Programmable logic controller (plc) for polymer mixing tank

Programmable Logic Controller (PLC) for Polymer
Mixing Tank
A’zraa Afhzan Ab Rahim, Mohd Hazwan Md Shah, Ili Shairah Abdul Halim, Siti Lailatul Mohd Hassan
Faculty of Electrical Engineering, Universiti Teknologi MARA,
40450 Shah Alam Malaysia
azraa.afhzan@yahoo.com , hazwan.mdshah@gmail.com, shairah@yahoo.com, sitilailatul@salam.uitm.edu.my
Abstract— This project focuses on improving the performance
of a plant’s sludge dewatering process by using Omron CP1E
Programmable Logic Controller (PLC) to increase the
efficiency of the process which leads to a reduction in cost of
the polymer product. The process requires manually mixing
the cationic polymer long chains with raw water to produce a
product that will be sent to the sludge tank process and filter
press process where the sludge will harden for disposal. The
addition of PLC into the process will reduce error caused by
human. The Omron PLC will control the water intake inlet and
pump for polymer needed to be mixed by measuring the level
of water inside the tank using the sensor to control amount of
water and polymer. The project works on upgrading an
established system that uses manual mix method to automated
method that will produce more accurate concentration of
polymer without any human error.
Keywords-PLC, polymer mixing, Jar test
I. INTRODUCTION
The polymer mixing preparation and dosing tank is a part
of the dewatering process. While treating waste water,
polluted products are removed whilst the treated water is
released in the environment. Sludge is formed from the
aerobic wastewater treatment which contains a mixture of
microorganism. Only the settled sludge will be decanted to
the sludge tank and treated. The polymer is used in
dewatering process for the sludge treatment where the
function of the polymer is to thicken the sludge before the
sludge goes into the filter press machine. The polymer
product output is a mixture of raw water and cationic
polymer long chain.
The main system is the Omron PLC that acts as a control
system to the electronic device or equipment to ensure the
accuracy, stability and smooth transition of the process [1].
Due to the rapid advancement of technologies, the PLC can
be used to complete complicated control task that uses
highly automated control system by using signal interfacing
device such as motor, solenoid valves and float sensors
where the capabilities of these devices can be implemented
to ensure the process runs in good coordination. The
proposed system will operate by using a magnetic float
sensor as a feedback to the controller to give signal to the
output section. The system uses PLC because of the
rustiness of the product and it is also suitable for fast
switching. Fast switching is appealing because the mixing
product concentration will be affected if either valve or
pump did not close at specific given time that based on the
sensor. The solenoid type valve is used as the main valve
because of the quick opening provided by the coil. Basically
this solenoid valve is normally closed. The agitator which is
used to mix the product of polymer and raw water uses
direct current motor where the optimum voltage has been set
to around 3.5V [2]. The product for polymer is a cationic
polymer long chain that will be mixed together with raw
water to produce an output that will harden the organic
sludge waste. All this system is a part of the dewatering
process in chemical waste treatment plant [3].
This system is used to mix chemical product to produce
an output that will harden the organic sludge. There are two
designated tanks that will store the chemical products which
are used for preparation and dosing [4]. Initially, raw water
will be filled up until it reaches 80 percent of the preparation
tank. Then the polymer with a concentration of 0.2 percent
will be dosed to the preparation tank. The motor mixer will
be turned on after dosing the polymer and will run for 2
minutes 16 seconds to obtain a chemical reaction that will
produce the desired output. The process will continue by
filling up the dosing tank where the polymer will then be
sent to the thickened sludge tank process and sludge tank
mixer. The process will be repeated as long as the dosing
tank level has not reached the maximum set level [1]. The
magnetic float sensor will be placed inside the two tanks to
control each designated level to give signal to the controller.
All this process is done automatically by the Omron CP1E
PLC.
II. METHODOLOGY
The project aims to design a polymer mixing system that
works automatically using the CP1E Omron PLC. There are
two 18 liter tanks that contain polymer with each tank
having its own function. The upper tank which is the main
tank will be used as a preparation tank for the polymer. The
lower tank is used as a reservoir tank to store the product
before the polymer will be dosed to other process such as
sludge mixing tank or table thickening sludge. The magnetic
float sensor will be used to send feedback signals to the
controller to detect changes in water level. The actuators
used are solenoid valves and direct current motor to control
the water flow and agitator as a stirrer inside the preparation

