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Displacement Losses from the Refueling Operation of Passenger Cars

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Abstract

Displacement losses occur when vapor from a fuel tank headspace is displaced by the incoming liquid to the tank. This study was undertaken in order to perform a calculation that is used to estimate the displaced hydrocarbon losses. In the calculation, a mixture of hydrocarbon vapor and air is considered as an ideal gas. The volume of vapor displaced equals the volume of liquid dispensed. An experimental study was conducted for measuring the displaced vapor loss to confirm the rcsults from the calculation. Activated carbon was used to absorb vapors that were emitted during refueling. The change of weiglrt of activated carbon was recorded by a digital balance. The loss, as derived by calculation, is compared with experiments carried out at a service station. The study shows that the preseit model can be used for estimating the displaced hydrocarbon loss during a refueling operation
Thammasat Int. J. Dc. Tech., Vol.2, No.l, January 1997
Displacement
Losses from the
Refueling
Operation
of Passenger Cars
S. Wongwises, S. Chanchlona, I. Rattanaprayura
Department of Mechanical Engineering
King Mongkut's Institute of Technology Thonburi
Bangmod, Bangkok 10140, Thailand
Abstract
Displacement losses occur when vapor from a fuel tank headspace
is displaced by the
incoming liquid to the tank. This study
was
undertaken
in order to perform
a calculation that is used
to estimate the displaced
hydrocarbon losses. In the calculation, a mixture of hydrocarbon vapor and
air is considered as an ideal
gas.
The volume of vapor displaced equals the volume
of liquid
dispensed. An experimental study
was
conducted
for measuring the displaced
vapor loss to confirm
the rcsults from the calculation. Activated
carbon was used to absorb vapors that
were emitted during
refueling. The change
of weiglrt of activated carbon was recorded by a digital balance.
The loss, as
derived by calculation, is compared
with experiments carried out at a service
station. The study shows
that the preseit model can be used for estimating the displaced
hydrocarbon loss during a refueling
operation
1. Introduction
Hydrocarbons
which contribute to air
pollution
may affect both public health and the
growth of vegetation. Total hydrocarbons are
divided between natural and man-made sources.
Man-made
sources
include
solvents,
automotive
emissions and oil industry refining and
distribution systems. The automobile is one
source of hydrocarbon emissions to the
atmosphere. Hydrocarbons from passenger
cars
are emitted in the exhaust
gases
and from the
evaporation of gasoline in the fuel system.
Hydrocarbon
loss during a refueling
operation
is called
"Refueling
Loss". The expelled vapor
during refueling is a mixture of hydrocarbons
and air which
are expelled during the refueling
operation.
A study
from abroad
[] showed
that
exposure to gasoline
vapor has contributed to
kidney tumors. This study also prompted
the
automobile industry to review the scientific
literature relating gasoline vapor exposure to
human cancer. Smith [2] investigated hydro-
carbon losses during the refueling of a
passenger
car. Loss measurements
were tested
in a small sealed enclosure by varying the
factors that may affect the magnitude of loss.
Statistics were used to analyse and find the
significant
variables and a mathematical model
was developed to estimate the hydrcicarbon
losses. Koehl et. al. [3] studied the onboard
refueling control system using a carbon canister
technology and the effectiveness of the
technology wab shown to comply with the
current US EPA (Environmental Protection
Agency) requirements for losses during
refueling operations.
The objective
of this work is to estimate
the gasoline
vapor emissions
from the refueling
operation ofa passenger
car.
22
2. Derivation of Loss Equation
. Consider
a tank (Figure l) which is open
to the atmosphere
and which is being filled with
a volatile liquid. Assume that the liquid and
vapor are initially at equilibrium, that is, the
partial
pressure
ofsubstances in the vapor
phase
is equal to the equlibrium
vapor pressure
of the
liquid. As the temperature and pressure
in the
tank are changed, a vapor with the same
chemical composition as the liquid will result
from the evaporation. The loss of vapor from
the tank sustained
during the filling operation is
called
displacement loss. The expelled
mass
of
component
i can be calculated
simply by this
equation
[4].
m; = AVCi
Thammasat Int. J. Dc. Tech., Vol.2, No.l, January 1997
- vr M; rr.
