Cement manufacturing process, advantages of traditional technology

Put a picture first, then look at the text, it will be clearer.

Cement production process:

1, pulverizing and pre-homogenizing

(1) In the process of producing crushed cement, most raw materials are crushed, such as limestone, clay, iron ore and coal. Limestone is the most used raw material in cement production. After mining, the particle size is large and the hardness is high, so the crushing of limestone plays an important role in the crushing of materials in cement plants.

(2) Pre-homogenization of raw materials Pre-homogenization technology is to realize the initial homogenization of raw materials by using scientific stacking technology in the process of raw material storage and retrieval, so that the raw material storage yard has both storage and homogenization functions.

2, raw meal preparation

In the process of cement slurry production, for every 65,438+0 tons of portland cement produced, at least 3 tons of materials (including various raw materials, fuels, clinker, mixtures and gypsum) are ground. According to statistics, the grinding operation of dry cement production line consumes more than 60% of the power of the whole plant, of which raw meal grinding accounts for more than 30%, pulverized coal grinding accounts for about 3%, and cement grinding accounts for about 40%. Therefore, it is of great significance to reasonably select grinding equipment and process flow, optimize process parameters and correctly operate and control the operating system to ensure product quality and reduce energy consumption.

3, raw meal homogenization

In the process of new dry cement production, stabilizing the composition of into the pit raw meal is the premise of stabilizing the thermal system of clinker burning, and the raw meal homogenization system plays the final role in stabilizing the composition of into the pit raw meal.

4, preheating decomposition

The preheating and partial decomposition of raw materials are completed by the preheater, which replaces some functions of the rotary kiln, thus shortening the time of returning to the kiln. At the same time, the heat exchange process of gas and material in the kiln is carried out in a stacked state and moved to the preheater in a suspended state, so that the raw materials are fully mixed with the hot gas discharged outside the kiln, the contact area between the gas and the material is increased, the heat transfer speed is high, and the heat exchange efficiency is high, thus achieving the purposes of improving the production efficiency of the kiln system and reducing the heat consumption of clinker burning.

(1) material dispersion

80% of the heat exchange is carried out in the inlet pipe. Under the impact of high-speed updraft, the raw meal entering the preheater pipeline turns upward and moves with the airflow, and is dispersed at the same time.

(2) gas-solid separation

When the airflow carries the powder into the cyclone cylinder, it is forced to rotate in the annular space between the cyclone cylinder and the inner cylinder (exhaust pipe), and moves downward while rotating, from the cylinder to the cone, to the cone end, and then turns upward and is discharged from the exhaust pipe.

(3) Pre-decomposition

The emergence of pre-decomposition technology is a technological leap in cement calcination process. A precalciner is added between the preheater and the rotary kiln, a flue rising at the kiln tail is used, and a fuel injection device is installed, so that the exothermic process of fuel combustion and the endothermic process of raw meal decomposition can be carried out rapidly in the precalciner in a suspended state or a fluidized state, and the decomposition rate of raw meal entering the kiln can be improved to over 90%. The carbonate decomposition task originally carried out in the rotary kiln was transferred to the decomposing furnace; Most of the fuel is added from the calciner and a small part is added from the kiln head, which reduces the heat load of the calcining zone in the kiln, prolongs the service life of the furnace lining and is beneficial to large-scale production; Because the fuel is evenly mixed with the raw meal, 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 properties and characteristics such as high quality, high efficiency and low consumption.

5. Combustion of cement clinker

After the raw meal is preheated and pre-decomposed in the cyclone preheater, the next process is to enter the rotary kiln for clinker sintering.

In the rotary kiln, carbonate is further rapidly decomposed and a series of solid-state reactions occur to produce minerals such as cement clinker. As the material temperature rises, etc. Minerals will become liquid phase, and those dissolved in the liquid phase will react to produce a large number of clinker. After the clinker is fired, the temperature begins to drop. Finally, the cement clinker cooler cools the high-temperature clinker discharged from the rotary kiln to the temperature that the downstream transportation, storage and cement grinding can bear, and at the same time recovers the sensible heat of the high-temperature clinker, thus improving the thermal efficiency and clinker quality of the system.

