ABSTRACT From this experiment, our objectives are to examine the effect of pulse input in a tubular flow reactor and to construct a residence time distribution (RTD) function for the tubular flow reactor. First of all, the equipment is set up before we can run the experiment. After that, we set up the flowrate that is 700mL/min. After the conductivity for inlet and outlet we collected are reaching to a constant value, the experiment is stopped. The conductivity for inlet and outlet after 5 minutes are 0.2mS/cm and 0.1mS/cm. The outlet conductivity, C(t) then is calculated and the value we get is 2.60. Then, we are able to determine the distribution of exit time, E(t). The E(t) is calculated for each 30 seconds until it reach 5 minutes interval. The sum of E(t) we get is 1.00 which is the residence time distribution. The mean residence time, t m for this experiment is 0.7652 minute. The variance, σ 2 and the skewness, s 3 are also then calculated. The value we get for σ 2 is 1.5112 and for the s 3 is 4.1752. Graphs for outlet conductivity, C(t) against time and distribution of exit time, E(t) against time is plotted. The graphs we get from this experiment are just the same with the graphs in the theory. The value of E(t) is depends on the value of C(t). 1
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ABSTRACT
From this experiment, our objectives are to examine the effect of pulse input in a tubular flow
reactor and to construct a residence time distribution (RTD) function for the tubular flow
reactor. First of all, the equipment is set up before we can run the experiment. After that, we
set up the flowrate that is 700mL/min. After the conductivity for inlet and outlet we collected
are reaching to a constant value, the experiment is stopped. The conductivity for inlet and
outlet after 5 minutes are 0.2mS/cm and 0.1mS/cm. The outlet conductivity, C(t) then is
calculated and the value we get is 2.60. Then, we are able to determine the distribution of exit
time, E(t). The E(t) is calculated for each 30 seconds until it reach 5 minutes interval. The
sum of E(t) we get is 1.00 which is the residence time distribution. The mean residence time,
tm for this experiment is 0.7652 minute. The variance, σ2 and the skewness, s3 are also then
calculated. The value we get for σ2 is 1.5112 and for the s3 is 4.1752. Graphs for outlet
conductivity, C(t) against time and distribution of exit time, E(t) against time is plotted. The
graphs we get from this experiment are just the same with the graphs in the theory. The value
of E(t) is depends on the value of C(t).
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INTRODUCTION
In the tubular reactor, the reactants are continually consumed as they flow down the length of
the reactor. Flow in tubular reactor can be laminar, as with viscous fluids in small-diameter
tubes, and greatly deviate from ideal plug-flow behaviour, or turbulent, as with gases.
Turbulent flow generally is preferred to laminar flow, because mixing and heat transfer are
improved. For slow reactions and especially in small laboratory and pilot-plant reactors,
establishing turbulent flow can result in conveniently long reactors or may require
unacceptable high feed rates.
However, many tubular reactors that are used to carry out a reaction do not fully conform to
this idealized flow concept. In an ideal plug flow reactor, a pulse of tracer injected at the inlet
would not undergo any dispersion as it passed through the reactor and would appear as a
pulse at the outlet. The degree of dispersion that occurs in a real reactor can be assessed by
following the concentration of tracer versus time at the exit. This procedure is called the
stimulus-response technique. The nature of the tracer peak gives an indication of the non-
ideal that would be characteristic of the reactor.
For most chemical reactions, it is impossible for the reaction to proceed to 100% completion.
The rate of reaction decreases as the percent completion increases until the point where the
system reaches dynamic equilibrium (no net reaction, or change in chemical species occurs).
The equilibrium point for most systems is less than 100% complete. For this reason a
separation process, such as distillation, often follows a chemical reactor in order to separate
any remaining reagents or by products from the desired product. These reagents may
sometimes be reused at the beginning of the process, such as in the Haber process.
Tubular flow reactors are usually used for this application which are:
1. Large scale reactions
2. Fast reactions
3. Homogeneous or heterogeneous reactions
4. Continuous production
5. High temperature reactions
Residence Time Distribution (RTD) analysis is a very efficient diagnosis tool that can be
used to inspect the malfunction of chemical reactors. It can also be very useful in modelling
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reactor behaviour and in the estimation of effluent properties. This technique is, thus, also
extremely important in teaching reaction engineering, in particular when the non-ideal
reactors become the issue. The work involves determining RTDs, both by impulse and step
tracer injection techniques, and applying them to the modelling of the reactor flow and to the
estimation of the behaviour of a nonlinear chemical transformation. The RTD technique has
also been used for the experimental characterization of flow pattern of a packed bed and a
tubular reactor that exhibit, respectively, axially dispersed plug flow and laminar flow
patterns (FEUP).
The concept of using a ‘tracer’ species to measure the mixing characteristics is not limited to
chemical reactors. In the area of pharmacokinetics, the time course of renal excretion of
species originating from intravenous injections in many ways resembles the input of a pulse
of tracer into a chemical reactor. Normally, a radioactive labelled (2H, 14C, 32P, etc.) version
of a drug is used to follow the pharmacokinetics of the drug in animals and human.
