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Company profile
Jaypee group is the 3rd largest cement producer in the country. The groups
cement facilities are located in the Satna Cluster (U.P), which has one of the
highest cement production growth rates in India.
The group produces special blend of Portland Pozzolana Cement under the brand
name ‘Jaypee Cement’ (PPC). Its Cement Division currently operates modern,
computerized process control cement plants with an aggregate capacity of 22.80
MnTPA*. The company is in the midst of capacity expansion of its cement
business in Northern, Southern, Central, Eastern and Western parts of the
country and is slated to be 37.55 MnTPA BY FY12 (EXPECTED) WITH CAPTIVE THERMAL
POWER PLANTS.
Keeping pace with the advancements in the IT industry, all the 140 cement
dumps are networked using TDM/TDMA VSATs along with a dedicated hub to
provide 24/7 connectivity between the plants and all the 120 points of cement
distribution in order to ensure “track – the – truck” initiative and provide
seamless integration. This initiative is the first of its kind in the cement industry in
India.
In the near future, the group plans to expand its cement capacities via acquisition
and greenfield additions to maximize economies of scale and build on vision to
focus on large size plants from inception.The Group is committed towards the
safety and health of employees and the public. Our motto is ' Work For Safe,
Healthy, Clean & Green Environment '.
Content Company profile
Introduction
Cement
Type of cement
Brief layout of cement plant
Cement manufacturing process
Thermal power plant
INTRODUCTION
CEMENT-:
In the most general sense of the word, a cement is a binder, a substance that sets
and hardens independently, and can bind other materials together. The volcanic
ash and pulverized brick additives that were added to the burnt lime to obtain a
hydraulic binder were later referred to as cement.
The most important use of cement is the production of mortar and concrete—the
bonding of natural or artificial aggregates to form a strong building material that
is durable in the face of normal environmental effects.
Concrete should not be confused with cement because the term cement refers
only to the anhydrous powder substance (ground clinker) used to bind the
aggregate materials of concrete. Upon the addition of water and/or additives the
cement mixture is referred to as concrete, especially if aggregates have been
added.
Cement
TYPES OF MODERN CEMENT
Portland cement
Cement is made by heating limestone (calcium carbonate), with small quantities
of other materials (such as clay) to 1450 °C in a kiln, in a process known
as calcination, whereby a molecule of carbon dioxide is liberated from the calcium
carbonate to form calcium oxide, or quicklime, which is then blended with the
other materials that have been included in the mix . The resulting hard substance,
called 'clinker', is then ground with a small amount of gypsum into a powder to
make 'Ordinary Portland Cement', the most commonly used type of cement
(often referred to as OPC).
Portland cement is a basic ingredient of concrete, mortar and most non-
speciality grout. The most common use for Portland cement is in the production
of concrete. Concrete is a composite material consisting
of aggregate (gravel and sand), cement, and water. As a construction material,
concrete can be cast in almost any shape desired, and once hardened, can
become a structural (load bearing) element. Portland cement may be gray or
white.
Portland cement blends
These are often available as inter-ground mixtures from cement manufacturers,
but similar formulations are often also mixed from the ground components at the
concrete mixing plant.[7]
Portland blastfurnace cement contains up to 70 % ground granulated blast
furnace slag, with the rest Portland clinker and a little gypsum. All compositions
produce high ultimate strength, but as slag content is increased, early strength is
reduced, while sulfate resistance increases and heat evolution diminishes. Used
as an economic alternative to Portland sulfate-resisting and low-heat cements.[8]
Portland flyash cement contains up to 30 % fly ash. The fly ash is pozzolanic, so
that ultimate strength is maintained. Because fly ash addition allows a lower
concrete water content, early strength can also be maintained. Where good
quality cheap fly ash is available, this can be an economic alternative to ordinary
Portland cement.[9]
Portland pozzolan cement includes fly ash cement, since fly ash is a pozzolan, but
also includes cements made from other natural or artificial pozzolans. In countries
where volcanic ashes are available (e.g. Italy, Chile, Mexico, the Philippines) these
cements are often the most common form in use.
Portland silica fume cement. Addition of silica fume can yield exceptionally high
strengths, and cements containing 5-20 % silica fume are occasionally produced.
However, silica fume is more usually added to Portland cement at the concrete
mixer.[10]
Masonry cements are used for preparing bricklaying mortars and stuccos, and
must not be used in concrete. They are usually complex proprietary formulations
containing Portland clinker and a number of other ingredients that may include
limestone, hydrated lime, air entrainers, retarders, waterproofers and coloring
agents. They are formulated to yield workable mortars that allow rapid and
consistent masonry work. Subtle variations of Masonry cement in the US are
Plastic Cements and Stucco Cements. These are designed to produce controlled
bond with masonry blocks.
Expansive cements contain, in addition to Portland clinker, expansive clinkers
(usually sulfoaluminate clinkers), and are designed to offset the effects of drying
shrinkage that is normally encountered with hydraulic cements. This allows large
floor slabs (up to 60 m square) to be prepared without contraction joints.
White blended cements may be made using white clinker and white
supplementary materials such as high-purity metakaolin.
Colored cements are used for decorative purposes. In some standards, the
addition of pigments to produce "colored Portland cement" is allowed. In other
standards (e.g. ASTM), pigments are not allowed constituents of Portland cement,
and colored cements are sold as "blended hydraulic cements".
Very finely ground cements are made from mixtures of cement with sand or with
slag or other pozzolan type minerals that are extremely finely ground together.
Such cements can have the same physical characteristics as normal cement but
with 50% less cement particularly due to their increased surface area for the
chemical reaction. Even with intensive grinding they can use up to 50% less
energy to fabricate than ordinary Portland cements.[11]
LAYOUT OF THE CEMENT PLANT
Cement Manufacturing Process
Mining
The cement manufacturing process starts from the mining of limestone,
which is the main raw material for making cement. Limestone is excavated
from open cast mines after drilling and blasting and loaded on to dumpers
which transport the material and unload into hoppers of the limestone
crushers.
