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Downcomer liquid level

The experimental equipment has proved exceedingly valuable in elucidating many of the factors such as hydraulic gradient, weeping" characteristics, effect of vapor velocity on foam height, weir performance under foaming conditions, downcomer liquid levels, effect of deviation from verticality, etc., which affect the hydraulic performance of various types of trays. [Pg.555]

Z Vertical elevation Zd Downcomer liquid level Zs Two phase level in separator Z Nonboiling (subcooled) length y Density ratio, p Density V Specific volume... [Pg.64]

Another important consideration in tower design is tray downcomers size. At high ratios of liquid flow to vapor flow a proportionally greater area on the tray must be allotted to the downcomer channel opening. Downcomers are designed from basic hydraulic calculations. If the downcomer is inadequately sized and becomes filled with liquid, liquid level will build on the tray above. This unstable situation will propagate its way up to the tower and result in a flooded tower condition. Excessive entrainment can also lead to this same condition and, in fact, is usually the cause of flooding. [Pg.87]

The bottom of the downcomer must be sealed below the operating liquid level on the tray. Due to tolerance in fabrication and tray level, it is customary to set the downcomer seal referenced to the weir height on the outlet side of the tray. Recommended seals, based on no inlet weir adjacent to the downcomer, and referenced as mentioned are given in Table 8-19. [Pg.168]

This is the case with diameter determination. The relation of Equation 8-250 for the perforated tray or sieve tray with downcomers can be used for the plate without downcomers. Generally, the liquid level and foam-froth height will be higher on this tray, hence the ralue of h., clear liquid on the tray, may range from 1-in. to 6-in. depending on the service. [Pg.203]

F = Free height in downcomer above clear liquid level (not froth level)... [Pg.222]

On the other hand, all trays in a tower below downcomer B will lose liquid levels and dry out, when flooding starts in downcomer B. Thus, the following rules apply ... [Pg.8]

As the liquid level on a tray increases, the height of liquid in the downcomer feeding this tray will increase by the same amount. Again, excessive downcomer liquid or froth levels result in flooding and loss of tray efficiency. [Pg.9]

This means that if we calculated a clear liquid level of 12 inches in our downcomer, then we would actually have a foam level in the downcomer of 12 in/0.50 = 24 in of foam. [Pg.11]

One of the most frequent causes of flooding is the use of carbon steel trays. Especially when the valve caps are also carbon steel, the valves have a tendency to stick in a partially closed position. This raises the pressure drop of the vapor flowing through the valves, which, in turn, pushes up the liquid level in the downcomer draining the tray. The liquid can then back up onto the tray deck, and promote jet flood, due to entrainment. [Pg.15]

The clear liquid height, or the liquid holdup, is the height to which the aerated mass would collapse in the absence of vapor flow. The clear liquid height gives a measure of the liquid level on the tray, and is used in efficiency, flooding, pressure drop, downcomer backup, weep-... [Pg.318]

The discharge end of the downcomer must project far enough into the tray liquid so that no gas bubbles can enter the open end and bypass the bubble caps. When the liquid contains no sediment, a seal pot or discharge weir is often placed around the discharge end of the downcomer to make certain that no free vapor can enter the open end. The distance between the liquid level on the loaded discharge plate and the bottom of the downcomer when no liquid is flowing is known as the downcomer liquid seal. A downcomer liquid seal, based on a perfectly level tray, in the range of to l in. is usually satisfactory. [Pg.685]

Above the limiting liquid load, the vapor is entrained downward in the downcomer, the tray liquid level builds up, and the liquid becomes entrained into the vapor stream. The tower floods with the liquid. [Pg.274]

The assembly is similar to a toadstool, with the hollow stem positioned off to one side of the cap about 1/4 of the way in from one edge. The top end of the tube projects above the plate surface the lower end stops just above the surface of the plate below. The tube is projected above the plate surface in order to form a miniature dam (called a "weir") to maintain a depth of liquid on the plate. As the liquid level rises, overflow occurs into the downcomer pipe to the next plate below. [Pg.9]

The discharge end of each downcomer pipe must be positioned close to the surface of the plate below, so that the free end will be immersed in the liquid level on that plate. This forms a liquid seal over the open end to keep vapor from entering the pipe. By positioning successive downcomer pipes on opposite sides of each sieve tray, the liquid flows across each plate, minimizing any stagnate flow sections and helping move any solids that might accumulate from the distillation column. [Pg.9]

The subcooM region is modelled separately along with the downcomer pipework. As far as the drum model is concerned, its sole contribution comes in determining liquid level, where it adds a constant term to the liquid volume. As mentioned previously, the subcooled region may make up typically about 10% or less of the water volume of the drum, and so its effect on steam drum dynamics is second-order only. [Pg.122]

Ultimately, purely mechanical difficulties arise. High pressure drop may lead directly to flooding. With a large pressure difference in the space between trays, the level of liquid leaving a tray at relatively low pressure and entering one of high pressure must necessarily assume an elevated position in the downspouts, as shown in Figure 4.6. As the pressure difference increases due to an increased rate of flow of the gas, the level in the downspout will rise further to permit the liquid to enter the lower tray. Ultimately, the liquid level in the downcomer may reach that on the tray above and the liquid will fill the entire space between the trays. The tower is then flooded, the tray efficiency falls to a very low value, the flow of gas is erratic, and liquid may be forced out of the gas exit pipe at the top of the tower. [Pg.250]

An overflow pipe (or downcomer), with an opening located below the top of the risers, is recommended for preventing liquid from overflowing the risers at high liquid levels (Fig. 4.10). The overflow pipe should be liquid-sealed at the bottom to avoid vapor rise through it. Two experiences have been described (57, 237) where failure to provide an overflow pipe caused liquid to overflow the risers and prematurely flood the column section above the chimney tray. In a third case (334), liquid overflowing the risers caused entrainment (Sec. 8.2). [Pg.109]

Downcomer trapouts seldom provide sufficient residence time for vapor disentrainment, and the venting process must be completed downstream of the column outlet. The vent-retum nozzles must always be located above the tray s liquid level. Downstream piping must be designed for self-venting flow (Fig. 4.5). [Pg.111]

The downcomer in Fig. 4.12a is likely to lose its seal whenever its liquid height drops below tray level. When the seal is lost, vapor fium the tray ascends the downcomer, which may cause flooding, cycling, and/or poor separation. Downcomer unsealing by this mechanism is most likely to occur when the liquid drawn constitutes a laige portion of the downcomer liquid flow, when the quantity drawn tends to fluctuate, and/or when excessive leakage takes place due to tray weeping or draw pan leaks. [Pg.111]


See other pages where Downcomer liquid level is mentioned: [Pg.157]    [Pg.170]    [Pg.7]    [Pg.26]    [Pg.29]    [Pg.274]    [Pg.334]    [Pg.157]    [Pg.170]    [Pg.1579]    [Pg.1582]    [Pg.486]    [Pg.494]    [Pg.495]    [Pg.498]    [Pg.43]    [Pg.1575]    [Pg.1578]    [Pg.40]    [Pg.359]    [Pg.98]    [Pg.109]    [Pg.110]    [Pg.110]    [Pg.127]    [Pg.129]   
See also in sourсe #XX -- [ Pg.8 ]




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