Unit Operation Laboratory 2 Myn Edited

7/24/2019 Unit Operation Laboratory 2 Myn Edited

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UNIT OPERATION LABORATORY 2

(CCB 3062)

EXPERIMENT 6:

CSTR DYNAMICS

GROUP 1 MEMBER :

1) ARVINDAN A/L GOPALAKRISHNAN 13!1

2) A"ESAH MASOR 11!

3) AI##AT BIN INCHE #AKUAN 16

) AHMAD SABRI MOHAMED #AID 16!$

%) AHMAD SYA#MIN BIN ISMAYUDDIN 1%33

LAB DEMONSTRATOR : MR& RI#'AN NASIR

DATE O SUBMISSION : 2% EBRUARY 2013


2/24

INTRODUCTION

The objective of the experiment is to study the transient behavior of three

Continuous Stirred-Tank Reactors connected in series by plotting the Residence Time

Distribution (RTD curve! Dynamic simulation is useful to design the control structure of

the process" study the performance of the controllers by subjecting the system to

various disturbances and to optimi#e the control parameters

V

=

$ith a vie$ to

develop an economic process!

Residence time" % is the amount of time a fluid spends in a reactor! &here ' is the

volume of the reactor and is the volumetric flo$ rate!

The RTD function" )(t describes the amount of time a fraction of fluid is present in the

reactor! &hen )(t vs! t is plotted! The area under the curve gives the fraction of

substance that has spent a certain amount of time in the reactor!

=0

1)( dttE

Since"

2

1

)(

t

t

dttE

Therefore" fraction of substance spent in a reactor $ithin a certain time is given

by"

*n this experiment" the RTD curves are determined using the Step and +ulse input

methods! ,or both methods" deioni#ed $ater is used as the bulk fluid and !./0

sodium chloride solution is used as the tracer! The conductivity is measured in all three

reactors in one minute intervals!


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SUMMARY

Continuous stirred tank reactors are used very commonly in industrial process! *n

our experiment" there are part 1 and part 2! The difference bet$een this both parts is

the rate of stirrer in rpm! ,or this type of reactor mixing is complete" so that the

temperature and the composition of the reaction mixture are uniform in all parts of the

vessel and are the same as those in the exit stream!

,or the part 1" the input that $e use is the same $hich is deioni#ed $ater and

Sodium Chloride (3aCl $ith the !./ 0! ,irst the $ater $ill be adding on the first

reactor and then continued until it reaches the third reactor! 4ntil no$" $e have to start

the stirrer and $ait until it productivity near to 5! This is because the productivity is

nearer to 5! Then $e $ill add the 3aCl for about 67 minutes and take the reading of

productivity!

,or part 2" the same procedure and also same material is used! 8o$ever" the

stirrer speed has been change a little bit! 9n this part" the same result that $e $ant

$hich is the productivity after 67 minutes has over! So basically" this experiment $ants

to investigate the differences $hen $e change the speed of the stirrer inside the reactor

although the same input have been used!

RESULTS CALCULATION


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S*+, I-,.*

Since conductivity" : of the !./0 sodium chloride solution $as not measured directly"

it $as estimated to be 3%00 S by looking at the e;uilibrium concentration on the

concentration vs! time graph and the corresponding conductivity!

4sing values from Reactor 5 as the basis"

1t t< !./0 and :>< ?/ =S

1ssuming the concentration is linearly proportional to the conductivity" the concentration

of the

=3500

025.0tt

C

tracer at time t can be determined by"

025.0)( t

o

t C

C

CtF ==

Therefore" the cumulative distribution" ,(t is simply"

dt

tdFtE

)()( =

,(t is the plotted and the e;uation if the curve is obtained! Then" the RTD

is given by"

P.+ I-,.*


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The concentration is determined from conductivity using the method used above!

=

0

)(

)()(

dttC

tCtE

Then" the RTD is determined by"

$hereby the denominator is solved using Simpson@s one-third rule!

,or consistency" the value of the denominator calculated for Reactor 5 $as used to

compute )(t values for the other t$o reactors!

