What are sieve trays and valve trays used for in crude oil distillation?

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Aerial view of an oil refinery complex near New Orleans, Louisiana, with storage tanks, industrial structures, and smoke rising from the facility, surrounded by open land. — petroleum refining Aerial view of an oil refinery near New Orleans.

In crude oil distillation, sieve and valve trays are essential components housed within the fractionating column to facilitate the separation of hydrocarbon components.1

These trays are designed to promote intimate contact between rising oil vapours and descending liquid, known as reflux. As the vapours pass through the openings in the trays, they undergo continuous condensation and reevaporation. This process allows the liquid to absorb heavier constituents from the vapour while simultaneously releasing lighter constituents into the vapour phase, eventually establishing a temperature and property gradient throughout the tower.1

The specific designs function as follows:
* Sieve trays: These consist of simple perforated plates featuring small holes, typically 5 to 6 mm (0.2 to 0.25 inch) in diameter.1
* Valve trays: These are similar to sieve trays but include small metal disks covering the perforations. These disks act to restrict the flow of vapours through the holes under specific process conditions.1