Hydrocarbon Mixture Processing System and Method using Vapor Recovery

Abstract

Systems and methods for processing a hydrocarbon mixture wherein heat is generated from compression of recovered natural gas vapors and used to provide a heating medium for a heat exchanger.

Description

The present application claims priority to U.S. Provisional Patent Application Ser. No. 611600,176 filed Feb. 17, 2012.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to systems and methods for processing hydrocarbons that are recovered from subterranean wells. In particular aspects, the invention relates to processing of hydrocarbon mixtures from a well to a storage point.

2. Description of the Related Art

Oil, natural gas and water are ordinarily produced in a hydrocarbon mixture from a subterranean well. Processing is done following production to help remove water and gas from the oil and its condensate.

SUMMARY OF THE INVENTION

Oil and natural gas processing methods and systems are described that remove water and natural gas from a hydrocarbon production mixture. The present invention provides exemplary hydrocarbon mixture processing systems and methods that employ heat generated by a vapor recovery compressor through the engine jacket water cooling system and the natural gas compression stages as a heating medium for an oil and condensate stabilization and treating process, Natural gas liquids (NGLs) are recovered from the vapor stream. Heat generated by compressing the natural gas vapor is reused to heat the oil and/or condensates produced from the subterranean wells. Because this heat is reused in the system, as opposed to burning direct fired heaters, there are fewer emissions of CO₂, SO₂, H₂S and other harmful gases that are typically released when fuel gas is used. Furthermore, the heated oil and/or condensates will more easily liberate natural gas vapors in the vapor recovery separator, allowing for reduced natural gas emissions in the storage tanks. In an exemplary embodiment, a system constructed and operated in accordance with the present invention produces greatly reduced emissions of these harmful gases through the elimination of flashed gases at a flare as well as through elimination of a direct fired heater, which is replaced by a heat exchanger that uses recovered waste heat.

An exemplary hydrocarbon mixture processing system is described that includes a liquid separator to separate gas, oil and water from a hydrocarbon mixture and a heat exchanger to heat the hydrocarbon mixture and supply it to the liquid separator. The exemplary system also includes a vapor recovery compressor to provide compression to return the natural gas vapors to the sales lines. The heat generated in this process is utilized as a heating medium to the heat exchanger to increase the oil and/or condensates temperature prior to entering the separator. The vapor recovery compressor receives natural gas vapor from the liquid separator and compresses the vapor, which heats the vapor. The heated vapor is provided from the vapor recovery compressor to the heat exchanger to add heat to the heat exchanger.

An exemplary multi-stage heat exchanger is described having at least one stage of heating that is powered by engine jacket water and at least one other stage of heating that is powered by discharge gas from a vapor recovery compressor. in particular embodiments, the vapor recovery compressor has a plurality of compressor stages, and each of the compressor stages provides heating for one of the heat exchanger stages.

An exemplary hydrocarbon mixture processing method is described in which a hydrocarbon mixture containing gas, oil, water and condensate is first heated with a heat exchanger. Thereafter, gas, oil and water is separated from the hydrocarbon mixture using liquid separator. Natural gas vapor is collected from the liquid separator and transmitted to a vapor recovery compressor which compresses the natural gas vapor. When the natural gas vapor is compressed, it is heated. Thereafter, the compressed natural gas vapor is provided to the heat exchanger and provides a heating medium for oil and condensate that has been removed from the hydrocarbon mixture. In particular embodiments, the heat exchanger has multiple stages and at least some of these stages use heat provided by compressed natural gas vapor from the vapor recovery compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

For detailed understanding of the invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings in which reference characters designate like or similar elements throughout the several figures of the drawings.

FIG. 1 is a schematic system diagram of an exemplary hydrocarbon mixture processing system in accordance with the present invention.

FIG. 2 is an enlarged schematic view of portions of the system shown in FIG. 1.

FIG. 3 is a flow chart depicting steps n an exemplary method in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts an exemplary hydrocarbon processing system that is constructed in accordance with the present invention. The system generally includes a production separator 16, a vapor recovery stabilizer unit 24 and oil/condensate storage vessels 52.

In accordance with an exemplary method of operation, a hydrocarbon mixture that includes oil, condensate, water and natural gas is transmitted from wells 12 along conduit 14 to a production separator 16 of a type known in the art for initial separation of the hydrocarbon mixture. The production separator 16 removes natural gas from the mixture and transmits the removed natural gas to a sales compressor as illustrated at 18. Water s removed from the mixture by the separator 16 to water tanks, as indicated at 20. Oil and condensate are transmitted from the separator 16 along conduit 22 to a vapor recovery stabilizer unit 24.

