What is a FLEXIFIBER Mist Eliminator?

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2 What is a Mist Eliminator? A mist eliminator is a fiber bed into which mist laden gases enter, and out of which emerges a clean gas stream and a separated liquid stream. Fiber packing in the bed is engineered to provide extremely high separation efficiencies. Figure 1 shows schematically a mist eliminator. As indicated, the bed consists of special fibers, which are densely packed between two screens. Mist-laden gases enter from the side of the bed and pass in a horizontal direction through the bed. Clean gases emerge from the bed and rise to exit from the mist eliminator. Separated liquids are directed downwards and towards the outer screen, and ultimately drain down the outer edge of the bed. SCREENS SPECIAL FIBER MIST LADEN GAS CLEAN GAS TO VENT mist eliminator type BD with stainless steel cage SEPARATED MIST TO COLLECTION Figure 1. Single stage vertical mist eliminator Typical Mist Eliminator Installations Figures 3. and 4. show typical mist eliminator installations. Basic components of this system are the FLEXI- FIBER element and the vessel. The element consists of two concentrically oriented cylindrical screens containing packed fibers in the annular area. The screens are connected to a flange at the top of the element, and the flange in turn is bolted to the tank tube sheet. Mist-laden gases commonly enter the tank at the base and pass through the bed towards the element core. Separated liquids drain downwards through the bed, through the drain leg, and are collected at the base of the tank. Clean gases exit at the top of the vessel. mist eliminator type BD with FRP cage 1

3 Basic Mechanism of Mist Separation The three basic mechanisms for mist separation can best be described by considering the following. A gas stream containing mist particles moves towards a fiber which is perpendicular to the direction of flow. As depicted in figure 2, the gas streamlines around the fiber. The momentum of larger particles, greater than about 1 micron, makes them deviate from the gas streamline and head for the fiber. The larger particles are thus separated through the principle of inertial impaction. Smaller particles, generally smaller than one micron in diameter, tend to follow the gas streamline around obstacles. However, as shown in figure 2, they show considerable Brownian movement and thus diffuse from the gas to the surface of the fiber. A particle having a 0.1 micron diameter will have approximately five times the Brownian displacement of a 1.0 micron particle and about 15 times the Brownian displacement of a 5.0 micron particle. Through proper fiber bed design, submicron particles can thus be effectively collected. With Brownian diffusion, the collection efficiency increases as the particle size decreases because the Brownian displacement actually increases with smaller particle size. Particles may also be collected by direct interception. The particle may follow a gas streamline and be collected without inertial impaction or Brownian diffusion if the streamline is relatively close to the fiber. Consider a particle with a diameter of 1 micron. If it follows a gas streamline which passes within 0.5 microns of the fiber, the particle will touch the fiber and be collected. Mist Laden Gas In Clean Gas Out PDI PDI VAPOR OUT Overflow Tube Sheet mist eliminator BD - SFF Figure 3. Typical mist eliminator assembly (forward flow installation). Drain Leg With Collected Liquid The three mechanisms previously discussed make mist eliminators highly efficient mechanical type liquid entrainment separators. While their primary purpose is to remove low micron and submicron liquid particles, they will also handle large particles at higher efficiencies. They can also handle either large quantities of soluble solids or small quantities of insoluble solids providing the particles are very small and there is sufficient liquid in the gas stream to flush the solids through the fiber beds. Small quantities of very large particles can be handled by collection on the surface of the bed. TUBE SHEET W/ DRAIN PIPE P Inertial Impaction FIBER SUMP FILL CONSTANT OVERFLOW CLEANOUT DRAIN SUMP SKIRT BASE RING P Brownian Diffusion FIBER VAPOR IN Direct Interception FIBER Figure 4. mist eliminator for lube oil tank vents on gas or steam turbines. Figure 2. Mechanisms for mist collection on fibers 2

