United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
January 1981
Air
v>EPA Guideline Series
Control of Volatile
Organic Emissions from
Volatile Organic Liquid
Storage in Floating and
Fixed Roof Tanks
Preliminary Draft
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453D81001
NOTICE
This document has not been formally released by EPA and should not now be construed to represent
Agency policy. It is being circulated for comment on its technical accuracy and policy implications.
Control of Volatile Organic
Emissions from Volatile Organic
Liquid Storage in Floating and
Fixed Roof Tanks
Emission Standards and Engineering Division
Contract No. 68-02-3168
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
January 1981
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GUIDELINE SERIES
The guideline series of reports is issued by the Office of Air Quality
Planning and Standards (OAQPS) to provide information to state and local
air pollution control agencies; for example, to provide guidance on the
acquisition and processing of air quality data and on the planning and
analysis requisite for the maintenance of air quality. Reports published
in this series will be available - as supplies permit - from the Library
Services Office (MD-35), U. S. Environmental Protection Agency, Research
Triangle Park, North Carolina 27711, or for a nominal fee, from the
National Technical Information Service, 5285 Port Royal Road, Springfield,
Virginia 22161.
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Table of Contents
Page
Li st of Tabl es vi
Li st of Fi gures V1 n 1
Chapter 1.0 Introduction and Summary 1-1
1.1 Introduction 1-1
1.2 Summary of Model Regulation 1-2
Chapter 2.0 Emissions from VOL Storage 2-1
2.1 Industry Description 2-1
2.2 Storage Tanks 2-1
2.2.1 Types of Storage Tanks 2-1
2.2.2 Types of Seals 2-3
2.2.3 Storage Tank Emissions and Emission
Equations 2-8
2.3 Model Tanks and Uncontrolled Emissions 2-12
2.3.1 Fixed Roof Tank 2-12
2.3.2 Floating Roof Tank 2-16
2.3.3 Small Tank 2-16
2.4 References for Chapter 2 2-17
Chapter 3.0 Emissions Control Techniques 3-1
3.1 Introduction 3-1
3.2 Emissions Control Techniques 3-1
3.2.1 Internal Floating Roofs in Fixed Roof
Tanks 3-2
3.2.2 Rim-Mounted Secondary Seals on External
Fl oati ng Roofs 3-3
iii
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Table of Contents (continued)
Page
3.2.3 Fixed Roofs on External Floating Roof
Tanks 3-3
3.2.4 Contact Internal Floatinq Roofs in
Non-Contact Internal Floating Roof Tanks... 3-5
3.2.5 Liquid-Mounted Primary Seals on
Contact Internal Floating Roofs 3-5
3.2.6 Rim-Mounted Secondary Seals on Contact
Internal Floating Roofs 3-5
3.3 Retrofit Considerations 3-7
3.3.1 Fixed Roof Tanks with Internal Floating
Roofs 3-7
3.3.2 Rim-Mounted Secondary Seals on External
Fl oati ng Roofs 3-7
3.3.3 Fixed Roofs on External Floating Roof
Tanks.. 3-7
3.3.4 Secondary Seals on non-contact Internal
Fl oati ng Roofs 3-8
3.4 References for Chapter 3 3-9
Chapter 4.0 Environmental Analysis of RACT 4-1
4.1 Air Pollution 4-1
4.2 Water Pollution 4-3
4.3 Solid Waste Disposal.. 4-3
4.4 Energy 4-3
4.5 References for Chapter 4 4-4
Chapter 5.0 Control Cost Analysis of RACT 5-1
5.1 Bases for Installed Capital Costs 5-1
5.1.1 Cost of Installing a Contact Internal
Floating Roof 5-1
iv
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Table of Contents (continued)
Page
5.1.2 Cost of Installing a Fixed Roof 5-4
5.1.3 Cost of Installing Secondary Seals 5-4
5.1.4 Cost of Cleaning, Degassing, and
Certification 5-4
5.2 Bases for Annualized Costs 5-4
5.2.1 Annual Capi tal Charges 5-10
5.2.2 Direct Operating Costs 5-10
5.2.3 Recovery Credits 5-11
5.3 Emission Control Costs 5-11
5.3.1 Small Model Storage Tank 5-11
5.3.2 Average Fixed Roof Model Storage Tank 5-11
5.3.3 Average Floating Roof Model Storage Tank... 5-15
5.4 Cost Effectiveness 5-15
5.5 References for Chapter 5 5-18
Chapter 6.0 Model Regulation and Discussion 6-1
6.1 Model Regulation 6-1
6.2 Discussion 6-6
6.2.1 Introduction 6-6
6.2.2 Review of the Records 6-6
6.2.3 Inspections 6-7
6.2.4. Equivalency 6-7
6.2.5 Compliance Schedule 6-9
6.3 References for Chapter 6 6-10
Appendix A Emission Source Test Data VOL Storage Tanks
Appendix B Example Calculations for Determining Reduction in
Emissions from Implementation of RACT
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LIST OF TABLES
Table 2-1
Table 2-2
Table 2-3
Table 2-4
Table 4-1
Table 5-1
Table 5-2
Table 5-3
Table 5-4
Table 5-5
Table 5-6
Table 5-7
Table 5-8
Table 5-9
Table A-l
Table A-2
Table A-3
Emission factors K and n
s
Summary of emission factors K. and m for floating
roofs
Fitting multipliers
Model tank parameters and emissions
Impact of RACT on VOC emissions from storage tanks.
Cost of installing a contact internal floating roof
in an existing fixed roof tank
Cost of installing a fixed roof on an existing
external floating roof tank
Cost of installing a secondary seal on an existing
internal or external floating roof
Cost of cleaning, degassing, and certification
of a storage tank
Bases for annual i zed cost estimates
Recovery credi ts
Installed capital costs
Annual i zed control costs for model storage tanks
Cost effectiveness for model storage tanks under
RACT
Summary of test conditions, for phase I,
contact- type internal floating roof
Summary of test conditions for phase II,
non-contact-type internal floating roof
Summary of test conditions for phase III, double
deck external floating roof
Page
2-13
2-13
2-14
2-15
4-2
5-2
5-2
5-6
5-6
5-9
5-12
5-13
5-14
5-16
A-7
A-12
A-14
VI
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LIST OF TABLES (continued)
Table A-4
Table A-5
Table A-6
Table A-7
Table A-8
Measured benzene emissions from EPA phase I
testing, contact-type internal floating roof
Measured benzene emissions from EPA phase III
testing double deck external floating roof
Seal loss factors for average seal gaps and the
basis of estimation
Measured and estimated breathing losses from
fixed-roof tanks
Comparison of measured losses with those calculated
usina API 2518
Page
A-16
A-17
A-19
A-22
A-25
Vll
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LIST OF FIGURES
Page
Figure 2-1 Typical fixed-roof tank 2-2
Figure 2-2 External floating roof tank (pontoon type) 2-4
Figure 2-3 Internal floating roof tanks 2-5
Figure 2-4 Primary seals 2-6
Figure 2-5 Typical flotation devices and perimeter seals
for internal f 1 oating roofs 2-9
Figure 3-1 Metallic shoe seal with shoe-mounted secondary seal. 3-4
Figure 3-2 Rim mounting of a secondary seal on an internal
floating roof 3-6
Figure 5-1 Cost of installing a contact internal floating roof
in an existing fixed roof tank 5-3
Figure 5-2 Cost of installing a fixed roof on an existing
external floating roof tank 5-5
Figure 5-3 Cost of installing a secondary seal on an existing
internal or external floating roof 5-7
Figure 5-4 Cost of cleaning, degassing, and certification 5-8
Figure A-l Simplified process and instrumentation schematic... A-2
Figure A-2 Position of the contact-type internal floating roof
within the emissions test tank A-5
Figure A-3 Rim mounting of the flapper secondary seal A-6
Figure A-4 Installed shingle-type seal A-8
Figure A-5 Position of the non-contact-type internal floating
roof within the emissions test tank A-9
Figure A-6 Cross-sectional view of the shingle-type seal
installation A-10
Figure A-7 Position of the double deck external floating roof
within the emissions test tank A-13
vm
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1.0 INTRODUCTION AND SUMMARY
1.1 INTRODUCTION
The Clean Air Act Amendments of 1977 require each State in which there
are areas in which the national ambient air quality standards (NAAQS) are
exceeded to adopt and submit revised State implementation plans (SIP) to
EPA. Revised SIP's were required to be submitted to EPA by January 1, 1979.
States which were unable to demonstrate attainment with the NAAQS for ozone
by the statutory deadline of December 31, 1982, could request extensions for
attainment with the standard. Such extensions could not go beyond
December 31, 1987. States granted such an extension are required to submit
a further revised SIP by July 1, 1982.
Section 172(a)(2) and (b)(3) of the Clean Air Act require that
nonattainment area SIP's include reasonably available control technology
(RACT) requirements for stationary sources. As explained in the "General
Preamble for Proposed Rulemaking on Approval of State Implementation Plan
Revisions for Nonattainment Areas," (44 FR 20372, April 4, 1979) for ozone
SIP's, EPA permitted states to defer the adoption of RACT regulations on a
category of stationary sources of volatile organic compounds (VOC) until
after EPA published a control techniques guideline (CTG) for that VOC source
category. See also 44 FR 53761 (September 17, 1979). This delay allowed
the states to make more technically sound decisions regarding the application
of RACT.
The CTG documents provide State and local air pollution control agencies
with an information base for proceeding with development and adoption of
regulations which reflect RACT for specific stationary sources. Consequently,
CTG documents review existing information and data concerning the technology
and cost of various control techniques to reduce emissions. CTG documents
also identify control techniques and suggest emission limitations which EPA
considers the "presumptive norm" broadly representative of RACT for the
entire stationary source category covered by a CTG document.
1-1
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The CTG documents are, of necessity, general in nature and do not fully
account for variations within a stationary source category. RACT, however,
is defined as the lowest emission limitation that a particular source is
capable of meeting by the application of emission control technology that is
reasonably available considering technical and economic feasibility. Thus,
reasons may exist for regulations developed by States to deviate from the
"presumptive norm" included in a CTG document. The CTG document, however,
is a part of the rulemaking record which EPA considers in reviewing revised
SIP's, and the information and data contained in the document is highly
relevant to EPA's decision to approve or disapprove a SIP revision. Where a
State adopts emission limitations that are consistent with the information
in the CTG, it may be able to rely solely on the information in the CTG to
support its determination of RACT. Where this is not the case, the State
must include documentation with its SIP revision to support and justify its
RACT determination.
This draft CTG document includes a model regulation based upon the
"presumptive norm" considered broadly representative of RACT for the
stationary source category covered by this document. The sole purpose of
this model regulation is to assist State and local agencies in development
and adoption of regulations for specific stationary sources. This model
regulation is not to be construed as rulemaking by EPA.
This CTG document is being released in working draft form to achieve
two objectives. First, to provide an opportunity for public review and
comment on the information and regulatory guidance contained in the document;
and second, to provide as much assistance and lead time as possible to State
and local agencies preparing RACT regulations for specific stationary
sources covered by this document.
1.2 SUMMARY OF MODEL REGULATION
The model regulation applies to storage tanks with a capacity larger
than 151,416 liters (40,000 gallons) storing a volatile organic liquid (VOL)
with an actual vapor pressure greater than 10.5 kPa (1.5 psia). Storage
tanks which are used to store petroleum liquids are excluded from the model
regulation.
1-2
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This model regulation requires that affected VOL storage tanks be
retrofitted with RACT. The RACT required by the model regulation is a
contact internal floating roof with primary and secondary seals. Tanks that
are currently equipped with an internal floating roof are exempt. Affected
fixed roof tanks must install a contact internal floating roof with a liquid-mounted
or metallic shoe primary seal and a continuous secondary seal. Affected
external floating roof tanks must install a fixed roof over the tank. The
model regulation does not require that existing primary seals which are not
RACT be removed and replaced by a liquid-mounted or metallic shoe primary
seal, or that existing secondary seals which are not RACT be removed and
replaced with a continuous secondary seal. However, when a primary seal is
replaced it must be replaced with a liquid-mounted or metallic shoe primary
seal and when a secondary seal is replaced, it must be replaced with a
continuous secondary seal.
The owner or operator of each storage tank is required to visually
inspect the internal floating roof, the primary seal, and the secondary seal
prior to initial fill and whenever the tank is emptied and degassed but at
least once every five years. If the owner or operator of the storage tank
finds any defects in the internal floating roof, or any holes, tears, or
other openings in the seals or seal fabric, the control equipment must be
repaired before filling the tank. More frequent inspections are not
required; however the tanks must be maintained in good repair as outlined in
the model regulation.
The recordkeeping requirements of the model regulation require that
each owner or operator of a storage tank storing a VOL with an actual vapor
pressure greater than 1.0 psia keep a record of the VOL being stored, the
average monthly storage temperature of the VOL, and the actual vapor
pressure of the liquid at the average monthly storage temperature.
No periodic reports are required in the model regulation. However, the
Director is to be notified in writing at least 30 days prior to the
refilling of the storage tank in order to afford the State air pollution
agency an opportunity to inspect the control equipment.
1-3
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Provisions are made in the model regulation for an owner or operator of
a storage tank to apply for an alternative control device. Alternative
control devices must reduce emissions by at least 90 percent. The emission
reduction efficiency of the alternative control device would be determined
by comparing emissions resulting from its use with emissions resulting from
use of a fixed-roof storage tank. The owner or operator must provide any
calculations, data, or other evidence which is necessary for determination
of control efficiency.
1-4
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2.0 EMISSIONS FROM VOL STORAGE
2.1 INDUSTRY DESCRIPTION
VOL storage tanks are primarily located at chemical manufacturing
facilities and bulk terminals. A terminal is a non-manufacturing site that
stores commodities in bulk quantity.
Tanks are used for storing a variety of materials: raw materials,
final products or usable by-products, as well as waste tars, residues, and
nonusable by-products. The vapor pressure of the material stored is a major
factor in the choice of tank type used. Other factors, such as material
stability, safety hazards, and multiple use, can also affect the choice of
tank type for a particular organic chemical.
2.2 STORAGE TANKS
2.2.1 Types of Storage Tanks
2.2.1.1 Fixed Roof Tanks. A typical fixed roof tank is shown in
Figure 2-1. This type of tank generally consists of a cylindrical steel
shell with a permanently affixed roof that varies from a cone-shaped to a
dome-shaped design.
Of presently employed tank designs, the fixed roof tank is the least
expensive to construct and is generally considered the minimum accepted
standard for storage of VOL. The tank is designed to operate at a slight
internal pressure above or below atmospheric pressure, and as a result,
emissions from breathing, filling, and emptying can be appreciable.
Breather valves (pressure-vacuum valves) are commonly installed on
many fixed roof tanks to prevent vapors from escaping due to temperature
and barometric pressure changes or very small liquid level fluctuations.
However, these valves vent vapors to the air during normal filling and
allow air into the tank during emptying.
2-1
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PRESSURE-VACUUM
VALVE
GAUGE HATCH
MANHOLE
MANHOLE
NOZZLE
(FOR SUBMERGED FILL
OR DRAINAGE)
Figure 2-1. Typical fixed-roof tank.
