Tanks Essentials Organic Liquid Above-Ground Storage Tank Basics - - PowerPoint PPT Presentation

Page 1 Tanks Essentials 3/31/18

Tanks Essentials

Organic Liquid Above-Ground Storage Tank Basics

Bart Leininger, P.E. Principal Ashworth Leininger Group Camarillo, CA

Jim Miller, P.E. Senior Air Quality Engineer (512) 297-6448

Special Note: Credit for the tank design diagrams and information used in this presentation is given to Rob Ferry, TGB Partnership and associated content used under the permission of the 4C Conference.

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Objectives

• Exposure to Tank Design Parameters
• Understand Source Emissions Driving Forces and Calculation Basics
• Evaluate Standard Practices for Emission Rate Determination
• Introduction to Federal Regulatory Requirements

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Tank Categories

API 650

• 0 to 2.5 psig, “atmospheric tanks”

API 620

• Up to 15 psig, “low-pressure tanks”

ASME Boiler and Pressure Vessel Code, Section 8

• Above 15 psig, “pressure vessels”

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Tank Design

• Types of Above-Ground Organic Liquid Storage Tanks
• Fixed-roof, IFR, EFR, Domed EFR
• Types of Floating Roofs
• IFR/EFR, bolted/welded, contact/noncontact
• Floating Roof Design Details
• Deck Seams, Rim Seals, Fittings

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Types of Above-Ground Storage Tanks

• Fixed-roof
• Fixed roof at the top of the shell; no floating roof
• Internal floating roof (IFR)
• Fixed roof and a light-duty floating roof
• External floating roof (EFR)
• Open top (no fixed roof), with a floating roof
• Covered (Domed) external floating roof
• Fixed roof and an external-type floating roof

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Fixed-Roof Tanks

• No floating roof
• Liquid surface is free to evaporate into the headspace
• Typically low-profile cone roof supported with columns
• Requires interior supports, frangible joint
• Vented to the atmosphere
• Open vents (gooseneck) or P/V breather vents

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Fixed-Roof Tanks

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Fixed-Roof Tank Driving Forces for Emissions: Working Losses

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Fixed-Roof Tank Driving Forces for Emissions: Standing Losses

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Fixed-Roof Tank Failures

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Fixed-Roof Tank Failures

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Fixed-Roof Tank Failures

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Fixed-Roof Tank Failures

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Internal Floating-Roof Tanks (IFRTs)

• Floating roof covers the liquid surface
• Greatly reducing free evaporation into the headspace
• Fixed roof is freely vented
• For maintaining vapors << LEL (unless gas blanketed)
• Floating roof deck is lightweight, per API 650, App. H
• Protection by the fixed roof allows lightweight design
• Some vapors escape past the floating roof
• At rim seals, deck fittings, & deck seams (if bolted)

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Internal Floating-Roof Tanks

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IFRT Summary

• Deck construction can be lightweight
• Short sleeves (housings) for deck support legs
• Deck seams may be bolted (typ. for aluminum)
• Fixed roof may require support columns
• Which penetrate the deck, creating paths for emissions
• Wind is not a factor in emissions
• Vapors escape past the floating roof independent of ambient wind speed, and

daily breathing results in enough air movement to carry vapors out of the tank

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External Floating-Roof Tanks (EFRTs)

• Floating roof covers the liquid surface
• Greatly reducing free evaporation
• Fixed roof is subject to wind action
• Tank shell provides a partial shield, but losses still wind driven
• Floating roof deck is heavyweight, per API 650, App. C
• Designed for external forces (e.g., snow, torrential rain)
• Some vapors escape past the floating roof
• At rim seals, deck fittings (but deck seams are welded)

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External Floating-Roof Tank

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EFRT Summary

• Deck construction is heavyweight
• Tall sleeves (housings) for deck support legs
• Welded deck seams
• No fixed roof; no support columns
• Typically fewer deck penetrations than for an IFRT
• Wind is a factor in emissions
• The rate at which vapors escape past the floating roof is very sensitive to

ambient wind speed

• Wind action offsets lower loss factors, fewer fittings

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Covered (Domed) External Floating-Roof Tanks

• Differs from IFRT in the type of floating roof
• EFR-type deck, w/ welded deck seams, tall leg sleeves
• Fixed roof is freely vented (as for IFRT)
• Typically an aluminum dome over an EFRT
• Particularly for retrofit applications, where a dome can be installed in-service
• Could be a steel cone roof, but this would typically involve installing out-of-

service, roof support columns

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Covered (Domed) External Floating-Roof Tank

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Domed External Floating-Roof Tank Summary

• Deck construction is heavyweight
• Tall sleeves (housings) for deck support legs
• Welded deck seams
• Typically with dome roof; no columns
• Means typically fewer deck penetrations than for an IFRT
• Wind is not a factor in emissions
• Lower loss factors, fewer fittings, and not subject to wind action – lowest emitting

type of construction.

