Home> Blog>How to choose thermal insulation refractories for new glass melting furnaces


The domestic float glass market is highly competitive, and the country's requirements for energy conservation and environmental protection are constantly improving. The melting furnace is one of the three major thermal equipments produced by float glass. About 30% of the heat entering the glass melting furnace is consumed in the heat dissipation of the kiln. This not only causes waste of energy, but also worsens the production and operation environment. Furnace insulation has become one of the effective energy-saving methods in the glass industry. Furnace insulation not only can greatly reduce the heat dissipation of the kiln to the outside, but also increase the heat capacity of the kiln, increase the flame temperature, increase the melting rate and improve the quality of the glass; at the same time reduce energy consumption and save fuel, thereby reducing production costs and saving Capital, ultimately improve the market competitiveness of enterprises.
       At present, the thermal insulation technology of the melting furnace is mainly from the structural design of the melting furnace and the selection of thermal insulation materials. Among them, the selection of thermal insulation materials plays an important role in the thermal insulation of the melting furnace.

1. Principles for selecting insulation materials for melting furnaces
       Due to the harsh environment in which the furnace insulation material is located, the following principles should be followed when selecting insulation materials:
       (1) It has good thermal insulation performance, that is, the thermal conductivity is 矣λ≤0.14W/(m·K) (350K);
       (2) It has a certain degree of refractoriness, especially under composite insulation, each insulation layer should meet the requirements of interface temperature, otherwise it will greatly affect the  temperature retention performance and even failure;
       (3) It has high temperature stability and can ensure no powdering or falling off under the use temperature conditions;
       (4) It has good chemical stability, and it must not be corroded or corroded by the body structure during use, and it can be fixedly attached to the refractory material;
       (5) It has certain impact strength and light weight;
       (6) The material allocation plan should be economical.
       The large dome, pool bottom and pool wall of the melting furnace are the most heat-dissipating parts, accounting for about 85% of the heat dissipation of the entire furnace kiln, and the heat transfer mode of the kiln body is convection heat transfer and radiation heat transfer. The surface temperature of the kiln body is related to the ambient temperature. The smaller the temperature difference between the surface temperature of the kiln body and the external environment, the lower the heat loss. Therefore, in order to achieve the purpose of heat preservation and energy saving, it is necessary to lower the temperature of the surface of the kiln. The decrease of the surface temperature of the kiln after heat preservation has a great relationship with the physical properties of the thermal insulation material, especially the thermal conductivity of the thermal insulation material, and the two have a positive correlation.

