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Liquid-Liquid Separation Technology Optimum Cost-Effectiveness of the Process

Liquid-Liquid Separation Technology Optimum Cost-Effectiveness of the Process

P ROCESSING A water wash has been avoids the need for thermal regeneration found that effectively recov- of the solvent. ers the solvent in the IFPEX-1 offers a number of benefits IFPEXOL process by pulling over glycol technology, including more dissolved into compact design with only one contactor Processing water for subsequent tower (good for offshore locations), no removal. required heating, no foaming in contac- The water-solvent mixture and hydro- tors, reduced corrosion and solvent degra- have a low interfacial tension that dation, and the ability to locate the cold often forms a stable emulsion and is diffi- section at a separate treating location. cult to separate by conventional settling Fig. 1 shows a schematic of IFPEX–1, processes. Effective separation of this emulsion and reuse of the methanol is critical in achieving Liquid-liquid separation technology optimum cost-effectiveness of the process. IFPEXOL is a cryogenic liquids-sepa- including the location for the advanced improves IFPEXOL ration process that uses methanol for coalescer technology. dew point suppression instead of glycol. The inlet is first split into process economics But the solvent losses resulting from the two streams. One, consisting of 50% of dissolution of methanol in the generat- the total flow, passes through the IFPEX-1 Peter Hampton Petro-Canada Oil & Gas ed liquids can be very contactor tower against rich methanol, Calgary costly. while the remainder of the gas stream bypasses the tower. Thierry Darde The process The bypass stream and the IFPEX-1 Pall Europe Developed by Institut Francais du contactor outlet stream are recombined, Saint Germain-En-Laye, France Petrole, IFPEXOL is capable of dehydrating makeup methanol is injected, and the gas Robert James (IFPEX-1) and sweetening (IFPEX-2) stream is then fed to a chiller. Pall (Canada) Ltd. sweet and sour natural gas and liquid Condensation of the water phase and Mississauga, Ont. streams.1 2 heavier occurs during pas- The IFPEX-1 process employs methanol sage through the chiller. Thomas H.Wines Pall Corp. instead of the commonly used triethylene The liquids are separated in the three- East Hills, NY glycol (TEG) to dehydrate the gas.This phase, low-temperature separator.

IFXPEX-1 PROCESS* Fig. 1

Make up methanol Cold process

Cold dry gas

Cold separator

Condensed hydrocarbons

Methanol-water Inlet raw wet gas Pall Aqua Sep liq.-liq. coalescer Pall prefilter

Water injection Water/LPG static mixer LPG product to storage

Recovered water Methanol-water *With LPG water wash and liquid/liquid coalescer.

