NO_x reduction by coupling combustion with recycling flue gas in iron ore sintering process

A new process called’NOx reduction by coupling combustion with recycling flue gas(RCCRF)’was proposed to decrease NOx emission during the iron ore sintering process.The simulation test of NOx reduction was performed over sintered ore and in the process of coke combustion.Experimentally,NOx reduction was also carried out by sintering pot test.For sintered ore,the amount of NOx emission is reduced by 15wt%-25wt% at 400-550oC using 2.0vol% H2 or 2.0vol% CO,or reduced by 10wt%-30wt% at 560-720oC using 0.15vol% NH3.NOx reduction is around 10wt% by coupling combustion of pyrolysis gas and coke,or around 16wt% by recycling flue gas into coke combustion.By RCCRF,the maximum NOx reduction ratio is about 23wt% in coke combustion experiment and over 40wt% in sintering pot test.     

Development of carbon composite iron ore micropellets by using the microfines of iron ore and carbon-bearing materials in iron making

Iron ore microfines and concentrate have very limited uses in sintering processes. They are used in pelletization; however, this process is cost intensive. Furthermore, the microfines of non-coking coal and other carbon-bearing materials, e.g., blast-furnace flue dust (BFD) and coke fines, are not used extensively in the metallurgical industry because of operational difficulties and handling problems. In the present work, to utilize these microfines, coal composite iron oxide micropellets (2-6 mm in size) were produced through an innovative technique in which lime and molasses were used as binding materials in the micropellets. The micropellets were subsequently treated with CO₂ or the industrial waste gas to induce the chemical bond formation. The results show that, at a very high carbon level of 22wt% (38wt% coal), the cold crushing strength and abrasion index of the micropellets are 2.5-3 kg/cm2 and 5wt%-9wt%, respectively; these values indicate that the pellets are suitable for cold handling. The developed micropellets have strong potential as a heat source in smelting reduction in iron making and sintering to reduce coke breeze. The micropellets produced with BFD and coke fines (8wt%-12wt%) were used in iron ore sintering and were observed to reduce the coke breeze consumption by 3%-4%. The quality of the produced sinter was at par with that of the conventional blast-furnace sinter.     

Influencing factor of sinter body strength and its effects on iron ore sintering indexes

Sinter body strength, which reflects the strength of sinter, plays an important role in the improvement of sinter. In this study, the sinter body strengths of iron ores were measured using a microsintering method. The relationship between the chemical composition and sinter body strength was discussed. Moreover, sinter-pot tests were performed. The effects of sinter body strength on the sintering indexes were then elucidated, and the bottom limit of sinter body strength of blending ores was confirmed. In the results, the compressive strengths (CSs) of iron ores are observed to decrease with the increasing of the contents of loss on ignition (LOI), SiO₂, and Al₂O₃; however, LOI of less than 3wt% does not substantially influence the CSs of fine ores. In the case of similar mineral composition, the porosity, in particular, the ratio between the number of large pores and the total number of pores, strongly influences the sinter body strength. With an increase of the blending-ore CSs used in sinter-pot tests, the yield, productivity, and tumbler strength increase, and the solid fuel consumption decreases. The CSs of the blending ores only slightly affect the sintering time. The CS bottom limit of the blending ores is 310 N. When the CSs of the blending ores increase by 10%, the yield, productivity, and tumbler index increase by 1.9%, 2.8%, and 2.0%, respectively, and the solid fuel consumption decreases by 1.9%.     

基于低镁烧结矿和熔剂性球团的综合炉料熔滴性能研究

A low MgO content in sinter is conducive to reduce the MgO content in blast furnace slag. This study investigated the effect of MgO content in sinter on the softening–melting behavior of the mixed burden based on fluxed pellets. When the MgO content increased from 1.31wt% to 1.55wt%, the melting temperature of sinter increased to 1521°C. Such an increase was due to the formation of the high-melting-point slag phase. The reduction degradation index of sinter with 1.31wt% MgO content was better than that of others. The initial softening temperature of the mixed burden increased from 1104 to 1126°C as MgO content in sinter increased from 1.31wt% to 1.55wt%, and the melting temperature decreased from 1494 to 1460°C. The permeability index (S-value) of mixed burden decreased to 594.46 kPa·°C under a high MgO content with 1.55wt%, indicating that the permeability was improved. The slag phase composition of burden was mainly akermarite (Ca₂MgSiO₇) when the MgO content in sinter was 1.55wt%. The melting point of akermarite is 1450°C, which is lower than other phases.     

