tceq- short-term emissions from floating roof storage tanks · apdg6419v1, released 02/18,...

APDG6419v1, Released 02/18, Short-term Emissions from Floating Roof Tanks Page i

Air Permit Reviewer Reference Guide

APDG 6419

Short-term Emissions from Floating Roof Storage Tanks

Air Permits Division Texas Commission on Environmental Quality

APDG6419v1, Released 02/18, Short-term Emissions from Floating Roof Tanks Page ii

Table of Contents

Introduction .......................................................................................................................................... 1

Total Short-term Losses ...................................................................................................................... 2

Withdrawal Loss .................................................................................................................................. 2

Rim Seal Loss ...................................................................................................................................... 3

Deck Fitting Loss ................................................................................................................................. 4

Deck Seam Loss .................................................................................................................................. 4

Ambient and Seasonal Adjustments .................................................................................................. 5

Adjustment for Material Temperature................................................................................................. 5

Best Available Control Technology (BACT) ....................................................................................... 6

APPENDIX A ............................................................................................................................................................7

APPENDIX B ............................................................................................................................................................8

APPENDIX C ......................................................................................................................................................... 14

APDG6419v1, Released 02/18, Short-term Emissions from Floating Roof Tanks Page 1 of 17 This form is for use by facilities subject to air quality permit requirements and may be revised periodically.

Short-term Emissions from Floating Roof Tanks

Introduction

The purpose of this document is to clarify current TCEQ Air Permits Division guidance on estimating short-term emissions from floating roof tanks. The parameters and methods herein are recommended for the purpose of establishing conservative emission rates that may be relied upon for health impacts analyses and other permitting requirements. The emission calculation procedures are generally based on equations found in EPA AP-42 Chapter 7 (November 2006 version). Note that this guidance does not address calculation of annual emissions. For guidance on estimating annual emissions, please refer to EPA AP-42 Chapter 7 or contact the Air Permits Division at (512) 239-1250.

This publication illustrates two acceptable methods for estimating short-term emissions from floating roof tanks: (1) a hand calculation method; and (2) a method using data generated by EPA Tanks 4.09D software. Please refer to Appendix B for the example calculations. Please note that other software or spreadsheet programs may also be used to estimate short-term emission rates, provided the methodology is based on EPA AP-42 equations using the worst-case parameters described below.

The most conservative value for short-term emissions can be determined using the maximum pump rate for withdrawal losses and the vapor pressure corresponding to the maximum liquid surface temperature. The maximum liquid surface temperature can be assumed to be 95°F for materials stored at ambient temperature for consistency with the guidance for fixed roof tanks (APDG 6250). As an alternative, a maximum liquid surface temperature can be determined from on-site monitoring of the actual temperature. As a third alternative, applicants can continue to calculate emissions using the “worst month” approach, which is equivalent to using the monthly average liquid surface temperature from the month that produces the highest emission rate.

For cases where EPA Tanks 4.09D is used to estimate emissions, the new example calculation includes a “worst-month selection” step to account for worst-case ambient conditions (see Ambient and Seasonal Adjustments, Page 5). This extra step results in a more conservative estimate of standing losses than using an annual average. Basing the short-term emission rate on the “worst month” at maximum throughput may also help account for seasonal variability in Reid vapor pressure at gasoline terminals.

This guidance also includes a vapor pressure scale-up procedure for scenarios where the tank or stored material is heated above ambient temperature.

The following short-term calculation procedures are intended to cover the most common floating roof tank scenarios. For special cases that may require unique considerations, please contact the Air Permits Division at (512) 239-1250.


Total Short-term Losses

Total short-term losses from floating roof tanks are a combination of withdrawal (working) losses and standing losses. Equation 2-1 of EPA AP-42, Chapter 7 expresses floating roof tank losses on an annual basis:

DFRWDT LLLLL +++= (Equation 1)

• LT is Total Loss (lb/year) • LWD is Withdrawal Loss (lb/year) • LR is Rim Seal Loss (lb/year) • LF is Deck Fitting Loss (lb/year) • LD is Deck Seam Loss (lb/year)

To obtain a short-term (lb/hr) emission rate, AP-42 equations for each loss type are used with certain worst-case parameters. For withdrawal loss, the equation is adjusted for maximum throughput. For standing losses (rim seal, deck fitting, and deck seam), the equations are adjusted to account for the vapor pressure corresponding to the maximum liquid surface temperature.