Ci \z)
vmolar,gas
where
yi = mole fraction of component
i in the vapor
Mi = molecular weight of component i,kg/
kmol
Vmotar,gas
: gas
molar volume,
m3/kmol
In low pressure
air pollution control, we
can assume with only a small error that the
vapor mixture behaves as a perfect gas,
and that
we can estimate
the content of a volatile liquid
into the vapor mixture using the laws' of
thermodynamics. Raoult's law states that the
vapor pressure
of component
i in a mixture is
Pi = *iR
pi = partial pressure
of comqonent
i in the
vapor mixture,N/m'
P1 = saturation pressure
of pure.component i
at existing temperature, N/m'
Xi = mole fraction of component
i in the liquid
Furthermore the relationship between
partial pressure
and total pressure
can be found
from Dalton's law which states that the total
pressure
of the vapor mixture is a sum of the
partial pressures
ofthe constituents.
The partial
pressure
of the component i is
Pi = YiPt (4)
Combining
Eq.(3) and (4), the mole fraction of
component i in the vapor is found.
yi
= -'fr
where
yt = mole fraction of component
i in the
vapor
Xi = mole fraction of component i in the
liquid
Pt = total pressure,
N/m'
Replacing the vapor mole fraction in Eq.
(2) and replacing the gas molar volume by the
perfect gas law, and substituting
in Eq. (l), we
find
(3)
(l)
where
m; = expelled mass of component
i, kg
AV = volume of air and vapor
of volatile liquid
expelled from the tank, m'
C1 concentration of component i in
displaced
gas,
kg/m'
A
Vapour out
Liquid in
Figure l. Displacement losses
occur when
tank is filled with liquid
Concentration C; can be expressed
as
(s)
23
mi = xi4Mi
AV RT
where
T = absolute temperature,
K
R = universal
gas
constant, 8.3
l4 kN.m/kmole'K
Eq. (6) is in a general form. It can be
applied in order to estimate
the total amount
of
gasoline
vapor emitted as
refueling losses when
gasoline is transferred from underground
storage tanks at a service station to the gasoline
tanks of the customers'
vehicles. The molecular
weight
ofthe hydrocarbon vapor is a function of
temperature and the l0 % point slope on the
curve
of distillation.It can be found in table 6. of
ref. [5]. For example, assuming Reid vapor
pressure,
Rvp = 8.0 psi (The vapor pressure
of
gasoline
is specified
by the Reid vapor pressure
which is found by a standard test [6])and ,S=3
(S is the average value of the 10 oh
point slope
for motor gasoline),
the molecular weight of
hydrocarbon vapor,
M; at 15.55
oC is 63. For the
value of S = 3, the molecular weight increases
or decreases by 0.1053 per degree of
temperature
change which can be calculated
by
Mi = 63+0.1053At where At = t - 15.55,
( t is
the
temperature
in deg C).The true vapor pressure,
Pi at the bulk liquid temperature
may also be
computed with the aid of the nomograph in
appendix
V ofref.[7] or the table 7 in ref. [5].
The sensitivity of the displacement loss to
Rvp for various temperatures is displayed in
(Figures 2 and 3). The effect of the Rvp is
plotted in (Figure 2) for fixed values of the
temperature
equal
to 20,25,30,35,40, and
45
oC . It may be seen
more clearly in (Figure 3),
where the displacement loss is plotted as a
function of the temperature for fixed values of
Rvp equal to 7,8,9, 10, ll,12,and 13
psi.
They show that the displacement
loss increases
with increasing Rvp. It should be noted in
practice that fuels which have volatilities
appropriate
to the seasonal temperatures
should
be used. To reduce the displacement losses,
both of them must be optimized.
3. Materials and Methods
To confirm the results from calculations,
an experimental study was obtained. A
Thammasat Int. J. Dc. Tech., Vol.2, No.l, January 1997
schematic diagram of the experimental set up
for the determination of displaced losses is
shown in (Figure 4). Details of this
experimental system
were also described in the
former paper [8].The system consists of two
main parts, the fuel tank and the carbon
canister. An ordinary fuel tank of 40 litres
capacity
was
used
with a small modification. On
the top of the tank there was a vapor vent, ll4
inch in diameter which was connected to the
canister by a transparent rubber tube. A
drainage valve was mounted at the bottom of
the tank. The inside diameter of the nozzle was
2.4 cm. All the valves were manually
controlled. The carbon canister was designed
and constructed for collecting the displaced
vapor from the refueling operation. The housing
of the canister
was fabricated from aluminium
sheet.
