Gypsum Powder Production Line: Overview and Process
Gypsum powder, also known as calcium sulfate hemihydrate, is widely used in the construction, agriculture, and chemical industries. A gypsum powder production line transforms raw gypsum rock or industrial by‑products into a fine, uniform powder suitable for a variety of end uses. This article outlines the key stages, equipment, and considerations involved in establishing and operating such a production line.
1. Raw Material Preparation
1.1 Source and Composition
Natural Gypsum: Extracted from geological deposits, typically containing 70–75% calcium sulfate dihydrate (CaSO₄·2H₂O) with minor impurities (clay, sand, and sulfides).
Synthetic Gypsum: Generated as a by‑product in industrial processes (e.g., flue gas desulfurization in power plants), often with higher purity.
1.2 Primary Crushing
Raw gypsum blocks are fed into a jaw crusher or impact crusher to reduce particle size to below 25 mm. This makes subsequent grinding more efficient and ensures consistent dehydration in the calcination stage.
1.3 Screening and Washing
Crushed gypsum is screened through vibrating screens to separate oversized particles and remove impurities. In some installations, a washing system eliminates clay and soluble salts, improving product quality and reducing wear on downstream equipment.
2. Drying and Calcination
2.1 Drying
Before calcination, gypsum must be dried to lower its moisture content to around 1–2%. Rotary dryers or flash dryers use hot air generated by gas or oil burners, ensuring uniform moisture reduction.
2.2 Calcination (Roasting)
Dried gypsum enters a rotary kiln or fluidized‑bed reactor, where it is heated to 150–180 °C. This step removes part of the water (one and a half molecules per gypsum molecule), yielding calcium sulfate hemihydrate (CaSO₄·0.5H₂O). Precise temperature and retention time control are essential to produce a consistent hemihydrate phase.
3. Grinding and Classification
3.1 Grinding
Calcined gypsum is ground in a ball mill, vertical roller mill, or Raymond mill to achieve the desired fineness. Typical target fineness ranges from 3% to 5% residue on a 45 µm sieve, depending on application requirements for setting time and strength.
3.2 Powder Classification
A classifier (air‑swept or static) separates fine powder from coarse particles. Coarse material is returned to the grinder for re‑processing. This closed‑loop system optimizes energy consumption and ensures a narrow particle size distribution.
4. Additive Dosing and Mixing
Gypsum powder properties can be adjusted with the addition of chemical retarders (e.g., starch ether, sodium citrate) to control setting time, as well as flow agents (e.g., surfactants) to improve workability. Precise dosing systems, such as screw feeders or loss‑in‑weight feeders, introduce additives into the powder stream. A paddle mixer or ribbon blender ensures homogeneous distribution.
5. Packaging and Storage
5.1 Packaging
Final gypsum powder is conveyed to a packing machine, where it is filled into bags (20–50 kg) at rates up to 1,000 bags per hour. Automated bagging lines include weighing scales, stitching or heat‑sealing units, and palletizing robots.
5.2 Storage
Finished goods are stored in a dry warehouse to prevent moisture uptake, which can alter setting characteristics. Warehousing systems may use stackers and reclaimers to manage inventory and support first‑in, first‑out rotation.
6. Quality Control
Quality assurance at each stage is vital for consistent performance:
Chemical Analysis: Regular sampling to verify calcium sulfate content, loss on ignition, and impurity levels.
Physical Tests: Measurement of setting time (initial and final), compressive strength after setting, and particle size distribution.
Moisture Monitoring: Ensuring low moisture in the final product to maintain shelf life and workability.
7. Environmental and Safety Considerations
Dust Management: Bag filters, cyclones, and wet scrubbers capture fine particles from crushers, mills, and kilns.
Emission Controls: Desulfurization systems on rotary kilns minimize sulfur dioxide emissions.
Waste Handling: Wash water from the screening stage is treated to remove suspended solids before discharge or reuse.
Operator Safety: Enclosures, ventilation hoods, and personal protective equipment reduce exposure to airborne dust.
8. Applications of Gypsum Powder
Gypsum powder is used in a range of products:
Construction: Drywall panels, plasterboard, gypsum blocks, and joint compounds.
Cement Industry: As a set regulator in Portland cement.
Agriculture: Soil amendment to improve structure and supply calcium and sulfur.
Dental and Medical: Casting molds and orthopedic plaster.
9. Conclusion
A gypsum powder production line integrates raw material handling, thermal processing, grinding, and packaging into a continuous workflow. Attention to process parameters, equipment selection, and quality control ensures a reliable product that meets the specifications of diverse end users. By optimizing energy efficiency and emissions control, such a facility can operate cost‑effectively while meeting environmental standards.
