WO1997029273A1 - Exhaust gas driven fuel gas pressure booster method and apparatus - Google Patents

Abstract

A method of increasing fuel gas pressure to a spark ignited internal combustion engine. The method includes delivering exhaust gas from the spark ignited internal combustion engine to at least one expansion turbine (22, 24). Each expansion turbine is powered by the exhaust gas. The power generated from each expansion turbine is transmitted to at least one compressor (26, 28). Fuel gas is delivered to each compressor to increase pressure prior to delivering the fuel gas to the spark ignited internal combustion engine. The pressure of the fuel gas is controlled prior to entering the spark ignited internal combustion engine in alternative ways.

Description

EXHAUST GAS DRIVEN FUEL GAS PRESSURE BOOSTER METHOD AND APPARATUS

BACKGROUND OF THE INVENTION

1. Field Of The Invention.

The present invention is directed to a method and apparatus for increasing fuel gas pressure to a spark ignited internal combustion engine using engine exhaust as the energy source for a turbocharger. In particular, the present invention is directed to a method and apparatus for increasing fuel gas pressure delivered to a spark ignited fuel internal combustion engine wherein the available fuel gas supply is at a pressure insufficient to fuel the engine. 2. Prior Art .

There are sites where flammable gas is available at low pressures in quantities sufficient to collect and use for generating power or to sell as fuel. For example, one of the by-products of large man-made landfills is production of methane gas. In some instances, this gas is simply burned off into the atmosphere.

Spark ignited gaseous fuel internal combustion engines use flammable gas as fuel to generate power or to run the machinery to collect the gaseous fuel. In some situations, the flammable gas pressure is insufficient to fuel the internal combustion engine without the gas pressure first being increased to a certain, adequate level. Examples of such sites are: landfills; oil and gas wells; vapor recovery from railroad tank cars, tanker ships and the like; and sewage treatment plants. At sites such as these, it is necessary to increase the pressure of the fuel gas by means of a compressor. For instance, at a landfill recovery site, the methane gas produced during the decomposition process may be at a low pressure. The methane gas is collected from the landfill and delivered to an engine where it is converted to electrical energy. Heretofore, fuel gas compressors used at these sites have been conventional blowers, screw compressors or positive displacement compressors driven by an electric motor. The energy that is used to operate the fuel gas compressor must either be purchased, such as electrical power, or generated on site. If the energy is generated on site, it then becomes unavailable to sell or use for other purposes. Whether the energy used to compress the engine fuel gas is generated or purchased, it adds directly to the cost of operating the site and, thus, adds to the cost of the energy produced. Cost of power, maintenance and installation of the conventional fuel gas compressor make it economically feasible to replace a conventional compressor with a turbine compressor system that utilizes engine exhaust energy to compress the fuel gas for delivery to the engine. The exhaust energy in these cases would otherwise be wasted.

It has also been known in the past to utilize turbochargers with internal combustion engines wherein air to the combustion chamber is increased in pressure. In addition to automobiles, examples are seen in Acheson et al . , U.S.

Patent No. 4,202,168 and Papsdorf, U.S. Patent No. 4,254,617.

One prior approach to increasing gas fuel pressure is shown in Faulkner, U.S. Patent No. 5,329,757. Faulkner's invention applies to a gas turbine engine as opposed to the present invention which utilizes a spark ignited internal combustion engine. Faulkner utilizes high pressure air bled from one of the turbines compressor stages in order to power the turbocharger. Faulkner's invention, thus, uses energy that would otherwise be available as engine shaft power. This is in contrast to the present invention which uses exhaust gas from a spark ignited internal combustion engine. The exhaust gas contains energy that the engine did not convert to shaft power. Accordingly, the present invention does not decrease the available shaft power of the engine. In many instances, this exhaust energy would not be recovered except for the present purpose. Therefore, it is a principal object and purpose of the present invention to increase fuel gas pressure to a spark ignited internal combustion engine using engine exhaust as the energy source for a turbocharger.

