Note: Descriptions are shown in the official language in which they were submitted.
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
METHOD AND APPARATUS FOR PROVIDING VENT SOURCE GASES
TO AN ENGINE
REFERENCE TO RELATED APPLICATION
This is a division of Canadian Application Serial No.
2,678,569 filed August 30, 2007 entitled CHECK VALVE FOR
FUGITIVE GAS FUEL SOURCE, now allowed, which application claims
priority from United States Provisional Application Serial No.
60/824,028 filed August 30, 2006.
INTRODUCTION
This invention relates to a method and apparatus for
providing fugitive or vent gases to an engine and, more
particularly, to such a method and apparatus wherein a first
duct provides a principal fuel to the engine and a secondary
duct provides the vent gases to the engine.
BACKGROUND OF THE INVENTION
Engines, turbines and heating units using natural gas
and other gaseous fuels are known and are used extensively,
particularly in locations where natural
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
- 2
gas production takes place. Such engines and turbines
range from 30HP to over 10000 HP and may conveniently be
used in powering gas compressors, pumps and electric
generators and which powered equipment is normally
associated with natural gas production. The heating
units are used in a wide range of industrial processes.
The natural gas or other gaseous fuel is introduced
directly to the cylinder of the natural gas engine or to
the intake manifold. A spark ignitor is typically used
to ignite the combustible natural gas and an air supply
adds the air necessary to support the combustion.
The gaseous fuel used for such engines, turbines
or heating units comes from a fuel source such as natural
gas and the air to support the combustion of the gas
comes from the atmosphere. Normally, the gaseous fuel is
under pressure and appropriate ducting extends from the
pressurized fuel supply to the engine. A carburetor,
valves or an electronic control mechanism is used to
regulate the quantity of natural gas provided to the
engine and the quantity of air added to the natural gas
for efficient combustion.
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
- 3 -
Various production processes in natural gas
production result in losses of combustible gases. Such
gaseous losses typically occur from compressors,
particularly where the packing is old or otherwise
deficient, from pneumatic instrumentation utilising
natural gas, from initiating or starting engine procedure
using natural gas, from gas dehydration units, from
engine crankcases and from petroleum liquid storage
tanks. These gas losses, typically called "fugitive
and/or vent emissions", are usually passed to the
atmosphere or to a stack for burning. In either case,
they are lost and the energy content of these gases which
can be considerable, is similarly lost. It is
disadvantageous and energy deficient to lose these
fugitive or vent gases.
It is known to use natural gas as a
supplementary fuel for =a diesel engine by adding natural
gas to the intake air. This natural gas, however, is not
a fugitive or vent gas and the gas is maintained under
pressure as a normal fuel source. The use of such fuel
does not lower costs by using a fuel normally lost or
deliberately discarded and such a fuel is not an emission
WO 2008/025158 PCT/CA2001/001529
-4-
resulting from venting or escaping gas. Fugitive gases have been
collected and used as a fuel source but such gases have been
collected and put under pressure. Such gases are not used as a
supplementary fuel source.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is
provided a method of providing vent gases to an engine, said engine
having an associated throttle, a principal source of fuel and a
secondary source of fuel, said secondary source of fuel comprising
said vent gases which are emitted from at least one component
associated with said engine and collected at a vent gas source
supply located near said engine, an air supply for providing air to
said engine, and an engine intake manifold associated with said
engine, a first duct to convey said principal source of fuel to
said engine intake manifold, a second duct to convey said secondary
source of fuel to said engine intake manifold, said vent gases
being introduced downstream of an air filter mounted so as to
filter said air of said air supply provided to said engine, and
upstream of said throttle, said method comprising allowing said
vent gases to pass through said second duct to said engine intake
manifold.
CA29053192017-10-03
WO 2008/025158 PCTICA2007/001520
-4A-
According to a further aspect of the invention there is
provided an apparatus for providing vent gases to an engine from a
secondary source of fuel which vent gases are collected in a
collector and which vent gases then pass to an engine through a
secondary fuel duct, an accumulator mounted in said secondary duct
to receive said secondary fuel and to pass said secondary fuel to
said engine through said secondary fuel duct to an engine intake
manifold, said secondary fuel duct acting to pass said secondary
fuel from said collector to said engine through said engine intake
manifold.
