On-line process analysers are nowcommonplace in industrialplants and are being increasinglyused in refineries. Over the last fewyears, they have become more complexand sensitive to contaminants in theinlet feed. One of the most critical issueswith the use of on-line sensors is theirvulnerability to fouling and thepotential harmful outcomes ofinaccurate measurements such as non-optimised process control, leading toloss of revenue. Also of concern is theneed for costly replacement parts due tocorrosion and maintenance related tofrequent repairs or cleaning.

However, advances in the separationtechnology of liquid/gas coalescers andliquid/liquid coalescers and theirapplication to sensor protection arechanging this situation. The use ofspecially engineered polymeric mediahas advanced the state-of-the-art forseparating liquid aerosols from gases andbreaking emulsions in liquid systems.

This case history of the OMV refineryin Burghausen, Germany documents asmall-flow, high-efficiency liquid/liquidcoalescer system installed to optimiseanalytical devices including a nearinfrared (NIR) spectrometer and pHsensor. In one case, water and particleshad affected the on-line measurement ofdifferent hydrocarbon streams. Inanother, hydrocarbons in the water haddamaged the pH sensor, making an on-line measurement impossible.

The use of high-efficiency liquid/liquid coalescers made it possible toremove any harmful traces of water fromhydrocarbons or hydrocarbons fromwater, enabling the analysers to operateat peak performance and provideaccurate and reliable measurements.This in turn allowed the processequipment to be adjusted using thesensor information, enabling bothcontinuous process control andimprovements in operation efficiency.The cost of each small-flow, high-efficiency liquid/liquid coalescer systemfor this application was less than $5000

and resulted in a quick return oninvestment (ROI).

OMV is the leading oil and naturalgas group in Central and EasternEurope. It is active in exploration andproduction worldwide and hasintegrated chemicals operations. OMVDeutschland, a subsidiary company ofthe international OMV Aktienge-sellschaft, processes mainly low-sulphurcrude. This crude is transported in theTrans-Alpine Pipeline (TAL) from Triesteto the Steinhöring tank farm and fromthere to Burghausen.

The OMV Burghausen refinery isstrategically located in the heart ofBavaria’s chemical industry. This refineryprocesses some 3.4 million metric tonsof crude oil annually and produces thebasic petrochemicals ethylene andpropylene, as well as extra-light heatingoil, diesel and aviation fuel, and coke forthe aluminium industry.

Coalescer technologiesCoalescers are designed to eitherseparate liquid aerosols from gas streamsor to break liquid/liquid emulsions. Theycan be constructed from fibres made ofvarious materials, including glass, metal,polymers and fluropolymers. Thecoalescer media can be configured aspleated sheets or as a depth type, buthave in common a pore gradient thatgoes from smaller to larger sizes in theflow direction and an outer coarse sleevematerial to complete the coalescingprocess. In principle, coalescers canoperate indefinitely as long as they arenot exposed to solid contaminants. Inpractice, coalescer systems, with properpre-filtration, typically achieve servicelives varying from six months to twoyears. They operate in three stages: — Separation of solids— Coalescence of small drops intolarger drops— Separation of the large drops fromthe purified continuous stream.

During the coalescing process, theinlet drop sizes are in the sub-micron tolow-micron size range; after passing

through the coalescer, they are in themillimetre range. Both liquid/gas andliquid/liquid coalescer technologies havebeen successfully applied to analysertechnology.

With the liquid/gas coalescer, poorliquid separation, which eats away theprofit margins, can be eliminated. Liquidaerosols dispersed in gases attack severalcritical areas within the process:compressors and turbo-equipment,amine-glycol contactors, burner andcombustion equipment, and desiccantand absorbent beds. This can result inany or all of the following:— Compressor valves that needchanging out more than once every twoyears— Turbo-equipment servicing morethan once a year— Plugging of reboiler heat exchangersor trays in contact towers— Frequent replacement of amines andglycols— Frequent foaming incidents— Loss of efficiency in burner andcombustion equipment— Frequent desiccant regeneration orreplacement.

