Wire mesh separators

Knitted wire mesh serves as an effective entrainment separator when it cannot easily be foiiled by sohds in the liquor. The mesh is available in woven metal wire of most alloys and is installed as a blanket across the top of the evaporator (Fig. ll-122d) or in a monitor of reduced diameter atop the vapor head. These separators have low-pressure drops, usually on the order of 13 mm [ M in) of water, and collection efficiency is above 99.8 percent in the range of vapor velocities from 2.5 to 6 iti/s (8 to 20 ft/s) [Carpenter and Othmer, Am. nsi. Chem. 

Entrainment Due to Gas Bubbling/Jetting through a Liquid Entrainment generally hmits the capacity of distiUation trays and is commonly a concern in vaporizers and evaporators. Fortunately, it is readily controllable bv simple inertial entrainment capture devices such as wire mesh pads in gravity separators. 

Surface-type filter media are distinguished by the fact that the solid particles of suspension on separation are mostly retained on the medium s surface. That is, particles do not penetrate into the pores. Common examples of this type of media are filter paper, filter cloths, and wire mesh. 

Figure 4-16. Diagram of action of wire mesh in liquid-vapor separation. Courtesy of Metal Textile Corp., Bulletin ME 9-58.

Figure 4-20. Typical pressure drop range for most wire mesh separators.

Figure 4-25. Specification design sheet for separator using wire mesh.

Figure 9-48. ACS maximum vapor velocity correction for L/G for woven/knitted wire mesh structured packing. Used by permission of ACS Industries, Inc., Separation Technology Division, Bull. B-129 (1992).

The basic purpose of an oil separator is to clean the pressurized air of any oil contamination, which is highly detrimental to pneumatically controlled instrumentation. A separator consists of an inlet, a series of internal baffle plates, a wire mesh screen, a sump, and an outlet. The pressurized air enters the separator and immediately passes through the baffle plates. As the air impinges on the baffle plates it is forced into making sharp directional changes as it passes through each baffle section. As a result, the oil droplets separate from the air and collect on the baffles before dropping into the separator s sump. 

Kfne = Proportionality factor in Stokes-Cunningham correction factor, dimensionless k = Constant for wire mesh separators 1 = Wire mesh thickness, ft L = Length of vessel from hydrocarbon inlet to hydrocarbon outlet, or length of decanter, ft L[ = Liquid entering Webre separator, lbs pel- minute per square foot of inlet pipe cross-section L, = EnLrainment from Webre unit, lb liquid per minute per square foot of inlet pipe cross section... 

Vmax = Calculated maximum allowable superficial gas velocity, ft/sec, or ft/min wire mesh pad Vs = Superficial gas velocity, ft/sec Vsa — Separator vapor velocity evaluated for air-water system, ft/sec... 

Impingement separators, 246, 257 Chevron style, 248, 255 Efficiencies, 246 Knitted wire mesh, 246 York-vane efficiencies, 248 Inertial centrifugal separators, 266, 268 Kinetic energy, pump system, 187 Lamella plate classifiers, 239 Line sizing work sheet, 107... 

Lines in vacuum service, 135—141 Line symbols, 17, 23 Numbering, 23 Lined centrifugal pumps, 171 Liquid-solid particle, separators, 228 Baffle type specifications, 248 Baffle type, 247, 248 Centrifugal, 256, 259-261 Chcvron-vanc, 248, 235 Comparison chart, 230 Cyclone, 259 Specification form, 268 Vane, 259 Wire mesh, 246 York-vane, 248 Low pressure storage... 

Chart, 204, 205, 207 Vortex, 190 Water hammer, 98 Wire mesh separators, 246, 247 Calculations, 247-254 Efficiency, 248, 250 Installation, 251-253 k-value for mesh, table, 249 Mesh patterns, 247 Pressure drop, 249, 251 Specifications form, 254 Vapor velocity, 247, 250 Wire mesh types, 248... 

A specimen of the sample is cooled under specified conditions and, at intervals of34°F (1°C), is drawn into a pipet under a controlled vacuum through a standardized wire mesh filter. The procedure is repeated, as the specimen continues to cool, for each 34°F (1°C) below the first test temperature. Testing is continued until the amount of wax crystals that have separated out of solution is sufficient to stop or slow down the flow so that the time taken to fill the pipet exceeds 60 seconds or the fuel fails to return completely to the test jar before the fuel has cooled by a further 34°F (1°C). The indicated temperature at which the last filtration was commenced is recorded as the CFPP. 

A second type of impingement separation device is a knitted wire mesh pad. The primary mechanism of separation in the knitted wire mesh is impingement. It also utilizes centrifugal and gravitational force in the collection of small liquid particles. 

The tests showed the knitted wire mesh has high gas and liquid handling capacities. It was also found to increase in removal efficiency with increased gas velocities when small droplets were involved, until the pad approached a flooding condition. As the flooding velocity-is approached, considerable liquid is held up within the pad between the wire. Since the area left for gas flow is decreased by the presence of the liquid, the gas velocity increases until large droplets are torn away from the back side of the pad and carried from the separator with the gas velocity. 

Impingement type mist extractor exemplified by knitted wire mesh pads are widely used in oilfield liquid and gas separation equipment. Their liquid and gas handling capacities are good with high liquid droplet removal efficiencies with small gas pressure drop. 

Centrifugal mist eliminators separate liquid dropi by centrifugal force. These can be more efficient than either wire mesh or mist eliminators, and are the least susceptible to plugging. However, they are not in common use in production operations because removal efficiencies are sensitive to small changes in flow. In addition, they require relatively large pressure drops to create the centrifugal force. 

The velocity constant" K varies from 0.30 to 0.45 ft/s for a wire-mesh surface in an impingement separator, and from 0.15 to 0.25 ft/s for a gravity settler. 

The mechanism of vapor-phase separation is illustrated in Fig. 1. Both stages—coalescence and disengagement followed by gravity settling—must be considered in sizing the drum and selecting the wire-mesh pad. 

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