Refractory for melting furnace

The temperature in the melting furnace is usually 1400~1700℃, sometimes as high as 1800℃. Therefore, it is necessary to choose refractories with good corrosion resistance. Moreover, the atmosphere in the furnace and the basicity of the molten material on the use of refractories also have a great impact, in the selection of materials must be carefully analyzed about the conditions.

Refractory materials for melting furnace are mostly aluminum oxide, Al2O3-MgO, Al2O3-Cr2O3, Al2O3-ZrO2, ZrO2, SiC-Al2O3, castable and firebrick.

Refractory materials containing a certain amount of Cr2O3 are highly corrosion-resistant in incinerators because they are widely used as lining materials, including refractory bricks containing Cr2O3 and amorphous refractory materials containing Cr2O3. Especially with the decrease of SiO2 content and the increase of Cr2O3 content in the material, its service life is doubled. This is mainly because with the decrease of SiO2 content, low melting point substances are difficult to produce, Al2O3 reacts with Cr2O3 to form a continuous solid solution with high corrosion resistance, and the viscosity of slag increases with the increase of Cr2O3, thus inhibiting the melting of furnace lining materials.

However, Cr2O3 in the dissolved slag may convert to the harmful chromium 6 in the calcium environment, which is easier at high temperatures than at room temperature. Therefore, chromium - containing materials should be avoided in general. In the oxidizing atmosphere can choose Al2O3, ZrO2, MgO and other oxide refractories, also has a good corrosion resistance. In the reducing atmosphere can also choose carbon and SiC refractories. For the time being, however, the durability of these materials is far from comparable to that of chromium-containing materials. This is an urgent problem to be studied and solved.

 

Factors influencing the use of refractories for melting furnaces

Effect of atmosphere in furnace on refractory

As a result of using melting method is different, the atmosphere inside the furnace is also different. Generally speaking, the electromelting mode using electrodes is easy to become a reducing atmosphere, while the burner mode using heavy oil is easy to become an oxidizing atmosphere. In the selection of materials, it is difficult to define the use of non-oxide refractory materials such as carbon bricks, silicon carbide bricks atmosphere limit, not only because of O2, H2O, CO2 and its oxidizing gas concentration, but also because of temperature, pressure, etc., will lead to subtle changes in the atmosphere.

The corrosion resistance of SiC bricks in oxidizing atmosphere is about 10 times larger than that in reducing atmosphere. Therefore, considering from practical experience, the critical condition for the use of SiC series refractory materials in incinerators and melting furnaces is about O2=3%~10%, which can be used according to service temperature; Metal oxides such as FeO; The use conditions of H2O, CO2 and other oxidizing gases determine the SiC content and material. In addition, SiC content and material. In addition, SiC furnace materials should not be used in the oxidation atmosphere layer above the slag line, and it is best to limit them to the parts covered by slag and metal at the bottom of the furnace, so they should be used in the reducing atmosphere.

B. Effect of service temperature on refractories

The maximum temperature in the melting furnace is usually 1400~1700℃, occasionally reaching above 1800℃. Moreover, the temperature of the metal layer below the slag line reaches 1200~1300℃, and all parts of the furnace are in the high temperature zone, which can be said to determine the life of refractories in the actual furnace is closely related to the maximum temperature. When the temperature of molten slag exceeds 1400~1500℃, the erosion ratio of refractory increases sharply, especially the clay-high alumina refractory is easily affected by temperature, and the amorphous refractory is more easily affected by temperature than the shaped brick. For example: in the actual furnace under the same conditions, the brick and castable mixed masonry of the same chemical composition, the brick life is 2~3 times that of the amorphous refractory plant.

Effect of fly ash alkalinity (CaO/SiO2) on refractories

Among oxide refractories, basic brick is the most difficult to be affected by CaO/SiO2, al2O3-Cr2O3 and other neutral refractories due to the increase of CaO/SiO2, the amount of corrosion will increase. In non-oxide refractory materials, C-SIC brick is less susceptible to CaO/SiO2 than SiC brick, but it will accelerate the erosion with the increase of temperature. It can be seen that CaO/SiO2=1.0 of the melted material becomes the critical point, above which MgO, spinel and C-series refractory materials have good effect. Below this critical point, it is better to use Al2O3, Cr2O3, SiC refractories.

D Chromium - free measures

As mentioned above, chromium-containing refractories are widely used due to their high fire resistance (melting point: 2275℃), high corrosion resistance and other properties. However, 3-valent stable chromium in the high temperature area and slag in CaO, Na2O, K2O and other alkaline reaction, the formation of harmful to human body 6-valent chromium. Therefore, from the perspective of environmental protection, we hope to develop and use non-chromium refractory materials. As a chrome free refractory, Al2O3 (melting point 2050℃), ZrO2 (melting point 2950℃), MgO (melting point 2800℃) and other oxide refractory can be selected in oxidizing atmosphere. In reducing atmosphere, C, SiC and other non - oxide refractories can be selected.