2. Classification of melting furnace insulation materials and introduction of new thermal insulation materials
       According to the development history of furnace insulation materials, it can be divided into traditional insulation materials that have been developed very early and new furnace insulation materials developed in recent years. The traditional furnace insulation materials mainly include: lightweight clay bricks, aluminum silicate fiberboard, light calcium silicate board, lightweight silica brick, high temperature resistant coatings, etc. The new nano-melting furnace insulation materials mainly include high-performance fiber spraying materials. Nano-scale microporous insulation board, titanium nano silicon nano insulation blanket, high emissivity energy-saving materials. Traditional insulation materials are familiar, and will not be described here, but focus on introducing new insulation materials.
       2.1 High performance fiber spray material
       Mainly used for the outer surface of the melting surface of the melting furnace, the product has excellent insulation and sealing performance, and the energy saving and environmental protection effect is remarkable.
       2.2 nanometer microporous insulation board
       The nano-scale air-insulation board is a new material made by the latest high-tech technology. It uses a special inorganic refractory powder to form a smiling super pore with a thermal conductivity smaller than that of still air. The product is in the form of a plate and can be combined with an outer protective layer material in the form of a PE plastic film, an aluminum foil, a fiber cloth or the like. How the product works:
       (1) Conductive heat transfer: nano-scale fine powder, the solid particles are very small, and the nano-level point contact thermal resistance is very large, so that the conduction heat transfer effect is small;
       (2) Convective heat transfer: nanometer pores average 20 nm. The average free motion of static air at normal temperature is 60 nm, and the air molecules are locked and cannot do convective heat transfer, so the convective heat transfer is very small;
       (3) Radiation heat transfer: The heat-insulating material is added with nano-scale anti-infrared radiation material, so that the radiation-based radiation heat transfer at high temperature is reduced to the lowest point.
       2.3 Titanium nanosilicone aerogel nano-insulation blanket
       Using the special nano-cavity structure inside the titanium-containing silica continuous material, the composition characteristics of the material: three-dimensional skeleton, nano-scale pores smaller than the air free path, high porosity make the thermal conductivity extremely low, and the products are mainly silicic acid. The aluminum fiber blanket layer and the high-efficiency heat-insulating aerogel layer are composited several times, and the performance parameters are as follows:
       (1) Low thermal conductivity, 0.012~0.016 W/(m ? K);
       (2) Class A1 is non-combustible and does not decompose at high temperatures;
       (3) Wide temperature range (0~1 050 °C);
       (4) Extremely strong resistance to pressure, shock, and expansion;
       (5) No moisture absorption, no aging, long-term use of insulation performance does not decrease;
       (6) The coefficient of thermal expansion is extremely small, avoiding the occurrence of fractures due to thermal expansion and contraction;
       (7) Small installation space, saving space and significantly reducing installation and transportation costs;
       (8) Extremely lightweight and flexible material, the construction is extremely simple, and it can be cut and tiled at will.
       2.4 High emissivity energy-saving materials
       The insulation mechanism of traditional insulation materials is to reduce heat transfer through heat insulation, which is generally used for the cold surface of refractory materials, while the high emissivity energy-saving materials are applied to the inner wall of the heat dissipation surface of the furnace in the furnace, which can increase the amount of heat radiation in the kiln. At the same time, reduce the amount of heat transferred by the glass. This not only reduces the amount of heat lost in the refractory above the liquid level, but also greatly reduces the amount of heat carried away in the flue gas. Its performance parameters are as follows:
       (1) Applicable to the surface of refractory materials, the thickness after spraying and curing is only 0.1 ~ 0.2 mm.
       (2) Strong thermal shock resistance and excellent ductility, which can be extended with the expansion of the sprayed substrate to offset the peeling force generated by thermal shock.
       (3) High acid and alkali corrosion resistance, suitable for complex combustion atmosphere in glass kiln.
       (4) High emissivity materials are distinguished from the above-mentioned several insulating materials, which are not themselves an insulating material. Instead, it absorbs the heat of radiation and convection at high temperatures and re-radiates 95% of it so that heat can circulate inside the furnace.
       (5) The emission coefficient is kept constant between 0.85 and 0.95 at high temperature, while the emission coefficient of general refractory materials under high temperature conditions is only between 0.2 and 0.3.

3. the choice of insulation materials
       3.1 Selection of insulation materials for different parts of the furnace
       (1) Since the top position of the crucible of the melting furnace is a curved surface, when selecting these parts of the thermal insulation material, a sprayable or blanket-like thermal insulation material should be used, and the plate-shaped thermal insulation material should not be used to prevent the material from being damaged by the bending. .
       (2) The temperature of the inner surface of each part of the melting furnace is quite different. Therefore, when selecting the insulating material (especially composite insulation), it must be considered whether the interface temperature between the layers is within the suitable operating temperature range. Prevent insulation performance from failing.
       3.2 Configuration of insulation materials use plan
       After determining the type of insulation material used, it is necessary to calculate the specification and dosage of the insulation material used.
       The heat transfer mechanism of the melting furnace can be simplified as follows: the heat transfer process of the inner wall of the melting furnace to the outer wall of the melting furnace and the heat transfer process of the outer wall of the melting furnace to the surrounding environment, ignoring the heat transfer of the melting hole of the melting furnace, the commutation, etc. Influence, establish an ideal melting furnace heat dissipation model. The model uses the heat transfer coefficient and the cold curvature temperature and the hot surface temperature as variables, establishes the heat balance formula through the thermodynamic equation, and then obtains the data set by the software programming calculation program. Finally, the curve of the three variables is obtained, and the heat preservation according to the furnace needs The hot part of the part and the temperature of the cold surface to be reached. The total heat transfer coefficient of the material of each part of the part can be obtained from the graph. With this heat transfer coefficient as the standard, the thermal insulation material specifications and the original refractory material are placed. The amount can be used.

4. Conclusion
      (1) By establishing an ideal glass melting furnace model, analyzing its heat transfer mechanism and heat balance formula, and proposing a heat transfer coefficient and temperature curve, it is convenient to calculate the thermal parameters of the furnace insulation.
      (2) The selection of new insulation materials should be determined by the outer surface morphology of the heat preservation part of the furnace and the temperature of use. The various new insulation materials mentioned in this paper have the characteristics of low thermal conductivity, high temperature resistance and high emissivity, so they are flexible. Designing a composite new insulation material application program can achieve better energy-saving insulation effect.
      (3) By comparing and analyzing the design schemes of new insulation materials and traditional insulation materials of the furnace, the heat dissipation of the furnace using the new insulation materials is significantly lower than that of the traditional insulation materials, the energy saving rate is higher, and the overall insulation performance is more sustainable.



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