Manufacturing Process

Portland Cement is a carefully blended combination of lime, silica, alumina and iron oxide. These components are found in materials which fall into two main categories; calcareous (or lime bearing), such as limestone, and argillaceous (or clay-like) such as shale.

The main raw material component of cement is Limestone, which is obtained from our Kleins Point Quarry on the Yorke Peninsula and shipped across St. Vincent Gulf on the Company’s ship M.V. Accolade II, to our Birkenhead plant.
Once the Accolade II reaches the Birkenhead plant, the Limestone is transported via conveyor belts to the Limestone Pre-blend Building, where it is stockpiled into pre-blended heaps of around 25,000 tonnes. A reclaimer (pictured in the diagram to the right) moves back and forth along the heap scraping a cross section of the limestone. As the newer raw material is stacked on top of older material, the cross-sectioned reclaiming process ensures an even blend of material is reclaimed.
The reclaimed limestone is then transported via belt conveyors to the weigh building where other raw materials, known as ‘fringe’ materials, such as shale, sand and iron oxide are added to the limestone. This blend of materials is fed into a ring roller mill, where it is dried and crushed to a fine state. This material is now referred to as raw meal and is the feed for the kiln. The drying process in the raw mill uses the hot gases from the kiln, which also transport the raw meal through large electrofilters which separate the solid particles from the gas, allowing the clean gasses to pass into the atmosphere.

The raw meal is then extracted from the electrofilters and conveyed to the 6,000 tonne blending silo. This silo serves, not only as a storage silo, but also thoroughly blends the raw meal into a physically and chemically consistent material, ensuring well controlled, quality product.

The raw meal travels through a preheating tower and reaches approximately 900°C before it enters the kiln. Once the raw meal reaches the rotating kiln, it is heated further which releases carbon dioxide from the limestone. As the heated raw meal proceeds further down the kiln into the burning zone, temperatures reach in excess of 1400°C causing chemical reactions which convert the raw meal into hard nodules ranging in size from 5-35mm in diameter known as clinker.

The clinker is then cooled, with the heat recovered from this process being re-used in the kiln to increase energy efficiency. After cooling, the clinker is transported from the storage area, via belt conveyers, to the cement mill. Just before entering the mill, other additives such as gypsum and limestone are added to the clinker in very specific quantities. The mill is a large rotating ball mill which is filled to a certain level with steel balls ranging in size from 17-90mm in diameter. The clinker and additives are crushed and ground between the steel balls until the desired fineness is attained. The resultant cement powder then exits the mill and passes through a separator, which extracts the coarse cement powder that has not been milled to the required fineness and returns it back into the mill for further milling. The cement meal that passes through the separator is stored in various silos, ranging in size from 500-30,000 tonnes, where it awaits bagging or bulk transportation.