The use and development of refractory linings for hot blast stoves, the selection of refractory materials for hot blast stoves is mainly determined by the temperature of the hot blast. When the air temperature is lower than 900℃, clay bricks are generally used, and the service life can reach about 20 years; when the air temperature is 900~1100℃, high-alumina bricks, mullite bricks or Sillimanite bricks; when the wind temperature is higher than 1100 ℃, high alumina bricks, mullite bricks and silica bricks are generally used as furnace lining or checker bricks.
In recent years, the newly built or rebuilt blast furnace hot blast stoves in various countries are mainly of the external combustion type, the air supply temperature is 1200~1350℃, and the vault temperature is generally 1500~1550℃, even close to 1600℃. Therefore, the high-temperature parts of the furnace lining and the upper layer of checker bricks are generally built with silica bricks, and the use effect is better.
Japan’s large-scale blast furnace hot blast stoves mainly use Coopers type hot blast stoves, and recently Nippon Steel has built more hot blast stoves; West Germany uses Coopers type or Maqin type hot blast stoves, and other countries in Western Europe mostly use Didier type hot blast stoves In addition to building some external-combustion hot-blast stoves, the United States attaches great importance to the transformation of internal-combustion hot-blast stoves, which can obtain higher air temperature and prolong the service life.
Before the 1960s in the United States, blast furnace hot blast stoves were mainly built with clay bricks and semi-silica bricks. After completing a single furnace operation in the blast furnace, the hot blast stove undergoes a maintenance process where only the upper section of the regenerator, specifically the 3-5m high checker bricks, is replaced, while the remaining passages of the checker bricks are cleaned and reused. The high-temperature sections of the hot blast stove typically utilize high-grade or super clay bricks, high-alumina bricks, and mullite bricks as lining materials.
In the 1970s, inexpensive silica bricks were commonly employed for the high-temperature sections of hot blast furnaces. When the temperature of the upper part of the regenerator exceeds 1420℃, periclase checker bricks with strong alkali corrosion resistance, good thermal conductivity and large heat storage are used. The table shows the performance of refractory bricks used in blast furnace hot blast stoves in the United States.
Black silica bricks are generally used for the dome, furnace wall and checker brick upper part of hot blast stoves in Western Europe. In black silica bricks, the content of iron oxide and titanium oxide is relatively high, which has a high specific gravity, good thermal conductivity, and strong heat storage capacity, so the thermal efficiency is high. The middle and lower furnace walls and checker bricks of the hot blast stove are made of high alumina bricks and clay bricks respectively.
In the past five years in West Germany, there have been no new changes in the refractory materials used in blast furnace hot blast stoves. Typical hot blast stove materials, from high temperature to low temperature, use silica bricks, sillimanite bricks, mullite bricks, high alumina bricks and clay bricks. The performance indicators of some bricks have been slightly improved.
The traditional material of the Soviet blast furnace hot blast stove is: the dome and the upper masonry are built with high-alumina bricks with an Al2O3 content of 62-72%, and the middle and lower masonry are made of clay bricks with an Al2O3 content of 38%. Recently, the hot blast stove Therefore, the dome and the upper part with a height of 6 to 7 meters are generally built with low-expansion silica bricks, and the rest of the parts are made of mullite bricks, corundum bricks, kaolin bricks and clay bricks according to the temperature.
China’s blast furnace hot blast stove is generally internal combustion type, and its lining and checker bricks are generally built with high alumina bricks and clay bricks; the high temperature parts of external combustion type hot blast stoves are generally built with silica bricks, and the medium and low temperature parts are in turn made of high temperature bricks. Aluminum bricks and clay bricks.
Japan Blast Furnace Hot Blast Stove selects different types and grades of refractory bricks for different parts of use to make the best use of them; at the same time, the high temperature creep performance of refractory bricks must be fully considered in order to ensure production safety during long-term work . In addition, the service life of Japanese hot blast stoves can generally be used by two blast furnaces, that is, 15 to 20 years.
