The cement manufacturing process is mainly composed of six steps:
Extraction of Raw Material
Crushing and Pre-homogenization
Raw Flour Milling
Packing and Dispatching
Every one of these stages goes through strict quality control to ensure and meet international standards for cements produced and a true commitment to environmental management.
1. Extraction of Raw Material
The main raw materials for cement manufacturing come directly from the quarries near the plant Bijao. These consist of limestone and shale that are extracted by means of tearing (tractors) or blasting (explosives).
2. Crushing and Pre-homogenization
The second stage of the process involves reducing the size of the rocks from the quarries, crushing through, from diameters of 1 meter to particles smaller than 1 inch. The product of this phase is stored in circular Pre-homogenization galleys in order to ensure greater uniformity in the chemical distribution of materials and reduce variations in material quality for batches as large as 18.000 tons, which are ready to be used in the next step.
3. Flour Milling Raw
This process continues the reduction of particle size and material drying, prior to subject it to high temperatures in high furnaces. From the high furnaces the mills then receive the crushed and pre-homogenized materials, where they are simultaneously mixed and sprayed together.
The chemical composition of mineral mixture is given online, through neutron analysis prior to entering the mill, which allows for the continuous adjustment of the raw flour milling process in the proportion of materials.
The product is a very fine powder called “raw flour” with a chemical composition suitable for the type of cement that is being produced. The reduction in the variation of the quality of the raw flour is made possible by storing it in special bins for homogenization. A second stage in the quality control of raw flour takes place in the product that is entering the silos, through an X-ray analyzer that can perform complete chemical analysis in very short time and with great precision
The raw flour from the silos is fed into rotary kilns where the material is charred and half-melted by subjecting to high temperatures (1450oC). Here are carried out chemical reactions between the different oxides of calcium, silicon, aluminum, iron and other minor trace elements that combine to form new compounds that are cooled quickly out of the oven. The cooled product out of the furnace is given the name of ‘clinker’ and is usually granular, rounded and dark gray. The Bijao plant has 2 furnaces with a total design capacity of 5,500 tonnes per day of clinker production and can use petroleum fuels, coal, petroleum coke and other alternative fuels.
5. Cement grinding
The next step in the production process is the grinding of cement clinker, together with other minerals that confer specific properties to cement. The cast, for example, is used to retard the setting time (or hardening) of the mixture of cement and water, and allow their management. You can also add other materials such as volcanic sands, which produce a more durable, waterproof concrete, with lower heat of hydration than an ordinary portland cement consisting only of clinker and plaster.
Again, the analysis of the product leaving the mill is a priority, so it is also carried out using X-ray analyzer, which allows adjustment in the proportions of the materials and the specific characteristics of the cement that is being produced. Control of particle size of ground cement is another variable of great importance, since it greatly affects its properties, so its measurement is considered frequently.
6. Packaging & Dispatch
Finally, the cement produced and stored in silos can be shipped in pipes in bulk for large consumers, or bagged.The net weight traditionally used in Central America for the bagged cement is 42.5 kilograms. (93.7lb.).
The Bijao plant has 2 packaging lines of 3,000 bags / hour each, one of them fully capable of automatically palletizing the product.