Reactor Design
‫الجمهور‪ :‬هو احنا هناخد إيه النهاردة؟‬
‫أنا‪ :‬هناخد ‪Reactor‬‬
‫الجمهور‪ :‬بس؟‬
‫أنا‪ :‬آه بس‬
‫الجمهور‪ :‬هو السكشن طويل‬
‫أنا‪ :‬آه‬
‫الجمهور‪ :‬يعني هناخد السكشن ونص‬
‫أنا‪ :‬آه‬
‫الجمهور‪ :‬بس احنا تعبانين‬
‫أنا‪ :‬وأنا تعبانة أكتر منكم‬
‫الجمهور‪ :‬بس احنا صايمين‬
‫أنا‪ :‬ربنا يتقبل إن شاء هللا‬
‫الجمهور‪ :‬طب احنا هناخد إيه في ال ‪Reactor‬؟‬
‫أنا‪Combined Reactors :‬‬
‫الجمهور‪ :‬بس احنا ما أخدناهاش في المحاضرة؟ وال ‪ gas phase‬هناخده امتى؟‬
‫أنا‪ :‬ماهي بتاخد في السكشن بس ‪ ،‬بعد العيد إن شاء هللا‬
Exercise
a) Calculate the volume of a PFR and a CSTR
required for 90% conversion of reactant by a
first-order reaction: 𝐴 → 𝐵 ; 𝑟𝐴 = 𝑘𝐶𝐴
𝑞
𝑘
= 1𝑚3 .
b) Calculate the total volume of two CSTRs
(both of the same volume) in series required
for 90% conversion.
WHAT IS THE BEST ARRANGEMENT FOR
REACTORS TO GET THE MAXIMUM
CONVERSION?
Order of Reaction
Reactor Arrangement
n=1
Equal size reactor
Order of Reaction
Reactor Arrangement
n>1
Smaller reactor should be put first
Order of Reaction
Reactor Arrangement
n<1
Larger reactor should be put first
SERIES COMBINATION OF CSTR AND
PFR
• When PFRs and CSTRs are both available and
to be used in series, the order of the reactors
can affect the total conversion, as the
conversion will be dependent on the inlet
concentration to each reactor. Therefore, the
overall will depend on the order in which the
reactors are placed.
• For first order reactions, the overall
conversion will be independent of reactors
order.
• For n > 1, PFR should be placed before CSTR,
Why?
High
rates
(at
high
concentrations) are required in
order
to
maximize
the
conversion. As PFR takes the
advantage of the high reaction
rates, it should be placed
before CSTR. The reverse occurs
when n <1.
• If we have more than one CSTR of different
sizes together with the PFR, the smallest one
should be placed immediately after the PFR so
as to keep higher concentrations and hence
higher rates of reaction.
WHAT ABOUT PARALLEL
CONFIGURATION FOR CSTRS AND PFRS
IN SERIES?
HIPPOPOTAMUS’S DIGESTIVE
SYSTEM
The hippopotamus digestive system is modeled as a CSTR and a PFR
in a
series. For the system above A represents the grass that
makes up the bulk of the hippos normal diet. F is the molar flow of
A, m is the mass flow and X represents the conversion of A into
proteins, vitamins, minerals and everything else that the hippo
needs to survive.
• Finding correct values of X is of course impossible
but fairly good estimates can be done. We further
assumed that about 75% of the total conversion
occurred in the first part of the digestive system,
i.e. the CSTR or the stomach, and 25% in the
second part, i.e. the PFR or the intestines. The
assumption is based on the volume ratio between
the two parts. Studies made of the stomach
contents of the hippo are not extensive enough to
make any final conclusions but at least the
protein contents in different parts of the stomach
are in concord with the aforementioned
assumption.
SHEET 5
1.
Pure A is fed at a volumetric flow rate of 5 lit/sec and a
concentration of 10 gmole/lit to an existing CSTR which is
connected to an existing tubular reactor in series. If the volume of
the CSTR is 20 lit, and the tubular reactor volume is 8 lit, what
are the intermediate and final conversions that can be achieved
with the existing system if the reaction:
𝑨→𝑷
is first order with k = 1 sec-1. What if the previous system is
reversed?
2. Consider the liquid phase reaction:
𝑨 → 𝟐𝑩
With the rate constant k = 2 sec-1 in a PFR of volume 1 m3. The
volumetric flow rate of feed is 0.5 m3/sec of pure A. It is
desired to replace the PFR with a cascade of 3 equal volumes
CSTR in series while maintaining the same outlet conversion.
What volume for each of the three CSTRs would be needed?
3.
It is desired to carry out the following first order reaction:
𝑨→𝑩
(K = 0.1 min-1 at the operating temperature). A CSTR of volume 100
lit is fed at a flow rate of 50 lit/min of fresh feed containing A in the
concentration of 5 gmole/lit. The outlet stream from this CSTR is fed
to a tubular reactor of total length 100 cm and cross-sectional area of
200 cm2. 25 lit/min of the effluent stream leaving the PFR is
recycled again to the CSTR, such that the net product stream from the
PFR flows at the rate of 50 lit/min. What are the outlet conversions
of the CSTR and the PFR?
4. The kinetics of the aqueous – phase decomposition of A is
investigated in two mixed reactors in series, the second
having twice the volume of the first reactor. At steady state
with a feed concentration of 1 mole A/lit. and mean
residence time of 96 sec in the first reactor, the
concentration in the first reactor is 0.5 mole A/lit. and in the
second is 0.25 mole A/lit. Find the kinetic equation for the
decomposition.