Coalescers

Coalescers are devices or media that promote coalescence of small droplets in a dispersed phase, forming larger droplets that can be removed by gravity, filtration, or drainage. They are used in liquid-liquid and gas-liquid separations, including oil-water emulsions and condensate removal from carrier streams.

Coalescence is aided by enhancing droplet contact, reducing interfacial resistance, and providing surfaces that encourage merging. Coalescers employ structured media, plate arrays, or porous filters to increase residence time and promote droplet-wall interactions. Surfactants can hinder coalescence; demulsants are sometimes used to improve performance.

Common configurations include gravity coalescers (tanks with media and baffles), plate coalescers (inclined plates or vertical arrays), tubular or honeycomb coalescers (high surface-area packings), cartridge coalescers (in-line porous media), and membrane coalescers (selective wetting to promote merging). Gas-phase coalescers are used for demisting and condensate removal in compressed air and natural gas streams.

Applications include crude oil dehydration, produced-water treatment, refinery effluent cleanup, natural gas sweetening, and general water purification. Performance is described by droplet-size distribution, separation efficiency, throughput, residence time, and pressure drop. Design factors include fluid properties, temperature, salinity, surfactants, and target moisture content.

Maintenance involves cleaning or replacing media, controlling fouling, and ensuring proper drainage. Coalescers reduce downstream energy needs and improve product quality, but can be sensitive to contaminants and deactivation over time.