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The gas generation from reactions between direct reduced iron (DRI) pellets and steelmaking slags is known to take place in two stages; (1) the reaction of FeO and carbon within DRI, i.e., pellet internal reaction, followed by (2) the reduction of slag FeO with DRI carbon at the pellet?Cslag interface, if any carbon remains from the first step. To understand the controlling mechanism of the reaction between FeO and C inside DRI, the rate of the gas release and the temperature of pellets suspended in a slag-free atmosphere were quantified. The results were used to determine the apparent thermal conductivity of DRI that showed values of approximately 0.5 to 2 W.m?1.K?1 for a temperature range of 573?K to 1273?K (300?°C to 1000?°C). Furthermore, it was found that the experimental gas evolution rates are consistent with the values predicted by a heat?Ctransfer based model, confirming that the FeO-C reaction within pellet is controlled by the rate of heat transfer from the slag to the DRI pellet. 相似文献
3.
Etsuro Shibata Haiping Sun Katsumi Mori 《Metallurgical and Materials Transactions B》1999,30(2):279-286
The oxidation rates of carbon, phosphorus, and silicon; the desulfurization rate of liquid iron; and the simultaneous reduction
rate of MnO from slag were examined at 1450 °C to 1550 °C by using high carbon iron alloys and CaO-SiO2-CaF2 slags containing MnO and FeO. The reaction rates were well reproduced by a kinetic model describing the reaction between
the slag and multicomponent iron alloys. The controlling steps applied for the reactions considered in the present kinetic
simulation were as follows. The rate of decarburization is controlled by the chemical reaction at the slag-metal interface,
and those of the other reactions are controlled by the transport in slag and metal phases. Both observation and simulation
results showed that MnO was not a strong oxidizer compared with FeO in the slag, but was an effective component for desulfurization.
The simulation results also showed that the interfacial oxygen activity using MnO-based slag was much lower than that using
FeO-based slag. The apparent equilibrium constants of phosphorus and sulfur, which were obtained by the kinetic modeling of
experimental results, were found to increase with increasing the (MnO + CaO)/SiO2 ratio of the slag. The controlling step(s) of each element transport across the slag-metal interface was discussed with the
aid of the kinetic model. 相似文献
4.
Nasser Towhidi 《国际钢铁研究》2003,74(10):595-600
Direct reduced iron (DRI) is the product of some commercial direct reduction (DR) of iron ore on base of natural gas. DRI tends to oxidize in air generally above 300 °C and then follows spontaneous combustion. To control the oxidation mechanism, several investigators have used different iron samples and methods. This paper gives the results of experimental work carried out for determination of DRI oxidation. The behaviour of DRI oxidation in air after isothermal reduction of hematite pellets with different size, temperature and H2 / CO mixture is investigated. 相似文献
5.
Huseyin Akarsu 《Mineral Processing and Extractive Metallurgy Review》2013,34(1):42-56
Additives can give rise to obvious, step-wise changes both in the oxidation process and in the sintering process. Therefore, the oxidation and sintering characteristics measured in dried pellets prepared from pure magnetite concentrates can not be representative for those characteristics in dried pellets containing additives. The oxidation and sintering characteristics of magnetite iron ore pellets balled with a novel complex binder (namely MHA) were mainly investigated by batch isothermal oxidation measurements in this research. Combined results reveal that the thermal decomposition of MHA binder influences the oxidation and sintering processes of dried pellets. Oxidation rate of pellets increases obviously with increasing the oxidation temperature in the range from 800°C to 1000°C. And the remaining FeO content declines gradually when separately heated for 10 min at low temperature (<1000°C). However, the oxidation rate of pellets decreases distinctly when oxidation temperature is higher than 1000°C. In addition, when oxidation temperature increases from 1000°C to 1250°C, the FeO content of pellets goes up obviously, particularly at 1250°C. The FeO content in the core of sintered pellets heated at 1250°C can even reach 29.68%. SEM spectrum analysis demonstrate that some iron appears in forms of wustite in sintered pellets, which indicates that the reduction reaction of iron oxide occurs during the high temperature sintering process. This is explained by the occurrence of reducing atmospheres because of the pyrogenic decomposition of MHA binder. 相似文献
6.
