EPA-453/R-94-001
Alternative Control Techniques Document:
Volatile Organic Liquid Storage
in Floating and Fixed Roof Tanks
Emissions Standards Division
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
January 1994
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TABLE OF CONTENTS
Page
1.0 INTRODUCTION .................... !_!
2.0 STORAGE TANK DESCRIPTIONS .............. 2-1
2.1 INTRODUCTION .................... 2-1
2.2 TYPES OF STORAGE TANKS ............ 2-1
2.2.1 Fixed-Roof Tanks ............ 2-1
2.2.2 'External Floating Roof Tanks .-.-. . . -. 2-2
2.2.3 Internal Floating Roof Tanks ...... 2-2
2.2.4 Horizontal Tanks ............ 2-5
2.3 TYPES OF FLOATING ROOF PERIMETER SEALS .... 2-5
2.3.1 External Floating Roof Seals ...... 2-5
2.3.2 Internal Floating Roof Seals ....... 2-8
2.4 TYPES OF FLOATING ROOF DECK FITTINGS ..... 2-10
2.4.1 External Floating Roof Fittings .... 2-10
2.4.2 Internal Floating Roof Fittings .... 2-13
2.5 REFERENCES .................. 2-33
3.0 EMISSION ESTIMATION PROCEDURES AND REGULATORY BASELINE 3-1
3 . 1 INTRODUCTION ........ " ......... 3^
3.2 STORAGE TANK EMISSIONS AND EMISSION EQUATIONS . 3-1
3.2.1 Fixed-Roof Tank Emissions ....... 3-1
3.2.2 Horizontal Tank Emissions ..... . ] 3.4
3.2.3 External Floating Roof Tank Emissions .* 3-5
3.2.4 Internal Floating Roof Tank Emissions . .3-15
3.3 REGULATORY BASELINE .............. 3.27
3.3.1 Petroleum Liquid Storage NSPS
(Subpart K) ......... ...'.-.. 3-28
3.3.2 Petroleum Liquid Fixed- Roof Tank CTG . . 3-28
3.3.3 Petroleum Liquid External Floating
Roof Tank CTG' ...... ......... 3-29
3.3.4 Subpart Ka NSPS ........ '.'.'.'.'. 3-29
3.3.5" Volatile Organic Liquid NSPS ...... 3-30
3.3.6 Results, of. Regulatory Actions ...'!.' 3-31
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TABLE OF CONTENTS (continued)
Bage
3..4 MODEL LIQUIDS AND MODEL TANKS 3-32
3.4.1 Model Liquids 3-32
3.4.2 Model Tanks . 3-33
3.5 REFERENCES - ...... 3-40
4.0 CONTROL TECHNIQUES 4-!
4.1 OVERVIEW *...... „ ........... .,_ . . . . 4-1
4.2 FIXED ROOF TANKS ....... 4-4
4.3 INTERNAL FLOATING ROOF TANKS ! 4.5
4.3.1 Controls for Fitting Losses 4-6
4.3.2 Controls for Seal Losses 4-6
4.3.3 Deck Seam Losses 4-8
4.4 EXTERNAL FLOATING ROOF TANKS 4-8
4.4.1 Controls for Fitting Losses 4-10
4.4.2 Controls for Withdrawal Losses 4-12
4.4.3 Controls For Rim or Seal Losses .... 4-12
4.5 VAPOR CONTROL OR RECOVERY SYSTEMS ON FIXED
ROOF TANKS "4-14
4.5.1 Carbon Adsorption 4-14
4.5.2 Oxidation Units '.'.'. 4-15
4.5.3 Refrigerated Vent Condensers ...'... 4-15
4.5.4 Control Efficiencies of Vapor
Recovery or Control Systems 4-16
4.6 RETROFIT CONSIDERATIONS 4_16
4.6.1 Fixed Roof Tanks With Internal
Floating Roofs 4-17
4.6.2 Secondary Seals on Existing Internal
Floating Roofs 4-17
4.6.3 Liquid-Mounted Seals on Existing
Internal Floating Roofs ..:..... 4-17
4.6.4. Rim-Mounted Secondary Seals on
External Floating Roofs ' 4-is
4.6.5 Self-Supporting Fixed Roofs on
External Floating Roof Tanks- 4-18
4.7 PROBLEM LIQUIDS AND MATERIALS OF
CONSTRUCTION 4 ia
4.8 REFERENCES 4 19
iii
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TABLE OF CONTENTS (continued)
Page
5.0 ENVIRONMENTAL IMPACTS OF CONTROL OPTIONS 5-1
5.1 ENVIRONMENTAL IMPACTS • 5-1
5.2 FIXED ROOF MODEL TANKS 5-1
5.2.1 Emissions Reductions 5-2
5.2.2 Secondary Impacts 5.3
5.3 INTERNAL FLOATING ROOF TANKS • 5-5
5.3.1 Emissions Reductions 5-6
5.3.2 Secondary Impacts 5-6
5.4 EXTERNAL FLOATING ROOF TANKS 5-6
5.4.1 Emissions Reductions 5-7
5.4.2 Secondary Impacts 5-7
5.5 NATIONWIDE IMPACTS OF CONTROL OPTIONS ..... 5-8
5.5.1 Fixed-Roof Tanks 5-10
5.5.2 Internal Floating Roof Tanks ...... 5-10
5.5.3 External Floating Roof Tanks 5-11
5.6 REFERENCES 5.34
6.0 COST ANALYSIS OF CONTROL OPTIONS 6-1
6.1 INTRODUCTION 6-1
6.2 EQUIPMENT COSTS '. 6-2
6.3 MODEL TANK COSTS ....... 6-4
6.4 NATIONWIDE COST IMPACTS -6-5
6.5 UNCERTAINTIES 6-6
6.6 REFERENCES ......... 6-33
APPENDIX A a ,
APPENDIX B '.'.'.'.'.'.'.'.'.'.'. B-l
iv
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LIST OF FIGURES
Page
Figure 2-1. Typical fixed roof tank 2-16
Figure 2-2. External floating roof tank (pontoon type) 2-17
Figure 2-3. External floating roof tank (double-deck
type) 2-18
Figure 2-4. Internal floating roof tanks 2-19
Figure "2-5. Typical underground storage tank .... . 2-20
Figure 2-6. A typical above-ground horizontal tank . . 2-21
Figure 2-7. Primary seals 2-22
Figure 2-8. Rim-mounted secondary seals on external
floating roofs 2-23
Figure 2-9. Metallic shoe seal with shoe-mounted
secondary seal 2-24
Figure 2-10. Typical flotation devices and
perimeter seals for internal floating
roofs 2-25
Figure 2-11. Rim-mounted secondary seal on internal
floating roof 2-26
Figure 2-12. Access hatch 2.27
Figure 2-13a. Unslotted guide-pole well 2-28
Figure 2-13b. Slotted guide-pole/sample well ...... 2-28
Figure 2-14a. Gauge-float well 2-29
Figure 2-l4b. Gauge-hatch/sample well 2-29
Figure 2-15. Vacuum breaker 2-30
Figure 2-16a. Overflow roof, drain .' 2-31
Figure 2-l6b. Roof leg 2_31
Figure 2-17. Rim vent. 2.32
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LIST OF FIGURES (continued)
Page
Figure 3-1. Total roof fitting loss factor
for typical fittings on pontoon
floating roofs 3-12
Figure 3-2. . Total roof fitting loss factor for
typical fittings on double-deck
floating roofs 3-13
Figure 3=3. Total deck fitting loss factor as a
function of tank diameter, for a
self-supporting fixed roof 3-25
Figure 3-4. Total deck fitting loss factor as a
function of tank diameter, for a
column-supported fixed roof 3-26
Figure 5-1. The effects' of turnover rates and stored
liquid vapor pressure on emissions
from fixed-roof tanks storing a model
VOL .- 5-12
Figure 5-2. The effects of turnover rates and stored
liquid vapor pressure on emissions
from fixed-roof tanks storing a model
crude oil 5-13
Figure 5-3. The effect of the control options on
emissions from fixed-roof tanks
storing VOL as a function of tank
volume 5-14
Figure 5-4. The effect of the control options on
emissions from fixed-roof tanks storing
VOL as a function of tank volume 5-15
Figure 5-5. The effect of the control options on
emissions from fixed-roof tanks storing
VOL as a function of tank volume ..... 5-16
Figure 5-6.' The effect of. the control options on
emissions from internal floating roof
tanks storing VOL as a function of tank
volume .................. 5-17
Figure 5-7. The effect of the control options on
emissions from internal floating roof
tanks storing crude oil as a function
of tank volume .. . 5-18
VI
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Figure 5-8.
LIST OF FIGURES (continued)
The effect of the control options on
emissions from external floating roof
tanks equipped with mechanical shoe
seals as a function of tank volume . ,
Page
5-19
Figure 5-9. The effect of the control options on
emissions from external floating roof
tanks equipped with vapor-mounted
primary seals as a function of tank
volume . . . ... ....". Y .""."". ".' . "."" 5-20
Figure 6-1. The cost-effectiveness of control
options on fixed-roof tanks storing VOL
as a function of tank volume : 6-7
Figure 6-2. The cost-effectiveness of control options
on fixed-roof tanks storing VOL as a
function of tank volume 6-8
Figure 6-3. The cost-effectiveness of control options
on fixed-roof tanks storing VOL as a
function of tank volume 6-9
Figure 6-4. The cost-effectiveness of control options
on fixed-roof tanks storing VOL as a
function of tank volume 6-10
Figure 6-5. The cost-effectiveness of control options
on fixed-roof tanks storing VOL as a
function of tank volume 6-11
Figure 6-6. The cost-effectiveness of control options
on fixed-roof tanks storing VOL as a
function of tank volume 6-12
Figure 6-7. The cost-effectiveness of control options
on fixed-roof tanks storing crude oil as a
function of tank volume 6-13
Figure 6-8. The cost-effectiveness of control options
on fixed-roof tanks storing crude oil as
a function of tank volume 6-14
Figure 6-9. The cost-effectiveness of control options
on fixed-roof tanks storing crude oil as
a function of tank volume 6-15
vii
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LIST OF FIGURES (continued)
Figure 6-10.
Figure 6-11.
Figure 6-12.
Figure 6-13.
Figure 6-14.
Figure 6-15.
Figure 6-16.
Figure 6-17.
Figure 6-18.
Figure 6-19.
Figure 6-20.
The cost-effectiveness of control options
on fixed-roof tanks storing crude oil as
a function of tank volume
The cost-effectiveness of control options
on fixed-roof tanks storing crude oil as a
function of tank volume .
The cost-effectiveness of control options
on' fixed-roof tanks storing-crude- oil as a
function of tank volume
The cost-effectiveness of control options
on internal floating roof tanks storing
VOL as a function of tank volume
The cost-effectiveness of control options
on internal floating roof tanks storing
VOL as.a function of tank volume .....
The cost-effectiveness of control options
on internal floating roof tanks storing
VOL as a function of tank volume
The cost-effectiveness of control options
on internal floating roof tanks storing
crude oil as a function of tank volume . .
The cost-effectiveness of control options
on internal floating roof tanks storing
crude oil as a function of tank volume . .
The cost-effectiveness of control
options on internal floating roof tanks
storing crude oil as a function of tank
volume
The cost-effectiveness of control
options on external floating roof
tanks equipped with mechanical shoe
primary seals storing VOL as a function
of tank volume and vapor pressure . . . .
The cost-effectiveness of control
options on external floating roof
tanks equipped with mechanical shoe
primary seals storing crude oil as a
function of tank volume and vapor
pressure
Page
6-16
6-17
6-18
6-19
6-20
6-21
6-22
6-23
6-24
6-25
6-26
viii
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LIST OF FIGURES (continued)
Figure 6-21,
The cost-effectiveness of control options
on external floating roof tanks equipped
with vapor-mounted primary seals storing
VOL as a function of tank volume and
vapor pressure
Figure 6-22,
The cost-effectiveness of control options
on external floating roof tanks equipped
with vapor-mounted primary seals storing
crude oil as a function of tank volume •
and vapor pressure
Page
6-27
6-28
IX
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LIST OF TABLES
- TABLE 3-1.
TABLE 3-2.
TABLE 3-3.
TABLE 3-4.
TABLE 3-5.
TABLE 3-6.
TABLE 3-7.
TABLE 3-8.
TABLE 3-9.
TABLE 3-10.
TABLE 3-11.
TABLE 3-12.
TABLE 4-1.
TABLE 4-2.
TABLE 4-3.
TABLE:4-4.
Page
PAINT FACTORS FOR FIXED-ROOF TANKS .... 3-3
RIM SEAL LOSS FACTORS, KR AND N 3.7
ROOF FITTING LOSS FACTORS, KFa, K^, AND
m, AND TYPICAL NUMBER OF ROOF
FITTINGS, NT 3.9
TYPICAL NUMBER OF VACUUM BREAKERS, NFfi,
AND ROOF DRAINS, N^ -.- . -. . . . . . ... 3-10
TYPICAL NUMBER OF ROOF LEGS, NF8 3-n
AVERAGE CLINGAGE FACTORS (C) bbl/1,000 ft2 3-16
PHYSICAL PROPERTIES OF SELECTED
PETROCHEMICALS 3.3.7
TYPICAL NUMBER OF COLUMNS AS A FUNCTION
OF TANK DIAMETERS 3-22
EFFECTIVE COLUMN DIAMETER (Fc) 3-22
SUMMARY OF DECK FITTING LOSS FACTORS
(KF) AND TYPICAL NUMBER OF FITTINGS (NF) . 3-24
FIXED ROOF MODEL TANKS 3.34
ANALYTICAL FRAMEWORK FOR INTERNAL
FLOATING ROOF AND EXTERNAL FLOATING
ROOF MODEL PLANTS 3.39
FIXED ROOF AND INTERNAL FLOATING ROOF
TANKS--HIERARCHY OF EQUIPMENT TYPES
BASED ON EMISSIONS RATE 4-2
EXTERNAL FLOATING ROOF TANKS -- HIERARCHY
OF EQUIPMENT TYPES BASED ON EMISSIONS
RATE 4_3
"CONTROLLED" AND "UNCONTROLLED" INTERNAL
FLOATING ROOF DECK FITTINGS 4.7
INTERNAL FLOATING ROOF RIM SEAL SYSTEMS
SEAL LOSS FACTORS AND CONTROL
EFFICIENCIES
4-9
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LIST OP TABLES (continued)
TABLE 4-5.
TABLE 4-6.
TABLE 5-1.
TABLE 5-2.
' TABLE 5-3.
TABLE 6-1.
TABLE 6-2.
TABLE 6-3.
TABLE 6-4.
TABLE B-l.
i
TABLE B-2.
TABLE B-3.
TABLE B-4.
TABLE B-5.
"CONTROLLED" AND "UNCONTROLLED" EXTERNAL
FLOATING ROOF DECK FITTINGS
EXTERNAL FLOATING ROOF TANK SEAL SYSTEM
CONTROL.EFFICIENCIES
NATIONWIDE ENVIRONMENTAL IMPACTS OF THE
FIXED-ROOF TANK CONTROL OPTIONS . . .
NATIONWIDE ENVIRONMENTAL IMPACTS OF--THE
INTERNAL FLOATING ROOF TANK CONTROL
OPTIONS ;
NATIONWIDE SECONDARY ENVIRONMENTAL
IMPACTS OF THE INTERNAL FLOATING ROOF TANK
CONTROL OPTIONS
ESTIMATED INSTALLED CAPITAL COST OF
INTERNAL FLOATING ROOFS (-1991 DOLLARS) . .
NATIONWIDE COST IMPACTS FOR FIXED-ROOF
TANK OPTIONS ......
NATIONWIDE COST IMPACTS FOR INTERNAL
FLOATING ROOF TANK OPTIONS ....
NATIONWIDE COST IMPACTS FOR EXTERNAL
FLOATING ROOF TANK OPTIONS
INCREMENTAL COST-EFFECTIVENESS WITHIN
EACH CONTROL OPTION FOR FIXED-ROOF
TANKS . .
INCREMENTAL COST-EFFECTIVENESS BETWEEN
EACH CONTROL OPTION FOR FIXED-ROOF
TANKS ' . . .
INCREMENTAL COST-EFFECTIVENESS WITHIN
EACH CONTROL OPTION FOR INTERNAL FLOATING
ROOF TANKS . . . .
INCREMENTAL COST-EFFECTIVENESS BETWEEN
EACH CONTROL OPTION FOR INTERNAL FLOATING
ROOF TANKS- .. .. .... . . ., ., .. . . . m . .
INCREMENTAL COST-EFFECTIVENESS WITHIN
EACH CONTROL OPTION FOR EXTERNAL FLOATING
ROOF TANKS .
4-11
4-13
5-21
5-22
5-23
6-29
6-30
6-31
6-32
B-2
B-3
3-4
B-5
B-6
xi
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1.0 INTRODUCTION
The purpose of this document is to provide information on
alternative control -techniques - (ACT) for volatile organic
compound (VOC) emissions from the storage of volatile organic
liquids. The control techniques described in this document
are applicable to storage tanks in all industries; however,
most tanks described in this document are located at petroleum
refineries, chemical plants, pipelines, and liquid terminals.'
This document contains information on emissions,
controls, control options, and costs that States can use in
developing rules based on reasonably available control
technology (RACT). The document presents options only, and
does not contain a recommendation on RACT.
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2.0 STORAGE TANK DESCRIPTIONS
2.1 INTRODUCTION
This chapter presents basic descriptions of fixed-roof
tanks, internal and external floating roof tanks, and horizontal
tanks. In addition, the chapter provides descriptions of
perimeter seals and fittings for both internal and external
floating roofs.
2.2 TYPES OF STORAGE TANKS
Three types of vessels are of concern in examining control
techniques for volatile organic liquid (VOL) storage vessels:
1. Fixed-roof tanks;
2. External floating roof tanks; and
3. Internal floating roof tanks.
These tanks are cylindrical in shape with the axis oriented
perpendicular to the foundation. The tanks are almost
exclusively above ground, although below-ground vessels and
horizontal vessels (i.e., with the axis parallel to the
foundation)- also can be used in VOL service. Controls that apply
to horizontal tanks primarily are limited to vapor recovery
systems as discussed in Chapter 4. Vapor recovery systems are
capable of collecting and processing VOC vapors and gases
discharged" from the^storage vessel so as to reduce their emission
to the atmosphere.
2 .2 .1.. Fixed-Roof Tanks -
Of currently used tank'designs, the- fixed-roof tank is the
least expensive-- to construct, and; is generally considered the
minimum acceptable equipment for storing VOL's. A typical
fixed-roof tank,, which is. shown in Figure• 2-1, consists of a
cylindrical steel, shell with a cone- or dome-shaped, roof that.is
2.-1
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permanently affixed to the tank shell. Most recently built tanks
are of all-welded construction and are designed to be both
liquid- and vapor-tight. However, older tanks may be of riveted
or bolted construction and may not be vapor-tight. A breather
valve (pressure-vacuum valve), which is commonly installed on
many fixed-roof tanks, allows the tank to operate at a slight
internal pressure or vacuum. Breather vents are typically set at
0.19 kiloPascals (kPa) (0.75 inches of water column [in. w-.c.])
on atmospheric pressure fixed-roof tanks.1 Because this valve
prevents the release of vapors during only very small changes in
temperature, barometric pressure, or liquid level, the emissions
from a fixed-roof tank can be appreciable. Additionally, gauge
hatches/sample wells, float gauges, and roof manholes provide
accessibility tp these tanks and also serve as potential sources
of volatile emissions.
2.2.2 External Floating Roof Tanks
Floating roofs are constructed of welded steel plates and
are of three general types: pan, pontoon, and double deck.
Although numerous pan-type floating roofs are currently in use,
the present trend is toward pontoon and double-deck floating
roofs.2 These two most common types of external floating-roof
tanks are shown in Figures 2-2 and 2-3. Manufacturers supply
various versions of these basic types of floating roofs, which
are tailored to emphasize particular features, such as full
liquid contact, load-carrying capacity, roof stability, or
pontoon arrangement.2 An external floating roof tank consists of
a cylindrical steel 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 slides
against the- tank wall as the roof is- raised "or lowered.
2-2•3 Internal Floating Roof Tanks
There are two-basic types of internal floating roof tanks:
tanks in which the fixed roof is supported by vertical columns
within the tank; and tanks, with a, self-supporting/ fixed- roof and,
2-2.
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no internal support columns. The fixed roof is not necessarily
free of openings but does span the entire open plan area -of the
vessel. Fixed roof tanks that have been retrofitted to employ an
internal floating roof are typically of the first type, while
external floating roof tanks that have been converted to an
internal floating roof tank typically have a self-supporting
roof. Tanks initially constructed with both a fixed roof and an
internal floating roof may be of either-type. An internal
floating roof tank has both a permanently affixed roof and a roof
that floats inside the tank on the liquid surface (contact roof)
or is supported on pontoons several inches above the liquid
surface (noncontact roof). The internal floating roof rises and
falls with the liquid level. Typical contact and noncontact
internal floating roof tanks are shown in Figures 2-4a and 2-4b,
respectively.
Contact-type roofs include (1) aluminum sandwich panel roofs
with a honeycombed aluminum core floating in contact with the
liquid; (2) resin-coated, fiberglass-reinforced polyester (FRP),
buoyant panels floating in contact with the liquid; and (3) pan-
type steel roofs, floating in contact with the liquid with or
without the aid of pontoons. The majority of contact internal
floating roofs currently in VOL service are pan-type steel or
aluminum sandwich panel type. The FRP roofs are less common..
Several variations of the pan-type contact steel roof exist.
The design may include bulkheads or open compartments around the
perimeter of the roof so that any liquid that may leak or spill
onto the deck is contained. Alternatively, the bulkheads may be
covered to form sealed compartments (i.e., pontoons), or the
entire pan may be covered to form a sealed, double-deck, steel
floating roof. Generally, construction is of welded steel.
Noncontact-type, roofs typically consist of an aluminum deck
laid on an aluminum grid framework supported above the liquid
surface by tubular aluminum pontoons. The- deck, skin for the
noncontact-type floating roofs is typically constructed of rolled
aluminum sheets (about 1.5 meters [m] [4.9 feet (ft)] wide, 2.3 m
[.?•. 5 ft] long and: 0.58-millimeter- [mm] [0.023 inches (in)]
2-3
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thick). The overlapping aluminum sheets are joined by bolted
aluminum clamping bars that run perpendicular to 'the. pontoons to
improve the rigidity of the frame. The deck skin seams can be
metal on metal or gasketed with a polymeric material. The
pontoons and clamping bars form the structural frame of the
floating roof. Deck.seams in the npncontact internal floating
roof design are a source of emissions. Aluminum sandwich panel
contact-type internal floating roofs also share this design
feature. The sandwich .panels are joined with bolted mechanical
fasteners that are similar in concept to the noncontact deck skin
clamping bars. Steel pan contact internal floating roofs are
constructed of welded steel sheets and therefore have no deck
seams. Similarly, the resin-coated, reinforced fiberglass panel
roofs have no apparent deck seams. .The panels are butted and
lapped with resin-impregnated fiberglass fabric strips. The
significance of deck seams with respect to emissions from
internal floating roof tanks is addressed in Chapter 4.
The internal floating roof physically occupies a finite
volume of space that reduces the'maximum liquid storage capacity
of the tank. When the tank is 'completely full, the floating roof
touches or nearly touches the fixed roof. Consequently, the
effective height of the tank decreases, thus limiting the storage
capacity. The reduction in the effective height varies from
about 0.15 to 0.6 m (0.5 to 2 ft), depending on the type and
design of the floating roof employed.
All types of internal floating roofs, like external floating
roofs, commonly incorporate flexible perimeter seals or wipers
that slide against the tank wall as the roof moves up and down.
These seals are discussed in detail in Section 2.3.2.
Circulation vents and an open vent at the top of the fixed roof
are generally provided to minimize the accumulation of
hydrocarbon vapors .in concentrations approaching the flammable
range.
Flame arrestors are an option that can be used to protect
the vessel from fire or explosion. ' When these are used,,
2-4
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circulation vents are not provided. Tank venting occurs through
a pressure -vacuum vent and flame arrest or.
2.2.4 Horizontal Tanks
Horizontal tanks are constructed for both above-ground and
underground service. Figures 2-5 and 2-6 present schematics of
typical underground and above-ground horizontal tanks.
Horizontal tanks are usually constructed of steel, steel with a
fiberglass overlay, or fiberglass -reinforced polyester.
Horizontal- tanks "are -generally --small -storage tanks with -
capacities of less than 75,710 liters (L) (20,000 gallons [gal]).
Horizontal tanks are constructed such that the length of the tank
is not greater than six times the diameter to ensure structural
integrity. Horizontal tanks are usually equipped with pressure -
vacuum vents, gauge "hatches and sample wells, and manholes to
provide accessibility to these tanks. In addition, underground
tanks are cathodically protected to prevent corrosion of the tank
shell. Cathodic protection is accomplished by placing
sacrificial anodes in the tank that are connected to an impressed
current system or by using galvanic anodes in the tank.
The potential emission sources for above-ground horizontal
tanks are the same as those for fixed- roof tanks. Emissions from
underground storage tanks are mainly associated with changes in
the liquid level in the tank. Losses due to changes in •
temperature or barometric pressure are minimal for underground
tanks because the surrounding earth limits the diurnal
temperature change and changes in the barometric pressure would
result in only small losses.
2.3 TYPES OF FLOATING ROOF PERIMETER SEALS '
2 -3'. 1 External Floating Roof
Regardless of tank design, a floating roof requires a device
to seal the gap between- the tank wall and the roof perimeter. A
seal, or in the- case- of a- two-seal system,, the lower (primary)
seal, can be made from, various materials suitable for organic
liquids service. The basic designs available for external
floating roof, seals are- (1): mechanical (metallic) shoe; seals,
(2) liquid- filled seals, and (3); (vapor- or liquid- mounted)
2-5
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resilient foam-filled seals. Figure 2-7 depicts these three
general types of seals.
One major difference in seal system design is the way in
which the seal is mounted with respect to the liquid.
