- Time:Jan 30, 2023
The main purpose of using refractory wear-resistant materials in circulating fluidized bed boilers is to prevent high temperature oxidation and corrosion and wear of metal components by high temperature flue gas and materials of boilers, which is an important measure to ensure the long-term safe operation of circulating fluidized bed boilers and is also the main feature of circulating fluidized bed boilers. The common refractory and wear-resistant materials used in circulating fluidized bed boilers include non-metallic refractory bricks, castables and plastic. These wear-resistant materials are subject to various degrees of wear and tear in actual application. The following summarizes the causes, hazards and preventive measures of damage to wear-resistant materials for CFB boilers.
A. Causes of damage to refractory wear-resistant materials
1、The wear caused by thermal stress and thermal shock. Mainly manifested as temperature cycle fluctuations, thermal shock and mechanical stress resulting in cracks and spalling of refractory wear-resistant materials.
2、Abrasion caused by solid material scouring. The main performance is the breakage caused by the strong scouring of the refractory wear-resistant material by the material. The refractory wear-resistant material in circulating fluidized bed boiler is easy to wear area including edge area, cyclone separator and solid material return line. In general, the wear of refractory wear-resistant materials increases with the increase of impact angle.
3、The wear caused by the change of the nature of the refractory and wear-resistant material. The main performance is the damage caused by the deterioration of the refractory wear-resistant material and the reduction of the physical and chemical properties. The penetration of alkali metal will cause the refractory wear-resistant material to deteriorate, and some refractory wear-resistant material and bonding agent strength decrease, or the oven does not meet the requirements, which will also cause the lining to delaminate and collapse.
B. The danger of wear-resistant materials falling off
Wear-resistant material shedding will cause the heated surface to be directly scoured by the high temperature flue gas, not only the thermal deviation of the heated surface will increase, but also the amount of tube wall wear will increase rapidly, which will easily cause pipe burst accidents. In addition, because of the wear-resistant material shedding of the re-feeder will cause poor fluidization of the bed material in the re-feeder, and in serious cases, the normal return of material cannot be achieved, which seriously threatens the operation of the boiler.
C. Causes and preventive measures for shedding of furnace chamber and dense phase area
1、Analysis of the causes of wear of refractory wear materials in the furnace chamber.
Circulating fluidized bed boilers have a combustion chamber temperature of 850 to 950°C during normal operation, and are subject to rapid start-up and shutdown to accommodate load changes or special operating conditions. The temperature change in the combustion chamber, the thermal shock from compression fire and hot start, and the thermal stress can cause damage to the refractory wear-resistant materials. Drying, shrinkage, thermal vibration and plastic deformation under various stresses can cause cracks in the refractory wear-resistant material, and excessive cracks and extrusion spalling can cause destruction of the refractory wear-resistant material.
Wear prevention and mitigation measures.
(1) Minimize the primary fluidization air speed while maintaining the normal fluidization air volume.
(2) Check the incoming coal and limestone granularity frequently to keep within the specified range.
(3) Improve the design and reduce the number of profiled tubes.
(4) Do not operate with too much air volume and try to reduce the flow rate of flue gas.
2. Dense phase area refractory wear-resistant material off damage cause analysis.
(1) unreasonable design, such as the pin, grab nail density, height, material selection is unreasonable.
(2) The composition of the refractory wear-resistant material does not meet the regulations, affecting the stability, compressive strength, flexural strength, wear resistance, thermal vibration stability and refired change rate and other indicators up to.
(3) poor construction techniques, such as mixing the water quality, water quantity, water temperature or ambient temperature, maintenance, mold removal, etc. did not follow the requirements of construction.
(4) Insufficient expansion gap reservation.
(5) the oven heating speed is too fast, constant temperature time is not enough.
(6) improper operation, such as starting and stopping the furnace during the rise and fall of temperature too fast, bed temperature rise and fall, etc.
Anti-wear measures.
Suitable refractory and wear-resistant materials should be selected according to the environment in which the equipment is located, and the materials must be high-strength refractory and wear-resistant materials with good bending strength. Adequate number of metal pins should be designed inside the refractory wear-resistant material, the length of which should basically run through the refractory wear-resistant layer, and sometimes stainless steel fibers can be added to the refractory wear-resistant material to ensure that a large area will not fall off when cracks are generated.
The maintenance of the refractory wear-resistant material is very important. During the baking period, the temperature rise of refractory wear-resistant materials should always be controlled within the range permitted by the manufacturer, and it is also very critical that the surface of the refractory wear-resistant layer reaches and exceeds the sintering temperature when baking. In actual operation, we must pay great attention to the maintenance of the refractory wear-resistant materials, and we cannot simply pursue the fast cooling after the furnace is raised and stopped, ignoring the law of temperature rise of the refractory wear-resistant materials, which will form fatal damage to the refractory wear-resistant materials and leave hidden problems for the long-term stable operation in the future.
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