Basic characteristics of Australian iron ore concentrate and its effects on sinter properties during the high-limonite sintering process

The basic characteristics of Australian iron ore concentrate (Ore-A) and its effects on sinter properties during a high-limonite sintering process were studied using micro-sinter and sinter pot methods. The results show that the Ore-A exhibits good granulation properties, strong liquid flow capability, high bonding phase strength and crystal strength, but poor assimilability. With increasing Ore-A ratio, the tumbler index and the reduction index (RI) of the sinter first increase and then decrease, whereas the softening interval (?T) and the softening start temperature (T_10%) of the sinter exhibit the opposite behavior; the reduction degradation index (RDI_+3.15) of the sinter increases linearly, but the sinter yield exhibits no obvious effects. With increasing Ore-A ratio, the distribution and crystallization of the minerals are improved, the main bonding phase first changes from silico-ferrite of calcium and aluminum (SFCA) to kirschsteinite, silicate, and SFCA and then transforms to 2CaO·SiO₂ and SFCA. Given the utilization of Ore-A and the improvement of the sinter properties, the Ore-A ratio in the high-limonite sintering process is suggested to be controlled at approximately 6wt%.     

Agglomeration Mechanism of Rich Hematite Sinter with Lowering SiO2 Content

The mini-sintering test was introduced. The experiments of specimens of rich hematite with lowering SiO₂ content were carried out by the mini-sintering test. The strength and mechanism of agglomeration were studied mainly when silica content in sintered specimens was decreased gradually. The relationships between SiO₂ volume and morphology of sinter were also investigated. It is considered that high grade sinter can be developed by raising sinter basicity so as to enhance complex calcium ferrite content or lowering sinter basicity so as to make Fe₂O₃ bonding for strength.     

Some basic properties of granules from ore blends consisting of ultrafine magnetite and hematite ores

Some basic properties of granules, including the granule size distribution, packed-bed permeability, and chemical composition of the adhering layer, were investigated in this study for four iron ore blends consisting of 5wt%, 25wt%, and 45wt% ultrafine magnetite and 25wt% ultrafine hematite concentrates. The effects of varying the sinter basicity (CaO/SiO₂ mass ratio=1.4 to 2.2) and adding ultrafine concentrates on the variation of the adhering-layer composition and granule microstructure were studied. Moreover, the effect of adhering-layer compositional changes on sintering reactions was discussed in combination with pot sintering results of ore blends. Increasing sinter basicity led to an increase in the basicities of both the adhering layer and the fine part of the sinter mix, which were higher than the overall sinter basicity. When the sinter chemistry was fixed and fine Si-bearing materials (e.g., quartz sand) were used, increasing the amount of ultrafine ores in the ore blends tended to reduce the adhering-layer basicity and increase the SiO₂ content in both the adhering layer and the fine part of the sinter mix, which will induce the formation of low-strength bonding phases and the deterioration of sinter strength. The adhering-layer composition in granules can be estimated in advance from the compositions of the -1 mm fractions of the raw materials.     

Softening–melting behavior of mixed burden based on low-magnesium sinter and fluxed pellets

A low MgO content in sinter is conducive to reduce the MgO content in blast furnace slag.This study investigated the effect of MgO content in sinter on the softening–melting behavior of the mixed burden based on fluxed pellets.When the MgO content increased from 1.31 wt% to 1.55 wt%, the melting temperature of sinter increased to 1521℃.Such an increase was due to the formation of the high-meltingpoint slag phase.The reduction degradation index of sinter with 1.31 wt% MgO content was better than that of others.The initial softening temperature of the mixed burden increased from 1104 to 1126℃ as MgO content in sinter increased from 1.31 wt% to 1.55 wt%, and the melting temperature decreased from 1494 to 1460℃.The permeability index(S-value) of mixed burden decreased to 594.46 kPa·℃ under a high MgO content with 1.55 wt%, indicating that the permeability was improved.The slag phase composition of burden was mainly akermarite(Ca_2MgSiO_7) when the MgO content in sinter was 1.55 wt%.The melting point of akermarite is 1450℃, which is lower than other phases.     

Effect of MgO content in sinter on the softening–melting behavior of mixed burden made from chromium-bearing vanadium–titanium magnetite

The effect of sinter with different MgO contents on the softening–melting behavior of mixed burden made from chromium- bearing vanadium–titanium magnetite was investigated. The results show that with increasing MgO content in the sinter, the softening interval and melting interval increased and the location of the cohesive zone shifted downward slightly and became moderately thicker. The softening–melting characteristic value was less pronounced when the MgO content in the sinter was 2.98wt%–3.40wt%. Increasing MgO content in the sinter reduced the content and recovery of V and Cr in the dripped iron. In addition, greater MgO contents in the sinter resulted in the generation of greater amounts of high-melting-point components, which adversely affected the permeability of the mixed burden. When the softening–melting behavior of the mixed burden and the recovery of valuable elements were taken into account, proper MgO contents in the sinter and slag ranged from 2.98wt% to 3.40wt% and from 11.46wt% to 12.72wt%, respectively, for the smelting of burden made from chromium-bearing vanadium–titanium magnetite in a blast furnace.     

