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A study of sieve‐tray efficiencies
Author(s) -
Hay J. M.,
Johnson A. I.
Publication year - 1960
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690060307
Subject(s) - tray , plate column , mass transfer , chemistry , sieve (category theory) , analytical chemistry (journal) , pressure drop , methanol , mechanics , pellets , superficial velocity , dimensionless quantity , leakage (economics) , materials science , chromatography , composite material , flow (mathematics) , mathematics , physics , organic chemistry , combinatorics , engineering , economics , macroeconomics , mechanical engineering
The performance of sieve trays in the rectification of the methanol‐water system without entrainment or leakage from the perforations was studied in an 8‐in.–diameter five‐tray column. The trays had a 2‐in. weir height and 4‐in. length of liquid path. Three tray geometries were studied: 1/4‐in. diameter holes on 3/4‐in. triangular spacing, 1/8‐in. holes on 3/8‐in. triangular spacing, and 3/16‐in. on 7/16‐in. triangular spacing. The superficial vapor velocity was varied from 2.2 ft./sec. to the limit of stable operation, which for this apparatus was 4.4 ft./sec. The ratio L M / V M within the column was varied from 1 to 0.5. The Murphree plate efficiency varied greatly from 105% at low concentration to 82% at high concentrations of methanol. Variations of 10 or 12 efficiency % were noted owing to changing velocities and tray geometries. Measurements of concentration gradients, foam heights, and gas pressure drops are also reported. This paper proposes a method of calculating the point efficiency and the number of individual‐phase mass transfer units independent of the actual concentration gradient on the tray. The method is applied to the methanol‐water data, and calculated point efficiencies range from 50 to 65%. The value of 1/ N L for the methanol‐water system is found to be small. The values of N G and the effect of the velocity on N G are believed to be the first in the literature for a tray in distillation operation. The effect of velocity is shown to be in agreement with the theory proposed by Gerster and co‐workers. It is shown that k G ' a G decreases for increasing free area and increasing hole size. Finally variation in L M / V M is shown to have little effect on E MV .