The hot blast stove of blast furnace is one of the important auxiliary equipments of blast furnace. It is a kind of regenerative heat exchanger, which can provide a certain temperature hot air for the effective operation of blast furnace, that is to say, it will be pumped into the blast furnace coke combustion of air from room temperature heating to high temperature (about 1200 something 1350 & amp; deg; C) , the wind should be adequate, continuous supply. Therefore, each blast furnace generally needs to be equipped with 3 × 4 hot-blast Stove, in order to heat and supply air energy alternately.
Recently, one of the contents of the modernization of blast furnace ironmaking technology is to adopt high blast temperature technology, which is one of the important conditions for ironmaking production. Therefore, regardless of foreign, domestic are always to raise the hot blast stove blast temperature work to the important agenda. It has been proved by practice that the increase of hot blast temperature can not only reduce coke ratio but also increase hot metal content. The results show that the coke ratio can be reduced by 15 ± 20 kg per ton of iron and the output can be increased by 3% when the blast furnace temperature is increased by 100 ° c within a certain temperature range. The blast temperature of many blast furnaces abroad has been over 1200 °C for a long time.
Refractory for stove body
In order to achieve high blast temperature of hot-blast Stove, besides operating conditions, high temperature heat source, structure of hot-blast Stove and other factors, it is necessary to have the Refractory which can bear high temperature for a long time and meet the technological requirements of hot-blast Stove. The Refractory used for hot blast stove should be able to withstand high temperature and high pressure, with good creep resistance at high temperature, large heat capacity of brick and good heat conductivity, which is favorable for heat exchange and raising wind temperature. When the temperature of hot air is lower than 900 °C, clay brick is usually used as masonry. When the temperature of hot air is higher than 900 °C, clay brick is usually used as masonry, and when the temperature of hot air is higher than 900 °C, clay brick is usually used as masonry, high-temperature lining and checker bricks are made of high-alumina brick, mullite brick, sillimanite brick and silica brick.
Different operating conditions and damage characteristics of different parts of the hot blast stove require different physical and chemical properties of the Refractory used. The brick used in hot blast stove can be divided into two parts: High temperature zone and middle and low temperature zone。
High Temperature Zone brick includes: Combustion Chamber upper brick, regenerator upper checker brick and upper large wall brick, furnace top brick, etc. . Middle and low temperature brick area includes: Middle and lower brick of combustion chamber, checker brick of middle and lower part of regenerator and large wall brick of middle and lower part of regenerator。
The medium-low temperature zone uses a large amount of bricks, accounting for about two-thirds of the total amount of bricks used in hot blast stoves. This part can be used relatively dense, clay bricks or high-alumina bricks. Because of the difference of production operation and air temperature level in high temperature area, the requirement of physical and chemical properties of refractory brick is different. For example, special attention should be paid to the thermal stability of the furnace top brick to prevent the brick from peeling off or breaking off due to sudden change of temperature, the upper part of the combustion chamber and the regenerator should have higher structural strength at high temperature, lower linear shrinkage during reburning, and good slag resistance, etc. , in order to prevent the combustion chamber high temperature deformation, tilt and lattice brick subsidence, lattice hole disorder. The lattice brick also requires good heat conductivity, heat capacity, heat absorption and heat release are relatively fast. These requirements shall be based on the air temperature level of the hot blast stove。
When the hot-blast Stove is working, the lining is affected by the rapid change of temperature in the heat exchange process, the chemical erosion of blast furnace gas with dust, the mechanical load and the erosion of combustion gas, etc.。
The main reasons for the damage of hot-blast Stove lining are as follows：
(1) thermal stress. When the hot-blast stove is heated, the temperature of the combustion chamber is very high, and the temperature of the top of the stove can reach 1500 ° 1560 ° C. The temperature decreases gradually from the top of the stove down along the furnace wall and lattice brick. Because of the continuous heating of the hot-blast Stove, the lining of the hot-blast stove and the checker bricks are often in a state of rapid cooling and rapid heating, cracks, cracks and spalling occur in the masonry.。