2-2
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2.2.1.2 External Floating Roof Tanks. A typical external floating
roof tank is shown in Figure 2-2. This type of tank consists of a steel
cylindrical shell equipped with a deck or roof that floats on the surface of
the stored liquid, rising and falling with the liquid level. The liquid
surface is completely covered by the floating roof except in the small
annular space between the roof and the shell. A seal attached to the roof
contacts the tank wall (except for small gaps in some cases) and covers the
remaining area. The seal slides against the tank wall as the roof is raised
or lowered.
2.2.1.3 Internal Floating Roof Tanks. An internal floating roof tank
is essentially a fixed roof tank with a cover floating on or several inches
above the liquid surface inside the tank. Internal floating roofs that
float on the liquid surface are contact roofs, as shown in Figure 2-3a.
Contact roofs include (1) aluminum sandwich panel roofs with a honeycombed
aluminum core floating in contact with the liquid, and (2) pan-type steel
roofs floating in contact with the liquid. Internal floating roofs that
float above the liquid surface are non-contact roofs, as shown in Figure 2-3b.
Non-contact type roofs typically consist of an aluminum deck on an aluminum
grid framework supported above the liquid surface by tubular aluminum pontoons.
The roof rises and falls with the liquid level. In addition, circulation
vents and an open vent at the top of the fixed roof are often provided to
minimize the possibility of hydrocarbon vapors accumulating in concentrations
approaching the explosive range.
2.2.2 Types of Seals
2.2.2.1 External Floating Roof Tank Seals. Regardless of tank design,
a floating roof requires a closure device to seal the gap between the tank
wall and the roof perimeter. Primary seals, the lower seal of a two seal
system, can be made from a variety of materials suitable for organic liquids.
The basic designs available are: (1) mechanical shoe seals, (2) liquid-filled
seals, and (3) resilient foam log seals. One major difference in seal
design is how the seal is mounted with respect to the liquid. Figure 2-4c exhibits
a vapor space between the liquid and seal, whereas in Figures 2-4b and
2-4d, the seals are resting on the liquid surface.
2-3
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ro
-P.
ROOF LEG SUPPORT
PRIMARY SHOE SEAL
AUTOMATIC
BLEEDER VENT
Figure 2-2. External floating roof tank (pontoon type).
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ANTI-ROTATION
ROOF FITTING
CENTER
VENT
PERIPHERAL
ROOF VENT/
INSPECTION HATCH
i INCH DIAMETER
SS GROUND CABLES
ANTI-ROTATION CABLE
GROUND CABLE ROOF
ATTACHMENT
OVERFLOW VENT
MANHOLE
a. Contact internal floating roof.
CENTER
VENT
GROUND CABLE
ROOF ATTACHMENT
PERIPHERAL ROOF VENT/
INSPECTION HATCH
i INCH DIAMETER
SS GROUND CABLES
PRIMARY SEAL-
RIM PLATE
MANHOLE
TANK SUPPORT COLUMN
WITH COLUMN WALL
ANTI-ROTATION
ROOF FITTING
OVERFLOW
VENT
ANTI-ROTATION CABLE
PASSES THROUGH
FITTING BOLTED
TO RIM PLATE
RIM PONTOONS
VAPOR SPACE
ANTI-ROTATION LUG
WELDED TO FLOOR
TANK SUPPORT COLUMN
WITH COLUMN WELL
b. Non-contact internal floating roof.
Figure 2-3. Internal floating roof tanks.
2-5
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a. Metallic shoe seal
b. Liquid-filled seal with
weather shield.
Floating Roof
Vapor Space
Tank
Wall
^
Scuff
Band —
^
Metallic Weather
« Shield
i
„ \
Floating roof
Liquid filled
^tube
_ >
—
' .. ..
c. Resilient foam-filled seal
with weather shield.
d. Resilient foam-filled seal
with weather shield.
Tank
Wall
Metallic Weather
^/Shield
Floating roof
Seal fabric
Resilient foam
log
Vapor space
Metallic Weather
Shield
Floating roof
fabric
Resilient foam
log
Figure 2-4. Primary seals.
2-6
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2.2.2.1.1 Mechanical shoe seal. The mechanical shoe seal, which is
shown in Figure 2-4a, is characterized by a 75 to 130 cm (30" to 51") high
metal sheet called the shoe which is held against the vertical tank wall.
The shoe is connected by braces to the floating roof and is held tightly
against the wall by springs or weighted levers. A flexible coated fabric
called the envelope is suspended from the shoe seal to the floating roof to
form a gastight cover over the annular space between the roof and the primary
seal.
2.2.2.1.2 Liquid-filled seal. A liquid-filled seal (Figure 2-4b) may
be a tough fabric band or envelope filled with a liquid, or it may be a 20
to 25 cm (8-10") diameter flexible polymeric tube filled with a liquid and
sheathed with a tough fabric scuff band. The liquid is commonly a petroleum
distillate or other liquid which would not contaminate the stored product if
the tube is ruptured. Liquid-filled seals are mounted on the product liquid
surface with no vapor space below the seal.
2.2.2.1.3 Resilient foam-filled seal. A resilient foam-filled seal is
similar to a liquid-filled seal except that a resilient foam log is used in
place of the liquid. The resiliency of the foam log permits the seal to
adapt itself to some imperfections in tank dimensions and to even partially
or completely fill some protrusions. The foam log may be mounted above the
liquid surface (vapor-mounted) or on the liquid surface (liquid-mounted).
Typical vapor-mounted and liquid-mounted seals are presented in Figures 2-4c
and 2-4d, respectively.
2.2.2.1.4 Weather shield. A weather shield (Figures 2-4b, 2-4c, and
2-4d) may be installed over the primary seal to protect it from deterioration
caused by debris and exposure to the elements. Typically, a weather shield
is an arrangement of overlapping thin metal sheets pivoted from the floating
roof to ride against the tank wall. This type of seal is also known as a
shingle seal.
2.2.2.2 Internal Floating Roof Tank Seals. Internal floating roofs
typically incorporate two types of flexible, product-resistant primary
seals: resilient foam-filled seals and wiper seals. Similar to those
employed on external floating roofs, these seals close the annular vapor
2-7
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space between the edge of the floating roof and the tank shell. They
compensate for tank shell irregularities, thus allowing the roof to move
freely up and down in the tank without binding.
2.2.2.2.1 Resilient foam-filled seal. A resilient foam-filled seal
used on an internal floating roof is similar in design to that described in
section 2.2.2.1.3. Two types of resilient foam-filled seals for internal
floating roofs are shown in Figures 2-5a and 2-5b. These seals can either
be several inches above the liquid surface (vapor-mounted) or mounted in
contact with the liquid surface (liquid-mounted).
2.2.2.2.2 Wiper seal. A closed-cell, or other type of elastomeric
wiper (Figure 2-5c) can also be used to close the annular vapor space.
This type of seal, which is generally vapor-mounted can fit continuously
around the circumference of the floating roof. One design consists of
overlapping segments of seal material (shingle-type seal).
2.2.3 Storage Tank Emissions and Emission Equations
2.2.3.1 Fixed Roof Tank Emissions. The two major types of emissions
from fixed roof tanks are breathing losses and working losses. Breathing
loss is the expulsion of vapor from a tank due to expansion and contraction
resulting from diurnal temperature and barometric pressure changes. The
emissions occur in the absence of any liquid level change in the tank.
Working losses consist of filling and emptying losses. Filling losses
are associated with an increase of the liquid level in the tank. The vapors
are expelled from the tank when the pressure inside the tank exceeds the
relief pressure as a result of filling. Emptying losses occur when air
drawn into the tank during liquid removal becomes saturated with hydrocarbon
vapor and expands, thus exceeding the capacity of the vapor space.
2.2.3.2 Fixed Roof Emission Equations. The EPA Report, Publication
No. AP-42, emission equations for breathing and working losses were used to
estimate VOL emissions from fixed roof tanks. However, breathing losses
calculated using these equations were discounted by a factor of four in
light of test results reported by EPA, the Western Oil and Gas Association
Q
(WOGA), and the German Society for Petroleum Science and Carbon Chemistry
(DGMK).9
2-8
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a. Resilient foam-filled seal (vapor-mounted).
Tank wall
\\v L
Resilient foam-filled seal
Contact internal floating roof
(aluminum sandwich papel roof)
b. Resilient foam-filled seal (liquid-mounted),
Resilient foam-filled seal
Contact internal floating roof
(pan-type steel roof) /
Tank wall
c. Elastomeric wioer seal.
Elastomeric wiper seal
(.-'' V
/
Non-contact internal floating roof
Pontoon
"Metal seal ring
Tank wall
(J
Pontoon
Note: v - vapor
L - liquid
Figure 2-5. Typical flotation devices and perimeter seals
for internal floating roofs.
2-9
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The equations used in determining the emission estimates for fixed roof
tanks, reflecting this change, follow:
LT = LB + L, (2-1)
LB = 9.15 x 10"6 M f(P) D1'73^.51!0-^ (2-2)
Lw = 1.09 x 10~8NPKnVN (2-3)
where, Ly = total loss (Mg/yr)
LB = breathing loss (Mg/yr)
L, = working loss (Mg/yr)
M = molecular weight of product vapor (Ib/lb mole); (avg. mol . wt. is 80)
P = true vapor pressure of product (psia)
/ P xO.68
\ ;
14.7-P
D = tank diameter (ft)
H = average vapor space; assumed tank height/2 (ft)
T = average diurnal temperature change in °F(avg. temp, change is 20°F)
F = paint factor; 1.0 for clean white paint
C = tank diameter factor;
for diameter >_ 30 feet, C = 1
for diameter < 30 feet,
C = 0.0771 D - 0.0013 (D2) - 0.1334
=. turnover factor
10
K
for turnovers > 36, k =
for turnovers < 36 k = 1
— n
6N
N = number of turnovers per year
V = tank capacity (gal)
2.2.3.3. External Floating Roof Tank Emissions. Standing-storage
losses, which result from causes other than breathing or change in the
liquid level, constitute the major source of emissions from floating roof
tanks. The largest potential source of these losses is an improper fit
between the seal and the tank shell (seal losses). As a result some liquid
surface is exposed to the atmosphere. When air flow across the tank creates
pressure differences around the floating roof, air flows into the annular
vapor space on the leeward side and an air-vapor mixture flows out on the
windward side.
2-10
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Withdrawal loss is another source of emissions from floating-roof
tanks. When liquid is withdrawn from a tank, the floating roof is lowered
and a wet portion of the tank wall is exposed. Withdrawal loss is the
vaporization of liquid from the wet tank wall.
2.2.3.4 Internal Floating Roof Tank Emissions. Internal floating
roof tanks generally give the same sources of emissions as external floating
roof tanks. Consequently, standing storage and withdrawal constitute two
sources of emissions from these tanks. Fitting loss, which is a result of
penetrations in the roof for deck fittings, roof column supports, or other
openings, can also account for significant emissions from internal floating
roof tanks.
2.2.3.5 Floating Roof Tank Emission Equations. VOL emissions from
external floating roofs and internal floating roofs, were estimated using
equations based on an EPA study of emissions from benzene storage tanks.
From the equations presented below, it was possible to estimate the
Total Evaporation Loss, Ly, which is the sum of the Withdrawal Loss, LW,
the Seal Loss, L<., and the Fitting Loss, Lp.
LT = Lw + LF * Ls (2-4)
Lw = 0.943 QCWL/2205D (2-5)
LS = KS VnMvD f(P)/2205 (2-6)
LF = NKF V^ f(P)/2205 (2-7)
where LT = total loss (Mg/yr)
LW = withdrawal loss (Mg/yr)
LS = seal loss (Hg/yr)
Lp = fitting loss (Mg/yr)
f(P) = 0.068P/((1 + (1 - 0.068P)0-5)2)
MV = molecular weight of product vapor (Ib/lb mole)
P = true vapor pressure of product (psia)
D = tank diameter (ft)
WL = density of product (Ib/gal); 8 Ibs/gal12
V = average wind speed for the tank site (mph);
12
10 mph average wind speed
Q = product average throughput (bbl/yr);
tank capacity (bbl/turnover) x Turnovers/yr
2-11
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KS = seal factor; see Table 2-1
KF = fitting factor; see Table 2-2
n = seal wind speed exponent, See Table 2-1
m = fitting wind speed exponent; See Table 2-2
c = product withdrawal shell clingage factor bbl/(ft2 x 103);
use 0.0015 bbl/(ft2 x 103) for VOL in a welded steel tank with
light rust
N = fitting multiplier; See Table 2-3
2.3 MODEL TANKS AND UNCONTROLLED EMISSIONS
This section describes the model tanks and presents the uncontrolled
emission rate from each model tank. There are three model tanks used in
subsequent analyses: a fixed roof tank, a floating roof tank, and a small
tank. The parameters for the fixed roof and floating roof tanks were deter-
mined from data obtained during an industry survey conducted for the U.S.
Environmental Protection Agency. These data show that floating roof tanks
are normally much larger than fixed roof tanks and frequently store liquids
of higher vapor pressure. A small tank was included in the model tanks to
illustrate the environmental and economic impact on a small tank.
The uncontrolled emission rate of a storage tank is largely dependent
upon the tank's turnover rate. The turnover rate is determined by dividing
the annual throughput of the tank by the capacity of the tank. A storage
tank at a chemical manufacturing plant usually has a higher annual turnover
rate than a tank at a storage terminal. In general the annual turnover rate
of a storage tank decreases as the tank capacity increases. The small fixed
roof tank and the average fixed roof tank have a turnover rate of 50 turnovers
per year. The average floating roof tank has a turnover rate of 10 turnovers
per year.
2.3.1. Fixed Roof Tank
The model fixed roof tank is not equipped with emission control
technology. The model tank representing average conditions has a capacity
of 480,747 liters (127,000 gallons) and stores a liquid with a vapor pressure
of 10.5 kPa (1.5 psia). This tank has a diameter of 8 meters (26 feet) and
a height of 10 meters (32 feet). Using equation 2-1 for fixed roof tanks,
the emissions for the model tank are 7.22 Mg/yr for 50 turnovers per year.
(See Table 2-4).
2-12
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Table 2-1. EMISSION FACTORS K, AND n
Type of roof K<.
Contact internal floating roof
Primary seal only 26.7 0.1
Primary and secondary seals 8.3 0.3
Non-contact internal floating roofs
(Primary and secondary seals) 7.3 1.2
External floating roof
Primary seal only 50.5 0.7
Primary and secondary seals 77.0 0.1
Table 2-2. SUMMARY OF EMISSION FACTORS Kp AND m FOR FLOATING ROOFS
Case
number
1
2
3
Pan roof
Roof
description
type internal floating roof
Bolted cover type internal floating roof
External
floating roof
KF
132
309
0
m
0
0.3
0
2-13
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TABLE 2-3. FITTING MULTIPLIERS
D N
tank diameter, fitting
ft multiplier
D < 20 0.5
20 £ D < 75 1
75 £ D < 100 2
100 £ D < 120 3
125 < D < 150 4
150 £ D < 175 5
175 < D < 200 6
2-14
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TABLE 2-4. MODEL TANK PARAMETERS AND EMISSIONS
ro
K-»
in
Model tank
Small tank3
Average fixed roof
Average floating roof0
Vapor
pressure
kPa (psia)
10.5
10.5
15.2
(1.5)
(1.5)
(2.2)
Capacity
liters (gal)
151,416 (40,000)
480,747 (127,000)
3,482,579 (920,000)
Emissions
Mg/yr
2.29
7.22
23.08
a5 m (17 ft) diameter; 7 m (24 ft) height; 50 turnovers/year.
b8 m (26 ft) diameter; 10 m (32 ft) height; 50 turnovers/.year."
