Presentation1 (1)-16-28.pdf

Raw materials The fundamental raw materials used for cement production are:  Calcium sources :Limestone (CaCO3), chalk, shells, shale or calcareous rock Silica sources: sand(SiO2), shale, clay or argillaceous rock Alumina sources: bauxite, recycled aluminum, clay Iron sources:...

Raw materials The fundamental raw materials used for cement production are:  Calcium sources :Limestone (CaCO3), chalk, shells, shale or calcareous rock Silica sources: sand(SiO2), shale, clay or argillaceous rock Alumina sources: bauxite, recycled aluminum, clay Iron sources: clay, iron ore, scrap iron and fly ash  Sulphate sources: Gypsum, CaSO4.2H20 found together with limestone  Dry cement production process There are three main process in cement production process. These are:  Raw materials preparation Burning or clinker production  Finish grinding and packing  1. Raw materials preparation The raw material preparation for cement production includes: 1.1 Raw materials exploration: identifies the type of raw materials at its right qualities and quantities ( lime stone , clay , sand, gypsum, pozzolan etc) In MCF main source CaO is lime stone and OB, SiO2 - LSOB or sand, Fe2O3 and Al2O3 is clay  1.2 Mining operation Over burden removal (Dozer, excavator, loader off highway truck etc  Drilling (Drilling machine)  Blasting (using explosives like, ANFO, power jell)(primary and secondary ) Loading and Hauling( excavator, loader off highway truck) Crushing ( single or double hammer crusher  1.3 crushing of raw materials Crushing: is the mechanisms of size reduction of raw materials and as a result of 85% less than 25mm 100% less than 50mm particle size. Why crushing of cement raw materials ? (For easy blending and transportation) Crusher used – old line 350t/h double hammer New line 900t/h single hammer crusher for lime stone, sand and gypsum. Roller crusher for clay 150t/h These machines can either be single-rotor or double-rotor type. In the single-rotor type the rotation is counterclockwise so that the hammers force the material downward. The bottom part of the crusher consists of longitudinal grid bars, and the distance between the bars and the speed at the hammer determine the maximum size of the crushed product.  Cont…. A double-hammer crusher with two rotors, the left-hand unit rotating clockwise and the right-hand unit counterclockwise, offers the possibility of handling larger feed size, larger output, and higher moisture content in feed material. After crushing materials transported to intermediate storage by belt conveyors. Currently in MCF lime stone, overburden and sand are from the same quarry 1.4 Storage stockpiles and stacker reclaimer systems Stacker Reclaimer Systems are storage and extraction systems for crushed and granular materials like crushed limestone, other raw materials and coal. They can handle material at high rates of feed and extraction because conveyors in the systems are belt conveyors. The most important purpose of stacker reclaimer systems, in addition to being a stock for the grinding process is to enable achieve a homogenized raw material in response to the variation of the supplied material composition which occurs due to the changes in mine face progresses. The two most common distinguished types of stock piles are the longitudinal stock piles and the circular stock pile. Each of these have different geometries of stacking and reclaiming materials  Longitudinal Stockpile Most commonly the longitudinal stockpile operates with two piles. One pile is stacked while the other is being reclaimed. The height above the crest of the pile is kept at a minimum to reduce dust emission. Reclaiming takes place from the face of a pile at the natural angle of material slide.  The advantages of this type of stock pile include;  It issuitable for dry to moderately sticky materials,  Direct feed of free flowing materials is possible,  Efficient adjustment of long term variations in chemical composition of raw materials,  The Store capacity can easily be expanded. A capacity of each pile covering 3½ to 7 days requirements is normally recommended for cement production. The material entering the store on a rubber belt conveyor is discharged from the jib of the stacker traveling on rails along Fig. 2 Longitudinal Stockpile  Circular Stockpile The material enters the store on a rubber belt conveyor and is discharged into a centrally positioned inlet hopper on the stacker jib. Reclaiming takes place at the natural angle of slide by using a bridge reclaimer which rotates anticlockwise around the central column In case of a circular stock pile, pile is formed to occupy three fourths of the circle. Pile is built up from one end and extracted from the other end. Main advantages of using circular stock piles are:  High continuous homogenizing effect,  Optimum utilization of space and fully automatic continuous operation,  with no change of piles, is achieved. The Circular Blending system is designed for continuous Chevron stacking in one ring shaped pile. Stacking is effected by a fan shaped sprinkling action in an arc determined by the type of material being processed to ensure appropriate homogenization. Reclaiming at the other end of the pile is effected by a bridge reclaimer working parallel to a radius line. For cement production the pile between the bridge scraper and the stacking zone is a buffer normally representing 3 1/2 to 7 days‘ consumption. ffi Fig.3 Circular Stockpile In the longitudinal store there are three types of stacking methods. These are: According to the Chevron method material is deposited by the stacker moving to and fro over the centre line of the pile. The Chevron stacking method causes segregation of the material with fine particles in the central part of the pile and coarse particles on the surface and at the bottom of the pile. To ensure proper blending a Chevron pile must therefore be reclaimed from the face of the pile, working across the entire cross section. According to the Windrow method material is deposited from a number of positions across the full width of the pile. The Windrow method prevents segregation and ensures more even distribution of fine and coarse particles across the pile. The Windrow method is preferred in cases where the reclaimer is only operating in one part of the pile cross section at a time or in cases where segregation would make an open pile base unacceptable – typically in coal stores. The Cone Shell method is often used in cases where homogenization is not necessary. The pile is formed by depositing material in a single cone from a fixed position