The tail fitting method as described in the textbook $as attempted in order to determine

the theoretical end-point i!e! the x-intercept for the Reactor . and ? curves! 8o$ever"

accurate results could not be obtained for both step and pulse input methods!


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S*+, I-,.*

R+*45 1 R+*45 2

T7+8 *

(7-)

C4-9.**;(S)

C4-+-*5*4- 4


7/24

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8/24

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9/24

A

6/!?.5/!.

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6.76!5

!./ !5?

AREA

UNDER

CUR

VE

57!BA

R+*45 3

T7+8 *

(7-)

C4-9.**;(S)

C4-+-*5*4- 4< T5+58

C(*) (M)

C.7.*+

D*5=.*4- (*)

R+9+-+ T7+ D*5=.*4-8 E(*) (7-"1)

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10/24

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11/24

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AREA

UNDER

CURVE


12/24

0.0 10.0 20.0 30.0 40.0 50.0

0.0000

0.0050

0.0100

0.0150

0.0200

0.0250

GRAPH OF TRACER CONCENTRATION vs TIME - STEP

Reactor 1

Reactor 2

Reactor 3

Time (min)

Tracer Concentration (M)


13/24

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

0.0000

0.0050

0.0100

0.0150

0.0200

0.0250

0.0300

0.0350

GRAPH OF E(t) VS TIME - STEP

Reactor 1

Reactor 2

Reactor 3

Time (min)

E(t) (min-)


14/24

P.+ I-,.*

R+*45 1

T7+8*

(7-)

C4-9.**; (S)

C4-+-*5*4- 4


15/24

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16/24

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17/24

AREAUNDE

RCURV

E

!5/6

5!

B!./7

R+*45 2 R+*45 3

C4-9.**; (S)

C4-+-*5*4- 4


18/24

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AREA

UND

!5.. 5! !5A 5!


19/24

ERCURVE


20/24

0.0 10.0 20.0 30.0 40.0 50.0

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

0.0014

0.0016

0.0018

GRAPH OF TRACER CONCENTRATION VS TIME - P!"SE

Reactor 1

Reactor 2

Reactor 3

Time(min)

Tracer Concentration (M)

0.0 5.0 10.015.020.025.0 30.035.040.045.0 50.0

0.0000

0.0200

0.0400

0.0600

0.0800

0.1000

0.1200

GRAPH OF E(t) VS TIME - P!"SE

Reactor 1

Reactor 2

Reactor 3

Time(min)

E(t) (min-)


21/24

DISCUSSION

The transient behavior of three Continuous Stirred-Tank Reactors connected in

series is being studied by using t$o types of solutions Deioni#ed $ater and a !./0

3aCl Solution! 2y measuring the conductivity at one point in each of the three reactors"$e can calculate the concentration at this point! Then" $e can obtain the Residence

Time Distribution (RTD curve!

)ach of the t$o experiments needs time to prepare the solution of !./0 3aCl!

Then" $aiting for the conductivity reaches its minimum value as the deioni#ed $ater

flo$s! 1fter the step change is made in the first experiment and the pulse change in the

second one" readings are recorded for a period of 6/ minutes and interval of 5 minute! *t

has been noticed that some time passes before the sensors detect the changes!

,or the first experiment Step change is employed and after performing

calculations of concentration as a function of conductivity" $e obtain the concentration

graphs $hich sho$ that concentration increases rapidly in tank 5 follo$ed by tank .

then tank ?! *t has also sho$ed continuous increment for the three reactors! 1fter

integration and obtaining the RTD graph" $hich is ;uantitative description of ho$ much

time the different fluid element have spent in the reactor" it can be concluded that

reactor 5 is the most $ell mixed reactor because it has increased and decreased rapidlycompared to tank . and tank ?! The smooth curves of the concentration vs! time graph

in both experiments indicate that the CSTR is $ell mixed!