To sum up, the refractory materials used in blast furnace hot blast stoves are similar in various countries. After the wind temperature increases, the furnace roof, furnace wall and checker bricks in the high temperature parts are generally built with silica bricks. Because the softening temperature of silica brick under load is high, almost close to its melting temperature; when it is above 600℃, its volume stability is good, the change of refiring line is equal to zero or slightly expanded, and it has strong alkali corrosion resistance. At the same time, the high-temperature creep performance of silica bricks is particularly good. The silica bricks are measured under the conditions of 1.0 kg/cm2 load and heating at 1550℃; 1350℃ and 1300℃.
However, the volume density of silica bricks is small, and the heat storage capacity is poor. When the temperature is below 600 ° C, it is easy to change the type and destroy the integrity of the masonry. Therefore, all countries have stipulated the minimum operating temperature of silica bricks, which should generally be greater than 600℃, while Japan stipulates that it should be greater than 800℃. In addition, when the oven is baked at the low temperature stage, it must be done carefully to ensure the slow transformation of the product type without damaging the masonry.
It should be pointed out that Western Europe, like the United States, has tried periclase bricks with a high heat capacity of 95-96% MgO content in the upper part of the hot blast stove regenerator, and cheap semi-silica bricks are generally used in the middle and lower parts. The high temperature creep and volume stability of semi-silica bricks are better than that of clay bricks, and the thermal energy stability is better than that of silica bricks. In addition, mullite bricks are also used in the upper part of the regenerator and the parts with large temperature changes.
The load softening temperature and high-temperature creep performance of mullite bricks are similar to those of silica bricks, and the volume stability is good at low temperatures, and it is more convenient to start and stop the furnace; the heat storage capacity per unit volume is large. For example, if the heat storage capacity of clay bricks is 1. The sillimanite brick is 1.14, the silica brick is only 0.85, and the mullite brick is 1.2.
However, when making mullite bricks, it consumes a lot of energy and the cost is much higher than that of silica bricks. The picture shows the relationship between the temperature of the hot blast stove and the material of the checker brick in various countries. The numbers indicated in the figure are the content of alumina. It can be seen from the figure that with the increase of the air temperature of the hot blast furnace, the quality of refractory bricks is also continuously improved. Taking the high temperature zone as an example, it develops from clay bricks to silica bricks, high alumina bricks, sillimanite bricks, andalusite bricks and molybdenum bricks. Come stone bricks. As mentioned earlier, the application of periclase bricks is also promising.
The shape, size and arrangement of checker bricks used in blast furnace hot blast stoves are different, and the heat transfer efficiency is also quite different. The United States, Japan, West Germany, China and other countries generally use honeycomb lattice bricks. In recent years, the Soviet Union has conducted extensive research on the shape and heat transfer efficiency of checker bricks, emphasizing the use of large porous checker bricks (with 12 or 27 holes and a diameter of 25 or 30 mm) and obtained good results.
At present, there are more than 190 external-combustion hot blast stoves in the world, and the development continues. At the same time, many countries have also carried out research and transformation on internal combustion hot blast stoves. Among them, the transformation design of Hogowen Company in the Netherlands is relatively successful, which can make the hot air reach about 1200 ℃. The hot blast stove is called the Hogovin type internal combustion hot blast stove. Its main technical measure is to change the metal burner into a ceramic burner, which can rationally organize the combustion, increase the combustion temperature, and reduce the pulsation phenomenon; in order to maintain the stability of the partition wall structure, To prevent cracks, “short circuits” and dumping, expansion joints should be reserved during masonry to allow free movement in both vertical and horizontal directions.
At the same time, lightweight bricks are built in the middle of the partition wall, and heat-resistant steel plates are placed on the low-temperature side. This can reduce the temperature gradient of the masonry, reduce thermal stress damage, and prevent short-circuit accidents; the furnace roof adopts mushroom-shaped vaults, and It is located on the box-shaped ring beam, and there is a moving gap between it and the large wall of the hot blast stove. This type of roof structure has uniform force and long service life, but the brick shape is more complicated. For this reason, simplifying the brick type of the furnace roof and building it into a conical vault has better heat exchange effect and longer service life, which is an important direction for future development.
