chp303.pdf

CHP 303 Chemical Reaction Engineering and Process Control (CRE + PC) Laboratory

Semester II: 2012-13

Instructors: Prof. A.N. Bhaskarwar (Thu)

Prof. Anurag S. Rathore (Wed, Fri) Dr. Gaurav Goel (Mon) Dr. Sudip Pattanayek (Fri) Dr. Munawar A. Shaik (Mon,Tue) Grading Policy: Regular Labwork: 60%

Quiz (end of semester): 40% There will be 12 practicals (6 each in CRE and PC) in all. The 60% of in-laboratory evaluation will be done with 5% weightage for each turn based on your weekly report that is submitted. The experiments will be conducted in groups of 3 or 4 students. Handouts of all experiments can be downloaded from the link http://privateweb.iitd.ac.in/~munawar/CHP303.pdf. All the students are required to come prepared for the experiment. A common cover page (as per template on page 2 of the document in link) is to be used while submitting report for each experiment All experiments, calculations and final report writing will have to be completed and submitted before leaving the laboratory. Each sub-group of students needs to submit only one report, but it must be a joint effort. If some experiment is not completed or only partially done, you have to submit the report for whatever was accomplished. As this is a lab course 100 % attendance (including make-up) is required. There will be one extra turn at the end of the semester for catching up or re-doing one experiment, only if needed, with prior permission of the instructor. Lack of attendance automatically gets you a zero score for that turn. This also includes absence from the laboratory without prior permission of the laboratory instructor/TA for some part or entire laboratory. List of CRE Experiments: • Kinetics of saponification reaction from a batch reactor (CRE1) • Kinetics of hydrogen peroxide decomposition in a batch reactor (CRE2) • Kinetics of saponification reaction from a semi-batch stirred reactor (CRE3) • Flow analogy for series and parallel reactions (CRE4) • Reaction kinetics from an adiabatic batch reactor (CRE5) • Kinetics of a gas-solid non-catalytic reaction (CRE6) List of PC Experiments: • Dynamics of lagged thermometer (PC 1) • Dynamics of a stirred tank heater (PC 2) • Temperature Control (PC 3) • Level Control (PC 4) • Pressure Control(PC 5) • Cascade Control (PC 6)

Dr. Munawar A. Shaik (Course Coordinator)

CHP 303: Chemical Reaction Engineering & Process Control Lab II Semester 2012 - 2013

EXPERIMENT NAME AND NO. (AS GIVEN IN HANDOUT):

GROUP NO.: SUBGROUP NO.:

DATE AND DAY (Submitted)

LAB TURN (date and day)

NAMES OF GROUP MEMBERS PRESENT ON THE LAB TURN:

REMARKS (IF ANY):

Name of LAB INSTRUCTOR:

MARKS (TO BE FILLED BY LAB INSTRUCTOR/TA):

1

CHP 303 – PROCESS CONTROL AND REACTION ENGINEERING LABORATORY

CRE1: Kinetics of saponification reaction from a batch reactor

AIM: To determine the kinetics of saponification reaction between ethyl acetate and

sodium hydroxide in a batch reactor.

APPARATUS: Reaction Flask/Reactor, Stirrer, Beakers, Burettes, Pipettes, Indicator

and ice bath

CHEMICALS: Ethyl acetate, Sodium hydroxide, Oxalic acid (or other standard acid

for making stock solution), Indicator.

PREPARATION:

(i) Prepare standard acid stock solution of 0.1N (contact lab. technician)

(ii) Prepare 1000 ml of sodium hydroxide solution of 0. 1N and determine its

exact normality with standard acid solution

(iii) Calculate volume of ethyl acetate required per 100 ml of sodium hydroxide

0.1N so that the normalities are 1:1 and 1:2.

EXPERIMENTAL PROCEDURE:

(i) Add 400 ml of sodium hydroxide solution into the reaction vessel and stir its

contents slowly with the stirrer

(ii) Add the calculated amount of ethyl acetate for concentration ratio of 1:1 or

1:2 into the reactor vessel and note the time as starting time for reaction.

Immediately take a simple of 2 ml from the reactor and quench it.

(iii) At specified time intervals, i.e. 1, 2, 3, 4, 5, 7, 10, 12, 15, 20, 25 min take

samples of 5 ml from the reactor and quench them in ice bath.

(iv) Titrate the samples with standard oxalic acid solution for determining the

concentration of the sodium hydroxide as a function of time.

2

THEORY:

Reaction : NaOH + CH3 COOC2 H5 → CH3 COONa + C2 H5 OH

(A) + (B) → (C) + (D)

It is reported that the reaction is irreversible and the reaction orders with

respect to the reactant is unity. The rate expression is given by (elementary reaction):

2

[ ( ) ] (1)

(2)

AA B A BO AO A AO BO

AA AO BO

dC k C C K C C C C for C CdtdC K C for C Cdt

− = = − + ≠

− = =

DATA AND CALCULATIONS:

From the titration results, calculate the concentrations of the reactant A (sodium

hydroxide) in the reaction mixture at zero time and at other times.

Differential Method:

(i) Plot CA vs. t data.

(ii) Draw tangents at different values of CA.

(iii) Calculate slopes (dCA /dt) at each value of CA.

(iv) Plot (dCA/dt) vs. f (CA ) = CA {(CBO - CAO ) + CA )

(v) Calculate the rate constant, if the data gives a straight line passing

through the origin, from the slope of the line.

(vi) When the reactants are present in equimolal concentrations, plot ln(-

dCA /dt) vs. ln CA and determine the rate constant from the slope and

the overall order from the intercept.

