Scaling‐up distillation efficiencies

Abstract

This paper describes a study of the possibility of using point efficiencies, measured in a small laboratory column, in the scale-up of distillation efficiencies. The conditions on a large rectangular tray were closely duplicated in a small glass Oldershaw column with one sieve tray having similar hole size and percent free area. Point efficiencies on the large rectangular sieve tray were deduced from the composition profiles and compared with the point efficiencies measured in the small column. A simple relationship between the two columns was found in terms of the froth heights and liquid holdups. The results demonstrate that the slightly lower point efficiencies measured in the Oldershaw column could be used in conjunction with a mathematical mass transfer model based on the eddy diffusion concept, to relate the point efficiencies to the tray efficiences, resulting in a conservative design provided either that allowance is made for other factors, such as nonuniform flow patterns and stagnant zones, or that these are eliminated. A wide range of composition was covered using the two systems MeOH-nPrOH and EtOH-nPrOH operating in the froth region. M. M. Dribika, M. W. BiddulphUniversity of Nottingham Department of Chemical Engineering University Park, Nottingham, England SCOPEThe prediction of the performance of a large-scale distillation tray column is difficult, particularly if a new system is being processed. It is a problem that has attracted a considerable amount of attention over many years. However, the prediction of tray efficiency is still a very uncertain part of the design unless operating data from a similar size column distilling a similar system are available. The problem is that both mass transfer characteristics and tray hydraulic considerations are involved, and so the tray efficiency is a function of system and tray size. This paper is concerned with the mass transfer part of the problem. It describes a study of the relationship betwen point efficiencies, measured in a small glass Oldershaw Column, and the efficiencies inferred at points along a rectangular tray with a liquid flow path length of about 1 m. The tray used is a sieve type with small hole sizes typical of those used in the cryogenic distillation of air. The hole sizes and percent free area in the two trays being compared are similar. CONCLUSIONS AND SIGNIFICANCEThe relationship between point efficiencies measured in a small laboratory column and the point efficiencies that actually exist on a large rectangular tray were studied using two systems, MeOH-nPrOH and EtOH-nPrOH, and covering a wide range of composition. The composition profiles across the tray were measured and used to infer the values of point efficiencies using a mathematical mass transfer model based on the eddy diffusion concept.Similar conditions to those on the large rectangular 1864November 1986 sieve tray were used in a small Oldershaw column with one sieve tray and external downcomers. The results indicate that the point efficiencies obtained on the large rectangu...

Effect of mixing on efficiencies for reactive tray contactors

“…For nonreactive systems, several methods are available for estimating the Murphree tray efficiency from point efficiency estimates made either from laboratory-scale measurements, such as using an Oldershaw column, or from published corre-Ž lations Dribika and Biddulph, 1986;Bennett and Grimm, . Ž .…”

Liquid-Phase Resistance to Mass Transfer on Distillation Trays

“…However, 6 G and 6L have not been determined by experiments. Consequently, a rather arbitrary assumption of 6 G = OL has been made by many investigators (Calderbank and Pereira, 1977;Lockett and Uddin, 1980;Neuburg and Chuang, 1982;Stichlmair, 1978;Dribika and Biddulph, 1986). If 8G = OL, eq 20 becomes for a typical distillation system, eq 21 would give LPR = 0.17 and GPR = 0.83, which might indicate that distillation is a gas-phase-controlled operation.…”

Scale‐up von Destillationskolonnen

“…[7], Spielmnnn [8], Wu u. Chen [9] sowie Biihlmann [ shaw"-Typ [13] den Punktwirkungsgraden in GroRkolonnen entsprechen. Weitere Moglichkeiten zum Scale-up von Bodenkolonnen wurden von Dribika u. Biddulph [14], Garrett et al [15] sowie Vertuzaev [16] diskutiert.…”

“…Billet [4], Billet u. Mackowiak [5], Billet u. Bravo [6] [14], Garrett et al [15] sowie Vertuzaev [16] Im weiteren wird ausschlieRlich die Bestimmung der Kolonnenhohe behandelt, was irn folgenden als Trennwirkungs-Scale-up bezeichnet wird. Dabei sol1 nur der experimentelle Weg uber den Laborversuch beschrieben werden, der in Abb.…”