Refractory castables are one of the most critical components affecting the operation cycle of circulating fluidized bed (CFB) boilers. The performance of these materials—such as refractoriness, thermal strength, shrinkage, casting quality, curing, and furnace-drying—directly determines the durability of the boiler lining. Proper selection, construction, and maintenance of refractory castables can significantly extend boiler service life, reduce unplanned shutdowns, and improve overall efficiency.
The lining of a CFB boiler is exposed to high temperatures, abrasive ash, and thermal cycling. If the refractory castable fails prematurely, it leads to:
Reduced operating cycle and boiler uptime
More frequent start-ups and shutdowns
Increased maintenance costs and operational risks
Safety issues due to cracks, leaks, or tube exposure
Poor insulation and uneven expansion during cold weather can also cause stress concentration at welded joints, leading to leaks and forced outages.
Key areas such as the furnace bed, furnace exit, and cyclone separator operate at 850–900 °C with gas velocities up to 9.5 m/s. These conditions cause severe wear and demand advanced abrasion resistance.
Many CFB boilers in captive power plants burn low-calorific fuels like coal slime and middlings. High ash content accelerates abrasion, especially at the furnace wear belt, flues, cyclone, and return legs.
Improper installation, short curing times, and incorrect furnace-drying curves reduce bonding strength and shorten castable life.
Rapid heating or cooling creates large thermal stresses. Load swings of 150 °C or more—caused by fuel variations—further damage the lining.
Material Composition: High-strength alumina–titania castables with phosphate or cement binders are widely used.
Critical Properties: Refractoriness, linear expansion, abrasion resistance, and thermal stability vary depending on manufacturing methods.
Phosphate-Bonded Castables: Offer excellent hardness and compatible expansion behavior, with strong adhesion to water-cooled walls when fixed with stainless steel anchors.
High-wear areas such as the furnace wear belt, cyclone separator, and return legs should use high-strength composite castables with superior abrasion and erosion resistance. Applying a thin layer of abrasion-resistant mortar during outages helps extend life.
Upgrade coal blending systems to stabilize calorific value.
Crush and screen fuel to reduce oversized particles.
Ensure consistent feeding to avoid load fluctuations.
Inspect and test all incoming materials.
Upgrade anchors from I-type to Y-type to improve bonding strength.
Follow proper casting, curing, and furnace-drying procedures strictly.
Heat up gradually (minimum 6 hours).
Control auxiliary fuel usage to avoid rapid temperature rise.
During shutdown, reduce coal and air gradually and avoid sudden cooling.
For power plants operating circulating fluidized bed boilers, refractory castables are more than just linings—they are the foundation of long-term reliability. Correct material selection, strict construction practices, stable operating parameters, and proper start-up/shutdown procedures are essential. With these measures, operators can achieve longer boiler service life, safer operation, and greater cost efficiency.