Integral Method:

Integration of the equations (1) and (2) gives the following equations.

ln )3()(}){(

tkCCCC

CCCCAOBO

ABO

AAOBOAO −=+−

1 1 (4)

A AO

K tC C

− =

3

(i) Plot

{( ) ]1 {

( )AO BO AO A

BO AO BO A

C C C Cln

C C C C− +

− vs. t

(ii) Calculate the rate constant from the slope of the line.

(iii) When the reactants are present in equimolal concentrations,

Plot 1/CA vs. t and calculate the rate constant from the slope of the line.

FURTHER WORK :

(a) Repeat the experiment with different initial concentrations of the reactant .

(b) Determine the order of reaction by half life method. Check the value of the

rate constant with that obtained above in your procedure.

(c) Repeat the experiment at different temperatures to completely determine the

rate equation, i.e. frequency factor and activation energy, and order of

reaction.

RELEVANT BACKGROUND READING:

Fogler, H. Scott, Elements of Chemical Reaction Engineering, 3rd Ed., PHI India Pvt.

Ltd. (1999).

(Chapters 3, 5)

Levenspiel, O., Chemical Reaction Engineering, 3rd Ed., John Wiley and Sons (1999).

(Chapter 3)

1


CRE2: Kinetics of hydrogen peroxide decomposition in a batch reactor

AIM: To determine the kinetics of hydrogen peroxide decomposition in a batch

reactor.

APPARATUS: Three- necked round bottom flask, condenser, gas volume

measuring unit at atmospheric pressure, constant temperature bath, thermometer,

stopwatch.

CHEMICALS: Hydrogen peroxide, Potassium iodide.

PREPARATION:

The gas volume measuring unit consists of a 1 liter capacity measuring cylinder

and a open mouth glass bottle both connected at the bottom by a rubber tube. The

top of the measuring cylinder is covered with a lid with a 3- way stop valve.

Fill the measuring jar and the bottle with water such that the levels in the jar and

the bottle correspond to 1000 ml mark in the measuring cylinder when the 3- way

stop cock is open to atmosphere. Then keep aside the glass bottle without pouring

out the water.

PROCEDURE:

(i) Connect the reaction flask and the gas measuring cylinder with rubber

tubing with the condenser in between.

(ii) Add 100/150 ml of distilled water in the flask and heat it up to the desired

temperature (i.e., 35° – 40° - 45° – 50° C) and add 5 to 10 ml of the given

H2O2 solution and a pinch of KI salt.

(iii) Immediately turn the 3-way stop cock to connect the reactor with the gas

measuring cylinder and note the time as zero time.

2

(iv) Keep the overflow glass bottle next to the measuring cylinder and note the

times for change in volume of gas in the measuring cylinder by

maintaining equal levels of water in the cylinder and bottle.

(v) Note the time and volume of the gas collected at regular volume change in

the cylinder also.

THEORY

Reaction :

2H2 O2 2H2 O + O2

(A) (B) + (O)

It is reported that the reaction is irreversible and first order. The rate equation is:

- AA Ck

dtdC

=

DATA AND CALCULATIONS

Calculate the initial concentration of the hydrogen peroxide solution from the total

volume of oxygen (VO2) obtained from known volume of H2O2 (5 ml). Gram-

moles of Hydrogen peroxide in 1 ml of the sample is given by

)/(5400,22

2222 mlmolegmVC O

OH ××

=

Concentration of H2 O2 in the initial reaction mixture:

( )2 2 2 2

2 2 2

0H O H O

AH O H O

C VC

V V×

=+

The concentration of hydrogen peroxide in the reaction mixture at any time is

given by:

AOt

A CV

VVC∞

∞ −=

where Vt = volume of O2 liberated at time t.

Show the derivation of the above relationships and establish their correctness.

3

Differential Method:

(1) Plot Vt vs. t

(2) Plot CA vs. t

(3) Draw tangents at different values of CA and calculate (-d CA /dt) values.

(4) Plot ln(-dcA /dt) vs. ln CA

(5) Calculate the order and the rate constant from the intercept and the slope

of the data line.

Integral Method:

Plot ln(CAO /CA ) vs. t.

The line should pass through origin and the rate constant is given by the slope of

the line.

Compare the rate constants obtained in the differential and integral cases and

commet.

FURTHER WORK

(a) Repeat the experiment at a fixed temperature and at 2-3 different initial

concentration of H2 O2 and determine order by half life method.

(b) Repeat the experiment at different temperatures and determine the activation

energy and frequency factors from Arrhenius plot.



Ltd. (1999).

(Chapters 3, 5)


(Chapter 3)

1


CRE3: Kinetics of saponification reaction from a semi-batch stirred reactor

AIM: To determine the reaction rate/rate constant for saponification reaction between

ethyl acetate and sodium hydroxide in semi-batch mode of contacting.

APPARATUS: Storage tanks for the reactants, Reactor, Stirrer, Rotameters, Burettes,

Pipettes, Conical flasks, Ice bath.

CHEMICALS: Ethy1 acetate, sodium hydroxide, oxalic acid (or other standard acid

for making stock solution), indicator.

PREPARATION:

(i) Prepare approximately 0.1N solution of sodium hydroxide and fill the storage

tank with it.

(ii) Prepare ethyl acetate solution of about 0.1N concentration and fill the storage

tank with it.

(iii) Prepare standard oxalic acid (or any other standard acid stock solution as

directed by the lab. technician) of about 0.1N.