Reprinted with revisions, from the April 16, 2001 edition of OIL & GAS JOURNAL Copyright 2001 by PennWell Corporation P ROCESSING Gas flows to sales, while liquid hydro- be successful with conventional separation Stages are further processed to produce devices, including gravity separators or The liquid-liquid coalescing system LPG with a defined specification. mesh pad coalescers. operates in three stages: separation of The heavy methanol, rich aqueous When the drop size created is in the solids, coalescence, and separation of coa- phase (75% MeOH) is recycled to the top micron size range, a stable emulsion lesced drops: of the IFPEX-1 contactor. As the gas rises forms that greatly enhances the extraction • Separation of solids. Solids can in- in the contactor, the methanol is vapor- process by increasing the contacting sur- crease the stability of an emulsion, and re- ized and stripped from the methanol-rich face area, allowing for a smaller overall moving solids can make coalescing easier. aqueous phase so that almost pure water extraction system. Generally, this step can be achieved by is collected from the bottom of the The difficulty then lies in the separa- a separate cartridge filter system or by a IFPEX-1 contactor.The methanol is recov- tion of the stable emulsion, and this can regenerable backwash filter system for ered by condensation in the cold process be accomplished with advanced poly- high levels of solids. In addition, the filtra- section. meric liquid-liquid coalescer technolo- tion stage protects the coalescer and The LPG can be further treated for gy. increases service life. additional methanol recovery with a mix • Coalescence. In the next step in the tank and water-wash stage to recover sol- Advanced technology process, primary coalescence, the pore uble and carryover methanol from the Traditional liquid-liquid coalescers have dimensions begin with a very fine struc- LPG. used glass fiber medium, which works ture and then become more open to allow A high-efficiency polymeric liquid-liq- well for emulsions that have interfacial for void space for the coalescing droplets. uid coalescer system is downstream of the tensions greater than 20 dyne/cm and for In the primary coalescence zone, the water-wash stage to separate water- systems that have neutral water as the dis- inlet droplet dispersion containing fine methanol-LPG emulsions formed in the persed phase. droplets in the size range of 0.2 to 50 µm washing stage. Pall Corp. has developed new coalescer is transformed into a suspension of The expected solubility of methanol media constructed with formulated poly- enlarged droplets in the size range of 500- in the LPG stream is 2,000 ppm under mers and fluoropolymers that are effective 5,000 µm. normal process conditions, and the for emulsions having interfacial tensions The coalescence mechanism involves methanol content can be much higher as low as 0.5 dyne/cm and for harsh adsorption of droplets to the coalescer when free methanol and water are chemical environments.3 4 fibers, followed by translation along the emulsified. Additional water extraction The Pall liquid-liquid coalescer has fibers, and collisions at the junctures can be performed to recover this produced clean with between fibers.The collisions result in the methanol. sodium levels less than 0.5 mg/l. and droplets merging or coalescing, and the The methanol-recovery process free water concentrations of less than15 viscous drag of the bulk fluid stream then involves the mixing of water with the ppm (vol). causes the enlarged drops to disengage methanol-rich LPG stream to allow for Fig. 2 shows a Pall AquaSep high-effi- from the fibers. sufficient mass transfer or extraction fol- ciency liquid-liquid coalescer in the verti- This process is repeated several times lowed by a final separation stage that cal configuration. through coalescer depth until the large breaks the immiscible mixture into an The system consists of a prefilter sec- coalesced drops exit the coalescer medium. organic and aqueous phase. tion followed by a vertical stacked coa- The necessary condition that droplet- Once the methanol-extract water lescer-separator cartridge stage that is a fiber adsorption occur for coalescing has stream is separated, it is injected into the patented design of Pall. been supported by a number of sources.5 6 IFPEX-1 contactor. Based on solubility The LPG and methanol-water emul- • Separation of coalesced droplets. Once limits of the natural gas feeding the sion first enters at the top of the coa- coalesced, the droplets are now assumed tower, the methanol is absorbed from the lescer housing and flows from the inside to be as large as possible for the given water into the gas while the stripped of the coalescer cartridges radially out- flow conditions.The separation stage is water is collected from the bottom of the ward, causing the enlargement or coa- achieved with hydrophobic separator car- tower. lescing of the inlet dispersion into large tridges that provide an effective barrier to It is possible that stable emulsions can droplets at the outlet of the coalescer car- aqueous coalesced drops but allow the be formed, depending on how the water- tridges. LPG to pass through them. wash stream is contacted with the The aqueous coalesced drops and LPG The methanol-water coalesced drops methanol-rich LPG. then flow axially