Figure 2-7c shows a vapor space between the liquid surface and
seal, whereas in Figures 2-7a and 2-7d, the seals rest on the
liquid surface. These liquid-filled and resilient foam-filled
seals are classified as liquid- or vapor-mounted seals, depending
on their location Mechanical - shoe-seals are.-different in design
from liquid-filled or resilient foam-filled seals and cannot be
characterized as liquid- or vapor-mounted. However, because the
shoe and envelope combination precludes contact between the
annular vapor space above the liquid and the atmosphere (see
Figure 2-715) , the emission rate of a mechanical shoe seal is
closer to that of a liquid-mounted seal than that of a
vapor-mounted seal.
2-3.1.1 Mechanical Shoe Seal. A mechanical shoe seal,
otherwise known as a "metallic shoe seal" (Figure 2-7b), is
characterized by a metallic sheet (the "shoe") that is held
against the vertical tank wall. Prior to 40 CFR 60 Subpart Ka,
the regulations did not specify a height for mechanical shoe
seals, however, shoe heights typically range from 75 to 130
centimeters (cm) (30 to 51 in). 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 (the
"envelope") is suspended from the shoe seal to the floating roof
to form a vapor barrier over the annular space between the roof
and the primary seal.
2-3.1.2 Liquid-Filled Seal. A. liquid-filled, seal
(Figure 2-7a) may consist of a tough fabric band or envelope
filled with a liquid, or it may consist of a-, flexible polymeric
tube 20. to: 25 cm (a, to 10 in) in, diameter filled with-a. liquid
and sheathed with a tough fabric, scuff band. The liquid is
• commonly a petroleum distillate or other .liquid that will not
contaminate the stored product if. the tube ruptures.
2-6
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Liquid-filled seals are mounted on the product liquid surface
with no vapor space below the seal.
2.3.1.3 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
minor imperfections in tank dimensions and in the tank shell.
The foam log may be mounted above the liquid surface
.. .(yapar-mounted) .or on the liquid surface (liquid-mounted).
Typical vapor-mounted and liquid-mounted seals are presented in
Figures 2-7c and 2-7d, respectively.
2.3.1.4 Secondary Seals on External Floating Roofs. A
secondary seal on an external floating roof consists of a
continuous seal mounted on the rim of the floating roof and
extending to the tank wall, covering the entire primary seal.
Secondary seals are normally'constructed of flexible polymeric
materials. Figure 2-8 depicts several primary and secondary seal
systems.. An alternative secondary seal design incorporates a
steel leaf to bridge the gap between the roof and the tank wall.
The leaf acts as a compression plate to hold a polymeric wiper
against the tank wall.
A rim-mounted secondary seal installed over a primary seal
provides a barrier for volatile organic compound (VOC) emissions
that escape from the small vapor space between the primary aeal
and the wall and through-any openings or tears in the seal
envelope of a metallic-shoe seal (Figure 2-8). Although not
shown in Figure 2-8, a secondary seal can be used in conjunction
with a weather shield as described in the following section.
Another type of secondary seal is a shoe-mounted secondary
seal. A shoe-mounted seal extends from the top of the shoe to
the tank wall (-Figure 2-9) . These seals do not provide
protection against VOC leakage through;the envelope. Holes,
gaps, tears; or other defects in the envelope can permit: direct
exchange between the saturated vapor under the envelope and the
atmosphere. Wind can enter this space through envelope defects,
2-7
-------
flow around the circumference of the tank, and exit saturated or
nearly saturated with VOC vapors.
2-3.1.5 Weather Shield. A weather shield (Figures 2-7a,
2-7c, and 2-7d) may be installed over the primary seal to protect
it from deterioration caused by debris and exposure to the
elements. Though the NSPS's 40 CFR 60 Subparts Ka and Kb do not
accept the installation of a weather shield as equivalent to a
secondary seal, there are a large number of existing tanks not
affected-by-the-NSPS that have this- configuration. Typically, a
weather shield is an arrangement of overlapping thin metal sheets
pivoted from the floating roof to ride against the tank wall.
The weather shield, by the nature of its design, is not an
effective vapor barrier. For this reason, it differs from the
secondary seal. Although the two devices are conceptually
similar in design> they are designed for and serve different
purposes.
2.3.2 Internal Floating Roof Seals
Internal floating roofs typically incorporate one.of two
types of flexible, product-resistant seals: resilient
foam-filled seals or wiper seals. Similar to those employed on
external floating roofs, each of these seals closes the annular
vapor space between the edge of the floating roof and the tank
shell to reduce evaporative losses. They are'designed to
compensate for small irregularities in the tank shell and allow
the roof to freely move up and down in the tank without binding.
2.3.2.1 Resilient Foam-Pilled Seal. A resilient
foam-filled seal used on an internal floating roof is similar in
design to that described in Section 2.3.1.3 for external floating
roofs. Two types of resilient foam-filled seals for internal
floating roofs are shown in Figures 2-10a and 2-lOb. These seals
can be mounted either in contact with the liquid surface
(liquid-mounted) or several centimeters above the liquid surface
(vapor-mounted).
Resilient foam-filled seals work because of the expansion
and contraction of a resilient material to maintain contact with
the tank shell while accommodating varying annular rim space:
2-3
-------
widths. These seals consist of a core of open-cell foam
encapsulated in a coated fabric. The elasticity of the foam core
pushes the fabric into contact with the tank shell. The seals
are attached to a mounting on the deck perimeter and are
continuous around the roof circumference. Polyurethane- coated
nylon fabric and polyurethane foam are commonly used materials
For emission control, it is important that the mounting and
radial seal joints be vapor- tight and that the seal be in
, subst.antial contac_t with the tank shell . 5
2.3.2.2 Wiper Seals. Wiper seals are' commonly used as
primary seals for internal floating roof tanks. This type of
seal is depicted in Figure 2-lOc.
Wiper seals generally consist of a continuous annular blade
of flexible material fastened to a mounting bracket on the deck
perimeter that spans the annular rim space and contacts the tank
shell. The mounting is such that the blade is flexed, and its
elasticity provides a sealing pressure against the tank shell
Such seals are vapor -mounted; a vapor space exists between the
ixquid stock and the bottom of the seal. For emission control
it is important that the mounting be vapor- tight, that the seal
be continuous around the circumference of the roof, and that the
blade be in substantial contact with the tank shell 5
Three types of materials are commonly used to make the
wipers, one type consists of a cellular, elastomeric material
tapered in cross section with the thicker portion at the
mounting. Buna-N rubber is a commonly used material. All radial
joints in the blade are joined.5
A second type of wiper seal construction uses. a foam core
wrapped witir a coated fabric. Polyurethane on nylon fabric and
polyurethane foam are common materials. The core provides the
flexibility: and. support,., while the fabric provides the vasor
barrier and wear surface-.5'
A. Ctiird type of. wiper:- seal, consists of overling
rom*!1^^- (ttia*1-t*«-*>- Shingle-type" seals
from the wiper seals discussed previously in that they do not
provide a, continuous, vapor barrier.
2-9-
-------
2.3.2.3 Secondary Seala for Internal Floating Roof
Secondary seals may be used to provide some additional
evaporative loss control over that achieved by the primary seal.
The secondary seal is mounted to an extended vertical rim plate,
above the primary seal, as shown in Figure 2-11. Secondary seals
can be either a resilient foam-filled seal or an elastomeric
wiper seal, as described in Sections 2.3.2.1 and 2.3.2.2,
respectively. For a given roof design, using a secondary seal
further limits the. operating....capacity, of a..tank- due,.to the need
to keep the seal from interfering with the fixed-roof rafters
when the tank is filled. Secondary seals are not commonly used
on internal floating roof tanks' that are not affected by the NSPS
(40 CFR 60 Subpart Kb).5
2.4 TYPES OF FLOATING ROOF DECK FITTINGS
2-4.1 External Floating Roof PJttinag
Numerous fittings penetrate or are attached to an external
floating roof. These fittings accommodate structural support
members or allow for operational functions. These fittings can
be a source of emissions in that they must penetrate the deck.
Other accessories are used that do not penetrate the deck and are
not, therefore, sources of evaporative loss. 'The most common
fittings relevant to controlling vapor losses are described in
the following sections.
2-4.1.1 Accesg Hatches.2 An access hatch consists of an
opening in the deck with a peripheral vertical well attached to
the deck and a removable cover to close the opening as shown in
Figure 2-12. An access hatch is typically sized to allow workers
and materials to pass through the deck for construction or
servicing. The cover can rest directly on the well, or a -
gasketed connection can be used to reduce evaporative loss.
Bolting the cover to the well reduces losses further.
2-4.1.,2 Slotted and Unslotted Guide-Pole Wella/Sanmle>
Hells.2 Antirotation devices are used to prevent floating roofs
from rotating and potentially damaging roof equipment and seal
systems. A commonly used antirotation device is a guide pole
chat is fixed at the top and bottom of .the tank (Figures 2-l3a
2-10
-------
and 2-13b). The guide pole passes through a well on the deck.
Rollers attached to the top of the well ride on the outside
surface of the guide pole to prevent the floating roof from
rotating. The guide pole well has a sliding cover to accommodate
limited radial movement of the roof. The sliding cover can be
equipped with a gasket between the guide polefand the cover to
reduce evaporative loss. The guide pole well can also be
equipped with a gasket between the sliding cover and the top of
,the .well to . reduce evaporative loss.-•- Openings -a-t - the top and
bottom of the guide pole provide a means of hand-gauging the tank
level and of taking bottom samples. In the slotted guide
pole/sample well application, the well of the guide pole is
constructed with a series of holes or slots that allow the
product to mix freely in the guide pole and thus have the same
composition and liquid level as the product in the tank. To
reduce evaporative loss caused by these openings, a removable
float is sometimes placed inside the guide pole.
2.4.1.3 Gauge Float Wells.2 Gauge floats are used to
indicate the level of stock within the tank. These usually
consist of a float residing within a well that passes through the
floating deck, as shown in Figure 2-14a. The float is connected
to an indicator on the exterior of the tank via a tape passing
through a guide system. The float rests on the stock surface
within the'well, which is-enclosed by a sliding cover. A cable
attaches to the float and passes through a hole located at the
center of" the cover. As with similar deck penetrations, the well
extends into the liquid stock on noncontact floating decks.
Evaporation loss can be reduced by gasketing and/or bolting the
connection between the cover and the rim of the well.
2.4.1.4 Gauge Hatch/Sample Wellg.2 Gauge hatch/sample
wells provide access for hand-gauging the level of stock in the
tank and for taking thief samples, of the tank contents. A gauge
hatch/sample well consists of, a pipe sleeve through the deck and
•a self-closing gasketed cover, as shown in Figure 2-l4b. Gauge
hatch/sample wells are usually located under the gauger's
platform, which is mounted on- the top of the tank, shell. The
2-11,
-------
cover may have a cord attached so that it can be opened from the
ganger's platform. A gasketed cover reduces evaporative losses.
2.4.1.5 Vacuum Breakers.2 The purpose of a vacuum breaker
is to allow for the exchange of vapor and air through the
internal floating roof tank during filling and emptying. Vacuum
breakers are designed to be activated by. changes in pressure or
liquid level, or strictly by mechanical means.
Mechanical vacuum breakers are activated when the external
floating deck- is -either- -being-- landed^ on-- its legs or floated o-ff- -
its legs to equalize the pressure of the vapor space across the
deck. This is accomplished by opening a deck penetration that
usually consists of a well formed of pipe or framing on which
rests a cover (Figure 2-15). Attached to the underside of the
cover is a guide leg long enough to contact the tank bottom as
the external floating deck approaches the tank bottom. When in
contact with the tank bottom, the guide leg mechanically opens
the breaker by lifting the cover off the well. When the leg is
not contacting the bottom, the penetration is closed by the cover
resting on the well. The closure may or may not have a gasket
between the cover and neck. Since the purpose of the vacuum
breaker is to allow the free exchange of air and/or vapor, the
well does not extend appreciably below the deck. The gasket on
the underside of the cover, or conversely on the upper rim of the
well, provides a-small measure of emission control during periods
when the roof is free floating and the breaker is closed.
2-4.1.6 Roof Drains.2 Roof drains permit removal of
rainwater from the surface of floating roofs. Two types of
floating roof drainage systems are currently used: closed and
open. Closed drainage systems carry rainwater from the surface
of the floating roof to the outside of the tank through a
flexible or articulated piping system or through a flexible hose
system located below the deck in the product space. Sinca
product does not enter this closed drainage system, there is no
associated evaporative loss. Open drainage systems, consisting
of an open pipe that extends a short distance below the bottom,of
the deck, permit rainwater to drain from,the surface of the
2-12
-------
floating roof into the product. Since these drainpipes are
filled with product to the product level in the tank, evaporative
loss occurs from the top of the drainpipes. Open drainage
systems are commonly used on double-deck and pontoon floating
roofs. Two types of roof drains are commonly used in open
drainage systems: flush drains and overflow drains. Flush
drains have a drain opening that is flush with the' top surface of
the double deck. They permit rainwater to drain into the
product. Overflow drains (Figure 2-16a) consist of.a drain
opening that is elevated above the top surface of the floating
roof, thereby limiting the maximum amount of rainwater that can
accumulate on the floating roof and providing emergency drainage
of rainwater. They are normally used in conjunction with a
closed drainage system. Some open-roof drains are equipped with
an insert to reduce the evaporative loss.
2.4.1.7 Roof Leaa.2 To prevent damage to fittings
underneath the deck and to allow for tank cleaning or repair,
supports are provided to hold the deck at a predetermined
distance off the tank bottom. These supports consist of
adjustable or fixed legs attached to the floating deck as shown
in Figure 2-16b. For adjustable legs, the load-carrying element
passes through a well or sleeve-in the deck.
2.4.1.8 Rim Vents.2 Rim vents are normally supplied only
on tanks equipped with a mechanical shoe primary seal. The rim
vent is connected to the rim vapor space by a pipe and releases
any excess pressure or vacuum that is present (Figure 2-17). The
rim vapor space is bounded by the floating roof rim, the primary-
seal shoe, the liquid surface, and the primary-seal fabric. Rim
vents usually consist of weighted, pallets that rest on the
gasketed surface.
•
2 ..4'.2. Internal Floating Roof Fittings5
Numerous, fittings penetrate- or are attached to an internal
floating; roof. These fittings serve to accommodate structural
support members or-to allow for operational functions. The
fittings can be a source of evaporative loss in that they require
penetrations in, .the. deck.- Other accessories are used, that do not
2.-13.
-------
penetrate the deck and are not, therefore, sources of .evaporative
loss. The most common fittings relevant to controlling vapor
losses are described in the following sections.
The access hatches, roof legs, vacuum breakers, and
automatic gauge float wells for internal floating roofs are
similar fittings to those described earlier for fitting control
of external floating roofs.
2.4.2.1 Column Wells.5 The most common fixed-roof designs
(Figure 2-1) are normally supported from inside the tank by means
of vertical columns, which necessarily penetrate an internal
floating deck. (Some fixed roofs are entirely self-supporting
and, therefore, have no support columns.) Columns are made of
pipe with circular cross sections or of structural shapes with
irregular cross sections (built-up). The number of columns
varies with tank diameter from a minimum of 1 to over 50 for very
large tanks.
The columns pass through deck openings via peripheral
vertical wells. With noncontact decks, the well should extend
down into the liquid stock. Generally, a closure device exists
between the top of the well and the column. Several proprietary
designs exist for this closure, including sliding covers and
fabric sleeves, which must accommodate the movements of the deck
relative to the column as the liquid level changes. A sliding
cover rests on the upper rim of the column well (which is '
normally fixed to the roof) and bridges the gap or space between
the column well and the column.. The cover, which has a cutout
or opening, around the column, slides vertically relative to the
column as the roof raises and lowers. At the same time, the
cover slides horizontally.relative to the rim of the well, which
is fxxed to the roof. A gasket around the" rim of the well
reduces emissions from this fitting. A flexible fabric sleeve
seal between the rim of the well and the column (with a cutout
or opening to allow vertical motion of the' seal relative to the
columns) similarly accommodates limited horizontal motion of the
roof relative to the column. A third design combines the
advantages of the flexible- fabric sleeve- seal with a well that
2-14
-------
excludes all but a small portion of the liquid surface from
direct exchange with the vapor space above the floating roof.
2.4.2.2 Sample Pipes or wella.5 A sample well may be
provided to allow liquid stock sampling. Typically, the well is
funnel-shaped to allow for easy entry of a sample thief. A
closure is provided, which is typically located at the lower.end
of the funnel and which frequently consists of a horizontal piece
of fabric slit radially to allow thief entry. The well should
extend- into the liquid -stock: on- noncontact decks-. ~- - . - ~
Alternately, a sample well may consist of a slotted pipe
extending into the liquid stock equipped with an ungasketed or
gasketed sliding cover.
2.4.2.3 Ladder Weila.5 Some tanks are equipped with
internal ladders that extend from a manhole in the fixed roof to
the tank bottom. The deck opening through which the ladder
passes is constructed with similar design details and
considerations to those for column wells, as discussed in
Section 2.4.2.2.
2-15
-------
RIM VENT
PONTOON ACCESS HATCH
WtNO GIRDER
VACUUM BREAKER
RIM SEAL
PONTOON ROOF LEG
CENTER ROOF LEG
ACCESS HATCH
GAUGER'S PLATFORM
GAUGE-FLOAT WELL
GUIDE POLE
GAUGE-HATCH/
SAMPLE WELL
ROLLING LADDER
ROOF DRAIN
LEG FLOOR PAD'
Figure 2-2. External floating roof tanJc (pontoon- type)
2-17
-------
RIM VENT
WIND GIRDER
VACUUM BREAKER
ROOF LEG
RIM SEAL
ACCESS HATCH
EMERGENCY ROOF DRAIN
GAUGER'S PLATFORM
GAUGE-FLOAT WELL
GUIDE POLE
GAUGE-HATCH/
SAMPLE WELL
ROLLING LADDER
ROOF DRAIN
LEG FLOOR PAD
Figure: 2.~3 ,,, External, floating, roof: cank- (double-deck type)
2-181
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Prim«yS«l
Manhole
Pwiphmrt
Root Vent
PrimuySMi
Manhoto
aim
tank Suoocit
Column w«n
Column Well
a. contact: intamal floating roof
Tank Support
Column win
Column W««
HMI POnBORB
b. iToncontact intarnal floating roof
Figure-2-4. Internal floating roof, tanks
2-19
-------
v«min*
Figure 2-5. Typical underground storage tank.3
2-20
-------
Manhole
Sourca: Ecology and Environment Inc., 1963.
Pressure
vacuum vent
•Containment
dikes
Figure 2-6. A typical above-ground horizontal tank.4
2-21
-------
• Tank Wall
. /—Metallic
Vy Weather Shield
Floating Roof
Scuff Band
- Liquid Filled
Tube
a. Liquid-filled seal with
weather shield.
Tank Wall
Floating Roof
b. Metallic shoe seal.
r—Tank Wall
\ T
Metallic
Weather Shield
Floating Roof
Seal Fabric
c. Vapor-mounted resilient
foam-filled seal with:
weather shield.
T—Tank Wall
M
/ Metallic
^y£ Weather Shield
v»
• Floating Roof
• Seal Fabric
• Resilient
Foam
d. Liquid-mounted resilient
foam-filled seal with weather
shield..
Figure 2,-7'. Primary seals.
2-22
-------
fitm-Mounied
Secondary Seat
Floating Roof
•Tank Wail
•ffim-Moumed
Secondary Seal
Floating Roof
Scuff Band
Liquid-Fined
Tuba
Shorn s«al with rim-mountad
sacondary s*al.
b. Liquid-fillad saal with rim-
mountad secondary saal.
Tank Watt
RIm-Mount»d
Secondary Seal
Floating Roof
>— Seal Fabric
Resilient
Foam Log
Vapor Spaca
-Tank Wail
Rtm-Mounted
Secondary Seat
Floating Roof
>-Seal Fabric
G.
Rrailivat foaa saal (vapor-
mounrad) wi-tii rim-aountad
secondary saal.
d. Raailiant foam a«al (liquid
aouxread) wita ria-aounrad
sacondary saal.
Figure 2-8 (a-d). Rim-mounted secondary seals on
external, floating roofs.
2-23
-------
Secondary Seal
(Wiper Type)
Envelope
Shoe
Floating Roof
Vapor Space
Figure 2-9, Metallic shoe seal with shoe-mounted secondary seal
2-24
-------
a. Resilient foam-filled seal (vapor-mounted).
•Tank Wail
Vapor
Liquid
Resilient foam-filled seal
•Contact internal floating roof
(aluminum sandwich panel roof)
7
b. Resilient foam-filled seal (liquid mounted).
Tank Wall
•Contact internal floating roof
(pan-type steel roof)
Resilient foam-filled seal
Liquid
c. Eiastomeric wiper seal.
•Tank Wail
•Eiastomeric wiper seal
Liquid
Vapor
Non-contact internal floating roof
•Pontoon Pontoon
•Metal seal ring
17
Figure 2-10.
Typical flotation devices and perimeter seal
for internal floating roofs. '
2-25
-------
Secondary seal
Primary seal immersed in VOL
ontact type internal floating roof
Figure 2-11. Rim-mounted secondary seal on
internal floating roof.
2-26
-------
Handle
Sotted cover
Gasket
Liquid level
Weil
Floating roof
Figure 2-12. Access hatch.2
2-27
-------
> Unsioned guide pole
• Sliding cover
•Well
Liquid level
Floating roof
Figure 2-13a. Unslotted guide-pole well.'
- Slotted guide pole
;
0°
0
n
n u
0
n u
n
0 ^
/
\
^— Sliding cover
/— Roating roof
/
— Liquid level
>
c
Opening
Figure 2-13b. Slotted guide-pole/sample well.2
2-28
-------
Sliding cmtr
•w««
^— Ptertngro* ^
Uquidtov*
-Float
Figure 2-14a. Gauge-float well.
S«H doting.
Coiti
QaskM
Figure 2-14b. Gauge-hatch/sample well.2
2-29
-------
Cover
Gasket
• Alternative pinhole
t M^^B
in
—4^.
r=4—J
Adjustaiaia leg
u
Figure 2-15. Vacuum breaker.2
2-30
-------
roett
Figure 2-16a. Overflow roof drain.2
0-.
U
Figure -2-16b. Roof leg.2
2-31.
-------
Rim vent
Tank shell
Primary-seal
fabric
Primary-seal
shoe
Boating-roof
rim
Rim vapor
space
Liquid surface
Note: Rim. vents are normally supplied only on tanks equipped with
a- mechanical-shoe-primary seal.
Figure 2-17. Rim vent.2
2-32-
-------
-------
2.5 REFERENCES
1. The American Petroleum Institute. Evaporative Loss from
Fixed-Roof Tanks, API Draft Publication 2518, Second
Edition, Washington, D.C. October 1991.
2. The American Petroleum Institute. Evaporative Loss From
External Floating Roof Tanks, API Publication 2517, Third
Edition. Washington, DC. February 1989.
3. Recommended Practices for Underground Storage of Petroleum.
New York State Department of Environmental Conservation.
Albany, NY. May 1984. p. 5.
4. Toxic Substance Storage Tank Containment. Ecology and
Environment, Inc. Whitman, Requardt and Associates, Park
Ridge, NJ. 1985. p. 121.
5. The American Petroleum Institute. Evaporation Loss From
Internal Floating Roof Tanks, API Publication 2519, Third
Edition. Washington, DC. June 1983.
2-33
-------
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3.0 EMISSION ESTIMATION PROCEDURES AND REGULATORY BASELINE
3.1 INTRODUCTION
This chapter outlines the procedures used to estimate
emissions from fixed-roof tanks, horizontal tanks, and external
floating roof and internal floating roof tanks. In addition,
this chapter presents the regulatory baseline and analytical
framework (i.e., model tanks and model liquids) used to estimate
emissions for each control option presented in Chapter 4.
3.2 STORAGE TANK EMISSIONS AND EMISSION EQUATIONS
3.2.1 Fixed-Roof Tank Emissions
The major types of emissions from fixed-roof tanks are
breathing and working losses. Breathing loss is the expulsion of
vapor from a tank vapor space that has expanded or contracted
because of daily changes in temperature and barometric pressure.
The emissions occur in the .absence of any liquid level change in
the tank.
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 the air that is
drawn into the tank during liquid removal saturates with
hydrocarbon vapor and expands, thus exceeding the fixed capacity
of the vapor space and overflowing through the pressure vacuum
valve. Combined filling and emptying losses are called "working
losses."
Emission; equations for breathing and working losses-were
developed for EPA Publication No. AP-42.1 The American Petroleum
institute (API) has recently revised its recommended procedures
3-1
-------
for estimating fixed roof tank breathing losses. The EPA has
reviewed this revised%procedure and incorporated it into a draft
-version of AP-42, which is currently undergoing external review.
(Note: This ACT was prepared during the review of the revised
procedure and uses the existing AP-42 to estimate emissions.
Because the differences in results are small compared to overall
fixed roof tank emissions, it was decided that the benefits of
revising the ACT to reflect the new procedure would be small
compared to the resources required to revise the calculations.)