C19 m (62 ft) diameter; 12 m (40 ft) height; 10 turnovers/year.
-------
2.3.2 Floating Roof Tank
The model floating roof tank is an external floating roof tank with
primary seals. This model tank has a capacity of 3,482,579 liters
(920,000 gallons) and stores a liquid with a vapor pressure of 15.2 kPa
(2.2 psia). It has a diameter of 19 meters (62 feet) and a height of 12 meters
(40 feet). Using equation 2-4 for floating roof tanks the emissions are
23.08 Mg/yr for 10 turnovers per year. (See Table 2-4).
2.3.3 Small Tank
The model tank representing small tanks is a fixed roof tank. The
majority of existing tanks in this size range are fixed roof tanks with no
control technology. The capacity of this tank is 151,416 liters
(40,000 gallons) and the liquid it stores has a vapor pressure of 10.5 kPa
(1.5 psia). This tank has a diameter of 5 meters (17 feet) and a height of
7 meters (24 feet). The emissions from this uncontrolled tank are 2.29 Mg/yr
for 50 turnovers per year. (See Table 2-4).
2-16
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2.4 REFERENCES FOR CHAPTER 2
1. Erickson, D.G., Emission Control Options for the Synthetic Organic
Manufacturing Industry, Hydroscience, Inc. Knoxville, Tennessee.
(Unpublished draft submitted in fulfillment of EPA contract no. 68-02-2577.)
2. Radian, Inc. The Revised Organic Chemical Producers Data Base System,
Final Interim Report. Austin, Texas, (submitted in fulfillment of EPA
contract no. 68-03-2623) March 1979.
3. Booz, Allen, and Hamilton, Foster D. Snell Division, Cost of Hydrocarbon
Emissions Control to the U.S. Chemical Industry (SIC 28), Manufacturing
Chemists Association. Florham Park, New Jersey. December 1977.
4. Letter from Rockstroh, M.A., TRW to Moody, W.T., TRW, February 1, 1980.
5. International Liquid Terminals Association. Bulk Liquid Terminals and
Storage Facilities, 1979 Directory. Washington, D.C. 1979, 85 p.
6. U.S. Environmental Protection Agency. Compilation of Air Pollution
Emission Factors. Research Triangle Park, North Carolina. Report No.
AP-42, August 1977.
7. Western Oil and Gas Association. Hydrocarbon Emissions from Fixed
Roof Petroleum Tanks, prepared by Engineering Science, Inc. Los
Angeles, California. July 1977.
8. U.S. Environmental Protection Agency. Emission Test Report-Breathing
Loss Emissions from Fixed Roof Petrochemical Storage Tanks. EMB
Report 78-OCM-5. Research Triangle Park, North Carolina. February 1979.
9. German Society for Petroleum Science and Carbon Chemistry (DGMK) and
the Federal Ministry of the Interior (BMI). Measurement and Determina-
tion of Hydrocarbon Emissions in the Course of Storage and Transfer in
Above-Ground Fixed Cover Tanks With and Without Floating Covers,
BMI-DGMK Joint Projects 4590-10 and 4590-11, Translated for EPA by
Literature Research Company, Annandale, Virginia.
10. Hydroscience, Inc. Emissions Control Options for the Synthetic Organic
Chemicals Manufacturing Industry: Storage and Handling Report, Draft
Report. Knoxville, Tennessee. October 1978.
11. U.S. Environmental Protection Agency. Measurement of Benzene Emissions
from a Floating Roof Test Tank. Publication No. EPA-450/3-79-020,
Research Triangle Park, North Carolina. June 1979.
12. See reference 10.
13. See reference 10.
2-17
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3.0 EMISSIONS CONTROL TECHNIQUES
3.1 INTRODUCTION
This chapter describes techniques for controlling emissions from VOL
storage tanks and discusses the relative emission reduction capabilities for
these control techniques.
As discussed in Chapter 2, there are three types of tanks which are
used to store volatile organic liquids: fixed roof tanks, external floating
roof tanks, and internal floating roof tanks. The various techniques
discussed in this chapter for controlling VOC emissions from these types of
storage tanks were chosen on the basis of tests conducted for EPA on a
6 meter (20 foot) diameter pilot test tank fitted with several different
floating roof and seal combinations (See Appendix A). The tests were
conducted on a storage tank containing benzene. It is believed that the
benzene test results can be applied to any tank storing VOL. The roof and
seal combinations tested and discussed in this chapter are: (1) an external
floating roof with a metallic shoe primary seal (EFRps); (2) an external
floating roof with a metallic shoe primary seal and a rim-mounted secondary
seal (EFRss); (3) a non-contact internal floating roof with shingled,
vapor-mounted primary and secondary seals (ncIFRss); (4) a contact internal
floating roof with a liquid-mounted primary seal (cIFRps); and (5) a contact
internal floating roof with a liquid-mounted primary seal and a continuous
secondary seal (cIFRss). Several roof and seal combinations which have not
been tested are also discussed.
3.2 EMISSIONS CONTROL TECHNIQUES
As discussed in Chapter 2, emissions from storage tanks are primarily a
function of tank capacity, vapor pressure of the liquid stored, and the
annual turnover rate. The VOC emissions from storage tanks increase with
increasing tank capacity, vapor pressure, and turnover rate. The emissions
reduction obtained through the use of various control techniques depends upon
3-1
-------
the type of tank and the roof and seal combination employed. A contact
internal floating roof with primary and secondary seals provides the greatest
emission reduction over all other roof and seal combinations. Emissions from
an external floating roof tank can be reduced by building a fixed roof over
the tank, which converts it to a contact internal floating roof tank. A
contact internal floating roof provides a greater emission reduction than a
non-contact internal floating roof. Installation of a secondary seal on a
floating roof with only a primary seal will also reduce the emissions.
3.2.1 Internal Floating Roofs in Fixed Roof Tanks
Fixed roof tank emissions can be reduced by installing internal floating
roofs and seals in the tanks to minimize evaporation of the product being
stored. Floating roof and seal combinations which have been tested for use
in fixed roof tanks, are (1) a non-contact internal floating roof with
shingled, vapor-mounted primary and secondary seals; (2) a contact internal
floating roof with a liquid-mounted primary seal; (3) a contact internal
floating roof with a liquid-mounted primary seal and a continuous secondary
seal. Based on these test results, a non-contact internal floating roof
with shingled, vapor-mounted primary and secondary seals is not as effective
in reducing emissions as a contact internal floating roof with a liquid-
mounted primary seal. Consequently, a larger emissions reduction can be
achieved by fitting a fixed roof tank with a contact internal floating roof
and a liquid-mounted primary seal rather than a non-contact internal floating
roof and shingled, vapor-mounted primary and secondary seals. Installation
of a continuous secondary seal on a contact internal floating roof showed
the best emissions reduction.
Several other roof and seal combinations, which have not been tested,
are also available for controlling the emissions from fixed roof tanks. Some
of these include: (1) a non-contact internal floating roof with a vapor-mounted
primary seal; (2) a contact internal floating roof with a vapor-mounted
primary seal; and (3) a contact internal floating roof with vapor-mounted
primary seal and a continuous secondary seal. Based on engineering judgment,
a non-contact roof with a vapor-mounted primary seal would be less effective
at reducing emissions than the non-contact roof tested, which was equipped
with both primary and secondary seals. In addition, information presented in
3-2
-------
2
American Petroleum Institute (API) Bulletin 2517 regarding the effectiveness
of liquid-mounted and vapor-mounted primary seals on external floating roofs
indicates that the contact internal floating with a liquid-mounted primary
seal which was tested would be more effective at reducing emissions than a
contact internal floating roof with a vapor-mounted primary seal. As was
also indicated in the testing of a contact internal floating roof, a secondary
seal over a vapor-mounted primary seal may be expected to result in even
larger emissions reduction.
3.2.2 Rim-Mounted Secondary Seals on External Floating Roofs
A rim-mounted secondary seal on an external floating roof is a continuous
seal which extends from the floating roof to the tank wall, covering the
entire primary seal. Installed over a mechanical shoe seal, this secondary
seal has been demonstrated to effectively control VOC emissions which escape
from the small vapor space between the shoe and the wall, and through any
openings or tears in the seal envelope (see Figure 2-4a). Rim-mounted
secondary seals should also be effective in controlling emissions from the
liquid- and vapor-mounted primary seals shown in Figures 2-4b, 2-4c, and
2-4d. However, their effectiveness has not been tested on external floating
roof tanks.
Another type of secondary seal, which has not been tested, is a
shoe-mounted secondary seal. A shoe-mounted seal extends from the top of the
shoe to the tank wall (see Figure 3-1). These seals do not provide protection
against VOC leakage through the envelope. Holes, gaps, tears, or other
defects in the envelope can allow direct interchange between the saturated
vapor under the envelope and the atmosphere; the wind can enter this space
through envelope defects, flow around the circumference, and exit with
saturated or near saturated VOC vapors. For these reasons a shoe mounted
secondary seal is not as effective as a rim-mounted secondary seal.
3.2.3 Fixed Roofs on External Floating Roof Tanks
Installing a fixed roof on an existing external floating roof tank would
reduce emissions by reducing the effect of wind sweeping vapors out of the
vapor space and into the atmosphere.
3-3
-------
Secondary Seal
(Wiper Type)
Floating Roof
Vapor Space
Figure 3-1. Metallic shoe seal with shoe-mounted
secondary seal.
3-4
-------
3.2.4 Contact Internal Floating Roofs in Non-Contact Internal Floating
Roof Tanks
The EPA tests on floating roofs have demonstrated that non-contact
internal floating roofs with shingled, vapor-mounted primary and secondary
seals may not be as effective in reducing emissions as contact internal
floating roofs with liquid-mounted primary seals. Based on these studies,
one emissions control technique for internal floating roof tanks is to use
contact internal floating roofs with liquid-mounted primary seals instead of
non-contact internal floating roofs with shingled, vapor-mounted primary and
secondary seals. The use of a continuous secondary seal on the contact
internal floating roof has been demonstrated to result in a"larger emissions
reduction.
Two roof and seal combinations, which have not been tested, are (1) a
contact internal floating roof with a vapor-mounted primary seal; and (2) a
contact internal floating roof with vapor-mounted primary and secondary
seals. Engineering judgement indicates that the use of either of these roof
and seal combinations would result in lower emissions than those associated
with the use of a non-contact roof with a vapor-mounted primary seal or
vapor-mounted primary and secondary seals.
3.2.5 Liquid-Mounted Primary Seals on Contact Internal Floating Roofs
p
Based on information reported in API Bulletin 2517 and engineering
judgement, vapor-mounted primary seals are not as effective in reducing
emissions as liquid-mounted primary seals. As a result, one technique to
reduce the emissions from tanks having contact internal floating roofs is to
use liquid-mounted rather than vapor-mounted primary seals.
3.2.6 Rim-Mounted Secondary Seals on Contact Internal Floating Roofs
Contact internal floating roofs, like other types of floating roofs, can
have not only a primary seal to cover the annular vapor space, but also a
rim-mounted secondary seal (Figure 3-2). This secondary seal, which is
typically a wiper seal or a resilient foam-filled seal, minimizes the effects
of the air currents inside the tank sweeping vapors out of the annular vapor
space. This type of seal is continuous and extends from the floating roof to
the tank wall, covering the entire primary seal.
3-5
-------
Secondary Seal
Primary Seal
Immersed In Liquid
Contact Type
Internal Floating Roof
Figure 3-2. Rim mounting of a secondary seal on an
internal floating roof.
3-6
-------
3,3 RETROFIT CONSIDERATIONS
This section will discuss possible considerations that fixed roof tank
owners and operators may have in retrofitting their tanks with internal
floating roofs. In addition, considerations associated with the retrofitting
of rim-mounted secondary seals on external floating roofs, and the conversion
of external floating roof tanks to internal floating roof tanks will be
discussed. Prior to retrofit construction, tank owners will have to schedule
time for the tank to be out of service. The tank and roof must then be
cleaned and degassed before workers may enter the tank to begin retrofitting.
3.3.1 Fixed Roof Tanks With Internal Floating Roofs
Several modifications may be necessary on a fixed roof tank before it
can be equipped with an internal floating roof. Tank shell deformations and
obstructions may require correction, and special structural modifications
such as bracing, reinforcing, and plumbing vertical columns may be necessary.
Anti-rotational guides should be installed to keep cover openings in alignment
with roof openings. Special vents must be installed on the fixed roof or on
the walls at the top. of the shell to minimize the possibility of VOL vapors
approaching the explosive range in the vapor space.
3.3.2 Rim-Mounted Secondary Seals on External Floating Roofs
Retrofitting problems may be encountered when a secondary seal is installed
above a primary seal. Some primary seals are designed to accommodate a large
amount of gap between the primary seal and the tank wall. Some secondary
seals may not be able to span as large a gap and, consequently, excessive
gaps may result between the secondary seal and the tank shell.
3.3.3 Fixed Roofs on External Floating Roof Tanks
In order to install a fixed roof on an existing external floating roof
tank, several tank modifications may be required. For example, special
structural modifications such as bracing and reinforcing may be necessary to
permit the external floating roof tank to accommodate the added weight of a
fixed roof.
3-7
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3.3.4 Secondary Seals on Non-Contact Internal Floating Roofs
Retrofitting problems may be encountered when installing a secondary
seal on a non-contact internal floating roof. Unlike the contact internal
floating roof, the non-contact internal floating roof does not have an outer
rim on which to attach a secondary seal. Extensive modifications to the
roof may be required in order to install a secondary seal on a non-contact
internal floating roof.
3-8
-------
3.4 REFERENCES FOR CHAPTER 3
1. U.S. Environmental Protection Agency. Measurement of Benzene Emissions
from a Floating Roof Test Tank. Publication No. EPA-450/3-79-020,
Research Triangle Park, North Carolina. June 1979.
2. American Petroleum Institute. Evaporation Loss from External Floating
Roof Tanks. API Bulletin 2517. February 1980.
3-9
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4.0 ENVIRONMENTAL ANALYSIS OF RACT
The environmental impacts that would result from implementing reasonably
available control technology (RACT) are examined in this chapter. Included
in this chapter are estimates of VOC emissions from storage tanks before and
after implementation of RACT. These emission estimates were calculated
12345
using the emission equations outlined in Chapter 2. The percent
reduction of VOC emissions that could be achieved with RACT is also presented.
The beneficial and adverse environmental impacts of RACT on air pollution,
water pollution, solid waste generation, and energy consumption are also
discussed.
4.1 AIR POLLUTION
Reasonably available control technology will affect fixed roof tanks
and external floating roof tanks. Fixed roof tanks that are equipped with
internal floating roofs are not affected. For a fixed roof tank RACT is a
contact internal floating roof with secondary seals. For an external
floating roof tank RACT is secondary seals and a fixed roof. An external
floating roof tank that has secondary seals will be retrofitted with a fixed
roof. An external floating roof with primary seals will be retrofitted with
secondary seals and a fixed roof.
