OCR Text |
Show prescriptiQns for how and when regulations are to be put into place for these emissions (see ( Quarles and Lewis, 1990, for an excellent summary). Species of concern under the CAA ammendments include light organics such as .formaldehyde and butadiene, single-ring aromatics such as benzene, toluene, and the xylenes, any of the polycyclic aromatic hydrocarbon (P AH) species, and many chlorinated and metalcontaining compounds. A Major Source is defined as any site emitting 10 tons/year of anyone species or 25 tons/year of all species combined. Major Sources will be regulated in two steps: In the first, referred to as MACT, for Maximum Achievable Control Technology, regulations will be promulgated which are expected to achieve a 75 to 90% reduction in emission of HAP species. In the second, referred to as Residual Risk, a risk assessment is to be conducted with the objective of ensuring that lifetime excess cancer risk to a maximally exposed individual does not exceed one part in one million. Additional regulation may then be required in order to ensure compliance with this limit While petroleum refmeries are immediately recognized as a major source of bigh-quality energy, it is less appreciated that the refining process is also a major consumer of energy. A single, large transportation fuels refmery might consume as much as 0.07 Quads (1015 Btu) of energy in a single year. For perspective, total U.S. refinery output in 1985 was about 31 Quads of petroleum products (DOFlEIA, 1986). Much of the energy consumed in refining (about 3/4) is supplied in the form of Refinery Fuel Gas (RFG), a process gas composed of the off-gas from the various processing streams. Although similar to natural . gas in heating value, RFG differs in that it usually contains a significant fraction of hydrogen, as well as components in the <; t~ C4 range, and even some small fraction at C6 and higher. Figure 1 shows the average RFG composition from 19 gas streams from 5 U.S. oil companies as well as an unweighted average composition for those streams. The streams are plotted from left to right in order of decreasing hydrogen content so that correlations between components may be observed. As apparent from the figure, hydrogen Fig. 1 content ranges from less than 10% (by mole) to almost 70% and is, in general, inversely -2- |