José María Ponce-Ortega

Optimal synthesis of heat exchanger networks involving isothermal process streams

This paper proposes a new MINLP model for heat exchanger network synthesis that includes streams with phase change. The model considers every possible combination of process streams that may arise within a chemical process: streams with sensible heat, streams with latent heat, and streams with both latent and sensible heat. As part of the optimization strategy, the superstructure is modeled with logical conditions that are used for the proper placement of heat integration for streams with change of phase. The proposed MINLP model provides the network structure that minimizes the total yearly cost. Several examples are presented to illustrate the capabilities of the proposed model.

Optimal planning for the sustainable utilization of municipal solid waste

The increasing generation of municipal solid waste (MSW) is a major problem particularly for large urban areas with insufficient landfill capacities and inefficient waste management systems. Several options associated to the supply chain for implementing a MSW management system are available, however to determine the optimal solution several technical, economic, environmental and social aspects must be considered. Therefore, this paper proposes a mathematical programming model for the optimal planning of the supply chain associated to the MSW management system to maximize the economic benefit while accounting for technical and environmental issues. The optimization model simultaneously selects the processing technologies and their location, the distribution of wastes from cities as well as the distribution of products to markets. The problem was formulated as a multi-objective mixed-integer linear programing problem to maximize the profit of the supply chain and the amount of recycled wastes, where the results are showed through Pareto curves that tradeoff economic and environmental aspects. The proposed approach is applied to a case study for the west-central part of Mexico to consider the integration of MSW from several cities to yield useful products. The results show that an integrated utilization of MSW can provide economic, environmental and social benefits.

Global optimization for the synthesis of property-based recycle and reuse networks including environmental constraints

This paper presents a new formulation and a mathematical programming model for the direct recycle and reuse of mass exchange networks considering simultaneously process and environmental constraints. The model is based on mass and property integration. The properties constrained by the sinks include composition, density, viscosity, pH, and reflectivity, whereas the environmental constraints include the composition for hazardous materials, toxicity, chemical oxygen demand, color, and odor. The model eliminates most of the nonlinearities of the system, and the bilinear terms that remain are handled with a relaxation approach that yields a global optimal solution. The model minimizes the total annual cost that includes the cost of fresh sources and the annualized cost for property interceptors. Two examples are presented to show the effectiveness of the proposed model. The results show that even for a large size problem, the computation effort is relatively small as a result of the linearization procedure.

Multi-objective optimization of process cogeneration systems with economic, environmental, and social tradeoffs

Process cogeneration is an effective strategy for exploiting the positive aspects of combined heat and power in the process industry. Traditionally, decisions for process cogeneration have been based mostly on economic criteria. With the growing interest in sustainability issues, there is need to consider economic, environmental, and social aspects of cogeneration. The objective of this article is to develop an optimization framework for the design of process cogeneration systems with economic, environmental, and social aspects. Process integration is used as the coordinating framework for the optimization formulation. First, heat integration is carried out to identify the heating utility requirements. Then, a multi-header steam system is designed and optimized for inlet steam characteristics and their impact on power, fixed and operating costs, greenhouse gas emissions, and jobs. A genetic algorithm is developed to solve the optimization problem. Multi-objective tradeoffs between the economic, environmental, and social aspects are studied through Pareto tradeoffs. A case study is solved to illustrate the applicability of the proposed procedure.

Optimization model for re-circulating cooling water systems

Abstract This paper presents an optimization model for the simultaneous synthesis and detailed design of re-circulating cooling water systems. A cooler network superstructure that embeds all network configurations of practical interest is used as part of the integrated model. Pressure drops in each cooler are treated as optimization variables, and design guidelines and constraints are included in order to provide practical and feasible units. The model is based on a generalized disjunctive programming formulation, which gives rise to a mixed-integer nonlinear programming problem. The objective is to find cooling water systems that minimize the total annual cost. Solution of this mathematical formulation provides the optimal system configuration as well as the optimal operating conditions and design parameters required for each cooler unit in the network and in the cooling tower. Three example problems are presented to show the application of the proposed approach.

