The equations estimate average annual losses from floating-roof tanks for various types of tank construction, floating-roof construction, rim-seal systems, and deck fittings, as well as
General
The total loss L T is the sum of the standing loss L S and the working loss L W :
Standing Loss L S
Standing loss pertains to evaporative loss of stock liquid from beneath the floating roof while it is floating
The standing loss L S can be estimated as follows:
F r is the total rim-seal loss factor, in pound-moles per year,
F f is the total deck-fitting loss factor, in pound-moles per year,
F d is the total deck-seam loss factor, in pound-moles per year,
P* is the vapor pressure function, dimensionless,
M V is the average molecular weight of stock vapor, in pounds per pound-mole,
K C is the product factor, dimensionless
The loss factors \( F_r \), \( F_f \), and \( F_d \) are associated with the design of the tank and floating roof, classified as equipment-related factors In contrast, the loss factors \( P^* \), \( M_V \), and \( K_C \) are linked to the properties of the stored liquid, categorized as stock-related factors To calculate the actual evaporative loss in pound-moles per year for a specific liquid product, the equipment-related factors, measured in pound-moles per year, must be multiplied by the dimensionless stock-related factors \( P^* \) and \( K_C \) Finally, to convert the actual pound-moles per year into pounds per year, one must multiply by the molecular weight of the product in its vapor phase.
M V , with molecular weight having units of pounds per pound-mole
The factors related to equipment, namely F r, F f, and F d, in the standing loss equation are solely determined by the characteristics of the tank and floating roof, and they do not depend on the type of liquid stored.
The rim seal loss factor F r can be estimated as follows:
K r is the rim seal loss per unit length factor (lb-mole/ft-yr),
D is the tank diameter (ft)
The rim seal loss factor K r can be estimated as follows:
K ra is the zero-wind-speed rim-seal loss factor (lb-mole/ft-yr); see Table 1,
K rb is the wind-dependent rim-seal loss factor (lb-mole/(mi/hr) n -ft-yr); see Table 1,
V is the average ambient wind speed at the tank site (mi/hr), n is the wind-dependent rim-seal loss exponent; see Table 1
E vaporative loss from floating roof tanks can be influenced by various factors, including the type of seals used Table 1 presents the rim-seal loss factors, highlighting the differences between average-fitting seals, tight-fitting seals, and the zero-wind speed loss factor Understanding these loss factors is crucial for effective management of vapor emissions in floating roof tank operations.
Wind- dep en de nt Loss Factor Wind- dep en de nt Loss Expo ne nt
Rim -seal Loss Factor K r (lb -m ol /ft -y r)
Ze ro -w in d S pee d Lo ss Fac to r Wind- dep en de nt Loss Fac to r
Wind- dep en de nt Loss Factor Rim -seal Loss Factor K r (lb -m ol /ft -y r) Ta nk Co nst ruc tio n an d Rim -se al S ys tem
K rb [lb-m ol/ (mph) n - ft-y r] n (di m en si on -les s) 0 (m ph ) 5 (m ph ) 10 (m ph ) 15 (m ph )
K ra (lb -m ol / ft- yr)
The data presented outlines the performance metrics of various seal types used in welded and riveted tanks, categorized by their mounting methods and primary or secondary seal classifications For welded tanks, mechanical-shoe seals demonstrate a range of efficiencies, with primary seals achieving up to 5.8 b c at 15 mph In contrast, vapor-mounted seals show significantly higher performance, with primary seals reaching 6.7 d at 15 mph Riveted tanks exhibit lower efficiency levels, with mechanical-shoe primary seals recording up to 10.8 b c It is noted that "tight-fitting" refers to a maximum gap of 1/8 inch between the rim seal and tank shell The data suggests that welded tanks with average-fitting seals are the most common configurations in use, while specific evaporative-loss information for riveted tanks remains unavailable.
