Application of polycrystalline mullite refractory fiber and its products in kiln

With the in-depth development of energy-saving technologies, investment in energy-saving measures has become more and more important. The material of the masonry furnace is one of the important factors that save energy and reduce consumption, affecting the thermal efficiency and service life of the kiln.

Polycrystalline mullite refractory fiber (PMF) is a new type of ultra-light, high-temperature and heat-resistant thermal insulation material. It is composed of mullite microcrystals and integrates the characteristics of crystal materials and fiber materials. It has excellent heat stability, long-term use temperature up to 1500oC, melting point of 1840oC, thermal conductivity of 1/6 of traditional refractory bricks, and its bulk density is only 1/25, which can be widely used in industrial kiln lining insulation. It is an ideal material for high-temperature kiln energy saving, high quality and high yield.

The development of domestic polycrystalline mullite fiber is one of the key scientific research projects during the national “six. five” period. Zhejiang Oushiman Crystal Fiber Co., Ltd. took the lead in passing the pilot production technology appraisal in September 1986, and became the designated bidder of the National Economic and Trade Commission for alumina fiber bidding, as well as the designated enterprises of the State Economic and Trade Commission and the Ministry of Metallurgical Industry. Polycrystalline mullite fiber is produced by chemical colloid method and is a technology-intensive product. With high thermal resistance and low heat capacity, it can reduce heat loss by 30%. It can be used on steel rolling furnaces with frequent changes in steel specifications. Its comprehensive energy saving can reach 5-6% for intermittent electric heating furnaces. The effect is more obvious, and the energy saving rate is about 30%.

1. Properties and characteristics of polycrystalline mullite fibers and their products (Table 1)

Among them, PMF-100: specific heat 1024kj/kg.k, thermal conductivity (W/MoC) 1000oC∽0.226 1200oC∽0.295 1300oC∽0.337 1400oC∽0.387

Second, the application of polycrystalline mullite fiber in high temperature heat treatment furnace

The 82m2 trolley heat treatment furnace of a large enterprise is a special heat treatment furnace. When the “wetting treatment” is carried out, the Shanghai Manda is as high as 1250. The furnace was upgraded in 1987 with a high-level technical transformation. The whole fiber composite structure, the furnace top is 14 meters long and 7 meters wide. The top of the furnace is divided into nine pieces (composite fiber structure) during construction. After the fiber is installed, it is assembled on the top of the furnace. The thickness is 180mm, in which the 40mm PMF-100 series stack is used as the working surface, and it is attached to the longitudinal section of the high aluminum fiber (120mm) about 120m2. The anchor structure is not visible on the entire top of the furnace, which avoids heat loss. The furnace wall is single-layered and pasted with a 30mm thick PMF-100 series. Thus the entire lining is a PMF structure. Due to the use of PMF's new ultra-lightweight material, the furnace structure is lighter. The weight of the top of the stove is 12 tons, which is 83% lower than that of the original furnace top (phosphate heat-resistant concrete precast block). The structure is simple and the heat insulation effect is very good. The furnace only uses 20 tons of steel, and the original furnace. Steel consumption decreased by 45% compared to 37.3 tons. Since the furnace was put into production in 1987, after five years of production practice, the PMF furnace lining has accelerated the heating rate of the furnace, and the energy saving effect is remarkable. The PMF of the nearly 240m2 lining is firmly adhered and intact, and still maintains its thermal insulation effect. The workpiece, the old and new furnaces have a fuel consumption difference of 38%.

Third, the application of polycrystalline mullite fiber in rolling steel heating furnace

In November 1987, Zhejiang Oushiman Crystal Fiber Co., Ltd. cooperated with Anshan Iron and Steel Design Institute and Anshan Iron and Steel Small Rolling Mill to carry out a transformation of PMF100 series polycrystalline mullite fiber on two step-type rolling steel heating furnaces in the second workshop of the small factory. (The furnace has entered the ranks of special furnaces of the Ministry of Metallurgy since 1985, and its average unit consumption has been maintained at 1.46GJ/t). After the transformation, it has achieved low consumption and high output.

