Coalescer

A coalescer is a device or medium that promotes coalescence of fine droplets in a dispersed liquid or aerosol, merging them into larger droplets that can be separated more readily by gravity, buoyancy, or filtration. Coalescers are used to enhance separation in liquid-liquid systems (such as water droplets in oil or oil droplets in water) and in gas streams containing liquid aerosols.

Common configurations include gravity coalescers that use porous media or packed beds to induce collisions and coalescence, and coalescing filters or demisters that remove droplets from gas streams. Other designs include plate or horizontal/vertical vessel coalescers and centrifugal coalescers that increase collision rates by rotation.

Mechanisms: droplets collide due to turbulence, flow shear, and differential velocity; upon contact with wetting surfaces they merge, forming larger droplets that settle more quickly or are captured by downstream devices. Media pore size, surface chemistry (wettability), temperature, and interfacial tension influence performance.

Applications: produced water treatment, oil-water separation in refineries and petrochemical processing, natural gas dehydration and sweetening, fuel purification, and air handling systems for mist and aerosol removal.

Design and operation considerations: typical performance depends on droplet size distributions and liquid properties; designers must manage flow rates and pressure drop, prevent channeling, maintain drainage, and plan for media cleaning or replacement to prevent fouling.