When blast furnaces are forced to run at high speed, one way of reducing their downtime, increasing their productivity, and lowering the cost of making pig iron is to improve the durability of the tuyeres. Experience shows that the main causes of tuyere failure are crack formation, wear, and burn-throughs. The durability of a tuyere and the type of problems encountered with it are significantly affected by the sophistication of the smelting technology that is used and the quality of the charge materials. Most tuyeres do not last longer than three months when the supply of raw materials to the furnace is unstable, and 20% of tuyeres (out of the total number that are replaced) have lasted less than half a month under such conditions. The amount of furnace downtime necessitated by the replacement of failed tuyere parts has reached 2.0-2.5% of nominal operating time, which has seriously hurt furnaces' technical-economic indices. Stabilization of the operation of blast furnaces at EZRAZ ZSMK has allowed the combine to work on improving the durability of the tuyeres by redesigning them, improving the quality of the work done in making them, and applying protective coatings (by plasma deposition, electron-beam hard facing, etc.). The combine's introduction of a new technology for making tuyeres and the strengthening of these pieces of equipment while ensuring a satisfactory cooling rate have made it possible to reduce the incidence of tuyere failure due to cracking. The number of tuyere replacements has declined during both normal and high-speed operation of the furnaces, which has in turn elevated tuyere service life to an average of 5-7 months and a maximum of 14-15 months.Having blast-furnace tuyeres that are durable reduces downtime, increases productivity, and lowers the cost of making pig iron during periods when the furnace is forced to operate at higher-than-normal smelting rates.Experience with the use of the tuyeres at the combine has shown that most of the damage done to tuyeres comes from cracks, wear, and burn-throughs. By cracks, we mean fractures of the tuyeres along the weld or base metal (copper). The wear that the tuyere undergoes is for the most part uniform (and occurs primarily in the tuyere's "snout" region). Burnthroughs occur when the tuyere is destroyed by the action of the molten pig iron.It has been established that the durability of tuyeres and the types of defects that take them out of service are influenced chiefly by the sophistication of the smelting technology that is used and the quality of the iron-bearing materials and coke in the charge. Studies have found a correlation (correlation coefficient 0.69, reliability criterion of the relationship 2.96) between the number of burned tuyeres and several parameters of the smelting operation: N = -1.29 + 6.02[Si] + 5.41B Σ -0.34Fe snt + 0.3M 10 , where N is the number of burnt tuyeres; [Si] is the silicon content of the pig iron, %; B Σ is the absolute value of slag basicity (CaO + MgO)/SiO 2 ; Fe snt is the iron content of the charge, %; and ...
Due to the acute shortage of coke for the blast furnaces at the West Siberian Metallurgical Combine, the combine has conducted trial heats with the use of fine fractions of coke (36-25 mm). The content of fines was increased to 30% of the total coke content of the charge (the transition was made during a period when the furnaces were operating satisfactorily). To maintain the existing smelting rate, steps were taken to stabilize the operation of the hearth and keep the furnaces running smoothly.To prevent blockage of the hearth, washing materials (scales, welding slag, converter slag) were included in the charges and a specific tapping schedule was followed. Also, theoretical combustion temperature at the tuyeres was kept 20-30~ higher than normal (2100-2150~by changing the ratio of the parameters of the combination blast, consisting of oxygen and natural gas.The charge for smelting contained local sinter (90-95%) of two fractions (15-30 mm and +30 mm) and Tashtagol ore (10-5%)coarser than 25 mm. The total content of iron-bearing materials in the rounds was 50-54 tons and the total content of coke was 13.5-15.0 tons. The burden ratio was varied from 3.50 to 3.82 tons/ton coke, depending on the degree of forcing of the smelting operation.It was found that the use of coke fines (36-25 mm) in the charge of a blast furnace having a standard bell-and-hopper charging apparatus without additional devices to regulate charge distribution resulted in a moderate decline in performance indices. For example, using from 5 to 30% fines in the coke portion of the charge led to the following: a reduction in actual productivity by 0.9--6.5%; a reduction in smelting rate based on the quantity of melted ore, total carbon input, and wind rate; more nonuniform distribution of the gas flow across the furnace; an increase in scatter of the temperatures of the peripheral gases to more than 120-130~ During the test periods, there was a 4.0-4.5% (abs.) increase in the content of carbon dioxide in the central zone of the furnaces (Fig. 1) and a decrease in the utilization of the reducing and heat energies of the gas flow. For example, use of the chemical energy of carbon monoxide during the test periods decreased by 0.12-0.90% and use of the chemical energy of hydrogen declined 1.0-3.4% (abs.). These changes were accompanied by a 5-20~ increase in top-gas temperature, which characterizes the degree to which the heat energy of the gas flow is being used. Actual unit coke consumption increased from 3.6 (0.81%) to 9.1 (2.0%) kg/ton pig, while coke consumption adjusted for the conditions of the base period (iron content of the charge, natural-gas consumption, hot-blast temperature, etc.) increased to 1.4%. Routine downtime increased by
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