Classification and introduction of tower equipment

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With the continuous development of chemical processing technologies, tower equipment has also developed a wide variety of structures and types to meet various process requirements. To facilitate research and comparison, tower equipment is classified from different perspectives. For example: Based on the operating pressure, they are classified into pressurized towers, atmospheric-pressure towers, and vacuum towers ； Classified by unit operations, they include distillation towers, absorption towers, desorption towers, extraction towers, reaction towers, and drying towers ； Based on the manner in which the interphase contact interface is formed, there are towers with a fixed phase interface and those in which the phase interface forms during the flow process, etc. Below, several common classifications of tower equipment are introduced. 1. Classification by purpose: (1) Distillation column – The process of separating the various liquid components in a mixture by taking advantage of their differences in volatility is called distillation. Repeating this distillation process multiple times is known as rectification, and the equipment used for carrying out this rectification process is called a distillation column. Devices such as the atmospheric tower and vacuum tower in atmospheric and vacuum distillation units can separate crude oil into gasoline, kerosene, diesel, lubricating oils, and so on ； The various distillation columns in platinum reforming units can separate benzene, toluene, xylene, and others. (2) Absorption tower, desorption tower: The process operation in which gases are separated using an absorbing liquid, taking advantage of the different solubilities of the various components in the mixture in solution, is called absorption ； The process of releasing the gases dissolved in the absorbent solution by means of heating or other methods is called desorption. The tower equipment used to carry out the absorption and desorption processes is called an absorption tower or a desorption tower. Absorption and desorption towers are needed for applications such as recovering gasoline from refinery gas, recovering ethylene and propylene from pyrolysis gas, as well as for gas purification in catalytic cracking units. (3) Extraction tower: For liquid mixtures in which the boiling points of the various components differ by very little, conventional distillation methods are not effective; in such cases, a solvent with a higher boiling point (referred to as an extractant) can be added to the liquid mixture ； By taking advantage of the differences in the solubility of various components in the mixture within the extractant, they can be separated. This method is called extraction (also known as distillation). The tower equipment used to carry out this extraction process is known as an extraction tower. Such as the extraction tower in a propane deasphalting unit. Pulsating towers and rotary disk towers are commonly used in extraction towers. (4) Scrubber: The process of using water to remove unwanted components or solid particles from gases is known as washing or dust removal, and the tower equipment used for this purpose is called a scrubber or dust removal tower. It should be specifically noted that some equipment, in terms of its appearance, belongs to the tower type; however, its actual function is not separation but heat exchange or reaction. For example, cooling towers are coolers, while the synthesis towers in ammonia synthesis plants are reactors. 2. Classification by operating pressure: Depending on the process operations they perform, tower equipment operates under different pressures and humidity levels. However, when phase equilibrium is reached, there is a certain relationship among pressure, temperature, gas-phase composition, and liquid-phase composition. In actual production, the composition and requirements of raw materials and products are determined by the process and cannot be changed arbitrarily. There is some flexibility regarding pressure and temperature, but the two are interrelated; once one is determined, the other can only be calculated using phase equilibrium relationships. From the perspective of operational convenience and simple equipment, operating at atmospheric pressure is the best option. Regarding the source of the coolant, it is generally advisable to keep the condensation temperature at the top of the tower between 30 and 40°C, so that inexpensive water or air can be used as the coolant. Therefore, depending on the specific process requirements as well as the equipment and operating costs, tower equipment can sometimes operate at atmospheric pressure, sometimes under pressure, and at other times it is necessary to operate it under reduced pressure. The corresponding tower equipment is referred to as a atmospheric tower, a pressurized tower, and a vacuum tower, respectively. 3. Classification of tower equipment by structural form: Although tower equipment is used for various purposes and operates under different conditions, its structure is generally similar, consisting mainly of a tower body, supports, internal components, and accessories. Based on the structure of the internal components of the tower, they can be divided into two main categories: plate towers and packed towers. In a plate tower, a certain number of trays are installed inside the tower; the gas passes over the liquid layer on these trays either by bubbling or spraying, thereby enabling close contact between the two phases and facilitating mass transfer. The component concentrations in the two phases change in a stepwise manner along the height of the tower. In a packed tower, a layer of packing is filled to a certain height inside the tower; the liquid moves downward in a film-like manner along the surface of the packing, while the gas in the continuous phase flows from bottom to top, undergoing counter-current mass transfer with the liquid. The component concentrations in the two phases vary continuously along the height of the tower. Based on the tray structure of plate towers and the packing used in packed towers, they can be further classified into different types of towers.