Property Integration Of Water Networks For Batch Process Based On The Interceptors In Semi-continuous Operation

The shortage of water resources is a worldwide challenge for now.The chemical industry uses a large amount of fresh water and produces more wastewater.More attention should be paid to the rational distribution and utilization of water sources.In addition to concentration of contaminant,stream properties such as toxicity,pH,chemical oxygen demand are also important characters indicating water quality.Such situation would make the design of water-using process just according to contaminant concentration fail to meet the increasingly stringent production and environmental requirements,and prompt it to be necessary to consider the simultaneous integration of stream properties in water network synthesis.In this paper,the superstructure of water network for truely batch process and water network consisting of continuous and batch units are established respectively.The method of multi-property simultaneous integration is proposed and the influence of scheduling is also considered on the basis of above research.The main contents of this paper are summarized as follows:(1)In order to effectively solve the problem of multi-property integration of batch process water network,a superstructure of water network including the property interceptors in semi-continuous operation is established in this thesis.Based on the environmental constraints,the minimum total annual cost is taken as objective function.In this research,the property interceptors can operate at various treating rates in different time intervals.A series of tanks are placed before and after the interceptors to satisfy the batch operation of process sources and sinks,in assistance of which the sources in the tanks in front of interceptors are allowed to be reused to sinks directly without treated by interceptors.Two examples from literature are illustrated,and results demonstrate the effectiveness and superiority of the proposed approach with receiving a water network featuring lower total annual cost and fewer interceptors.(2)Considering that both batch process units and continuous process units exist in the practical production,the continuous unit is divided into several semi-continuous units to solve the problem of multi-property integration of water network involving continuous and batch units.The rules of treatment and reuse of semi-continuous sources are proposed in this thesis.Furthermore,the connecting relationships between tanks and interceptors are also optimized.The integrated design for water network is carried out with the objective of minimum fresh water consumption and minimum total annual cost,respectively.A single-property example and a multi-property example show that the proposed method can effectively reduce the fresh water consumption and annual total cost of the water network.(3)On the basis of property integration for water network involving continuous and batch units,the effect of scheduling on water network structure is further investigated.In this thesis,the starting and ending time of batch unit and semi-continuous unit are regarded as optimization variables by discrete time representation,and corresponding constraints are set to ensure that they meet the operation sequence of technological process,in order to achieve the simultaneous optimization of scheduling of process and design of water allocation network.The water network is optimized with the objective of minimizing the usage of fresh water and the annual total cost,respectively.The results of examples show that considering both scheduling and water network design can effectively reduce the usage of fresh water and the load of storage tanks,then further reduce the annual total cost of the network.