It is an additional object and purpose of the present invention to control pressure of fuel gas delivered to a spark ignited internal combustion engine using alternate control mechanisms.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for increasing the pressure of fuel gas delivered to a fuel system of a spark ignited gaseous fuel internal combustion engine. Exhaust gas from a spark ignited internal combustion engine is conducted through an exhaust gas conduit to a back pressure creating device, such as a waste gate, to selectively seal the exhaust gas conduit. By this procedure, a source of high pressure exhaust gas is created.

The high pressure exhaust gas is allowed to flow through conduits to a plurality of expansion turbines. Each expansion turbine produces rotary motion of a shaft .

After passing through the turbines, the exhaust gas exits and is thereafter conducted downstream of the back pressure creating device by return conduits. Power generated by the exhaust gas from the expansion turbines is transmitted mechanically to corresponding compressors. Rotating shafts of the turbines are directly coupled to shafts of the compressors.

Low pressure fuel gas from a source is conducted through gas source conduits. The gas source conduits deliver the fuel gas into the compressors. After compression, the fuel gas is discharged from the compressors and is delivered by conduits to the internal combustion engine fuel gas system.

Alternate pressure control mechanisms are provided to control the pressure of the fuel gas entering the fuel gas system. In one mechanism, a portion of fuel gas is bypassed from the inlet of the engine fuel gas system to a point downstream of the fuel gas source by a bypass conduit. Alternatively, pressure of the fuel gas entering the fuel gas system can be controlled indirectly by restricting the flow of engine exhaust gas to the turbines.

Fuel gas pressure control at the internal combustion engine inlet is thereby altered by either bypassing fuel gas around the compressors or by restricting exhaust gas flow through the turbines.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of an initial, preferred embodiment of the invention showing a method and apparatus for increasing the pressure fuel gas delivered to a fuel system of the spark ignited gaseous fuel internal combustion engine wherein fuel gas compressors are arranged in parallel in the fuel gas stream;

Figure 2 is a schematic diagram of another, alternate embodiment of the present invention showing a method and apparatus wherein the compressors are arranged in series in the fuel gas stream; and

Figure 3 is a top view and Figure 4 is a side view of the embodiment shown in Figure 1 of the method and apparatus of the present invention for increasing the fuel gas pressure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings in detail, Figure 1 is a schematic diagram of an initial, preferred embodiment 10 of the present invention showing a method and apparatus for increasing the pressure of fuel gas delivered to a fuel system of a spark ignited gaseous fuel internal combustion engine utilizing exhaust gas from the engine. The embodiments described are particularly useful for landfill gas recovery processes although other uses are possible. As will be described in detail, the fuel gas compressors in Figure 1 are arranged in parallel in the fuel gas stream.

Exhaust gas from a spark ignited internal combustion engine represented by box 12 is conducted through an exhaust gas conduit 14 to a back pressure creating device 16, such as a control valve or a waste gate or a means of otherwise selectively sealing the exhaust gas conduit 14. By this procedure, a source of high pressure exhaust gas is created.

High pressure exhaust gas in the conduit 14 between the engine 12 and the back pressure device 16 is allowed to flow through a pair of conduits 18 and 20 to a plurality of expansion turbines, represented by dashed line boxes 22 and 24, respectively. Each turbine 22 and 24 has a plurality of turbine wheels and accompanying stages. Each turbine produces rotary motion of a shaft by rings of blades mounted on a rotor. Exhaust gas is, thus, delivered to the turbines where it is used to rotate the shafts.

After passing through the turbines 22 and 24, the exhaust gas exits the turbines and is thereafter conducted downstream via return conduits 23 and 25. The power generated by the exhaust gas from the expansion turbines 22 and 24 is transmitted mechanically to corresponding compressors represented by dashed line boxes 26 and 28. The rotating shafts of the turbines are directly coupled to shafts of the compressors. Each compressor 26 and 28 has a plurality of compressor wheels and accompanying stages.

The present invention is capable of utilizing low pressure gas not otherwise usable at the input to an internal combustion engine. Fuel gas from a source shown by box 30 is conducted through gas source conduits 32 and 34 which may, as an option, include conditioners 36 which may include separators for contaminant removal. The conditioners may also include filters.