Rim-seal loss factors are applicable only for ambient wind speeds ranging from 0 mph to 15 mph In cases where the average ambient wind speed \( V \) at the tank site is unavailable, approximations can be made using wind-speed data from the nearest local weather station or values from API MPMS Ch 19.4, 3rd Edition, Table 1 For Internal Floating Roof Tanks (IFRTs) and domed External Floating Roof Tanks (EFRTs), ambient wind speed is not a critical factor, and thus, \( V \) is set to zero.
Rim-seal systems are detailed in section 6.1.3, where it is emphasized that loss factors for average-fitting seals are suitable for standard rim-seal conditions These factors should be utilized unless the rim-seal system is confirmed to be consistently tight-fitting, defined as having no gaps wider than 1/8 inch between the rim seal and the tank shell In cases where the fit of the rim seal is uncertain, it is recommended to apply the loss factors for average-fitting seals.
The deck-fitting loss factor F f can be estimated as follows:
The variable \( N_{fi} \) represents the quantity of deck fittings of type \( i \) If the value of \( N_{fi} \) is not known, it can be obtained from Table 2, where \( i \) ranges from 1 to \( k \), with \( k \) indicating the total number of distinct types of deck fittings.
K fi is the loss factor for type i deck fitting (lb-mole/yr) (see Table 2)
The deck fitting loss factor K fi can be estimated as follows:
K fai is the zero-wind-speed loss factor for type i deck fitting (lb-mole/yr); see Table 2,
K fbi is the wind-dependent loss factor for type i deck fitting (lb-mole/(mi/hr) m -yr); see Table 2,
K v is the fitting wind-speed correction factor, given a value of 0.7,
V is the average ambient wind speed at the tank site (mi/hr), m i is the wind-dependent loss exponent for type i deck fitting (dimensionless); see Table 2
Deck-fitting loss factors are applicable only for ambient wind speeds ranging from 0 mph to 15 mph In cases where the average ambient wind speed \( V \) at the tank site is unavailable, approximations can be made using wind-speed data from the nearest local weather station or values from API MPMS Ch 19.4, 3rd Edition, Table 1 For Internal Floating Roof Tanks (IFRTs) and domed External Floating Roof Tanks (EFRTs), ambient wind speed is not a critical factor, and the value of \( V \) is considered to be zero.
Table 2 outlines the most common types of deck fittings and their associated loss factors for different construction details Section 6.1.4 provides descriptions of these deck fittings For configurations not included in Table 2, loss factors can be estimated based on a zero miles-per-hour wind speed condition.
(IFRTs and domed EFRTs) from the following:
A fi represents the liquid surface area within a type i deck fitting, measured in square inches This area is defined as the space inside the deck fitting well or leg sleeve, excluding any portions occupied by obstructions such as fixed-roof support columns, unslotted guidepoles, guidepole floats, or deck support legs.
The coefficient, 0.27, has units of pound-moles per (square inch) 0.86 -year, and the exponent, 0.86, is dimensionless
Equation (9) is valid only when the distance from the liquid surface to the top of the deck-fitting well or leg sleeve is 12 inches or more Deck-fitting wells or leg sleeves that are shorter may lead to increased loss rates Currently, there are no algorithms available to estimate loss factors for these shorter configurations.
Equation (9) pertains to an uncontrolled deck fitting, suggesting that effective deck-fitting controls could lead to lower loss factors than those predicted by this equation However, there are currently no algorithms available to estimate the effectiveness of these deck-fitting controls.
