Factors driving refinery CO2 intensity, with allocation into products

Background and scopeAttempts to develop adequate allocation methods for CO2 emissions from petroleum products have been reported in the literature. The common features in those studies are the use of energy, mass, and/or market prices as parameters to allocate the emissions to individual products. The crude barrel is changing, as are refinery complexities and the severity of conversion to gasoline or diesel leading to changes in the emissions intensity of refining. This paper estimates the consequences for CO2 emissions at refineries of allowing these parameters to vary.Materials and methodsA detailed model of a typical refinery was used to determine CO2 emissions as a function of key operational parameters. Once that functionality was determined, an allocation scheme was developed which calculated CO2 intensity of the various products consistent with the actual refinery CO2 functionality.ResultsThe results reveal that the most important factor driving the refinery energy requirement is the H2 content of the products in relation to the H2 content of the crude. Refinery energy use is increased either by heavier crude or by increasing the conversion of residual products into transportation fuels. It was observed that the total refinery emissions did not change as refinery shifted from gasoline to diesel production.DiscussionThe energy allocation method fails to properly allocate the refinery emissions associated with H2 production. It can be concluded that the reformer from a refinery energy and CO2 emissions standpoint is an energy/CO2-equalizing device, shifting energy/CO2 from gasoline into distillates. A modified allocation method is proposed, including a hydrogen transfer term, which would give results consistent with the refinery behavior.ConclusionsThe results indicate that the refinery CO2 emissions are not affected by the ratio of gasoline to distillate production. The most important factors driving the CO2 emissions are the refinery configuration (crude heaviness and residual upgrading) which link to the refinery H2 requirement. Using the H2-energy equivalent allocation proposed in this study provides a more reliable method to correctly allocate CO2 emissions to products in a refinery in a transparent way, which follows the ISO recommendations of cause-effect and physical relationship between emissions and products.Recommendations and perspectivesRegulatory activity should recognize that there is no functional relationship between refinery CO2 emissions and the production ratio of gasoline, jet, and diesel, and adopt a methodology which more accurately mirrors actual refinery behavior.