Optimal Design of Water Desalination Systems Involving Waste Heat Recovery

Water desalination appears as an attractive alternative to provide fresh water in several parts of the world. However, this process is very expensive due to the high-energy consumption, and as consequence, significant pollution is produced due to the burning of fossil fuels that yield huge emissions of CO₂. Furthermore, most of the desalination processes yield a lot of waste heat at low temperature, which can be recovered. Therefore, this paper presents an optimization approach for designing water desalination systems involving heat integration and waste heat recovery to reduce the desalination cost, energy consumption, and overall greenhouse gas emissions. The proposed approach accounts for the optimal selection of existing and emerging desalination technologies based on the heating and cooling requirements and incorporating waste heat recovery systems. The integration of the proposed systems provides power and thermal energy to the desalination task. Also, the proposed approach includes the optimal selection of fossil fuels, biofuels, and solar energy as energy sources. The proposed approach was applied to a case study, and the results show that the system that involves the multiple-effect distillation and thermal membrane distillation shows the best economic and environmental benefits involving water sales, power production, and energy savings

Optimal Synthesis of Property-Based Water Networks Considering Growing Demand Projections

This paper presents a mathematical programming model for the optimal synthesis and retrofitting of water networks based on the properties of the streams that impact the processing in the plant and the environment. One important feature of the proposed approach is that it accounts for changes in the operation through a time horizon with growing demands. The optimization formulation considers changes in the demands and accounts for time-based variations in the flow rates required for the process sinks and constraints for properties in the process sinks and in the environment. Furthermore, the proposed model allows the installation of different units and the retrofitting of the water network over the considered time horizon. The objective function minimizes the total cost associated with the entire life of the project while accounting for the time value of money and the specific demands for the process and the environment that change through the life of the project. Two case studies are solved to show the applicability of the proposed approach

Multiobjective Optimization of Dual-Purpose Power Plants and Water Distribution Networks

This paper presents a multiobjective optimization approach for synthesizing water distribution networks involving dual-purpose power plants. The proposed model accounts for environmental, economic, and social objectives by accounting for greenhouse gas emissions, jobs, and net profit. The model considers water and energy demands for domestic, agricultural, and industrial users. Energy is provided through several alternatives including fossil fuels (i.e., natural gas and oil), biofuels (i.e., biomass, biogas, biodiesel, and bioethanol), and solar energy. Water demands are satisfied by fresh water from dams, lakes, rivers, aquifers, and artificial storage tanks. The proposed model is applied to a case study from the Mexican State of Sonora. The results show the viability of the dual-purpose power–water plants, the merits of incorporating solar energy in the system, and the economic, environmental, and social benefits of applying the proposed approach. The optimal solution yields a total annual profit of $MM 1,545.9, it generates 1.37 × 10⁷ ton CO₂ equiv/y and 19 781 jobs

Strategic Planning for Managing Municipal Solid Wastes with Consideration of Multiple Stakeholders

Management of municipal solid waste (MSW) involves multiple stakeholders such as government agencies, suppliers, consumers, providers of treatment/recycle services, and transporters. An optimal management strategy should be based on creating synergistic opportunities that benefit the multiple participants. This paper presents a multi-objective optimization approach for the strategic planning of a municipal solid waste management system. The formulation considers the involved tasks such as recycle, reuse, transportation, separation, and distribution. The proposed approach also accounts for the multiple stakeholders with the objective of maximizing the benefit to all the participating stakeholders. The Latin Hypercube sampling technique is adopted to systematically generate weights for the different stakeholders. A case study from Mexico is analyzed where three scenarios are considered. The first one considers that the separation cost is absorbed by each recycling company. The second one assumes that the government is responsible for the separation cost. The third one requires household inhabitants to carry out waste sorting. The optimization approach is used to analyze the results of the various scenarios and to deduce valuable insights on the interaction among the various stakeholders and the building blocks of the supply chain of MSW management systems

