Annex 49 Complementary information to source category 7f Petroleum Industry
Oil refineries are large scale plants, processing about a hundred thousand to several hundred thousand barrels of crude oil a day. There are 655 refineries worldwide, located in 116 countries that collectively have a daily capacity of about 88 million barrels per day (b/d). Because of the high capacity, many of the units operate continuously, as opposed to processing in batches, at steady state or nearly steady state for months to years. There are three broad categories of refining processes:
- Separation: The oil is separated into its constituents by distillation, and some of these components (such as the refinery gas) are further separated with chemical reactions and by using solvents that dissolve one component of a mixture significantly better than another.
- Conversion: The various hydrocarbons produced are then chemically altered to make them more suitable for their intended purpose. Prior to conversion, sulfur must be removed from the hydrocarbons because these reactions often require catalysts that are deactivated by sulfur.
- Purification: The hydrogen sulfide gas that was extracted from the refinery gas is converted to sulfur, which is sold in liquid form to fertiliser manufacturers. Detailed descriptions of refinery processes can be found in the European Commission’s Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for Mineral Oil and Gas Refineries (EC 2003).
Derivation of emission factors
Release to Air
For catalytic reforming units, off-gas was reported to have a PCDD/PCDF concentration of 131 ng I-TEQ/Nm³ (Jansson 1999). The California Air Resources Board (1999) determined an EFAir 3.04 ng TEQ/barrel for the catalytic reforming unit at one U.S. refinery. Both CONCAWE (2009) and USEPA (2006a) derived an EFAir of 1.52 ng TEQ/barrel for these units. It is important to note that USEPA (2004) reports that some refineries vent off-gases from these units directly to the air.
For refinery coking units, RTI (2011) derived an EFAir of 56.2 ng TEQ/barrel (353.5 ng/m³ oil).
For flares at Danish refineries, Henriksen et al. (2006) derived an EFAir of 0.25 μg TEQ/TJ of fuel.
EFAir of 2.28 ng TEQ/barrel (0.0143 μg TEQ/m³ oil; 0.0168 μg TEQ/t oil) for catalytic reforming unit catalyst regenerators, based on the mid-point of the values presented by CARB (1999), CONCAWE (2009) and USEPA (2005a).
EFAir of 56.2 ng TEQ/barrel (0.353 μg TEQ/m³ oil; 0.413 μg TEQ/t oil) for refinery coking units, based on the value derived by RTI (2011).
EFAir of 0.25 μg TEQ/TJ of fuel for flares at oil refineries, based on value presented by Henriksen et al. (2006).
Release to Water
Data obtained from four U.S. refineries found PCDD/PCDF concentrations ranging from 0 to 394,000 pg TEQ/L, with a median of 2,975 pg TEQ/L in wastewater from their catalytic reforming units (USEPA 2004).The data also include PCDD/PCDF concentrations ranging from 0 to 37.9 pg TEQ/L, with a mean of 3.5 pg TEQ/L, in the final effluent of nine refineries. At one refinery, stormwater run-off was identified as the source of 50% of PCDD/PCDF in the final effluent with coke pond and clean canal forebay as the source of 45%. Karras (1998) reported a PCDD/PCDF concentration of 7.86 pg TEQ/L in the wastewater effluent of a U.S. refinery.
Release in Residues
Data describing PCDD/PCDF concentrations in the final wastewater treatment sludge of refineries were not available. However, PCDD/PCDF concentrations ranging from 3 to 356 ng TEQ/kg, with a median of 13.61 ng TEQ/kg were measured in sludge generated by oil and solids removal (API) separators at catalytic reforming units (USEPA 2004).
Refinery boilers and process heaters may produce fly ash and bottom ash as residues, but there is no information on their PCDD/PCDF content, generation rates and fate (see also Source Group 3). Spent catalyst generated is around 20-25 tons per year for a 5-million-tons-per-year refinery. Spent catalyst is typically regenerated and catalyst fines from that process are likely to be captured by abatement systems. With dry abatement systems, the catalyst fines become a discrete residue; if wet, the fines accumulate in wastewater treatment sludge.
EFResidue of 13.61 ng TEQ/kg for sludge from API separator of catalytic reforming unit, based on value determined by USEPA (2004).