Crushing Stacking & Reclaiming of Limestone
The LS Crushers crush the limestone to minus 80 mm size and discharge
the material onto a belt conveyor which takes it to the stacker via the Bulk
material analyser. The material is stacked in longitudinal stockpiles.
Limestone is extracted transversely from the stockpiles by the reclaimers
and conveyed to the Raw Mill hoppers for grinding of raw meal.
Crushing Stacking & Reclaiming of Coal
The process of making cement clinker requires heat. Coal is used as the
fuel for providing heat. Raw Coal received from the collieries is stored in a
coal yard. Raw Coal is dropped on a belt conveyor from a hopper and is
taken to and crushed in a crusher. Crushed coal discharged from the Coal
Crusher is stored in a longitudinal stockpile from where it is reclaimed by a
reclaimer and taken to the coal mill hoppers for grinding of fine coal.
Raw Meal Drying/Grinding & Homogenisation
Reclaimed limestone along with some laterite stored in their respective
hoppers is fed to the Raw Mill for fine grinding. The hot gasses coming
from the clinkerisation section are used in the raw mill for drying and
transport of the ground raw meal to the Electrostatic Precipitator / Bag
House, where it is collected and then stored and homogenised in the
concrete silo. Raw Meal extracted from the silo (now called Kiln feed) is
fed to the top of the Preheater for Pyroprocessing.
Clinkerisation
Cement Clinker is made by pyroprocessing of Kiln feed in the preheater
and the rotary kiln. Fine coal is fired as fuel to provide the necessary heat
in the kiln and the Precalciner located at the bottom of the 5/6 stage
preheater. Hot clinker discharged from the Kiln drops on the grate cooler
and gets cooled. The cooler discharges the clinker onto the pan / bucket
conveyor and it is transported to the clinker stockpiles / silos. The clinker
is taken from the stockpile / silo to the ball mill hoppers for cement
grinding.
Cement Grinding & Storage
Clinker and Gypsum (for OPC) and also Pozzolana (for PPC) are extracted
from their respective hoppers and fed to the Cement Mills. These Ball
Mills grind the feed to a fine powder and the Mill discharge is fed to an
elevator, which takes the material to a separator, which separates fine
product and the coarse. The latter is sent to the mill inlet for regrinding
and the fine product is stored in concrete silos.
Packing
Cement extracted from silos is conveyed to the automatic electronic
packers where it is packed in 50 Kgs. Polythene bags and dispatched in
trucks.
Electrical Power
For total power requirement of 90 MW (Jaypee Rewa Plant and Jaypee
Bela Plant), we have
CPP 1 - 25.0 MW
CPP 2 - 25.0 MW
CPP 3 - 37.0 MW
CEMENT MILL
Conveyor
A conveyor belt (or belt conveyor) consists of two or morepulleys, with a
continuous loop of material - the conveyor belt - that rotates about them. One or
both of the pulleys are powered, moving the belt and the material on the belt
forward. The powered pulley is called the drive pulley while the unpowered pulley
is called the idler. There are two main industrial classes of belt conveyors; Those
in general material handling such as those moving boxes along inside a factory
and bulk material handling such as those used to transport industrial and
agricultural materials, such as grain, coal, ores, etc. generally in outdoor locations.
Generally companies providing general material handling type belt conveyors do
not provide the conveyors for bulk material handling. In addition there are a
number of commercial applications of belt conveyors such as those in grocery
stores.
The belt consists of one or more layers of material they can be made out
of rubber. Many belts in general material handling have two layers. An under
layer of material to provide linear strength and shape called a carcass and an over
layer called the cover. The carcass is often a cotton or plastic web or mesh. The
cover is often various rubber or plastic compounds specified by use of the belt.
Covers can be made from more exotic materials for unusual applications such as
silicone for heat or gum rubber when traction is essential.
Material flowing over the belt may be weighed in transit using a beltweigher.
Belts with regularly spaced partitions, known as elevator belts, are used for
transporting loose materials up steep inclines. Belt Conveyors are used in self-
unloading bulk freighters and in live bottom trucks. Conveyor technology is also
used in conveyor transport such as moving sidewalks or escalators, as well as on
many manufacturing assembly lines. Stores often have conveyor belts at
the check-out counter to move shopping items. Ski areas also use conveyor belts
to transport skiers up the hill.
A wide variety of related conveying machines are available, different as regards
principle of operation, means and direction of conveyance, including screw
conveyors, vibrating conveyors, pneumatic conveyors, the moving floor system,
which uses reciprocating slats to move cargo, and roller conveyor system, which
uses a series of powered rollers to convey boxes or pallets.
TYPE OF CONVEYOR
1. APRON (PAN) CONVEYOR
2. BELT CONVEYOR
3. SCREW CONVEYOR
4. AIR SLIDE
5. BUCKET ELEVETOR
Apron Conveyors
With our expertise in the domain, we offer precision engineered apron
conveyor, a metallic belt conveyor. The metal aprons with or without
side walls are fixed on two strands of chains running around end
sprockets. The conveyors find application for handling heavy, hot,
abrasive material. It is also used for continuous duty in hostile working
atmosphere. The MOC used for manufacturing the conveyor is to suit
the duty condition. The range is available in various configuration and
profile as required.
Our range is widely used in steel plant, fertilizer industries, collieries,
cement plants, heavy chemical plants, mines, wood handling, aggregate
handling, quarries and many others.
WEIGH FEEDER
The series of Weigh Feeders developed at Mil Mech are designed
according to the users need. The weigh feeders provide accurate
and dependable performance combining the simplicity and
cleanliness of a vibratory conveyor with robust weighing
capabilities. With only one mobile part, these weigh feeders are
compact in design and occupies too little space as compared to
other heavy duty weigh feeders, but with equal productivity.
