Abstract
Studies are reported on the characteristics of two sieve trays containing 1-inch-diameter holes. Little is known about the performance of such trays. A pilot plant was built containing two columns one 'rectangular' and the other 'round'. The trays had downcomers as would be the case in practice. The investigations are divided into four main sections: (i) Hydrodynamic studies of gas/liquid interactions on the tray. These include the measurements of liquid heads, froth heights, pressure drops, aeration and froth density factors, weeping and entrainment on the tray and liquid heads froth heights and froth density factors in the downcomer. (ii) Measurement of liquid residence time and degree of relative mixing on the tray using a dye injection technique. (iii) Mass transfer and efficiency studies with the system air/CO2 water, and (iv) Measurement of liquid/gas interfacial areas employing the system air/CO2/NaOH solution. The values of 'a' the interfacial area, obtained were combined with the mass transfer coefficient 'kla' obtained from efficiency studies to give values of Where possible, the results of the hydrodynamic studies have been reported in the form of correlation equations suitable for design purposes. A novel method was arrived at to sample the vapour stream for entrained liquid and the results although not yet complete enough for direct design purposes are very encouraging. A new criterion, pzf, has been introduced and the values obtained for it confirm the correlation proposed by FAIR. The extent of relative liquid mixing on the tray was determined using the variance of the residence time distribution. Graphical correlations of the mean liquid residence time and the extent of mixing have been presented. The validity of the method for obtaining the eddy diffusion coefficient from the variance of residence time distribution has been discussed. An accurate sampling and analysing technique was used in the efficiency and mass transfer studies. For the latter, operating conditions were selected such that the second order reaction between CO2 and NaOH solution could be regarded as pseudo-first order. The values of the interfacial area 'a' obtained were found to vary slightly with liquid and vapour flows. The values lie in the range 1.5 to 2.8 cm-1 for the rectangular columns 0.5 to 1.0 cm-1 for the round column. The kl values lie in the ranges 0.05 to 0.1 cm/sec and 0.20 to 0.35 cm/sec respectively. The interrelations between liquid mixing, liquid residence time, and the tray performance measured in terms of efficiency and mass transfer have also been examined in depth.