Overview of a Gypsum Powder Production Line

Gypsum powder is widely used in construction, agriculture, and various industrial applications. A well-designed production line ensures consistent product quality, operational safety, and efficient resource utilization. This article outlines the key components, production steps, and quality control measures of a gypsum powder production line.

1. Raw Materials and Preparation

• Gypsum Rock or FGD Gypsum: The primary feedstock can be natural gypsum rock or by-product gypsum from flue gas desulfurization (FGD). Grade and purity vary, so consistent sampling is important.

• Auxiliary Additives: Small amounts of setting modifiers, retarders, or flow enhancers may be added depending on the intended application.

• Size Reduction: Large gypsum lumps are crushed to a uniform size (typically under 20 mm) using a jaw crusher or impact crusher. This improves the efficiency of subsequent calcination.

2. Drying and Grinding

1. Drying

• The crushed gypsum may contain moisture up to 15–20%. A rotary dryer or belt dryer reduces moisture content to under 1–2% for efficient calcination and milling.

2. Grinding

• A vertical roller mill or Raymond mill reduces the dried gypsum to a fine powder. Mill parameters—such as roller pressure, separator speed, and feed rate—are adjusted to achieve a target fineness (typically 2–5% residue on 45 μm sieve).

3. Calcination Process

Calcination transforms gypsum dihydrate (CaSO₄·2H₂O) into hemihydrate (CaSO₄·½H₂O). Two common methods:

• Wet Process
  Slurry is heated under controlled pressure and temperature in autoclaves. The resulting hemihydrate is filtered, dried, and milled.

• Dry Process
  Dried gypsum powder is fed into a calcining furnace—such as a flash or rotary kiln—at temperatures between 150 °C and 180 °C. Residence time and air flow are optimized to prevent over-baking.

4. Grinding and Classification

After calcination, the hemihydrate gypsum is ground once more:

• Re-Grinding Mill
  A mill fitted with high-efficiency separators produces gypsum powder with uniform particle size distribution.

• Air Classifier
  Fine particles are separated automatically, while coarse particles return to the mill for further grinding.

5. Packaging and Storage

• Automatic Packaging
  Packaged in paper bags, valve bags, or bulk containers through an automated weighing and filling system.

• Storage
  Finished powder is stored in a dry warehouse to prevent moisture pickup and maintain flow properties.

6. Quality Control and Testing

Quality parameters are monitored throughout production:

• Chemical Composition
  Sulfate content, loss on ignition, and impurities (e.g., chlorides, fluorides).

• Physical Properties
  Particle size distribution, setting time, water requirement, and compressive strength of hardened samples.

• Routine Inspections
  In-line sensors and periodic laboratory tests ensure compliance with relevant standards (e.g., ASTM C471, EN 13279).

7. Environmental and Safety Considerations

• Dust Control
  Baghouse filters or electrostatic precipitators capture airborne particulates at key emission points.

• Waste Management
  Wastewater from wet processes is treated for suspended solids before discharge. Solid residues may be reused in backfill or other applications.

• Safety Measures
  Adequate ventilation, explosion-proof equipment, and personal protective equipment protect operators from inhalation hazards.

8. Applications of Gypsum Powder

• Construction
  Plaster, drywall, and cement additives.

• Agriculture
  Soil conditioner to improve structure and supply calcium and sulfur.

• Industrial Uses
  Casting molds, coatings, and as a component in various chemical processes.