The Mil Mech Weigh Feeders are simple in-line weighing conveyor
designed to feed products by weight.
In order to achieve the desired setting qualities in the finished product, a
quantity (2-8%, but typically 5%) of calcium sulfate (usually gypsum or anhydrite)
is added to the clinker and the mixture is finely ground to form the finished
cement powder. This is achieved in a cement mill. The grinding process is
controlled to obtain a powder with a broad particle size range, in which typically
15% by mass consists of particles below 5 μm diameter, and 5% of particles above
45 μm. The measure of fineness usually used is the "specific surface area", which
is the total particle surface area of a unit mass of cement. The rate of initial
reaction (up to 24 hours) of the cement on addition of water is directly
proportional to the specific surface area. Typical values are 320–380 m2·kg−1 for
general purpose cements, and 450–650 m2·kg−1 for "rapid hardening" cements.
The cement is conveyed by belt or powder pump to a silo for storage. Cement
plants normally have sufficient silo space for 1–20 weeks production, depending
upon local demand cycles. The cement is delivered to end-users either in bags or
as bulk powder blown from a pressure vehicle into the customer's silo. In
industrial countries, 80% or more of cement is delivered in bulk.
Ball mill
A typical type of fine grinder is the ball mill. A slightly inclined or
horizontal rotating cylinder is partially filled with balls,
usually stone or metal, which grinds material to the necessary
fineness by friction and impact with the tumbling balls. The feed is
at one end of the cylinder and the discharge is at the other. Ball
mills are commonly used in the manufacture of Portland cement.
These industrial ball mills are mainly big machines. Small versions
of ball mills can be found in laboratories where they are used for
grinding sample material for quality assurance.
Specification of BALL MILL -3
TYPE-TWO CHAMBER BALL MILL
SIZE-
1. DIAMETRE- 4.8 METRE
2. LENGTH- 14 METRE
SPEED- 14.8 rpm
CAPASITY- 150 TPH
PRINCIPLES OF GRINDING
SPEED OF MILL
Experimental work conducted in our laboratory and supplemented by
our pictures in slow motion definitely indicates that the action inside
the Mill drum is not a haphazard stirring and throwing of the charge.
There is a specific operating speed for most efficient grinding. At a
certain point, controlled by the Mill speed, the load nearest the wall of
the cylinder breaks free and it is so quickly followed by other sections in
the top curves as to form a cascading, sliding stream containing several
layers of balls separated by material of varying thickness. The top layers
in the stream travel at a faster speed than the lower layers thus causing
a grinding action between them. There is also some action caused by
the gyration of individual balls or pebbles and secondary movements
having the nature of rubbing or rolling contacts occur inside the main
contact line.
It is important to fix the point where the charge, as it is carried upward,
breaks away from the periphery of the Mill. We call this the “break
point”, or “angle of break” because we measure it in degrees. It is
measured up the periphery of the Mill from the horizontal.
There are four factors affecting the angle of break:
1. Speed of Mill
2. Amount of grinding media
3. Amount of material
4. In wet grinding, the consistency or viscosity
As this section deals entirely with speeds, we will confine our discussion
to this item and cover the other factors in their respective categories.
While, in the old days, operating speeds were determined by trial and
error, we have been able to establish practical operating speeds
through correlation with the critical speed, which is the speed at which
the grinding media, without material, begin to centrifuge. Therefore, to
determine the critical speed for any given size Mill, we use the
following formula: 54.19 divided by the square root of the radius in
feet.
The smaller the Mill the faster in RPM it must run to attain critical
speed. Our 4.5” diameter Specimen Jar has a critical speed of 125 RPM,
and our size #00 90” diameter Ball Mill 28 RPM.
For most grinding and dispersing problems, we strive to attain the
cascading, sliding action described earlier, and to accomplish this we
have found that the most desirable angle of break ranges from 50 to 60
degrees from the horizontal.
The lower range is recommended for most wet grinding operations like
paints and soft dry materials, and the higher break point (which
provides a more severe grinding action) for most dry materials and wet
grinding such hard products as enamel frit and glaze.
It is also known that the grinding action in a larger Mill is more severe
than in the smaller sizes and, consequently, we are of the opinion that
the angle of break should be lower for the larger Mills than for the
smaller.
The rule of speed applies regardless of the type of grinding media.
A Pebble Mill the same size as a Ball Mill is expected to run at a slightly
faster speed. This is due to the smaller inside diameter of the Pebble
Mill with its lining, which is lacking in the Ball Mill.
In the production of bronze and aluminum powders, the Mills are run
almost a critical speed so that the balls are drooped to give the same
effect as a hammer blow. Without this action the product grinds finely
but no flaking of any consequence can be obtained and aluminum or
bronze powders are only effective as coatings when they are used in
flake form.
TYPE OF GRINDING
WET GRINDING
The void volume between the grinding media, with the mill half
charged, represents approximately 20% of the total volume of the mill
– and with a one-third charge of grinding media 13 ½%.
Fastest grinding occurs where there is just sufficient material in a batch
to fill all voids and slightly cover the grinding media. This equals
approximately 25% of the total volume with a half ball charge and 18%
with a one-third ball charge. The material should never be allowed to
drop below the surface of the grinding media, because when this
happens, excessive wear occurs to the Mill and grinding media and
contaminates the material itself. The largest size batches should not
exceed 60% of total Mill volume which corresponds with our catalog
rating.
There are occasions where additional thinning of the batch after
grinding may be done to increase the yield of the Mill. For example: A
Paul O. Abbé #3-C lined Pebble Mill has a volume of 450 gallons. A
minimum 25% material charge for this Mill would be 112 gallons and
the maximum 60% charge 270 gallons. After grinding, if the Mill were
loaded to the extreme top with thinner, the yield produced would be
315 gallons, or 70% of the total volume of the Mill.
