mini project-process control

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UNIVERSITI MALAYSIA PERLISPUSAT PENGAJIAN KEJURUTERAAN ALAM SEKITAR

School of Environmental Engineering

EAT 449

ENVIRONMENTAL PROCESS CONTROL

AND INSTRUMENTATION

Title : pH Control in Fermentation Process

Lecturer : Dr. Fahmi Muhammad Ridwan

Group members No.matric

LIEW JEUN YANG 101130420

THENMOLHI A/P RAVINDER 101131300

ROSNAH BINTI HAMID 101131123

NUR FALAHI BINTI MOHAMMED 111131334


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Content

Chapter 1 : Introduction

1.1Background1.2pH monitoring devices1.3Background of fermentation in plants1.4 pH control

Chapter 2: Process control and instrumentation

Chapter 3 : Process Description and modeling

3.1 Process Description

3.2 Process Modelling

Chapter 4 : Process control Design

4.1 Equation for acid,

4.2 Equation for alkaline ,

4.3 Calculation part

4.4 Characteristic equation

4.5 Routh Array

4.6 Root locus

Chapter 5 : Conclusion

References


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CHAPTER 1

INTRODUCTION

1.1BACKGROUNDIn the general aspects of process control, there are also focuses on process

control applications in the chemical process industries (CPI) and biotechnology

industries. The chemical process industries represents a range of industries that are

use processing units to produces a wide range of products such as hydrocarbon

fuels, petrochemical products, concrete, pharmaceutical products, paper products, manmade fibers and films, agrochemical products and ceramics. Biotechnology is the

technology that uses microbial species or any other living organisms or part of

them to produce useful products (Atkinson et al, 1992).

Fermentation is a another type of chemical process and its also engineering

that help in the development and regulation of biological processes. There are

possibilities in applying ideas and techniques developed for more conventional

chemical system (Gaden, JR., et al, 1959).

There are three types of fermentation methods such as batch fermentation, fed

batch fermentation processes and continuous fermentation. The batch fermentation can

be refers as a partially closed system and requires materials are loaded onto the

fermenter, decontaminated before process starts and then removed at the end. The

regulation of batch fermentation process variables are temperature, dissolved oxygen

and the traces which determined by initial conditions (micobiological basis). Fed-

batch fermentation is a production technique which lies between batch and

continuous fermentation which related to the presence of production of high

concentrations of substrates. The presence of concentration can be avoided by

limiting the amounts that required in biochemical production (R.M. Dekkers, 1979)

In addition, the control process of variables which we distinguishing between

batch and fed-batch / continuous fermentation are similar with closed loops cases

such as temperature, pH and possible dissolved oxygen.


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Figure 1 shows typical industrial fermentation and typical process

measurements that are availables. The typical measurements can be differentiate as

on-line and off-line. The industrial fermenter control can be divided into three

categories such as on-line environmental control (examples: pH and temperature),

off-line environmental-control (examples: nutrient concentration and precursor

concentration) and off-line organism state control (examples: biomass concentration

and hyphal length distribution) (Gary A. Montague et al)

.

1.2pH monitoring devicesA pH measurement is a determination of the activity of hydrogen ions

in an aqueous solution. Many important properties of a solution can be determined

from an accurate measurement of pH, including the acidity of a solution and extent

of a reaction in the solution. Many chemical processes and properties, such as the

spees of a reaction and the solubility of a compound, can also depend greatly on

the pH of a solution. In application ranging from industrial opertaions to biological

processes, it is important to have an accurate and precise measurement of pH.

Most modern pH electrodes consist of a single combination reference and

sensing electrode instead of separate electrodes. This type of pH electrode is much

easier to use and less expensive than electrode pair. A combination electrode is

functionally the same as an electrode pair.


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Figure 2 (a) glass electrode (b) combined electrode

Any pH electrode requires both a sensing electrode and a reference

electrode. The sensing electrode consists of a thin hydrogen permeable membrane

containing a solution and electrode. The membrane of the sensing electrode allows

hydrogen to slowly pass, creating a positive voltage across the membrane. The

voltagecreated in this electrode is then compared to the voltage in the refences

electrode. The voltage difference between the two electrode is then used to

determine the pH of the unknown solution using the Nernst equation.

E(pH) = E(constant) + (2.3* RT/nF) * log [H+] (5)

Where:

E (pH) = Voltage difference between sensing electrode and Reference electrode (V)

E (constant) = Voltage difference in a solution with pH = 7 (V)

R = Gas Constant (8.314 J/K*mole)

T = Temperature in Kelvin (K)


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n = Number of Valence Electrons per Mole (1 for H+)

F = Faradays Constant (96500 J/V * mole e-)

1.3Background of fermentation in plants

A typical batch fermentation process starts with sterilization so that all

micro-organisms found in the mash and reactor are completely destroyed. The mash

heated in the fermenter or a special cooking vessel by injecting live steam or by

means of steam coils set in the vessel. Holding the temperature at 121C (250 F)

for 30 miunutes is usually adequate to destroy all living organism in the mash.