It had a cubical form (0.2mx0.2mx0.23
m). To increase the efficiency of the carbon
canister, a two-pass design
was performed.
The
inside of the canister was divided into two
spaces by a baffle. Two ball valves were
mounted on the top of the canister
for vapor
entry and exit. The inlet valve was
connected
to
the vapor vent of the fuel tank. The canister
contained approximately 3 kg of activatec
carbon which had an apparent density of 0.28-
0.35 g/cc and a particle size 8x30 mesh.
Thermocouples were used to measure the
ambient, displaced vapor and tank fuel
temperatures.
Five litres of gasoline were introduced
into the fuel tank. The tank was shaken so that
the liquid was vaporized within the tank.
Subsequently, the fuel was drained out. The
tank was then placed in the experimenta,
position
as shown in (Figure
4). Thirry litres of
gasoline
from an underground storage tank were
dispensed through a hose at a flow rate
controlled automatically by the nozzle. The
flow rate of gasoline was kept constant
throughout
this experiment.
The weight of the
canister was recorded every l0 seconds by
digital balance until the end of the filling
operation. The ambient temperature,
the fue-
temperature in the tank and
the displaced vapor
temperature were measured during the
experiment.
(6)
24
Thammasat
Int. J. Dc.
Tech., Vol.2,
No.l, January
1997
bo
b
o
a
o
o
o
t2-oo
10.00
8.00
6.00
4.00
2.00
0.00
10 ll
Reid Vapor Pressure
(psi)
T=20C T=25C T=30C
T=35C --- T=40C
-T= 45C.
Frgure 2 Sensitivity of displacement loss to Rvp at various values of temperature
t3
bo
o0
o
(.)
12.00
10.00
8.00
6.00
4.00
2-0/.)
0.00
15 20 25 30 35 40 45 50
Vapor temerature (C)
RVP=7psi RVP=8Psi RVP=9Psi
RVP
= 10
psi - - - RVP
= 1l psi
-RVP = 12
psi
Figure 3 Sensitivity
of displacement
loss
to temperature at vanous values of Rvp
10
25
Canist'er
\
Electronic
Balance
Thammasat
Int.
J.
Dc. Tech.,
Vol.2, No.l, January
1997
Fuel
Temperature
Recorder
Figure
4 Schematic diagram
of experimental
apparatus
40
2<
2n
za
20
iq
10
c
0GP2 GP3 ULR1 ULR2
Type of gasoline
and test
no.
GP : Premium
motor
gasoline
ULR : Unleaded
regular
gasoline
Figure
5 Comparison
of measured displacement
loss with calculated
losses.
Nozzle
1O
Experiment
1
lr91gl3l9!_l
qt
o
o
o
o
t
26
4. Results and Discussion
Figure 5 shows
the results of the refueling
tests. Both unleaded and leaded gasoline were
used. The experimental data were compared
with the results from the calculation. The
theoretical model has consistently
underpredicted the displacement loss. The
losses from experiment were generally greater
than
the calculations
by about l2 %. This makes
sense begause the total real losses during
refueling operation may not include only the
displaced fuel tank vapor but also the entrained
fuel droplets in the displaced vapor, and the
liquid spills. The model approximates
evaporative vapor loss only. However the
model may be used to predict the losses. The
same calculation is used to estimate the total
amount of gasoline vapor emitted as
displacement losses at service stations in
Thailand when gasoline is transferred from the
storage tank to the gasoline tanks of the
customers'
vehicles.
Assuming
RvP = 3 Psi,
T=30 "C and S=3.
Vapor pressure
and molecular.weight can be
estimated as 44.78 kN/m' and 64.52
respectively. The concentration of gasoline in
the displaced vapor is^
calculated
by Eq. (6) as
l.l5 kg gasoline / m' vapor. Multiplying this
concentration by 6300x10o
litres
which was the
total amount of gasoline used in 1995 in
Thailand, the total displacement loss is
estimated at 7300 tons/vear or about 90x106
baht/year.
