Computers and Chemical Engineering 44 (2012) 11–19 Contents lists available at SciVerse ScienceDirect Computers and Chemical Engineering jo u rn al hom epa ge : www.elsevier.com/locate/compchemeng Synthesis of mass integration networks: Integrated approach to optimization of stream matching for a metal pickling process Kamil M. Wagialla ∗ Chemical Engineering Department, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia a r t i c l e i n f o Article history: Received 20 December 2011 Received in revised form 20 April 2012 Accepted 25 April 2012 Available online 8 May 2012 Keywords: MILP MINLP Mass and property integration Pinch point Stream matching Techno-economic feasibility a b s t r a c t The purpose of this techno-economic feasibility study is to develop a procedure for the cost-effective synthesis and optimization of schemes to recover in-plant a valuable ingredient from waste streams and at the same time reduce the COD property. MILP and MINLP algorithms are used. The model minimizes the total annualized cost of the mass exchange network (MEN). The procedure involves a two-stage process: first, using the MILP, the pinch point location is identified along with the selection of an optimal set of mass separating agents (MSAs). At this stage the effect of each selected MSA on COD is scrutinized. In the second stage, the MINLP is applied to realize the optimal matching of waste and lean streams through the direct minimization of equipment capital cost. An example is presented to show the applicability and advantages of the proposed novel procedure. The project was found to be highly profitable. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction The problem of synthesizing mass exchange networks (MENs) has been studied by several investigators (Azeez, Isafiade, & Fraser, 2012; Dunn & El-Halwagi, 2003; El-Halwagi, 1997; El- Halwagi, 2006; El-Halwagi, 2012; El-Halwagi & Manousiouthakis, 1989; Gabriel & El-Halwagi, 2005; Lovelady, El-Halwagi, & Krishnagopalan, 2007; Noureldin & El-Halwagi, 2000; Wagialla, in press; Wagialla, El-Halwagi, & Ponce-Ortega, 2012). Fig. 1 shows an overall scheme of a MEN system. Synthesis of networks is carried out after identification of pinch point location and selection of an optimum set of MSAs. The performance of chemical processes depends ultimately on functionalities and properties. Design specifications may be based on properties, not chemical components (e.g. vapor pressure in con- densation, relative volatility in distillation, Henry’s coefficient in absorption). Properties of pollutants such as volatility and solubility can affect quantities of plant emissions. Property integration is thus more general than mass integration which is in fact a special case of property integration. The concept of property integration was introduced by El-Halwagi and co-workers (El-Halwagi, Glasgow, Eden, & Qin, 2004; Kazantzi & El-Halwagi, 2005; Kazantzi, Harell, Gabriel, Qin, & El-Halwagi, 2004; Kazantzi, Qin, Gabriel, Harell, & El-Halwagi, 2004). Grooms, Kazantzi, and El-Halwagi (2005) ∗ Tel.: +966 508422167; fax: +966 14678770. E-mail address: wagialla@ksu.edu.sa introduced the problem of synthesizing a network of property- modifying units and scheduling operating schemes. The authors developed a mixed-integer nonlinear programming formulation to minimize the total annualized cost of the system, synthesize the network, and determine its optimal operating schedule. Prop- erty integration is a generic systematic design methodology for allocation and manipulation of streams and process units which is based on properties and functionalities rather than on chemi- cal composition alone. Tracking properties through this approach is manageable while tracking numerous chemical pollutants is prohibitively difficult. Property integration should be considered when: (a) process constraints are given in terms of properties, (b) units’ performances are assessed on the basis of properties, not chemical constituents (c) with complex mixtures of numerous compounds such as complex hydrocarbons and (d) when environ- mental regulations for process discharges are based on properties (e.g. COD, BOD, pH, color, odor, etc.). Recent research consid- ers simultaneously process and environmental constraints (Azeez et al., 2012; El-Halwagi, 2012; Nápoles-Rivera, Ponce-Ortega, El- Halwagi, & Jiménez-Gutiérrez, 2010; Ng, Foo, Tan, & El-Halwagi, 2010; Ponce-Ortega, El-Halwagi, & Jimenez-Gutierrez, 2010). 2. Problem statement The problem addressed in this paper consists of designing a cost-effective network of mass exchangers that can preferentially transfer in-plant a specific ingredient from the waste streams to the MSAs. Notwithstanding the numerous efforts made in the literature 0098-1354/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compchemeng.2012.04.012