Desulfurization gypsum drying
Desulfurization gypsum (FGD gypsum) drying is an essential industrial process that removes excess moisture from the wet byproduct (calcium sulfate dihydrate, CaSO₄·2H₂O) generated by flue gas desulfurization (FGD) systems in coal-fired power plants and industrial boilers. Common Drying Methods:
Desulfurization gypsum (FGD gypsum) drying is an essential industrial process that removes excess moisture from the wet byproduct (calcium sulfate dihydrate, CaSO₄·2H₂O) generated by flue gas desulfurization (FGD) systems in coal-fired power plants and industrial boilers. This slurry, initially containing 40–60% moisture, must be dried to transform it into a stable, handleable material for recycling or disposal.
Purpose & Key Objectives:
Recycling Preparation: Enable reuse as a raw material (e.g., in cement production, wallboard/gypsum board, soil amendment).
Volume/Weight Reduction: Cut transportation and storage costs.
Stabilization: Prevent caking, hardening, and secondary leaching during storage.
Quality Control: Ensure consistency for industrial applications.
Common Drying Methods:
Rotary Calcining Kiln:
The rotary dryer operates by uniformly feeding materials to be dried into the kiln body through a chute inside the kiln head cover. The inclined rotation of the drum, driven by the rotary kiln’s rotating mechanism, causes loose powders or fine particles to spiral forward while continuously rolling and flowing within the drum. This movement ensures even heat distribution from hot air, leading to thorough drying as materials progress through the kiln.
Critical Technical Considerations:
Temperature Sensitivity: Strict limit of ≤65°C to avoid premature dehydration to hemihydrate (CaSO₄·0.5H₂O) or anhydrite (CaSO₄), which compromises setting properties for construction.
Abrasion & Corrosion: Equipment must resist abrasive gypsum crystals and residual acidic compounds (e.g., chlorides, fluorides).
Moisture Target: Final moisture ≤10% (often 5–8%) for most reuse applications.
Energy Use: Significant thermal input required; waste heat recovery from power plants is increasingly utilized.
Dust Control: Closed systems with bag filters prevent particulate emissions.
Challenges:
Variable Feed: Moisture/content fluctuates based on FGD system efficiency and coal composition.
Adhesion/Stickiness: Wet gypsum can adhere to dryer surfaces, reducing efficiency.
Impurities: Trace elements (e.g., mercury, selenium) require management in emissions/residue.
Significance & Applications:
Dried FGD gypsum is pivotal for:
Circular Economy: Diverts waste from landfills (~200 million tons/year globally).
Construction Industry: Primary substitute for natural gypsum in wallboard (≈90% of recycled FGD gypsum in some regions) and cement retarders.
Agriculture: Soil conditioner providing calcium and sulfur.
Environmental Compliance: Meets regulations for byproduct utilization (e.g., EU Waste Framework Directive).
Conclusion:
Desulfurization gypsum drying bridges environmental protection and resource efficiency. By converting a high-moisture slurry into a standardized, marketable product through controlled thermal processes like rotary or flash drying, it transforms an industrial waste stream into a valuable secondary raw material. Precise temperature and moisture control are paramount to preserve the gypsum's crystal structure and reactivity, enabling its critical role in sustainable construction and closing industrial loops.
