Reactor
The reactor is the heart of a chemical process. It is the only place in the process where
raw materials are converted into products, and reactor design is a vital step in the
overall design of the process.
The design of an industrial chemical reactor must satisfy the following requirements:
1. The chemical factors: The kinetics of the reaction. The design must provide
sufficient residence time for the desired reaction to proceed to the required
degree of conversion.
2. The mass transfer factors: With heterogeneous reactions the reaction rate may
be controlled by the rates of diffusion of the reacting species, rather than the
chemical kinetics.
3. The heat transfer factors: The removal, or addition, of the heat of reaction.
4. The safety factors: The confinement of hazardous reactants and products, and
the control of the reaction and the process conditions.
The need to satisfy these interrelated and often contradictory factors makes reactor
design a complex and difficult task. However, in many instances one of the factors
will predominate and will determine the choice of reactor type and the design method.
The following characteristics are normally used to classify reactor designs:
1. Mode of operation: batch or continuous.
2. Phases present: homogeneous or heterogeneous.
3. Reactor geometry: flow pattern and manner of contacting the phases:
i. Stirred tank reactor;
ii. Tubular reactor;
iii. Packed bed, fixed and moving;
iv. Fluidized bed.
Fluidized-Bed Reactors
For other topics on fluidization, see Fluidized bed technology, Fluidized bed
combustion and Fluidization.
A fluidized bed reactor (FBR) is a type of reactor device that can be used to carry
out a variety of multiphase chemical reactions. In this type of reactor, a fluid (gas or
liquid) is passed through a granular solid material (usually a catalyst possibly shaped
as tiny spheres) at high enough velocities to suspend the solid and cause it to behave
as though it were a fluid. This process, known as fluidization, imparts many important
advantages to the FBR. As a result, the fluidized bed reactor is now used in many
industrial applications.
Figure (3-1) Fluidized Bed Reactor Design
The essential feature of a fluidized-bed reactor is that the solids are held in suspension
by the upward flow of the reacting fluid; this promotes high mass and heat transfer
rates and good mixing. Heat transfer coefficients in the order of 200W/m28C to
jackets and internal coils are typically obtained. The solids may be a catalyst, a
reactant in fluidized combustion processes, or an inert powder added to promote
heat transfer.
Though the principal advantage of a fluidized bed over a fixed bed is the higher
heat transfer rate, fluidized beds are also useful where it is necessary to transport large
quantities of solids as part of the reaction processes, such as where catalysts are
transferred to another vessel for regeneration.
Fluidization can be used only with relatively small-sized particles, <300 mm with
gases.
A great deal of research and development work has been done on fluidized-bed
reactors in recent years, but the design and scale-up of large diameter reactors is still
an uncertain process and design methods are largely empirical.
The principles of fluidization processes are described in Richardson et al. (2002).
The design of fluidized bed reactors is discussed by Rase (1977).
Reactor R-101:
HYSYS data
FA0 (Kgmol/hr)
126.07
T0 (C)
451
T (C)
548
PT0 (psia)
40
PT (psia)
35
X
0.997
yA0
0.2534
yB0
0.7056
Table (3-1) Hysys reactor worksheet
C6H5NO2 + 3H2 - C6H5NH2 + 2H2O
The initial conversions and the initial reaction rates at different reaction conditions
were obtained by extrapolating the conversion curves to time t=0 min. It could be
shown that hydrogenation of nitrobenzene on the fresh catalyst follows a Langmuir
Hinshelwood mechanism considering the surface reaction of the adsorbed
nitrobenzene molecule and one adsorbed hydrogen atom as the rate determining step
(Amon et al., 1999a):
.
Parameter
k0 (Kmol/Kgcat.s)
EA (KJ/mol)
KNB (Kpa-1)
KH2 (Kpa-0.5)
Value of estimation
1.86x10-4
10
1.51x10-2
0.14
Standard deviation
1.27x10-5
0.9
2.98x10-3
0.02
Table ( 3-2 ) Kinetic constants of the initial reaction rate
rA = kKNBKH2PNBPH20.5/(1+ KNBPNB + KH2PH20.5)2
PA0  y A0 PT 0  10.136 psia
  y A0 = 0.534*(1+2-3-1) = -0.534
A 
y A0
=1
y A0
B 
y B0
 0.7056 / 0.2534  2.78453
y A0
PA  PA0
 A  x  T0  P 
   = PNB
1  x  T  P0 
 0.04682907 psia = 0.3227 Kpa
PB  PA0
 B  x  T0  P 
   = PH2
1  x  T  P0 
 27.9 psia = 192.263 Kpa
Kinetic Data:
k = 1.642x10-7 Kmol/Kgcat.s
-rA = kKNBKH2PNBPH20.5/(1+ KNBPNB + KH2PH20.5)2
= (1.642x10-7*1.51x10-2*0.14*0.3227*192.2630.5) / (1+ 1.51x10-2*0.3227 +
0.14*192.2630.5)2 = 1.79x10-10 Kmol/Kgcat.s
= 1.79x10-7 mol/Kgcat.s
= 6.45X10-4 mol/Kgcat.hr
dx  rA

dW FA0
W
FA0 ( x)
 194827 Kg
 rA
Wcopper = 15% of the total weight = 29224 Kg
Wsilica = 1548.211376 – 29224 = 165603 Kg

 ( Bulk )  100 lb / ft 3 = 45.359237 Kg/ft3

 = 0.3
 V (column) 

W
 6136 ft 3 = 173.75 m3
(1   ) * 
V 
D 
 

1/ 3
 3.81 m
L  6D  22.86 m
Equipment Name
Reactor
Objective
Convert nitrobenzene to aniline
Equipment Number
R-101
Designer
Abdulaziz Alshomer
Type
Fluidized bed vapor catalytic reactor
Material of Construction
stain steel
Table (3-3) reactor 101 information
Refrrences
Book
Chemical engineering design,sinnot&towler,5th edition,reactor ,page 666
websites
http://www.lossinweightfeeder.com/standards/documents/1500-C01-2.pdf
http://144.206.159.178/FT/158/35028/599706.pdf
C6H5NO2 + S ↔ C6H5NO2.S
-rNB = kNB (PNB Cv - CNB.s/KNB)
-rNB/kNB = 0
CNB.s = KNB PNB Cv
0.5H2 + S ↔ H.S
-rH2 = kH2 (PH20.5 Cv – CH.s/KH2)
-rH2/kH2 = 0
CH.s = KH2 PH20.5 Cv
C6H5NO2.S + H.S  C6H5NH2 + H2O + 2S
-ra = K CNB.s CH.s
Ct = CNB.s + CH.s + Cv
Ct = KNB PNB Cv + KH2 PH20.5 Cv + Cv
Cv = Ct / (1 + KNB PNB + KH2 PH20.5 )
Surface Reaction rate limiting
-ra = rs = Ks Ct KNB KH2 PNB PH20.5 / (1 + KNB PNB + KH2 PH20.5 )2
Let k = Ks Ct
-rA = kKNBKH2PNBPH20.5/(1+ KNBPNB + KH2PH20.5)2