(iv) Determine the normality of the sodium hydroxide solution prepared.

PROCEDURE:

(i) Take NaOH in the reactor to fill it to an appreciable level (seek guidance from

the lab. technician or instructor).

(ii) Start the stirrer slowly and maintain a suitable speed so as not to spill the

liquid in the reactor.

(iii) Adjust the flow rate of the ethyl acetate solution from the storage tank to about

30-50 ml/min.

(iv) Allow the ethyl acetate flow to the reactor at the prefixed flow rate.

2

(v) When the reaction mixture starts overflowing, start collecting samples of 2 ml

and quench in ice bath (note that the reactor is operating in semi-batch mode).

(vi) Start collecting the samples from the exit overflow until steady state is

attained, i.e. the composition of the last two samples has the same value (and

essentially the NaOH, which was in batch, has been flushed out of the system

by the flowing ethyl acetate solution).

(vii) Titrate the samples obtained with standard acid for determining the

concentration of the sodium hydroxide.

THEORY:

Reaction:

NaOH + CH3COOC2H5 → CH3COONa + C2H5OH

(A) + (B) → (C) + (D)

Rate equation = (-rA) = k CA CB (1)

Design equations for semi-batch reactor need to be derived from first principles, with

help from books by Fogler and Levenspiel. The derivation should be shown in the

report.


Calculate the steady state exit concentration/conversion of the reactant (A) ie. Sodium

hydroxide. Measure the volume of the reactor and volumetric flow rate of the

reactants. Calculate the rate constant from the equations derived above.

FURTHER WORK:

Repeat the experiment with different flow rates/concentrations of the reactants and

verify the rate constant.



Ltd. (1999).

(Chapter 4)

1


CRE4: Flow analogy for series and parallel reactions

AIM: To study series and parallel reactions using fluid flow analogy and determine

the rate constants.

APPARATUS: Burettes, Capillary tubes and stop watch.

CHEMICALS: Water.

PREPARATION:

Connect the burettes with the capillary tubes, measure the I.D. and lengths of the

capillary tubes. Setup is already prepared in the laboratory.

PROCEDURE:

(i) Empty all the three burettes.

(ii) Adjust the capillary tubes such that they are in zero/50 ml mark level in the

burettes and the liquid flows through them into the subsequent burettes

(burettes kept downstream), smoothly.

(iii) Close the stop-cocks of the burettes and fill the top most burette to the zero

level mark.

(iv) Open the stop cocks of the burettes except the lower-most burette and note

down times for changes in water levels of known values in each of the

burettes.

Note: To avoid the difficulty of noting level vs. time data in the three burettes

simultaneously, first note time vs. level in the top most burette only. Repeat the

experiment noting down level vs. time in the middle burette. The level vs. time data in

the lower most burette can be determined from material balance for the three burettes.

The level vs. time data in the first burette is independent of the flows into the second

and third burettes.

2

(v) Repeat the same procedure for parallel reaction arrangement of

burettes/capillary tubes also, designed to mimic a parallel reaction scheme.

THEORY:

Series Reaction: → →

Assuming first order reactions, the rate equations are:

(1)

(2)

(3)

At t = 0, CA = CA0 and CB = CC = 0. Using these initial conditions, the solution to

equations (1)-(3) can be found by integration over time:

exp (4) exp exp (5)

(6)

The maximum concentration of the intermediate and the time at which the maximum

occurs are, respectively, given by: / (7)

(8) ‘

Please derive these relationships in your report.

We draw an analogy of the above reaction scheme with the burette-capillary

arrangement. The first burette empties into the second via flow through the capillary.

Resistance to flow in the capillary determines the speed of the emptying of the first

burette. Thus, the first burette may be taken to the first reactant A, and the rate

constant of flow through the first capillary may be taken to be the first rate constant

k1. Similarly, for the second and third burettes and capillaries. Thus, the envisioned

fluid mechanical apparatus provides an analogy to the series reaction network.

3

From fluid mechanics principles, a first order irreversible reaction can be represented

by emptying of a tank with a pipe line having laminar flow conditions (through

Hagen-Poiseulle’s equation). The equation relating level fall with time is given by

(please derive this relationship in your report):

)10(32/'

)9('

241

1

DLdgk

hkdtdh

μρ=

=−

D = tank (burette) diameter

d = pipe (capillary tube) diameter

L = length of the pipe (capillary tube)

h = level in tank (burette) – function of time

µ = viscosity of liquid (water)

ρ = density of liquid (water)

Parallel Reaction Network:

A

Assuming first order the rate equations are given by:

1 2

1

2

( ) (1)

(2)

(3)

AA

BA

CA

dC k k Cdt

dC k Cdt

dC k Cdt

− = +

=

=

At t = 0, CA = CA0 and CB = CC = 0. Using these initial conditions, the solution to

equations (1)-(3) can be found by integration over time: exp (4) 1 exp (5) 1 exp (6)

Please derive these relationships in your report.

B

C

k1

k2

4


Series Reaction Network:

(i) Measure the height of the burettes w.r.t. the capillary tube level (centerline of

horizontal capillary). Measure the length and diameter of the capillary tube.

(ii) Plot h vs. t for three burettes on a single graph.

(iii) Plot - ln(h/h0) vs. t for the first burette data.

(iv) Note down the value of hmax for the second burette and the corresponding time.

(v) Determine the value of k1 from the slope of the second plot.

(vi) Calculate k1 /k2 ratio from equation (7) or (8) by trial and error.

(vii) Calculate the k2 from the above values.