However dome processes require higher temperature, as shown in figure 2 which a

heating/cooling jacket maintains the temperature of the fermentor.

A fermentation cycle can be divided into two phases are (a) the

growth phase and (2) the production phase. During the growth phase, cells grow

very slowly because its adapting to the reactor environment. After the adaption

period, the cell culture grows exponentially, releasing enzymes as a byproduct of

the metabolic process. During the production the molecular products are formedthrough a series of chemical reations catalyzed by the enzymes. For many

fermentation processes, these two phases are con-current.

1.4pH control

pH is the one of the most important chemical environmental

measurements used to indicate the course of the fermentation process. It detects the

presence of specific chemical factors that influence growth, metabolism and final

product. For example, the pH of commercial mash of P.chrysogenum (penicillin

production) should be closely monitored and controlled in both the growing phase

and the production phase. Initiation of the growth phase, the ph of the mash is

carefully maintained between 4.5 and 5.5, depending on the mash formulation. The

range is set to ensure the most favourable condition for growth. The metabolism

of glucose and rapid consumption of ammonia during this phase adversely affect


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the medium by lowering the pH. If the medium is not adjusted, growth may be

inhibited and the fermentation may take a long time to reach the optimal range

required for penicillin production.

In the production phase, the organism starts to metabolize other sugars

(lactose) and amino compounds because of the depletion of glucose. The liberation

and accumulation of ammonia from the metabolism of amino compounds will

cause the pH to slowly rise. The pH is allowed to about 7 and is controlled at

this point until the end of production. Depending on the culture and several other

factors, it has been found that the optimum range of penicillin production lies

between 6.8 and 7.8. the pH is monitored and controlled in this range by the

addition of sulfonic acid. Finally at the end of the fermentation, the pH rises and

production stops. Figure 2 shows that the pH control loop implemented on a

standard fermentor.

Figure 2


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Chapter 2

Process control diagram and Instrumentation

pH is read by the measurement of an electric potential generated at a pair of electrodes, which

are wetted by the sample stream. All pH instruments use a buffer solution, which is generally

pumped to the electrodes in very small volumes by the controller. The solution must be

replenished at intervals.

1. A needle valve and rotameter should be provided to adjust the flowrate past theelectrodes so that it falls in the range required by the manufacturer. If necessary, a

pressure reducing valve should be installed upstream of the needle valve to make the

flowrate adjustment easier.

2. If the sensor element could become clogged with silt, a filter should be providedupstream. The sensor elements are generally very fragile, so flush lines should only be

provided where the electrodes can be completely removed from service during

flushing.

3. The liquid stream is contaminated with buffer solution during the measurement; thestream should be discharged to waste.

4. If the controller includes an alarm contact to warn of low buffer solution level, thecontact should be tied into the alarm system to remind the operator to refill the

controller.

5. The sense element must not be mounted far from the controller because of the verylow-level signals involved. If necessary, the sample line should be routed to a location

where the sense probe and the controller may be located near each other.

6. The controller should include a display, and should be installed so that the display iseasily read.


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Process control diagram to control pH


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CHAPTER 3

PROCESS DESCRIPTION AND MODELLING

3.1 Process Description

The Reactor Tank

The reactor tank is very crucial in this research as this is where the neutralization reaction

process takes place and where the output measurements are taken. Figure shows the

simplified diagram of the physical arrangement of the reactor tank and a photograph of the

actual reactor tank on the pH neutralization pilot plant.

The reactor tank

The outlet point is positioned to provide a maximum storage volume for this tank of 80L. The

minimum operating volume is 30L, as the agitator will not be able to mix the solution

properly if the volume is smaller than this value. Thus most of the simulation and

experimental results are based on a volume of mixing solution of approximately 80L. As

shown in the figure, the pH meter (AT 122) and the agitator (AG 120) are installed near the

acid feed stream inlet. The main purpose of this agitator is to mix both solutions completely

and homogeneously. In addition to that, it will also accelerate the neutralization reaction

process. The agitator produces some turbulence in the tank in order to mix the solution

satisfactorily. The pH value from the online pH meter is also relatively consistent, indicating


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that the agitator works adequately and its turbulence does not adversely affect the measured

signals.

3.2 Process Modelling

The first principle that is applied is known as the conservation balance principle. The

conservation balance equations that are commonly used in process control are the equations

for conservation of material, energy and momentum. As far as this research is concerned the

variables involved relate to the total liquid mass in the reactor tank and the principle of

conservation of material is used in the derivation of the basic equations of the process. The

general equation for the conservation of material for the pH process may be written as

follows:

( ) ( )

As described earlier, the volume V represents a constant volume of 80L of the reactor tank.

The flowrates for the acid and alkaline streams are F1 and F2 respectively. The concentration

for acid in tank is C1 and the concentration of alkaline in tank is C2.

