(271f) 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-Halwagi^b,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.