What is the cement clinker? As we know, the cement production process is mainly divided into raw material preparation, clinker calcination, and cement grinding. Clinker is the material produced in the calcination stage and is usually used as the binder in many cement products. In other words, it is a semi-finished cement product by preparing limestone, clay, iron raw materials, etc., in proper proportion, calcining them to partial or full melting, and finally cooling to normal temperature.
In the cement industry, the main chemical components of the most commonly used Portland cement clinker are calcium oxide, silica and a small amount of alumina and iron oxide. Its particles are usually of diameter 3-25 mm and dark grey. It can be stored for long periods in a dry condition without reduction of quality, thus it is traded internationally and used by cement manufacturers when raw materials are found to be scarce.
The production of cement can be divided into dry process and wet process, while because of the high output, low heat consumption and steady running, the dry process has become the most commonly used manufacturing method in cement plant, mainly includes three models: dry process rotary kiln production, suspension preheating kiln production, and pre-decomposition kiln production. Of these models, the clinker calcination can be divided into preheating and pre-calcining, clinker sintering, and clinker cooling three stages.
Clinker Production Processes & Necessary Machines
Step 1: preheating and pre-calcining
The preheating and pre-calcining of raw meal replace partial functions and shorten the length of the cement kiln. It improves cement production efficiency and reduces heat consumption.
In the cement production line, we usually set a preheater and a precalciner before the cement kiln. After raw meal enters the preheater, they will be heated to about 750℃ by the hot air blown from the kiln, and then enter the precalciner to mix with the fuel injected from outside so that the exothermic process of fuel combustion and the endothermic process of carbonate decomposition in the raw meal are carried out rapidly in a suspended state, so the decomposition rate of raw meal before entering the kiln can reach 90%. This kind of rotary kiln with preheater and precalciner is called a pre-decomposition kiln. If only preheater is set, we call it suspension preheating kiln.
The production process of preheating and pre-calcining makes the thermal layout of the calcination system more reasonable, improves the production efficiency and product quality, reduces the energy consumption, meanwhile, it also has more superior performance in many aspects such as environmental protection.
Cyclone preheater, also called suspension preheater, is the essential cement equipment in the preheating and pre-calcining process. Different from the stacked heat transfer mode in the rotary kiln, the material in preheater is in full contact with the hot air under a suspended state. Due to the large contact area, its heat transfer speed is fast and the heat exchange efficiency is high.
The five-stage cyclone preheater produced by AGICO merges preheater and precalciner into a single. It has a small space occupation and adopts the automatic control system to make the production process more convenient. For different areas and capacity needs, AGICO provides a custom-designed solution to your cement plant.
Step 2: clinker sintering
Clinker sintering is a crucial link in clinker calcination, which mainly occurs in the cement kiln. Inside the kiln, raw meals are heated by rising temperature and generate a series of physical and chemical reactions. When the temperature reaches its peak, the clinker will be produced by rapid cooling. These reactions can be expressed as follow：
The moisture content in the raw meal is evaporated with the temperature rising. When the temperature rises to 100-150 ℃, almost all the free moisture is removed. Especially in the wet method production, the water content of slurry can reach more than 30%, so the heat consumption of this drying process is very large.
When the temperature of the raw meal rises to 450 ℃, the kaolin will be removed all the chemical combined water. At 900-950℃, amorphous materials are transformed into crystals, and the heat will be released at the same time.
- Carbonate decomposition
Calcium carbonate and magnesium carbonate will decompose at 600 ℃. When the temperature reaches 750℃ and 900℃, they start to decompose rapidly.
- Solid-phase reaction
When the temperature reaches 800-1300 ℃, the main mineral in the cement clinker will be formed by the interaction of solid substances.
- Formation of tricalcium silicate
When the temperature increased to nearly 1300 ℃, a large number of solvents began to turn into liquid phase, and the tricalcium silicate starts to form.
- Clinker cooling
In the cooling process, some of the flux minerals transfer into crystals and the other part is in a glassy state. To prevent the clinker from becoming powdery, it needs to be rapidly cooled when the temperature lower than 500 ° C.
Cement kiln is the main equipment for clinker sintering. From structure, it can be divided into rotary cement kiln and shaft kiln, while, from the working principle, it can be divided into the dry method and wet method kiln.
AGICO offers different types of cement kilns from 10-5000t/d with steady running, high efficiency and large output. We adopt the most advanced calcination technology so that the production investment of clinker is small and the income is high.
Step 3: clinker cooling
Clinker cooling is the final step in clinker production. This process aims to recycle heat, preheat the secondary air, and improve the quality and grindability of the clinker. Besides, the rapid cooling of the clinker in this process is convenient for cement storage and transportation.
Clinker cooler is also called cement cooler, which set behind the cement kiln for clinker cooling. In cement plants, we usually adopt the rotary cooler and grate cooler for daily production. Inside the cooler, hot clinker will direct contact with the cooled air blown from the air blower to realize fast cooling.
AGICO provides different models of rotary coolers and grate coolers. They are all made of high-strength and high-temperature resistant alloy cast steel and has the advantages of high efficiency and long service life. For your different capacity needs and layout design, we can customize the equipment most suitable for you.
AGICO Cement is a cement plant equipment manufacturer committed to development and innovation. We can provide the production, transportation, installation and many other services of the equipment needed in the cement clinker production process. In addition, we also provide the construction of large cement plants. We are a trustworthy partner!