Another important field of RTD applications lies in the prediction of the real reactor
performance, since the known project equations for ideal reactor are no longer valid. Now the
concepts of macro and micro mixing are fundamental. For each macro mixing level,
expressed in the form of a specific RTD, there is a given micro mixing level, which lies
between two limiting cases, complete segregation and perfect micro mixing.
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OBJECTIVES
The objectives of this experiment are:
1. To examined the effect of pulse input in a tubular flow reactor.
2. To construct a residence time distribution (RTD) function for the tubular flow reactor.
THEORY
In a tubular flow reactor, the feed enters at one end of a cylindrical tube and the product
stream leaves at the other end. The long tube and the lack of provision for stirring prevent
complete mixing of the fluid in the tube. Hence the properties of the flowing stream will vary
from one point to another, namely in both radial and axial directions. It is often not necessary
to know details of the entire flow fluid but rather only how long fluid elements reside in the
reactor (i.e. the distribution of residence times). This information can be used as a diagnostic
tool to ascertain flow characteristics of a particular reactor.
The ‘age’ of a fluid element is defined as the time it has resided within the reactor. The
concept of a fluid element being a small volume relative to the size of the reactor yet
sufficiently large to exhibit continuous properties such as density and concentration was first
put forth by Danckwerts in 1953.
In order to analyze the residence time distribution of the fluid in a reactor the following
relationships have been developed. Fluid elements may require differing lengths of time to
travel through the reactor. The distribution of the exit times, defined as the E(t) curve, is the
RTD of the fluid. The outlet conductivity of a tracer species C(t) can be used to define E(t).
That is:
E (t )≈Cout
t (t)
∫0
∞
Coutt (t ) dt
Based on the data collected, a graph of conductivity versus time could be draw to obtain the
C(t) curve and data of the integral C(t) could be calculate.
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∫0
∞
C ( t ) dt=∑C i ∆ t=Area
Figure 1: Theory of graph with its formula area under the graph
Other things that are needs to be determined in this experiment are:
Mean Residence Time = t E(t).dt =∑ tiEi(t)
Second moment Variance, σ2 = (t - tm)2 E(t).dt =∑ (t - tm)2 E(t)
Third Moment Skewness, s3 = (t - tm)3 E(t).dt =∑ (t - tm)3 E(t)
If the RTD function, E(t), is very broad, however, it may be difficult to inject an amount of
tracer that is sufficiently large so as to keep the outlet concentration sufficiently high to be
measured accurately.
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Figure 2: Example of graph when distribution exit time is very abroad
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APPARATUS
1. Soltec Tubular Flow Reactor instrument
2. Clock watch
3. Solution 0.025M Sodium Chloride and De-ionized water.
Figure 3: Soltec Tubular Flow Reactor instrument
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EXPERIMENTAL PROCEDURES
General Start-Ups
1. All valves are initially closed except valves V7.2. 20Liters of salt solution is prepared3. Feed tank B2 is filled with the sodium chloride solution.4. The ON power button is turn.5. The water De-ionizer is connected to the laboratory water supply. Valve V3 is opened
and the feed tank B1 is allowed to feed with the water. Valve V3 is closed as the water level reached the tank mark.
6. Valve V2 and V10 is opened and pump P1 is switched on. From observing the flow meter F1-01 value, The P1 pump is adjusted by controlling the flow controller to obtain a flow rate of approximately 700mL/min.
7. V6 and V12 are opened and pump 2 P2 is switched on. From observing the flow meter F1-02 value, The P2 pump is adjusted by controlling the flow controller to obtain a flow rate of approximately 700mL/min. Then the valve V12 is closed and pump P2 is turn off.
8. The experiment can now be carried out.
Experiment 1:0.0486 Pulse input in a Tubular Flow Reactor.
1. Valve V9 is opened and pump P1 is switched on.2. The P1 pump is adjusted by controlling the flow controller to obtain a flow rate of
approximately 700mL/min of de-ionized water into the reactor R1.3. The de-ionized water is allowed to continue flowing through the reactor until the inlet
(Q1-01) and outlet (Q1-02) conductivity values are stable at low levels. Both conductivity values is recorded.
4. Valve V9 is closed and pump P1 is switched off.5. Valve V11 is opened and pump P2 is switched on. The timer is simultaneously
started.6. Pump P2 flow controller is adjusted to give a constant flow rate of salt solution into
the reactor R1 at 700mL/min at F1-02.7. The salt solution is allowed to flow for 1minute, the timer is reset and restarted. This
will start the time at the average pulse input.8. Valve V11 is closed and pump P2 is switched off. Valve V9 is quickly opened and
pump P1 is switch on.9. By adjusting pump P1 flow controller, the de-ionized water flow rate is always
maintained at 700mL/min.10. The inlet (Q1-01) and outlet (Q1-02) conductivity values are recorded at regular
interval of 30 seconds.11. The conductivity values are recorded until all readings are almost constant and
approach stable low level values.
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RESULTS
Experiment 1: Pulse Input in a Turbular Flow Reactor