| Pulverized coal injection(PCI)into blast furnace(BF)not only reduce coke ratio and pig iron cost,but also improve hearth working condition and make BF run smoothly.The gasification and combustion of pulverized coal will reduce the theoretical combustion temperature in front of tuyere,create favorable conditions for high blast temperature and oxygen-enriched blast,and be beneficial to ore reduction and improvement of BF operation indexes.At present,the PCI technology which is used by almost all large and medium-sized blast furnaces at home and abroad has become a very universal and the PCI ratio is on the rise.Compared with the high PCI rate in some BF,the PCI rate in most domestic BF can still be increased..Therefore,to further improve the coal injection rate has become one of the important measures to reduce the cost of pig iron for most iron and steel enterprises.However,with the increase of PCI rate,pulverized coal not be fully burned in the tuyere raceway resulting in unburnt pulverized coal(UPC)and the accumulation of UPC in the BF limits the increase of the PCI rate.In this paper,the method of increasing PCI rate in BF is studied by improving the burning rate of pulverized coal in tuyere raceway and the distribution of UPC in blast furnace,which provides theoretical basis and reference for BF production.The main research contents and results of this paper are as follows:1.The experimental study of the transportation and combustion properties of five kinds of pulverized coal as raw materials and its mixed coal powder was carried out.The results show that:(1)The Carr'flowability index and floodability index of binary blended pulverized coal are mostly between the single pulverized coal's index,but they are not the linear addition of single pulverized coal index.(2)The pulverized coal combustion rate in tuyere raceway can be increased by optimizing pulverized coal selection,blending pulverized coal and oxygen enrichment,and the PCI rate can be increased,but the increase is limited.2.The accumulation of UPC in BF limits the further increase of PCI.In order to study the accumulation and distribution of UPC in BF,Euler-Euler method was used to simulate the distribution of UPC in BF.Simulation results show that:(1)The UPC is mainly accumulated below the cohesive zone of BF.The deadman,the region below the raceway,cohesive area and the top and root of the cohesive zone are the main regions where the UPC easily accumulates.The accumulation of UPC underneath the raceway is mainly affected by the raceway.Comparing the distribution of UPC in three kinds of different cohesive zone in BF,The distribution of UPC in BF with W type cohesive zone is relatively uniform and more UPC can be accumulated in BF under the same condition.(2)The effect of the cohesive zone parameters on the accumulation and distribution of UPC in the BF is mainly in the cohesive zone and its lower part.Properly raising the root of the cohesive zone can increase the accumulation of UPC in the BF,when the root is too high,the accumulation of UPC increases slightly,but the central pressure difference increases significantly.When the cohesive zone is narrow,the accumulation of UPC in BF can be increased and the pressure difference can be reduced.The accumulation area of UPC increases of furnace hearth with the increase of the diameter of deadman of BF,which has no obvious effect on the distribution of UPC in the cohesive zone and its upper area.(3)As the diameter of UPC decreases,the accumulation of UPC in BF decreases.The accumulation area of UPC in the middle area of the dropping zone of the BF is obviously smaller.The particle size of pulverized coal has an effect on the motion pattern of pulverized coal in the raceway of tuyere,and the movement pattern of pulverized coal in the raceway affects the distribution of pulverized coal in BF.The particle size diameter of UPC increases from 120 ?m to 170 ?m,and the accumulation of unburned pulverized coal changes little,while the pressure difference increases significantly.Therefore,the particle size of PCI is less than 120 ?m,which is beneficial to blast furnace production.3.The bisegment pulverized coal injection(Bi-PCI)process can change the distribution of UPC in the blast furnace and improve the air permeability of the blast furnace by changing the position of pulverized coal entering the BF and the amount of pulverized coal through the tuyere.In order to better master the Bi-PCI technology,the simulation study and industrial practice of Bi-PCI process were carried out.The results show that:(1)In the Bi-PCI experiment,the pulverized coal accumulation in the lower part of the tuyere of the blast furnace model decreases significantly,the pulverized coal accumulation in furnace bosh and furnace belly of decreases,and the amount of pulverized coal in the furnace shaft increases.(2)Compared with the conventional PCI process,the BF adopting Bi-PCI process operates smoothly and the daily output of iron increases,the coal ratio increased by 11.35 kg·t-1 and the coke ratio decreased by 9.87 kg·t-1.The pulverized coal injected into the blast furnace by the secondary lances can be fully utilized and will not escape from the BF with the gas.The BI-PCI process is able to protect the coke strength effectively and improve the operational indices of the BF.(3)When the coarser pulverized coal in the range of 75?170 ?m was injected into BF by the secondary lance,more pulverized coal is deposited in the BF shaft,which is more beneficial to the Bi-PCI process.When the particle size of pulverized coal is 75 ?m and the solid-gas ratio of the second lances is in the range of 15?20 kg·kg-1,the change of solid-gas ratio has little effect on the accumulation of pulverized coal injected by the secondary lance in the furnace shaft. |
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