25
CA 2905319 2017-10-03
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
-5-
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Specific embodiments of the invention will now be
described, by way of example only, with the use of drawings in
which:
Figure 1 is a diagrammatic illustration of a typical
building housing an engine and a compressor driven by the engine
and which illustrates various sources of fugitive combustible
gases which may be used as a supplementary fuel source for the
engine according to the invention;
Figure 2 is a diagrammatic illustration of a typical
control circuit used to regulate the input of fugitive
combustible gases to the engine according to the invention;
Figures 3A-3E diagrammatically illustrate various
control techniques when fugitive gases are used as a
supplementary fuel source for the engine according
30
40
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/0111529
- 6 -
to the invention;
Figure 4 is a table illustrating fugitive gas
emissions taken from various sources in a typical
operating environment during experimentation;
Figure 5 is a side diagrammatic view which
illustrates a building which encloses various sources of
fugitive gas emissions which pass into the atmosphere of
the building and are diluted thereby and which are
collected near the ceiling or upper portion of the
enclosed building according to a further aspeIct of the
invention;
Figure 6 is a diagrammatic schematic view
particularly illustrating a check valve positioned in an
exhaust stack according to the invention;
Figure 7 is a diagrammatic schematic view of an
accumulator positioned between the exhaust stack of an
engine and the intake of the engine according to the
invention; and
CA 02905319 2015-09-10
=
WO 2008/025158
PCT/CA2007/001529
- 7 -
Figure 8 is an enlarged view of the check valve
of Figure 6 but illustrating the typical operation of
such check valve.
DESCRIPTION OF SPECIFIC EMBODIMENT
The terms "fugitive gases" or "fugitive
combustible gases" or "fugitive emissions" or "fugitive
gases" or "vent gases" or "vent emissions" are used
throughout this specification. The terms are used
interchangeably and, by the use of such terms, it is
intended to include combustible gases which escape from
various apparatuses or which are released deliberately
into the atmosphere. Such combustible gases normally
exist at or near atmospheric pressure in the vicinity of
the sources from where they originate. These fugitive
gases are intended to be collected and to be used as a
supplementary fuel supply for an engine which,
conveniently, uses natural gas as its primary fuel supply
and which natural gas is pressurized before entering the
engine. The various apparatuses from which the fugitive
gases may escape include compressor cylinder packings,
instruments, starting gas sources for the engine, gas
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
- 8 -
dehydration units, crankcases, petroleum liquid storage
tanks and the like.
Referring to the drawings, an engine is shown
generally at 101 in Figure 1. The engine 101 is
conveniently a natural gas powered engine normally
located at a place of natural gas production. The engine
101 powers a compressor generally illustrated at 102.
The engine 101 and compressor 102 are normally located
within a building 100. As is usual, an outside location
for cooling apparatus 103 assists in drawing cooler air
or cooling water for cooling purposes.
A cabinet 104 for housing various
instrumentation used in support of the engine 101 and
compressor 102 is located near the engine 101. A
petroleum liquid storage tank 110 is also conveniently
located within the building 100.
Emissions of fugitive combustible gases are
shown as originating from four (4) sources in Figure 1. Vi
represents the gases released from the petroleum liquid
storage tank 110. Vm and Vm leakages originte from the
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
- 9 -
compressor 102 which gases are routed into the petroleum
liquid storage tank 110 and leave with leakage 1/1.
Leakages NT" and Vu, represent leakages from the various
packings used to seal the compressor 102 thereby to
prevent the escape of gases. 112 represents the fugitive
emissions released from the crankcase of the engine 101.
V3 represents the gases released from the pneumatic
control of a control valve 105 and V4 represents the
emissions released from the instrumentation used in
support of the engine 101 and compressor 102, housed in
cabinet 104.
Referring to Figure 2, the fugitive gases shown
as being emitted from various locations within the
building 100 of Figure 1 are collected into a collector
source 111 by way of appropriately sized and
appropriately located ducting, piping, tubing and the
like. These collected fugitive gases are fe4 into
ducting 131 extending to a diverter valve 112 which, in a
first configuration, passes the fugitive emissions to the
normal vent or stack 113 to bypass the engine 101 and
which, in a second configuration, pass the gases to a
flow meter 114 and thence to the air intake 120 of the
CA 02905319 2015-09-10
W02008/025158
NEVCA207/001529
- 10 -
engine 101. The fugitive gases and the air enter the
engine 101 from the air intake 120 through a control
valve 133.
