factnt3.txt
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TNRCC REGULATORY GUIDANCE New Source Review RG-138 November, 1995 SUBJECT: Gasoline Terminal Loading Emissions Process Description During the loading of tank trucks at bulk gasoline storage terminals, emissions occur which can be estimated utilizing the methods outlined here. Other gasoline terminal emission sources such as fugitive (e.g., valve, flange, and pumps) and tank emissions may be estimated utilizing factors readily available in Petroleum Marketing Terminal Factors or from TNRCC approved equivalent industrially derived sources and will not be discussed here. Gasoline "spills" or other upset emissions are also not considered in this analysis. Emissions Uncontrolled emissions are estimated utilizing the latest edition of AP-42, Section 4.4. Emissions are calculated using the equation: LL = (12.46)(SPM)/T Where: LL = Loading loss, lb/thousand gallons of gasoline loaded S = A saturation factor, see AP-42 P = True vapor pressure at maximum temperature of gasoline to be loaded, psia. M = Molecular weight of gasoline vapors, lb/lb-mole T = Temperature of bulk gasoline loaded, degrees Rankine. Hourly emissions are based on the highest emissions for any 60-minute period. The permit, when issued, would thus restrict the maximum gallons loaded in an hour to the basis of permit review for the hourly period. Similarly, the annual throughput in gallons would be limited to the maximum throughput involved in the representations for annual emissions. Collection efficiencies (vapor collected to a BACT control device) are as follows: Collection Efficiency Unenhanced Loading 65% Enhanced Loading (+3.0 to +5.0 inches water back pressure, blower, etc.) 85% Annual truck leak checking* 95% Leak checks every six months* 97.5% Vacuum loading 100% * Leak checking as required by NSPS Subpart XX Air Pollution Controls The BACT guideline for gasoline terminal loading emissions is either a thermal oxidizer (99.9% VOC destruction efficiency), carbon adsorption (0.04 - 0.09 lb gasoline per 1,000 gallons loaded), or flaring (98.0% destruction efficiency). These factors are applied to the collected uncontrolled gasoline vapors. Chemicals which may be emitted from a gasoline terminal include benzene, butane, methyl-tert-butyl ether, and tertiary butyl alcohol. Benzene emissions must be speciated so that an emission rate, hourly and annually, is available. Sample calculation: If uncontrolled gasoline emissions are 10 lb/hr and truck tanks are leak-checked annually, uncollected emissions are: (1 - 0.95)(10) = (0.05)(10) = 0.5 lb/hr. Utilizing a flare for the collected emissions, flare emissions would be: (1 - 0.98)(10 - 0.5) = 0.02(9.5) = 0.19 lb/hr. Total gasoline emissions are, therefore: 0.5 + 0.19 = 0.69 lb/hr gasoline vapors. If: Benzene is 0.68%(w) of the gasoline liquid, and Mol. Wt. benzene = 78 lb/lb mole Mol. Wt. gasoline (liquid) = 92.2 lb/lb mole Vapor Pressure of benzene @ 90F = 2.6 psia. Vapor Pressure of gasoline @ 90F = 8.8 psia. then: Mole % benzene in liquid = (0.68)(92.2) (78) = 0.804 Raoult's Law: Pb/Pbo = Xb Where: Pb = Partial pressure of benzene in the gasoline vapor Pbo = Vapor pressure of pure benzene Xb = Mole fraction of benzene in the gasoline liquid Then: Pb =(Pbo)(Xb) = (2.6 psia.)(0.00804) = 0.0209 psia. Dalton's Law: Pb/Pt = Yb Where: Pt = Vapor pressure of the gasoline Yb = Mole fraction of benzene in the gasoline liquid Mol. Wt. gasoline (vapor) = 66 lb/lb mole then: Yb = 0.0209/8.8 = 0.0024, and the weight percent benzene in gasoline vapor becomes: =(100)(0.0024)(78)/66 = 0.28 wt. % Benzene emissions then are: (0.0028)(0.69) = 0.0019 lb/hr benzene Permit Requirements After September 1, 1971, all new or modified sources of air contaminants to include gasoline terminals must obtain a permit from the TNRCC or meet the requirements of a TNRCC standard exemption in effect at the time the source, i.e., terminals, is constructed. Should federal emission significance levels be triggered, a federal PSD or nonattainment permit may also be required. An increase in throughput is considered a probable modification and must be reviewed by the TNRCC New Source Review Program. Federal Standards New Source Performance Standards for Bulk Gasoline Terminals, Subpart XX References AP-42, Environmental Protection Agency, Compilation of Air Pollutant Emission Factors, Volume I EPA Document, Bulk Gasoline Terminals- Background Information for Proposed Standards, EPA-450/3-80-038a, December 1980. -TNRCC Regulations V and VI -TNRCC General Rules -OAQPS TNN Electronic Bulletin Commission (AQPS TNN/CHIEF/AP42/Q&As/LEAKS-rd.txt) TNRCC Contact New Source Review Division, Core Section or Chemical Section