Synthesis of heat exchanger networks with economic and environmental assessment using fuzzy-Analytic Hierarchy Process

Abstract

In the present paper we propose an optimization model based on fuzzy-Analytic Hierarchy Process (AHP) programming in which the external costs associated with the environmental impacts caused by energy generation and equipment construction were explicitly incorporated in the synthesis of Heat Exchanger Networks (HEN) using the eco-costs methodology. The damage categories that compose the environmental and economic objective functions were human health (HH), ecosystem quality (EQ), resources depletion (RD), greenhouse gases (GW) impacts and HEN cost. The inclusion of the impact in the optimal synthesis of HEN was performed considering the most used fuels in industries: hard coal, heavy and light fuel oil and natural gas. Boilers operating with each one of the cited fuels were considered, and three different technologies for boiler operating with natural gas were included (low NOx natural gas, modulating and non-modulating natural gas boilers). The weights were obtained through a questionnaire directed to a multidisciplinary group of specialists. A case study with two hot and one cold streams was used to test the efficiency of the model and results were compared to a single-objective model and to a model not considering impacts in the objective function. Results showed that the fuzzy-AHP programming model was not able to find HEN costs lower than those obtained by the single-objective model for HENs operating with heavy and light fuel oil. For the HENs operating with hard coal and natural gas, HEN costs were lower than those obtained by the single objective model. The same HEN configuration was obtained for all fuels considered.