EPA Tanks 4.09D or the hand calculation method can be used to identify or calculate maximum monthly emissions. The emissions from the worst-case month are multiplied by 12 months per year and divided by 8,760 hours per year to determine the worst-case (or maximum potential) short-term hourly rate (lb/hr). An additional scale-up factor is applied if the tank is heated. The scale-up factor may also be applied if the applicant chooses to calculate emissions more conservatively using a maximum liquid surface temperature of 95°F.

Please refer to Appendix B for an illustration of each method.

Withdrawal Loss

Withdrawal loss does not depend on the stock vapor pressure. It is the only component of total short-term losses that depends on the fill/withdrawal rate. In order to simulate worst-case conditions, we first determine a maximum annual throughput based on the maximum pumping rate and assuming throughput occurs on a continuous basis:

)/8760( yrhrPRQ MMAX ×= (Equation 2)

• QMAX is Maximum Throughput (bbl/year) • PRM is Maximum Pumping Rate (bbl/hr)

Note: For internal floating roof tanks, use the greater of the maximum fill rate or maximum withdrawal rate; for external floating roof tanks, use the maximum withdrawal rate.

Withdrawal loss is then calculated as follows:

+=

DFN

DWCQL CCLMAX

WD 1943.0 S (Equation 3)

• LWD is Withdrawal Loss (lb/year) • 0.943 is Constant (103 ft3 gal/bbl2)


• CS is Shell Clingage factor (bbl/103 ft2 – See Table 7.1-10 from AP-42) • WL is Liquid Density (lb/gal) • NC is Number of Fixed Roof Support Columns (Table 7.1-11 from AP-42); NC = 0 for

self-supported or cable-suspended roof • FC is Effective Column Diameter (ft) • D is Tank Diameter (ft)

Rim Seal Loss

Rim seal loss depends on the vapor pressure of the material being stored, and is not affected by the fill/withdrawal rate.

( ) CVnRRR KMDPvKKL ba*+= (Equation 4)

• LR is Rim Seal Loss (lb/year) • KRa is Zero Wind Speed Loss Factor ((lb-mole)/(ft·yr)) • KRb is Wind Dependent Loss Factor ((lb-mole/((mph)n (ft·yr))) • For KRa, KRb, and n, Use Table 7.1-8 from AP-42, Chapter 7 • v is Worst Month Wind Speed (mph)(1)(2) – See Appendix A or Use Data from the National

Oceanic and Atmospheric Administration (www.ncdc.noaa.gov/sites/default/files/attachments/wind1996.pdf)

NOTE (1): v = 0 for internal or domed external floating roof tank. NOTE (2): While AP-42 indicates average ambient wind speed for annual calculations, please use the worst month wind speed for short-term calculations.

• n is Wind Dependent Loss Exponent (dimensionless) • D is Tank Diameter (ft) • P* is Vapor Pressure Function (Eqn. 5, dimensionless) • MV is Vapor Molecular Weight (lb/lb-mol) • KC is Product Factor (0.6 crude oil(3); 1.0 other)

NOTE (3): For the crude oil product factor (KC), use 0.6 for short-term (lb/hr) calculations and 0.4 for annual (tpy) calculations as recommended by API Technical Report 2576.

( )25.0

*

11

−+

=

AVA

AVA

PP

PP

P (Equation 5)

• PVA is Vapor Pressure at Maximum Liquid Surface Temperature, psia • PA is Atmospheric Pressure, psia

http://www.ncdc.noaa.gov/sites/default/files/attachments/wind1996.pdf


Deck Fitting Loss

Deck fitting losses depend on the vapor pressure of the stored material. Applicants should provide a completed Table 7(c) and/or Table 7(d) with the permit application to summarize tank fittings. If there are tank fittings not found in Table 7(d), use the values from AP-42 (Table 7.1-12) to calculate long-term emissions from floating roof tanks. Tables 7(c) and 7(d) are available on the TCEQ website. (www.tceq.texas.gov/permitting/air/forms/newsourcereview/tables/nsr_table2.html)