Comparison of reduction disintegration characteristics of TiO2-rich burdens prepared with sintering process and composite agglomeration process

To reveal the impact of the composite agglomeration process (CAP) on the reduction disintegration properties of TiO₂-rich ironmaking burden for a blast furnace, the reduction disintegration indices (RDIs), mineral constituents, and microstructure of the products prepared by the CAP and the traditional sintering process (TSP) were investigated. The results showed that, compared to the sinter with a basicity of 2.0 prepared by the TSP, the RDI_+6.3 and the RDI_+3.15 of the CAP product with the same basicity increased by 28.2wt% and 13.7wt%, respectively, whereas the RDI_-0.5 decreased by 2.7wt%. The analysis of the mineral constituents and microstructure of the products indicated that the decreasing titanohematite content decreased the volume expansion during reduction. Meanwhile, the decreasing perovskite content decreased its detrimental effect on the reduction disintegration properties. In addition, the higher silicoferrite of calcium and aluminum (SFCA) content improved the strength of the CAP product. Together, these factors result in an improvement of the RDI of the CAP products. In addition, compared to the sinter, the reduced CAP products clearly contained fewer cracks, which also led to mitigation of reduction disintegration.     

Reduction of NO_x emission based on optimized proportions of mill scale and coke breeze in sintering process

Reducing NO_x emission of iron ore sintering process in a cost effective manner is a challenge for the iron and steel industry at present. Effects of the proportion of mill scale and coke breeze on the NO_x emission, strength of sinter, and sinter indexes were studied by combustion and sinter pot tests. Results showed that the peak value of NO concentration, total of NO emission, and fuel-N conversion rate gradually decreased as the proportions of the mill scale increased because NO was reduced to N_2 by Fe_3O_4, FeO, and Fe in the mill scale. The strength of sinter reached the highest value at 8.0 wt% mill scale due to the formation of minerals with low melting point. The fuel-N conversion rate slightly fluctuated and total NO_x emission significantly decreased with the decreased proportions of coke breeze because CO formation and content of N element in the sintered mixture decreased. However, the sinter strength also decreased due to the decrease in the amount of the melting minerals. Furthermore, results of the sinter pot tests indicated that NO_x emission decreased. The sinter indexes performed well when the proportions of mill scale and coke breeze were 8.0 wt% and 3.70 wt% respectively in the sintered mixture.     

焦炭固定床燃烧氮氧化物排放实验研究

为降低锅炉NO的排放,研究焦炭在固定床中燃烧时的氮氧化物排放特性,分析焦炭数量对NO排放的影响。在其他条件不变的情况下,取焦炭质量分别为0．5、1．0和2．0g的煤样进行燃烧实验。结果表明：焦炭燃烧NOx排放与燃烧过程密切相关,在固定床中有还原层存在时,NO排放处于低水平稳定状态。随着焦炭还原层的消失,NO转化率迅速增加。在设计层燃燃烧锅炉时。加大燃煤炉中焦炭层的厚度．可以降低锅炉NO的排放．焦炭层厚度增加4倍．NOx排放降低73．86％．     

NOx reduction in the sintering process

A new process, NO_x reduction with recycling flue gas and modifying coke breeze, was proposed. The effects of modified coke breeze and recycled flue gas on NO_x reduction were investigated by sinter pot tests. The results show that the NO_x reduction rate is over 10wt% in the sintering of modified coke breeze, the effects of the additives on NO_x reduction are: CeO₂>CaO>K₂CO₃. The NO_x reduction rate increases with the amount of recycled flue gas, and is 22.35wt% in the sintering with recycling 30vol% of the flue gas. When 30vol% of the flue gas is recycled into the sintering of CeO₂, CaO, and K₂CO₃ modified coke breeze, the NO_x reduction rates are 36.10wt%, 32.56wt%, and 32.17wt%, respectively.     

