Method and system for providing compressed substantially oxygen-free exhaust gas for industrial purposes

A method and system of providing compressed substantially oxygen-free exhaust gas for industrial purposes including the steps of extracting exhaust gas from a lean burn engine consuming a mixture of natural gas fuel and air, passing the extracted exhaust gas through a cooling step to cause entrained water vapor therein to condense out, separating and disposing of the condensed water, measuring the oxygen content of the exhaust gas, using the measurement to regulate the quantity of natural gas fed into an igniter into which the exhaust gas is also fed so that substantially all of the oxygen in the exhaust gas is consumed by combustion with the natural gas in the igniter to provide at an outlet of the igniter substantially oxygen-free exhaust gas, and compressing the substantially oxygen-free exhaust gas to provide compressed exhaust gas for industrial applications.

REFERENCE TO PENDING APPLICATIONS

This is application is not related for purposes of priority to any existing United States or foreign patent application.

REFERENCE TO MICROFICHE APPENDIX

This application is not referenced to any microfiche appendix.

FIELD OF THE INVENTION

The present invention is generally directed toward a method of providing compressed substantially oxygen-free exhaust gas for industrial purposes. More specifically, the present invention is directed toward a system for providing substantially dry oxygen-free exhaust gas that employs a combustor to burn natural gas with the exhaust gas from a lean burn engine to produce substantially oxygen-free exhaust gas.

BACKGROUND OF THE INVENTION

Most oil producing subterranean formations are characterized by pressurized gas. In some parts of the work hydrocarbon bearing formations have pressures sufficient to force liquid hydrocarbons (crude oil) to the earth's surface. In other parts of the world, the gas pressure is not sufficient to force liquid hydrocarbons to the earth's surface. However, in such formations, the presence of gas is nevertheless important since in many formations a gas drive is required to move liquid hydrocarbons from within the formation to the site of a producing well or wells.

As crude oil is extracted from a subterranean reservoir, the reservoir gas pressure decreases. As the gas pressure decreases, crude oil production rates usually fall. For these and other reasons, it has been found desirable in producing many subterranean formations to maintain gas pressure within the formations.

The characteristics of gas injected into a well can be critical. Free oxygen contained in injected gas can cause plugging of formations. Further free oxygen can result in bacteria growth that can plug a producing formation, and corrode tubulars in the producing well.

Ideally, gas injected into a reservoir to augment the production of liquid hydrocarbons should be oxygen-free. Therefore, when treating gas prior to injection, a most important step is to remove substantially all free oxygen.

The present invention provides a process for generating substantially oxygen-free exhaust gas that is particularly useful for injection into hydrocarbon bearing formations.

Examples of the use of exhaust gas from an engine for industrial purposes and examples of the use of exhaust gas to augment liquid hydrocarbon production are found in the following United States patents:

U.S.PAT. NO.INVENTOR(S)TITLE1,868,755MountDehydrator1,945,407Adair et al.Process of Purifying Gases2,240,550Conlon, Jr.Method of Retuning Gas to Gas-ProducingFormations2,825,408WatsonOil Recovery By Subsurface ThermalProcessing3,004,601BodineMethod and Apparatus for Augmenting OilRecovery from Wells by Refrigeration3,100,528Plummer, et al.Method for Using Inert Gas3,137,344WiemerMinimizing Loss of Driving Fluids inSecondary Recovery3,381,523NettlesMethod and Apparatus for Supplying GasUnder Pressure3,653,438WagnerMethod of Recovery of Petroleum Deposits3,908,762RedfordMethod for Establishing CommunicationPath in viscous Petroleum-ContainingFormations Including Tar Sand Deposits forUse in Oil Recovery Operations4,324,291Wong et al.Viscous Oil Recovery Method4,325,432HenryMethod of Oil Recovery4,533,374HaagMethod for Reducing Air Pollution4,546,829Martin et al.Enhanced Oil Recovery Process4,593,763BurkeCarbon Dioxide Well Injection Method4,891,939BrighentiSystem for the Cryogenic Processing andStorage of Combustion Products of HeatEngines5,232,049Christiansen,Sequentially flooding a Subterraneanet al.Hydrocarbon-Bearing Formation with aRepeating Cycle of Immiscible DisplacementGases5,988,280Crawford et al.Use of Engine Heat in Treating a Well Bore6,039,116Stevenson et al.Oil and Gas Production with Periodic GasInjection

