Study On The Improvement Of Absorption Process Based On Liquid Gas Jet Technology

Absorption is an important chemical operating unit. It rely on countercurrent contacting of gas and liquid in tower equipment to complete the mass transfer of gas to liquid, so as to purify gas or obtain target component of gas. Due to the limitation of trays’ structure and non forced gravity mixing contact, the flow velocity of liquid and gas and surface renewal velocity of liquid phase are decreased, which reduce the speed of mass transfer and increase the cost of equipment investment and operation. Therefore, it is of great significance to enhance the mass transfer in absorption.In view of the characteristics and advantages of liquid gas jet pump(LGJ), an improved absorption process(IAP) is proposed based on analysis of absorption in this paper. It adds some parts, and takes the absorbent of tower’s bottom as working fluid to inhale and compress gas. Compared with traditional process, advantages of IAP are: 1) the energy required to compress liquid is much lower than that of compressing gas, so it can reduce the cost of improving operating pressure in absorption tower; 2) forced turbulent mixing of gas and liquid in LGJ increases the contact area of liqud and gas and enhances the mass transfer of gas to liqud. Under the same conditions, IAP can reduce the energy of compressor, the number of trays in absorption tower and the flow rate of circulating absorbent, which can save investment and reduce energy consumption.In order to verify IAP in this paper, four models of absorption tower, LGJ, compressor and centrifugal pump are established first. Then, Sequential modular approach is used to solve IAP and IAP is divided into four subsystems based on topological analysis. In this paper, a virtual theoretical tray N+1 is proposed to simplify the calculation of the absorption tower subsystem. And a solution procedure of an integrated model is determined after simplification. At last, IAP optimization design based on LGJ optimization design is proposed in this paper. An optimization strategy is established, the number of theoretical trays N, the operating pressure PT of absorption tower and the inlet pressure PS of LGJ’s suction chamber are chosen as optimization variables, GA as optimization tool, and comprehensive cost including investment and energy consumption as objective function.A case about ethylene recovery from 11.6×104t/a catalytic dry gas is used to IAP’s optimization design. Compared to the existing process, the calculation results show that the IAP reduces 8 theoretical trays and 84.7 kmol/h absorbent and save comprehensive cost 2151000 yuan/a when the number of theoretical trays N is 10, the operating pressure PT of absorption tower is 4.9MPa and the inlet pressure PS of LGJ’s suction chamber is 4.4MPa.