Cement, Coal and Minerals Resource Library
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The cement production process
The cement production process begins with the extraction of limestone and clay from the quarry. The material is then blended, crushed and fed to the kiln. Post-kiln, the clinker is cooled and goes through a final grinding method before it is ready to ship. Portland cement, the most common type of cement, is formulated in a variety of strengths and colors, depending on its intended use. Cement composition is based upon their customer’s requests, each requiring a different elemental chemistry in recipe.
Here are the five stages of cement production and the steps to maintain consistent raw material quality with minimal chemistry deviation, from quarry to silo to customer.
The first step in the cement process is to extract limestone and clay from the earth. The key elemental components for cement are Ca, Al, Fe and Si. However, sometimes unwanted elements such as MgO, and alkalis such as Na, K, and sulfur, exist within the limestone, clay and sandstone that are adverse to the process and reduce the mineability of the quarry. In these cases, online elemental analyzers using PGNAA technology allow the end user to monitor MgO levels in the limestone and adjust accordingly.
Belt scales help to measure the amount of materials that is being mined, and tramp metal detectors can help find any unwanted metals in the raw material, which is extremely important for safety and the protection of the conveyor belt. In addition, handheld XRF analyzers can quickly measure areas in the quarry and any samples that may be taken.
| Extraction of Raw Materials | Desired elements include |
| • Limestone | • CaO |
| • Clay | • Al2O3 |
| • Fe2O3 | |
| • SiO2 |
After the material is extracted from the earth, it is crushed to reduce the particle sizes. The materials are stocked into a special pile and blended to reduce the variability in cement composition. The proportions of this raw material blend are dependent upon the elemental composition of the limestone and raw materials that are available within the quarry. The material is then reclaimed from a rake, then fed onto a conveyor that transports the material to another control point called the raw mix proportioning area.
Additional raw materials, often referred to as “additives,” are needed to supplement the limestone and clay. Generally these additives are sand and iron ore, but other types of raw materials are used as well, such as marl, shale and fly ash. Cement composition will vary from plant to plant depending on the quality of the limestone in that specific quarry and the availability of additives in that area. These additives, along with the limestone, are fed from bins to the raw mill. An extremely important step in the cement process is to proportionally feed these materials to the raw mill to ensure the correct “blend” of these materials. One can think of this process as a “recipe” for making various types of cement. Generally, cement customers are looking to control Lime Saturation Factor (LSF), Silica Modulus (SM) and Iron Modulus (IM). The raw materials, now known as kiln feed, enter a raw mill that consists of a drying chamber and a grinding chamber. The heat required for this process comes from recirculating heat from the kiln and also from the clinker cooler.
The kiln feed is then fed into a rotary kiln, a large chemical reaction chamber with temperature reaching approximately 1400 degrees C. This forms the clinker components C3A, C4AF, C2S, and C3S. The heat source can be either coal, natural gas, and/or biofuels. In addition, the consistency of the mix is extremely important because a consistent blend not only makes for better clinker, but also has profound effects on the kiln as it requires less energy from the kiln and also extends the life of the refractory bricks that line the inside of the kiln.
Coal is still used in approximately 90% of cement plants globally to deliver the energy needed for the heat inside the kiln. Online coal analyzers using PGNAA technology are used to control the coal blend to a specific GCV in addition to the ash value of the coal as this adds raw materials to the process as well. This allows cement producers to “mix” low cost coals with higher costs coals to provide additional cost savings in fuel and to allow a consistent feed to the kiln. Additionally, belt scales and tramp metal detectors provide value in production and safety.
While the cement production process before the kiln is focused on the elemental make-up and proportions of the raw materials, after the clinker is produced, the focus shifts to the molecules these elements form. As an example, Iron (Fe) is present in the raw mix and is required in a certain proportion in the raw mix, but the same iron in clinker can be present as Fe2O3, FeO or Fe3O4, the concentration of each of which plays an important role in the physical characteristics of cement such as color and strength.
The cement analysis procedure can be achieved using XRF analyzers, while the phases are identified using the XRD platform. The final stage is to grind the cooled clinker into a fine particle and add gypsum to control the setting time of the cement. Mineralogy is important at this stage as well and is measured in the lab by XRD technology.
The first step in the cement process is to extract limestone and clay from the earth. The key elemental components for cement are Ca, Al, Fe and Si. However, sometimes unwanted elements such as MgO, and alkalis such as Na, K, and sulfur, exist within the limestone, clay and sandstone that are adverse to the process and reduce the mineability of the quarry. In these cases, online elemental analyzers using PGNAA technology allow the end user to monitor MgO levels in the limestone and adjust accordingly.
Belt scales help to measure the amount of materials that is being mined, and tramp metal detectors can help find any unwanted metals in the raw material, which is extremely important for safety and the protection of the conveyor belt. In addition, handheld XRF analyzers can quickly measure areas in the quarry and any samples that may be taken.
| Extraction of Raw Materials | Desired elements include |
| • Limestone | • CaO |
| • Clay | • Al2O3 |
| • Fe2O3 | |
| • SiO2 |
After the material is extracted from the earth, it is crushed to reduce the particle sizes. The materials are stocked into a special pile and blended to reduce the variability in cement composition. The proportions of this raw material blend are dependent upon the elemental composition of the limestone and raw materials that are available within the quarry. The material is then reclaimed from a rake, then fed onto a conveyor that transports the material to another control point called the raw mix proportioning area.