(viii) Calculate the numerical values of k1’ and k2’ from equation (10) and verify

with the above values.

Parallel Reaction Network:

(i) Plot h vs. t for the three burettes on a single graph.

(ii) Plot - ln(h/h0) vs. t data of the first burette.

(iii) Calculate (k1 + k2) from the slope of the line of the above plot.

(iv) Calculate (k1/k2) ratio from the ratio of the maximum heights of the plot of the

graphs of the second and third burettes (CB and CC).

(v) Calculate individual values of k1 and k2.

FURTHER WORK

Repeat the experiment with some liquid initially present in the second and third

burettes, i.e. CBO = 0 and CC0 = 0 at t = 0 and verify h vs. t data from the solutions of

the equation (1), (2) and (3).



Ltd. (1999).

(Chapter 6)


(Chapter 8)

1


CRE5: Reaction kinetics from an adiabatic batch reactor

AIM: To determine the kinetics of the reaction between hydrogen peroxide and

sodium thiosulphate in a batch reactor under adiabatic conditions.

APPARATUS: Reaction vessel (Thermos Flask), Thermocouple or thermometer.

CHEMICALS: Sodium thiosulphate solution and hydrogen peroxide solution.

PREPARATION: Take 1M H2 O2 solution and 0.5M Na2 S2 O3 solutions (100 ml

each).

PROCEDURE:

(i) Add the two reactants into the reaction flask and close the lid. Note the time as

the starting time for reaction.

(ii) Note the temperature vs. time date at regular intervals until there is no change

in the temperature of the reaction mixture.

THEORY:

A simple thermos flask acts as a very good adiabatic batch reactor, particularly is the

reaction is fast and the rate of heat transfer from the flask is slow in comparison.

Reaction:

2 Na2 S2 O3 + 4 H2 O2 → Na 2 S3 O6 + Na 2 SO4 + 4 H2 O

It is reported that the reaction is irreversible and first order w.r.to each reactant.

Rate equation is:

-rA = k CA CB (1)

Under adiabatic conditions, the heat balance gives:

dT/dt = ( )(/)() pTA CMrH −Δ− (2)

where, MT = total mass/moles of reaction mixture.

Cp = avg. specific heat (mass/mole basis)

2

ΔH = heat of reaction

Note that the reaction rate constant k, itself is a function of temperature, and is

related via Arrhenius law:

= /

Taking the reactants in stoichiometric proportions, the rate equation (1) can be

expressed as:

- rA = k 2AC (3)

Solving equations (2) and (3) together with the boundary condition:

At t = 0, T = T0 and CA = CA0

Gives:

RTE

O

AO eTT

CkdtdT

TT/0

2 .))(

1 −

∞∞ −=

− (4)

When reactants are not in stoichiometric proportions, i.e., when ≠ 2 , the

temperature variation is given by:

RTE

O

O

AO

BOAOO e

TTTT

CC

TTCkdtdT /]

)()(2

[)( −

∞∞ −

−−−= (5)


(i) Plot t vs. T data.

(ii) At different values of T calculate dT/dt by graphical method.

(iii) Plot ln[T

vsdtdT

TT1].

)1

2−∞

.

(iv) Calculate the activation energy from the slope of the line.

(v) Calculate the frequency factor from equation (4).

(vi) Repeat the similar procedure for the case of non-stoichiometric proportions,

in which case you have to get the parameters from equation (5).

FURTHER WORK:

Repeat the experiment with different initial concentrations of the reactants such that ≠ 2 and calculate the rate constant using equation (5).



Ltd. (1999). (Chapter 8)


3

(Chapter 9)

1


CRE6: Kinetics of a gas-solid non-catalytic reaction

AIM: To determine the rate parameters, i.e. reaction rate constant and effective

diffusion coefficient for the reaction of calcium carbonate decomposition (gas-solid

non-catalytic reaction).

APPARATUS: Furnace, pelletizer, holders, microbalance, stop watch, thermocouple.

CHEMICALS: Calcium carbonate powder, or chalk.

PREPARATION: Prepare one dimensional pellets by compacting the reactant

powder in the pellet holder using the bench-vice under uniform pressure. The

diameter, thickness and weight of the pellets are then measured.

Alternatively, if plain chalk is supplied to you, then cut them into precise cylindrical

shapes and weigh them in the microbalance to ensure that you know the precise

weight.

PROCEDURE:

Number the pellets (pellet holder) for identification. Raise the furnace temperature to

the desired reaction temperature. Keep all the pellets in the furnace at one time (try to

make sure that they all have similar dimensions and initial weights). Remove each

pellet after keeping them in the furnace for different reaction times and put them

immediately in a desiccator for cooling. Then, measure the weight loss of the pellets

corresponding to different reaction times.

THEORY:

Reaction: CaCO3 → CaO + CO2

B(S) → C(S) + A(g)

The reaction is assumed to proceed according to shrinking core model.

2

For chemical reaction rate controlling, the time of reaction for conversion X is given

by:

t = )1(r

B

KXLρ

For mass transfer controlling, the time of reaction is:

)2(2

2

AEeff

B

AEg

B

CDXL

CKL

xt ρρ

+=

Where:

B = molar density of the solid

L = thickness of the pellet

X = conversion

Kg = mass transfer coefficient, m/sec

Kr = reaction rate constant, kg.mol/m2 sec

Deff = effective diffusion coefficient, m2/sec

CAE = equilibrium CO2 concentration at any given temperature.

