GUIDANCE DOCUMENT April 6, Guidance on Estimating Condensate and Crude Oil Loading Losses from Tank Trucks

Transcription

1 OKLAHOMA DEPARTMENT OF ENVIRONMENTAL QUALITY AIR QUALITY DIVISION GUIDANCE DOCUMENT April 6, 207 SUBJECT: Guidance on Estimating Condensate and Crude Oil Loading Losses from Tank Trucks SECTION I. INTRODUCTION The purpose of this guidance document is to provide general guidance on estimating condensate and crude oil 2 evaporative emissions from tank trucks during loading operations. The Air Quality Division (AQD) has received permit applications requesting the use of a reduction factor for estimating tank truck loading loss emissions to account for methane and ethane entrained in the petroleum liquid and that are released in the vapors as the petroleum liquid is loaded. In some cases, the proposed reduction factor represents a combined methane and ethane vapor concentration of greater than 30% by weight. The majority of permitted loading losses have been calculated assuming negligible concentrations of methane and/or ethane. Due to the high concentrations of methane and ethane proposed, a review of the calculation methodology was conducted and resulted in this guidance document. SECTION II. BACKGROUND DISCUSSION As stated in AP-42 (6/08), Section 5.2: Transportation and Marketing of Petroleum Liquids: Loading losses are the primary source of evaporative emissions from rail tank car, tank truck, and marine vessel operations. Loading losses occur as organic vapors in empty cargo tanks are displaced to the atmosphere by the liquid being loaded into the tanks. These vapors are a composite of () vapors formed in the empty tank by evaporation of residual product from previous loads, (2) vapors transferred to the tank in vapor balance systems as product is being unloaded, and (3) vapors generated in the tank as new product is being loaded. The quantity of evaporative losses from loading operations is, therefore, a function of the following parameters: Physical and chemical characteristics of the previous cargo; OAC 65:0--2 defines condensate as a liquid hydrocarbon which: (A) [w]as produced as a liquid at the surface, (B) [e]xisted as a gas in the reservoir, and (C) [h]as an API gravity greater than or equal to fifty degrees, unless otherwise proven. 2 OAC 65:0--2 defines crude oil as any petroleum hydrocarbon, except condensate, produced from a well in liquid form by ordinary production methods. Air Quality Division, Oklahoma DEQ Page of 7

2 Method of unloading previous cargo; Operations to transport the empty carrier to a loading terminal; Method of loading the new cargo; and Physical and chemical characteristics of the new cargo. Variation in these parameters can result in the release of different quantities of actual volatile organic compound (VOC) emissions. For example: A tank truck recently cleaned or previously carrying nonvolatile liquids loading volatile liquids will emit less VOC emissions. This is because the vapors in the tank truck prior to loading contain little to no VOCs. A tank truck previously carrying a more volatile liquid than the liquid being loaded loading a nonvolatile liquid will have greater VOC emissions. This is because the vapors in the tank truck prior to loading have a high concentration of VOCs. A tank truck being loaded that had been utilizing a vapor balance system when unloading would result in a greater saturation factor and increased emissions. SECTION III. EMISSION FACTOR CALCULATION Emissions from tank truck loading losses are usually calculated using Equation of AP-42 (6/2008), Section 5.2. AP-42 indicates the equation (which is based on the Ideal Gas Law) has a probable error of ±30 percent. Loading operations can be controlled through the use of various control measures and control equipment. When estimating emissions from controlled loading operation, AP-42 (6/2008), Section 5.2 recommends multiplying the uncontrolled emission rate by an overall reduction efficiency term. Pairing the AP-42 equation with the reduction efficiency term results in the following equation: Where: L L = 2.46 SPM T eff ( 00 ) LL = Loading loss, pounds per,000 gallons (lb/0 3 gal) of liquid loaded; S = Saturation factor; P = True vapor pressure (TVP) of liquid loaded, pounds per square inch absolute (psia); M = Molecular weight of vapors, pounds per pound-mole (lb/lb-mol); T = Temperature of bulk liquid loaded, R ( F +460); and 2.46 = Conversion factor which incorporates the ideal gas constant (0.73 ft 3 psia/ R lb-mole) and a conversion from cubic feet to,000 gallons; eff = Overall reduction efficiency (should include collection and control efficiency). Air Quality Division, Oklahoma DEQ Page 2 of 7

