Inlet Air Cooling System

This invention relates generally to an internal combustion engine inlet air system and more particularly to an inlet air system driven by gas turbines.

It is conventional for supercharged or turbocharged engines to have a system for cooling the inlet air to approximately the temperature of the ambient air adjacent the engine. Otherwise, the inlet air would be at a higher temperature due to the heat of compression, which could result in poor engine operation. It is also recognized that engines benefit from the inlet air being cooled below the ambient air temperature. In particular, refrigeration below ambient can provide a combination of reduced specific NO.sub.x emissions, increased specific power and increased efficiency. The method most generally used for reducing specific NO.sub.x emissions, leaning the engine mixture, causes a reduction in specific power and may cause a loss of efficiency.

Natural gas is moved in large quantities through pipelines by means of compressor stations along the pipelines. These compressor stations use reciprocating or gas turbine engines which are fueled by the pipeline gas itself. As part of the national and international effort to reduce air pollution, the exhaust emissions from these engines are coming under increasingly strict limits. Reducing NO.sub.x emissions from reciprocating engines has proved to be fairly difficult, and in some cases, existing installed engines must be shut down, resulting in an economic loss to the operator.

A primary strategy for NO.sub.x reduction in reciprocating engines that has been identified by recent research is to operate the engine with a substantially leaner fuel/air mixture. If the engine air flow is maintained constant and the fuel flow is reduced to lean the mixture, there will be a loss of engine power output roughly proportional to the reduction in fuel flow. Therefore, to make up this loss in engine power, it is desirable to increase the air flow through the turbocharger compressor. However, when the mixture is leaned with constant air flow, the engine exhaust temperature decreases, and hence the power available in the turbocharger turbine will decrease. Therefore, often the turbocharger turbine cannot produce the additional power. In this case, the desired NO.sub.x reduction is achieved, but at the cost of reduced power available from the engine.

In some cases, the reduction in engine exhaust temperature is such that the turbocharger turbine cannot maintain the original air flow through the compressor. Thus, the compressor air flow falls as the fuel flow is reduced, and the desired lean fuel/air ratio can never be reached. In this case, the desired NO.sub.x reduction cannot be achieved and the engine may have to be shut down.

The foregoing illustrates limitations known to exist in present inlet air systems. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.

In one aspect of the present invention, this is accomplished by providing an inlet air compression means for compressing inlet air supplied to the engine, the inlet air compression means including a turbocharger driven by engine exhaust gas and an expansion turbine driven by a source of compressed gas, the expansion turbine being mechanically connected to the turbocharger.

The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.

FIG. 1 is a schematic drawing of a system employing the concepts of this invention;

FIG. 2 is a schematic drawing showing the details of a hydrocarbon leakage collection system;

FIG. 3 is a schematic drawing of a second embodiment of a system incorporating the hydrocarbon leakage system;

FIG. 4 is a schematic drawing of an alternate embodiment of the system shown in FIG. 1; and

FIG. 5 is a schematic drawing of an alternate embodiment of an engine inlet air system.

One embodiment of this invention, shown in FIG. 1, is a combined system for use on internal combustion engines in natural gas compression service. In the preferred embodiment, this combined cycle provides both inlet air refrigeration for the internal combustion engine and additional natural gas compression. Also provided is a leakage control system for any natural gas or hydrocarbon leakage from the combined cycle system. The leakage is collected and introduced into a low pressure portion of the engine air intake system where it is burned along with the normal engine fuel.

In the embodiment shown in FIG. 1, a combined cycle inlet air cooling system and gas compression system is shown. Natural gas is used as the refrigerant fluid. The natural gas refrigerant fluid circulates in a typical gas refrigeration cycle, transferring heat from the intake air to the ambient atmosphere, either directly or via an intermediate coolant, such as water. The natural gas compressor in the refrigerant circuit is oversized, and the refrigeration cycle is connected to the station high and low pressure gas mains. Therefore, this natural gas compressor augments the compression capacity provided by the internal combustion engine. The refrigeration system and the natural gas compressor receive power from the engine exhaust turbine and the refrigeration turbine. There may also be an additional turbine in the inlet stream to drop the inlet temperature further and provide additional power for the refrigeration system. The various compressors and turbines could be combined on a single shaft. The additional gas compression capacity assures that the maximum practical fraction of all the energy available in the exhaust system is utilized, without the use of additional components. The compressors and turbines may be of either the roto-dynamic or positive displacement type.

