What are Cement Clinkers?

Cement clinker uses limestone, clay, and iron as the main raw materials. It is prepared into a raw material at an appropriate ratio, and is partially or completely melted and cooled to obtain a semi-finished product. In the cement industry, the main chemical components of Portland cement clinker are calcium oxide, silica, and a small amount of alumina and iron oxide. The main mineral composition is tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium iron aluminate. Portland cement clinker is ground together with an appropriate amount of gypsum to become portland cement. In English, cement is sometimes written as caement to refer to cement. ^[1]

Cement clinker

(1) Chemical composition

It is mainly composed of CaO.SiO2.Al2O3 and Fe2O3, and the total content is usually above 95%.

(2) Mineral composition

The formation process of cement clinker

1. Water evaporation:

Free moisture gradually evaporates with the temperature of the material. When the temperature rises to 100 ~ 150 , all the free moisture in the raw material is eliminated.

In wet production, the slurry can reach 32-40%, so the drying process has a great impact on yield, quality and heat consumption.

2,

The motor is driven by a reduction gear

In the cement production process, at least 3 tons of materials (including various raw materials, fuels, clinkers, mixtures, and gypsum) must be ground for each ton of portland cement. According to statistics, the grinding process of dry cement production lines requires consumption of Power accounts for more than 60% of the plant's power, of which raw meal grinding accounts for more than 30%, coal grinding accounts for approximately 3%, and cement grinding accounts for approximately 40%. Therefore, reasonable selection of grinding equipment and process flow, optimization of process parameters, correct operation, and control of the operating system are of great significance for ensuring product quality and reducing energy consumption.

(1) Broken

During cement production, most raw materials are crushed, such as limestone, clay, iron ore, and coal. Limestone is the raw material that produces the largest amount of cement. After mining, the particle size is larger and the hardness is higher. Therefore, the crushing of limestone occupies a relatively important position in the crushing of the materials in the cement plant. The crushing process is more economical and convenient than the grinding process. It is very important to choose crushing equipment and grinding equipment reasonably. Before the material enters the grinding equipment, as much as possible, crush large pieces of material to a small, uniform size to reduce the load on the grinding equipment and increase the output of the honing machine. After the material is broken, the phenomenon of separation of different granularity materials during transportation and storage can be reduced, and raw materials with uniform composition can be obtained to improve the accuracy of batching.

(2) Pre-homogenization of raw materials

The pre-homogenization technology is to use the scientific stacking and reclaiming technology during the storage and retrieval of raw materials to achieve the initial homogenization of the raw materials, so that the raw material storage yard has the functions of storage and homogenization. The basic principle of raw material pre-homogenization is that when the materials are stacked, the incoming materials are continuously stacked by the stocker into a certain number of layers that are parallel to each other, overlap each other, and have the same thickness. When taking the material, in a direction perpendicular to the material layer, cut all the material layers at the same time as far as possible, and cut them in turn until they are finished, that is, tiling straight.

Features

(1) Homogenize raw material components, reduce quality fluctuations, and help to produce higher quality clinker, and stabilize the production of the firing system.

(2) Expand the use of mining resources, improve mining efficiency, maximize the coverage and interlayers of the mine, and produce no or less waste rock during the mining process.

(3) The quality and control requirements of mining can be relaxed, and the mining cost of mining can be reduced.

(4) Strong adaptability to sticky materials.

(5) Provide long-term and stable raw materials for the factory. It is also possible to batch the raw materials of different components in the yard to make it a pre-dosed yard, creating conditions for stable production and improving the equipment operating rate.

(6) High degree of automation.

Cement clinker homogenization

In the new dry cement production process, the stability of the raw material composition in the pit is the prerequisite for the stable clinker firing thermal system. The raw material homogenization system plays the final role of stabilizing the raw material composition in the pit.

