DESIGN CRITERIA

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STAGE IVAPOR CONTROL SYSTEMS

GASOLINE SERVICE STATIONS

U. S. ENVIRONMENTAL PROTECTION AGENCY OFFICE OF A I R QUALITY PLANNING AND STANDARDS M I S S I O N STANDARDS AND ENGINEERING D I V I S I O N RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711

NOVEMBER 1975

CRITERIA FOR STAGE I SERVICE STATION CONTROL SYSTEMS

Background

Transportation Control Plans (TPC's) promul gated by EPA in 1973 and 1974 include requirements for the control of gasoline vapors a t service stations in some 17 Air Quality Control Regions (AQCR's) throughout the nation. In a l l cases, control of gasoline vapors during storage tank f i l l i ng (Stage I sources) i s required. In many areas, control of vehicle fueling (Stage 11 sources) i s also required. For storage tank f i l l i ng , EPA regulations prohibit the release of more than 10 percent by weight of displaced organic vapors.

Nhile Stage I vapor control syStems are relatively new, there has been substantial testing which shows that compliance with prescribed limits can be c o plish d a t comrnerical service stations. Tests by oil companies,f,Eq3 P A , ' and a local control agency5 indicate that efficiencies qreater than 90 percent are effected with simple balance systems i f certain common design elements are employed a n d i f the equipment i s properly maintained and operated. Based primarily on this testing, c r i t e r i a have been developed for Stage I control systems. The purpose of this document i s t o provide direction t o operators who are required t o instal l vapor recovery systems.

These c r i t e r i a l i s t the key features of systems which have been found to meet Stage I requirements. Systems incorporating different c r i te r ia may be installed i f t e s t data are supplied to show that they m e t the emission limitation and other provisions of the Stage I regulations.

All current systems used t o control emissions from storgage tank f i l l i ng return displaced vapors t o the tank truck. Vapor balance (displacement) systems re1 ease any excess vapors t o t h e atmosphere; vacuum ass is t systems process excess vapors i n secondary recovery units.

As shown i n the vapor balance systems of Figures 1 and 2 and the secondary system in Figure 3, f lexible hoses carry liquid gasoline from t h e tank truck down a drop tube t o the underground tank. Entering liquid forces t he air-hydrocarbon mixture in the tank out t h r o u g h a f lexible hose t o the tank truck. Alternately, the vapors may ex i t from the underground tank through a vent pipe (about 2 inches in diameter) extending a t least 12 fee t above ground level (OSHA and National Fire Protection Code 30 requirement). A t the truck, the vapor hose i s connected t o a pipinq manifold which may serve as a rollover ra i l t o prevent damage t o the tank in case the truck i s overturned. The ro l l - over r a i l pipinq i s interconnected with the truck compartments by vents

which are opened selectively durinq truck unloadins, allowina returnina vapors from the underground tank t o enter respective product comoartments on the truck.

Two-Point Systems

The most effective method of conductinq displaced vapors from the underaround tank to the truck i s by means of a separate connection t o the underuround tank for the 3-inch vapor return hose, as shown in Fiqure 1 . The vast majority of the tes t s showina comoliance with prescribed limits are from systems util izing th i s feature.

Concentric or Coaxial Systems

However, i n some cases a separate entry i s not available or the operator desires to avoid the excavation necessary to reach an unused entry. For these cases, coaxial devices have been developed t o remove the vapors throuqh the same openinq throuqh which the fuel i s delivered.

I n one system, shown in Figure 4, a droo tube of smaller diameter i s inserted in the existing fuel r i ser . The vapors ex i t through the annular space. A coaxial adaptor f i t s on t h e r i ser and provides connections for the fuel delivery hose and the vaoor return hose. In another system, shown in Fiqure 5, the fuel and vapor passaqes are separated i n a "Y" f i t t i n g which i s permanently attached to the underground tank. The f i t t i nqs for t h e hose connections are located in a conventional manhole. A 6-inch coaxial f i t t i n g i s shown in Figure 7. Yost of these devices arovides less cross-sectional area in the vapor return passaae than do separate connectors and tend t o reduce vapor recovery efficiency to some extent. Vent pipe restr ic t ions will improve efficiencies.

