Refractory material for common boiler wall

Because a furnace wall material can not have both heat resistance, insulation and sealing three good properties, so the same furnace wall should often use several materials. Usually, the furnace wall is divided into three layers from inside to outside along the thickness of heat resistance, insulation and sealing, respectively, using heat resistance, insulation and sealing materials. But the division of this kind of level is relative and should be changed according to the actual situation. For example, the heat resistant layer can be removed for the furnace wall in the low temperature zone; In the brick furnace wall, in order to simplify the structure, the insulation layer and the sealing layer can also be combined with one material.

Boiler furnace wall is divided into all kinds of refractory materials, thermal insulation materials and sealing materials three categories. The commonly used refractory materials are firebrick, common clay brick (including red brick), refractory concrete, refractory plastic material, etc. Thermal insulation materials are thermal insulation brick, thermal insulation board, thermal insulation tile and all kinds of thermal insulation concrete and fibrous (glass wool, slag wool, asbestos, etc.) thermal insulation materials, sealing materials have a variety of sealing coating and coating materials.

(1) refractory materials include the following:

1) Firebrick. Boiler firebrick with a certain acid - resistant, alkali - resistant neutral brick as well. Usually industrial boiler using firebrick is clay brick, brick contains about 30%~45% of the Al₂O₃ and about 50%~65% of the SIO ₂. It belongs to weak acid refractory material, can resist the erosion of acid slag, but the resistance to alkaline slag is slightly poor.

2) light firebrick for boiler, with the advantages of light weight, small thermal conductivity and high refractoriness. But its disadvantages are large air permeability, loose structure, low mechanical strength, poor slag resistance and anti-harmful gas erosion ability, long-term use is easy to damage, so generally the density of 0.4~0.8g/cm³ products as high temperature insulation components, the density of 1.0~1.3g/cm³ products as the insulation wall between industrial boiler pipes. Light firebrick presses raw material different, have light silicon brick, light high aluminum brick and light clay brick to wait. There are five grades of light clay refractories commonly used for boiler walls.

3) Ordinary red brick. Common red brick is made of common clay with a small amount of sand. Its composition AL ₂O₃ is 16%~24%; The SiO is 60% ~ 80%; Other oxides 10%~20%. Standard brick size is 250mm*120mm*65mm.

(2) refractory concrete. Refractory concrete has the advantages of simple process, convenient construction, good integrity, high refractoriness at high temperature, good thermal stability, and small residual shrinkage performance, has been widely used in boiler furnace wall. The most commonly used binders in boilers are bauxite cement and Portland cement. The concrete prepared with these two kinds of cement is bauxite cement refractory concrete and Portland cement concrete, respectively. The scope of use of bauxite cement refractory concrete is: the working temperature of 1200~1300℃. The use range of Portland cement refractory concrete is: the working temperature is below 1200℃.

The common refractory castable in boiler is mainly bauxite cement and Portland cement as binder. The operating temperature of bauxite cement refractory castable is below 1200℃, and that of Portland cement refractory castable is below 1100℃.

(3) Thermal insulation materials include the following:

1) diatomaceous earth products. Diatomite is a kind of biochemical sedimentary rock formed by crustal changes after the decay of aquatic algae. It has many micropores and is an excellent natural insulation material. Diatomite brick is made of diatomite, its composition SIO ₂ is 80%~83%; Al ₂ O ₃ is 5% ~ 6%; Other oxides are 3%~5%. Standard brick size: 250mm*120mm*65mm. Diatomite products include diatomite brick, diatomite board and diatomite tile. They are all made of diatomite as raw material, which is added with burnable combustible materials, and roasted at a certain temperature.

2) expanded perlite and its products. Perlite is an acidic aqueous volcanic lava, it is calcined at 850~1050℃, the water vaporization in the lava produced pressure, the volume of the perlite rapidly expanded, the formation of porous soft perlite after cooling, said: "expanded perlite". It has the advantages of small bulk density, small thermal conductivity, fearless, non-toxic, no combustion, no corrosion, is a new type of thermal insulation material, has been widely used in China.

3) Expanded vermiculite and its products. Vermiculite is an aqueous silicate aluminate. At high temperature (850~1000℃), the water vapor escape between the silicate and aluminate layers was blocked, resulting in increased pressure of water vapor between layers, resulting in violent expansion of vermiculite and many times increase in volume, resulting in the formation of expanded vermiculite. It has the advantages of small density, small thermal conductivity, is a good thermal insulation material.

4) microporous calcium silicate products. This is a new type of insulation material, made of lime, silica, asbestos and adhesive, stirred and heated. It is dried. Its density is small, can be made into a density of 0.18g/cm³ below the product, compressive strength is greater than 5MPa, the cost is not high, is one of the better molding insulation materials.

5) Insulated concrete. The adiabatic concrete is made of diatomite, expanded perlite, expanded vermiculite as aggregate, and Portland cement as binder and water. After casting, curing can be made into any shape of thermal insulation materials, can be used as boiler wall high temperature insulation materials, and fire concrete layer closely adhered.

6) Fibrous moisturizer. The main raw materials of fibrous insulation materials are: rock, slag, glass and other additions. After batching, it is burned into a molten state at high temperature, and released by the flow trough, and then blown into filamentous or flocculent fibers with hot air or steam, which are respectively called mineral cotton, slag cotton and glass wool. They have the advantages of small density, small thermal conductivity, not easy to burn and so on. They are ideal materials for furnace wall insulation and thermal pipe insulation. The main disadvantage of this kind of products is poor temperature resistance, and they have a slight irritation to human skin during construction.

7) aluminum silicate refractory fiber, also known as "ceramic fiber", is a kind of high temperature resistant fiber insulation material, the use of temperature up to 1000℃. Aluminium silicate refractory fiber has the properties of fire resistance and heat preservation, and is often used for heat preservation of high temperature pipelines.

(4) sealing materials. Sealing material is divided into the "heat-resistant sealing coating" used in the high temperature area and the "sealing coating" used in the low temperature area. They are mainly used as the sealing layer outside the insulation layer of the light concrete furnace wall and the tube furnace wall, the sealing layer of the horizontal and inclined roof of the light brick structure, the coating of the outer layer of the heavy furnace wall, etc. With the extensive application of concrete furnace wall, there are many formulations of sealing coating, which can be prepared and substituted in accordance with local conditions.

(5) mortar. Mortar is a kind of furnace wall material used to fill the brick joints, to combine the bricks into a whole, and to prevent the furnace wall from being ventilated. The mortar should have a certain bonding strength, and the mortar material suitable for different masonry kilns should be used. The mortar consists of: 1) refractory mortar, also known as "clay refractory mud", used in the masonry of firebricks. It is made of refractory clay clinker and raw refractory clay in a certain proportion. 2) Insulation mortar, used for masonry molding insulation products, such as diatomite products, expanded perlite products, expanded vermiculite products, etc. 3) Cement slurry, used for masonry temperature below 200℃ and wet areas of common clay bricks.