Trays caps, selection

From the residence time in dorvneomers for bubble cap trays, and at the very low tray spacing of 9 inches, select an allowable liquid velocity of 0.1 ft/sec. 

Kister et al. [136] prepared one of the few comprehensive distillation studies for the application selection of valve and sieve trays compared to random or structured packing. This reference is based on a more comprehensive evaluation of accumulated data by the same authors [137]. Many separate studies have been conducted for trays [138] including bubble caps as well as various packings, but few, if any attempt to establish similar conditions to make a viable comparison as is attempted in References 136, 137. There are four main differences related to capacity and separation [136] when considering ... 

Select an Lm equation in accordance with the number of tray liquid passes, Eqs. (3.53) through (3.56). Execute the equation the same as for valve-type trays, determining Lm for the bubble cap tray. 

The number of valve caps that can be fitted on a tray is at best an estimate unless a detailed tray layout is prepared. However, a standard has evolved for low- and moderate-pressure operations a 3 x 2 y2 in pattern that is the tightest arrangement available, accommodating about 14caps/ft2 (150 caps/m2). The active area does not take into account liquid-distribution areas at the inlet and outlet, nor edge losses due to support rings, nor unavailable space over tray-support beams. In smaller columns, it is possible that as much as 25 percent of the active tray area may not be available for functioning valves. For this column, which operates at low pressure, select the standard 3 x 2 /2 in pitch. 

The mass-transfer devices may be sieves (holes), fixed valves, moveable valves, or bubble caps. Fig. 2 shows a selection of mass-transfer devices. The purpose of the device is intimate mixing of the vapor and liquid on the tray deck. An ideal device has high capacity, high flexibility, low leakage, low pressure drop, and low cost. 

The sample boat with reagents is placed at the entrance of the combustion tube and slid into the heated zone with a long fork. The cap at the entrance to the combustion tube is screwed into place, heating mode "3" is selected, and the start button is pressed. The mercury response values from this measuring cycle are discarded. While the first boat is being heated, a second sample boat is prepared with reagents in a similar manner. At the end of the cycle, the first boat is removed and allowed to cool in a covered tray. The second boat is also subjected to one heating cycle. 

Five bubble size distributions were selected from the literature to compare with the binary and cluster coalescence models. Four were measured in small-scale bubble column test sections and one in a sieve tray. Newtonian systems of air-water, oxygen-water, and oxygen-glycol, and a non-Newtonian oxygen-PAA solution were used. The data sets are described in Table 1. The mean bubble diameter is the equivalent diameter of a sphere of equal volume. Bubble shapes are generally ellipsoidal, though larger cap bubbles of -2 cm in diameter appear in several tests. 

FURFURAL. C5H4O . In laboratory tests, alloy 3(X)3 was resistant to solutions of furfural at ambient temperature and 200 C (392°F).. Aluminum storage tanks, evaporators, condensers, valves and pumps have been used to handle gasoline-furfural mixtures. Aluminum bubble caps, trays and heat exchangers have been used where furfural is used a.s the selective solvent. Pure furfural for pharmaceuticals has been stored in aluminum.. Alloy 35o.O valves have been used for handling furfural. See also Ref (1) p. 133. l2)p. 325.(3) p. 148. Op. 95. 

Random-packed absorption columns have seldom been used for large commercial-size dehydrators because of the very low liquid flow rates usually employed. As pointed out in Chapter I, a low liquid flow rate normally leads to the selection of a bubble-cap column. The recent trend toward extremely low dew-point requirements (-40°F and below) has resulted in a reexamination of contactor designs to attain more theoretical stages at a reasonable cost. Structured packing, which is offered by several vendors, is claimed to offer greatly increased throughput, lower pressure drop, and lower column height than bubble-cap trays for the same service. 

---