How a mist eliminator works: three mechanisms without magic

Short answer: a mist eliminator separates liquid drops from the gas stream because a drop is heavier than air and does not have time to repeat all the turns of the channel. Three mechanisms are at work: inertial deposition, interception (capturing) and coalescence.

The three mechanisms

• Inertia. At a channel turn the drop keeps moving in a straight line and touches the wall (vane, mesh). This is how a vane pack works: zigzag channels with a small turn radius.
• Interception. A drop moving close to a wire or wall and touching it — the basis of mesh packs.
• Coalescence. In a fiber layer small drops merge on the fibers into large ones that can already be removed by gravity or a second stage.

What is important to understand

1. A mist eliminator captures liquid drops; water vapor is a gas, and “catching vapor” is beyond a mist eliminator.
2. The design determines applicability: vanes — for large drops in horizontal flow; mesh — broader over the droplet fraction but more sensitive to fouling; a coalescer — for fine mist.
3. Numerical efficiency (percentages, maximum velocities) is a parameter of the specific model from the data sheet: comparing models without documents is incorrect.

Common mistakes

• mixing up “vapor” and “drops” in the specification;
• transferring data sheet velocities of one model to another;
• vertical upward flow over vanes without drainage solutions from the manufacturer.