4 Mist Eliminator type BD (Brownian Diffusion) Utilizing the Brownian Diffusion mechanism, BD is able to achieve collection efficiencies of up to 99.95% on all submicron liquid or soluble solid particles. BD elements are normally cylindrical in shape, and are available in a wide variety of materials and sizes. Operating pressure drops are normally designed in the range of 50 to 500 mm (2-20 inch) W.G. An interesting feature of the Flexifiber bed system is that, with submicron particles, the collection efficiencies are actually increased slightly as the gas flow rate through the bed is reduced. This occurs because at reduced flow rates there is a greater exposure time to the fibers. Probability of contact of the particles with the individual fibers through Brownian Movement is thus increased. The type BD fiber beds are also constructed using carbon fibers for applications that involve fluoride concentrations, high ph service (typically greater than 9-10 depending on temperature), and for some applications that involve the hydroxyl group. Carbon fibers resist corrosion for these applications that typically attack glass fibers. Many times one will see this type of situation in metallurgical acid plants, spent acid plants, ammonia scrubbing applications, and the digesting of wood pulp. Mist Eliminator type IC (Impaction Cylinder) Utilizing primarily the impaction mechanism, IC fiber beds are designed to capture and collect particles in the 1 to 3 micron range economically. Collection efficiencies on 1 micron particles will vary from 90% on liquid mists with a specific gravity of 1.0 to 97% on liquid mists with a specific gravity of 1.8. Operating pressure drops are in the range of 100 to 220 mm (4-9 inch) W.G. Elements are normally cylindrical in shape and available in a variety of materials and sizes. The type IC-K fiber beds are constructed with a co-knit wire mesh interior consisting of alloy 20 and fiberglass. The type IC-M fiber beds are constructed with a glass fiber interior. The exterior of both elements are wrapped with additional alloy mesh to control liquid reintrainment and promote drainage. Using this type of construction allows maximum operating time between washing of sulfates in sulfuric acid drying towers or absorption towers which are its primary applications. IC BD with Glass Fibers IC-K Primary Collection Mechanism Particle Size (Microns) Collection Efficiency Efficiency* (%) Element Pressure Drop mm W.G. (inches W.G.) Bed Velocity m/sec (ft./min.) BD with Carbon Fibers BD IC Brownian Diffusion Impaction Cylinder >3 <3 >3 1-3 Essentially 100 Up to Essentially (2-20) (4-10) (5-40) ( ) IP Impaction Panel (5-7) ( ) * In H2SO4 Service Table 1. Comparison of Element s. 3

5 % Design Flow 1 25% 2 100% 3 110% Fractional Efficiency (%) % Design Flow 4 75% 5 100% 6 110% Microns TYPE BD Microns TYPE IC Typical performance curves for mist eliminators BD-FRF MK II Mist Eliminator type IP (Impaction Panel) BD-FRF MK I IP fiber beds are most commonly used in sulfuric acid plants. Utilizing primarily the impaction mechanism, collec-tion efficiencies on 98% sulfuric acid mist are essentially 100% on all particles greater than 3 microns, 85 to 99% on all particles 1 to 3 microns, and 55 to 85% on all particles 0.5 to 1.0 microns. Operating pressure drops are normally 50 to 170 mm (2-7 inch) W.G. Elements are normally rectangular in shape and are available in various metals. IC-SRF The mist eliminator elements cages are available in the following materials: Carbon steel Stainless steel Special alloy steel FRP Polypropylene PVDF PTFE We use a large variety of special fibers to suit the chemistry of various chemical processes. The ph of collected liquid and its chemical aggressiveness are parameters taken into consideration to determine the proper fiber to be used in mist eliminator elements. IP BD-SRF MK I 4

6 TYPICAL APPLICATIONS sulfuric acid LOCATION PROBLEM Drying tower Acid mists foul catalyst and type IC-K or corrode downstream DEMISTER equipment Interpass Acid mists corrode expensive type BD Absorption Tower downstream equipment LOCATION PROBLEM Final Acid mists cause air pollution type BD Absorption Tower or IC-M Oleum storage SO3 from vents mixes with and loading area moisture to form acid creating type BD safety in air and corrosion problems. BLOWER DRYING S BURNER 8-11% e SO2 TYPICALLY 10% CONVERTER OLEUM ABSORPTION HEAT EXCHANGER CONVERTER FINAL ammonia scrubber LOCATION PROBLEM SO 2 Absorber Ammonium sulfite particles type BD are exhausted causing plume and pollution DRYING BLOWER S BURNER BOILER CONVERTER SO 2 SO 2 H 2 O NH 3 5

7 chlorine plant LOCATION PROBLEM Wet end Brine mists foul drying tower type BD and increase sulfuric acid consumption in drying gas Wet end H2 gas carries caustic type BD LOCATION PROBLEM Dry End Acid mists corrode type BD compressor and reduce product quality BRINE ANODE (+) (Na CI & H 2 0) CATHODE (-) H 0 VAPOR & SALT 2 CI 2 CELL Na OH CONVERSION TO CAUSTIC H 2 COOLERS H 2 WET CI 2 H 2 TO ABSORTION DRYING S ALT.2 ALT.1 LIQUID SEAL COMPRESSOR DRY CI 2 DRY CI2 CENTRIFUGAL RECIPROCATING COMPRESSOR LIQUEFACTION LIQUEFACTION TO TO ammonium nitrate LOCATION PROBLEM Neutralizer AN is carried out by type BD exhausting gas causing product loss and pollution Prill tower Visible plume caused by AN salts in exhaust gas type BD LOCATION PROBLEM Evaporator Product loss and pollution type BD or IC VENT VENT AMMONIA NH3 NITRIC ACID HN03 NEUTRALIZER EVAPORATOR CONCENTRATOR PRILL AMMONIA NITRATE 6

