共查询到20条相似文献,搜索用时 31 毫秒
1.
V. V. Solonenko E. V. Protopopov S. V. Feiler M. V. Temlyantsev N. F. Yakushevich 《Steel in Translation》2017,47(10):650-657
Thermodynamic analysis is applied to the physicochemical processes in the converter bath when intensifying bath heating by means of gas–oxygen burners. In the converter’s working space, when the combustion flames interact with the liquid bath, the oxygen and natural gas supplied through the burners and the oxygen supplied through the tuyere interact in a bubbling slag–metal emulsion. As a result, iron and the impurities are oxidized. The use of such burners changes the gas composition: not only O2, CO, and CO2 are present, but also H2 and H2O, which changes the oxidative capacity of the gas phase. The presence of solid carbon (for example, pulverized coal) in the burner flame may be used to control and intensify the combustion process. Combustion is most effective in the oxidation of carbon to CO when the oxygen excess is less than 1.0. The oxidation conditions of carbon in the melt change with variation in its activity as a function of its concentration and the temperature. The equilibrium in the M–O–C system may be described by the oxygen partial pressure \({P_{{O_2}}}\), which may be regarded as a universal characteristic. In addition, the equilibrium may be assessed on the basis of the associated ratios \({P_{CO}}/{P_{C{O_2}}}\) and \({P_{{H_2}}}/{P_{{H_2}O}}\) It is found that iron may be oxidized by oxygen and, to some extent, by carbon dioxide. At 1600–2000 K, there is practically no oxidation of iron by steam. The carbon dissolved in the steel is oxidized relatively effectively by oxygen and carbon dioxide until its concentration is less than 0.1% C. Steam oxidizes carbon very poorly and is not much more effective with manganese and silicon. With increase in temperature, the rate at which carbon dissolved in steel is oxidized by oxygen increases, while the oxidation rate of manganese and silicon falls. Above 1800 K, superoxidized slag with a high FeO content actively oxidizes silicon (to <2% Si), manganese (to <1% Mn), and carbon (to <1.5% C). 相似文献
2.
Post combustion in the top space of iron bath smelting reduction furnaces is analysed with three-dimensional mathematical modelling. Momentum transport and continuity equations in combination with a k-? model of turbulence are numerically solved for the gas flow field. Combustion reactions are modelled by a set of transport equations based on the SCRS combustion model and its extension to the k-?-g model. A two-stage combustion scheme is formulated to include carbon transfer and combustion. Heat transfer to bath and droplets is approximated including radiation. Computation results for rectangular reactors are presented with velocity patterns and combustion fields. The complex shapes of post combustion flames are demonstrated. Process parameters are varied to study their influence on combustion and heat transfer to the bath. Effects of the injection geometry are illustrated. 相似文献
3.
The oxidation kinetics of molten Cu2S baths, during top lancing with oxygen/nitrogen (argon) mixtures, have been investigated as a function of oxygen partial
pressure (0.2 to 0.78), bath temperature (1200 °C to 1300 °C), gas flow rate (1 to 4 L/min), and bath mixing. Surface-tension-driven
flows (the Marangoni effect) were observed both visually and photographically. Thus, the oxidation of molten Cu2S was found to progress in two distinct stages, the kinetics of which are limited by the mass transfer of oxygen in the gas
phase to the melt surface. During the primary stage, the melt is partially desulfurized while oxygen dissolves in the liquid
sulfide. Upon saturation of the melt with oxygen, the secondary stage commences in which surface and bath reactions proceed
to generate copper and SO2 electrochemically. A mathematical model of the reaction kinetics has been formulated and tested against the measurements.
The results of this study shed light on the process kinetics of the copper blow in a Peirce-Smith converter or Mitsubishi
reactor. 相似文献
4.