为了降低直接还原铁能耗,根据试验数据研究了煤制气直接还原铁两段串联流程。串联流程中第一段竖炉用煤制气粗煤气余热和含碳球团冶炼直接还原铁,含碳球团以焦粉、半焦粉或无烟煤粉为还原剂,铁精矿、无机黏结剂混合后加压制作,电炉熔化直接还原、脱硫和生产水渣。串联流程中第二段竖炉以第一段净化后的炉顶煤气为第二段直接还原铁还原气,以氧化球团为原料。结果表明,煤制气直接还原铁两段串联流程估算能耗为394.8kg/t;与铁水比可比能耗为487.8kg/t,比高炉低41.2kg/t,生产过程中产生的污染物和温室气体排放低于高炉,接近天然气直接还原铁。 相似文献
7.
In the iron smelting, or bath smelting, process the tapped metal contains high amounts of sulfur and the slag contains high amounts of FeO, relative to blast furnace slag. After tapping, the FeO can be further reduced by carbon in the metal, which will also lead to better desulfurization. Although there have been many studies of the reaction of carbon in iron with FeO in slag, discrepancies exist with regards to the effect of carbon in iron on the rate of FeO reduction in slag, which is the subject of this study. Experiments were conducted at 1723 K, using a slag with basicity close to one with an FeO mass content of 5 %. The rate of reduction was measured using a pressure increase technique. For moderate and high sulfur contents, as in the case of iron smelting, the rate is primarily controlled by the dissociation of CO2 on the surface of the molten iron. Furthermore, if the effect of carbon on sulfur is taken into account, for the range of carbon mass contents of 2 to 4.5 %, there is no effect of the carbon level on the rate of FeO reduction. At low sulfur contents it was found that there is considerable slag foaming, which inhibits mass transfer of FeO in the slag, and significantly reduces the rate. Even when there is no slag foaming at low sulfur contents, mass transfer of FeO in the slag can influence the rate of FeO reduction. 相似文献
8.
Rate of reduction of iron oxide in iron and steelmaking slags by mass contents of dissolved carbon (>3%) in molten iron depends upon activity of FeO, temperature, mixing of bulk slag and other experimental conditions. A general kinetic model is developed by considering mass transfer of FeO in slag, chemical reaction at gas-metal interface and chemical reaction at gas-slag interface, respectively, as the three rate controlling steps. A critical analysis of the experimental data reported in literature has been done. It is shown that in the case of slags containing mass contents of less than 5% FeO, the reduction of FeO is controlled by mass transfer of FeO in slag plus chemical reaction at gas-metal interface; when slags contain more than 40% FeO, the reduction of FeO is controlled by chemical reaction at gas-metal interface plus chemical reaction at gas-slag interface; at intermediate FeO mass contents (between ~ 5 and 40% FeO), the reduction of FeO is controlled by all three steps, namely, mass transfer of FeO in slag, chemical reaction at gas-metal interface and chemical reaction at gas-slag interface. The temperature dependence of rate constant for the gas-slag reaction is obtained as: In k2 = –32345.4(&6128)/ T + 19.0(&3.42); σlnk2,1/T = &0.3. where k2 is expressed in mol m-2 s-1 bar-1. The mass transfer coefficient of iron oxide in bulk slag is found to vary in the range 1.5 × 10-5 to 5.0 × 10-5 m/s, depending upon the slag composition as well as experimental conditions. 相似文献
9.
Mohammed Meraikib 《国际钢铁研究》1986,57(12):626-635
Test charges containing sponge iron proportions varying from 38.7–95.4 wt% of the metallic input were melted in a UHP electric arc furnace with a design capacity of 70 tons per heat. After melting started, samples of molten metal and the corresponding slag were taken simultaneously at different time intervals and analysed. The time dependence of the chemical composition of the metal and slag as well as the variation of the temperature of the melt with time are given. Thermodynamic calculations using different methods for finding the activity of ferrous oxide show that there is a linear relationship between a(FeO) and the total ferrous oxide content in the slag. It is also found that the total ferrous oxide content in the slag and the oxygen concentration in the metal vary linearly with the iron proportion from sponge iron in the metallic input. The activity of ferrous oxide decreases with increasing slag basicity due to the formation of calcium ferrites. The relationship between the oxygen concentration and the reciprocal of the carbon content in liquid steel is almost linear. A formula showing the influence of some important factors on the oxygen content in molten steel is given. The effect of sponge iron on the sulphur concentration in the steel is also investigated. The present results indicate that the sulphur content in the steel can be reduced from 0.02 to 0.004 wt% by increasing the iron proportion from sponge iron in the metallic input from 35 to 95 wt %. Using the boundary layer diffusion model, it is found that the rate of decarburization of a steel bath is enhanced by increasing the sponge iron proportion in the metallic input. The activation energy of the decarburization reaction is found to be 56.9 kJ/mol and the mass transfer coefficient of carbon has a value of 0.0161 cm/s at 1 600°C. In a way similar to that used for decarburization, it is also found that the rate of oxidation of manganese dissolved in the bath is enhanced by increasing the sponge iron proportion in the metallic input. 相似文献
10.
