Optimization Of Water-allocation Network For Batch Processes

Wastewater minimization has received significant attention from both academic and industrial researchers due to the scarcity of freshwater and severe environmental pollution.Over the past decades,much focus has been paid on water network synthesis of continuous manufacturing industries.However,the synthesis of batch water network is also important,because the batch production has been increasingly applied in process industries and tends to generate wastewater with high-concentration toxic substance.With the development of the research,methods for the synthesis of batch water network need to be extended to tackle with more complex and practical problems,such as: selection and integration among various regeneration technologies,the impact of contaminants and integration between production and water-allocation network.Thus,this article mainly focuses on these intractable issues,and the major content of the article is stated as follows.1.This article proposed a systematic approach to study different regeneration modes and technologies.Multiple wastewater regeneration modules with various candidate technologies are taken into account,and the regeneration modules are divided into batch and semi-continuous operating modes.The integration of these modules with specific regeneration technologies could further reduce freshwater consumption and wastewater generation.Hence,a modified state-space superstructure incorporating a water-using subsystem with buffer tanks and a regeneration subsystem is adopted to capture all realistic potential configurations.Correspondingly,a mixed-integer nonlinear programming model embedded with the scheduling of regeneration subsystem and buffer tanks are formulated to minimize the total annualized cost.In addition,a heuristic rule based solution procedure is developed to reduce the computation complexity and three illustrative examples are presented to demonstrate the effectiveness of the proposed methodology.2.To bridge the gap to industrial applications,impacts of contaminants on water-allocation system are considered,including the inhibitory impact of toxic substances on regeneration and its variable removal efficiencies for different types of contaminants.In addition,concentrate streams of two outflows regeneration modules are allowed to be reused and further purified,in order to minimize the consumption of fresh water and effluent discharge.On these basises,corresponding mixed-integer nonlinear programming(MINLP)is formulated.Ultimately,a case study is studied and the results show that cost-optimal network configuration can be achieved when considering the effects of contaminants.3.Recently,many researchers have simultaneously optimized batch production schedule and water-using network,and the majority of these methods are based on the single time representation.To overcome the drawbacks of literature models: high complexity of global continuous time model and solution space reduction of unit-specific event point model,a hybrid time representation is proposed which consists of unit-specific event point for schedule model,non-uniform discrete time for water-using network model and auxiliary time correlation constraints.A MINLP model is then formulated based on the proposed hybrid time representation.Finally,the results of two illustrative examples demonstrate that simultaneous optimization decreases water consumption but causes higher complexity of the model,compared to hierarchical method.And the results also show that the proposed methodology can avoid loss of solution space as well as reduce computational complexity.