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Floating Roof Tank Driving Forces for Emissions: Working Losses

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Floating Roof Tank Driving Forces for Emissions: Standing Losses

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Floating Roof Features

• Emissions sources
• Withdrawals
• Deck Seams (bolted decks only)
• Rim Seals
• Deck Fittings
• Controls
• Rim Seals
• Deck Fittings

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Types of Floating Roof Decks

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Floating Roof Cutaway

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Pan Deck

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Bulkheaded Deck

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Pontoon Deck

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Pontoon Deck

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Double-Deck

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Double Deck

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On-Floats Deck

• aka skin & pontoon, or noncontact

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On-Floats Deck

• aka skin & pontoon, or noncontact

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Sandwich Panel Deck

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Sandwich Panel Deck

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Floating Roof Considerations

• Design:
• External floating roofs per API 650, Appendix C
• Internal floating roofs per API 650, Appendix H
• Costs
• Environmental
• Fire Safety

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External Floating Roofs

• Potentially more economical to initially construct versus IFR
• But future costs may be unacceptable:
• Problems associated with water intrusion
• Drain lines pose maintenance problems
• Snow load poses maintenance problems
• Higher liquid surface temp = higher emissions
• This is not presently accounted for in the emission factors, but an API study is seeking to

quantify this

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Floating Roof Considerations

• Design:
• External floating roofs per API 650, Appendix C
• Internal floating roofs per API 650, Appendix H
• Costs
• Environmental
• Fire Safety

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Rainwater Problems with an EFRT

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EFR Drain Line Problems

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Snow Problems with an EFRT

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Emissions Increased with an EFRT

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Fixed Roofs for Floating Roof Tanks

• Steel cone roof
• Typically column supported
• Requires painting for maintenance
• Retrofit installation requires out-of-service
• Aluminum dome roof
• Self-supporting (no interior columns)
• No painting necessary
• Retrofit installation may be done in-service

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Problems with Support Columns

• Increased air emissions
• Due to penetrations through the floating roof
• May involve significant foundation costs
• Soft soils may require piles under each column.
• High corrosion potential/unable to inspect
• Bottom corrosion & leaks are accelerated at columns
• Interfere with secondary bottom installation

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Support Columns

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IFR Comparison

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Limitations for Pan-Type

• Does not meet NFPA 30 criteria
• Nor does the bulkheaded, as noted in the prior table - they do not have enclosed

flotation compartments

• Does not provide redundant buoyancy
• A single leak can flood the entire deck, whereas other designs still float with two

flooded compartments.

• Is readily sunk by upsets or turbulence
• Unsymmetrical loading may buckle the rim of the deck, allowing it to fold up like a

taco.

• Foam system must be for full surface area.

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Floating Roof “Taco” Failure

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Costs of Steel IFRs

• Higher than aluminum for initial installation
• More loss of capacity than aluminum
• Heavier material displaces more liquid
• Doorsheet escalates replacement costs
• The doorsheet itself involves additional construction
• A hydrotest is required when complete
• To test the integrity of the doorsheet, and
• To stress relieve the doorsheet welds

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Comparison of Aluminum IFRs

• Sandwich panel type:
• More expensive than skin and pontoon,
• More length of deck seams (higher emissions),
• May require doorsheet/hydrotest to replace
• If closed cell core, inherent safety concerns
• Appendix H states that this type is “permitted however…enclosed spaces within a

module may result in undetectable combustible gas.”

• This type, then, does not provide the safety implicit in H.4.1.7

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Comparison of Aluminum IFRs

• Skin and pontoon type:
• Least expensive,
• Lower emissions than sandwich panel,
• Replace without doorsheet or roof hole,
• Foam system must be designed for full surface
• Skin and pontoon type decks cost less than other types both initially and for replacement,

but if a foam system is required for fire protection the foam system will cost more for skin and pontoon aluminum than for steel pontoon or doubledeck.

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Aluminum Skin & Pontoon

• If best, why are others even considered?
• Seems to be clear choice from value engineering
• Negative perceptions in the market:
• Flexibility is disconcerting for personnel.
• Reputation of poor service history.
• The Question: Are they inherently flimsy,

OR have they been underdesigned?

