Property Integration And Scheduling Of Water Networks For Batch Processes In Multiple Production Lines

Nowadays,the shortage of water resources has increasingly become a major problem that restricts human development.The huge consumption of industrial water raises up higher requirements for improving the efficiency of water resource utilization.With the development of environmental protection,not only the stream components,but also the corresponding physical and chemical properties(density,viscosity,odor,toxicity,p H,chemical oxygen demand,etc.)need to be considered.It is necessary to make reasonable scheduling and to design the overall water network based on various factors,such as impurity concentration,property,unit operation mode,and operation time.This paper establishes a water network superstructure of different batch production lines,where one-direction intermediate storage tanks among different lines is considered.Then,connections between intermediate storage tanks are modified and network structure is optimized from the first period to the stable period.Multi-property integration and actual multi-period scheduling optimization are also considered.The main contents are as follows:(1)In order to realize the optimal distribution of water resources,this article introduces intermediate storage tanks for indirect reuse of water streams within and between production lines,while considering the environmental limitation of various properties.With the aim of minimum total annual cost,a superstructure including intermediate storage tanks,interceptors in semi-continuous operation,and buffer tanks before and after the interceptors is established.Finally,two examples verify the effectiveness of the proposed method.(2)Considering that different quality streams are over-mixed and difficult to reuse in actual water networks,this article further introduces one-direction intermediate storage tanks among different lines,to splits the functions of intermediate storage tanks,and constructs a matching relationship of one-way flow between lines,to reduce the total annual cost.Meanwhile,the water network structure is optimized from the start-up period to the stable period.Finally,the superiority of the split tank function is verified by two examples.(3)The different operation time of water inlet and outlet will affect the water network structure.This article investigates the impact of operation time scheduling on the water network based on the previous studies.Discrete time model is used as the time expression method,and the operation time is served as unknown variables to be optimized.The opportunities for further reuse caused by the overlap of different cycle lengths,are also considered,while following the process production sequence.The results show that the scheduling can break through the limitation of operation time on water reuse,reduce the use of fresh water,and thus reduce the total annual cost.