The rate parameters are obtained by data according to equation (1) and (2). For

determining the chemical reaction rate constant, the experiments are conducted at

lower temperature 650-7500C and mass transfer coefficients the temperature are 750

to 9000C.


From the experiments with each pellet, the time versus weight loss is determined.

Then conversion is given by:

X = )3(∞−

−WWWW

O

tO

Where W0, Wt, W∞ are weight of the solid at zero time, any time and infinite time

i.e. completion of reaction. The time versus conversion for the different pellets is used

to calculate the rate parameters corresponding to one temperature.

For the calculations, the molecular diffusion coefficient DCO2-air can be calculated

using Chapman-Enskog equation and porosity can be calculated from true density and

bulk densities of the solid pellet and assuming tortuosity factor as 2.

3

τε /2 airCOeff DD −= (4)

The Deff values can be compared with the experimental value obtained according to

equation (2).

FURTHER WORK: Repeat the experiments at other temperatures for determining

the activation energies for reaction and diffusion constants.



Ltd. (1999). (Chapter 11)


(Chapter 25)

CHP 303: PROCESS CONTROL AND REACTION ENGINEERING LAB

PC 1: EXPERIMENT: TRANSIENT RESPONSE OF A LAGGED THERMOMETER

OBJECTIVE : To determine the transient response of a distributed parameter system and to

show that it can be approximated by a first order system followed by a time delay and n-first

order systems in series using a lagged thermometer.

EXPERIMENTAL SETUP: A mercury thermometer is embedded in a long cylindrical wooden

block. The transient response to change in the surrounding temperature is determined by the

temperature at the centre line of this block. A hot temperature bath is provided for this

purpose. You may try different types of materials around the thermometer.

THEORY: If several identical interacting systems are arranged in series, the response is

practically the same as that of a distributed system, which is one where resistance and

capacity are associated with each incremental length of the system. That is to say that transfer

function of a distributed parameter system can be approximated by

( )( ) = ( ) as n→∞ (1)

Where is the time constant of a first order system. Another useful approximation of the

transfer function of a distributed parameter system is a first order system followed by a time

lag, i.e;

( )( ) = (2)

Where Td is the time delay and τ is the time constant of the first order system.

PROCEDURE : Measure the initial reading of the thermometer and then place the lagged

thermometer inside the hot bath which is maintained at constant temperature. Measure the

temperature with time until the steady state has been reached. This completes one set of the

experiment. Remove the lagged thermometer from the hot bath and allow it to cool in the

atmosphere. Once again, note the temperature versus time until the new steady state has

been reached.

RESULTS TO BE REPORTED:

1. Plot Q = vs t for both heating and cooling experiments. Here and are

the initial and ultimate temperatures respectively.

2. To approximate the response of two and three first order systems in series, determine

the time to reach 74% and 80% response respectively. Let these be t0.74 and t0.8. Then

time constant of two first order systems in series will be approximately, τ = . /4

and the time constant for three first order systems in series will be, τ = . /9. Using these time constants, determine the theoretical response from equation (1) and

match with the actual responses and comment.

3. To approximate the response by a first order system followed by a time delay, find the

inflection point of the transient response plot and draw a tangent at the inflection

point. The intercept of the x-axis provides the value of Td, while the inverse of the

slope gives the value of the time constant. Using the values of and Td plot the

theoretical response from equation (2) and match with the actual response and

comment.


PC 2: EXPERIMENT: DYNAMICS OF STIRRED TANK HEATER

OBJECTIVE: To study the response of a stirred tank heater using a step change in heater input.

EXPERIMENTAL SET-UP: The stirred tank has a diameter of 22.6 cm and a height of 28 cm. Water is

filled upto a certain level and is continuously agitated by a stirrer with a diameter of 5 cm rotating at

1100 rpm. The bottom of the tank contains heating coils whose input is controlled by means of variac.

Cooling water flows through a long helical coil. There are 15 turns in all, the diameter of the helix being

4.2 cm and the coil thickness is 6mm. Cooling water is obtained from an overhead tank and there is a

valve to regulate the flow. Temperature of the tank is measured using a thermometer.

THEORY: Draw a block diagram of the stirred tank heater. Cooling water enters at a temperature Ti

and mass flow rate Mc (measured using measuring cylinder). The outlet temperature of the cooling

water changes when a step change is introduced into the system by altering the heater input Q. Derive

the transfer function (refer any book on process control like “Coughanowr”) between the tank

temperature T and the heater input Q.

The following assumptions can be made:

1. The temperature of water in the cooling coil is the average of inlet and outlet temperatures.

2. Perfect mixing exists in the tank i.e. same temperature throughout.

The value of heat transfer coefficient between tank and coil, U, is a function of several parameters like

stirrer rpm and diameter, Prandtl number etc. The exact correlation can be obtained from Perry’s

handbook.

PROCEDURE: The study is to be conducted by changing the heater input in a step fashion and

noting the change in tank temperature. (It is also possible to change cooling water flowrate and note

the resultant effect on the system)

1. Set up the apparatus and start the flow of cooling water.

2. Set variac reading (say 80 V) and wait for steady state to be attained.

3. Give a step change to the variac reading (hence heater input ) and start noting temperature

vs time.

4. Plot the temperature vs time curve. Compare the experimental and theoretical curves (with

the one obtained from the transfer function). Identify possible sources of error.


PC-3: EXPERIMENT: Temperature Control

OBJECTIVE: To study the tuning of PID controller by Open Loop method using (a) Cohen and Coon (C-C) (b) Ziegler-Nichols (Z-N) tuning rules.

APPARATUS: Process tank having temperature controlling unit.