L.F. Nascimento R.F. Martins O.A. Serra 《中国稀土学报(英文版)》2014,32(7):610-620
We employed modified substrates as outer heterogeneous catalysts to reduce the soot originating from the incomplete diesel combustion. Here, we proposed that ceria(CeO2)-based catalysts could lower the temperature at which soot combustion occurred from 610 oC to values included in the operation range of diesel exhausts(270–400 oC). Here, we used the sol-gel method to synthesize catalysts based on mixed oxides(ZnO:CeO2) deposited on cordierite substrates, and modified by ruthenium nanoparticles. The presence of ZnO in these mixed oxides produced defects associated with oxygen vacancies, improving thermal stability, redox potential, sulfur resistance, and oxygen storage. We evaluated the morphological and structural properties of the material by X-ray diffraction(XRD), Brumauer-emmett-teller method(BET), temperature programmed reduction(H2-TPR), scanning electron microscopy(SEM), and transmission electron microscopy(TEM). We investigated how the addition of Ru(0.5 wt.%) affected the catalytic activity of ZnO:CeO2 in terms of soot combustion. Thermogravimetric analysis(TG/DTA) revealed that presence of the catalyst decreased the soot combustion temperature by 250 oC, indicating that the oxygen species arose at low temperatures, which was the main reason for the high reactivity of the oxidation reactions. Comparative analysis of soot emission by diffuse reflectance spectroscopy(DRS) showed that the catalyst containing Ru on the mixed oxide-impregnated cordierite samples efficiently oxidized soot in a diesel stationary motor: soot emission decreased 80%. 相似文献
5.
H. T. Abuluwefa R. I. L. Guthrie F. Ajersch 《Metallurgical and Materials Transactions A》1997,28(8):1633-1641
The article describes rates of oxidation of low carbon steel in various nitrogen-based atmospheres of O2, CO2, and H2O in the temperature range 800 °C to 1150 °C. In characterizing the oxidation process, the weight gains of the samples per
unit surface area vs time data were analyzed. Reaction rates during oxidation in the binary atmospheres of CO2-N2 and H2O-N2 followed a linear rate law and were found to be proportional to the partial pressures of CO2 or H2O. These rates were controlled by rate of reactions at the oxide surface and were highly dependent on oxidation temperature.
The activation energies of the phase boundary reactions obtained were approximately 274 and 264 kJ/mole, for oxidation in
CO2 and H2O atmospheres, respectively. Oxidation in gases containing free oxygen showed that the main oxidizing agent was the free oxygen
and that additions of CO2 and H2O had little effect on the magnitude of the initial oxidation rates. Experiments for oxidation in multicomponent gases showed
that the overall oxidation rates were the additions of rates resulting from oxidation with the individual gaseous species
O2, CO2, and H2O. Oxidation in these atmospheres exhibited an initial linear rate law which gradually transformed into a parabolic. Examination
of scale microstructure after 1 hour of oxidation showed that, for oxidation in carbon dioxide and water vapor atmospheres,
only wustite was present, while in atmospheres containing free oxygen, all three iron oxides, wustite, magnetite, and hematite,
were present. 相似文献
6.
A simulation model on bath smelting processes for the production of iron was developed which predicts the coal, flux, ore, and oxygen consumptions and the off gas volume, temperature and composition. The model is comprehensive in that it takes into account all of the important variables including coal composition, metal composition, ore composition, slag basicity, post combustion ratio, (PCR), prereduction degree (PRD), heat transfer coefficient (HTC), flux, scrap charge, and heat losses. Four basic cases were considered: I. 30% PRD–50% PCR; II. 90% PRD–0% PCR; III. 60% PRD–30% PCR; and IV. 0% PRD–50% PCR. Several different coals were considered and a sensitivity analysis of the critical variables was performed. The model also estimates the sulfur content of the metal. The major conclusions are: Post combustion siginificantly reduces coal consumption but above 20% PCR little reduction of FeO to Fe can be performed with the off gas. Prereducing to FeO (case I) and having as much post combustion as consistent with good heat transfer is an attractive process. This process only requires a simple prereducer, uses less coal, and is relatively insensitive to the type of coal used. High off-gas temperatures may pose a potential problem. The off-gas temperature can be reduced by using an O2–air mixture for post combustion, limiting post combustion or adding water to the gas. The use of CaCO3 in place of CaO or of supplemental electricity does not appear attractive. The melting unit is theoretically an energy efficient scrap melter. For case I using 200 kg of scrap as part of the charge the coal consumption decreases by about 80 kg. With PCR > 30% the FeO content of the slag is expected to be 2–5%, and the metal will not be saturated with carbon. These factors and the increased sulfur load since coal is the fuel indicate the sulfur content of the metal may exceed 0.25%. 相似文献
7.
