Working principle and type classification of recovery tower: design points of distillation tower and absorption tower

The recovery tower is a key equipment used to separate and recover valuable components in the chemical production process. It plays an irreplaceable role in the fields of solvent recovery, organic matter purification, waste gas purification and comprehensive utilization of resources. In the production units of fine chemicals, pharmaceutical intermediates, flavors and fragrances, pesticide solvent recovery, and coal chemical industries, recovery towers are almost indispensable core unit equipment.

Separation principles and main types

The distillation tower utilizes the differences in boiling points of each component to achieve separation through repeated partial vaporization and partial condensation. It is the most commonly used type of recovery tower. Methanol recovery tower, ethanol recovery tower, acetone recovery tower, etc. all belong to the category of distillation towers. Organic solvents are separated from the water phase or other low-volatility components through distillation operations. The absorption tower uses the different solubility characteristics of each component in the gas mixture in a specific absorbent to selectively absorb the target gas component. The desorption tower is often combined with the absorption tower to form a complete absorption tower.-Desorption process flow.

Tower internals design

The tray is the core mass transfer element of the plate tower. Common types include sieve plate tower, float valve tower, bubble cap tower and floating valve tower. The sieve plate tower has the simplest structure and the lowest cost. It is suitable for clean materials and has a wide operating flexibility range. The float valve tower has superior comprehensive performance, large operating flexibility and high separation efficiency. It is currently the most widely used tray type in chemical plants. The packed tower uses the packing as the mass transfer surface for gas-liquid contact. The structured packing has a large specific surface area and high mass transfer efficiency, and is especially suitable for vacuum distillation of heat-sensitive materials.

Design selection and energy saving optimization

The design and selection of the recovery tower requires comprehensive consideration of various factors such as separation tasks, equipment investment, and operating energy consumption. The first step is to perform a material balance and heat balance to determine the required number of theoretical plates and reflux ratio. For azeotropic systems or difficult-to-separate substances, special distillation techniques such as extractive distillation or azeotropic distillation may be needed to break through the azeotropic limit. Energy-saving optimization of tower equipment is an important way to reduce operating costs. By optimizing the reflux ratio, using intermediate reboilers and intermediate condensers, and using waste heat as the heat source of the reboiler, the unit product energy consumption of the recovery tower can be significantly reduced.