Liquid/gas coalescers are the latestdevelopment in the history of liquid/gasseparation units. Their performance issuperior to knockout drums, vaneseparators, mesh pads, and combinat-ions of filter separators and vane or meshpacks. These older devices rely oninternal separation mechanisms andwork well for larger aerosol droplets(>5µm), but lose efficiency at reducedflow rates.

High-efficiency, vertical liquid/gascoalescers have been used extensively ingas processing in the last decade. Theyoffer the advantage of increased removalcapability of fine droplets (down to0.3µm in size and to levels as low as3ppb) and are able to operate efficientlyat low flow rates. A recent innovation inliquid/gas coalescer design is to use asurface treatment to prevent the wettingof the coalescer media with aerosolliquids, thereby increasing the allowable

High-efficiency coalescersfor analyser protection

Coalescers are designed to either separate liquid aerosols from gas streams or tobreak liquid/liquid emulsions. Both liquid/gas and liquid/liquid coalescer

technologies have been successfully applied to analyser technology

Hans Thoma OMV Burghausen Refinery Verena Titzenthaler and Thomas Reisenhofer Pall Corporation

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flux, decreasing fouling tendency andlowering pressure drop losses.

Liquid/liquid coalescer systems arefrequently used to dry jet fuel and arefinding increasing applications forrefinery and chemical process streams.These systems can be divided into twobroad categories: vertical with separatorstage and horizontal with gravityseparation. Schematics of typicalvertical and horizontal configurationsare provided in Figures 1 and 2.

Both configurations employ acoalescence stage. In the verticalconfiguration, a hydrophobic barrierrepels the coalesced aqueous drops in asecond separation stage. The verticaldesign is used to separate water fromhydrocarbons when the interfacial

tension is greater than 3dyne/cm. In the horizontal configuration, a

settling zone achieves separation bygravity. This configuration is used whenthe interfacial tension is less than3dyne/cm or for the separation of oilfrom the water phase. Typically, themain stream leaving the liquid/liquidcoalescer will have a concentration ofless than 15ppmv of undissolvedcontaminant. The liquid/liquid coalescercan only remove the free/undissolvedcontaminant phase.

Traditional coalescers have used glassfibre media, which works well foremulsions that have interfacial tensionsgreater than 20dyne/cm. New coalescermedia, constructed with advancedformulated polymers and fluoro-

polymers, are effective for emulsionshaving interfacial tensions as low as0.5dyne/cm. Newer designs of verticalliquid/liquid coalescers have thecoalescers stacked on top of theseparators. In older designs, theseparators are located in a separatesection of the housing. The new designsimprove the flow distribution and,consequently, increase separator use.The new coalescer media enables betterliquid/liquid separation to optimise theprocess and cure a variety of costlyproblems that may not be obvious.These include:— Hazy product (not bright and clear)— Sodium levels in gasoline above1ppm— High solvent losses downstream ofliquid/liquid extraction units— High caustic carryover from gasoline,LPG or kerosene treating unit— Carryover of amine in LPG— Oil and hydrocarbon in water andother aqueous streams.

Problems created atliquid/liquid interfacesSurfactants are naturally present in crudeoil and, as a result, in refined petroleumproducts. During the oxidation processand the caustic recirculation in sulphur-removal processes, surfactants can beconcentrated to high levels.

Surfactants that have been identifiedin caustic treaters include sulphides,mercaptides, naphthenic acids, cresylicacids and phenol homologs. Petroleumnaphtha sulphonates have been identif-ied as naturally-occurring petroleumsurfactants that are especially detri-mental to conventional glass fibrecoalescers. The surfactants can adsorb atthe solid/liquid interface (coalescerfibres) or at the liquid/liquid interface(water/oil).

