What are the effects of shaft furnace pelletizing on blast furnace?

Pelletizing is another method of finely grinding iron concentrate or other iron-containing materials into blocks. The mixture of concentrate powder and flux (sometimes binder and fuel) is rolled into green pellets with a diameter of 8- 15 mm (larger for steelmaking) in a pelletizing machine, and then dried, roasted and solidified to form high-quality iron-containing raw materials with good metallurgical properties, which can be supplied to iron and steel smelting. I. Structure of Pellet Shaft Furnace According to its cross-sectional shape, there are two kinds of shaft furnaces: round and rectangular. Round shaft furnaces appeared in the early days, and now Switzerland is almost rectangular except for a few. The disadvantages of foreign shaft furnaces are: (1) high power consumption. According to the analysis of LKAB company in Sweden, its power consumption is as high as 50 kW h/. The main reason of high power consumption is its high material column. When the cold air passes upward through the roasting zone, the gas velocity in the material layer is high, the resistance is high, and the working pressure of the main fan is high, so the power consumption is high. (2) Foreign shaft furnace pellets generally use high calorific value fuel, heavy oil or natural gas, which is limited to roasting magnetite pellets. (3) The feeding speed is uneven, and the roasting consolidation is uneven, which affects the pellet quality. The foreign shaft furnace itself is a silo structure. When pellets with the same cross section are discharged, the discharge speed is uneven, the center of the discharge port is faster and the two sides are slower, which makes the pellets stay in the furnace for different times, so the roasting consolidation is uneven and affects the pellet quality. (4) In foreign shaft furnaces, two movable adhesive tapes are generally used to distribute cloth in a "B" shape. A shaft furnace with a width of 2.44 m and a length of 6.4m needs 140s at a time, and the distribution truck has to go back and forth eight times along the width direction. If the furnace type is expanded again, the distribution cycle must be extended, so it is difficult to keep the surface temperature distribution of the material uniform, which is not conducive to operation and affects the pellet quality. The main feature of shaft furnace in China is that shaft furnace pellets use blast furnace gas as fuel, unlike foreign shaft furnaces which use high calorific value fuel (heavy oil) or natural gas and coke oven gas. This is because the new furnace structure in China has improved the air permeability in the furnace, increased the penetration ability of combustion waste gas and cooling air, uniform airflow distribution, reasonable roasting system and stable uniform zone, which has created conditions for recrystallization and grain growth and consolidation of pellets. Two. Working environment of each part of pellet shaft furnace (I) Combustion chamber In China, 8m2 pellet shaft furnace usually adopts rectangular combustion chambers, which are arranged on both sides of the shaft furnace hearth. Most of the combustion chambers burn blast furnace gas, and the waste gas after combustion forms a certain pressure, which is sprayed into the furnace from the vertical furnace mouth to roast pellets, and finally reaches the top of the furnace, and is discharged into the atmosphere after dust removal. A prominent feature of the combustion chamber is positive pressure operation. Therefore, the combustion chamber must be well sealed and there can be no gas leakage. Practice has proved that the combustion chamber is the weak link of the shaft furnace body. At present, the first generation life of shaft furnace is short, only 1 ~ 3 years, which is closely related to the combustion chamber and determined by the harsh working environment of the combustion chamber. The combustion chamber bears the high temperature of11120℃ and the pressure of 10 ~ 20 kpa. If the masonry quality is not good, it is easy to leak and catch fire, so the combustion chamber may sometimes burn through, which seriously affects the normal operation of the shaft furnace. In addition, the temperature of the combustion chamber is high, and the whole masonry is displaced due to thermal expansion. The existing combustion chamber underframe is freely placed on the concrete platform, and the surface of the platform is rough, and the friction caused by thermal expansion is large, which is easy to cause cracking of the top masonry. The combustion chamber not only operates under positive pressure, but also bears certain pressure, which is easy to burn through. The burn-through parts are mostly vault, arch foot, burner, air inlet and so on. Once burned through, the pressure will drop sharply, and the ability of exhaust gas to penetrate the material column will be affected, so the combustion chamber must be sealed. In addition, the combustion chamber is also affected by the horizontal thrust of the arch foot and the gas side pressure of the furnace wall. The closure of the shaft furnace also caused some