Enhanced vapor containment and monitoring

Details Enhanced vapor containment and monitoring Enhanced vapor containment and monitoring

2002-06-26

2004-12-28

Hoff, Marc S. (Department: 2857)

Data processing: measuring, calibrating, or testing

Measurement system in a specific environment

Chemical analysis

C702S024000, C702S031000, C702S032000, C702S084000, C073S024040, C073S025040, C073S029010, C073S061770, C324S464000, C324S089000, C141S007000, C141S044000, C141S059000, C141S290000

Reexamination Certificate

active

06836732

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to the commercial distribution and sales of volatile motor fuels and more specifically to systems and methods for increasing overall vapor recovery efficiency and ensuring storage tank integrity at such volatile motor fuel dispensing facilities.
BACKGROUND OF THE INVENTION
Various stationary and mobile tanks are used in the production, storage and distribution of volatile organic compounds such as fuels, solvents and chemical feedstocks. When transferring a volatile fuel such as gasoline from a fixed roof storage tank to a fixed roof receiving tank, two events simultaneously occur. Vapors in the receiving tank ullage (space above the liquid) are displaced by the incoming liquid, and a negative pressure in the storage tank is developed in response to the dropping liquid level. The negative pressure in the storage tank is offset by either the ingestion of atmospheric air, or in the case of facilities equipped with Stage II vapor recovery systems, a hydrocarbon/air mixture. If the hydrocarbon concentration in the storage tank ullage is reduced below the naturally occurring equilibrium concentration dictated by the volatility and temperature of the fuel, a driving force for evaporation of valuable liquid gasoline is established. As the storage tank liquid evaporates to re-establish the equilibrium hydrocarbon concentration in the ullage space, the volume expansion of liquid to vapor measures approximately 520:1, and the resulting large volume of vapor is exhaled until equilibrium is achieved. These emissions are comprised of VOC's (Volatile Organic Compounds) which are ozone precursors and hazardous air pollutants (HAPS) such as benzene. These gasoline vapor emissions represent an economic loss to the retailer, an environmental hazard and a negative impact on human health since benzene is a known human carcinogen.
Accordingly, vapor losses from fixed-roof gasoline storage tanks includes displacement losses caused by inflow of liquid, breathing losses caused by temperature and atmospheric pressure variations, and emptying losses caused by evaporation of liquid after the transfer of product occurring during the interval between the next product delivery.
Capture of displacement losses in the United States petroleum industry has been addressed by Stage I, Stage II and ORVR vapor recovery systems. The Stage I systems return vapors displaced from the large capacity storage tanks to the ullage space of the high volume tanker truck. Stage II systems return vapors displaced from vehicle fuel tanks to the storage tanks, and ORVR (On-board refueling Vapor Recovery) systems capture vapors displaced from vehicle fuel tanks within a canister, located within the vehicle, containing selectively adsorbent material.
The overall vapor recovery efficiency at the refueling station depends upon the vapor emissions at the nozzle/automobile fillpipe interface and on the vapor emissions from the storage tanks both during and in the interval between bulk product deliveries. In addition, other factors such as liquid spillage must be taken into account. In conjunction with
FIG. 5
, the following equations apply:
E
(
UNC
)=
E
(
R
1
)+
E
(
V
1
)+
E
(
F
1
)+
E
(
SL
1
)  (1)
E
(
C
)=
E
(
R
2
)+
E
(
V
2
)+
E
(
F
2
)+
E
(
SL
2
)  (2)
where;
Efficiency (
n
)=(
E
(
UNC
)−
E
(
C
))/
E
(
UNC
)×100%  (3)
E
UNC
=Total Uncontrolled Emissions from a petrol filling station using Stage I vapor recovery, but no Stage II and open vent lines,
E
R1
=Uncontrolled refueling emissions from vehicle tank
E
V1
=Measured vapor emissions expelled from manifolded storage tank vent lines. These losses include tank breathing losses caused by atmospheric pressure variations, wet-stock evaporative losses caused by air ingestion and excess vapor volumes developed during a bulk drop, even with Stage I vapor balance piping installed.
E
F1
=Fugitive emissions expelled from the combined vapor space of the petrol station storage tank and delivery piping system. These emissions occur in the vapor space before reaching the vent. Fugitive emissions can be estimated by conducting a pressure decay test on the enclosed vapor space of the storage tank and vapor piping system.
E
SL1
=Spillage emissions are caused by liquid product dripping from nozzles and nozzle/fillpipe interface
The equation describing the losses after control measures are installed is as follows:
E
C
=E
R2
+E
V2
+E
F2
+E
SL2
; where  (4)
E
R2
=Vehicle refueling emissions measured at the nozzle/fillpipe interface after the installation of Stage II vapor recovery systems which allow the return of vapors displaced from the vehicle fuel tank to the petrol stations storage tanks.
E
V2
=Measured vapor emissions at storage tank vent lines which are manifolded and are kept closed by the use of a pressure/vacuum valve (“p/v”). The p/v valve provides for a slight increase in Stage I collection efficiency and allows for the establishment of a small positive or negative pressure on the entire vapor space. All measured vapors expelled from the valve or valves must be included in the emissions inventory; this includes tank breathing losses, wet-stock evaporative losses and the vapors expelled during bulk tanker drops, even with Stage I balance piping installed. If processing units are installed on the manifolded vent lines, the exhaust lines of the units must be measured for vapor emissions and included in EV
2
.
E
F2
=Fugitive emissions are calculated in the same manner as previously described for uncontrolled sites.
E
SL2
=Spilled liquid emissions are estimated from published figures unless other lower parameters can be proved.
As seen in the above equations, the key parameters which must be measured are EV
1
, ER
2
and EV
2
(ER
1
is assumed relatively constant while EF
1
, EF
2
, ESL
1
and ESL
2
are smaller contributors—see Table 1 in the Appendix for listing of typical figures for these parameters).
Historically, the focus has been on systems or piping configurations which capture vapors and systems designed to ensure containment of the captured vapors and mitigate breathing and emptying losses from storage tanks located at dispensing facilities have not been widely discussed or pursued. This focus has recently changed since newly promulgated Enhanced Vapor Recovery (EVR) regulations by the California Air Resources Board (CARB) are scheduled to take effect by April 2003. In addition, the San Diego Air Pollution Control District (APCD) is presently investigating in detail various loss modes in the storage and transfer of petroleum liquids. Moreover, NESCAUM (Northeast States for Coordinated Air Use Management) has recently asked the USEPA to accurately measure storage tank vapor emissions.
The lack of attention to these loss modes can be largely attributed to loss factors quantified in a Journal article published in 1963, Chass, R. L., et al., “Emissions from Underground Gasoline Storage Tanks”, J. Air Pollution Control Association, 13 (11), 524-530. The relatively small figures of 1 pound of hydrocarbon evaporated for every 1,000 gallons of fuel dispensed have been recently challenged. The author's research has consistently measured and modeled a figure of at least 8 pounds of hydrocarbons evaporated for every 1,000 gallons of fuel dispensed. A recent study in Australia reports a figure of approximately 28 pounds of HC per 1,000 gallons dispensed, and a recent analysis done on a Chevron-Texaco site in the USA yielded an even higher figure.
The above mentioned CARB regulations require certain refinements to existing hardware and monitoring methods to meet the new EVR standards. One technique involves the use of a selectively permeable membrane to reduce EV
1
, EV
2
, EF
1
, and EF
2
emissions (see U.S. Pat. No. 6,059,856, “Method and Apparatus for Reducing Emissions from Breather Lines of Storage Tanks,” describing the use of a GKSS mem

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