downward where the are carried with the downward convective Mixing tanks, contactor columns, or flow then goes from the outside of the flow of the LPG and accumulate in a lower static in-line mixing devices can be used separator to the inside. collection sump.The purified LPG passes to increase the surface area of contact The large coalesced drops are repelled through the separators and exits at the between the two phases and enhance by the separators and collected in the bot- bottom of the housing.The methanol- extraction. tom sump. water in the collection sump can be man- Often it is necessary to keep the size of The purified LPG passes through the ually drained periodically or equipped the emulsified drops in the hundreds-of- separators and exits at the bottom of the with an automatic level control and drain micron size range so that separation can housing. system. Emulsion formation, stability cially detrimental to conventional glass Brazeu River gas plant Emulsion formation and stability can fiber coalescers.7 The surfactants can Petro-Canada Oil & Gas operates the be greatly affected by the addition of adsorb at the solid-liquid interface (coa- Brazeau River gas plant in .The methanol. lescer fibers) or at the liquid/liquid inter- plant processes a water-rich natural gas Methanol acts as a surfactant and face (water/oil). flow of 6,100 kg/hr (70 MMscfd) and a increases the solubility of the water in the When surfactants concentrate on the water-rich LPG flow of 38.5 kg/hr. LPG, thereby bridging the gap between coalescer fibers, this is known as “disarm- The IFPEX-1 process was selected so the two immiscible fluids (LPG and water) ing,” and the coalescer fibers are shielded that the existing plant infrastructure could and consequently strongly reduces the from the passing aqueous droplets.This be utilized, even though the capacity of interfacial tension. results in poor separation efficiency. the new facility was 300% larger than the Pall Corp. conducted a study with pen- Generally, the disarming phenomenon previous facility that utilized a convention- tane on the effect of methanol concentra- does not occur unless the interfacial ten- al glycol configuration. tion in water on the interfacial tension sion between the water and is less The initial start-up of the IFPEX unit (IFT).The study substituted for than 20 dyne/cm. Disarming was not went smoothly. Consumption of methanol LPG (propane- mixture) because it observed when specially formulated poly- was about 45 kg/hr, before the methanol- remains a liquid at atmospheric pressure. meric coalescer medium was used instead recovery technology was brought on-line. Fig. 3 plots the IFT data showing the of glass fiber.3 4 This methanol was leaving the system as a dramatic effect of increasing the methanol The coalescing performance of a poly- vapor in the natural gas sales stream and content on lowering the IFT, thereby mak- meric medium can be greatly enhanced by also in the LPG mix product due to solu- ing it more difficult to separate emulsions. modification of surface properties, which bility and entrainment caused by ineffi- These results were generated with high- cannot be accomplished with glass fiber cient operation of the low-temperature purity chemicals and water. For real world medium. separator. systems, the IFT values will be even lower. Surfactants can also concentrate at the The IFPEX-1 process for the Brazeau In addition to methanol, surfactants are water-fuel interface, and this can lead to River gas plant was expected to have a present naturally in crude oil and, as a very small droplets and stable emulsions. methanol solubility of about 2,000 ppm result, can make their way into refined Separating these types of emulsions in the LPG based on IFPEX operating petroleum products. Well-treating fluids requires special consideration applied to experience elsewhere. and corrosion inhibitors used in gas the pore size and distribution in the coa- During the design phase of the Brazeau pipelines can also act as emulsifiers. lescer medium to intercept and coalesce IFPEX unit, Petro-Canada anticipated the Petroleum naphtha sulfonates are espe- the small droplets. need for reduced methanol consumption to reduce the variable operating cost of the facility. Petro-Canada designed and IGH-EFFICIENCY, LIQUID-LIQUID COALESCER Fig. 2 H added a methanol-recovery unit to the process for this reason. Key to the success of the unit was installation of a high-efficiency polymeric liquid-liquid coalescer system to separate the emulsified methanol–water phase Prefilter from the LPG mix product. Coalescer Petro-Canada determined that a water wash could effectively be used to extract the methanol in solution with the LPG mix. A simple water injector and mixer were used to raise the water content in the LPG mix to about 10%. Separator Subsequent removal of the water- methanol mixture would purify the LPG mix, but a viable technology would be needed to remove essentially all of the LPG outlet free water-methanol mixture from the LPG mix to meet product specification. Conventional glass fiber liquid-liquid coalescing technology is known not to LPG/water-methanol inlet work under these circumstances because of the low interfacial tension of the water- Methanol-water outlet methanol mixture in the LPG. Petro-Canada utilized high-efficiency polymeric P ROCESSING