The EPA is considering incorporating this revised procedure for
AP-42, and may adopt this procedure at the next revision of
AP-42. For the purposes of estimating emission rates, the
equations used for fixed-roof tanks storing volatile organic
liquids (VOL) are:
LT =. LB + Lw, (3-1)
LB m 1.02 x lO'5 Mv (P/(14.7-P))0-68D1.73H0.51T0.5FpCKcf (3_2)
Lw » 1.09 x 10"8MVPVNKNKC/ (•*.•*}
** ^ • \ -5 - o)
• where:
Lw
Mv
D
H
total loss (megagrams per year [Mg/yr]);
breathing loss (Mg/yr);
working loss (Mg/yr);
molecular weight of product vapor
(pounds per pound-mole [Ib/lb mole]);
•true vapor pressure of product
(pounds per square inch absolute [psia]);
tank diameter (feet [ft]);
average vapor space height (ft); use tank-specific
values or an assumed value of one-half the tank
height;
average diurnal temperature change (°F); assume 20°F
as a typical value;
paint factor (dimensionless); see Table 3-1;
tank diameter factor (dimensionless)
for diameter, D ^30 ft, C =» l,
for diameter, 6 ft ^D <30 ft,
C - 0.0771' D - 0.0013(D2) - 0.0.334;
3-2
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TABLE 3-1. PAINT FACTORS FOR FIXED-ROOF TANKS
Tank color
Roof
White
Aluminum (specular)
White
Aluminum (specular)
White
Aluminum (diffuse)
White
Light gray
Medium gray
Shell
White
White
Aluminum (specular)
-Aluminum- (specular)
Aluminum (diffuse)
Aluminum (diffuse)
Gray
Light gray
Medium gray
Paint factors (Fp)
Paint condition
Good
1.00
1.04
1.16
•1.20
1.30
1.39
1.30
1.33
1.46
1.15
1.18
1.24
1.29
1.38
1.46
1.38
1.44a
1.58a
Estimated from the ratios of the first seven paint factors.
3-3
-------
K
V
N
•N
product factor (dimensionless) - 1.0 for VOL,
0.65 for crude oil breathing losses, and
0.84 for crude oil working losses;
tank capacity (gallons [gal]);
number of turnovers per year (dimensionless); and
turnover factor (dimensionless)
180 + N
for turnovers >36, K,
and
6N
•1.-
f or turnovers -,<36 •, KJJ
3.2.2 Horizontal Tank Emissions
The fixed-roof tank emission equations presented above in
Section 3.2.1 were modified to estimate emissions from horizontal
tanks. The procedure presented below is to be used only as a
screening to estimate emissions from horizontal tanks, and will
most likely result in an over-estimation of emissions. The
modifications to the breathing loss emission estimation equation
and the methodology used to calculate emissions from horizontal
above-ground tanks are presented below:
1. Calculate the liquid surface area and then calculate the
diameter of a circle with this same surface area. Substitute the
calculated diameter of the circle for the effective tank diameter
in the breathing loss equation. The liquid surface area is equal
to the length of the tank multiplied by the tank diameter.
Therefore, the effective diameter can be calculated using the
following equation:
Do =
L D
0.785
(3-4)
where:
De
L
D
2.
effective tank diameter (ft) ;
length of tank (ft); and
actual diameter of tank (ft).
Use half the diameter of the tank as the average vapor
space'height (H =» 0.5D).
3-4
-------
For underground tanks, assume that no breathing losses occur
because the insulating nature of the earth limits the diurnal
temperature change. No modifications to the working loss
equation are necessary for either above-ground or underground
horizontal tanks.
3-2.3 External Floating Roof Tank Emissions
Standing storage losses, which result from causes other than
a change in the liquid level, constitute the major source of
emissions from external - floating roof. tanks. ".. The largest
potential source of these losses is an improper fit between the
seal and.the tank shell (seal losses), resulting in portions of
the liquid surface being exposed to the atmosphere. Air flowing
over the tank creates pressure differentials 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.
Standing storage losses of VOC vapors from under the
floating- roof also occur through openings in the deck- required
for various types of fittings (fitting losses).
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.
From the equations presented below, it is possible to
estimate the total evaporation loss for external floating roof
tanks, LT, which is the sum, of the standing storage loss, LS, and
the withdrawal loss, 1^. The equations presented in the
following sections in large part are extracted from AP-42 and API
Publication No. 2517.1'2
3-2.3.1 Standing Storage Loaa. The standing storage loss,
Lg, includes losses from the rim seal and the roof fittings. The
following equations can be; used to/estimate the independent
coneributions of rim seal and roof fitting losses to the overall
standing storage loss:
3-5
-------
LR
FRD
where:
P *MVKC/2,205; and
FpP* MyKc/2,205,
(3-5)
(3-6)
p*
rim seal loss (Mg/yr);
rim seal loss factor (pound-moles per "foot-year
[Ib-mole/ft-yr]);
tank diameter (ft) ;
total roof-fitting loss factor (Ib-mole/yr);
vapor pressure function" (dimensionless) ;
average molecular weight of stock vapor
(Ib/lb-mole);
product"factor (dimensionless); and
Lp - total roof fitting loss (Mg/yr).
Therefore, the overall standing storage loss can be estimated as
follows:
jp - (FRD -i- FF) P* MyKc/2,205
3.2.3.1.1 Rim seal loss factor.
can be estimated as follows:
where:
FR - KR V'
(3-7)
The rim seal loss factor,
(3-8)
KR -
V
N
rim seal loss factor (Ib-mole/ft-yr);
rim seal loss factor (pound-moles per [miles per
hour]Nfoot-year [lb-mole/(mi/hr)N ft-yr]); see
Table 3-2;
average wind speed (mi/hr); and
rim seal-related wind speed exponent (dimen-
sionless) ; see Table 3-2.
The rim seal loss factors apply only for wind speeds from 2 to
15 miles per hour.
3.2.3.1.2 Roof fitting logs factor. The total roof fitting
loss factor, Fp, can be estimated as follows:
where:
Fp = [(NplKpl + Np2
5 )
*Fi
total roof fitting loss factor (Ib-mole/yr);
number of roof fittings of a particular type
(dimensionless);
3-6
-------
TABLE 3-2. RIM-SEAL LOSS FACTORS, KR/ AND N
Tank construction and
rim- seal system
Average- fitting seals
Kp
(lb-mol/[mi/hr]N-ft-vr)
N
(dimensionless)
WELDED TANKS
Mechanical shoe seal
Primary only
Shoe -mounted secondary
Rim-mounted secondary
Liquid -mounted
resilient- filled seal
Primary only
Weather -shield
Rim-mounted secondary
Vapor-mounted resilient -
filled seal
Primary only
Weather shield
Rim-mounted secondary
1.2*
0.8
0.2
1.1
0.8
0.7
1.2
0.9
0.2
1.5a
1.2
1.0
1.0
0.9
0.4
2.3
2.2
2.6
RIVETED TANKS
Mechanical shoe seal
Primary only
Shoe -mounted secondary
Rim-mounted secondary
1.3
1.4
0.2
1.5
1.2
1.6
— - — ' !
Note: The rim-seal loss factors KR and N may only be used for wind
speeds from 2 to 15 miles per hour.
alf no specific information is available, a welded tank with an
average-fitting mechanical-shoe primary seal only can be assumed
to represent the most common or typical construction and rim-seal
system in use.
3-7
-------
K
•Fi
i
k
loss factor for a particular type of roof fitting
(Ib-mole/yr);
1,2, . . . , k (dimensionless); and
total number of different types of roof fittings
(dimensionless).
The loss factor for a particular type of roof fitting,
K
be estimated as follows:
•Fi''
K
where :
Fai
K
•Fbi
Vmi,
can
(3-10)
K
•Fi
K
K
•Fai
•Fbi
mi
i
V
loss factor for a particular type bf"rbof"fitting
(Ib-mole/yr);
loss factor for a particular type of roof fitting
(Ib-mole/yr);
loss factor for a particular type of roof fitting
(lb-mole/[mi/hr]m-yr);
loss factor for a particular type of roof fitting
(dimensionless);
1/2, . . . , k (dimensionless); and
average wind speed, (mi/hr).
The most common roof fittings are listed in Table 3-3 along with
the associated roof fitting-related loss factors, - Kpa, Kpb, and
m, for various types of construction details. These factors
apply to typical roof fitting conditions. The roof fitting loss
factors may only be used for wind speeds from 2 to 15 mi/hr.
Since the number of each type of roof fitting can vary
significantly from tank to tank, Np values for each type of roof
.fitting should be determined for the tank under consideration.
If this information is not available, typical Np values are given
in Tables 3-3, 3-4, and 3-5. If no information is available
about the- specific type and number of roof fittings, a typical
total roof fitting loss factor, Fp, can be read from^ either
Figure 3-1 or 3-2 for the type of external floating roof deck.
These figures, show; the total roof, fitting: loss factor, F^, as a
function of tank diameter, D, for pontoon and double-deck
floating roofs, respectively.
3-8
-------
TABLE 3-3. ROOF FITTING LOSS FACTORS, KFa, KFb, AND m,
AND TYPICAL NUMBER OF ROOF FITTINGS, My.
Fitting type and construction details
Access hatch (24-inch-diameter well)
Bolted cover, gasketed
Unbolted cover, ungasketed
Unbolted cover, gasketed
Unslotted guide-pole well
(8-inch-diameterunslotted pole, 21-inch-diameterweil)
Ungasketed sliding cover
Oasketed sliding cover - - •- -•
Slotted guide-pole/sample well
(8-inch-diameterunslotted pole, 21-inch-diameterwell)
Ungasketed sliding cover, without float
Ungasketed sliding cover, with float
Oasketed sliding cover, without float
Oasketed sliding cover, with float
Gauge-float well (20-inch diameter)
Unbolted cover, ungasketed
Unbolted cover, gasketed
Bolted cover, gasketed
Gauge-hatch/sample well (8-inch diameter)
Weighted mechanical actuation, gasketed
Weighted mechanical actuation, ungasketed
Vacuum breaker (10-inch-diameter well)
Weighted mechanical actuation, gasketed
Weighted mechanical actuation, ungasketed
Roof drain (3-inch diameter)
Open
90 percent closed
Roof leg (3-inch diameter)
Adjustable, pontoon area
Adjustable, center area
Adjustable, double-deck roofs
Fixed
Roof leg (2Vi-inch diameter)
Adjustable, pontoon area
Adjustable, center area
Adjustable, double-deck roofs
Fixed
Rim vent (6-inch diameter)
Weighted mechanical actuation, gasketed
Weighted mechanical actuation, ungasketed
Loss factors
KF.
(Ib-mole/yr
0
2.7
2.9
0
0
0
0
0
0
2.3
2.4
0
0.95
0.91
1.2
1.1
0
0.51
1.5
0.25
0.25
0
1.7
0.41
0.41
0
0.71
0.68
KFb
(lb-mole/(mi/hr]m-yr)
0
7.1
0.41
67
3.0
310
29
260
8.5
5.9
0.34
0
0.14
2.4
0.17
3.0
7.0
0.81
0.20
0.067
0.067
0
0
0
0
0
0.10
l.S
m
(dimensionless)
0«
1.0
1.0
0.98*
1.4
1.2
2.0
1.2
2.4
1,0*
1.0
0
1.0a
1.0
1.0a
1.0
.4
.0
.oa
.0"
.0
0
0
0
0
0
1.0*
1.0
Typical number
of fittings, My
1
1
b
1
1
NF6 (Table 3-4)
Npj (Table 3-4)
NFg
(Table 3-5)c
NF8 c
(Table 3-5)°
1"
Note: The roof fitting loss factors, KFm, Kj^, and m, may only be used for wind speeds from 2 to 15 miles per hour
If no specie mformatton is available, this value can be assumed to represent the most common or typical roof fittings currently in
A slotted guide-poie/sample well is an optional fitting and is not typically used.
'The most common roof leg diameter is 3 inches. The loss factors for 2'A-inch-diameter roof legs are provided for use if this smaller
size roof leg is used on a particular floating roof.
Rim vents are used only with mechanical-shoe primary seals.
3-9
-------
TABLE 3-4.
TYPICAL NUMBER OF VACUUM BREAKERS,
AND ROOF DRAINS,
Tank diameter,
D (feet)a
50
100
150
200
250
300
350
400
No. of vacuum breakers, N^c
Pontoon roof
1
1
2
3
4
5
6
7
Double -deck
roof
1
1
2
2
3
3
4
4
No. of roof
drains , NP7
(double -deck
roof)
1
1
2
3
5
7
Note: This table was derived from a survey of users and
manufacturers. The actual number of vacuum breakers may
vary greatly depending on throughput and manufacturing
prerogatives. The actual number of roof drains may also
vary greatly depending on the design rainfall and
manufacturing prerogatives. For tanks more than 300 feet in
diameter, actual tank data or the manufacturer's recommenda-
tions may be needed for the number of roof drains. This
table should not supersede information based on actual tank
data.
alf the actual diameter is between the diameters listed, the
closest diameter listed should be used. If the actual diameter
is midway between the diameters listed, the next larger diameter
should be used.
3-10
-------
TABLE 3-5. TYPICAL NUMBER OF ROOF LEGS,
N
F8
Tank
diameter, D
(feet) a
30
40
50 '
60
70
80
- 90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
280
290
300
310
320
330
340
350
360
370
380
390
400
Pontoon roof
No. of pontoon
leqs
4
4
6
9
13
15
~ 16
17
18
19
20
21
23
26
27
28
29
30
31
32
33
34
35
36
36
37
38
38
39
39
40
41
42
44
45
46
. 47
48
No. of center
leers
2
4
6
7
9
10
12
16
20
24
28
33
38
42
49
56
62
69
77
83
92
101
109
118
128
138
148
156
168
179
190
202
213
226
238
252
266
281
No. of legs on
double -deck
roof
6
7-
8
10
13
16
20
25
29
34
40
46
52
58
66
74
82
90
98
107
115
127
138
"149
162
173
186
200
213
226
240
255
270
285
300
315
330
345
Note: This table was, derived from a survey of users and manufac-
turers. The actual number of roof legs may vary qreatlv
depending on age,, style of floating roof, loading specifica-
tions, and manufacturing prerogatives. This table should not
supersede: information based on actual tank data
Si^1 diaf2ter is- between the diameters listed, the
diameter listed.should be used. If the actual diameter
diameters listed, the next larger diameJSr
3-11
-------
3500
3000
i
2500
2000
i
10 mife* per tour}—
1500
1000
100 150 200
Tank diameter, D (feet)
250 300
Figure 3-1..
Total roof fitting loss factor for typical
on pontoon floating roofs.2 cypicaj-
3-12
-------
3500
3000
i
2500
2000
i
i
I
1500
1000
500
' ' ' ' ' ' ' ! ' ' ' ' • '
100 150 200
Tank diameter, O (f««t)
250 300
Figure 3-2,
Total roof fitting loss factor for typical
on- double-deck floating roofs.2 Yplcai
3-13
-------
3.2.3.1.3 Vapor pressure function. The vapor pressure
function, P*, can be determined as follows:
P* =
0.068P
[1 -i- (1 - 0.068P)0-5]2
(3-11)
where:
P* =• vapor pressure function (dimensionless); and
P - the true vapor pressure of the materials stored
(psia).
3.2.3.1.4 Product faster- The product 'factor, K'c, accounts
for the effect of different types of product liquids on
emissions. Product factors have been developed for
multicomponent hydrocarbon mixtures, including refined products
(such as gasolines and naphthas), crude oils, and single-
component VOL's (such as petrochemicals):
KC * 1-° for refined products and single-component VOL's
» 0.4 for crude oils.
3-2-3.2 Withdrawal Loaa. The withdrawal loss, LW, pertains
to the evaporation of liquid that clings to the tank shell while
the liquid is withdrawn. The withdrawal loss can be estimated as
follows:
0.943 Q C W1
2205 D
(3-12
where:
D
0.943
withdrawal loss (Mg/yr);
annual net throughput (associated with lowering
the liquid stock level in the tank) (barrels per
year [bbl/yr]) ;
clingage factor (barrels per 1,000 square feet
[bbl/1,000 ft2]),
average liquid density at the average storage
temperature (Ib/gal);
tank diameter (ft); and
constant (1,000 cubic feet x gallons per barrel
squared [1,000 ft3 x (gal/bbl)2]).
3-14
-------
The annual net throughput, Q, is the total volume of stock
withdrawn from the tank per year that results in a decrease in
the level of the liquid in the tank. If filling and withdrawal
occur equally and simultaneously so that the liquid level does
not change, the net throughput is zero.
The clingage factors, C, for steel tanks with light rust,
dense rust, and gunite lining in gasoline, single-component VOL,
and crude oil service are presented in Table 3-6.
For refined petroleum-products and crude oil; the 'density of
the condensed vapor, Wv, is lower than the density of the stored
liquid. If the density of the condensed vapor is not known-, it
can be approximated as follows:
where:
Wy - O.OSMy, (3-13)
Wv = density of condensed vapor (Ib/gal); and
My m vapor molecular weight (Ib/lb-mole).
For single-component VOL's, the density of the condensed vapor is
equal to the density of the liquid, w^ The physical properties
of selected petrochemicals are given in Table 3-7.
3-2.3.3 Total" Loss. The total loss, LT, in megagrams per
year, can be estimated as follows:
where:
LT (Mg/yr) — Lg + L^, ' (3-14)
LT » total loss (Mg/yr);
Lg =. standing storage loss (Mg/yr) ; and
LW - withdrawal loss (Mg/yr).
3-2.4 Internal Floating Roof Tank Emiggion.ci
As ambient wind flows over the exterior of an internal
floating roof tank, air flows into the enclosed space between the
fixed and floating roofs through some of the shell vents and out
of the enclosed space through, other vents. Any VOC vapors that
have evaporated from the exposed liquid surface and that have not
been contained by the floating deck will be swept out of the
enclosed space. Vapors- may also be expelled by the expansion of
3-15
-------
TABLE 3-6. AVERAGE CLINGAGE FACTORS (C) bbl/1,000 ft2
Product
Gasoline
Single- component
stocks
Crude oil
. Shell condition
Light rusta
0.0015
0.0015
0.0060
Dense rust
0.0075
0.0075
0.030
Gunite- lined
0.15
0.15
0.60
alf no specific information is available, these values can be
assumed to represent the most common/typical condition of tanks
currently in use. •
3-16
-------
or
i-^
rt
g
O
B
u
04
Q
12
u
H
•4
H
CO
CO
a
H
a
u
H
2
S
O4
n
a
"
o
is-J,
si
Hi
3-17
-------
(1)
•H
.U
a
o
o
n
II
3s
2 3
S 5
X
o
5
0
J
-,
5
?
jj
il
II
- o
i
I.*
3-18
-------
air in the enclosed space due to diurnal temperature changes
(breathing).
Losses of VOC vapors from under the floating roof occur in
one of four ways:
1. Through the annular rim space around the perimeter of
the floating roof (rim or seal losses);
2. Through the openings in the deck required for various
types of fittings (fitting losses);
3. Through the. .nonwelded seams formed when "joining -•_••-
sections of the deck material (deck seam losses); and
4. Through evaporation of liquid left on the tank wall and
columns following withdrawal of liquid from the tank (withdrawal
loss) .
The withdrawal loss from an internal floating roof tank is
similar to that discussed in the previous section for external
floating roofs. The other losses--seal losses, fitting losses,
and deck seam losses--occur not only during the working
operations of the tank but also during free-standing periods.
The mechanisms and loss rates of internal floating roof tanks
were studied in detail by the Chicago Bridge and Iron Company for
the American Petroleum Institute.3 The result of this work forms
the following internal floating roof emissions discussion.
Several potential mechanisms for vapor loss from the rim
seal area of an internal floating roof tank can be postulated.
Among them are:
1. Circumferential vapor movement underneath vapor-mounted
rim seals;
2... Vertical mixing, due to diffusion or air turbulence, of
the vapor in gaps that may exist between any type of rim seal and
the tank shell;
3. Expansion of vapor spaces in the rim area due to
temperature or pressure changes;
4. Varying solubility of gases, such as air, in the rim
space liquid due to temperature and pressure changes;•
5,. Wicking of the rim space liquid up the tank shell; and
S-.. Vapor permeation through the sealing material.
3-19
-------
For external floating roof tanks, wind-generated air
movement across the roof is the dominant factor affecting rim
seal loss. In comparison, freely vented internal floating roof
tanks significantly reduce air movement and have no clearly
dominant loss mechanism.3
Vapor permeability is the only potential rim seal area loss '
mechanism that is readily amenable to independent investigation.
Seal fabrics are generally reported to have very low permeability
to typical hydrocarbon vapors, such that this source of loss is
not considered to be significant. However, if a seal material is
used that is highly permeable to the vapor from the stored stock,
the rim seal loss could be significantly higher than that
estimated from the rim seal loss equation presented later in this
section.3 Additional loss data including permeability data for
VOL/seal material combinations are not available to fully
characterize the significance of permeability losses.
The extent to which any or all of these mechanisms
contribute to the total fitting loss also is not known. The
relative importance of the various mechanisms depends on the type
of fitting and the design of the fitting seal.3
Floating decks are typically made by joining several
sections of deck material together, resulting in seams in the
deck. Because these seams are not completely vapor tight, they
become a source of loss.
••
Emissions from internal floating roof tanks can be estimated
from the equations in the following subsections.1'3 (Note that
these equations apply only to freely vented internal floating
roof tanks.J
(3-15
where:
the total loss (Mg/yr);
=• the withdrawal loss (Mg/yr) ;
= the rim seal loss (Mg/yr);
=• the deck, fitting loss (Mg/yr)
3 the deck seam loss (Mg/yr).
and
3-20
-------
3.2.4.1 Withdrawal Loss . The withdrawal loss,
calculated from the following equation:
(0.943)QCWL [1 + NCFC] /22Q5.
D D
is
(3-16)
where :
N
Wr
c -
3.2.4.2
withdrawal loss (Mg/yr);
tank diameter (ft) ;
number -of -columns;, see—Table 3^8-;—.
effective column diameter (ft); see Table 3-9;
density of product (Ib/gal);
product average throughput (bbl/yr); (bbl/turnover) x
(turnovers/yr); and
clingage factor (bbl/1,000 ft2); see Table 3-6.
Rim Seal Loss. The rim seal loss, LR, is
calculated from the following equation:
where:
KT
LR = (KRD)P*MVKC/22051
(3-17)
rim seal loss (Mg/yr);
the rim seal loss factor (Ib-mole/ft-yr); rim seal
loss factors for average fitting seals are as
follows:
Seal system description
Vapor-mounted primary seal only
Liquid-mounted primary seal'only
Vapor-mounted primary seal plus
secondary seal
Liquid-mpunted primary seal plus
secondary seal
(Ib-mole/ft-yr)
6.7
3.0
2.5
1.6
tank diameter, ft;
the vapor pressure function (dimensionless)
P.* =» 0.068 P/([l + (1 - O.Q68 P)°-5]2) and
P- =• the true vapor pressure of. the material stored
(psia);
the average molecular weight of the product vapor
(Ib/lb-mole); and
the product factor (dimensionless).
3-21
-------
TABLE 3-8.
TYPICAL NUMBER OF COLUMNS AS A FUNCTION OF TANK
DIAMETERS1
Tank diameter range D, ft
Typical number columns, Nf
0 < D <. 85
85 < D <. 100
100 < D < 120
120 < D <. 135
135 < D <. 150
150 < D <. 170
170 < D < 190
190 < D <, 220
220 < D <. 235
235 < D < 270
270 < D <. 275
275 < D < 290
290 < D <. 330
330 < D < 360
360 < D < 400
1
6
7
8
9
16
19
22
31
37
43
49
61
71
81
Note:
This table was derived from a survey of users and manufac-
turers. The actual number of columns in a particular tank
may vary greatly depending on age, roof style, loadincr
specifications, and manufacturing prerogatives. This table
should not supersede information based on actual tank data.
TABLE 3 -9. EFFECTIVE
Type
COLUMN DIAMETER (Ff
F~, ft
9-inch by 7-inch built-up
columns
1.1
8-inch-diameter pipe columns
0.7
No construction details known
3-22
-------
The product factor, KC, is equal to 1.0 for VOL and refined
products and 0.4 for crude oil.
3.2.4.3 Fitting Loaa. The fitting loss, Lp, is calculated
from the following equation:
LF - (FF)P* My Kc/2205, (3-18)
where:
LF =» fitting loss (Mg/yr) ;
Fp m total deck fitting loss factor (Ib-mole/yr);
P - the vapor pressure function; see Section 3.2.4.2 for
the vapor pressure function calculation;
My = average molecular weight of product vapor
(Ib/lb-mole); and
KC = the product factor (dimensionless).
The total deck fitting loss factor, Ff, is equal to:
n
FF = E
i=l
where:
F,,
(NFi KFi) = [(NF1 KF1) + (NF2 KF2)
(3-19)
N.
= total deck fitting loss factor (Ib-mole/yr);
Fi = number of fittings of a particular type
(dimensionless). NFi is determined for the specific
tank or estimated from Tables 3-8 and 3-10. In the
case of an external floating roof tank that has been
converted to an internal floating roof tank by
retrofitting with a self-supporting fixed roof,
Tables 3-3, 3-4, and 3-5 can be used to estimate the
number of fittings.
- deck fitting loss factor for a particular type fitting
(Ib-mole/yr); K?i is determined for each fitting type
from Table 3-10; and
» number of different types of fittings (dimensionless).
Alternatively, the total deck fitting loss factor can be
estimated from: either Figure 3-3 or 3-4, depending upon the type
of deck, and roof: configuration.
n
3-23
-------
TABLE 3-10.
SUMMARY OF DECK PITTING LOSS FACTORS (Kw) AND
TYPICAL NUMBER OF FITTINGS (N«)
1.
2.
3.
4.
5.
6.
7.
8.
Deck fitting type
Access batch
a. Bolted cover, gasketed
b. Unbolted cover, gasketed
c. Unbolted cover, 'ungasketed
Automatic gauge float well
a. Bolted cover, gasketed
b. Unbolted cover, gasketed
c. Unbolted cover, ungasketed
Column well
a. Built-up column, sliding cover, gasketed
b. Built-up column, sliding cover, ungasketed
c. Pipe column, flexible fabric sleeve seal
d. Pipe column, sliding cover, gasketed
e. Pipe column, sliding cover, ungasketed
Ladder well
a. Sliding cover, gasketed
b. Sliding cover, ungasketed
Roof leg or .hanger well
a. Adjustable
b. Fixed
Sample pipe or well
a. Slotted pipe, sliding cover, gasketed
b. Slotted pipe, sliding cover, ungasketed
c. Sample well, slit fabric seal, 10 percent open area
Stub drain, 1-inch diameter1
*•
Vacuum breaker
a. Weighted mechanical actuation, gasketed
b. Weighted mechanical actuation, ungasketed
Deck fitting
loss factor,
Kp (Ib-
mole/yr)
1.6
11
25
5.i
15
28
33
47
10
19
32
56
76
7.9
0
44
57
12
1.2
0.7
0.9
Typical number of
fittings, NF
1
• 1
(see Table 3-8)
1
-------
4SOO
Basis:
4000
3SOO
3000
2SOO
2000
1500
r
BOLTED DECK
(0.0228)Z>2 + (0.79)D + 105.2
1000
WELDED DECK (St» Now)
(0.0132)Z>2 + (0.79)0 + 105.2
100 180 200 290 300
TANK DIAMETER, D (feet)
400
Fitting! include: (1) access hatch with ungasketed, unbolted cover, (2) adjustable deck legs; (3) gauge float wcl
with unguketed, unbolted cover, (4) sample well with slit fabric seal (10% open area); (5) 1-inch-diameter stub
drains (only on bolted deck); and (6) vacuum breaker with guketed weighted mechanical actuation. This basis
was derived from a survey of user* and manufacturers. Other fitting* may be typically used within particular
companies or organizations to reflect standards and/or specifications of that group. This figure should not
supersede information based on actual tank data.
