Get Price

Requirements of autoclaved aerated concrete production line for quicklime

September 22, 2021
Quicklime is one of the indispensable raw materials in the production of autoclaved aerated concrete. Quicklime provides an important calcareous material for the production of autoclaved aerated concrete. Therefore, the performance of quicklime is an important factor to ensure the stability of production process and product quality.
Next, Bona will give you a detailed introduction to the specific requirements for quicklime in the autoclaved aerated plate production line and autoclaved aerated block production line
Quicklime is generated by calcining limestone, dolomite or shell at high temperature. Quicklime used in autoclaved aerated concrete and plate production is mainly obtained by calcining limestone and dolomite.
Limestone and quicklime are described in detail below through the requirements of the standard.
1、 Requirements for limestone
The limestone for calcined lime is divided into ordinary limestone and magnesia limestone, and its chemical composition indexes are Cao, MgO, SiO2, P and s. The quality of limestone is mainly related to the quality of limestone, the particle size of lime stone, the temperature in the kiln and the firing time.
2、 Quicklime requirements
The chemical composition of lime is mainly Cao, and also contains a small amount of MgO, Fe2O3 and SiO2. Due to incomplete decomposition of CaCO3 during calcination, lime contains undissolved CaCO3 and other compounds. Therefore, the composition of lime includes two parts: one is the inactive part, including undissolved CaCO3, which does not participate in the hydrothermal synthesis reaction, so do not use total calcium in calculating the calcium silicon ratio; The second is the active part, which is the free CaO decomposed from CaCO3. It is the active part used in the production of aerated concrete blocks, including effective calcium oxide and free calcium oxide.
The role of quicklime in the production of aerated concrete blocks mainly includes two aspects:
First, provide calcium. The effective calcium oxide in quicklime reacts with SiO2 and Al2O3 in siliceous materials under hydrothermal conditions to form crystalline or colloidal hydrated calcium silicate and calcium aluminosilicate products;
Second, adjust the gas generation and thickening speed of slurry in the production process. On the one hand, improve the alkalinity of the slurry to make the aluminum powder gas; On the other hand, the heat released by digestion accelerates the gasification, thickening and hardening of slurry.
Reference standard for requirements of quicklime for autoclaved aerated concrete: JC / T 621-2009 lime for silicate building products, as shown in the table above.
1. A (CaO + MgO) mass fraction
Available calcium oxide and magnesium oxide are the main effective components in quicklime. They can react with SiO2 to produce silicate under hydrothermal conditions. The quality of quicklime is determined by its content.
If the content of effective calcium oxide and magnesium oxide is low, the amount of quicklime can be appropriately increased. The method in the appendix of JC / T 621-2009 standard is used for analysis. Since this analysis method detects the total amount of both, it is generally suitable for the analysis of calcareous lime. The analysis method of effective calcium oxide is carried out according to standard {JC / T 478-2013, test method for Building lime}.
2. MgO mass fraction
According to the MgO content, it can be divided into: ① calcareous lime: the MgO content is not more than 5%, which is obtained by calcining limestone; ② Magnesia lime: the MgO content is greater than 5%. Magnesia lime is obtained by calcining dolomite, or limestone will also lead to high MgO content when it is not fully burned. Calcareous lime is generally used in production, because most of MgO in lime is in overburned state, which will lead to expansion and cracking of green body after entering the kettle; If plates are produced, magnesia lime with appropriate MgO content can be used.
3. SiO2 mass fraction
SiO2 in quicklime comes from limestone. Generally, on the premise that the total amount of effective calcium meets the requirements, the total amount of SiO2 can be relaxed slightly, because it can participate in the reaction in the hydrothermal synthesis process, not harmful substances.
4. CO2 mass fraction
The mass fraction of CO2 is mainly determined by the amount of uncooked CaCO3 in lime, which can reflect the quickness of lime to a certain extent. The high mass fraction of CO2 indicates that there are more quicklime. Due to the complexity of measuring CO2 content, when the test conditions are not available, it can be roughly replaced by loss on ignition.
5. Digestion speed
The standard requires that the lime digestion speed of aerated concrete is 5 min ~ 15 min. for production, the lime of 5 min is generally too fast, resulting in insufficient afterforce of lime and affecting the hardening of green body; At the same time, the fineness of lime has an effect on the digestion rate.
6. Digestion temperature
The standard requires that the lime digestion temperature for aerated concrete is 60 ℃ ~ 90 ℃, and the temperature rise curve of lime for production is preferably flat.
7. Mass fraction of undigested residue
The main components of undigested residue are quicklime and superheated lime. Too high content will affect the quality of lime and the instability of process.
8. Fineness
The fineness of lime will affect the reaction speed. If it is too coarse, it is easy to produce white spots. Generally, the residue of 180 mesh sieve is controlled at 10% ~ 20%. The fast ash can be coarser and the slow ash can be finer.