Use of cement

Production process:

The production process of silicate cement is representative in cement production, which is made of limestone and clay as the main raw materials, broken, proportioned, and ground into raw materials, and then fed into the cement kiln to calcined mature materials, and then the clinker with an appropriate amount of gypsum (and sometimes mixed materials or admixtures).

Cement production can be divided into dry method (including semi-dry method) and wet method (including semi-wet method) with different raw material preparation methods.

① Dry production. The method of drying and grinding raw materials at the same time, or first drying and grinding into raw powder and then feeding into a dry kiln to calcinate the mature material. However, there is also a method of adding raw powder to an appropriate amount of water to make raw ball and sending it into the Lipol kiln to calcinate the mature material, which is called semi-dry method and still belongs to one of the dry production methods.

New dry process cement

The new dry cement production line refers to the cement produced by the new process of decomposition outside the kiln. Its production to suspension preheater and kiln decomposition technology as the core, the use of new raw materials, fuel homogenization and energy-saving grinding technology and equipment, the whole line uses computer distributed control, to achieve the cement production process automation and high efficiency, high quality, low consumption, environmental protection.

The new dry process cement production technology was developed in the 1950s, Japan, Germany and other developed countries, with suspension preheating and pre-decomposition as the core of the new dry process cement clinker production equipment accounted for 95%, China's first set of suspension preheating and pre-decomposition kiln put into operation in 1976. The advantages of this technology are: rapid heat transfer, high thermal efficiency, larger output per unit volume than wet cement, and low heat consumption.

② Wet production. The method of grinding raw material with gouache into raw pulp and feeding it into wet kiln for calcining mature material. There is also a method of dewatering the raw slurry prepared by the wet method and making the raw material block into the kiln to calcinate the mature material, which is called the semi-wet method, which is still one of the wet production.

The main advantage of dry production is low heat consumption (such as the heat consumption of dry kiln clinker with preheater is 3140 ~ 3768 coke/kg), the disadvantage is that the raw material composition is not easy to uniform, the workshop dust, high power consumption. Wet production has the advantages of simple operation, easy control of raw material composition, good product quality, convenient slurry transport, less workshop dust, etc. The disadvantage is high heat consumption (clinker heat consumption is usually 5234 ~ 6490 coke/kg).

The production of cement can generally be divided into three processes, such as raw material preparation, clinker calcination and cement production, and the entire production process can be summarized as "two grinding and one burning".

Raw material grinding

There are dry and wet methods. Dry method generally adopts closed-circuit operating system, that is, after the raw material is refined by the mill, it enters the separator for sorting, and the coarse powder flows back into the mill and then grinds, and most of the materials are dried and grinned in the mill at the same time, the equipment used is tube grinding, middle discharge grinding and roll grinding. The wet method usually uses open circuit systems such as tube grinding and baseball grinding that no longer flow through the mill at one time, but there are also closed circuit systems with graders or curved screens.

Cement History:

In 1756, the British engineer J. Smeaton found that in order to obtain hydraulic lime, limestone containing clay must be fired; The ideal composition of masonry mortar for underwater construction is a combination of hydraulic lime and volcanic ash. This important discovery laid a theoretical foundation for the research and development of modern cement.

In 1796, the British J. Parker made a kind of cement with marl firing, brown in appearance, much like the lime and volcanic ash mixture of ancient Rome, named Roman cement. Because it is made of natural marl as raw material and is fired directly without ingredients, it is also known as natural cement. With good hydraulic and fast setting characteristics, especially suitable for projects in contact with water.

In 1813, French civil engineer Biggar discovered that the cement made by mixing lime and clay by a ratio of three to one has the best performance.

In 1824, English construction worker Joseph Aspdin invented cement and patented Portland cement. He used limestone and clay as raw materials, after a certain proportion of the combination, in a shaft kiln similar to the burning of lime calcined mature materials, and then ground fine to make cement. It was named Portland cement because the color of the hardened cement was similar to the stone used for construction in Portland, England. It has excellent construction performance and has epoch-making significance in the history of cement.