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Aluminum Skin & Pontoon – Negative Perceptions

• Flexibility is disconcerting for personnel.
• Workers feel uneasy walking on it
• Safe, but sensation like walking on a huge waterbed
• A moot point in light of Confined Space Entry
• Workmen generally not allowed to enter any IFRT
• Reputation for poor service history.
• API 650 Appendix H has had a design loophole.
• Only required to support 500 pounds.

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API 650, Appendix H pre-Revision

• Design standard for all IFRs
• Allowed waiver of uniform live load
• If equipped with deck drains
• Only design load was then 500 pound load
• As a result, some manufacturers use few legs
• ‘Typical’ tributary area assumed for emission estimates is about 400 square feet per leg

(an area 40 ft x 10 ft)

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API 650, Appendix H post-Revision

• All IFRs to support uniform live load:
• Still 12.5 psf if no deck drains.
• Now 5 psf with deck drains.
• This translates to 2,000 lbs for a 400 sq.ft. area.
• Most failures have had too few deck legs.
• Legs on 40 ft spacing would now need 10 ft spacing, or
• Support 4-times more load than previously.

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Aluminum Skin & Pontoon - Summary of Service History

• Frequent failures occur with poor designs
• Successful deck leg design has featured:
• Limit on tributary area of about 200 square feet
• Designed to support 1000 pounds {5 psf}
• Designed for real world load conditions
• (i.e., out-of-plumb, out-of-level, & subject to cyclic loads)
• Properly designed skin & pontoon IFRs can last longer w/o major repairs

than the tank

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Summary of IFR Types

• Steel pontoon and double deck:
• Most durable, lowest emissions, best fire safety
• Most expensive
• Aluminum skin-and-pontoon:
• Best value for many applications IF well made
• Quality varies greatly
• Higher emissions
• Other designs:
• May suit limited or specialized applications

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Floating Roof Features

• Points of emissions from floating roofs
• Deck seams (if bolted), rim seals, deck fittings
• Types of devices to control emissions
• Features of common rim seals and deck fitting controls

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Points of Emissions from Floating Roofs

• Deck Seams
• Contribute to emissions if bolted; but not if welded
• Rim Seals
• This is the closure device between the deck and tank
• Deck Fittings
• Only those features that open through the deck to the stored liquid are

considered to be deck fittings for emissions purposes

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Deck Seams – Sheet Construction

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Deck Seams – Panel Construction

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Rim Seals

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Rim Seal Vapor Space

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Rim Seal Emissions

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Types of Primary Rim Seals

• Vapor-mounted:
• Highest emissions - Fair service history
• Liquid-mounted:
• Lowest emissions - Poorest service history
• Mechanical-shoe:
• Fairly low emissions - Best service history
• Note that, in California, a mechanical-shoe seal is considered a type of liquid-mounted

seal, rather than a separate category of rim seal.

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Vapor-Mounted Rim Seal

• Bottom is not in contact with the liquid surface
• Annular vapor space beneath the rim seal
• Between the rim of the deck and the shell of the tank
• Two common types:
• Flexible-wiper (blade)
• Continuous wiper blade around the rim of the deck
• Resilient-filled type
• A foam log within an elastomeric-coated fabric envelope
• The envelope protects the foam core from liquid & abrasion

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Vapor-Mounted Rim Seal – Flexible-Wiper Type

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Vapor-Mounted Rim Seal – Resilient-Filled Type

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Liquid-Mounted Rim Seal

• Bottom of the seal contacts the liquid surface
• The rim vapor space is virtually eliminated
• Resilient-filled design
• Typically a foam log in an elastomeric-coated fabric
• Differs from resilient-filled vapor-mounted rim seal in its position relative to

the liquid

• i.e., whether or not the bottom of the seal contacts the liquid surface

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Liquid-Mounted Rim Seal

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Mechanical-Shoe Rim Seal

• Metallic shoe - slides against the tank shell
• A series of overlapping sheets form a ring inside the shell
• Mechanical device - pushing the shoe outward
• Regularly spaced devices hold the shoe against the shell
• Primary seal fabric - to cover the annular space
• An elastomeric-coated fabric closes the annular space between the metallic shoe

and the rim of the deck

• In California, mechanical-shoe is considered a type of liquid-mounted seal,

rather than a separate category

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Mechanical-Shoe Rim Seal

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Strategies to Improve Rim Seal Effectiveness

