Table of Contents

1 Table of Contents Organic Liquid Storage Tanks .. 3. General .. 3. Scope .. 3. Process Description .. 4. Emission Mechanisms And Control .. 8. Fixed roof Tanks .. 8. floating roof 9. Emission Estimation 14. Routine Losses From Fixed roof 16. Routine Losses From floating roof Tanks .. 31. floating roof Landing Losses .. 38. Tank Cleaning 38. Flashing Loss .. 56. Variable Vapor Space 56. Pressure Tanks .. 57. Variations Of Emission Estimation Procedures .. 58. Speciation Methodology .. 63. Figure Typical fixed- roof 67. Figure External floating roof tank (pontoon type) .. 68. Figure External floating roof tank (double deck) .. 69. Figure Internal floating roof tank .. 70. Figure Domed external floating roof tank .. 71. Figure Vapor-mounted primary seals .. 72. Figure Liquid-mounted and mechanical shoe primary seals.

2 73. Figure Secondary rim 74. Figure Deck fittings for floating roof tanks .. 75. Figure Deck fittings for floating roof tanks .. 76. Figure Slotted and unslotted guidepoles .. 77. Figure Ladder 78. Figure True vapor pressure of crude oils with a Reid vapor pressure of 2 to 15 pounds per square inch .. 79. Figure True vapor pressure of crude oils with a Reid vapor pressure of 2 to 15 pounds per square 79. Figure True vapor pressure of refined petroleum stocks with a Reid vapor pressure of 1 to 20. pounds per square 80. Figure Equation for true vapor pressure of crude oils with a Reid vapor pressure of 2 to 15. pounds per square 82. Figure Equation for true vapor pressure of refined petroleum stocks with a Reid vapor pressure of 1 to 20 pounds per square inch .. 82. Figure Equations to determine vapor pressure constants A and B for refined.

3 82. Figure Equations to determine vapor pressure Constants A and B for crude oil stocks .. 83. Figure Equations for the average daily maximum and minimum liquid surface temperatures .. 83. Figure Reserved.. 84. Figure Vapor pressure function .. 85. Figure Bottom conditions for landing loss .. 86. Figure Ladder-slotted guidepole combination with ladder sleeve .. 86. Figure Slotted-guidepole with flexible enclosure .. 87. 06/2020 Liquid Storage Tanks Table LIST OF ABBREVIATIONS USED IN THE TANK EQUATIONS .. 90. Table PROPERTIES (MV, ML, PVA, WL) OF SELECTED PETROLEUM LIQUIDS .. 92. Table PHYSICAL PROPERTIES OF SELECTED PETROCHEMICALS .. 93. Table Height of the Liquid Heel and vapor space under a landed floating roof .. 100. Table LEL VALUES FOR SELECTED COMPOUNDS .. 101. Table PAINT SOLAR ABSORPTANCE .. 102. Table METEOROLOGICAL DATA (TAX, TAN, V, I, PA) FOR SELECTED LOCATIONS.

4 103. Table RIM-SEAL LOSS FACTORS, KRa, KRb, and n, FOR floating roof TANKS .. 140. Table RESERVED .. 141. Table AVERAGE CLINGAGE FACTORS, CS .. 142. Table TYPICAL NUMBER OF COLUMNS AS A FUNCTION OF TANK DIAMETER FOR. INTERNAL floating roof TANKS WITH COLUMN- SUPPORTED FIXED ROOFS .. 142. Table DECK-FITTING LOSS FACTORS, KFa, KFb, AND m, AND TYPICAL NUMBER OF. DECK FITTINGS, NF .. 143. Table EXTERNAL floating roof TANKS: TYPICAL NUMBER OF VACUUM. BREAKERS, Nvb, AND DECK DRAINS, Nd .. 146. Table EXTERNAL floating roof TANKS: TYPICAL NUMBER OF roof LEGS, Nl .. 147. Table INTERNAL floating roof TANKS: TYPICAL NUMBER OF DECK LEGS, N1, AND STUB DRAINS, Nd .. 148. Table DECK SEAM LENGTH FACTORS (SD) FOR TYPICAL DECK CONSTRUCTIONS. FOR INTERNAL floating roof TANKS .. 148. Table roof LANDING LOSSES FOR INTERNAL OR DOMED EXTERNAL floating .