In this paper, a series of Rh/CeO2 catalysts with three-dimensional porous nanorod frameworks and large specific surface area were prepared by chemical dealloying Al–Ce–Rh precursor alloys and then calcining in pure O2. The effects of the Rh content and calcination temperature on CO oxidation and CH4 combustion were studied, and the results reveal that the Rh/CeO2 catalysts produced by dealloying melt-spun Al91.3Ce8Rh0.7 alloy ribbons and then calcining at 500 °C exhibit the best catalytic activity, the reaction temperatures for the complete conversion of CO and CH4 are as low as 90 and 400 °C, respectively. Furthermore, after 150 h of continuous testing at high concentrations of H2O and CO2, the nature of the catalyst is not irreversibly destroyed and can still return to its initial level of activity. This excellent catalytic activity is attributed to a portion of Rh being uniformly distributed on the CeO2 nanorod surface in the form of nanoparticles, forming strong Rh–CeO2 interfacial synergy. Another portion of Rh permeated into the CeO2 lattice, which results in a significant increase in the number of oxygen vacancies in CeO2, thus allowing more surface active oxygen to be adsorbed and converted from the gas phase. Moreover, the catalytic reaction can proceed even in an oxygen-free environment due to the excellent oxygen storage performance of the Rh/CeO2 catalyst. 相似文献
8.
HIsarna technology combines the cyclone converter furnace (CCF) technology owned by Tata Steel and the HIsmelt technology owned by RioTinto. The CCF is mainly a prereduction vessel that prereduces and melts the iron ore particles, while the final reduction to metallic iron takes place in the smelt reduction vessel. The off-gases from the smelt reduction vessel undergo post-combustion in the CCF. Depending on the operating conditions of the HIsarna process, the off-gases may still contain small amounts of unburnt carbon and hydrogen; hence, for process safety and environmental reasons, they are passed through an incinerator that needs to be operated within a temperature window that will guarantee full combustion of the off-gases. In one of the HIsarna campaigns, it was observed that the temperatures in the incinerator dropped significantly during short periods of production. In order to avoid this phenomenon, the HIsarna process can be adjusted to meet the design conditions in the incinerator, but this is not a preferred option. A computational fluid dynamics study of the incinerator was carried out with different compositions of off-gases from the CCF with varying degrees of post-combustion and flowrates, in order to improve its design and operation. The combustion model predicted complete burn out of CO, CH4 and H2 when sufficient air/O2 was injected. The computational fluid dynamics study showed that in all the cases, the flow pattern of the gases remained asymmetric. The temperature in the incinerator was generally higher if natural gas was mixed with the cyclone off-gas and much higher if oxygen was also injected. Modifications to the incinerator layout were recommended. In subsequent HIsarna trials, the new design was successfully implemented. 相似文献
9.
