Optimal Design And Flexibility Analysis Of Hydrogen Network Integra Ted With PSA Unit

Hydrogen is widely used in hydrocracking and hydro-treating processes in refineries.During the past decade,the proportion of high-sulfur crude oil and heavy crude oil obtained by refineries has been increased gradually,leading to the increase of hydrogen consumption in refineries.In addition,the demand of hydrogen has further gone up due to stricter air emission regulations which is enacted to reduce sulfur content in fuel products.The cost of hydrogen becomes a major component of refinery operating costs.To alleviate the hydrogen demand gap,it is necessary to optimize the hydrogen distribution networks and recycle hydrogen from refinery off-gas by purification technics.Pressure swing adsorption(PSA)is a commonly used technique in hydrogen purification.Simultaneous optimization of hydrogen network and PSA unit is of great significance,which can improve the utilization rate of hydrogen resources and reduce production costs.On the basis of the predecessors,a layered two-bed PSA process was established to separate hydrogen from methane steam reforming off gas.The operation conditions were optimized to achieve high recovery and purity,and the effects of changes in feed composition on purification performance was further analyzed.Based on the obtained PSA process,the kriging based surrogate model is applied to simplify the rigorous mathematical model.Then it is combined with the hydrogen network model to achieve simultaneous optimization of both PSA unit and network structure.In order to adapt to varying operating conditions,a flexible design method is proposed to improve the flexibility of the integrated hydrogen network and ensure the stable operation of the hydrogen system.The main contents of the work are as follows:(1)Since the PSA unit is located downstream of the methane steam reforming unit,its feed concentration will vary with the operation conditions of the reforming process.However,little research has been done on the changed feed composition system.In this work,a layered two-bed PSA process was bulit to separate hydrogen from methane steam reforming off gas,and the operation parameters were optimized to obtain hydrogen product with purity greater than 99.5%and recovery greater than 80%.The effect of feed composition change on purification performance was further analyzed.(2)Shortcut models of PSA are commonly used in hydrogen network optimization process,which can not achieve the optimal design of PSA unit and may cause the mismatch of hydrogen demands.To address such problem,the surrogate modeling technique was adopted to replace the conventional PSA shortcut model in hydrogen network.As PSA design is of great value for hydrogen recovery and resource conservation in refineries,it is optimized simultaneously with hydrogen network.The results of a case study show that the integrated model can reduce the total annual cost by 16%compared to the shortcut model.(3)As the operating state of the refinery changes frequently,the parameters of the hydrogen system fluctuate accordingly.In order to ensure the stability of the hydrogen system,the flexibility index was introduced to measure the adaptability of the network structure and PSA equipment.A flexible design method was further proposed to improve the flexibility of hydrogen system,and realize the operation safety of the obtained hydrogen system.