Sidhee Cement - Production Process

PROCESS: -

The process of clinker /Cement production at Saurashtra Cement Limited Sidheegram can be briefly described as follows.

MINING: -

The rich captive mines have vast reserves of high purity lime stone. In these captive mines, almost all the grades of limestone is available and a very little quantity of additive is to be obtained from outside. Mining is done by surface mining technology which is environment friendly.

CRUSHING, STACKING & RECLAIMING: -

The mined limestone is hauled through Dumpers to a rotary hammer - impact type crusher that crushes the limestone to a size up to - 75 mm (minimum 80%). Additive material is added to the crushed limestone through crusher hopper. The material is passed on to the stacker via belt conveyors, which stocks the material in longitudinal layers. The stacked material is lifted by the reclaimer, which reclaims by cutting transversely the longitudinal stacked layers ensuring perfect blending and homogenizing

RAW MEAL GRINDING: -

The desired material is drawn from lime stone reclaimer pile through the Box feeder and is fed to the vertical roller mill through air locking feeder. The vertical mill consists of a rotating table upon which 3 rotating rollers are hydraulically pressed. The material is dried and transported by the hot kiln exit gases. The size of the pulverized material is controlled by a static separator, which separates the oversized grits and sends it back on the table for further grinding. The pulverized material is transported to the C.F. Silo via energy efficient bucket elevators.

STORAGE & BLENDING: - (CAPACITY 20,000 M.T.)

The pulverized material is stored and blended in the controlled flow silo. The Blending action is achieved by extracting the material from the 7 outlets at a different rate. The extracted material is conveyed to a weighing bin where it is further blended. The operation of extraction is controlled by a PLC. The blended material is fed to the pre heater for preheating via bucket elevator.

PREHEATING, CLINKERISATION AND COOLING: -

The kiln feed from the C.F silo is fed into the both strings of pre heaters. Approximately 40% of the feed is given to the pre heater string where it gets preheated by the hot kiln exit gases and gets calcined up to 30% approximately. The balance 60% feed is fed to the calciner string where coal is fired in the calciner and the 30% calcined feed from the pre heater string is also added to the calciner. Here, about 90% calcination is achieved. The calcined feed is transferred to the kiln for the remaining calcination process and sintering where the flux materials and silica melt and react with lime to form clinker constituents. This is achieved by firing pulverised coal in the rotary kiln with use of advanced combustion burners. The clinker coming out of the rotary kiln is at a temperature of 13000 -1400 0C and hence cooling of the same is required and the hot gases are recouped. This is achieved by pumping atmospheric air in the reciprocating grate cooler by centrifugal fans. The clinker gets cooled and the air gets heated up and the excess air is vented out at a lower temperature. The recuperation of the heat in the cooler is very effective and thus energy efficient.

CLINKER STORAGE & TRANSPORT: -

The clinker is transported to the clinker storage silo by deep bucket conveyors. The silo for clinker has a capacity of 40,000 M.T and is a salient feature of the plant to retain clinker freshness. Another smaller silo of 2000 M.T. Capacity is provided to store special products/non conforming products (if, any). The clinker from the clinker silo is transported to the clinker hopper of the cement mills for finish grinding.

CEMENT MILLS:-

The clinker is ground along with gypsum ( for OPC) and Fly ash (for PPC) at desired proportion in the highly efficient combidan mills. The cement mills are two compartment tube mills. In the first compartment, the grinding is done by impact with balls and in the second compartment it is done by attrition with smaller grinding media. The mill is swept with air, which transports the material through the mill. The cement is pumped to the cement silos with the help of airlifts. There are four silos for cement of 5000 M.T. capacities each for storing different grades/types of cement.

PACKING PLANT: -

The packing is done by automatic rotary packers, which have a capacity of 90 TPH each. There is total No. of 5 packers. The packed bags are directly loaded into the trucks by belt conveyors. Separate system is made for loose cement loading.

RAW COAL & FINE COAL PLANT: -

Raw coal is also stacked and reclaimed by a stacker and reclaimer hence ensuring a perfectly blended Raw Coal. This is a unique feature of the plant. The Raw Coal is pulverized in a vertical roller mill, which is similar to that for the limestone.

