Cement Plant Process and Instruments Used

Plant Process & Instruments
Used
Ravi Roy
Dept-Instrumentation

What is cement?
The term cement is commonly used to refer to
powdered materials which develop strong
adhesive qualities when combined with water.
Cement is a fine grayish powder which, when
mixed with water, forms a thick paste. When this
paste is mixed with sand and gravel and allowed
to dry it is called concrete.

Limestone Quarry and Crushing Plant
The major raw material for cement production is limestone.The
limestone most suitable for cement production must have some
ingredients in specified quantities i.e., calcium carbonates, silica,
alumina, iron, etc..
Quarrying is done through drilling and subsequently, using heavy
earth moving equipment such as bulldozers, payloaders and
dumpers.

The quarried limestone is normally in the form of big boulders,
ranging from a few inches to meters in size.These varying sizes of
limestone need to be crushed to a size of about 10 mm in order to be
prepared for finish-grinding.
Crushing is done either in two stages or in a single stage. In the two
stage crushing system, a impact type crusher is used in the first
stage for raw crushing, followed by hammer crusher in the second
stage.

STACKER AND RECLAIMER
A stacker is a large machine used in bulk material handling. Its
function is to pile bulk material such as limestone, ores and cereals
on to a stockpile.
Stackers normally travel on a rail between stockpiles in the
stockyard. A stacker can usually move in at least two directions:
horizontally along the rail and vertically by luffing (raising and
lowering) its boom. Luffing of the boom minimises dust by reducing
the distance that material such as coal needs to fall to the top of the
stockpile.The boom is luffed upwards as the height of the stockpile
increases.

A reclaimer can be used to recover the material.

Limestone Bunker
It is used for the storage of crushed limestone.The material is fed
into bunker from reclaimer followed by belt conveyor.

The Ball Mill contains 3chambers:-Dry, coarse, fine. The material is
fed to the ball mill in the inlet side and the hot gas from preheater
outlet is also fed in the inlet of ball mill. The material is moved
through all the 3chambers before giving it to silo. Once the material
is moved through all the 3 chambers, the coarse material is fed to
bucket elevator which is then moved to separator1 and then again
back to inlet of ball mill through returning belt. The fine material is
moved up by separator2, out of which still some coarse material is
fed on the returning belt which again moves towards ball mill inlet,
and the extra fine material is then fed to cyclones which is then
released through air slide and the very fine material is moved to
RABH.

The Reverse Air Bag House is a modular type dust collector in which
each module act as a device which accepts the dust-laden gases,
filters it, collects the dust and discharges the clean air.
The dirty air enters the side of the hopper so that, due to the low
velocity, much of the entrained dust (particularly the large size of the
dust particles) will drop directly into the hopper. Continuing upward,
the air encounters the tube sheet where it passes the filter bags. The
dust in the air does not penetrate the bags and remains as a deposit
on their inside surfaces. The air itself, however, does pass through
the bag material, then continues upward and out through the top of
the compartment from there it is directed through an exhaust
manifold.

At specific intervals, a cleaning cycle is initiated in which the
air flow through the module is stopped and air moving in the
opposite direction is introduced. This reversed flow and the
partial collapse of the bag which it produces causes the
accumulated dust to break loose and fall out of the bags. The
dislodged dust drops in to the hopper and is removed by dust
handling equipment. After the dust had a few moments to
settle, the valves are reset to their position for filtering.

CF Silo
It’s a large storage of Rawmeal which comes from Rawmeal. It is
made up of concrete and can store Rawmeal for long time.

The material stored in silo is fed to the bin with the help of
airslide which containes butterfly valve, pneumatic gate and
dossive valve.Continuous air is blown to the bin through
bottom of the bin so that material is not dried or get stuck to
the walls of bin. It is then moved to the kilin feed1&2 and then
moved to preheater1&2 with the help of bucket elevator.

PREHEATER
The purpose of preheater is to increase the temperature of
rawmill material through the incoming hot air from kilin and
transfer air duct.

Rotary Kiln
Kiln is cylindrical rotary equipment rotating on supporting rollers.
Due to the inclination of the cylinder and slow rotation of the
material, the materials roll in hoop direction. On the other hand, the
materials move from the high end to the low end, where they are
decomposed, burnt, cooled in succession. Thus they become
cement clinker, and are discharged from the low end of the cylinder
finally, they enter the cooling device.The heating source is sprayed
into kiln by the burner barrel in the nose area of the kiln the exhaust
gas are discharged.