Manifolded Vent Lines

Several schemes have been used t o manifold vents from two or more tanks to a common vapor hose connection. Manifolding may he above or below grade. A number of configurations are acceptable for use w i t h suitable vent restr ic t ions as shown i n Fiaure 8. The 3-way connector of Fiaure 9 provides the most effective arranaement since connection of t he vapor hose t o t h e common connector blocks flow t o the atmosphere and routes a l l displaced vapor to the tank truck. In any manifold piaing system, care must be exercised t o prevent contamination of "no-lead" gas01ine nroduct.

Objectives of Pesiqn Criteria

Design cr i te r ia presently included in this document pertain primarily t o commercial stations where f i l l i n g conditions are most severe. Here there are usually two or three storaoe tanks, each of which ranne u p t o 10,000 gallons i n c a ~ a c i t y . They are normally f i l l ed from a tank truck

of about 4,000-gallon capacity i f a single tanker or 8,000-sallon capacity i f a t r a i l e r i s added. Each truck and t r a i l e r i s compartmented such that different grades of gas01 ine can be transported without cominal ing .

Normal practice a t commercial stations i s t o f i l l storage tanks a t a rate of 200 to 500 gallons per minute, Thus, a typical 4,000-aallon drop may be accam~lished in 10 t o 20 minutes. The drop ra te i s c r i t ica l since i t governs the rate of vapor transfer. Where slower f i l l rates a re used, it may he possible t o use smaller transfer hoses and connections. Also, leakage a t storage tanks and tank trucks tends t o be of lesser magnitude a t slower f i l l ing rates.

Criteria were developed t o accompl ish the following:

l a ) assure submerged f i l l , i . e . , discharge liquid below the gasoline surface in the storaae t a n k ,

( 5 ) assure that the vapor return l ine and connections are o f sufficient size and sufficiently free o f restrictions t o allow transfer of vapor to the truck tank and achieve the desi red recovery,

( c ] assure that there are no sianificant leaks in t h e system or the tank truck which reduce vacuum in the truck or otherwise inhibit vapor transfer,

( d ) assure that the vapor return l ine will be connected during tank f i l l ina.

In addition, coqnizance has been taken of safety requirements of the Occupational Safety and Health Administration (OSHA) and the recomrnendatf ons of the National Fire Protection Association.

Desiqn Criteria

1. .Drop Tube S ecifications. Submerqed f i l l i s specifically required '

by certain TP-hile others are s i l en t on the method of f i l l i n s . ,411 tes t data submitted t o EPA were obtained from systems util izing submerged f i l l . If subrneraed f i l l i s n o t used, t e s t data must be submitted t o show the required recovery will be obtained. The submerged f i l l requirement i s i n t e r ~ r e t e d to mean a drop tube atending t o within 6 inches of the tank bottom, l!nder normal industrypractices, a tube meeting this snecification wi 11 a1 ways be submersed since the tanks are not ournped dr-y.

Deviation from the c r i t e r i a will be a1 lowed i f the owner/o~erator shows that a shorter tube will quarantee suhmerqed f i l l . In such instance, the owner/operator i s required to present records which show

t h a t the level i n the tank never f a l l s below the droo tube. Exceptions also will be allowed for t anks which cannot be converted t o submersed f i l l , e . g . , tanks with offset f i l l lines or Door accessibil i ty.

2. Cause \dell. I f a qauqe well separate from the f i l l tube i s used, it must be ~rovidedw i t h a drop tube which extends t o within 6 inches of the tank bottom. This will prevent vaoor emissions in case the qauge we1 1 cap i s not replaced durina a droo.

3. Va~or Hose Return. Existinp data indicate that a 3-inch ID hose i s needed t o transfer vapors from the storaqe tank t o the truck when a 4-inch d r o ~ tube i s used. Smaller diameter hoses may be satisfactory where f i l l rates are appreciably less than 400 aallons per minute. If a hose smaller than 3 inches i s t o be used, the owner/operator i s required to show that the hose will achieve the required vapor recovery.