8 plastic manufacturing LOCATION PROBLEM Curing Ovens Extruders Injection Molding Calendering Plasticizer vapors condense in type BD and IP air causing visible plume and product loss EXTRUDER COOLING CHAMBER COOLING PLASTISOL COATING APPLIED CURING OVEN PLASTICIZER RECOVERY compressed gas VENT LOCATION PROBLEM Compressor Oil from the lubricating type BD reservoir creates pollution problem & decreases life of dryers TO COMPRESSOR LUBRICATION OIL RESERVOIR sulfonation plant RECOVERED OIL LOCATION PROBLEM Oleum or SO 3 SO 3 mixes with moisture in air type BD storage and forming acid creating safety unloading areas and corrosion problems ORGANICS Before Reactor Sulfuric acid mist in SO 3 gas type BD causes hazy appearance in final product SO3 SOURCE REACTOR After Reactor Sulfuric acid mist causes type BD pollution 7

9 pulp and paper ammonia based sulfite recovery LOCATION PROBLEM After SO 2 Cooler Particulate carry-over type BD resulting in severe opacity GAS COOLER MULTI CLONES SO2 COOLER EXHAUST GAS RECOVERY BOILER (NH4)2 SO3 SOLUTIONS SULFUR SULFUR BURNER NH4 HSO3 SULFONATION DIGESTER BLOW TANK FORTIFICATION EVAPORATOR WOOD CHIPS FIBER TO PAPER MAKING PROCESS nitric acid LOCATION PROBLEM Ammonia Iron catalyst and oil particles type BD Feed Line cause decomposition of the ammonia andcontamination of the platinum gauze Air Feed Line Iron catalyst and oil particles cause decomposition of the type BD ammonia and contamination of the platinum gauze LOCATION PROBLEM After Waste Loss of platinum burned off type pt filter Heat Boiler the gauze during normal operation Tail Gas Nitric acid mist that is carried over from the absorption type IC tower or formed by reaction or BD of NO 2 nd H 2 O corrodes downstream equipment LIQUID AMMONIA WATER TAIL GAS VAPORIZER GASEOUS AMMONIA AMMONIA STATIC MIXER CONVERTER HEAT RECOVERY TRAIN PT. HEAT EXCHANGER LIQUID SEPARATOR ABSORPTION NO2 ABATEMENT DEVICE TURBINE COMPRESSOR NITRIC ACID PRODUCTS STEAM 8

10 asphalt LOCATION PROBLEM Asphalt Storage Vapors condense in air type BD and loading area causing plume and pollution LOCATION PROBLEM Saturating Vapors and oil mist cause type BD and coating plume and pollution VACUUM BREAKER TANK VENT TANK FROM OTHER TANKS LOADING NOZZLE ANNULAR HOOD AROUND NOZZLE TRUCK TANK HEADER TO OTHER LOADING NOZZLES H 2 ASPHALT SYSTEMS ASPHALT LOADING RACK PRE H 2 ASPHALT SATURATOR ROLL WINDER ASPHALT SATURATING AND COATING phosphoric acid LOCATION PROBLEM Absorption Tower Acid mists cause air pollution type BD or IC problem HYDRATOR BURNER PHOSPHORUS PHOSPHORIC ACID PUMP 9

11 urea LOCATION PROBLEM Carbon dioxide Oil or water carryover Compressor contaminates reaction and type BD corrodes equipment Prill tower Visible plume and pollution type BD LOCATION PROBLEM Evaporator Product loss and pollution type BD AMMONIA NH3 ABSORBERS COMPRESSOR REACTOR UREA SOLUTION PRILL CO2 CARBON DIOXIDE DECOMPOSERS STEAM CONCENTRATOR power generation LOCATION PROBLEM Turbine oil reservoir vent line Visible emission plume type BD compressor crankcase vent line along with loss of lube oil gearbox vent line resulting in oil coating vacuum pump exhaust equipment, roofs, and creating safety hazards RECOVERED OIL RECOVERED OIL OIL RESERVOIR TURBINE Crankcase vent or Exhaust Recip, or centrifugal compressor, vacuum pump 10

12 KOCH-OTTO YORK Design & Service Leader in Separations Technology. Members of the Koch-Glitsch Business Group 42 Intervale Road P.O. Box 3100 Parsippany, NJ TEL: FAX: Killough Road Houston, TX TEL: FAX: E. 37th St. North Wichita, KS TEL: FAX: Koch-Glitsch Italia S.r.l. Via Tonale 50 P.O. Box Albano S. Alessandro (Bergamo) Italy TEL: FAX: Koch-Otto York BVBA Bijkhoevelaan 12 B Wijnegem, Belgium TEL: FAX: Otto York Asia Pacific 260 Orchard Road, #11-01/09 The Heeren Singapore TEL: FAX: Visit us on the internet: KOCH-OTTO YORK, A Koch-Glitsch Business Group DEMISTER, FLEXICHEVRON and are registered trademarks. COALEX, YORKMESH, YORK-AXIFLOW, SPIRAFLOW and DEMISTER-PLUS are trademarks for our mist eliminators. All data in this brochure are for general information only and are based on tests carried out under conditions which may or may not apply to your requirements. No warranties or guarantees are expressed or implied. No information contained in this brochure constitutes an invitation to infringe any patent, whether now issued or issued hereafter. All descriptions and specifications are subject to change without notice. Printed in the USA. Bulletin FF M0502B Printed in U.S.A. Copyright 2002 Koch-Otto York