The reduction of CaO-SiO2-Al2O3-FeO slags containing less than 10 wt pct FeO by solid carbonaceous materials such as graphite, coke, and coal char was investigated at reaction temperatures of 1400 °C to 1450 °C. The carbon monoxide evolution rate from the system was measured using stationary and rotating carbon rods, stationary horizontal carbon surfaces, and pinned stationary spheres as the reductants. The measured reaction rate ranged from 3.25 × 10?7 mol cm?2 s?1 at 2.1 pct FeO under static conditions to 3.6 × 10?6 mol cm?2 s?1 at 9.5 pct FeO for a rotating rod experiment. Visualization of the experiment using X-ray fluoroscopy showed that gas evolution from the reduction reaction caused the slag to foam during the experiment and that a gas film formed between the carbon surface and the slag at all times during experimentation. The reaction rate increased with increased slag FeO contents under all experimental conditions; however, this variation was not linear with FeO content. The reaction rate also increased with the rotation speed of the carbon rod at a given FeO content. A small increase in the reaction rate, at a given FeO content, was found when horizontal coke surfaces and coke spheres were used as the reductant as compared to graphite and coal char. The results of these experiments do not fit the traditional mass transfer correlations due to the evolution of gas during the experiment. The experimental results are consistent, however, with the hypothesis that liquid phase mass transfer of iron oxide is a major factor in the rate of reduction of iron oxide from slags by carbonaceous materials. In a second article, the individual rates of the possible limiting steps will be compared and a mixed control model will be used to explain the measured reaction rates. 相似文献
11.
George N. Shannon R. J. Fruehan Seetharaman Sridhar 《Metallurgical and Materials Transactions B》2009,40(5):727-737
It is possible, in some cases, for ground coal particles to react with gasifier gas during combustion, allowing the ash material
in the coal to form phases besides the expected slag phase. One of these phases is metallic iron, because some gasifiers are
designed to operate under a reducing atmosphere (pO2{p_{\rm {O}_{2}}} of approximately 10−4 atm). Metallic iron can become entrained in the gas stream and deposit on, and foul, downstream equipment. To improve the
understanding of the reaction between different metallic iron particles and gas, which eventually oxidizes them, and the slag
that the resulting oxide dissolves in, the kinetics of iron reaction on slag were predicted using gas-phase mass-transfer
limitations for the reaction and were compared with diffusion in the slag; the reaction itself was observed under confocal
scanning laser microscopy. The expected rates for iron droplet removal are provided based on the size and effective partial
pressure of oxygen, and it is found that decarburization occurs before iron reaction, leading to an extra 30- to 100-second
delay for carbon-saturated particles vs pure iron particles. A pure metallic iron particle of 0.5 mg should be removed in about 220 seconds at 1400 °C and in 160 seconds
at 1600 °C. 相似文献
12.
Kezhuan Gu Neslihan Dogan Kenneth S. Coley 《Metallurgical and Materials Transactions B》2017,48(5):2343-2353
The bloating behavior of metal droplets and the dephosphorization behavior of bloated droplets at 1853 K (1580 °C) were investigated using X-ray fluoroscopy coupled with constant volume pressure change measurements and chemical analysis of quenched samples. The effect of sulfur content on dephosphorization kinetics was studied during the decarburization period. The slag foamed during the reaction forming a foamy layer over a dense layer. After a short incubation period, the droplets became bloated due to internal decarburization. The bloated droplets floated from the dense slag into the foamy slag. The behavioral changes are directly related to the effect of sulfur on the incubation time for swelling. The dephosphorization reaction was very fast; droplets with low sulfur contents experienced phosphorus reversion shortly after entering the foamy slag, while those with higher sulfur content took a longer time to swell and went through reversion before they entered the foam. The dephosphorization rate and maximum phosphorus partition were higher at lower CO evolution rates because the dynamic interfacial oxygen potential increased with the decreasing oxygen consumption rate. The rate controlling step for dephosphorization was initially a combination of mass transport in both the metal and the slag. As the iron oxide in the slag was depleted, the rate control shifted to mass transport in slag. 相似文献
13.
