| Iron and steel industry has always been an important symbol to measure the level of a country’s industrialization.As a pillar industry of the country,it plays a pivotal role in the national economy.In recent years,with the lack of high quality iron ore resources,makes the continuous increasing of our country’s dependence on imported ore at the same time with the increase of coal injection quantity,low grade iron ore increased usage and so on,makes the charging of Al2O3 proportion rising raw materials,parts of Al2O3 content in blast furnace slag has reached to 20%,resulting in a decline in slag metallurgical properties.The extensive use of high Al2O3 content iron ore will bring a series of problems to the smelting process.In order to ensure the smooth running of blast furnace,MgO is usually used to improve the metallurgical properties of slag.However,the addition of MgO will worsen the metallurgical properties of sinter and increase the production cost.Therefore,it is of great research significance to explore suitable M/A smelting.In this paper,the reasonability of using low MgO sinter and reducing blast furnace slag M/A smelting in A specific iron and steel enterprise is studied.The influence of reducing MgO content on sinter strength,mineral phase composition and metallurgical properties is analyzed in detail.At the same time,the soft melting properties of composite charge with low MgO content were studied.However,the reduction of MgO content in raw materials is bound to have A certain impact on the metallurgical properties of slag.The change of metallurgical properties of slag after the reduction of M/A is studied on the basis of on-site slag.The following results are obtained:(1)After reducing the amount of MgO flux brought into the sintering process and the content of MgO in the sinter,the utilization coefficient of sintering increases from 1.885t/m2·h to 1.978t/m2·h;Moreover,with the decrease of MgO ratio,the iron grade of sinter also increases by 0.92%.Sinter drum index(T1)increased from 72.1%to 75.5%,up 3.4%,improved strength,mainly because when MgO style content is higher in sinter,MgO style in the sinter,dissolve into calcium ferrite bonded phase in the formation of magnesium spinel and destruction of the sinter intensity of binding phase,deterioration in the sinter strength,thus reduce the content of MgO style in sinter can improve the sinter drum strength;Field of sinter is particle size distribution uneven phenomenon,mainly related to sinter cooling systems of enterprises,through the comparative study of sinter ore phase under different cooling systems,found under the quench system of sinter internal proportion of glass phase(C2S)will greatly enhance,destroy the sinter strength,therefore the change of sinter cooling system can optimize the graded levels.(2)The main binding phase of the sinter of this enterprise is the typical composite calcium ferrite(SFCA)binding phase,which is the main binding phase of the high alkalinity sinter at present.However,compared with the sinter of advanced enterprises,the ratio of composite calcium ferrite(SFCA)binding phase is relatively low,so the ratio has room for further increase.After MgO content in sinter is reduced,the type of binding phase does not change significantly,and the main binding phase is still calcium ferrite,while the proportion of calcium ferrite binding phase(SFCA)in sinter increases from 25.3%to 29.3%,with an increase of 4%.In the sinter,the proportion of hematite is relatively low,and the proportion of magnetite phase(MF)is relatively high.Because MgO can form a stable SOLID solution MF phase with Fe3O4(magnetite)solid solution,MgO has the function of stabilizing magnetite.Therefore,the excessive content of MgO in the sinter is a major reason for the excessive magnetite phase proportion.(3)By studying the metallurgical properties of iron making raw materials,the low temperature reduction degradation index(RDI-3.15)of sinter is 24.3%,and the CONTENT of MgO is reduced from 2.8%to 2.0%.The low temperature reduction degradation index of sinter is 24.8%,no obvious deterioration occurs,and it still remains within the range of less than 35%,meeting the smelting requirements of blast furnace.The reduction index of sinter is 70.3%,which meets the requirements for sinter reduction in blast furnace production.After MgO is reduced,the reduction index is increased to 73.3%,and the reduction of sinter can be improved after MgO content is reduced.The initial softening temperature T10 and dripping temperature TD are moderate,while the temperature range of soft melt belt(TD-T10)is small,which is 283.0℃.There is no obvious deterioration of metallurgical properties of sinter after MgO reduction,so it provides possibility for low magnesium aluminum ratio sm elting in blast furnace.The reduction pulverization rate(RDI-3.15)of this enterprise is 11.16%,which meets the production requirements,but the reduction expansion rate(RSI)is 18.43%,which is slightly higher than that of advanced enterprises.Pellets have poor reduction RI,which is only 50.70%.The soft melting characteristics of pellets are typical acidic materials,and the temperature at the beginning and end of the soft melting are respectively 1082.0℃ and 1175.1℃,both of which are relatively low.Soft melting characteristics of the composite burden at present belongs to the condition of reasonable,compared with low content of MgO style sinter burden structure can be found with soft melting temperature interval(TD-T10)narrowed by 8.4℃,the maximum differential pressure ΔPmax relative decline 2.92%,preliminary prediction using low after M/A burden structure inside the blast furnace permeability is good.(4)is obtained by laboratory test with slag slag basicity R=1.20,from 0.75 to 0.60 M/A,the slag melting temperature is reduced after the first rise trend,through the analysis of the phase diagram of slag is within the range of 0.75 to 0.65 M/A rhodonite belongs to magnesium slag series,with the reduction of M/A slag melting of elevated temperature from 1380℃ to 1386℃,and M/A to 0.6 after slag into melilite area,slag melting temperature to 1377℃,the two kinds of slag are all belong to blast furnace Tony department,to meet the requirements of the blast furnace smelting;When basicity R=1.25,the melting temperature of slag decreases from 1393℃ to 1366℃ with the decrease of M/A,which also meets the requirements of blast furnace smelting.So it is possible to carry out low M/A smelting in blast furnace.The mineral analysis of two groups of blast furnace slag before and after MgO reduction was carried out on site,and it was found that the blast furnace slag system of the yellow feldspar type was mainly common.The melting temperature of the slag system in the quaternary phase diagram was lower than 1400℃,so the slag system was suitable to be used as the main slag system of the blast furnace slag.After the adjustment of M/A,the melting temperature of slag tends to be stable with little variation range,and the iron output temperature of the blast furnace in this enterprise is above 1450℃,so reducing M/A slag can still maintain good metallurgical properties. |
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