(203i) Sustainable Integration of Heat Exchanger Networks and Utility Systems

This work deals with the problem of synthesizing sustainable integrated systems consisting of heat engines, absorption refrigeration (AR) subsystems and heat exchanger networks. The proposed integration scheme is shown in Figure 1. Notice that a Rankine cycle provides the energy required by the absorption refrigeration subsystem, the hot utility (i.e. steam) required for providing the necessary heating in the heat exchanger network in addition to the heat demanded to run an organic Rankine cycle (ORC) used to produce electricity. The proposed configuration allows the heat exchange between the process streams and the ORC, as well as with the AR subsystem. The optimal configuration simultaneously maximizes the total annual profit (TAP), minimizes the greenhouse gas emissions (GHGE) and, at the same time, maximizes the number of generation of jobs (NJOBS) in the entire life cycle of the system. The proposed formulation is aimed at finding the optimal demand of each primary energy source (solar energy, biofuels and fossil fuels) to provide the heat required by the Rankine cycle, which supplies the heating needed for the operation of the AR, ORC and the heat exchanger network. The economic objective function accounts for the sale of power produced by the Rankine cycle and the ORC as well as the tax credits obtained by the reduction of greenhouse gas emissions minus the costs associated to the primary energy sources selected as well as the capital costs needed for the system implementation.

Figure 1. Schematic representation for the proposed integrated energy system.

Additionally, Figure 2 shows the proposed superstructure for the energy integration, which considers the heat exchange between hot process streams (HPS) with cold process streams (CPS), AR subsystem, ORC and the cold water (cold utility) as well as the refrigeration requirement for the HPS. The superstructure also takes into account the heat integration between the CPS and the ORC, in addition to the hot utility (provided by the Rankine cycle) to achieve the target temperatures. On the other hand, the proposed approach considers the possible installation of a solar collector and a disjunctive programming model determines if it is required or not, as well as its optimal size. Furthermore, since the solar radiation depends on the season of the year and the availability of the biofuels is limited during the year, the model also considers the burning of fossil fuels to fully satisfy the energy demanded by the system. In addition to the economic and environmental metrics, the social issues are also considered as an important issue of sustainability. Results show that the proposed approach allows to obtain significant economic benefits and at the same time decreasing the environmental impact accounting for the generated jobs.

Figure 2. Superstructure for the energy integration.