Implementation of RACT will have a significant beneficial impact on air
pollution emissions from VOL storage tanks. The annual emissions from each
model tank outlined in Chapter 2 before and after control by RACT are
presented in Table 4-1. Implementation of RACT will reduce VOC emissions
from the small tank, which is a fixed roof tank, 85 percent from 2.29 Mg/yr
to 0.35 Mg/yr. Implementation of RACT will reduce emissions from the
average model fixed roof tank 92 percent from 7.22 Mg/yr to 0.58 Mg/yr.
For the average external floating roof tank with primary seals, RACT will
reduce emissions 93 percent from 23.08 Mg/yr to 1.57 Mg/yr. There are no
adverse air pollution impacts associated with RACT.
4-1
-------
TABLE 4-1. IMPACT OF RACT ON VOC EMISSIONS FROM STORAGE TANKS
Model tank
Small tank3
Average fixed roof
Average floating roofc
Emissions
before
RACT
(Mg/yr)
2.29
7.22
23.08
Emissions
after
RACT
(Mg/yr)
0.35
0.58
1.57
Emissions
reduction
(Mg/yr)
1.94
6.64
21.51
Percent
reduction
(*)
85
92
93
The capacity of this tank is 151,416 liters (40,000 gallons); the vapor
pressure is 10.5 kPa (1.5 psia); the diameter is 5 meters (17 feet); the
height is 7 meters (24 feet); the annual turnover rate is 50.
capacity of this tank is 480,747 liters (127,000 gallons); the vapor
pressure is 10.5 kPa (1.5 psia); the diameter is 8 meters (26 feet); the
height is 10 meters (32 feet); the annual turnover rate is 50.
CVOC emissions for a floating roof tank are based on an external floating
roof with primary seals. The capacity of this tank is 3,482,579 liters
(920,000 gallons); the vapor pressure is 15.2 kPa (2.2 psia); the diameter.
is 19 meters (62 feet); the height is 12 meters (40 feet); the annual
turnover rate is 10.
4-2
-------
4.2 WATER POLLUTION
Implementation of RACT would result in no adverse water pollution
impacts. Wastewater is not generated during the storage of VOL. Retrofitting
a tank with RACT will not generate wastewater.
4.3 SOLID WASTE DISPOSAL
Implementation of RACT would result in an insignificant amount of solid
waste. Normal operation of a floating roof results in wear on the roof and
especially on the seals. Solid waste in the form of worn out roofs and
seals is generated when the roof or seals of a tank are replaced.
4.4 ENERGY
The implementation of RACT calls for an emission control technique that
requires no additional energy consumption. A beneficial impact would be
experienced by saving VOL that has already been manufactured and transported
to fixed roof and external floating roof tanks.
4-3
-------
4.5 REFERENCES FOR CHAPTER 4
1. U.S. Environmental Protection Agency. Compilation of Air Pollution
Emission Factors. Research Triangle Park, North Carolina. Report
No. AP-42. August 1977.
2. Engineering Science, Inc. Hydrocarbon Emissions from Fixed-Roof
Petroleum Tanks. Western Oil and Gas Association. Los Angeles,
California. July 1977.
3. U.S. Environmental Protection Agency. Emission Test Report—Breathing
Loss Emissions from Fixed-Roof Petrochemical Storage Tanks. Research
Triangle Park, North Carolina. EMB Report 78-OCM-5, February 1979.
4. German Society for Petroleum Science and Carbon Chemistry (DGMK) and
the Federal Ministry of the Interior (BMI). Measurement and Deter-
mination of Hydrocarbon Emissions in the Course of Storage and Transfer
in Above-Ground Fixed Cover Tanks With and Without Floating Covers.
BMI-DGMK Joint Projects 4590-10 and 4590-11. (Translated for EPA by
Literature Research Company, Annandale, Virginia.)
5. U.S. Environmental Protection Agency. Measurements of Benzene Emissions
from a Floating-Roof Test Tank. Research Triangle Park, North Carolina.
Report No. EPA-450/3-79-020. June 1979.
4-4
-------
5.0 CONTROL COST ANALYSIS OF RACT
The cost of implementing RACT for volatile organic compound (VOC)
emissions from volatile organic liquid (VOL) storage tanks is presented in
this chapter. The bases for the installed capital cost estimates presented
in this chapter will be identified and discussed. This chapter will discuss
the bases for the annualized costs, including product recovery credits. The
estimated emission control costs associated with control by RACT will be
presented for each of the model tanks discussed in Chapter 2. This Chapter
will also present the cost effectiveness of RACT for each of the model
tanks.
5.1 BASES FOR INSTALLED CAPITAL COSTS
Installed capital costs represent the total investment required for
installing retrofit VOC control equipment on existing VOL storage tanks.
This includes the cost of the equipment, materials, labor for installation,
and other associated costs. The capital costs presented in this chapter
123
were obtained through vendor quotes and EPA reports. ' ' The capital costs
of implementing RACT affect two types of tanks: fixed roof tanks and external
floating roof tanks. This section describes the installed capital costs
associated with each type of tank. These costs have been updated to
4
second-quarter 1980 dollars.
5.1.1 Cost of Installing a Contact Internal Floating Roof
The installed capital costs of retrofitting a fixed roof tank with a
5
contact internal floating roof are shown in Table 5-1. These costs represent
the total cost of installing a contact internal floating roof including the
purchased equipment, equipment installation, and design engineering. These
costs do not include cleaning, degassing, and certification of the tank or
the cost-of taking the tank out of service. The installed capital cost of
the contact internal floating roof is a function of the diameter of the tank
as shown in Figure 5-1.
5-1
-------
TABLE 5-1. COST OF INSTALLING A CONTACT INTERNAL FLOATING ROOF
IN AN EXISTING FIXED ROOF TANKa
Tank u
dimensions
(meters)
8 x 12
13 x 15
14 x 17
21 x 12
27 x 15
Installed capital
cost of a
contact internal
floating roofc
$10,700
$17,600
$20,200
$37,300
$56,300
aCosts are in second-quarter 1980 dollars and do not include cleaning,
degassing, and certification.
Diameter x height.
cBased on cost of an aluminum contact internal floating roof (Ref. 5).
TABLE 5-2. COST OF INSTALLING A FIXED ROOF ON AN EXISTING
EXTERNAL FLOATING ROOF TANK9
Tank .
dimensions
(meters)
8 x 12
13 x 15
14 x 17
21 x 12
27 x 15
Installed capital
cost of
fixed roof
$ 8,700
$15,900
$18,200
$37,500
$57,600
aCosts are in second-quarter 1980 dollars and do not include cleaning.
degassing, and certification.
Diameter x height.
cBased on cost of an aluminum dome (Ref. 6),
5-2
-------
en
CJ
o
u-§
o »
o
i o
Q O
UJ __l
t/1
60
50
40
30
20
10
10 15 20
TANK DIAMETER (m)
25
30
35
Figure 5-1. Cost of installing a contact internal floating roof in an existing
fixed roof tank (second-quarter 1980 dollars).5
-------
5.1.2 Cost of Installing a Fixed Roof
The installed capital costs of retrofitting an external floating roof
tank with a fixed roof are shown in Table 5-2. These costs represent the
total cost of installing the fixed roof including the purchased equipment,
equipment installation, and design engineering. These costs do not include
cleaning, degassing, and certification of the tank or the cost for taking
the tank out of service. The installed capital cost of the fixed roof is a
function of tank diameter as shown in Figure 5-2.
5.1.3 Cost of Installing Secondary Seals
The installed capital costs of retrofitting an internal or external
floating roof with secondary seals are shown in Table 5-3 . These costs
represent the total cost of installing the secondary seal including
purchased equipment, equipment installation, and design engineering. These
costs do not include cleaning, degassing, and certification of the tank or
the cost for taking the tank out of service. The installed capital cost of
the secondary seal is a function of tank diameter as shown in Figure 5-3.
5.1.4 Cost of Cleaning, Degassing, and Certification of a Tank
The capital costs of cleaning, degassing, and certification of a
Q
storage tank are shown in Table 5-4. The storage tank must be emptied,
cleaned, and degassed before workers can begin to retrofit the tank with
RACT. This cost does not include the cost of taking the tank out of service.
The cost of cleaning, degassing, and certifying the tank is a function of
tank capacity as shown in Figure 5-4.
5.2 BASES FOR ANNUALIZED COSTS
The annualized cost of an air pollution control system is the total
annual expenditure required to build, operate, and maintain the system
minus the value of the recovered product. The annualized cost consists
of the annual capital charges, the direct operating costs, and the recovery
credits. The bases used to estimate annualized costs in this section are
presented in Table 5-5.
5-4
-------
60 I
O
CD
O
50
o
s
Q
UJ
X
40
30
CJl
I
en
O
o
U 20
D-
O
Q
10
10 15 20
TANK DIAMETER (m)
25
30
35
.Figure 5-2.
Cost of installing a fixed roof on an existing external
floating roof tank (second-quarter 1980 dollars)I6
-------
TABLE 5-3. COST OF INSTALLING A SECONDARY SEAL ON AN EXISTING INTERNAL
OR EXTERNAL FLOATING ROOF3
Tank L
dimensions
(meters)
8 x 12
13 x 15
14 x 17
21 x 12
27 x 15
Installed
capital cost
of secondary
seal 7
$ 4,380
$ 6,350
$ 7,360
$ 9,990
$12,100
aCosts are in second quarter 1980 dollars and do not include cleaning,
degassing and certification.
Diameter x height.
TABLE 5-4. COST OF CLEANING, DEGASSING, AND CERTIFICATION
OF A STORAGE TANK3
Tank ,
dimensions
(meters)
8 x 12
13 x 15
14 x 17
21 x 12
27 x 15
Tank
capacity
(liters)
602,000
2,000,000
2,610,000
4,160,000
8,590,000
Cost of cleaning,
degassing, and
certification®
$1,495
$2,300
$2,875
$3,910
$7,070
aCosts are in second-quarter 1980 dollars,
Diameter x height.
5-6
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o
o
o
LU
CO
-------
o
o
o
on
oo
8
I
I
I
1000 2000
3000 4000 5000 6000
CAPACITY OF TANK (TO3 LITERS)
I
7000 8000 9000
Figure 5->4. Cost of Cleaning, Degassing,' and Certification
(second-quarter 1980 dollars)'.8
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TABLE 5-5. BASES FOR ANNUALIZED COST ESTIMATES
Item
Cost basis
1.
2.
Annual capital charges
a. Capital recovery
Contact internal floating
roof
Fixed roof
Secondary seals
Cleaning, degassing, and
certification
b. Annual charges for taxes,
insurance, and administration
Direct operating costs
a. Annual maintenance charges
b. Annual inspection charges
3. Annual recovery credit
0.1175* x installed capital cost
0.1175. x installed capital cost
0.1628 x installed capital cost
0.1628 x installed capital cost
0.04 x total installed capital cost0
0.05 x total installed capital cost0
0.01 x total installed capital cost0
$330/Megagram
Capital recovery factor based on 20 year life and 10 percent interest rate.
DCapital recovery factor based on 10 year life and 10 percent interest rate.
fS
"Reference 9.
4
Reference 10.
5-9
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5.2.1 Annual Capital Charges
Annual capital charges consist of capital recovery and annual-charges
for taxes, insurance, and administration.
The capital recovery is obtained from annualizing the installed capital
cost for control equipment. The installed capital cost is annualized by
using a capital recovery factor (CRF). The CRF is a function of the .
interest rate and useful equipment lifetime. The capital recovery for each
component is determined by multiplying the CRF for that component by the
installed capital cost for that component. The total capital recovery is
determined by summing the capital recoveries of all the components of the
installed capital costs. The equation for the capital recovery factor is:
1(1 + i)"
CRF =
(1 + i)" -1
where i = interest rate, expressed as a decimal
n = economic life of the equipment in years.
The capital recovery factors used to annualize the intalled capital costs of
the control equipment are summarized in Table 5-5. The interest rate is
assumed to be ten percent. The useful lifetime of the installed contact
12
internal floating roof and the installed fixed roof is 20 years. The
useful lifetime of the secondary seals is 10 years. The cost of cleaning,
degassing and certification of the tank is annualized over 10 years because
that is the minimum lifetime of the secondary seals. The installed equip-
ment has no salvage value.
The annual costs for taxes, insurance, and administration are assumed
14
to be 4 percent of the installed capital cost.
5.2.2 Direct Operating Costs
The annual direct operating costs for the control equipment include the
cost of maintaining the equipment and periodic inspection of the equipment.
15
The maintenance cost is five percent of the installed capital cost. The
inspection cost is one percent of the installed capital cost.
5-10
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5.2.3 Recovery Credits
Implementation of RACT decreases the amount of VOL lost through
evaporation. The value of the VOL saved is a product recovery credit. This
product recovery credit is used in determining the net annualized cost of
the control equipment. The credit is based on a VOL value of $330/Mg.
The recovery credits for each model tank are presented in Table 5-6.
5.3 EMISSION CONTROL COSTS
This section will present and discuss the estimated emission control
costs of RACT for each of the model storage tanks developed in Chapter 2.
The installed capital costs for each model storage tank are summarized in
Table 5-7. The annualized costs for each model tank are summarized in
Table 5-8.
5.3.1 Small Model Storage Tank
The installed capital cost of RACT for the small model storage tank is
based on a fixed roof tank. This tank has a capacity of 151,416 liters
(40,000 gallons). The diameter of the tank is 5 meters (17 feet) and the
height is 7 meters (24 feet). Most tanks of this size are fixed roof tanks.
As can be seen in Table 5-7 the installed capital cost of $12,540 consists
of the installed costs for the contact internal floating roof, the secondary
seal, and the cost of cleaning, degassing, and certifying the tank. The net
annualized cost, including the product recovery credit, is $2,288 as shown
in Table 5-8.
5.3.2 Average Fixed Roof Model Storage Tank
The installed capital cost of RACT for the average fixed roof model
storage tank is $16,670. The capacity of this tank is 480,747 liters
(127,000 gallons). The diameter of the tank is 8 meters (26 feet) and the
height is 10 meters (32 feet). The installed capital cost consists of the
installed costs for the contact internal floating roof, the secondary seal,
and the cost of cleaning, degassing, and certifying the tank. The net
annualized cost, including the product recovery credit, is $1703 as shown in
Table 5-8.
5-11
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TABLE 5-6. RECOVERY CREDITS
Model
storage
tanks
Emissions3
before
RACT
(Mg/yr)
Emissions
after
RACT
(Mg/yr)
Emission
reduction
(Mg/yr)
Emission
reduction
(*)
Recovered
product
value,
($/yr)
Small tank
Average .
fixed roof
Average
floating roof
2.29
7.22
23.08
0.35
0.58
1.57
1.94
6.64
21.51
85
92
93
640
2,191
7,098
Emissions were calculated using the emissions equations outlined in Chapter 2
(Ref. 18, 19, 20, 21, 22).
Based on an average price of $330/Mg (Ref. 17).
CVOC emissions for a small tank are based on a fixed roof tank. The capacity
of this tank is 151,416 liters (40,000 gallons); the vapor pressure is 10.5 kPa
(1.5 psia); the diameter is 5 meters (17 feet); the height is 7 meters (24 feet);
the annual turnover rate is 50.