5. Method to Reduce the Emissions
The above example considers only the
losses from the transfer of gasoline from the
underground
storage at the service station to the
customer.
This is the final operation. In reality,
there are many transfers of gasoline everyday;
from the refinery or depot to the tank truck, and
from the tank truck to the tank at the service
station. Because the loss mechanism is the
same,
we can use the same method to calculate
the total losses.
To reduce the losses incurred when
transfering gasoline from the underground
storage tank to the customer's vehicle at the
service stations. a scheme such as shown in
Thammasat
Int.
J. Dc. Tech.,
Vol.2,
No.l, January
1997
(Figure 6) can be used. The vapor from the
customer's tank is forced back into the
underground tank by the positive pressure
caused by pumping gasoline
into the customer's
tank .or by a blower which is added to the
system. In this system
a special design of hose
and
nozzle must be used.
The same
kind of technology can bq used
for the transfer of gasoline from tank trucks to
underground storage tanks at service stations
(Figure 6)or the storage tank at the depot to the
tank trucks (Figure 7). The vapor displaced
from the tank is returned to the tank being
emptied.
Additionally the return vapor can be
sent to a vapor recovery unit which can restore
the vapor to liquid which then flows to a bulk
gasoline
storage tank
(Figure
7).
6. Recommendation for Further Studies
The loss
of the entrained
fuel droplets in
the displaced vapor and
liquid spill losses
which
result from fuel spillage from the fuel tank or
nozzle should be studied.
The breathing losses from the fuel tank
which are associated
with the thermbl expansion
and contraction of the vapor space resulting
from the daily temperature
cycle should be
studied.
The technical and economic feasibility
of using the vapor recovery system should
be determined.
7. Conclusion
This paper presents new data for
displacement
losses from a vehicle gasoline
tank during refueling.
The work was
underta[en
to investigate the displaced
hydrocarbon losses
obtained during the refueling of passenger
cars.
A calculation method
was developed based on
thermodynamic theory. An experimental study
was conducted t6 verifu the results from
calculations. Calculated
losses
were compared
with measured
losses. Factors influencing
losses
are the temperature of the vapor and liquic,
vapor pressure and molecular weight. The
magnitude of the average observed loss was
about
40 g for filling 30 litres of gasoline.
27
Thammasat
Int.
J.
Dc. Tech.,
Vol.2, No.l, January 1997
From
Gasoline
Deliveries
From
Breathing
Losses
fi
tl
Vapour
Return Line l.i
Truck
Refinery
and Distribution
Terminal
Vapour
Return
Line
Figure 6 Vapor return
system in service station
[4]
Spillage
Emissions
Gasoline
Pump
Air
and
Unrecovered
Gasoline Vapour
Vented
tolAtmosphere
Figure 7 Vapor
rccovery system
Recovered
Gasoline
(Storage
Tank)
28
The results can be used to predict the total
displacement losses
in Thailand when gasoline
is transferred from the underground storage
tanks at service stations to the gasoline
tanks of
the passenger
cars.
Total national
displacement
losses
from the refueling
operation ofpassenger
cars in 1995 are estimated
as 7300 ton/year or
about 90x106 bahUyear.The
results
shouid be of
concern
to vehicle manufacturers,
the petroleum
industry
and also to government
agencies
with a
view to promote
regulations
in Thailand.
8. Acknowledgement
This work was given financial support by
the Petroleum Authority of Thailand (PIT),
whose
assistance is gratefully
acknowledged.
9. References
[] MacFarland,
H.N.
et. al.
(1984),
A Chronic
Inhalation Study with Unleaded Gasoline
Vapor, J. Am. College Tox.,
Vol.3,
p.23
L
[2] Smith, M , An Investigation
of Passenger
Car Refueling Losses, SAE Paper 720931,pp.
2693-2703.
Thammasat
Int. J. Dc. Tech.,
Vol.2, No.l, January
1997
[3] Koehl,
W.J. et.al.
(1986),
Vehicle
Onboard
Control of Refueling Emissions-System
Demonstration on a 1985 Vehicle, Paper
861551 Presentedat International
Fuels and
Lubricants Meeting and Exposition,
Philadelphia.
