Wear Mechanism of Power Plant Boiler Lining and Selection of Castables

Wear Mechanism of Power Plant Boiler Lining

There are two main types of boilers in power plants, one is pulverized coal boiler and the other is circulating fluidized bed boiler. The lining material of the boiler is an important factor that determines its service life. The choice of lining castable should be determined according to the damage mechanism of the furnace type. The wear mechanism of the circulating fluidized bed boiler is that the bed material in the furnace is carried along the furnace by the flue gas, and enters the separator through the upper outlet of the furnace. The two-phase separation of gas and solid is carried out in the middle, and the separated flue gas enters the flue at the tail of the boiler, and the separated solid particles return to the lower part of the furnace through the return valve. In the closed loop of furnace-separator-return valve-furnace, it is in constant high-temperature circulating flow, and the combustion and desulfurization reaction is carried out at a high rate of 850~900 °C in the furnace. In addition to the external circulation flow of the bed material in this circuit, the bed material is continuously circulated in the furnace under the action of gravity. Therefore, wear will inevitably occur in the corresponding parts of the circulation loop. Wear not only affects the safe operation of the boiler, but also limits the exertion of some advantages of this type of boiler; the direct harm caused by wear to the boiler is to reduce the wall thickness of the metal pipes on the heating surface under internal pressure until the tube bursts and stop the furnace; wear makes the boiler The cost of operation and maintenance increases and the utilization rate of the unit decreases, causing huge losses to users.

Wear is the impact of coal or ash particles on the surface of the pipe on the heating surface at a certain angle, causing erosion and wear, resulting in the loss of metal on the surface of the pipe. The wear of the boiler heating surface pipes is affected by the concentration of coal particles and ash particles, particle characteristics, and in the area with high solid particle concentration, the wear mainly depends on the convective movement of the solid particles and the flue gas flow and the heating surface pipes, and the wear is closely related to the flue gas flow rate. Relatedly, the velocity of solid particles is the main factor affecting wear, so the parts of severe wear usually occur in the region of sudden change in particle flow rate. Wear mainly occurs in the lower part of the combustion chamber, around the upper outlet of the furnace, and at the lower part of the heating surface of the combustion chamber. At this stage, the wear-resistant materials used for the lining of circulating fluidized bed boilers are mostly wear-resistant plastics or wear-resistant castables.

How to choose castables for power plant boilers?

The choice of castables will have a great impact on the quality of these two boilers. The construction of the power plant boiler lining is extremely complicated, and the material flow rate in the circulation system is high and the flow rate is large. The refractory material for lining is required to have high strength, good wear resistance and excellent workability. The high-strength wear-resistant castable is made of corundum, silicon carbide, and dead-burned bauxite as the main raw materials, with superfine powder and composite admixtures. It has the characteristics of high early medium temperature, good high temperature performance, stable volume, strong resistance to slag penetration and erosion, erosion resistance, convenient construction, and strong lining structure integrity. grinding material.

Commonly used castables for power plant boilers:

(1) Corundum self-flow wear-resistant castable. According to different grades, this product uses various artificial synthetic materials such as high alumina bauxite, corundum, silicon carbide as the main material, and is equipped with various additives, water reducing agents, flow agents, etc. As a result, the material flow properties are improved. Its main features are: under the condition of not increasing water consumption, only relying on the self-weight of the material itself and the promotion of potential energy difference to generate flow, in the state of no vibration, it can be constructed in the cracks and places that cannot be vibrated, and it has good performance. Construction performance, mainly used for lining difficult to construct, serious erosion and wear parts.

(2) Thermal shock-resistant castable, this product is made of artificial synthetic material as the main raw material, added with composite binder and ultra-fine powder. The product has the characteristics of excellent thermal shock stability, high refractoriness and high strength. It can ensure the overall structure of the lining of the circulating fluidized bed boiler, and is especially suitable for harsh environments such as ignition air ducts and water-cooled air chambers with large temperature fluctuations of the boiler.

(3) High-strength and high-alumina refractory castables and corundum-mullite high-strength wear-resistant refractory castables are also power plant boiler castables. High-strength and high-alumina refractory castables have the characteristics of anti-penetration, corrosion resistance, impact resistance, wear resistance, high strength, etc., and are widely used in power station boilers and other thermal furnaces.

(4) Corundum and mullite castables use corundum and mullite as the main raw materials, cultivate ultrafine powder, and use composite binders and additives to combine. It has the characteristics of high strength and wear resistance and good thermal shock performance. It can also be used as a kind of boiler castable, suitable for boiler lining.