The vapor recovery stabilizer unit 24 includes vapor recovery stabilizer product heat exchanger 26. Preferably, the heat exchanger 26 has multiple stages, and in the depicted embodiment, there are three stages of heat exchangers 26a, 26b and 26c. Oil and condensate that was removed from the production separator 16 is transmitted to the heat exchangers 26 whereby engine jacket water (EJW) coolant from the vapor recovery compressor driver 47 heats the oil and condensate in the first heat exchanger 26a. The compressor driver 47 may be in the form of an engine or motor of types known in the art. The oil and condensate then flow into exchanger 26b where they are heated further by the first stage discharge gas from the vapor recovery compressor stage 46a. The oil and condensate then flow into exchanger 26c where they are heated yet further by the second stage discharge gas from the vapor recovery compressor stage 46b.

The temperature of the oil and condensate exiting the heat exchangers 26 is regulated by a temperature transmitter 28. In a particular embodiment, the temperature transmitter 28 includes or is operably associated with programmable logic controllers of a type known in the art. The temperature transmitter 28 controls the temperature via temperature controllers 30 which will be selectively opened to allow the gas or fluid heating medium to bypass their respective heat exchangers 26a, 26b or 26c and go directly to a forced draft compressor cooler 32 when the oil and condensate have reached the desired temperature. The programmable logic controller will first open the engine coolant temperature bypass valve 34 until it is fully opened. Next, the first stage discharge temperature bypass valve 36 is opened. Thereafter, the second stage discharge temperature bypass valve 38 is opened. Optionally, an engine water coolant auxiliary pump 40 may be used to help compensate for pressure drop and circulate engine water coolant through the heat exchanger 26a.

Heated oil and condensate depart the heat exchangers 26 and enter a vapor recovery separator 42. The vapor recovery separator 42 operates in pressure ranges of about 35 psi to about 125 psi temperature ranges from about 150° F. to about 250° F. The vapor recovery separator 42 removes additional natural gas from the heated oil and condensate that are liberated from the process of heating of the oil and condensate by the heat exchangers 26, This natural gas is removed by suction line 44 to the suction of the second stage of a vapor recovery compressor 46 of a type known in the art.

Stabilization is the removal of natural gas and natural gas liquids at higher temperatures so that they are not liberated in lower pressure storage tanks where lower pressure vapors would either “flash” to atmosphere or be more difficult to compress back to the pipeline pressure due to their lower starting point pressure being near atmospheric pressure. Heated and stabilized oil and condensate are removed from the vapor recovery separator 42 via level control valve 48 and conduit 50 to oil and condensate storage tanks 52. Any remaining natural gas vapors in the oil and condensate storage tanks 52 are flowed back through conduit 54 to the first stage of the vapor recovery compressor 46 where they are compressed, taken through the first stage heat exchanger 26b then returned to the suction of the second stage of the vapor recovery compressor 26c where they are combined with the natural gas vapors from the vapor recovery separator 42. After being compressed and heated again by the second stage of the vapor recovery compressor 46, the natural gas passes through the second stage heat exchanger 26c as the heating source and then is discharged to sales or an existing sales compressor. The use of heated, compressed vapor from vapor recovery compressor 46 as a heating medium for the heat exchanger 26 results in greatly reduced emissions from the hydrocarbon processing system. The recovered heat allows for the elimination of a direct fired heater for the heat exchanger 26. Emissions are also reduced since gas that would otherwise be burned off at a flare during normal operations is used to provide heat to the heat exchanger 26 and natural gas liquids can be reclaimed therefrom.

A forced draft compressor cooler 32 is used to further reduce the engine jacket water coolant and first and second stage discharge natural gas temperatures to ensure that the engine water, first stage discharge and second stage discharge natural gas remains within the acceptable operating limits for the vapor recovery compressor 46. Furthermore, this additional cooling will promote improved recovery of natural gas liquids (NGLs) in the interstage separators 57a and 57b.

After the natural gas vapors are cooled and condensed by forced draft compressor cooler 32, the condensed natural gas liquids (NGLs) and water are removed by two phase separation 57a and 57b and taken to the three phase NGL separator 58. There, the NGLs and water are separated from each other and the NGL is either recovered and taken to an onsite storage vessel or pumped directly back to the gas to sales line 18 depending on user preference, Should there be any residual natural gas vapor from the NGL separator 58, it will be returned to the natural gas vapor to first suction line 54.

The back pressure regulator safety valve 56 exists for circumstances when the vapor recovery compressor 46 is not in operation such that the vapor recovery separator 42 will not overpressure.

It can be seen that the invention provides methods for processing a hydrocarbon mixture to separate gas, oil and water from the mixture. According to an exemplary method of processing 70, illustrated in FIG. 3, a hydrocarbon mixture which contains gas, oil, water and condensate is heated utilizing waste heat from vapor recovery compressor 46 (step 72) via a heat exchanger 26. Thereafter, gas, oil and water are separated from the hydrocarbon mixture using liquid separator 42 (step 74). Natural gas vapor is collected from the liquid separator and transmitted to a vapor recovery compressor 46 which compresses the natural gas vapor (step 76). When the natural gas vapor compressed, it is heated. Thereafter, the compressed natural gas vapor is flowed through the heat exchanger 26 and provides a heating medium for oil and condensate that has been removed from the hydrocarbon mixture (step 78). In particular embodiments, the heat exchanger 26 has multiple stages 26a, 26b and 26c and at least some of these stages (26B and 26C) use heat provided by compressed natural gas vapor from the vapor recovery compressor 46. Also in particular embodiments, the vapor recovery compressor 46 has multiple stages 46A, 46B, and at least one of the stages is used to supply heat to one of the stages 26B or 26C of the heat exchanger 26. According to step 80 of the exemplary process 70, natural gas liquids are collected from the compressed natural gas vapor.

