The drying kiln is actually a combustion chamber. The drying temperature is generally controlled between 300 and 600 °C. When building the kiln, the outer layer is made of red brick, and the inner layer is generally made of clay refractory bricks, clay refractory mud or refractory concrete，etc.
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Clay refractory bricks are made of refractory clay mixed with calcined refractory clay. The content of SiO2 is below 65%, and the content of Al2O3 is 35~48%. It has high resistance to rapid cooling and rapid heating, and has sufficient fire resistance temperature (1610°C). Clay refractory mud should have certain cohesiveness, permeability, refractoriness and mechanical strength when used as mud, and should be close to the corresponding properties of the refractory bricks to be laid. Refractory concrete is also commonly used for repairing and drying. Dry kiln, especially the kiln roof with large span, is usually formed by pouring steel bars mixed with refractory concrete at one time. Refractory concrete is made of cementitious substances (10-20% cement) plus refractory aggregates (clay clinker or waste refractory bricks). A kind of artificial refractory material obtained after mixing, forming and hardening of admixture (the same material as aggregate) and water in a certain proportion. Compared with refractory brick, refractory concrete simplifies the manufacturing process, The manufacturing cost is reduced, the kiln-laying operation is innovated, and the kiln body is integrated. However, the refractoriness is slightly lower than that of the same-sprayed refractory brick. When the drying kiln is used as a qualitative kiln, it is not suitable to use refractory concrete.
The specific maintenance method of the drying kiln varies with the structure of the kiln body. But in general, building a drying kiln should meet the following requirements:
(1) Try not to use cut refractory bricks.
(2) The width of the brick joints should meet the following requirements: 3mm for clay refractory bricks and 5-7 mm for red bricks.
(3) Expansion joints should be reserved when laying bricks, and the average length of expansion joints for each meter of bricks is 5-6 mm.
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(4) Expansion joints are often filled with cooked refractory clay. Because the mud used for bricklaying has secondary shrinkage, it is best to add asbestos accounting for 25 to 30 O of the total volume.
(5) In principle, expansion joints should be left in layers, but expansion joints are only left in the inner layer of the underground masonry that is in contact with the flue gas.
(6) The spacing of each expansion joint is generally 2.5 to 3.5 meters.
(7) The staggered distance between the two-layer expansion joints is generally not less than 232 mm.
(8) The expansion joints at both ends of the arch are generally not left at the connection between the arch and the wall. When staggered, the expansion joint should be at least three arch rings away from the wall.
(9) For the furnace wall composed of refractory bricks and red bricks, because the brick layers of red bricks and refractory bricks are different in size, when determining the size of the red brick masonry, it should be uniformly calculated according to the size of the refractory brick masonry.
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