Equation (9) is for the zero miles-per-hour wind speed condition There are no algorithms available for estimating loss factors at non-zero wind speeds (EFRTs)
Table 2—Deck-Fitting Loss Factors Table 2A—Other-than-guidepole deck fittings
Zero-wind Speed Loss Factor
Typical Number of Deck Fittings
(lb-mol/yr) Deck-fitting Type and
Unbolted cover, ungasketed 36 5.9 1.2 36 63 97 140 Unbolted cover, gasketed 31 5.2 1.3 31 58 96 140 Bolted cover, gasketed 1.6 0.0 0.0 1.6 1.6 1.6 1.6 Fixed-roof support columns N fc : note a, Table 3
Round pipe, ungasketed sliding cover
Round pipe, gasketed sliding cover 25 25
Round pipe, flexible fabric sleeve seal
Built-up column, ungasketed sliding cover
Built-up column, gasketed sliding cover
Gauge floats (automatic gauge) N fgf = 1
Unbolted cover, ungasketed 14 5.4 1.1 14 35 60 86 Unbolted cover, gasketed 4.3 17 0.38 4.3 32 40 46 Bolted cover, gasketed 2.8 0.0 0.0 2.8 2.8 2.8 2.8
Gauge hatch/sample ports N fsp = 1
Slit fabric seal (10 % open area) 12 b b 12
Vacuum breakers N fvb : note c, Table 4
Deck drains (opening which drains directly into the product) N fdd : note d, Table 4
3-in diameter, open 1.5 0.21 1.7 1.5 3.3 7.2 13 3-in diameter (10 % open area) 1.8 0.14 1.1 1.8 2.4 3.0 3.7
C-type, double-deck roofs and center area of pontoon roofs)
Ungasketed, no sock 0.82 0.53 0.14 0.8 1.5 1.5 1.6 Gasketed, no sock 0.53 0.11 0.13 0.5 0.7 0.7 0.7 With sock, no gasket 0.49 0.16 0.14 0.5 0.7 0.7 0.7 Adjustable (API 650, Appendix
C-type, pontoon area of pontoon roofs)
Table 2A—Other-than-guidepole deck fittings
Zero-wind Speed Loss Factor Wind-dependent
Wind- dependent Loss Exponent Typical Number of
(lb-mol/yr) Deck-fitting Type and
Ladder/guidepole combinations N flg = 0, note g
Ladder sleeve with ungasketed sliding cover
Ladder sleeve with gasketed sliding cover 60 b b 60
Unslotted (Unperforated) Guidepoles: Zero-wind
Slotted (Perforated) Guidepoles: Zero-wind
15 (mph) YES or NO m NO NO NO 43 270 1.4 43 1600 4200 7300
YES or NO m YES l NO NO 31 36 2.0 31 470 1800 4000
Columns are not utilized in tanks with self-supporting fixed roofs, such as domed EFRTs, or in tanks lacking fixed roofs Additionally, this feature is generally not applied to API 650, Appendix C decks, and there is no available data regarding wind-dependent evaporative loss from this type of fitting construction For API 650, Appendix H decks (IFRTs), the number of vacuum breakers can be estimated.
N fvb = 1 d The number of deck drains on API 650, Appendix H decks (IFRTs) can be assumed to be:
N fdd = D 2 /125 for bolted decks, where D = tank diameter (ft) e The number of deck legs on API 650, Appendix H decks (IFRTs) can be assumed to be:
N fdl = (5 + D/10 + D 2 /600), where D = tank diameter (ft) f The deck legs tested for API 650, Appendix H decks (IFRTs) had 12-in tall leg sleeves The deck legs tested for API 650, Appendix
C decks, including EFRTs and domed EFRTs, feature 30-inch tall leg sleeves for pontoon roof areas and 48-inch tall leg sleeves for double-deck roofs and the center of pontoon roofs Additionally, ladder and guidepole combinations that penetrate the deck are generally not utilized on open-top tanks with API 650, Appendix C decks.
EFRTs utilize rim vents exclusively with certain mechanical-shoe primary seals Vertical ladders that extend through the deck are generally not employed on open-top tanks featuring API 650, Appendix C decks In contrast, the quantity of ladders on API 650, Appendix H decks (IFRTs) can be estimated accordingly.
Working Loss L W
Working or withdrawal loss refers to the evaporation of liquid stock that adheres to the tank shell and fixed-roof support columns during the withdrawal process, which occurs as the liquid level decreases The working loss, denoted as \( L_W \), can be estimated using specific calculations.
