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7/27/2019 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.