U.S. patent application number 10/943706 was filed with the patent office on 2005-04-14 for enhanced vapor containment and monitoring.
Invention is credited to Tiberi, Tedmund P..
Application Number | 20050080589 10/943706 |
Document ID | / |
Family ID | 29778888 |
Filed Date | 2005-04-14 |
United States Patent
Application |
20050080589 |
Kind Code |
A1 |
Tiberi, Tedmund P. |
April 14, 2005 |
Enhanced vapor containment and monitoring
Abstract
An apparatus and method for ensuring effective and efficient
vehicle vapor recovery performance, storage tank system integrity
relative to both vapor and liquid containment and for reducing the
probability that inaccurate information causes companies to
undertake unnecessary, expensive and wasteful loss investigations
at gasoline dispensing facilities. A fuel storage and delivery
system is transformed from an "open system" communicating directly
with the environment to a "closed system" which ensures capture,
containment and accurate accounting of both hydrocarbon vapors and
liquid phase product.
Inventors: |
Tiberi, Tedmund P.;
(Brookfield, IL) |
Correspondence
Address: |
PATENT DEPARTMENT
SKADDEN, ARPS, SLATE, MEAGHER & FLOM LLP
FOUR TIMES SQUARE
NEW YORK
NY
10036
US
|
Family ID: |
29778888 |
Appl. No.: |
10/943706 |
Filed: |
September 17, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10943706 |
Sep 17, 2004 |
|
|
|
10180238 |
Jun 26, 2002 |
|
|
|
6836732 |
|
|
|
|
Current U.S.
Class: |
702/140 |
Current CPC
Class: |
B67D 7/0496 20130101;
B67D 7/0486 20130101 |
Class at
Publication: |
702/140 |
International
Class: |
G01L 011/00 |
Claims
1-2. (canceled)
3. A method for conducting a vapor containment test, comprising:
identifying the start of an idle dispensing period, when no liquid
is transferred from a storage tank to a receiving tank; as long as
the idle dispensing period continues, measuring storage tank
pressure in the ullage space to provide a storage tank pressure
measurement associated with a point in time (P tank, t); measuring
atmospheric pressure at the same point in time (P atm, t);
determining the variation of storage tank pressure and atmospheric
pressure during the idle period by comparing measurements of
storage tank pressure and atmospheric pressure for different times;
in response to detecting that the idle dispensing period is
complete, generating a pressure versus time curve based on the
monitored variations; and determining the acceptability of vapor
containment in the ullage space of the facility to test vapor
containment by reference to the generated pressure versus time
profile.
4. The method of claim 3, further comprising comparing a standard
deviation of storage tank pressure with a standard deviation of
atmospheric pressure, (P tank-P atm), if said standard deviation is
below a threshold, and the average of (P tank-P atmosphere) is
below a threshold, indicating that the storage tank system is
leaky.
5. The method of claim 3, further comprising: comparing a sum of
atmospheric pressure and storage tank pressure (P atm+P tank) at
various time intervals chosen to avoid the impact of temperature
variation; and if sums of (P atm+P tank) are not constant over the
chosen time interval, indicating that the storage tank system is
leaky.
6. A method for directly calculating a vapor growth rate in a
storage tank system, comprising: identifying the ullage tank volume
(Vullage0) at the beginning of a time period (t0), said period
including both idle and active dispensing activity; measuring the
atmospheric pressure (P atm0); measuring the ullage tank pressure
(P tank0); calculating a volume of vapor occupying the ullage
volume (Vullage0) at the beginning of the period, (V0), by the
relationship V0=(P tank0+Patm0)/P atm0.times.Vullage0 at t0;
identifying the ullage volume at the end of the time period
(Vullage1, t1), said period including idle and active dispensing
activity; measuring the atmospheric pressure at the end of the
period (P atm1, t1); measuring the ullage tank pressure at the end
of the period (P tank1, t1); calculating a volume of vapor
occupying the ullage volume at the end of the period (V1) by the
relationship V1=(P tank1+Patm1)/P atm1.times.Vullage1 at t1; and
determining a volume growth rate (VGR) by the relationship
VGR=(V1-V0)/delta t, where delta t is the difference between t1 and
t0.