Additional raw materials, often referred to as “additives,” are needed to supplement the limestone and clay. Generally these additives are sand and iron ore, but other types of raw materials are used as well, such as marl, shale and fly ash. Cement composition will vary from plant to plant depending on the quality of the limestone in that specific quarry and the availability of additives in that area. These additives, along with the limestone, are fed from bins to the raw mill. An extremely important step in the cement process is to proportionally feed these materials to the raw mill to ensure the correct “blend” of these materials. One can think of this process as a “recipe” for making various types of cement. Generally, cement customers are looking to control Lime Saturation Factor (LSF), Silica Modulus (SM) and Iron Modulus (IM). The raw materials, now known as kiln feed, enter a raw mill that consists of a drying chamber and a grinding chamber. The heat required for this process comes from recirculating heat from the kiln and also from the clinker cooler.
The kiln feed is then fed into a rotary kiln, a large chemical reaction chamber with temperature reaching approximately 1400 degrees C. This forms the clinker components C3A, C4AF, C2S, and C3S. The heat source can be either coal, natural gas, and/or biofuels. In addition, the consistency of the mix is extremely important because a consistent blend not only makes for better clinker, but also has profound effects on the kiln as it requires less energy from the kiln and also extends the life of the refractory bricks that line the inside of the kiln.
Coal is still used in approximately 90% of cement plants globally to deliver the energy needed for the heat inside the kiln. Online coal analyzers using PGNAA technology are used to control the coal blend to a specific GCV in addition to the ash value of the coal as this adds raw materials to the process as well. This allows cement producers to “mix” low cost coals with higher costs coals to provide additional cost savings in fuel and to allow a consistent feed to the kiln. Additionally, belt scales and tramp metal detectors provide value in production and safety.
While the cement production process before the kiln is focused on the elemental make-up and proportions of the raw materials, after the clinker is produced, the focus shifts to the molecules these elements form. As an example, Iron (Fe) is present in the raw mix and is required in a certain proportion in the raw mix, but the same iron in clinker can be present as Fe2O3, FeO or Fe3O4, the concentration of each of which plays an important role in the physical characteristics of cement such as color and strength.
The cement analysis procedure can be achieved using XRF analyzers, while the phases are identified using the XRD platform. The final stage is to grind the cooled clinker into a fine particle and add gypsum to control the setting time of the cement. Mineralogy is important at this stage as well and is measured in the lab by XRD technology.
From the coal mill to raw materials storage or the cement mill – learn more how Thermo Scientific bulk material handling equipment and PGNAA/PFTNA analyzers help optimizing the Cement manufacturing process. Learn more how we help you optimize your cement operation.
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Learn everything you need to know to improve product quality, boost efficiency, lower productions costs, and create safer, cleaner cement production lines. Download the free eBook, A Practical Guide to Improving Cement Manufacturing Processes and Production.
Online elemental analyzers based on PGNAA or PFTNA technology can help help cement, coal, and steel producers achieve consistent raw material quality, boost efficiency, and lower productions costs.
To learn more about how PGNAA and PFTNA technology works, download our free eBook, A Guide to PGNAA and PFTNA Technology for Non-Scientists.
Visit the Advancing Mining blog for news and information about the latest topics in cement manufacturing and production. Learn about technologies and equipment used in the cement process including elemental online analyzers, x-ray analyzers, belt scales, weigh belt feeders, level sensors and indicators, impact weighers, stack emission gas detectors, and material storage tracking software.
Ensure complete regulatory compliance
Cement manufacturing is the source of 5% of global CO2 emissions. 60% of emissions are due to the transformation of raw materials at high temperatures and 40% results from the combustion required to heat the cement kilns to 1500°C. Therefore emissions monitoring is extremely critical for cement plants to meet regulatory requirements. There are even provinces in China that are only allowing cement plants to operate 9 months out of the year to curb some of the unwanted emissions. Continuous Emissions monitoring systems are critical for cement plants to monitor harmful emissions such as CO2, Nox, SOx and Hg as well as other particulate matters.
Types of Portland Cement
- Type I - For use when the special properties specified for any other type are not required.
- Type IA - Air-entraining cement for the same uses as Type I, where air-entrainment is desired.
- Type II - For general use, more especially when moderate sulfate resistance is desired.
- Type IIA - Air-entraining cement for the same uses as Type II, where air-entrainment is desired.
- Type II(MH) - For general use, more especially when moderate heat of hydration and moderate sulfate resistance are desired.
- Type II(MH)A - Air-entraining cement for the same uses as Type II(MH), where air-entrainment is desired.
- Type III - For use when high early strength is desired.
- Type IIIA - Air-entraining cement for the same use as Type III, where air-entrainment is desired.
- Type IV - For use when a low heat of hydration is desired.
- Type V - For use when high sulfate resistance is desired.