Q N is the net stock throughput associated with decreasing the liquid level in the tank (bbl/yr),
C L is the clingage factor (bbl/1000 ft 2 ),
W L is the average stock liquid density at 60°F (lb/gal),
N fc is the number of fixed-roof support columns (dimensionless),
D C is the effective column diameter (ft),
D is the tank diameter (ft)
The constant 0.943 has units of thousand cubic foot-gallons per barrel 2
The net stock throughput Q N is:
Q N = 0.1781 (ΣH Q ) (π D 2 /4) (20) where ΣH Q = annual sum of the decreases in liquid level (ft/yr)
The constant 0.1781 has units of barrels per cubic foot
The stock throughput, denoted as Q N, is linked to the reduction of the liquid level in the tank In cases where Q N is not known, it is advisable to use the stock throughput Q as a substitute However, it is important to note that using Q may lead to an overestimation of Q N if the product is being pumped into and out of the tank at the same time.
The clingage factor C L is given in Table 7
Table 7—Clingage Factors C L for Steel Tanks (bbl/1000 ft 2 )
Product Stored light rust dense rust gunite lining gasoline 0.0015 0.0075 0.15 single-component stocks 0.0015 0.0075 0.15 crude oil 0.0060 0.030 0.60
For selected petroleum liquids (multicomponent stocks), the stock liquid density W L is given in API MPMS
Ch 19.4, 3 rd Edition, Table 2 The stock liquid density W L of selected petrochemicals (single component stocks) is given in API MPMS Ch 19.4, 3 rd Edition, Table 3
4.3.5 Number of Fixed-Roof Support Columns N fc
To determine the number of fixed-roof support columns (\$N_{fc}\$) for tanks, refer to Table 3 if the value is unknown It is important to note that only tanks with column-supported fixed roofs, commonly found in Internal Floating Roof Tanks (IFRTs), will have these columns, while tanks with self-supporting fixed roofs do not.
(typical of domed EFRTs) and tanks without fixed roofs (EFRTs) do not have fixed-roof support columns
The effective column diameter D C is:
Table 8—Effective Column Diameter D C for Typical Column Construction
9 in × 7 in built up column 1.1
General
The total evaporative loss is the sum of the standing loss and the working loss
This article presents sample problems that demonstrate the process of estimating evaporative loss, including an EFRT problem in section 5.2, an IFRT problem in section 5.3, and a domed EFRT problem in section 5.4 The estimated emissions are reported to two significant figures, as higher precision is not feasible due to the limitations of the empirically-derived emission factors.
EFRT Sample Problem
Estimate the total annual evaporative loss, in pounds per year, given the following information
A well-maintained welded EFRT features a 100 ft diameter, an aluminum-colored shell with a shiny finish, and a single-deck pontoon floating roof It is equipped with a mechanical-shoe primary seal but lacks a secondary seal Additionally, it has an unslotted guidepole without controls, such as a well gasket, pole wiper, or pole sleeve, and construction details for other deck fittings are provided in the calculations below.
The motor gasoline in the tank exhibits key characteristics, including a Reid vapor pressure of 10 psi, a stock liquid density of 6.1 lb/gal, and an average net throughput of 1.5 million barrels per year.
The ambient conditions include an average annual temperature of 60 °F, an atmospheric pressure of 14.7 psia, an average wind speed of 10 mph, and a daily total insolation of 1300 Btu/(ft² day) on a horizontal surface.
