TFR experiment

7/30/2019 TFR experiment

1/25

1

TABLE OF CONTENTS

CONTENTS PAGE

Abstract/Summary 2

Introduction 3

Aims/Objectives 4

Theory 5

Apparatus 8

Methodology/Procedure 9

Results 13

Calculations 15

Discussion 22

Conclusion 23

Recommendations 24

Reference 24

Appendices 25


2/25

2

ABSTRACT

There are 2 experiment that had to be done for tubular flow reactor (TFR). The first

experiment was conducted to examine the effect of a pulse input in tubular flow reactor

and to construct a residence time distribution (RTD) function for the tubular reactor.

While the second objective for experiment 2 is to examine the effect of a step change

input in tubular flow reactor and to construct a residence time distribution (RTD)

function for the tubular flow reactor. From the graph of first experiment, it can be seen

that the residence time distribution (RTD) for pulse input increased with time. However

after a few minutes, it will slowly decreases until the value of zero. Besides that, for the

second experiment, it can be seen that the value slowly increase of output conductivity

and E(t) until it is constant. The mean residence time, second moment (Variance) and

third moment (Skewness) were calculated was calculated from the graph. For the first

experiment, the value of residence time is 0.151 min, the second moment (Variance) is

0.0369 min2 and the third moment (Skewness) is 0.0129 min5/2. For the experiment 2,

the mean residence time, the second moment (Variance) and third moment (Skewness)

is 0.0998 min, 7.99 10 min2 and 3.197 10 min5/2 respectively.


3/25

3

INTRODUCTION

A tubular reactoris a vessel through which flow is continuous, usually at steadystate, and

configured so that conversion of the chemicals and other dependent variables are

functions of position within the reactor rather than of time. In the ideal tubular reactor, the

fluids flow as if they were solid plugs or pistons, and reaction time is the same for all

flowing material at any given tube cross section. Tubular reactors resemble batch reactors

in providing initially high driving forces, which diminish as the reactions progress down

the tubes.

Flow in tubular reactors can be laminar, as with viscous fluids in small-diameter tubes,

and greatly deviate from ideal plug-flow behavior, orturbulent, 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 inconveniently long reactors or may require

unacceptably 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
http://en.wikipedia.org/wiki/Plug_flow_reactor_modelhttp://en.wikipedia.org/wiki/Steady_statehttp://en.wikipedia.org/wiki/Steady_statehttp://en.wikipedia.org/wiki/Steady_statehttp://en.wikipedia.org/wiki/Laminarhttp://en.wikipedia.org/wiki/Turbulenthttp://en.wikipedia.org/wiki/Turbulenthttp://en.wikipedia.org/wiki/Laminarhttp://en.wikipedia.org/wiki/Steady_statehttp://en.wikipedia.org/wiki/Plug_flow_reactor_model


4/25

4

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 reactions2. Fast reactions.3. Homogeneous or heterogeneous reactions4. Continuous production5. High temperature reactions

OBJECTIVE

Experiment 1:

1. To examine the effect of a pulse input in tubular flow reactor.2. To construct a residence time distribution (RTD) function for thetubular reactor.

Experiment 2:

1. To examine the effect of a step change input in tubular flow reactor.2. To construct a residence time distribution (RTD) function for thetubular flow reactor.
http://en.wikipedia.org/wiki/Distillationhttp://en.wikipedia.org/wiki/Haber_processhttp://en.wikipedia.org/wiki/Haber_processhttp://en.wikipedia.org/wiki/Haber_processhttp://en.wikipedia.org/wiki/Haber_processhttp://en.wikipedia.org/wiki/Distillation


5/25

5

THEORY

The residence-time distribution (RTD) of a reactor is a characteristic of the mixing that

occurs in the chemical reactor. The RTD is determined experimentally by injecting an

inert chemical, molecule, or atom, called a tracer, into the reactor at some time t = 0 and

then measuring the tracer concentration, C, in the effluent stream as a function of time.