tank respectively. This entire signal will be sent to the
Omron CP1E PLC. Figure 1 shows the block diagram of the
general process flow of the polymer mixing process.
Analysis then is carried out on the valve flow rate, the
sequence timing and chemical concentration.
Figure 1 General process flow
A. Software development
This part involves ladder diagram programming of the
CX programmer for the Omron CP1E programmable logic
controller. This software is developed to interface with the
sensor and the actuators of the process:
i. Siemens LOGO simulation
A computer program that uses ladder diagram symbols
to construct instruction for the PLC. This computer
program can simulate the ladder diagram instruction to
predict the outcome for input and output.
Figure 2 Overall flow chart of the Polymer
mixing process
B. Hardware development
The hardware part consists of two designated tank
of 18 liters which will be used as preparation tank and
dosing tank. The tank level will be controlled by the
three magnetic level sensors where each of the level as it
own function to interlock with the controller. The PLC
acts as the brain for the hardware part where it receives
signal from the inputs and process it for outputs signal to
be send. So basically, the float sensor is the main
feedback of the process that will interlock with the
actuators.
i. Magnetic float sensor
The float sensor is a device that will detect a
change in water level. The sensors will send the
signal back to the programmable logic controller
to be processed. The magnetic float sensor is one
of the smallest in the world and suitable for this
project scale. Figure 3 shows the dimension of
the sensors.
Figure 3 Magnetic level sensor diagram [5]
ii. Solenoid Valve
The solenoid valve uses an electrical coil that
will convert electrical into mechanical energy
that will open or shut off the valve. The valve
was chosen based on fast opening characteristics.
Fill 80% of tank
with raw water
Polymer dosing at 0.2 %
concentration
Mixing process for 2 minutes 16
seconds
Filling up the dosing tank
Dosing products to other process
End

Figure 4 Solenoid valves [5]
iii. DC motor (stirrer)
Using a direct current motor for the agitator part
so that the mixture can diffuse much better. The
motor was chosen because the stirring part does
not require much torque where it can affect the
polymer quality.
iv. AC Pump
AC pump was used to supply the polymer to the
tank at normal flow rate from the polymer
container. The pump is used only at the
preparation tank parts, where polymer been mix.
v. Omron CP1E Programmable Logic Controller
(PLC).
The programmable logic controller is used as
control system to control the sequence transition
smoothly. The PLC is designed for multiple
inputs and outputs arrangement where the output
response to the input conditions.
Figure 5 Input block arrangement
Figure 6 Output block arrangement
Figure 7 General diagram of the hardware
Table 1 Description table for Figure 7
Term Description
VA Valve A
VB Valve B
LL Low Level
LP Process Level
LH High Level
Table 2 Discrete state table for mixing
polymer tank

Figure 8 Flow chart of the P
process
III. RESULTS AND DISCUSSION
A. Results
i. Flow rate
Flow rate is the amount of f
through a certain given surface
this project, flow rate is defi
minutes. The flow rate is determ
11 litre container and stopwatc
standard water flow rate. Table
below will show two kinds of
standard water hose and soleno
shows the different methods of
using solenoid valve and sta
shows that the flow rate with
employed to fill water is m
without solenoid valve, which i
solenoid valve helps speed up th
Table 3 Flow rate t
olymer mixing
fluid that passes
per unit time. In
ined as liter per
mined by using an
h to measure the
e 3 and Figure 9
testing using the
id valve. Table 3
filling raw water
andard valve. It
h solenoid valve
much faster than
indicates that the
he process.
test
Figure 9 Flow
ii. Jar test
Jar tests are test
effectiveness of che
treatment facility. M
to water can be eva
scale by the usin
important of these c
coagulation such a
Using the jar test th
be approximated.
coagulant dosages
dosing flow rate, d
outlet water quality
of chemical used an
flow at the meterin
with regards to the
quality taken from
Under dosing or
(coagulant & floccu
chemical processes
Table 4, Table 5 a
results of the test.
Table 4 Jar Test 1
C
Table 5 Jar Test 2
C
0
0.5
1
1.5
2
2.5
1 2 3 4 5 6 7
Minutes
Litres
w rate graph
ts designed to show the
emical treatment in a water
Many of the chemical added
aluated on a small laboratory
ng the jar test. The most
chemicals are those used for
as coagulant and polymers.
he correct coagulant dose can
Jar test results includes
and settle water pH, pump
dissolved air flotation (DAF)
and actual volume /quantity
nd cost. The actual chemical
ng pump are then calculated
e optimum dosing and water
m the same water sample.
overdosing of chemicals
ulants) will upset the chain in
and increase operational cost.
nd Table 6 below show the
(pH=6.63, Turbidity=34.2,
OD=5510)
(pH=4.87, Turbidity=41,
OD=4130)
7 8 9 10
with
solenoid
valve
without
solenoid
valve