Differential grinding of coal is done. For calciner, the coal is pulverized to a coarser size while for kiln it is ground finer and stored separately. Pneumatic screw pumps fire the coal.

CONTROL SYSTEM: -

The plant is centrally controlled except the packing plant. The control is achieved by DCS and color videography system. FUZZY LOGIC controls the kiln & cooler operation.

QUALITY CONTROL: -

The quality control is achieved with the help of an X-Ray analyzer, which gives accurate and fast results. However, a fully equipped chemical and physical laboratory is also provided to comply all National standard.

QUALITY MANAGEMENT: -

The organization was first certified for ISO 9001 : 2000 Quality Management System by TUV, Germany in March 1995. Saurashtra Cement Limited is an IMS certified company (Integrated Management System combining ISO 9001 : 2015 , ISO 14001 : 2015 and ISO 45001 : 2018 for environment and other safety related standards)

POLLUTION CONTROL EQUIPMENTS: -

The plant employs the relates state of art pollution control equipments like ESPS, Bag filters & Chemjets. The old generation pulse energized ESP has been modified to the latest generation ESP. The controller for the transformers has been changed and a variable inductance is provided. M/s. BHA, USA, supplied the equipment. Also the gas conditioning system supplied by M/s. Chemstrol Samil, India has been installed with this system, which conditions the gases in the down comer duct itself rather than the Gas Conditioning Tower in a conventional way.

Unit Operation

UNIT OPERATION	DESCRIPTION	CHEMICAL REACTION	TIME REQUIRED
Mining	Mining of Limestone from the Mines & hauling to crusher.	No chemical reaction
CRUSHING	Crushing of the limestone from a bigger to a smaller size & adding additive material.	No chemical reaction
STACKING	Stacking of the crushed limestone in longitudinal layers to form a stockpile.	No chemical reaction
RECLAIMING	Reclaiming of the longitudinally stacked material by cutting it transversely to ensure blending.	No chemical reaction
RAW GRINDING	The material from the pile is pulverized to a very fine powder & is stored in a Controlled Flow Silo.	No chemical reaction
PYRO PROCESSING	The Raw Meal is extracted from the silo & it is Preheated in the PREHEATER where it gets calcined up to approx. 90% and enters the KILN for further calcinations & sintering. Sintering is the process wherein the clay components melt & form a liquid, which reacts with lime to form the potential clinker components.	ATTACHED SEPARATELY	RETENTION TIME IN KILN IS APPX. 29 MINUTES.
COOLING	The clinker thus formed is very hot and hence pumping cold air in the cooler through fans, which cools the clinker & heats up the combustion air, cools it. The extra cooling air is vented out through an ESP.	No chemical reaction	RETENTION TIME APPX. 20 MINUTES.
GRINDING	The cooled clinker is drawn from the silo & is pulverized to a very fine powder. Also, Gypsum is mixed at the inlet of the mill.	No chemical reaction	RETENTION TIME APPROX. 30 MINUTES
PACKING	Packing of cement form silos im bags is done by notary packers.	No chemical reaction
COAL HANDLING	The coal received is stacked in piles with the help of a Stacker & is again reclaimed with Reclaimer and fed to the Coal Mill Storage Hopper.	No chemical reaction
COAL GRINDING	Raw coal is pulv. To a fine powder in order to facilitate fast ignition of coal in a vertical mill.	No chemical reaction

TRI-CALCIUM SILICATE (C3S)	3CaO.SiO2
BI-CALCIUM SILICATE (C2S)	2CaO.SiO2
TRI-CALCIUM SLUMINATE (C3A)	3CaO.Al203
TETRA CALCIUM ALUMINO FERRATE (C4AF)	4CaO.Al203.Fe2O3

S.N.	Temperature	CHEMICAL REACTION
1)	Below 800oC	Decomposition of limestone & formation of CaO.Al203 begins
2)	900 - 1100oC	• Decomposition of Calcium Carbonate is complete.
		• Formation & Decomposition of Gehlenite (2CaO+Al2O3+SiO2)
		• Formation of C3A, C4AF starts.
3)	1000 - 1200oC	Formation of C2S, C3A & C4AF is nearly complete.
4)	1200 - 1300oC	Liquid formation starts.
5)	1200 - 1450oC	Assimilation of CaO through solid-liquid reactions & formation of C3S