• Minimize gaps between rim seal and tank shell
• Seek to keep the rim seal firmly against the tank shell
• Minimize the rim space tributary to a gap
• Fill the rim space or provide a baffle to isolate it
• Provide secondary closure of the rim space
• Equip the floating roof with a secondary rim seal

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Minimize Rim Seal Gaps

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Baffle-Type Controls

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Rim Seal Gaps – Mechanical-shoe Seal

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Eliminate the Rim Space (Filling It)

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Rim Seal Gaps – Liquid-mounted Seal

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Secondary Rim Seals

• Purpose is to reduce emissions
• Particularly effective for external floating roofs
• Mounted above the primary seal
• The secondary is the upper seal in a double seal system
• May be added to any type of primary seal
• Mounted sufficiently high to not interfere w/the primary
• Generally results in loss of tank capacity
• Particularly with internal floating roofs, where the fixed roof limits upward travel of

the floating roof

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Secondary Rim Seals – Rim-Mounted Secondary; Mechanical Shoe Primary

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Secondary Rim Seals – Shoe-Mounted Secondary; Mechanical Shoe Primary

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Secondary Rim Seals – Wiper Secondary; Log Seal Primary

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Secondary Rim Seals – Wiper Secondary; Wiper Primary

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Deck Fittings – Common Features

• Only create emissions if through to liquid
• Deck opening may be round or square
• Shape of opening is a matter of fabricator preference
• Bottom of opening (for most) extends below the liquid surface
• Noncontact decks require a well extension or skirt
• If for a penetration, deck cover must be loose
• The cover must be allowed to slide for out-of-plumbness

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Deck Fittings

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Not Deck Fittings

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Deck Fittings

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Deck Fittings – Basic Categories

• Small opening (nozzle or pipe sleeve) type
• e.g., deck support legs, gauge hatches, deck drains.
• Vent devices
• Not required to extend below the liquid surface
• Large opening (well) type
• e.g., manways, gauge float wells, column wells, and vertical ladders
• Guidepoles–aka gaugepoles, gaugepipes, etc.
• Important enough to be a category unto themselves

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Deck Fittings – Support Legs

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Deck Support Legs – Control Options

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Sample Ports

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Effectiveness of Slit Fabric/Slotted Membrane

• There is no apparent benefit to 90% closure at 0 mph wind
• By comparison, emission factor for an uncontrolled slotted guidepole at 10

mph is 4200 lb-mol/yr

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Deck Drains

(that empty into stored liquid)

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Rim Space Vents

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Vacuum Breaker (Automatic Bleeder Vent)

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Vacuum Breaker (Automatic Bleeder Vent)

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Access Hatch (Manway)

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Gauge Float (Automatic Tank Gauge)

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Fixed Roof Support Column

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Fixed Roof Support Column

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Fixed Roof Support Column

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Fixed Roof Support Column

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Vertical Ladder

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Guidepoles

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Guidepole Functions

• Anti-rotation devices
• Sampling location
• Level gauge location

To measure the level of the liquid in the tank

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Unslotted Guidepoles

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Slotted Guidepoles

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Function of Slots in a Guidepole

• Allow bulk liquid to flow freely into the pole
• To achieve accurate sampling
• To achieve accurate level gauging
• Avoid confined space entry
• Definition of a slotted guidepole: (Per Generic MACT, 63 Subpart WW)
• A guidepole or gaugepole that has slots or holes through the wall of the pole

[that] allow the stored liquid to flow into the pole at liquid levels above the lowest

• perating level

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Unslotted Guidepole

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Unslotted Guidepole

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Unslotted Guidepole

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Slotted Guidepole

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Slotted Guidepole

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Slotted Guidepole

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Pole Float

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Pole Float

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Short Pole Float

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Pole Sleeve

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Flexible Enclosure (Accordion)

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Guidepole/Ladder Combination

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Guidepole/Ladder Combination

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Guidepole/Ladder Combination

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Estimating Storage Tank Air Emissions

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Brief History of Calculation Development

• Data from testing for over 20 years
• Sponsored by API, in cooperation with EPA
• Published by both API and EPA
• Chapter 19 of API’s MPMS
• Section 7.1 of EPA’s AP-42
• liquid in the tank

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Brief History of API Research

• Pilot tank testing in the late 1970’s
• Yielded useful results, such as effect of ambient wind
• Not feasible for isolating components
• Wind tunnel and bench scale tests
• Testing of individual deck fittings and rim seals
• Testing at various wind speeds
• ‘Zero wind speed’: frequent air changes (not still air)
• Bolted deck seams the most difficult to standardize