Fuel from the normal fuel source 121,
conveniently natural gas in the case of a natural gas
powered engine 101, passes to a fuel meter 122 and,
thereafter, to the engine 101 through a control valve
134. Combustion products from engine 101 are exhausted
through an exhaust stack 123. An exhaust analyzer 130
may monitor the combustion products from the engine 101
passing through the exhaust stack 123.
Various control techniques are contemplated as
will be explained in greater detail. A control unit 124
is operatively connected to the fuel meter 122 and to the
valves 133, 134 which control unit 124 controls the
quantity of inletted fugitive gases and air and fuel from
the normal fuel supply 121, respectively. Exhaust
analyzer 130 may also be associated with the control unit
124. If, for example, the fugitive gases entering air
intake 120 and engine 101 provide increased richness in
the exhaust stack 123 as indicated by the exhaust sensor
CA 02905319 2015-09-10
V1/132WM/025158
KIICA2007/01529
- 11 -
130, the control unit 124 may adjust the quantity of air
passing through valve 133 thereby maintaining the proper
air-fuel ratio for efficient combustion within the engine
101.
OPERATION
With reference to Figures 1 and 2, the operation
of engine 101 is initiated and will be operating with the
normal fuel source 121 and the normal air supply entering
the engine 101. The emissions of the fugitive gases from
the various apparatuses 110, 101, 105 and 104 as
represented by III, Võ V3 and V4f respectively, will be
collected with appropriate ducting and piping at fugitive
emission collector source 111. The fugitive gases are
then conveyed to the air intake 120 of engine 101 through
ducting 131, diverter valve 112 and flow meter 114.
For safety reasons, the diverter valve 112 will
normally divert the fugitive gases through stack 113 when
the engine 101 is not running and the fugitive gases are
still being collected. Alternatively, a holding
container (not illustrated) may store the gases until the
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
- 12 -
engine 101 commences operation. Or, the fugitive gases
may be diverted to a flare stack (not illustrated) where
they are burned.
Following the startup of engine 101, the
position of diverter valve 112 is changed either manually
or otherwise, so that the fugitive gases flow directly to
the air intake 120 through ducting 132 and flow meter
114. Flow meter 114, located between the diverter valve
112 and the air intake 120, operates to measure the flow
of the fugitive gases entering the air intake 120. The
use of the fugitive gases operates to increase the fuel
supply which enriches the fuel flow to the engine 101
thereby creating an increased engine speed. ;A governor
(not illustrated) for measuring and controlling engine
speed is operably connected to the engine 101 and the
valve 134. As the engine speed increases, the governor
will reduce the normal fuel supplied to the engine 101 by
way of partially closing valve 134. This will act to
reduce the normal fuel supplied to the engine 101 and
return the engine speed to that desired. The reduced
normal fuel supplied to the engine 101 will be replaced
with that energy supplied by the fugitive gases thereby
W02008/025158
PCT/CA2007/001529
-13-
resulting in less use of normal fuel in the engine 101.
Depending upon the quantity of fugitive emissions
available, the rate of flow of such emissions and the existing air-
fuel control method for the combustion process, a variety of
control techniques are available to adjust the normal fuel supplied
to the engine 101 when the fugitive gases are being used as a
supplementary fuel source.
For example and as previously described, an exhaust
sensor 130 may be operably associated with the exhaust stack 123.
The exhaust sensor 130 monitors the components in the exhaust of
exhaust stack 123. If the exhaust sensor 130 senses hydrocarbon
and/or oxygen content greater than desired, appropriate adjustment
will be provided to either the air or fuel supply, the
adjustment changing the percentage of hydrocarbons and/or oxygen in
the exhaust stack thereby contributing to combustion of increased
efficiency.
A further application utilises the techniques disclosed
in United States Patent 6,340,005 Maim et al).
