The circulating fluidized bed (CFB) boiler technology is a relatively mature Yanhao combustion technology. The CFB boiler has excellent fuel adaptability and can burn almost any fossil fuel. The limestone can be directly discharged into the furnace to remove 90% of the S02. The emission concentration of the N0x is low, only 1/4 of the pulverized coal furnace. The boiler ash has good activity and can be used as a building filling material. Among them, the heat-insulating refractory material has become an integral part of the boiler with its effects of fire resistance, wear resistance and heat preservation. Due to the different roles of the circulating fluidized bed boilers, the insulation refractories required for each position of the boiler are not the same.
1 boiler structure
The 75t/h circulating fluidized bed boiler of Tangshan Zhongrun Coal Chemical Co., Ltd. is produced by Taiyuan Boiler Group Co., Ltd. The design fuel is bituminous coal, which can be mixed with a certain proportion of gas. The amount of fuel blended by the boiler is 30% of the total fuel (calculated by heat). The boiler is suitable for semi-open spaces. The boiler adopts the fixed method of combining the front and rear branches, and the boiler operating layer has an elevation of 7m. The boiler adopts a single-pot simple, natural circulation, distributed down-flow pipe, balanced ventilation, adiabatic cyclone gas-solid separator, and circulating fluidized bed combustion mode, and a convection heating surface is arranged in the convection shaft flue.
2 reasons for boiler refractory damage
The damage of refractory materials is divided into two cases: wear of refractory materials; destruction of refractory materials.
2.1 The wear of the refractory material causes the wear condition of the fired material to be: the working temperature in the boiler furnace is 900~1050; the redox atmosphere in the furnace; the smoke scouring and impact: the furnace is generally 3~6m/s, The separator is 20 to 30 m/s.
Flue gas scouring and impact refers to the abrasion caused by the impact of fluid or solid particles on the surface of the material at a certain speed and angle. Scour wear: The impact angle of the particles and the solid surface is small and nearly parallel. Under the combined force of the vertical splitting speed and the tangent splitting speed, the particles form a planing action on the solid surface, thereby gradually destroying the refractory material. Impact wear: The impact angle is large and close to vertical. The particles impact the solid surface at a certain speed to cause cracks and deformation. Long-term impact destroys the solid surface and the deformed layer will fall off.
2.2 Refractory damage (flaking)
There are several types of refractory damage: hot peeling; structural spalling; mechanical stress spalling. The thermal peeling is caused by the temperature change and the uneven heating due to the boiler starting and stopping, which causes a temperature difference inside the refractory material, thereby generating stress, which causes the refractory material to crack and peel off. Structural spalling is the change of material composition (mass change) in the long-term use of the material, and the surface material is peeled off. The reason why the mechanical stress causes the refractory material to peel off is caused by the difference in thermal expansion coefficient between the refractory material and the metal structure (temperature measuring, load cell, refractory pinching, etc.) passing through the refractory material.
3 working conditions of each position of the boiler
3.1Ignition air duct The 75t/h boiler of the company is under the bed. When the ignition method under the bed is adopted, the temperature rises quickly. The maximum temperature during ignition can reach 1200~1400. The temperature changes quickly and has high thermal shock resistance. Fall off. Due to the small number of particles, the wear resistance is low, and a high temperature resistant castable can be selected.
3.2 Fluidized bed bed fluidized bed surface working temperature is between 800~1100, wear-resistant refractory material is laid between the fluidized bed hood.
3.3 Boiler Furnace Circulating Fluidized Bed Boiler The working temperature of the furnace is between 900 and 1000. The dense phase and semi-dense phase layer materials and ash concentration are very large, and the airflow direction changes frequently during continuous boiling and circulation. The requirements for fluidized bed four-wall refractories are very high, requiring greater fire resistance and adhesion, as well as high wear resistance. The structure type adopts the method of applying refractory plastic to the welding pin on the water wall tube.
3.4 The flue gas turns at the top of the furnace roof of the furnace roof, the working temperature is 850~1100. The refractory wear-resistant layer of the furnace top adopts the following types, namely refractory castable casting or profiled brick laying or fire-resistant wear-resistant plastic (with the film wall when the spike is added)
3.5 Cyclone separator straight and cone circulating fluidized bed boiler Cyclone separator is designed to separate carbon particles and ash particles in the flue gas. The particles in the separator have a high speed, the working strip is bad, and the working temperature is 800~ 950, and there is the possibility of secondary combustion, the lining material must have a relatively high wear resistance. Most use high-aluminum or steel jade castables.
3.6 The riser and the returner have a working temperature of 800-950, and the particle concentration is high, but the particle size is fine, the heat capacity of the ash is large, and the thermal shock to the lining is large. The working conditions are not bad, generally high-aluminum materials are used. However, the construction conditions of these parts are poor, and special attention should be paid to the construction process to ensure the construction quality.
3.7 The temperature of the tail flue is low, and the wear of the lining is small. It can be built with ordinary refractory bricks.
4 selection of parts
The refractory materials used in the company's 75t/h circulating fluidized bed boiler are: corundum wear-resistant plastic, diatomite insulation castable, high-strength wear-resistant castable, phosphate refractory concrete, lightweight insulation brick, diatomaceous earth Insulation bricks, refractory bricks, etc.
The lower wear layer of the furnace and the furnace outlet mainly use corundum wear-resistant plastic; the high-strength wear-resistant castable is used in the inlet flue and target area of the separator; the lightweight insulation brick is used inside the separator cylinder and the cone, and the surface is separated Intensity wear-resistant castables; phosphate refractory concrete for air distribution devices, ignition ducts, and furnace doors; diatomaceous earth insulation bricks and refractory bricks are mainly used for the heating surfaces of the tail.
5 problems in the use of refractory materials
You must use clean water, add 6% to 8% of water; with a forced blender, all mixing tools must be clean. Mixing until the material is even; when mixing, the amount of material added is not less than the whole package, dry mixing for 15 minutes before adding water to achieve the purpose of uniform mixing;
A large number of pins are reinforced with the metal surface of the boiler. The pin is made of metal material, and the coefficient of thermal expansion is much larger than that of refractory material. Therefore, the pin needs to be pre-heat treated before installation; all the casting surfaces of the mold should be coated with a layer of oil; each batch must be poured within 10-30 minutes after the mixing is completed. It should be poured to the specified thickness at one time and vibrated until it is completely sealed; the mold is released 24 hours after pouring, and the total curing time is 3 days.
6 Conclusion
More than 50% of the problems of CFB boilers are on the castables. The choice and construction of castables has a decisive influence on the service life of CFB boilers. Only a good understanding of the working principle, wear characteristics and characteristics of various castables of CFB boilers can ensure the construction quality and increase the service life of CFB boilers.
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