Attock Cement Maintenance
Attock Cement Maintenance
Attock Cement Maintenance
PREVENTIVE MAINTENANCE
ATTOCK CEMENT PAKISTAN LIMITED
GROUP MEMBERS
ME-171
ME-173
ME-178
ME-188
ME-193
ME-206
ME-309
ME-310
ME-315
ME-324
ME-338
Introduction
The journey of Attock Cement started from the year 1981 and the
company started its commercial production in 1988. In 25 years, company
has shown steady growth. ACPL has attained new peaks every year
through strong team work, continuous modernization of plant to
improve efficiency and with utmost hard work. ACPL has cemented its
place not only in the local market but also in the regional markets through
selling quality products. ACPL’s current production capacity is 2,400
MTPD. Due to an overall surge in cement demand in the country over the
last couple of years coupled by growth in regional market, ACPL has
decided to increase its production capacity to 5,400 MTPD by setting up a
new plant with a capacity of 3,000 MTPD. The new plant started operation
in June 2003.
We visited the cement plant of attock industries for the sole purpose of
understanding the working and maintenance strategies followed by the
engineers and maintenance staff with regard to the different machineries
operated in day to day production to meet the increasing demand of
cement in modern day.
To understand the working of maintenance schedules in a cement industry,
one must first be aware of the processes carried out in order to produce
different types of cements. Attock Cement produces three types of
products under cement category namely
Wet process
When chalk is used, it is finely
broken up and dispersed in water in a
washmill. The clay is also broken up
and mixed with water, usually in a
similar washmill. The two mixtures
are now pumped so as to mix in
predetermined proportions and pass through a series of screens. The
resulting – cement slurry – flows into storage tanks.
When limestone is used, it has to be blasted, then crushed, usually in two
progressively smaller crushers (initial and secondary crushers), and then
fed into a ball mill with the clay dispersed in water. The resultant slurry is
pumped into storage tanks. From here onwards, the process is the same
regardless of the original nature of the raw materials.
The slurry is a liquid of creamy consistency, with water content of
between 35 and 50%, and only a small fraction of material – about 2% -
larger than a 90 µm (sieve No. 170).
The slurry mix mechanically in the storage tanks, and the sedimentation of
the suspended solids being prevented by bubbling by compressed air
pumped from bottom of the tanks.
The slurry analyze chemically to check the achievement of the required
chemical composition, and if necessary changing the mix constituents to
attain the required chemical composition.
Finally, the slurry with the desired
lime content passes into the rotary
kiln. This is a large, refractory-
lined steel cylinder, up to 8 m in
diameter, sometimes as long as 230
m, which is slightly inclined to the
horizontal.
The slurry is fed in at the upper end
while pulverized coal (oil or
natural gas also might be used as a
fuel) is blown in by an air blast at
the lower end of the kiln, where the
temperature reaches about 1450oC.
The slurry, in its movement down
the kiln, encounters a progressively
higher temperature. At first, the water is driven off and COR 2R is
liberated; further on, the dry material undergoes a series of chemical
reactions until finally, in the hottest part of the kiln, some 20 to 30% of the
material becomes liquid, and lime, silica and alumina recombine. The
mass then fuses into balls, 3 to 25 mm in diameter, known as clinker. The
clinker drops into coolers.
Dry process
The raw materials are crushed and fed in the correct proportions into a
grinding mill, where they are dried and reduced in size to a fine powder.
The dry powder, called raw meal, is then pumped to a blending silo, and
final adjustment is now made in the proportions of the materials required
for the manufacture of cement. To obtain a uniform mixture, the raw meal
is blended in the silo, usually by means of compressed air.
The blended meal is sieved and fed into a rotating dish called a granulator,
water weighing about 12% of the meal being added at the same time. In
this manner, hard pellets about 15 mm in diameter are formed.
The pellets are baked hard in a pre-heating grate by means of hot gases
from the kiln. The pellets then enter the kiln, and subsequence operations
are the same as in the wet process of manufacture.
Grinding of the clinker
The cool clinker (produced by wet or dry process), which is
characteristically black and hard, is underground with gypsum
CaSO4.2H2O in order to prevent flash setting of the cement, and to
facilitate the grinding process. The grinding is done in a ball mill. The
cement discharged by the mill is passed through a separator, fine particles
being removed to the storage silo by an air current, while the coarser
particles are passed through the mill once again.
Apron Conveyors:
Apron conveyors consist of endless
chains with attached overlapping and
interlocking plates to provide a
continuous-carrying surface that
forms a leakproof bed suitable for
bulk materials without containers.
Move loose bulk materials like coal,
lime, sand, stone, and sugar cane
along horizontal or inclined
conveyors. Apron Conveyors are
especially useful as feeders to
elevating systems, for picking tables
and loading booms, and for long
horizontal or inclined conveyors. In
cement industry, it is used to feed the
raw material into the gypsum crusher.
There are three areas where the inspection is performed on yearly basis
which includes the drive, driven sprocket bearing and gear box bearing
and internals
Problem Potential cause Solution
Chain rises off Excess chain slack. Adjust the amount of
sprocket Excess wear at the bases slack.
of Replace the sprocket.
sprocket teeth. Replace the chain.
Excess chain extension. Remove the foreign
Foreign material stuck to material
the from the bases of the
bases of sprocket teeth. teeth.
CEMENT MILL
CEMENT MILL PROCESS
The clinker is stored in two silos of clinker and storage.
