Cement is a finely milled and water-absorbent powder which is basically made of limestone, clay, and marl combined with shale, clay, slate, blast furnace slag, silica sand, and iron ore. These ingredients, when heated at high temperatures form a rock-like substance that is ground into the fine powder that is commonly known as cement. Mixed with water, cement serves as an adhesive to bind sand, gravel, and hard rock in concrete. Cement hardens both in the air and under water, and reaches its hardened state to 70 percent of its final compressive strength after 28 days depending on the type and mixture.
Production process of cement in MOMTAZAN CEMENT PLANT
Preparation of raw material:
After examining the quality of raw material and their exact required volume, they are selected from the relevant depot and passed through a crusher, made by German Hazemag, with a capacity of 400 t/h. This crusher is capable of grinding large masses of up to 1 meter in size to particles of maximum 8 cm. Fine raw materials which are fine enough pass through the roller screen of the crusher. This adds to the capacity of the crusher to 1200 t/h meanwhile efficiently saving energy. Afterwards the output material is conveyed to the mixing unit.
Primary raw-material mixing unit:
The primary raw material mixing unit is a barn-like covered space with the dimensions of 280 m in length, 55m in width and 20 m in height, with a storing capacity of 60000 tons of material in two depots of 30000 tons, each is called a pile. Two machines are installed in this unit; one for stacking and one for reclaiming up the material. The stacking machine or stacker, designed by Germany’s SCHADE, piles up the material in layers. When one pile is ready, the reclaimer , designed and manufactured by Germany’s SCHADE, collects the material with a capacity of 700 tons and conveys it to the feeder silo of raw mill.
Unlike the stacker, reclaimer collects the material in width which allows it to take up different layers simultaneously and thus the first stage of homogenization takes place. As the reclaimer is recovering the material from the stockpile, the stacker is preparing a new pile. When the second pile is stacked, the reclaimer can be moved to a new pile, while stacker has started a third one. With continuous replacement of these two machines, the process of preparation and adjustment of raw material continues.
Material coming from the primary mixing unit requires another step to be prepared for the burning processin the kiln. It has to be ground into powder. The grinding stage is performed in the raw mill. The mill is of rotary kind, designed and manufactured by Pfeiffer, Germany. The milling capacity is 310 t/h. Reclaimed material is carried to the mill feeder by special conveyor belts. Four funnels are provided to feed the mill, one of which is the main funnel containing material from the mixing unit. Other three funnels are used for probable necessary adjustments, containing iron, silica and limestone. The material enters the mill, and is ground by 3 rollers each weighing 60 tons which are positioned on the mill tray. Then it is guided towards the separator, where fine and coarse particles are separated. The fine particles which are suitable for clinker production is conveyed to the raw material silo. Coarse particles are again fed to the mill to be ground and reach a suitable size and shape.
Raw Material Silos:
Fine material from the separator which is suitable for the burning process is then directed to the raw material silos for storage and further homogenization. In MOMTAZAN CEMENT FACTORY two silos, designed by Germany’s IBAU with a capacity of 8000 tons each, are used for this crucial step.
The output material from silos is to be transformed to the burning process. To doso the material must reach a suitable temperature prior to being fed to the kiln. This takes place in the pre-heater section. The kiln feed is firstly conveyed to the top of pre-heater by airlift and moves down towards the bottom, passing through various cyclones, due to the weight of particles. Hot gas is ousted from the kiln at the bottom of the pre heater and moves up toward the top, passing through cyclones. The contact between material and the gas provides an exchange of heat and the material heats up. The warm material is guided into a calciner. With appropriate fuel consumption the temperature is raised to approximately 900 degree C, so that the carbonates are calcined and then fed into the kiln.
Dust Trapping System:
The output gas which has conducted most of its heat to the material has cooled to about 300 degree C. As a result of direct contact with the material, this gas contains very fine, tiny particles which have to be separated from the gas suitably. To do this, the gas is moved through a cooling tower, and the temperature is reduced to around 150 degrees C by water spraying. Then it is injected into the dust trapping system, of electro filter type. In the elector filter, strong magnetic fields of about 50000 volts charge particles allowing them to be absorbed by special sheets and are entered into the production process anew. This is a highly crucial step both economically and environmentally.
The kiln in MOMTAZAN CEMENT FACTORY was designed and manufactured by KHD Germany,which is 52 m in length with a diameter of 4.4 m. It is installed on two rings with a 3% tilt, rotating 0.1 to 3.5 rpm using a powerful engine. As the kiln is rotating, the material moves towards the exit. A torch is installed at the end of the kiln. The temperature is increased to 1450 degrees C. while material is passing through the burning zone, chemical reactions are completed which results in producing a granular material called clinker. Internal wall of the kiln is covered with alumina bricks and refractories which protect the steel structure and reduce energy waste. MOMTAZAN CEMENT FACTROY kiln is capable of producing 3300 tons of clinker per day and is working 24/7 non-stop.
The output of the kiln is clinker with a temperature of up to 1100 degrees C, which must be cooled appropriately in order to safeguard the phases. This is performed in the grate cooler by applying cool air current. Ambient air is fanned into the lower section of the cooler which absorbs the heat of the clinker as it moves through it and cools it down. Some of the heated air is reused as secondary for the torch in kiln. Some other heated air is directed via tertiary pipes towards the pre heater and extra air is released after the dust trapping process. Cooled clinker which has a temperature of 100 degrees C, is conveyed to the clinker silos after being grated for large particles by Amond band.
Three silos are used for storing the clinker. One silo with a capacity of 3000 tons is specializedfor particular occasions and products in order to export or for other uses. The output can be loaded by a backhoe or a bulldozer.
Two other silos are similar in shape, each with a capacity of 25000 tons.
Sampling is performed from the produced clinker every hour which is transformed to the lab for quality control tests.
The produced clinker needs to go through a grinding step to turn into cement. This is done in the cement mill, designed and made by KHD Germany, with a capacity of 210 t/h. This is one of the biggest of its kind in the Middle East.
The clinker is fed to the mill along with the required amount of raw gypsum to control setting. If necessary, in order to produce special cement, other additives are passed into the mill after going through weighing instruments and reach an appropriate graining.
Sampling is performed hourly which is sent to the labs for quality control tests.
The output cement is then transformed to the silos for storage according to type. In MOMTAZAN CEMENT FACTORY three silos each with a capacity of 7800 tons are being used. These silos were designed and made by IBAU Germany.
Cement is packed in the packing department to be delivered to the customers. In MOMTAZAN CEMENT FACTORY, cement can be delivered in four ways: in bulk, sacks, palletized, and jumbo bags. For bulk loading, two separate truck lines are provided for each silo or product. Both lines are equipped with weighbridge systems which adjusts the tonnage to be loaded into trucks or bunkers.
In bag packing, the most cutting edge technologies are used in two roto- packers, each with a capacity of 2400 bags per hour which is equal to 120 t/h. The packing machine is designed and made by Germany’s Haver&Bocker. At the request of customers, palletized delivery is as well possible using the palletizer machine with a capacity of 700 tons per day.
Jumbo bags of 1 and 1.5 tons are also other methods of delivery.
To ensure highest quality, sampling is performed on loaded and packed cement every day, which is sent to labs for physical and chemical parameters testing.