THEORY: The open loop method of tuning in which the control action is removed from the controller by placing it in manual mode and an open loop transient is induced by a step change in the signal. Fig.1 shows a typical control loop in which the control action is removed and the loop opened for the purpose of introducing a step change (M/S). The step response is recorded at the output of the measuring element. The step change to the valve is conveniently provided by the output from the controller, which is in manual mode. The response of the system is called the process reaction curve.

Fig: 1. Block Diagram of a Control Loop for measurement of Process reaction curve.

A typical process curve exhibits an S- shape as shown in Fig: 2. It is represented by equation (1).

( )1

L seG s KTs

−

=+

(1)

Zeigler and Nichols suggested setting the values of Kc, Ti, Td according to the formula shown in Table 1. Refer Fig. 2 for symbol meaning for tuning the controller via Z-N settings.

Table 1. Z-N Settings for tuning different Controllers

Type of Controller Kc Ti Td Proportional (P) T/L Proportional - Integral (PI) 0.9T/L L/0.3 Proportional - Integral – Derivative (PID) 1.2T/L 2L 0.5L

Fig: 2.Typical process reaction curve (First Order with Transportation lag)

Similarly, Cohen and Coon suggested controller parameters as given in Table 2.

Table 2. C-C settings for tuning different controllers

Types of Control Parameter Settings Proportional (P) Kc = (T/(Kp*L) ) * ( 1+L/3T) Proportional - Integral (PI) Kc = (T/(Kp*L)) * (0.9 + L/12T) Ti = L * (30 + 3L/T) / (9 +20L/T) Proportional - Derivative (PD) Kc = (T/(Kp*L))* (1.25 + L/6T) Td = L*(6-2L/T) / (22+3L/T) Proportional - Integral – Derivative (PID) Kc = (T/(Kp*L)) * (1.33 + L/4T) Ti = L*(32 + 6L/T) / ( 13 +8L/T) Td = 4L / (11 + 2L/T)

The value of Kp can be found using Kp = Bu / M, where Bu is the ultimate value of B at large time t. (Refer to Fig. 1).

PROCEDURE :

1. Process Tank filled with liquid water is made available. Temperature Control Trainer is active.

2. Log in the system and select “INTERFACE” mode for experimentation. 3. Turn on the water supply and maintain the inlet flow rate of water to process tank to

approximately 600-700 mL per min. Please note that attached Rotameter is not calibrated. Corresponding reading in Rotameter will be around 20-25 LPM. Please verify it.

4. Due to some external disturbances, liquid flow rate may show some significant change in its value. Please keep an eye on the rotameter reading to dampen such

changes by careful adjustment of rotameter itself. Please note that change in mass flow rate is not desired in the undertaken experiment.

5. Run the process as directed below: o Select the MANUAL MODE with controller output 0 %. o Wait till steady state is reached. o Log on to a file for saving transient data. o Start saving data. Wait for approximately 5 mins. o Give a STEP RESPONSE to controller output. Change it from 0% to 100%. o Wait till steady state is reached. Please do not rush. o Log Off from data saving procedure.

6. With the help of saved data file, draw the Process Reaction Curve. 7. Find the control setting parameters from Cohen-Coon (C-C) & Ziegler-Nichols (Z-N)

rules. 8. Tabulate the control setting parameters for each type of controlling mode e.g. P-

mode, PI-mode, PID-mode; obtained from both the rules, C-C & Z-N. 9. Run the process with the suggested controlling parameters for each type of control

mode, obtained from both the methods. Please follow the instructions directed below carefully.

• Select the MANUAL MODE with controller output 0%. • Have the set point of 25 oC. • Wait till steady state is reached. • Select the AUTO MODE. • Set P / PI / PID parameters as obtained from Z-N rules. For the first time, set

for P-mode. You will have the opportunity of tuning PI & PID mode in next RUN sequences.

• Wait till steady state is reached. Please do not rush. • Once steady state is reached, LOG on to a file for saving transient response of

system. It is advised to save the data file with name explaining: controller mode, set pointy change, control parameter values.

• Start saving data, with file name as suggested above, if possible. • Wait till approximately 5 mins. • Give a STEP change by changing the set point from 25 oC to 35 oC. • Wait till steady state is reached. Please do not rush. • Log Off from data saving procedure.

10. Repeat the procedure mentioned in STEP-8 for obtaining the process transient

response for different control mode e.g. PI and PID. 11. Repeat STEP-8 and STEP-9 for controlling parameters as obtained previously from C-

C rules. 12. Draw the excel plots for all the above set of transient responses. Plot process value

and set point of the process on the same graph against time. 13. Report the best possible controlling mode for the step change made. Justify your

decision on both, qualitative and quantitative scale.

14. Last step of experiment is to observe the frequency response of the system. Do as directed below:

• Select AUTO MODE. • Set for PI Mode of control. Set the controlling parameters with Kc= 4*Kc(Z-

N) and Ti = 1.85*Ti (Z-N). • Turn on Function Generator. • Select Signal type as “Sine Wave” of Amplitude: 5, Period: 10 sec, Reference

point 30. • Wait for steady state. • Log on to data file for saving data. • Save the transient frequency response for approximately 15 mins. • Log Off from data saving procedure. • Shut down the unit. Please make sure “Heater” is turned off. • Make a plot showing the transient response of process value, set point

value and control output value against time. Please make sure that they are plotted on same graph.


PC 4: EXPERIMENT: Level Control Trainer: Experiment & Simulation

OBJECTIVE: Optimizing the tuning parameters of Level Control Trainer via simulation interface and comparing the transient response obtained from the simulation with real time response for the same set of controlling parameters obtained as above.

