Optimal design of solar-assisted industrial processes considering heat pumping: Case study of a dairy

Pinch analysis and Mixed Integer Linear Programming (MILP) have been extensively studied for optimization of industrial processes addressing heat recovery, utility selection and sizing. Analysis of renewable utility integration, such as solar thermal or photovoltaics, introduces several obstacles for established methods: the time-dependency of resources, storage inertia and losses, and intrinsic non-linearities of the system performance are difficult to represent by linearized, time-invariant MILP equations. Moreover, waste heat recovery options such as heat pumping cannot be neglected as a potential competitor to solar heat. This work presents a set of multi-period MILP equations for solar technologies as well as a superstructure for optimization of heat pump cycles. Additionally, a methodology is proposed and applied to simultaneously optimize the process' refrigeration and renewable utility system using ɛ-constrained parametric optimization. The proposed methodology is illustrated on the basis of a dairy plant for which the different utility technologies are compared and evaluated based on economic and environmental criteria. It is illustrated that integration of solar energy can contribute to strongly reduce the environmental impact of the process (65–75% reduction in CO2 equivalent emissions), but only in combination with heat recovery (27%) and an improved heat pump system (33%). Heat recovery and heat pump placement for industrial processes are hereby shown to reduce exergy destruction and total cost while improving system energy efficiency by means of thermo-economic optimization. The solutions show that investment in solar energy can be economically and environmentally attractive for industrial processes by considering the whole system and ensuring that solar energy is optimally integrated and utilized.

Process design methods for sustainable energy systems

François Maréchal

Today, energy is the driver of the modern society, allowing for transforming raw materials and resources into ``useful'' products and services. Concerns on climate change and resources scarcity together with the increasing importance put on the environmental impacts are redefining the problem of the energy usage in the society. In this context, developing a sustainable energy systems means designing the system that will convert in an optimal way the available resources into useful products and services, reaching the maximization of the resources productivity and minimizing its environmental impact. In a given socio-economical and environmental context, the goal of the process design is to select the type and the size of the technologies, the way they are interconnected and the way they are operated. A computer aided methodology and the corresponding process system engineering tools for the analysis and the synthesis of efficient processes and energy conversion systems will be presented. It combines the use of thermo-economic and environomic models of sub-systems that are structured in an equipment data base. These models include the representation of the possible interfaces that a technology will present when it is integrated to build the integrated system. A systematic method based on process integration and optimization techniques is then used to generate process superstructure and process configurations. Models are then used to calculate the system performances in terms of thermodynamic performances, operating and investment cost together with Life cycle impact assessment indicators. Multi-objective optimization techniques are then used to decide the best values of the design decision variables and to generate thermo-economic Pareto sets of process configurations where the trade-off between economical criteria and thermodynamical or environmental impact criteria are represented. Such tools are used to support decisions in the process engineering work. In this iterative procedure, one has to recognize that the problem is never perfectly defined at the beginning of the project. The methodology includes therefore solutions analysis tools such as exergy analysis and sensitivity analysis and graphical representations that are used to understand the energetics of the solutions and refine the process design problem definition. The tools developed are applied in different fields : rational use of energy, water and waste management in the industrial processes, energy conversion systems design like power plants with

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capture, fuel cell systems and biofuels production and in the study of urban energy systems. In the presentation, examples of the biofuel production process design will be used to illustrates the different steps of the methodology and demonstrate the role of process design in the development of sustainable energy systems.

2011

A systematic methodology for the synthesis of unit process chains using Life Cycle Assessment and Industrial Ecology Principles

Léda Gerber, François Maréchal, Jérôme Mayer

The integration of environmental impacts in the conceptual process design procedure can be achieved by combining Life Cycle Assessment (LCA) tools with flowsheeting software and process integration techniques. However, current LCI databases assume a given unit process chain for each product or waste, and do not allow for the systematic synthesis of the process chain minimizing the environmental impacts of raw materials or auxiliary flows, accounting systematically for the different alternatives and recyclings. This paper presents a methodology for systematically designing process units LCI database for the optimal design of integrated systems with a life cycle perspective.

Elsevier Science, Reg Sales Off, Customer Support Dept, 655 Ave Of The Americas, New York, Ny 10010 Usa2011

Process design methods for sustainable energy systems

François Maréchal

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2011