In the present work, a modified thermal analysis technique was used for studying the heat effect of slag foaming with carbonates
addition. Experiments were conducted by sinking limestone and dolomite pieces of defined shapes (together with iron sinkers)
in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. The heat effects of dolomite
and limestone decompositions were determined at 1623 K (1350 °C) and 1673 K (1400 °C). It was found that the decomposition
energy for dolomite and limestone for the studied slag composition is in the range of 56 to 79 pct of theoretical values,
which is linked to the energy-saving effect of slag foaming. No influence of sample shape on decomposition energy was found
for both limestone and dolomite. 相似文献
14.
An experimental study was conducted to determine the reduction behaviour of olivine iron ore pellets and associated reduction mechanisms in the experimental blast furnace (EBF) located at Luleå. Two sets of EBF samples, namely slowly annealed excavated samples and rapidly quenched probe samples of olivine bearing iron ore pellets were examined in detail. Pellet samples were analysed using SEM, XRD and SIROQUANT analysis to quantitatively determine iron ore phase transformations during descent in the EBF. In the tested EBF campaign, up to 75% of reduction occurred at less than 1100°C, i.e. before the pellet reached the cohesive zone while rest of 25% reduction was completed when pellets reached a temperature of 1300°C and hence within the cohesive zone. The reduction degree of pellets was found to have a linear correlation with distance from the stock line of the EBF. This study showed that the presence of olivine did not have a significant effect on reduction degree for temperatures less than 1100°C in the upper zone of the EBF. However, olivine increased the reduction rate in the final stage of reduction for temperatures in excess of 1100°C in the cohesive zone, which was attributed to the formation of an increased amount of molten FeO containing slag within the pellet. This study is expected to make important contributions towards further improvements in the pellet design as well as the optimization of blast furnace operation and efficiency. 相似文献
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16.
Kinetics of Oxidation of Divalent Iron to Trivalent State in Liquid FeO-CaO-SiO<Subscript>2</Subscript> Slags 总被引:1,自引:0,他引:1
Anna Semykina Volodymyr Shatokha Masanori Iwase Seshadri Seetharaman 《Metallurgical and Materials Transactions B》2010,41(6):1230-1239
This work was devoted to the kinetics studies of the oxidation of divalent iron in liquid FeO-CaO-SiO2 slags to the trivalent state. The experiments were carried out using a thermogravimetric technique (TGA) in the temperature
range of 1623 K to 1773 K (1350 °C to 1500 °C) in an oxidizing atmosphere. The reaction products after oxidation were analyzed
by X-ray diffraction and optical and scanning electron microscopy. The results obtained show that during the first 10 to 15 minutes
of oxidation, 70 to 90 pct of the Fe2+ in the slag was oxidized. Kinetic analysis of the TGA results indicates that the oxidation process may consist of three distinct
steps, viz an initial incubation period, followed by a chemical-reaction-controlled stage, and later, a diffusion-control stage. Appropriate
mathematical relationships were set up for the first two consecutive steps. After combining these equations suitably as the
mechanism of oxidation shifts from one form to another, the experimental results for the first two parts could be reproduced.
A linear correlation was found between the thermodynamic activity of FeO in the slag and the degree of oxidation. 相似文献
17.
Jafar Safarian Leiv Kolbeinsen Merete Tangstad Gabriella Tranell 《Metallurgical and Materials Transactions B》2009,40(6):929-939
The carbothermic reduction of 38.7 pct MnO-12.1 pct CaO-5.4 pct MgO-9.3 pct Al2O3-24.1 pct SiO2-10.4 pct FeO slag in Ar at 1600 °C was studied using the sessile drop wettability technique. Pure graphite, coke, and charcoal
were used as the carbon material substrates. The reduction rates were evaluated by sampling at different reduction times and
by analyzing the chemical compositions of the reduced slag and the produced metal. The carbothermic FeO reduction from slag
is initially fast followed by a much slower reduction rate. However, the rate of the MnO reduction is slow in the fast FeO
reduction stage, and it starts to increase significantly during the slow FeO reduction stage. The kinetics of FeO and MnO
reduction are affected by the type of carbonaceous materials. Moreover, the rate of the carbon dissolution/transfer into the
produced metal phase and the amount of the transferred manganese to the metal phase depend on the type of carbon. Based on
the experimental observations and the thermodynamic calculations, a mechanism for MnO reduction was proposed. According to
this mechanism, MnO is mainly reduced through a metallothermic reduction by Fe and the rate of MnO reduction is controlled
by the rate of the consumption of FeO from the slag, which takes place simultaneously. In contrast, the rate of FeO reduction
in the fast initial reduction stage is controlled by the rate of the carbon dissolution/transfer into the metal phase. However,
at the second slow FeO reduction stage, it is reduced mainly by the solid carbon. 相似文献
18.