6, cement grinding

Cement grinding is the last process of cement manufacturing, and it also consumes the most electricity. Its main function is to grind cement clinker (and cementing agent, performance adjusting material, etc.). ) to a suitable particle size (expressed by fineness and specific surface area, etc.). ), form a certain particle gradation, increase its hydration area, accelerate the hydration speed, and meet the requirements of setting and hardening of cement paste.

7, cement packaging

Cement can be transported in bags and in bulk.

Cement production technology

manufacturing method

The production technology of portland cement is representative in cement production. Limestone and clay are used as the main raw materials, which are crushed, mixed and ground into raw materials, and then sent to a cement kiln to calcine the mature materials, and then the clinker is ground with a proper amount of gypsum (sometimes a mixture or additive).

Cement production can be divided into dry method (including semi-dry method) and wet method (including semi-wet method) according to different preparation methods of raw materials.

① Dry production. A method of drying and grinding raw materials at the same time, or a method of drying and grinding them into raw meal powder and then sending them into a dry kiln to calcine mature materials. However, there is also a method that raw meal balls are made by adding proper amount of water into raw meal powder and sent to Lipper kiln to calcine mature materials. This method is called semi-dry method and is still one of the dry production methods.

② Wet production. A method of grinding raw materials into raw slurry with water and sending them into a wet kiln to calcine mature materials. Another method is to dehydrate the raw slurry prepared by wet method, make it into raw material blocks, and put it into a kiln for calcination, which is called semi-wet method and still belongs to one of wet production.

The main advantage of dry production is low heat consumption (for example, the heat consumption of dry kiln clinker with preheater is 3 140 ~ 3768 coke /kg), but the disadvantages are uneven raw material composition, large dust in the workshop and high power consumption. Wet production has the advantages of simple operation, easy control of raw material composition, good product quality, convenient slurry transportation and less dust in the workshop, but the disadvantage is high heat consumption (clinker heat consumption is usually 5234 ~ 6490 coke /kg).

production process

Cement production can generally be divided into three processes: raw material preparation, clinker calcination and cement production.

(1) raw meal grinding

There are two kinds: dry method and wet method. Dry method generally adopts closed-circuit operation system, that is, raw materials are finely ground by a mill, then separated by a classifier, and coarse powder is returned to the mill for grinding, and most of them adopt the process of drying and grinding materials in the mill at the same time. The equipment used includes tube mill, intermediate discharge mill and roller mill. Wet process usually adopts open-circuit systems such as tube mill and rod ball mill, which pass through the mill once without reflux, but there are also closed-circuit systems with classifier or arc screen.

(2) calcination

There are mainly two kinds of equipment for calcining clinker: vertical kiln and rotary kiln. Vertical kilns are suitable for small factories, and rotary kilns are suitable for large and medium-sized factories.

(1) shaft kiln:

Kilns that do not rotate vertically are called vertical kilns. Divided into ordinary shaft kiln and mechanized shaft kiln. Ordinary vertical kiln is manual feeding and manual unloading or mechanical feeding and manual unloading; Mechanical vertical kiln is mechanical feeding and mechanical unloading. The output, quality and labor productivity of mechanical shaft kiln are higher than those of ordinary shaft kiln. In recent years, most foreign vertical kilns have been replaced by rotary kilns, but in China's current cement industry, vertical kilns still occupy an important position. According to the technical policy requirements of building materials, small cement plants gradually replace ordinary vertical kilns with mechanized vertical kilns.

② Rotary kiln:

The kiln barrel is horizontal (slightly inclined, about 3%) and can make rotary motion, which is called rotary kiln. It can be divided into dry kiln for calcining raw meal powder and wet kiln for calcining slurry (water content is usually around 35%).

