| Crude oil is becoming heavier and more inferior.The environmental regulations and policies on sulfide and aromatics contained in product oil became tighter recently.Therefore,refineries have been increasing the processing ratio of hydrotreating and hydrocracking processes,which aggravates the fresh hydrogen shortage in refineries,forcing refineries to use hydrogen more efficiency.Process integration which has been widely addressed both in academic and industrial sector has become a research spot in the hydrogen conservation in the process industry.Up to now,most researches focus on the optimization of single hydrogen system and the comprehensive researches on single hydrogen system and interplant hydrogen systems with direct reuse/recycle and purification reuse/recycle is insufficient.Interplant hydrogen system integration has been a promising work.It focuses on multiple hydrogen systems,and regards overall hydrogen systems as the research object.With the introduction of hydrogen stream to each other,the overall hydrogen utility flow rates can be reduced and the cost of hydrogen production can be saved.For example,in petro-chemical park,rich hydrogen gas stream from chemical plant(ethylene plant,fertilizer plant,etc.)can be reused/recycle to refinery to reduce the flowrate of hydrogen utility of refinery.In addition,no researsh on using Pinch technology to optimize hydrogen system with intermediate header is reported yet,and researches on optimizing compression workcan be improved.In this paper,firstly,IPT is utilized to locate the flowrate targets of hydrogen system(i.e.the flowrate of hydrogen utility)with direct reuse/recycle and identify the flow rate and impurity of purged streams.The generalized procedures of IPT are introduced.Two scenarios(Scenario ? and ?)of interplant hydrogen integration with direct reuse/recycle are investigated.Three classical examples,which are marked as Plant A,Plant B and Plant C,are extracted from literatures to do the case studies.Then,combined with material balance analysis,the procedures of optimization for hydrogen system with purification reuse/recycle are observed.The Excel Goal Seek feature is utilized to check the feasibility and figure out the optimal results.The case study shows that the conservation ratio of the flowrate of hydrogen utility in Scenario ? is greater than that in Scenario ?:The total flowrate of hydrogen utility for Plants A and B reduced from 111657 Nm3/h to 107096 Nm3/h(the conservation is 4.1%,compared with the results before optimization)after individual hydrogen integration and to 103774 Nm3/h(7.1%,in Scenario I)and 102698 Nm3/h(8.0%,in Scenario ?)after interplant hydrogen integration with direct reuse/recycle.For interplant hydrogen integration of Plants A-B-C,the total flowrates of hydrogen utilities for Scenario ?(10097 Nm3/h(0.001)+ 97298 Nm3/h(0.05))is slightly better than those for Scenario ?(10097 Nm3/h(0.001)+ 98374 Nm3/h(0.05)).Note that,the flowrate of hydrogen utility in Scenario ? can be equal to that in Scenario I:The total flowrates of hydrogen utilities for Plants A-C are both 10097 Nm3/h(0.001)+80502 Nm3/h(0.05)and for Plants B-C are both 10097 Nm3/h(0.001)+16275 Nm3/h(0.05)in Scenario ? and ?.Compared with the results of individual hydrogen integration with direct reuse/recycle,the results of the flowrate of hydrogen utility for Plant A after individual hydrogen integration with purification reuse/recycle is reduced by 15197 Nm3/h,from 85418 Nm3/h to 70220 Nm3/h.For Plants A-B,the total flowrate of hydrogen utilities reduced by 21210 Nm3/h,from 107096 Nm3/h to 85886 Nm3/h after interplant integration with purification reuse/recycle,compared with interplant integration with direct reuse/recycle.According to IPT,Limiting Composite Curves and Optimal Hydrogen Supply Lines for each case study are ploted.And Nearest Neighbors Algorithm is utilized to design the hydrogen network according to the optimal results.Then,based on the literature research and case studies,IPT is utilized to locate the flowrate targets of hydrogen system with intermediate header.The case studies can be categorized into hydrogen system with direct reuse/recycle and with purification reuse/recycle.The problems of pure pattern and mixed pattern,one intermediate header and two intermediate headers are considered.The results indicate that,without considering concentration distribution in the intermediate header,the intermediate header in mixed pattern amount to a hydrogen mixer and spliter,which means that the placement of the intermediate header in the hydrogen system has no effect on the optimization results.For example,the optimization result of Plant B(21678 Nm3/h)in mixed pattern is same to the result after single hydrogen integration with direct reuse/recycle(21678 Nm3/h).Thehydrogen network with pure hydrogen header can be simplified,while the flowrate of hydrogen utility is increased sharply,take Plant B as an example,the flowrate of hydrogen utility increased from 21678 Nm3/h(conventional hydrogen network)to 40853 Nm3/h(mixed pattern hydrogen network with one hydrogen header).For optimization of hydrogen system with purification reuse/recycle,the parameters of purification unit are set firstly(i.e.the purification recovery and impurity of hydrogen product are set as 0.9 and 0.01),then the initial impurity of intermediate header is assumed,and the optimization results(the minimum flowrate of hydrogen utility FHU=16139 Nm3/h,the impurity of purification feed yheader =0.106,the minimum flowrate of purification product Fprod=104747 Nm3/h)can be determined by IPT integrated with Excel Goal Seek tool.Finally,on the basis of literature research on calculating the minimum compression work and nearest neighbors algorithm,a novel nearest neighbors algorithm as well as pressure-impurity graph are proposed to design hydrogen network with minimum compression work.Example studies include conventional hydrogen system and hydrogen system with intermediate header.For the conventional hydrogen system,the minimum compression work is located as 15.069 MJ and the number of compressors is 9.For hydrogen system with intermediate header,the minimum compression work is 1 MJ and it is slighter higher than that for the conventional hydrogen system.The number of compressors is reduced further to be 8. |
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