In addition to being a nonreactive species that is easily detectable, the tracer should

have physical properties similar to those of the reacting mixture and be completely

soluble in the mixture. It also should not adsorb on the walls or other surfaces in the

reactor. The latter requirements are needed so that the tracers behavior will honestly

reflect that of the material flowing through the reactor. Colored and radioactive

materials along with inert gases are the most common types of tracers. The two most

used methods of injection are pulse input and step change input.

In a pulse input, an amount of tracers N0 is suddenly injected in one shot into the

feedstream entering the reactor in a short time as possible. The outlet concentration is

then measured as a function of time. The effluent concentration-time curve is referred to

the as the C curve in RTD analysis. The injection of a tracer pulse for a single input and

output system is analyzed which only flow carries the tracer material across system

boundaries.

= () =

()

For pulse injection we defined;

() = ()


6/25

6

= ()

The quantity E(t) is called residence-time distribution function. It is the function that

describes in a quantitative manner how much time different fluid elements have spent in

the reactor. The quantity E(t)dt is the fraction of fluid exiting the reactor that has spent

between time t and and t + dt inside the reactor.

In Step Change input, the equation goes;

() = (

)(

)

We can now analyze a step change input in the tracer concentration for a system with a

constant volumetric flow rate. Consider a constant rate of tracer addition to a feed that is

initiated at time t = 0. Before this time no tracer was added to the feed. Stated

symbolically, we have;

() = {0, < 0(), 0

The concentration of tracer in the feed to the reactor is kept at this level until the

concentration in the effluent is indistinguishable from that in the feed; the test may then

be discontinued. Take C0 outside from the integral sign, that is;

() = ()

[()

] = (

)

= ()

() = [() ]To obtain RTD function E(t);

() = [() ]

As for mean residence time, it is shown that, in the absence of dispersion, and for

constant volumetric flow (v=v0) no matter what RTD exists for a particular reactor, ideal


7/25

7

or nonideal, the nominal space time, , is equal to the mean residence time, tm.

= ()

() = ()

We also usually compare RTDs by using their moments instead of trying to compare

their entire distributions. For this, we used three moments. First is mean residence time.

The second moment commonly used is taken about mean and is called the variance, or

square of the standard deviation.

= ( )() The magnitude of this moment is an indication of the spread of the distribution; the

greater the value of this moment is, the greater a distributions spread will be.

= 1 ( )()

This moment measures the extent that a distribution is skewed in one direction or

another in reference to the mean. It is called the skewness.


8/25

8

APPARATUS

Tubular Flow Reactor SOLTEQ BP 101-B


9/25

9

PROCEDURE

General Start-Up Procedures

1. All valves were ensured initially closed except valve V7.2. 20 liter of salt solution was prepared. For example, sodium chloride, NaCl

(0.025M).

3. The feed tank B2 was filled with the NaCl solution.4. The power for the control panel was turned up.5. The water de-ionizer was connected to the laboratory water supply. Valve V3

was opened and feed tank B1 was filled up with the de-ionized water. Valve

V3 was closed.

6. Valves V2 and V10 were opened. Pump P1 was switched on. P1 flowcontroller was adjusted to obtain a flow rate of approximately 700 ml/min at

flow meter F1-01. The conductivity display was observed at low value then a

valve V10 was closed and pump P1 was switched off.

7. Valves V6 and V12 were opened. Pump P2 was switched on. P2 flowcontroller was adjusted to obtain a flow rate of approximately 700 ml/min at

flow meter F1-02. A valve V12 was closed and pump P2 was switched off.

8. The unit was ready for experiment.


10/25

10

General Shut-Down Procedures

1. Both pump P1, P2 and P3 were switched off. Valves V2 and V6 wereclosed.

2. The heaters were switched off.3. The cooling water was kept circulating through the reactor while the

stirrer motor is running to allow the water jacket to cool down to room

temperature.

4. All liquid were drained from the unit by opening valves V1 and V16 if theequipment is not going to be used for long period of time. The feed tanks

were rinsed with clean water.

5. The power for the control panel was turned off.


11/25

11

Experiment 1: Pulse Input

1. General start-up procedures are performed.2. Valve V9 is opened and pump P1 is switched on.3. Pump P1 flow controller is adjusted to give a constant flow rate of de-ionized

water into reactor R1 at approximately 700 mL/min at Fl-01.

