Evaporator Mist Eliminator Selection for Salt and Scaling Service

Evaporators and crystallizers are difficult mist-elimination duties because the droplets may carry salts, solids or scaling species. Selection has to consider not only initial capture but whether the internal keeps an effective open flow area through operation and washing.

Define where deposits originate

An evaporator demister can receive entrained liquor, crystals, foam and solids, while local evaporation or cooling can also precipitate material on the separator. Identify the liquor composition, concentration factor, boiling regime, antifoam use, temperature profile and location of the pad relative to the vapor outlet. “Salt service” does not define one fouling mechanism.

Product-purity loss, downstream exchanger scaling, compressor or ejector contamination and capacity loss are different consequences. State which result the project must control and how it is observed.

Mesh versus vane

Knitted mesh can capture fine droplets in clean vapor, but salt or crystal carryover can bridge the mesh and raise pressure drop. Vane packs or washable plastic internals are often considered where fouling tolerance is more important.

If a mesh pad is used, lower density, wash access and easy removal may matter more than maximum catalog efficiency.

Open vanes can improve wash access and stable flow area, but blade geometry and spacing still determine droplet range and drainage. A combined mesh and vane system may be considered where both fine-mist agglomeration and liquid handling are needed; include the pressure drop and cleaning of both stages.

In vacuum evaporators, evaluate the separator pressure drop within the complete pressure balance. Use vapor flow and density at the local operating condition, not standard flow. A clean dry supplier value should not be compared directly with a wet end-of-run plant measurement.

Material selection

Chloride-rich service can challenge common stainless grades. Duplex stainless, titanium, PP, PTFE or other materials may be considered depending on temperature, chemistry and mechanical loading.

A plastic demister must have its raw material producer, named commercial grade and continuous and upset temperature limits locked. PP can be considered for some wet corrosive services, but the polymer type by itself does not establish suitability.

Review mesh, vane, grids, tie wires, fasteners and support contact as one material set. Concentrated liquor and deposits can create a more severe local environment than feed analysis suggests. For polymers, include creep, thermal expansion, support spacing and cleaning exposure as well as chemical compatibility.

Washing and drainage review

Confirm wash medium, temperature, chemical compatibility, nozzle coverage, direction, frequency, available pressure and route for removed solids. If washing dissolves a deposit, check where the concentrated solution drains and whether it can re-precipitate. A pad that is easy to spray but has no clear drain path is not maintainable.

Track clean and end-of-run pressure drop, wash response, product contamination and run length. These trends help determine whether the limitation is deposit growth, hydraulic overload or bypass.

Information to send

Provide brine or liquor chemistry, temperature, pressure, vapor flow, solids or scaling risk, wash system details, vessel diameter, available height and required material documents.

For replacement, the scale pattern is useful evidence. Uniform scale points towards chemistry or wash capability; edge deposits point towards bypass or poor liquid distribution. Neither pattern establishes a single cause on appearance alone.

Add minimum and maximum vapor cases, liquor concentration and viscosity, boiling or foaming behavior, crystal or solids size where known, pressure-drop limit, downstream purity symptom, run length, cleaning method, support survey and manway path. Photograph both faces and section joints before cleaning.

Procurement decision

Freeze media family and offered geometry, material set, flow direction, dimensions, support and hold-down interface, section map, wall seals, wash interface, inspection points and packing. If the supplier is only reproducing a controlled drawing, do not imply evaporation performance. A performance route needs operating cases, inlet droplets and loading, purity or carryover criterion, allowable pressure drop and acceptance method.

Use the vacuum tower guide for pressure-drop-sensitive service and the fouling guide for deposit investigation.

Engineering source and limits

Koch-Glitsch’s Severe Services identifies evaporators and high-vacuum service as duties where low pressure drop, open paths, irrigation and fouling resistance can justify vane internals. This supports the decision framework. Named proprietary blade performance does not transfer to a different profile, and no media choice substitutes for liquor chemistry and wash review.