Gas expansion device and method for expanding gas

Abstract

Gas expansion device for expanding a gas or a gas-liquid mixture, where the gas expansion device includes a gas expansion element with an inlet port for the gas to be expanded and an inlet pipe for the gas to be expanded. The inlet pipe is connected to the inlet port where the gas expansion device includes a first liquid injection point for the injection of liquid, where the first liquid injection point is at a position level with the inlet port or upstream from the inlet port.

Claims

1. A gas expansion device for expanding a gas or a gas-liquid mixture, whereby the gas expansion device comprises a gas expansion element with an inlet port for the gas to be expanded and an inlet pipe for the gas to be expanded, whereby the inlet pipe is connected to the inlet port, whereby the gas expansion device comprises a first liquid injection point for the injection of liquid, wherein the first liquid injection point is in the inlet pipe, and the expansion device is provided with a liquid separator for separating liquid from gas that is expanded in the gas expansion element, whereby the first liquid injection point is connected to a liquid outlet of the liquid separator, wherein the gas expansion device is provided with a supply pipe for the said liquid, whereby the first liquid injection point and a second liquid injection point are both connected to the supply pipe and wherein said means comprises a three-way valve with three connecting ports, whereby a first of the connecting ports is connected to the supply pipe and other connecting ports are each connected to one of the said liquid injection points.

2. The gas expansion device according to claim 1, wherein the liquid is oil.

3. The gas expansion device according to claim 2, wherein the gas expansion element is a double screw gas expansion element.

4. The gas expansion device according to claim 2, wherein the gas expansion device is provided with means for starting up and switching off a flow of the said liquid to the first liquid injection point.

5. The gas expansion device according to claim 1, wherein the gas expansion element is a double screw gas expansion element.

6. The gas expansion device according to claim 5, wherein the gas expansion device is provided with means for starting up and switching off a flow of the said liquid to the first liquid injection point.

7. The gas expansion device according to claim 1, wherein the gas expansion device is provided with means for starting up and switching off a flow of the said liquid to the first liquid injection point.

8. The gas expansion device according to claim 7, wherein the gas expansion device comprises a control unit to control the said means.

9. The gas expansion device according to claim 8, wherein the gas expansion element is coupled to a generator, such that the expansion element can drive the generator, whereby the control unit is connected in a data-transferring way to the generator.

10. The gas expansion device according to claim 1, wherein the second liquid injection point is configured to inject the said-liquid into the gas expansion element at a position downstream from the inlet port.

11. A method for expanding a gas in which this gas is guided by a gas expansion device according to claim 1, in which liquid is only injected via the first liquid injection point upon the detection of an exceptional operating condition, wherein said exceptional operating condition comprises a first threshold value of a torque being exceeded.

12. A method for expanding a gas in which this gas is guided by a gas expansion device according to claim 1, in which liquid is only injected via the first liquid injection point upon the detection of an exceptional operating condition, wherein said exceptional operating condition comprises a threshold value of a speed of rotation of the expansion element being exceeded.

13. A method for expanding a gas in which this gas is guided by a gas expansion device according to claim 1, in which liquid is only injected via the first liquid injection point upon the detection of an exceptional operating condition, wherein said exceptional operating condition comprises a threshold value of a generated electric power being exceeded.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) With the intention of better showing the characteristics of the invention, a preferred embodiment of a gas expansion device according to the invention and an accompanying method are described hereinafter by way of an example without any limiting nature, with reference to the accompanying drawings, wherein:

(2) FIG. 1 schematically shows a gas expansion device according to the invention;

(3) FIG. 2 illustrates the operating principle of the gas expansion device.

DETAILED DESCRIPTION OF THE INVENTION

(4) In this example the gas expansion device 1 is a double screw natural gas expansion device with oil injection to the expansion.

(5) However, the invention can be similarly applied to other types of volumetric expansion machines and other fluids than oil and natural gas.

(6) The gas expansion device 1, as shown in FIG. 1, comprises a double screw expansion element 2 and an electricity generator 3 that are mechanically coupled together.

(7) The expansion element 2 comprises an inlet port 4 for natural gas that is connected to an inlet pipe 5 for natural gas. A shut-off valve 6 is provided in the inlet pipe 5.

(8) An oil separator 7 for separating oil and gas is provided downstream from the expansion element 2. This has an outlet 8 for expanded gas and an outlet 9 for oil.

(9) The outlet 9 for oil is connected via an oil pump 11 to a first connecting port of a three-way valve 12.

(10) The two other connecting ports of the three-way valve 12 are connected to liquid injection points.

(11) More specifically this concerns a first liquid injection point 13 that is affixed just upstream from the inlet port 4 in the expansion element 2 or in the inlet pipe 5, and a second liquid injection point 14 that is affixed downstream from the inlet port 4.

(12) The first liquid injection point 13 hereby has an injection direction that is opposite to the flow direction of the gas.

(13) The gas expansion device 1 is further provided with an electronic control unit 15 that is connected in a data-transferring way to the shut-off valve 6, the three-way valve 12 and the generator 3.

(14) The operation of the gas expansion device 1 is simple and as follows.

(15) In the event of normal operation, i.e. when a higher torque than desired is not detected, the three-way valve 12 is set such that all oil is driven to the second liquid injection point 14. The operation is then analogous to a traditional gas expansion device.

(16) This is schematically shown in FIG. 2. The horizontal axis indicates the progress of the rotation of a rotor of the expansion element 2. The vertical axis indicates the volume of an expansion chamber.

(17) Hereby the inlet port 4 is open to the expansion chamber between the points indicated by A and B. Just after the inlet port 4 is closed, oil is injected via the second liquid injection point 14, schematically indicated by the interval from point C to point D.

(18) This is done in this way because, for a cost efficient application of a screw expansion device, the peripheral speed of the rotors must be as high as possible. Hence the oil injection to the inlet of the machine must be minimised to limit the friction losses that reduce an optimum filling of the expansion chamber. Hence, the oil injection is generally controlled such that the oil gets in the expansion chamber after the inlet port is closed, when the oil has no further effect on the filling process of the chamber with gas.

(19) In order to obtain a good effect of the injected oil, it is often injected at high pressure, immediately after the inlet port is closed. The oil pressure is generally higher than the gas pressure at the inlet of the piping, despite the fact that the chamber pressure is reduced immediately after the inlet port closes.

(20) In a first exceptional operating condition, i.e. if a higher than desired torque is measured or calculated in the generator 3 by the control unit 15, the three-way valve 12 is set such that all oil flows to the first liquid injection point 13.

(21) This has two effects. The first effect is that upon injection, the oil experiences a narrowing and change of direction due to the gas flowing past so that the effective inlet pressure of the gas is reduced. The second effect is that the oil flows in the expansion chamber of the expansion element, so that there is less room for the gas. With a high speed of rotation in the first effect will significantly gain the upper hand and at a low speed of rotation the second effect will significantly gain the upper hand.

(22) In both cases the torque is reduced so that an overload of the gas expansion device 1 is prevented.

(23) In a second exceptional operating condition, upon detection of an emergency situation, the three-way valve 12 is also set such that all oil flows to the first liquid injection point 13, with the above-mentioned effects, and additionally the shut-off valve 6 is closed by the control unit 15, so that the gas expansion device 1 quickly comes to a stop in a way that does not cause any damage to the gas expansion device 1.

(24) In the above, downstream and upstream refer to the flow direction of the gas.

(25) The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but a gas expansion device and method according to the invention can be realised in all kinds of forms and dimensions without departing from the scope of the invention.