The primary purpose of using wear-resistant refractory materials as linings in circulating fluidized bed (CFB) boilers is to protect the steel shell of the furnace from erosion and abrasion caused by the combustion materials.
The most commonly used linings in boilers are monolithic refractories, including wear-resistant castables, plastic refractories, low-cement castables, corundum castables, steel fiber reinforced castables, and lightweight insulating castables.
A typical power generation boiler consists of the combustion chamber, water-cooled walls, superheater, economizer, air preheater, and steam drum. The combustion chamber usually reaches temperatures around 1550°C. However, due to the presence of water-cooled tubes close to the furnace wall, the inner wall temperature is significantly lower—typically not exceeding 900°C. In membrane wall structures, the wall temperature can drop to as low as 500–600°C or even lower.
For chain grate boilers or pulverized coal boilers, the working temperature is generally around 1000°C. In contrast, fluidized bed boilers operate at higher temperatures and have many pipes penetrating the furnace walls, necessitating the use of higher-grade refractory castables for linings.
For small-sized or lightweight boilers, the working layer of the lining is often made of fireclay castables or plastic refractories. The insulation layer may use lightweight castables, insulating boards, or ceramic fiber wool. Some manufacturers also apply a sealing coating to the outer surface of the boiler shell to enhance air-tightness and improve insulation performance, thereby reducing fuel consumption.
In pulverized coal boilers, where coal particles and airflow cause simultaneous abrasion, high alumina or fireclay castables are used for lining, and high alumina plastic is rammed into the furnace roof. When severe wear occurs from coal particles or dust-laden gas streams, silicon carbide-based wear-resistant castables are used as the working layer lining to extend service life.
Refractory bricks are typically used in specific parts of the CFB boiler such as the return feeder, economizer furnace wall, mixing and combustion zones, flue ducts, and chimney linings.
Wear-resistant castables are primarily applied in key components such as the cyclone separator, combustion chamber, dense phase zone, furnace outlet, water-cooled air chamber, ash cooler, return feeder, and ignition air ducts. High alumina castables are used in boiler flue corners, air chambers, economizer shields, and fire doors. Lightweight insulating castables are used for thermal insulation of boiler roofs and walls.
Wear-resistant plastic refractories offer easy construction, fast repairs, high strength, excellent thermal shock resistance, and tight sealing performance. They are mainly used for repairs and localized ramming in fluidized bed boilers. Micro-expansion plastic refractories feature strong plasticity at ambient temperature, excellent bonding, high strength after natural drying, and slight expansion at high temperatures. These offer good refractoriness and sealing, and are easy to apply. Corrosion- and wear-resistant ramming materials with good thermal conductivity help improve heat transfer and are ideal for areas in CFB boilers that demand both wear and corrosion resistance.
Of course, the choice of castables and refractory bricks depends on the type and size of the boiler. Each application requires careful selection based on operational needs and performance demands.
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