Performance assessment of an inline horizontal swirl tube cyclone for gas-liquid separation at high

Available online at www.sciencedirect.comJURALOFScienceDirectC}NATURAL GASCHEMISTRYEL SEVIERJournal of Natural Gas Chemistry 20(2011)565- -567www.elsevier.com/locate/jngcCommunicationPerformance assessment of an inline horizontal swirl tube cyclonefor gas-liquid separation at high pressureNurhayati Mellon*，Azmi M. ShariffDepartment of Chemical Engineering, Universi Teknologi PETRONAS, Bandar Sri Iskandar, Perak 31750, Malaysia[Manuscript received July 25, 2011; revised August 30, 2011 ]AbstractThe application of swirl tube cyclone for gas-liquid separation is atractive due to its small size and weight. However, very scarce informationon the performance of the swirl tube cyclonc especially at high operating pressure cmulating actual field condition was published in jourmals.Performance asessment was usually done at a low operating pressure using either air-water, air-fine particle mixtures or dense gas such as SF6.This paper flls the existing gaps and reports the initial findings on the performance asessment of a horizontal swirl tube cyclone for gas-liquidseparation operating at a flow rate of 5 MMSCFD at 40 -60 bar operating pressure.Key wordscompact separator; cyclone; swirl tube; natural gas separationThe increasing energy demand worldwide and the deple-an important parameter in influencing the droplet size andtion of economically accessible natural gas resources have ini-its distribution. Fluid with low interfacial tension tends totiated the motive to explore new reservoirs in the remote andform small droplets that are difficult to separate. Hence, thehostile environment. This demands a new technology portfo-proper test fluid is important to reflect the actual performancelio that gives space and weight savings, and superior separa-of the separator.tion performance and reliability with minimum maintenanceThe availability of data and analysis on the separationrequirement to ensure the production economically feasibleefficiency of the compact separator operating at a high pres-and attainable.sure condition using hydrocarbon fluid in the public domainTest on separation efficiency of the compact separator isis very scarce. The earliest published report found was onusually carried out using a mixture of air-water [1] or air-fineGasunie cyclone [3] operating at 40 bar using processed natu-solid particle [2] at low operating pressure. In certain cases,ral gas. Another study reported the application of SPLIT-FLOSF6 gases were used to simulate the flow and separation be-compact separator operating at 17 bar using three types of hy-havior of high pressure natural gas at low pressure due to itsdrocarbon fluid [4]. Chin et al. [5] reported the applicationhigh density at low pressure. Using this approach, the re-of the inline Degasser operating at 40 bar to reduce the bot-ported separation performance in certain cases is as high astleneck of existing separation equipment. Rawlins and Ting99.9%. However, the actual separation performance will vary[6] reported the results on the daily performance of an inlinefrom the test condition due to the difference in fluid physi-rotary separator operating at a pressure up to 77 bar.cal properties such as densities, liquid viscosities and inter-The most extensive study so far on compact separator wasfacial tension. A reduction in the density difference of thedone by Austrheim [7] for an axial flow cyclone installed ontwo components reduces the forces available for separation totop of an existing gas scrubber and acted as the final demistingoccur. Liquid viscosities affect the flow dynamics of fluid,device to increase the overall efficiency of the gas scrubber.which may as well influence the separation efficiency. InThe highest oergtinr nrasra etudied was 114 bar using liveterms of the gas-liquid separation, the interfacial tension isnatural gas中国煤化工ange of 0.070 -0.095●Coresponding author. Tel: +605-3687643; Fax: +605- 36561 76; E-mail: norhaye@petronas|YHCNM HGThis work was supported by the Universiti Teknologi PETRONAS.CopyrightO201 1, Dalian Institute of Chemical Physics, Chinese Academy of Scicnces. All rights reserved.doi:10.1016/S1003- 9953(10)60245-9566Nurhayati Mellon et al./ Journal