Design, Construction and Maintenance of Wear-resistant Materials for CFB Boilers

In a CFB boiler, on the one hand, a large number of high-temperature solid particles moving at high speed continuously wash away the wear-resistant materials and destroy them; on the other hand, the wear-resistant materials crack and peel due to temperature fluctuations, thermal shock and mechanical stress in the furnace. At the same time, the penetration of alkali metals, etc. can also easily cause the failure and damage of wear-resistant materials.

01 Design of wear-resistant materials

In CFB boilers, the wear-prone areas mainly include the water wall and the heating surface arranged in the furnace, the separation return system, the tail flue inlet and the slag discharge system.

Considering the characteristics of wear in CFB boilers, the physical properties of wear-resistant materials and construction characteristics, single or multi-layer wear-resistant refractory materials are generally used. Single-layer laying areas include water-cooled walls, screen heating surfaces, water-cooled partition walls, double-sided water-cooled walls, steam-cooled separators and other thin linings. Use φ6 or φ10 cylindrical pins (or Y-shaped V-shaped pins) to support the wear-resistant refractory castable on the flue gas side of the pipe wall. The thin lining can better withstand the rapid thermal shock when the boiler starts and stops. At the same time, in order to enhance its rigidity and impact capability, stainless steel fibers need to be added to the castable. The thick lining is divided into two or three layers. The flue gas side is made of wear-resistant and high-temperature resistant refractory bricks or wear-resistant plastic casting. The purpose of the lining's insulation material is to reduce heat loss and lower the shell temperature.

02 Construction and maintenance of wear-resistant refractory materials

1) Setting of expansion joints

Construction joints are also expansion joints. For areas where the castable area is too large, construction should be carried out alternately, construction joints should be left between blocks, and construction joints should be staggered.

2) Handling of metal anchors

Due to the difference in linear expansion coefficients between metal materials and wear-resistant materials after heating, asphalt must be applied to the surface of metal materials (including pins, pallets and pipes) before construction of wear-resistant refractory materials.

3) Vibration

If the vibration is insufficient, the density of the wear-resistant castable cannot meet the requirements or is uneven, which may cause insufficient strength of the castable and make it difficult to play an anti-wear role.

4) Thermal maintenance of wear-resistant refractory materials

Since the base-free mineral raw materials contain a certain amount of water, a certain amount of water is added as a solvent during the preparation of castables. This water needs to be discharged through natural drying and thermal curing. Because the wear-resistant refractory castable has a high density and its crystal water is inside its molecular structure, the thermal curing oven is a process that requires sufficient time. Although thermal curing uses controlled temperature hot flue gas curing, water still needs to be added to the heating surface of the boiler during curing to protect its safety. After thermal curing, all pouring holes opened in the sealed box need to be closed and welded, and all steam channels opened for thermal curing should be sealed and welded.

Doing a good job in shutting down and maintaining the boiler is extremely important to ensure the long-term economic operation of the boiler; it can also maintain and extend the service life of the boiler.