Water-using Network Synthesis For Batch Processes Involving Regeneration Operations

Currently,the problem of water scarcity and water pollution is increasingly severe.Reusing regenerated wastewater is an effective way of fresh water conservation and environmental protection.Batch operation mode has fine operating elasticity and great production flexibility.It has been widely applied in the manufacturing process of low-volume,multi-variety,and high value-added chemicals.However,compared with the continuous processes,the wastewater from batch processes generally has higher pollution and toxicity.Therefore,it is of great significance to work on water-using network synthesis for batch processes involving wastewater regeneration system.This study focuses on water-using system for batch processes.A superstructure of water-using network is proposed including regeneration unit and the mathematical formulation is based on a continuous time representation.The optimization and design water-using network are solved in GAMS.The main research content of this dissertation is summarized as follows:(1)In order to achieve reasonable utilization of process sources with different qualities for maximum reuse of water in batch processes,a superstructure of water-using network is proposed involving source-sink,source-intermediate storage tank-sink,source-continuous regeneration system-sink and source-wastewater disposal system.Based on current resources distribution in our country and the practical need of industry,water-using network are synthesized from two perspectives of resources and economy.Additionally,in consideration of multiple batch cycles in practical,the design,analysis and optimization of water-using network are carried out for the whole process from start-up to the steady state in this paper.Two cases are solved to demonstrate the effectiveness of the proposed approach.(2)Regeneration techniques often have the selectivity to the types of contaminants.A new superstructure of batch water-using network including regeneration units in series and parallel is constructed for multiple contaminants problem.On one hand,it can remove varieties of contaminants effectively and meet the demand of high quality water.On the other hand,it can ensure the quantity of regeneration at a reasonable level and avoid over-treatment of wasterwater.The integrated design of water network is carried out from the perspective of minimum fresh water consumption and minimum total annual cost.This study also investigates the water using batch plan of multi-cycle.Two cases are solved to demonstrate the proposed method,which can achieve effective treatment and reasonable reuse of wastewater.(3)For the sake of water integration between batch processes and continuous processes,this work transforms mixing system water network synthesis to batch water network design problem,by regarding continuous processes in mixing system as a special case of semi-continuous processes.Concurrently,in order to reduce the amount of freshwater consumption and wastewater discharge,this paper ameliorates current superstructure of water-using network for mixed system by adding a regeneration unit which runs in continuous mode.Water sources that come from processes can be regenerated and reused back to the water-using system,so as to achieve water-saving and emission reduction of chemical production.Finally,three examples are solved to demonstrate the validity of the proposed method.