Design elements of chemical industry packing absorption towers

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The last edit to this post was made by B0SS on 2017-8-10 at 20:59. The design of chemical filler absorption towers mainly consists of two aspects: the calculation of the absorption process and the design of the absorption tower itself. Based on parameters such as the properties of the material system in the absorption system, the separation purity of the component to be absorbed, and operating conditions, mass and heat balance calculations are carried out for the absorption process; mass transfer calculations determine the required height of the packing layer; structural calculations for the tower equipment are performed to determine the diameter and height of the tower, as well as to properly design the liquid and gas distributors and other internal components of the tower. I. Tower diameter calculation: For bulk packing, the tower diameter should be 8-10 times larger than the diameter of the packing. Good design requires not only the selection of appropriate packing and tower diameter, but also consideration of the economic and stability aspects of tower operation. Economic factors refer to the fact that the selected tower diameter results in the lowest total operating cost; the operating gas velocity of the tower at this point is known as the economic gas velocity. II. Calculation of tower height: The height of the packing required for the absorption process is influenced by factors such as material properties, product purity, the type of packing used, and the flow conditions within the tower; typically, it is necessary to determine the mass transfer coefficient or the height of the mass transfer unit in practice. Since regression equations based on experimental data are often used in theoretical calculations, a certain safety factor must be taken into account for the filler height calculated in the design. III. Design conditions: First, it is necessary to clarify the design requirements, determining the volume and composition of the feed gas; specify the separation requirements, such as the concentration of the components to be separated in the purified gas or the recovery rate of those components; the concentration of soluble components in the solution entering the tower; the operating temperature and pressure of the tower; the temperature and pressure of the gas and liquid phases entering the tower; and others requirements related to the absorption process, such as any special requirements regarding the total pressure drop across the tower, the presence of heat-sensitive substances, and the corrosiveness of the materials involved. IV. Material balance calculation: The absorption process occurs because of the differences in the solubility of various components in a mixed gas within a certain solvent (absorbent). Since the solubility of soluble gases is greater than that of inert gases, these soluble gases are absorbed by the solvent, thereby achieving the separation of the mixed gas. V. The selection of packing requires considering factors such as the properties of the system, the difficulty of separation, operating conditions, and the corrosive nature of the system in order to determine the type, size, and material of the packing. The packing can be either structured packing or loose packing. Structured packing has a high porosity, low pressure drop, and high flow capacity; it is suitable for difficult separation systems where gas film control is required. However, compared to random packing, structured packing is more expensive and its manufacturing and installation are more complicated. Bulk packing materials are widely used in absorption processes; they have strong adaptability, are inexpensive, and are easy to manufacture, install, and clean. Whether it is structured packing or bulk packing, there are various models and sizes available, and the hydrodynamic properties, mass transfer performance, and operational flexibility of these packings differ significantly; therefore, several types of packing can be selected as a preliminary choice. Perform tower makeup and pressure drop calculations, estimate the investment and operating costs of the equipment, conduct optimization comparisons to determine the type and size of the packing; generally, since the volume of liquid in the absorption process is large, packing of larger size is advisable. Regarding the material of the filler, metals, plastics, and ceramics can all be used for the absorption process, depending on the properties of the medium to be separated and the operating conditions. Metal materials typically include stainless steel, carbon steel, aluminum, copper, and low-alloy steel, while plastic materials include polyethylene, polyvinyl chloride, polypropylene, and polytetrafluoroethylene. Ceramic materials include acid-resistant ceramics and alkali-resistant ceramics. Materials should be selected based on the degree of corrosion of the system, and for plastic materials, their heat resistance also needs to be taken into account.