Construction Technology of Wear-resisting Refractory Material for Circulating Fluidized Bed Boiler

September 14, 2021
When the circulating fluidized bed boiler is in operation, the material in the boiler furnace is in a circulating flow state. Among them, the materials containing fuel, fuel ash, limestone and their reaction products are part of the external circulation in the circulation process, that is, in the closed loop of the furnace-cyclone-return valve-furnace at a constant high speed Circulating fluidization state; part of it is internal circulation, that is, materials with larger particles fall back in the furnace under the action of gravity. If the selection of refractory and wear-resistant materials is inappropriate, the construction quality is not high, and the quality of the oven does not meet the regulatory requirements, it will seriously affect the normal operation of the circulating fluidized bed boiler.
1. Construction of wear-resistant and refractory castables
Castable construction focuses on several links such as pin welding, bitumen painting, water mixing, mold fixing, vibrating, mold release protection, size assurance, and accuracy of measuring points, and the implementation is carried out in strict accordance with the requirements of the material manufacturer and the boiler factory.
1) Pin and grab nail installation
Before the water pressure, the pins in the relevant areas such as the welding joints of the heating surface and the combined welding joints and the joints of the heating surface during the transportation and installation process should be filled up. Repair welding and grab nails to ensure that the pins are arranged according to the designed density. Before pouring, apply a layer of asphalt paint with a thickness of> 1mm on all embedded metal parts, nails and other metal surfaces or wrap combustible materials.
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2) Ingredients, water distribution, mixing control


The ingredients are weighed and the water is distributed in strict accordance with the requirements of the material manual of the material manufacturer, and a designated person is responsible for the accurate measurement. The water used for mixing castables must be clean water (such as drinking water), with a pH of 6~8. Pay attention to the order of adding water and the mixing and mixing time. It is not allowed to add water at will, and it is not allowed to advance or extend the mixing time arbitrarily. The amount of water must not be added to one place, and the castable must be fully mixed. It is necessary to add steel fiber to the castable during the process of adding water and mixing, and shall not be mixed in agglomerates. The well-mixed pouring material that meets the requirements should be transported away immediately after being poured out. After the pouring material is poured out of the barrel, whether it is transported away or not, it is not allowed to return to the barrel for repeated mixing and use; after each construction, it should be timely The barrel is cleaned and ready for next use; record the amount of water added to the ingredients, mixing time and other records.


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3) Template control


Castable mold making is a very critical process, and the quality of the mold plate directly affects the quality of the castable. The template control focuses on the acceptance of its firmness and dimensional accuracy. The template must be firm and tightly assembled to ensure that there is no displacement or looseness during pouring. The wooden mold should be laid out according to the geometric dimensions of the construction drawing and the pouring thickness, prefabricated and assembled, and the interface is tight. The mold is made with a 15 cm template and a wooden square, with a width of ≤500mm; the special-shaped mold is made of a wooden square and covered with a surface Layered three-centimetre board, the surface is brushed with two release agents to ensure the thickness of the castable and the surface after construction is smooth and clean without pitting. The formwork must be checked and accepted before construction.


4) Pouring control


When pouring the castable, the height of each feed is controlled in the range of 200~300mm, the part with thickness greater than 50mm is poured with an inserted vibrator vibrating, and the "fast in and slow out" method is used to vibrate continuously during vibrating to prevent retention For the lower hole and leakage vibration, the vibration time of each point should not be too long to prevent the fine powder from floating. During the vibration process, the vibrating rod must not hit the template and hook nails too much. When pouring castables greater than 50mm thick, the area greater than 10m2 should be constructed at two points at the same time; to ensure that the mixed materials are poured within the specified time, the pouring of the parts less than 50mm thick is preferred to be self-leveling and automatic Degassed self-flowing castable construction. Use vibrating castable with ordinary fluidity, use φ35mm vibrating rod when vibrating, weld φ16mm round steel 300mm long at the end of the rod head, extend it into the template to vibrate, or use a wooden hammer to gently move it to the side in the horizontal direction Vibrate the template to ensure the compactness of the castable and no honeycomb pitted surface, but it is not suitable for over-frequency and heavy percussion, and it is not allowed to percussion on the vertical die surface to prevent serious flooding on the die surface. After the construction of the castable, it is strictly forbidden to repair and level the surface after the second construction.