Deepak Kumar Raghavendra R. Adharapurapu Tresa M. Pollock Gary S. Was 《Metallurgical and Materials Transactions A》2011,42(5):1245-1265
The objective of this study was to determine the mechanisms of carburization and decarburization of alloy 617 in impure helium.
To avoid the coupling of multiple gas/metal reactions that occurs in impure helium, oxidation studies were conducted in binary
He + CO + CO2 gas mixtures with CO/CO2 ratios of 9 and 1272 in the temperature range 1123 K to 1273 K (850 °C to 1000 °C). The mechanisms were corroborated through
measurements of oxidation kinetics, gas-phase analysis, and surface/bulk microstructure examination. A critical temperature
corresponding to the equilibrium of the reaction 27Cr + 6CO ↔ 2Cr2O3 + Cr23C6 was identified to lie between 1173 K and 1223 K (900 °C and 950 °C) at CO/CO2 ratio 9, above which decarburization of the alloy occurred via a kinetic competition between two simultaneous surface reactions: chromia formation and chromia reduction. The reduction
rate exceeded the formation rate, preventing the growth of a stable chromia film until carbon in the sample was depleted.
Surface and bulk carburization of the samples occurred for a CO/CO2 ratio of 1272 at all temperatures. The surface carbide, Cr7C3, was metastable and nucleated due to preferential adsorption of carbon on the chromia surface. The Cr7C3 precipitates grew at the gas/scale interface via outward diffusion of Cr cations through the chromia scale until the activity of Cr at the reaction site fell below a critical
value. The decrease in activity of chromium triggered a reaction between chromia and carbide: Cr2O3 + Cr7C3 → 9Cr+3CO, which resulted in a porous surface scale. The results show that the industrial application of the alloy 617 at
T > 1173 K (900 °C) in impure helium will be limited by oxidation. 相似文献
19.
It is considered that the use of prereduced ferrous materials and sources of metallic iron such as direct reduced iron (DRI)
or hot briquetted iron (HBI) improves the productivity of the blast furnace (BF). However, oxidation of DRI/HBI can occur
in the upper zone of the BF, which may increase the content of the reducing gases but may not decrease the coke rate substantially.
The behavior of DRI and HBI was investigated by measuring the rate of oxidation of the materials in CO2 gas in a temperature range of 400 °C to 900 °C. In addition, the microstructure of “as-received” and oxidized materials was
examined. The iron oxide phases formed due to oxidation were determined using X-ray diffraction (XRD) and a vibrating sample
magnetometer. The results of isothermal experiments indicated that the kinetics of oxidation of metallic iron is slow at 400
°C. In DRI samples, the initial rate is controlled by the limited mixed control of chemical kinetics at the iron/iron oxide
interface and pore mass transfer, whereas gas diffusion in pores is the rate governing step during the final stages of oxidation.
The oxidation of wustite from iron is found to be faster than the oxidation of the former to magnetite. The structure of DRI
after oxidation resembled a “reverse topochemical-oxide on the surface metal in the center” structure at 600 °C to 700 °C.
The final iron oxide phase formed in DRI after oxidation was magnetite and not hematite. The oxidation of HBI was limited
to the surface of the samples at lower temperatures; at 900 °C, moderate oxidation was observed and a topochemical iron oxide
layer was formed. 相似文献
20.
Rodrigo Corbari Hiroyuki Matsuura Sabuj Halder Matthew Walker Richard J. Fruehan 《Metallurgical and Materials Transactions B》2009,40(6):940-948
Foaming in the electric arc furnace is achieved by injecting carbon into slag, where the resulting reaction of the carbon
with FeO dissolved in the slag generates gas (CO) that causes the slag to foam. In this research, the rate of the reaction
of FeO in slag with carbon and the resulting foam height were measured. In these experiments, the FeO content of the slag
ranged from 15 to 45 mass pct, and several different types of carbon were used including graphite, coals, and chars. The rate
of the slag-carbon reaction and the consequent CO generation increased with FeO content of the slag from 15 to 45 mass pct.
However, the slag foam height reached a maximum at about 25 mass pct FeO and decreased at higher FeO contents. The decrease
in foaming is apparently due to a decrease in the foam index or foamability caused by a decrease in viscosity and an increase
in density of the slag with FeO content. The results of this work indicate that the foam height is influenced more significantly
by the decrease in the foam index compared to the increase in the CO gas generation rate at higher FeO contents. The decrease
in the foam index with FeO agrees with that predicted from the slag properties. 相似文献