A. heating the drying chamber

Dry kiln can be divided into hollow kiln, waste heat boiler kiln, suspended preheater kiln and suspended decomposition kiln. Around 1970s, a kind of calcination technology-out-of-kiln decomposition technology was developed, which can greatly increase the output of rotary kiln. Characterized in that a precalciner kiln is adopted, and a precalciner furnace is added between the preheater and the kiln on the basis of hanging the preheater kiln. Fuel accounting for 50-60% of the total fuel consumption is added into the calciner, so that the fuel combustion process, preheating of raw materials and carbonate decomposition process are moved from the area with low heat transfer efficiency in the kiln to the calciner, and the raw materials exchange heat with hot air in the suspended state or boiling state, which improves the heat transfer efficiency, makes the decomposition rate of calcium carbonate reach over 80% before the raw materials enter the kiln, reduces the heat load of the kiln, prolongs the service life of kiln lining and the operation cycle of the kiln, and maintains the heat transfer efficiency.

B. wet kiln

The cement kiln used in wet production is called wet kiln, and wet production is to make raw materials into slurry with water content of 32%~40%. Due to the preparation of slurry with fluidity, the raw materials are evenly mixed, the composition of raw materials is uniform and the quality of sintered clinker is high, which is the main advantage of wet production.

Wet kiln can be divided into long wet kiln and short wet kiln with slurry evaporator. Long kilns are widely used, while short kilns are rarely used at present. In order to reduce the heat consumption of wet long kiln, various types of heat exchangers are installed in the kiln, such as chain type, slurry filtration preheater, metal or ceramic heat exchanger, etc.

(3) grinding

The fine grinding of cement clinker usually adopts circulating grinding process (that is, closed-circuit operating system). In order to prevent dust flying in production, cement plants are equipped with dust removal equipment. Dust collectors commonly used in cement plants include electrostatic precipitator, bag dust collector and cyclone dust collector.

In recent years, due to the adoption of new technologies and equipment in raw material pre-homogenization, raw meal powder homogenization and dust collection, especially the appearance of decomposition technology outside the kiln, a new dry production process has emerged. Using this new process, the quality of clinker produced by dry method is no less than that of wet method, and the power consumption is also reduced, which has become the development trend of cement industry in various countries.

Example of production process

After the raw materials and fuel enter the factory, they are sampled, analyzed and tested by the laboratory, homogenized according to quality and stored in the raw material shed. Clay, coal and pyrite powder are dried by the dryer to the process index value, and lifted to the corresponding raw material warehouse by the hoist. After two-stage crushing, limestone, fluorite and gypsum are sent to their respective warehouses by hoists. According to the quality of limestone, clay, anthracite, fluorite and pyrite powder, the laboratory calculates the process formula. Raw meal is mixed with black raw meal through microcomputer batching system and ground by raw meal mill. Sampling and testing the percentage content of calcium oxide and iron oxide and the fineness of raw meal every hour, and adjusting them in time to make all the data meet the requirements of process formula. The ground black raw meal is lifted to the raw meal bin by the bucket elevator. According to the quality of raw meal after grinding, the laboratory homogenized the raw meal through multi-bin proportioning and mechanical dumping, and then lifted it to two raw meal homogenizing bins by elevator. The raw meal is lifted to the pelletizing bin by the cooperation of two homogenization bins. The pre-added water pelletizing control device installed on the kiln surface of the vertical kiln is used for the proportion of raw meal and water, and the raw meal is pelletized through the pelletizing tray. The raw meal balls are distributed to different positions in the kiln by the vertical kiln distributor for calcination, and the calcined clinker is sent to the clinker crusher through the discharge pipe and the weighing machine for crushing, and the laboratory samples every hour for chemical and physical analysis. According to the quality of clinker, it is put into the corresponding clinker warehouse by the hoist. At the same time, according to the requirements of production and operation and the building materials market, the laboratory mixes clinker, gypsum and slag with cement through the clinker microcomputer batching system, and the cement mill grinds 425 and 525 ordinary portland cement respectively, and samples are taken every hour for analysis and inspection. The ground cement is lifted by bucket elevator to three cement warehouses. According to the quality of grinding cement, the laboratory adopts the way of multi-storehouse collocation and mechanical dumping to homogenize cement. It is sent to two cement homogenizing bins by a hoist and then matched with the two cement homogenizing bins. The packaging machine is controlled by microcomputer to package cement, and the packaged bagged cement is stored in the finished product warehouse. After the test and sampling inspection are qualified, the cement factory notice will be issued.