Incorporating life cycle assessment eco-costs in the optimization of heat exchanger networks

Abstract

A substantial amount of research on heat exchanger networks (HEN) synthesis has concentrated on minimizing the total cost as unique criterion, thereby disregarding their negative environmental effects. In the present paper the external costs associated with the environmental impacts caused by energy generation and equipment construction were incorporated explicitly in the HEN synthesis task using the eco-costs methodology. The inclusion of the impact costs in the optimal synthesis of HEN was performed considering the most used fuels in chemical and petrochemical industries: hard coal, heavy and light fuel oil and natural gas. Boilers operating with each one of these 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 influence of the impact assessment on total area, area cost and HEN cost were observed. Results show that the inclusion of indirect costs (externalities) in the optimization procedure can affect significantly the characteristics of the minimum cost design, the operational conditions and HEN topology. HEN operating with hard coal has the second lowest HEN cost, but the higher impact cost. Greenhouse gases and ecosystems impacts had the largest costs for all the cases considered. The HEN operating with heavy and light fuel oil have the highest HEN costs and the second and third total impact costs and this HEN may become less competitive when compared with cheaper fuels, due to its relatively high cost. HEN operating with natural gas is the most competitive alternative, since it has the lowest total impact cost and HEN area cost. For these fuels, results demonstrate that the reduction of total impact is affected more by the increase of the total area than by the utilities consumption.