MOTE: If no specification information is available, assume bolted deck* are the most common/typical type currently in
use in tanks with column-supported fixed roots.
Figure 3-3.- _Total deck fitting loss factor, as a function of
. tank diameter, for a self-supporting fixed roof.^
3-25
-------
Basis:
NOTE:
asm
am
7SOO
7000
8800
(000
MOO
5000
4400
4000
MOO
*
;
.
•
;
,
..^
1 1 1 .1
»
r>-(O.C
^x
^•^
1 1 1 1
XTEOOl
U8l)D2 •
/,
f
1 1 t 1
CX(S4Wl>
*• (1.392)
/
//
y
D + 134.
/
//
/
2 /
^ /
/
/
• 1
1 1
/
/
1
1
1
1 /
/
1
'/ ^ waoeooecK
/Ff (0.0385)D3 •)• (1.392)D + 12
(4.2
100 iso an ao wo
TANK DIAMETER, O (feet)
3fO
400
Fittings include: (1) access hatch with ungmsketed, unbolted cover, (2) built-up column wells with ungasketed
unbolted cover, (3) adjiutable deck legs; (4) guige float well wiA ungasketed, unbolted cover, (5) ladder well
with ungmtketed sliding cover; (6) sample well with slit fabric seal (10 5S open area); (7) 1-iacfa-diameter stub
drains (only on bolted deck); and (8) vacuum breaker win gaskeced weighted mechanical actuation. This basis
was derived from * survey of users and manufacturers. Other fittings may be typically used within pardcular
companiesor organizations to reflect standards and/or specifications of that group. This figure should not
supersede information based on actual tank data.
If no specification information is available, assume bolted decks are the most common/typical type currently in
use in tanks whh column-supported fixed roofs.
Figure 3-4. Total deck fitting loss factor as a; function of
tank diameter, for a column-supported fixed' roof.^
3-26
-------
3.2.4.4 Dec* seam T.OSH. The deck seam loss factor, LD, can
be calculated from the following equation:
LD = (SDKDD2) P*M7Kc/2205f (3-20)
where
where:
L
A
deck seam loss (Mg/yr);
the deck seam length factor (ft/ft2)
(L/A)
D
*
K
seam length (ft) and
deck area .(ft2);
the deck seam loss factor (Ib-mole/ft-yr),
0.34 for nonwelded decks; and
0 for welded decks;
tank diameter, ft;
vapor pressure function (as described previously);
average molecular weight of product vapor (Ib/lb-mole)-
and '
the product factor (dimensionless).
If total length of deck seam is unknown, use:
D = 0.14, for a deck constructed from continuous metal
sheets with a 7-ft spacing between seams;
=• 0.17, for a deck constructed from continuous metal
sheets with a 6- ft spacing between seams;
- 0.33, for a deck constructed from rectangular panels
5 ft by 7.S ft;
= 0.28, for a deck constructed from rectangular panels
5 ft by 12 ft; and
- 0.20, an approximate value for use when no construction
details are known, and for a deck constructed from
continuous, metal sheets with a 5- ft spacing between
seams.
3.3 REGULATORY BASELINE
The Environmental Protection Agency (EPA) has published two
control technique, guideline documents (CTG's) and promulgated
three new^source performance standards (NSPS) that establish the
ma3pr components of the regulatory baseline. These regulatory
actions are summarized in the following sections.
3-27
-------
3.3.1 Petroleum Liquid Storage NSPS (Subpart m4
The Petroleum Liquid Storage NSPS(K) (effective March 1974
for tanks between 40,000 gal and 65,000 gal; June 11, 1973 for
tanks greater than 65,000 gal) marks the Agency's first
regulatory action on storage tanks. Only petroleum liquids
stored in tanks with volumes of 40,000 gallons and greater were
affected. Petroleum liquid was defined as petroleum, condensate,
and finished or intermediate refined products. The required
control .was the..installati.on.,,af _.a..,fLoating. roof 'or vapor recovery-
system if the vapor pressure of the stored liquid was greater
than 1.5 psia but less than 11.1 psia. In addition, the NSPS did
not have any equipment specifications for the floating roofs.
Tanks storing liquids with vapor pressures of 11.l psia and
greater were required to install vapor control devices with no
specification on type or efficiency.
3-3.2 Petroleum Liquid Fixed-Roof Tank cw;5
This CTG was published in December 1977 and required fixed-
roof tanks with volumes greater than or equal to 40,000 gal
storing petroleum liquids with true vapor pressures greater than
1.5 psia to reduce emissions by equipping the tank with an
internal floating roof. The CTG did not specify the type of
deck, fittings, or seal system. Because the CTG applied only to
petroleum liquids, the CTG did not apply to products manufactured
at chemical plants (e.g., methyl ethyl ketone [MEK]) even if the
tank volume and vapor pressure of the stored liquid were within
the applicability range of the CTG. However, in implementing
this CTG, most States expanded the applicability beyond petroleum
liquids and in fact regulated all VOC-emitting tanks. Some
States further strengthened their regulations beyond the CTG by
requiring internal floating roof.controls for smaller tanks
(e.g., Texas requires internal floating roof controls on tanks
with volumes of 25,000 gal and greater in nonattainment areas;
New Jersey has a sliding volume-vapor pressure applicability).
3-28
-------
3.3.3 Petroleum Liquid External Floating Roof Tank
This CTG was published in December 1978 and required
external floating roof tanks with volumes of 40,000 gal or
greater to control emissions by installing a rim-mounted
secondary seal. Control of fitting emissions was not required,
and applicability was limited to petroleum liquids (as defined in
the fixed-roof tank CTG and the Subpart K NSPS), although "heavy,
waxy, pour.crudes" were specifically exempted. The vapor
"pressure at "which- controls- must-be -installed varied -as.follows: - -
1. Tanks with vapor-mounted primary seals became affected
at 1.5 psia;
2. Tanks with shoe- or liquid-mounted primary seals became
affected at 4.0 psia; and
3. Riveted tanks with primary shoe seals or liquid-mounted
seals became affected at 1.5 psia.
As with the fixed-roof tank CTG, the majority of States in
implementing the external floating roof tank CTG broadened its
applicability by controlling volatile organic compound (VOC)-
emitting tanks, and they selected 40,000 gal and 1.5 psia as the
cutoff point.
It is important to note that the CTG which required
secondary seals for external floating roof tanks is more
stringent than the Subpart K NSPS which only required the
installation of a floating roof. This CTG resulted in a retrofit
of tanks complying with the NSPS in nonattainment areas.
The Subpart Ka NSPS (May 1978 for tanks constructed,
reconstructed or modified) affected only petroleum liquids and
contained more detailed specifications than the previous
regulatory actions. The volume and vapor pressure cutoffs were
40,000 gal and 1.5 psia, respectively.. The requirements for
external floating roofs were very detailed and included
requirements for rim-mounted secondary seals and gap
specifications .for both the primary and secondary seals. The
Agency distinguished between vapor-mounted primary seals and
other seal types by requiring a tighter fit for both the vapor-
3-29
-------
mounted primary and the secondary seal. In addition, some
requirements were included on fitting controls for external
floating roof tanks. In general, all openings in the roof except
for automatic bleeder vents, rim vents, and leg sleeves had to be
equipped with a cover, seal, or lid, which was to be maintained
in a closed position at all times except when the device was in
actual use or as otherwise specified by the NSPS(Ka).
Few specifications were set for internal floating roofs.
Seal and deck type were not specified, nor was any requirement
included to control fitting emissions.
Vapor control devices were allowed if the control efficiency
was 95 percent by weight. Vapor control was required if the
vapor pressure of the stored liquid exceeded 11.1 psia.
• 3 •3 • 5 Volatile Organic Liquid N.ciP.c!8
The VOL NSPS (July 1984, 40 CPR Part 60 Subpart Kb)
controlled VOC emissions from storage vessels regardless of
liquid origin (i.e., both petroleum and nonpetroleum liquids were
affected). The control applicability is as follows:
1. Tanks of 40,000 gal and greater storing liquids with
vapor pressures of 0.75 psia and greater and
2. Tanks with volumes between 20,000 and 40,000 gal storing
liquids with vapor pressures of 4 psia and greater.
The NSPS control options are:
1. An internal floating roof with controlled fittings and
one of the following seal systems:
a. A vapor-mounted primary seal with a secondary seal or
b. A liquid-mounted or shoe primary seal only;
2. An external floating roof equipped with a shoe or
liquid-mounted primary seal and a secondary seal; and
3. A 95 percent-by-weight vapor control system.
Vapor control was required for all affected tanks storing liquids
with vapor pressures of 11.1 psia or greater.
Although the NSPS specified equipment to control internal
floating roof fitting losses, no controls were required beyond
those previously specified by the Subpart Ka NSPS for external
3-30
-------
floating roof fittings. Also, the NSPS made no provisions to
. exempt heavy, waxy, pour crude oils.
The shoe seal was allowed for internal floating roofs, in
part to allow the storage of problem liquids and to allow for the
conversion from an external floating roof tank to an internal
floating roof tank by retrofitting with a self-supporting fixed
roof. Shoe seals are made of steel and can be used with welded
steel internal floating roofs. If the liquid can be stored in a
steel tank, this type of system should be appropriate. . The only
potential problem is ensuring the seal fabric is compatible with
the product vapor.
3.3.6 Results of Regulatory Actions
The history of regulatory action makes the baseline control
scenario complex. Due to the fixed-roof tank CTG, it is
reasonable to assume that all fixed-roof tanks with volumes of
40,000 gal and greater storing liquids with true vapor pressures
of 1.5 psia or greater were converted to internal floating roof
tanks in nonattainment areas. This conversion occurred because
the majority of the States did not distinguish between petroleum
liquids and other VOL's in implementing the CTG. Because the
control cutoffs of the petroleum NSPS are also 40,000 gal and
1.5 psia, and compliance for all three regulatory actions could
be achieved with a low-cost, noncontact internal floating roof
with a vapor-mounted primary seal only and uncontrolled fittings,
it is reasonable to assume this type of internal floating roof
tank as the baseline, as opposed to other, higher-cost control
options. Below 40,000 gal or 1.5 psia, few States require
controls. Therefore, it is reasonable to assume only fixed-roof
tanks exist with volumes less than 40,000 gal or volumes above
40,000 gal storing liquids less than 1.5 psia.
The external floating roof baseline cases are more complex
because of previous regulatory actions affecting these tanks.
First,, as a result of the CTG and the NSPS(Xa), it is reasonable
to assume riveted external floating roof tanks in nonattainment
areas are controlled with rim-mounted secondary seals at vapor
3-31
-------
pressures of 1.5 psia and greater. For.these riveted tanks, it
is reasonable to assume a shoe seal as the primary seal. Second,
some welded tanks are equipped with vapor-mounted primary seals.
These are divided into a controlled (rim-mounted secondary seal)
subgroup, which can be defined as having liquid vapor pressures
of 1.5 psia and greater, and an uncontrolled subgroup, with vapor
pressures less than 1.5 psia. Third, the populations of external
floating roofs with liquid-mounted or shoe seals may be
categorized as: (l) tanks uncontrolled by both the NSPS(Ka) and
the CTG (i.e., vapor pressures less than 1.5 psia or vapor ' " "
.pressures less than 4.0 psia constructed prior to May 8, 1978);
(2) tanks controlled by both the NSPS(Ka) and the CTG
(i.e., tanks storing liquids with vapor pressures exceeding
4.0 psia); and (3) tanks controlled by the NSPS(Ka) but not
controlled by the CTG (i.e., tanks storing liquids with vapor
pressures between 1.5 psia and 4 psia constructed after May 8,
1978).
3.4 MODEL LIQUIDS AND MODEL TANKS
3-4.1 Model Liquids
The emissions estimation procedures distinguish between
crude oils and other single-component or refined stocks.
Therefore, a series of model crude oils and single-component
stocks have been provided to represent the range of stored
liquids. Further information on these model liquids is presented
in the following sections.
3-4.1.1 Mpflel Crude Qil . The properties of crude oils vary
widely. For the purpose of this analysis, the physical
properties of crude oil Reid vapor pressure (RVP) 5 were
selected. Crude oil RVP 5 has a molecular weight of 50 and a
density of 7.1 Ib/gal. The total vapor pressure in the analysis
varied from 0.10 to 5.0 psia. The product value used in
analyzing crude oil was $15.00/bbl.
3.4,1.2 Model VOL-3. To represent single-component liquids
and refined products, two model VOL's have also been used in "the
analysis. One model VOL is representative of nonhalogenated
compounds, and the other is representative of halogenated
3-32
-------
compounds. Two model VOL's were chosen because of the effect of
the physical properties of the stored liquid on emissions and the
compatibility of the liquid with the materials of construction.
The model nonhalogenated compound has a molecular weight of 60
and a density of 6.6 Ib/gal, whereas the model halogenated VOL
has a molecular weight of 100 and a density of 10.5 Ib/gal. The
vapor pressures examined in the analysis for the model
nonhalogenated VOL ranged from 0.1 to 5.0 psia. The vapor
pressures, examined..for..the model halogenated VOL were lower,
, ranging from 0.1 to 1.0 psia. The vapor pressure range for the
model halogenated VOL is lower than that of the model
nonhalogenated VOL because halogenated compounds typically have
much lower vapor pressures than nonhalogenated compounds. The
product value selected for both the halogenated and •
nonhalogenated VOL's was $0.71/lb. This value is representative
of the most common VOL compounds used in industry.
3.4.2 Model Tanks
Table 3-11 presents the analytical framework for fixed-roof
tanks. Eleven model tanks were selected to represent typical
storage tank sizes. The model tanks range in size from
approximately 10,000 gal up to 2 million gal. Model annual
turnover rates were also developed for fixed-roof tanks. Annual
turnover rates of 10, 25, 30, 50, and 100 were selected for tanks
less than 40,000 gal. Annual turnovers rates of 5, 10, 20, and
, 30 were selected for tanks greater than 40,000 gal. These values
are believed to be representative of the tanks that are discussed
in this ACT. The turnover rate values may not be representative
of large chemical production facilities that conceivably could
have annual turnover rates as high as 400. However, Che turnover
rates, selected for analyses would be more representative of
chemical users than producers. The model liquids and vapor
pressure ranges examined in the analysis for each model tank are-
also shown in Table 3-11. The model liquid and vapor pressure
ranges were selected considering the current regulatory baseline.
For instance, the fixed-roof tank CTG requires all fixed-roof,
tanks above 40,000 gal that store liquids
3-33
-------
I
;§•
oil
de
•8
rude
e o
i
O
0
1
in
O
I/I
6
a
-
OS
v
en
en
O
o\
VO
6
to
I
Q
W
H
fa
•a
i
00
:
—
O
o
Cd
)
i
a.
I
o
n
oo
oo
ON
ON
3-34
-------
T3
0)
a
o
o
m
ta
i
cu
u
>
+*
*s
s
s
o
'3
0.
OJ
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1
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to
8
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SO
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o
en
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en
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o
o
ON
VOL/crade
«n
0
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en
'3
VOL/crade
jq
o
r-
••
'c
VOL/crade
0
0
ON
VO
0
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-------
3-36
-------
with true vapor pressures above 1.5 psia to install either an
internal floating roof or a vapor recovery system. Therefore,
the vapor pressure range examined for tanks greater than
40,000 gal was limited to tanks storing liquids below 1.5 psia,
Table 3-12 presents the analytical framework for internal
and external floating roof tanks. Eight model tanks.were
developed to represent typical tank sizes. The vapor pressure
range and model liquids examined for each model tank were
selected considering the existing regulatory baseline-as-with
fixed-roof tanks.
3-37
-------
3-38
-------
•o
0>
•H
U
a
o
o
CN
I
CO
2
m
CU
?
a-
'3
EC
1
3
"o
1
u.
T»
1
ol
.8,
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2
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a
Q
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00
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o
o
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-------
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3.5
1.
4
5,
7.
8.
REFERENCES
U. S. Environmental Protection Agency. Compilation of Air
Pollution Emission Factors, Report No. AP-42, Supplement 12
Research Triangle Park, NC. April 1981.
The American Petroleum Institute. Evaporative Loss From
External Floating Roof Tanks, API Publication 2517, Third
Edition. Washington, DC. February 1989.
The American Petroleum Institute. Evaporation Loss From
Internal Floating Roof Tanks, API Publication 2519, Third
Edition. Washington, DC-. June 1983. --
40 CFR Part 60 Subpart K; promulgated March 8, 1974.
The Control of Volatile Organic Emissions From Storage of
Petroleum Liquids in Fixed Roof Tanks. EPA-450/2-77-036
Research Triangle Park, NC. December 1977.
Control of Volatile Organic Emissions From Petroleum Liquid
Storage in External Floating Roof Tanks. EPA-450/2-78-047
Research Triangle Park, NC. December 1978.
40 CFR Part SO Subpart Ka; promulgated April 4, 1980.
40 CFR Part 60 Subpart Kb; promulgated April 8, 1987.
3-40
-------
-------
4.0 CONTROL TECHNIQUES
4.1 OVERVIEW
This section describes the control.-techniques .that-.-apply-feo .
volatile organic compound (VOC) emissions from storing volatile
organic liquids (VOL's).
As discussed in Chapter 2, three major types of vessels are
used to store VOL's: fixed roof tanks, internal floating roof
tanks, and external floating roof tanks. "in addition, optional
equxpment designs exist within each major tank type' (e g seal
design, roof fabrication, and fittings closure). Each tank type
and equipment option has its own associated emission rate in
effect, there is a spectrum of equipment options, with a
corresponding spectrum of emission rates.
Considering the optional types of equipment that can be used
to store VOL's, a general hierarchy, or ranking, of equipment
alternatives can be developed for fixed roof tanks, internal
floating roof tanks, and external floating roof tanks based on
emission rates. These hierarchies, in order of decreasing
emission rates, are listed in Tables 4-1 and 4-2. There are
other ranking scenarios that could be developed depending on the
specific types of fittings used, however, the hierarchy of
options presented in this document are meant to represent general
groups,of equipment alternatives. Comparison of actual control
performance should use actual tank data. Chapter 3 outlines
equations for estimating the emission rate for each of the major
tank types, and the equipment options that are- available These
equations-, and-the- test data, used, to develop the eouations for.
the basis, for evaluating the effectiveness of the control
techniques discussed in this chapter.
4-1
-------
TABLE 4-1. FIXED ROOF AND INTERNAL FLOATING ROOF TANKS-
HIERARCHY OF EQUIPMENT TYPES BASED ON EMISSIONS RATEa'b
Control
option
Equipment description
Abbreviated
notation
Fixed roof tank (baseline)
Fixed roof tank
Internal floating roof tank, bolted
construction (contact or
noncontact), vapo'r-mounted primary
seal with uncontrolled deck
fittings0
bIFRvm,uf
Internal floating roof tank, bolted
construction (contact or
noncontact), vapor-mounted primary
and secondary seals with controlled
deck fittings
bIFRvm,ss,cf
Internal floating roof tank, bolted
construction (contact or
noncontact) , liquid-mounted n-r
bIFRlm,ss,cf
Internal floating roof tank, welded
wIFRlm,ss,cf
deck) . liquid-mounted or shoe
primary and secondary seals, with
controlled deck fittings
*n °rder °J decreasing emission rates with Control
11 rate and contro1
For new installations, some vendors of internal floating roofs
supply the roofs with both vapor-mounted primary and se?ondSr?
seals at no additional cost beyond the basic rc?f ?ost ^
4-2
-------
TABLE 4-2. EXTERNAL FLOATING ROOF TANKS-
HIERARCHY OF EQUIPMENT TYPES BASED ON EMISSIONS RATEa'b
^^^^^^^^^^^^^^^B B^S^giLii^j^- . . .^=B=.__
Control
option
nent description
Baseline: External floating roof
tank, riveted construction with
mechanical shoe primary seal
External floating roof tank,
riveted construction with
mechanical shoe primary seal and
secondary seal with nnntrolled
•F-l »"f- •{ -i-irvc*
Baseline: External floating roof
tank, welded construction with
vapor-mounted primary seal.
External
Abbreviation
notation
EFRms
EFRms,cf,ss
EFRvm,cf,ss
EFRlm,cf,ss
............
,inu°rder of Decreasing emission rates with Control
1
o
Conversion to an internal floating roof tank
would
-------
Decreasing the annual turnover rate decreases the emission
rate for fixed roof tanks. Conversely, the turnover rate has
little effect on internal and external floating roof tank
emission rates. Therefore,. the higher the turnover rate, the
larger the difference between fixed roof and floating roof tank
emission rates.
The vapor pressure of the stored VOL has an effect on the "
relative emission rates of the equipment options. As the vapor
pressure, of .the. stored- liquid-increases, -.-the-: emission rates from
both fixed and floating roof tanks increase. However, the vapor
pressure functions in the equations used to estimate losses from
fixed and floating roof tanks are different and the percent
increase in floating roof tank emissions is greater than the
percent increase in fixed roof tank emissions for a similar
increment in vapor pressure. Within the range of conditions
commonly found in VOL storage vessels, however, neither the
effect of the vapor pressure nor the turnover rate changes the
rank of the fixed roof tank and floating roof tank equipment
options.
4.2 FIXED ROOF TANKS
A fixed roof tank is the minimum acceptable equipment
currently employed for storing VOL. The discussion of control
techniques, therefore, relates the effectiveness of alternative
storage equipment types to the effectiveness of fixed roof tanks.
Working and breathing losses normally incurred from storing VOL
in fixed roof tanks can be reduced in the following ways:
1. By installing an internal floating roof with appropriate
fittings and one of the seal systems previously discussed in
Chapter 2; or
2. By installing and using a vapor recovery system (e.cr. ,
carbon adsorption or refrigerated condensation) or a vapor
control system (e.g.,. incineration).
This list defines only the major types of control techniques
.that apply to VOL storage-. Optional equipment designs that
influence the effectiveness of minimizing VOL emissions exist
within each major type of control technique. The- following:
4-4
-------
sections discuss the relative effectiveness of these equipment
options.
4.3 INTERNAL FLOATING ROOF TANKS
Internal floating roof tanks with rim seal systems emit less
VOC per unit of storage than fixed roof tanks. Internal floating
roofs can be used directly as a control device for existing fixed
roof tanks.
Depending on the type of roof and seal system selected, the
number; Of "turnovers ,-•. tank- volume, - and- liquid type, installing an
internal floating roof in a model fixed roof tank reduces the
emission rate by 69 to 98 percent. An internal floating roof,
regardless of design, reduces the area of exposed liquid surface
in the tank. Reducing the area of exposed liquid surface, in
turn, decreases the evaporative losses. The majority of the
emissions reduction is achieved through the floating roof vapor
barrier that precludes direct contact between a large portion of
the liquid surface and the atmosphere. All floating roofs share
this design benefit. The relative effectiveness of one floating
roof design over another, therefore, is a function of how well
the floating roof'can be sealed.
i
From an emissions standpoint, the most basic internal
floating roof design is the noncontact, bolted, aluminum internal
floating roof with a single vapor-mounted wiper seal and
uncontrolled fittings. Though the NSPS (40 CFR 60 Subpart Kb)
requires the use of a secondary seal with vapor-mounted primary
seals, there are many existing tanks not covered by NSPS that
have only a single vapor-mounted primary seal. As discussed in
Chapter 3, there are four types of losses from this design.
These losses, with an estimate of their respective percentage
contributions to the total loss from an internal floating roof
tank (volume = 481 cubic meters [m3]- (16,980 cubic feet [ft3]);
vapor pressure =6.9 kiloPascals [kPa] (1 pound per square inches
[psia]), are as follows:
1. Rim or seal losses--35 percent;
2. Fitting losses--35 percent;
3. Deck seam losses--18 percent; and
4-5
-------
4. Withdrawal losses--12 percent.
These percentages will vary as a function of tank diameter,
equipment type, and throughput.
With the exception of withdrawal losses, which are inherent
in all floating roof designs, the losses listed above can be
reduced by using roofs with alternative design features. The
following sections elaborate on the alternative equipment that
can be employed on internal floating roofs. The discussion is
arranged according to the major emissions categories.
4.3.1 Controls for Fitting Losses
Fitting losses occur through the penetrations in an internal
floating deck. Penetrations exist to accommodate the various
types of fittings that are required for proper operation of an
internal floating' roof. Fitting losses can be controlled with
gasketing and sealing techniques or by substituting a lower-
emitting fitting type that serves, the same purpose. Table 4-3
lists the fitting types-that are pertinent to emissions and an
abbreviated description of the equipment that is considered to be
representative of "uncontrolled" fittings and "controlled"
fittings.1 Certain fitting types are not amenable to control.
These are not listed in .Table 4-3.
4.3.2 Controls for Seal Losses
Internal floating roof seal losses can be minimized in
either one of two ways or their combination:
1. By employing liquid-mounted primary seals instead of
vapor-mounted seals; arid/or
2. By employing secondary seals in addition to primary
seals.
