The importance of energy crisis and global warming necessitates presenting strategies in order to decrease the amount of emissions as well as fuel consumption in large and complex industries such as refineries and petrochemical industries. Generally, refinery steam networks are regarded as units which consume fuel enormously. In this paper, the steam network of Tehran Oil Refinery is considered as an industrial case study. Then, various scenarios are proposed to modify the network. In this

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... d, the network and suggested scenarios are initially modeled into STAR software environment. Next, they are simulated to estimate process parameters and costs. Afterwards, each scenario is separately optimized and, after comparison, the best scenario is chosen from the viewpoint of total annualized cost (TAC). The objective function of optimization is to minimize TAC. At the second stage, the amount of carbon dioxide production is calculated for all the proposed scenarios, before and after optimization. In addition, the tax of production (Kyoto Protocol) is added to the TAC of each scenario. Since in this version of STAR software, the effects of CO2 emission have not been taken into account, a combination of the results of TAC in the software considering CO2 and its effect on TAC has been considered as a new investigation. In fact, both economical and environmental issues are taken into account. Moreover, the scenarios are simultaneously compared with each other and the best scenario is chosen with considering carbon dioxide taxes.