Why is liquid carrying over past my demister pad?

The symptom

Droplets reach equipment the demister is supposed to protect: fouled compressor blades, off-spec overhead product, corrosion in downstream lines. The pad looks intact at the last inspection, yet the carry-over continues.

Root causes

1. 01 Gas velocity outside the design window: too fast re-entrains captured liquid off the pad face, too slow lets fine droplets follow the gas around the wires instead of hitting them.
2. 02 Wall bypass: gaps between pad segments or at the vessel wall give the gas a free path; a few percent of open bypass can defeat an otherwise perfect pad.
3. 03 Wrong density or thickness for the droplet spectrum: a pad sized for coarse mist will pass the fine fraction generated by a new upstream condition.
4. 04 Fouling: polymer, salts or coke bridge the wire structure, raise local velocity and turn the pad into a re-entrainment source.

The mesh solution

• ▸ Re-rate the pad against actual operating data, not the original design case: density, thickness and free area must match today's gas rate and droplet size.
• ▸ Close the bypass: properly engineered support grids, segment overlap and wall sealing make the gas pass through the pad, not around it.
• ▸ For fine mists, step up in density or add a co-knit layer (wire plus yarn) sized for the small-droplet fraction.
• ▸ For fouling service, choose an open, thicker pad that tolerates deposits, and plan cleaning access into the design.

Prevention

• ⊕ Record gas rate at every process change: demisters fail by drift, one debottlenecking at a time.
• ⊕ Inspect segment joints and wall clearance at every entry, not just the pad surface.
• ⊕ Replace pads as engineered assemblies (pad plus grid plus sealing), not as loose mesh cut to fit on site.