Comparison before and after the transformation of rolling steel heating furnace (Table 2)

As can be seen from Table 2, the increase in production is much larger than the energy consumption, and the energy saving rate is 6.88%. This is a new indicator reached in the special furnace. Due to the use of a full-fiber top, the heat sensitivity of the furnace is improved, and the time from the ignition to the tapping of the cold furnace is shortened by nearly two hours, resulting in a significant increase in production efficiency. At the beginning of 1989, the whole fiber furnace was changed into a whole watering, and a 50mm thick PMF (still a flat flame burner) was placed inside. When not pasted, the gas consumption is 2600m3/h, and after the paste is reduced to 2400-2450m3/h, the energy saving rate is 6-8%. When the furnace is ignited to the tapping, the sticking fiber is 1 hour ahead of the unattached. The No. 5 Steel Plant also uses the PMF series on the rolling steel heating furnace to replace the high temperature mixed refractory fiber (NONOFRAX) of Toshiba Electroforming Refractory Co., Ltd. as the heating furnace lining.

Fourth, the application of polycrystalline mullite refractory fiber products in a full hydrogen hood furnace

Annealing of hood furnaces for cold rolled strip is one of the key processes in the production of cold rolled sheets. In 1988, when Anshan Iron and Steel Cold Rolling Sheet Plant introduced 40 full hydrogen hood furnaces from abroad, the refractory materials of the furnace were made of lightweight refractory bricks and imported polycrystalline mullite products. After several years of use, light refractory bricks were found. There are many problems with the hood furnace. To this end, when the project of 36 full-hydrogen hood furnaces was introduced again in 1993, Angang Cold Rolled Sheet Plant cooperated with Anshan Iron and Steel Design Institute and Zhejiang Oushiman Crystal Fiber Co., Ltd. to solve the problem of polycrystalline mullite refractory fiber products instead of import. Refractory materials and lightweight refractory bricks, the application technology of polycrystalline mullite refractory fiber products is based on the National Science and Technology Commission document (Guo Ke Fa Cheng Zi [1996] No. 349) on the release of the "Ninth Five-Year National Science and Technology Achievements Key Promotion Plan Guide In the project > (2) new materials and new products of 97070101A project, mainly use polycrystalline Mo industrial area stone refractory fiber products for hot cover burner area lining instead of lightweight refractory bricks to cover the furnace heating cover burner area lining The use of this polycrystalline mullite refractory fiber product has achieved considerable economic and social benefits since it was put into production in 1995. The annual operating time of the equipment has increased by 5,640 hours and the annual production capacity has increased by 19,740 tons. The energy saving effect is 18%, and the quality of the steel plate product is improved.

Main features of polycrystalline mullite crystal fiber products: low thermal conductivity, thermal shock resistance, easy processing, and low heat storage.

Main performance: bulk density: 200-600kg/m3

Operating temperature: 1500oC

Thermal conductivity (W/MoC); 1000oC-0.16 1250oC-0.22 1350oC-0.25

Through the introduction of the hood furnace in the early stage of the Angang Steel Cold Rolled Sheet Plant, the use of lightweight refractory brick lining and the introduction of a fully integrated hydrogen furnace using polycrystalline mullite refractory fiber composite precast block lining and imported refractory lining production practice, The following conclusions can be drawn:

1. The domestic polycrystalline mullite crystal fiber vacuum forming block meets the requirements of the refractory material in the burner area of ​​the full hydrogen hood furnace heating cover, and can completely replace the imported refractory material.

2. In the area of ​​the heating cap burner for the full hydrogen hood furnace, compared with the lightweight refractory brick, the polycrystalline mullite crystal fiber vacuum forming block can reduce the repair time, improve the equipment operation time and increase the production capacity. To save energy and reduce the consumption of spare parts for imported equipment.

3. The polycrystalline mullite crystal fiber vacuum forming block is used as the lining of the full hydrogen hood furnace burner area, and the economic benefit is remarkable.

To this end, Benxi Steel, Wuhan Iron and Steel and other enterprises have also carried out the transformation of the full hydrogen hood furnace, using polycrystalline mullite fiber products for the lining of imported refractory materials, and achieved good results.

5. Application of polycrystalline mullite fiber in bell jar kiln

In December 1989, Zhejiang Oushiman Crystal Fiber Co., Ltd. and the State-owned 999 Factory Design Co., Ltd. cooperated to build two bell jar kiln with a temperature of 1400oC intermittent full fiber furnace. The lining material in the furnace was made of polycrystalline Moola. Stone fiber hard product PMF-300 series (capacity 300kg/m3), which is made of polycrystalline mullite fiber loose cotton added with special binder by vacuum suction filtration. The total thickness of the lining is 180mm, and the top of the PMF product is 70mm. Thick, furnace wall 60mm thick, after nearly two years of high temperature continuous operation, fiber furnace lining intact, achieved very obvious comprehensive economic benefits, energy saving rate of more than 30%, improve the yield rate of 30-40%. The bell jar kiln has achieved remarkable technological progress due to the adoption of the PMF series, reaching the international advanced level. In 1990, it passed the identification of electromechanical technology and was the demonstration furnace of the bell and kiln of the Ministry of Electrical and Mechanical Engineering.

