Cement Manufacturing Process

Author : SBM Time: Oct 15, 2021 Concurrent Readers:

Summary: In brief, cement production has the following 7 steps: crushing and pre-homogenization, raw meal preparation, homogenization of raw meal, preheating decomposition, firing of cement clinker, cement grinding and cement package....

Cement is a powdery hydraulic inorganic cementing material. After adding water and stirring, it becomes slurry, which can harden in the air or in water, and can firmly bond sand, stone and other materials together.

Cement is an important material to make concrete and has wide application in civil engineering, water conservancy, national defense and other projects.

Raw materials for producing cement

The main raw material for producing cement is lime.

Raw materials for cement production mainly include limestone (the main source of CaO), clay raw materials (supplying SiO₂, Al₂O₃ and a small amount of Fe₂O₃), corrective raw materials (for supplementing insufficient components), and auxiliary raw materials such as mineralizers, fluxes and grinding aids.

Generally speaking, limestone accounts for 80% of the raw materials for cement manufacturing, which is the main material for cement manufacturing.

Classification of cement

According to application and performance, cement can be divided into:

(1) General cement: Ordinary cement is commonly used in general civil engineering. General cement mainly refers to the six major types of cement specified in GB 175-2007, namely Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement and composite Portland cement.

(2) Special cement: Cements with special properties or special purposes include G-grade oil well cement, rapid-hardening Portland cement, road Portland cement, aluminate cement and sulphoaluminate cement.

What is the manufacturing process of cement?

As one of the most commonly used raw materials, cement plays an important role in the construction of projects, civil industry, transportation and other industries. In the cement production process, do we need crushing and grinding equipment? Are they important?

In brief, cement production has the following 7 steps: crushing and pre-homogenization, raw meal preparation, homogenization of raw meal, preheating decomposition, firing of cement clinker, cement grinding and cement package.

cement manufacturing process

1. Crushing and pre-homogenization

(1) Crushing.

In cement production process, most of the raw materials need to be crushed, such as limestone, clay, iron ore and coal. Limestone is the largest-consumption raw material for cement production. After mining, limestone has large particle size and high hardness. Therefore, the crushing of limestone occupies a relatively important position in the material crushing of cement production.

Pre-homogenization of raw materials. The pre-homogenization technology is to use scientific stacking and reclaiming technology to realize the preliminary homogenization of the raw materials during the storage and retrieval process of the raw materials, so that the raw material storage yard has the functions of storage and homogenization at the same time.

Advantages of pre-homogenization:

1) Homogenize the raw material composition to reduce quality fluctuations to facilitate the production of higher quality clinker and stabilize the production of the firing system.

2) Expand the utilization of mineral resources, improve mining efficiency, fully exploit overburden and interlayer resources, and reduce or eliminate waste rock discharge during mining.

3) The quality requirements for mining can be relaxed, and the mining cost of the mine can be reduced.

4) Strong adaptability to sticky and wet materials.

5) Provide long-term stable raw materials for the factory, and can also batch raw materials of different components in the yard, making it a pre-batch yard, creating conditions for stable production and improving equipment operation rate.

6) High degree of automation.

2. Raw meal preparation

In the cement production process, to produce every 1 ton of Portland cement, we need to grind at least 3 tons of materials (including various raw materials, fuels, clinkers, mixtures, and gypsum). According to statistics, the power consumed by grinding operations in dry-process cement production lines accounts for over 60% of the total power consumption of the entire plant. Among this proportion, raw meal grinding accounts for more than 30%, coal grinding about 3%, and cement grinding around 40%. Therefore, reasonable selection of grinding equipment and process flow, optimization of process parameters, correct operation, and control of the operating system are of great significance for ensuring product quality and reducing energy consumption.

3. Homogenization of raw meal

In the new dry-process cement production, stabilizing the composition of kiln feed raw meal is the prerequisite for maintaining a stable thermal system during clinker firing. The raw meal homogenization system acts as the final control link to stabilize kiln feed quality.

4. Preheating decomposition

The preheater completes the preheating and partial decomposition of raw meal, replacing part of the functions of the rotary kiln. This shortens the kiln length and transfers the gas‑solid heat exchange process from the accumulation state inside the rotary kiln to the suspended state in the preheater. In this way, raw meal is fully mixed with high‑temperature flue gas discharged from the kiln, which greatly increases the gas‑solid contact area, accelerates heat transfer, and improves heat exchange efficiency. Ultimately, the production capacity of the kiln system is enhanced, and the heat consumption of clinker calcination is reduced.

5. Firing of cement clinker

After the raw meal is preheated and pre-decomposed in the cyclone preheater, the next step is to enter the rotary kiln for clinker firing. In the rotary kiln, the carbonate is further rapidly decomposed and a series of solid phase reactions occur to generate minerals in the cement clinker. As the material temperature increases, mineral components enter the liquid phase, and abundant clinker is formed through chemical reactions. 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 a temperature suitable for downstream transportation, storage and cement grinding. Meanwhile, it recovers the sensible heat of high-temperature clinker, improving the overall thermal efficiency of the system and clinker quality.

rotary kiln

cooler

6. Cement grinding

Cement grinding is the last process in cement manufacturing and the process that consumes the most electricity. Its main function is to grind cement clinker (gelling agent, performance adjustment material, etc.) to a suitable particle size (expressed in fineness, specific surface area, etc.) to form a certain particle gradation, increase its hydration area, and accelerate hydration speed, to meet the requirements of cement slurry condensation, hardening.