All seal systems should be designed, installed, and
maintained to minimize the gap between the seals and the tank
shell. Data from emission tests conducted on internal floating
roof tanks support the general conclusion that seal losses
increase rapidly when .the seal gap exceeds 63.5 square
centimeters per meter (em2/m) (3 square inches per foot [in2/ft] )
of tank diameter. Below this level, the effect of seal gap on
seal loss is much less pronounced-.
4-6
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TABLE 4-3. "CONTROLLED" AND "UNCONTROLLED" INTERNAL FLOATING
ROOF DECK FITTINGS1
Deck fitting type
1. Access hatch
2. Automatic gauge
float well
. 3. Column well
4. Ladder well
5. Sample pipe or well
6.- Vacuum breaker
Equipment descriptions
Uncontrolled
Unbolted, ungasketed cover*; or
unbolted, gasketed cover
Unbolted, ungasketed cover*; or
unbolted, gasketed cover
Built-up column-sliding cover,
ungasketed ;
Ungasketed sliding cover*
Slotted pipe-sliding cover, ungasketed;
or slotted pipe-sliding cover, gasketed
Weighted mechanical actuation,
ungasketed
Controlled
Bolted, gasketed cover
Bolted, gasketed cover
Built-up column-sliding cover,
gasketed; or
Pipe column-flexible fabric
sleeve seal for tanks with pipe
columns
Gasketed sliding cover
Sample well with slit fabric
seal, 10% open area
Weighted mechanical actuation,
gasketed
The fittings assumed in the uncontrolled case for estimating the effectiveness of fittings controls are marked
with a single asterisk in the above table. This fittings scenario is representative of no single tank, but rather is
the composite of what is estimated based on a survey of users and manufacturers to be typical of fittings on the
majority of tanks currently in service. Note that the sample well with slit fabric seal was used in the
"uncontrolled" case for calculating emissions because it is in common use. It was also used in the "controlled"
case because it is the lowers emitting fitting type.
4-7
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The effectiveness of alternate internal floating roof seal
systems can be evaluated through inspection of the rim seal loss
factors (KR) that have been developed based on test data for
estimating losses for-various seal systems. These factors are
- listed in Table 4-4.
4.3.3 Deck- Seam Losses
Depending on the type of floating roof employed, deck seam
• losses can contribute to the total loss from an internal floating
roof. For the model tank used as a basis for comparison
throughout this section (i.e., blFR^) , deck seam losses are
18 percent of the total loss.
Deck seam losses are inherent in several floating roof
types. Any roof constructed of sheets or panels fastened by
mechanical fasteners (bolted) is expected to experience deck seam
losses. Deck seam losses are considered to be a function of the
length of the seams only and not the type of the seam or its
position relative to the liquid surface. Selecting a welded roof
rather than a bolted roof eliminates deck seam losses.
4.4 EXTERNAL FLOATING ROOF TANKS
Most external floating roof tanks are constructed of welded
steel and are equipped with shoe primary seal systems. There are
still a significant number of tanks storing liquids with vapor
pressures less than 1.5 psia with no secondary seal. Because
these tanks do not experience deck seam losses, there are only
three types of losses that can result from this roof design:
1. Rim or seal losses;
2. Fitting losses; and •
3. Withdrawal losses.
These losses,, with an estimate of their respective contributions
to the total loss from an external floating roof tank
(volume = 481 m3 ;• vapor pressure = 6.9 kPa [the same capacity and
vapor pressure as the tank used to estimate internal floating
roof tank emissions]) are as follows:
1. Rim or seal losses--68 percent;
2. Fitting losses--28 percent; and
3.. Withdrawal losses---4, percent.
4-8
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TABLE 4-4.
INTERNAL FLOATING ROOF RIM SEAL SYSTEMS SEAL LOSS
FACTORS AND CONTROL EFFICIENCIES
Seal system
Vapor-mounted
primary seal only
Liquid mounted or
shoe primary seal
only -'••"• •
Vapor - mounted
primary and
secondary seals
Liquid-mounted or
shoe primary and
secondary seals
KR
(Ib-mole/ft-year)
6.7
3.0
2.5
1.6
Seal loss control
efficiency related
to baseline
IFR .baseline (0%)
55%
63%
76%
4-9
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These percentages can vary drastically according to tank
diameter, equipment type, and throughput.
With the exception of withdrawal losses, which are inherent
in all floating roof designs, the losses listed above can be
reduced by employing roofs with alternative design features. The
following sections elaborate on the alternative equipment that
can be used on external floating roofs. The discussion is
arranged according to the major emissions categories.
Rim seal losses that are 'similar in nature to those
experienced by internal floating roof tanks also occur with
external floating roof tanks. The only difference in this
respect between external floating roofs and internal floating
roofs is that the external floating roof seal losses are believed
to be dominated by wind- induced mechanisms.
4.4.1 Controls for Fitting Losses
Fitting losses from external floating roof tanks occur in
the same manner as fitting losses from internal floating roof
tanks: through the penetrations in the floating roof deck. As
mentioned earlier, these fittings are necessary for the normal
operation of the external floating roof. However, these fitting
losses can be controlled with gasketing and sealing techniques or
by the substitution of a lower emitting fitting type that serves
the same purpose. Table 4-5 lists the fitting types that are
pertinent to emissions and an abbreviated description of the
equipment that is considered to be representative of
"uncontrolled" fittings and "controlled" fittings. Certain
fitting types are not amenable to control and are not listed in
Table 4-5.
4.4.2 Controls for Withdrawal
Withdrawal losses in external floating roof tanks, as with
internal floating roof tanks, are entirely a function of the
turnover rate and inherent tank shell characteristics. No
applicable control measures have been identified to reduce
withdrawal losses from floating roof tanks.
4-10
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TABLE 4-5. "CONTROLLED" AND "UNCONTROLLED" EXTERNAT *ro .
j ROOF DECK FITTINGSJT 2 EXTERNAL FLOATING
Access hatch
^^—-i^^^s
.Equipment description^
Uncontrolled IZZc
Unbolted, ungasketed cover- Ho1 ..^ !
or unbolted, gasketed covlr «ver*' 9asketed
2: Gauge float in Unbolted, ungasketed
COVer : Of lintel . a
3 . Guide -
pole/sample
well**
Sample well
• •
Vacuum breaker
—
Jtoof drain
^^^"^"•"""•^•'-••"^Mr--
Rim vent13
—* **' ••'"yaB.isececi
cover ; or unbolted,
gasketed cover
e—C"-• *-***ycL».l^6
—-, cover with or
without float; or unslotted
Pipe-sliding cover
ungasketed*
• ____
Weighted mechanical
_actuation^
Weighted mechanical
actuation,
ungasketed
Weighted mechanical
actuation- ungasketed
.
Bolted, gasketed cover
—
Unslotted pipe-sliding
cover, gasketed
^^^"^^•m
Weighted mechanical
actuation, crasleat-orn
Weighted mechanical
actuation,
gasketed*
^^^""""^••"^""•^•••••B
closed
——•MM.™_ ^^
Weighted mechanical
jactuation, make*.***
fittings assumed in th. - ' ^"'^
'
4-11.
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4.4.3 Controls For Rim or Seal Losses
Rim seal losses from external floating roof tanks vary
depending on the type of seal system employed. As with internal
floating roof rim seal systems, the location of the seal (i.e.,
vapor- or liquid-mounted) is the most important factor affecting
the effectiveness of resilient seals for external floating roof
tanks. Liquid-mounted seals are more effective than
vapor-mounted seals at reducing rim seal losses. Metallic shoe
seals, which commonl y, are. -employed, on. jexternal.... float ing, roof
tanks, are more effective than vapor-mounted resilient seals but
less effective than liquid-mounted resilient seals.
The relative effectiveness of the various types of seals can
be evaluated by analyzing the seal factors (KR factor and wind
velocity exponent, N) contained in Table 3-2 of the previous
chapter. These seal factors were developed on the basis of
emission tests conducted on a pilot-scale tank. The results of
the emission tests are published in an American Petroleum
Institute bulletin.2 To compare the relative effectiveness of
the alternate seal systems, the seal factors were used with an
assumed wind velocity (10 miles per hour) to generate directly
comparable emission factors. These factors, which have meaning
only in comparison to one another, are listed in Table 4-6 for
alternative seal systems. From the information in Table 4-6, it
is clear that vapor-mounted primary seals on external floating
roof tanks are significantly less effective than liquid-mounted
or metallic shoe primary seals. Further, secondary seals provide
an additional measure of control. Retrofitting an external
floating roof tank with a self-supporting fixed roof would
convert the tank to an internal floating roof tank and eliminate
the wind influence thereby reducing the rim seal losses.
4.5 VAPOR CONTROL OR RECOVERY SYSTEMS ON FIXED ROOF TANKS
Losses from fixed roof tanks can be reduced by collecting
the vapors.and- either recovering or oxidizing the VOC. In a.
typical vapor control system, vapors remain in the tank until the
internal pressure reaches a preset level. A pressure switch,
which senses;the pressure buildup in the tank, then"activates
4-12
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TABLE 4-6.
EXTERNAL FLOATING ROOF TANK SEAL SYSTEM CONTROL
EFFICIENCIES51'b
Seal system description.
Vapor-mounted resilient
primary seal only
Vapor-mounted resilient
primary seal and
. secondary seal
Metallic shoe primary
seal only
Metallic shoe primary
seal with a shoe -mounted
wiper seal
Liquid -mounted resilient
primary seal only
Metallic shoe primary
seal with rim-mounted
secondary seal
Liquid -mounted resilient
primary seal with rim-
mounted secondary seal
Emissions
factor,a
(10)N6KP
239
80
38
13
11
2.0
1.8
Seal loss control
ef ficiencyc
EFR baseline (0%)
66%
84%
95%
95%
99%
99%
aFor well designed seal systems with "average" gaps between the
seal and the tank shell. Calculated from Kp and N values listed
listed in Table 3-2. K
External floating roof tanks can be converted to an internal
floating roof tank by retrofitting with a self-supporting fixed
roof. This would eliminate wind influences thereby reducing rim
seal losses.
GRim seal loss control efficiency relative to the least effective
seal alternative.
4-13
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blowers to collect and transfer the vapors through a closed vent
system. A redundant blower system may be provided in this
service to ensure that no vapors will be released to the
atmosphere in the event of a primary blower malfunction. The
closed vent system ducts the vapors to a recovery or oxidizer
unit.
To prevent flashbacks from the control equipment, systems
can be designed to operate so that vapor levels are above the
upper explosive limit, enriched with natural gas to 1.2 times the
upper explosive limit (21 percent), or inerted with nitrogen or
inert flue gas. Other safety precautions are also exercised such
as nitrogen blanketing and using flame arrestors. The particular
precautions employed'vary widely depending on the design of
individual systems and the operating preference of individual
companies.
4.5.1 Carbon Adsorption
Although there is little commercial operating experience for
VOL applications of carbon adsorption, oarbon adsorption has been
demonstrated in the recovery of other organic vapors, and
applying this technology to VOL recovery should not be
difficult.3 Application of this vapor control technology,
however, is probably more widespread in the chemical industry
that in the petroleum industry. The general principle of
adsorption is described below to facilitate the description of a
carbon adsorption unit.
Carbon adsorption uses the principle of carbon's affinity
for nonpolar hydrocarbons to remove VOC's from the vapor phase.
Activated carbon is the adsorbent; the VOC vapor that is removed
from the airstream is referred to as the adsorbate. The VOC
vapor is adsorbed by a physical process at the surface of the
adsorbent. The VOC carbon adsorption unit consists of a minimum
of two carbon beds plus a regeneration system. Two or more beds
are necessary to ansura that one bed will be available for use'.
while the other is being regenerated.
The carbon beds can be regenerated using either steam or
vacuum. In steam regeneration, steam is circulated through the.
4-14
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bed, raising the VOC vapor pressure. The vaporized VOC is then
removed from the steam: the steam-VOC mixture is condensed,
usually by an indirect cooling water stream, and routed to a
separator. The VOL is then decanted and returned to storage, and
the contaminated water is sent to the plant wastewater system for
treatment. Cooling water, electricity, and steam are the
required utilities for a steam regeneration system. The other
method of regenerating the carbon, vacuum regeneration, is
performed by pulling a high vacuum on the - carbon-bed. The-VOG
vapor desorbed by this process is condensed and returned to
storage.
4.5.2 Oxidation Units
Thermal and catalytic oxidizers have been used successfully
to dispose of VOC vapors in other industries." Thermal oxidation
is the -most, direct means of VOC vapor disposal and uses the
fewest moving parts. The vapor mixture is injected via a burner
manifold into the. combustion area of the incinerator. Pilot
burners provide the ignition source, and supplementally fueled
burners add heat when required. 'The amount of combustion air
needed is regulated by temperature-controlled dampers.
A water-seal flame arrestor can be used to ensure that flashbacks
do not spread from the burner to the rest of the closed vent
system. As mentioned, safety practices and equipment vary widely
depending on system design and the operating preference of
individual companies. A significant advantage of thermal
oxidizers is that they can dispose of a wide range of VOC's.
Fuel consumption and catalyst replacement are the major cost
factors in considering thermal and catalytic oxidation.
4'-5.3' Refrigerated Vent Condensers
A refrigerated vent condenser collects the VOL vapors
exiting through the vents and condenses them. The vents open and
close.-asvthe pressure within the tank increases and decreases.
?ressure changes occur when the tank, is being filled or ampciad
or when the temperature changes. Condensers should be designed
to handle the maximum flow rate expected at any given time, which
usually, occurs during filling. Freezing of moisture is handled
4-15
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by a defrost-separation-recovery system. The efficiency of vent
condensers depends upon the vapor concentration and the
condensing temperature.
4-5-4 Control Efficiencies of Vapor Recovery or Control Systems
The carbon adsorption vapor control system is estimated to
reduce emissions from the VOL storage vessel by approximately
95 percent or greater. This efficiency is based on a measured
carbon adsorption unit efficiency of 98 percent during gasoline
loading operations.4 ..._ , ..._...-•. _r.-
The refrigerated vent condenser is capable of achieving
emission reductions of greater than 90 percent from VOL storage
vessels. However, as explained in the previous section, the
condenser efficiency depends on the vapor concentration of the
emission stream and the designed condensation temperature.
The thermal oxidation vapor control system is capable of
achieving emission reductions of 98 percent or greater from VOL
storage vessels. This efficiency is based on a measured thermal
oxidation unit efficiency of 98 percent during a wide variety of
operations.5'6 At very low flow rates or at low VOC inlet
concentrations, somewhat less than 98 percent of the VOC vapors
leaving the storage vessel may be incinerated.
4.6 RETROFIT CONSIDERATIONS
This section discusses possible considerations that owners
and operators may have in retrofitting their tanks with
alternative design equipment. 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.
4-5-1 Fixed Roof Tanks with Internal Floating Rnn-fg
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. Antirotational
guides should be installed to keep floating roof openings in
alignment with fixed roof openings.
4-
-------
Special vents may 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.
Alternatively, other fire protection devices such as flame
arresters may be provided instead of circulation vents.
4.6.2 Secondary Seals on Existing Internal Floating Roofs
Retrofitting problems may be encountered when installing a
secondary seal on a noncontact internal floating roof. Unlike
some contact internal floating roofs, 'the noncontact "internal -
floating roof generally does not have an outer rim on which to
attach a secondary seal. Extensive modifications to the
noncontact internal floating roof may be required in order to
install a secondary seal. This problem may also occur on some
designs of contact internal floating roofs. Additional rim
flotation may be required when retrofitting a secondary seal on a
contact or noncontact internal floating roof to ensure that the
roof will remain buoyant with the additional weight of the
secondary seal.
4.6.3 Liquid-Mounted Seals on Existing Internal Floating Roofs
Liquid-mounted seals are generally heavier and exert more
compressive force than vapor-mounted seals, particularly
wiper-type seals. When retrofitting existing internal floating
roofs, rim flotation may become a problem, particularly in the
noncontact-type designs. The heavier seal may cause the rim of
the noncontact deck to sink below the liquid surface.
4.6.4 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. When adding a
secondary seal it is not always necessary to degas the tank
because there is typically a predrilled horizontal flange on
which the seal can be attached.7 However, if the flange has to
be repaired or modified to be able to properly mount the
4-17
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secondary seal, this may require hot work and the tank should be
cleaned and degassed prior to the installation.
4.6.5 Self-Supportinq Fixed Roofs on External Floating Roof
Tanks
Several design issues are encountered in the retrofit of a
self-supporting fixed-roof to an existing open top tank. For
example, the weight of the fixed roof produces localized loading
on the tank. The self-supporting fixed roofs are typically made
of aluminum, .which results _in_the_potential_.for differential
movement between the aluminum fixed roof and the steel tank
shell due to the difference in their coefficients of thermal
expansion.
4.7 PROBLEM LIQUIDS AND MATERIALS OF CONSTRUCTION
Many liquids such as chlorinated organic solvents cannot
utilize the same control technologies previously mentioned.
These problem liquids are corrosive in nature and may degrade
certain metals as well as seal materials. For problem liquids
that corrode aluminum, a welded steel floating roof with a
specialty seal that can withstand attack by the liquid can be
used to reduce emissions. If the liquid is too corrosive to
utilize a welded-steel floating roof or specialty seal, or is
stored in a fiberglass fixed roof tank, an applicable control
technology is to vent emissions to an add-on pollution control
device such as an incinerator or a stainless steel condenser.
4-18
-------
4.8 REFERENCES
1.
2.
3.'
4.
5.
6.
7.
The American Petroleum Institute. Evaporative Loss From
Internal Floating-Roof Tanks. API Publication 2519, Third
Edition. June 1982.
The American Petroleum Institute. Evaporative Loss From
External Float-ing-Roof Tanks.. API Publication No 2517
Third Edition. February 1989. '
U. S. Environmental Protection Agency. Evaluation of
Control Technology From .Benzene Transfer-Operations. ....
Research Triangle Park, NC. EPA-450/3-78-018. April 1978.
Letter from McLaughlin, N., EPA, to D. Ailor, TRW Inc.
May 3, 1979. Comments on the benzene storage model plant
package.
Letter and attachments from Mascone, D. EPA/CPB, to Farmer
J. _EPA/OAQPS.. June 11, 1980. Memo concerning thermal
incinerator performance for NSPS.
U. S. Environmental Protection Agency. Organic Chemical
Manufacturing, Volume 4: Combustion Control Devices
Research Triangle Park, NC. Publication No.
EPA-450/3-80-026. December 1980.
Telecon. deOlloqui. V., MRI with Moffit, L.
Pittsburgh-Desmoines Corp. Discussion about retrofitting a
secondary seal on an external floating roof tank.
June 26, 1991.
4-19
-------
-------
5.0 ENVIRONMENTAL IMPACTS OF CONTROL OPTIONS
5.1 ENVIRONMENTAL IMPACTS
Two types of environmental impacts result from controlling
VOL storage tanks: (1) impacts from reducing VOC emissions from
the tank and (2) secondary impacts from implementing the control
' options. The secondary impacts result from cleaning and
degassing the tank prior to installing some types of equipment
such as an internal floating roof or replacing a primary seal.
Impacts were developed for model tanks (defined in
Chapter 3) by analyzing the control options applicable to fixed-
roof, internal floating roof, and external floating roof tanks
described in Chapter 4. Nationwide emissions estimates and tank
populations for each tank type were estimated from information
developed in the 1984 background information document for VOL
storage tanks.1 Nationwide secondary environmental impacts for
each tank type were estimated by determining the secondary
impacts of the control options for a typical size model tank,
then multiplying the impacts for this tank by the estimated
number of tanks affected at the stored liquid vapor pressure and '
tank capacity cutoffs'of each specific control option. The
following sections present the model tank and nationwide
environmental impacts of each control option.
5.2 FIXED ROOF MODEL TANKS
Control equipment for fixed roof model tanks is described, in
Chapter 4, Section 4.2. The control equipment hierarchies
outlined in. Table- 4-1 were organized into control options.
Specific options considered include:
1. A bolted construction internal floating roof with a
vapor-mounted, primary seal and uncontrolled fittings (Option I)•
5-1
-------
2. A bolted construction internal floating roof with a
vapor-mounted primary and secondary seals with controlled
fittings(Option II);
3. A bolted construction internal floating roof with a
liquid-mounted primary and secondary seals with controlled
fittings (Option III); or
4. A welded construction internal floating roof (steel pan
or fiberglass-reinforced plastic [FRP] deck) with a liquid-
mounted primary and secondary seals with controlled fittings
(Option IV).
5.2.1 Emissions Reductions
These control options were applied to the model tanks
described in Chapter 3 and emissions profiles were generated.
Figure 5-1 presents the VOC emissions from the model fixed-roof
tanks greater than 151,420 liters (L) (40,000 gallons [gal])
storing a model VOL at vapor pressures of 3.4, 5.2, and
6.9 kiloPascals (kPa) [0.5, 0.75 and 1 pound per square inch
absolute (psia)] at 10 and 50 turnovers per year. Figure 5-1
shows that fixed roof tank emissions increase significantly with
an increase in turnovers or an increase in vapor pressure.
Figure 5-2 presents model tank emissions for the same tank
capacities, vapor pressures, and turnovers as Figure 5-1 but for
a model crude oil. A comparison of the VOC emissions from the
model VOL and crude oil tanks at the same turnover rates and
vapor pressures shows that the model crude oil tanks emit less
VOC than the model VOL tanks.
The effect of the control options on fixed-roof tank
emissions is shown in Figure 5-3. This figure shows that for
50 turnovers per year and an absolute liquid vapor pressure of'
6.9 kPa (l.O psia), the installation of a basic internal floating
roof provides a significant emission reduction for fixed-roof
tanks. However, applying additional controls to the internal
floating roof such as controlling fittings or adding a secondary
seal does not provide any significant emission reduction beyond
that achieved by the installation of the internal floating roof.
5-2
-------
Figures 5-4 and 5-5 present emissions for Options I - V at
10 and 50 turnovers per year. A comparison of these figures
shows that the turnover rate does not significantly effect
emissions from internal floating roof tanks, which is opposite
from that shown in Figure 5-2 for fixed-roof tanks where the
.turnover rate significantly effects emissions. Therefore, the.
working or withdrawal losses, which are dependent upon the
turnover rate or throughput, account for a significantly larger
percentage of. emissions-: -front-a. fixed---roof- -tank- than- an- internal -
floating roof tank.
Figures 5-4 and 5-5 also present the incremental emission
reductions achieved by Options II through V beyond that achieved
by Option I, the installation of an internal floating roof. The
data presented in these figures reaffirms that the incremental
emission reduction achieved by additional controls is small
compared to the emission reduction achieved by the installation
of the internal floating roof.
For fixed-roof tanks with capacities ranging from 75,700 to
151,420 L (20,000 to 40,000 gal), the same control options apply
as those shown in Figures 5-4 and 5-5 and the effects of the
control options on emissions are similar. However, for fixed-
roof tanks less than 75,700 L (20,000 gal), the only control
option examined was the installation of a condenser with a
required control efficiency of 90 percent. This was the only
control option-examined because most storage tanks below 75,700 L
(20,000 gal) are horizontal rather than vertical tanks and a
large percentage of these tanks are also underground; therefore,
the installation of internal floating roofs is not practical.
5-2.2 Secondary Impacts
Secondary impacts are those impacts not directly associated
with the VOC emission reductions; described in the preceding
section, but rather those with implementing the control option.
The* following- sections- describe the secondary environmental
impacts associated with implementing the control options for
fixed-roof .tanks.
5-3
-------
5.2.2.1 VOC Emissions from Degassing and Sludcre Handling.
Prior to installing an internal floating roof in a fixed-roof
tank, the tank needs to be cleaned and degassed. Cleaning and
degassing is necessary to allow the tank to be modified to
install an internal floating roof and to allow workers to enter
the tank. The degassing emissions are those emissions that will
be released from the tanks' vapor space prior to cleaning, and
sludge handling emissions are released from the tank in the
process of removing sludge from the tank during cleaning. Sludge
handling emissions are difficult to quantify because they depend
entirely on the care the tank service company takes in removing
the sludge from the tank.
Emission estimates for.degassing and sludge handling were
estimated based on the quantities of rinseate required to clean
the tank and the amount of residual sludge in the bottom of the
tank. Estimates obtained from a tank service company indicate
that 7,570 L (2,000 gal) of sludge and 3,790 L (1,000 gal) of
rinseate would result from cleaning a 757,000 L (200,000 gal)
tank.2 Based on these values, it was estimated that 1 Mg
(1.1 ton) of VOC emissions are released during degassing of the
tank. Additional VOC emissions could be released during the
sludge handling operations but the quantity of these emissions is
unknown
5-2.2.2 Solid and Hazardous Waste. ..Another possible source
of secondary emissions is the treatment, storage or disposal of
tank sludges and the rinseate used to clean the tank. The exact
regulatory status of the sludge and rinseate will be a function
of the contents of the tank and the properties of these
materials.
The sludge generated from the tank cleaning process could be
up to 90 percent liquid. Independent of any VOC emitted from the
liquid portion of the sludge, 11,360 L (3,000 gal) of solid waste
will be produced from cleaning a 757,000 L (200,000 gal) tank.1
This material may be industrial solid waste regulated under
provisions authorized by Subtitle D of RCRA; or alternatively it
may be a hazardous waste in which case treatment, storage, and
5-4
-------
disposal of this material would be regulated in accord with
regulations authorized by Subtitle C of RCRA. To the extent that
these materials are hazardous wastes, RCRA regulations would
require reduction of secondary emissions by prohibiting the use
of high emitting treatment, storage, and disposal techniques,
such as the use of land farming. Furthermore, secondary
emissions would be reduced by limiting emissions from other types
of treatment, storage, and disposal techniques. A variety of
methods-such, as incineration-are available to-treat, store, and-
dispose of hazardous waste sludge. If a facility were to
incinerate the sludge, there would potentially be minimal
emissions from the hazardous waste treatment, storage, and
disposal. The only emissions would be from degassing and sludge
handling. However, if a facility were to landfarm a Subtitle D
(nonhazardous) waste, virtually all of the emissions from the
sludge might be released to the atmosphere.