BRIEF SUMMARY OF THE INVENTION

This invention is a method and a system for providing substantially oxygen-free exhaust gas useful for industrial purposes and particularly useful for injection into subterranean formations to augment the production of hydrocarbons. The method includes the steps of: 1) extracting exhaust gas from a lean burn natural gas fuel consuming engine; 2) passing the gas from Step 1 through a catalytic converter; 3) cooling the gas from Step 2 to provide a cooled exhaust gas; 4) passing the cooled exhaust gas from Step 3 through a scrubber/separator by which entrained water is extracted to provide dry exhaust gas; 5) conducting the dry exhaust gas into an igniter vessel; (6) flowing natural gas into the igniter vessel in proportion to the level of oxygen in the exhaust gas; (7) combusting the natural gas and oxygen in the exhaust gas; and (8) compressing the substantially oxygen-free exhaust gas for industrial purposes such as for injecting into a hydrocarbon producing formation.

A system for practicing the method of this invention includes a lean burn natural gas fuel consuming engine that produces exhaust gas. A catalytic converter is connected to receive the exhaust gas from the engine. An air cooler is employed by which water vapor is extracted to thereby provide substantially water-free exhaust gas. The oxygen content of the substantially water-free exhaust gas is measured by use of an oxygen analyzer. This measurement is used to regulate the ratio of exhaust gas and natural gas in an igniter where the oxygen is consumed by combustion with the natural gas. The exhaust gas, having minimal oxygen, is then passed through compression and cooling steps to cause any remaining entrained water vapor to condense out. The extracted water vapor is separated and disposed of to provide substantially dry and substantially oxygen-free exhaust gas, which is then compressed so that it can be used industrially, such as for injecting into a producing oil or gas-bearing formation.

A better understanding of the invention will be obtained from the following description and claims taken in conjunction with the attached drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing is a block diagram that may also be described as a flow diagram that illustrates a method and a system employing a lean burn natural gas combustion engine having a drive shaft connected to a multi-stage compressor. Exhaust gas from the engine is passed through a catalytic converter, cooled and then subjected to compression. Condensed water is extracted to provide a substantially water-free exhaust gas. The exhaust gas is then measured to detect the oxygen content thereof. The exhaust gas is then fed into an igniter that also receives a controlled quantity of natural gas. Combustion within the igniter consumes any and substantially all the oxygen remaining in the exhaust gas to provide substantially oxygen-free exhaust gas for industrial purposes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, and first toFIG. 1, a system that can be used for practicing a method of this invention is shown. The system makes use of the exhaust gas output of a lean burn internal combustion natural gas engine, the engine being indicated by the numeral10. Such an engine can be the kind utilized in an automobile, a truck or an industrial engine. The size of the engine will be determined by the quantity of gas required. If more gas is required than can be produced by a single engine, then multiple separate engines may be utilized. The engine10utilizes natural gas fuel mixed with ambient air that is combusted within the engine to produce energy output in the form of a rotating drive shaft12. As a consequence of the combustion of the fuel and air within engine10, exhaust gas is produced at an exhaust14.

Gas from exhaust14is passed through a catalytic converter16. In the catalytic converter, heated catalysts react with deleterious components of the exhaust gas to substantially neutralize such components to provide an output from the catalytic converter that is more environmentally acceptable.

The exhaust gas having passed through catalytic converter16is reduced to a lower temperature in an air cooler18. From air cooler18, the exhaust gas is fed into a scrubber/separator20in which any entrained water is separated with the water passing out through a discharge line22and the exhaust gas passing through a conduit24. Exhaust gas produced by lean burn engines characteristically has excess oxygen that is not sufficiently removed merely by a sequence of compressing and cooling steps. The essence of this invention is a provision of a method and system whereby exhaust gas from a lean burn engine can be treated in such a way that it is useful for industrial applications including, as a specific but not limiting example, introduction into subterranean oil or gas producing formations to augment production.

For this purpose, exhaust gas appearing in conduit24is fed into a gas igniter/combustion chamber which, for brevity, will hereinafter be referred to as a combustion chamber26. Combustion chamber26is a system that mixes any significant oxygen contained within the exhaust gas stream in conduit24with a gas fuel so that, by combustion, the oxygen is depleted. For this purpose an igniter that constantly provides a spark or other means for initiating combustion is provided within the combustion chamber26.

