended solids or are prone to polymerization; it is not suitable for complex distillation processes involving side feed and withdrawal. 2. Plate distillation tower: A plate tower is a type of equipment for gas-liquid mass transfer through stepwise contact; it is primarily composed of a cylindrical shell, tray plates, overflow weirs, downcomers, and liquid collection trays. Principle: Under the action of gravity, the liquid flows from the downcomer of the upper tray to the tray drain of the lower tray, then flows horizontally across the tray and goes to the next lower tray via the downcomer on the other side. The function of the overflow weir is to maintain a certain thickness of liquid layer on the tray. The gas, driven by the pressure difference, moves from bottom to top through the gas channels in each tray layer (such as bubbles, sieve pores, or floating valves), breaking up into small streams of gas that bubble through the liquid layers in each tray layer. On the tray, the gas and liquid phases come into close contact, allowing for the exchange of heat and mass. In a plate tower, the gas and liquid phases come into contact stage by stage, with the composition of the two phases changing in a stepped manner along the height of the tower. Under normal operating conditions, the liquid phase is the continuous phase, while the gas phase is the dispersed phase. 3. Gas cooling tower: Function of the cooling tower: The waste heat generated during industrial production generally needs to be removed using cooling water. The function of a cooling tower is to allow the cooling water carrying waste heat to exchange heat with air inside the tower, thereby transferring the waste heat to the air and releasing it into the atmosphere. For example, in a thermal power plant, the boiler heats water to produce high-temperature, high-pressure steam, which drives the turbine to generate power and thus power the generator. The waste steam resulting from the operation of the turbine is sent to a condenser, where it exchanges heat with cooling water and turns back into water, which is then pumped back to the boiler for reuse. During this process, the waste heat from the waste steam is transferred to the cooling water, raising its temperature. The cooling water, carrying this waste heat, transfers the heat to the air in the cooling tower, and it is then released into the atmosphere through the exhaust vents. Applications of cooling towers: They are primarily used in air conditioning cooling systems, refrigeration systems, injection molding, leather processing, foam production, power generation, steam turbines, aluminum profile processing, air compressors, and industrial water cooling. The most common applications are in air conditioning cooling, refrigeration, and the plastic and chemical industries. 4. Screen plate extraction tower: Features include large processing capacity, simple structure, and low cost; it is widely used in chemical production processes. The flow pattern of the liquid-liquid two-phase flow inside the tower has a significant impact on the mass transfer efficiency, while the flow pattern of the continuous phase is closely related to the structure of the tower internals. 5. Packing extraction tower – Working principle: The structure of a packing extraction tower is essentially the same as that of a packing tower used in distillation or absorption processes; appropriate packing is installed inside the tower, with the light liquid phase entering at the bottom of the tower and exiting from the top ； The heavy liquid phase enters from the top of the tower and is discharged from the bottom. During the extraction process, the continuous phase fills the entire tower, while the dispersed phase is broken up into droplets by a distributor and enters the packing layer, where it comes into contact with the continuous liquid phase for mass transfer. 6. Working principle of the reciprocating sieve plate extractor: The reciprocating sieve plate extractor is also known as a vibrating sieve plate tower. The tower is equipped with an extraction device featuring a reciprocating central shaft equipped with numerous sieve plates; the central shaft, driven by a mechanism at the top of the tower, causes these plates to move up and down vertically within the tower, thereby stirring and dispersing the two liquid phases that flow in counterflow within the tower. The amplitude and frequency of the reciprocating motion of the plates can be adjusted. Due to its advantages such as large processing capacity, high efficiency, operational flexibility, and simple structure, the reciprocating sieve plate extraction tower is widely used in industrial sectors such as pharmaceuticals, petrochemicals, hydrometallurgy, and wastewater treatment. 