The Grate cooler operates with crosscurrent principle in
which the clinker is moved across the grate while cooling air
blow in from below through the grate and clinker layer.The
hot clinker falls from the kilin and forms clinker bed on the
grate and transported through the cooler over fixed and
reciprocating grates. At the inlet of first great clinker is
quenched and spread across the cooler width by increasing
the cooling air. During the clinker transport from the cooler
a part of dust and small clinker fall from the gates and gets
collected in the hopper below, which is then transported to
clinker silo and clinker stock pile with the help of DBC.

ESP(Electrostatic Precipitator)

Electrostatic precipitator is commonly used as the final dust removal device for
flue gases. It consists of chambers each of which contains a series of collection
plates and an overhead framework of suspended rigid high-voltage electrodes.
Particles in the gas stream are charged by a high-voltage, direct current field
which is generated from the discharge electrodes, suspended between the
collector plates. Current applied directly to the discharge electrodes manifests a
highly active and visible glow in the electrode known as the "corona". In the
strong electrical field region near the electrode-emitting surface, large numbers
of both positive and negative ions are formed. As the discharge electrodes have
a negative polarity, the positive ions are attracted to them. Both negative and
positive ions are formed in equal amounts directly in the corona region near the
discharge electrodes and over 99 percent of the gas space between the
discharge electrodes and the collector plates contain only negative ions. As the
particles entrained in the gas stream pass through the corona field, they are
bombarded by negative ions and become charged in a fraction of a second.
They are then attracted to the grounded collector plates where they are
collected and then transported to clinker silo through DBC.Particulate matter on
the collecting plates and high voltage electrodes is removed by the impact of
"rapper" mechanisms. Dislodged particles from the high voltage electrodes and
collector plates fall into a hopper directly below each precipitator chamber,
which is then moved to clinker stock pile and clinker silo with the help of
conveyor belt and DBC.

The clinker, gypsum, flyash with the help of hopper
is fed on the feeding belt from where with the help
of conveyor belt is fed into the hoppers from where
it is moved to the ball mill, flyash is fed if the
cement is PPC and clay is fed if cement is OPC. The
course material once moved from the outlet is
moved to the bucket elevator through air slide.,
from where it is again proceeded to ball mill with
the help of separator and returning belt. The fine
material at the discharge of ball mill moves to the
bag filter proceeded by bucket elevator through air
slide to silo.

The material from silo through bucket elevator is moved to
the vibrating screen from where it is moved to hopper
proceeded by bin with the help of dossive valve.The
material then with the help of rotopacker is packed into the
bag(50kg each) and then loaded into the trucks wih the help
of belt conveyor.The fine cement while packing is absorbed
by the bag filter and also the material fallen below the
rotopacker with the help of screw conveyor is again sent to
the bucket elevator to repeat the same process.

ZERO SPEED SWITCH(ZSS)
Zero speed switches (ZSS) are used to detect the stoppage or
unacceptably slow movement of a rotating shaft. In
various machines, conveyors, power plants, and in industries involving
the production of cement, sugar, textiles, paper, etc. Zero speed
switches mainly use electromechanical, electronic,
or magnetic proximity technologies.

BELT SWAY SWITCH(BSS)
The switch allows smooth running of the conveyor and
protects it from damages by over swaying which can
occur due to uneven loading of material, worn out idler
roller bearings etc. Belt sway switch is also known as Run
Off Switch.

Pull Cord Switch
Pull Cord Switch is an emergency switch to stop the belt
conveyor instantly when an accident happens. Since the
Pull Cord Switch is so designed that it should be installed
at the side of belt conveyor and the pull cord should be
mounted along conveyor, the switch can be actuated at
any position.

LIMIT SWITCH
Rotary Lever Operating Head
Rotary lever operating heads are available in spring return and
maintained type. The rotary shaft can be readily changed to
operate clockwise, counter clockwise or both. The operating
levers may be rotated and locked in any position through 3600.
The operating head can be positioned in any of the four sides.
The lever rollers are 19mm diameter and 8mm thickness. The
levers are available fixed and adjustable lengths.

Thermocouple
Thermocouples are the most commonly used
temperature sensors.
OPERATION
A thermocouple is created when two dissimilar metals
touch and the contact point produces a small open-circuit
voltage as a function of temperature. This thermo-electric
voltage is known as Seebeck voltage.

Resistance Temperature Detector(RTD)
A resistance temperature detector (RTD) can also be
called a resistance thermometer as the temperature
measurement will be a measure of the output resistance.
OPERATION
RTDs work on a basic correlation between metals and
temperature. As the temperature of a metal increases, the
metal's resistance to the flow of electricity increases.
Similarly, as the temperature of the RTD resistance
element increases, the electrical resistance, measured in
ohms (Ω), increases. RTD elements are commonly
specified according to their resistance in ohms at zero
degrees Celsius (0° C). The most common RTD
specification is 100 Ω, which means that at 0° C the RTD
element should demonstrate 100 Ω of resistance.