The preferred embodiment also includes a hydrocarbon leakage control system. Recently, there has been greatly increased attention to minimizing the release of various gases into the atmosphere, including hydrocarbons. Inlet refrigeration systems require shaft seals which will inevitably leak slightly. However, for most refrigeration systems, the lowest pressure in the refrigeration system will be higher than the lowest pressure in the engine intake system. Therefore, any leakage can be arranged to flow into the engine intake, and then into the engine, to be burned along with the normal fuel. Normal leakage rates will not change the mixture ratio of the engine significantly. This hydrocarbon leakage control system is illustrated in FIGS. 1 and 2.

The hydrocarbon leakage control system may also be used with the normal engine compressor configuration typically used for natural gas compression service, as shown in FIG. 3.

The preferred embodiment of the system of this invention is shown schematically in FIG. 1 and includes an internal combustion engine 5 including an inlet air conduit 32 and an engine exhaust conduit 34. An exhaust gas turbine 10 is connected to the exhaust conduit 34 and is driven by the exhaust gas flowing from the engine 5.

A rotary inlet compressor 12 is connected to the inlet air conduit 32 for compressing the inlet air entering the inlet air conduit 32. Air is supplied to the inlet compressor 12 by an air conduit 30. This compressor, along with the other compressors and turbine expanders in this system may either be of the roto-dynamic type or of the positive displacement type. The preferred embodiment uses rotary compressors and turbine expanders. The inlet compressor 12 is mechanically driven by the exhaust turbine 10. As shown in FIG. 1, the inlet compressor 12 is connected to exhaust turbine 10 by direct drive shaft 11.

The compressed inlet air then flows through an inlet cooler 20 for extracting heat from the inlet air. Heat removal from the inlet air cooler 20 is provided by an inlet air cooling system 25. The inlet air cooling system 25 uses a hydrocarbon as a refrigerant. The preferred embodiment uses natural gas as the hydrocarbon refrigerant. The cooled compressed inlet air is then introduced into the engine intake system by inlet air conduit 32. If further cooling of the inlet air is desired, an inlet expander turbine 18 is provided to expand the compressed cooled inlet air, thereby further reducing the temperature. This optional inlet expander turbine 18 is mechanically connected to a gas compressor 14 and a refrigeration turbine 16, thus using some of the energy from the compressed inlet air to provide additional power for the inlet air cooling system 25. If the inlet expander turbine 18 is not provided, the power for the inlet air cooling system 25 is provided by the exhaust turbine 10 and the refrigeration turbine 16. The exhaust turbine 10 or the direct drive shaft 11 is mechanically connected to the inlet air cooling system by means such as shaft connection 24. The inlet air cooling system 25 can be driven by either the exhaust turbine 10 or the inlet expander turbine 18 or by both the exhaust turbine 10 and the inlet expander turbine 18.

The inlet air cooling system 25 is comprised of a gas compressor 14, a refrigeration turbine 16, the inlet cooler 20, a refrigeration cooler 22 and, if provided, the inlet expander turbine 18. The present invention is intended to be used in conjunction with a natural gas compression service. The source of the refrigerant, natural gas, is the station low pressure gas main 40. Typical station low pressure gas main pressures are 200 to 500 psi. Gas compressor 14 receives low pressure natural gas from the station low pressure gas main 40 and boosts the pressure to or above the pressure of the station high pressure gas main 50. Typical station high pressure gas main 50 pressures are 500 to 1200 psi. The heat of compression is removed from the compressed natural gas by the refrigeration cooler 22. The refrigeration cooler 22 is cooled by an outside source such as water or ambient air 26. The cooled compressed natural gas is then expanded in the refrigeration turbine 16, further reducing the natural gas temperature. The cooled low pressure natural gas then flows through the inlet cooler 20, removing the heat of compression from the compressed inlet air. The natural gas is then returned to the gas compressor 14.

Check valves 66 are provided in the station low pressure gas main 40 and the station high pressure gas main 50 to prevent backflow from the inlet air cooling system into the station low pressure gas main 40 and to prevent backflow from the station high pressure gas main 50 into the inlet air cooling system 25.

