An exergy based approach to determine production cost and CO2 allocation for petroleum derived fuels

The renewable and non-renewable exergy and CO2 costs of petroleum derived fuels produced in Brazil are evaluated using exergoeconomy to rationally distribute the exergy costs and the CO2 emitted in processes with more than one product. An iterative procedure is used to take into account the cyclic interactions of the processed fuels. The renewable and non-renewable exergy costs together with the CO2 cost provide a reasonable way to compare different fuels and can be used to assess an enormous quantity of processes that make use of petroleum derived products. The system considers Brazilian typical processes and distances: offshore oil and gas production, transportation by shuttle tankers and pipelines, and refining. It was observed that the renewable exergy cost contribution in the total exergy cost of petroleum derived fuels is negligible. On average, the refining process is responsible, for 85% of the total unit exergy cost. Total unit exergy costs of gasoline, liquefied petroleum gas, natural gas and fuel oil were found to be: 1.081 MJ/MJ, 1.074 MJ/MJ, 1.064 MJ/MJ, 1.05 MJ/MJ, respectively. The hydrotreatment process increases diesel cost from 1.038 MJ/MJ to 1.11 MJ/MJ in order to decrease its sulphur content. The CO2 cost reflects the extent of processing as well as the C/H ratio of the used fuel. Hence, coke followed by hydrotreated diesel have the largest CO2 cost among the fuels, 91 gCO2/MJ and 79 gCO2/MJ, respectively.