CVFF KMPFL *= (Equation 6)

• LF is Deck Fitting Loss (lb/year) • FF is Fitting Loss Factor(1)(2) – calculated from Form 7(d) (lb-mol/yr) or AP-42 Table 7.1-12 • KC is Product Factor (0.6 crude oil; 1.0 other)

NOTE (1): Please note that wind speed will affect the calculation of FF for external floating roof tanks. See AP-42 Chapter 7, Equations 2-5 through 2-8 and AP-42 Chapter 7, Sample Calculations, Example 3. NOTE (2): Please note that actual tank fitting types must be used when calculating the fitting loss factor (FF). Fittings must also be in compliance with rules and current BACT.

Deck Seam Loss

Deck seam losses are zero for external floating roof tanks and for welded decks on internal floating roof tanks. For bolted decks on internal floating roof tanks, the losses depend on the vapor pressure of the stored material and the square of the diameter of the tank.

CVDDD KMPDSKL *2= (Equation 7)

• LD is Deck Seam Loss (lb/year) • KD is Deck Seam Loss per Unit Seam Length Factor

= 0.0 for Welded Deck; = 0.14 for Bolted Deck • SD = Lseam/Adeck (ft-1)

Where: Lseam = total length of deck seams (ft)

Adeck = area of deck (ft2) = �14�𝜋𝜋𝐷𝐷2

http://www.tceq.texas.gov/permitting/air/forms/newsourcereview/tables/nsr_table2.html


Ambient and Seasonal Adjustments

Using Tanks 4.09D

EPA Tanks 4.09D automatically calculates withdrawal, rim seal, deck fitting, and deck seam losses based on monthly average temperatures and wind speeds for the selected geographic location. In order to determine worst-case hourly emissions from non-heated tanks using Tanks 4.09D results, an adjustment should be made to reflect worst-case ambient conditions (temperature and/or wind speed). Using QMAX and selecting the Emissions Report - Detail Format” spreadsheet generated by the Tanks 4.09D software, examine the total losses calculated for each individual month. The highest monthly emission rate can then be multiplied by 12 mo/yr and divided by 8,760 hr/yr to determine a worst case hourly emission rate.

For All Calculation Methods

Please note that if the material characteristics vary by month or season due to regulatory requirements (such as Reid Vapor Pressure limits at gasoline terminals), the worst-case month for emissions may not necessarily correspond to the warmest ambient conditions. In the case of external floating roof tanks, please note that both temperature and wind speed will affect standing losses, and the highest ambient temperature and highest wind speed may not necessarily occur in the same month. These and other variable factors may be accounted for by calculating emissions for each month separately (using QMAX) and choosing the month with the highest emissions as the basis for the short-term emission rate. The variables should be considered regardless of the calculation method used (hand method, Tanks 4.09D, or other AP-42 based program).

Adjustment for Material Temperature

If the floating roof tank or its material is heated, or if the material enters the tank above ambient temperature, the short-term standing loss calculations should be adjusted to account for the vapor pressure at the worst-case liquid surface temperature. This approach may also be used for ambient temperature tanks when a more conservative assumption is selected (e.g., using 95oF for the liquid surface temperature).

In the hand calculation method, the worst-case vapor pressure is plugged into the vapor pressure function equation (Equation 5, or AP-42 Equation 2-3).

If Tanks 4.09D is used to estimate emissions, a suggested scale-up factor should be applied to the standing losses as follows:

LSTANDING MAX, HEATED (lb/mo) = (P*MAX/P*) x [(LR WORST MONTH + LF WORST MONTH + LD WORST MONTH)]

• P*MAX is Vapor Pressure Function (Eqn. 5, dimensionless) Using Worst-Case Vapor Pressure • P* is Vapor Pressure Function (Eqn. 5, dimensionless)

For the total short-term losses, add the scaled-up standing losses to the withdrawal losses at maximum throughput:

LT MAX, HEATED (lb/hr) = [LSTANDING MAX, HEATED (lb/mo) + LWD MAX (lb/mo)] x [(12 mo/yr) x (1 yr/8,760 hr)]


The material temperature adjustment for floating roof tank scenarios is further illustrated in Appendix B, Example Calculations.