3 Saturation Factor (S) AP-42 (6/2008), Section 5.2 defines the saturation factor as representing the expelled vapor s fractional approach to saturation, and it accounts for the variations observed in emission rates from the different unloading and loading methods. Although several methods of loading tank trucks are described in Section 5.2, it is standard industry practice to conduct submerged fill loading. Most tank trucks are equipped with pups that pump the liquids into the bottom of the tank truck. AP-42 (6/2008), Section 5.2 suggests the following factors for submerged loading: True Vapor Pressure (P) AP-42 Suggested Saturation Factors for Submerged Loading Service Type S Dedicated Normal Service 0.6 Dedicated Vapor Balance Service.0 The true vapor pressure of the liquid being loaded should be calculated at the temperature used to calculate emissions. The true vapor pressures for crude oil (RVP 5) are shown below at different temperatures. Crude Oil (RVP 5) True Vapor Pressure at Selected Temperatures Temperature ( F) True Vapor Pressure (psia) AP-42 (/2006), Section 7., Table Vapor Molecular Weight (M) For crude oil, the default value is the vapor molecular weight given in AP-42 (/2006), Table 7.-2 for crude oil (RVP 5) at 60 F of 50 lb/lb-mole. For condensate, the default value is the vapor molecular weight given in AP-42 (/2006), Table 7.-2 for gasoline (RVP 7) at 60 F of 68 lb/lb-mole. Vapor molecular weight data generated by process simulators based on sales liquid speciation data can be used. Liquid Surface Temperature (T) For the state of Oklahoma, the average liquid surface temperature is approximately 70 F as calculated by Tanks 4.0b. Average Ambient and Corresponding Average Liquid Surface Temp for Crude Oil in Oklahoma City, State Average Ambient Temp Average Liquid Surface Temp Oklahoma City, Oklahoma Tulsa, Oklahoma This data was generated using Tanks 4.09d and crude oil (RVP 5). Air Quality Division, Oklahoma DEQ Page 3 of 7

4 Loading loss calculations may also be performed using the API standard temperature (60 F) or actual local temperature data can be used to calculate the average liquid surface temperature. Long-Term vs. Short-Term Emission Factors Loading loss emission factors will differ between long-term and short-term based estimates. A long-term emission factor (used to estimate ton per year (TPY) emission rates) should incorporate the annual average liquid surface temperature of the liquid being loaded. Accordingly, since true vapor pressure varies with temperature, the corresponding true vapor pressure at the selected liquid surface temperature should be utilized. Short-term emission factors (used to estimate lb/hr emission rates) should be based on the maximum loading rate and the worst case loading factor parameters (i.e. highest temperature and associated vapor pressure). Although a lower liquid surface temperature would in itself result in a higher calculated emission rate, the corresponding true vapor pressure must also be considered. The pressure to temperature ratio for crude oil was calculated to show that when correlated, the emissions would be greater at higher temperatures. The following table presents the pressure to temperature ratio (P/T) for crude oil with a Reid vapor pressure (RVP) of 5 psi. Crude Oil (RVP 5) Pressure/Temperature Ratio Temperature, T ( F) Temperature, T ( R) TVP, P (psia) P/T ratio, (psi/ R) Based on data from AP-42 (/2006), Section 7. As long as the true vapor pressure is correlated with the temperature used, the higher liquid surface temperature will result in a higher emission factor and thus a higher emission rate. Summary Based on the properties presented in AP-42 (/2006), Section 7., AP-42 (6/2008), Section 5.2 suggests the following loading emission factors for uncontrolled tank trucks: AP-42 Suggested Loading Loss Factors for Submerged Loading Service Type LL (lb/0 3 gallons) Dedicated Normal Service (S = 0.6) Crude Oil 2 2 Gasoline 3 5 Dedicated Vapor Balance Service (S =.0) Crude Oil 2 3 Gasoline 3 8 Rounded to nearest whole number. 2 Based on crude oil with an RVP of 5 psia at 60 F. 3 Based on gasoline with an RVP of 0 psia at 60 F. Air Quality Division, Oklahoma DEQ Page 4 of 7

5 Review of AQD s Emissions Inventory Database indicates that loading loss emission factors used to report emissions for crude oil loading were between 2 and 3 lb/0 3 gallons on average and ranged up to 4.5 lb/0 3 gallons. Loading loss emissions factors used to report emissions for condensate loading were between 3 and 4 lb/0 3 gallons on average and ranged up to 7.5 lb/0 3 gallons. These loading loss factors are within the range of the AP-42 referenced factors. Weight Percent Reduction As noted in AP-42 (6/2008), Section 5.2, VOC factors for crude oil can be assumed to be 5% lower than the total organic factors, to account for the methane and ethane content of the crude oil evaporative emissions. All other products should be assumed to have VOC factors equal to total organics. Applications have been submitted with various speciated analyses: () pressurized separator gas streams, (2) pressurized separator liquids streams, and (3) other various pressurized spot sampling locations for pipeline gas streams. Typical flash residual atmospheric hydrocarbon liquids analyses generally identify non-detectable amounts of methane and minimal amounts of ethane still present in the liquids after complete flashing has occurred. Utilizing a limited number of speciated analyses, the speciation calculation methodology presented in AP-42 (/2006), Section 7., and calculated vapor pressures (Perry 2-50), the amount of ethane in the vapor was estimated at 5% by weight. A review of speciated analyses from production site atmospheric storage tank vapors indicates a concentration of up to 5% by weight for methane and ethane combined. The boiling point of methane and ethane are F and F, respectively (Perry 2-37 and 2-40). Therefore, it is assumed that most of the methane and ethane in the liquids is driven off when the liquid reaches atmospheric temperature and pressure except that due to solubility, some small amount of the methane and ethane may still remain dissolved in the liquids after flashing has occurred. The solubility of methane and ethane in petroleum liquids is dependent on the composition of the liquids and the temperature and pressure of the liquid. Crude oil from production facilities will generally contain higher concentrations of more volatile components (i.e., methane and ethane). Over time, the liquids become weathered and the more volatile components are lost to evaporation. Liquids being loaded at non-production sites will have negligible concentrations of methane and ethane. The retention time of liquids in a tank prior to being loaded into a tank truck should also be taken into account. If petroleum liquids are loaded into tank trucks shortly after being sent to on-site atmospheric storage tanks, the residual methane and ethane in the liquids may not have had sufficient time to evaporate. However, petroleum liquids that remain in an on-site atmospheric storage tank for an extended period of time will have had sufficient time for the methane and ethane to separate and evaporate from the liquids. Air Quality Division, Oklahoma DEQ Page 5 of 7

