Plate spacing

Packed vs Plate Columns. Relative to plate towers, packed towers are more useful for multipurpose distillations, usually in small (under 0.5 m) towers or for the following specific appHcations severe corrosion environment where some corrosion-resistant materials, such as plastics, ceramics, and certain metaUics, can easily be fabricated into packing but may be difficult to fabricate into plates vacuum operation where a low pressure drop per theoretical plate is a critical requirement high (eg, above 49,000 kg/(hm ) (- 10, 000 lb/(hft )) Hquid rates foaming systems or debottlenecking plate towers having plate spacings that are relatively close, under 0.3 m. 

Weir height is less than 15 percent of plate spacing... 

Comparison of Efficiency of Various Plates Several studies of various plates have been carried out under conditions such that direct and meaningful comparisons are possible. Required conditions include identical system, same pressure, same column diameter, and equivalent submergence. Standart and coworkers [B/ Chem. Eng., 11 (11), 1370 (1966) Sep. Sci, 2, 439 (1967)] used the methanol-water system at atmospheric pressure in a 1.0-m (3.3-ft) column. For a plate spacing of 0.4 m (15.7 in) they studied the following ... 

Billet and cowodcers [Chem. Jng. Tech., 38, 825 (1966) Jnstn. Chem. Engrs. Symp. Set No. 32, 5, 111 (1969] used the ethylbenzene/ styrene system at 100 torr and a 0.8-m column with 500-mm plate spacing. Two weir heights were used, 19 and 38 mm. Operation was at... 

Column diameter in. Amplitude, in. Plate spacing, in. Agitator speed, strokes/min Extractant Dispersed phase Minimum HETS Throughput, gal hr- ft-2 Volumetric efficiencies V/HETS,h" ... 

Curve No. Column diam, in phase dispersed phase extractant Double amplitude, in Plate spacing, in Total throughput gal/(li)(fr)... 

The following parameters are kept constant on the scale-up total throughput per unit area, plate spacing, and stroke length. The... 

For two-stage precipitators with close collec ting-plate spacings (Figs. 20-152, 20-153), the gas flow is substantially streamline, and no 01001 110 wind exists. Consequently, with reentrainment neglected, collec tion efficiency may be expressed as [Penny, Electi Eng, 56, 159 (1937)]... 

Ward [187] reports the best fits for the curves at tray (or plate) spacing in the range of 0.5 to 3.0 feet, and at the ends of the curves. 

Liquid entrainment mass velocity corrected for liquid properties and plate spacing, lb entrainment/(hr) (ft ), based on net tray area as for Wg... 

A note of caution on the use of photo-etched channels has been offered by RAMSHAWfl3 ) who points out that the system is attractive in principle provided that severe practical problems such as fouling are not encountered. With laminar flow in matrices with a mean plate spacing of 0.3-1 mm, volumetric heat transfer coefficients of 7 MW/m3 K have been obtained with modest pressure drops. Such values compare with 0.2 MW/m3 K for shell and tube exchangers and 1.2 MW/m3 K for plate heat exchangers. 

Reciprocating tray towers can have holes 9/16 in. dia, 50-60% open area, stroke length 0.75 in., 100-150 strokes/min, plate spacing normally 2 in. but in the range 1-6 in. In a 30 in. dia tower, NETS is 20-25 in. and throughput is 2000 gal/(hr)(sqft). Power requirements are much less than of pulsed towers. 

GL 13] [R 1] [P 12] By using a nickel plate, space-time yields up to 401 mol 1 h were achieved in the falling film micro reactor [6]. Control experiments in a batch reactor at a 30 min reaction time resulted in a space-time yield of only 1.3 mol 1 h , hence orders of magnitude smaller. By using an iron plate, space-time yields up to 346 mol h were achieved in the falling film micro reactor. 

Where a side-stream is withdrawn from the column the plate design must be modified to provide a liquid seal at the take-off pipe. A typical design is shown in Figure 11.25a. When the feed stream is liquid it will be normally introduced into the downcomer leading to the feed plate, and the plate spacing increased at this point Figure 11.25A... 

Optimise design repeat steps 3 to 12 to find smallest diameter and plate spacing acceptable (lowest cost). 

Weir height less than 15 per cent of the plate spacing. 

The downcomer area and plate spacing must be such that the level of the liquid and froth in the downcomer is well below the top of the outlet weir on the plate above. If the level rises above the outlet weir the column will flood. 

This value is also taken as the mean density of the fluid in the downcomer which means that for safe design the clear liquid back-up, calculated from equation 11.91, should not exceed half the plate spacing lt, to avoid flooding. 

This criterion is, if anything, oversafe, and where close plate spacing is desired a better estimate of the froth density in the downcomer should be made. The method proposed by Thomas and Shah (1964) is recommended. 

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