Note: In cases where mixtures are stored, please also account for any variations in vapor phase molecular weight (Mv) due to heating.

Best Available Control Technology (BACT)

All new or modified storage tanks must meet current Best Available Control Technology (BACT) requirements. For information on current BACT requirements for storage tanks, please contact the TCEQ Air Permits Division at (512) 239-1250 or visit the following on-line resources:

www.tceq.texas.gov/permitting/air/nav/air_bact_chemsource.html

www.tceq.texas.gov/assets/public/permitting/air/Guidance/NewSourceReview/bact/bact_tanks.pdf

_______________________ Equation References Equation 1: AP-42, Chapter 7.1.3.2.1, Equation 2-1 Equation 2: TCEQ Draft RG-166, Equation V-2 Equation 3: AP-42, Chapter 7.1.3.2.1, Equation 2-4 Equation 4: AP-42, Chapter 7.1.3.2.1, Equation 2-2 Equation 5: AP-42, Chapter 7.1.3.2.1, Equation 2-3 Equation 6: AP-42, Chapter 7.1.3.2.1, Equation 2-5 Equation 7: AP-42, Chapter 7.1.3.2.1, Equation 2-9

http://www.tceq.texas.gov/permitting/air/nav/air_bact_chemsource.html

http://www.tceq.texas.gov/assets/public/permitting/air/Guidance/NewSourceReview/bact/bact_tanks.pdf

APDG6419v1, Revised 02/18, Short-term Emissions from Floating Roof Tanks Page 7 of 17 This form is for use by facilities subject to air quality permit requirements and may be revised periodically.

APPENDIX A Wind Speed Data for Texas*

(Unit:mph)

PLACE JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANN Abilene 12 13 14 14 13 13 11 10 11 11 12 12 12

Amarillo 13 14 15 15 14 14 12 11 12 13 13 13 13

Austin 10 10 11 10 9 9 8 8 8 8 9 9 9

Brownsville 11 12 13 14 13 12 12 10 9 10 11 11 11

Corpus Christi 12 13 14 14 13 12 12 11 10 11 12 12 12

Dallas/ Ft.Worth 11 12 13 12 11 11 10 9 10 10 11 11 11

Del Rio 9 10 11 11 11 11 11 10 9 9 9 8 10

EI Paso 8 9 11 11 10 9 8 8 8 8 8 8 9

Galveston 12 12 12 12 12 11 10 9 10 10 11 11 11

Houston 8 9 9 9 8 8 7 6 7 7 8 8 8

Laredo AFB 9 10 12 13 14 14 14 13 10 10 9 9 12

Lubbock 13 14 15 15 15 14 12 10 11 12 13 13 13

Midland/ Odessa 10 11 13 13 13 12 11 10 10 10 10 10 11

Port Arthur 11 11 11 12 10 9 7 7 8 9 10 10 10

San Angelo 10 11 12 12 12 11 10 9 9 9 10 10 10

San Antonio 9 9 10 10 10 10 9 8 8 8 8 8 9

Sherman 12 12 13 13 12 10 9 9 9 9 10 10 10

Waco 12 12 13 13 12 11 11 10 10 10 11 11 11

Wichita Falls 11 12 13 13 12 12 11 10 10 11 11 11 11

*Reproduced from Climatic Wind Data for the United States

Original Link: www.ncdc.noaa.gov/sites/default/files/attachments/wind1996.pdf

http://www.ncdc.noaa.gov/sites/default/files/attachments/wind1996.pdf


APPENDIX B Short-term Emissions from Floating Roof Tanks

Example Calculations

Short-term emissions from floating roof tanks may be calculated using equations from AP-42 Chapter 7 with some value substitutions to reflect worst-case parameters and conditions. TCEQ recommends the following calculation steps:

EXAMPLE SCENARIO: Internal Floating Roof (IFR) Tank - heated such that the maximum liquid surface temperature = 100oF.