APPARATUS: Process tank having level control trainer, rotameter, pump, sump-tank etc.

THEORY: The open loop method of tuning in which the control action is removed from the controller by placing it in manual mode and an open loop transient is induced by a step change in the signal. Fig.1 shows a typical control loop in which the control action is removed and the loop opened for the purpose of introducing a step change (M/S). The step response is recorded at the output of the measuring element. The step change to the valve is conveniently provided by the output from the controller, which is in manual mode. The response of the system is called the process reaction curve.



( )1

L seG s KTs

−

=+

(1)

Zeigler and Nichols suggested setting the values of Kc, Ti, Td according to the formula shown in Table 1. Refer Fig. 2 for symbol meaning for tuning the controller via Z-N settings.




Similarly, Cohen and Coon suggested controller parameters as given in Table 2.

Table 2. C-C settings for tuning different controllers

Types of Control Parameter Settings Proportional (P) Kc = (T/(Kp*L)) * ( 1+L/3T) Proportional - Integral (PI) Kc = (T/(Kp*L)) * (0.9 + L/12T) Ti = L * (30 + 3L/T) / (9 +20L/T) Proportional – Derivative (PD) Kc = (T/(Kp*L)) * (1.25 + L/6T) Td = L*(6-2L/T) / (22+3L/T) Proportional - Integral – Derivative (PID) Kc = (T/(Kp*L)) * (1.33 + L/4T) Ti = L*(32 + 6L/T) / ( 13 +8L/T) Td = 4L / (11 + 2L/T)

The value of Kp can be found using Kp = Bu / M, where Bu is the ultimate value of B at large time t. (Refer to Fig. 1).

It is the open loop method of tuning control parameter, which is widely used in industrial practices. However, we will divert from this approach in this experiment. Students will have an opportunity to exercise the above mentioned open loop algorithm in “Temperature Control Trainer” experimentation.

Currently, the area of focus will be doing a set of suggested simulation on “INTERFACE” panel of the trainer. Transient data will be observed and analyzed for step, frequency & square wave responses given to the system. You will be given a set of controlling parameters for different modes of controller. You are required to come up with the best control logic from the given set.

Having done with search for best controlling action, students are advised to replicate their simulations model for real time experimentation. This will help in realizing and appreciating the real time differences with ideal simulation conditions, if any.

EXPERIMENTAL PROCEDURE :

1. Run the process with the suggested controlling parameters (same as for simulation) for each type of control mode. Please follow the instructions directed below carefully.

2. Log in the system with “INTERFACE” mode this time. 3. Select AUTO mode. 4. Make sure all the system component e.g. pump, rotameter, sump-tank are in

working conditions. 5. Repeat step 4 for real time analysis for all the above done simulations. 6. Plot the responses, both simulation & experiments, on the same graph for

comparison. 7. Plot the Bode diagram for frequency response. 8. Explain the effect of increasing value of Kc for P-mode controller, both qualitatively

and quantitatively. 9. What happens to phase lag with decrease in frequency of the sine wave signal.

Justify your reasoning on simulation and experimental results obtained. SIMULATION PROCEDURE:

1. “Level Control Interface Panel” is made available. 2. Log in the system and select “SIMULATION” mode 3. Select AUTO mode. 4. Do as directed below:

o Adjust set point to 30%. o Select P-mode of controller with Kc = 1.0. o Wait for steady state. Please do not rush. o Log on to a file for saving system transient response. o Induce a step change by changing set point to 50%. o Wait for steady state. Please do not rush. o Log off from data saving protocol.

5. Repeat step 4 for Kc = 2, 10, 30. 6. Please observe the sustained oscillations for Kc = 30. Justify it. 7. Turn ON the Function Generator module.

OPTIONAL:

Table 3. Input Response Parameter for Simulation

S.No. Signal Type Amplitude Period Reference Point Control Mode 1. Sine Wave 10 10 40 a. P-mode

Kc = 1 b. P-mode

Kc = 5 c. P-mode

Kc = 50 2. Sine Wave 10 100 40 P-mode

Kc = 5 3. Triangle

Wave 10 10 40 PI-mode;

Kc= 100, Ti = 10.

8. Repeat step 4 for simulation conditions as mentioned in Table 3.


PC 5: EXPERIMENT: Pressure Control Trainer: Experiment & Simulation

OBJECTIVE: Optimizing the tuning parameters of PID controller for Pressure Control Trainer via simulation interface using Ziegler-Nichols (Z-N) tuning rules and to study the closed loop response for servo and regulatory problems.

APPARATUS: Process tank having pressure control trainer, interfacing unit with computer, air supply through compressor.

The basic objective is to control the pressure in the process tank shown in Fig. 1. The interfacing unit is basically a medium for communicating with the equipment from the computer. The assembly has various supporting components on the front panel i.e. pressure gauges which is used to measure the pressure, current to pressure converter in the range 3 to 15 psi for current in the range of 4 to 20 mA which is given to the I/P converter by digital indicating controller. The setup also contains a pneumatic actuator. The pressure in the process tank is sensed by the pressure transmitter with the help of pressure sensor fitted in the line. The data is transmitted by the pressure transmitter to the computer through the interfacing unit which shows the value of the process variable. The control valve performs the function of controlling the input of air pressure in the process tank. It has a diaphragm type pneumatic actuator which varies the flow of air according to the movement of the stem at a pressure range of 3 – 15 psi received from I/P converter.