5 roof TANK WITH A LIQUID 149. Table roof LANDING LOSSES FOR EXTERNAL floating roof TANK WITH A. LIQUID 149. Table roof LANDING LOSSES FOR ALL DRAIN-DRY TANKS .. 151. Table TANK CLEANING EQUATIONS VAPOR SPACE PURGE EMISSIONS .. 152. Table TANK CLEANING EQUATIONS CONTINUED FORCED VENTILATION. EMISSIONS .. 153. Sample 154. Historical Equations .. 200. Average Daily Vapor Pressure 200. Fixed roof Tank Working 200. 06/2020 Liquid Storage Tanks Organic Liquid Storage Tanks General Scope Section presents emissions estimating methodologies for storage tanks of various types and operating conditions. The methodologies are intended for storage tanks that are properly maintained and in normal working condition. The methodologies do not address conditions of deteriorated or otherwise damaged materials of construction, nor do they address operating conditions that differ significantly from the scenarios described herein.

6 To estimate losses that occur from underground gasoline storage tanks at service stations, please see AP-42 Section , Transportation and Marketing of Petroleum Liquids.. Sections and present emissions estimating methodologies for routine emissions from fixed roof tanks and floating roof tanks. Use of the terminology routine emissions to refer to standing and working losses applies only for the purposes of this document, and not for any other air quality purposes such as New Source Review (NSR) permitting. The equations for routine emissions were developed to estimate average annual losses for storage tanks, but provisions for applying the equations to shorter periods of time are addressed in Section The equations for routine emissions are a function of temperatures that are derived from a theoretical energy transfer model.

7 In order to simplify the calculations, default values were assigned to certain parameters in the energy transfer equations. The accuracy of the resultant equations for an individual tank depends upon how closely that tank fits the assumptions inherent to these default values. The associated uncertainty may be mitigated by using measured values for the liquid bulk temperature. The equations for routine emissions are not intended to include emissions from the following events (these are addressed separately): a) To estimate losses that result from the landing of a floating roof . A separate methodology is presented for floating roof landing losses in Section b) To estimate losses that result from cleaning a tank. A separate methodology is presented for tank cleaning losses in Section c) To estimate losses from variable vapor space tanks.

8 Variable vapor space tanks are discussed in Section d) To estimate losses from equipment leaks associated with pressure tanks designed as closed systems without emissions to the atmosphere. Pressure tanks are discussed in Section Section addresses the following additional scenarios that are outside the scope of the methodologies for routine emissions presented in Sections and e) Time periods shorter than one year. Certain assumptions in the equations for routine emissions are based on annual averages, and thus the equations have greater uncertainty for a period of time less than a year. Section addresses application of the equations to time periods shorter than one year, with the caveat that a one-month time frame is recommended as the shortest time period for which routine emissions should be estimated using these methodologies.

9 F) Internal floating roof tanks with closed vent systems. The equations for routine emissions from internal floating roof tanks assume that the tank has open vents in the fixed roof . 06/2020 Liquid Storage Tanks Section addresses estimation of emissions when an internal floating roof tank has closed pressure/vacuum vents. g) Case-specific liquid surface temperature determination. Several parameters pertaining to liquid surface temperature are assigned default values for incorporation into the equations for routine emissions. Section presents methodology to account for these parameters as variables in the estimation of emissions from a particular storage tank at a particular location. h) Heating cycles in fixed roof tanks. The equations for standing loss from fixed roof tanks are based on a daily cycle of warming and cooling of the vapor space due to heat exchange between the vapor space and ambient air through the shell and roof of the tank.

10 This heat exchange results in daytime expansion and nighttime contraction of vapors in the vapor space, with each expansion causing some portion of the vapors to be expelled from the vapor space. A similar cycle of expansion and contraction of the vapors may be driven by cyclic heating of the bulk liquid. Section provides guidance for adapting the equations for fixed roof tank standing loss to the case of cyclic heating of the bulk liquid. Section presents calculations for applying Raoult's Law to calculate the contribution of individual chemical species to the total emissions. Section presents worked examples, with estimated emissions shown to two significant figures. This level of precision is chosen arbitrarily and may overstate the accuracy of the loss estimates given the uncertainty associated with the multiple parameters affecting emissions from storage tanks.