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High Alumina Cement is a type of cement prepared from high-purity alumina bauxite and a certain amount of limestone. The preparation process mainly includes the following steps:
Raw Material Preparation
High alumina bauxite and limestone are selected as the main raw materials. High alumina bauxite contains high aluminum oxide, providing high refractoriness and resistance to chemical erosion. Limestone provides sufficient calcium oxide for the reaction to form active compounds in the cement stone.
Raw Material Crushing and Mixing
The high alumina bauxite and limestone are respectively crushed to appropriate particle sizes, and then mixed. Usually, a ball mill is used to grind the raw materials into powder to improve their reactivity.
Calcination
The mixed raw materials are sent into a rotary kiln for calcination. The calcination process controls the formation of active compounds in the cement stone and the growth of crystals. At high temperatures, the bauxite and limestone undergo chemical reactions to generate the main components of the cement stone, such as tricalcium aluminate and higher alumina phases.
Grinding
The clinker produced by calcination needs to be ground to improve the fineness and activity of the cement. Common grinding equipment includes coal mills and roller presses. Grinding increases the surface area of the cement, making it easier to react with water, thereby improving the strength and durability of the cement.
Packaging and Storage
After the grinding process is completed, the high alumina cement is packed into bags, jars, or silos for storage. During storage, attention should be paid to moisture-proofing and avoiding contact with moisture to ensure the quality of the cement.
Selection and Proportioning of Raw Materials
The main raw materials of high alumina cement are gangue, bauxite, chalk, and clinker. Among them, gangue and bauxite have the highest content. The proportions are: gangue 50%~60%, bauxite 30%~40%, chalk 10%~20%. When selecting raw materials, attention should be paid to the grinding fineness and calcination temperature of the gangue, the aluminum and iron content of the bauxite, and the quality and content of the chalk.
Clinker Preparation
High alumina cement clinker is obtained from the thermal reaction of limestone, chalk, and bauxite, producing clinker primarily composed of dialuminum trioxide (C3A) and dicalcium silicate (C2S). It is produced using rotary kilns. The clinker needs a high calcination temperature and good maturity.
Raw Material Mixture Preparation
High alumina cement raw material mixture preparation involves preheating and pre-decomposition of raw materials used to make the clinker before thermal treatment in the kiln. The raw mixture has high viscosity, is prone to caking, and has poor flowability. Adding appropriate amounts of low-calorific value and low ash content fuel to the raw mixture can effectively raise the temperature, promoting decomposition reactions, and ensuring the raw material is properly sintered.
Sintering Technology
High alumina cement sintering is performed using rotary kilns. The sintering temperature generally is 1450℃, and the sintering time is 60~70 minutes. During the sintering of high alumina cement, it is crucial to control the aluminum oxide content to avoid excessive reduction and further oxidation.
In summary, the production of high alumina cement mainly includes steps such as raw material preparation, raw material crushing and mixing, calcination, grinding, packaging, and storage. These steps enable high alumina bauxite and limestone to form cement stone through a series of chemical reactions, thereby possessing high refractoriness, resistance to chemical erosion, and strength. The formula and technology of high alumina cement include aspects such as the selection and proportioning of raw materials, clinker preparation, raw material mixture preparation, and sintering technology. It is necessary to pay attention to the process parameters at each stage to produce high-quality high alumina cement.