losses. The combustion chamber of shaft furnace is generally built with a 60-degree vault. Due to the existence of vault, a certain horizontal thrust is generated. The heavier the vault, the greater the horizontal thrust. The shaft furnace operates under positive pressure, gas is injected into the combustion chamber for combustion under a certain pressure, and the generated hot waste gas is injected into the furnace chamber from the flue of the combustion chamber. It can be seen that if the combustion chamber is not tightly sealed, enough pressure can not be formed and the technological requirements of roasting pellets can not be met. According to the calculation, the gas pressure generated by the side wall is very high. The shaft furnace production needs to be stopped, which has the greatest damage to the combustion chamber. The shaft furnace has been in production for a long time, and the combustion chamber is in high temperature. The expansion of refractory bricks stops when they reach a certain size, which is relatively stable. However, if the furnace is stopped, the temperature of the combustion chamber will drop, especially to normal temperature, and the masonry will naturally shrink. Open and stop the shaft furnace. Masonry will expand and contract, and cracks will appear after repeated several times, especially when the arch foot and vault move, which will burn through. Therefore, to ensure the long life of the combustion chamber, not only the masonry meets the requirements, but also the sealing is good. But also improve that operation rate of the shaft furnace. This is very important to prolong the life of the combustion chamber. To sum up, the combustion chamber is a weak link of shaft furnace, which is in a high temperature state for a long time and the working environment is relatively bad. (2) Air guide wall: Air guide wall is another weak link of shaft furnace. It is supported by the metal water beam below, often eroded by high temperature and dust airflow, and also bears the lateral pressure of the burden. Therefore, the working environment of the air guide wall is also very bad. The junction of water beam and masonry, especially the masonry under 1m, is the easiest to fall off. Therefore, it is very important to choose the material, unit size and hole wall thickness of the air guide wall. 3. Refractory material for shaft furnace (1) Combustion chamber is the main masonry body of shaft furnace, and it is usually built with clay bricks or high alumina bricks. For example, the bricklaying amount of two combustion chambers in Hangzhou Iron and Steel Company is about 120t ... The joint is less than 2mm, 70 1 mortar is used in important parts such as vault, and ordinary mud is used in furnace bottom and other parts. In the process of bricklaying, due to the large working face and many bricks, if there is one place that can't meet the quality requirements of bricklaying (such as large cracks in bricks and insufficient mud, etc.). ), the hot gas will pass through these weak points and move along the inner wall of the furnace shell, and leak out from the loose part of the metal furnace shell. The expansion problem mainly depends on the fillers such as insulation bricks and feather ash outside the masonry to buffer the expansion or contraction of refractory brick masonry. The cross-section of the baking zone of Benxi Steel 168m2 shaft furnace is 2.088m wide and 7.056m long. Height of arch trunk zone 1.260 m, height of preheating roasting zone 2.660 m, height of soaking zone 2.570 m, height of cooling zone 3.500m, height from center line of ore drum to furnace mouth 12.8 10 m, and volume 190m3. The nozzle is made of refractory bricks above and high alumina bricks below. The combustion chamber adopts a rectangular combustion chamber with a semicircular vault, which has simple structure, compact preparation, good sealing performance and low combustion chamber pressure. In order to ensure its air tightness, each layer of brick is built with phosphate mud, and the brick joint is not more than 2 m. The whole combustion chamber masonry adopts peripheral expansion joints. In addition, multiple groups of multidirectional sliding bearings are installed at the bottom of the combustion chamber. On the one hand, it is simple and reliable to compensate the displacement caused by thermal expansion, on the other hand, it can reduce the tamping combustion chamber. (2) The shaft furnace with air guide wall adopts air guide wall technology, which is an innovation in China. Its existence is that there are channels in the furnace, which effectively shortens the material layer through which the cooling air passes, greatly reduces the resistance, relatively increases the cooling air volume, improves the cooling effect, and greatly reduces the power consumption of the main fan. The working conditions of the air guide wall are bad, which not only bears the erosion of high temperature airflow, but also bears huge lateral pressure and projectile wear. Therefore, bricks for air guide walls are required to have excellent performance, and high-quality clay bricks or high-alumina bricks are generally used.