CA 2905319 2017-10-03
W02008/025158 PCT/CA2007/001529
-14-
The flow of the fugitive gases added to the inlet 120 of the engine
101 may be measured by a flow meter 114 as earlier set forth. As
the rate of flow of the fugitive gases increases, the rate of flow
of the normal pressurized fuel will decrease thereby causing the
normal control system based on the quantity of normal pressurized
fuel relative to the air supplied to deliver too little air. By
combining the fugitive gas flow with the normal pressurized fuel
flow, the control unit 124 will maintain the proper fuel-air ratio
in engine 101 to provide for appropriate and efficient combustion.
Thus, the normal fuel entering the engine 101 through fuel meter
122 is replaced by the supplementary fuel supply provided by the
fugitive gas emissions and measured by flow meter 114. The fuel
flow meter 114 can also be calibrated to ensure that the quantity
of fuel added to the engine 101 by the fugitive emissions does not
exceed the fuel supply required by the engine 101.
Yet a further control application is illustrated in
Figure 3A where manual control is used for the fugitive gases
entering the air intake 204. A diverter
CA 2905319 2017-10-03
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
- 15 -
valve 201 is provided which allows the fugitive gases to
pass to the normal fugitive gas vent or stack 202 which
may vent or burn the fugitive gases. A control signal
211 may provide that the diverter valve 201 pass all
fugitive gases to the stack 202 in the event there is an
engine failure or an engine shutdown. A three-way manual
valve 203 is provided downstream of the diverter valve
201. This valve 203 provides for the entry of fugitive
gases to the air intake 204 of the engine and it can be
adjusted to regulate the quantity of fugitive gases to
the air inlet 204 and to the fugitive gas stack 202
through piping 210. A slow addition of fugitive gases
passed to the air intake 204 by adjusting valve 203 will
minimize the engine speed change and will allow the
operator to manually adjust the air-fuel ratio to account
for the addition of the fugitive gases. When engine
operation ceases, a control signal 211 moves the diverter
valve 201 so that the fugitive gases vent to stack 202 in
the normal manner. The three-way valve 203 should be
selected so that the flow path of the fugitive gases is
not blocked in any valve position which would stop the
flow of fugitive gases and contribute to pressure buildup
in the collection system 111 (Figure 2). This technique
CA 02905319 2015-09-10
WO 2008/025158
PCUCA207/(0)1529
- 16 -
is relatively simple and inexpensive and, under certain
gas flow conditions, it is contemplated that the diverter
valve 201 and the three-way valve 203 could be combined
into a single valve.
A further embodiment of the control technology
is contemplated wherein an exhaust gas sensor is provided
which initiates a signal related to the amount of oxygen
and/or unburned fuel in the combustion exhaust.
Normally, this technique would use the signal to control
the air/fuel ratio for the combustion. If the signal
advised that the mixture was too rich, the normal air
supplied to the engine would be increased and if the
signal advised that the air/fuel ratio was too lean, the
normal air supplied to the engine could be decreased.
Similarly, the proportion of fugitive gases could be
increased or decreased relative to the normal fuel entry.
This control technique is generally referred to a closed
loop air/fuel control.
A further control technique is illustrated in
Figure 3B wherein automatic control of the three way
valve 203 is provided which allows the control system to
CA 02905319 2015-09-10
WO 208/025158
PCFCA2007/001 52 9
- 17 -
control the quantity of fugitive emissions diverted to
the combustion air intake 204. If the addition of
fugitive gases to the air intake 204 through valve 203 is
excessive thereby prohibiting the engine speed from
otherwise being automatically adjusted, a control signal
advises the three-way valve 203 that any excessive
quantity of fugitive gases are to be diverted to the
fugitive gas stack 202. In this embodiment, it is
contemplated that the diverter valve 201 could be deleted
with control of the fugitive gases provided wholly by the
three-way valve 203.
In yet a further control technique illustrated
in Figure 3C, a flow meter 220 is added upstream of the
engine air intake 204 and downstream of three-way valve
203 to measure the quantity of fugitive gases added to
the air intake 204. The information obtained from the
flow meter 220 can be used to determine general operating
characteristics and/or to determine the fraction of fuel
used by the engine which originates with the fugitive
gases. In this embodiment, the diverter valve 201 could
be deleted with control provided solely by the flow meter
220 which would provide appropriate control signals to
CA 02905319 2015-09-10
WO 208/025158
PCUCA207/001 52 9
- 18 -
three-way valve 203.