Estimate the standing loss from Equation (2):
The variables in Equation (2) can be determined as follows:
Total Rim-Seal Loss Factor
= 4400 lb-mol/yr [from Equation (3) for an average-fitting primary only mechanical-shoe seal, with
= 44 (lb-mol/ft-yr) [for a welded tank with a mechanical-shoe primary seal, from Equation (4) and Table 1, or directly from Table 1],
Total Deck-Fitting Loss Factor
= 2500 lb-mol/yr [from Equation (6), with V = 10 mph] where
= 1.6 lb-mol/yr [for bolted, gasketed access hatches, from Equation (7) and Table 2, or directly from
N fc K fc = (not used on EFRTs)
= 0 lb-mol/yr (for fixed-roof support columns)
= 60 lb-mol/yr [for unbolted, ungasketed gauge floats, from Equation (7) and Table 2, or directly from
= 0.6 lb-mol/yr [for gasketed gauge hatch/sample ports, from Equation (7) and Table 2, or directly from Table 2]
= 14 lb-mol/yr [for gasketed vacuum breakers, K fvb , from Equation (7) and Table 2, or directly from
N fdd K fdd = (not typically used on pontoon (single-deck) floating roofs )
= 0 lb-mol/yr [for open deck drains]
= 95 lb-mol/yr [for deck legs, K fdl from Equation (7) and Table 2, or directly from Table 2, N fdl from
= 1.4 lb-mol/yr [for gasketed rim vents, from Equation (7) and Table 2, or directly from Table 2]
N fl K fl = (not typically used on EFRTs)
= 0 lb-mol/yr (for vertical ladders)
= 2300 lb-mol/yr [for unslotted guidepoles with no well gasket, pole wiper or pole sleeve, from
Equation (7) and Table 2, or directly from Table 2]
N fsgp K fsgp = (not present in this example)
= 0 lb-mol/yr (for slotted guide-poles)
Total Deck-Seam Loss Factor
= 0 lb-mol/yr [from Equation (11) for a welded deck]
= 0.125 [for P = 5.8 psia, from Equation (13)] where
T B = 61.6 °F [from Equation (18), with T AA = 60 °F, α = 0.44]; α = 0.44 [for aluminum specular paint in average condition, from API MPMS Ch 19.4, 3 rd Edition, Table 7];
P VA = 5.8 psia [for gasoline with RVP = 10 psi and T LA = 65.4 °F, from API MPMS Ch 19.4, 3 rd Edition, Section 4.2];
M V = 66 lb/lb-mol [for gasoline, from API MPMS Ch 19.4, 3 rd Edition, Table 2]
To estimate the standing loss in pounds per year, substitute the values above into Equation (2):
Estimate the working loss from Equation (19):
The variables in Equation (19) can be determined as follows:
C L = 0.0015 bbl/1000 ft 2 (for gasoline in a lightly rusted tank, from Table 7);
To estimate the working loss in pounds per year, substitute the values above into Equation (19):
Estimate the total loss from Equation (1):
In this EFRT sample problem, the impact of the working loss is minimal Emissions are estimated with two significant figures, as higher precision is constrained by the limitations of the empirically-derived emission factors.
IFRT Sample Problem
Estimate the total annual evaporative loss, in pounds per year, given the following information
A well-maintained welded shell, known as IFRT, features a diameter of 100 feet, built-up fixed-roof support columns, and an aluminum-colored shell with a shiny finish in average condition It is equipped with a noncontact aluminum floating roof and a wiper-type primary seal, lacking a secondary seal Additionally, the deck seams are bolted, and construction details for deck fittings are provided in the calculations below.
The motor gasoline in the tank exhibits key characteristics, including a Reid vapor pressure of 10 psi, a stock liquid density of 6.1 lb/gal, and an average net throughput of 1.5 million barrels per year.