The Hogovin-type internal combustion hot blast stove was put into production in 1973. The temperature of the dome can reach 1500℃, and the temperature of the hot air is about 1200℃. Inspection after four years of production, the partition wall is not bent, cracked or leaked, and other furnace linings are in good condition. The hot blast stove is widely used in blast furnaces in the Netherlands, and 13 of them have been established in countries such as the United States, Britain, Australia, Mexico, and Canada, which meet the high blast temperature requirements for blast furnace operation.
China also adopts a design scheme similar to that of the Netherlands in the transformation of internal combustion hot blast stoves for blast furnaces. The furnace has high air temperature and long service life and saves about 30% of investment compared with newly built external combustion hot blast stoves.
As we all know, both the external-combustion hot blast stove and the Hogovin type internal-combustion hot blast stove can provide hot air at a higher temperature, but the former occupies a large area, requires a lot of investment, and the life of the masonry at the furnace top node is relatively low, while the latter has a complicated partition wall structure. The airflow distribution is uneven, and the further increase of wind temperature is limited to a certain extent.
Therefore, various countries are studying hot blast stoves without body structure, that is, top-combustion hot blast stoves. The capacity of the No. 2 blast furnace of China Capital Iron and Steel Company is 1327 m3, and the top-fired hot blast stove was successfully used for the first time, and the blast temperature can reach above 1200 ℃. The high temperature zone of the furnace is built with silica bricks, and the burner is poured with refractory castables around the circumference.
If the blast furnace hot blast stove uses lightweight refractory bricks, it should be compatible with the material of the working layer, that is, silica brick lining, and lightweight silica bricks should be used as the insulation layer.
After the air temperature of the blast furnace hot blast stove is increased, the spherical top furnace shell is corroded by the acid condensate in the furnace gas, resulting in intergranular stress, resulting in cracks or cracks. This phenomenon is more serious when the furnace top insulation layer is too thick. For this reason, many countries have adopted many protective measures, such as laying a layer of aluminum corrugated board to prevent the overflow of acid gas after laying lightweight refractory bricks, and then building a working lining: West Germany sprayed a layer of aluminum on the spherical top furnace shell. A layer of silicon acid-resistant spray paint, Japan and the United States and other countries use modified resin to prepare high-temperature resistant acid-resistant paint, which is applied to the inner surface of the furnace shell at high temperature to prevent acid erosion.
The structure type and operation system of the burner have a great influence on the work of the blast furnace hot blast stove. At present, ceramic burners are generally used in large and medium-sized blast furnace hot blast stoves. This type of burner is built with refractory materials in the combustion chamber, the work is cyclical, the temperature fluctuation is about 600 ℃, and it is affected by air flow scour and chemical erosion, so the use condition is poor.
Since the appearance of ceramic burners in the early 1960s, the air gas channels are generally built with high alumina bricks and clay bricks, and the parts with radiation holes are built with mullite bricks or mullite corundum bricks; It is generally prefabricated into large blocks with refractory castables, which can be hoisted on site.
The construction speed is fast and the use effect is good; the Azov Steel Plant in the Soviet Union used MKB-72 inchstone bricks to build the upper part of the ceramic burner on the No. 4 blast furnace hot blast stove. At the nozzle, cracks appeared in the masonry after 13 months of use, but it can still be used; when it was built with MKF-80 mullite corundum bricks, it was put into production in January 1976. After 3.5 years of use, the lining is still intact of. The properties of these two bricks are shown in the table.