“Disarming” occurs when surfactantsconcentrate on the coalescer fibres.These fibres are shielded from passingaqueous droplets, resulting in poorseparation efficiency. Generally,disarming does not occur unless theinterfacial tension between the waterand fuel is less than 20dyne/cm.However, when specially formulatedpolymeric coalescer medium was usedinstead of glass fibre, disarming did notoccur at all. The performance of thismedium can be greatly enhanced by themodification of surface properties thatcannot be accomplished with the glassfibre medium.

Surfactants can also concentrate at thewater/fuel interface, leading to verysmall droplets and stable emulsions. Asurvey of caustic hydrocarbon emulsionsshowed the interfacial tensions variedfrom 0.5–12.4dyne/cm. To separate thesetypes of emulsions, special consideration

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Figure 1 Vertical liquid/liquid coalescer

Figure 2 Horizontal liquid/liquid coalescer system

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must be given to the pore size anddistribution in order for the coalescermedia to intercept and coalesce thesmall droplets.

Equipment for small flow ratesTo apply coalescing technology toanalyser protection, scaled-downversions of the industrial systems arerequired. The use of fast loop samplingsystems is critical to ensure thatrepresentative (fresh) fluid is analysedfor real-time optimal process control.Here, a high flow rate is maintained in aloop that goes through the pre-filter andcoalescer and is than re-routed back tothe process (Figure 3). A smaller streamof the purified fluid is drawn off foranalysis.

An important distinction between theuse of coalescers in analyser protectionand full-scale industrial applications isthat the contaminant phase re-routesback into the process stream duringanalyser protection. This configurationallows for less instrumentation, as it isnot critical to monitor the separatedcontaminant fluid for level controlbecause it is continuously purged back toprocess. This leads to a different flowpath in the coalescer housing, where thefast loop flow rate is passing throughnormal coalescer sump connections backto the process, while a smaller samplingflow is leaving the normal main outletport.

For the small-flow systems, Pallcreated a small coalescer cartridge (6in

long with 3–3/4in diameter) used in astandard stainless steel housing. Toprotect the fine coalescer media, anabsolute-rated pre-filter is needed (ie,Beta 5000 greater or equal to the ratingas determined using a modified OSU-F2laboratory test). Therefore, a 5µm(99.98% retention of 5µm particles)rated proprietary Nylon Profile filter isused. The pre-filter cartridge is 10in longwith 2.5in diameter. The filter materialis compatible with hydrocarbon streamsup to 150°C. The coalescer media is thesame as for the process applications(Table 1).

Case 1Separation of water phase from

hydrocarbonsThe OMV Burghausen refinery installedsix small-flow liquid/liquid coalescer

systems, each consisting of one pre-filterand one vertical coalescer housingequipped with one pre-filter element,one coalescer and one separator element(part number and design characteristicsshown in Table 1) to protect their NIRanalysers (analyser type: ABB BomemFTSW100).

NIR analysers are a relatively newtechnology for refineries to monitormain product, intermediate streams andunit feed. The specially designed Pallcoalescer media is suitable for use indifferent streams with a large variety ofinterfacial values. The analyser is offeredas a low-cost alternative to traditionalgas chromatographs or distillationanalysers. With the new generation ofNIR spectrometers, a large number oftypical and characteristic fluid valuescan be calculated (T10, T95, Cloud

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Fast loop to process

(Hydrocarbon + aqueous)

Clean hydrocarbon

100ml/min

From process

Pre-filter Coalescer

to analyser approx.

approx. 4-12lpm

Figure 3 Fast loop for liquid/liquid coalescer

Cartridges: Part number Description Max. Initial pressure Recommended

temperature drop* change-out dPRGN1FN050 Nylon Profile filter 150°C 20mbar 3.4 bar LCS06B1AH AquaSepPlus Coalescer 65°C 140mbar 1 barLSS06F1H Separator 65°C 140mbar 1 barLCS06H1AH PhaseSep Coalescer 65°C 140mbar 1 bar* The initial pressure drop values are likely to vary case to case.

