Chemical Engineering September 2021 - 26

Cover Story
Sieve Tray Stability
Factor Based on
Efficiency Data
Using a vast collection of experimental distillation-column data, sieve tray stability, and its
influence on efficiency, are explored in terms of several physical and mechanical properties
Dan Summers
Sulzer Chemtech, Ret.
IN BRIEF
STABILITY, ∆P AND
HYDROSTATIC HEAD
DISCUSSION
PHYSICAL PROPERTY
IMPACT
MECHANICAL PROPERTY
INFLUENCES
OBSERVATIONS
ALTERNATIVE EQUATION
F
or trayed distillation columns, the
concept of tray stability was introduced
by the author back in 2010
[1]. The data used to determine this
modified Froude number term were based
on simulator data, and the tray hydraulic parameter
examined was weeping. This work
serves to validate this stability factor concept
by demonstrating when tray efficiency data
" falls off " as one turns down the capacity
of a trayed distillation tower. That information
is readily available for sieve trays from
the publicly disclosed data that have been
collected by Fractionation Research Inc.
(FRI; Stillwater, Okla.; www.fri.org) over the
past 70 years [2]. Table 1 shows a small
selection of these data sets, which were
used to generate some of the charts in
this article.
The FRI data sets are also used in this article
to demonstrate that there is a relationship
between tray stability and tray efficiency, and
determine which physical properties
and mechanical design features most
impact that relationship. An equation
is presented that defines the minimum
tray stability factor value for sieve
trays. The applicability of this equation
covers a wide range of physical
and mechanical parameters,
using
FRI data to expand upon the author's
FRI Run
Number
14,115
14,116
14,117
14,118
14,119
26
Liquid
density,
lb/ft3
30.6
30.6
30.5
30.5
30.5
Vapor
density,
lb/ft3
Flowrate,
lb/h
Efficiency,
%
Weir
load,
1.7640
59,170 113
1.7680 46,770 112
1.8000 31,580 103
1.8000 22,580
1.8840 13,870
95
62
GPM/in.
6.52
5.16
3.49
2.49
1.54
drop, in.
of liquid
1.373
0.856
0.384
0.197
0.071
Ub,
ft/s
FIGURE 1. FRI run numbers 1,323 to 1,329, from January
1957, showing tray efficiency (black diamonds) and tray pressure
drop (blue circles)
STABILITY FACTOR, ∆P & HEAD EQUATIONS
ƞ = [∆PDry ρW / (ρLHS)] 0.5
(1)
∆PDry = 12 ρV( VH / CV)2 / (2gCρW) (2)
CV = K (Dp/Pitch) 0.10
(3)
K = 0.997 - {0.34 / [1 + (4.925TT/Dp)3.582]} (4)
HS = (α How) + K0 [(α0.5 / Cd )(GPM/Bw)] 2/3 (5)
TABLE 1. SELECTED FRI RUN DATA (REFERENCED IN FIGURE 2)
Dry
ε
1.007
0.794
0.527
0.377
0.221
3.761
3.130
2.284
1.749
1.157
Froth
height,
in.
7.83
6.71
5.27
4.40
3.53
α
Cd HS, in.
of liquid
0.2100 0.8433 1.645
0.2422 0.7982 1.624
0.3045 0.7409 1.605
0.3638 0.7060 1.600
0.4637 0.6713 1.638
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
Stability
0.913
0.726
0.489
0.350
0.209
SEPTEMBER 2021

http://www.fri.org http://WWW.CHEMENGONLINE.COM

Chemical Engineering September 2021

Table of Contents for the Digital Edition of Chemical Engineering September 2021

Contents
Chemical Engineering September 2021 - Cover1
Chemical Engineering September 2021 - Cover2
Chemical Engineering September 2021 - Contents
Chemical Engineering September 2021 - 2
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