PROCESS INTEGRATION IN WASTE WATER MINIMIZATION

Abstract

Water is widely used in chemical process industries, for example in product preparation, product separation and product finishing, etc. We treat water system design as a problem of mass transfer i.e. from a contaminant-rich process stream to a contaminant- lean water stream. The Water network design problems are tackled by a number of approaches such as Hierarchical design approach, Graphical approach and Mathematical Programming approach. In present work Graphical approach, based on the Pinch Technology is applied to design water- reuse networks. The present study is related to the use of water resources to maximize water reuse, minimize waste water regeneration, reduce effluent treatment and design of optimal water network at minimum annual cost. The problem is tackled in two steps. During the first step, a feasible target is established by integrating streams and utilities based on the Pinch Technology. In the second step, a network is designed to satisfy the targeted parameters and finally water network is fine-tuned to get an optimal water- reuse network at minimum annual cost. Generally water-system design network problems are of two types: the first type is related to the design of a water-system design network for a new plant which is in the design stage and second type is to retrofit an already existing water system network in a plant to reduce its consumption. These problems are computationally intensive and need specialized approach as for its solution. The Pinch Technology and Graphical Approach for solving water-system network problems are specially attractive. It provides a considerable flexibility to the designer and allows him to participate in the decision taking process. It also saves the designer from setting up superstructures of equations and development of complex codes for solution. Due to these attractive features in the present work, three water-system design problems were taken from a fertilizer plant for its solution as discussed. iii