The systems and methods of the present invention result in a savings of energy and greatly reduced emissions. A processing system constructed and operated in accordance with the present invention has significantly reduced emissions of CO2, SO₂, H₂S and other harmful gases that are typically released when excess gas is otherwise burned off at separation facility flares. In a particular embodiment, the emissions of CO₂, SO₂ and H₂S from the processing system 10 are dramatically reduced during typical operation, being limited to only the vapor recovery compressor 46 emissions. FIG. 1 depicts a conduit 60 that transmits gas from the back pressure regulator safety valve 56 to a flare wherein gas is burned off. This allows for burning off of excess gas in instances where the vapor recovery compressor 46 is not running or inoperable and gas has to be flared so that oil production can continue.

The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiments set forth above are possible without departing from the scope and the spirit of the invention.

Claims

1. A system for separating components of a hydrocarbon mixture, the system comprising:

a liquid separator to separate gas, oil and water from the hydrocarbon mixture;

a heat exchanger to heat and supply the hydrocarbon mixture to the liquid separator;

a vapor recovery compressor to compress natural gas vapors from the heat exchanger and provide a heating medium to the heat exchanger, the vapor recovery compressor receiving natural gas vapor from the liquid separator and compressing the natural gas vapor to heat it; and

to the heated vapor is provided from the vapor recovery compressor to the heat exchanger to add heat to the hydrocarbon mixture.

2. The system of claim 1 wherein the vapor recovery compressor also receives vapor from oil condensate storage tanks.

3. The system of claim 1 wherein the system has reduced emissions of CO2, SO2 or H2S during operation due to elimination of a direct tired heater for the system.

4. The system of claim 1 wherein the system has reduced emissions of CO2, SO2 or H2S during operation due to elimination of gases burned off at a flare.

5. The system of claim 1 wherein the heat exchanger comprises:

a plurality of heat exchanger stages;

at least one of the heat exchanger stages having heat supplied by engine jacket water; and

at least one of the heat exchanger stages having heat supplied by the vapor recovery compressor.

6. The system of claim 5 wherein the vapor recovery compressor has a plurality of compressor stages and each of the compressor stages provides a heating medium to one of the plurality of heat exchanger stages.

7. The system of claim 1 further comprising a forced draft compressor cooler for condensing natural gas liquids from natural gas vapor that has been compressed by the vapor recovery compressor.

8. A system for separating components of a hydrocarbon mixture, the system comprising:

a liquid separator to separate gas, oil and water from the hydrocarbon mixture;

a heat exchanger to heat and supply the hydrocarbon mixture to the liquid separator, the heat exchanger having a plurality of heat exchanger stages;

a vapor recovery compressor to compress natural gas vapors from the heat exchanger and provide a heating medium to the heat exchanger, the vapor recovery compressor receiving natural gas vapor from the liquid separator and compressing the natural gas vapor to heat it; and

the heated vapor is provided from the vapor recovery compressor to the heat exchanger to add heat to the hydrocarbon mixture.

9. The system of claim 8 wherein the vapor recovery compressor also receives vapor from oil condensate storage tanks.

10. The system of claim 8 wherein the system has reduced emissions of CO2, SO2 or H2S during operation due to elimination of a direct fired heater for the system.

11. The system of claim 8 wherein the system has reduced emissions of CO2, SO2 or H2S during operation due to elimination of gases burned off at a flare.

12. The system of claim 8 wherein the heat exchanger comprises:

a plurality of heat exchanger stages;

at least one of the heat exchanger stages having heat supplied by engine jacket water; and

at least one of the heat exchanger stages having heat supplied by the vapor recovery compressor.

13. The system of claim 12 wherein the vapor recovery compressor has a plurality of compressor stages and each of the compressor stages provides a heating medium to one of the plurality of heat exchanger stages.

14. The system of claim 8 further comprising a forced draft compressor cooler for condensing natural gas liquids from natural gas vapor that has been compressed by the vapor recovery compressor.

15. A method of processing a hydrocarbon mixture to separate gas, oil and water from the mixture, the method comprising the steps of:

heating the hydrocarbon mixture with a heat exchanger;

separating gas, oil and water from the hydrocarbon mixture using a liquid separator;

compressing natural gas vapor from the liquid separator with a vapor recovery compressor; and

providing the compressed natural gas vapor to the heat exchanger for heating the hydrocarbon mixture.

16. The method of claim 15 further comprising the step of collecting natural gas liquids from the natural gas vapor after it is compressed.