The ambient conditions are as follows: a) an average annual ambient temperature of 60 °F, b) an atmospheric pressure of 14.7 psia c) an average daily total insolation on a horizontal surface of 1300 Btu/(ft 2 day)
Estimate the standing loss from Equation (2):
L S = (F r + F f + F d ) P* M V K C (2) The variables in Equation (2) can be determined as follows
Total Rim-Seal Loss Factor
= 670 lb-mol/yr [from Equation (3) for an average-fitting primary only vapor-mounted seal] where
K r = 6.7 (lb-mol/ft-yr) [for an average-fitting primary only vapor-mounted seal, from Equation (5) and Table 1, or directly from Table 1];
Total Deck-Fitting Loss Factor
= 820 lb-mol/yr [from Equation (6)] where
= 36 lb-mol/yr [for unbolted cover, ungasketed access hatches, from Equation (8) and Table 2],
= 310 lb-mol/yr [for built-up columns, ungasketed sliding covers, from Equation (8) and Table 2 and
= 14 lb-mol/yr [for unbolted, ungasketed gauge floats, from Equation (8) and Table 2],
= 12 lb-mol/yr [for gauge hatch/sample ports with slit fabric seals, from Equation (8) and Table 2],
= 6.2 lb-mol/yr [for gasketed vacuum breakers, from Equation (8) and Table 2],
= 96 lb-mol/yr [for 1-in deck drains, from Equation (8) and Table 2],
= 250 lb-mol/yr [for adjustable deck legs, from Equation (8) and Table 2],
N frv K frv = (not used with vapor-mounted rim seals)
= 0 lb-mol/yr (for rim vents),
= 98 lb-mol/yr [for vertical ladders, sliding ungasketed cover, from Equation (8) and Table 2],
N fugp K fugp = (not present in this example)
= 0 lb-mol/yr (for unslotted guidepoles),
N fsgp K fsgp = (not present in this example)
= 0 lb-mol/yr (for slotted guidepoles)
Total Deck-Seam Loss Factor
= 680 lb-mol/yr [from Equation (11) and Table 6 for a bolted noncontact deck with 5-ft wide sheets]
= 0.125 [for P = 5.8 psia, from Equation (13)] where
T B = 61.6 °F [from Equation (18), with T AA = 60 °F, α = 0.44]; α = 0.44 [for aluminum specular paint in average condition, from API MPMS Ch 19.4, 3 rd Edition, Table 7];
P VA = 5.8 psia [for gasoline with RVP = 10 psi and T LA = 65.4 °F, from API MPMS Ch 19.4, 3 rd Edition, Section 4.2];
M V = 66 lb/lb-mol [for gasoline, from API MPMS Ch 19.4, 3 rd Edition, Table 2]
To estimate the standing loss in pounds per year, substitute the values above into Equation (2):
Estimate the working loss from Equation (19):
The variables in Equation (19) can be determined as follows:
C L = 0.0015 bbl/1000 ft 2 (for gasoline in a lightly rusted tank, from Table 7);
N fc = 6 (from Table 3 for a 100-ft tank);
D C = 1.1 ft (for typical built-up columns)
To estimate the working loss in pounds per year, substitute the values above into Equation (19):
Estimate the total loss from Equation (1):
In this IFRT sample problem, the impact of the working loss is minimal Emissions are estimated with two significant figures, as higher precision is not feasible due to the limitations of the empirically-derived emission factors.
Domed EFRT Sample Problem
Estimate the total annual evaporative loss, in pounds per year, given the following information
A well-maintained welded shell, domed EFRT features a 100 ft diameter, an aluminum-colored shell with a shiny finish, and a single-deck floating roof built per API 650, Appendix C It includes a mechanical-shoe primary seal without a secondary seal, an unslotted guidepole lacking controls such as a well gasket or pole wiper, and construction details for other deck fittings as outlined in the calculations Additionally, it boasts a self-supporting aluminum dome roof.
The motor gasoline in the tank exhibits key characteristics, including a Reid vapor pressure of 10 psi, a stock liquid density of 6.1 lb/gal, and an average net throughput of 1.5 million barrels per year.