Pressure Switch
A pressure switch is used to detect the presence of fluid
pressure. Most pressure switch uses a diaphragm, piston
or bellow as the sensing element. The movement of this
sensing element is used to actuate one or more switch
contacts to indicate one or more alarm or control actions.

RF LEVEL SWITCH
The probe comprises sense and shield electrodes
electrically isolated from the metallic tank by means of
suitable insulators.The sense electrode of the switch and
the vessel wall serve as the two electrodes of a capacitor
with the service material as the dielectric. A change in
material level causes a change in dielectric, which in turn
causes a change in admittance of this tank capacitor.
The processed signal is used to energize or de-energize a
relay whose output contacts are available for annunciation
or control.

VIBRATION FORK LEVEL SWITCH
The tuning fork is piezoelectrically energized and vibrates
at its mechanical resonance frequency. (of approx. 1200
Hz.) The piezos are fixed mechanically and therefore are
not subject to temperature shock limitations. The
frequency changes when the tuning fork is covered by the
medium. This change is detected by the integrated
oscillator and converted into a switching command.
Typical applications are overfill and dry run protection.
They are used in silos and hoppers to know if its full or not
to prevent overfill.

BOOT LEVEL SWITCH(BLS)
Diaphragm Level Switch is used for detecting the
clogging of material on screw conveyor, boot level
detection of bucket elevator and to detect level of
food grain in hopper. The pressure of the product
on the membrane operates a limit switch inside the
switch compartment. The contact of limit switch is
used for control action

RADAR LEVEL SENSOR
In continuous non-contact level measurement with
radar, the sensor sends microwave signals towards
the medium from above. The surface of the
medium reflects the signals back in the direction of
the sensor. Using the received microwave signals,
the sensor determines the distance to the product
surface and calculates the level from it.

ELECTRONIC EAR
Electronic ear is used to know whether the ball mill is full
empty or rather the amount of material inside the ball mill
can be analyzed.

LOAD CELL
A load cell is a transducer that is used to create
an electrical signal whose magnitude is directly
proportional to the force being measured.
Strain gauge load cells work on the principle that the strain
gauge(a planar resistor) deforms/stretches/contracts when
the material of the load cells deforms appropriately.These
values are extremely small and are relational to the stress
and/or strain that the material load cell is undergoing at the
time.The change in resistance of the strain gauge provides
an electrical value change that is calibrated to the load
placed on the load cell.

FLOW SWITCH
Vane Operated Flow Switch is a reliable mechanical device that
uses the force of the fluid velocity exerted against a vane (a
paddle mounted on a vertical pivot point) inserted into the flow
stream to activate/deactivate an electric switch at a
predetermined flow rate.

TEMPERATURE SWITCH
Temperature Switches have a vapour filled
thermostatic element, which consists of a sensing
bulb, capillary tube and a bellows element. The
entire element contains a charge which reacts to
temperature variations at the sensing bulb, so that
pressure on the bellows increases on rising
temperature. The bellows movement due to this
increase in pressure is utilised to operate the
switch.
It is mostly used in bag house of coal mill.

DIFFERENTIAL PRESSURE TRANSDUCER
The most common and useful industrial pressure
measuring instrument is the differential pressure
transmitter. This equipment will sense the
difference in pressure between two ports and
produce an output signal with reference to a
calibrated pressure range.

PRESSURE GAUGE
It is used to indicate the value of pressure with the help of
the scale on it.

BAG FILTER SEQUENTIALTIMER CARD
Bag Filter Controller (BFC) is Solid State SequentialTimer, without
Digital Display.This is designed to control the cleaning cycle of On-Line
Bag Filters with adjustable ON, OFF & PauseTiming. It is available in
various models to suit different output requirements viz.Triac Output
and Relay Output. Custom BuiltTimer Panels are also available, which
are designed as per customer specification.
The card can be either phase looping or neutral looping. If it is phase
looping then connect the negative of the solenoids in the different
channels and all the phase short together in the phase channel and a
loop from phase channel to the com on the card and vice versa for the
neutral looping.
The timer energizes a solenoid valve, thus triggering the momentary
pulse of high pressure compressed air down into a row of filter bags.
This pulse of air will expel the dust from the surface of the filter.The
timer closes the valve after a specified time and the filter starts working
in the ventilation mode.

CO AND O2 GAS ANALYSER
Carbon monoxide (CO) and oxygen (O2)
concentrations allow the plant operator to optimize
the combustion in the rotary kiln with respect to
clinker quality compliance, toxic emissions reduction,
and fuel consumption minimization.