We find that the most general batch size is about 30% for products that
are hard to grind like enamel frit and glazes and 40 t0 45% for products
like the average high grade paint and enamel. Larger batches are run
where a good mix rather than a grind is involved or where grinding time
is not a particularly important factor. A general rule in determining the
grinding efficiency for different size batches is to figure that a 40%
batch takes twice as long as the 25% and the 60% batch four times as
long when a 50% charge of grinding media is used. This is particularly
applicable to high grade dispersions. When grinding material such as
enamel frit, it is unlikely that the extreme upper limit in batch size will
ever grind.
It is a practical plan to establish the batch size consistent with the
allowable running time. For example: Assuming that a 25% batch takes
9 hours, this would be too long for an 8 hour shift. Therefore, it is
usually advisable to increase the batch size and continue running the
Mill to the next working day. Assuming again that 40% batch takes 9
hours, then a slight cutback should make it possible to turn out a batch
within an 8 hour working day. It is therefore; always wise to do a little
experimenting with the batch size to try to develop a system that will
work out best under your particular grinding conditions. The one
principal rule to remember is that the grinding media must be covered
with material.
CONSISTENCY OR VISCOSITY OF MATERIAL – The most important
element in wet grinding is the consistency, or viscosity, of the batch.
Low viscosity materials permit the grinding media to move with
excessive speed and this combined with the thin protective film around
the media, may cause abnormal wear, contamination and heat build-
up. If the low viscosities cannot be avoided then it is imperative that
small grinding media be used.
With high viscosities free movement of the grinding media is impeded.
This can cause a carrying over and “throw” of the media resulting in
inefficiencies and contamination.
Based on accepted milling techniques, we have found the following
consistencies measured at milling temperature usually work out best:
For flint pebbles and porcelain balls 75 to 90 Kreb Units, 600 to 1100
centipoises
For high density balls 90 to 100 Krebs Units, 1100 to 2100 centipoises
For steel balls 90 to 115 Krebs Units, 1100 to 2400 centipoises
These viscosities are based on using 1 to 1 ½” flint pebbles – 1 to 1 ½”
porcelain balls – ½ to ¾” steel balls. The smaller sizes for the lower
viscosities and the larger sizes for the higher viscosities.
Some producers of high density media have been recommending a
higher viscosity range than the figures we have indicated. In effect, this
merely increases the thickness of the film surrounding the media
thereby providing more cushion against impact. We find this desirable
where a shearing action is only required to obtain results. However,
impact is one of the most important advantages of Ball Mill and Pebble
Mill operations, consequently, excessive restriction of media
movement should be avoided for highest operating efficiency. This
same rule also applies where other types of media are used.
Our viscosity readings were made on a Stormer Impeller type
Viscometer. We have found this accurate on both high and low shear
materials, as well as on products of a thixotropic nature, whether
acqueous or non-acqueous mixtures.
WETTING AGENTS -- The use of wetting agents has greatly increased
the capacity of Ball Mills and Pebble Mills without altering the viscosity
during the grind. A typical example is the case of one operator who,
prior to the use of wetting agents, could load no more than 50% solids
to retain a suitable working viscosity. By adding the proper wetting
agent he was able to increase his solids content to 85%.
It has generally been found that, combined with the increased
production, the grinding operation can be performed in a much faster
time because the wetting agents aid in breaking down the surface
tensions of the aggregated particles and the finished product has
greater stability.
DILUTION BEFORE DISCHARGE – Where the product being ground has
a heavy consistency which makes it difficult to discharge, it is
sometimes advisable to add sufficient additional liquid to thin down the
batch. If the mill is equipped with a discharge valve, the liquid is best
added to the batch through the valve. The reason for suggesting this is
that there is likely to be some unground material packed between the
flanges of the manhole frame and cover. To prevent dropping this
material into a finished batch, try to avoid disturbing the cover until the
ground material has been removed.
If there is any surging of the liquid as it is being loaded into the mill, the
brass vent plug on the head of the mill, the brass vent plug on the head
of the mill should first be removed. BE SURE TO REPLACE PLUG BEFORE
RE-STARTING THE MILL. If the mill is not equipped with a discharge
valve, extra liquids must be added through the manhole opening.
The mill should be run form 10 to 15 minutes with the added thinner.
The mill can be comple tely full after the additional thinner is added. In
some cases, the minimum 25% grinding charge of semi-paste material
is being ground first and additional liquid to fill the remaining 45% of
total volume of the mill is added later to make the finished mix. Where
still further thinning is desired, this can only be accomplished by
unloading the batch of material and adding the extra thinner in mixing
tanks.
Another method is to discharge part of the grinding slurry, mix thinner
into the remainder in the mill, discharge this material into the receiver
holding the first portion, and finally mix the entire batch with a portable
mixer. A variation of this is to be discharge as much of the grinding
slurry as possible, and then make the thinner serve the twofold
purpose of washing the mill out and finally thinning the entire batch.
COATINGS COMPRISING PAINT, INK AND SIMILAR MATERIALS– While
we recognize that actual grinding, i.e. – size reduction of some
pigments is not required, the action of Ball and Pebble Mills embodies a
combination of impact, shear and attrition. Therefore, it is the
utilization of all these forces that insures the best performance of these
Mills.
Most desirable applications for Ball and Pebble Mills are on pigments
requiring further reduction -- Non-uniform pigments that must be
made uniform in the finished product, -- Agglomerated pigments
resulting from storage and handling -- Manufactured agglomerates
such as carbon beads – Raw materials lacking complete compatibility --
Grinding inexpensive coarse extender pigments in the batch giving
more hiding power to expensive pigments, -- Where uniformity and
stability of the finished product are essential and must be constant,
batch after batch.