[4] de Nevers,
N. (1995),
Air Pollution
Control
Engineering,
McGraw-Hill lnc., pp.27
5-327 .
[5] Koehl, W.J.
(1969),
Mathematical
Models
for Prediction of Fuel Tank and Caburetor
Evaporative Losses, SAE Paper 690506
Presented
at Mid-Year Meeting, Chicago.
[6] Standard Test Method for Vapor Pressure
of
Petroleum Products (Reid Method), ASTM,
Publ., D 323-72,1973.
[7] Tentative Methods of Measuring
Evaporative Loss From Petroleum Tanks and
Transportation
Equipment, API Bulletin 2512,
July
1957.
l8l Wongwises,
S. et.al. (1996), Hydrocarbon
Emissions from a Vehicle Gasoline Tank
During Refueling, Proceedings
of the 6 th
International Energy Conference and
Exposition, Beijing, China, June 3-7, pp.582-
586.
29
... -Check condition of existing seals -Replace vapor mounted primary seal with liquid mounted seal -Install secondary rim seal -Install vapor recovery/destruction system A future method for controlling evaporative losses is to adapt a vapor recovery system. The cost of this method is quite high because it needs special equipment to convert hydrocarbon vapor to liquid before liquid fuel is sent back to the storage tank [6]. ...
... -Check condition of existing seals -Replace vapor mounted primary seal with liquid mounted seal -Install secondary rim seal -Install vapor recovery/destruction system A future method for controlling evaporative losses is to adapt a vapor recovery system. The cost of this method is quite high because it needs special equipment to convert hydrocarbon vapor to liquid before liquid fuel is sent back to the storage tank [6]. ...
Article
Full-text available
Gasoline is a volatile organic compound (VOCs) which consists of different hydrocarbons with different boiling points in the range of 30-200 o C. The light compounds that have boiling point of less than 40 o C constitute about 10%. Khartoum, Sudan is characterized with an average of 10 hrs of sunshine and solar radiation of 3.05-7.62 kWh/m 2 /day and average temperature of 32 to 40 o C. Under these conditions high evaporation rate is expected from storage tanks. The objective of this study is to evaluate the evaporation loss of gasoline from internal floating roof storage tank. The case study is based on metrological and operation data for the year 2008. The result revealed that the total evaporation loss is 0.5%. This is significantly higher than that set by the ministry of energy [i.e.0.25%]. The results should be of concern to the petroleum industries and government. The reduction of evaporation loss of gasoline will give attractive economic returns as well as reducing air pollution and hazards.
... -Check condition of existing seals -Replace vapor mounted primary seal with liquid mounted seal -Install secondary rim seal -Install vapor recovery/destruction system A future method for controlling evaporative losses is to adapt a vapor recovery system. The cost of this method is quite high because it needs special equipment to convert hydrocarbon vapor to liquid before liquid fuel is sent back to the storage tank [6]. ...
Article
Full-text available
ABSTRACT Gasoline is a volatile organic compound (VOCs) which consists of different hydrocarbons with different boiling points in the range of 30-200oC. The light compounds that have boiling point of less than 40oC constitute about 10%. Khartoum, Sudan is characterized with an average of 10 hrs of sunshine and solar radiation of 3.05-7.62 kWh/m2/day and average temperature of 32 to 40oC. Under these conditions high evaporation rate is expected from storage tanks. The objective of this study is to evaluate the evaporation loss of gasoline from internal floating roof storage tank. The case study is based on metrological and operation data for the year 2008. The result revealed that the total evaporation loss is 0.5%. This is significantly higher than that set by the ministry of energy [i.e.0.25%]. The results should be of concern to the petroleum industries and government. The reduction of evaporation loss of gasoline will give attractive economic returns as well as reducing air pollution and hazards.