7. A method for estimating the vapor growth rate in a storage tank
system, comprising; identifying the average dispensing rate within
a given time interval (D); measuring the atmospheric pressure at
the beginning of the time interval (P atm0, t0); measuring the
ullage tank pressure at the beginning of the time interval (P
tank0, t0); assuming at least one or a range of ullage volume
values (Vullage0) between 0 and the total storage tank system
capacity; measuring the atmospheric pressure at the end of the time
interval (P atm1, t1); measuring the storage tank pressure at the
end of the time interval (P tank1, t1); for each assumed initial
ullage volume, calculate a ullage volume at the end of the interval
by the relationship Vullage1=Vullage0+(D.times.delta t), where
delta t is the difference between t1 and t0; and for each pair of
beginning and ending ullage volume values, calculate a vapor growth
rate (VGR) according the following relationships: V0=(P tank0+P
atm0)/P atm0.times.V ullage0, where Vullage0 is the assumed ullage
volume at time t0; V1=(P tank1+P atm1)/P atm1.times.(Vullage1),
where Delta V=V1-V0 and delta t=t1-t 0; and
VGR=(V1-V0)/(t1-t0).
8. The method according to claim 7, further comprising indicating
that leaks may be present when VGR is less than a predetermined
threshold of expected VGR.
9. The method according to claim 7, further comprising indicating
that other anomalies may be present when VGR is greater than a
predetermined threshold of expected VGR.
10. The method according to claim 7, further comprising indicating
that a change in system dynamics may have occurred when VGR is
greater than a predetermined threshold of expected VGR.
11. A method for monitoring the ullage space, comprising: recording
values of storage tank pressure versus time at regularly spaced
time intervals at a facility; determining a pressure profile
signature developed for a specific gasoline dispensing facility
relative to the history of storage tank pressure versus time for
the facility; observing variations from the pressure profile
signature; and indicating the presence of anomalies at the
dispensing facility in response to said observed variations.
12. The method of claim 11, further comprising identifying
anomalies which trigger closer physical inspection of potential
leak sources in response to said observed variations.
13. The method of claim 11, further comprising identifying hardware
operating problems in response to said observed variations;
14. The method of claim 11, further comprising identifying
anomalies which trigger predetermined safety measures if measured
values fall outside of a given threshold value, thus providing an
immediate response for corrective action to anomalies.
15. The method of claim 11, further comprising identifying
anomalies which trigger remote alert notification if measured
values fall outside of a given threshold value, thus providing an
immediate response for corrective action to anomalies.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of and claims priority
from U.S. patent application Ser. No. 10/180,238, entitled
"Enhanced Vapor Containment and Monitoring" filed Jun. 26, 2002,
now pending, which is incorporated herein by reference.
TECHNICAL FIELD
[0002] 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
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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(R1)+E(V1)+E(F1)+E(SL1) (1)
E(C)=E(R2)+E(V2)+E(F2)+E(SL2) (2)
[0007] where;
Efficiency (n)=(E(UNC)-E (C))/E (UNC).times.100% (3)
[0008] E .sub.UNC=Total Uncontrolled Emissions from a petrol
filling station using Stage I vapor recovery, but no Stage II and
open vent lines,
[0009] E .sub.R 1=Uncontrolled refueling emissions from vehicle
tank
[0010] E .sub.v 1=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.
[0011] E .sub.F 1=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.
[0012] E .sub.SL 1=Spillage emissions are caused by liquid product
dripping from nozzles and nozzle/fillpipe interface.
[0013] The equation describing the losses after control measures
are installed is as follows:
E.sub.C=E.sub.R 2+E.sub.V 2+E.sub.F 2+E.sub.SL 2; where (4)
[0014] E .sub.R 2=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.
[0015] E .sub.V 2=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 EV2.
[0016] E .sub.F 2=Fugitive emissions are calculated in the same
manner as previously described for uncontrolled sites.
[0017] E .sub.SL 2=Spilled liquid emissions are estimated from
published figures unless other lower parameters can be proved.
[0018] As seen in the above equations, the key parameters which
must be measured are EV1, ER2 and EV2 (ER1 is assumed relatively
constant while EF1, EF2, ESL1 and ESL2 are smaller
contributors--see Table 1 in the Appendix for listing of typical
figures for these parameters).
[0019] 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.
[0020] 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.