8o$ever" for pulse change in second experiment" similar behavior bet$een

concentration and RTD graphs cannot be noticed! The concentration increases in the

beginning" $ith a rapid increment for tank 5" then it tends to increase! &e also notice

that the concentration change becomes slo$er in reactor . and even slo$er in reactor

?! The trend of graph for pulse change and step change is different because in pulse

change the injection of 3aCl $as different! *t is injected in one shot in the reactor feed

stream for only . seconds compared to step change $hich is injected continuously into

the reactor!


22/24

The principal difficulty $ith the pulse techni;ue lies in obtaining a reasonable

pulse at the reactor@s entrance as the injection must take place over a short period! &e

can observe that the trend of the graphs is similar to expected theoretical results! The

slight deviation is attributed to the follo$ing

ERROR AND RECOMMENDATIONS

2ased on the experiment that $e had done" there are several factor that contribute to

the error! Therefore" $e stated some recommendation on ho$ to prevent this type of

error from happening

5! E5545 The three tanks readings (CT5" CT." and CT? are not started $ith a

stable reading at the lo$est values due to not enough time for it to stabilise!

R+477+-9*4- extend the time for the lab so that $e can $ait until the

system is stabilised!

.! E5545: The value of the flo$ rate sometimes varies due to the bubbles in the

pipe!

R+477+-9*4- The bubbles in the pipe should be removed before the

experiment is started!

?! E5545: There are still impurities in the tank that is left from the previous

experiment!

R+477+-9*4-: The tank should be cleaned $ith distilled $ater after each

experiment is done!

6! E5545 The reading from the digital monitor and the analogue monitor is not the

same!

Recommendation 2oth of the monitor should be calibrated so that it can display

a same reading!


23/24

/! E5545: The solution of 3aCl that $as prepared $as not accurate as it re;uired a

high volume of solution! The concentration of the 3aCl may deviate from the

desired value due to this error!

R+477+-9*4-:&e should use a more accurate instrument to produce a

more accurate concentration of 3aCl or $e can also use a small volume

measuring cylinder so that the concentration that is produced does not deviate to

far from the desired value!

CONCLUSION

2ased on the experiment that $e had done $e had been able to make some

observation! ,rom the first experiment" $e can see $hen step change is employed and

after performing calculations of concentration as a function of conductivity" $e obtain the

concentration graphs $hich sho$ that concentration increases rapidly in tank 5 follo$ed

by tank . then tank ?! *t also sho$s that there are continuous increments for all three

reactors! The experiment also sho$s that the no 5 reactor is the best mixed reactor

compared to reactor . and ?! 8o$ever" for pulse change in experiment ." similar

behavior bet$een concentration and RTD graphs can be noticed! The concentration

increases in the beginning" $ith a rapid increment for tank 5" then it tends to increase!

&e also notice that the concentration change becomes slo$er in reactor . and even

slo$er in reactor ?!

*n conclusion" the experiment results are relevant since the deviation from the

theory is considerable! &e can say that the deviations are caused by some errors that

happened during the experiment! The objective of the experiment that is to study thetransient behavior of three Continuous Stirred-Tank Reactors connected in series by

plotting the Residence Time Distribution (RTD curve is achieved best on the results

that $e got!


24/24

REERENCE

,ogler" 8!S!" )lements of Chemical Reaction )ngineering E Chapter 5?" 6 th)dition"

+rentice 8all +TR" .7!

(5B December .5.! ResidenceTime Distribution.&ikipedia! Retrieved ,ebruary A"

.5?" from httpFFen!$ikipedia!orgF$ikiFResidenceGtimeGdistribution

Residence Time Distribution Hpdf documentI! Chemical )ngineering **T 2ombay!

Retrieved from $$$!che!iitb!ac!inFcoursesFuglabFcl6?5Fms65-rtd!pdf
http://en.wikipedia.org/wiki/Residence_time_distributionhttp://www.che.iitb.ac.in/courses/uglab/cl431/ms401-rtd.pdfhttp://www.che.iitb.ac.in/courses/uglab/cl431/ms401-rtd.pdfhttp://en.wikipedia.org/wiki/Residence_time_distribution

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