Engineering

Cement Manufacturing Process A Complete Guide

Written by Thalib Tantary

The production of cement is a complex and energy-intensive process. In the past decades, the industry has become more and more a high-tech industry. The raw materials for cement are extracted in the quarry. There, the material is loosened either by blasting or with heavy machinery and then transported with wheel loaders and heavy trucks to the crusher and crushed there to gravel.

The raw ballast is brought via conveyor belts or by cable and railways in the ballast hall of the cement plant. Here it is stored in a mixed bed silo and homogenized. After extraction, extraction, commutation and homogenization, the raw material is ground to raw meal, acidified and then burned in the rotary kiln at about 1,450 degrees to cement clinker, which is then cooled and ground. Details of the individual process steps are explained below:

1. RAW MATERIAL EXTRACTION AND PROCESSING

The main cement raw materials limestone, clay and their natural mixture Limestone marls are extracted in quarries mainly by blasting. Depending on the size of the plant, each amount of rock falls to 50,000 tons per blast. After transport, the coarse-grained rock is crushed in crushing plants to crushed stone of about 30 millimeters edge length.

An essential feature for the later cement quality is the constant composition of the raw material ready for the oven. Since the deposits can naturally have variations in the chemical composition, the raw ballast is usually homogenized. For this purpose, successively two or more mixed beds are piled up layer by layer according to different patterns. The heaps usually hold the gravel stock for a week; depending on the size of the factory, about 20,000 to 80,000 tons. Each finished heap is removed again across the layers, which homogenization degrees of about 70 to 90 percent can be achieved and variations in the occurrence are already largely offset.

The homogenized raw material is processed almost exclusively dry in Germany. For this purpose, the raw material is dried during commutation in a rolling or ball mill with hot gas, usually from the exhaust gas of the furnace system. Occasionally, correction components such as silica sand or iron ore are added to adjust the required chemical composition of the raw meal. Alternative raw materials can also be added to the raw mill in order to achieve optimal mixing with the other raw materials. Today, large roller mills grind up to 500 tons of raw meal per hour and have an energy requirement of about 10 to 16 kilowatt hours per ton (kWh / t) of raw meal. Remaining fluctuations in the raw meal are compensated in homogenizing silos.

2. BURNING THE CEMENT CLINKER

Cement clinker is produced in Germany almost exclusively by the dry process in rotary kilns with warm and possibly a calcine. These rotary kiln plants can be dimensioned smaller and compared to plants of the same power without calcine smaller and thus cost-effective to build and operate. The pre-calcination (deacidification) of the raw meal achieves uniform kiln operation, which is an important prerequisite for low fuel energy consumption while at the same time contributing to emission reduction in a process-integrated manner.

