Top 4 Upgrading Tips For Limestone Crushing Plant In Lime Preparation

There are many aspects to consider for using lime kiln (rotary and vertical) to calcine active lime, in which the limestone selection is the key to obtaining qualified quick lime product in the limestone preparation process. To Make it easy to understand, AGICO has summed up 4 essential tips to improve lime material purity in limestone crushing plant. The second is the calcination equipment and calcination method according to limestone conditions.

4 Tips in Limestone Preparation Process

1.Limestone Types – Raw Material Selection

Chalk Coquina, Travertine, Fossiliferous Limestone, Oolitic Limestone, Tufa, Lithographic Limestone, Crystalline Limestone

Limestone Types

In quicklime production, the raw materials used to produce active lime are mainly carbonate rocks, which is what we usually call limestone. There are many types of limestone, the most common types are: granular crystalline limestone, dense limestone, porous limestone, earthy limestone, marly limestone, chalk, dolomite, shell-limestone river pebbles, etc.

Limestone Physical and Chemical Indicators - Limestone Purity Requirement

Among the main chemical components of active lime, CaO content is required to be high, generally reaching more than 90%. At the same time, the content of impurities such as S (sulfur) and P (phosphorus) is required to be as low as possible. Therefore, there are specific requirements for the limestone.

In the selection of limestones, the CaO content shall at least be greater than 54%, and low impurity content, such as SiO2 (silicon dioxide), S (sulfur), P (phosphorus), MgO (magnesium oxide), Fe2O3 (ferric oxide), Al2O3 (aluminum oxide) is often used as the raw material for calcining active lime.

To meet the requirements of the properties of quicklime products, the main raw materials for producing metallurgical lime or active lime have long been dense limestone or called ordinary limestone. The dense limestone has a unique advantage for its dense and fine-grained crystal structure and low hardness, making it suitable for calcining active lime.

2.Limestone Crushing and Grinding

---

Particle Size Can Affect Calcination Speed

Limestone shall be crushed and ground into small particles before the calcination, to produce quicklime is achieved by heating to remove CO2 in quick lime. Since the separation of CO2 is carried out slowly from the surface of limestone to its interior, if the limestone particles are too large, the heat transfer decomposition process will be slowed, and the calcination temperature needs to be higher to generate a higher reaction pressure.

Lime Calcination for Steel Plant

From the perspective of lime application, when lime is used as a slag-forming agent in converter steelmaking, the smelting of steel has time requirements within a certain temperature range. This also determines that time is limited when lime reacts with molten steel and completes slag formation.

In short, the requirement for limestone particle size shall consider the following aspects:

• User's needs for lime product particle size,
• The molding rate and availability of the limestone mining process.
• Maintain long-term usability.

3. Impurities Treatment of Limestone - Washing and Screening

The raw material used to produce active lime is natural mineral - limestone. The melting point of pure CaCO3 is 1339℃. Quicklime is composed of CaO as the main component with other substances, and the melting point of pure CaO is 2550℃. However, limestone is not a pure substance, and its internal structure contains various impurities. To produce active lime and high-quality quicklime, the impurities shall be removed by washing and screening process.
The most common impurities in limestone are: SiO2, Al2O3, Fe2O3, MgCO3, S, P, Na2O and K2O.

Limestone Process in Steel-making

When lime is used in steel-making, the impurity requirements focus on the low content of S and P impurities. In the alkali industry, the impurity requirements for lime are Mn (manganese), Cr (chromium), Ba (barium), As (arsenic) and other heavy metal indicators.
Any type of limestone material contains different types and levels of impurities. The sources of these impurities are classified as follows:

1. Exist in limestone.
2. Adheres to the surface of limestone.

Impurities that Affect Lime Calcination Process

In limestone, the harmful impurities that can affect the calcination process are mainly: SiO2, Al2O3, Fe2O3, Na2O, K2O, etc. These elements can react with CaO at a relatively low temperature (around 900°C), causing the fusion and shrinking of CaO particles, making the grains coarse, and finally increasing the slag rate. They are one of the important factors that cause the formation of rings and nodules in the limestone during the calcination process.

4.Limestone Quality Testing

How Washing Process Can Improve Limestone Purity

After the raw materials are mined or before they are put into the kiln for calcination, they are usually washed with water to ensure the cleanliness of the limestone surface and reduce the presence of impurities.
Multipal Impurities: The soil wrapped around the limestone surface often contains SiO2, potassium, sodium oxides and other impurities. SiO2 is harmful to both the quality of lime in the calcining process and stable operation.
Avoid Ring Formation: Although the content of potassium and sodium oxides contained in limestone impurities is very small (<1%), their oxides or other compounds have extremely low melting points, which is one of the reasons for the formation of rings in the kiln.
The moisture content in limestone has little effect on the final calcination result of lime. The purpose of controlling moisture is to stabilize thermal efficiency. Especially in the preheater, it can help to prevent the material from sticking together due to fluffy materials.
Limestone with proper particle size can be obtained by screening after the washing process. All of these are to calcine qualified active lime and facilitate the calcination operation.

Limestone Physical and Chemical Indicators

According to the needs of active lime products and calcination, there are basic requirements for the limestone selection. The physical properties and chemical components are classified into the following requirements: