SEVERAL MEASURES TO PROLONG THE SERVICE LIFE OF BOILER LINING CASTABLES

The refractory castable of the circulating fluidized bed boiler is an important part that affects the operation cycle of the boiler. The refractory degree, thermal strength, shrinkage rate, pouring quality, maintenance and oven of the castable directly affect the strength and life of the boiler wall. Affects the operation cycle of the boiler, and at the same time, the quality of heat preservation and protection outside the furnace body restricts the expansion of the boiler, especially in winter when the temperature is lower than minus 5 degrees, due to the asynchronous expansion uniformity, it is easy to cause stress in the weld joints of relevant parts of the pipeline. Centralized and leaked furnace shutdown reduces the operation cycle, increases the number of furnaces and the input of furnaces, affects the smooth operation of the system unit, and increases the operation risk. Through the problems found during the actual operation of the boiler and during the shutdown and maintenance, the castable was partially damaged during construction, and there was no reserved expansion gap during construction and improper external insulation caused large temperature differences between the inside and outside. The main reasons for the damage are cracks. By discussing the material mechanism, using parts, and strengthening the link control, it is hoped to achieve the purpose of improving the service life.
Analysis of Current Situation of Circulating Fluidized Bed
The load capacity of the coal mine’s own power plant boilers is relatively low, most of which are circulating fluidized bed boilers with comprehensive utilization properties that use inferior fuels, and the evaporation capacity is mostly 75t/h and 130t/h. Due to the use of inferior fuel, the calorific value is low, the ash content is high, the boiler slag nozzle, the furnace folded flame angle, the wear-resistant castable at the column legs of the coal feeder and the cyclone separator are prone to cracks, wear and tear, wear-resistant Castable is the main factor restricting the long-term operation of the boiler; the selection of external protection and insulation materials and the quality of construction of the boiler are the loss of heat, and the welding joint where stress concentration is easily caused by the heating of the spot furnace and the sudden drop in the external ambient temperature. At the same time, with the increasingly strict environmental protection requirements, when the Ca/S=1.5-2.0 of the boiler with calcium injection desulfurization in the furnace, the desulfurization efficiency can reach 85-90 %, the utilization rate of limestone powder is nearly double that of conventional fluidized bed boiler, but the input of desulfurizer increases the amount of bed material and circulating material, and increases the wear of furnace wall castables. The wear of wear-resistant castables exposes the water-cooled film wall and the outer guard plate. In severe cases, the guard plate is burned, deformed, cracked, and the pressure-bearing pipe fittings leak due to the reduced wear strength, which greatly shortens the operation period, increases the accident rate, and affects the Safe production and increased material and labor input.
Performance analysis of wear-resistant castables in important parts of boilers
The furnace wall of the low magnification circulating fluidized bed boiler adopts the tube-laying light furnace wall, the cyclone separator, the inclined flue, the furnace top and the tail flue are built with refractory castables, phosphate bricks and aluminum silicate insulation materials. High-strength composite refractory castables are poured into the lower part of the membrane-type water-cooled wall of the furnace. Different forms of refractory materials are selected and used according to the fluidization rate, flue gas flow rate, and refractory degree, so as to reduce construction and maintenance costs while ensuring service life and wear resistance. . The wear-resistant castable is made by mixing oxides and binders. The fluidized bed boiler furnace uses high-strength refractory castables with good fluidity. There are great differences in wear resistance, etc., which affect the boiler operation cycle. The refractory materials in the high temperature zone of the circulating fluidized bed boiler are mainly high-strength refractory castables. The main components are Al2O3+TiO2, and Portland cement is blended in a certain proportion. Due to different processes, the refractoriness, linear expansion rate, wear resistance There is a big difference in strength, which affects the service life of the boiler. The composition (quality parameter) of the alum clinker should be Al2O3>60%, SiO2<20%, Fe2O3<3%; the concrete should be dried to remove moisture, and the basic refractory Do not dry when cemented with phosphoric acid. When acid and neutral refractories are cemented with phosphoric acid, immediately dry at 350℃<450℃<. (The phosphate solution is adjusted with 50% phosphoric acid and industrial aluminum hydroxide in a mass ratio of 7:1) According to the comparison of the physical properties of the castable, the phosphate refractory castable has high strength and hardness, and has a good linear expansion coefficient. To meet the requirements of use, it is fixed on the pressure furnace wall by 1Cr18Ni9Ti stainless steel nails, and has good adhesion with the furnace wall 20G membrane water cooling wall.
The main factors affecting the life of wear-resistant castables
1. The influence of the boiler structure
According to the structural characteristics of the boiler, the circulating fluidized bed boiler mainly uses the ash burned in the furnace to go up with the hot air, and the cyclone at the exit of the furnace produces rotary cutting and sinking, and the return material flows into the furnace through the return air , the temperature of the three parts with higher boiler temperature during normal operation are: (1), furnace run: 900 ℃ (2), furnace outlet: 892 ℃ ⑶, cyclone separator: 852 ℃. The smoke velocity is: furnace 5m/s, furnace exit 5m/s, and cyclone separator 9.5m/s. Higher temperature and smoke velocity will increase the wear of wear-resistant castables, and wear-resistant treatment must be strengthened.
2. The effect of fuel
The boiler fuel is the by-products of coal preparation plant washing gangue, coal slime and washing mixed coal, with low calorific value and high ash content, which will cause wear to the wear-resistant castables and water-cooled wall pipes of the furnace during boiling combustion. The wear of wear-resistant castables of cyclone separator and return material is particularly serious. Damage to the castables can easily cause the outer guard plate to be directly heated, deformed and cracked, and the phenomenon of smoke leakage and ash leakage occurs. Affect the normal operation of the boiler, and the site environment becomes worse.
3. The impact of construction quality
Construction quality is the main factor affecting the service life of boiler wear-resistant castables. The necessary construction measures are not taken for seasonal construction, the construction process does not meet the standard requirements, the maintenance period is short, and the oven cannot be baked in strict accordance with the given oven curve, resulting in The bonding force and wear resistance of wear-resistant castables cannot meet the design requirements.
4. The influence of load fluctuations on the castables during boiler start-up, shutdown and operation stages
Poor control of the heating and cooling rate when the boiler is heating up and shutting down to cool down will cause a large temperature difference between the inside and outside to form a large thermal stress. The failure of the coal feeding equipment and the large change in coal quality during operation will cause the temperature of the furnace to fluctuate. There are bed temperature fluctuations of 150°C. First, it affects the steam parameters. Second, the air volume needs to be adjusted in time. The fluctuation of the air-to-coal ratio causes the disturbance of the combustion state, which causes the castable to be eroded to the fire and affects the use of wear-resistant castables. life.