Given: General = AAAA Corporation located in Galveston, Texas. Tank Type = Internal Floating Roof Tank Diameter = 60 ft TCG = 846,100 gal Q = 10,000,000 gal/yr QMAX = PRM (gal/hr) x 8,760 hr/yr PRM = 5,000 gal/hr (needed for QMAX) Roof = Not Self Supporting No. Columns = 1 Column Dia. = 1 ft Internal Shell = Light Rust Shell Col/Shade = White/White Shell Cond. = Good Roof Col/Shade = White/White Roof Cond. = Good Primary Seal = Liquid-Mounted Sec. Seal = None Deck Type = Welded Deck Fittings = See Below Contents = 100% n-Heptane MV = 100.204 lb/lbmol Heated? = Yes TMAX = Maximum Liquid Surface Temperature = 100oF VPMAX = Vapor Pressure at TMAX = 1.62 psia WL = Liquid Density at 100oF = 5.597 lb/gal

Deck Fitting Information

Deck Fitting Status Quantity

Access Hatch (24-in. Diam.) Bolted Cover, Gasketed 1

Automatic Gauge Float Well Bolted Cover, Gasketed 1

Column Well (24-in. Diam.) Built-Up Col.-Sliding Cover, Gasketed 1

Ladder Well (36-in. Diam.) Sliding Cover, Gasketed 1

Roof Leg or Hanger Well Adjustable 17

Sample Pipe or Well (24-in. Diam.) Slit Fabric Seal 10% Open 1

Vacuum Breaker (10-in. Diam.) Weighted Mech. Actuation, Gask. 1


Find: Worst-case short-term VOC emission rate (lb/hr).

Solution A: Using Hand Calculation Method (Heated IFR Tank)

1) Withdrawal (Working) Loss (LWD)

Calculate the maximum throughput (QMAX), based on the worst-case hourly pump rate (PRM): QMAX (bbl/yr) = PRM (bbl/hr) × 8,760 (hr/yr)

In this example: QMAX (bbl/yr) = (5,000 gal/hr) × (1 bbl/42 gal) × 8,760 hr/yr

= 1,042,857.14 bbl/yr (or 43,800,000 gal/yr)

Note: For internal floating roof tanks, use the greater of the maximum fill rate or maximum withdrawal rate for PRM; for external floating roof tanks, use the maximum withdrawal rate for PRM.

Using an estimation method incorporating AP-42, Chapter 7.1, Equation 2-4 and QMAX as indicated above, calculate worst-case working (withdrawal) losses (LWD MAX):

LWD MAX (lb/yr) = [(0.943)(QMAX)(CS)(WL)/D] × [1 + (NCFC)/D]

Where: 0.943 = constant (103 ft3 gal/bbl2)

QMAX = maximum throughput (bbl/yr, see above) CS = shell clingage factor (bbl/103 ft2, AP-42 Table 7.1- 10) WL = liquid density (lb/gal) NC = number of fixed roof support columns (AP-42 Table 7.1- 11)

= 0 for self-supported or cable-suspended roof FC = effective column diameter (ft) D = tank diameter (ft)

LWD MAX (lb/yr) = [(0.943 (103 ft3 gal/bbl2))(1,042,857.14 bbl/yr)(0.0015 bbl/103 ft2)(5.597 lb/gal)/60 ft] × [1 + (1)(1 ft)/(60 ft)]

LWD MAX = 139.90 lb/yr

2) Rim Seal Loss (LR)

L R (lb/yr) = (K R a + (K Rb vn)) D P* M V K C

Where: KRa = Zero Wind Speed Loss Factor ((lb-mole)/(ft·yr))

KRb = Wind Dependent Loss Factor ((lb-mole/((mph)n (ft·yr))) For KRa, KRb, and n use Tbl 7.1-8

v = Worst Month Wind Speed (mph)

See Appendix A or Use Data from the National Oceanic and Atmospheric Administration.

