WASTE WATER MINIMIZATION USING WATER PINCH TECHNOLOGY

Abstract

Water is a vital component for many industrial operations, and is utilized for a wide range of purposes in industrial processes. The rapid growth in population, coupled with industrialization and urbanization, resulted in an increased demand for water, leading to serious consequences on the environment. The cost and scarcity of water beside stricter regulations on industrial effluents have become a significant factor in commodity material manufacturing. As water supply and treatment costs increase, there will be increasing pressure on the chemical process industries to reduce water consumption. There are many types of technologies/methodologies available to save fresh water and reduce waste water generation. Water Pinch is one of the most important technologies for wastewater minimization, treats the water utilization processes of an industry as an organic whole, and considers how to allocate the water quantity and quality to each water using unit, so that water reuse is maximized within the system and simultaneously the wastewater generation is minimized. In this dissertation, sincere efforts had been put to demonstrate, the potential of water pinch technology at real world of industries. Different case studies are discussed in detail. All cases had been considered as retrofitting problems and had been solved very meticulously considering existing piping and plant layouts, present cost of power and recent market price of different sizes of pipes. Two industries mainly targeted due to accessibility of data: (1) Starch Industry from Gujarat and (2) Glass Industry from Uttarakhand. Four different cases of starch industry had been solved which are based on conventional water pinch problems. The case of glass industry is based on special case of water conservation through energy management. iv • The first problem is viewed as a single contaminant problem and all the three modes of water integration i.e. reuse, regeneration-reuse, regeneration —recycling are demonstrated. The DM water consumption is 50 tph before modification and after modification using water pinch it reduces to 31.9 tph (reuse), 21.6 tph (regeneration-reuse) and 12 tph (regeneration-recycling). The results obtained from the present analysis are compared well with the results obtained from well established software ASPEN WATER which uses mathematical programming approach based on MINLP. The cost benefit analysis illustrates that the profit obtained in the case of reuse is 22,01,914 INR per year and the pay back period for the regeneration-reuse and regeneration —recycling are 2.5 and 2.3 month. The second problem is also viewed as a single contaminant problem and all the three modes of water integration i.e. reuse, regeneration-reuse, regeneration —recycling are applied. The DM water consumption is 69 tph before modification and after modification using water pinch it reduces to 59.8 tph (reuse), 34.5 tph (regeneration-reuse) and 30 tph (regeneration-recycling). The cost benefit analysis illustrates that the profit obtained in the case of reuse is 17,63,914 INR per year and the pay back period for the regeneration-reuse and regeneration —recycling are 1.8 and 1.1 month. The third problem is tackled as a single contaminant problem which involves ten operations and only approach of water reuse is applied. The DM water consumption is 337 tph before modification and after modification using water pinch it reduces to 221.5 tph (reuse). The cost benefit analysis illustrates that the profit obtained in the case of reuse is 5,43,120 INR per year. The fourth problem is identified as a multi contaminant, reuse problem. The fresh water consumption and DM water consumption are 100 tph and 51 tph respectively before modification and the network is dealing with three major contaminant such as total organic content (TOC), total dissolved solids (TDS) and total suspended solids (TSS). The improved water using network designed for the present work consumed less DM & fresh water. The reductions are of the tune of 28% and 64.38 % for DM and fresh water respectively. Due to alteration in piping, there will be a saving of 4,06,026 INR per year, which will be utilized for development of efficient environment policy for the company. The concept of water-pinch coupled with thermal analysis is applied on cooling water networks of different sections, namely, furnace melting, neck- refining & spout and tin bath, of a Glass industry of India commissioned in the year 2006. The analysis takes in to account mixing of multiple intermediate cooling water streams to satisfy the constraints of the network. Different proposal had been worked out and different strategies had been proposed for summer and winter season. The results are very encouraging and there will be huge benefit in terms of power and fresh water consumption, if the proposed modified networks have been put into real operations. Two different operational strategies have been proposed to achieve maximum reuse of water. The maximum projected savings will be of 11,55,978 INR for summer season and 14,16,846 INR for winter season operations. vi