The Quarry
The Quarry is situated to the Northeast of the plant. The principal limestone is nearly horizontal series of seams with a total thickness of 70 to 75 feet (21 to 23 m). The titration of the limestone is high, (about 90%) with a variation of a few percent. The limestone is drilled with ( 108 mm Ø holes ) and blasted. The yield is 7-10 Tons of limestone Kilogram explosive. The fragmentation is very good.
It is then loaded by shovels and loaders on 35-ton dumpers and dropped into the apron feeder of the crusher.
Crushing
The crushing of limestone and shale is done separately in an Appareils Dragon, France double hammer mill with a normal capacity of 250 Tons/Hr. The limestone (or shale) is fed to an apron feeder from where it is discharged onto a Hevitt Robins scalper. The scalper was originally fitted with a top deck of steel bars and a lower deck of strong wire mesh. The material passing the wire mesh fell directly to the conveyor belt, which also transports the crushed stone to concrete hopper. Now the screen has been modified to work with only an upper deck. This is made of heavy steel plate perforated by dia 60 mm holes. The material, which passes this plate, is taken by the conveyor belt to the hopper.
The crushing installation is working three shifts a day and six days a week.
Transport of Raw Materials
The crushed products are taken from the storage hopper by ropeway to the overhead crane store at the plant. The ropeway loading station is at 2200', and the discharge at the crane store at level 1300'. The ropeway is working three shifts a day and six days a week. The installed capacity is 290 Tons/Hr and now the operating actual capacity is not more than 225 Tons/Hr. Maintenance of the ropeway takes 6 hours a day. Thus, 18 hours a day are available for production.
Beside the ropeway unloading point at the plant there is an 80 Tons/Hr. dragon hammer mill for crushing gypsum.
Raw Material Grinding
The plant has 3 identical raw mills 12.75m x 2.90m Ø for slurry grinding. The mills are 3 compartment mills having capacity 55 Tons/Hr each. An overhead crane fills material into the mill feed hoppers. The feed tend to block during the rainy season, especially the shale hopper. The feed is taken from the feed hoppers to the mills conveyor belts. A steel plate at the hopper outlet controls the feed rate manually.
Much care is taken to keep the slurry moisture content as low as possible. No instruments are available to control the slurry moisture or viscosity but the care exercised by the attendants seems fully satisfactory without the use of instruments.
Homogenistation
The slurry is being homogenized in 8 silos with a capacity of 1225 Tons each and in two slurry basins with stirring performed by mechanical device and through air injection. The composition of slurry silos is being checked by analysis of nearly full silos and corrected composition slurry in silos is transferred to one of the basins.
This slurry is then used as kiln feed. Normally first basin is used for blending and second as Kiln Feed. Each basin has a capacity of 9400 Tons and much care is taken to ensure that the basins are kept will filled at all times.
Clinker Burning
The three kilns are 3.75 x 3.40 x 3.75 x 135 m working with Fuller grate coolers, type 744. The rated production of the each kiln is 600 Tons per 24 Hrs, The kilns are fitted with a chain system composed of chains suspended at one end on circular rings. The temperature of the exit gases is about 175°C, which indicates an efficient chain system.
The slurry fed to the kilns is controlled by the speed of a scoop wheel working in a pond of slurry. Coal or natural gas is used as fuel. The material residue time is about 180 minutes. During which clinker formation took place & clinker is then cooled in clinker cooler.
Fuller Cooler
The clinker coolers are a Fuller coolers type 744 with horizontal grate.The cooler becomes very hot when the kiln output has been raised above 600 Tons clinker per 24 Hrs. Cooler exist hot gases at present are being used in coal grinding mills.
The clinker is taken from the Fuller cooler to the clinker store by drag chains. In order to further cool the clinker, water is sprayed on the drag chains. The overhead crane lifts the clinker into the feed hoppers for the three cement mills.
Cement Mills
The three cement mills are all of the same size, 12.75m x 2.90 m, having each 38 Tons/Hr capacity. They are open circuit grinding mills having cooling devices by spraying water on the mill shell. After grinding the cement is transported by Fuller pumps to the cement silos. We have three cement storage silos of capacity 4500 Tons each. Hence total storage capacity is 13,500 Tons.
The mill feed is controlled by adjusting the opening of the sluice gate below the feed hoppers. The blain is kept at 3000 cm²/gm. The particle size distribution is the finished cement is not uniform. Residue is high, its conversions to close circuit is essential for good quality cement.
Packing
Cement from silo is extracted and filled in bins of packing machine 2x90 Tons/Hr capacity. Here cement is packed in 50kg bags and loaded on trucks for further transportation to the market. |