of Natural Gas Chemistry Vol. 20No.6 2011vol% at liquid superficial velocity between 5.4 and 9.0 m/s.ter into the gas stream. The gas flow rate could be var-This study reports the initial findings on the performanceied from 5- 15 m/s via a multistage compressor capable ofof an inline horizontal swirl tube cyclone for the separationoperating up to 100 bar pressure. This allows the oper-of natural gas- water mixture operating at 40 to 60 bar. Theating condition of the test rig to be as close as possiblestudy was carried out in a pilot scale test rig as shown in .to the actual field condition. However, initial study onlyFigure 1 with volumetric flow up to 5 MMSCD and inletcovers liquid ratio of 1 vol% and maximum operating pressuremethane concentration up to 92 mol%. The water injec-up to 60 bar, similar to an existing field condition at offshoretion system was capable of injecting up to 4 vol% of wa-Malaysia.Feed top-upointFeed gasstorage母母OInline, swirltube separatorAdsorptionCompressorWatejectionWater.pointWaterfeed tankknock ouldrum.● Drain女pump甲甲甲Legend:P口Pressure indicatorF∞Flowmeter indicatorT口Temperature indicator.L - Level indicatordP - Differential pressure indicatorFigure 1. Simplified schematic diagram of the high pressure test rigFigure 2 shows that the separation performance of theThe poor performance at low gas superficial velocity and op-horizontal swirl tube cyclone is improved at higher operatingerating pressure of 40 bar can be related to the fact that thepressure, indicating the strong connection between the separa-energy produced by the gas stream is insufficient for optimumtion efficiency and the kinetic energy of the feed stream. Theseparation to occur.feed stream enters the horizontal swirl tube cyclone through aA quadratic trend was observed in terms of the separa-static vane, which forces the stream to move in circular mo-tion performance with respect to liquid flow rate for all rangetion, producing the required centrifugal force for separation.of operating pressure considered as shown in Figure 3. TheThe separation efficiency at 40 bar shows the lowest trend.separation efficiency first increases with liquid load, before00 r0山o分8t00966t;94 F■40ba”40bar， 50 bar92 t50 bar .s60ba60 bar中国煤化工0.000一YHCNMH Gu uputstus uy (m/s)Gas superficial velocity (m/s)Figure 3. The variation of separation eficiency with respect to liquidFigure 2. The variation of separation eficiency with respect to operating gassuperficial velocity at various pressures (gas velocity remains constant atvelocity at various pressures and water load of 1 vol%10 m/s)Joumal of Natural Gas Chenistry Vol. 20 No.62011567reaching a maximum point, and then starts to decrease. Theat higher liquid load as well as investigating the probability ofpositive trending shows that the liquid particles tend to coa-liquid entrainment through the separator.lesce with each other as the liquid load increases. This formslarger particle size, which is easier to be removed from theReferencesgas stream. After reaching the optimum point, the separa-tion efficiency starts to decrease. This observation may be[1] Movafaghian S, Jaua-Marturet J A, Mohan R S,' Shoham O,attributed to either the liquid entrainment through the separa-Kouba E. Int J Multiphase Flow, 2000, 26(6): 999tor or insufficient centrifugal force of the gas stream leading[2] Mondt E, van Kemenade E, Schook R. Chem Eng Technol, 2006,to poor separation. More detailed experiments are required29(3): 375to further analyze the relationship between poor performance[3] Oranje L. Oil GasJ, 1990, 88(4): 54and probability of liquid entrainment, especially at low oper-ating pressure.www.hudsonproducts.com/products/splitflo/dpb%204. _98.pdfIn conclusion, the performance of the horizontal swirl[5] Chin R w, Stanbridge D I, Schook R. In: SPE Annual Technicaltube cyclone is favourable at high operating pressure, whichConference and Exhibition, 2002may be due to higher dynamic pressure of the incoming gas[6] Rawlins H, Ting F In: Proceeding of 52nd Annual Laurancestream for incoming liquid load of 1 vol%. Further experimentReid Gas Conditioning Conference. Oklahoma, 2002is required to extensively evaluate the separation performance[7] Austrheim T. [PhD Thesis]. Bergen: University of Bergen, 2006中国煤化工MHCNM HG