6 SECTION IV. CONCLUSION Based on AQD s review of the AP-42 calculation methodology additional considerations for estimating evaporative emissions from petroleum liquids loaded into tank trucks, the following general assumptions may be made: Tank trucks are in dedicated normal service (i.e. that they handle petroleum liquids with similar component compositions), and The vapors from working and breathing losses will be similar to that of the vapors displaced in from the tank truck during loading operations. Vapors in the tank headspace resulting from flashing will not be similar to the vapors from truck loading operations. The appropriate saturation factor (S) from AP-42 should be utilized. Molecular weight (M) of the vapors being expelled can be: o The default values given in AP-42 (/06), Section 7. for a representative petroleum liquid, o Values determined using an approved process simulator, or o Values determined from speciated laboratory analysis of representative on-site atmospheric storage tank vapors (not to include vapor generated during flashing). The average liquid surface Temperature (T) can be: o For long term calculations: The annual average liquid surface temperature for Oklahoma City (70 F), or The API standard temperature (60 F) as long as the vapor pressure is based on the same value. o For short-term calculations: the highest liquid surface temperature for Oklahoma City (93 F). o Can be based on actual temperature data for a specific location. The true vapor pressure (P) of the liquid being loaded should correspond with the temperature being utilized (long-term or short-term) in the emission calculation. VOC content in the loading loss vapors: o For crude oil (API gravity less than 50 ), a loading loss vapor VOC content of 85% by weight (i.e., 5% by weight methane and ethane) may be assumed prior to lease custody transfer as long as the loading loss emission factor is equal to or greater than the default AP-42 loading factor (2 lb/0 3 gallons). o All other petroleum liquids being loaded should assume a vapor VOC content of 00%. If an applicant wishes to claim a loading loss vapor VOC content of less than 85% by weight (i.e., reduction factor greater than 5% by weight) for crude oils prior to lease custody transfer or a VOC content of less than 00% by weight for any other petroleum liquids being loaded to account for methane and ethane, site-specific documentation will be required to substantiate the claim. Documentation from a similar facility will not be sufficient. One of the following methods are required to support the use of a reduction factor to account for the presence of methane and ethane: Air Quality Division, Oklahoma DEQ Page 6 of 7

7 Speciated laboratory analysis of liquids from an on-site atmospheric storage tank which have been standing idle for at least 24-hours. o May utilize speciation calculation methodology outlined in AP-42 (/06), Section 7. to estimate the concentration of non-volatile organic components in the vapor. Speciated laboratory analysis of vapor headspace from an on-site atmospheric storage tank which has standing idle for at least 24-hours then vacated. Speciated laboratory analysis of the vapors being displaced and emitted from a tank truck being loaded. Sampling and testing protocols should be submitted 30-days prior to the sampling to allow AQD to review and approve the analysis methodology. Contingent on AQD review and approval, the applicant may propose an alternative sampling methodology. SECTION V. REFERENCES Oklahoma Administrative Code, Title 65: Corporation Commission, Chapter 0: Oil and Gas Conservation, Subchapter, OAC 65:0-, August 25, 206. Perry, Robert H., et al. Perry s Chemical Engineers Handbook. 7 th ed., McGraw-Hill, 997. U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Fifth Edition Compilation of Air Pollutant Emission Factors, Volume : Stationary Point and Area Sources, Publication AP-42, Research Triangle Park, North Carolina, January Who Can I Contact for More Information? For assistance, contact the Air Quality Division at (405) and ask to speak with a permit writer. Oklahoma Department of Environmental Quality Air Quality Division Permitting Group 707 N. Robinson, Suite 400 P.O. BOX 677 Oklahoma City, Oklahoma Air Quality Division, Oklahoma DEQ Page 7 of 7