[0021] 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 EV1, EV2, EF1, and EF2 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 membrane). It should be noted that even without the
recent regulatory requirements, the installation of a selectively
permeable membrane system on the combined ullage space of storage
tanks yields attractive economic returns to the party that owns the
gasoline in the storage tanks.
[0022] A major concern among regulators and petroleum marketers
alike is ensuring that numerous installed vapor recovery systems
are performing effectively over an on-going, continuous interval.
Coupled with this concern is the need for confidence in the storage
tank system integrity--in terms of both vapor and liquid
containment. To achieve the latter objectives, petroleum marketers
have made substantial investments in storage tank and product line
leak detection systems, Automatic Tank Gauges (ATG's) and
Statistical Inventory Reconciliation (SIR) algorithms. Ostensibly,
these hardware devices and software algorithms appear effective in
meeting the above needs. However, upon closer examination, the
existing products and services suffer serious flaws.
[0023] The key governing equation for storage tank systems is as
follows:
INPUT-OUTPUT=ACCUMULATION (5)
[0024] If the owner or operator of a gasoline refueling station is
confident that liquid leaks are not present, the other means of
apparent or measured loss of mass are through evaporation loss,
meter miscalibration, invoice errors, theft or volumetric changes
due to temperature variation. Variations of these techniques are
presently approved by USEPA for tank monitoring protocols designed
to detect liquid leaks and thereby avoid major environmental spills
and their associated costly remediation.
[0025] However, for the material balance to generate accurate
results, temperature compensation is necessary to avoid significant
calculation errors caused by volume growth or contraction of liquid
gasoline. It is known in the art that typical gasoline blends
experience a volume change of approximately 0.70% upon undergoing a
temperature change of 10 F. A consistent and accurate inventory
balance can also provide the refueling site owner/operator with an
extra level of confidence that liquid leaks are not being masked by
volume expansion of liquid gasoline. Moreover, this technique will
allow for continuous verification that the vapor recovery system,
liquid leak detection system and associated diagnostic monitors are
working properly. Without temperature compensation and isolation of
inventory discrepancies, one can never be sure if inventory
shortfalls or gains are the result of liquid leaks, meter
inaccuracies, theft, product evaporation or invoicing errors from
the wholesaler. The algorithms presently used by most SIR service
providers do not typically isolate individual components of
inventory variation. In fact, USEPA regulations allow up to 1%+130
gallons unexplained variation in inventory reconciliation. For a
site with throughput of 2 million gallons per year, this
discrepancy totals 20,000 gallons, or 3 full tanker trucks per
year. Considering aggregate United States gasoline average annual
consumption of 130 billion gallons via approximately 170,000
dispensing facilities, these unexplained losses total 1.322 billion
gallons. Viewed in another manner, this quantity of fuel represents
220,350 full tanker trucks. If parked end-to-end, this line of bulk
tanker trucks would stretch from Chicago to San Francisco.
[0026] To ensure efficient, on-going vapor recovery and containment
system performance within prescribed confidence intervals, various
techniques have been proposed, with similar fundamental
characteristics and associated shortcomings. U.S. Pat. No.
5,860,457 (Andersson), proposes measuring the flow of a mixture of
air and gasoline from a vehicle tank and then determining the
density of the gasoline vapor in the mixture. A variable flow valve
is proposed to vary flow of the mixture based on vapor density. If
such a technique is employed, it seems clear from FIG. 5 and
equations (3) and (4) that ER2 and EV2 will increase, and the
overall recovery efficiency will be proportionally reduced. In a
similar manner, U.S. Pat. No. 6,240,982 (Bonne), proposes a
variable vapor return rate contingent upon atmospheric temperature
conditions. Again, if ER2 and EV2 are increased, overall recovery
efficiency will decline.
[0027] Pending US applications by Pope, 20010004909, Nanaji,
20010020493 and Hart, 20010039978, disclose the use of various
sensors to measure flow and/or hydrocarbon concentration in various
vapor pathways connected to the storage tank system. The similar
thread of measuring an air to liquid (A/L) or vapor to liquid (V/L)
ratio are disclosed. The shortcomings of such an approach are
numerous. Among the primary limitations are the following: (1) to
calculate an overall vapor recovery efficiency, ER2 must be
measured. These techniques only seek to measure a V/L or A/L ratio.