4. The de-ionized water is allowed to continue flowing through the reactor untilthe inlet (Ql-01) and outlet (Ql-02) conductivity values are stable at low levels.

Both conductivity values are recorded.

5. Valve V5 is closed and pump P1 is switched off.6. Valve V11 is opened and pump P2 is switched on. The timer is started

simultaneously.

7. Pump P2 flow controller is adjusted to give a constant flow rate of salt solutioninto the reactor R1 at 700 mL/min at Fl-02.

8. The salt solution is allowed to flow for 1 minute, then reset and restart the timer.This is the start time of the average pulse input.

9. Valve V11 is closed and pump P2 is switched off. Then, valve V9 is quicklyopened and pump P1 is switched on.

10.The de-ionized water flow rate is made sure to be maintained at 700 mL/minby adjusting P1 flow controller.

11.Both the inlet (Ql-01) and outlet (Ql-02) conductivity values are recorded atregular intervals of 30 seconds.

12.The recording of the conductivity values is continued until all readings are


12/25

12

almost constant and approach the stable low level values.

Experiment 2 : Step Change Input

1. Valve V9 is opened and pump P1 is switched on.2. Pump P1 flow controller is adjusted to give a constant flow rate of de-ionized

water into the reactor R1 at approximately 700 mL/min at Fl-01.

3. The de-ionized water is allowed to continue flowing through the reactor untilthe inlet (Ql-01) and outlet (Ql-02) conductivity values are stable at low levels.

Both conductivity values are 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 started

simultaneously.

6. Both the inlet (Ql-01) and outlet (Ql-02) conductivity values are recorded atregular intervals of 30 seconds.

7. The recording of the conductivity values is continued until all readings arealmost constant.

8. General shut-down procedures are performed


13/25

13

RESULTS


Time (min) Conductivity (ms/cm) E(t) min-1

Input Output

0 0.0 0.0 0.0

0.5 0.0 1.4 0.651

1.0 0.0 2.0 0.930

1.5 0.0 0.7 0.326

2.0 0.0 0.2 0.093

2.5 0.0 0.0 0.0

3.0 0.0 0.0 0.0

3.5 0.0 0.0 0.0

4.0 0.0 0.0 0.0

4.5 0.0 0.0 0.0


14/25

14

Experiment 2: Step change input

Time (min) Conductivity (ms/cm) E(t) min-1

input output

0.5 0.0 0.0 0.0

1.0 2.0 0.0 0.0

1.5 2.3 0.0 0.0

2.0 2.4 0.9 0.212

2.5 2.5 1.3 0.306

3.0 2.3 1.5 0.353

3.5 2.2 1.6 0.376

4.0 2.1 1.6 0.376

4.5 2.1 1.6 0.376


15/25

15

SAMPLE CALCULATION


() =

= 0.5

() = (

0 + 1 . 4 + 2 . 0 + 0 . 7 + 0 . 2 + 0 + 0 + 0 + 0 + 0 ) ( 0 . 5 )

()=2.15

Divide each value of C(t) with the integral to obtain a value E(t)

() = ()

()

() = 1.42.15

() =0.651


16/25

16

-0.5

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

outpu

tconductivity

(ms/cm

)

time (min)

output conductivity vs time

-0.2

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

E(t)(

min-1)

time (min)

E(t) vs time


17/25

17

Mean residence time

= . ()

= ()

= 0.5 0.6512.15

= 0.151

Second moment, Variance

= ( ) () = ( ) ()

= ( ) ()

= (0.50.151) (0.651)2.15

=0.0369


18/25

18

Third moment, Skewness

=

( ) () =( ) ()

= ( ) ()

= (0.50.151) (0.651)2.15

=0.0129


19/25

19

Experiment 2: Step change input

() =

= 0.5

() = (

0+0+0+0+0. 9+1. 3+1. 5+1. 6+1. 6 +1. 6 ) ( 0. 5)

() = 4.25Divide each value of C(t) with the integral to obtain a value E(t)

() = ()

()

() = 0.94.25

() =0.212


20/25

20

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5outputconductivity

(ms/cm

)