The gas source conduits 32 and 34 deliver the fuel gas into the compressors 26 and 28. Between each stage of compression, further conditioning of the fuel may occur as illustrated by boxes 38 and 40. The conditioners 38 and 40 may include heat exchangers to either cool or heat the fuel gas, or separators to remove any liquid condensation, or both. In a preferred embodiment, air or water heat exchangers are utilized to cool the fuel gas prior to the next stage.

Thereafter, the fuel gas is delivered via conduits 42 and 44 to the internal combustion engine fuel gas system 46. The fuel gas passes through inlet conduit 45 as it enters the fuel gas system 46. After compression, the fuel gas is discharged from the compressors and may be further conditioned as at box 41.

Alternate pressure control mechanisms are provided to control the pressure of the fuel gas entering the fuel gas system 46. In one manner, this is accomplished by bypassing a portion of fuel gas from the inlet of the engine fuel gas system 46 to a point downstream of the fuel gas source 30 by a bypass conduit 48. The bypass conduit 48 is in communication with the inlet conduit 45 and the fuel gas source conduit 32. A valve 50 controls the amount of fuel gas bypassed. A controller having a sensor 52, in fluid communication with the inlet conduit 45 into the fuel gas system 46, senses engine fuel system inlet pressure, controls the valve 50 and, in turn, controls the size of the fuel gas conduit 48. The volume of fuel bypassed is, thus, controlled.

Alternatively, pressure of the fuel gas entering the fuel system can be controlled indirectly by restricting the flow of engine exhaust gas to the turbines 22 and 24. An additional controller 54 is in fluid communication with the inlet conduit 45 of the inlet of the fuel gas system 46. The amount of exhaust gas flowing through the turbines 22 and 24 is controlled by valves 56 and 58 in exhaust gas conduits 18 and 20, respectively, prior to introduction into the turbines. Controller having a sensor 54 senses engine fuel system inlet pressure and controls the flow of the exhaust gas, thereby controlling the turbines and compressors and maintaining a predetermined pressure at the engine fuel system inlet.

Fuel gas pressure control at the engine inlet is thereby altered by either bypassing fuel gas around the compressors or by restricting exhaust gas flow through the turbines.

A mechanism is provided for supplying adequately compressed fuel gas during engine start up. An auxiliary fuel source 60 may be utilized during start up conditions before an adequate exhaust gas supply is built up. Gaseous fuel can be supplied from storage tanks or another suitable gaseous fuel source. The auxiliary fuel source 60 is conducted by a conduit 62 where it connects to the incoming fuel gas line 45. A valve 64 may be used to control the admission of auxiliary fuel to the system. A one way check valve 66 in the inlet conduit 45 prevents flow of any auxiliary fuel backwards into or through the compressors 26 and 28.

In summary, once the fuel gas from the low pressure source, such as the landfill, is compressed to an adequate pressure, it is delivered to the engine which generates power.

Figure 2 is a schematic diagram of another alternate embodiment 70 of the present invention wherein the compressors are arranged in series in the fuel gas stream and fuel gas pressure is controlled by either bypassing fuel gas from the discharge to the inlet of the compressors or restricting exhaust gas flow to the turbines . Exhaust gas from a spark ignited internal combustion engine 72 is conducted through an exhaust conduit 74 to a back pressure creating device 76 such as a control valve, a waste gate, or other means of selectively sealing the conduit. High pressure exhaust gas in the conduit between the engine and the back pressure device thereby flows through conduit 78 and 80 to a plurality of expansion turbines 82 and 84 (illustrated by dashed lines) . Each turbine 82 and 84 has a plurality of turbine wheels or stages. After passing through the turbines 82 and 84, the exhaust gas exists the turbines and is thereafter conducted downstream. The power generated by the exhaust gas in the expansion turbines is transmitted mechanically to compressors 86 and 88 respectively. Each compressor has a plurality of compressor wheels or stages. Fuel gas from a source 90 is conducted through a conduit 92 past a conditioner 94, which may be a separator for contaminant removal. The fuel is thereafter delivered to compressor 88. Between stages of compression, further conditioning of the fuel may occur in conditioners 96 which may be heat exchangers to cool or heat the gas, separators to remove condensate or both. After the gas passes through the first set of compressors 88 it is discharged and conducted through conduit 98 past conditioner 100 and thereafter to compressor 86. Between stages of compression, further conditioning of the fuel gas may occur in conditioners 97. After the fuel gas passes through the compressor 86 it is discharged from the second compressor after further conditioning at 102. The compressed fuel gas is finally delivered to the engine fuel gas system 104.