煤层燃过程中热解气燃烧氮氧化物排放实验

我国大气中的氮氧化物污染日益严重,燃煤是大气中氮氧化物的主要来源之一。为研究燃煤过程中氮氧化物的排放规律,设计了双层固定床反应器,对煤燃烧产生的热解气和焦炭的燃烧情况分别进行研究。利用实验研究分析煤燃烧时煤中氮元素的分配、热解气析出特性及热解气燃烧时的氮氧化物排放规律。结果表明:煤热解过程中进入热解气和留在焦炭内的N分别为38%和62%。实验结果为分析煤炭层燃过程中NOx排放规律奠定了基础。     

粉末冶金制备的AISI 8620钢渗碳后的磨损和力学性能

The effect of carburization on the tensile strength and wear resistance of AISI 8620 steel produced via powder metallurgy was investigated. Alloys 1 and 2 (with 0.2wt% C and 0.25wt% C, respectively) were first pressed at 700 MPa and then sintered at 1300, 1400, or 1500°C for 1 h. The ideal sintering temperature of 1400°C was determined. Afterward, Alloys 1 and 2 sintered at 1400°C were carburized at 925°C for 4 h. The microstructure characterization of alloys was performed via optical microscopy and scanning electron microscopy. The mechanical and wear behavior of carburized and noncarburized alloys were investigated via hardness, tensile, and wear tests. After carburization, the ultimate tensile strength of Alloys 1 and 2 increased to 134.4% and 138.1%, respectively. However, the elongation rate of Alloys 1 and 2 decreased to 62.6% and 64.7%, respectively. The wear depth values of Alloy 2 under noncarburized and carburized conditions and a load of 30 N were 231.2 and 100.1 μm, respectively. Oxidative wear changed to abrasive wear when the load transitioned from 15 to 30 N.     

Mechanical properties and friction behaviors of CNT/AlSi10Mg composites produced by spark plasma sintering

The mechanical properties and friction behaviors of CNT/AlSi10Mg composites produced by spark plasma sintering (SPS) were investigated.The results showed that the densities of the sintered composites gradually increased with increasing sintering temperature and that the highest microhardness and compressive strength were achieved in the specimen sintered at 450℃.CNTs dispersed uniformly in the AlSi10Mg matrix when the addition of CNTs was less than 1.5wt％.However,when the addition of CNTs exceeded 1.5wt％,the aggregation of CNTs was clearly observed.Moreover,the mechanical properties (including the densities,compressive strength,and microhardness) of the composites changed with CNT content and reached a maximum value when the CNT content was 1.5wt％.Meanwhile,the minimum average friction coefficient and wear rate of the CNT/AlSi10Mg composites were obtained with 1.0wt％ CNTs.     

Effects of SiO2 on the preparation and metallurgical properties of acid oxidized pellets

The effects of SiO₂ content on the preparation process and metallurgical properties of acid oxidized pellets, including compressive strength, reduction, and softening–melting behaviors, were systematically investigated.Mineralogical structures, elemental distribution, and pore size distribution were varied to analyze the mechanism of the effects.The results show that with an increase in SiO₂ content from 3.51 wt%to 7.18 wt%, compressive strength decreases from 3150 N/pellet to 2100 N/pellet and reducibility decreases from 76.5% to 71.4%.The microstructure showed that pellets with high SiO₂ content contained more magnetite in the mineralogical structures.Additionally, some liquid phases appeared, which hindered the continuous crystallization of hematite.Also, the softening–melting properties of the pellets clearly deteriorated as the SiO₂ content increased.With increasing SiO₂ content, the temperature range of the softening–melting zone decreased, and the maximum differential pressure and the comprehensive permeability index increased significantly.When acid oxidized pellets are used as the raw materials for blast furnace smelting, it should be combined with high basicity sinters to improve the softening–melting behaviors of the comprehensive charge.     

机械合金化法制备的Cu/SiC纳米复合材料的组织、热性能和力学性能评估

Nano-sized silicon carbide (SiC: 0wt%, 1wt%, 2wt%, 4wt%, and 8wt%) reinforced copper (Cu) matrix nanocomposites were manufactured, pressed, and sintered at 775 and 875°C in an argon atmosphere. X-ray diffraction (XRD) and scanning electron microscopy were performed to characterize the microstructural evolution. The density, thermal expansion, mechanical, and electrical properties were studied. XRD analyses showed that with increasing SiC content, the microstrain and dislocation density increased, while the crystal size decreased. The coefficient of thermal expansion (CTE) of the nanocomposites was less than that of the Cu matrix. The improvement in the CTE with increasing sintering temperature may be because of densification of the microstructure. Moreover, the mechanical properties of these nanocomposites showed noticeable enhancements with the addition of SiC and sintering temperatures, where the microhardness and apparent strengthening efficiency of nanocomposites containing 8wt% SiC and sintered at 875°C were 958.7 MPa and 1.07 vol%?1, respectively. The electrical conductivity of the sample slightly decreased with additional SiC and increased with sintering temperature. The prepared Cu/SiC nanocomposites possessed good electrical conductivity, high thermal stability, and excellent mechanical properties.