Trays valve

This type of tray is designed to allow for wide variations in liquid and vapor flow. One typical design of a valve vapor opening consists of a one- to two-inch diameter orifice in the tray plate, an orifice cover, and a travel stop. At low vapor rates, the orifice cover is settled in its lower position. In this position, slots in the orifice cover allow small amounts of vapor to be distributed evenly. At higher vapor rates, the orifice cover is elevated to its upper position set by the travel stop. In this position, large amounts of vapor can flow through the valves. 

Maximum efficiency at low loads and high efficiency at conditions 5 to 10 percent below flooding results in usable capacity. 

A combination of lower pressure drop per stage and high efficiency for vacuum systems results in low tower pressure drops. 

The mechanical design of the tabs are such as to virtually eliminate sticking problems. At zero to relatively low vapor rates, the V-type unit is sealed on 

Some specific claims of Koch Engineering11 are as follows  

Flexitrays can handle loads up to 10 percent higher than sieve trays and 15 to 20 percent higher than bubble-cap trays. 

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Cast-iron column shells are satisfactory, but stainless-steel bubble or valve trays are preferred. A flow sheet of a typical tar acid extraction and refining plant is shown in Figure 3. 

Float Valve Tray Design Manual, Nutter Engineering Co., Tulsa, OHa., 1976. 

A wide range of loadabihty (turndown ratio) is required. Valve trays are particiilarly desirable in this case. 

Fractionation Research, Inc. Report of Tests of Nutter Type B Float Valve Tray, July 2, 1964 from Nutter Engineering Co. 

Downcomer Backup Flood. For downcomer backup. Equation 4 can be used. Reference 15 states that if the downcomer backup for valve trays exceeds 40% of tray spacing for high vapor density systems I3.01bs/ft-), 50% for medium vapor densities, and 60% for vapor densities... 

Valve trays Minimum liquid head on liquid distributor, in. 0.75-1 ... 

If the absorber has aceess manways, blank off a portion of the bubble eaps or valve trays. 

In valve trays, perforations are covered by liftable caps. Vapor flows lifts the caps, thus self creating a flow area for the passage of vapor. The lifting cap directs the vapor to flow horizontally into the liquid, thus providing better mixing than is possible in sieve trays. 

Trays operate within a hydraulic envelope. At excessively high vapor rates, liquid is carried upward from one tray to the next (essentially back mixing the liquid phase in the tower). For valve trays and sieve trays,. i capacity limit can be reached at low vapor rates when liquid falls through the rray floor rather than being forced across the active area into tlic downcomers. Because the liquid does not flow across the trays, it rass.scs contact with the vapor, and the separation efficiency drops dramatically. ... 

At low vapor rates, valve trays will weep. Bubble cap trays cannot weep (unless they are damaged). For this reason, it is generally assumed that bubble cap trays have nearly an infinite turndown ratio. This is true in absorption processes (e.g., glycol dehydration), in which it is more important to contact the vapor with liquid than the liquid with vapor. However, this is not true of distillation processes (e.g., stabilization), in which it is more important to contact the liquid with the vapor. 

Bubble Cap Figures 8-63, 64, 66 Several Med. to 60% Good low flows, exceeds Valve Tray High Good... 

Nye Tray, 10-20% increased tray (over sieve or valve) capacity and good efficiency. More capacity from existing column. Improved inlet area for sieve or valve tray with greater area for vapor-liquid disengagement. 

Figure 8-69A. Nutter BDH Float valve tray with downcomer. Used by permission, Nutter Engineering, Harsco Corp.

Figure 8-71 A. Nutter MVO high performance fixed valve tray with 4 1 turndown ratio. Used in new installations and to replace sieve trays. Used by permission, Nutter Engineering, Harsco Corp., Bui. CN-4.

Figure 8-78. Glitsch Nye Tray action to improve conventional sieve and valve tray performance by 10-20%. Used by permission, Glitsch, Inc., Bui. GLI-5138.

Specifically, the Nye Tray achieves this Improvement by using a patented inlet area on a sieve or valve tray, which increases the area available for vapor-llquid disengagement. 

Figure 8-80. Typical Norton Valve Tray Valves. Used by permission, Norton Chemical Process Products Corp., Stow, Ohio., Bui. FT-2.

Turndown can be applied to all types/styles of tray columns however, it is more relevant to sieve and valve trays. The generally accepted explanation of turndown is as follows [199] (also see Figure 8-101) ... 

The performance analysis of these trays is quite similar to bubble caps, but more so to valve trays, because the tray has the same basic mechanical features. The difference being that bubble caps and valves are replaced by perforations or holes in the tray for entrance of the gas to the liquid on the tray. Figures 8-67A and 8-118 and 119 represent the general construction of a sieve tray. 

Hsieh and McNulty [210] developed a new correlation for weeping of sieve and valve trays based on experimental research and published data. For sieve trays the estimation of the weeping rate and weep point is recommended using a two-phase countercurrent flow limitation model, CCFL. 

The weep point for sieve or valve trays is the vapor rate at which the liquid weeping rate is diminished to zero. Thus, J L approaches zero asJ G is increased [210]. For a vapor rate that leads to J g higher than the weep point value, then there should be no weeping. 

The equivalent hole diameter for use in the equation for Z when considering the two types of valve trays studied here is given by ... 

For the valve tray equivalent hole diameter, see illustration. 

Fv = valve tray F-factor, ft- /min/valve Fvm = valve tray F-factor at the beginning of the valve open region, fr /min/valve g = gravitational constant, ft/s he = clear liquid height, in. ho = dry tray pressure drop, in. 

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