The furnace wall around the hot air outlet, as well as the lining at the interface with the main air duct and the corner of the air duct, are generally built with high alumina bricks or mullite bricks. Due to the complex structure and high temperature here, when bricks with poor creep resistance are used, bricks often fall off, causing the furnace shell or tube shell to turn red, and they are forced to cool down and operate until the furnace is shut down. For example, the average air temperature of a blast furnace external combustion hot blast stove in West Germany is 1246℃, and the highest temperature is 1380℃.
When the lining around the tuyere and at the joint or corner of the air duct is built with andalusite bricks with an Al2O3 content of 70%, the bricks will fall off within 12 months of production; after using sintered corundum bricks, use The service life is 15 to 27 months; when high alumina bricks or mullite bricks are used to build the furnace wall around the tuyere, and black silica bricks are used to build the lining of the main air duct, excellent results have been obtained.
When the lining body at the tuyere of the hot blast stove or other holes is partially damaged, Japan uses water glass aluminum silicate press-in materials for repair, and good results have been achieved. For example, near the temperature measuring hole of No. 1 hot blast stove in a factory 25 meters from the ground, the temperature of the furnace shell reached 180-270℃, which affected production.
For this purpose, holes are drilled on the furnace shell around the temperature measuring hole, and nozzles are installed, and 1570 kg of refractory pressure material is squeezed in at a pressure of 1.0 kg/cm. After the repair, the temperature of the furnace shell was reduced to 60~90℃. After more than a year of use, the temperature has not risen, that is, the lining repaired by refractory press-fit material is good.
Blast furnace hot air surrounding pipes and other parts are generally built with refractory bricks. The working layer of clay bricks is 170 mm thick, and the thickness of the lightweight brick insulation layer is 350 mm. If it is carefully built according to the construction regulations, the surface temperature of the shell is generally lower than 100 ℃.
The linings of air supply branch pipes and hot air valves are generally poured with refractory castables. The material should have the characteristics of good volume stability, high strength, low thermal conductivity, good thermal shock stability and convenient construction. During the production process, the lining will not peel off or crack and have a long service life.
For example, the large-scale blast furnace air supply pipe system of more than 4,000 m3 in Japan generally uses the brand BPC-1 ultra-high aluminum refractory castable as the lining. The material uses high-grade aluminate cement as the binder, alumina powder as the powder, and corundum as the refractory aggregate. The lining made of this material has a long service life, but it has high thermal conductivity, fast heat dissipation, and high shell temperature; It is made of CN140 and H160-1 refractory castables, and has achieved good results.
The elbow, the upper spherical surface, the nozzle seat, the lower spherical surface and the working lining of the nozzle are poured with refractory castables, and their thicknesses are 75~110, 75, 75~95, 75 and 40mm respectively; the heat insulation layer is made of light refractory The castables are poured, and the thicknesses are 50~110, 50, 50, 50 and 33 mm respectively.
The Japanese blast furnace hot air valve is made of special steel, and the surface is poured with refractory castable lining, and the service life is generally about 2.5 years.
Recently, in order to improve the service life and energy saving of the direct injection pipe, Japan Bomo Refractory Co., Ltd. adopts a centrifugal molding machine to make a double-layer refractory castable pipe lining. First, place the direct injection pipe on the molding machine, pour in light refractory castables with a thermal conductivity of 0.18 kcal/m·h·℃, and centrifugally form the heat insulation layer (thickness is 20~40mm); after curing, reshape Refractory castable working layer (thickness 40~50mm).
The average service life of the pipe lining constructed by the ordinary pouring method is 72 months; the average service life of the pipe lining formed by the centrifugal method is 13.8 months at the beginning, and after improvement, the average service life reaches 38.4 months. The shell surface temperature dropped from 354℃ to 268℃.
A large-scale blast furnace hot blast pipe and air supply branch pipe of a large-scale blast furnace in China are lined with high-alumina phosphate refractory castables. Using one furnace, there is only slight wear and tear. The direct injection pipe is also made by hand with the same material, and the service life Better than refractory brick lining.
Production practice has proved that in the blast furnace system of various countries, amorphous refractory materials are used as linings in many parts, and good results have been achieved.