Each Silo has six extraction holes. 4 belt conveyers overtake the extraction
clinker, 3 extractions for in belt conveyer. The 4-belt conveyers discharge
the clinker onto the long belt conveyer, which leads it to the clinker
hopper.
Clinker extraction de-dusted by the two-bag filter installation and fans.
The extraction clinker and gypsum are stored into corresponding hopper.
These are metal hopper mounted on load cells (one load cell and 2 fix
propying for each hopper).
The clinker hopper has the capacity of 180 tons and while the gypsum has
110 tons capacity hopper. The hoppers are connected to a de-dusting and
fans.
The material is extracted from each hopper by means of weigh feeder and
introduced into the mill-feeding funnel.
The clinker and gypsum are ground in a closed circuit mill system,
composed of;
Ball mill dia 4.2 x 13.0m length
Bucket elevator of 450t/h
Separator diameter 5m with satellite cyclones and a separator fan. Air slide
for feeding the elevator and separator and for conveying coarse and fine
material.
CONVEYORS:
Clinker extraction belt conveyor take the clinker out of Air quenched
clinker cooler and feed it into the main belt which led to weigh feeder.
Inspection the these conveyors include the yearly checking of drive drum
bearing, tensioning drum bearing and gear box internals and bearing in the
clinker extraction bearing. Snub pulley bearing is also checked in the
inspection of main clinker long belt conveyor along with other bearings. In
weigh feeder, same components as the first bearing is inspected. All the
inspection is done visually or through the concern problem detection
technique which may include vibration analysis, or NDT- techniques.
GRINDING MILL:
A Ball mill is a horizontal cylinder partly filled with steel balls (or
occasionally other shapes) that rotates on its axis, imparting a tumbling
and cascading action to the balls. Material fed through the mill is crushed
by impact and ground by attrition between the balls. The grinding media
are usually made of high-chromium steel. The smaller grades are
occasionally cylindrical ("pebs") rather than spherical. There exists a speed
of rotation (the "critical speed") at which the contents of the mill would
simply ride over the roof of the mill due to centrifugal action. The critical
speed (rpm) is given by: nC = 42.29/√d, where d is the internal diameter in
metres. Ball mills are normally operated at around 75% of critical speed,
so a mill with diameter 5 metres will turn at around 14 rpm.
Inspection of Grinding mills include the various components of the
grinding mill, air slide blower and bucket elevator such as Ultra sonic
inspection inlet/outlet trunnion, Dye Penetrant (DP Test) inlet/outlet
trunnion, Mill Trunnion White Metal Bearings, Pinion Shaft Bearings (04
Nos), Transmission Shaft Bearings (04 Nos), Drive 1 Gear Box Internals
& Bearings, Drive 2 Gear Box Internals & Bearings etc. these inspection is
yearly, semiannually, monthly or semimonthly depend upon the severity of
the equipment.
DYNAMIC SEPARATOR:
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 separated 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.
In inspection of dynamic separator or separator fan includes yearly
inspection and rectification of the following components:
1. Vertical Shaft Bearings
2. Gear Box Internals & Bearings
3. Vane & Casing
4. Rotary Locks Internals & Brgs (08 Nos)
5. Shaft Bearings
6. Damper Inspection
7. Impeller Inspection
8. Inspection of Casing & Foundation Pads
Iron remover:
The purpose of iron remover is to remove any metallic part from the
cement and it is done by using magnetic techniques.
Inspection and rectification of the iron remover includes visual inspection
and vibration analysis of:
1. Drive Drum Bearings
2. Driven Drum Bearings
3. Gear Box Internals & bearings
4. Drive Pulley and V-Belt
Roller Press:
These consist of a pair of rollers set 8–30 mm apart and counter-rotating
with surface speed around 0.9 - 1.8 m.s−1. The bearings of the rollers are
designed to deliver a pressure of 50 MPa or more. The bed of material
drawn between the rollers emerges as a slab-like agglomeration of highly
fractured particles. The energy efficiency of this process is comparatively
high. Systems have been designed, including a de-agglomerator and
separator, that will deliver material of cement fineness. However, particle
size distribution is again a problem, and roll presses are now increasingly
popular as a "pre-grind" process, with the cement finished in a single
chamber ball mill. This gives good cement performance, and reduces
energy consumption by 20-40% compared with a standard ball mill
system.
Inspection of Roller Press Includes the visual and visual aid inspection of
the following components:
1. Universal Couplings
2. Planetry Gear # 01 Internal/bearings
3. Planetry Gear # 02 Internal/bearings
4. Fix Roller bearings
5. Moveable Roller bearings
6. Torque Supports arrangement
7. Rollers Hard facing condition
8. Hydraulic System
9. Lubrication system (Gear)
Inspection carried out, under Inspection carried out, Inspection not carried out, give
Colour Codes Inspection carried out, found O.K.
observation rectification required reasons
4 Cement Grinding Mill Drive 1 Gear Box Internals & Bearings Apr-15 6M
Inspection carried out, under Inspection carried out, Inspection not carried
Colour Codes Inspection carried out, found O.K.
observation rectification required out, give reasons
PREVENTIVE MAINTENANCE SCHEDULE OF PACKING AREA
PACKING AREA
Inspection Schedule
Last
History Insp Remarks / Reasons for Inspection carried out before/after
S.# Eqpt Name / # Inspection Details Insp. Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
File # Freq the schedule dates or not carried out
Date
15 15 15 15 15 15 16 16 16 16 16 16
Deduster bags Y
1 Cement Mill Deduster Rotary Valve Gear Box 2Y