5.3 INTERNAL FLOATING ROOF TANKS
Control options for internal floating roof tanks are almost
identical to the control options for fixed-roof tanks and consist
of equipping the tank with:
1. A bolted construction internal floating roof with a
vapor-mounted primary seal and controlled fittings {Option I);
2. A bolted construction internal floating roof with a
vapor-mounted primary and secondary seals with controlled
fittings (Option II) ;
3. A bolted construction internal floating roof with a
liquid-mounted primary and secondary seals with controlled
fittings (Option III); or
4. A welded construction internal, floating roof (steel pan
or FRP deck) with a liquid mounted primary and secondary seals
with controlled fittings (Option IV).
The baseline internal floating roof tank -configuration was
assumed, to consist of a bolted-construction internal floating
roof with a vapor-mounted primary seal.
5-5
-------
5.3.1 Emissions Reductions
These control options were applied to the internal floating
roof (IFR) model tanks presented in Chapter 3. The VOC emission
reduction from the baseline IFR tanks for each emission control
option are shown in Figures 5-6 and 5-7 for a model VOL and crude
oil, respectively. As stated earlier, VOC emissions from
internal floating roof tanks do not depend as much on the number
of tank turnovers per year as the liquid vapor pressure and tank
capacity The Incremental .emissions reductions between
increasingly more stringent control options is relatively small
ranging from 5 to 20 kilograms (kg) [11 to 44 pounds (Ib)].
5.3.2 Secondary Impacts
5.3.2.1 VOC Emissions from Degassing and Sludae Handling.
All of the, control options for internal floating roof tanks
require cleaning and degassing the tank. Therefore, these
emissions will have to be considered when applying these control
options. Referring to the emissions estimates developed for a
757,000 L (200,000 gal) tank in Section 5.2.2, 1 Mg (1.1 ton) may
be released from degassing the tank. Depending on the method of
disposal, the sum of the cleaning and degassing emissions may be
greater than the emission reductions obtained from the
implementation of the control options (<1 Mg [l.l ton]). For
this reason, it may be necessary to minimize the environmental
impacts associated with cleaning and degassing by requiring
internal floating roof tanks to implement the control options
when the tanks are out of service for their regularly scheduled
cleaning.
5.3.2.2 Hazardous Waste. The amount of hazardous waste
generated from disposing of the tank sludge and rinseate is
equivalent to that from fixed-roof tanks. Again, the method of
treatment, storage, and disposal of the waste is the determining
factor as to the quantity of VOC-emitted to the -atmosphere.
5.4 EXTERNAL FLOATING ROOF TANKS
Control equipment for external floating roof tanks is
discussed in Chapter 4, and the control options are described in
Table 4-2. The control option for an external floating- roof.
5-6
-------
(EFR) tank equipped with a mechanical shoe primary seal consists
of adding a secondary seal and controlling fittings. Two control
options exist for an EFR tank equipped with a vapor-mounted
primary seal only;. (1) adding a secondary seal and controlling
' fittings, and (2) replacing the vapor-mounted primary seal with a
liquid-mounted primary seal, adding a secondary seal, and
controlling fittings.
5.4.1 Emissions Reductions
The control options presented above were applied-to the -
model tanks described in Chapter 3. The emissions for the two
baseline EFR tank configurations and the corresponding control
option(s) are shown in Figures 5-8 and 5-9, respectively. From
Figure 5-8 it is shown that the greatest emission reduction for a
baseline external floating roof tank with metallic shoe primary
seal is obtained from the addition of a secondary seal and
controlled fittings. From Figure 5-9 it is shown that the
greatest emission reduction for a baseline external floating roof
tank with a vapor-mounted primary seal is obtained by the
substitution of a liquid-mounted primary for the vapor-mounted
primary seal in conjunction with the addition of secondary seals
and controlled fittings.
5.4.2 Secondary Impacts
5.4.2.1 VOC Emissions from Degassing and Sludae Handling.
In order to install a secondary seal in an external floating roof
tank, a tank may not always have to be cleaned and degassed.
This is because the external floating roof tanks are typically
equipped with a flange on which the secondary seal can be
bolted.3 This may eliminate the need for cutting, welding, or
drilling,-, therefore, there may be no need to clean and degas the
tank.. However, if the flange is in poor condition or if the
flange is unsuitable for the installation.of a secondary seal,
the tank would have to be cleaned and degassed prior to the
necessary welding. For the purposes of this ACT, it has been
assumed that degassing would be required prior to installing a
secondary seal. In addition, no modifications that would require
degassing, of the= tank, are-needed-', to control fittings. For
5-7
-------
purposes of assessing secondary impacts, the quantity of
emissions released from an external floating roof tank as a
result of degassing were the same as those described previously
for similar sized fixed-roof and internal floating roof tanks.
5-4.2.2 Hazardous Waste. The amount of solid waste
generated from treatment, storage, and disposal of the tank
sludge and rinseate is equivalent to that from'fixed-roof or
internal floating roof tanks of a similar size. As stated
previously, the disposal method is the determining, factor as to_
the quantity of VOC emitted to the atmosphere as a result of
solid waste treatment, storage, and disposal.
5.5 NATIONWIDE IMPACTS OF CONTROL OPTIONS
Nationwide environmental impacts were determined for each of
the three tank types and their associated control options. The
nationwide number of tanks and the amount of VOC emissions
associated with the three tank configurations (fixed, internal
floating, and external floating roofs) were estimated by taking
the tank population and emissions estimates developed for the
Volatile Organic Liquid NSPS and accounting for:
l. Tanks in nonattainment areas;
2. Tanks already regulated by either an existing CTG or
NSPS; and
3. Tanks not considered in the specific control option
because,the tanks were outside the tank capacity and vapor
pressure cutoffs of the control options.1
The tank capacity and vapor pressure cutoffs for each
control option were determined based on the combined
environmental and cost impacts of these options on a model tank
basis, once the number of affected tanks and the nationwide
emissions levels were determined for each option, nationwide
secondary impacts were then calculated. Secondary impacts were
assessed for a representative tank in each category and
multiplied by the number of affected tanks to obtain nationwide
impacts;
Tanks in nonattainment areas were determined from industry
profiles contained in the -198.7-Census-of Manufacturers Data and
5-8
-------
from a 1991 EPA database of county ozone nonattainment status.4 A
database was developed from this information that contains the
number of facilities by county and standard industry
classification (SIC) codes, and includes a classification of each
county as an attainment or nonattainment area. The total number
of facilities in SIC codes- 2911 (petroleum refining), 2861 (gum
and wood chemicals), 2865 (cyclic crudes and intermediates), and
2869 (industrial organic chemicals) were then compiled. After
compiling these estimates for each industrial segment, -the •"--•-'• •• -
percentages of the facilities located in nonattainment areas was
determined. These percentages (about 45 percent for the
petroleum industry and about 55 percent for the chemical
industry) were then applied to the tank population and emissions
estimates previously derived to obtain the base number of
affected tanks and emissions levels for each industrial
category.
Because the control options were segregated by tank capacity
and vapor pressure of the liquid stored in the tank, the base
number of tanks and corresponding emissions estimates for each
category had to be apportioned in a similar manner. Tank
population data apportioned by tank capacity and vapor pressure
was available to a limited extent. However, this information was
insufficient to apportion the tank population into the narrow
tank capacity and vapor pressure ranges required by the control
options. For example, tank population data was available for
tanks storing liquids in the vapor pressure range of 3.4 to
6.9 kPa (0.5 to 1.0 psia) at various tank capacity cutoffs.
However, the vapor pressure cutoffs required an estimate of the
tank population in the vapor pressure ranges from 3.4 to 5.2 kPa
(0.5 to 0.75 psia). and 5.2 to 6/9 kPa (0.75 to 1,0 psia).
Therefore, it was assumed that the number of affected tanks
within, the broader vapor pressure- ranges were distributed eoually
across the range. Using this approach, if 1,000 tanks were
within the broad range of 3.4 to 6.9 kPa (0.5 to 1.0 psia), then
500, tanks were- assumed to be in the range from, 3.4 to- 5.2. kPa
(0-.5- to 0.75 psia) and 500 tanks in the range from 3.4 to 6.9 kPa
5-9
-------
(0.75 to 1.0 psia). However, nationwide emissions estimates from
these tanks were apportioned into smaller vapor pressure ranges
according to ratios developed between the emissions levels and
the vapor pressure function, so that as the vapor pressure
increased the emissions estimates increased.
5.5.1 Fixed-Roof Tanks
The representative tank used to develop nationwide secondary
impacts for fixed-roof tanks was a 4.9 million liter (1.3 million
gallon) tank with a diameter of about 20 meters (m) (60 feet
[ft]) and a height of 15 m (48 ft). - The model liquid used to
determine nationwide impacts is jet naphtha that has the
following properties: (1) a molecular weight of 80 grams per
gram-mole (80 pounds per pound-mole); (2) a density of
0.72 kilograms per liter (kg/LJ (6 pounds per gallon (6 Ib/gal);
and (3) a product recovery factor of 350 dollars per megagram
($/Mg) (320 dollars per ton [$/ton]).
The nationwide impacts for fixed-roof tank control options
are presented in Table 5-1 and are listed from least to most
stringent. The total number of affected tanks estimated at the
vapor pressure cutoffs of 3.4, 5.2, 6.9 kPa (0.5, 0.75, 1.0 psia)
£s 3,000, 2,300, and 1,700 tanks, respectively. Of these totals,
approximately'70 to 75 percent are storing petroleum products and
the remaining 25 to 30 percent are storing organic chemical
products •.
5.5.2 Internal Floating Roof Tanka
The representative internal floating roof tank was the same
size as that of the representative fixed-roof tank.' This
representative tank is also storing the same model liquid as the
representative fixed-roof tank. The nationwide impacts^ for
internal floating roof tank control options is presented in
Tables 5-2 and 5-3. • The total number of affected tanks estimated
at the vapor pressure cutoffs of 3.4, S.6-,r 6.9., and 10,3 kPa
(0.5, 0.75, 1.0, and 1.5 psia) is 6,000, 5,300, 5,600, and 5,500,
respectively. Of these totals, approximately 75 percent are
storing petroleum products and the remaining 25 percent are
storing organic chemical products.
5-10
-------
The nationwide secondary environmental impacts for internal
floating roof tank options presented in Table 5-3 are provided
for informational purposes only. In implementing these control
options, the required control equipment would not be installed
until the IFR tanks are degassed and cleaned during the next
normal maintenance period for the tanks.
5.5.3 External Floating Roof Tanks
Neither nationwide emissions estimates nor secondary impacts
could be quantified"for external floating roof tanks because no
data was available that could be used to determine the number of
tanks in each vapor pressure range according to seal type.
However, the nationwide emission reductions obtained from
applying secondary seals and controlling fittings could be
approximated based on the number of EFR tanks. At vapor pressure
cutoffs of 3.4, 5.2, 6.9, and 10.3 kPa (0.5, 0.75, 1.0, and
1.5 psia) and greater and tank capacity cutoffs of 151,420 L
(40,000 gal) and greater at each vapor pressure, the estimated
nationwide emission reductions are 9,390, 9,260, 9,060, and
8,210 Mg/yr (10,330, 10,180, 9,960, and 9,030 tons/yr),
respectively. The estimated number of affected tanks at these
same vapor pressure cutoffs is estimated at 6,600, 6,400, 6,300,
and 6,000, respectively.
5-11
-------
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TABLE 5-2. NATIONWIDE ENVIRONMENTAL IMPACTS OF THE INTERNAL
FLOATING ROOF TANK CONTROL OPTIONS
Nationwide emission estimates
Mg/yr (tons/yr)
Nationwide emissions reduction,
Mg/yr (tons/yr)
Control options/cutoff values
VP = 0.5a
VP a 0.75b
VP = 1.0C
VP = 1.5d
Control Option I
16,430 (18,070)
16,260 (17,890)
16,010 (17,610)
15,620(17,180)
VP = 0.5a
VP = 0.75b
VP = 1.0C
VP a 1.5d
Control Ontion n
15,570(17,120)
15,410 (16,950)
15,160(16,670)
14,780 (16,260)
860 (950)
850 (940)
850 (940)
840 (920)
VP a 0.5a
VP a 0.75b
VP a l.QC
LS
Control Ontion TTT§
11,680(12,840)
11,540(12,700)
11,320(12,450)
10,990 (12,090)
4,750 (5,230)
4,720(5,190)
4,690(5,160)
4,630 (5,090)
VP a Q.5a
VP = 0.75b
VP » 1.0°
VP m l.5d
Control Ontion I\
10,140(11,150)
10,000(11,000)
9,800 (10,780)
9,490 (10,440)
6,290 (6,920)
6,260 (6,890)
6,210 (6,830)
6.130(6,740)
VP = 0.5a
VP a 0.75b
VP - 1.0C
VP = 1.5d
4,560 (5,010)
4,450 (4,900)
4,290 (4,720)
4,050 (4,450)
11,870(13,060)
11,810(12,990)
11,720(12,890)
11,570(12,730)
aBased on a vapor pressure cutoff value of 0.5 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
bBased on a vapor pressure cutoff value of 0.75 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
cBased on a vapor pressure cutoff value of 1.0 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
Based on a vapor pressure cutoff value of 1.5 psia and a tank capacity cutoff value of 40,000 gallons and
greater. . °
'Control Option I a control fittings.
Control Option n = control fittings and add a secondary seal.
SControl Option in = replace vapor-mounted primary seal with liquid-mounted primary seal, secondary seals
ana controlled fittings.
Control Option IV . npi^ noncontact IFR with a welded steel contact EFR with liquid-mounted primary
seals, secondary seals, and controlled fittings. f «™uy
5-22
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TABLE 5-3. NATIONWIDE SECONDARY ENVIRONMENTAL IMPACTS OF THE
INTERNAL FLOATING. ROOF TANK CONTROL OPTIONS
Control options/cutoff values
Baseline
VP = 0.5a
VP = 0.75b
VP = 1.0C
VP = 1.5d
Control Option Je
VP = 0.5a
VP = 0.75b
VP = 1.0C
VP = 1.5d
Control Option IP
VP = 0.5a
VP = 0.75b
VP = 1.0°
VP = 1.5d
Control Option HIS
VP = 0.5a
VP = 0.75b
VP = 1.0C
VP = 1.5d
Control Ootion IVn
VP = 0.5a
VP = 0.75b
YP = 1.0°
VP = 1.5d
Nationwide secondary emissions,
Mg/yr (tons/yr)
_ —
6,780-81,360 (7,458-89,500)
6,590-79,020 (7,240-86,922)
6,390-76,690 (7,030-84,360)
6,150-73,850 (6,770-81,240)
6,780-81,360 (7,458-89,500)
6,590-79,020 (7,240-86,922)
6,390-76,690 (7,030-84,360)
6,150-73,850 (6,770-81,240)
6,780-81,360 (7,458-89,500)
6,590-79,020 (7,240-86,922)
6,390-76,690 (7,030-84,360)
6,150-73,850 (6,770-81,240)
6,780-81,360 (7,458-89,500)
6,590-79,020 (7,240-86,922)
6,390-76,690 (7,030-84,360)
6,150-73,850 (6,770-81,240)
Nationwide hazardous waste
disposal I /gal
—
41 x 106 (37 x 106)
40 x 106 (36 x 106)
38 x 106 (35 x 106)
37 x 106 (34 x 106)
41 x 106 (37 x 106)
40 x 106 (36 x 106)
38 x 106 (35 x 106)
37 x 106 (34 x 106)
41 x 106 (37 x 106)
40 x 106 (36 x 106)
38 x 106 (35 x 106)
37 x 106 (34 x 106)
41 x 106 (37 x 106)
40 x 106 (36 x 106)
38 x 106 (35 x 106)
37 x 106 (34 x 106)
aBased on a vapor pressure cutoff value of 0.5 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
bBased on a vapor pressure cutoff value of 0.75 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
°Based on a.vapor pressure cutoff value.of 1.0 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
Based on a vapor pressure cutoff value of 1.5 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
eControi Option I = control fittings.
Control Option IL= control fittings and add a secondary seaL
^Control Option HI" = replace vapor-mounted primary seal with liquid-mounted primary seal, secondary seals.
and controlled fittings.
Control Option IV = replace noncontact IFR with a welded steel contact IFR with liquid-mounted primary
seals, secondary seals, and controlled fittings.
5-23
-------
-------
5.6 REFERENCES
1.
2.
3.
4.
U. S. Environmental Protection Agency. VOC Emissions from
Volatile Organic Liquid Storage Tanks--Background Information
for Proposed Standards. EPA-450/3-81/003a. Research
Triangle Park, NC. June 1984.
Telecon. deOllogui, V., MRI, to McManus, E., Four Seasons
Industrial- Services, Greensboro, North Carolina. June 1991
Information on cleaning and degassing of storage tanks.
Telecon. deOlloqui, V., MRI, to Mbffit, L., Pittsburgh/Des
Moines, Inc., Pittsburgh, Pennsylvania, -June 26, 1991 -
Information on the requirements for cleaning and degassing
prior to the installation of control equipment on external
floating roof tanks.
U. S. Environmental Protection Agency. 1991 Ozone
Nonattainment Status Data Base. National Air Data Branch,
5-24
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6.0 COST ANALYSIS OF CONTROL OPTIONS
6.1 INTRODUCTION .- •- .
This chapter presents the costs of equipping fixed-roof
(FR), internal floating roof (IFR), and external floating roof
(EFR) tanks with the control equipment described in Chapter 4.
Three types of cost data are presented:
1. Capital cost;
2. Annual cost; and
3. Cost effectiveness.
The cost analysis follows a prescribed approach. Capital
costs, which represent the initial investment for control
equipment and installation, are estimated based on vendor quotes
and EPA protocols. From these estimates, correlations and
factors have been developed to approximate capital costs for the
range of tank sizes commonly used in the industry. The capital
cost is annualized by applying a capital recovery factor, which
is based on an estimated equipment lifetime, and the interest
rate on the capital, and by adding costs for taxes and insurance.
The total annualized cost, excluding product recovery credits,
attributable to each type of control is estimated by adding
operating costs to the annualized capital cost. The total or net
annualized,cost, including product recovery credits, is estimated
by subtracting the value of the recovered product from the
annualized cost.. The amount of recovered product is equal to the
difference: in emissions between, the baseline and the control
option levels. Cost, effectiveness is the total annualized cost
divided by the emission reduction obtained by each control
technology ...
6-1
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6.2 EQUIPMENT COSTS
Capital equipment costs that depend on tank size were
obtained from vendors for various tank capacities and tank
diameters.1'3 A regression analysis was then performed on the
data to obtain an equation that could be used to develop capital
equipment costs for any tank capacity. The costs provided by
vendors and the equations used to develop model tank costs for
installing an IFR in a FR tank and for retrofitting a noncontact
IFR tank with a contact IFR are presented in Table 6-1. The cost
difference of--constructing-a .liquid-mounted primary seal rather
than a vapor-mounted primary seal is $65 per linear meter
($20 per linear foot).1 The additional cost of controlling
, fittings is estimated at $200 for newly installed floating roofs
and $600 for existing floating roofs.1 The installation of
secondary seals on existing internal floating roofs is estimated
at $83 per linear meter ($26/ft).1,2 On new installations there
is no additional charge for the secondary seals.
The retrofit cost to add secondary seals to an external
floating roof is estimated at $180 per linear meter ($54/ft).2
The additional cost of controlling fittings is estimated at $680,
which is mainly for controlling the guidepole fitting since other
EFR fittings are typically controlled already. The retrofit cost
for replacing a vapor-mounted primary seal with a liquid-mounted
primary seal on EFR tanks is estimated at $260 per linear meter
($80/ft).2
Cleaning and degassing costs can be subdivided into two
separate costs: (l) cleaning and (2) hazardous waste disposal
costs. An estimated cleaning and degassing cost of $18,000 to
$20,000 was obtained from a tank service company for a
757,090-liter (1) (200,000-gallon [gal]) tank.* For the purposes
of this analysis, it was, assumed that the sludge and rinseate
generated from cleaning the tank will have to be treated, stored,
and disposed as a hazardous waste. The hazardous waste generated
from cleaning this size tank was estimated at 11,370 1
(3,000 gal), which consists of 3,790 1 (1,000 gal) of rinseate
and 7,570 1 (2,000 gal) of sludge. A tank service company-
6-2
-------
estimated the hazardous waste disposal costs at $1.30/1
($5/gal).4 Because cost estimates were only provided by one
tank service- company for one tank size, cleaning and degassing
costs were not estimated for each model tank. Instead estimates
for these services were developed for representative tanks which
were then used to determine the nationwide cost impacts presented
in Section 6-4. In examining the effect of the cleaning and
hazardous waste disposal costs, it was determined that these
costs comprise the majority of the capital cost associated with
•-installing,.eontro_l: equipment- when cleaning and degassing is- • -
necessary. Therefore, the capital and annualized costs for the
control options that include cleaning and degassing prior to the
installation of controls are largely dependent on the cleaning
and disposal costs.
Annual costs for equipment were developed assuming an
equipment life of 10 years and an interest rate of 10 percent.
Capital recovery costs, which are the cost of capital spread over
the depreciable life of the control equipment, were calculated
using the following equation:5
CRC = [TCC] [(i{l+i}n)/({l-t.i}n-l)]
where,
CRC
TCC
i
n
capital recovery cost, $/yr
total capital cost, $
annual interest rate, 10 percent
depreciable"life, 10 years.
The annualized cost without product recovery credits is
calculated by adding the annualized capital cost to the costs for
taxes, insurance and administration (4 percent of the capital
costs) and the operating costs. Operating costs include the
yearly maintenance charge of 5 percent of the capital cost, and
an inspection charge of 1 percent of the capital cost. However,
when annualizing the cost of cleaning and degassing the storage
tank and'hazardous, waste disposal, additional allowances for
taxes, insurance, and administration costs were not applied
because this work would be provided by a tank service company and
is already considered in the cost of the service.
6-3
-------
The total annualized cost with product recovery credits is
calculated by accounting for the value of any recovered product.
The recovered product costs were based on average product values
for petroleum liquids and organic chemicals.6'7 A price of
$350 per megagram ($/Mg) ($320 dollars per ton [$/ton]) was
estimated for tanks storing petroleum products and $l,5io/Mg
($l,370/ton) was estimated for tanks storing organic chemical
products.6'7 The amount of recovered product was assumed equal
to the emissions difference between the baseline uncontrolled
emissions and the control option emissions.
6.3 MODEL TANK COSTS
Model tank costs were calculated for each of the control
options under consideration for fixed-roof, internal floating
roof, and external floating roof tanks. The model tanks are
presented in Chapter 3, and the control options for each tank
type are presented in Chapters 4 and 5. Figures 6-1 through 6-12
display the effect of tank volume' on the cost effectiveness of
fixed roof tanks for three vapor pressures, two turnover rates,
and two liquid types. Cost effectiveness is reported on the
figures in units of dollars'per megagrams ($/Mg), which is
equivalent to dollars per megagram per year annualized over a ten
year period.
In the analysis for internal floating roof tanks, the base
case is assumed to be an internal floating roof with a vapor-
mounted primary seal and typical fittings. Figures 6-13
through 6-18 display the effect of tank volume on the cost
effectiveness of internal floating roof tanks for three vapor
pressures and two liquid types.
In the analysis for external floating roof tanks, two base
cases were assumed: (l) an external floating roof with mechanical
shoe primary seals; and (2) an external floating roof with vapor-
mounted primary seals. Figures 6-19 and 6-20 display the effect
of tank volume on the cost effectiveness of external floating
roof tanks with mechanical shoe primary seals for three vapor:
pressures and two liquid types. Figures 6-21 and 6-22 display
the effect of the tank volume on the cost effectiveness.of
6-4
-------
external floating roof tanks with vapor-mounted primary seals for
three vapor pressures and two liquid types.
6.4 NATIONWIDE COST IMPACTS
Nationwide cost impacts were -calculated in a similar manner
as that described in Chapter 5 for secondary environmental
impacts. Briefly, capital and annualized costs for a
representative tank of each tank type were determined and then
multiplied by the estimated number of affected tanks for the
given control option to obtain nationwide cost impacts. The
nationwide cost-effectiveness values were" then- determine-d' by -
dividing the nationwide annual cost by the nationwide emissions
reduction obtained by the control options. The nationwide cost
impacts for fixed-roof, internal floating roof, and external
floating roof tanks are shown in Table 6-2 through 6-4,
respectively.
All of the control options for fixed-roof tanks include
degassing costs. For the representative fixed-roof tank with a
tank capacity of 4.9 million liters (1.3 million gallons), it was
estimated that cleaning costs were approximately $30,000 and
hazardous'waste disposal costs were'estimated at an additional
$30,000 based on the disposal of 22,710 L (6,000 gal) of
hazardous waste. Therefore, a total of $60,000 was attributed to
cleaning and degassing cost. Also, to account for problem
liquids it was assumed that for any option, 50 percent of the
tanks in the chemical industry would be controlled with welded
steel IFR's With a seal cost of $335 per linear meter ($l05/ft).
However, the impacts presented for internal and external floating
roof tanks do not include degassing costs. Although the majority
of control options for internal floating roof tanks and Control
Option, II for external floating roof tanks equipped with vapor-
mounted primary seals require degassing, the costs associated
with this, service were not included because it is assumed that
Che control equipment, will be installed on the tank following a
regularly scheduled degassing. Most storage tanks are degassed
and cleaned every 5 to 10 years.
6-5
-------
The nationwide cost-effectiveness values for internal
»
floating roof tanks are lower than the cost-effectiveness values
for individual model tanks shown in Figures 6-13 through 6-18
because the majority of IFR tanks "(90 to 95 percent) are storing
liquids with vapor pressures at or above 10.3 kPa (1.5 psia) and
the lower cost-effectiveness values for these tanks offset the
higher cost-effectiveness values for the remaining affected tanks
at the lower vapor pressures (10.3 kPa [1.5 psia] and below).