Pressure of the fuel gas is controlled by a control mechanism. A portion of the fuel gas is bypassed from the inlet of the fuel gas system 104 to a point downstream of the fuel source 90 by a conduit 106. A controller having a sensor 108 senses the inlet pressure of the fuel system and controls restriction of a valve 110 to maintain a predetermined pressure at the engine fuel system inlet .

An alternate fuel gas pressure control is also provided in the present invention. Fuel gas entering the system is controlled by restricting the flow of engine exhaust gas through the turbines 82 and 84. The amount of exhaust gas flowing through the turbines is controlled by valves 112 and 114 in conduit 78 and 80. A controller 116, in communication with the gas line senses engine fuel system inlet pressure and controls the amount of restriction of the valves 112 and 114, thereby trying to maintain a predetermined pressure of the fuel system inlet. In general, fuel gas control at the engine inlet is affected by either of these control mechanisms and both are not utilized at the same time.

During start up of the system, adequate exhaust gas to power the compressor systems may not be available. For engine start up, an auxiliary fuel source 120 may be provided. The auxiliary fuel source is at an adequate pressure for delivery to the engine. The auxiliary fuel is conducted by a conduit 122 to communicate with the engine fuel system 104. A valve 124 and conduit 122 is used to control the admission of auxiliary fuel to the system. An additional check valve 126 prevents flow of the auxiliary fuel gas backward through the compressors .

Figure 3 illustrates a top view and Figure 4 illustrates a side view of the method and apparatus for increasing pressure of fuel gas to a fuel system of a turbocharged spark ignited gaseous fuel internal combustion engine as shown in Figure 1. The spark ignited internal combustion engine 12 is shown in outline. Exhaust gas from the engine 12 is conducted through a conduit to a back pressure creating device 16. An existing air turbocharger 130 is in parallel with the existing waste gate 16. High pressure exhaust gas is allowed to flow through conduit 18 to expansion turbine 22 in parallel with the existing turbocharger. After passing through the turbine, exhaust gas is discharged to the engine exhaust conduit 14 by return conduit 23. Power generated by the exhaust gas from the expansion turbine 22 is transmitted mechanically to a corresponding compressor 26. Fuel gas from a source 30 passes through conduit 32. The fuel gas is delivered to the compressor 26. The fuel is thereafter delivered through a check valve 66 to the internal combustion engine fuel gas system 46. An optional heat exchanger 41 cools the fuel. A pressure control mechanism controls pressure of the fuel gas entering the fuel gas system 46. A portion of the fuel gas from the inlet of the fuel gas system is bypassed via conduit 48 through regulator 58 to a point downstream of the fuel gas source and upstream of the compressor.

An auxiliary fuel source is delivered by conduit 62 and valve 64.

The feasibility of the present invention has been studied using some of the excess exhaust energy of a turbocharged, spark ignited, internal combustion engine to raise the pressure of low pressure fuel gas to a level suitable for introduction into the engine fuel system. In the study, the engine analyzed is a Caterpillar 3516 low BTU engine. The fuel gas being compressed is of the sort typically extracted from landfills. The engine is a turbocharged and aftercooled engine designed for low heating value fuel gas. The turbocharger is powered by the engine exhaust stream. Part of the exhaust stream is diverted to the turbocharger and the rest is diverted to a valve, called a waste gate, that is in parallel with the turbocharger. By varying the opening of the waste gate, the intake manifold boost supplied by the turbocharger can be regulated. The mass flow of exhaust gas flowing through the turbocharger and the shaft power transferred from the turbine side to the compressor side of the turbocharger is calculated using manufacturer supplied data.

