koalescers

Koalescers are devices or vessels designed to promote the coalescence of small droplets within an immiscible liquid system, producing larger droplets that can then separate by gravity or simple phase separation. They are used to remove dispersed droplets of one liquid from another, most commonly water droplets in oil or fuel, but also in gas streams where liquid aerosols must be eliminated. In many industries, coalescers are paired with filtration media to improve separation efficiency.

How they work varies by type. In media-based coalescers, a porous or woven medium provides surfaces for tiny droplets to contact, merge, and grow into larger droplets that settle or rise out of the continuous phase. Gravity-based designs include plate or tubular coalescers, where flow is arranged to maximize droplet contact and residence time. Electrostatic coalescers apply an electric field to induce droplet polarization and collision, accelerating coalescence, especially for difficult emulsions. Coalescing filters combine separation and filtration, using a coalescing media to merge droplets followed by a final filtration step to capture residual particles.

Common applications span petroleum processing, natural gas dehydration, aviation fuel polishing, wastewater treatment, and chemical processing. In oil and gas, coalescers remove free and emulsified water from crude or condensate streams. In aviation and industrial fuels, they protect engines and systems from water contamination. In wastewater, they help separate oil from water for recycling or disposal.

Key design considerations include droplet size distribution, phase viscosities and interfacial tension, flow rate and residence time, temperature, and potential fouling of the media. Performance is typically measured by removal efficiency and pressure drop across the unit.