275109 Sustainable Design of Integrated Absorption Refrigeration Systems
Sustainable Design of Integrated Absorption Refrigeration Systems
Luis Fernando Lira-Barragán,a José María Ortega-Ponce,a Medardo Serna-González,a Mahmoud M. El-Halwagib,c
a Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Mich., México
b Chemical Engineering Department, Texas A&M University, College Station, TX, USA
c Adjunct Faculty at the Chemical and Materials Engineering Department, King Abdulaziz University, Jeddah, Saudi Arabia
This paper deals with the problem of synthesizing sustainable absorption refrigeration cycles that are integrated with industrial processes that require refrigeration. The proposed methodology is based on a mathematical programming formulation considering the superstructure shown in Figure 1. This superstructure allows the heat integration of a set of hot and cold process streams and, at the same time, accounts for multiple energy sources to run the stripper required by the absorption refrigeration cycle that provides the refrigeration requirements by a given process. The energy sources considered are the hot process streams connecting the hot end of the heat exchanger network with the absorption refrigeration cycle, solar energy, fossil fuels and biofuels, which have different environmental and social impacts. With exception of hot process streams, when it is necessary, the energy sources can also be used to generate the hot utility required by the cold process streams. Therefore, the proposed formulation addresses the optimization of absorption refrigeration cycles and heat exchanger networks simultaneously (i.e., it optimizes simultaneously the configuration and parameters of the overall system) and thus can evaluate appropriately the trade-off between capital and operational costs, as well as the environmental and social impacts of integrated absorption refrigeration systems. As shown in Figure 1 several options for the energy integration between the process streams and the utility system are considered and optimized taking into account thermodynamic feasibility constraints as well as operational constraints. Additionally, the cooling and heating subsystems of the heat exchanger network are interconnected through the absorption refrigeration cycle.
The proposed formulation is aimed at finding the optimal demand of each energy source to provide the heat required by the absorption refrigeration cycle and the heat exchanger network as well as the refrigeration requirement of the network. The optimal configuration of the integrated absorption refrigeration system simultaneously minimizes the total annual cost and the greenhouse gas emissions and, at the same time, maximizes the number of jobs generated by the project in the entire life cycle. The economic function accounts for the tax credit obtained by the reduction of greenhouse gas emissions when clean energies are used. The proposed approach considers different types of solar collectors, which are optimized through a disjunctive programming model to determine the type and area required. Furthermore, because of the solar radiation depends on the season of the year, the model also considers the combination of fossil fuels and biofuels to complement the energy required for the heat utility system. In addition to the economic and environmental metrics, the social issues are also considered as an important element of sustainability. The approach accounts for the social metric associated with the number of jobs that can be created by each type of energy (solar, fossil and biofuels) to identify the best scenarios for their possible implementation. The results are shown in Pareto curves that allow to consider the trade-offs for the different objectives. Several example problems are presented to show the applicability of the proposed methodology.
Figure 1. Superstructure for the integrated refrigeration system.