A global optimal formulation for the water integration in eco-industrial parks considering multiple pollutants

Abstract A mathematical programming formulation for the water integration in eco-industrial parks considering streams with several pollutants is presented. The formulation is based on a superstructure that allows the wastewater reuse in the same plant, the water exchange with different plants, and a shared set of interceptors that must be selected to determine the network configuration that satisfies process equipments and environmental constraints. The model formulation considers wastewater with several pollutants, and optimizes the network according to the minimum total annual cost, which includes the costs of fresh water, piping and regeneration. A new discretization approach is also proposed to handle the large set of bilinear terms that appear in the model in order to yield a near global optimal solution. The results obtained in several examples show considerable savings with respect to the solutions of the individual plant integration policy commonly employed for these types of problems.

Optimal reconfiguration of multi-plant water networks into an eco-industrial park

Abstract This paper presents an MINLP model to design an eco-industrial plant by retrofitting existing water networks from different industrial plants in the same industrial zone. The proposed model is based on a superstructure and takes into account both in-plant and inter-plant structural modifications, such as the placement/reassignment of existing treatment units, the required increase of capacity and/or efficiency of existing treatment units, the placement of new treatment units either within the participating plants or in a new shared wastewater treatment facility, and the stream re-piping associated with installing new treatment units and retrofitting existing treatment units. The model allows the tracking of changes in the process performance as a result of the stream re-routing and retrofitting activities. Two examples were solved, and the results show the economic and environmental benefits of the retrofitted networks within an eco-industrial park compared to the stand-alone retrofitted networks.

Industrial waste heat recovery and cogeneration involving organic Rankine cycles

This paper proposes a systematic approach for energy integration involving waste heat recovery through an organic Rankine cycle (ORC). The proposed approach is based on a two-stage procedure. In the first stage, heating and cooling targets are determined through heat integration. This enables the identification of the excess process heat available for use in the ORC. The optimization of the operating conditions and design of the cogeneration system are carried out in the second stage using genetic algorithms. A modular sequential simulation approach is proposed including several correlations to determine the properties for the streams in the ORC. The proposed approach is applied to a case study which addresses the tradeoffs among the different forms of energy and associated costs. The results show that the optimal selection of the operating conditions and working fluid is very important to reduce the costs associated to the process.

Synthesis of water networks considering the sustainability of the surrounding watershed

Abstract This paper presents a new mathematical programming model for the optimal synthesis of recycle and reuse networks considering simultaneously the integration of the water network system and the surrounding watershed to satisfy process and environmental constraints. The model considers the optimal location of the new industrial facility to integrate its wastewater discharge to the environment with the surrounding watershed through a disjunctive formulation. The pollutants discharged for the new plant are tracked simultaneously with the other discharges to the watershed (i.e., residential, sanitary, industrial and extractions), and the natural phenomena that affect the composition of the watershed (i.e., evaporation, filtration, etc.), in addition to the chemical reactions that are carried out in the rivers. The objective function consists in minimizing the total annual cost that is constituted by the installation of the new plant cost (including the transportation for raw materials, products and services, as well as the land cost), the wastewater treatment costs (including the piping cost) and the fresh sources cost. Two example problems were used to show the applicability of the proposed methodology.

An MINLP model for the simultaneous integration of energy, mass and properties in water networks

Abstract A model for the synthesis of water networks with a simultaneous integration of energy, mass and properties is presented. The model is formulated within a mixed-integer nonlinear programming framework where the objective function accounts for the minimization for the total annual cost satisfying energy, mass and property constraints for the water streams involved in the network. To accomplish this task, a new superstructure is proposed, in which a first stage for energy integration before mixing streams was considered, followed by a mass and property integration network, and placing finally a second energy integration network. Within this approach, the optimization model identifies when a stream can be used as a hot or a cold stream as part of the energy integration. The proposed approach was applied to two case studies, and the results show that there are significant advantages for the simultaneous implementation of the energy, mass and property integration strategies.