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API’s MPMS Chapter 19

Manual of Petroleum Measurement Standards Chapter 19 – Evaporative Loss Measurement

• 19.1 Evaporative Loss from Fixed-Roof Tanks
• 19.2 Evaporative Loss from Floating-Roof Tanks
• 19.3 Loss Factor Certification Program
• Parts A-E are test methods
• Parts F-H are for administration of the tests
• 19.4 Evaporative Loss Reference Information and Speciation Methodology

(Oct. 2012)

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EPA’s AP-42

Compilation of Air Pollutant Emission Factors

• Volume I: Stationary Point and Area Sources
• Contains emission factors for all sorts of sources
• Section 7.1 – Organic Liquid Storage Tanks
• Fifth Edition, Supplement D – September ’97
• 2006 Revision added Floating Roof Landing Losses
• But Landing Losses not in TANKS 4.09D
• Most agencies reference AP-42 equations

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MPMS 19 versus AP-42 7.1

• The loss factors and equations used are identical, with the following

exception:

• Bolted deck seam loss factor
• EPA reduced this factor by about 60% (0.14 vs 0.34) in response to data from testing in

the late 1990’s.

• API has not changed from the earlier value of 0.34
• Liquid surface temperature – no longer different
• Had been different for floating-roof tanks, but the API method was reconciled to

the EPA method in the Oct 2012 revisions to API MPMS 19.2 and 19.4

• Most agencies refer to emissions equations in AP-42

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Emissions Driving Forces Review

• Losses due to liquid throughputs
• Fixed-roof: working loss (filling)
• Floating-roof: withdrawal loss (clingage)
• Losses when tank is static
• Fixed-roof: standing loss (breathing)
• Floating-roof: standing loss
• Due to vapors escaping past the rim seal and through deck fittings (and deck seams, if

bolted)

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Fixed-Roof Tank: Filling Loss

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Fixed-Roof Tank Filling (Working) Loss

Equation (1-35) for estimating working loss, LW: LW = N [ HLX (π/4) D2 ] KN KP WV KB

where N = turnover rate [turnovers/year] HLX = maximum liquid height [feet] D = tank diameter [feet] KN = working loss turnover (saturation) factor [dimensionless] KP = working loss product factor [dimensionless] (0.75 or 1) WV = stock vapor density [lb/ft3] KB = vent setting correction factor [dimensionless]

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Fixed-Roof Tank Saturation Factor

KN = working loss turnover (saturation) factor [dimensionless] For turnovers ≤36: KN = 1 For turnovers >36: KN = (180 + N)/6N Asymptotically approaches 0.167

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Fixed-Roof Tank Filling (Working) Loss

• Stock vapor density, WV [lb/ft3] (Equation 1-21)

WV = MV PVA / (R TLA)

where:

• MV = vapor molecular weight [lb/lb-mole]
• R = the ideal gas constant (10.731 psia ft3/lb-mole °R)
• PVA = vapor pressure at daily avg liquid surface temperature [psia]
• TLA = daily average liquid surface temperature [°R]

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Fixed-Roof Tank Filling (Working) Loss

• Vent setting correction factor, KB

(Eq 1-37)

(Only used if breather vent settings are greater than the typical ±0.3 psig)

KB = [(PI + PA) / KN – PVA] / (PBP + PA - PVA)

where:

• PI = pressure of the vapor space at normal operating conditions [psig] (0 if

tank is atmospheric: not held at constant pres/vac)

• PA = atmospheric pressure [psia]
• KN = working loss turnover (saturation) factor [dimensionless]
• PVA = vapor pressure at the daily average liquid surface temperature [psia]
• PBP = breather vent pressure setting [psig]

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Fixed-Roof Tank Standing Losses

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Fixed-Roof Tank Standing (Breathing) Loss

Equation (1-4) for estimating standing loss, LS: LS = 365 KE (π/4 D2) HVO KS WV

where 365 = number of daily events per year [year -1] KE = vapor space expansion factor [dimensionless] (1-5, 1-7) D = tank diameter [feet] HVO = vapor space outage [feet] (1-15) KS = vented vapor saturation factor [dimensionless] (1-20) WV = stock vapor density [lb/ft3] (1-21)

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Fixed-Roof Tank Standing (Breathing) Loss

