Application of Polycrystalline Mullite Fiber in Steelmaking Production

The second steelmaking plant of Angang built a large open hearth furnace-billet continuous casting production line in March 1986, and has achieved certain production results.
Production practice has proved that the key to limit and affect the yield and quality of billets is molten steel testing. In order to provide qualified molten steel, our factory and other domestic manufacturers have adopted the method of tapping temperature rather high than low. As a result, the energy consumption of steelmaking increases and the inclusion of molten steel increases, which not only affects the rapid delivery of steel and other troughs, but the baking of ladle by our own and traditional ladle baking equipment still fails to achieve the desired effect.
In the face of the above situation, after careful analysis, we realize that: from raising the ladle temperature, to maintain the temperature of molten steel, but also to achieve a more ideal effect. To this end, we designed and developed a new ladle baking equipment. The cover body of this equipment is both the cover and the heat exchanger, and also has a certain service life. For this reason, the cover must be made of refractory materials for thermal insulation and keep the cover unchanged. After a variety of long-term tests, it is confirmed that the use of polycrystalline mullite fiber for the ladle cover insulation material is better.
Characteristics of 1. polycrystalline mullite fibers
Polycrystalline mullite fiber has stable chemical properties and is not corroded by acid, alkali and reducing chlorine. The main components are Al2O3 accounting for 72%-75%,Al2O3 + SiO2 is more than 99.6, the main crystal phase is AsS2, the melting point is 1850 ℃, and the specific surface is 35.5M2/G at 1000 ℃.
The newly developed ladle baking equipment in our factory is to paste polycrystalline mullite fiber stacking blocks on the lining surface of the ladle lid by pasting method. Its specific heat is 1.24KJ/KG.℃. The thermal conductivity is 0.24 W/M.℃(1200 ℃).
Polycrystalline mullite fiber has low heat capacity, small thermal conductivity and large surface area. Pasting it on the inner surface of the cover can effectively convert the sensible heat of the gas into strong radiant energy. Therefore, polycrystalline mullite fiber can be used as the heat insulation radiator of the cover for heat preservation and energy saving.
2. Use of Polycrystalline Mullite Fiber as Cover Insulating Radiators
The equipment with polycrystalline mullite fiber as the insulation radiator covered was put into trial use on November 6, 89. The trial situation was tracked and tested, and hundreds of sets of data were obtained. In the process of using the equipment, it is found that the pasting process is the key problem. The pasting must be carried out strictly according to the process requirements. There must be no raised sharp objects along the ladle. Otherwise, it is easy to scrape off the Moye stone fiber. Once scraped off, it can be repaired and used. This fiber is afraid of humid gas, so it cannot be baked and overhauled ladles by hand.
The equipment using polycrystalline mullite fiber as the covering heat insulating radiator is 4.7 ℃ lower than the original equipment for baking ladles with average temperature. The termination temperature is increased by 13%, the time is shortened by 56%, and the gas consumption is reduced by more than 50%. According to the average temperature rise rate, the original equipment using polycrystalline mullite fiber to cover the new equipment is increased by 2.98 times on average.
Compared with the ladle baked with the original equipment, the ladle baked with the new equipment provides the best level of molten steel continuously in 89 years and 10 parts. The comparison is as follows: the tapping temperature is reduced by 1.2 ℃, the average temperature at the argon blowing station is increased by 4.5 ℃, the argon blowing time is prolonged by 1.13min, the temperature is reduced, the ladle body stores more heat, and the molten steel heat loss is less. This is to reduce the tapping temperature and improve the life of furnace body, reduce energy consumption laid the foundation, while the qualified for continuous casting negative water temperature increased by more than 1.97. In this way, our factory can arrange more than 50000 tons of T high-temperature molten steel in open hearth.
3. energy saving benefit
The use of polycrystalline mullite fiber as a cover of the insulation radiator, energy-saving effect is more significant. According to the actual situation of our factory, if we use this new equipment to bake ladles, we can save 247530GJ of gas in baking ladles every year and 8455.83 standard coal.
Because the average temperature of the ladle has increased by 110-130°C (referring to the intermediate temperature of the ladle lining). The ladle body increases the heat storage of 1303096KJ. When 100T of molten steel is filled, it is equivalent to the loss of 1303096KJ of heat from the steel, then the molten steel can be reduced by 15.6 ℃, and the open hearth can consume 20016T less heavy oil and 2852.6T less standard coal per year.
In the whole year, more than 50000 t of high-temperature molten steel can be smelted less, 157.5t of heavy oil can be consumed less, and 222.5t of standard coal can be converted.
Due to the decrease of tapping temperature, the life of the furnace body is relatively prolonged, which can save more than 4000 T of refractory materials and more than 3000 standard coal indirectly.
In short, the use of polycrystalline mullite fiber stacking paste cover lining, its comprehensive energy-saving benefits can reach 14530.93T/standard coal. Value 3.63 million yuan/A.
Therefore, polycrystalline mullite fiber has high use value.