ER2 is a mass, not a volumetric flow rate. (2) the V/L or A/L ratio
and corresponding HC concentrations are not constant values
throughout the refueling event. In order to record accurate
results, one would need extremely high sampling rate to record
changes of both flow rate and hydrocarbon concentration with time.
Also, time lag in measuring the data presents problems with
correlating proper flow and HC concentration values
(Mass=flow.times.HC Concentration). (3) V/L and A/L ratios show
only that air or vapors are being transferred to the storage tank,
but no additional information on the storage tank environment is
provided. (4) the "L" value is liquid flow rate determined by
dispenser meters which are not temperature compensated, thus
introducing a volumetric error even before associated HC masses are
tabulated. (5) The "A" or "V" values are volumetric flow rates of
air or hydrocarbon/air mixtures which vary in both temperature and
concentration, introducing additional measurement errors. (6)
Impact of ORVR equipped vehicles on returned flow rates is
uncertain. (7) The assumption of a properly functioning vapor
recovery system operating at an A/L ratio of 1:1 is not valid. The
vapor generation rate is a function of RVP, temperature, altitude,
ORVR population, and ORVR design type. Measured figures have been
shown to exceed a 1:1 ratio by a large margin.
[0028] The present invention provides a real-time system for
detecting leaks from product tanks due to evaporation, volume
discrepancies from flow meters out of calibration, improperly
functioning vapor recovery equipment and other irregularities.
[0029] The method of the invention also identifies system anomalies
to a specific storage tank to accelerate any subsequent
investigative procedures. The storage tank discrepancy can be
further partitioned to identify a malfunctioning fueling point or
specific nozzle.
[0030] The system of the invention remotely monitors storage tanks
to maximize usage, prevent overflow, and ensure EPA compliance. The
system also employs the data to generate the overall material
balance for the site.
[0031] The system is adapted to remotely monitor proper operation
of processor systems designed to mitigate evaporative losses and
subsequent storage tank pressurization by logging critical
variables and maintaining historical logs for CARB, EPA and local
air quality enforcement organization inspection.
[0032] The system maintains historical logs which provide a
documented record of saved product volumes; such volumes may form
the basis for certain processor system payment options.
[0033] The system notifies maintenance and on-site personnel via
alarms, pager, e-mail, phone, fax, or the like, if system anomalies
are recorded.
[0034] The system sends local site data to regional or national
data warehouses for management reporting, trend analysis and
regulatory compliance verification.
[0035] Finally, the system logs performance data of processor and
other systems to predict preventive maintenance schedules.
[0036] Accordingly, a continuing and heretofore unaddressed need
exists for a gasoline vapor recovery, containment and monitoring
methodology wherein the above discussed problems associated with
verifying vapor collection efficiency from the tanker truck and
nozzle/automobile fill-pipe are minimized, short-comings of
complicated and expensive sensors to monitor V/L, A/L and HC
concentrations are eliminated, and lack of confidence in storage
tank system integrity and expensive investigative procedures for
both vapor and liquid containment are eliminated. In addition,
there is a need for a system that can interface with existing
equipment capable of serial communication and can be installed at
existing service stations with a minimum amount of disruption to
commerce.
SUMMARY OF THE INVENTION
[0037] Briefly described, the present invention comprises a method
of transforming an "open" gasoline storage and transfer system to a
"closed" system. The method includes providing a selectively
permeable membrane processor on the combined storage tank ullage
space in conjunction with the installation of a p/v valve on the
combined storage tank vent lines. The normal vent to atmosphere is
fitted with the p/v valve such that the storage tank system becomes
a closed system, sealed off from the atmosphere. A pressure sensor
is installed to measure and monitor the pressure differential
between the combined storage tank ullage and prevailing atmospheric
pressure. When the pressure differential reaches a prescribed
value, the membrane processor is actuated to exhaust to the
atmosphere air which has been depleted of hydrocarbons and return
vapors, enriched with hydrocarbons to the combined ullage
space.
[0038] In order to ensure proper operation of the vapor recovery
and containment system as well as storage tank system integrity,
two techniques can be employed. First a statistical inventory
reconciliation (SIR) technique is employed which uses trend
smoothing and statistics to isolate specific inventory variations
in the distribution chain such as evaporative losses in transit and
storage, terminal meter variation, dispenser meter variation, and
temperature variation.
