Raw Materials
The main raw materials used in the cement manufacturing procedure are limestone, sand, shale, clay, and iron ore. The primary material, limestone, is generally mined on site whilst the other minor materials might be mined either on site or in nearby quarries. Another source of raw supplies is industrial by-products. The use of by-product materials to replace natural raw supplies is a key element in achieving sustainable improvement.
Raw Material Preparation
Mining of limestone requires the use of drilling and blasting techniques. The blasting methods use the newest technology to insure vibration, dust, and noise emissions are kept at a minimum. Blasting produces materials in a wide range of sizes from approximately 1.5 meters in diameter to little particles less than a couple of millimeters in diameter.
Material is loaded at the blasting face into trucks for transportation towards the crushing plant. Via a series of crushers and screens, the limestone is reduced to a size much less than 100 mm and stored till required.
Based on size, the minor materials (sand, shale, clay, and iron ore) might or may not be crushed before becoming stored in separate locations till needed.
Raw Grinding
In the wet procedure, each raw material is proportioned to meet a desired chemical composition and fed to a rotating ball mill with water. The raw materials are ground to a size exactly where the majority of the materials are less than 75 microns. Supplies exiting the mill are known as “slurry” and have flowability characteristics. This slurry is pumped to blending tanks and homogenized to insure the chemical composition of the slurry is right. Following the homogenization process, the slurry is stored in tanks till needed.
Within the dry procedure, every raw material is proportioned to meet a desired chemical composition and fed to either a rotating ball mill or vertical roller mill. The raw materials are dried with waste procedure gases and ground to a size where the majority of the supplies are less than 75 microns. The dry materials exiting either kind of mill are called “kiln feed”. The kiln feed is pneumatically blended to insure the chemical composition of the kiln feed is nicely homogenized after which stored in silos till required.
Pyroprocessing
Whether or not the procedure is wet or dry, the same chemical reactions take place. Basic chemical reactions are: evaporating all moisture, calcining the limestone to produce totally free calcium oxide, and reacting the calcium oxide with the minor supplies (sand, shale, clay, and iron). This outcomes in a final black, nodular item known as “clinker” which has the desired hydraulic properties.
Within the wet process, the slurry is fed to a rotary kiln, which can be from 3.0 m to five.0 m in diameter and from 120.0 m to 165.0 m in length. The rotary kiln is made of steel and lined with unique refractory supplies to protect it from the high procedure temperatures. Process temperatures can reach as high as 1450oC during the clinker generating process.
In the dry procedure, kiln feed is fed to a preheater tower, which could be as high as 150.0 meters. Material from the preheater tower is discharged to a rotary kiln with can have exactly the same diameter as a wet procedure kiln but the length is much shorter at roughly 45.0 m. The preheater tower and rotary kiln are made of steel and lined with special refractory supplies to protect it from the high process temperatures.
Regardless of the process, the rotary kiln is fired with an intense flame, produced by burning coal, coke, oil, gas or waste fuels. Preheater towers can be equipped with firing also.
The rotary kiln discharges the red-hot clinker under the intense flame into a clinker cooler. The clinker cooler recovers heat from the clinker and returns the heat to the pyroprocessing system therefore decreasing fuel consumption and enhancing energy efficiency. Clinker leaving the clinker cooler is at a temperature conducive to being handled on regular conveying equipment.
Finish Grinding and Distribution
The black, nodular clinker is stored on site in silos or clinker domes till needed for cement production. Clinker, gypsum, along with other process additions are ground together in ball mills to form the final cement goods. Fineness of the final products, quantity of gypsum added, and the amount of process additions added are all varied to develop a desired efficiency in every of the final cement goods.
Every cement item is stored in an individual bulk silo until needed by the customer. Bulk cement can be distributed in bulk by truck, rail, or water based on the customer’s requirements. Cement may also be packaged with or without color addition and distributed by truck or rail.