(2) chemical erosion. Coal Gas and combustion air contain a certain amount of Basic oxide, and the ash after combustion contains 20% iron oxide, 20% zinc oxide and 10% Basic oxide, most of which is discharged from the furnace, however, a few components adhere to the surface of the masonry and penetrate into the brick body. Over time, this leads to damage to the lining, cracking, and loss of strength。
(3) mechanical loading. Hot-blast stove is a kind of high structure, its height is generally between 35 ° and 50 meters. The maximum static load of the lower part of the checker brick in the regenerator is 0.8 MPA, and the static load of the lower part of the combustion chamber is also higher。
(4) stress. The hot-blast stove periodically carries on the combustion and the air supply, the combustion period is in the low pressure state, the air supply period is in the high pressure state. In the traditional structure of large wall and vault, there is a large space between the vault and the shell, and the filler layer of the wall and the Shell is set up, which also leaves a certain space after shrinking and natural compaction under long-term high temperature. Because of the existence of these spaces, under the pressure of high-pressure gas, the masonry is subjected to a great outward push, which easily causes the masonry to incline, crack and loosen, and then the space outside the masonry is periodically filled with and relieved of pressure through the brick joints, and then intensify the damage to the masonry。
The function of Refractory for hot blast stove is to insulate heat and bear high temperature load. Therefore, when determining the material and thickness of lining materials for each part of Stove, the requirements of temperature, load and heat insulation for Masonry shall be taken into account, and smoke on the physical and chemical effects of Masonry and other conditions。
The top, Wall and upper part of lattice brick of hot-blast stove in western European countries are generally made of Silica brick, while the middle and lower parts of hot-blast stove are made of high-alumina brick and clay brick respectively. The traditional materials of hot blast stoves in Russia are: the Top and top of the stove are built with high aluminium bricks (AL203) of 62% and 72% respectively, and the middle and bottom of the stove with clay bricks (AL203) of 38% respectively, therefore, the top of the furnace and the upper part of the 607m high part of the General Use of low, expansive Silica Brick Masonry, the rest of the different temperatures, respectively, using mullite brick, corundum brick, Kaolin brick and clay, earth brick。
The Japanese hot-blast stove selects different kinds and brands of firebrick according to different use parts, so as to make the best use of the firebrick, at the same time, the high temperature creep property of firebrick should be fully considered in order to ensure production safety in long-term work. Table 4 shows the performance and using position of refractory brick used in hot blast stove of blast furnace in Japan。
1 furnace top
The top of the hot blast stove is the high temperature zone in the stove. The Refractory at the top of the stove, especially the brick layer which is in direct contact with the hot air and the hot smoke, must have good thermal shock resistance and creep resistance. Generally uses the silica brick or the low creep high aluminum brick, the heat insulation layer is the clay heat insulation brick. When choosing insulation materials, special attention should be paid to the work of the hot surface temperature should not be higher than its allowed, the use of temperature。
2Hot Blast Stove Wall
The lining of a hot-blast stove comprises a working layer firebrick, a heat-insulating layer light brick and a filler. The upper part of the wall bears the higher temperature, while the lower part bears the lower wind temperature. The upper working layer of the big wall generally adopts low creep high aluminum brick or silicon brick, and the middle and lower part of the big wall generally adopts high aluminum brick and clay brick. Insulation layer, generally according to different parts of the use of different grades of insulation brick, fire-resistant ceramic fiber or filler。
3 hot blast stove partition
The hot blast stove partition wall is the fireproof wall which separates the combustion chamber and the regenerator. The partition wall and the top of the furnace can not be completely bricked to death, there should be a certain expansion joint (200 something 250 mm) , in order to make the air distribution even, the partition wall should be 400 something 700 mm higher than the checker brick of the regenerator. The lower part of the partition wall, the temperature difference between the two sides is very large, the difference of thermal expansion is also very large, so that the partition wall masonry continued to produce bending cracks. The upper part of the partition wall generally uses low creep high aluminum brick or silica brick, the middle and lower part generally uses high aluminum brick and clay brick.
