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(11) | EP 0 105 593 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Dispersing liquid slugs in gas pipelines |
| (57) Liquid slugs in gas pipelines (1) are dispersed by injecting gas into the liquid,
producing a compressible gas-liquid mixture. Placed upstream of a compressor station
(2), the present invention can be used to protect valves (4) and separators (3) from
the destructive effect of liquid slugs. |
[0001] This invention relates to dispersing liquid slugs in gas pipelines in order to reduce the destructive effect on components in the pipeline.
[0002] In gas pipelines, condensed gas and water form a liquid fraction which can, under certain conditions, form slugs that are carried along by the gas at the velocity of the gas. The impact of such slugs can damage components in the pipeline, such as separators or valves as found at a compressor station.
[0003] It is an object of the present invention to enable liquid slugs to be dispersed and thereby reduce the destructive effect thereof.
[0004] The present invention provides an apparatus for dispersing liquid slugs in a gas pipeline comprising a gas emitting device communicating with said pipeline, said device having a plurality of outlets for emitting gas, and means for connecting said chamber with a source of gas.
[0005] The invention further provides a method of dispersing liquid slugs in a gas pipeline comprising introducing a gas into the liquid to form a gas-liquid mixture.
[0006] It has been found that, by injecting gas into a gas pipeline upstream of a component or components to be protected, liquid slugs in the pipeline can be dispersed. The gas introduction generates bubbles and breaks up the slugged flow to form a compressible gas-liquid mixture, substantially reducing the potential for damaging components in the pipeline.
[0007] By way of example, embodiments of the invention will be described with reference to the accompanying drawings, in which:
Figure 1 is a schematic diagram illustrating a compressor station incorporating the present invention.
Figure 2 is an enlarged cross-sectional view showing details of one form of gas emitting device mounted in a gas pipeline.
Figure 3 is a cross-sectional view of another form of gas emitting device mounted in a gas pipeline.
Figure 4 is a partly sectional view of another form of the gas emitting device associated with a gas pipeline.
Figure 5 is a sectional view taken at 5-5 of Figure 4.
[0008] Referring to Figure 1, a typical compressor station for a gas pipeline 1 includes a turbo-compressor 2, a separator 3 and a valve 4. A gas emitting device 5 is positioned upstream of the components to be protected, namely the valve 4 and separator 3. As shown, gas is supplied to the gas emitting device 5 from the turbo-compressor outlet by means of a suitable conduit 6.
[0009] Figure 2 shows the gas emitting device 5 and the effect on liquid slugs in the pipeline 1. One slug 10 is shown approaching the gas emitting device 5 while another slug is being dispersed in region 11. The gas emitting device 5 comprises a porous chamber defining a plurality of outlets 7. Each outlet or pore 7 provides a nucleation site for a bubble in the liquid. The emitted bubbles break up the incompressible liquid slug to form a compressible gas-liquid mixture.
[0010] After formation, the bubbles begin to coalesce into large bubbles and flow will subsequently revert to separated gas and liquid, and again be suseptible to slugging. In order to prolong the duration of compressible gas-liquid mixture mode of flow, the pores should be as small and numerous as practical. The outlet diameter should be less than 1% of the pipeline diameter.
[0011] Since flow will eventually revert to the slugging mode, the distance the gas emitting device can be placed upstream of the components to be protected is limited. It appears that protection against slugging can be provided for a distance up to 60 pipeline diameters, but preferably the emitting device should be placed within 30 diameters of the component or components to be protected.
[0012] The gas emitting device and outlets may take various forms. In the embodiment of figure 2, the emitting device may be formed of woven stainless steel wire mesh or grid, or sintered stainless steel. With such construction, the outlet or pore size can be made less than 50 pm.
[0013] Figure 3 shows an alternate embodiment for the gas emitting device, in the form of a sparger.tube 15 provided with outlets 17 and supplied with gas through inlet 16.
[0014] Figures 4 and 5 illustrate another embodiment of the gas emitting device. Gas is introduced into the pipeline 20 through outlets 27 of a perforated section 25 of the pipeline. The perforated section 25 is enclosed by manifold 28 to which gas is supplied through inlet 26.
[0015] With reference to figure 1, gas may be supplied to the emitting device 5 on a continuous basis, for example, when the incidence of slugging is high, or only when a slug is approaching. For the latter, a slug detector 12 is provided a suitable distance upstream. An actuator 14, in response to a signal from the detector 12, opens the normally closed valve 13 when a slug is detected. The detector 12 may take various forms such as a conductance probe, acoustic sensor or radio-frequency densitometer.
[0016] Although even small amounts of gas introduced by the gas emitting device provides some attenuation of the distructive effects of slugs, it appears that at least 5X of the gas flow rate is required to provide a significant degree of protection. On the other hand, it appears impractical to exceed 25X of the gas flow rate, since little additional protection against slugs is provided, and because additional gas introduced increases pressure losses that reduce the overall efficiency of the compressor station. The optimum amount of gas introduction appears to be in the range of 15 to 25X of the gas flow rate. The actual amount of gas introduced in a particular application will depend on various factors such as the degree of protection desired, or whether the system will operate in a continuous mode, or on an intermittent basis with a slug detector as described above.
1. An apparatus for dispersing liquid slugs in a gas pipeline comprising a gas emitting
device communicating with said pipeline, said device having a plurality of outlets
for emitting gas, and means for connecting said chamber with a source of gas.
2. The apparatus of claim 1 wherein the outlets'of the gas emitting device have diameters
less than 1% of the pipeline diameter.
3. The apparatus of claim 1 wherein the outlets have a diameter less than 50 µm.
4. The apparatus of claim 1 wherein said gas emitting device comprises a porous chamber
defining the outlets for the gas.
5. The apparatus of claim 1 wherein said gas emitting device is disposed within 60
pipeline diameters of a component to be protected.
6. The apparatus of claim 1 wherein said gas emitting device is disposed within 30
pipeline diameters of a component to be protected.
7. The apparatus of claim 1 wherein the length of the gas emitting device is not less
than 5 times the diameter of the pipeline.
8. A method of dispersing liquid slugs in a gas pipeline comprising introducing a
gas into the liquid to form a gas-liquid mixture.
9. The method of claim 8 wherein the gas is introduced within 60 pipeline diameters
of a component to be protected.
10. The method of claim 8 wherein the gas is introduced within 30 pipeline diameters
of a component to be protected.
11. The method of claim 8 wherein gas is introduced at a rate of from 5 to 25X of
the gas flow rate in the pipeline.
12. The method of claim 8 wherein gas is introduced at a rate of from 15 to 25X of
the gas flow rate in the pipeline.