5) Reservation of expansion joints


Because the expansion coefficient of the castable is inconsistent with the expansion coefficient of the steel, it is about half of that of the steel. In general, there are four ways to solve the expansion of the castable: one is to paint the asphalt paint on the pin and metal surface, the thickness is not less than 1mm. The second is the large-area pouring part, which is poured in blocks every 800~1000×400, and the expansion joint material is pasted from the side to leave the expansion joint. The third is to wind ceramic fiber paper with a thickness of 2mm on the surface of the hood, instrument pipe fittings, and metal wall penetration parts as expansion joints. Fourth, a knife can be used to cut out a half-thickness gap during construction of the plastic, or a hole can be punched in the plastic to solve the problem of expansion.


2. Furnace wall brick masonry construction


1) Masonry of wear-resistant refractory bricks


Masonry wear-resistant refractory bricks are made of high-strength wear-resistant mud. The strength of the mud (under 1000℃) is> 3MPa, the bonding time is> 90s, and it has good workability and spreadability. The barreled mud should be used as soon as possible after opening. , If you find agglomeration or poor spreadability, stop using it. When using dry powder to prepare mud, clean water should be used, weighed accurately, and mixed evenly. Do not add water or binders to the prepared mud arbitrarily. Mud of different types and brands should not be mixed, and the mud that is stirred on the same day must be used up on the same day. The joints between masonry bricks should be ≤2 mm, and the joints between the bricks should be kept uniform, and no joints ≥3 mm are allowed. The masonry of special-shaped bricks shall be constructed in strict accordance with the drawings. If the joints of individual special-shaped bricks are larger than 3 mm, the slurry used must be separately prepared.


2) Refractory insulation brick masonry


Refractory insulation brick masonry adopts insulation refractory mud. Expansion joints should be left in the furnace wall according to the design position and requirements of the equipment drawings. The width error is ±3 mm, and the boundary misalignment is ≤2 mm; no debris, such as mortar, bricks, etc., should be included in the expansion joints, and the filling diameter of the joints The dust-free asbestos rope or aluminum silicate fiberboard that is slightly larger than the gap distance should be aligned with the plane of the refractory brick wall, and there should be no overhanging or concave phenomenon. The internal walls of refractory bricks and the external walls of thermal insulation bricks are generally not allowed to be involved in masonry, except as specified in the equipment technical documents. The two opposing pull hook bricks should be aligned, and the fire facing surface should be on the same plane as the wall where the pull hook brick is located. The end of the pull hook brick leaning against the fire surface should be slightly lower, generally 10 mm is appropriate. The gap between the pull hook brick and the fixed pipe Fill it with insulation materials.


In order to ensure that the cross-sectional dimension error of the masonry after masonry is within the allowable range and effectively eliminate the deformation of the shell, the refractory bricks should be laid first, and then the thermal insulation bricks should be laid. The gap between the insulation brick and the silica-calcium board is tightly filled with No. 13 insulation material. For circular structures, lock bricks must be used to ensure the stability of the masonry. The lock brick has a wedge-shaped structure, with the big end facing inward and the small end as the working surface.


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With the widespread application of circulating fluidized bed boilers, the discussion on the construction technology of circulating fluidized bed boilers has become more and more in-depth, especially the construction of wear-resistant refractory materials directly affects the economic and safe operation of the boiler. For circulating fluidized bed boilers, the quality of wear-resistant refractory materials, the rationality of on-site construction measures and the overall process control of construction are the keys to the safe operation of circulating fluidized bed boilers.

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