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Pellet shaft furnace

Pellet shaft furnace

Key words: pellet shaft furnace;

【 Application of Refractory Materials 】 August 2006 14 14:06

Pelletizing is another method of finely grinding iron concentrate or other iron-containing materials into blocks. The mixture of concentrate powder and flux (sometimes binder and fuel) is rolled into green pellets with a diameter of 8- 15 mm (larger for steelmaking) in a pelletizing machine, and then dried, roasted and solidified to form high-quality iron-containing raw materials with good metallurgical properties, which can be supplied to iron and steel smelting. I. Structure of Pellet Shaft Furnace According to its cross-sectional shape, there are two kinds of shaft furnaces: round and rectangular. Round shaft furnaces appeared in the early days, and now Switzerland is almost rectangular except for a few. The disadvantages of foreign shaft furnaces are: (1) high power consumption. According to the analysis of LKAB company in Sweden, its power consumption is as high as 50 kW h/. The main reason of high power consumption is its high material column. When the cold air passes upward through the roasting zone, the gas velocity in the material layer is high, the resistance is high, and the working pressure of the main fan is high, so the power consumption is high. (2) Foreign shaft furnace pellets generally use high calorific value fuel, heavy oil or natural gas, which is limited to roasting magnetite pellets. (3) The feeding speed is uneven, and the roasting consolidation is uneven, which affects the pellet quality. The foreign shaft furnace itself is a silo structure. When pellets with the same cross section are discharged, the discharge speed is uneven, the center of the discharge port is faster and the two sides are slower, which makes the pellets stay in the furnace for different times, so the roasting consolidation is uneven and affects the pellet quality. (4) In foreign shaft furnaces, two movable adhesive tapes are generally used to distribute cloth in a "B" shape. A shaft furnace with a width of 2.44 m and a length of 6.4m needs 140s at a time, and the distribution truck has to go back and forth eight times along the width direction. If the furnace type is expanded again, the distribution cycle must be extended, so it is difficult to keep the surface temperature distribution of the material uniform, which is not conducive to operation and affects the pellet quality. The main feature of shaft furnace in China is that shaft furnace pellets use blast furnace gas as fuel, unlike foreign shaft furnaces which use high calorific value fuel (heavy oil) or natural gas and coke oven gas. This is because the new furnace structure in China has improved the air permeability in the furnace, increased the penetration ability of combustion waste gas and cooling air, uniform airflow distribution, reasonable roasting system and stable uniform zone, which has created conditions for recrystallization and grain growth and consolidation of pellets. Two. Working environment of each part of pellet shaft furnace (I) Combustion chamber In China, 8m2 pellet shaft furnace usually adopts rectangular combustion chambers, which are arranged on both sides of the shaft furnace hearth. Most of the combustion chambers burn blast furnace gas, and the waste gas after combustion forms a certain pressure, which is sprayed into the furnace from the vertical furnace mouth to roast pellets, and finally reaches the top of the furnace, and is discharged into the atmosphere after dust removal. A prominent feature of the combustion chamber is positive pressure operation. Therefore, the combustion chamber must be well sealed and there can be no gas leakage. Practice has proved that the combustion chamber is the weak link of the shaft furnace body. At present, the first generation life of shaft furnace is short, only 1 ~ 3 years, which is closely related to the combustion chamber and determined by the harsh working environment of the combustion chamber. The combustion chamber bears the high temperature of11120℃ and the pressure of 10 ~ 20 kpa. If the masonry quality is not good, it is easy to leak and catch fire, so the combustion chamber may sometimes burn through, which seriously affects the normal operation of the shaft furnace. In addition, the temperature of the combustion chamber is high, and the whole masonry is displaced due to thermal expansion. The existing combustion chamber underframe is freely placed on the concrete platform, and the surface of the platform is rough, and the friction caused by thermal expansion is large, which is easy to cause cracking of the top masonry. The combustion chamber not only operates under positive pressure, but also bears certain pressure, which is easy to burn through. The burn-through parts are mostly vault, arch foot, burner, air inlet and so on. Once burned through, the pressure will drop sharply, and the ability of exhaust gas to penetrate the material column will be affected, so the combustion chamber must be sealed. In addition, the combustion chamber is also affected by the horizontal thrust of the arch foot and the gas side pressure of the