The method of this invention includes the steps of supplying a gaseous fuel into combustion chamber26to combine with oxygen contained within the exhaust gas appearing in conduit24. For this reason, a source of natural gas28is utilized. When the system of this invention is employed in an oil field to augment the secondary recovery of petroleum, a source of natural gas is frequently inherently available. In other instances, the source of natural gas may be from a supply line used to supply gas for residential or industrial heating purposes.

The quantity of flow from the source of natural gas28is regulated by a control valve30, the output at32which represents a controlled gas source.

Gas from control gas source32flows into exhaust conduit24to intimately mix with the exhaust gas passing out of scrubber/separator20and passing into combustion chamber26. Thus, the inflow into combustion chamber26is exhaust gas having natural gas admixed therewith, the purpose of the natural gas is to combine, by combustion, with oxygen found within the exhaust gas stream appearing at exhaust gas conduit24to thereby burn and neutralize the oxygen content.

The output of combustion chamber26includes the exhaust gases from conduit24plus the results of combustion of natural gas flowing into the combustion chamber from gas source32. This oxygen-neutralized exhaust gas flows through conduit34to a scrubber/separator36of the type similar to that identified by the numeral20. From scrubber/separator entrained water is carried away by water pipe38that feeds into a water disposal40along with the water from the first scrubber/separator20conveyed by water discharge line22. The purpose of combustion chamber26is to mix oxygen occurring in the exhaust gas stream from lean burn engine10with gas and the mixture combusted—that is, neutralized, to form substantially nitrogen and carbon dioxide. It is important that the correct quantity of natural gas be supplied from the gas source28—that is, it is important that control valve30be accurately and continuously operated in such a way as to introduce a quantity of natural gas into combustor chamber26as is required for complete combustion of oxygen contained in the exhaust gas stream. For this purpose, an oxygen analyzer42is connected to sample gas flowing through conduit34. Oxygen analyzer42provides an electrical signal by way of conductor44connected to a controller46that in turn provides a signal at48to regulate control valve30. More specifically, controller46responds to the electrical signal appearing at conductor44to provide a control signal at48that may be electrical or hydraulic, depending upon the type of control valve30. When oxygen analyzer42detects the presence of oxygen in the exhaust gas flowing through conduit24, a signal is sent to controller.46to open control valve30to a greater degree, to allow more natural gas to be introduced into combustion chamber26to thereby combine with and neutralize the oxygen. On the other hand, if oxygen analyzer42detects a reduced amount of oxygen in the exhaust gas appearing in conduit34, then a reduced quantity of natural gas is supplied to the combustion chamber. In other words, the closed circuit function of oxygen analyzer42, controller46, control valve30and combustion chamber26is to continuously regulate the amount of natural gas supplied to the combustion chamber to substantially neutralize oxygen occurring within the exhaust gas stream at conduit24to thereby provide gas that flows through conduit34to scrubber/separator36that is substantially oxygen-free.

Oxygen neutralized exhaust gas appearing at the outlet conduit50from scrubber/separator36is fed into the input of a multi-stage compressor51. In the arrangement as illustrated, compressor51has four stages of compression with intermediate coolers52,54and56. Cooler52is between first compressor stage1and second compressor stage2; cooler54is between compressor stage2and compressor stage3; and cooler56is between compressor stages3and4. The compressed gas at the output58of the 4thcompression stage is substantially oxygen-free and at an elevated pressure suitable to be used for industrial purposes. As previously stated, an example of an ideal use of the substantially oxygen-free exhaust gas at output58is injection into a subterranean hydrocarbon producing formation to maintain the pressure of the formation to thereby augment the production of liquefied petroleum.

The use of a multi-stage compressor51with its companion coolers52,54and56is by example only. However, for most efficient generation of engine exhaust gas, it is preferable that engine10have a load—that is, that it does work. This is achieved by using the available energy from engine10to drive compressor51to produce the ultimate pressure required at output58.

The substantially oxygen-free exhaust gas appearing at58and as produced by the system and method of this invention as illustrated in the drawing is substantially composed of nitrogen and carbon dioxide. The system confines the carbon dioxide and nitrogen as produced by the engine for industrial use such as injection into a subterranean formation and thereby makes use of the carbon dioxide and nitrogen that would otherwise pass to the atmosphere.

The claims and the specification describe the invention presented and the terms that are employed in the claims draw their meaning from the use of such terms in the specification. The same terms employed in the prior art may be broader in meaning than specifically employed herein. Whenever there is a question between the broader definition of such terms used in the prior art and the more specific use of the terms herein, the more specific meaning is meant.