was able to reduce the 6. Basu, S., “A Study on the Effect of Wetting EFFECT OF METHANOL ON H2O-C5 INTERFACIAL TENSION Fig. 3 aqueous-phase content on the Mechanism of Coalescence,” Journal 55 of the LPG from as of Colloid and Interface Science, 1993,Vol. high as 20% down to 159, p. 68. 50 300 ppm total water. 7. Hughes,V.B., “Aviation Fuel Handling: New 45 This reduction Mechanism Insight into the Effect of dropped the methanol Surfactants on Water Coalescer 40 consumption from 45 Performance,” presented at the 2nd kg/hr down to 15 International Filtration Conference, San 35 kg/hr. Antonio, April 1997. Based on a 30 methanol cost of The authors Peter Hampton is a team leader in the Wildcat Hills devel- $0.35/l. (Canadian), 25 opment and operations group within this represents a sav- Petro-Canada. He has been with the 20 ings of more than company for 19 years working in off- Interfacial tension, dyne/cm $90,000/year for shore drilling, offshore and land pro- duction operations, sour-gas plant 15 Petro-Canada, result- operations, and sour-gas plant supervi- ing in a payback time sion. He holds a BSc (1978) in 10 of less than 1 year. mechanical from the The liquid-liquid University of Alberta and is a mem- 5 coalescer system has ber of Association of Professional Engineers Geologists & 0 20406080been on-line for 2 Geophysicists of Alberta (APEGGA). Methanol in water, vol % years and has sur- Thierry Darde is global marketing manager for the hydro- passed all expectations. carbon business of Pall Corp., which liquid/liquid coalescer effectively to remove Service life on the coalescers is more than he joined in 1995 as European mar- the water-methanol mixture from the LPG. 2 years, with four sets of prefilters being keting manager. He served as head of Alternative approaches that could be used annually. ✦ economics and scheduling at Shell's used to remove the methanol include the Berre (1993-1995), plant manager for Shell's Reichstett refinery, use of a wash tower instead of the injector References (1989-1992) and was also a process and mixer previously described.The mixer 1. Holcek, R.G., Minkkinen, A., and Larue, J., engineer at the refinery (1987- was used due to the significantly lower “The IFPEX-1 Process for Natural Gas 1989). Darde holds a PhD and DsC capital cost. Dehydration/Hydrate Inhibition—The in chemical engineering from Nancy University,France. Use of a tower would reduce the water North American Experience,” Laurance Reid load to the filters to a few hundred ppm Natural Gas Conditioning Conference, Robert H. James is vice-president, general industrial, for Pall (Canada) Ltd., Mississauga, Ont. He but would not reduce the need for Norman, Okla., 1996. has also served as sales manager, advanced coalescer technology to ensure 2. Minkkinene, A., and Jonchera, J.P., industrial process; market sales man- that the LPG met product specification. “Methanol Simplifies Gas Processing,” GPA ager, industrial process; marketing 76th Annual Convention, San Antonio, manager; and applications engineer. Plant coalescer operation March 1997. He holds a B Eng (1983) in mechanical engineering from McGill Petro-Canada installed a liquid-liquid 3. Brown, R.L., and Wines,T.H., “Improve University,Montreal, and is a member coalescer system designed by Pall Corp. in Suspended Water Removal From Fuels,” of Professional Engineers Ontario and 1996, that contained four, 20-in. long Hydrocarbon Processing, December 1993, the Canadian Professional Sales Association (CPSA). AquaSep coalescer cartridges and separa- Vol. 72, No. 12, p. 95. tors. In addition, a prefilter was installed 4. Wines,T.H., and Brown, R.L., “Difficult Thomas H.Wines is a senior marketing manager for the fuels and chemicals group at Pall to remove solid particulate from the LPG Liquid-Liquid Separations,” Chemical Corp., East Hills, NY. He has also mix and precondition the emulsion for Engineering, December 1997,Vol. 104, No. served as senior staff engineer, staff coalescing. 12, p. 104. engineer, and senior test engineer in The methanol recovery and AquaSep 5. Jeater, P., Rushton, E., and Davies, G.A., the scientific and laboratory services liquid-liquid coalescer system installed in “Coalescence in Fiber Beds,” Filtration & department. He holds a BS in chem- the Petro-Canada Brazeau River gas plant Separation, March-April 1980, p. 129. istry from Fordham University and an MS in chemical engineering from Columbia University.He is complet- ing studies for a PhD in chemical engineering at Columbia University. Wines is a member of AIChE and ACS.

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