A slugcatcher is a unit in a gas refinery (or other aspect of the petroleum industry) in which "slugs" are collected or caught at the outlet of pipelines. 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. 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 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. 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. These pipes slope down away from the inlet, they can typically be 100 to 250 metres in length. 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. 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. +CountryNameRemarkBottlesLength [m]LatitudeLongitudeARRio Cullen Slug Catcher4240 -52.90317 -68.35208AUGorgon Slug Catcher 112205 -20.78881115.44490AUGorgon Slug Catcher 214110 -20.78884115.44423AUKarratha Slug Catcher 1Volume 5000m3?14345 -20.58892116.77609AUKarratha Slug Catcher 28225 -20.58565116.77904AUKarratha Slug Catcher 316315 -20.61163116.76680AUWheatstone Slug CatcherWheatstone LNG Gas plant24300 -21.69308114.99779AZSangachal Slug Catcher 1Shan Deniz 1 sub sea pipeline1213040.1890049.46417AZSangachal Slug Catcher 2Shan Deniz 2 sub sea pipeline813040.1938049.47019BNSlug Catcher 18704.66855114.45955BNSlug Catcher 261354.66821114.46046BNSlug Catcher 3181504.67457114.46744CNZhuhai Gaolan Slug Catcher2816521.88548113.26463DKSlug catcher Nybro411555.672128.36611EGIdku Slug Catcher 11210331.3576930.32672EGIdku Slug Catcher 2617031.3619830.33079EGIdku Slug Catcher 3612531.3650830.33215EGIdku Slug Catcher 4128831.3704130.32940EGIdku Slug Catcher 51210331.3608230.32693EGSlug Catcher 1411531.3415832.10563EGSlug Catcher 2821531.3415232.10544EGZohr Slug Catcher 1413031.3207132.14526EGZohr Slug Catcher 2413031.3205532.14516EGZohr Slug Catcher 3413031.3192432.14787EGZohr Slug Catcher 4413031.3190932.14777IEBellenaboy Bridge Slug Catcher9554.23347 -9.74356IEBellenaboy Bridge Slug Catcher9554.23347 -9.74356ILSharon Udasin Slug Catcher47031.8494534.67977IRSlug CatcherGas pipeline to Turkey411039.3966544.39614IRSlug Catcher 1637027.6914052.24349IRSlug Catcher 2637027.6914052.24349IRSlug Catcher 3637027.6885152.25925IRSlug Catcher 4637027.6885152.25925IRSlug Catcher 5637027.7165952.20021IRSlug Catcher 6637027.7165952.20021IRSlug Catcher 7637027.7265352.17832IRSlug Catcher 8637027.7265352.17832IRSlug Catcher 9637027.7265352.17832ITSlug Catcher 144037.6673012.53984ITSlug Catcher 244037.6673012.53984ITSlug Catcher 344037.6673012.53984LYSlug Catcher 132.8589112.24242LYSlug Catcher 232.8589112.24242MOTamane Slug Catcher -21.7470135.05903MYBintulu Slug Catcher 13.28802113.07969MYBintulu Slug Catcher 23.29392113.08913MYBintulu Slug Catcher 33.29329113.08778MYBintulu Slug Catcher 43.28757113.07892MYKimanis Slug Catcher 182055.64175115.88684MYKimanis Slug Catcher 282055.64100115.88684NGBonny GTS-2/44.423267.15990NGBonny NLNG GTS-14.424117.15917NGBonny OGGS GTS-34.424057.16031NGKwaleKwale AHL Gas plant5.725526.39195NLHarlingen53.188615.43573NLNAM52.920284.79385NLNAM52.920284.79385NOHammerfest Slug Catcher 189570.6840923.59074NOHammerfest Slug Catcher 289570.6819923.58454NONyhamna Slug Catcher 1 Ormen Lange gas field1416062.848516.93893NONyhamna Slug Catcher 2 Ormen Lange gas field1416062.848056.94050PEKinteroni Field Slug Catcher -11.83780 -72.94533PKDhodak Plant Slug Catcher30.8164270.48968PKKunnar Slug Catcher 125.3836968.58074PKKunnar Slug Catcher 225.3836968.58074PKQadirpur Slug Catcher28.0547369.36721QASlug Catcher 125.8896551.53810QASlug Catcher 225.8877151.54215QASlug Catcher 325.8864451.54472TMSlug catcher Dragon OilDragon Oil611039.4011753.18819TMSlug cather43338.5143254.21043TMSlug catcher 1 PetronasPetronas Carigali GTPOGT812040.1678952.76912TMSlug catcher 2 PetronasPetronas Carigali GTPOGT1023040.1631852.77123TRBlue Stream Slug CatcherBlue stream413041.3598536.71042UEHabshan 5 plant Slug Catcher23.9076653.71354UEHabshan Slug Catcher 1GASCO Habsan plant23.8373453.65407UEHabshan Slug Catcher 2GASCO Habsan plant23.8370453.65426UAZirku Island Slug Catcher24.8707253.07181UKBacton Slug Catchers52.859841.46191UKEasington Slug Catcher53.362250.23492UKHull Slug Catcher53.661800.10998USCanyon Midstream Cryoplant Slug Catcher36.43756 -99.15882USCanyon Redcliff Plant Slug CatcherVolume 2500 bbl613536.21184 -99.15533USSlug Catcher31.27392 -103.10827
References
http://www.glossary.oilfield.slb.com/en/Terms/s/slug_flow.aspx