The capacity of this tank is 480,747 liters (127,000 gallons); the vapor pressure
is 10.5 kPa (1.5 psia); the diameter is 8 meters (26 feet); the height is 10 meters
(32 feet); the annual turnover rate is 50.
eVOC emissions for a floating roof tank are based on an external floating roof
with primary seals. The capacity of this tank is 3,482,579 liters (920,000 gallons);
the vapor pressure is 15.2 kPa (2.2 psia); the diameter is 19 meters (62 feet);
the height is 12 meters (40 feet); the annual turnover rate is 10.
5-12
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TABLE 5-7. INSTALLED CAPITAL COSTS'
Cost item
Installed floating roof ($)
Installed fixed roof ($)
Installed secondary seals ($)
Cleaning, degassing, and
certification ($)
Total ($)
Small
tankb
8,120
3,310
1,110
12,540
Model storage tank
Average
f i xed
roofc
10,800
4,530
1,340
16,670
Average
floating
roof"
30,660
9,020
3,450
43,130
Costs are in second-quarter 1980 dollars.
3Instaned capital costs for a small tank are based on retrofitting a fixed
roof tank with a capacity of 151,416 liters (40,000 gallons) and a diameter
of 5 meters (17 feet).
"Installed capital costs are based on retrofitting a tank with a capacity of
480,747 liters (127,000 gallons) and a diameter of 8 meters (26 feet).
Installed capital costs for a floating roof tank are based on retrofitting
a tank with a capacity of 3,482,579 liters (920,000 gallons) and a diameter
of 19 meters (62 feet).
5-13
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TABLE 5-8. ANNUALIZED CONTROL COSTS FOR MODEL STORAGE TANKS'
Model storage tank
Small
Cost parameter tank"
Average
f i xed
roofc
Average
floating
roofd
Installed capital costs
Annualized costs
Annual capital charges
12,540
16,670
43,130
Capital recovery
Taxes, insurance and
administration
Subtotal
Direct operating costs
Maintenance
Inspection
Subtotal
Total annual i zed cost
Annual recovery credit
Net annual i zed cost
1,674
502
2,176
627
125
752
2,928
(640)
2,288
2,226
667
2,893
834
167
1,001
3,894
(2,191)
1,703
5,633
1,725
7,358
2,156
431
2,587
9,945
(7,098)
2,847
Costs are in second-quarter 1980 dollars.
Annualized control costs for a small tank are based on retrofitting a fixed
roof tank with a capacity of 151,416 liters (40,000 gallons) and a diameter
of 5 meters (17 feet).
GAnnualized control costs are based on retrofitting a tank with a capacity
of 480,747 liters (127,000 gallons) and a diameter of 8 meters (26 feet).
Annualized control costs for a floating roof tank are based on retrofitting
a tank with a capacity of 3,482,579 liters (920,000 gallons) and a diameter
of 19 meters (62 feet).
eCosts in parentheses are cost credits.
5-14
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5.3.3 Average Floating Roof Model Storage Tank
The installed capital cost of RACT for the average floating roof model
storage tank is $43,130. The capacity of this tank is 3,482,579 liters
(920,000 gallons). The diameter of the tank is 19 meters (62 feet) and the
height is 12 meters (40 feet). The installed capital cost consists of the
installed costs for the fixed roof, the secondary seal, and the cost of
cleaning, degassing, and certifying the tank. The net annualized cost,
including the product recovery credit, is $2847 as shown in Table 5-8.
5.4 COST EFFECTIVENESS
Cost effectiveness is the net annual ized cost per megagram of VOC
controlled annually. The cost effectiveness of RACT for each model storage
tank is the net annualized cost for implementing RACT divided by the
emission reduction gained under RACT. The cost effectiveness of RACT is
summarized in Table 5-9.
The implementation of RACT on the small model storage tank which is a
fixed roof tank results in a net annual cost of $2,288 and an emission
reduction of 1.94 Mg/yr. This results in a net cost effectiveness of
$l,179/Mg.
The implementation of RACT in the case of the average fixed roof model
storage tank results in a net annual cost of $1,703 and an emission reduction
of 6.64 Mg/yr. This results in a net cost effectiveness of $256/Mg.
The implementation of RACT in the case of the average floating roof
model storage tank results in a net annual cost of $2847 and an emission
reduction of 21.51 Mg/yr. This results in a net cost effectiveness of
$132/Mg.
A comparison of the cost effectiveness of RACT for each model storage
tank reveals that cost effectiveness improves as the model tank size,
turnover rate, and the vapor pressure of the liquid being stored increases.
As the tank size, turnover rate, and vapor pressure of the liquid being
stored increase the emissions and the emission reduction increase
5-15
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TABLE 5-9. COST EFFECTIVENESS FOR MODEL STORAGE TANKS UNDER RACT
Small
tankb
Model storage tank
Average
fixed
roofc
Average
floating
roofd
Total annualized
cost ($)
Total annual recovery
credit ($)a
Net annualized cost ($)
Total VOL reduction
2,928
(640)
2,288
3,894
(2,191)
1,703
9,945
(7,098)
2,847
(Mg/yr)
Cost effectiveness
(annual $/Mg VOL)
1.94
1,179
6.64
256
21.51
132
Values in parentheses indicate cost credits.
n"he cost effectiveness for a small tank is based on a fixed roof tank with a
capacity of 151,416 liters (40,000 gallons) and a diameter of 5 meters (17 feet),
cThe cost effectiveness of this tank is based on a capacity of 480,747 liters
(127,000 gallons) and a diameter of 8 meters (26 feet).
The cost effectiveness of this tank is based on a capacity of 3,482,579 liters
(920,000 gallons) and a diameter of 19 meters (62 feet).
5-16
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which affects the cost effectiveness. As the tank diameter increases the
annual costs for the control equipment increases. However, the increase in
annual emission reduction is greater relative to the increase in annual
cost so that there is an overall improvement in cost effectiveness. The
cost effectiveness is also sensitive to the value of the product being
stored. The cost effectiveness of the control equipment improves as the
value of the product being stored increases.
5-17
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5.5 REFERENCES FOR CHAPTER 5
1. Letter and attachments from Roney, E.W., PETREX, Inc., (Warren, Pennsylvania),
to D.C. Ailor, TRW, Inc., (Research Triangle Park, North Carolina).
February 28, 1979. Features of PETREX Internal Floating Roofs.
2. Telecon. G.N. Houser, TRW, Inc., (Research Triangle Park, North Carolina),
to Ken Wilson, Pittsburgh Des-Moines Steel Company, (Des-Moines, Iowa).
January 25, 1979. Cost of installing an aluminum dome roof over an
external floating roof.
3. U.S. Environmental Protection Agency. Control of Volatile Organic
Emissions from Petroleum Liquid Storage in External Floating Roof Tanks.
Report No. EPA-560/2-78-047. Research Triangle Park, North Carolina.
December 1978.
4. Chemical Engineering/Economic Indicators. 87J21):7. October 20, 1980.
87(8):7. April 21, 1980. 85(0):7
5. See reference 1.
6. See reference 2.
7. See reference 3.
8. See reference 3.
9. U.S. Environmental Protection Agency. Draft Report - Volatile Organic
Compound Emissions From Volatile Organic Liquid Storage Vessels -
Background Information for Proposed Standards. EPA Contract No. 68-02-2063.
September 1980.
10. Telecon. R.E. Sommer, GCA/Technology Division, (Chapel Hill, North
Carolina), to W.T. Moody, TRW, Inc., (Research Triangle Park, North
Carolina). November 6, 1980. Value of VOL to be used in calculation of
recovery credits.
11. See reference 9.
12. See reference 9.
13. See reference 9.
14. See reference 9.
15. See reference 9.
16. See reference 9.
5-18
-------
17. See reference 10.
18. U.S. Environmental Protection Agency. Compilation of Air Pollution
Emission Factors. Research Triangle Park, North Carolina. Report
No. AP-42. August 1977.
19. Engineering Science, Inc. Hydrocarbon Emissions from Fixed-Roof
Petroleum Tanks. Western Oil and Gas Association. Los Angeles,
California. July 1977.
20. U.S. Environmental Protection Agency. Emission Test Report—Breathing
Loss Emissions from Fixed-Roof Petrochemical Storage Tanks. Research
Triangle Park, North Carolina. EMB Report 78-OCM-5, February 1979.
21. German Society for Petroleum Science and Carbon Chemistry (DGMK) and the
Federal Ministry of the Interior (BMI). Measurement and Determination
of Hydrocarbon Emissions in the Course of Storage and Transfer in
Above-Ground Fixed Cover Tanks With and Without Floating Covers.
BMI-DGMK Joint Projects 4590-10 and 4590-11. (Translated for EPA by
Literature Research Company, Anhadale, Virginia.)
22. U.S. Environmental Protection Agency. Measurements of Benzene Emissions
from a Floating-Roof Test Tank. Research Triangle Park, North Carolina.
Report No. EPA-450/3-79-020. June 1979.
5-19
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6.0 MODEL REGULATION AND DISCUSSION
6.1 MODEL REGULATION
This chapter includes a model regulation based on the "presumptive norm"
which is considered broadly representative of RACT for storage of volatile
organic liquids (VOL). The model regulation is included solely as guidance
to assist state and local agencies in drafting their own specific RACT.
Consequently, the model regulation is illustrative in nature and is not to be
construed as rulemaking by EPA.
§XX.010 Applicability
(A) This regulation applies to all volatile organic liquid storage
tanks having capacities greater than 151,416 liters (40,000 gallons)
and storing volatile organic liquids with an actual vapor pressure
greater than 10.5 kilo Pascals (1.5 psia).
(B) This regulation exempts storage tanks which are used to store
petroleum liquids, or which are equipped with an internal floating
roof.
(C) This regulation is applicable to all volatile organic liquid
storage tanks in the following areas:
§XX.020 Definitions
Except as otherwise required by the context, terms used in this
Regulation are defined in the General Statutes, the General Provisions,
or in this section as follows:
"Actual vapor pressure" means the pressure exerted by a
volatile organic liquid when it is in equilibrium with its own
vapor at the temperature of the volatile organic liquid in the
storage tank.
6-1
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"Alternative control technology" means any device or procedure
which reduces volatile organic compound emissions from storage
tanks other than floating roof control equipment.
"External floating roof" means a storage tank cover in an open
top tank consisting of a double deck or pontoon single deck which
rests upon and is supported by the liquid being contained and is
equipped with a closure seal or seals to close the space between
the roof edge and tank wall.
"Internal floating roof" means a storage tank cover that
rests partially or completely upon the liquid surface inside a
storage tank with a permanently affixed roof.
"Liquid-mounted seal" means a foam-filled or liquid-filled
primary seal mounted in contact with the liquid between the tank
wall and the floating roof continuously around the circumference
of the tank.
"Metallic shoe seal" includes, but is not limited to, a metal
sheet held vertically against the wall of the storage tank by
springs or weighted levers which is connected by braces to the
floating roof. A flexible, coated fabric (envelope) spans the
annular space between the metal sheet and the floating roof.
"Petroleum liquids" mean crude oil, condensate, and any
finished or intermediate products manufactured or extracted in a
petroleum refinery.
"Primary seal" means the lower seal forming a closure between
the wall of the storage tank and the internal floating roof.
"Secondary seal" means the upper seal forming a closure that
completely covers the space between the wall of the storage tank
and the internal floating roof.
"Storage tank" means each tank used for the storage of volatile
organic liquid, but does not include pressure vessels designed to
operate without emission to the atmosphere except under emergency
conditions.
6-2
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"Volatile organic compound" means any organic compound which
participates in atmospheric photochemical reactions or is measured
by the applicable test method or equivalent State methods.
"Volatile organic liquid" means any organic liquid that
produces volatile organic compounds as vapors.
§XX.030 Standards
(A) The owner or operator of each storage tank to which this regulation
applies shall equip each storage tank with the following:
(1) A fixed roof in combination with an internal floating roof
with a primary seal and a continuous secondary seal, meeting
the following specifications:
(a) The internal floating roof shall be of the type that
rests completely on the surface of the volatile organic
liquid inside the storage tank at all times except
during initial filling and during those intervals when
the storage tank is completely emptied and subsequently
refi11ed.
(b) The primary seal shall be a liquid-mounted primary seal
or a metallic shoe primary seal except where the floating
roof is already equipped with a primary seal. When a
primary seal is replaced the primary seal shall be
replaced with a liquid-mounted primary seal or metallic
shoe primary seal.
(c) Each opening in the internal floating roof, except for
automatic bleeder vents and leg sleeves, shall be equipped
with a cover, seal, or lid which is in a closed position
at all times (i.e., no visible gap), except when the
device is in actual use. Automatic bleeder vents are to
be closed at all times when the roof is floating, except
when the roof is being floated off or is being landed on
the roof leg supports.
6-3
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(2) An alternative control technology which achieves an overall
emission reduction efficiency of at least 90 percent by
weight. The overall emission reduction efficiency will be
determined by comparing volatile organic compound emissions
to the atmosphere resulting from use of the alternative
control technology with volatile organic compound emissions
to the atmosphere resulting from storage of the volatile
organic liquid(s) in question in a fixed roof storage tank
fitted with a conservation vent. The owner or operator shall
provide any calculations, data, or other evidence which is
necessary for determination of overall emission reduction
efficiency.
(B) The owner or operator shall maintain each storage tank so that the
following conditions are met:
(1) No visible holes, tears, or other openings in the secondary
seal or seal fabric;
(2) No volatile organic liquid accumulated on or defects in the
internal floating roof; and
(3) No visible gaps between the secondary seal and the wall of
the storage tank.
§XX.040 Inspection
(A) After installing the control equipment specified in §XX.030(A)
and prior to filling the storage tank, the owner or operator of
each affected storage tank shall visually inspect the internal
floating roof, primary seal, and secondary seal. If the owner or
operator finds holes, tears, or other openings in the primary
seal, the secondary seal, or the seal fabric, or defects in the
internal floating roof, or both, the owner or operator shall
repair the items before filling the storage tank.
(B) The owner or operator of each affected storage tank shall visually
inspect the internal floating roof, the primary seal, and the
secondary seal whenever the storage tank is emptied and degassed,
but at least once every 5 years after installing the control
6-4
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equipment. In the case of the periodic 5 year inspection, the
owner or operator shall notify the Director in writing at least
30 days prior to the refilling of each storage tank to afford the
Director the opportunity to have an observer present for inspecting
the floating roof and seals. If the owner or operator finds that
the internal floating roof has defects, the primary seal or the
secondary seal has holes, tears, or other openings in the seal or
the seal fabric, the owner or operator shall repair the items so
that they meet the requirements of §XX.030(B) before refilling the
storage tank.
§XX.050 Recordkeeping
(A) The owner or operator of each storage tank storing a volatile
organic liquid with an actual vapor pressure greater than 7.0 kilo
Pascals (1.0 psia) shall maintain a record of the volatile organic
liquid being stored, the average monthly storage temperature of
the volatile organic liquid, and the average monthly actual vapor
pressure of that liquid.
