Plant For Separating Oil From A Gas Mixture, And A Method For Separating Oil From A Gas Mixture

PATENT
Plant For Separating Oil From A Gas Mixture, And A Method For Separating Oil From A Gas Mixture
United States Patent Application 20120031270
Inventors:Carlsoon, Claes-göran (Tullinge, SE)
Ström, Göran (Ronninge, SE)
Application Number:13/147404 Publication Date:02/09/2012 Filing Date:01/26/2010 Export Citation:Click for automatic bibliography generation Assignee:ALFA LAVAL CORPORATE AB (LUND, SE)
Abstract:
The invention refers to a plant and a method for separating oil in form of particles and/or mist from a fossil gas mixture for obtaining a separated gas. The plant comprises a centrifugal separator with a stationary casing defining a separation space. The casing permits a pressure of at least 10 bars in the separation space. The centrifugal separator comprises an inlet for the gas mixture, a gas outlet for the separated gas and an oil outlet for discharging separated oil. A separating member for separating the gas mixture comprises a plurality of separating discs and is provided in the separation space. A drive motor is connected to the separating member via a spindle and rotate the separating member about an axis (x) of rotation.
FIELD OF THE INVENTION
The present invention refers to cleaning of natural gas, and especially separating oil from natural gas. Furthermore, the invention refers to separating oil in the form of particles, preferably liquid particles, and/or mist from a fossil gas mixture by means of a centrifugal separator comprising a stationary casing defining a separation space permitting a gas flow therethrough. The invention also refers to a method for separating oil in the form of particles and/or mist gas from a fossil gas mixture.

BACKGROUND OF THE INVENTION
When producing natural gas for delivery via for instance a gas conduit, the natural gas is received from the source at a very high pressure. The natural gas comprises larger or smaller amounts of undesired substances, such as oil, water, heavier hydrocarbons etc., in the form of liquid particles. Before delivery of the natural gas, for instance via a pipe line, the gas has to be treated and undesired substances, such as oil, be removed. Thereafter, the pressure has to be reduced to a manageable level. Today separating members in the form of so-called scrubbers for separating oil from the natural gas are used. The expression fossil gas mixture can in the present application refer to natural gas. The expression may also refer to the gas or gas mixture which is obtained during production of oil from natural oil sources. Such a gas or gas mixture may contain large amounts of liquid particles.

WO 2008/111909 discloses a particle separator for separating particles from a gas mixture. The separator comprises a stationary casing, defining a separation space permitting a gas flow therethrough, and an inlet for the gas mixture through the casing into the separation space. A rotation member is provided in the separation space downstream the inlet with respect to the gas flow and arranged to cause the gas mixture to rotate. A separating member for separating the gas mixture comprises a spindle with a plurality of separating discs and is provided in the separation space downstream the rotation member with respect to the gas flow. A drive motor is connected to the spindle and arranged, during the separation, to rotate the separating member via the spindle in a direction of rotation about an axis of rotation at a number of revolutions lying within a range of revolutions. The separating member is configured to separate particles from the gas mixture by means of centrifugal forces. Furthermore, a gas outlet is provided downstream the separating member with respect to the gas flow for discharge of the separated gas. An oil outlet for discharge of oil extends through the casing. The separator disclosed is not suitable for treating a fossil gas mixture, and especially not for separating oil from the fossil gas mixture.

U.S. Pat. No. 4,687,585 discloses a plant and a method for separating at least one component from a fossil fluid, such as crude oil or natural gas, during utilization of a device comprising a centrifuge rotor. The centrifuge rotor in the known device comprises a central hollow inlet chamber and a number of conical separating discs. The fossil fluid is conveyed centrally into the central chamber and then flows radially outwardly in the interspaces between the separating discs.

U.S. Pat. No. 5,755,096 discloses a dynamic filter arranged to be connected to a natural gas source. The dynamic filter comprises a stationary casing with a rotating separating rotor comprising separating discs extending mainly axially. The separating member seems to driven by means of the flow of natural gas.

FR-A-2 476 505 discloses a cyclone for separating particles from a gas. The cyclone comprises a rotor member, which comprises a number of discs and which is provided in the cyclone immediately inside the outlet of the cyclone for cleaned gas.

