the same as in the original reactor where it is injected as
air. The number of indicated stages include the first
injection stage near the bottom of the reactor in all cases.
Table 3 lists the results; they indicate that both con-
version and yield can be improved by this revamp, with
maximum benefit seen from two-stage oxygen injection.
However, it also indicates that this is achieved at the
expense of lower selectivities. Furthermore, the benefits
of higher conversion and yield may also be partially off-
set due to a lower MTY or a higher catalyst demand.
Revamp Option 2--Higher feed concentration
with n-butane recycle. Two feed n-butane concen-
trations (fresh feed + recycle)
-
50% and 100% higher
than the original are examined, assuming that these
higher concentrations are acceptable from a safety point
of view. In Table 3, the results show that although both
conversion and yield decline with this revamp, selec-
tivity is significantly improved. Furthermore, the reac-
tor throughput or MA productivity increases dramati-
cally due to higher feed concentrations, as reflected by
the increase in MTY values.
Revamp Option 3--Higher feed concentration
with n-butane recycle and lower bed tempera-
ture. Two bed temperatures--one 10°C and the other
20°C lower than the original value (T
BC
)--are used in
this option along with twice the original (base case) n-
butane feed concentration. The results shown in Table
3 indicate that although the conversions are decreased
due to lower temperatures, they are compensated by a
substantial increase in both selectivities and MTY.
Lower operating temperatures are also preferable from
the reactor safety point of view. Therefore, option 3 is a
clearly a better choice over option 2.
Model validation.
As shown by previous illustrations,
a general reactor model can examine various reactor
designs or design modifications before final choices
are made. However, the model projections must be val-
idated through testing in appropriate test units before
implementing any revamp option. This is particularly
true for reaction systems for which the mechanism
and kinetics have not been established. Mechanical,
detailed safety analysis and measures, and economics
are obviously the final factors in the revamp decision.
Many choices.
There are many choices when it comes
to revamp reactors--whether to boost the capacity of
the current reactor to meet increased demand, to make
up for out-dated design or to correct for design mis-
takes made originally. A general reactor model can help
discriminate between these choices, explore hidden
options and guide one to the best revamp possible. In
many cases, the cost and effort involved is minimal
when compared to the boost in productivity and profit
that can be achieved.
LITERATURE CITED
1
Dutta, S. and R. Gualy, "General Reactor Model Improves HPI Applications," Hydrocar-
bon Processing, July 1999.
2
Dutta, S. and G. D. Suciu, "Unified Model Applied to the Scale-up of Catalytic Fluid Bed
Reactors of Commercial Importance," Fluidization VI, J. R. Grace et al., Eds., Engineer-
ing Foundation, NY, pp. 311318, 1989.
Dr. Dutta is a senior staff consultant for
GTC Technology Corp., specializing in
designing and implementing reactor models
to industry. He has published more than 30
papers and a book chapter describing work
in reactor modeling. He has served numer-
ous times on advisory boards and research
teams across the globe, addressing aspects
of chemical engineering and process mod-
eling. Dr. Dutta has a long history of indus-
try experience, spanning over 30 years, having held senior
positions for Simulations Sciences, SABIC Research and Devel-
opment, Engelhard, Fluor Daniel and CE Lummus Crest.
Ron Gualy is the general manager of the
Chemicals Group for GTC Technology. His
responsibilities include business unit mar-
keting, sales and licensing of the tech-
nologies. He also manages business devel-
opment and strategy, coordination and
negotiation of strategic alliances, definition
of research activities, and growth of the
business. Mr. Gualy holds a BS degree in
chemical engineering from Texas A&M
University and is a registered professional engineer. He is a
member of AIChE and the American Management Associa-
tion. Mr. Gualy holds four patents concerning carboxylic acid
recovery and has other patents pending. He has been with
GTC Technology since its beginning six years ago.
Reprinted from Hydrocarbon Processing ® magazine, September 1999 issue, pgs. 43-50. Used with permission.
F/1M/1099 Copyright © 1999 by Gulf Publishing Company. All rights reserved. Printed in USA.