Use of Nonlinear Membership Functions and the Water Stress Index for the Environmentally Conscious Management of Urban Water Systems: Application to the City of Morelia

This article proposes a multiobjective optimization strategy based on a fuzzy formulation for the sustainable design and planning of water supply chains in urban areas that considers simultaneously economic and environmental objectives. Harvested rainwater and reclaimed water are considered as alternative sources to reduce freshwater consumption while maximizing water revenues and minimizing land usage. As opposed to other models that attempt to minimize water consumption, this work seeks to minimize the water stress index, which quantifies the impact of freshwater consumption with respect to the specific location where the withdrawals take place. We illustrate the capabilities of this approach through its application to a real case study based on the city of Morelia in Mexico, in which we show that the use of alternative water sources along with an appropriate water distribution plan can reduce the impact over natural reservoirs

Strategic Planning for the Supply Chain of Aviation Biofuel with Consideration of Hydrogen Production

Substitution of petro-based aviation fuel with biomass-derived aviation fuel is an emerging strategy to reduce the carbon footprint associated with the aviation sector. There are several pathways for the production of aviation biofuel, and most of them require the use of hydrogen. Therefore, the analysis of the aviation biofuel supply chain must incorporate the production of hydrogen. This paper presents an optimization approach for the strategic planning of aviation fuel supply chains, which considers hydrogen production from fossil and renewable raw materials. The approach also considers extraction of fossil materials, growth of biomass, selection and several processing routes of the feedstock, along with the distribution of products. As a case study, the strategic planning of aviation biofuels in Mexico considering the generation of biomass and the hydrogen production is selected. The results show that significant decreases in producing costs and CO₂ emissions can be obtained if aviation fuel is generated from renewable raw materials. This finding is quite important, because in Mexico 90% of the consumed energy proceed from fossil sources. Several scenarios are addressed to assess the key factors in the design of the supply chain, reconciling the economic and environmental objectives; and also an analysis for the integration of the infrastructures of the fossil fuels and biorefineries is presented

Optimization of Pathways for Biorefineries Involving the Selection of Feedstocks, Products, and Processing Steps

This paper presents a systematic approach to identify the optimal pathway configurations of a biorefinery while incorporating technical, economic, and environmental objectives. This problem is formulated as a generalized disjunctive programming model which accounts for the simultaneous selection of products, feedstocks, and processing steps. The optimal solution can involve multiproduct and multifeedstock biorefineries. The optimization model takes into account two potentially conflicting objectives, the maximization of the net profit and the minimization of the greenhouse gas emissions, while considering the number of processing steps. The environmental criterion is measured using the life cycle assessment methodology. The ε-constraint method is used to determine the Pareto curves of this multiobjective optimization problem and to show the trade-offs between the competing objectives. A case study is presented to illustrate the applicability of the proposed methodology for the optimal selection of the biorefinery configuration for the conditions of Mexico under several scenarios. The results show that the optimal combination of different feedstocks and products allows for proper trade-off between the economic and environmental objectives. Results also show that bioethanol, biodiesel, and biohydrogen usually appear as products, whereas sugar cane, jatropha, and microalgae appear as feedstocks in the optimal pathways

Optimal Synthesis of Refinery Property-Based Water Networks with Electrocoagulation Treatment Systems

This paper presents an optimization approach to the incorporation of electrocoagulation in the design of integrated water networks for oil refineries. A disjunctive programming formulation is developed to minimize the cost of the water-management system while including the characteristics of process water streams, recycle, reuse, and treatment of wastewater streams, performance of candidate technologies, and composition and property constraints for the process units and the environmental discharges. The performance of electrocoagulation was related to temperature pH and the concentration of phenols and sodium chloride. Ancillary units including pH adjustment, reverse osmosis, and heat exchangers were used to support the electrocoagulation unit. Two case studies are presented to show the applicability of the proposed model and the feasibility of using electrocoagulation as part of an integrated water management scheme for oil refineries