On the other hand, simple dispersions can be quickly and easily
accomplished in a consistent, productive fashion without the need for
elaborate controls or supervision.
One of the most successful techniques employed in the dispersion of
pigment in vehicle and solvent is known as low solids grinding. Utilizing
this procedure offers two distinct advantages:
1. Dispersion is accomplished in a fraction of the time formerly
required. Typical results include a white architectural enamel 8 +
grind in one hour with flint pebbles. Light green trim enamel 6 +
grind in one hour with steel balls. Yellow enamel to 7 grind in 2 ½
hours with steel balls.
2. A greater pigment quantity can be dispersed in a mill batch than
the ultimate formula requires. The remainder of the formula, i.e.:
vehic le and solvent, is then added when the dispersion is
complete. Many instances are known where mills have yielded
two to four times the actual batch loading in finished product.
Excellent papers covering this subject have been presented to the
Federation of Societies for Paint Technology.
The first article presented by Frederick K. Daniel describes the “Flow
Point” method of determining the optimum relationship of pigment –
binder and solvents.
A second article also presented in October 1950 by R.B. Shurtz gives
further data on the “Flow Point” method with tables and graphs
showing results on many combinations. If this method of determining
pigment concentration or percentage of vehicular solids is used, the
danger of seeding or pigment shock is decreased. However, to reduce
this danger further it is frequently advantageous to step load the
balance of the vehicle solids and solvent with the temperature as close
as possible to the mill temperature.
A third paper presented by Frederick K. Daniel in October 1956
discusses the effect on seeding by the solvents utilized in the mill base
and let-down phase.
While the use of all forces comprising the action of ball and pebble mills
is beneficial on most pigmented products, there are a few pigments on
which it is desirable to avoid direct impact and attrition and rely mostly
on shear.
For example, one of these is toluidine red. Excessive grinding through
impact can destroy the pigment structure thereby reducing its hiding
power. To avoid excessive grinding by impact the consistency should be
heavier than for normal operation and the size batch should be
sufficient to induce spreading of the grinding media in order to prevent
direct contact and merely induce a shearing action.
Other operating suggestions of value include the following:
Most operators prefer to first charge the liquids and follow this with
the pigment. They find they get faster initial wetting and there is less
danger of pigment balls forming
Step loading is more advantageous than tightly packing a bulky pigment
to try and get it all in the Mill in one loading. Pigment manufacturers
report that excessive packing can cause reaggregation of pigment
particles.
Most operators prefer to first charge the liquids and follow this with
the pigment. They find they get faster initial wetting and there is less
danger of pigment balls forming Step loading is more advantageous
than tightly packing a bulky pigment to try and get it all in the Mill in
one loading. Pigment manufacturers report that excessive packing can
cause reaggregation of pigment particles.
Wetting or dispersing agents have a definite place in formulating
techniques. There are many types on the market and the manufactures
of these should be consulted in determining their application.
DRY GRINDING
Whenever there is a choice between grinding a product wet or grinding
it dry, wet grinding will generally prove better. However, in many cases,
it is impractical to grind wet due to the nature of the process or
product.
The void volume between the grinding media, with the mill half
charged, represents approximately 20% of the total volume of the mill-
and with a one-third charge of grinding media 13 1/3%.
We usually try to limit the size of the batch to 25% of the total Mill
volume which is sufficient to fill all voids and slightly cover the grind ing
media. Any larger batches cause the pebbles to spread out through the
mass of solids so they cannot make effective contact with each other,
because of the layers of material between them. This greatly reduces
the grinding efficiency of the mill and, in some cases, makes it
impossible to attain the desired results. The only occasion for larger
batches than 25% of total volume, is on products requiring a good mix
rather than a grinding action or on products that are soft and easy to
grind and the grind ing media do not necessarily have to make close
contact with each other.
The feed material should preferably be about 8 mesh or smaller,
although many operators start with much larger pieces. Having the feed
material as fine as possible enable the use of smaller sizes of grinding
media, which are always best for fine Uniform grinding and dispersions.
For hard material, it is especially advantageous to start with a fairly fine
product.
Clogging of material in the Mill makes further operation harmful. This is
generally caused by moisture of fat, as in oily seeds. Possible remedies
include:
1. Taking the material out and thoroughly drying it.
2. Adding a dry filler to absorb the excessive moisture while the
batch is being ground.
3. Adding a few pieces of steel angle, bar, or chain which can slide
along the Mill surface and scrape off any materials starting to
pack.
4. If the material is packing due to particle size alone, grinding
should be stopped prior to this point. The material should then be
screened and tailings returned to the mill.
GRINDING MEDIA
In the grinding mill numbers of solid metel ball are use for
grinding the raw material.these are called grinding media.
QUANTITY OF GRINDING MEDIA
For the most efficient results, the Mill should be at least half filled with
grinding media. Some operators prefer to go a little beyond the halfway
mark to compensate for wear. There is no objection to this and we have
been suggesting a limit of about 5 percent.
In steel ball grinding, many operators, especially in the paint industry,
are satisfied to run with a smaller ball charge ranging as low as one-
third the volume of the Mill. They find the smaller charge gives them
the required grind within allowable limits of grinding time and the extra
space gives them more loading room.
There is no objection to this practice when the grinding cycle falls
within the desired working limits. Where speed of grind is of utmost
importance, larger ball charges ranging up to the recommended 50%
for other types of grinding media are advisable. The logic in this system
is best illustrated as follows:
5/8” steel balls are one of the most popular sizes, and there are 36 of
these per pound. In a 54” x 60” Steel Ball Mill, for example, the
difference between the weight of a one-third and one-half ball charge is
3,970 pounds, or 103,220 balls. The ½” steel ball is another very
popular size and, as there 53 of these per pound, the difference would
amount to 200,410 balls. It s therefore, reasonable to expect (and
experience has proven this to be true) that any addition above the
minimum limits prescribed can only result in increased grinding
efficiency. This improvement is usually related to the surface area of
the media involved.