[0039] If the SIR technique indicates an inventory variation in a
particular storage tank, which falls outside of prescribed
statistical limits, then a mass integrity test such as that offered
by Masstech International, Ltd of the United Kingdom is employed to
ensure that the specific storage tank identified for further
investigation has both liquid and vapor storage integrity; in other
words, no liquid or vapor leaks are present. These techniques are
well known in the art, but their use in conjunction with an overall
material balance is unique and valuable.
[0040] The inventory reconciliation is carried out by accessing
volumetric data from a given refueling site by conducting
reconciliation calculations on each individual storage tank
employed at the site. This volumetric data includes gasoline
dispensed, delivered, and opening and closing inventory levels in
the each tank. Temperature variations are important since a 10 F
change will result in a 0.7% change in gasoline volume. Without a
common temperature basis, temperature variation can mask
evaporative losses and/or liquid leaks. These data are obtained by
presently existing hardware used in the dispenser, POS
(point-of-sale) and ATG systems such as those provided by Incon
(Franklin Fueling Systems), EBW (Franklin Fueling Systems), Emco
Electronics (Dover Resources) and Veeder-Root (Danaher).
[0041] The combination of membrane based vapor processor hardware,
a trend smoothed temperature compensated inventory reconciliation
algorithm, tank, and line leak detection techniques will provide a
continuous, on-going diagnostic of vapor recovery system
performance as well as ensuring storage tank system integrity
relative to vapor and liquid containment. As such, costly,
cumbersome, inaccurate and maintenance intensive flow and
concentration sensors are not required by petroleum marketers. A
direct linkage is established between storage tank, interconnection
piping leak detection, statistical inventory reconciliation, bulk
tanker vapor recovery, vehicle vapor recovery system performance
and storage tank vapor containment processor system performance.
Each component is a key contributor to the overall integrated vapor
recovery and containment at a given refueling site.
[0042] This technique is especially valuable since system upsets or
anomalies will manifest themselves by disrupting the fundamental
overall material balance and observed differential pressure
profile. If inventory variations from a median value are greater
than a statistically derived standard deviation, additional
investigative procedures can be undertaken to determine the primary
failure mode of the integrated storage tank and delivery system.
This technique is especially powerful since system anomalies are
rapidly isolated and pinpointed to a specific storage tank at a
given refueling site.
[0043] The integrity of the overall system is further enhanced by
the use of a pressure monitor on the combined storage tank ullage
and on the permeate vacuum pump. Also, cumulative run time of the
vacuum pump motor is recorded. In addition to logging and reporting
process conditions via various communication systems, such as via
local or internet protocols, the system can be configured to
automatically initiate predetermined safety measures such as
shutting down dispenser pumps, sending emails or other types of
alerts to service technicians, and actuating audible or visual
alarms at the site. Such an approach leverages the value of
presently required methods and enables the petroleum marketer to
earn an economic return while at the same time taking steps
favorable to the environment. Another commercial advantage earned
by petroleum marketers is the flexibility and vendor options
provided by such an approach.
DESCRIPTION OF DRAWINGS
[0044] FIG. 1 illustrates a typical refueling station arrangement
including liquid and vapor interface;
[0045] FIG. 2 illustrates the various emission points associated
with a refueling station;
[0046] FIG. 3 illustrates a control processor and associated data
in accordance with the invention;
[0047] FIG. 4 illustrates a first embodiment of a refueling station
of the invention;
[0048] FIG. 5 illustrates a second embodiment of a refueling
station of the invention; and
[0049] FIG. 6 illustrates a third embodiment of a refueling station
of the invention.
DETAILED DESCRIPTION
[0050] As seen in FIGS. 4-6, a refueling station storage tank
system is equipped with a membrane system (1), a vacuum pump (2),
an ATG console (3) and a data acquisition module (4). Two storage
tanks (5) and (6) are shown. The selectively permeable membrane (1)
was referenced previously and is shown connected to the combined
vapor space or "ullage" of tanks (5) and (6). Tanks (5) and (6) are
shown with their ullage spaces connected by conduit (7). (The
figures show the tanks manifolded underground with individual vent
lines; other piping combinations are contemplated as well). The
combined ullage space is kept closed by the installation of p/v
valves (8) and (9). In the United States, these valves have a
typical setting of +3 inches water column and -8 inches water
column. Such valves are commercially available from suppliers such
as Husky, Hazlett Engineering and OPW Fueling Components. Also note
in FIGS. 5 and 6 is a "front-end" vehicle vapor recovery system
commonly known as a Stage II vapor recovery system. This system may
be a balance system, or dispenser based vacuum assisted system
provided by companies such as Tokheim, Gilbarco and Dresser/Wayne.