furnace wall. The closure of the shaft furnace also caused some losses. The combustion chamber of shaft furnace is generally built with a 60-degree vault. Due to the existence of vault, a certain horizontal thrust is generated. The heavier the vault, the greater the horizontal thrust. The shaft furnace operates under positive pressure, gas is injected into the combustion chamber for combustion under a certain pressure, and the generated hot waste gas is injected into the furnace chamber from the flue of the combustion chamber. It can be seen that if the combustion chamber is not tightly sealed, enough pressure can not be formed and the technological requirements of roasting pellets can not be met. According to the calculation, the gas pressure generated by the side wall is very high. The shaft furnace production needs to be stopped, which has the greatest damage to the combustion chamber. The shaft furnace has been in production for a long time, and the combustion chamber is in high temperature. The expansion of refractory bricks stops when they reach a certain size, which is relatively stable. However, if the furnace is stopped, the temperature of the combustion chamber will drop, especially to normal temperature, and the masonry will naturally shrink. Open and stop the shaft furnace. Masonry will expand and contract, and cracks will appear after repeated several times, especially when the arch foot and vault move, which will burn through. Therefore, to ensure the long life of the combustion chamber, not only the masonry meets the requirements, but also the sealing is good. But also improve that operation rate of the shaft furnace. This is very important to prolong the life of the combustion chamber. To sum up, the combustion chamber is a weak link of shaft furnace, which is in a high temperature state for a long time and the working environment is relatively bad. (2) Air guide wall: Air guide wall is another weak link of shaft furnace. It is supported by the metal water beam below, often eroded by high temperature and dust airflow, and also bears the lateral pressure of the burden. Therefore, the working environment of the air guide wall is also very bad. The junction of water beam and masonry, especially the masonry under 1m, is the easiest to fall off. Therefore, it is very important to choose the material, unit size and hole wall thickness of the air guide wall. 3. Refractory material for shaft furnace (1) Combustion chamber is the main masonry body of shaft furnace, and it is usually built with clay bricks or high alumina bricks. For example, the bricklaying amount of two combustion chambers in Hangzhou Iron and Steel Company is about 120t ... The joint is less than 2mm, 70 1 mortar is used in important parts such as vault, and ordinary mud is used in furnace bottom and other parts. In the process of bricklaying, due to the large working face and many bricks, if there is one place that can't meet the quality requirements of bricklaying (such as large cracks in bricks and insufficient mud, etc.). ), the hot gas will pass through these weak points and move along the inner wall of the furnace shell, and leak out from the loose part of the metal furnace shell. The expansion problem mainly depends on the fillers such as insulation bricks and feather ash outside the masonry to buffer the expansion or contraction of refractory brick masonry. The cross-section of the baking zone of Benxi Steel 168m2 shaft furnace is 2.088m wide and 7.056m long. Height of arch trunk zone 1.260 m, height of preheating roasting zone 2.660 m, height of soaking zone 2.570 m, height of cooling zone 3.500m, height from center line of ore drum to furnace mouth 12.8 10 m, and volume 190m3. The nozzle is made of refractory bricks above and high alumina bricks below. The combustion chamber adopts a rectangular combustion chamber with a semicircular vault, which has simple structure, compact preparation, good sealing performance and low combustion chamber pressure. In order to ensure its air tightness, each layer of brick is built with phosphate mud, and the brick joint is not more than 2 m. The whole combustion chamber masonry adopts peripheral expansion joints. In addition, multiple groups of multidirectional sliding bearings are installed at the bottom of the combustion chamber. On the one hand, it is simple and reliable to compensate the displacement caused by thermal expansion, on the other hand, it can reduce the tamping combustion chamber. (2) The shaft furnace with air guide wall adopts air guide wall technology, which is an innovation in China. Its existence is that there are channels in the furnace, which effectively shortens the material layer through which the cooling air passes, greatly reduces the resistance, relatively increases the cooling air volume, improves the cooling effect, and greatly reduces the power consumption of the main fan. The working conditions of the air guide wall are bad, which not only bears the erosion of high temperature airflow, but also bears huge lateral pressure and projectile wear. Therefore, bricks for air guide walls are required to have excellent performance, and high-quality clay bricks or high-alumina bricks are generally used.