It is not true that a one-half ball charge consumes proportionately more
power than a one-third ball charge. The difference in weight between
the tow charges is about 50% but the center of gravity of the larger is
nearer the center of rotation of the Mill. Consequently, the power
required to turn the larger charge only runs between 15 and 20% more.
The grinding efficiency of the one-half charge is considerably greater
than for the one-third and, therefore it ca be expected that power
consumption per gallon output will actually be less than with the
smaller charge.
Grinding media should be periodically checked. Reduction in the
quantity and size of the grinding media will result in poor grinding. We
suggest a maximum schedule of once every six months, but any
established procedure should be decided by individual experience. In
some cases, where abrasive materials are involved, once a month is not
too often and, in a few cases, even shorter intervals are indicated.
A simple method for checking is to have a rod cut indication the
distance from the top of the grinding media to the underside of the
manhole opening and use this for checking the depth of the charge.
When grinding enamel frit, wear to the porcelain balls is quite excessive
because to the abrasive nature of the frit. Consequently, many
operators have been able to closely determine the ball wear per batch
and, when a batch of frit is loaded for grinding, a quantity of new balls
is added equaling the weight lost during the previous grind. However,
even with this system, we still advise an occasional check with the
measuring rod because there is no positive guarantee that all balls will
wear the same.
We also advocate dumping the charge once a year, or as often as
experience indicates, and removing any grinding media found to be
excessively worn or damaged.
1. Special note: No matter how good the metal ball might be, care
must be exercised in the operation of the Mill if excessive wear
with its resultant contamination is to be avoided. (See other
sections in this chapter; also sections on Cleaning and
Discharging.)
The following general rules should be carefully adhered to regardless of
the type media used.
1. There should be enough material in the batch to cover the
grinding media.
2. Grinding time must be watched carefully to avoid excessive
grinding.
3. Excessive buildup of heat should be avoided. In paint grinding, this
may lower the operating viscosity beyond the critical point. A
reduction in Mill speed may help to avoid overheating, but it is
more desirable to circulate a cooling medium around the cylinder.
If the Mill is not jacketed, a water spray can be used with
satisfaction.
4. The smallest grinding media should be employed. These not only
reduce the danger of overheating but, as is well known, the
smaller grinding media provide faster and better results.
5. When using extenders, their abrasive nature may cause excessive
wear. To avoid this, some operators are able to hold out the
extenders until the grinding is almost completed and then add
them for the final operation.
SIZE OF GRINDING MEDIA
Probably the most common cause for faulty operation and complaints
has been due to the size of grinding media. It is strongly recommended
that the smallest feasible grinding media be used in all cases. The
optimum size of media should not change with Mill size. If the
laboratory Pebble or small Ball successfully grinds a sample batch in a
lab Mill, the same size grinding media will do the best job in a
production Mill whether the Mill is one foot or eight feet in diameter.
Small grinding media are recommended because:
1. They provide many more grinding contacts per revolution than
larger media. This results in much quicker grinding action.
2. They provide smaller voids, limiting the size of particles or
agglomerates which can exist there.
3. They do not create excessive energy which cannot be utilized.
Oversized grinding media frequently develop more grinding
energy than is needed for the job. This excess merely builds up
heat and wears down the media and lining, introducing
contamination in the batch. Using an extremely large grinding
media is somewhat like using a sledgehammer to drive in a carpet
tack.
The chief disadvantage of the smallest size grinding media is that
discharging takes somewhat longer due to increased surface tension in
the smaller voids. Almost invariably, however, the reduced grinding
time realized by smaller media more that offsets this disadvantage.
Slight air pressure may be used to assist in more rapid discharge.
Using extremely small media, with their greater surface area for the
material to adhere to, may yield a smaller initial batch. Subsequent
batches will be of normal size, however.
When steel balls are used, the optimum sizes we have usually been
recommending have been ½ and 5/8”. However, many operators are
now using media as small as ¼” in production mills and find these
extremely advantageous where exceptionally fine grinds are required.
Generally, the viscosities must be slightly lower for the small size balls
than we would recommend for the more popular ½ and 5/8” sizes.
CEMENT MILL DRIVE & LUBRICATION SYSTEM
Technical Data
The gearbox comprises two co-axial planetary stages arranged one
behind the other. Both stages are straight-toothed planetary gears with
fixed ring gear and rotating planet carrier.
The drive is achieved through the sun pinion. The rotating planet
carrier is, at the same time, also the output drive shaft of the first stage.
The planetary gears are supported on planetary gear axles in the planet
carrier. All bearings in the first stage are plain bearings. The fist stage is
provided with its own housing which is bolted to the second stage.
The second stage is a straight-toothed planetary gear with fixed ring
gear and rotating planet carrier. The drive is achieved through the sun
pinion, which is driven by the planet carrier of the first stage via a
toothed coupling. The rotating planet carrier is, at the same time, also
the output drive shaft of the first stage. The planetary gears are
supported on planetary gear axles in the planet carrier. All bearings in
the second stage are slide bearings.
Gearing
The spur teeth of the sun pinion and the planet wheels are case-
hardened and grinded. The toothed flanks of the sun pinions have both
profile and longitudinal corrections to fully compensate for
deformations occuring under load. This method guarantees optimum
tooth flank contact and very long life. The inner gear rings are heat
treated.
Gear Unit Types
Make- MAAG
Drive- General Drive
Power-4650 kw
R.P.M-14.8 rpm
Additional Components
Auxiliary Drive
During maintenance of the ball mill different jobs need to be
performed, such as cooling down, level out, clean and position the mill.