The cyclone preheats consist of four to six cyclone stages, which are arranged one above the other in towers 50 to 120 meters high. The different stages are flowed through from bottom to top of the exhaust gas of the rotary kiln. By contrast, the raw meal is introduced in the uppermost stage and passes through the cyclone preheated in the opposite direction to the exhaust gas flow and is heated to higher temperatures in each stage. The limestone contained in the raw meal is already partially acidified. The residual deacidification takes place in a calcine or in the calcining zone of the rotary kiln. Here, the emerging from the second lowest cyclone stage hot meal is untrained by understatement hot gas and fed into the calcine. This is a shaft in which furnace gas and fuel are introduced and mix intensively. The furnace exhaust gas is abruptly cooled from about 1100 ° C to 1200 ° C to the deacidification temperature of about 830 ° C. In order to maintain the endothermic deacidification reaction, fuels are added in the calcine whose heat input, depending on the kiln plant, can amount to up to 60 percent of the total fuel energy requirement. Compared to conventional systems, the degree of pre-deacidification of the raw meal by the calcine increases to more than 90 percent. As a result, the rotary kiln can be made smaller or operated at the same dimensions with higher power. Due to the temperature range of only 830 ° C to 950 ° C required for deacidification, this technology allows the flexible use of low-caloric, high-carbon fuels, such as ash-rich coals or certain alternative fuels. 200 ° C to the deacidification temperature of about 830 ° C cooled. In order to maintain the endothermic deacidification reaction, fuels are added in the calcine whose heat input, depending on the kiln plant, can amount to up to 60 percent of the total fuel energy requirement. Compared to conventional systems, the degree of pre-deacidification of the raw meal by the calcine increases to more than 90 percent. As a result, the rotary kiln can be made smaller or operated at the same dimensions with higher power. Due to the temperature range of only 830 ° C to 950 ° C required for deacidification, this technology allows the flexible use of low-caloric, high-carbon fuels, such as ash-rich coals or certain alternative fuels. 200 ° C to the deacidification temperature of about 830 ° C cooled. In order to maintain the endothermic deacidification reaction, fuels are added in the calcine whose heat input, depending on the kiln plant, can amount to up to 60 percent of the total fuel energy requirement. Compared to conventional systems, the degree of pre-deacidification of the raw meal by the calcine increases to more than 90 percent. As a result, the rotary kiln can be made smaller or operated at the same dimensions with higher power. Due to the temperature range of only 830 ° C to 950 ° C required for deacidification, this technology allows the flexible use of low-caloric, high-carbon fuels, such as ash-rich coals or certain alternative fuels. In order to maintain the endothermic de-acidification reaction, fuels are added in the calciner whose heat input, depending on the kiln plant, can amount to up to 60 percent of the total fuel energy requirement. Compared to conventional systems, the degree of pre-deacidification of the raw meal by the calcine increases to more than 90 percent. As a result, the rotary kiln can be made smaller or operated at the same dimensions with higher power. Due to the temperature range of only 830 ° C to 950 ° C required for de-acidification, this technology allows the flexible use of low-caloric, high-carbon fuels, such as ash-rich coals or certain alternative fuels. In order to maintain the endothermic deacidification reaction, fuels are added in the calcine whose heat input, depending on the kiln plant, can amount to up to 60 percent of the total fuel energy requirement. Compared to conventional systems, the degree of pre-deacidification of the raw meal by the calcine increases to more than 90 percent. As a result, the rotary kiln can be made smaller or operated at the same dimensions with higher power. Due to the temperature range of only 830 ° C to 950 ° C required for deacidification, this technology allows the flexible use of low-caloric, high-carbon fuels, such as ash-rich coals or certain alternative fuels. depending on the kiln plant, their heat input can amount to up to 60 percent of the total fuel energy requirement. Compared to conventional systems, the degree of pre-deacidification of the raw meal by the calcine increases to more than 90 percent. As a result, the rotary kiln can be made smaller or operated at the same dimensions with higher power. Due to the temperature range of only 830 ° C to 950 ° C required for deacidification, this technology allows the flexible use of low-caloric, high-carbon fuels, such as ash-rich coals or certain alternative fuels. depending on the kiln plant, their heat input can amount to up to 60 percent of the total fuel energy requirement. Compared to conventional systems, the degree of pre-deacidification of the raw meal by the calcine increases to more than 90 percent. As a result, the rotary kiln can be made smaller or operated at the same dimensions with higher power. Due to the temperature range of only 830 ° C to 950 ° C required for de-acidification, this technology allows the flexible use of low-caloric, high-carbon fuels, such as ash-rich coals or certain alternative fuels. As a result, the rotary kiln can be made smaller or operated at the same dimensions with higher power. Due to the temperature range of only 830 ° C to 950 ° C required for de-acidification, this technology allows the flexible use of low-caloric, high-carbon fuels, such as ash-rich coals or certain alternative fuels. As a result, the rotary kiln can be made smaller or operated at the same dimensions with higher power. Due to the temperature range of only 830 ° C to 950 ° C required for de-acidification, this technology allows the flexible use of low-caloric, high-carbon fuels, such as ash-rich coals or certain alternative fuels.

The material emerging from the lower cyclone stage of the pre-heater enters the rotary kiln of the kiln plant. Rotary ovens are slightly inclined, refractory lined tubes with diameters of up to 6 meters rotating at 1.3 to 3.5 revolutions per minute. By the rotation and the inclination of the kiln is moved from the kiln inlet in the direction of the burner installed at the kiln outlet. In the so-called splintering zone, the kiln reaches temperatures of about 1,450 ° C; the gas temperature is up to 2,000 ° C. The flow time of the material through the oven is about 20 to 40 minutes. The combustion air is supplied to the rotary kiln mainly as preheated air (secondary air) from the clinker cooler with temperatures of 600 ° C to 1,000 ° C. Only a share of 6 to 13 percent is injected directly through the burner (primary air). The kiln outlet is followed by a clinker cooler. In the frequently used grate coolers, the cement clinker moved on a transport grate is cooled with air. Most of the heated cooling air is used as combustion air in the furnace (secondary air) and in the calcine (tertiary air). The excess amount of air can be used in addition to the drying of the raw material or the fuels. After cooling, the clinker has a temperature of 80 ° C to 200 ° C. The excess amount of air can be used in addition to the drying of the raw material or the fuels. After cooling, the clinker has a temperature of 80 ° C to 200 ° C. The excess amount of air can be used in addition to the drying of the raw material or the fuels. After cooling, the clinker has a temperature of 80 ° C to 200 ° C.