Some of the exhaust that is bypassed around the turbocharger by the waste gate is used to power an additional smaller turbocharger that will be used to compress the engine fuel gas. The fuel gas is extracted from a landfill at a known pressure. The required fuel flow and pressure required by the engine is obtained from Caterpillar supplied data. These calculations show that there is sufficient energy in the portion of the exhaust stream bypassed through the waste gate to power the fuel gas turbocharger. The exhaust bypassed through the waste gate represents wasted energy. Ambient Conditions: P_atm=14.38psi Assumed Atmospheric Pressure

T_amb=537°R Assumed Ambient Temperature

Air-Fuel Compressor Analysis:

The fuel gas is mixed with the air before it is compressed by the turbocharger. Therefore, the combined mass flow of the inlet air and fuel gas passes through the air compressor. The compressor outlet temperature is calculated from the published aftercooler heat rejection and inlet manifold temperature. Since the fuel gas mass flow is only a small part of the total mass flow, the thermodynamic properties of the inlet stream are assumed to be those of air.

c pa=196.538 ft -lbf Assumed Specific Heat at Constant lb°R Pressure For Air-Fuel Mixture

-..=1.38 Assumed Ratio of Specific Heats For Air-Fuel Mixture Q=6746Btu-min^" =159. lhp Published Aftercooler Heat Rejection Rate

-iι_ac=10767 lb-hr Published Air-Fuel Mass Flow

P_acin=0.98-P_at_=14.09 Inlet Pressure With Assumed Pressure Drop

_β«,_ut⁼l-05<69- tfgr)=72.45^•Hg Outlet Pressure, Published Manifold Pressure With Assumed Pressure Drop

T_a a_tc.x_tn_n¹-T_Λ ai_mm_h)+5 °J?=542 ° R Inlet Temperature With Assumed Pre-heat

^■ acout -+590^oi?=738 . 8 °.R Outlet Temperature:^maX^Cpa (Calculated From AC Heat Rejection)

^_aci_„⁼™_βc-c_M-(2^,_aeoιIt-r_acill)=210.4Λ Shaft Work In

i *_saci-=πι_ac-c_pa-r_acin "acout I . =168.3 tip Isentropic Work

wk_c

^ l_aa_cc⁼-_wj. =0.8 Adiabatic Efficiency of Air-Fuel Compressor

Air Turbine Analysis: .'2744_l^B_b^to^u_R Assumed Exhaust Gas Specific Heat At Constant Pressure

¹ -³³³ Assumed Specific Heat Ratio of Exhaust Gas

T_Λtout^~1240 °R Published Outlet Temperature T_atιn= (1495-10 ) °R Turbine Inlet Temperature, Measured

Manifold Temperature Less Assumed Loss

P_atout=P_atm+l =15.38 Assumed Outlet Pressure

Assumed Turbine Adiabatic Efficiency

_•v*_atout=l-01-ϊv'/e_ac__l„=212.5i-p Assumed Shaft Work Out, Considering

Losses Between Compressor And Turbine

Q_atout= 0 . 1 - wk_atout=2 l . 3tιp Assumed Heat Loss Through Turbine

Casing

m =^w aattoouut⁺ *** a^at^to^ou^ut^t _₌Q₈._Q84Λ_C6..₁Λ₀33 -*■-^*-*_{Mass Flow} through Turbine

^CDe^' ' -' ati" *" atout ) "^r

T - T Ts_out=T_at-ιπ-^{at n} -----_=1090°i? Isentropic Discharge Temperature

^"at

_______

( Ta.₊t- ,n K - l

P atxn=P atout =53.07 Inlet Pressure ~"^Sout j

Fuel Gas Compressor Analysis: c =258.3 A- =1.26 Assumed Fuel Gas Properties^pg IJ -J?^?

The fuel gas compressor is assumed to have the same efficiencies as the air-fuel compressor.