A further control technique using a combination
of fuel. flow measurement and manual control for the
fugitive gases is illustrated in Figure 3D. In this
embodiment, as the fuel flow comprising normal fuel and
fugitive gases increases, the control system will
increase the air flow to the air intake 204. If the flow
of fugitive gases is relatively constant, following the
initiation of the fugitive gas flow, the control system
can be adjusted to compensate for the addition of the
fugitive gases. Diverter valve 201 ensures that the
fugitive gases are vented in the event of engine shutdown
or a safety hazard arising. Any changes in the rate of
flow of the fugitive gases will be done manually since no
automatic adjustment of the fugitive gas flow rate is
provided in this case.
A further control technique is illustrated in
Figure 3E. The control system 230 utilises fuel flow
measurement and fugitive flow measurement with the air-
fuel ratio being controlled by the rate of air flow to
the combustion process. To maintain the desired air-fuel
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
- 19 -
ratio, a fugitive gas flow meter 220 is required. The
fugitive gas flow measured by meter 220 is added to the
normal combustion fuel flow value and the control system
230 will use the input from flow meter 220 to determine
the proper quantity of air to be added to the air intake
204. In the event, for example, that the fugitive gas
flow is small, the control system 230 is contemplated to
be sufficient to determine the correct air quantity
without the use of flow meter 220. For higher flows of
fugitive gases, however, the fugitive gas flow signal
from flow meter 220 can be used as a feed-forward signal
to adjust the combustion fuel control valve (not
illustrated) coincident with the addition or removal of
the fugitive gases. This fugitive gas flow value is
again useful for operating information and/or to
determine the fraction of fuel used by the engine which
may come from the fugitive gases.
In the interest of full disclosure, experiments
which have been performed by the applicant are set forth
below. In addition, the potential savings thought to be
achievable by using fugitive emissions as a supplement
fuel source are calculated. It is emphasized that these
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
- 20 -
experiments and calculated possible savings have not been
measured in a technically rigorous manner, nor have they
been corroborated. Rather, the experiments conducted and
the subsequent discussions based on those experiments are
included here as being corroborative of the advantages
thought to be achievable only. Applicant would not want
to be bound by the experimental results given hereafter
if subsequent measurements or calculations are found to
be more precise or if subsequent experiments and
calculations adversely affect the results described and
the discussions based on those results.
EXAMPLE 1
For a typical 1000 HP natural gas engine, the
amount of methane used would be approximately 1000 x
7500/900 = 8300 scf/h = 139 scf/m where scf/m = standard
cubic feet per minute. The average packing leak as found
in reciprocating compressors is described in "Cost
Effective Leak Mitigation at Natural Gas Transmission
Compressor Stations", Howard et al, Pipeline Research
Council International, Inc., (PRCI) Catalogue No.
L51802e, the contents of which are herein incorporated by
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
- 21 -
reference. The measurements reveal that the leaks amount
to approximately 1.65 scf/m per rod packing. For a
four(4) throw compressor, this would amount to 6.60 scf/m
or 5% of the fuel required for the above-identified
engine. If natural gas is used for the pneumatic
instrumentation, gas venting can increase to 10 scf/m or
more. In addition to packing leaks, other sources of
fugitive hydrocarbon gas emissions include the engine
crankcase, the compressor crankcase, glycol dehydrators,
petroleum liquid storage tanks, engine starting systems
and unit blow downs during gas venting operations.
EXAMPLE 2
Other sources of fugitive gases in a typical
operating environment such as the engine compressor unit
located within the compressor building 100 illustrated in
Figure 1 were measured. The results of those
measurements are given and set forth in Figure 4. The
vent flow measurements were taken by a rotometer which
was calibrated for air and then multiplied by a
correction factor for natural gas. It will be seen from
Figure 4 that the total estimated fugitive emissions by
CA 02905319 2015-09-10
WO 2008/025158 PCT/CA2007/001529
- 22 -
the sources measured amount to approximately 9 scf/m
which is the value used in the calculations given
hereafter. It will further be noted the term 546 I/P
stands for a Fisher 546 model current/pressure
transducer. A current to pressure transducer (ZIP) takes
a 4 to 20 ma control signal from the controller and
coverts it to a proportional gas pressure. This gas
pressure then controls a diaphragm on a conttol valve.
