CA2905319C - Method and apparatus for providing vent source gases to an engine - Google Patents

Abstract

A check valve installed in an exhaust stack prevents the ingress of atmospheric air which would otherwise be mixed with fugitive gases supplied as a fuel source to an engine. An accumulator is positioned within the ducting which conveys the fugitive gases to the engine from the source of fugitive gases thereby to prevent excessive flow fluctuations of fugitive gas to the engine. Measurement and control of the fugitive gases and engine operation is enhanced.

Description

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 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.

- 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

-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.

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.

-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

- 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 =

- 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

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

- 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

- 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

- 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

- 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

-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).

-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

- 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 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

- 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

- 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

- 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

- 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.

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

- 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.

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

- 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.

A test was undertaken to add fugitive gases to

- 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

- 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.

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

- 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.

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.

- 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

- 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,

- 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.

- 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

- 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.

- 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.

- 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

- 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.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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.

2. A method as in claim 1 wherein said flow of said vent gases has fluctuations and an accumulator is positioned within said second duct for smoothing said fluctuations of said flow of said vent gases to said engine intake manifold.

3. A method of providing vent gases to an engine as in claim 1 wherein said engine is a natural gas engine and a stack is provided to allow at least a portion of said vent gases to pass to the atmosphere and bypass said engine.

4. A method as in claim 3 wherein said stack further includes means for allowing or prohibiting said vent gases to pass through said stack to said atmosphere.

5. A method as in claim 4 wherein said means for allowing or prohibiting said vent gases to pass through said stack to said atmosphere is a pressure relief device.

6. A method as in claim 4 wherein said means for allowing or prohibiting said vent gases to pass through said stack to said atmosphere is a check valve.

7. A method as in claim 5 wherein said vent gases are emitted from said secondary source of fuel at approximately atmospheric pressure.

8. 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.

9. Apparatus as in claim 8 and further comprising a stack associated with said secondary fuel duct, said stack allowing said secondary fuel to escape to the atmosphere.

10. Apparatus as in claim 9 and further comprising means to prevent said secondary fuel from escaping from said stack.

11. Apparatus as in claim 10 wherein said means to prevent said secondary fuel from escaping from said stack is a pressure relief valve.

12. Apparatus as in claim 11 wherein said pressure relief valve is a check valve.

13. Apparatus as in claim 10 wherein said engine is a natural gas engine.

14. Apparatus as in claim 13 wherein said natural gas engine has an air filter mounted on said engine intake manifold and a throttle in said engine intake manifold downstream of said air filter, said engine intake manifold allowing air to enter said engine intake manifold through said air filter, said secondary fuel duct entering said engine intake manifold downstream of said air filter and upstream of said throttle.