Mahmoud M. El-Halwagi

Automatic synthesis of mass-exchange networks with single-component targets

This paper addresses the problem of automatically synthesizing mass-exchange networks in which the mass of a single (key) component is exchanged between a set of rich streams and a set of lean streams. In the first part of this paper we present a two-stage synthesis procedure that employs one minimum allowable composition difference for all possible rich-lean stream pairs. In the first stage, a linear programming problem is solved to determine the minimum cost of mass-separating agents and to locate thermodynamic bottlenecks (pinch points) which restrict the exchange of mass between the rich and the lean streams. This formulation can also preclude (preassign) any specified forbidden (compulsory) matches between streams. In the second stage, a mixed-integer linear program is solved to yield minimum-utility cost networks in which the number of mass-exchanger units is minimized. In the second part of this paper we present a more general, yet computationally intensive, procedure that employs one minimum allowable composition difference for each possible rich-lean stream pair. These degrees of freedom are then used to minimize the annualized total cost of the network. An additional merit of the latter methodology is its potential as an improved approach for the synthesis of optimal heat-exchange networks. Several examples with industrial relevance are solved to demonstrate the usefulness of the notion of synthesizing mass-exchange networks and to illustrate the computational effectiveness of the proposed synthesis strategy.

Automated targeting technique for concentration- and property-based total resource conservation network

Resource conservation networks (RCNs) are among the most effective systems for reducing the consumption of fresh materials and the discharge of waste streams. A typical RCN involves multiple elements of resource pre-treatment, material reuse/recycle, regeneration/interception, and waste treatment for final discharge. Due to the close interactions among these individual elements, simultaneous synthesis of a total RCN is necessary. This paper presents an optimisation-based procedure known as automated targeting technique to locate the minimum resource usage or total cost of a concentration- or property-based total RCNs. This optimisation-based approach provides the same benefits as conventional pinch analysis techniques in yielding various network targets prior to detailed design. Additionally, this approach offers more advantages than the conventional pinch-based techniques through its flexibility in setting an objective function and the ability to handle different impurities/properties for reuse/recycle and waste treatment networks. Furthermore, the concentration-based RCN is treated as the special case of property integration, and solved by the same model. Literature examples are solved to illustrate the proposed approach.

Techno-economic analysis for a sugarcane biorefinery: Colombian case

In this paper a techno-economic analysis for a sugarcane biorefinery is presented for the Colombian case. It is shown two scenarios for different conversion pathways as function of feedstock distribution and technologies for sugar, fuel ethanol, PHB, anthocyanins and electricity production. These scenarios are compared with the Colombian base case which simultaneously produce sugar, fuel ethanol and electricity. A simulation procedure was used in order to evaluate biorefinery schemes for all the scenarios, using Aspen Plus software, that include productivity analysis, energy calculations and economic evaluation for each process configuration. The results showed that the configuration with the best economic, environmental and social performance is the one that considers fuel ethanol and PHB production from combined cane bagasse and molasses. This result served as the basis to draw recommendations on technological and economic feasibility as well as social aspects for the implementation of such type of biorefinery in Colombia.

A shortcut method for the preliminary synthesis of process-technology pathways: An optimization approach and application for the conceptual design of integrated biorefineries

Abstract Synthesis and screening of technology alternatives is a key process-development activity in the process industries. Recently, this has become particularly important for the conceptual design of biorefineries. This work introduces a shortcut method for the synthesis and screening of integrated biorefineries. A structural representation (referred to as the chemical species/conversion operator) is introduced. It is used to track individual chemicals while allowing for the processing of multiple chemicals in processing technologies. The representation is used to embed potential configurations of interest. An optimization approach is developed to screen and determine optimum network configurations for various technology pathways using simple data. The solution to the optimization formulation provides a quick and effective method for screening and interconnecting the technological pathways and to distributing the flows over the network. Case studies are solved to illustrate the applicability of the proposed approach.

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.

An integrated approach to the optimisation of water usage and discharge in pulp and paper plants

This paper is aimed at developing a systematic methodology for the cost-effective reduction of water usage and discharge in pulp and paper plants. As the industry moves towards increased system closure, the build-up of Non-Process Elements (NPEs) leads to serious consequences on the process equipment. In response, this paper achieves the following: a mathematical model to track water and primary NPEs throughout the pulping process; rigorous targeting for water usage and discharge; a systematic framework for water reduction using mass integration strategies including no/low cost techniques as well as capital-based techniques; an optimisation model for the optimisation of allocation, recycle and separation of aqueous streams. A case study for water management in a kraft pulping process has been solved to highlight the usefulness of the devised approach.

An algebraic targeting approach to resource conservation via material recycle/reuse

In this paper, an algebraic approach to the targeting of material recycle/reuse is developed. A cascade analysis is developed to maximise the recycle of process streams. Feasibility constraints and optimality conditions are derived based on insights from the graphical representation of material recycle pinch diagrams. The devised method is non-iterative, systematic and leads to the identification of rigorous targets for minimum usage of fresh resources, maximum recycle of process resources, and minimum discharge of waste. All these targets are determined ahead of detailed design of the recycle/reuse network. Two case studies are solved to illustrate the ease, rigour, and applicability of the developed targeting technique.

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.