| Industrial park as a carrier of economic growth contributes to the economy meanwhile causing a certain burden on the environment.Under the background of increasing shortage of water resources and increasingly stringent environmental protection regulations,the optimization of the water system in the industrial park is of great importance since it can effectively save water resources and relieve the water pressure in the chemical park.The up-to-date approaches to optimizing water system only include freshwater,regenerated water and wastewater and ignore other types of water in refinery,i.e.desalted water,deaerated water,circulated cooling water,steam with different pressure levels and condensate water.Therefore,the existing mathematical model for water system optimizaiton is not directly applicable for the optimization of practical refinery water system.To overcome the limitation and bridge the theory and application,this thesis firstly presents a generalized model of water-using process including multiple types of water and a general superstructure for the optimization of refinery water system.The replacement ratio of altered type of water is also introduced in the flowrate balance equations for water reuse/recycling and it avoids the imprecise data extraction of limiting water quality for the inlets of water-using processes.It presents two mathematical models with different objective functions(minimum flowrate of water resource(Scenario 1)and minimum partial annualized cost(Scenario 2)).The proposed models are applied for the optimization of water system of a large-scale refinery in China.Results show that water system with minimum flowrate of water source can be obtained in Scenario 1 with the water-saving ratio of 21.6%.In Scenario 2,the profit of water conversation for five strategies cannot offset the investment cost of added pipelines,and their actual replacement ratios are zero.It leads to an economic and simpler water system with slightly higher flowrate of water resource.Traditional industrial water network only consists of water-using processes and water treatment processes.The practical water-using processes may use fresh water,desalted water,condensation water,steam,circulating cooling water etc.and those are typically water utilities.It is not considered in the up-to-date model of industrial water network.To overcome the limitation,this thesis proposes a novel superstructure of property-based industrial water system and it consists of water utility,water-using and water treatment sub-systems.The water system of a certain coal-based chemical complex in China is optimized to illustrate the proposed model.The results show that the total annualized cost of the water system is reduced from 1.825×10~8 CNY/y(preliminary design)to 1.494×10~8 CNY/y(optimum design)and the flowrate of water resource is decreased from 1369.855 t/h to 1030.498 t/h.Based on the research of water system optimization in a single plant,this thesis develops the superstructure of the industrial park water system optimization as well as the general mathematical model.The model includes water utility system,water-using system and water treatment system for each single plant.It considers the water integration within a single plant and between different plants.The results of the case study show that the optimal solution is obtained by implementing water system integration within the scope of the entire industrial park with the minimum total annual cost as the objective function.All plants in the industrial park can share a desalted water station from plant 2 and it achieves the goal of the sharing of utility in the industrial park.Inter-plant water integration and equipment integration are also proven feasible. |
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