Design Of Hybrid Separation Process For Refinery-off Gas And Optimization Of Hydrogen System

With the increasing capacity of high-sulfur and heavy crude oil,the hydrogenation process has been more and more widely used in refineries.In the case of increasing consumption of hydrogen,it becomes more important to optimize the refinery hydrogen network.How to recover the high value-added components in the refinery gas,improve the product quality and optimize the industrial structure is of great significance.In this paper,the recovery of hydrogen and other high value-added components in refinery-off gas is studied.The hybrid separation process of refinery-off gas is introduced.In addition,the optimization of the minimum compression work for the hydrogen network is investigated and the energy consumption can be further reduced with the minimum hydrogen utility.In this paper,the retrofit procedure of refinery hydrogen network integrated with light hydrocarbons recovery is firstly proposed.The minimum hydrogen utility of hydrogen network is determined by using the improved problem table method.Streams with rich light hydrocarbons are delivered to the light hydrocarbons recovery process which is simulated by Aspen HYSYS.Based on the simulation results,three retrofit schemes of integrated hydrogen network are designed.The hydrogen network of one real refinery plant is retrofitted according to the proposed procedure.Results show that,in the integrated light hydrocarbons recovery Scheme 3,the benifit of recovery hydrogen achieves 36.75 Million CNY/y.The total benefit reaches 111.63 Million CNY/y.The utilization ratio of hydrogen can be increased from 85.62%to 88.28%.The hydrogen network integrated with light hydrocarbons recovery has better economic benefit and higher hydrogen utilization ratio.The compression work plays an important role in the operation cost of hydrogen network.Moreover,in the case of minimum hydrogen utility consumption,there are still various of optimized hydrogen network structures with different compression work.To solve this problem,a mathematical model for optimizing the minimum hydrogen network compression is established and solved by using GAMS software.The proposed mathematical model can be used to design the hydrogen network with the minimum hydrogen utility and the minimun compression work.The calculation results of a literature example show that the hydrogen utility of the optimized network is 14.598Sm³·s^-1,and the minimum compression work of the optimized network is 15.094 MW,which is consistent with the literature data.19 different network structures with minimum hydrogen utility are designed and compression work for each structure is calculated.Results show that the minimum compression work among the 19 situations is identical with the calculated value by the mathematical model.The correctness of the proposed model is verified.Finally,the hybrid separation process of refinery gas is designed and simulated.The refinery-off gas separation system is divided into hydrogen production system,hydrogenation unit system and non-hydrogenation unit system.The separation process includes pressure swing adsorption,membrane separation,adsorption/desorption,low temperature distillation and so on.According to different types of refinery-off gas,a suitable hybrid separation process is designed to maximize the recovery of hydrogen and produce other high value-added components.Based on the case data,the hybrid process is simulated by Aspen Plus.Results show that the utilization ratio of hydrogen in the refinery with the hybrid separation process can reach 97.4%.The annual economic benefit of the recovered product is 1.383 billion CNY.The economic benefit is considerable.At the same time,it avoids the waste caused by the emission of high value-added components into the fuel system.The hybrid separation process for refinery-off gas provides a better comprehensive optimization scheme for the construction of resource-saving refineries.