.n_fc=1267 lh -hr^Λ Published Fuel Gas Mass Flow

T_fcιn=r_amb+5⁰R=542°P Assumed Inlet Temperature 1^=11.56 Assumed Inlet Pressure, Absolute

P_fcout = 1.05-(P_{atjn +} 9 )=24 Assumed Outlet Pressure,

Published Pressure With Assumed Pressure Drop

( P^r f ÷cout

-*^• ~out - fcin =633.082 °R Isentropic Outlet Temperature

^•P σin

τ~ — T T_fco -'T_f i_n- °^U-^f "=655.856°R Actual Outlet Temperature

^_fcin-m_fc-c_pg-(T_fcout- T_fcin)-18.819-hp Shaft Work In

Fuel Gas Turbine Analysis:

The efficiency is assumed to be that of the air-fuel turbine. Therefore the ratio of mass flows through the fuel gas and main turbine will be proportional to the shaft powers.

wk m fcin ft^'■m_at =791.3112j -hr Fuel Gas Turbine Mass Flow wk„„.

^mac--^ma -^mft⁼¹-¹³-¹°^{3 lb ,Λr} Waste gate flow

The positive waste gate flow demonstrates that there is sufficient energy in the exhaust stream to power the apparatus described herein.

Whereas, the present invention has been described in relation to the drawings attached hereto, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.

Claims

WHAT IS CLAIMED:

1. A method of increasing fuel gas pressure to a spark ignited internal combustion engine, which method comprises:

delivering exhaust gas from said spark ignited internal combustion engine to at least one expansion turbine;

powering each said expansion turbine by said exhaust gas;

transmitting power generated from each said expansion turbine to at least one fuel gas compressor;

delivering said fuel gas to each said compressor to increase gas pressure prior to delivering said fuel gas to said spark ignited internal combustion engine; and

controlling said pressure of said compressed fuel gas prior to entering said spark ignited internal combustion engine.

2. A method of increasing fuel gas pressure as set forth in Claim 1 including the additional step of initially pressurizing said exhaust gas prior to delivering to each said turbine.

3. A method of increasing fuel gas pressure as set forth in Claim 1 wherein controlling said fuel gas pressure is accomplished by bypassing a portion of said fuel gas after compression in said compressor prior to delivering to said engine.

4. A method of increasing fuel gas pressure as set forth in Claim 1 wherein controlling said fuel gas pressure is accomplished by controlling the flow of said exhaust gas delivered to each said turbine.

5. A method of increasing fuel gas pressure as set forth in Claim 1 including a plurality of said expansion turbines and a plurality of said compressors arranged in parallel.

6. A method of increasing fuel gas pressure as set forth in Claim 1 including a plurality of said expansion turbines and a plurality of said compressors arranged in series.

7. A method of increasing fuel gas pressure as set forth in Claim 1 including the additional step of introducing pressurized fuel gas from an auxiliary source during engine start up.

8. A method for increasing fuel gas pressure as set forth in Claim 7 including a valve to control admission of auxiliary fuel gas to the system.

9. An apparatus to increase fuel gas pressure to a spark ignited internal combustion engine, which apparatus comprises:

at least one expansion turbine in communication with exhaust gas from said internal combustion engine;

at least one compressor powered by said expansion turbine;

means to pass said fuel gas through said compressor, thereby increasing the fuel gas pressure;

means to deliver said compressed fuel gas to said spark ignited internal combustion engine; and

means to control pressure of said fuel gas prior to entering said internal combustion engine.

10. An apparatus to increase fuel gas pressure as set forth in Claim 9 wherein said means to control said fuel gas pressure includes a controller having a sensor which operates a valve to bypass a portion of said fuel gas after compression and prior to delivering to said internal combustion engine.

11. An apparatus to increase fuel gas pressure as set forth in Claim 9 wherein said means to control said fuel gas pressure includes a controller having a sensor which restricts the flow of said exhaust gas to each said turbine.

12. An apparatus to increase fuel gas pressure as set forth in Claim 9 including a plurality of said turbines and wherein each said turbine is mechanically linked to one said compressor and said turbines are arranged in parallel.

13. An apparatus to increase fuel gas pressure as set forth in Claim 9 including a plurality of said turbines and wherein each said turbine is mechanically linked to one said compressor and said turbines are arranged in series.