The preferred embodiment of the present invention uses a gas compressor 14 which is oversized and provides more natural gas compression than is required to cool the inlet air for the engine 5. The excess compressed natural gas is introduced into the station high pressure gas main 50. This system, therefore, uses some of the exhaust gas pressure from the engine 5 to provide additional natural gas compression.

FIG. 2 illustrates an embodiment of a gas leakage collection system. Although FIG. 2 shows a single compressor, the gas leakage collection system is connected to many potential leakage sources. At any point in the inlet air cooling system 25 where significant natural gas leakage may occur, such as a shaft seal, a controlled leakage seal 60 is used. The controlled leakage seal 60 collects the natural gas which may leak past a shaft seal and directs the leakage to a controlled leakage collection system 62a, 62b. FIG. 2 shows the portion of the controlled leakage collection system 62a connected to the controlled leakage seal 60. There may be multiple portions of the controlled leakage system 62a, each being connected to a different controlled leakage seal 60. The portions 62a of the controlled leakage system are brought together to a single point 62b which is connected to a low pressure portion of the engine intake system. Depending upon the relative pressures, the controlled leakage system 62b may be connected to the inlet air conduit 32 or may be connected to another portion of the engine intake system.

In most refrigeration systems, the lowest pressure in the refrigeration cycle will be higher than the lowest pressure in the engine intake system. This controlled leakage collection system is arranged to cause any leakage to flow into the engine intake. By using this controlled leakage collection system, any natural gas leakage is collected and then burned in the engine along with the normal engine fuel. Normal leakage rates will not change the mixture ratio of the engine significantly. Although this system is shown in combination with a natural gas inlet air refrigeration system, it can be used with any refrigeration system which uses a refrigerant which can be burned in the engine.

An alternate embodiment of the controlled leakage collection system is shown in FIG. 3. The engine 5 and the station compressor 6 are typical natural gas compression service components. The controlled leakage collection system 62a, 62b is used to collect any natural gas leakage from the compressor 6. The leakage is introduced into the engine intake system as discussed above.

FIG. 4 shows an alternate embodiment of an inlet air cooling system for use with an internal combustion engine. The primary difference between the alternate embodiment and the embodiment shown in FIG. 1 is the alternate embodiment does not contain a separate compressor for compressing the natural gas refrigerant.

High pressure natural gas is supplied to the inlet air cooling system 25 by the station high pressure gas main 50. The high pressure natural gas is cooled in refrigeration cooler 22, which is in turn cooled by either water or air 26. The cooled high pressure natural gas is then expanded in refrigeration turbine 16, further reducing the natural gas temperature.

Inlet air for the engine 5 is compressed by an inlet compressor 12 and then cooled in inlet cooler 20. The cooled expanded natural gas is used to remove the heat of compression from the compressed inlet air. The inlet compressor 12 is mechanically connected to the refrigeration turbine 16, which drives the inlet compressor 12. The natural gas is returned to the station low pressure gas main 40 after cooling the compressed inlet air.

An exhaust turbine 10 may also be used to provide additional power to the inlet compressor 12. The exhaust turbine is connected to the engine exhaust conduit 34 to be driven by the engine exhaust. The exhaust turbine is also mechanically connected to the inlet compressor 12.

FIG. 5 shows a further embodiment of an inlet air system 75 for use with an internal combustion engine 5.

Inlet air for the engine 5 is compressed by an inlet compressor 12 and then cooled in an inlet cooler 20, which is in turn cooled by either water or air 26. An exhaust turbine 10 is used to power the inlet compressor 12. In the preferred embodiment, the inlet compressor 12 and the exhaust turbine 10 are a unitary turbocharger.

An expansion turbine 16, powered by a source of compressed gas 50, provides additional power to the inlet compressor 12. In the preferred embodiment, a station compressor 6, mechanically driven by the engine 5, compresses low pressure hydrocarbon gas from the station low pressure gas main 40 and discharges the compressed gas into the station high pressure gas main 50. The station high pressure gas main 50 is then the source of compressed gas to the expansion turbine 16. The exhaust of the expansion turbine 16 is returned to the station low pressure gas main 40.