The fuel flow consumption was approximately 138
kg/h at 932 rpm. The estimated load percentage based on
fuel was 72% by using the manufacturer's specifications
for the maximum load capacity and comparing it with the
actual load for the engine estimated from the operating
conditions. Using a fuel density of 0.79 kg/m3, the fuel
flow is (138 kg/h/0.790kg/m3) x (35.3 ft3/m3)/60 min/h =
103 scf/m. Thus, the fugitive emissions released at this
location amounted to approximately 8:7% (9 sdf/m/103
scf/m = 8.7%) of the total engine fuel consumption.
EXAMPLE 3
A test was undertaken to add fugitive gases to
CA 02905319 2015-09-10
WO 2008/025158
PCT/CA2007/001529
- 23 -
the engine inlet of a Waukesha 7042 GSI engine modified
for lean operation which powered a four(4) throw, two(2)
stage Ariel JGK-4 compressor. Only the vent gas V4 from
the instrument cabinet 104 (Figure 1) was used. This was
so because the cabinet 104 used for housing the
instruments provided a convenient source for fugitive
gases from the instrumentation and a convenient place to
connect a rubber hose for conveying the gases first to a
three-way valve and then to the engine air intake. The
three way valve was positioned in the hose between the
cabinet and engine air intake thereby allowing the gas to
be vented or directed to the air intake and which also
allowed a sample of the gas to be taken. A subsequent
gas analysis confirmed that the fugitive or vent gas
measured was principally a combustible hydrocarbon
mixture. The speed of the Waukesha engine was set to 932
rpm and the measured suction pressure at the compressor
intake remained relatively constant during the test,
ranging between 347 to 358 kPa, which confirmed the
relatively constant engine load during the test.
When the fugitive gases from the instrument
cabinet 104 were initially directed to the air intake of
CA 02905319 2015-09-10
WO 2008/025158
ITT/CA2007O1 52 9
- 24 -
the engine, the engine speed initially increased and then
recovered to the set point of 932 rpm. The fuel flow
recorded by the engine flow meter dropped from 126.6 kg/h
to 115.2 kg/h which indicated a potential fuel saving of
about 10 kg/h. The exhaust oxygen dropped from 7.6% to
6.6%. The air control valve was then adjusted to bring
the exhaust oxygen percentage back to the approximate
starting value. The decrease in fuel flow for the engine
operating with the same exhaust oxygen percentage was
(126.6 - 118.6) = 8 kg/h which was a decrease of
approximately 6.3%. To check this value, the gas flow
through the vent was measured at a value of 5.6 scf/m
(air) or 6.6 scf/m (gas). Converting this flow to metric
mass flow gave a value of 8.8 kg/h. This correlated with
the decrease in fuel flow observed with fuel enrichment
by way of the fugitive gas supply to the air inlet.
EXAMPLE 4
Based on the measurements given above, the
savings in fuel would be in the range of CDN$20000.00 to
CDN$30000.00 per year for this engine. Since the
fugitive gas emissions are normally vented and lost, and
CA 02905319 2015-09-10
WO 2008/025158 PCT/CA2007/001529
- 25 -
assuming the gas price of $5.00/GJ(Giga Joule) =
5.27/MMBTU(mi1lion British Thermal Units) =
$4.79/Mscf(thousand standard cubic feet) (GHV(Gross
Heating Value) = 1100 BTU/scf), the lost value of the
vented gas is CDN$3100/year for gas vented at 1 scf/m.
Thus, the value of the vented gas from the compressor
building alone was calculated to be approximately
CDN$25,000.00 per year.
EXAMPLE 5
In this case, the fugitive emissions were mostly
methane. These emissions contribute to greenhouse
gas(GHG)emissions. A calculation reveals that the
fugitive emissions and the engine CO2 result in the
equivalent or estimated GHG emission(CO2(e)) of 4900
Tonnes per year ( = CO2 mass/y + 21 x CH4 mass/year). If
the fugitive emissions are used as fuel by the engine,
the CO2(e) would drop to 3010 Tonnes per year, a decrease
of 40% or 1890 T/y. Thus, this is contemplated to
provide a good technique for the reduction of greenhouse
gases.