Weigh Feeder, BeltWeigher
The most typical application is for feeding / weighing
into a continuous process.The controller
continuously compares the actual weight with the
setpoint weight, and automatically adjusts the motor
speed to either increase or decrease belt speed, in
order to maintain a constant feedrate.Any variation
in the density of the material is reflected as a change
in belt loading, which is compensated for by
adjusting the belt speed.

Drop test calibration
Set the intecont controller in the keyboard mode.
Enter the password 07734.
Keep the mode gravimetric mode.
Go to Z1 counter by clicking on the DAT(green button) and
reset it by pressing ∑=0.
Set certain value of z1 and start by pressing I.
After the z value is achieved, checked how much material
has passed over the belt.
Check the difference between actual and shown value.
Divide them to get a specific value and multiply it with
correction factor which was earlier set.
After changing d02 value in the parameter in the calibration
option under programming in the intecont plus, test one
more time to get accurate value of actual and value shown
in intecont plus.

Tare calibration
Set the intecont controller in the keyboard mode.
Enter the password 07734.
Change the mode to volumetric mode from gravimetric mode.
Start the belt
Go to the tare option in the calibration and press on tare option.
After tarring once note down the abw value.
See how much percentage error has achieved.
If not satisfied then once again tare it and again and see the abw value and error
percentage.
If satisfied then press enter otherwise continue with the same process until you
get minimum error.
Still some changes or more accuracy can be achieved by changing tare weight
value.
Subtlewieh Feeders
Check weight Calibration
Check if the belt is empty, and the rollers, load cell are properly aligned.
Do dynamic tare once.
Put 10k/20K weight on the belt exactly at the center on the roller.
Check linear weight value.
Compare the original value and the weight showing on panel.
Calculate the difference, and according change the C.F to get the correct value.

DCS (DISTRIBUTED CONTROL SYSTEM)
MODEL ABB 5.1

AO(ANALOG OUTPUT)
AO or analog output is the type of DCS output which used to control
analog device. AO send command to device in form of electrical current
(4 - 20 mA) or electrical voltage. DAC (Digital to Analog Converter)
inside DCS will convert digital value to current or voltage and send it to
controlled device through AO channel. Example ofAO device is control
valve, DCS could control opening percentage of control valve BY
sending 4 - 20 mA current which represent 0 - 100% open command.
AI(ANALOG INPUT)
AI or analog input is the type of DCS input which used to read value
from sensor.AI will receive value from sensor in form of electrical
current (4-20 ma) or electrical voltage (1-24V). Example of sensor is
temperature transmitter/sensor.Temperature sensor will measure
temperature and send measurement value to AI channel in form of
current or voltage.

DI(DIGITAL INPUT)
DI or discrete/digital input is the type of DSC input which used to
read status of digital input
devices. Digital input device only have 2 status,ON or OFF. ON
state mean DCS DI point received status in form of electrical
power (can be 24VDC, 220VAC, etc.) and OFF state mean DCS DI
point received no power from devices.The 230VAC volt coming
from the field is converted to 24VDC and given to DI module.
DO(DIGITAL OUTPUT)
DO or discrete/digital output is the type of DCS output which
used to control digital output devices. Digital output devices only
have 2 status, ON or OFF. ON command mean DCS DO point
send command in form of electrical power and OFF command
mean DCS DO send no power to devices.The DCS command is
sent as 24VDC from the module and is converted to 220VAC with
the help of relay and given to the electrical feeders.

PROFIBUS (Process Field Bus) CONNECTOR
4 LEDs for bus/device status:
- Connector power supply (PWR).
-Transmission activity (TxD).
-Termination status (Term).
- Wrong termination resistance or false surge impedance (ERR).
Product features
General
• PG socket
• Fast Connect
• Switchable terminating resistor
• 12 Mbps
• Cable diameter: 8 mm
• Metal case (die-cast zinc)
• IP 20
• Status monitoring via LEDs
Ambient conditions
• Operating temperature: -20..+75 °C
Dimensions
• Dimensions (WxHxD) : +31 x 65 x 15.8 mm

DISADVANTAGES OF PROFIBUS CABLE
Profibus communication is not suitable for more
distance
and will be get affected by emf.signal strength. So its
better to use OFC (Optical fiber cable) cable as a
redundancy atleast.

Conclusion
Instrumentation will continue to become more
reliable and user-friendly for the cement industry.
Smart sensors, as well as advances in
communication capabilities, will allow users to
obtain much more information from field devices
in addition to the process measurement.
Programming options using process device
managers will enable plant personnel to better
maintain field instrumentation. Measurements in
the cement process will always tend to be rather
difficult because of the aggressive environment.
Solutions will improve as field device suppliers
focus on the specific needs of the cement industry.

Cement Plant Process and Instruments Used

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