Article
Full-text available
The determination of volatile organic compounds (VOCs) at selected pump stations in Skudai, Johor Bahru was investigated. About 27 chemicals substances in petrol and 24 chemicals substances in diesel with different concentration have been identified in each pump station. Benzene, toluene, ethylbenzene and xylene (BTEX) and MTBE have been chosen as VOCs of interests because of their toxicity properties that can gives hazardous to human health. The exposures of benzene at all three pump stations during refuelling the liquid fuel have potential to cause cancer riskwhile, ethylbenzene stated as acceptable risk to the people health.As for noncarcinogenic substances, the exposure of toluene, xylene and MTBE were recorded as acceptable risk to the people health at all the studied pump stations. Besides, there is a great correlation between physical environment factors; temperature, relative humidity and wind speed typically with total volatile organic compounds that evaporate into the ambient air during refuelling activities.
Article
Volatile nature of gasoline is the prime reason for various kinds of losses, which occur during the course of retailing operation. Standing storage or breathing loss, the expulsion of hydrocarbon vapors, occurs during tranquil condition from the gasoline storage tank. Estimation of breathing loss is vital as it occurs endlessly, consequently affecting the environment and economy of the nation. Present study proposes an empirical model to evaluate breathing loss of under ground storage (UGS) and above ground storage (AGS) tanks using easily accessible variables.
Conference Paper
This paper presents the findings of the second year of a planned three-year program to investigate the hydrocarbon losses sustained during the refueling of passenger cars. The magnitude and frequency of occurrence of spills by type of spill were estimated from observations of refueling operations during a five-city, four-season field survey. The magnitude of the average observed loss due to spills was 10. 6 g and the probability of a spill loss was 0. 329. The average spill loss was 3. 5 g per refueling operation or 0. 3 g/gal of dispensed gasoline. A sample of 732 measurements of dispensed fuel and displaced vapor temperature, taken during daylight hours only, yielded a preliminary estimate of 5 g/gal of dispensed gasoline for the average displaced loss.
Conference Paper
Two technologies for controlling vehicle refueling emissions have been under consideration by the U.S. Environmental Protection Agency. They are vehicle onboard systems and Stage II service station vapor recovery. A 1978 program showed that onboard systems are very effective in controlling refueling emissions with no significant effect on exhaust emissions. The work reported herein shows that vehicle onboard technology can be applied equally well to a car meeting more stringent 1985 exhaust and evaporative emission standards with the latest engine and emission control technology. This work also shows that a vehicle onboard refueling control system can provide substantially improved control of evaporative emissions.
Tentative Evaporative Loss From Petroleum Tanks and Transportation Equipment Methods of Measuring l8l Wongwises, Hydrocarbon Emissions from a Vehicle Gasoline Tank During Refueling Conference and 29
  • S Et
Tentative Evaporative Loss From Petroleum Tanks and Transportation Equipment, API Bulletin 2512, July 1957. Methods of Measuring l8l Wongwises, S. et.al. (1996), Hydrocarbon Emissions from a Vehicle Gasoline Tank During Refueling, Proceedings of the 6 th International Energy Exposition, Beijing, China, June 3-7, pp.582- 586. Conference and 29
Tentative Methods of Measuring Evaporative Loss From Petroleum Tanks and Transportation Equipment
[7] Tentative Methods of Measuring Evaporative Loss From Petroleum Tanks and Transportation Equipment, API Bulletin 2512, July 1957.
Vehicle Onboard Control of Refueling Emissions-System Demonstration on a 1985 Vehicle, Paper 861551 Presentedat International Fuels and Lubricants Meeting and Exposition
  • W J Koehl
Koehl, W.J. et.al. (1986), Vehicle Onboard Control of Refueling Emissions-System Demonstration on a 1985 Vehicle, Paper 861551 Presentedat International Fuels and Lubricants Meeting and Exposition, Philadelphia.
Mathematical Models for Prediction of Fuel Tank and Caburetor Evaporative Losses, SAE Paper 690506 Presented at Mid-Year Meeting
  • W J Koehl
Koehl, W.J. (1969), Mathematical Models for Prediction of Fuel Tank and Caburetor Evaporative Losses, SAE Paper 690506 Presented at Mid-Year Meeting, Chicago.
A Chronic Inhalation Study with Unleaded Gasoline Vapor
  • References
  • H N Macfarland
References [] MacFarland, H.N. et. al. (1984), A Chronic Inhalation Study with Unleaded Gasoline Vapor, J. Am. College Tox., Vol.3, p.23 L