The ambient conditions are as follows: a) an average annual ambient temperature of 60 °F; b) an atmospheric pressure of 14.7 psia c) an average daily total insolation on a horizontal surface of 1300 Btu/(ft 2 day)
Estimate the standing loss from Equation (2):
L S = (F r + F f + F d ) P* M V K C (2) The variables in Equation (2) can be determined as follows
Total Rim-Seal Loss Factor
= 580 lb-mol/yr [from Equation (3) for an average-fitting primary only mechanical-shoe seal, with
K r = 5.8 (lb-mol/ft-yr) [for a welded tank with a mechanical-shoe primary seal, from Equation (5) and Table 1, or directly from Table 1];
Total Deck-Fitting Loss Factor
F f = N f1 K f1 + N f2 K f2 + … + N fk K fk (6) = 100 lb-mol/yr [from Equation (6), with V = 0 mph] where
= 1.6 lb-mol/yr [for bolted, gasketed access hatches, from Equation (8) and Table 2];
N fc K fc = (not used on self-supporting fixed roofs)
= 0 lb-mol/yr (for fixed-roof support columns);
= 14 lb-mol/yr [for unbolted, ungasketed gauge floats, from Equation (8) and Table 2];
= 0.47 lb-mol/yr [for gasketed gauge hatch/sample ports, from Equation (8) and Table 2];
= 6.2 lb-mol/yr [for gasketed vacuum breakers, from Equation (8) and Table 2 and Table 4];
N fdd K fdd = (not typically used on pontoon (single-deck) floating roofs)
= 0 lb-mol/yr [for open deck drains];
= 47 lb-mol/yr [for deck legs, from Equation (8) and Table 2 and Table 5];
= 0.71 lb-mol/yr [for gasketed rim vents, from Equation (8) and Table 2];
N fl K fl = (not present in this example)
= 0 lb-mol/yr (for vertical ladders);
= 31 lb-mol/yr [for unslotted guidepoles with no well gasket, pole wiper or pole sleeve, from Equation
N fsgp K fsgp = (not present in this example)
= 0 lb-mol/yr (for slotted guidepoles)
Total Deck-Seam Loss Factor
= 0 lb-mol/yr [from Equation (11) for a welded deck]
= 0.125 [for P = 5.8 psia, from Equation (13)] where
T B = 61.6 °F [from Equation (18), with T AA = 60 °F, α = 0.44]; α = 0.44 [for aluminum specular paint in average condition, from API MPMS Ch 19.4, 3 rd Edition, Table 7];
P VA = 5.8 psia [for gasoline with RVP = 10 psi and T LA = 65.4 °F, from API MPMS Ch 19.4, 3 rd Edition, Section 4.2];
M V = 66 lb/lb-mol [for gasoline, from API MPMS Ch 19.4, 3 rd Edition, Table 2]
To estimate the standing loss in pounds per year, substitute the values above into Equation (2):
Estimate the working loss from Equation (19):
The variables in Equation (19) can be determined as follows:
C L = 0.0015 bbl/1000 ft 2 (for gasoline in a lightly rusted tank, from Table 7);
To estimate the working loss in pounds per year, substitute the values above into Equation (19):
Estimate the total loss from Equation (1):
Estimated emissions are expressed to two significant figures, in that greater precision cannot be supported due to limitations in the precision of the empirically-derived emission factors
Components
Floating-roof tanks are designed with specific construction features to minimize evaporative losses These tanks consist of a vertical cylindrical shell and a roof that floats on the liquid's surface, which can be complemented by a fixed roof attached to the top.
The essential elements of a floating roof consist of a floating deck, an annular rim seal that is affixed to the edge of the deck, and various fittings that penetrate the deck for specific functions.
This section outlines the various types of components available in commercial designs, highlighting their potential for evaporative loss along with key design and operational characteristics While tank maintenance and safety are crucial considerations in the design and selection of tank equipment, they are not covered in this publication.
Floating decks effectively minimize evaporative stock loss by covering the liquid surface, which reduces the area exposed to evaporation These decks can either rest directly on the liquid surface or create a layer of saturated vapor beneath them, supported by floats (IFRTs) This design significantly reduces vapor loss typically caused by filling and breathing in fixed-roof tanks However, some evaporative loss can still occur during standing storage through the annular rim space, deck fittings, and occasionally, deck seams (IFRTs).