4. Vapor Line Connections. Where separate vapor lines are used with 4-inch product tubes, nominal 3-inch or larqer connections should be u t i l ized a t the storaqe tank and truck-trailer. Uhen smal l e r product tubes are used, a smaller vapor l ine connection may be used, provided the ratio of the cross-sectional area of the connection t o the cross-sectional area of the product tube i s 1 :2 or qreater. If the ra t io i s smaller, t e s t data must be provided t o show the required recovery efficiency will be met.

yaaor l ines from two or more tanks may be manifolded t o a common vapor hose connector usinq confiaurations tyaified by Figures 8 and 9 .

For concentric or other tube-in-tube f i t t i nqs , operatina characteristics are unique t o the particular desiqn. To date , adequate t e s t data have been supplied for 4-inch and 6-inch tube-in-tube adapters. These are l is ted i n Attachment A. Other f i t t i nqs will be added t o Attachment A when supporting data are supplied. If f i t t i n a s not l i s ted are t o be used, test data must be provided.

5. Type of Liquid Fill Connection. Vapor t ight caos are required for the liquid f i l l connection for a l l systems. A positive closure ut i l iz inp a gasket or other similar sealina surface i s necessary t o prevent vapors from b e i n q emitted a t around level. Cam-lock closures meet this requirement. Dry-break closures also are accep tab le , b u t are n o t required.

6. Tank Truck Inspection. Vapor t i ah t tank trucks are specifically required by TCP regulations. !his i s interpreted to mean that the truck compartments won't vent qases or draw in a i r unless the s e t t i n p s of the pressure-vacuum rel ief valves are exceeded. An i n s~ec t ion procedure should be submitted t o include frequent visual inspection and leak test ins a t least twice per year. Leak testing should demonstrate that the tank truck when oressurized t o 5 inches W.C. will n o t leak t o a pressure of 2 inches W.C. in less than

3 minutes. Frequent visual inspection i s necessary t o insure proper operation of manifol ding and re1 ief valves.

7 . Closures or Interlocks on Underground Tank Vapor Hose Connectors. Closures or interlocks are required t o assure transfer of displaced vapors t o the truck and t o prevent ground level gasoline vapor emissions due t o fa i lure t o connect the vapor return l ine t o the underground tanks. These devices must be designed: ( a ) t o keep the storaae t a n k sealed unless the vapor hose i s connected t o i t ; or (b ) t o prevent delivery of fuel until the vapor hose i s connected, i . e . , an interlock. Tank openings designed for combined f i l l and vapor recover shall also be protected against vapor release unless connection o f the liquid delivery l ine t o the f i l l pipe simultaneously connects the vapor recovery 1ine, e.g., an interlock. All connections must be vapor tight.

8. Vapor Hose Connection t o the Tank Truck. A means must be provided t o assure t h a t the vapor hose i s connected t o the truck before fuel i s delivered. ~cceptable means of providing th is assurance include: ( a ) permanent connection of the vapor hose t o the truck; ( b ) an inter-lock which prevents fuel delivery unless the vapor hose i s connected, Such as a bracket t o which the product and vapor hose are permanently attached so t h a t neither hose can be connected separately; a n d ( c ) a closure in the vapor hose which remains closed unless the hose i s attached t o the vapor f i t t i ng on t h e truck.

9. Vent Line Restrictions. Vent line restr ic t ions improve recovery efficiency and provide assurance t h a t t h e vapor return l ine will be connected during transfer. I f the liquid f i l l l ine were attached t o the underground tank and the vapor return 1 ine disconnected, closures would seal the vapor return p a t h t o the truck forcing a l l vapors out the vent l ine. Restriction of t h e vent l ine through the use of an or i f ice or pressure-re1 ief valve greatly reduces f i l l rate in such instances warning the operator that the vapor 1ine i s n o t connected.