Equation (1-5) for estimating vapor space expansion factor for products with PV < 0.1 psia: KE = 0.0018 [0.72 (TAX − TAN) + 0.028 α I]

where TAX = daily maximum ambient temperature [°R] TAN = daily minimum ambient temperature [°R] α = tank paint solar absorptance [dimensionless] I = daily total solar insolation on a horizontal surface [Btu/(ft2 day)] 0.0018 = constant, [(°R)-1] 0.72 = constant [dimensionless] 0.028 = constant [(°R ft2 day)/Btu]

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Fixed-Roof Tank Standing (Breathing) Loss

Equation (1-7) for estimating vapor space expansion factor for products with PV > 0.1 psia: KE = Δ TV / TLA + (Δ PV - Δ PB) / (PA - PVA) > 0

where Δ TV = daily vapor temperature range [°R] = (0.72 Δ TA + 0.028 α I) Δ PV = daily vapor pressure range [psi] Δ PB = breather vent pressure setting range [psi] PA = atmospheric pressure [psia] PVA = vapor pressure at daily average liquid surface temperature, [psia] TLA = daily average liquid surface temperature [°R]

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Fixed-Roof Tank Standing (Breathing) Loss

Equation (1-20) for estimating vented vapor saturation factor: KS = 1 / (1 + 0.053 PVA HVO)

where PVA = vapor pressure at daily avg liquid surface temperature, [psia] HVO = vapor space outage [ft] 0.053 = constant [(psia-ft)-1]

Page 142 Tanks Essentials 3/31/18

Fixed-Roof Tank Vapor Space Expansion Factor

HVO

Page 143 Tanks Essentials 3/31/18

Fixed-Roof Tank Emissions Strategy

Compliance calculations Minimum data needs:

• Tank design parameters (diameter, color, shell height)
• Material properties (liquid density, MWs, vapor pressure

curve data)

• Operating parameters (liquid level, breather vent

settings, monthly throughput)

Page 144 Tanks Essentials 3/31/18

Fixed-Roof Tank Emissions Strategy

Compliance calculations Specific data for special cases:

• Tank design parameters (paint and insulation specifics)
• Operating parameters (constant level, temperature

data)

• Material properties (monthly average sampling data –

vapor pressure and/or speciation)

Page 145 Tanks Essentials 3/31/18

Fixed-Roof Tank Emissions Strategy

Permit calculation considerations Compliance challenges and NSR challenges:

• Maximize emissions? Capping emissions?

Annual calculation strategy:

• Total throughput on a tank basis (how one divides these into the month

can create flexibility, particularly when > 36 t/o per year)

• Total throughput on a product cap basis (greater flexibility)
• Product vapor pressures (or use maximum regulatory limit of 0.5 psia)

and speciations

• New, average, poor paint factors

Page 146 Tanks Essentials 3/31/18

Fixed-Roof Tank Emissions Strategy

Permit calculation considerations Un-capped Options:

• Divide annual throughput evenly into each month (1/12)
• Normalize for number of days in month (31/365,

28/365,…)

• Total annual in each month, then use maximum working

loss

• Total annual in each month, then use max working loss

/ KN (hybrid)

Page 147 Tanks Essentials 3/31/18

Fixed-Roof Tank Emissions Strategy

Permit calculation considerations Un-capped Options:

Page 148 Tanks Essentials 3/31/18

Fixed-Roof Tank Emissions Strategy

Permit calculation considerations Hourly emissions:

• Use working loss equation only (neglect breathing)
• Use greater liquid surface temperature of either 95⁰F or maximum monthly

liquid surface temperature

• Use annual throughput based on maximum fill rate
• Set KN, KP, and KB = 1
• New after Dec. 2016, set KP = 0.6 for crude oil (was 0.4)

LW,MAX = N [ HLX (π/4) D2 ] KN KP WV KB / 8760 LW,MAX = 5.614 QMAX KP WV / 8760 [lb/hr]

5.614 Q 1 1

Page 149 Tanks Essentials 3/31/18

Floating Roof Tank: Working Losses

Page 150 Tanks Essentials 3/31/18

Floating-Roof Tank Withdrawal (Clingage) Loss Equation (2-4) for estimating withdrawal loss, LWD: LWD = 0.943 Q/D CS WL [ 1 + NC FC / D ]

where 0.943 = constant [1000 ft3-gal/bbl2] Q = annual throughput [bbl/year] D = tank diameter [feet] CS = shell clingage factor [bbl/1000 ft3] (product and lining dependent) WL = organic liquid density [lb/gal] NC = number of support columns [dimensionless] FC = effective column diameter [feet]

