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These damages are common in refractory castables in fluidized bed boilers.
Dec 05, 2018

The function of the lining of the circulating fluid bed boiler is to prevent high temperature oxidation and wear of high temperature flue gas and materials on the metal outer wall, and at the same time to insulate and heat the materials in the boiler. Most of the boiler linings are made of wear-resistant castables. In actual use, the common problems of wear-resistant castables in circulating fluidized bed boilers are as follows:


1. The castable material in the dense phase zone of the boiler often shows the phenomenon of falling off the castable material, which causes the water wall to burst.


2. The castable in the slag area of the air distribution plate is frequently peeled off.


3. The expansion joint is unreasonably reserved for cracking of the castable.


4. The boiler is heated too fast and the castable falls off.


5. Collapse caused by the operation of the cyclone separator casting material and the rubber leakage of the insulation material will directly cause a shutdown accident.


The castable lining of the fluidized bed boiler unit is one of the most important components of the CFB boiler. The selection of the lining material and the maintenance and construction process directly affect the safe production and normal operation of the boiler.


During the operation of the boiler, the internal environment is not bad, not only the bed material is washed, but also the partial vortex generated by the secondary air and the tertiary air, which causes wear on the castable. Therefore, the lining material used is required to have a high degree of refractoriness, a high softening temperature, and a high resistance to quenching and quenching, and chemical resistance.


The spalling of the castable in the boiler is generally caused by the following conditions:


1. Hot peeling, when the furnace is stopped, due to temperature fluctuations and thermal shock, a large temperature gradient is generated on the surface and inside of the castable, which causes the castable to crack and peel off.


2. Structural spalling, generally due to the change of composition and crystal phase structure of the castable during long-term operation, causing the surface to fall off.


3. Mechanical stress spalling, which is generally caused by the difference in thermal expansion coefficient between the castable and the fixed metal parts during construction.


Henan Nexian New Material Co., Ltd. can analyze and propose specific solutions for refractory castables for circulating fluidized bed boiler lining. For example, the material at the secondary air vent is seriously worn, and the cause of this wear is as follows: :


1. Material falling along the furnace wall and local eddy currents generated by the secondary air. 2. Airflow angle problem; 3. Wear caused by material flowing down the water wall; 4. Impact of material on lining refractory castable, and scouring caused by high velocity airflow carrying solid material.


In response to this wear, technicians in Henan's selection of new materials proposed improvements from the following aspects: 1. flue gas flow rate; 2. fly ash concentration; 3. hardness, temperature, shape and size of fly ash particles.


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