The auxiliary drive facilitates these operations by providing: interval mill
turning, smooth start, position hold with brakes, automatic auxiliary
drive disengagement at main motor start-up and level out function.
FLSmidth MAAG Gear is able to provide all the necessary turning
functions for your maintenance operations. Personal safety, an
essential requirement for your staff, is given top priority.
Coupling ZCF
The ZCF toothed coupling installed between the mill and the gearbox is
a unique FLSmidth MAAG Gear design combining a high degree of
freedom (alignement) with efficient torque transmission. Thermal
expansions and mechanical deflections resulting from operating
conditions are safely absorbed by the ZCF coupling, and only the torque
is transmitted to the gearbox through a torsion shaft. Upon request a
water injection system can be installed. During gearbox maintenance
the ZCF coupling remains in place.
Coupling ZEXF
The gearbox to motor coupling ZEXF is a toothed coupling specially
designed by FLSmidth MAAG Gear. The coupling has a limited axial
displacement and therefore requires an axial bearing on either the
motor or gearbox side. The easy disassembly of the coupling spool
piece allows the first planetary stage to be displaced towards the motor
side for maintenance purposes, allowing the main motor to remain in
place during maintenance works. With this coupling the gearbox is
electrically insulated from the motor.
Lubrication System
The gearbox is lubricated by a closed circuit oil system which is ideally
located beneath the mill drive motor. The design of the lubricant
system is standardised thus it is applicable for several gear types. This
ensures an easy handling, optimal insertion and lower costs. Also the
components of the lubrication system as instrumentation, filter and
cooling/heating system are consistent. The oil system is monitored with
digital indication on site. Top priority is given to guarantee operational
reliability.
General bearing lubrication specification-:
Lubricating oil-: ISo VG-46
Oil flow-:12.0 lpm
Oil pressure-:0.2 bar
Air classifier {separator}
An air classifier is an industrial machine which sorts materials by a
combination of size, shape, and density. It works by injecting the
material stream to be sorted into a chamber which contains a column
of rising air. Inside the separation chamber, air drag on the objects
supplies an upward force which counteracts the force of gravity and
lifts the material to be sorted up into the air. Due to the dependence of
air drag on object size and shape, the objects in the moving air column
are sorted vertically and can be separated in this manner.
Air classifiers are commonly employed in industrial processes where a
large volume of mixed materials with differing physical characteristics
need to be sorted quickly and efficiently. One such example is
in recycling centers, where various types of metal, paper,
and plastics arrive mixed together and need to be sorted before further
processing can take place.
Types of dust collectors
Five principal types of industrial dust collectors are:
Inertial separators
Fabric filters
Wet scrubbers
Electrostatic precipitators
Unit collectors
Inertial separators
Inertial separators separate dust from gas streams using a combination of forces,
such as centrifugal, gravitational, and inertial. These forces move the dust to an
area where the forces exerted by the gas stream are minimal. The separated dust
is moved by gravity into a hopper, where it is temporarily stored.The three
primary types of inertial separators are:
Settling chambers
Baffle chambers
Centrifugal collectors
Neither settling chambers nor baffle chambers are commonly used in the minerals
processing industry. However, their principles of operation are often incorporated
into the design of more efficient dust collectors.
Settling chamber
A settling chamber consists of a large box installed in the ductwork. The sudden
expansion of size at the chamber reduces the speed of the dust-filled airstream
and heavier particles settle out.
Settling chambers are simple in design and can be manufactured from almost any
material. However, they are seldom used as primary dust collectors because of
their large space requirements and low efficiency. A practical use is as precleaners
for more efficient collectors.
Baffle chamber
Baffle chambers use a fixed baffle plate that causes the conveying gas stream to
make a sudden change of direction. Large-diameter particles do not follow the gas
stream but continue into a dead air space and settle. Baffle chambers are used as
precleaners
CYCLONE
Centrifugal collectors
Centrifugal collectors use cyclonic action to separate dust particles from the gas
stream. In a typical cyclone, the dust gas stream enters at an angle and is spun
rapidly. The centrifugal force created by the circular flow throws the dust particles
toward the wall of the cyclone. After striking the wall, these particles fall into a
hopper located undern eath
.
The most common types of centrifugal, or inertial, collectors in use today are:
Single-cyclone separators
They create a dual vortex to separate coarse from fine dust. The main vortex
spirals downward and carries most of the coarser dust particles. The inner vortex,
created near the bottom of the cyclone spirals upward and carries finer dust
particles,.
Multiple-cyclone separators
Also known as multiclones®, consist of a number of small-diameter cyclones,
operating in parallel and having a common gas inlet and outlet, as shown in the
figure. Multiclones® operate on the same principle as cyclones—creating a main
downward vortex and an ascending inner vortex
.
Multiclones® are more efficient than single cyclones because they are longer and
smaller in diameter. The longer length provides longer residence time while the
smaller diameter creates greater centrifugal force. These two factors result in
better separation of dust particulates. The pressure drop of multiclone® collectors
is higher than that of single-cyclone separators.
Babcock & Wilcox is the original manufacturer and trademark holder of
Multiclone® dust collectors and replacement parts formerly offered by Western
Precipitation. Multiclone® dust collectors are found in all types of power and
industrial applications, including pulp and paper plants, cement plants, steel mills,
petroleum coke plants, metallurgical plants, saw mills and other kinds of facilities
that process dust.
Secondary Air Flow Separators
This type of cyclone uses a secondary air flow, injected into the cyclone to
accomplish several things. The secondary air flow increases the speed of the
cyclonic action making the separator more efficient; it intercepts the particulate
before it reaches the interior walls of the unit; and it forces the separated
particulate toward the collection area. The secondary air flow protects the
separator from particulate abrasion and allows the separator to be installed
horizontally because gravity is not depended upon to move the separated
particulate downward.