CA 02905319 2015-09-10
WO 2008/025158 PCT/CA2007/001529
- 26 -
Many modifications may readily be contemplated
to the invention. Although the teachings are
specifically directed to a natural gas engine where
natural gas is used as the normal fuel, the fugitive
gases are contemplated to be a useful supplementary fuel
source for other engines, including diesel and gasoline
powered engines and turbines. Indeed, with appropriate
controls, it is contemplated that the fugitive gases may
be usefully added as a supplementary ,fuel to virtually
any device using the combustion of air and fuel where the
fuel may be liquid or gaseous so long as the fuel is
combustible.
In addition, although the invention has been
described as providing for the fugitive gases to emanate
from a storage tank to an engine and compressor located
within a building, the presence of a building is of
course unnecessary and quite optional. The engine and/or
compressor and/or storage tank may be instead located in
the open.
Yet a further embodiment of the invention is
contemplated where the fugitive gases may have been
CA 02905319 2015-09-10
WO 2008/025158 PCT/CA2007/001529
- 27 -
diluted by air as is illustrated in Figure 5. Such
fugitive gases may have escaped from various sources such
as block and control valves, pressure relief valves,
regulators, flange connections, compressor seals,
compressor valve stems and valve caps, coal mines,
livestock and sewage treatment and the like without such
list being all inclusive. Sources for such fugitive
gases are described in "Catalytic Solutions for Fugitive
Methane Emissions in the Oil and Gas Sector", Hayes,
R.E., Chemical Engineering Science 59 (2004) 4073-4080.
While Hayes describes the source of such dilute fugitive
gases, he does not contemplate that the dilute fugitive
gases could be used as a supplemental fuel source for an
engine or turbine.
The fugitive gas emissions which are diluted by
air may occur in buildings where the sources of gas
Prnissions are located. Typically, the air in such
buildings is replaced constantly with the use of fans or
ventilators using atmospheric air which is provided to
the building and which replaces the internal air of the
building together with the escaped fugitive gases. A
fugitive gas of considerable interest is methane which,
CA 02905319 2015-09-10
WO 2008/025158 PCT/CA2007/001529
- 28 -
being of a density which is lighter than air, passes to
the inside ceiling of the building before being replaced
by external air and evacuated to the atmosphere.
It is contemplated that such methane and other
dilute fugitive gases being of a density lighter than air
can be collected and used as intake air for the engine or
turbine in which the fuel is used and thereby serve as a
supplementary fuel for the engine or turbine similar to
the procedure desired above where an exhaust .gas oxygen
sensor is described. The use of methane as a
supplemental fuel source is particularly attractive since
methane is a greenhouse gas. The combustion of such
methane is beneficial to reduce greenhouse gas emissions.
Reference is made to Figure 5 where the fugitive
gases are shown as being emitted from various locations
within the building 300 which gases particularly will
usually include methane and which gases are shown by the
broken lines V5, V5 and V, The fugitive gases. migrate to
the inside ceiling of the building 300 because they will
include, typically, methane which is of a density lighter
than air. They are collected there by a collector 311.
CA 02905319 2015-09-10
WO 2008/025158 PCT/CA2007/001529
- 29 -
These collected dilute fugitive gases are fed into
ducting 311 extending to a diverter valve 312 which, in a
first configuration, is positioned such that all of the
engine intake air is drawn via a duct 313 from outside
the building. The exhaust fan 324 is turned on to ensure
the dilute fugitive gases are drawn from the building.
In a second configuration, the diverter valve is moved to
draw all or part of the engine intake gases from the
collector 311. The control and inletting of natural gas
or other fuel together with control processes provided
for the collected and dilute fugitive gases is similar to
the embodiments earlier described to obtain the desired
air-fuel control for the engine or turbine which utilises
the dilute fugitive gases as a supplemental fuel source.
The diverter valve 312 is controlled (manually or by a
control system) to achieve the .desired amount of outside
intake air and intake air, which may contain diluted
fugitive gases. An exhaust sensor 330 may conveniently
be associated with the exhaust stack 323 to monitor the
components in the exhaust of exhaust stack 323 as
previous described.