Nationwide cost impacts are not presented for the control
options for the baseline-.external .float ing-.roof, tank--with-vapor--
mounted primary seals because no data were available that could
be used to determine the number of tanks in each vapor pressure
range according to seal type. Therefore, it was assumed that all
EFR tanks are equipped with mechanical shoe primary seals, which
is the most typical primary seal used on EFR tanks. It-was also
assumed that all EFR tanks storing liquids with vapor pressures
above 10.3 kPa (1.5 psia) were already equipped with secondary
seals, because the States in implementing the- EFR CTG did not
distinguish between seal types in requiring secondary seals on
tanks storing liquids with vapor pressures at or above 10.3 kPa
(1.5 psia). Therefore, nationwide cost-effectiveness values for
EFR tanks are lower than those presented earlier for individual
model tanks, because the majority of EFR tanks store liquids
above 10.3 kPa (1.5 psia) and the cost associated with fitting
control is relatively low.
6.5 UNCERTAINTIES
The costs that are provided in this chapter represent an
estimation of the potential nationwide impacts of implementing
the control options. These costs are only estimations
representing average control cost. For example, costs may be
greater for tanks storing problem liquids due to increased
material costs, or alternatively, costs may be less than
estimated due to less sludge and. therefore less sludge disposal
costs.
6-6
-------
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6-28
-------
TABLE 6-1. ESTIMATED INSTALLED CAPITAL COST OF
INTERNAL FLOATING ROOFS (1991 DOLLARS)
Tank diameter, m
(ft)
3.7 (12)
4.6 (15)
6.1 (20)
- 7.6 (25)
9.1 (30)
10.7(35)
12.2 (40)
15.2 (50)
18.3 (60)
30.5 (100)
Tank capacity, 1 (gal)
38,420(10,150)
80,060(21,150)
213,500 (56,400)
333,610(88,130)
720,600 (190,360)
980,810(259,100)
1,281,030(338,410)
2,001,630(528,770)
3,843,090 (1,015,230)
11,120,070(2,937,590)
Basic roof cost
aluminum,
noncontact, $a •
6,923
7,510
8,670
. .- - . • 9,894
10,816
11,949
13,505
16,770
20,048
38,960
=====5-
Basic cost of welded
steel contact IFR's,
$b
36,650
38,475
41,975
45,850
49,650
53,825
58,750
66,975
76,525
132,170
Cost (including
retrofit) of welded
steel contact IFR's,
$°
46,970
49,475
54,595
59,310
65,070
70,945
77,990
90,445 *
105,985
189,040
1
Equation developed from cost data for any tank capacity: Cost ($) = 3.19 (D2) + 7,734; where D = tank
diameter in feet; with the correlation coefficient ? = 0.993. This correlation generates installed cost estimates
for an aluminum noncontact.internal floating roof with a vapor-mounted primary seal and a secondary seal
Equation developed from cost data for any tank capacity: Cost ($) = 9.46 (D2) + 40,013; where D = tank
diameter m feet; with the correlation coefficient r* = 0.989. This correlation generates installed cost estimates
tor a welded steel contact internal floating roof and primary seal.
'Equation developed from cost data for any tank capacity: Cost ($) = 14.14 (D2) + 50,976; where D = tank
diameter in feet; with the correlation coefficient ? = 0.992. This correlation generates installed cost estimates
tor replacing an aluminum noncontact IFR with a welded steel contact EFR.
6-29
-------
TABLE 6-2.
Nationwide
annual cost,
Nationwide
emissions reduction,
Control options/
cutoff values
Nationwide capital
Cost effectiveness,
$/Mg ($/ton)
VP = o.5a
VP * 0.75b
VP « 1.0°
51,960 (57,730)
47,950 (53,280)
41,970 (46,630)
590 (530)
510 (460)
430 (380)
Control Option T]re
VP = 0.5a
VP s o.75b
VP = i.oc
52,650 (58,500)
48,630 (54,030)
42,450(47,170)
580 (520)
500 (450)
420 (380)
Control Option nr
VP = 0.5a
VP = 0.75b
VP = l.oc
52,780 (58,640)
48,670 (54,080)
42,540 (47,270)
650 (590)
560 (500)
470 (420)
Control Qpt,-nn rvg
53,690 (59,650)
49,460 (54,960)
43,170(47,970)
1,700 (1,530)
1,460 (1,320)
1.230(1,110)
CUIoff val
—-
6-30
-------
TABLE 6-3. NATIONWIDE COST IMPACTS FOR INTERNAL FLOATING
ROOF TANK OPTIONS
Control options/
cutoff values
Control Option Ia
VP = 0.5b
VP = 0.75C
VP = 1.0d
VP = 1.5e
Control Option nf
VP = 0.5b
VP = 0.75C
VP = 1.0d
VP = 1.5°
Control Option fflS
VP = 0.5b
VP = 0.75°
VP = 1.0d
VP = 1.5e
Control Ootion IVfl
VP = 0.5b
VP = 0.75°
VP = 1.0d
VP = 1.5e
Nationwide
capital costs, $
(millions)
4.1
4.0
3.8
3.7
42.9
41.6
40.4
38.9
144.2
140.0
135.9
130.9
876.5
851.3
826.2
795.6
Nationwide
annual cost,
$/yr (millions)
0.4
0.4
0.4
0.4
8.8
8.4
8.2
7.9
35
34
33
32
226
219
213
205
Nationwide emissions
reduction, Mg/yr
(tons/yr)
860 (950)
850 (940)
850 (940)
840 (920)
4,750 (5,230)
4,720(5,190)
4,690(5,160)
4,630 (5,090)
6,290 (6,920)
6,260 (6,890)
6,210 (6,830)
6,130 (6,740)
11,870(13,060)
11,810(12,990)
11,720(12,890)
11,570(12,730)
Cost effectiveness,
$/Mg ($/ton)
470 (420)
470 (420)
470 (420)
480 (430)
1,850 (1,680)
1,780 (1,620)
1,750 (1,590)
1,710 (1,550)
5,560 (5,060)
5,430 (4,930)
5,310 (4,830)
5,220 (4,750)
19,040 (17,300)
18,540 (16,860)
18,170(16,520)
17,720(16,100)
aControl Option I = control fittings.
bBased on a vapor pressure cutoff value of 0.5 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
cBased on a vapor pressure cutoff value of 0.75 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
Based on a vapor pressure cutoff value of 1.0 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
^ased on a vapor pressure cutoff value of 1.5 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
Control Option fl = control fittings and add a secondary seal.
^Control Option ffl = replace vapor-mounted primary seal with liquid-mounted primary seal, secondary seals,
and controlled fittings.
Control Option IV = replace noncontact IFR with a welded steel contact IFR with .liquid-mounted primary
seals, secondary seals, and controlled fittings.
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TABLE 6-4.
NATIONWIDE COST IMPACTS FOR EXTERNAL FLOATING ROOF
TANK OPTIONS
Control options/
cutoff values
Mechanical shoe primary seals2-
Control Option Ib
VP = 0.5°
VP « 0.75d
VP = 1.0e
VP = 1.5f
Nationwide
capital costs,
$ (millions)
13.4
11.7
10.0
4.8
Nationwide
annual cost,
$/yr (millions)
-1.0
-1.3
-1.7
-2.8
Nationwide
emissions
reduction, Mg/yr
(tons/yr)
11,050(12,160)
10,910 (12,000)
10,710 (11,780)
9,880 (10,870)
Cost
effectiveness,
$/Mg ($/ton)
. -90 (-80)
-120 (-110)
-160 (-140)
-280 (-260)
aFor base case of external floating roof with mechanical shoe primary seals. Assumes all EFR tanks are
equipped with mechanical shoe primary seals.
"Option I = Control fittings and add a secondary seal.
°Based on a vapor pressure cutoff value of 0.5 psia and a tank capacity cutoff value of 40,000 gallons.
Based on a vapor pressure cutoff value of 0.75 psia and a tank capacity cutoff value of 40,000 gallons.
^Based on a vapor pressure cutoff value of 1.0 psia and a tank capacity cutoff value of 40,000 gallons.
'Based on a vapor pressure cutoff value of 1.5 psia and a tank capacity cutoff value of 40,000 gallons.
6-32
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6.6. REFERENCES
1.
2.
3.
4.
5.
6.
7.
Cost Enclosure for Storage Tanks, Ultraflote Corporation
Houston, Texas. Prepared for U. S. Environmental Protection
Agency, Research Triangle Park, North Carolina.
.May 22, 1991.
Cost Enclosure for Storage Tanks, Chicago Bridge and Iron
Corporation. Oak Brook, Illinois. Prepares-for U. S.
Environmental Protection Agency, Research Triangle Park
North Carolina. .April 8, 1991.
Cost Enclosure for Storage.Tanks, Pittsburgh-Des Moines
Corporation. Pittsburgh, Pennsylvania. Prepared for U S
Environmental Protection Agency, Research Triangle Park'
North Carolina. March 6, 1991.
Telecon. deOlloqui, V., MRI, to McManus, E., Four Seasons
Industrial Services. Greensboro, North Carolina. June 1991
Information on cleaning and degassing of storage tanks.
EAB Control Cost Manual (Fourth Edition), U. S. Environmental
Protection Agency, Research Triangle Park, North Carolina
Publication No. EPA 450/3-90-006. January 1990.
Hazardous Air Pollutant Emissions from Process Units in the
Synthetic Organic Chemical Manufacturing Industry--Background
Information for Proposed Standards. U. S. Environmental
Protection Agency, Research Triangle Park, North Carolina
Publication No. EPA 453/D-92-0168. November 1992.
Energy Information Administration. Petroleum Marketing
Monthly and Petroleum Marketing Annual. U. S. Department of
Energy, Washington, D.C. 1987-1990.
6-33
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APPENDIX A
VOL STORAGE VESSEL EXAMPLE RULE
This appendix presents an example rule limiting VOC
emissions from VOL storage vessels. The example rule is for
informational purposes only; it is intended to provide
information concerning factors that need to be considered in
writing a rule to ensure that it is enforceable.
This example rule is general in nature; that is, the -
applicability of the rule, and thus the stringency, are
determined.when the volume and vapor pressure "cutoffs" are
chosen by a State or local agency. As mentioned in Chapter 1,
this document does not contain a recommendation on RACT;
therefore, the cutoffs in the example rule appear as variables.
The general framework presented in this example rule is
consistent with the NSPS(Kb) and the Hazardous Organic NESHAP
(HON) proposed rule (57 PR 62608) for Synthetic Organic Chemical
Manufacturing Industry (SOCMI) plants.
A-l.
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Control of Volatile Organic Compound Emissions from Volatile
Organic Liquid Storage Vessels
§XX.110b Applicability and designation of affected facility.
(a) Except as provided in paragraphs (b), (c), and (d) of
this section, the affected facility to which this rule applies is
each storage vessel with a capacity greater than or equal to
[Volume cutoff] .gallons... (gall that is used to store volatile
__ organic liquids (VOL's) .
(b) Except as specified in paragraphs (a) and (b) of
§XX.116b storage vessels with design capacity less than [Volume
cutoff] gal are exempt from the provisions of this rule.
(c) Except as specified in paragraphs (a) and (b) of
§XX.ll6b, vessels with a capacity greater than or equal to
[Volume cutoff] gal storing a liquid with a maximum true vapor
pressure less than [Vapor pressure cutoff 1] psia are exempt from
the provisions of this rule.
(d) This rule does not apply to the following:
[This section includes exemptions from the rule.]
§XX.lllb Definitions.
Terms used in this rule are defined as follows:
(a) "Bulk gasoline plant." means any gasoline distribution
facility that has a gasoline throughput less than or equal to
75,700 liters per day. Gasoline throughput shall be the maximum
calculated design throughput as may be limited by compliance with
an; enforceable condition under Federal requirement or Federal,
State or local law, and discoverable by the Agency and any other
person.
(b) "Condensate" means hydrocarbon liquid separated from
natural gas that condenses due to changes in the temperature or
pressure, or both, and remains liquid at standard conditions.
(c), -"Custody transfer" means the transfer of produced
petroleum,and/or condensate-,. after-processing and/or treatment in
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the producing operations, from storage vessels or automatic
transfer facilities to pipelines or any other forms of
• transportation.
(d) "Fill" means the introduction of VOL into a storage
vessel but not necessarily to complete capacity.
(e) "Gasoline service station" means any site where
gasoline is dispensed to motor vehicle fuel tanks,from stationary
storage tanks.
(f) "Maximum true vapor pressure" means the equilibrium
partial pressure exerted by the stored VOL, at the temperature
equal to the highest calendar-month average of the VOL storage
temperature for VOL's stored above or below the ambient
temperature or at the local maximum monthly average temperature
as reported by the National Weather Service for VOL's stored at
the ambient temperature, as determined:
(1) In accordance with methods described in American
Petroleum institute Bulletin 2517, Evaporation Loss From
1 External Floating Roof Tanks;
(2) As obtained from standard reference texts; or
{3} As determined by ASTM Method D2879-83;
(4) Any other method approved by the Agency.
(g) "Reid vapor pressure" means the absolute vapor pressure
of volatile crude oil and volatile nonviscous petroleum liquids
except liquified petroleum gases, as determined by ASTM D323-82
(incorporated by reference-see §XX.17).
(h) "Petroleum" means the crude oil removed from the earth
and the oils derived from tar sands, shale, and coal.
(i) "Petroleum liquids" means petroleum, condensate, and
any finished or intermediate products manufactured in a petroleum
refinery.
(j) "Storage vessel" means each tank, reservoir,, or
container used for the storage of volatile organic liquids but
does not include:
(1) Frames, housing, auxiliary supports, or other
components that are not directly involved in the containment of
liquids or vapors; or
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(2) Subsurface caverns or porous rock reservoirs.
(k) "Volatile organic liquid" (VOL) means any organic
liquid which can emit volatile organic compounds into the
atmosphere except those VOL's that emit only those compounds
which the Agency has determined do not contribute appreciably to
the formation of ozone. These compounds are -identified in EPA
statements on ozone abatement policy for SIP revisions
(42 FR 35314, 44 FR 32042, 45 FR.32424, and 45 FR 48941).
(1) "Waste" means any liquid resulting from industrial,
, commercial, mining or agricultural operations, or from community
activities that is discarded or is being accumulated, stored, or
physically, chemically, or biologically treated prior to being
discarded or recycled.
SXX.112b Standard for volatile organic compounds (VOC).
(a) The owner or operator of each storage vessel either
with a design capacity greater than or equal to [Volume cutoff]
gal containing a VOL that, as stored, has a maximum true vapor
pressure equal to or greater than [Vapor pressure cutoff 2] psia
but less than 11.1 psia shall reduce VOC emissions as follows:
(1) Each fixed roof tank shall be equipped with an internal
floating roof meeting the following specifications or a vapor
control system meeting the specifications contained in
paragraph (4).
(i) The internal floating roof shall rest or float on the
liquid surface (but not necessarily in complete contact with it)
inside a storage vessel that has a fixed roof. The internal
floating roof shall be floating on the liquid surface at all
times, except during initial fill and during those intervals when
the storage vessel is completely emptied or subsequently emptied
and refilled., When the roof is resting on the leg supports, the-
process of filling, emptying, or refilling shall be continuous,
and shall be accomplished as rapidly as possible.
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(ii) Each internal floating roof shall be equipped with one
of the following closure devices between the wall of the storage
-vessel and the edge of the internal floating roof:
(A) A foam-oar liquid-filled seal mounted in contact with
the liquid (liquid-mounted seal). A liquid-mounted seal means a
foam-or liquid-filled seal -mounted in contact with the liquid
between the wall of the storage vessel and the floating'roof
continuously around the circumference of the tank.
(B) TWO seals mounted .one above the other so-that-each
forms a continuous closure that completely covers the space
between the wall of the storage vessel and the edge of the
internal floating roof. The lower seal may be vapor-mounted, but
both must be continuous.
(0 A mechanical shoe seal. A mechanical shoe seal is a
metal sheet held vertically against the wall of the storage
vessel by springs or weighted levers and 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.
(iii) Each opening in a noncontact interval floating roof
except for automatic bleeder vents (vacuum breaker vents) and the
rim space vents is to provide a projection below the liquid
surface.
(iv) Each opening in the internal floating roof except for
leg sleeves, automatic bleeder vents, rim space vents, column
wells, ladder wells, sample wells, and stub drains is to be
equipped with a cover or lid which is to be maintained in a
closed position at all times (i.e., no visible gap) except when
the devxce is in actual use. The cover or lid shall be equipped
wxth a gasket. Covers on each access hatch and. automatic gauge
float well shall be bolted except when they are in use
(v) Automatic bleeder vents shall be. equipped with a. gasket
and 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.
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(vi) Rim space vents shall be equipped with a gasket and are
to be set to open only when the internal floating roof is not
floating or at the manufacturer's recommended setting.
(vii) Each penetration of the internal floating roof for the
purpose of sampling shall be a sample well. The sample well
shall have a slit fabric cover that covers at least 90 percent of
the opening.
(viii) Each penetration of the internal floating roof that
allows for passage of a ladder shall have-a.gasketed sliding
cover.
(2) After the next scheduled tank cleaning, but no later
than 10 years after the effective date of this rule, each
internal floating roof tank shall meet the following
specifications:
(i) The internal floating roof shall be floating on the
liquid surface at all times except during those intervals when
the storage vessel is completely emptied or subsequently emptied
and refilled. When the roof is resting on the leg supports, the
process of filling, emptying, or refilling shall be continuous
and shall be accomplished as rapidly as possible.
(ii) Each internal floating roof shall be equipped with one
of the following closure devices between the wall of the storage
vessel and the edge of the internal floating roof:
(A) A foam-or liquid-filled seal mounted in contact with
the liquid (liquid-mounted seal). A liquid-mounted seal means a
foam-or liquid-filled seal mounted in contact with the liquid
between the wall of the storage vessel and the floating roof
continuously around the circumference of the tank.
. (B) Two. seals.mounted one above the other so that each
forms a continuous closure that completely covers the space
between the wall of the storage vessel and the edge of the
internal floating, roof. The^. lower seal may be vapor-mounted, but
both, must be. continuous.
(C) A mechanical shoe-seal.
(iii) Each opening, in a noncontact interval, floating roof
except; for automatic bleeder vents (vacuum breaker vents) and the
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rim space vents is to provide a projection below the liquid
surface.
(iv) Each opening in the internal floating roof except for
leg sleeves, automatic bleeder vents, rim space vents, column
wells, ladder wells, sample wells, and stub drains is to be
equipped with a cover or lid which is to be maintained in a
closed position at all times (i.e., no visible gap) except when
the device is in actual use. The cover or lid shall be equipped
with a gasket. Covers on each access hatch and automatic gauge
float well shall be bolted except when they are in use.
(v) Automatic bleeder vents shall be equipped with a gasket
and 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.
(vi) Rim space vents shall be equipped with a gasket and are
to be set to open only when the internal floating roof is not
floating or at the manufacturer's recommended setting.
(vii) Each penetration of the internal floating roof that
allows for passage of a ladder shall have a gasketed sliding
cover.
(3) Each external floating roof tank shall meet the
following specifications:
(i) Each external floating roof shall be equipped with a
closure device between the wall of the storage vessel and the
roof edge. The closure device is to consist of two seals, one
above the other. The lower seal is referred to as the primary
seal, and the upper seal is referred to as the secondary seal.
(A) Except as provided in §XX.113b(b)(4), the primary seal
shall completely cover the annular space between the edge of the
floating roof and tank wall and shall be either a liquid mounted
seal or a shoe seal.
(B) The secondary seal shall completely cover the annular
space between the external floating roof and the wall of the
storage vessel in a^continuous fashion except as allowed in
§XX.-li3b(b) (4) .
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(0 The tank shall be equipped with the closure device
after the next .scheduled tank cleaning, but no later than
10 years after the effective date of this rule.
(ii) Except for automatic bleeder vents and rim space vents
each opening in a noncontact external floating roof shall provide
a projection below the liquid surface. Except for automatic
bleeder vents, rim space vents, roof drains, and leg sleeves
each opening in the roof is to be equipped with a gasketed cover
seal, or lid that is to be maintained in a closed position at all
' txmes (z.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. Rim vents are to be
set to open when the roof is being floated off the roof leg
supports or at the manufacturer's recommended setting. Automatic
bleeder vents and rim space vents are to be gasketed. Each
emergency roof drain is to be provided with a slotted membrane
fabric cover that covers at least 90 percent of the area of the
opening.
(iii) The roof shall be floating on the liquid at all times
(i.e., off the roof leg supports) except when the tank is
completely emptied and subsequently refilled. The process of
filling, emptying, or refilling when the roof is resting on the
leg supports shall be - continuous and shall be accomplished as
rapidly as possible.
(4) A closed vent system and control device meeting the
following specifications:
^ (±) *** Cl°Sed VSnt SVStem sha11 ** designed to collect all
VOC vapors and gases discharged from the storage vessel and
operated with no detectable emission as indicated by an
instrument reading of less than 500 ppm above background and
visual inspections, as determined by the methods- specified in
Part 60, Subpart. W, §60.485(c).
(ii) The control device shall be designed and operated to
reduce inlet VOC emissions- by 95 percent or greater, if a flare
as. the-control device, it: shall meet the specifications
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described in the general control device requirements (§60.18)of
the General Provisions.
(5) A system equivalent to those described in paragraphs
(a)(1), (a)(2), (a)(3), or (a)(4) of this section as provided in
§XX.114b of this rule.
(b) The owner or operator of each storage vessel with a
design capacity greater than or equal to [Volume cutoff] gal
which contains a VOL that, as stored, has a maximum true vapor
pressure greater than or equal to 11.1 psia shall equip each
storage vessel with one of the following:
(1) A closed vent system and control device as specified in
§XX.112b(a) (3) .
(2) A system equivalent to that described in paragraph
(b)(1) as provided in §XX.114b of this rule.
SXX.113b Testing and procedures.
The owner or operator of each storage vessel as specified in
§XX.112b(a) shall meet the requirements of paragraph (a), (b), or
(c) of this section. The applicable paragraph for a particular
storage vessel depends on the control equipment installed to meet
the requirements of §XX.112b.
(a) After installing the control equipment required to meet
§XX.112b(a)(1) or (2) (permanently affixed roof and internal
floating roof), each owner or operator shall:
(1) Visually inspect the internal floating roof, the
primary seal, and the secondary seal (if one is in service),
prior to filling the storage vessel with VOL. If there are
holes, tears, or other openings in the primary seal, Che
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 vessel.
(2) For vessels equipped with a liquid-mounted- or
mechanical shoe primary seal,, visually inspect the internal
floating roof and the primary seal or the secondary seal (if one
is in service) through manholes, and; roof hatches on the fixed
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roof at least once every 12 months after initial fill, if the
internal floating roof is not resting on the surface of the VOL
inside the storage vessel, or there is liquid accumulated on the
roof, or the seal is detached, or there are holes or tears in the
seal fabric, the owner or operator shall repair the items or
empty and remove the storage vessel from service within 45 days.
If a failure that is detected during inspections required in this
paragraph cannot be repaired within 45 days and if the vessel
cannot be emptied within 45 days, a.,30-.day extension may be
requested from the Agency in the inspection report required in
- §XX.ll5b(a)(3). Such a request for an extension must document
that alternate storage capacity is unavailable and specify a
schedule of actions the company will take that will assure that
the control equipment will be repaired or the vessel will be
emptied as soon as possible.
(3) For vessels equipped with both primary and secondary
seals:
(i) Visually inspect the vessel as specified in paragraph
(a)(4) of this section at least every 5 years; or
(ii) Visually inspect the vessel as specified in paragraph
(a)(2) of this section.
(4) Visually inspect the internal floating roof, the
primary seal, the secondary seal (if one is in service), gaskets
slotted membranes and sleeve seals (if any) each time the storage
vessel is emptied and-degassed. If the internal floating roof
- has defects, the primary seal has holes, tears, or other openings
xn the seal or the seal fabric, or the secondary seal has holes
tears, or other openings in the seal or the seal fabric, or the
gaskets no longer close off the liquid- surfaces from the
atmosphere, or the slotted membrane has more than 10 percent open
area, the owner or operator shall repair the items as necessary
so that none of the^ conditions specified in- this paragraph exist
before refilling the storage; vessel with-VOL. m no «vent afaair
inspections conducted in accordance with this provision occur at
intervals greater than 10 years in'the case of vessels conducting
the annual, visual inspection, as specified in paragraphs- (a) (2)
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and (a)(3)(ii) of this section and at intervals no greater than 5
years in the case of vessels specified in paragraph (a)(3)(i) of
this section.
(5) Notify the Agency in writing at least 30 days prior to
the filling or refilling of each storage vessel for which an
inspection is required by, paragraphs (a) (1) and (a) (4) of this
section to afford the Agency the opportunity to have an observer
present.- If the inspection required by paragraph (a)(4) of this
section is not planned and the owner or operator could not have
known about the inspection 30 days in advance or refilling the
tank, the owner or operator shall notify the Agency at least 7
days prior to the refilling of the storage vessel. Notification
shall be made by telephone immediately followed by written
documentation demonstrating why the inspection was unplanned.
Alternatively, this notification including the written
documentation may be made in writing and sent by express mail so
that it is received by the Agency at least 7 days prior to the
refilling.
(b) The owner or operator of external floating roof tanks
shall:
(1) Determine the gap areas and maximum gap widths, between
the primary seal and the wall of the storage vessel and between
the second seal and the wall of the storage vessel according to
the following frequency.
(i) Measurements of gaps between the tank wall and the
primary seal (seal gaps) shall be performed during the
hydrostatic testing of the vessel or within 60 days of the
initial fill with VOL and at least,once every 5 years thereafter.
(ii) Measurements of gaps between the- tank wall, and the
secondary seal shall be performed within 60 days of the initial
fill with VOL and at least once per year thereafter.
(iii) If any source ceases*:-to.-store VOL. for a period of
1 year or more, subsequent introduction of. VOL.-into. the-, vessel.
shall be considered an initial fill for the purposes of
paragraphs (b) (1) (i) and (b*) (l) (ii) of this section.
A-11.
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(2) Determine gap widths and areas in the primary and
secondary seals individually by the following procedures:
(i) Measure seal gaps, if any, at one or more floating roof
levels when the roof is floating off the roof leg supports.
