Trays chimney

Pipe downcomers from chimney tray too small for flow. Poor separation. Slightly higher pressure drop. Design error. 

Hats on chimney tray excessively restricted vapor resulting in liquid entrainment. Design error. 

Commonly, amine absorbers include an integral gas. scrubber section in the bottom of the tower. This scrubber would be the same diameter as required for the tower. The gas entering the tower would have to pass through a mist eliminator and then a chimney tray. The purpose of this scrubber is to remove entrained water and hydrocarbon liquids from the gas to protect the amine solution from contamination. 

Wheeler, D. E., Design Criteria For Chimney Trays, Hydrocarbon Processing July, (1968) p. 119. 

The sum of APv + APL is the total height of liquid on the chimney tray. Let us assume that this total height is 6 in of liquid ... 

Figure 7.4 shows a modern, narrow-trough, liquid collector-vapor distributor chimney tray. While the initial vapor distribution through a packed bed is not quite so critical or difficult as the liquid distribution, it is still important. 

The narrow-trough vapor distributor shown in Fig. 7.4 is intended to disperse the vapor evenly across the bottom of the packed bed. The width of the chimney does not exceed 6 in. The older-style chimney trays, which may have had a few large round or square chimneys, reduced the separation efficiency of the packing. To work properly, the vapor distributor has to have a reasonable pressure drop, in comparison to the pressure drop of the packed bed. For example, if the expected pressure drop of a 12-ft packed bed is 10 in of liquid, the pressure drop of the vapor distributor ought to be about 3 to 4 in of liquid. 

In practice, the most common reason why vapor flow is maldistrib-uted as it escapes from a well-designed chimney tray is distortion of the hats. I believe this is due mostly to workers stepping on the hats during unit turnarounds. The hat support brackets are designed to support a 20-lb hat, not a 200-lb welder. 

FIG. 14-72 Chimney tray vapor distributor. (Reprinted courtesy of Koch-Glitsch LP.)... 

Liquid collectors are installed when liquid must be collected for redistribution or drawoff (e.g., for external cooling). The common device used is a chimney tray, which is similar to an orifice redistributor, but without perforations. Another common device is the Chevron-type collector, which is a series of Chevron blades, with liquid being collected at the bottom of the blades. 

Intermediate liquid outlets. Liquid may be withdrawn using a chimney tray or from a downcomer. A chimney tray is a flat, unperforated plate with vapor risers. It permits total withdrawal of liquid a downcomer drawoff permits only partial withdrawal because some weeping occurs through the tray. A downcomer drawoff may contain some entrained gas, which must be separated downstream or allowed for in downstream equipment design. 

Low-velocity vapor-only feeds often enter via bare nozzles or V baffles (above). At higher velocities, perforated vapor spargers are used. At high velocities, vapor horns and Schoepentoeters are often preferred. Alternatively or additionally, a vapor distributor may be mounted above the feed. The vapor distributor is a chimney tray (Fig. 14-72) where liquid is collected on the deck and flows via downcom-... 

Under normal service conditions, the liquid collector is a separate tray from any liquid distribution device. The basic collector is a chimney tray with a sump (Fig. 9). The chimneys provide passage for vapor rising through the tray. The sump(s) provides for liquid drainage into a draw nozzle (for product draw) or... 

Passages on chimney trays should be designed so that liquid can easily flow into product draws and sumps. If blockage of liquid draws is a potential... 

Weir redistributors These are identical to notched-trough distributors. Because weir redistributors cannot collect liquid from the upper section, a liquid collector such as a chimney tray or chevron collector (Chap. 4) or a collecting support plate (e.g., the upper plate in Fig. 3.8c) is usually required above the redistributor. 

Most vapor distributors are essentially chimney trays (Chap. 4) specifically designed to promote vapor distribution. A typical vapor distributor contains a large number of uniformly spaced vapor risers and... 

Arrangements such as bottom sumps, chimney trays, side-draw drums, and surge drums are usually designed for avoiding the presence of vapor in the liquid outlet. On the other hand, downcomer trapouts are usually designed to allow for the presence of vapor in the outlet liquid. 

Providing adequate residence time is a primary consideration in arrangements that avoid vapor in liquid outlets. Such arrangements t )-ically include bottom sumps, chimney trays, external side-drawoff drums, or surge drums. Sufficient residence time must be provided in the liquid-drawoff sump for one or more reasons ... 

Guidelines for sump residence time are scarce in the published literature. Those given by Wheeler (420) for chimney trays are the only detailed list available (Table 4.1). Wheeler (420) did not state the residence time definition on which his guidelines are based. The author believes that their application with the above definition is reasonable for chimney trays, bottom sumps, and side-draw drums. Caution is needed when these guidelines are applied, particularly when the main consideration is to buffer upsets. 

A residence time smaller than 1 minute using the above definition may be satisfactory on chimney trays that are used for withdrawing pumparound liquid in nonfoaming services. Because of the large circulation rate ts pical in such applications, a 1-minute residence time may require an excessively tall chimney tray. Since pumps used in such applications t3q>ically develop low heads, they usually can tolerate some entrained vapor. 

Once-through reboiler arrangement Here reboiler liquid is withdrawn from the bottom downcomer or from a chimney tray located above the bottom sump. Typical arrangements are shown in Fig. 4.7. 

In tray columns, liquid to once-through reboilers (Fig. 4.7a to c), as well as liquid to many recirculating reboilers (Fig. 4.7cf), is normally withdrawn from the bottom tray via a trapout pan. In packed columns, a chimney tray is usually preferred for this purpose. This trapout pan can often be troublesome. Successful operation requires close attention to the following guidelines ... 

Chimney trays (Fig. 4.10a, 6) are used for withdrawing intermediate liquid streams from the column in a packed tower, they are also used as liquid collectors or vapor distributors. Alternative devices used for liquid withdrawal are downcomer trapouts in tray columns, chevron collectors, and some redistributors in packed columns. Compared to these alternative devices, chimney trays have the following advantages ... 

In packed columns, chimney trays are the most effective liquid collection devices for high liquid flow rate services, for interreboilers, and for once-through reboilers. They are also sometimes used for collecting liquid from an upper bed for redistribution (when the redistributor is not self-collecting), and as vapor distributors. 

In tray columns, chimney trays do not suffer from unsealing problems and are generally less troublesome than downcomer trapouts. 

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