01 / TOWER INTERNALS · TRAY
Tray Column Internals
Tray decks and their fittings, engineered to stage gas–liquid contact at every level of a distillation or absorption column — bubble cap, sieve, floating valve and tongue trays.
How a tray column works
In a tray (plate) column, gas–liquid contact happens on a series of horizontal tray decks stacked up the column. Liquid flows across each tray and down to the next through a downcomer, while vapour rises through holes, valves or caps in the deck and bubbles up through the liquid layer at every stage. The tray type sets how the vapour passes through the liquid — and therefore the column’s capacity, turndown, pressure drop and resistance to fouling. PCX supplies tray internals (ถาดในหอกลั่น) sourced from qualified international manufacturing partners, engineered to your column loads.
BUBBLE CAP TRAY
Bubble Cap Tray
Vapour rises through a riser in the tray deck and is redirected downward by a cap sitting over it, forcing the gas to bubble out beneath the cap and up through the liquid layer on the tray. Because the cap always covers the riser, the tray cannot weep at low gas rates the way a sieve tray can — giving a very wide, stable operating range at the cost of more complex construction and higher pressure drop.
- Very wide operating range, stable at low and high vapour rates
- Wide gas-to-liquid ratio tolerance — no dumping or weeping
- More resistant to clogging than small-hole tray types
Applications: columns needing very wide turndown and stable operation across variable loads
Documentation
Catalogs and technical documentation are available upon request. Please contact our team for product information, specifications, and documentation.
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SIEVE TRAY
Sieve Tray
The simplest tray deck — a perforated plate with no moving parts. Vapour passes straight up through a regular pattern of small holes, bubbling through the liquid layer held on the tray by a weir and directed to the tray below via a downcomer. With few components it is the least expensive and easiest tray to fabricate, and remains the most widely used design across the industry.
- Simple, low-cost construction — easy maintenance
- Higher capacity than a bubble cap tray for a given diameter
- Low pressure drop — well suited to vacuum distillation
Applications: general distillation and absorption duty, vacuum columns, cost-sensitive projects
Documentation
Catalogs and technical documentation are available upon request. Please contact our team for product information, specifications, and documentation.
Contact UsFLOATING VALVE TRAY
Floating Valve Tray
A sieve-type deck with movable discs that open with vapour flow. Each valve hole carries a disc that lifts as vapour flow increases and settles back down as it falls, so the open area for gas passage adjusts itself to the vapour rate. Legs under each disc limit how far it can rise; small tabs around its edge keep it from sitting flush against the deck at very low gas rates.
- High capacity and good tray efficiency
- Wider turndown than a sieve tray
- Lighter and simpler to install than bubble cap trays
Applications: general-purpose columns needing wide turndown with high capacity
Documentation
Catalogs and technical documentation are available upon request. Please contact our team for product information, specifications, and documentation.
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TONGUE TRAY
Tongue Tray
An early inclined-jet design using angled tongue-shaped louvres. Gas passes through tongue-shaped louvres punched out of the tray deck and tilted at a fixed angle, so gas jets emerge in the same direction as the liquid flow across the tray — originally developed to limit excessive liquid entrainment carried up by the rising gas. Simple to build, though largely superseded by valve and sieve trays for demanding duty.
- Simple deck construction — easy to install and maintain
- Directional gas jetting reduces liquid entrainment
- Best suited to steady, less demanding duty
Applications: simpler columns and steady-load duty where entrainment control matters
Documentation
Catalogs and technical documentation are available upon request. Please contact our team for product information, specifications, and documentation.
Contact UsCOMPARISON
Tray Types Compared
| Tray type | Advantages | Limitations | Best suited to |
|---|---|---|---|
| Bubble cap | Widest turndown; no weeping or dumping; clog-resistant | Complex, costly; highest pressure drop; harder to maintain | Very wide, variable operating range |
| Sieve | Simple, low-cost; high capacity; low pressure drop | Weeps at low vapour rates; narrow turndown; small holes can clog | General duty and vacuum distillation |
| Floating valve | High capacity; wide turndown; good efficiency | Some weeping at low gas rates; valves can stick; higher ΔP than sieve | General-purpose columns needing wide turndown |
| Tongue | Simple deck; directional jetting cuts entrainment | Narrow load range; lower efficiency; largely superseded | Steady, less demanding duty |
Ratings are for general guidance; actual performance depends on the specific tray design, materials and column loads. Tray deck type, hole / valve layout and downcomer sizing are engineered to each column at quotation stage.
Frequently Asked Questions
Bubble cap vs sieve vs valve tray — what is the difference?
All three stage gas–liquid contact across a tray deck, but handle vapour differently. A bubble cap tray uses caps over risers, so gas always bubbles through the liquid and the tray cannot weep at low vapour rates — the widest turndown, but the most complex and costly. A sieve tray is just a perforated plate: simplest and cheapest, high capacity and low pressure drop, but it weeps at low vapour rates and has a narrower turndown. A floating valve tray sits between them — movable discs open and close with vapour flow, giving wide turndown and high capacity at moderate cost. See the comparison table above.
Which tray type is best for vacuum distillation?
Vacuum service rewards low pressure drop, which favours a sieve tray (or a low-pressure-drop valve tray). A bubble cap tray has the highest gas-phase pressure drop of the three and is usually avoided in vacuum columns unless its very wide turndown is specifically needed.
What is tray weeping and which trays are prone to it?
Weeping is liquid draining down through the tray deck instead of flowing across it and down the downcomer, which happens when vapour velocity is too low to hold the liquid up. Sieve trays are the most prone to weeping at low vapour rates; floating valve trays weep less because the valves close down; bubble cap trays effectively cannot weep because the cap always covers the riser.
What is a floating valve tray and when is it used?
A floating valve tray is a sieve-type deck where each hole carries a disc (valve) that lifts as vapour flow increases and settles back as it falls, so the open area adjusts itself to the vapour rate. This gives a wider turndown than a plain sieve tray with high capacity and good efficiency, at a lower cost and weight than bubble cap trays — which is why it is a common general-purpose choice. Legs under each disc limit its lift and edge tabs stop it sitting flush at very low gas rates.
How are trays specified and quoted?
Tray deck type, hole or valve layout and downcomer sizing are engineered to the specific vapour and liquid loads of each column — there is no fixed size table. PCX sources trays from qualified international manufacturing partners and supplies to your drawing or specification. Send the column diameter, number of trays, materials and vapour / liquid loads and we will return a quotation.
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