3. REACTIONS WHEN BURNING AND COOLING

During the firing process, various chemical reactions take place in the kiln – partly successively, partly parallel to one another. When heating the fuel escapes first at temperatures up to 200 ° C, the liquid water. Between 100 ° C and 400 ° C, the clay minerals release their absorptively bound water. At higher temperatures between about 400 ° C and 750 ° C, the clay minerals are decomposed and the chemically bound water expelled. The decomposition of the calcium carbonate contained in the raw meal into CaO and CO 2 , the deacidification of the limestone, begins in the presence of SiO 2 , Al 23 and Fe 2 O 3 already at 550 ° C to 600 ° C and runs above 900 ° C. very fast.

These endothermic reactions are counteracted by new formation reactions, some of which are exothermic and parallel to the dissociation processes. This produces di-calcium silicate (C 2 S) from calcium oxide and silicon dioxide as well as various Al 2 O 3 – and Fe 23 -containing intermediate compounds, which, however, decay again at about 1280 ° C. with the onset of melt formation. In the presence of the melt whose proportion in the kiln at the sintering temperature of 1450 ° C is about 15 to 25 mass percent and in which the predominant portion of the aluminum and iron oxide originally contained in the raw materials, calcium oxide reacts with the dicalcium silicate to form tricalcium silicate ( C 3S). During the subsequent cooling of the clinker, crystallization of the melt results in tricalcium aluminate (C 3 A) and calcium aluminate ferrite C 4 AF. The energy required for the clinker burning process is more than 50 percent needed for drying and heating the raw material, the dissociation of the calcium carbonate and to cover the heat losses.

The cooling rate significantly influences the properties of the clinker. Fine-grained and C 4 AF -grown C 3 A reacts more slowly with water than coarsely crystalline C 3 A, which is formed at low cooling rates. In order for the tri-calcium aluminate and the calcium aluminate ferrite to crystallize as fine-grained as possible, it is necessary to cool the clinker from splintering temperature to 1,200 ° C. with sufficient rapidity. In general, rapid cooling of the clinker in the high-temperature range reduces the water requirement of the cement. With sulfate-optimized cement, the faster cooling is all the more advantageous for the solidification behavior and the strength development of the cement, the higher the C 3 S and C 3A content of the clinker is.

4. GRINDING, MIXING AND TRANSPORT

After firing and cooling, the clinker is stored in silos or closed halls in order to avoid emissions of clinker dust as much as possible. The clinker grains have grain sizes of up to 50 millimeters. For the production of cement, the clinker is finely ground alone or with other main components – for example, granulated blast furnace or fly ash. In this case, a sulfate carrier is added to the mill base to control the solidification. For this one uses gypsum or an hydrite from natural occurrences; To protect natural resources but also gypsum from flue gas desulfurization is used.

For more than 100 years, ball mills have been used to grind cement raw materials and cement. They are characterized by high availability and robustness. The mills are built with a pipe diameter of up to 6 meters and a pipe length of up to 20 meters. They are filled with grinding balls with up to 30 percent and achieve throughput rates of up to 200 tons per hour. The material to be ground is comminuted by the rotational movement of the tube and the resulting rolling and falling movement of the grinding balls. In comparison with other mill types, ball mills have the lowest grinding efficiency. For this reason, the more efficient high-pressure roller mills and vertical roller mills are used today for cement grinding.

5. Storage of Packing

The finally ground cement is stored in cement silos from which it is packed of 50kg in each bag.

About the author

Thalib Tantary

My name is Thalib Mushtaq Tantary and i am the founder of this very site. I am a medical or civil engineering student and i love to help people get out of trouble they counter in their lives.
Since most often students find it difficult to understand their text books or even there many who can not afford such books, therefore we prepared ourselves to solve this problem faced by them.

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