Housings:Part number Max. temperature Max. pressure Material1PH4F1F11 140°C 16 barg 316L SS1AQ4F1F11 140°C 16 barg 316L SS

Part numbers/design parameter

Table 1

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Point, Freezing Point and Flashpoint). Inorder to apply the best efficiency, a fastloop sampling is installed as previouslydescribed in Figure 3.

For the correct measurement of NIRspectra, it is critical to have water- andparticle-free samples. The transmissionvalue (how clean and anhydrous the cellis) is needed to know if the product is inthe given spectrum. Water and particlesdisturb the measurement and must beremoved. Without a continuous trans-mission, no on-hand readings can bedone.

In the past, OMV used a salt filter. Themajor disadvantages were that there wasno control of these values and the filterhad to be changed every two to threedays. The content of the water was notverified during this time. With theinstallation of the coalescer system, thelifetime of the filter system hasincreased, the samples are reproducible,and the water content is controlledeffectively.

The Bomen Gran ABB NIR spectro-meter has six “in channels” and isconnected to the refinery’s computersystem. With reference spectra, it ispossible to calculate the Cloud Point,T10, T95, Freezing Point and Flashpoint(Table 2).

With better control of the column,the OMV refinery could increase theoutput of kerosene by 5–6%, whichoffers a fast ROI. This is due to theoptimisation of production throughadvanced control in the gas oil and cokergas oil streams.

Case 2Hydrocarbons from water phase

The aim is to protect the pH sensor fromhydrocarbons being used in the coolingwater cycle for dosage NaCl constant tothe system. Hydrocarbons destroy thesensitive pH meter. In the past, only off-line measurements were possible (point-wise measurement) and the sensor wasdamaged by long-term contact withhydrocarbon in the stream. The usage ofa new pH sensor was required everythree months.

By using the small-flow liquid/liquidcoalescer system, a constant on-linemeasurement is possible and the pHsensor does not need to be changed formore than one-and-a-half years. Theflow rate of the described installation is10l/hr by the pH sensor.

ResultsDue to the installation of six small-flowliquid/liquid coalescer systems, the OMV

Burghausen refinery is able to make acontinuous and correct on-line measure-ment of its hydrocarbon streams. Withthe result of these measurements, therefinery controls its column properlyand is able to produce 5–6% morekerosene. The Pall system will removefree liquid contaminant to levels of15ppmv and below over a wide range ofconditions such as:— Inlet liquid contaminant concentra-tions as high as 10%— Interfacial tensions as low as0.5dyne/cm.

The use of the fast loop configurationwith the small-scale liquid/liquidcoalescer system has resulted in simpleseparation systems that do not requirelevel controls or automated dischargevalves.

Nylon Profile filter, AquaSepPlus Coalescerand PhaseSep Coalescer are trademarks ofPall Corporation.

Hans Thoma is the head of the processanalytic and optimisation department,OMV Burghausen refinery. Thoma hasbeen working since 1981 for the refinery atthe Burghausen site. Email: hans.thoma@omv.comVerena Titzenthaler is a sales engineer,fuels and chemicals, Pall Corporation,Germany since 2001. Titzenthaler earneda PhD in organic chemistry and organicanalytics from University of Regensburg.Email: verena.titzenthaler@europe.pall.comThomas Reisenhofer is market manager,refineries, fuels and chemicals/CentralEurope, Pall Corporation, Austria.Reisenhofer manages and co-ordinates theinternational sales teams, and has beenworking for Pall since 1995. Email:Thomas.reisenhofer@europe.pall.com

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Stream Flow through Flow through Converted coalescer NIR data

HDS diesel outlet, l/h 40 3–8 Cloud Point; T10; T95HDS inlet, l/h 40 3–8 Cloud Point; T10; T95Gas oil I outlet, l/h 40 3–8 Cloud Point; T10; T95Coker gas oil outlet, l/h 40 3–8 Cloud Point; T10; T95Heating oil outlet, l/h 40 3–8 Cloud Point; T10; T95Kerosene outlet, l/h 40 3–8 Freezing Point,

Flashpoint

Converted data available per individual stream

Table 2

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