In the H2–O2–C system, in the general case, two reversible reactions of carbon gasification and the water gas reaction, the gas mixture H2–H2O–CO–CO2 is formed at high temperatures. In this mixture, the very low content of oxygen formed by the dissociation of H2O and CO2 is represented by the oxygen potential log (\({p_{{O_2}}}\), atm). Thus, the redox properties may be assessed in terms of the oxygen potential. In any gas mixture containing H2O and/or CO2, it may be calculated from the equations ;.In the present work, possible compositions of the H2–O2–C system at 700–1500 K and a total pressure of 1 atm are considered: H2–H2O, CO–CO2, CO–CO2–C, H2O–CO2–O2, H2–CO–C, H2–H2O–CO–CO2, and H2–H2O–CO–CO2–C. Analysis yields two nomograms in the following coordinates: log(\({x_{{H_2}O}}\)/\({x_{{H_2}}}\))–log\({p_{{O_2}}}\)–T and log(\({x_{C{O_2}}}\)/xCO)–log\({p_{{O_2}}}\)–T. Using the nomograms and reference information regarding the dissociation pressure of metal oxides, the redox properties of the gas mixtures with respect to those oxides may be assessed. In CO–CO2 systems without hydrogen that are obtained in the combustion of CO, carbon may be formed as soot. This explains the existence of a limited region of gas-phase compositions and log\({p_{{O_2}}}\) in the corresponding nomogram and hence the limited potential for the reduction of some metal oxides in CO–CO2–C systems. The introduction of hydrogen permits the creation of gas mixtures with extremely low oxygen pressure and hence increases the thermodynamic probability of reduction for any metal oxide. Hydrogen may be introduced in the system by methods that differ in economic expediency: from the use of pure hydrogen to the production of gas mixtures as a result of the reaction between water vapor and carbon. In the first case, the reduction of the oxide by hydrogen in the MeO–C–H2 system activates the gasification of carbon by water vapor, the water gas reaction, the reduction of carbon monoxide, and the gasification of carbon dioxide. In the second case, practically pure H2–CO mixture may be obtained above 1300 K. The utility of representing the results on a three-dimensional diagram based on the H2–O2–C concentration triangle is analyzed. If methane formation is taken into account, the equilibrium parameters of gas mixtures are changed markedly only at temperatures below about 900 K.
相似文献
$${\log [{p_{{O_2}}},atm] = 2\log (\frac{{{x_{{H_2}O}}}}{{{x_{{H_2}}}}}) - \frac{{25708}}{T} + 5.563}$$
$$\log [{p_{{O_2}}},atm] = 2\log (\frac{{{x_{C{O_2}}}}}{{{x_{CO}}}}) - \frac{{29529}}{T} + 9.149$$
10.
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
11.
Igor Wilkomirsky Alfonso Otero Eduardo Balladares 《Metallurgical and Materials Transactions B》2010,41(1):63-73
The kinetics and reaction mechanism of the flash oxidation of +35/–53 μm molybdenite particles in air, as well as in 25, 50, and 100 pct oxygen higher than 800 K, has been investigated using a
stagnant gas reactor and a laminar flow reactor coupled to a fast-response, two-wavelength pyrometer. The changes in the morphology
and in the chemical composition of partially reacted particles were also investigated by scanning electron microscopy (SEM),
X-ray diffraction (XRD), differential thermal analysis (DTA), and electron microprobe. High-speed photography was also used
to characterize the particle combustion phenomena. The effects of oxygen concentration and gas temperature on ignition and
peak combustion temperatures were studied. The experimental results indicate that MoS2 goes through a process of ignition/combustion with the formation of gaseous MoO3 and SO2 with no evidence of formation of a molten phase, although the reacting molybdenite particles reach temperatures much higher
than their melting temperature. This effect may be a result of the combustion of gaseous sulfur from partial decomposition
of molybdenite to Mo2S3 under a high gas temperature and 100 pct oxygen. In some cases, the partial fragmentation and distortion of particles also
takes place. The transformation can be approximated to the unreacted core model with chemical control and with activation
energy of 104.0 ± 4 kJ/mol at the actual temperature of the reacting particles. The reaction was found to be first order with
respect to the oxygen concentration. The rate constant calculated at the actual temperatures of the reacting particles shows
a good agreement with kinetic data obtained at lower temperatures. The ignition temperature of molybdenite shows an inverse
relationship with the gas temperature and oxygen content, with the lowest ignition temperature of 1120 K for 100 pct oxygen.
Increasing the oxygen content from 21 to 100 pct increases the particle combustion temperature from 1600 K to more than 2600 K.
A high oxygen content also resulted in a change of the reaction mechanism from relatively constant combustion temperatures
in air to much faster transient combustion pulses in pure oxygen. 相似文献
12.