Fig. 1. Schematic diagram of experimental setup

THEORY: In the open loop method of tuning the control action is removed from the controller by placing it in manual mode and an open loop transient is induced by a step change in the signal. Fig.2 shows a typical control loop in which the control action is removed and the loop opened for the purpose of introducing a step change (M/S). The step response is recorded at the output of the measuring element. The step change to the valve is conveniently provided by the output from the controller, which is in manual mode. The response of the system is called the process reaction curve.



( )1

L seG s KTs

−

=+

(1)

Zeigler and Nichols suggested setting the values of Kc, Ti, Td according to the formula shown in Table 1. Refer to Fig. 3 for meaning of symbols for tuning the controller via Z-N settings.




The value of K can be found using K = Bu / M, where Bu is the ultimate value of B at large time t. (Refer to Fig. 2).

Start-up:

1. All the drains should be closed. 2. Switch on the main supply. 3. Check whether all the valves are properly working or not. 4. Switch on computer and the interfacing unit. 5. Select the auto mode to perform experiment automatically and in manual mode to

change the values manually. 6. Connect the equipment with compressed air supply.

Shut-down:

1. Exit from the software. 2. Switch off the interfacing unit.

Procedure:

1. Start the set-up (as mentioned in start-up) 2. Select open loop option for control. 3. Select a value of set point to some desired value. 4. Apply 20-30 % change to controller output. Record the step response. Wait for the

steady state. 5. Start data logging and from the readings draw the step response curve. 6. Calculate T and L (refer to Fig.3) 7. Calculate PID settings from Table 1. 8. Now select auto mode option for control. 9. Change the set point. And input the controller settings calculated earlier. Plot the

closed loop response. 10. Repeat the same for regulatory problem by changing the disturbance.


PC 6: EXPERIMENT: Flow-Level Control Trainer: Cascade Control

OBJECTIVE: Optimizing the tuning parameters of Flow-Level Control Trainer via simulation interface and comparing the transient response obtained from the simulation with real time response using Cascade control scheme.

APPARATUS: Process tank having flow and level control trainer.

THEORY: In cascade control an intermediate process variable is used that responds to both the manipulated variable and some disturbances to achieve more effective control over the primary process variable. Fig.1 shows the general block diagram of a cascade control scheme.

Fig: 1. Block Diagram for Cascade Control Loop

Two controllers are used but only one process variable is manipulated. The output of one controller can be used to manipulate the set point of another. Each controller has its own measurement input, but only the primary controller has an independent set point and only the secondary controller has an output to the process. The advantages are that the disturbances affecting secondary variable can be connected by the secondary controller before a pronounced effect is felt by the primary variable. Also closing the control loop around the secondary part of the process reduces the phase lag of primary controller and this increases speed of response.

In this experiment, cascading of flow and level controllers is done. Level controller is the primary controller with an independent set point, and controlling level in the tank is the primary variable. The level transmitter transmits the level of tank to primary controller which gives its output as set point to the secondary controller i.e. the flow controller. The flow controller gets the process value of flow from the flow transmitter. Responding to both it gives an output to the control valve through an E/P converter and adjusts the flow into the level tank. The flow transmitter forms the secondary loop while level transmitter forms primary loop.

PROCEDURE: Cascade control using PC as PID controller

switch position mains OFF pump OFF flow-cascade / level PC level PC PID / PC PC FR knob (E/P in) Fully anti clockwise

1. Ensure that the drain valve of sump tank (V1) is fully closed. 2. Close the bypass valve (V2) partially. Partially open the drain valve (V3) of the level tank. 3. Fill clean water in the sump tank till the maximum level of the sump tank. 4. Connect the communication cable from output of the interface card to PC. 5. Connect the 230 V A.C. supply to the trainer. Switch ON the “Mains supply”. 6. Ensure that pneumatic supply (to the trainer) is ON and it is more than 2 kg/cm2. 7. Ensure that position of the switches is as per the table mentioned above 8. Switch on the pump on the panel marked as “PUMP” 9. Gradually turn the knob of FR clockwise till the pressure gauge marked “E/P IN” shows

20 psi. (WARNING: Sudden application of pressure or application of high pressure may damage E/P converter.)

10. Switch ON the PC and the interface device. Select the experiment ‘Cascade Flow/Level’. 11. Make following settings. (Take two readings with set points 200 and 300)

Primary loop (level loop): set point: 300, PB: 80%, It: 10 s-1, Dt: 0 s-1. Secondary Loop (flow loop): PB: 25%, It: 45 s-1, Dt: 5 s-1. Low alarm: 275 lph, High alarm: 400 lph

12. Ensure that both the PID controllers are in ‘Manual Mode’. Keep the output of the secondary loop to 0 %. This means the control valve is fully open. Let the level reach near set point.

13. Change the secondary PID and primary PID to ‘Auto mode’ 14. See the graphical trend display where you will observe graphs of level vs time, set point

vs time, output vs time, etc. Observe if the level is under control. Note if there are oscillations or offset, note if the response time is faster or slower. Depending on this data, tune the PID controller.

15. Once control is achieved and fine tuning is done, create a disturbance in secondary loop (flow loop) and observe its effect on the level. To do this open the valve V2 slightly and observe the flow and level. This will increase the flow momentarily leading to increase in level. However, the primary loop takes care of the minor changes here on its own and the effect of this is not passed on to secondary loop (level loop). Please note that the disturbance in the flow should not be more than 10 % of the present value of flow.

16. Switch OFF the pump and shut down the system.

chp303.pdf

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