Explain the roles of filters and coalescers in oil-water separation trains.

• A. Filters remove solids; coalescers promote droplet coalescence to form larger droplets, improving downstream separation.
• B. Filters promote droplet coalescence; coalescers remove solids.
• C. Filters remove water; coalescers dissolve emulsions.
• D. Filters and coalescers both remove gas.

Answer: (A)

In oil-water separation trains, you want both solids removed and the oil droplets in the water encouraged to separate quickly. Filters remove solids from the flow, protecting equipment and preventing fouling downstream. Coalescers, by contrast, promote collisions and merging of dispersed oil droplets so they form larger droplets. Those larger droplets rise or settle more rapidly in the next stage, making the separation more efficient and reliable. The combination is practical: solids are filtered out first, then coalescing accelerates the actual oil–water separation. The other descriptions miss essential roles—coalescers don’t remove solids, filters don’t remove water, and neither device is used for dissolving emulsions or removing gas.