Slugcatcher

Slug Catcher is the name of a unit in the gas refinery or petroleum industry in which slugs at the outlet of pipelines are collected or caught. A slug is a large quantity of a liquid that exists in a multi-phase pipeline.

Slugs

Pipelines that transport both gas and liquids together, known as two-phase flow, can operate in a flow regime known as slugging flow or slug flow. Under the influence of gravity, liquids will tend to settle on the bottom of the pipeline, while the gases occupy the top section of the pipeline. Under certain operating conditions gas and liquid are not evenly distributed throughout the pipeline, but travel as large plugs with mostly liquids or mostly gases through the pipeline. These large plugs are called slugs.

Slugs exiting the pipeline can overload the gas/liquid handling capacity of the plant at the pipeline outlet, as they are often produced at a much larger rate than the equipment is designed for.

Slugs can be generated by different mechanisms in a pipeline:

  • Terrain slugging is caused by the elevations in the pipeline, which follows the ground elevation or the sea bed. Liquid can accumulate at a low point of the pipeline until sufficient pressure builds up behind it. Once the liquid is pushed out of the low point, it can form a slug.
  • Hydrodynamic slugging is caused by gas flowing at a fast rate over a slower flowing liquid phase. The gas will form waves on the liquid surface, which may grow to bridge the whole cross-section of the line. This creates a blockage on the gas flow, which travels as a slug through the line.
  • Riser-based slugging, also known as severe slugging, is associated with the pipeline risers often found in offshore oil production facilities.[1] Liquids accumulate at the bottom of the riser until sufficient pressure is generated behind it to push the liquids over the top of the riser, overcoming the static head. Behind this slug of liquid follows a slug of gas, until sufficient liquids have accumulated at the bottom to form a new liquid slug.
  • Pigging slugs are caused by pigging operations in the pipeline. The pig is designed to push all or most of the liquids contents of the pipeline to the outlet. This intentionally creates a liquid slug.

Slugs formed by terrain slugging, hydrodynamic slugging or riser-based slugging are periodical in nature. Whether a slug is able to reach the outlet of the pipeline depends on the rate at which liquids are added to the slug at the front (i.e. in the direction of flow) and the rate at which liquids leave the slug at the back. Some slugs will grow as they travel the pipeline, while others are damped and disappear before reaching the outlet of the pipeline.

Purpose of the slug catcher

A slug catcher is a vessel with sufficient buffer volume to store the largest slugs expected from the upstream system. The slug catcher is located between the outlet of the pipeline and the processing equipment. The buffered liquids can be drained to the processing equipment at a much slower rate to prevent overloading the system. As slugs are a periodical phenomenon, the slug catcher should be emptied before the next slug arrives

Slug catchers can be used continuously or on-demand. A slug catcher permanently connected to the pipeline will buffer all production, including the slugs, before it is sent to the gas and liquid handling facilities. This is used for difficult to predict slugging behaviour found in terrain slugging, hydrodynamic slugging or riser-based slugging. Alternatively, the slug catcher can be bypassed in normal operation and be brought online when a slug is expected, usually during pigging operations. An advantage of this set-up is that inspection and maintenance on the slug catcher can be done without interrupting the normal operation.