NOTE: v = 0 for internal or domed external floating roof tank.

n = Wind Dependent Loss Exponent imensionless) D = Tank Diameter (ft) P* = Vapor Pressure Function (based on maximum

liquid surface temperature, see note below)


PVA = Vapor Pressure at Maximum Liquid Surface Temperature, psia (needed for P*)

PA = Atmospheric Pressure, psia (needed for P*) MV = Vapor Molecular Weight (lb/lb-mol) KC = Product Factor (0.6 crude oil; 1.0 other)

IMPORTANT NOTE: For P*, use the vapor pressure at the maximum liquid surface temperature. In this example, the tank is heated to 100oF, with a corresponding vapor pressure of 1.62 psia:

P* = [1.62 psia/14.7 psia] [1 + (1 – (1.62 psia/14.7 psia)) 0.5]2

= 0.02918

LR = [1.6 ((lb-mole)/(ft·yr)) + 0.3 ((lb-mole/((mph)n (ft·yr))) (60 ft)(0.02918)(100.204 lb/lbmol)(1.0)

LR = 280.70 lb/yr

3) Deck Fitting Loss (LF)

LF (lb/yr) = FF P* MV KC

Where: FF = Total Fitting Loss Factor (lb-mol/yr)

P* = Vapor Pressure Function (based on maximum liquid surface temperature, see above)

MV = Vapor Molecular Weight (lb/lb-mol) KC = Product Factor (0.6 crude oil; 1.0 other)

IMPORTANT NOTE: Please note that actual tank fitting types must be used when calculating the fitting loss factor (FF). Fittings must also be in compliance with rules and current BACT.

From AP-42 Chapter 7, Equation 2-6:

FF = [(NFiKFi) + (NF2KF2) + (NFfKFf)]

Where: NFi = Number of Fittings of a Particular Type (dimensionless) KFi = Deck Fitting Loss Factor for a Particular Type

(lb-mol/yr) – See AP-42, Chapter 7, Equation 2-7.

From AP-42 Chapter 7, Equation 2-7:

KFi = KFai + KFbi(KVv)mi

Where: KFi = Deck Fitting Loss Factor for a ParticularType (lb-mol/yr)

KFai = Zero Wind Speed Loss Factor for a Particular Type Fitting (lb-mol/yr)

KFbi = Wind Speed Dependent Loss Factor for a Particular Type Fitting (lb-mol/((mph)myr)

mi = Loss Factor for a Particular Type Fitting (dimensionless) i = 1, 2, n (dimensionless) KV = Wind Speed Correction Factor (dimensionless) v = Worst Month Wind Speed (mph)

For Internal Floating Roof Tanks, v = 0, so:

KFi = KFai


Using AP-42, Chapter 7, Table 7.1-12:

FF = [(1)(1.6) + (1)(2.8) + (1)(33) + (1)(56) + (17)(7.9) + (1)(12) + (1)(6.2)] lb-mol/yr

FF = 245.9 lb-mol/yr LF = (245.9 lb-mol/yr)( 0.02918)(100.204 lb/lb-mol)(1.0) LF = 719.00 lb/yr

4) Deck Seam Loss (LD)

LD (lb/yr) = KD SD D2 P* MV KC

Where: LD = Deck Seam Loss (lb/year)

KD = Deck Seam Loss per Unit Seam Length Factor (lb-mole/ft-yr)

= 0.0 for Welded Deck; = 0.14 for Bolted Deck

For D, P* (max), and KC, see above.

SD = Lseam/Adeck (ft-1)

Where:

Lseam = total length of deck seams (ft) Adeck = area of deck (ft2) = �1

4� 𝜋𝜋𝐷𝐷2

This example indicates a welded deck. Therefore, KD = 0.0, and thus:

LD = 0.00 lb/yr

5) Combine Losses

Add the worst-case working losses and worst-case standing losses:

LT MAX (lb/yr) = LWD + LR + LF + LD

In this example:

LT MAX (lb/yr) = 139.90 lb/yr + 280.70 lb/yr + 719.00 lb/yr + 0.00 lb/yr = 1,139.60 lb/yr

To obtain the worst-case lb/hr:

LT MAX (lb/hr) = LT MAX (lb/yr)/(8,760 hr/yr) LT MAX (lb/hr) = (1,139.60 lb/yr)/ (8,760 hr/yr)

LT MAX (lb/hr) = 0.13 lb/hr VOC

NOTE: The above example assumes a heated tank at constant temperature. For ambient storage scenarios, calculations may be performed for multiple months to determine worst-case short-term emissions.