Floating decks are essential for managing volatile stock services, particularly for stocks with a true vapor pressure below atmospheric pressure These decks are available in a wide range of commercial tank sizes, from approximately 20 ft to 400 ft in diameter, with modified designs suitable for tanks as small as 8 ft Advanced methods and materials have been developed to effectively seal the annular rim space between the tank shell and the deck rim, as well as to secure fittings that penetrate the floating deck.
Floating decks are constructed by joining sheets or panels of deck material, often using mechanical methods like bolting or welding Bolted seams, commonly made of aluminum, are detailed in sections 6.1.5.2 and 6.1.5.3, while welded decks, typically made of steel plates but potentially using other materials, are covered in section 6.1.5.4.
Floating decks are sometimes characterized by the location of the deck relative to the stock liquid surface
A noncontact deck is supported above the stock liquid surface by buoyant structures, while a contact deck floats directly on the liquid surface Typically, steel decks are designed as contact decks, whereas nonferrous materials like aluminum are utilized in both noncontact and contact designs.
API 650 includes two appendices for designing floating roofs Appendix C is used for decks with heavy construction that can support environmental loads like rainfall In contrast, lighter construction decks are designed according to Appendix H, intended for tanks with a fixed roof that protects the floating deck from environmental exposure.
Tanks with a heavier floating deck and no fixed roof are classified as EFRTs, while those with a lighter floating deck and a fixed roof are known as IFRTs Additionally, tanks featuring a heavier external floating roof along with a fixed roof are referred to as domed EFRTs.
The article outlines the various types of floating decks utilized in EFRTs, detailed in section 6.2.1, and illustrated in Figures 1 and 2 It also covers the floating decks used for IFRTs in section 6.2.2, with a reference to Figure 3 Additionally, domed EFRTs, discussed in section 6.2.3, employ the same floating deck types as those found in EFRTs, as shown in Figure 4.
Floating roofs feature an annular space between the deck's perimeter and the tank shell, allowing for movement within the tank To minimize evaporative loss from this rim space, a rim-seal system is implemented An effective rim-seal system effectively closes the rim space, accommodates any irregularities between the floating roof and the tank shell, aids in centering the roof, and allows for normal roof movement.
A rim-seal system can consist of one or two separate seals: a) the primary seal and b) the secondary seal, which is mounted above the primary seal
Three basic types of primary seals are currently in widespread use: a) vapor mounted, b) liquid mounted, and c) mechanical shoe
1—EFRT wi y represent the m th Pontoon most common or t n Floating R typical features i
NOTE De etails shown do n
EFRT with D epresent the mos
Double-deck st common or typ k Floating R pical features in
Figu o not necessarily re 3—IFRT y represent the m with Nonco most common or t ontact Deck typical features i k [12] in use
Vapor-mou differentiate mounted on rim seal are a liquid-mo primarily of
Two basic mounted In primary and widespread rim-seal sys
Dented and liquefied materials in floating configurations are associated with mounted seals Additionally, secondary seals are utilized in various applications It is important to consider the current specifications, as the details provided do not apply to fluid-mounted systems Mechanical seals, particularly those made from specific materials, have been shown to have potential for various uses, although they may not always be applicable in every situation.
The primary seals' location is crucial for vapor containment in floating-roof tanks Proper selection of seal types is essential to ensure effective performance and minimize chemical incompatibility These seals play a significant role in preventing emissions and maintaining safety standards in storage facilities.
Domed EF rim seal systems are currently being developed to enhance compatibility and efficiency These systems feature a unique design that addresses common issues found in traditional rim seal technologies The advancements in these seals aim to improve performance and reliability in various applications.
Rim seals are essential components in various construction applications, particularly in the context of weather shields These seals are typically made from nonmetallic materials that provide effective protection against environmental elements The construction of rim seals involves the use of specific stock liquids, which enhance their durability and functionality While traditional shoe-type rim seals are commonly used, there are other types that are not currently prevalent in the market Understanding the characteristics and applications of these seals is crucial for ensuring the integrity and longevity of the products they are designed to protect.
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-mounted P ositioned suff wiper seals rimary Sea fficiently abov ls [12] ve the liquid surface