Industrial water management by multiobjective optimization: from individual to collective solution through eco-industrial parks.

Industrial water networks are designed in the first part by a multiobjective optimization strategy, where fresh water, regenerated water flow rates as well as the number of network connections (integer variables) are minimized. The problem is formulated as a Mixed-Integer Linear Programming problem (MILP) and solved by the ε-constraint method. The linearization of the problem is based on the necessary conditions of optimality defined by Savelski and Bagajewicz (2000). The approach is validated on a published example involving only one contaminant. In the second part the MILP strategy is implemented for designing an Eco-Industrial Park (EIP) involving three companies. Three scenarios are considered: EIP without regeneration unit, EIP where each company owns its regeneration unit and EIP where the three companies share regeneration unit(s). Three possible regeneration units can be chosen, and the MILP is solved under two kinds of conditions: limited or unlimited number of connections, same or different gains for each company. All these cases are compared according to the global equivalent cost expressed in fresh water and taking also into account the network complexity through the number of connections. The best EIP solution for the three companies can be determined

Optimization of Water Network Retrofit Design for Petroleum Refineries with Water Reuse, Regeneration, and Recycle Strategies (W3R)

Water is a key element in the operation of petroleum refineries. In the past, wastewater was typically piped to a centralized treatment plant and research efforts were focused mainly on improving treatment technologies. It was later recognized that distributed wastewater treatment networks in which wastewater streams are treated separately may be preferable to the centralized approach. Moreover, scarcities in freshwater supply and increasingly stringent rules on wastewater discharge have emerges as issues of major concerns to plant operators, along with an increased awareness in the need to support sustainable development initiatives and minimization of water footprint. In line with these development, there are increased interests to incorporate water reuse, regeneration (i.e, treatment), and recycle (W3R) approaches in the design of refinery water network systems, with the aim of minimizing freshwater consumption and wastewater generation. This work presents an optimization model to determine the optimal design of refinery water network systems. The integrated model explicitly considers the incorporation of water minimization strategies by first postulating a source-interceptorsink superstructure that embeds many possible feasible tlowsheet alternatives for the implementation of potential W3R approaches. Subsequently, a mixed-integer nonlinear programming (MINLP) model is formulated based on the superstructure to determine the optimal water network structure in terms of the continuous variables of total stream tlowrates, contaminant concentrations and the 0-l binary variables of stream interconnections in the piping network. The superstructure and the MINLP model explicitly handles the membrane-based interceptors (primarily ultrafiltration and reverse osmosis units) and the non-membrane-based interceptors, in which in the former, the feed, permeate, and reject streams are assumed as an individual process units. The objective of the model is to minimize the fixed capital costs of installing piping interconnections and the variable cost of operating all stream interconnections while reducing the pollutants level to within limits by environmental regulations under all the associated material balances of flows and concentrations. The proposed modeling approach is implemented on an industrially-significant numerical example using the GAMS/BARON global optimization platform to obtain a globally cost-optimal water network topology

Optimization with Integrated Offline Parametric Optimization of Detailed Process Model of an Interceptor Unit for Water Network Synthesis and Retrofit Design

Petroleum refineries is a prime example of industrial plants that demand high quantities of water for process consumption and generate volumes of highly contaminated industrial eflluents and wastewaters. Scarcity of freshwater resources and increasingly stringent environmental regulations on industrial effluents have motivated refineries to develop water reuse technologies for sustainability of plant operations. The technology concept can be characterized into three (3) strategies: reuse, regeneration, and recycle (W3R). The major contribution of this work is to consider the design of alternative refinery water network structures that incorporate the detailed design of wastewater treatment technology (or interceptor) in an optimization-based modeling framework as an offline parameter optimization problem. For this purpose, a source-interceptor -sink superstructure representation is adopted that embeds many feasibly possible alternative water network configurations. A mixed-integer nonlinear programming (MINLP) optimization model is formulated based on the superstructure with the objective of minimizing freshwater import, wastewater generation, piping interconnections, and the total cost of installing and operating the treatment technology. The parametric optimization problem comprising of material balances and the detailed phenomena model for interceptor, specifically for a single-stage hollow fiber reverse osmosis (HFRO) membrane module, is incorporated in the overall MINLP framework. The modeling approach is developed in conjunction with its implementation into general algebraic modeling system (GAMS), using data of a real operating refinery situation. The model is solved iteratively by branch and reduce optimization navigator (BARON), resulting in freshwater consumption requirements to be 296.2 m3 /h at the optimal refinery water network structure and operating conditions, which accounts for nearly 61% of water recovery compared to current operating requirements (before the integration and retrofit initiatives based on W3R)

Synthesis of Heat-Integrated Water Allocation Networks: A Meta-Analysis of Solution Strategies and Network Features

Industries consume large quantities of energy and water in their processes which are often considered to be peripheral to the process operation. Energy is used to heat or cool water for process use; additionally, water is frequently used in production support or utility networks as steam or cooling water. This enunciates the interconnectedness of water and energy and illustrates the necessity of their simultaneous treatment to improve energy and resource efficiency in industrial processes. Since the seminal work of Savulescu and Smith in 1998 introducing a graphical approach, many authors have contributed to this field by proposing graphically- or optimization-based methodologies. The latter encourages development of mathematical superstructures encompassing all possible interconnections. While a large body of research has focused on improving the superstructure development, solution strategies to tackle such optimization problems have also received significant attention. The goal of the current article is to study the proposed methodologies with special focus on mathematical approaches, their key features and solution strategies. Following the convention of Jeżowski, solution strategies are categorized into: decomposition, sequential, simultaneous, meta-heuristics and a more novel strategy of relaxation/transformation. A detailed, feature-based review of all the main contributions has also been provided in two tables. Several gaps have been highlighted as future research direction