Page 151 Tanks Essentials 3/31/18

Floating-Roof Tank Withdrawal (Clingage) Loss Note: When speciating emissions from floating roof tank withdrawal losses, the liquid phase concentrations must be applied (This would not be appropriate for standing losses)

Page 152 Tanks Essentials 3/31/18

Floating Roof Tank Driving Forces for Emissions: Standing Losses

Page 153 Tanks Essentials 3/31/18

Floating-Roof Tank Standing Loss Equation for estimating standing storage loss, LS: LS = [LR + LF + LD]

where LR = total rim seal loss [lb/year] (2-2) FF = total deck fitting loss [lb/year] (2-5) FD = total deck seam loss [lb/year] (2-9)

Page 154 Tanks Essentials 3/31/18

Floating-Roof Tank Rim Seal Loss Equation (2-2) for estimating rim seal loss, LR: LR = [KRa + KRb Vn] D P* MV KC

where KRa = zero wind speed rim seal loss factor [lbmol/ft-year] (Table 7.1-8) KRb = wind dependent rim seal loss factor [lbmol/(mph)n-ft-year] V = average ambient wind speed at tank site [mph] n = seal-related wind speed exponent [dimensionless] P* = vapor pressure function [dimensionless] (2-3) MV = stock vapor molecular weight [lb/lbmol] KC = product factor [dimensionless – 0.4 or 1]

Page 155 Tanks Essentials 3/31/18

Floating-Roof Tank Rim Seal Loss Equation (2-2) for estimating rim seal loss, LR: P* = (PVA / PA) / [1 + (1 - PVA / PA )0.5]2

where PVA = vapor pressure at daily average liquid surface temperature [psia] PA = atmospheric pressure [psia]

Page 156 Tanks Essentials 3/31/18

Floating-Roof Tank Deck Fitting Loss Equation (2-5) for estimating deck fitting loss, LF: LF = FF P* MV KC

where FF = total deck fitting loss factor [lbmol/year] (2-6, 2-7) P* = vapor pressure function [dimensionless] (2-3) MV = stock vapor molecular weight [lb/lbmol] KC = product factor [dimensionless – 0.4 or 1]

Page 157 Tanks Essentials 3/31/18

Floating-Roof Tank Deck Fitting Loss Equation (2-6) for estimating total deck fitting loss factor, FF: FF = [(NF1 KF1) + (NF2 KF2) +…+ (NFf KFf)]

where NFi = number of fittings (i = 0, 1, 2,…,nf) [dimensionless] KFi = deck fitting loss factor [lbmol/year] (2-7)

Page 158 Tanks Essentials 3/31/18

Floating-Roof Tank Deck Fitting Loss Equation (2-7) for estimating deck fitting loss factor, KFi: KFi = Kfai + Kfbi (KV V)mi

where Kfai = zero wind speed loss factor for fitting [lbmol/year] Kfbi = wind speed dependent loss factor for fitting [lbmol/year] KV = fitting wind speed correction factor [dimensionless – 0.7 or 0] V = average ambient wind speed [mph] mi = loss factor for deck fitting [dimensionless]

Page 159 Tanks Essentials 3/31/18

Floating-Roof Tank Deck Fitting Loss

AP-42, Table 7.1-12

Page 160 Tanks Essentials 3/31/18

Floating-Roof Tank (Relative) Guidepole Losses

Page 161 Tanks Essentials 3/31/18

Floating-Roof Tank Deck Seam Loss Equation (2-9) for estimating deck seam loss, LD: LD = KD SD D2 P* MV KC

where KD = deck seam loss factor [lbmol/ft-year] SD = deck seam length factor [ft/ft2] D = tank diameter [ft] P* = vapor pressure function [dimensionless] (2-3) MV = stock vapor molecular weight [lb/lbmol] KC = product factor [dimensionless – 0.4 or 1]

Page 162 Tanks Essentials 3/31/18

Floating-Roof Tank Emissions Strategy Permit calculation considerations

Compliance challenges and NSR challenges:

• Maximize flexibility? Capping emissions?
• Minimize emissions increases?

Annual calculation strategy:

• Total throughput on a tank basis (how one divides these into the

month can create issues for cascading tanks)

• Cap total throughput on a product basis (greater flexibility)
• Actual product vapor pressures (vs use maximum regulatory limit
• f 11.0 psia) and speciation
• New, average, poor paint factors

Page 163 Tanks Essentials 3/31/18

Floating-Roof Tank Emissions Strategy What about those throughput options?