The non-reactant components in the system are for acid and for alkaline.

= [ H2SO4] + [HSO-4] + [SO

-24]

= [Na+

]


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The next step is to identify and derive the electroneutrality condition of the nonreactant

components. Based on the principle of electroneutrality all solutions are electrically neutral.

There is no solution containing a detectable excess of positive or negative charge because thesum of positive charges equals the sum of negative charges.

The total electro neutrality condition is,

[] [] [] [] []The equilibrium constant expressions that apply to the acid-base system,

i. Water (H2O)Kw= [H

+] [OH-]

ii. Sulphuric acid (H2SO4) [][]

[

][

]

The quantity Kw (the constant value for the ionic product of water), is equal to 1.0 x 1014.

There are two acid dissociation constants for sulphuric acidK1= 1.0 x 103 andK2=1.2 x 10-2

since sulphuric acid falls under category of a diprotic acid, having two equilibrium points or

dissociation points. However for this case, the first point is negligible as the first dissociation

constant,K1 is too large. Theoretically the titration curve for this acid-base reaction process

will only show one break point or equilibrium point.


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The pH scale is a measure of the hydrogen ion concentration, thus the pH value can be

calculated by using the equation below.

[

]

pH equation,

[] [] [] [] a1= K1+

a2 = K1+ K1K2KwK1

a3 = K1K2+ K1Kw2K1K2

a4= - K1K2Kw


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Chapter 4

Process control Design

4.1 Equation for acid,

V = F1C1 - (F1+ F2)

= ( ) ()

S [(s) (0)] = ( ) ()

(s) [S + ( ) ] = + (0)

(s) =

()( )

(s) = * + ()[ ] ) . Equation for acid (1)


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4.2 Equation for alkaline,

V = F2C2 - (F1+ F2)

= ( ) ()

S [(s) (0)] = ( )()

(s) [S +( ) ] = + (0)

(s) = ()( )

(s) =* + ()[ ] ) . Equation for alkaline (2)


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4.3 Calculation part

Assume that :-

V = 80 l

F1 = 300 l/h C1 = 0.5 M

F2 = 350 l/h C2 = 0.5 M

= 3 = 11

For acid,

Gp =* + ()* + )

= * + [ ] =

= So,

Kp = 0.5

tp = 0.1


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For alkaline,

Gp = *

+ ()*

+ ) =* + [ ] =

=

So ,

Kp= 1.7

tp = 0.1

Gs ,

Ks =

=

= 1.14

Assume time delay , ts = 3

Gs =

Ga = 1

Gc= Kc


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4.4 Characterisation Equation

(Kc) ( Ga) (Gp) (Gs) + 1 = 0

(Kc) (1) ( ) ( ) + 1 = 0 ( )( ) ( )

( )

Kc + = 0 ( ) 4.5 Routh Array

n

A1 =( )( ) A2 = 0

= ( ) =

= 3.150.05Kc

B1 =[()()

B2 = 0

= 1+ Kc


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Therefore ,

=

3.150.05 Kc 0 1 + Kc 0

-0.05 Kc -3.15 Kc -1

Kc 63

4.6 Root Locus

Kc R1 R2 R3

0 -0.33 -10 -

-2 0.3 -10.31 -10.31-2.53i

-1 -10.17 + 1.82i -10.17-1.82i 0

2 -1.19 -6.79 -12.35

4 -13.22 -3.33 -3.78


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Chapter 5

Conclusion

A fermenter is a vessel which does not permit contamination but provides

conditions necessary for the maximum production of the desired product. The use of

software sensors, which combine signals already available on-line with mathematical

models, should be a valuable tool for process development. The possibility to obtain

more information throughout the process using software sensors, without sampling and

off-line analysis, generates a demand for efficient tools for data evaluation by

muitivariate analaysis and data presentation.

In conclusion , it is important to recognize the major advances in biosensors

technology and how much instruments contribute to the overall control scheme. A

significant conclusion is that in order to achieve improved control, process must

become more computerized in their operation. The levels of computerization of

bioprocess plants are very low compared to their chemical equilkvalent and in order

to improve operability, this problem must be rectified. Greater computer application

leading to improved data .


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References and Appendices

1. Atkinson, R., Baulch, D.L.,Cox, R.A.,Hampson, R.F.,Kerr,J.A.r and Troe,J., 1992,Evaluated kinetic and photochemical data for atmospheric chemistry supplement IV

Atmos.Environ., 26A, No.7, 1187-1230

2. Gaden, E.L., Jr.Chem & Ind (Rev.) (1955) , 1543. Gary A.Montague, A.J.M., and John R Bush (1966). Considerations in Control

Scheme Development for Fermentation Process Control, IEEE Control Systems

Magazine , C30(88)

4. R.M. Dekkers, State Estimeation of a Fed-Batch Fermentation Process, Proc.1stIFAC on Modelling and Control of biotechnical Processes, Helsinki, Pergamon

Press, pp.201-211,1979.

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