7. Principle of operation of the rotary disk sieve tray extractor: The rotary disk extractor is a type of tower extraction equipment that uses mechanical stirring; it consists of three sections: an upper clarification section, a mixing section, and a lower clarification section. The mixing section is cylindrical in shape, and its interior is divided into a series of extraction chambers by stationary ring baffles. Between the two stationary ring baffles lies a fixed rotating disk that rotates together with the stirring shaft. During operation, the heavy phase (aqueous phase) and the light phase (organic phase) enter from the top and bottom of the tower respectively, where they come into contact in counterflow within the tower. Under the agitation of the fixed rotor, the dispersed phase forms small droplets, increasing the mass transfer area. After the extraction process is complete, the light phase and the heavy phase flow out through the outlets at the top and bottom of the tower, respectively. 8. F1 type floating tower: Features include high production capacity, stable tray efficiency, great operational flexibility, low cost, and ease of maintenance and cleaning; therefore, it is widely used. 9. Bubble column – Working principle: It is commonly used to bring steam (or gas) into close contact with a liquid in order to facilitate mass transfer between them. The tower is equipped with multiple layers of horizontal trays, on which there are several short tubes through which steam (or gas) can pass. These tubes are covered with bubble caps having toothed edges or small grooves, and the tower is also fitted with overflow pipes. During operation, the liquid enters continuously from the upper part of the tower, flows down layer by layer through the overflow pipes, and accumulates in layers on each plate, thus forming a liquid seal ； Steam (or gas) enters at the bottom of the tower, is dispersed into small bubbles through the gaps or slots on the bottom edge of the bubble cap, thereby coming into full contact with the liquid; it then passes through the liquid layer to reach the surface, and rises to the upper tray. When the short tube is installed inside the tower, it is called an internal overflow type ； There are also those installed outside the tower, known as external overflow type. Bubble columns are widely used in distillation and gas absorption. The bubble column has a high degree of operational flexibility and its trays are not prone to clogging; however, it has a complex structure and high costs. The liquid layer on the trays is thick, resulting in high pressure drops across the trays, and thus its production capacity and tray efficiency are relatively low. 10. Turbulent ball tower dust collector – Principle: A certain amount of polyethylene spherical filler is placed inside the tower; when the gas velocity reaches a specific value, these small balls remain suspended and move violently, rotating and colliding with each other, thereby achieving mass transfer and dust removal. Features: It overcomes the drawbacks of traditional tower units, such as easy scaling and clogging, low desulfurization efficiency, unstable operation, and high operating costs. At the same time, it reduces the liquid-to-gas ratio to a minimum of 1–3 L/m3, resulting in lower operating costs as well. 11. Introduction to the scrubber tower: The scrubber tower is a new type of gas purification equipment. It is an improvement based on the floating packing layer gas purifier, and is widely used for pre-treatment in areas such as industrial waste gas purification and dust removal, offering excellent purification results. For gasification processes, gas washing is inevitable, as this unit operation is used in every type of gasification technology. It is called a washing tower because its working principle is similar to that of a washing process. Features: 1) Wash-type exhaust gas treatment system, low cost and simple treatment process ； 2) The upright structure is most suitable for installation in compact spaces ； 3) Suitable for gaseous and liquid pollution sources ； 4) Treating a single pollution source ； 5) Suitable for medium to low air volume ； 12. Fractionating tower – Principle: Within a limited space, the heat exchange area for liquid mixtures is increased as much as possible. Mixtures used for distillation are generally organic azeotropes; these azeotropes rise from the reaction vessel to the fractionation section once heated. Those with lower boiling points continue to rise. Since the temperature at the top of the tower becomes equal to that of the low-boiling-point substances due to heat transfer, these low-boiling-point substances are separated out. Higher-boiling-point substances, not having reached their corresponding boiling points, are cooled and sent back to the reaction vessel or the lower part of the fractionation column. Once all the low-boiling-point substances have been distilled off, the higher-boiling-point substances are separated one after another, followed by the distillation of the highest-boiling-point substances. Finally, what remains at the bottom of the reaction vessel is residue. 13. Other tower equipment such as continuous liquid-liquid extraction towers, ZST vibrating sieve plate extraction towers, and various new types of tower equipment