THE BEST PARTNER HANBIT SOLTECH
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|Type||Bubble-cap tray||Sieve tray||Valve tray||Dual-flow tray|
|Capacity||Moderate||High||High to very high||Very high|
|Efficiency||Moderate||High||High to very high||Lower than other types|
|Turndown||Excellent (10:1)||About 2:1||4:1, up to 6-7:1||Low|
|Entrainment||High||Moderately high||Moderate||Low to moderate|
|Pressure drop||High||Moderately high||Moderate||Low|
|Maintenance||Relatively high||Low||Low to moderate||Low|
|Fouling Tendency||High||Low||Moderate||Extremely low|
|Cost||High||Low||Low to moderate||Very low|
Bubble Cap Tray
Bubble cap tray is a flat perforated plate with risers around the holes, and caps in the form of inverted cups over the risers. The caps are usually equipped with slots through which the vapor comes out. Liquid and froth are trapped on the tray to a depth at least equal to the weir height or riser height, giving the Bubble cap tray a unique ability to operate at low vapor and liquid rates.
Main Applications✔ Extremely low flow conditions
Advantage• Well known performance
Disadvantage• High material cost
Sieve tray is a flat perforated plate. Vapor issues from the holes to give a multi-orifice effect. The vapor velocity keeps the liquid from flowing down through the holes. At low vapor velocity, liquid weeps through the holes, bypassing some of the tray and reducing efficiency, giving sieve trays relatively poor turndown. Sieve trays are simple and easy to fabricate, and are therefore relatively inexpensive.
Main Applications✔ Most columns when turndown is not critical
Advantage• High capacity than bubble cap tray
Disadvantage• Low turndown ratio (2:1)
Floating Valve Tray
Floating valve tray has round movable valves with or without a caging structure on perforated plate. The valve disks rise as vapor rate is increased. The upper limit of opening is controlled by a caging structure or by restrictive legs at the bottom of the valve unit. As vapor rate falls, the disk openings are reduced, or they may settle intermittently over the holes. This stops the liquid from weeping and gives the valve tray its main advantage; good operation at low flow rates, and therefore, a high turndown.
Main Applications✔ Most columns
Advantage• More capacity than sieve or bubble cap tray
Disadvantage• Can plug
Dual Flow Tray
Dual flow tray is a sieve tray with no downcomers. Tray Holes have a dual function to pass both liquid and vapor. This tray operates with liquid continuously weeping through the holes, hence its low efficiency. Tray froth height diminishes rapidly when vapor velocity is reduced, causing further efficiency deterioration upon turndown. Turndown of a dual flow tray is even poorer than that of a sieve tray with downcomers. Dual flow trays are prone to channeling, and are therefore sensitive to out of levelness and to liquid distribution.
Main Applications✔ Capacity revamps where efficiency and turndown can be sacrificed
Advantage• Greater capacity than common valve tray
Disadvantage• Relatively low efficiency
Baffle trays are arranged in a tower in such a manner that the liquid flows down the column by splashing from one baffle to the next lower baffle and the ascending gas or vapor passes through the “curtains” of liquid spray descending from baffle to baffle.
Main Applications✔ Heavy oil refining and petrochemical industries in heat transfer applications
Advantage• Very high capacity
Disadvantage• Poor efficiency (due to the low contact area)