BAG FILTER & BAGHOUSE
Fabric filters
Commonly known as baghouses, fabric collectors use filtration to separate dust
particulates from dusty gases. They are one of the most efficient and cost
effective types of dust collectors available and can achieve a collection efficiency
of more than 99% for very fine particulates.
Dust-laden gases enter the baghouse and pass through fabric bags that act as
filters. The bags can be of woven or felted cotton, synthetic, or glass-fiber
material in either a tube or envelope shape.
The high efficiency of these collectors is due to the dust cake formed on the
surfaces of the bags. The fabric primarily provides a surface on which dust
particulates collect through the following four mechanisms:
Inertial collection - Dust particles strike the fibers placed perpendicular to the
gas-flow direction instead of changing direction with the gas stream.
Interception - Particles that do not cross the fluid streamlines come in contact
with fibers because of the fiber size.
Brownian movement - Submicrometre particles are diffused, increasing the
probability of contact between the particles and collecting surfaces.
Electrostatic forces - The presence of an electrostatic charge on the particles
and the filter can increase dust capture.
A combination of these mechanisms results in formation of the dust cake on the
filter, which eventually increases the resistance to gas flow. The filter must be
cleaned periodically.
Types of baghouses
As classified by cleaning method, three common types of baghouses are:
Mechanical shaker
In mechanical-shaker baghouses, tubular filter bags are fastened onto a cell plate
at the bottom of the baghouse and suspended from horizontal beams at the top.
Dirty gas enters the bottom of the baghouse and passes through the filter, and
the dust collects on the inside surface of the bags.
Cleaning a mechanical-shaker baghouse is accomplished by shaking the top
horizontal bar from which the bags are suspended. Vibration produced by a
motor-driven shaft and cam creates waves in the bags to shake off the dust cake.
Shaker baghouses range in size from small, handshaker devices to large,
compartmentalized units. They can operate intermittently or continuously.
Intermittent units can be used when processes operate on a batch basis-when a
batch is completed, the baghouse can be cleaned. Continuous processes use
compartmentalized baghouses; when one compartment is being cleaned, the
airflow can be diverted to other compartments.
In shaker baghouses, there must be no positive pressure inside the bags during
the shake cycle. Pressures as low as 0.02 in. wg can interfere with cleaning.
The air to cloth ratio for shaker baghouses is relatively low, hence the space
requirements are quite high. However, because of the simplicity of design, they
are popular in the minerals processing industry.
Reverse air
In reverse-air baghouses, the bags are fastened onto a cell plate at the bottom of
the baghouse and suspended from an adjustable hanger frame at the top. Dirty
gas flow normally enters the baghouse and passes through the bag from the
inside, and the dust collects on the inside of the bags.
Reverse-air baghouses are compartmentalized to allow continuous operation.
Before a cleaning cycle begins, filtration is stopped in the compartment to be
cleaned. Bags are cleaned by injecting clean air into the dust collector in a reverse
direction, which pressurizes the compartment. The pressure makes the bags
collapse partially, causing the dust cake to crack and fall into the hopper below. At
the end of the cleaning cycle, reverse airflow is discontinued, and the
compartment is returned to the main stream.
The flow of the dirty gas helps maintain the shape of the bag. However, to
prevent total collapse and fabric chafing during the cleaning cycle, rigid rings are
sewn into the bags at intervals.
Space requirements for a reverse-air baghouse are comparable to those
of a shaker baghouse; however, maintenance needs are somewhat
greater.
Electrostatic precipitators (ESP)
Electrostatic precipitators use electrostatic forces to separate dust particles from
exhaust gases. A number of high-voltage, direct-current discharge electrodes are
placed between grounded collecting electrodes. The contaminated gases flow
through the passage formed by the discharge and collecting electrodes.
Electrostatic precipitators operate on the same principle as home "Ionic" air
purifiers.
The airborne particles receive a negative charge as they pass through the ionized
field between the electrodes. These charged particles are then attracted to a
grounded or positively charged electrode and adhere to it.
The collected material on the electrodes is removed by rapping or vibrating the
collecting electrodes either continuously or at a predetermined interval. Cleaning
a precipitator can usually be done without interrupting the airflow.
The four main components of all electrostatic precipitators are-
Power supply unit, to provide high-voltage DC power
Ionizing section, to impart a charge to particulates in the gas stream
A means of removing the collected particulates
A housing to enclose the precipitator zone
The following factors affect the efficiency of electrostatic precipitators:
Larger collection-surface areas and lower gas-flow rates increase efficiency
because of the increased time available for electrical activity to treat the dust
particles.
An increase in the dust-particle migration velocity to the collecting electrodes
increases efficiency. The migration velocity can be increased by-
Decreasing the gas viscosity
Increasing the gas temperature
Increasing the voltage field
Enexco is a pioneer in silo feeding, storage and extraction systems for
flat bottom as well as inverted cone silos. Enexco has to its credit the
expertise in designing and supplying various types of silos for indian as
well as overseas clients. We offer clients a wide range of machine that
meet the requirements of cement, flyash, opc & slag processing the
range offered by us include silo storage plants, mixers, solid flow
meters and others. Our process expertise also allow us to offer these in
other customized specifications as desired by the clients.
Enexco offers complete equipment required for the silo system
including open and closed airslide, manual & pneumatic cut off gate,
dosing valves, parallel distributors, adaptor box, bin weighing and
aeration system, solid flow feeders, control panels, piping etc.
Types of silos-
Rcc silos and steel silos
Inverted cone, normal cone and flat bottom silos
Continuous blending silo
Clinker silo with dustless extraction gates
Single compartments, ring and multi compartment silos for
storage of cement / flyash / ground slag
Advantages of storage silos-
High extraction efficiency (guarantee emptiness 99% in case of
inverted cone)
Low
References-