It is further contemplated that the animal
CA 02905319 2015-09-10
WO 2008/025158 PCT/CA2007/001529
- 30 -
husbandry may be a source of methane and that the
building 300 may be a barn, for example, with cattle or
other animals being located therein. The methane
produced by the animals would be collected in a similar
manner to that described and inputted to an engine
or turbine 303.
Yet a further embodiment of the invention is
illustrated in Figure 6. With the engine in operation,
there is a negative pressure at the intake to the engine
which tends to draw in the collected fugitive gases which
are subsequently used as a fuel source. The negative
pressure tends not only to draw in the fugitive gases but
it also tends to draw in air through the exhaust stack
which otherwise would vent the fugitive gases to the
atmosphere when the engine is not in operation. In
accordance therewith, Figure 6 illustrates an exhaust
stack 600 and a passive check valve 601 which is
installed in the exhaust stack 600. The check valve 601
prevents the ingress of air into the intake ducting 602
which extends to the engine 603 and which otherwise
allows atmospheric air passing through air filter 604 to
the intake ducting 602.
CA 02905319 2015-09-10
WO 2008/025158 PCT/CA2007/001529
- 31 -
The passive check valve 601 is operable to
maintain a maximum positive pressure at the source 610 of
fugitive gases of 1 to 5 inches of water (H20) where the
pressures are here stated as inches of water column with
27.7 inches of water column equaling 1 psi or 6,895
kiloPascals.
A control or on/off valve 611 is closed when it
is not desired to use the fugitive gases as a fuel source
such as when the engine 603 is not in operation. The
fugitive gases will thereby pass directly to the stack
600 and vent to the atmosphere and the back pressure
exerted by the check valve 601 is of a value that it will
not adversely affect this passage of the fugitive gases
to the atmosphere through stack 600.
When the control valve 611 is open and the
engine 603 is in operation, the fugitive gases will pass
directly to the engine air intake 602. The slight
negative pressure created by engine operation will
provide additional force on check valve 601 to maintain
it in its closed position thereby preventing backflow of
air through the stack 600 and into the air intake 602.
CA 02905319 2015-09-10
V1/32MM/0251M NEVCA2007/01529
- 32 -
With the flow of atmospheric air transmitted through the
control valve 611, fugitive gas flow into the engine 602
can be measured and better controlled.
Yet a further embodiment of the invention
relates to the addition of an accumulator 612 within the
duct 613 extending from the fugitive gas source to the
engine 603 as illustrated in Figure 7. The use of an
accumulator 612 is valuable if the flow of fugitive gas
is variable on a short term basis. The accumulator 612
will smooth out the fluctuations in fugitive gas flow to
the engine 603 thereby obviating excessive instrument and
control variations. The volume of the accumulator 612
selected is calculated based upon the volume of gas flow
from the fugitive gas source. 610 and the expected time
variables involved in such flow.
In operation and when the control valve 611 is
open and the engine 602 is in operation, the normal
pressure in the accumulator 612 will be similar to the
pressure in the air intake, typically 3 to 15 " H20 below
atmospheric pressure. If there is a burst of fugitive
gases, the pressure in the accumulator 612 will rise to a
CA 02905319 2015-09-10
WO 2008/025158 MUCA207/001529
- 33 -
maximum determined by the check valve 601. When the
check valve 601 opens, the excess gas is vented through
stack 600 to the atmosphere. If the fugitive gas burst
is small relative to the volume of the accumulator 612,
the fugitive gases will all be consumed by the engine 603
due to the storage capacity of the accumulator 612.
The check valve 601 is conveniently better
illustrated in more detail in Figure 8 wherein one
embodiment is shown. A seal 621 is conveniently provided
to prevent the ingress of air and for reliability
purposes, no spring is used and the weight of the movable
member 620 is designed to provide a force equivalent to a
pressure of 1 to 2" H210 closure force on the check valve
601. A pliable material is conveniently provided to
ensure seal integrity for the small forces involved.
=
Many further modifications will readily occur to
those skilled in the art to which the invention relates
and the specific embodiments herein described should be
taken as illustrative Of the invention only and not as
limiting its scope as defined in accordance with the
accompanying claims.