(1) For a single-component volatile organic liquid the actual
vapor pressure may be obtained from standard reference texts
or determined by ASTM (American Society of Testing and Materials)
Method D-2879-75 (1980).
(2) For a volatile organic liquid mixture, the actual vapor
pressure shall be taken as the lesser of the following:
(a) The sum of the actual vapor pressures of each component
weighted by its mole fraction, or
(b) The sum of the actual vapor pressures of each organic
component weighted by its mole fraction.
(c) Or as obtained from standard reference texts or as
measured by an appropriate method approved by the Director.
These records shall be kept for two years.
6-5
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§XX.060 Compliance Schedule
The owner or operator of a volatile organic liquid storage tank
subject to this regulation shall meet the applicable increments of
progress contained in the following schedule for installation of a
VOC control device:
(A) Submit final plans for the emission control equipment
[four months after implementation of regulation].
(B) Award contracts for the emission control equipment
[three months after submittal of final control plan].
(C) Initiate on-site construction or installation of the emission
control equipment [four months after the contract for
the emission control equipment is awarded].
(D) Complete on-site construction or installation of the emission
control equipment [two months after the on-site
construction begins].
(E) Achieve final compliance with the regulation [one month
after installing the control equipment].
6.2 DISCUSSION
6.2.1 Introduction
Adequate enforcement of the regulation consists of determining that all
tanks affected by the regulation are retrofitted to RACT and that RACT is
adequately maintained to reduce VOC emissions. Review of the records will
ensure that tanks larger than 151,416 liters (40,000 gallons) storing a
liquid with a vapor pressure greater than 10.5 kPa (1.5 psia) are equipped
with RACT. Inspection of the tanks will ensure that the internal floating
roofs and seals are being inspected and maintained as required by the
regulation.
6.2.2 Review of the Records
During an inspection by a State representative a review of the records
kept by the owner or operator of the storage tank should be made. These
records should have data on the VOL stored, the average monthly storage
6-6
-------
temperature of the liquid, and the average monthly actual vapor pressure of
the liquid at that temperature for all tanks storing a VOL with an actual
vapor pressure greater than 7.0 kPa (1.0 psia).
During a review of the records the State representative should determine
if all applicable storage tanks are in compliance. The actual vapor pressure
of the stored liquid should be calculated and recorded at the average monthly
temperature of the stored liquid. The inspector may wish to review the
method the owner or operator used to determine the actual vapor pressure.
Several methods are available for determination of the actual vapor pressure.
If the actual vapor pressure were calculated, the inspector may check that
the procedure used in the calculations is correct. In the previous CTG
documents the term "true vapor pressure" was used instead of "actual vapor
pressure." The term "actual vapor pressure" is used in this document to
explicitly describe the vapor pressure of the VOL stored as the vapor pressure
at the actual conditions at which the VOL is stored.
6.2.3 Inspections
Inspections should be made as frequently as required for adequate
enforcement of the regulation. An inspection of the facility should include
a thorough review of the records and a visual inspection of as many tanks as
the Director or inspector deems necessary. Once every five years all
affected storage tanks are required to be emptied, cleaned, and degassed and
an inspection of the control equipment made. The tank owner or operator
must notify the Director at least 30 days prior to refilling the tank. This
opportunity should be taken by the Director to inspect, from within the
tank, the internal floating roof, the primary seal, and the secondary seal.
To conduct a visual inspection of the control equipment the inspector should
be equipped with an explosion proof flashlight and other appropriate safety
equipment.
6.2.4 Equivalency
The purpose of the equivalency provision in the model regulation is to
allow a tank owner or operator to develop an equally effective alternative
volatile organic compound control technology for a specific tank or group of
tanks. An alternative control technology is any means of VOC emission
6-7
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reduction other than floating roof control equipment. If a floating roof is
to be installed as RACT then the model regulation requires that it be a
contact internal floating roof with a liquid-mounted or metallic-shoe primary
seal and a continuous secondary seal.
A tank owner or operator may be able to design an alternative technology
to control VOC's from storage tanks which will result in less cost to the
tank owner or operator. For equivalency, the tank owner or operator must
demonstrate that emissions from an alternative control technology are less
than or equal to the emissions from a storage tank which meet the requirements
of the State regulation. Equivalent vapor control technologies must be
approved by the Director.
Typical add-on alternative controls which may be demonstrated as equivalent
to RACT are carbon adsorbers, thermal and catalytic incinerators, and
refrigerated condensers. In a typical add-on control system, vapors remain
in the tank until the internal pressure reaches a preset level. A pressure
switch then activates blowers to collect and transfer the vapors. Both
carbon adsorbers and condensers allow the VOC to be recovered. Thermal and
catalytic incinerators destroy the VOC vapors.
The model regulation requires that alternative control devices reduce
emissions of VOC's by at least 90 percent. The emission reduction performance
of alternative control devices is determined by comparing the estimated VOC
emissions from the alternative control device with the uncontrolled VOC
emissions from a fixed roof storage tank with a conservation vent. The
uncontrolled emissions can be calculated from the emission equations for
i
fixed roof tanks presented in Chapter 2 and Appendix B. The uncontrolled VOC
emissions from the fixed roof storage tank are calculated based on the
actual vapor pressure of the volatile organic liquid(s) that are stored at
the anticipated highest average monthly temperature. The controlled emission
rates from the alternative control device will normally be determined from
engineering calculations or emission test data.
i
1
6-8
-------
Two typical control procedures which reduce the formation of VOC's are
pressurized tanks and refrigerated tanks. When filling a storage tank with
VOL the liquid normally displaces vapor in the tank. A pressurized tank is
designed to operate without venting the displaced vapor. The vapor remains
in the tank and the internal pressure builds up. Pressurized storage tanks
designed to operate without emissions to the atmosphere except under emergency
conditions are exempt in the model regulation. A refrigerated tank can also
be used to prevent VOC vapor formation. The vapor pressure of a VOL is
temperature dependent. If the VOL is sufficiently refrigerated the maximum
temperature of the stored VOL will be low enough to ensure that the actual
vapor pressure of the VOL is less than 10.5 kPa (1.5 psia). A storage tank
storing a VOL with an actual vapor pressure of less than 10.5 kPa (1.5 psia)
at the stored temperature is exempt in the model regulation.
6.2.5 Compliance Schedule
The compliance schedule in the model regulation is based on estimates
from equipment vendors and construction contractors on the length of time
1-12
required to retrofit a tank with RACT. This compliance schedule reflects
the time required to retrofit a single tank with RACT considering the demand
for RACT equipment as of December, 1980. The compliance schedule in the
model regulation may have to be modified for a particular area or situation
depending upon the availability of RACT equipment and the number of tanks
which must be retrofitted at any given location or plant. For example, when
the State regulations become effective there may be an immediate increase in
the demand for RACT equipment resulting in a backlog of orders. Additionally,
there may be a limited number of local construction contractors capable of
retrofitting VOL storage tanks with RACT which would also impact on the time
required to retrofit tanks with RACT. Another consideration when determining
the compliance schedule is the number of tanks at a particular site which
must be retrofitted with RACT. A tank owner or operator with a large number
of tanks may not be able to have all tanks to which RACT is applicable
install RACT concurrently. Therefore, an extended compliance schedule may
be necessary for these tank owners or operators.
6-9
-------
6.3 References for Chapter 6
1. Telecon. R.E. Sommer, GCA/Technology Division, (Chapel Hill, North
Carolina), to Mike Curtis, Conservatek, (Conroe, Texas). November 14, 1980.
Time required to purchase and install an aluminum dome for an external
floating roof tank.
2. Telecon. T. Epstein, GCA/Technology Division, (Chapel Hill, North Caroline),
to Bill Wagner, Petrex, (Warren, Pennsylvania). December 5, 1980.
Internal floating roof compliance schedule.
3. Telecon. T. Epstein, GCA/Technology Division, (Chapel Hill, North Carolina),
to Thomas Smith, Mayflower Vapor Seal Corporation, (Little Ferry, New Jersey).
December 5, 1980. Internal floating roof compliance schedule.
4. Telecon. T. Epstein, GCA/Technology Division, (Chapel Hill, North Carolina),
to Mike Curtis, Conservatek, (Conroe, Texas). December 5, 1980. Internal
floating roof compliance schedule.
5. Telecon. T. Epstein, GCA/Technology Division, (Chapel Hill, North Carolina),
to Fred Coon, Brown Minneapolis Tank Manufacturing Company, (St. Paul,
Minnesota). December 9, 1980. Internal floating roof compliance schedule.
6. Telecon. T. Epstein, GCA/Technology Division. (Chapel Hill, North Carolina),
to Ron Brown, GATX Tank Erection Corporation, (Chicago, Illinois).
December 9, 1980. Internal floating roof compliance schedule.
7. Telecon. T. Epstein, GCA/Technology Division (Chapel Hill, North Carolina)-
to Dick Reimers, Pittsburgh Des-Moines Steel Company, (Pittsburgh,
Pennsylvania). December 9, 1980. Internal floating roof compliance
schedule.
8. Telecon. T. Epstein. GCA/Technology Division, (Chapel Hill, Ncrth Carolina),
to Doyle West, Tank Service, Incorporated, (Tulsa, Oklahoma), December 9, 1980.
Internal floating roof compliance schedule.
9. Telecon. T. Epstein, GCA/Technology Division, (Chapel Hill, North
Carolina), to Jim Hart, Ultrafloat Corporation, (Houston, Texas).
December 9, 1980. Internal floating roof compliance schedule.
10. Telecon. T. Epstein, GCA/Technology Division, (Chapel Hill, North
Carolina), to LC.Creith, Altech Industries, (Allentown, Pennsylvania).
December 9, 1980. Internal floating roof compliance schedule.
11. Telecon. T. Epstein, GCA/Technology Division, (Chapel Hill, North Carolina),
to William Cook, Sandford Floating Roof, (Gushing, Oklahoma). December 9, 1980.
Internal floating roof compliance schedule.
12. Telecon. T. Epstein, GCA/Technology Division, (Chapel Hill, North Carolina),
to Victor Gazgi, Stoplos Company, (East Orange, New Jersey). December 9, 1980.
Internal floating roof compliance schedule.
6-10
-------
APPENDIX A - EMISSION SOURCE TEST DATA
-------
APPENDIX A - EMISSION SOURCE TEST DATA
A.I INTRODUCTION
This appendix describes the emissions source test data obtained by a
U.S. Environmental Protection Agency test program and used in the development
of this control techniques guideline (CTG) document. The facilities tested
are described, the test methods used are identified, and the data obtained
presented.
A.2 ESTIMATING EMISSIONS FROM FLOATING ROOF TANKS
The emissions from external and internal floating roof tanks storing
VOL were estimated using equations developed for EPA by the Chicago Bridge
and Iron Company (CBI). This section summarizes the test methods, test
results, and conclusions from this study.
A.2.1 Description of Test Facility
The VOL emissions test program was performed in a test tank which
contained benzene at CBI's research facility in Plainfield, Illinois. The
test tank was 20 feet in diameter and had a 9 foot shell height (see
Figure A-l). The lower 5'-3" of the tank shell was provided with a
heating/cooling jacket through which a heated or cooled water/ethylene
glycol mixture was continuously circulated to control the product temperature.
The effect of wind blowing across the open top of a floating roof tank
was simulated by means of a blower connected to the tank by either a 30-inch
or 12-inch diameter duct. An inlet plenum with rectangular openings was
used to distribute the air entering the test tank shell. This air exited
from the tank through a similar plenum into a 30-inch diameter exit duct.
The 12-inch diameter air inlet duct was used for the internal floating roof
simulation tests, and the 30-inch diameter inlet duct was used for the
external floating roof simulation tests (which required larger air flow
rates). While one size of inlet duct was in use, the other size was always
closed.
A-l
-------
INLET
CONCENTRATION
BLOWER
OUTLET
TEMP
OUTLET
CONCENTRATION
I
AIR FLOW
'CONTROL
VALVE
FLOW RATE
i
IN3
RIM HEATING
SUPPLY TEMP
PRODUCT
TEMPERATURE
__js"/ ^r ,k ir
BLOWER
DISCHARGE
PRESSURE
\
VON
/OFF
AIR BLOWER
FLOATING ROOF TANK
20'dia. x 5' high
SHELL HEATING SUPPLY
SHELL HEATING
SUPPLY TEMP
SHELL HEATING RETURN
Figure A-l. Simplified process and instrumentation schematic.
-------
A.2.1.1 Principal Instrumentation. The principal instrumentation
consisted of the following equipment:
1. The air speed in the inlet duct was measured with a Flow Technology,
Inc., air velometer, Model No. FTP-16H2000-GJS-12.
2. The total hydrocarbon concentrations were measured with Beckman
Instruments, Inc., Model 400, total hydrocarbon analyzers. Two
instruments were used, one for the inlet and one for the outlet.
3. The airborne benzene concentration at the test facility was
measured with an HNU Systems, Inc., portable analyzer, Model
PI 101.
4. The local barometric pressure was measured with a Fortin, Model 453,
mercury barometer.
5. During unmanned periods (nights and weekends), the barometric
pressure was measured with a Taylor Instruments, aneroid baro-
meter, Weather-Hawk Stormoscope Barometex No. 6450.
6. The temperatures were measured with copper/constantan thermo-
couples and recorded with a multipoint potentiometer, Doric
Scientific Corp., Digitrend, Model 210.
A.2.1.1.1 Analyzer calibration. Calibration gas mixtures were provided
by Matheson Gas Products Company for the purpose of calibrating both the
total hydrocarbon analyzers and the portable analyzer. Gas mixtures of
three different benzene concentrations in ultra zero air were used:
0.894 ppmv
8.98 ppmv
88.6 ppmv
The inlet air analyzer and the portable analyzer were routinely calibrated
with the 0.894 ppmv benzene calibration gas. The outlet air analyzer was
calibrated with the gas mixture closest to the concentration currently being
measured by the analyzer. Both total hydrocarbon analyzers were calibrated
at the beginning of each 8-hour shift, and the portable analyzer was calibrated
at least twice a week.
A.2.1.2 Product Description. The benzene used during the testing
program was nitration grade benzene, as defined in ASTM-D-835-77.
A-3
-------
A.2.2 Test Method
The testing was done in three phases, each using a different type of
floating roof. Phase I used a contact-type internal floating roof. Phase II
used a noncontact-type internal floating roof. Phase III used a double-deck
external floating roof.
A total of 29 tests were conducted during the three phases. Conditions
were varied to determine the following:
o Emissions from a tight primary seal.
o Emissions from a tight primary seal and secondary seal.
o Effect of gaps in the primary and/or the secondary seal.
o Contribution of deck fittings (penetrations) to emissions.
o Effect of vapor pressure (temperature) on emissions.
A.2.2.1 Description of Floating Roof and Seals.
A.2.2.1.1 Phase I. contact-type internal floating roof. A cross-
sectional view of the position of the floating roof within the test tank is
shown in Figure A-2.
A flapper secondary seal was used during some of the tests. This seal
was 15 inches wide, with internal stainless steel reinforcing fingers. A
sketch of its installation on the rim of the contact-type internal floating
roof is shown in Figure A-3.
Description of test conditions--The test conditions for Phase I are
summarized in Table A-l. This table presents a brief overview of the various
temperatures, seal configurations, and deck fitting sealing conditions for
the Phase I emissions tests.