Solution B: Using Tanks 4.09D (Heated IFR Tank)

1) Withdrawal (Working) Loss

Calculate the maximum throughput (QMAX), based on the worst-case hourly pump rate (PRM): QMAX (bbl/yr) = PRM (bbl/hr) × 8,760 (hr/yr)

In this example: QMAX (bbl/yr) = (5,000 gal/hr) × (1 bbl/42 gal) × 8,760 hr/yr

= 1,042,857.14 bbl/yr (or 43,800,000 gal/yr)

Note: For internal floating roof tanks, use the greater of the maximum fill rate or maximum withdrawal rate for PRM; for external floating roof tanks, use the maximum withdrawal rate for PRM.

In this example, EPA TANKS 4.09D software is used to assist in emissions estimation. Please refer to the Tank 4.09D Report included in APPENDIX C. Please contact the Air Permits Division at (512)239-1250 to obtain a larger printed version of Appendix C. [NOTE: Other software or spreadsheet programs that incorporate AP-42 equations may also be used.] TANKS 4.09D indicates:

LWD MAX (lb/yr) = 143.15 lb/yr (or 11.93 lb/mo)

Note: The TANKS 4.09 program uses an average liquid density of 5.727 lb/gal. This yields a slightly higher value for LWD MAX versus Solution A above, which uses a liquid density of 5.597 lb/gal corresponding to the maximum temperature.

2) Standing Losses (Rim Seal, Deck Fitting, and Deck Seam)

In this example, EPA TANKS 4.09D software is used to assist in emissions estimation. Based on a review of the detailed monthly calculation breakdown from Tanks 4.09D, it is noted that July would yield the highest hourly emission rate. Standing losses are therefore based upon the month of July.

LSTANDING MAX (lb/mo) = 14.5980 lb/mo (LR WORST MONTH) + 37.3922 lb/mo (LF WORST MONTH) + 0.0000 (LD WORST MONTH)

= 51.9902 lb/mo

3) Adjust Standing Losses for Heating

If the floating roof tank or its material is heated, or if the material enters the tank hot from the process, scale up the standing losses to account for a worst-case vapor pressure:

LSTANDING MAX, HEATED (lb/mo = (P*MAX/P*) × [(LR WORST MONTH +

LF WORST MONTH + LD WORST

MONTH)

Where: P*MAX = Vapor Pressure Function (AP-42 Ch. 7.1, Eq. 2-3)

Using Worst-Case Vapor Pressure at Maximum Liquid Surface Temperature

P* = Vapor Pressure Function (AP-42 Ch. 7.1, Eq. 2-3)


In this example, EPA TANKS 4.09D indicates that the vapor pressure function (P*) during the worst month for standing losses (July) equals 0.0182.

For P*MAX:

P* MAX = [VPMAX/PATMOSPHERIC]/[1 + (1 - (VPMAX/ PATMOSPHERIC))0.5]2

= [1.62 psia/14.7 psia]/[1 + (1 – (1.62 psia/14.7 psia)) 0.5]2

= 0.02918

In this example, the scaled-up standing losses to account for tank heating would therefore be:

LSTANDING MAX, HEATED (lb/mo) = (0.02918/0.0182) x 51.9902 lb/mo (from July) = 83.36 lb/mo

4) Combine Losses

Add the worst-case working losses and worst-case standing losses:

LT MAX (lb/mo) = LWORKING MAX (lb/mo) + LSTANDING MAX, HEATED (lb/mo)

In this example:

LT MA (lb/mo) = 11.93 lb/mo + 83.36 lb/mo = 95.29 lb/mo

To obtain the worst-case lb/hr:

LT MAX (lb/hr) = LT MAX (lb/mo) x (12 mo/yr) x (1 yr/8760 hr)

In this example (using July):

LT MAX (lb/hr) = (95.29 lb/mo) x (12 mo/yr) x (1 yr/8760 hr)

LT MAX (lb/hr) = 0.13 lb/hr VOC


APPENDIX C Example Emissions Report – TANKS 4.09d

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