As seen in FIGS. 5 and 6, the Stage II vapor recovery system
returns vapors recovered during vehicle refueling to storage tank
(5).
[0051] The system shown in FIG. 4 uses the developed ullage tank
pressure to actuate and feed the membrane system as shown. The
system shown in FIG. 5 employs a blower (10) on the feed stream of
the membrane to allow the ullage pressure to be driven below
prevailing atmospheric pressure. The system shown in FIG. 6 uses a
vacuum pump or blower (11) on the exhaust side of the membrane to
allow for drawing the ullage pressure below prevailing atmospheric
pressure. In FIGS. 4-6, the ATG (automatic tank gauge) probe (12)
and console (3) are shown. The tank probe is shown only in one
storage tank for clarity, but in practice, each tank is equipped
with such a probe. Also in FIGS. 4-6, the combined ullage pressure
sensor (13) is shown connected to the feed side of the membrane
(14) and the data acquisition module (4).
[0052] FIG. 3 schematically depicts the inputs to the data
acquisition and processing system as well as the output decision
logic of the subject invention. Dispensed and delivered volumes are
tracked from dispenser meters, automatic tank gauge systems and/or
delivery manifests. Residual tank levels are quantified by manual
sticking or electronic tank gauges. These readings make up the raw
data inputs for a trend-smoothed statistical inventory
reconciliation technique such as that employed by various
statistical techniques, such as the RedOne algorithm employed by
Leighton O'Brien of Melbourne Australia. The trend smoothed data is
analyzed on a continuous basis (perhaps monthly) to ensure that
discrepancies do not exceed an acceptable range. At the same time,
simple parameters are monitored, logged and remotely accessed to
ensure proper operation of a vapor processor, such as a membrane
based system. The critical variables are combined ullage
differential pressure relative to atmosphere; permeate vacuum pump
level, altitude, cumulative run time on vacuum pump motor, and
atmospheric pressure.
[0053] These variables are continuously measured, logged and
recorded to provide an on-going operating history of the system
dynamics. With proper operation, one would expect storage tank
pressures never to exceed the UCL (Upper Control Limit) of the
membrane processing system. Also, while the storage tank pressure
is being reduced, the permeate vacuum level should register a value
within an acceptable band and the cumulative run time meter should
also show an increase. The combination of these variables with the
inventory reconciliation provides a reliable, simple technique for
ensuring efficient and effective operation of the vapor recovery
and containment system.
[0054] As seen in FIG. 3, the typical inputs and output of the data
acquisition system show the raw data and calculated trend loss for
a refueling site. So called trigger values are set based on RVP and
temperature conditions for a given site. If these values are
approached or exceeded, a loss investigation procedure is
recommended to ensure that a liquid leak is not present. Alarms
will be actuated, and depending on the severity of the anomaly,
fueling operations will be interrupted for a short period of time
until appropriate actions are taken by on-site or off-site
personnel in acknowledging the upset and taking corrective
measures.
[0055] Although the specification and illustrations of the
invention contain many particulars, these should not be construed
as limiting the scope of the invention but as merely providing an
illustration of some of the preferred embodiments of the invention.
Thus, one skilled in the art should interpret the claims as
encompassing all features of patentable novelty that reside in the
present inventions, including all features that would be treated as
equivalents by those skilled in the art.
1TABLE 1 Appendix Uncontrolled Emissions Source Magnitude (mg
HC/liter fuel dispensed) ER1 750-1200 EV1 350-1200 EF1 0 (Open vent
line) ESL1 50 Stage II System - no processor Source Magnitude (mg
HC/liter fuel dispensed) ER2 2-154 EV2 350-1200 EF2 10-750 ESL2 50
Stage II System - with processor Source Magnitude (mg HC/liter fuel
dispensed) ER2 2-154 EV2 4-6 EF2 0 ESL2 50
* * * * *