According to the US Dept. of Energy's Energy Information Administration (EIA), in 2006 global, energy-related emissions of CO₂ totaled 29.195B mt, and petroleum refining was responsible for approximately 5% of this total. Refinery emissions can be almost entirely attributed to fuel combustion, which is in turn affected by the types of crudes processed and the product slates chosen.

More specifically, most of the emissions of CO₂ from refineries are due to stationary combustion devices. These emissions are also referred to as energy-related emissions. At a hypothetical 250K-b/d refinery with a hydrogen plant and an FCCU, the CO₂ emissions from various sources, as estimated by the American Petroleum Institute, are listed in the following table.

Refinery fuels include: coke; light hydrocarbon gases and liquid fuels, both of which are internally produced; and imported natural gas. It is clear that, per unit of energy, the refinery fuels differ significantly in the amounts of CO₂ that are produced by their combustion, with natural gas having about one half the emissions of coke, as illustrated in the table below.

As is known in the refining industry, crude quality plays a major role in determining refinery GHG emissions; lower API gravity and higher sulfur content correlate to increased refinery CO₂ emissions. Not surprisingly, crudes with lower API gravity and higher sulfur content also correlate to greater energy intensity (energy per barrel of crude processed) and process intensity (combined capacity of vacuum distillation, coking, thermal cracking, FCC, and hydrocracking divided by the capacity of the atmospheric distillation unit). These correlations are thought to be attributed to two major factors. First, lighter, sweeter crudes require less conversion and desulfurization; and second, for lighter, sweeter crudes, the refinery's energy requirements are met by more low-carbon fuel gas and less coke, fuel oil, and other higher-carbon streams. On the other hand, many heavy, sour crudes will also contain high levels of nitrogen and metals, requiring further processing and adding to refinery CO₂ emissions per barrel of crude processed. However, even crudes with similar API gravity, sulfur, nitrogen, and metals content will not necessarily yield similar amounts of CO₂ per unit of product produced, because other crude properties such as the distribution of hydrocarbons (i.e., naphtha, distillates, gas oil), and the type of heteroatom compounds play a role in emissions, as well.

A refiner can perform a life-cycle assessment (LCA) or "well-to-wheels" analysis of the environmental impacts of different transportation fuels. In fact, the allocation of refinery CO₂ emissions to individual petroleum products is extremely useful when a refinery wants to control its variable costs associated with CO₂ emissions from different products. The complexity of today's refineries—in which a given product (e.g., gasoline) is involved with several refining units and a given refining unit produces multiple products—means that there is no unique way to allocate emissions to finished products. One approach that has been used is to perform the allocation in a way that reflects how the refinery's emissions would be changed by a quantitative variation in the product slate, as discussed in this Report. An example is shown in the following table.

However, there are concerns with the allocations mentioned above. One is that they might not reflect what happens when marginal changes occur in the product slate. At present, schemes are being developed that use optimization routines.

This Report looks at how production of CO₂ by refineries is being impacted by the fuels that are being used, the crudes that are being processed, and the product slate that is being produced. The allocations of emissions to specific refinery fuels and products are also covered. There are detailed discussions on the implementation of refinery carbon accounting; i.e., means for monitoring and estimating CO₂ emissions. Furthermore, case studies are presented to examine the costs and benefits of various options and to identify competition in market supply and demand of combustion fuel, crude oils, and refined products on regional and global bases.

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