Time (min)

output conductivity vs time

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

E(t)(min-1)

Time (min)

E(t) vs Time


21/25

21

Mean residence time

= . ()

= () = 2.0 0.2124.25

= 0.0998

Second moment, Variance

= ( ) () = ( )

()

= ( ) () = (0.50.0998) (0.212)4.25

=7.99 10

Third moment, Skewness

= ( ) () =( ) ()

= ( ) () = (0.50.0998) (0.212)4.25

=3.197 10


22/25

22

DISCUSSION

There are two 2 experiment that had to be done using turbular flow reactor (TFR). For

the first experiment the objective are to examine the effect of a pulse input in tubular

flow reactor and to construct a residence time distribution (RTD) function for the

tubular reactor. While for the second experiment, the objective are to examine the effect

of a step change input in tubular flow reactor and to construct a residence time

distribution (RTD) function for the tubular flow reactor.

From the theory, the residence time distribution (RTD) is a function to describe time of

fluid inside the reactor. According to the graph of residence time distribution (RTD)

function which is E(t) versus time that had been plotted, for the first experiment, it

shows that the trend of RTD for pulse input increased with time. However after a few

minutes, it slowly decrease until the value become zero. Besides that, for the second

experiment, the graph show an increase of RTD value until the value of output

conductivity and E(t) is constant.

After the graph was plotted, the mean residence time, second moment (Variance) and

third moment (Skewness) were calculated. For the first experiment, the value of mean

residence time is 0.151 min, the second moment (Variance) is 0.0369 min2 and the third

moment (Skewness) is 0.0129 min5/2. For the experiment 2, the mean residence time,

the second moment (Variance) and third moment (Skewness) is 0.0998 min, 7.99 10 min2 and 3.197 10 min5/2 respectively.In this experiment, it can be seen that pulse input and step change in tubular reactor

method has a few differences. For pulse input method, it can be seen the inlet tracer

concentration is suddenly change from zero value to the large value and return it to zero

after a short time. While for the step input change method the feed tracer is suddenly


23/25

23

changed from steady C0 to steady value at Ct after time reached to zero.

CONCLUSION

The first experiment was conducted to examine the effect of a pulse input in tubular

flow reactor and to construct a residence time distribution (RTD) function for the

tubular reactor. While the second objective for experiment 2 is to examine the effect of a

step change input in tubular flow reactor and to construct a residence time distribution

(RTD) function for the tubular flow reactor. From the graph of first experiment, it can

be seen that the residence time distribution (RTD) for pulse input increased with time.

However after a few minutes, it will slowly decreases until the value of zero. Besides

that, for the second experiment, it can be seen that the value slowly increase of output

conductivity and E(t) until it is constant. The mean residence time, second moment

(Variance) and third moment (Skewness) were calculated was calculated from the graph.

For the first experiment, the value of residence time is 0.151 min, the second moment

(Variance) is 0.0369 min2 and the third moment (Skewness) is 0.0129 min5/2. For the

experiment 2, the mean residence time, the second moment (Variance) and third

moment (Skewness) is 0.0998 min, 7.99 10 min2 and 3.197 10 min5/2respectively.


24/25

24

RECOMMENDATION

1. Make sure Tank 1 and Tank 2 are full with sodium chloride and deionisedwater respectively

2. Ensure that there are no leakage at the valve. This is to prevent it fromeffecting the result of the experiment.

3. Make sure that the valve is open or close according to the general start-upprocedure carefully.

4. For both experiments, do more trial to get average of conductivity for bothinlet (Qi-01) and outlet (QI-02) conductivity values in order to get more

accurate results.

REFERENCES

1. Levenspiel, O., Chemical Reaction Engineering(3rd edition). John Wiley &Sons, USA (1999).

2. Douglas, J. M. Conceptual Design of Chemical Processes, McGraw-Hill: NewYork, 1988.

3. http://solve.nitk.ac.in/dmdocuments/Chemical/theory_plugflow.pdf4. Fogler H.S., Elements of Chemical Reaction Engineering, 3rd Ed., Prentice

Hall (USA), 1999


25/25

25

APPENDICES

TFR experiment

Documents

Transcript of TFR experiment