4 Burner
A burner is a device used to mix gas with air and send it to a combustion chamber for combustion. In terms of materials, there are metal (mechanical) burners and ceramic burners. At present, ceramic burners are mostly used. During the air supply period, the temperature of the upper surface of the ceramic burner is slightly lower than that of the air; during the combustion period, the temperature is slightly higher than that before the air or gas enters the burner, the temperature of the upper part of the burner rises (or falls) very rapidly. In order to ensure the gas tightness, integrity and service life of the burner masonry, the linear expansion coefficient of the Refractory is required to be small and the creep resistance is good. Before the 1980s, almost all ceramic burners in China used high aluminum phosphorus, acid refractory castable or bauxite refractory precast parts, this material is suitable for the hot blast stove of medium and small blast furnaces and the ceramic burner with a blast temperature of about 1100 °C. When high aluminum phosphate refractory castable is used, it should be baked to about 600 °C before bricklaying to prevent the preform cracking in installation and use. Since the 1990s, due to the large-scale hot-blast Stove and the requirement of high air temperature, high-alumina cordierite is now used as Refractory, a few ceramic burners are made of mullite cordierite, and the lower part of ceramic burners is made of sillimanite except a few, almost all of them are high aluminum or clay Refractory。
5 Latticed bricks and fireballs
The main requirements of high temperature area latticed brick in regenerator are high temperature volume stability, corrosion resistance and creep resistance. Silicon brick has these characteristics and its price is cheap, therefore, it is widely used in hot blast stove with high blast temperature at home and abroad. According to the specific situation in China, when the design temperature of the top of the hot-blast stove is not less than 1400 °C, on the premise that the fuel is well burned and the operation level is high, the preferred Refractory in the high temperature zone of the hot-blast stove should be silica brick, at the same time, the residual quartz of Silica brick must be controlled not more than 2% . It is necessary to carefully determine the lower limit of the use of silica brick in the hot-blast stove using silica brick, and to set up a reliable temperature detection device to ensure that the lowest use temperature of silica brick is not lower than 800 ° °C in the production operation (including blowing-off) . When the design temperature of hot blast stove top is not higher than 1400 °c, the low creep and high density Refractory is more suitable for our country and can make full use of our country's rich bauxite resources. At present, the creep resistance of high aluminum Refractory has reached a better level abroad, such as HD brick in Hogovin, the Netherlands at 1350 °C, 0. The creep rate of AC-8M brick in Shinagawa-ku, Japan is 1300 ° C, 0.2 MPA and 50 H, respectively. 2% ; at present, the creep rate of high alumina Refractory in China is less than 1% under the corresponding conditions, which is still far from the advanced level in the world, and in view of the present situation of low creep high alumina brick production in China, it is necessary to control the content of impurities, especially Alkali metal and alkaline earth metal, while strictly checking the creep index of brick.
High Aluminum and clay Refractory are usually used for the lower and middle latticed tiles of the regenerator. With the increase of the regenerator height of the large hot blast stove, the pressure of the upper checker brick on the lower refractory is also increasing. In addition, according to the investigation of the damage of the checker brick of the large hot blast stove abroad, the cracking and breaking of the lower checker brick caused by the periodic temperature fluctuation are increasing. Therefore, in addition to the creep properties of the lower clay brick, the normal temperature compressive strength and thermal shock stability of the product should be controlled, qualitative Times (resistance to rapid cooling and heating) put forward higher requirements. In the regenerator of the ball-type hot air stove, the fire-resistant ball is used instead of the checker brick. The hot blast stove with fireball instead of lattice brick has been used in small blast furnace. The fireball has the advantages of large heat surface area, large heat capacity, large heat exchange area and high air temperature. In the high temperature zone, the refractory ball material is usually high aluminum Refractory, and in the low temperature zone, clay Refractory.
6 Combined Brick for each hole of hot blast stove
There are many holes in hot-blast stove, and the working condition is very bad, so the life of the hole is often the weak link in the whole structure. In order to improve its life, people try every means to improve its integrity, stability and the use of high-temperature refractory characteristics. Combined brick technology is a comprehensive technology which integrates these measures. The technology of combined brick has been widely used abroad, and it has been popularized and widely used in China since the introduction of this technology in Baosteel.
7Spray coating and acid resistant coating on hot blast stove shell
In order to reduce the surface temperature of the shell and pipes of hot-blast stove, to prolong its service life and reduce the heat loss, at present, most hot-blast stove adopts many kinds of fire-resistant spraying materials. For example, four 4000M3 blast furnaces at Baosteel have been sprayed with acid-resistant spray paint (thickness 50? ? 70? MM) on the combustion chamber, the top of the ball and the connecting pipe of the regenerator of the hot blast furnace, and medium and heavy-duty spray paint on the straight barrel of the combustion chamber and the middle of the regenerator, the thickness is 45 × 77 mm, the lower part of regenerator is sprayed with slag wool material, the thickness is 46 × 51 mm, the high temperature zone of hot blast furnace is sprayed with acid resistant coating, the thickness is 65 mm, the middle and low temperature zone is sprayed with coating, the thickness is 50 mm; The hot blast stove of masteel 2500M3 blast furnace also adopts advanced spraying, coating technology and coating materials, among which the hot blast stove ball item is 130 acid-resistant coating, the other parts are common coating.