(ii) Measure seal gaps around the entire circumference of
the tank in each place where a 1/8 inch (in) diameter uniform
probe passes freely (without forcing or binding against seal)
between the seal and the wall of the storage vessel and measure
the circumferential-distance of each such location.
(iii) The total surface area of each gap described in
paragraph (b)(2)(ii) of this section shall be determined by using
probes of various widths to measure accurately the actual
- distance from the tank wall to the seal and multiplying each such
width by its respective circumferential distance.
(3) Add the gap surface area of each gap location for the
primary seal and the secondary seal individually and divide the
sum for each by the nominal diameter of the tank and compare each
ratio to the respective standards in paragraphs (b)(4) of this
section.
(4) Make necessary repairs or empty the storage vessel
within 45 days of identification in any inspection for seals not
meeting the requirements listed in (b) (4) (i) and (ii) of this
section:
(i) The accumulated area of gaps between the tank wall and
the mechanical shoe or liquid-mounted primary seal shall not
exceed 10 in2 per foot of tank diameter, and the width of any
portion of any gap shall not exceed 1.5 in. There are to be no
holes, tears, or other openings in the shoe, seal fabric, or seal
envelope.
(ii) The secondary seal is to meet the following
requirements:
(A) The secondary seal is to.be installed above the primary
seal so that it completely covers the space between the roof edge
and the tank wall except as provided in paragraph (b)(2)(iii) Of
this section.
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(B) The accumulated area of gaps between the tank wall and
the secondary seal used in combination with a metallic shoe or
liquid mounted primary seal shall not exceed 1.0 in2 per foot of
tank diameter, and the width of any portion of any gap shall not
^ exceed 0.5 in. There"shall be no gaps between the tank wall and
the secondary seal when used in combination with a vapor mounted
primary seal.
(C) There are to be no holes, tears, or other openings in
the seal or seal fabric.
(iii) If a failure that is detected during inspections
required in paragraph (b)(1) of §XX.113b(b) cannot be repaired
within 45 days and if the vessel cannot be emptied within
45 days, a 30-day extension may be requested from the Agency in
the inspection report required in §XX.115b(b)(4). Such extension
request must include a demonstration of unavailability of
alternate storage capacity and a specification of a schedule that
will assure that the control equipment will be repaired or the
vessel will be emptied as soon as possible.
(5) Notify the Agency 30 days in advance of any gap
^ measurements required'by paragraph (b)(l) of this section to
afford the Agency the opportunity to have an observer present.
(6) Visually inspect the external floating roof, the
primary seal, secondary seal, and fittings each time the vessel
is emptied and degassed.
(i) If the external floating roof has defects, the primary
seal has holes, tears, or other openings in the seal or the seal
fabric, 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 as necessary so that none of the conditions
specified in this paragraph exist before filling or refilling the
storage vessel with VOL.
(ii) For all the inspections required by paragraph (b)(6) of
this section, the owner or operator shall notify the Agency in
writing at least 30 days prior to the filling or refilling of
, each storage vessel to afford the Agency the opportunity to
-------
Aspect the storage vessel prior to refilling. if the Inspection
reared by paragraph « d««iP«:ion of the parameter or parameters to'be" "
monitored to ensure that the control device will be operated in
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conformance with its design and an explanation of the criteria
used for selection of that parameter (or parameters) .
(2) Operate the closed vent system and control device and
monitor the parameters of the closed vent system and control
f device in accordance with the operating plan submitted to the
Agency in accordance with paragraph (c) (l) of this section
unless the plan was modified by the Agency during the review
process. In this case, the modified plan applies.
(d) The owner or operator of each source that is equipped
wxth a closed. vent system and -a -flare- to meet the -requxremehts in
§XX.ii2b (a) (4) or (b) (2) shall meet the requirements as specified
in the general control device requirements, §60.18 (e) and (f ) .
SXX.114b Alternative means of emission limitation.
(a) If, in the Agency's judgment, an alternative means of
emission limitation will achieve a reduction in emissions at
least equivalent to the reduction in emissions achieved by any
requirement in §XX.ll2b, the Agency will publish in the
a notice permitting the use of the alterative means for
purposes of compliance with that requirement.
(b) Any notice under paragraph (a) of .this section will be
published only after notice and an opportunity for a hearing.
(0 Any person seeking permission under this section shall
submxt to the Agency a written application including:
(1) An actual emissions test that uses a full-sized or
scale-model storage vessel that accurately collects and measures
all VOC enussions from a given control device and that accurately
simulates wind and accounts- for other emission, varxabies- such as
temperature and barometric pressure.
(2) An engineering evaluation that the Agency deiermxnes is
an accurate method of determining equivalence.
(d) The Agency may condition the permission on r8oniraments
that may be necessary to ensure operation and maintenance to
achxeve the same emissions reduction as specified in §XX H2b
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SXX.llSb Reporting and recordkeeping requirements.
The owner or operator of each storage vessel as specified in
§XX.ll2b(a) shall keep records and furnish reports as required by
paragraphs (a), (b), or (c) of this section depending upon the
control equipment installed to meet the requirements of §XX.H2b
The owner or operator shall keep copies of all reports and
records required by this section, except for the records required
by (c)(l), for at least 2 years. The record required by (c)(l)
will be kept for the life of the control" equipment".
(a) After installing control equipment in accordance with
§XX.ll2b(a)(1) or (2)-(fixed roof and internal floating roof)
• the owner or operator shall meet the following requirements.
(1) Furnish the Agency with a report that describes the
control equipment and certifies that the control equipment meets
the specifications of §XX.H2b(a) (1) and §XX.H3b(a) (1) .
(2) Keep a record of each inspection performed as required
by SXX.li3b(a)(1). (a)(2). (a)(3), and (a)(4). Each record shall
identify the storage vessel on which the inspection was performed
and shall contain the date the vessel was inspected and the
observed condition of each component of the control equipment
(seals, internal floating roof, and fittings).
(3) If any of the conditions described in §XX.H3b(a) (2)
are detected during the annual visual inspection required by
.§XX.H3b(a) (2), a report shall be furnished to the Agency within
30 days of the inspection. Each report shall identify the
storage vessel, the nature of the defects, and the date the
storage vessel was emptied or the nature of and date the repair
was made.
(4) After each inspection required by §XX.H3b(a) (3) that
finds holes or tears in the seal or seal fabric, or defects in
the internal floating roof, or other control equipment defects
ixsted in §XX,ll3b(a)(3)(ii), a report shall be furnished to the
Agency within 30 days of the inspection. The report shall
identify the storage vessel and the reason it did not meet the
A- is:
-------
specifications of §61.ll2b(a)(l) or (2) or §XX.113b(a) and list
each repair made.
(b) After installing control equipment in accordance with
§61.1l2b(a)(3) (external floating roof), the owner or operator
shall meet the following requirements.
(1) Furnish the Agency with a report that describes the
control equipment and certifies that the control equipment meets
the specifications of §XX.ll2b(a)(3) and §XX.ll3b(b)(2), (b)(3),
and (b)(4).
(2) Within 60 days of performing the seal gap measurements
required by §XX.ll3b(b)(1), furnish the Agency with a report that
contains:
(i) The date of measurement.
(ii) The raw data obtained in the measurement.
(iii) The calculations described in §XX.ll3b (b)(2) and
(b) (3).
(3) Keep a record of each gap measurement performed as
required by §XX.ll3b(b). Each record shall identify the storage
vessel in which the measurement was performed and shall contain:
(i) The date, of "measurement.
*
(ii) The raw data obtained in the measurement.
(iii) The calculations described in §XX.ll3b (b)(2) and
(b) (3) .
(4) After each seal gap measurement that detects gaps
exceeding the limitations specified by §XX.H3b(b)(4), submit a
report to the Agency within 30 days of the inspection. The
report will identify the vessel and contain the information
specified in paragraph (b)(2) of this section and the date the
vessel was emptied or the repairs made and date of repair.
(c) After installing control equipment in accordance with
§XX.112b (a)(4) or (b)(l) (closed vent system and control device
other than a flare). the owner or operator shall keep the
following records.
(1) A copy *o£ the operating plan.
(2) A record of"the measured values of the parameters
monitored in accordance with §XX.113b(c) (2) ...
A-17
-------
(d) After installing a closed vent system and flare to
comply with §XX.112b, the owner or operator shall meet the
following requirements.
(1) A report containing the measurements required by
§60.18(f)(l>, (2), (3), (4), (5), and (6) shall be furnished to
the Agency as required by §60.8 of the General Provisions. This
report shall be submitted within 6 months of the initial start-up
date. . *
(2) Records shall be kept of all periods of operation
during which the flare pilot flame is absent.
(3) Semiannual reports of all periods recorded under
§60.1l5b(b)(d)(2) in which the pilot flame was absent shall be
furnished to the Agency.
§XX.116b Monitoring of operations.
(a) The owner or operator shall keep copies of all records
required by this section, except for the record required by
paragraph (b) of this section, for at least 2 years. The record
required by paragraph (b) of this section will be kept for the
life of the source.
(b) The owner or operator of each storage vessel as
specified in §XX.llOb(a) shall keep readily accessible records
showing the dimension of the storage vessel and an analysis
showing the capacity of the storage vessel. Each storage vessel
with a design capacity less than [Volume cutoff] gal is subject
to no provision of this rule other than those required-by this
paragraph.
(O Except as provided in paragraphs (f) and (g) of this
section, the owner or operator of each storage vessel either with
a desxgn capacity, greater than or equal to [Volume cutoff] gal
storing a liquid with a maximum true vapor pressure greater than
or equal to [Vapor pressure cutoff 13 pgia but less than (Vaoor
pressure cutoff 2] psia shall maintain a record of the VOL
storage, the period of storage, and the maximum true vapor
pressure- of that VOL during, the respective: storage period.
A-18
-------
(d) Except as provided in paragraph (g) of this section,
the owner or operator of each storage vessel either with a design
capacity greater than or equal to [Volume cutoff] gal storing a
liquid with a maximum true vapor pressure that is normally less
than [Vapor pressure cutoff 2] psia shall notify the Agency
within 30 days when the maximum true vapor pressure of the liquid
exceeds [Vapor pressure cutoff 2] psia.
(e) Available data on the storage temperature may be used
to determine the maximum true vapor pressure as determined below.
(1) For vessels operated .above or below ambient
temperatures, the maximum true vapor pressure is calculated based
. upon the highest expected calendar-month average of the storage
temperature. For vessels operated at ambient temperatures, the
maximum true vapor pressure is calculated based upon the maximum
local monthly average ambient temperature as reported by the
National Weather Service.
(2) For local crude oil or refined petroleum products the
vapor pressure may be obtained by the following:
(i) Available data on the Reid vapor pressure and the
maximum expected storage temperature based on the highest
expected calendar-month average temperature of the stored product
may be used to determine the maximum true vapor pressure from
nomographs contained in API Bulletin 2517 unless the Agency
specifically requests that the liquid be sampled, the actual
storage temperature determined, and the Reid vapor pressure
determined from the sample(s).
(ii) The true vapor pressure of each type'of crude oil with
a Reid vapor pressure less than 2 psi or with physical properties
that preclude determination by- the- recommended-method is, to. be-
determined from available data and recorded if the estimated
maximum true vapor pressure is greater than 0.5 psia.
(3) For other liquids,, the vapor pressure:-
(i) Maybe obtained, from standard rafarenca texts, or
(ii) Determined by ASTM Method D2879-83; or
A-19'
-------
(iii) Measured by an appropriate method approved by the
Agency; or
(iv) Calculated by an appropriate method approved by the
Agency.
(f) The owner or operator of each vessel storing a waste
mixture of indeterminate or variable composition shall be subject
to the following requirements'.
(1) Prior to the initial filling of the vessel, the highest
maximum true vapor pressure for the range, of..antlc±patad-l±quld
compositions to be stored will be determined using the methods
described in paragraph (e) of this section.
(2) For vessels in which the vapor pressure of the
anticipated liquid composition is above the cutoff for monitoring
but below the cutoff for controls as defined in §XX.li2b(a), an
initial physical test of the vapor pressure is required; and a
physical test at least once every 6 months thereafter is required
as determined by the following methods:
(i) ASTM Method D2879-83; or
(ii) ASTM Method D323-82; or
(iii) As measured by an appropriate method as approved by the
Agency.
(g) The owner or operator of each vessel equipped with a
closed vent system and control device meeting the specifications
of §XX.ll2b is exempt from the requirements of paragraphs (c) and
(d) of this section.
A-20
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APPENDIX B
INCREMENTAL COST-EFFECTIVENESS TABLES
This appendix contains more detailed cost information than
was presented in Chapter-6,,,-SPecifically,,,,this appendix, presents
the-incremental cost-effectiveness values between the different
control options and within control options for the different tank
types.
The columns labelled "cost-effectiveness" contain estimates
of average cost-effectiveness values, i.e., costs per megagram of
emission reductions to implement the particular control option at
a specific vapor pressure "cutoff." These values were included
in the tables in Chapter 6.
The columns labelled "incremental cost-effectiveness"
contain estimates of costs per megagram of emission reductions to
select a more stringent alternative. For example, in Table B-l
("within option" table) for fixed roof tanks, it costs 24.2
million dollars per year to implement Control Option II for tanks
at or above 0.75 psia, which results in emission reductions of
48,S30 per year. It costs 17.9 million dollars per year to
implement the same option for tanks at or above 1.0 psia, which
results in emission reductions of 42,450 megagrams per year. The
incremental cost-effectiveness is the cost per megagram of
emission reductions to control the fixed roof tanks in the ranae
of 0.75 psia to l.O psia, and is calculated as follows:
($24>2 million - $17.9 million)/(48630 Mg - 42450 Mg) =
$l,-020/Mg
The incremental cost-effectiveness values given in the
"between option" tables represent costs: per megagram of emission
reductions to. implement, a particular control option instead of
B-l
-------
another. For example, in Table B-2 for fixed roof tanks, there
is a credit of $150 per megagram of emissions reduced for
implementing Option II at 0.75 psia rather than implementing
Option I at the same vapor pressure.
B-2
-------
TABLE B-l.
INCREMENTAL COST-EFFECTIVENESS WITHIN EACH CONTROL
OPTION FOR FIXED-ROOF TANKS
Control options/
cutoff values
Control Option I*1
VP 3 0.5*
VP = 0.75b
VP = 1.0C
Control Option if
VP = 0.5*
VP = 0.75b
VP - 1.0C
Control Ontinn ITT*
VP = 0.5*
VP = 0.75b
VP = 1.0C
Control Ootion IV&
VP « 0.5*
VP = 0.75b
VP = 1.0C
Nationwide capital
costs, $ (millions)
280
222
163
281
222
164
295
234
172
513
406
299
=====
Nationwide annual
cost,
$/yr (millions)
30.7
24.3
17.9.
30.6
24.2
17.9
34.4
27.2
20.0
91.4
72.3
53.3
=^==
Nationwide
emissions reduction,
Mg/yr (tons/yr)
51,960(57,730)
47,950 (53,280)
41,970(46,630)
52,650 (58,500)
48,630 (54,030)
42,450(47,170)
52,780 (58,640)
48,670 (54,080)
42,540 (47,270)
53,690 (59,650)
49,460 (54,960)
43,170(47,970)
^ «m-^lu^^ j^^
Cost-effectiveness,
590 (530)
510 (460)
430 (380)
580 (520)
500(450)
420 (380)
650 (590)
560(500)
470 (420)
1,700(1,530)
1,460(1,320)
1,230(1,110)
=======3=5=
Incremental cost
effectiveness, $/Mg
($/ton)
1,600(1,460)
1,070(960)
1,590(1,450)
1,020 (920)
1,750(1,590)
1,170(1,060)
4,520(4,110)
3,020 (2,720)
Based on a vapor pressure cutoff value of 0.5 psia and a tank capacity cutoff value of 40,000 gallons
cBased on a vapor pressure cutoff value of 0.75 psia and a tank capacity cutoff value of 40,000 gallons
Based on a vapor pressure cutoff value of 1.0 psia and a tank capacity cutoff value of 40,000 gallons
Control Option I = installation of an aluminum noncontact IFR with vapor-mounted primary seals and
uncontrolled fittings. ft
Control Option H = installation of an aluminum noncontact IFR with vapor-mounted primary seals, secondary
seals, and controlled fittings. ^^
Control Option ffl = installation of an aluminum noncontact IFR with liquid-mounted primary seals, secondary
seals, and controlled fittings. }
^Control Option IV = installation of a welded steel contact IFR with liquid-mounted primary seals, secondary
seals, and controlled fittings. y
a-3-
-------
TABLE B-2.
INCREMENTAL COST-EFFECTIVENESS BETWEEN EACH CONTROL
OPTION FOR FIXED-ROOF TANKS
Control options/
cutoff valuei
Control Option r
VP - 0.5*
VP =• 0.75b
VP - 1.0C
Control Option 0s
VP - 0.5*
VP - 0.75b
VP =» 1.0e
Control Option HI
VP = 0.5*
VP - 0.75b
VP - 1.0C
Control Option IV*
VP « 0.5*
VP - 0.75b
VP - 1.0C
Nationwide capital
com, $ (millions)
280
222
163
281
222
164
295
234
172
513
406
299
Nationwide
annual con,
S/yr (millions)
30.7
24.3
17.9
30.6
24.2
17.9
34.4
27.2 •
20.0
91.4
72.3
53.3
Nationwide emission!
reduction, Mg/yr (toni/yr)
51,960(57,730)
47,950 (53,280)
41,970(46,630)
52,650 (58,500)
48,630 (54,030)
42,450(47,170)
52,780 (58,640)
48,670 (54,080)
42,540 (47,270)
53,690 (59,650)
49,460 (54,960)
43,170(47,970)
Cost-efTectiveneu,
$/Mg ($/ton)
590 (530)
510 (460)
430 (380)
580 (520)
500(450)
420 (380)
650 (590)
560(500)
. 470(420)
1,700(1,530)
1,460 (1,320)
1,230(1,110)
Incremental coat
effectiveness, $/Mg
($/ton)
—
-140 (-130)
-150 (-130)
0(0)
29,200 (26,570)
75,000 (68,250)
23,330 (21.200)
62,600 (56,970)
57,100(51,960)
52,900(48,140)
fBased on a vapor pressure cutoff value of 0.5 psia and a tank capacity cutoff value of 40,000 gallons.
"Based on a vapor pressure cutoff value of 0.75 psia and a tank capacity cutoff value of 40,000 gallons.
°Based on a vapor pressure cutoff value of 1.0 psia and a tank capacity cutoff value of 40,000 gallons.
Control Option I = installation of an aluminum noncontact EFR with vapor-mounted primary seals and
uncontrolled fittings.
eControl Option n = installation of an aluminum noncontact IFR with vapor-mounted primary seals, secondary
seals, and controlled fittings.
Control Option HI = installation of an aluminum noncontact IFR with liquid-mounted primary seals, secondary
seals, and controlled fittings.
^Control Option IV = installation of a welded steel contact IFR with liquid-mounted primary seals, secondary
seals, and controlled fittings.
B-4
-------
TABLE B-3.
r=s=s=s==^*B=x
|| Control options/
cutoffvalues
[1 Control Option 1*
VP - 0.5b
VP = 0.75C
VP =» 1.0d
VP =. 1.5*
Control Option Ir
VP = 0.5b
| VP = 0.75C
VP =. 1.0d
VP =. 1.5"
Control Ootion m*
VP =» 0.5b
VP - 0.75C
VP = 1.0d
VP = 1.5C
Control Ontion IV"
VP = 0.5b
VP = 0.75C
VP = 1.0d
VP = 1.5«
======
OPTION FO
=====
Nationwide
capital costs, $
(millions)
4.1
4.0
3.8
3.7
42.9
41.6
40.4
38.9
144.2
140.0
135.9
130.9
876.5
851.3
826.2
795.6
=====
R INTERN?
=====
Nationwide
annual cost*
$/yr (millions)
0.44 .
0.43
0.42
0.40
8.8
8.4
8.2
7.9
35
34
33
32
226
219
213
205
\L FLOATING
========3===SS£SS
Nationwide
emissions reduction,
Mg/yr (tons/yr)
860(950)
850(940)
850(940)
840(920)
4,750 (5,230)
4,720(5,190)
4,690 (5,160)
4,630 (5,090)
6,290 (6,920)
6,260 (6,890)
6,210 (6,830)
6,130(6,740)
11,870(13,060)
11,810(12,990)
11,720(12,890)
11,570(12,730)
===== '
ROOF TANKS
—
Cost-effectiveness,
$/Mg ($/ton)
510 (470)
500(460)
500(460)
480(440)
1,850 (1,680)
1,780(1,620)
1,750(1,590)
1,710(1,550)
5,560 (5,060)
5,430 (4,930)
5,310(4,830)
5,220 (4,750)
19,040 (17,300)
18,540 (16,860)
18,170 (16,520)
17,720(16,100)
—
-
Incremental cost
effectiveness, $/Mg
(J/ton)
2,500 (2,280)
1,670(1,520)
2,000 (1,820)
— — — _i_____
13,300(12,100)
6,670 (6,070)
5,000 (4,550)
33,300 (30,300)
20,000 (18,200)
12,500(11,380)
— — — — . __
116,670(106,170)
66,670 (60,670)
53,330 (48,480)
fControl Option I = control fittings.
Based on a vapor pressure cutoff value of 0.5 psia and a tank capacity cutoff value of 40,000 gallons and
°B*a* on a vapor pressure cutoff value of 0.75 psia and a tank capacity cutoff value of 40,000 gallons and
Based on a vapor pressure cutoff value of 1.0 psia and a tank capacity cutoff value of 40,000 gallons and
n a vapor pressure cutoff value of 1.5. psia and a tank capacity cutoff value of 40,000 gallons and
Control Option H = control fittings and add a secondary seal
—
B-5
-------
TABLE 'B-4.
INCREMENTAL COST-EFFECTIVENESS BETWEEN EACH CONTROL
OPTION FOR INTERNAL FLOATING ROOF TANKS
Control options/
cutoff values
Control OotJon I*
VP - 0.5b.
VP - 0.75C
VP - 1.0d
VP - 1.5*
Control Option jf
VP - O.Sb
VP - 0.75C
VP - t.0d
VP =- 1.5*
Control Option ffl*
VP - 0.5b
VP - 0.75*
VP - I.0d
VP =• 1.5*
Control Option TV*1
VP - 0.5b
VP = 0.75C
VP - 1.0d
VP=» 1.5*
Nationwide
capital cotu, $
(millions)
4.1
4.0
3.8
3.7
42.9
41.6
40.4
38.9
144.2
140.0
135.9
130.9
876.5
851.3
826.2
795.6
Nationwide
annual cost,
S/yr (millions)
0.44
0.43
0.42
0.40
8.8
8.4
8.2
7.9
35
34
33
32
' 226
219
213
205
Nationwide
emissions reduction,
Mg/yr (tons/yr)
860(950)
850 (940)
850 (940)
840 (920)
4,750 (5,230)
4,720 (5,190)
4,690(5,160)
4,630 (5,090)
6,290 (6,920)
6,260 (6,890)
6,210 (6,830)
6,130(6,740)
11,870(13,060)
11,810(12,990)
11,720(12,890)
11,570(12,730)
Cost-effectiveness,
$/Mg (S/ton)
510 (470)
500(460)
500(460)
480 (440)
1,850(1,680)
1,780(1,620)
1,750(1,590)
1,710(1,550)
5,560 (5,060)
5,430 (4,930)
5,310(4,830)
5,220 (4,750)
19,040 (17,300)
18,540 (16,860)
18,170 (16,520)
17,720(16,100)
Incremental cost
effectiveness,
$/Mg ($/ton)
2,140(1,940)
2,070(1,880)
2,030(1,850)
1,980(1,800)
17,010 (15,480)
16,620(15,120)
16,320 (14,850)
16,070 (14,620)
34,230(31.150)
33,330 (30,330)
32,670 (29,730)
31,800(28,940)
"Control Option I = control fittings.
"Based on a vapor pressure cutoff value of O.S psia and a tank capacity cutoff value of 40,000 gallons and
greater.
C6ased on a vapor pressure cutoff value of 0.75 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
"Based on a vapor pressure cutoff value of 1.0 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
eBased on a vapor pressure cutoff value of 1.5 psia and a tank capacity cutoff value of 40,000 gallons and
greater.
'Control Option n = control fittings and add a secondary seal.
^Control Option HI = replace vapor-mounted primary seal with liquid-mounted primary seal, secondary seals,
and controlled fittings.
"Control Option IV = replace noncontact IFR with a welded steel contact IFR with liquid-mounted primary
seals, secondary seals, and controlled fittings.
B-6
-------
TABLE B-5.
INCREMENTAL COST-EFFECTIVENESS WITHIN
OPTION FOR EXTERNAL FLOATIN^In^
Control optioni/
cutoff value*
——-^—_____
M«chmtc«l shoe prinury
uali*
Control Onrion I**
VP - 0.5C
VP » 0.75d
VP » 1.0*
VP - 1.5f
—^•i^Hi^^^Bs^^sss
Nationwide
capital cow. $
(millioni)
•— — • — — — i
13.4
11.7
10.0
4.8
B^ssss:^^3-ss
SKB^SS-SEX—
Nationwide
annual eott,
$/yr
(millions)
^•—~—~~m^*^*
-1.0
-1.3 .
•i.7
-2.3
=aBaoea«S
^^••B^^^MsaH'1^ fiyt^g^Ti
Nationwide
reduction, Mg/yr
(toni/yr)
^"•^^
11,050(12.160)
10,910 (12,000)
10,710(11.780)
9,880 (10,870)
Co«
S/Mg (S/ton)
-90 (-80)
-120 (-110)
-160 (-140)
-280 (-260)
—
Incremental COM
•ffectivenet!, S/M
(S/ton)
a*sa=*&>^^^ai^mtm^n^aa^amt
2,140(1,950
2,000(1,820
1,330(1,210
„
*For base
equipped ^ ^ ^
cOption I =» Control fittings andradd a secondary seal
B-7
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