Design And Optimization Of Refrigeration Process Of Refinery Gas Shallow Condensation Process

With the lightening of ethylene raw materials and the intensive decommissioning of propane dehydrogenation projects,the demand for LPG also increases significantly.At the same time,about 5%of the petroleum resources in petrochemical production are discharged as refinery gas,which contains high value-added components such as hydrogen and light hydrocarbons.Therefore,the recovery of light hydrocarbons in refinery gas will help ease the demand for LPG in China.At present,the shallow condensation process is the mainst method for recovering lighter hydrocarbons in refineries.It uses propane as a refrigerant to condense light hydrocarbons in the feed gas,but its temperature matching between the isothermal phase change process and the refinery gas liquefaction process is poor,The irreversible loss of the cold box is large and the cooling efficiency of the refrigeration system is low.This article mainly researches from the aspects of refrigeration structure and refrigerating working substance.It can reduce the irreversible loss of the cold box and enhance the cooling efficiency of the refrigeration system by reducing the heat transfer temperature difference between cold and hot streams in the cold box.Finally,the purpose of reducing the energy consumption of the shallow condensation process is achieved.Firstly,the traditional shallow condensation process is improved from the perspective of system configuration.Two-stage shallow condensation process is designed by changing the single-stage cooling of the cooling section to two-stage cooling.Optimize the important parameters of the process with the minimum unit energy consumption as the objective function,and determine the operating pressure and primary and secondary refrigeration temperatures for the supercooled process of 100 kmol/h crude oil and vacuum distillation towers,and determine the primary and secondary refrigeration temperatures.A comparative analysis of unit energy consumption,loss of available energy,and economic performance was conducted.Compared to the traditional shallow-cooling process,the unit energy consumption is reduced by 16.5%,and the effective energy of each device is reduced to varying degrees.In addition,the comparison of economical parameters shows that although the two-stage shallow condensation process adds a cold box,resulting in increased investment in equipment costs,but due to lower energy consumption of compressors in the refrigeration section,the utility costs are lower than the traditional shallow condensation process,and ultimately its annual economic benefits increases of 1.24 million yuan per year compared to traditional shallow condensation process.Secondly,the traditional shallow condensation process is improved by useing the mixed refrigerant.By using a mixed refrigerant instead of a single propane refrigerant,the main operating parameters of a 100 kmol/h crude oil and vacuum-cooled distillation tower overhead gas mixed refrigerant shallow cooling process are determined.It was determined that the composition of the mixed refrigerant was C₃H₈/i-C₄H₁₀/n-C₄H₁₀/i-C₅H₁₂ of0.24/0.18/0.31/0.27.The unit energy consumption was selected as the objective function of the optimization of process parameters.The genetic algorithm was used to optimize.The unit energy consumption was 2.92 kW·h/kmol,which was 29.3%lower than the traditional process.Through comparison and analysis of the three processes,it is known that the effective energy loss of the mixed refrigerant shallow condensation process is the smallest,and the effective energy loss of the cold box heat exchanger is reduced by 77.8%compared to the traditional shallow condensation process,and its annual economic benefit increases of5.56 million yuan per year compared to traditional technology.Finally,due to the genetic algorithm’s optimization of mixed refrigerant ratios takes a long time,based on the refrigeration principle of each component in the mixed refrigerant in different temperature zones,a mixed refrigerant ratio optimization method using a stepwise approach is proposed.It is compared with the genetic algorithm.Taking the recovery of 100kmol/h light crude hydrocarbons in the normal and vacuum tower top gas as an example,a new optimization method is used in combination with the genetic algorithm optimization,and the unit energy consumption optimized by the genetic algorithm algorithm is the same,but the calculation time is shortened from 4 h to 1.5h,while ensuring the accuracy of the results,greatly improving the efficiency of the operation.