Homogenization principle

Using air agitation and gravity, it produces a "funnel effect", so that when the raw meal powder is unloaded downwards, it is possible to cut the multi-layer material surface as much as possible to fully mix it. Different fluidized air is used to cause different sizes of fluidized expansion of the parallel material surface in the warehouse. Some areas are unloaded and some areas are fluidized, so that the material surface in the warehouse is inclined to perform radial mixing and homogenization.

Preheating of cement clinker

process

The preheater and partial decomposition of the raw material are completed by the preheater, which replaces some functions of the rotary kiln to shorten the length of the return kiln. At the same time, the kiln is stacked for gas-material heat exchange process and moved to the preheater in suspension The next step is to make the raw material fully mix with the hot gas discharged from the kiln, increase the contact area of the gas material, fast heat transfer speed, high heat exchange efficiency, and achieve the improvement of kiln system production efficiency and reduction of clinker burning heat consumption. purpose.

working principle

The main function of the preheater is to make full use of the waste heat from the rotary kiln and the decomposition furnace to heat the raw material, so as to preheat the raw material and partially decompose the carbonate. In order to maximize the heat exchange efficiency between gas and solid, and realize the high quality, high output and low consumption of the entire calcining system, it must have three functions: uniform gas-solid dispersion, rapid heat exchange and efficient separation. (1) 80% of the material dispersion heat exchange is performed in the inlet pipeline. Under the impact of high-speed updraft air, the raw material fed into the preheater pipe moves along with the airflow and is dispersed at the same time. (2) Gas-solid separation When the airflow carries the powder into the cyclone, it is forced to make a rotating flow in the annular space between the cyclone cylinder and the inner cylinder (exhaust pipe), and moves downward while rotating, From the barrel to the cone, it can be extended to the end of the cone, and then turned upward to rotate and rise, and is discharged by the exhaust pipe. (3) Pre-decomposition The emergence of pre-decomposition technology is a technological leap in the cement calcination process. It is to add a decomposition furnace between the preheater and the rotary kiln, and use the tail of the kiln to raise the flue, and set up a fuel injection device, so that the heat release process of fuel combustion and the endothermic process of carbonate decomposition of raw materials, The furnace is rapidly carried out in a suspended state or a fluidized state, so that the decomposition rate of the raw material into the kiln is increased to more than 90%. The carbonate decomposition task originally performed in the rotary kiln was moved to the decomposition furnace; most of the fuel was added from the decomposition furnace, and a small part was added from the kiln head, which reduced the heat load of the calcination zone in the kiln and extended the lining. Material life is conducive to large-scale production; because the fuel and raw material are mixed uniformly, the combustion heat of the fuel is transferred to the material in time, so that the combustion, heat exchange and carbonate decomposition processes are optimized. Therefore, it has a series of excellent performance and characteristics such as high quality, high efficiency, and low consumption.

Cement clinker firing

After the raw materials are preheated and decomposed in the cyclone preheater, the next step is to enter the rotary kiln for firing the clinker. In the rotary kiln, the carbonate is further rapidly decomposed and a series of solid-phase reactions occur to generate minerals in the cement clinker. As the temperature of the material rises, the mineral will change into a liquid phase, and it will dissolve in the liquid phase and react to form a large amount (clinker). After the clinker is fired, the temperature starts to decrease. Finally, the high temperature clinker discharged from the rotary kiln is cooled by the cement clinker cooler to a temperature that can be endured by downstream conveying, storage and cement mills, and the sensible heat of the high temperature clinker is recovered, improving the thermal efficiency and clinker quality of the system.

Clinker grinding

Cement grinding is the last process of cement manufacturing, and it is also the process that consumes the most electricity. Its main function is to grind cement clinker (and gelling agent, performance adjustment materials, etc.) to an appropriate particle size (represented by fineness, specific surface area, etc.) to form a certain particle gradation and increase its hydration area. Accelerate the rate of hydration to meet the requirements of cement slurry setting and hardening.