Sui tab1 e restr ic t ive or i f ices or pressure-re1 i ef valves are required wherever the systems would otherwise be incapable of achieving 90 percentcontrol or would otherwise n o t assure that the vapor return l ine i s connected. For available hardware this means that these restr ic t ive devices are necessary for a l l except systems with interlock connections a t b o t h the truck a n d s torage tank.

Either o f the following res t r ic t ive devices are acceptable:

(a) Orifice of 1 /2 to 3/4 inch ID.

(b) Pressure-vacuum r e l i e f valve s e t to open a t 8 oz. persquare inch or greater pressure and 4 oz. per square inch or greater vacuum. The vacuum r e l i e f feature o f a P-V valve i s not required fo r Stage I recovery purposes b u t may be required by safe ty author i t ies .

The NFPA Interim Amendments (April 1975) t o Code 30 require tha t when vent res t r i c t ion devices are used the tank and associated piping be protected t o l imi t back pressure development to less than the maximum working pressure o f the tank and equipment by the provision of pressure vacuum vents, rupture discs or other tank venting devices ins ta l l ed i n the tank ven t l ines , and that these devices shall be protected to minimize the poss ib i l i ty o f blockage from weather, d i r t , or insect nests. Local f i r e marshals should be consulted regarding the use of these devices in your area . References

Performance of Service Station Vapor Control Concepts, Scott Research Laboratories f o r the American Petroleum In s t i t u t e , Interim Report, June 26, 1974.

Service S t a t i on Vapor Recovery, At1 antic-F!i ch f ie l d Company, April 8, 1974.

Presten, J . E. e t a l , The "Displacement" System: An Effective Method of Controlling Hydrocarbons, November 1973.

TRW Contract Test, June 1974, San Diego, California.

Bay Area Air Pol lu t ion Control D i s t r i c t , 1974.

- 7 - O r i f i c e or P-V Va lve Unless Product and

Compart~ent Vdpor Hoses a r e Inter locked.

U. G . Tank

To Islands

Figure 1. Vapor balancing w i t h separate l i q u i d - vapor r i s e r s .

O r i f i c e or P-V Valve

Figure 4. Coaxial F i t t i n g and F i 11 Tube Adapter . Emco Wheaton Inc.

MISTING CAP AND ADAPTOR OR

NEW OPW 634-TT-4" CAP AND

633-T-4" x 4" ADAPTOR

0 R 62-TT-4" CAP OR 62-4" CAP

AND 61-AS-4" x 4 " ADAPTOR-

NEW OPW 318-V-4" I 4" x 3"

" Y " Tube-in -Return F i t ting. ration/OPW

- .C o a x i a i -1 t t i n g for 6 " w i s e r P i p e s . Parker Hanni f! n , i n c .

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Figure 9. Aboveground , ' 4 a n i f o l d i n g o f Vapor Lines.

Concen t r i c a r d t u b e - i n - t u b e couplers f o r k i h i c h t e s t d a t a show acceptab le perforrr!ance:

1. Ercco b!neaton & i n c h Coax ia l F i t t i n g F-27Ls, adap t e r a n d Crcp T u b e k s e r b l y ,470-PC! .

3. D o v e r Corporat ion/CPh P i v i s i ~ n4- inch Tube-In-Tute Y-Fi t t i r ~ "0. 318 w i t h 61-TC-4 Inch Drop P ipe .

+ I . P a r k e r : a n n i f i c E - i nch Ccaxial Fi t t i ~ ci - S 1 $ ?;itla, a 5-:KC?, S t r a i g h t R i s e r or a 6 - i n c h by 4- inch Riser.

5. U n i v e r s a l Va l ve 4 - inch F i l l / V a p o r Return F i t t i n g Ro. 715.

"t1:io* T h i s attachrent has no r e l a t ion t o 5c iv l i : z y s t e ~ s ,; , P . . s y s t e r s 4. '\;:i'ch s e ~ a - r a t ~c c n r ? ~ c t i c r ,f c r t b e v a y r rettirn i-i:se ,c. ti;^ a i : f~ r$ rc l ; i ; i

t a n k . Such sys tems a r e t o be evs lua ted by t h s Cri te r i a .