Designing plant scale process integration for water management in an Indian paper mill Sudheer Kumar Shukla a, * , Vivek Kumar b , B. Chakradhar c , Taesung Kim a, d , M.C. Bansal b a School of Mechanical Engineering, Sungkyunkwan University, Republic of Korea b Department of Paper Technology, Indian Institute of Technology Roorkee, Saharanpur Campus, Saharanpur 247001, India c Ramky Enviro Engineers Ltd., Hyderabad, India d SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon, Republic of Korea article info Article history: Received 13 November 2011 Received in revised form 31 May 2013 Accepted 16 June 2013 Available online 8 July 2013 Keywords: Paper mill effluent Process integration Water cascade analysis Water network Water pinch analysis abstract In the present study, plant-scale process integration was applied to an Indian paper mill using the water cascade analysis (WCA) technique. Three limiting constraints, chemical oxygen demand (COD), total dissolved solids (TDS), and adsorbable organic halides (AOX), were considered for the study. A nearest neighbor algorithm was used to distribute the freshwater and recycled water among the plant opera- tions. It was found that the limiting critical constraint depends upon the types of processes and streams involved in the integration. The limiting critical constraint can differ for different sections of the same industry, and can differ in different schemes of integration. After process integration, a 55.6% reduction in effluent flow, a 36% reduction in COD, and a 73% reduction in AOX were observed. After process inte- gration, a 35.21% reduction in pollution costs can be achieved and, assuming the average production of the mill to be 225 tons per day, a savings of Indian rupees (INR) 1.73 per kg of paper produced can be achieved by employing process integration. The water cess was calculated as INR 3024.77 per day without integration for the sections that were considered for integration, while after integration, a 41.53% savings in the form of water cess was calculated. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction System closure in pulp and paper mills consists of optimizing the internal reutilization of used water to reduce freshwater con- sumption and enhance energy and material efficiency, while adhering to process constraints. Total system closure, or zero effluent, is generally not a practical objective because of technical and economic factors (Bajpai, 2012). Furthermore, the optimum closure target is specific to each mill because of the considerable differences in process configurations. Many Indian mills have made significant progress over the years by applying conventional process analysis and engineering tech- niques. Significant gains can still be accomplished by implementing innovative system closure strategies. Process integration methods and tools can yield interesting results in such endeavors. One strategy is to generate process water in the thickening and dewatering stages of the papermaking process and recycle the water in different loops of the water circuit of the system before disposal. The loops are separated by the thickening/dewatering process stages (disc filter plus wire press or screw press). The fil- trates of these stages are sent backward through the same loop for dilution purposes. The excess water (usually clear filtrate from the disc filter) replenishes the preceding loop. Similar to other industries, successful applications of water network synthesis in pulp and paper mills have also been docu- mented (Tripathi, 1996; Tainsh and Rudman, 1999; ’dard et al., 1999; Yang et al., 2000; Parthasarathy and Krishnagopalan, 2001; Andersen et al., 2002; Jacob et al., 2002; Koppol et al., 2003; Shafiei et al., 2004; Tan and Manan, 2003; Manan and Tan, 2004; Lovelady et al., 2007; Manan et al., 2007; Foo et al., 2006b; Delgado et al., 2006; Chiang et al., 2006). Despite the widespread application of water network synthesis techniques, considerably less work has been reported on the special case of water network synthesis, i.e., threshold problems, or on cross-plant water integration, known as plant-wide integration. Flow rate targeting for water network synthesis with threshold problems was first addressed by Foo (2008). Unlike many water networks that normally require fresh- water intake and discharge wastewater, a water network with * Corresponding author. Tel.: þ82 31 290 7466; fax: þ82 31 299 4751. E-mail addresses: sudheerkrshukla@gmail.com, shuklasudheer@rediffmail.com (S.K. Shukla), vivekfpt@gmail.com (V. Kumar), drchakradhar@ramky.com (B. Chakradhar), tkim@skku.edu (T. Kim), mukeshcbansal@hotmail.com (M.C. Bansal). Contents lists available at SciVerse ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman 0301-4797/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvman.2013.06.012 Journal of Environmental Management 128 (2013) 602e614