A.2.2.1.2 Phase II, noncontact-type internal floating roof. The
internal floating roof for the Phase II tests was fitted with shingled,
flapper type primary and secondary seals. A plan view sketch of a portion
of the shingle-type seal is shown in Figure A-4. Also, the dimensions of a
single piece, or shingle, of the seal is shown. Figures A-5 and A-6
illustrate the details of the shingled, flapper type seal that was installed
in lieu of the single continuous flapper seal used during the propane/octane
tests. Figure A-5 shows a cross-sectional view of the position of the
noncontact-type internal roof within the emissions test tank.
A-4
-------
30" Diameter
\Air Duct
Removable External
Cone Roof
Air Plenum
Rim Space Heating
& Cooling
Shell
Heating £
Cooling'
Jacket
N
SR-8 Resilient
Foam Seal
Product level
\Contact-type
internal floating
roof
Figure A-2. Position of the contact-type internal floating roof
within the emissions test tank.
A-5
-------
Bottom of Air Opening
Flapper-Type
Secondary Seal
Clips on 3" Centers Fastening
'Secondary Seal to Rim of Roof
,Primary Seal Immersed in Benzene
•Contact-type
Internal Floating Roof
Figure A-3. Rim mounting of the flapper secondary seal
A-6
-------
Table A-1. SUMMARY OF TEST CONDITIONS FOR PHASE I,
CONTACT-TYPE INTERNAL FLOATING ROOF
Test
No.
EPA-1
EPA-2
EPA- 3
EPA-4
EPA- 5
EPA-6
EPA -7
EPA-8
EPA- 9
EPA-10
EPA- 11
EPA-12
EPA-13
EPA-1 4
EPA-1 5
EPA-16
Prod.
Temp.
«F)
80
80
100
100
100
100
100
80
60
75
80
75
75
75
75
75
Primary
Seal
Gaps
None
None
None
None
None
4-l«i"x72"
None
None
None
None
l-lJj"x72"
None
4-lJj"x72"
1-1TX72"
None
S-Vx24"
Sec.
Seal
None
None
None
None
None
None
None
None
None
Yes
None
Yes
Yes
Yes
None
None
Sec.
Seal
Gaps
None
None
None
None
None
None
None
None
None
None
None
None
None
4-lJjBx72'
None
None
Gage
Hatch
Unsealed
Sealed
Sealed
Sealed
Sealed
Sealed
Unsealed
Sealed
Sealed
: Sealed
Sealed
i
Sealed
Sealed
Scaled
Sealed
Sealed
Deck
Fittings
Unsealed
Unsealed
Unsealed
Sealed
Sealed
Sealed
Unsealed
Sealed
Sealed
Sealed
Sealed
Sealed
Sealed
Sealed
Sealed
Sealed
Notes
Partial Test
Partial Test
Partial Test
Partial Test
Void Test
-------
m
12
INDIVIDUAL PIECE OF SHINGLE-TYPE SEAL
Tank Shell
Rim Plate
Steel Clamp Bar
PLAN VIEW
(the same detail was used for both
primary and secondary seals)
Figure A-4. Installed shingle-type seal.
A-8
-------
30" Diameter
Air Duct
Removable External
Cone Roof
Air Plenum
S
Space Heating^
ooling Coils^.^
'
"n
ID
*>
Shell
Heating &
Cooling
Jacket' — '
\
Air Opening
Non-Contact-Type
Internal
Floating Roof
(O
CO
0)
LL
Figure A-5. Position of the non-contact-type internal floating
roof within the emissions test tank.
A-9
-------
C71
C
QJ
Q.
o
S-
•r-
<
SecondaryvSeal
Foam Tape
Steel Clamp Bar
olted Joint
Primary Seal
Foam Tape
Rim Plate
Fabric Seal for Mounting Bracket
Mounting Bracket for
Secondary Seal
Deck Skin
Deck Skin Clamp Beam Assembly
Deck Skin
\
Figure A-6. Cross-sectional view of the shingle-type
seal installation.
A-10
-------
Description of test conditions—A description of test conditions for
Phase II are summarized in Table A-2. This table presents a brief overview
of the various temperatures, seal configurations, and deck fitting sealing
condition for the Phase II emissions tests.
A.2.2.1.3 Phase III, external double deck floating roof. A cross-
sectional view of the position of the double deck roof within the test tank
is shown in Figure A-7. This figure also illustrates a metallic shoe seal
mounted on a double deck external floating roof. When a secondary seal was
required, the flapper type secondary seal from Phase I was reused. However,
in order to fit it to the double deck roof, the length of the secondary seal
had to be shortened, because of the slightly smaller diameter of the double
deck roof.
Description of test conditions—The test conditions for Phase III are
summarized in Table A-3. This table presents a brief overview of the various
temperatures, seal configurations, and deck fitting sealing condition for
the Phase III emissions tests.
A.2.3 Emissions Test Data
A.2.3.1 The Effect of Vapor Pressure on Emissions. Several emissions
tests (EPA-5, EPA-9, and EPA-15) were initially conducted to determine the
effect of the product vapor pressure, P, on the emissions rate. This relationship
was evaluated during these tests by varying the product temperature in the
pilot test tank which had been fitted with a contact-type internal floating
roof and a liquid-mounted primary seal. The product temperatures maintained
during the three respective tests were 100°F (EPA-5), 60°F (EPA-9), and 75°F
(EPA-15). Based on these tests, the emissions are directly related to the
vapor pressure function, f(P):
f(P) = 14'7
P \°.5 2
A. 2. 3. 2 The Effect of Seal Gap Area on Emissions. Several tests were
performed to determine the rates of emission as a function of seal gap area.
A-ll
-------
Table A-2. SUMMARY OF TEST CONDITIONS FOR PHASE II,
NON-CONTACT-TYPE INTERNAL FLOATING ROOF
>
>—>
ro
Test
No.
EPA- 17
EPA-18
EPA-19
EPA-20
EPA-21
EPA-22
Product
Temp.
(°F)
75
75
75
75
75
75
Primary
Seal
Gaps
None
2-1/2 "x24"
None
None
None
None
Sec.
Seal
Yes
Yes
Yes
Yes
Yes
Yes
Sec.
Seal
Gaps
None
2-1/2 "x24"
None
None
None
None
Deck
Fittings
Sealed
Sealed
Sealed
Sealed
Sealed
Unsealed
Notes
Rim space temporarily sealed
with plastic film.
Rim space temporarily sealed
with plastic film, and deck
seams also sealed.
Same conditions as EPA-20, but
with additional sealing of deck
seams.
Same conditions as EPA-21, but
with all the temporary seals
removed from the deck fitting*.
-------
Removable External
Cone Roof
Air Plenum
30" Diameter
Air Duct
Double Deck External
Floatinq Roof
Rim Space Heating
& Cooling Coils
Shell
Heating &
Cooling
Jacket
LL
Figure A-7. Position of the double deck external floating roof
within the emissions test tank.
A-13
-------
Table A-3. SUMMARY OF TEST CONDITIONS FOR PHASE III,
DOUBLE DECK EXTERNAL FLOATING ROOF
Test
No.
EPA-23
EPA-24
EPA-25P
EPA-25
EPA-26
EPA-27
EPA-28
EPA-29
Product
Temp.
(°F)
75
75
75
75
75
75
75
75
Primary
Seal
Gaps
None
2-l"x24"
2-l"x24"
2-l"x24"
2-l"x24"
None
4-1 1/2 "x7 2"
4-1 1/2 "x72"
Sea.
Seal
None
None
Yes
Yes
Yes
Yes
Yes
None
Sec.
Seal
Gaps
None
None
1-1 l/4"x
377"
None
2-1/2 "x24"
None
2-1/2 "x24«
None
Notes
Deck fittings sealed for all
tests.
-------
Table A-4 presents the seal gap areas tested and the measured emissions
for the Phase I testing of a contact-type internal floating roof. Several
conclusions are apparent from these tests:
1. A comparison of the emissions measured during tests EPA-5, EPA-9,
and EPA-15 with the emissions measured during tests EPA-11 and
EPA-16 clearly demonstrates that increasing gap areas in the
primary seal increases emissions.
2. A comparison of the emissions measured during tests EPA-5, EPA-9,
and EPA-15 with the emissions measured during test EPA-12, in
addition to a comparison of the emissions measured during tests
EPA-11 and EPA-13, demonstrates that the addition of a secondary
seal reduces emissions.
3. A comparison of the emissions measured during tests EPA-12 and
EPA-13 shows that, as long as the secondary seal has no gaps, the
emissions rate is generally independent of the amount of gap in
the primary seal.
No relationship between seal gap area and emissions could be established
from the Phase II testing of a noncontact-type internal floating roof. This
was probably a result of the shingle-type primary and secondary seals used
during the tests.
Table A-5 presents the seal gap areas and the measured emissions for
the Phase III testing of a double deck external floating roof. Several
conclusions are apparent from these tests:
1. A comparison of the emissions measured during tests EPA-23 and
EPA-24 demonstrates that small gap areas in the primary shoe seal
do not increase emissions.
2. A comparison of the emissions measured during tests EPA-23 and
EPA-27, in addition to a comparison of the emissions measured
during tests EPA-24 and EPA-25, demonstrates that the addition of
a secondary seal reduces emissions.
3. A comparison between similar cases in Tables A-4 and A-5 demon-
strates that the emissions from an external floating roof tank are
higher than the emissions from a contact-type internal floating
roof tank similarly equipped.
A-15
-------
Table A-4. MEASURED BENZENE EMISSIONS FROM EPA PHASE I TESTING
CONTACT-TYPE INTERNAL FLOATING ROOF
Test
Primary seal
number
of gaps
total gap
size
(inVft)
Secondary seal
number
of gaps
total gap
size
(1nz/ft)
Emissions
Mhs/dav^
5 mph 10 mph 15 mph
I
t—>
cr>
EPA- 5,
EPA- 9,
EPA-153
EPA- 11
EPA-16
EPA-12
EPA-13
0
4
2
0
4
— •
21
1.3
~ •
21
b
b
b
0
0
2.7
5.8
4.8
0 1.0
0 1.0
3.3
10.1
5.8
1.7
Y-7
3.7
14.0
7.2
2.3
2.3
Calculated as benzene at 1.75 psia TVP from the 20 foot diameter test tank.
No secondary seal.
-------
Table A-5. MEASURED BENZENE EMISSIONS FROM EPA PHASE III TESTING,
DOUBLE DECK EXTERNAL FLOATING ROOF
Test
Primary seal
number
of gaps
total
qap9size
(inVft)
Secondary seal
number
of gaps
total
qap9size
(inVft)
Emissions
Mbs/day^
5 mph 10 mph 15 mph
EPA-23
EPA-27
EPA-24
EPA-25
EPA-26
0
0
2
2
2
—
—
3.4
3.4
3.4
a
0
a
0
2
20
9.3
20
9.3
1.3 17.4
32
10.0
32
10.0
23
43
10.4
43
10.4
27
No secondary seal.
-------
A.2.3.3 The Development of Seal Factors (K ) and Hind Speed Exponents (n).
" " j ' """
The emission factors (K and n) for internal and external floating
roofs with primary seals and primary and secondary seals were developed from
the emissions test data previously discussed. The emissions factors for
contact internal floating roofs and external floating roofs having primary
seals and primary and secondary seals are average seal factors developed
from the emission test data and field tank gap measurement data. Using a
methodology similar to one discussed in American Petroleum Institute (API)
Publication 2517, the test data from selected EPA Phase I and Phase III
tests were weighted to represent gap measurement data collected by the
California Air Resources Board (CARB) during seal gap area surveys on
external floating roof tanks. Based on engineering judgment, it is reasonable
to assume that they are also representative of the seal gaps on internal
floating roof tanks.
Consequently, the emission factors for a contact-type internal floating
roof with a primary seal (cIFRps) were estimated based on the weighted
average of tests EPA-15 and EPA-16, which have no measurable seal gap and
1.3 square inches of seal gap per foot of tank diameter, respectively.
Because 65 percent of the tanks surveyed by CARB had no measurable gaps, the
emissions measured during test EPA-15, the test with no measurable gap, was
weighted at 65 percent. The remaining 35 percent was assigned to the emissions
measured during test EPA-16.
The General Linear Models (GLM) procedure of the Statistical Analysis
System (SAS) was employed for the analysis. Each data set was assigned a
weight value corresponding to the seal gap occurrence frequency found in the
CARB measurements. The K and n values were then determined by a linear
o
regression of the common logarithm of the emissions versus the common logarithm
of the windspeed.
Similarly, the emission factors for a contact-type internal floating
roof with primary and secondary seals (cIFRss), an external floating roof
with a primary seal (EFRps), and an external floating roof with primary and
secondary seals (EFRss) were estimated by applying appropriate weighting
factors to the EPA test data to represent the CARB tank survey data.
Table A-6 summarizes the emission factors for internal and external floating
roofs.
A-18
-------
Table A-6. SEAL LOSS FACTORS FOR AVERAGE SEAL GAPS
AND THE BASIS OF ESTIMATION^
Roof and
seal3
cIFRps
cIFRss
ncIFRss
EFRps
EFRss
EPA i
test
EPA-15
EPA-16
EPA-13
EPA-14
EPA- 17, 18
EPA-23
EPA-24
EPA- 29
EPA-25
EPA-26
Primary Secondary
seal gap, seal gap, Weighting
n2/ft tank in2/ft tank factors
diameter diameter (%)
0 no seal
1.3 no seal
21 0
21 21
0, 1.3 0, 1.3
0 no seal
3.4 no seal
14.4 no seal
3.4 0
3.4 1.3
65
35
95
5
NAb
10
85
5
75
25
Emission
Factors
Ks
26.7 0.1
8.3 0.2
7.3 1.2
50.5 0.7
77.0 0.1
cIFRps = contact internal floating roof with a primary seal; cIFRss =
contact internal floating roof with primary and secondary seals;
ncIFRss = noncontact internal floating roof with primary and secondary
seals; EFRps = external floating roof with a primary seal; EFRss =
external floating roof with primary and secondary seals.
3Not applicable. Tests weighted equally.
A-19
-------
Some of the data collected during the Phase I and Phase III tests were
not used to develop emission factors. Data collected during Phase I tests
EPA-1 through EPA-4 were not used because these tests were performed primarily
to evaluate the performance of the test facility. Data collected during
test EPA-10 were voided because the secondary seal was incompatible with
benzene. Data collected during test EPA-11 were not used because the seal
gap area was unrealistically large.
Data collected during Phase III test EPA-25P were not used because of a
failure of the secondary seal. Data collected during test EPA-28 were not
used because the seal gap area was unrealistically large.
Additionally, while the testing did not specifically address the
control effectiveness of placing a fixed roof over an external floating
roof, it is reasonable to assume that the emissions from a tank so modified
would be equivalent to the emissions from a contact internal floating roof
tank similarly equipped.
A.3 ESTIMATING EMISSIONS FROM FIXED-ROOF TANKS
As discussed in Chapter 2, the working and breathing loss equations
from AP-42 were used to estimate benzene emissions from fixed-roof tanks
storing benzene. However, breathing losses estimated using these equations
were discounted by a factor of 4, based on recent fixed-roof tank tests
conducted for the Western Oil and Gas Association (WOGA), EPA, and the
German Society for Petroleum Science and Carbon Chemistry (DGMK).
