KNITTED WIRE MESH MIST ELIMINATORS

Jonell CANADA INC

There are several important applica-tions in which mesh and vane mist eliminators are placed in tandem. When the mesh pad is placed up-stream of the vane element it coa-lesces fine mist droplets into a spray of coarse particles which are readily re-moved by the downstream vane ele-ment. This is precisely the approach used in filter-separators in which the gas-coalescing media is placed up-stream of mesh or vane.

Jonell CANADA INC 3513 - 62nd Avenue S.E. Calgary, Alberta. T2C 1P5 PH: 403 313-1559 FAX: 403 280-7926 Email: sales@jonellcanada.com

The contactor section of a glycol dehydrator is a perfect candidate for an assembly. In such packed dehys, gas handling capacity is deter-mined by the hydraulics of the packing, and the mist eliminator must accommodate this flow. This translates into a flow rate much higher than allowable for mesh, but a vane allows too much carryover. The solution is an assembly. In this application, glycol losses of 0.01 to 0.001 gal/mmscfd can be achieved. For Vertical Gas Separators protecting down-stream compressor equipment and operating at moderate to high pressures, and with vessel di-ameter almost exclusively determined by the ca-pacity of the mist eliminator, higher capacity mist eliminators provide for smaller shells. While vane separators offer the capacity, their droplet removal performance drops off at higher pres-sures and turndown is often a concern. Again, assemblies combine not only the operating range of mesh and capacity of vane, but the op-erating range of both to ensure mist removal over broad operating ranges. As an example, if the optimum velocity through the vane and mesh are approximately 10 and 5.5 fps respectively, the assembly offers optimum performance over the range of 1.6-11 fps. Shown to the right is an assembly with multi-layer high efficiency mesh and a downstream vane with overall thickness of 8” to fit a vane housing for an 18” Sch. 60 pipe shell.

Mesh-Vane Assemblies

General Jonell mesh pads can be made of any material which is ductile enough to be drawn into wire. Although Jonell Canada knits 300 stainless series mesh and maintains in-ventory, special order for monel, inconel, alloy 20, duplex stainless, nickel and other materials is available upon special request. Mesh pads are fabricated to meet virtually any vessel geometry and orientation. Jonell Canada Inc. designers can determine the size and style of mist eliminator re-quired to meet process requirements or customer specifications.

Construction Jonell mist eliminators are made of layered or coiled socks of knitted mesh which are individually crimped to the proper height to maintain density and specific surface area requirements. In alloys, standard 0.011” and 0.006” wire is used, while co-knits of vari-ous materials are also available. Mesh pads are made in one piece for pipe-sized flanged vessels or segmented in nu-merous sections to facilitate handling and passage through a vessel manway. Standard grids using 1” x 1/8” flatbar and nominal 1/4” rod are typically used. Grating or expanded metal grids are also offered. For smaller mesh pads or in cases in which overall mist eliminator height is limited, rod-only grids may be used on top and/or bot-tom faces. Intermediate Rod-only grids are sometimes used for mesh pads of thickness 10” or greater.

Jonell CANADA INC

Mesh-Pad Nomenclature Common mesh pad styles correlate with those of most other vendors. For instance, JCI equivalent to industry “standard” 9-lb density mesh (ACS 4CA or Otto-York 431) is style 85, which happens to be the specific surface area of 0.011” wire crimped to 9-lb density JCI Style Mass Wire Void

(or Specific Surface Density Diameter SpaceArea in ft2/ft3) (lb/ft3) (inches) (%)

235 14 0.006 97.2200 12 0.006 97.6120 7 0.006 98.5115 12 0.011 97.595 10 0.011 97.285 9 0.011 98.265 7 0.011 98.545 5 0.001 99

PERFORMANCE

Wire mesh mist eliminators have been used to remove entrained droplets from a vapor stream since the late 1940’s. Droplets collide on wire surfaces and coalesce together to form larger droplets which then drain to the bottom of the pad and rain off. The first step in designing a mist eliminator is to determine the cross-sectional area required by using the Souders-Brown equation. Procedure for this is given in most references and is found in GPSA Section 7. JCI Style

Typically the mesh density is specified, and all too often what is used is 9-lb density mesh of 0.011” diameter wire. Removal efficiency however is not affected by mass density per se, but rather by the diameter of wire used and the specific surface area. The chart above lists several common mesh densities along with key parameters. Note that 12-lb density mesh exhibits 115 sq-ft/cu-ft if made of 0.011” diameter wire, or 200 if made of 0.006” wire. For this reason, Jonell Canada styles correspond not to mass density of mesh, but rather to specific surface area of wire in the mesh. In the graph above, from front to back, are compared the removal efficiency in a natu-ral gas application at 350 psia of style 45, 85 115 and 200. The higher the specific sur-face area, the better the performance. This affect is accentuated at elevated pres-sures. For example, at 950 psia, standard 9-lb density mesh removes 99.9% or droplets only at ~25 µm, where as 12-lb density mesh style 200 (with 0.006” wire) achieves this at only 9-10 µm.

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