SE-525 432 discloses a centrifugal separator for cleaning of pressurised air from a compressor and to a brake system of a motor vehicle. The centrifugal separator is arranged to remove impurities from the compressor.

SUMMARY OF THE INVENTION
One object of the present invention is to provide an efficient separation of oil from a fossil gas mixture, such as for instance natural gas. Furthermore, it is aimed at an efficient separation immediately or substantially immediately after the fossil gas mixture has been extracted from the source, i.e. an efficient separation under a high pressure.

Since the stationary casing is configured in such a way that it permits a pressure of at least 10 bars, or preferably at least 20 bars, in the separation space during the separation, the centrifugal separator can be used for an efficient separation of oil from a fossil gas mixture, or natural gas, just after the extraction of the gas mixture. The centrifugal separator enables separation directly after the gas mixture has been extracted or after one or a small number of preceding treatment stages, for instance a preceding separation of oil in a scrubber.

According to one aspect of present the invention, the plant is configured for counter flow separation, which means that the rotating gas mixture is guided into the separating member radially from outside the periphery of the separating member and into the gaps present between the separating discs towards the centre and the central outlet chamber. The oil and possible other substances which are present in the gas mixture will get attached to the separating discs and be conveyed outwardly and thrown towards the inner wall of the stationary casing at the same time as the cleaned gas is conveyed inwardly into the central outlet chamber and from there out through the outlet.

According to an embodiment of the invention, the gas outlet comprises a gas outlet pipe which is arranged to permit connection to the gas conduit for receiving the separated gas from the centrifugal separator, wherein this connection is configured to resist said pressure. The pressure in the gas conduit and in the separation space is the same, and the stationary casing shall thus have the same pressure strength as the gas conduit transporting the gas. Furthermore, also the inlet may comprise an inlet pipe which is arranged to permit connection to the gas conduit for supply of the gas mixture to the centrifugal separator, wherein this connection also is configured to resist said pressure.

According to an embodiment of the invention, the centrifugal separator comprises a rotation member, which is provided in the separation space downstream the inlet and upstream the separating member with respect to the gas flow and arranged to cause the gas mixture to rotate. Thanks to such a rotation member, the incoming gas mixture obtains an initial rotary motion which contributes to a certain separation of oil and possibly other liquid or particulate substances from the gas. Consequently, a higher cleaning degree is achieved in the separating member. The kinetic energy of the incoming gas mixture may in this manner also contribute to a lower energy consumption for the driving of the separating member. Advantageously, the rotation member has a tangential opening configured to guide the gas mixture in a tangential direction from the inlet into the separation space so that the gas mixture is caused to rotate. By means of such a rotation, at least a part of the oil will be separated from the gas mixture and by the centrifugal force moved outwardly towards an inner wall of the separation space. The rotation member may also, as a supplement or alternative, comprise a turbine wheel which is provided on the spindle. Such a turbine wheel will in a similar way as the cyclone-like design cause the gas mixture to rotate and provide an initial separation of oil from the gas mixture. Advantageously, the drive motor may be provided to drive the separating member during the separation in cooperation with the turbine wheel. The turbine wheel will due to the flow velocity of the gas mixture be caused to rotate by the flowing gas mixture. This rotation can be used for the driving of the separating member.

According to an embodiment of the invention, the range of revolutions is 1000 to 3000 revolutions/minute. The separating member thus rotates at a relatively low rotary velocity.

According to an embodiment of the invention, the drive motor comprises a hydraulic motor. It is to be noted that also other kinds of motors may be used, for instance an electric motor or a pneumatic motor. It is also possible to drive the separating member and the spindle by means of a turbine.

According to an embodiment of the invention, the drive motor is provided inside the stationary casing. In such a way, the spindle is completely enclosed in the stationary casing. Thus there is no need for any passage of moving parts through the stationary casing. This is advantageous due to the high pressure prevailing in the separation space and being substantially higher than the surrounding pressure.

According to an embodiment of the invention, the centrifugal separator is configured to be provided in such a way that the axis of rotation extends substantially vertically.

According to an embodiment of the invention, the centrifugal separator is configured to be provided in such a way that the axis of rotation extends substantially horizontally.

According to an embodiment of the invention, the plant comprises a separating device provided on the gas conduit upstream the centrifugal separator. The separating device may comprise a scrubber.

The object is also achieved by the initially defined method defined in claim 14.
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