A.3.1 WOGA and EPA Studies
During 1977 and 1978, 56 fixed-roof tanks were tested for WOGA and
EPA. Fifty of these tanks, which were tested for WOGA, were located in
Southern California and contained mostly California crudes, fuel oils, and
diesel and jet fuel. These tanks were in typical refinery, pipeline, and
production services. The remaining six tanks, which were tested for EPA,
contained isopropanol, ethanol, acetic acid, ethyl benzene, cyclohexane, and
formaldehyde, respectively.
A.3.1.1 Test Methods For The HOGA and EPA Studies. The test methods
for the WOGA and EPA studies followed the methods described in the American
Petroleum Institute (API) Bulletin 2512, "Tentative Methods of Measuring
A-20
-------
Evaporative Loss from Petroleum Tanks and Transportation Equipment," Part II,
Sections E and F. This document recommends that the emissions from a fixed-
roof tank be estimated by measuring the hydrocarbon concentrations and flow
rates leaving the tank.
In the WOGA study, the volume of vapors expelled from a tank was measured
using a large and a small positive displacement diaphragm meter and a turbine
meter connected in parallel. Three meters were used to cover the potential
range of flow rates. These meters were connected to the tank with flexible
tubing. Vapor samples, which were taken from the tank using a heated sample
line, were analyzed continuously with a total hydrocarbon analyzer. With
continuous monitoring, fluctuations in the hydrocarbon concentration could
be noted. Periodically, grab samples were taken and analyzed with a gas
chromatograph, providing details on hydrocarbon speciation.
In the EPA study, the volume of vapor emitted from a tank was measured
by positive displacement meters of either the bellows or rotary-type, depending
on flow rate. Both meters were mounted so they could be manually switched
for positive and negative flow through a one-way valve which was weighted,
when applicable, to simulate the action of a pressure-vacuum valve. Vapors
from the tank were sampled using a heated sample line (to reduce condensation
in these lines), and then monitored with a total hydrocarbon analyzer calibrated
specifically for the chemical in the tank. For the formaldehyde tank, a
thermal conductivity gas chromatograph was used instead of a flame ionization
detection gas chromatograph.
A.3.1.2 Test Data and Conclusions from the WOGA and EPA Studies. In
these studies, 33 tank tests were available for correlation with the API 2518
breathing loss equation which is the basis for the breathing loss equation
in AP-42. Table A-7 lists the emissions measured during each of these tests
and the emissions calculated using the API equation. Measured versus calculated
emissions for each of these tanks are also presented in Table A-7. Of the
33 tanks tested, only two had measured emissions larger than those calculated
using the API breathing loss equation. In general, the API equation overestimated
breathing losses by approximately a factor of four.
An additional 13 tank tests from the WOGA study were available for
evaluating the emissions from a fixed-roof tank in continuous working operation.
However, because of limited and scattered data, and the fact that breathing
A-2:1
-------
Table A-7. MEASURED AND ESTIMATED BREATHING
LOSSES FROM FIXED-ROOF TANKS
Test
No. Type of product
Measured
Breathing Calculated
loss, breathing loss,
(kg/day) (kg/day)
Measured/loss
calculated loss
EPA Study:
1
2
3
4
5
6
7
8
9
10
11
12
WOGA
1
2
3
4
5
6
7
8
9
Isopropanol
Isopropanol
Ethanol
Ethanol
Ethanol
Acetic acid,
glacial
Acetic acid,
glacial
Ethyl benzene
Ethyl benzene
Cyclohexane
Cyclohexane
Cyclohexane
Study:
Crude
Crude
Fuel oil
Crude
Fuel oil
Deisel
Crude
Crude
Crude
6.8
7.7
2.7
1.5
2.6
10.9
20.4
5.0
6.8
9.1
7.7
6.3
0
0
0
0
4.5
0
60.3
43.5
54.0
(continued)
A-22
16.3
15.0
18.2
20.4
17.2
34.5
42.7
14.5
16.8
70.1
56.3
61.7
3.6
8.6
10.0
1.4
30.4
14.5
175.2
72.2
187
0.42
0.52
0.15
0.08
0.15
0.32
0.48
0.34
0.41
0.13
0.14
0.10
0.00
0.00
0.00
0.00
0.01
0.00
0.34
0.60
0.29
-------
Table A-7. Concluded
Test
No.
10
11
12
13
14
15
16
17
18
19
20
21
Average
Type of product
Jet component
Crude
Crude
Crude
Fuel oil
Crude
Crude
Crude
Crude
Crude
Crude
Diesel
Measured
Breathing Calculated
loss, breathing loss,
(kg/day) (kg/day)
0
0
2.3
62.6
0.9
20
102
261
0
2.7
0
5.4
13.2
3.2
15.4
49.0
10.4
30.0
134.3
172.5
6.4
64.5
0.5
14.1
Measured/loss
calculated loss
0.00
0.00
0.15
1.28
0.09
0.67
0.76
1.51
0.00
0.04
0.00
0.39
0728
A-23
-------
losses could not be separated out of the emissions, no suggestions were made
for developing a new correlation for working losses from fixed-roof tanks.
A.3.2 DGMK Study
During 1974 and 1975, emissions tests were conducted by the German
Society for Petroleum Science and Carbon Chemistry (DGMK) on a 3,000 cubic
meter fixed-roof tank storing gasoline. The tests were designed to evaluate
the effects of both climate and method of operation on the emissions from
the tank over a long period of time.
A.3.2.1 Test Methods for the DGMK Study. A large number of parameters
were measured and recorded during the tests, including the volume of vapor
leaving the tank, concentration of hydrocarbons in the emitted vapor, gas
pressure and temperature in the tank, liquid temperature, liquid level,
ambient temperature, air pressure, and solar radiation. In addition, using
discontinuous measurements, vapor samples were analyzed in a laboratory for
speciation and total hydrocarbons.
The flow rates from the tank were measured using three bellows gas
counters connected to the breathing valves on the tank. Three gas counters
were used so that extremely high and extremely low volume flows could be
determined. The three bellows gas counters were installed on the roof of
the tank. The pressure drop across the counters was 20 mm water on the
column at full load. The additional pressure drop caused by the counters
was compensated for by installing a new set of breathing valves.
An electrically heated sampling line was connected from the outlet of
each of the bellows gas counters to the measurement room. The vapors were
analyzed with a flame ionization detector (FID) for total hydrocarbon content.
Grab samples were also analyzed using two different gas chromatographic
techniques to determine total hydrocarbons and individual components.
A.3.2.2 Test Data and Conclusions from the DGMK Study. Table A-8
presents the measured breathing and working losses and the losses calculated
using the API 2518 breathing and working loss equations. A comparison of
the measured and calculated losses indicates that the measured breathing
losses are only 24 percent of the estimated breathing losses. In addition,
measured working losses are approximately 96 percent of the working losses
estimated using API 2518.
A-24
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Table A-8. COMPARISON OF MEASURED LOSSES WITH
THOSE CALCULATED USING API 2518
Time
period
(days)
Breathing
69
46
45
160
Measured
(Mg)
lossb
2.0
0.6
0.7
3.3
Calculated3
(Mg)
6.6
3.9
3.2
13.7
Measured/cal cul ated
0.30
0.15
0.22
0.24
Working loss
69
46
45
160
12.2
11.3
5.9
29.4
12.2
12.9
5.6
30.7
1.0
0.88
1.05
0.96
aAPI Bulletin 2518, "Evaporation Loss from Fixed-Roof
Tanks."
Includes withdrawal loss.
A-25
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A.4 REFERENCES FOR APPENDIX A
1. American Petroleum Institute. Evaporation Loss from External
Floating-Roof Tanks. API Publication 2517. February 1980.
2. Letter from Tedone, M., TRW, Incorporated, to VOL Docket.
August 12, 1980. Emission Factors for VOL and Benzene.
A-26
-------
APPENDIX B - EXAMPLE CALCULATIONS
FOR DETERMINING REDUCTION IN EMISSIONS
FROM IMPLEMENTATION OF RACT
-------
APPENDIX B
EXAMPLE CALCULATIONS FOR DETERMINING REDUCTION IN
EMISSIONS FROM IMPLEMENTATION OF RACT
The purpose of this appendix is to provide example calculations and
procedures for computing the emissions before and after the implementation
of reasonably available control technology (RACT) for volatile organic
liquid storage tanks. The equations used to calculate emissions from
storage tanks were presented in Chapter 2. They are presented again in this
appendix with an example calculation to illustrate the calculation of
emissions from storage tanks. To calculate an emission reduction one first
calculates the emissions before implementation of RACT. The emissions after
the installation of RACT are then calculated. The emission reduction is
computed by subtracting the emissions before implementation of RACT from the
emissions after the implementation of RACT. The emissions from the imple-
mentation of RACT are from a contact internal floating roof tank with
primary and secondary seals. The emissions before the implementation of
RACT are typically from a fixed roof tank or an external floating roof tank.
The parameters needed to calculate the emissions from a fixed roof tank
are the molecular weight, the average monthly vapor pressure of the liquid
being stored, the tank diameter, height, and capacity, the average diurnal
temperature change, the color of the paint on the tank, and the annual
turnover rate for the tank. The parameters needed to calculate the emissions
from a floating roof tank (internal or external) are the molecular weight,
the vapor pressure, the density of the liquid being stored at the average
monthly temperature of the liquid, the diameter and capacity of the tank,
the average windspeed at the tank site, and the annual turnover rate for the
tank. The average diurnal temperature change and the average windspeed in
the area where a tank is located can be obtained from historical meteorological
data. The tank parameters such as diameter, height, capacity, average
B-l
-------
turnover rate, and color of external paint on the tank can be obtained from
the tank owner or operator. The properties of the liquid being stored such
as average monthly vapor pressure, density, and molecular weight at the
average monthly temperature of the liquid can be obtained from standard
reference texts.
Example Calculation
An example calculation is presented assuming the storage tank before
implementation of RACT is a fixed roof tank and implementation of PACT
changes this tank to an internal floating roof tank with primary and
secondary seals.
For this illustration a storage tank with a capacity of 6,427,376 liters
(1,697,933 gallons), a diameter of 25.9 meters (85 feet), and a height of
12.2 meters (40 feet) is used. The tank is storing methyl ethyl ketone
(2 butanone) having an average monthly liquid temperature of 25°C (77°F).
At this temperature the liquid has an actual vapor pressure of 13.4 kPa
(1.9 psia), a density of 0.805 kg/ml (6.72 Ib/gal), and a molecular weight
of 98.96 kg/kg mole (Ib/lb mole). This tank has an average annual turnover
rate of 15 and is located in an area where the average diurnal temperature
change is 11°C (20°F).
Calculation of Emissions Before Implementation of RACT
The equations used in determining the example emission estimates before
implementation of RACT are for fixed roof tanks as follow:
l- LT=LB+LW 6
2. LB = 9.15 x 10" M f(P) D1-7^0-51!0-^
3. Lw = 1.09 x 10" MPKnVN
where, Lj = total loss (Mg/yr)
Ln = breathing loss (Mg/yr)
LW = working loss (Mg/yr)
M = molecular weight of product vapor (Ib/lb mole); 98.96 Ib/lb mole
P = true vapor pressure of product (psia); 1.9 psia
f(P) = (i/TTlp- >°'68 ; °'2733
D = tank diameter (ft); 85 feet
H = average vapor space; assumed tank height/2 (ft); 20 feet
T = average diurnal temperature change in °F; 20°F
B-2
-------
F = paint factor; 1.0 for clean white paint
C = tank diameter factor;
for diameter >_ 30 feet, C = 1
for diameter < 30 feet,
C = 0.0771 D - 0.0013 (D2) - 0.1334
K = turnover factor
for turnovers > 36, kn = 18°6* N
for turnovers <_ 36 k = 1
N = number of turnovers per year ; 15
V = tank capacity (gal) ; 1,697,933 gallons
Substituting the numbers into the equations yields:
LB = (9.15 x 10"6)(98.96)(.2733)(85)1.73(20)°.51(20)°.5(1.0)(1.0)
LB =9.72 Mg/yr
Lw = (1.09 x 10"8)(98.96)(1.9)(1.0)(1,697,933)(15)
Lw =52.20 Mg/yr
LT = LB + Lw = 61.92 Mg/yr
If the storage tank before the implementation of RACT is an external
floating roof tank, then the emission estimates are calculated using the
equations presented in Chapter 2 for floating roof tanks. The equations for
calculating emissions from an external roof tank are the same as the equations
presented in the next section for calculating emissions from an internal
floating roof tank except that different values for certain parameters
(i.e., KS Kp, m, n) are used in the equations. :
Calculation of Emissions After Implementation of RACT
The equations used in determining the example emission estimates from
implementation of RACT are for a contact internal floating roof with primary
and secondary seals and are given by the following equations for emissions
from floating roof tanks:
i. LT =LW + LS + LF
2. Lw = 0.943 QCWL/2205D
3. Ls = Ks VnMvD f(P)/2205
4' LF = NKVmM f(P)/2205
B-3
-------
where LT = total loss (Mg/yr)
LW = withdrawal!oss (Mg/yr)
LS = seal loss (Mg/yr)
Lp = fitting loss (Mg/yr)
f(P) = 0.068P/((1 + (1 - 0.068P)0-5)2); 0.0346
MV = molecular weight of product vapor (Ib/lb mole); 98.96 Ib/lb
mole
P = true vapor pressure of product (psia); 1.9 psia
D = tank diameter (ft); 85 feet
WL = density of product (Ib/gal); 6.72 Ib/gal
V = average wind speed for the tank site (mph); 10 mph
Q = product average throughput (bbl/yr); 606,400 bbl/yr
(tank capacity (bbl/turnover) x Turnovers/yr)
KS = seal factor; 8.3 (see Table 2-1)
KF = fitting factor; 132 (ses Table 2-2)
n = seal wind speed exponent; 0.3 (see Table 2-1)
m = fitting wind speed exponent; 0.0 (see Table 2-2)
c = product withdrawal shell clingage factor bbl/(ft2 x 103);
use 0.0015 bbl/(ft2 x 103) for VOL in a welded steel tank
with light rust
N = fitting multiplier; 2 (see Table 2-3)
Substituting the numbers into the equations yields:
Lw = (0.943)(606,400)(.0015)(6.72)/(2205)(85)
Lw =0.03 Mg/yr
Ls = (8.3)(10)°-3(98.96)(85)(0.0346)/(2205)
Ls =2.19 Mg/yr
LF = (2)(132)(10)°'°(98.96)(0.0346)/(2205)
LF =0.41 Mg/yr
LT = Lw + Ls + LF = 2.63 Mg/yr
Emission Reduction from Implementation of RACT
The errission reduction is computed by subtracting the emissions after
implementation of RACT from the emissions before implementation of RACT.
B-4
-------
ER = 61.92 - 2.63 = 59.29 Mg/yr
ED(«) = ^-^ (100) = 96%
K 61.92
The total VOC emission reduction from all affected storage tanks in a
State is the sum of the emission reductions from each storage tank to which
RACT applies which is in the areas of nonattainment with the national ambient
air quality standard for ozone.
B-5
------- |