6. Application of polycrystalline mullite fiber products in thermal insulation cover and tunnel kiln, gas energy-saving intermittent kiln

1. The original design of the thermal insulation cover of the continuous steel ladle rotary tower of WISCO is made of castable. Because of the large material capacity (compared with fiber products), it is easy to fall off during use and endanger safety. In view of this, at the end of 1996, a polycrystalline mullite fiber composite structure was used as a heat insulating cover. After more than three years of practical use, the effect is good, which can effectively reduce the heat loss of molten steel and improve the service life and safety of the thermal insulation cover.

2. The gas-fired energy-saving intermittent kiln produced by the Jiangxi Ceramic Research Institute has won the national utility model patent and has won many provincial and provincial awards. The kiln body adopts a polycrystalline mullite fiber product and a lightweight refractory brick composite structure, that is, the fiber product is attached to the lightweight brick wall with a high-temperature adhesive, and the flame is directly connected to the flame. The crystal fabrics of Jingmolai Factory not only have the characteristics of high temperature resistance, low heat shrinkage rate, low heat dissipation, firm adhesion, no slag and long service life, but also significant energy saving effects, especially between 1450oC-1470oC. The fibrous product still maintains good performance under the atmosphere. Undoubtedly, it has created favorable conditions for the technical distribution of ceramic thermal equipment and energy conservation, and the market prospect is very broad.

3. In May 1996, the Dehua Dayi Kiln Material Application Technology Research Institute of Fujian Province applied polycrystalline mullite fiber and its products to the high temperature parts of ceramic tunnel kiln and shuttle kiln. The examples of use are:

In May 1996, polycrystalline mullite fibers and products were applied to the tunnel kiln of Dehua Huisheng Ceramics Co., Ltd. The kiln is 2500×400×600, and the fired products are ceramic western toys. Before the transformation: the firing temperature is 1250-1350C, the fuel is zero diesel, the kilowatt porcelain fuel consumption is 0.2385, and the high temperature section surface temperature is 96oC. After the transformation, the same firing temperature, fuel and products, kilogram porcelain fuel consumption Only 0.1852, the surface temperature of the high temperature section fell to 41oC, the fuel economy rate reached 28.78%, and the high temperature section is still intact.

However, when applying polycrystalline mullite fibers and products, it should be reasonably distributed according to the firing temperature, which is economically feasible, and correspondingly improve the position and volume of the combustion chamber. After more than three years of use, the energy-saving effect is fully proved. Significant, economical and long service life, and the “Application of polycrystalline mullite fiber in ceramic shuttle kiln” was also designated by the State Science and Technology Commission in March 1998 as “1998 National Science and Technology Achievements Promotion Project Plan”. (Project number is 98E061D7200074).

The above examples are just a few examples of polycrystalline mullite fibers that are typical in industrial applications. Other metallurgical heating furnaces in Anshan Iron and Steel, Wuhan Iron and Steel, Baotou Steel, Maanshan Iron and Steel, Jinan Iron and Steel, as well as more than 900 enterprises and scientific research institutes in chemical industry, machinery, ceramics, glass, building materials, electronics, military, etc. have been widely used. And try, practice proves:

1. Because the polycrystalline stone fiber is loose and porous, it has the characteristics of low thermal conductivity and high blackness coefficient. In addition, its high temperature stability and rapid cold resistance and rapid heat resistance are currently used in high temperature furnaces for a wide range of working surfaces. Its energy saving effect is very obvious.

2. The energy-saving effect of polycrystalline mullite fiber in high-temperature furnace window is better than that of general refractory brick or high-temperature coating. The energy saving is far greater than the heat loss. The reason is not only because the heat loss is reduced, but mainly Since the convective heat transfer of the furnace gas to the furnace wall is enhanced, the furnace wall can obtain more heat, and then the radiation is transmitted to the material, thereby improving the heating speed and production capacity of the material.

Therefore, the use of polycrystalline mullite fibers and their products have achieved the same satisfactory energy-saving effect, effectively promoting the light weight and technological progress of high-temperature furnaces in China, especially in today's high-energy era, more national energy Savings have contributed. To this end, Zhejiang Oushi Man Group Deqing Crystal Fiber Factory has also been recognized by the State Science and Technology Commission as the technical support unit for the “National Key Scientific and Technological Achievements Promotion Plan” project “Production and Application Technology of Polycrystalline Mullite Fiber and Its Products”.

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