• Divide annual throughput evenly into each month (1/12)
• Normalize for number of days in month (31/365, 28/365,…)
• Total annual in each month, then use maximum working loss
• Total annual / “x” in each month, then use “x” max working losses

(hybrid)

Page 164 Tanks Essentials 3/31/18

Floating-Roof Tank Emissions Strategy Permit calculation considerations Hourly emissions:

Use total emissions (working and breathing) Use maximum monthly emission rate divided by hours in the month

Hottest month for IFR tank Not necessarily hottest month for EFR tank

Use throughput based on maximum withdrawal rate for EFR tank, fill/withdrawal rate for IFR tank (TCEQ guidance)

Page 165 Tanks Essentials 3/31/18

Tank Emissions Speciation

• Guidance given in API MPMS 19.4
• Generally perform Partial Speciation to obtain emissions
• f selected compounds (HAPs, Toxics, etc.)
• Requires knowing the concentration of the compounds of

interest in the liquid phase of the mixture

• Speciate fixed roof tank emissions based on vapor phase
• Speciate floating roof standing emissions based on vapor phase
• Speciate floating roof withdrawal emissions based on liquid phase

Page 166 Tanks Essentials 3/31/18

Air Regulations Introduction

Page 167 Tanks Essentials 3/31/18

Page 168 Tanks Essentials 3/31/18

Regulatory Basics

• The rules are confusing
• Even EPA staff have called them “incomprehensible”
• The rules are complex
• 16 or more air rules may apply to a floating-roof tank
• The rules are conflicting
• Requirements from one rule to the next are inconsistent
• The rules are cumbersome
• Monitoring/Inspection, Recordkeeping, and Reporting

Page 169 Tanks Essentials 3/31/18

Regulatory Basics – Common Considerations

• First step is determining applicability
• Is the tank new, newly modified/reconstructed, or existing?
• Is the site a major source of HAPs or a named industry in

the MACT/GACT rules?

• Are there state rules, permit conditions, or consent decrees

that might affect applicability?

• Most rules have a minimum applicable volume and vapor

pressure for triggering controls/inspection/reporting

• MACT may also have minimum HAPs concentration limits

Page 170 Tanks Essentials 3/31/18

Regulatory Basics – Common Considerations

• For new tanks, New Source Performance Standards (NSPS),

60 Supbart Kb, may apply

• Check with your environmental expert to determine additional

rule overlap

• Most* rules have vapor pressure cutoffs of 0.5 psia and 11.0

psia

• Below 0.5 psia, no floating roof required
• Above 0.5 psia, floating roof required
• Above 11.0 psia, add-on closed-vent to controls required
• *Be very careful to check when dealing with NESHAPs tanks,

MACT sites, or permit/applicability concerns

Page 171 Tanks Essentials 3/31/18

Regulatory Basics – Common Considerations

• Most tanks below 20K gallons will be exempt
• Some tanks between 20K gallons and 40K gallons will be

exempt

• Most tanks above 40K gallons will be applicable
• Applicable tanks will have monitoring and reporting

requirements

Page 172 Tanks Essentials 3/31/18

Regulatory Basics – “Universal” Controls

For floating roof tanks controls, as specified in MACT WW (63 Subpart WW), are:

• IFR Rim seal: liquid mounted, mechanical shoe, or vapor

mounted primary with a secondary wiper

• EFR Rim seal: liquid mounted primary with a secondary;

mechanical shoe primary with a secondary

• All fittings except rim vents and vacuum breakers should

have wells that extend into liquid surface

Page 173 Tanks Essentials 3/31/18

Regulatory Basics – “Universal” Controls

• All fitting wells (except roof legs and emergency drains),

should be equipped with gasketed covers, closure device, etc.

• May elect slotted membrane (90% closed) for sample wells
• May elect covers equivalent 90% closed for deck drains
• Gauge float and manway lids: gasketed and bolted/latched

Page 174 Tanks Essentials 3/31/18

Regulatory Basics – “Universal” Controls

• Unslotted guidepoles:
• Gasketed lid, wiper, and welded lid or gasketed hatch at top of

pole

• Slotted guidepoles:
• Gasketed lid, wiper, pole sleeve
• Gasketed lid, wiper, pole float

Page 175 Tanks Essentials 3/31/18

Open Discussion

Jim Miller, PE (512) 297-6448

Special Note: Credit for the tank design diagrams and information used in this presentation is given to Rob Ferry, TGB Partnership and associated content used under the permission of the 4C Conference.