The working principle and process of gypsum powder calcination equipment are mainly based on thermodynamically driven dehydration reaction, which achieves the conversion of dihydrate gypsum to hemihydrate gypsum by controlling parameters such as temperature and pressure. The following are the core points:
1、 Working principle
Fluidized bed calcination (boiling furnace)
The boiling furnace adopts fluidized bed technology, where gas flows through porous plates to make gypsum powder move in a fluidized state. The heating tube (steam or thermal oil) evenly transfers heat to the particles, achieving rapid dehydration. The bed layer is divided into dense phase zone (low porosity) and dilute phase zone (bubble zone), and gypsum powder completes the phase transition of β - type hemihydrate gypsum above 160 ℃.
Rotary kiln calcination
By rotating the cylinder, gypsum powder is fully in contact with high-temperature airflow, suitable for desulfurization gypsum and other raw materials. It supports indirect heating for precise temperature control and avoids overburning.
Temperature and Phase Change Control
The dehydration stage of gypsum is carried out: lattice water migration is initiated at 100 ℃, crystal nuclei are formed at 120 ℃, and semi hydrated gypsum transformation is completed above 160 ℃. Low pressure environment can accelerate the continuous dehydration process.
2、 Key process parameters
Temperature range: usually controlled between 120-180 ℃, excessive temperature can lead to the formation of anhydrous gypsum (CaSO ₄).
Water vapor pressure: Low pressure calcination can improve the purity of semi hydrated gypsum (≥ 75%).
Equipment selection: Boiling furnace is suitable for large-scale continuous production, rotary kiln is suitable for high humidity raw materials, and electric heating furnace is used for precision experiments.
3、 Process flow diagram
Raw material pretreatment: crushing and grinding (Raymond mill, etc.) to the appropriate particle size.
Calcination stage:
Boiling furnace: fluidized bed dehydration → overflow discharge → cooling and screening.
Rotary kiln: integrated drying and calcination → cooling and conveying.
Post processing: graded by a powder selector and stored in the clinker silo.
4、 Precautions
It is necessary to avoid high temperatures (>200 ℃) that can cause calcium sulfate to decompose into calcium oxide, which can affect the gelling properties.
Industrial by-products such as desulfurization gypsum need to be pretreated to remove impurities.
The above process integrates fluidized heat transfer and phase change control to ensure the stable physical properties of gypsum powder.