HANBIT SOLTECH

Conventional Trays

Trays are a mass transfer device, primarily used for cross-current vapor/liquid contact consisting of inlet area (inlet deck), active area (active deck) and outlet area (exit weir and downcomer). There are many design options which need to be considered for each of these basic tray units.

Trays are designed primarily from a hydraulic standpoint with the belief that a hydraulically well designed tray will achieve the optimum efficiency for a given tower diameter and tray spacing. Also the tray design parameters involved are many and any of these parameters can affect efficiency. Therefore tray designs require a thorough understanding of many relevant hydraulic parameters in order to quantify their performance characteristics.

The three main tray types in the market today are the bubble cap tray, the sieve tray, and the valve tray. Each has relative advantages and disadvantages although the valve tray is by far the most widely used. We offer a complete line of conventional trays including dual-flow, baffle trays and related equipment.

Comparison of the Common Tray Types

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Comparison of the Common Tray Types
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.

It is able to operate over a wide range of loads with turndowns at least in the range of 10:1. This is due to the good liquid seal resulting from the cap design itself which acts like a diving bell when setting in a liquid pool. The bubble cap tray provides a fairly high liquid pool to operate which is an advantage for systems requiring high liquid residence times for chemical reaction.

Due to their ability to operate at low vapor and liquid rates, bubble cap trays are used primarily when large turndown ratios are required. This tray is the most expensive option and it has lower capacity compared to sieve and valve trays. Bubble cap can be offered in 3”, 4”, 6” OD and custom sizes as well.

Main Applications

✔ Extremely low flow conditions
✔ Where leakage must be minimized

Advantage

• Well known performance
• Good liquid seal
• High turndown (10:1)
• High liquid residence time

Disadvantage

• High material cost
• High installation cost
• Long installation period
• Low capacity than sieve tray
• Non-uniform flow due to high liquid gradient

Sieve Tray

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.

The large hole size sieve trays (hole diameters range from 1/8” to 1” with 1/2” being standard) offer good fouling resistance. Sieve trays also have higher capacity than bubble cap trays. The only major disadvantage of the sieve tray is its poor turndown characteristics which is typically not much better than 2:1.

Sieve trays have been used widely in the petroleum and chemical industries for many years because they are the most economical trays when low turndown is required. When properly designed, they have a capacity and efficiency equivalent to other types of general purpose trays. They can also be used in moderately dirty services.

Main Applications

✔ Most columns when turndown is not critical

Advantage

• High capacity than bubble cap tray
• Low liquid gradient
• Fouling resistance (with large orifice hole)
• Relatively low cost

Disadvantage

• Low turndown ratio (2:1)
• Prone to vibration at low rate

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.

The valve tray was developed to overcome the turndown limitations of the sieve tray. Because of the valve’s ability to open or close at various loading conditions the design turndown range increased to about 4:1. Two different weight valves are used to allow a wider flexibility of operating range, which gives more turndown ratio.

Floating valve tray exhibits lower entrainment than sieve tray because the flow of vapor through the holes is horizontal by valve unit. They have an efficient operating range (turnodwn) superior to a sieve tray when both are designed for the same maximum capacity. They are a much simpler, lower pressure drop and lower cost alternate to the bubble cap tray. The only drawback to using the floating valve tray is that valves can plug and they are difficult to clean when plugged.

Main Applications

✔ Most columns
✔ Services where turndown is important

Advantage

• More capacity than sieve or bubble cap tray
• Good turndown (4:1, up to 6-7:1)
• Good efficiency
• Same cost as sieve tray

Disadvantage

• Can plug
• Difficult to clean when plugged

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.

Due to the absence of downcomers, dual flow trays give more tray area, and therefore have a greater capacity than any of the common tray types. This makes them an ideal revamp tool if some efficiency can be sacrificed. The absence of downcomers, and the larger open areas, renders dual flow trays the most suitable to handle highly fouling services, slurries, and corrosive services. Dual flow trays are also the least expensive to make, and easiest to install and maintain.

As such, the use of dual flow trays may be more advantageous than other contacting devices, especially dual flow trays are now primarily utilized for fractionation of polymerizable compounds because of their low hold-up and ease of cleaning.

Main Applications

✔ Capacity revamps where efficiency and turndown can be sacrificed
✔ Highly fouling and corrosive services

Advantage

• Greater capacity than common valve tray
• Fouling resistance
• Low pressure drop
• Relatively low cost

Disadvantage

• Relatively low efficiency
• Low turndown ratio (smaller than sieve tray)
• Sensitive to leveling

Baffle Tray

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.

Tray decks may be level or slightly inclined and typically occupy 40-60% of the tower cross-sectional area. A shower-deck tray is a special type of side-to-side baffle tray with baffles extended to create overlapped baffles; the overlapped sections are perforated and have a weir that forces the liquid flow through the holes. Because of their open design, baffle trays are used in applications requiring high capacity, fouling resistance and low pressure drop.

Baffle trays are generally designed to give a maximum dispersion of liquid and an optimum contact of liquid and vapor with high capacities. They are well suited for heat transfer applications including heavy oil refining with high solids.

Main Applications

✔ Heavy oil refining and petrochemical industries in heat transfer applications

Advantage

• Very high capacity
• Fouling resistance
• Very low pressure drop
• Relatively low cost

Disadvantage

• Poor efficiency (due to the low contact area)

Conventional TraysTHE BEST PARTNER HANBIT SOLTECH Introduction Bubble Cap Tray Sieve Tray Floating Valve Tray Dual Flow Tray Baffle Tray

Conventional Trays
THE BEST PARTNER HANBIT SOLTECH

Introduction Bubble Cap Tray Sieve Tray Floating Valve Tray Dual Flow Tray Baffle Tray