Slug catcher types

Finger type slug catcher at the Qadirpur Gas Field

Slug catchers are designed in different forms,

  • A vessel type slug catcher is essentially a conventional vessel. This type is simple in design and maintenance.
  • A finger type slug catcher consists of several long pieces of pipe ('fingers'), which together form the buffer volume. The advantage of this type of slug catcher is that pipe segments are simpler to design for high pressures, which are often encountered in pipeline systems, than a large vessel. A disadvantage is that its footprint can become excessively large. An example of a large finger-type slug catcher can be seen in Den Helder, The Netherlands, using Google Maps. The incoming pipeline containing gas and liquid is routed to the inlet of the slug catcher. The inlet comprises a large diameter manifold and splitter section where the gas/liquid is divided into 2, 4, 6 or 8 horizontal pipes of 24, 30, 36, 42 or 48-inch diameter.[2] Gas/liquid separation takes place in these pipes with the liquid dropping to the bottom of the pipes with the gas above. Liquid-free gas is drawn off at the far end of the separation pipes by risers at the top of the pipes. The risers are manifolded together and the gas is routed to further treatment. From the base of the separation pipes liquids flow through down-comers into a further, lower array of horizontal pipes.[3] These pipes slope down away from the inlet, they can typically be 100 to 250 metres in length.[4] The initial section of the lower pipes provides for further gas/liquid separation and the far end provides a buffer storage volume for the liquids which are drawn off at a steady rate for further treatment.[3] The operating pressure in the slug catcher is maintained by a pressure controller and pressure control valve in the gas outlet. The liquid level in the storage end of the slug catcher is controlled by a liquid level controller and level control valve in the liquid outlet.
  • A Parking Loop slug catcher combines features of the vessel and finger types. The Gas/Liquid Separation occurs in the Vessel, while the Liquid is stored in the parking loop shaped fingers.
  • A Hybrid Slug Catcher combines the high efficiency of a vessel separator and the large storage volume of a harp slug catcher.

Slug catcher locations

Finger type slug catchers are large in size and can be observed on satellite images. The following table is generated using Google Earth and gives an overview of slug catchers in the world. The slug catcher length is determined using measurement tool in Google Earth and is estimated to be +/- 5 meters accurate.