Table 6 Jar Test 3 (pH=6.07, Turbidity=15
COD=5270)
B. Discussion
Based on the test results, design of the prototype
can be made using the variables available in
Table 4, Table 5 and Table 6. The filling process
time for an 11 liter container has an average of
1.38 minutes using solenoid valve where 11 liter
without solenoid valve has an average of 1.89
minutes. The actual flow rate is 70000 liter per
60 minutes, where in one minute it can fill up to
1,166.67 liter. The final flow rate is
approximately 8.33 liter per minute.
The jar test is used as a reference for the
coagulant dosing rate where all the calculations
are based on actual results. The yellow
highlighted in the table shows the optimum plant
performance based on chemical oxygen demand
(COD). A small value of COD is a good
indicator for the water disposal because the
small COD contain small amount of carbon
inside the water, where high carbon will affect
the amount of oxygen for the aquatic life. The
entire jar test had been done three times to vary
the water quality during each test. The standard
end result for the water quality is COD value
below 6000mg/l, turbidity below 20 ntu and the
pH is around 6-7. So the 7ml of coagulant and
1mg/l of polymer is the optimum quantity based
on the results given.
The plant should dose the coagulant at 120000
liter per hour with regard to the water quality.
The flow rate can be calculated using Equation
(1).
F = DI (Flow rate 70m3
/hr) (1)
1000 x SG
F = Flow rate of the pump
D = Dosage of the chemical
SG =Fixed variable for the chemical
I = flow rate of the plant
Table 7 Result for flow rate and dosage
Calculation F
(L/hr)
D
(g/m3)
I
(m3/hr)
SG
1 3.13 60 70 1.34
2 9.91 190 70 1.34
3 6.30 120 70 1.34
i. Cost calculation
Saving
= (9.91 - 6.3 ) L/hr
= 3.6 L/hr x 24 x RM 2.75/kg x 1.34
= RM 318 / day
From Table 7, three calculations have been carried
out. The first shows the dosage is under dosed at 60 g/m3
and metering pump set at 3.13 L/hr. The second calculation
shows the dosage is overdosed at 190 g/m3
and metering
pump set at 9.91 L/hr. The plant optimum dosage should be
120 g/m3
and the pump metering flow should be set to 6.30
L/hr. At 120 g/m3
the plant can save cost at least RM
318/day based on the calculation above.
From all the calculations done, the flow rate of the
water at house and plant can be compared having a ratio of
1:140 for the coagulant dosing rate. Using an 18 liter tank,
the polymer should be filled with 36 g per liter at about
0.2 % concentration. The Jar test had shown the actual result
to determine how much coagulant and polymer need to be
used by measuring the liquid chemical oxygen demand
(COD). The calculation method above shows how to
measure and adjust the pump setting to get the desired
output needed.
IV.CONCLUSION
Nowadays, most of the control system operation in
industries uses PLC as a controller to control the process. It
is available in the process control, transportation, domestic
appliances, production lines and many others.
From the experiment and testing, the PLC system can be
implemented using the existing standard procedure. The
automated system can improve the performance of the
process whereas it erased mostly the existing manual system.
The PLC also manages to work efficiently based on the
feedback from the sensor and works well with the actuators
such as solenoid valves and DC motor. It can be concluded
that the objective of this project to upgrade an established
system that uses manual mix method to automated method
that will produce more accurate concentration of polymer
without any human error and improve the process in terms
of time saving for preparation is achieved.
In future work, this system can be improved by
connecting it to the distributed control system (DCS) where
the operator can monitor the mixing process just by looking
to the monitor. The operator also can make changes much

easier to the process. Besides that the control variable and
manipulated variable can be control more efficiently.
ACKNOWLEDGMENT
The authors would like to the acknowledge Redzarul
Redzuan, process engineer of Veolia Water (M) Sdn.Bhd for
his dedication , guidance, advice and the generous amount
of time he spent. The authors would also like to
acknowledge Veolia water plant laboratory technician for
their support of using the lab equipment as well as Faculty
of Electrical Engineering, UiTM for supporting this project.
REFERENCE
[1] P. Programming, "pacontrol," 7 May 2000. [Online].
Available:
http://www.pacontrol.com/download/OMRON-PLC-
Programming.pdf. [Accessed 2012].
[2] C. D.Johnson, "Actuators," in Process Control
Instrumentation Technology, Pearson/Prentice Hall,
2006, 2006, pp. 358-367.
[3] V. Water, Polymer Standard Procedure, Veolia Water
(M).
[4] L. G. W. rossman, "Scale-model studies of mixing in
drinking water storage tanks," Journal of
Environmental Engineering, no. 125(8), pp. 755-761.
[5] R. Components, Magnetic Float sensors, RS.

Programmable logic controller (plc) for polymer mixing tank

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