Country Name Remark Bottles Length [m] Latitude Longitude
AR Rio Cullen Slug Catcher 4 240 -52.90317 -68.35208
AU Gorgon Slug Catcher 1 12 205 -20.78881 115.44490
AU Gorgon Slug Catcher 2 14 110 -20.78884 115.44423
AU Karratha Slug Catcher 1 Volume 5000m3? 14 345 -20.58892 116.77609
AU Karratha Slug Catcher 2 8 225 -20.58565 116.77904
AU Karratha Slug Catcher 3 16 315 -20.61163 116.76680
AU Wheatstone Slug Catcher Wheatstone LNG Gas plant 24 300 -21.69308 114.99779
AZ Sangachal Slug Catcher 1 Shan Deniz 1 sub sea pipeline 12 130 40.18900 49.46417
AZ Sangachal Slug Catcher 2 Shan Deniz 2 sub sea pipeline 8 130 40.19380 49.47019
BN Slug Catcher 1 8 70 4.66855 114.45955
BN Slug Catcher 2 6 135 4.66821 114.46046
BN Slug Catcher 3 18 150 4.67457 114.46744
CN Zhuhai Gaolan Slug Catcher 28 165 21.88548 113.26463
DK Slug catcher Nybro 4 115 55.67212 8.36611
EG Idku Slug Catcher 1 12 103 31.35769 30.32672
EG Idku Slug Catcher 2 6 170 31.36198 30.33079
EG Idku Slug Catcher 3 6 125 31.36508 30.33215
EG Idku Slug Catcher 4 12 88 31.37041 30.32940
EG Idku Slug Catcher 5 12 103 31.36082 30.32693
EG Slug Catcher 1 4 115 31.34158 32.10563
EG Slug Catcher 2 8 215 31.34152 32.10544
EG Zohr Slug Catcher 1 4 130 31.32071 32.14526
EG Zohr Slug Catcher 2 4 130 31.32055 32.14516
EG Zohr Slug Catcher 3 4 130 31.31924 32.14787
EG Zohr Slug Catcher 4 4 130 31.31909 32.14777
IE Bellenaboy Bridge Slug Catcher 95 54.23347 -9.74356
IE Bellenaboy Bridge Slug Catcher 95 54.23347 -9.74356
IL Sharon Udasin Slug Catcher 4 70 31.84945 34.67977
IR Slug Catcher Gas pipeline to Turkey 4 110 39.39665 44.39614
IR Slug Catcher 1 27.69140 52.24349
IR Slug Catcher 2 27.69140 52.24349
IR Slug Catcher 3 27.68851 52.25925
IR Slug Catcher 4 27.68851 52.25925
IR Slug Catcher 5 27.71659 52.20021
IR Slug Catcher 6 27.71659 52.20021
IR Slug Catcher 7 27.72653 52.17832
IR Slug Catcher 8 27.72653 52.17832
IR Slug Catcher 9 27.72653 52.17832
IT Slug Catcher 1 4 40 37.66730 12.53984
IT Slug Catcher 2 4 40 37.66730 12.53984
IT Slug Catcher 3 4 40 37.66730 12.53984
LY Slug Catcher 1 32.85891 12.24242
LY Slug Catcher 2 32.85891 12.24242
MO Tamane Slug Catcher -21.74701 35.05903
MY Bintulu Slug Catcher 1 3.28802 113.07969
MY Bintulu Slug Catcher 2 3.29392 113.08913
MY Bintulu Slug Catcher 3 3.29329 113.08778
MY Bintulu Slug Catcher 4 3.28757 113.07892
MY Kimanis Slug Catcher 1 8 205 5.64175 115.88684
MY Kimanis Slug Catcher 2 8 205 5.64100 115.88684
NG Bonny GTS-2/4 4.42326 7.15990
NG Bonny NLNG GTS-1 4.42411 7.15917
NG Bonny OGGS GTS-3 4.42405 7.16031
NG Kwale Kwale AHL Gas plant 5.72552 6.39195
NL Harlingen 53.18861 5.43573
NL NAM 52.92028 4.79385
NL NAM 52.92028 4.79385
NO Hammerfest Slug Catcher 1 8 95 70.68409 23.59074
NO Hammerfest Slug Catcher 2 8 95 70.68199 23.58454
NO Nyhamna Slug Catcher 1 Ormen Lange gas field 14 160 62.84851 6.93893
NO Nyhamna Slug Catcher 2 Ormen Lange gas field 14 160 62.84805 6.94050
PE Kinteroni Field Slug Catcher -11.83780 -72.94533
PK Dhodak Plant Slug Catcher 30.81642 70.48968
PK Kunnar Slug Catcher 1 25.38369 68.58074
PK Kunnar Slug Catcher 2 25.38369 68.58074
PK Qadirpur Slug Catcher 28.05473 69.36721
QA Slug Catcher 1 25.88965 51.53810
QA Slug Catcher 2 25.88771 51.54215
QA Slug Catcher 3 25.88644 51.54472
TM Slug catcher Dragon Oil Dragon Oil 6 110 39.40117 53.18819
TM Slug cather 4 33 38.51432 54.21043
TM Slug catcher 1 Petronas Petronas Carigali GTPOGT 8 120 40.16789 52.76912
TM Slug catcher 2 Petronas Petronas Carigali GTPOGT 10 230 40.16318 52.77123
TR Blue Stream Slug Catcher Blue stream 4 130 41.35985 36.71042
UE Habshan 5 plant Slug Catcher 23.90766 53.71354
UE Habshan Slug Catcher 1 GASCO Habsan plant 23.83734 53.65407
UE Habshan Slug Catcher 2 GASCO Habsan plant 23.83704 53.65426
UA Zirku Island Slug Catcher 24.87072 53.07181
UK Bacton Slug Catchers 52.85984 1.46191
UK Easington Slug Catcher 53.36225 0.23492
UK Hull Slug Catcher 53.66180 0.10998
US Canyon Midstream Cryoplant Slug Catcher 36.43756 -99.15882
US Canyon Redcliff Plant Slug Catcher Volume 2500 bbl 6 135 36.21184 -99.15533
US Slug Catcher 31.27392 -103.10827

References

  1. Eaton, A. (2015). "Post-installed fiber optic pressure sensors on subsea production risers for severe slugging control" (PDF). OMAE 2015 Proceedings, St. John's, Canada.
  2. "Science direct slug catcher". science direct. Retrieved 29 September 2020.
  3. "Gas processing and LNG". Gas processing news. Retrieved 29 September 2020.
  4. "Gas terminal Bacton Norfolk UK". Google Maps. Retrieved 29 September 2020.

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