《Acta Metallurgica》1986,34(1):139-145
An experimental study of equilibrium thermodynamic properties of oxygen in pure tantalum and tantalum alloyed with V, Nb or Mo was made by EMF measurements on solid electrolytic cells over the temperature range of 873–1373 K (600–1100°C). The solubility of oxygen in pure tantalum in equilibrium with Ta2O5 was determined to be Cs = 12.4exp[−(16 kJ/mol)/(RT)] over the experimental temperature range. It was concluded that oxygen obeys Henry's law for concentrations up to the terminal solubility in tantalum for the temperature range 873–1373 K (600–1100°C). The oxygen activity coefficient increased with Mo content in TaMo alloys and decreased with V content in TaV alloys. The equilibrium results showed virtually no change in thermodynamic behavior of the oxygen solution by adding Nb to TaO alloys. The positive deviation of the oxygen activity coefficient in TaMo alloys is evidence of a repulsive interaction between molybdenum and oxygen atoms. The interaction energy was calculated assuming that the interaction extends to third nearest neighbors. It may, in fact, extend to fourth or higher neighboring shells of atoms. 相似文献
13.
Paul Chiriță 《Mineral Processing and Extractive Metallurgy Review》2016,37(5):305-310
Aqueous oxidation of iron monosulfide (FeS) by oxygen at initial pH between 2.5 and 5 was investigated in a closed system at different temperatures (25, 35, and 40°C). It was found that the rate of aqueous oxidation of FeS increases when initial [H+] and temperature increase. The reaction order with respect to [H+] was 0.16 ± 0.02 at 25°C. The activation energy was found to be 23 ± 5 kJ mol–1 at initial pH 2.5. This value suggests that aqueous oxidation of FeS by oxygen is controlled by a mixed regime of diffusion and surface reaction control. FTIR analysis of the initial and reacted FeS samples has shown that during the aqueous oxidation of FeS by O2 a sulfur-rich layer is formed on the mineral surface. The experimental results indicate that the protons adsorb on the mineral surface and catalyze Fe2+ release into solution (by Couloumbic repulsion) and S(-II) oxidation to higher oxidation states. 相似文献
14.
Zhichao Shang Yong Yu Hang Yang Zhongxiang Yang Yang Xiao Xiaohong Wang 《中国稀土学报(英文版)》2023,41(2):250-258
The Cu/CeO2 nanoporous composite material was prepared via a one-step and energy-saving method of solution combustion synthesis(SCS).The phase composition,surface morphology and optical characteristics of Cu/CeO2 were studied.The results show that the SCS products are composed of cubic fluorite CeO2 and Cu.Due to the generation and escape of gas during the synthetic reaction,the SCS CeO2 shows porous structure,in which the mesopores(diameter 10-17 nm) ... 相似文献
15.
A series of Ce-Fe-Zr-O(x)/MgO (x denotes the mass fraction of Ce-Fe-Zr-O, x=10%, 15%, 20%, 25%, 30%) complex oxide oxygen carriers for selective oxidation of methane to synthesis gas were prepared by the co-precipitation method. The catalysts were characterized by means of X-ray diffraction (XRD) and H2-TPR. The XRD measurements showed that MgFeO4 particles were formed and Fe2O3 particles well dispersed on the oxygen carriers. The reactions between methane diluted by argon (10% CH4) and oxygen carriers were investigated. Suitable content of CeO2/Fe2O3/ZrO2 mixed oxides could promote the reaction between methane and oxygen carriers. There are mainly two kinds of oxygen of carriers: surface lattice oxygen which had higher activity but lower selectivity, and bulk lattice oxygen which had lower activity but higher selectivity. Among all the catalysts, Ce-Fe-Zr-O(20%)/MgO exhibited the best catalytic performance. The conversion of the methane was above 56%, and the selectivity of the H2 and CO were both above 93%, the ratio of H2/CO was stable and approached to 2 for a long time. 相似文献
16.
Environmental contamination such as soot particles and NOx has aroused extensive attraction recently.However,the main challenge lies in the oxidation of soot at mild temperature with the assistance of NOx.Here,a series of core-shell MnCeOx catalysts were successfully synthesized by hydrothermal method and employed for low-temperature catalytic oxidation of soot in the presence of NOx.X-ray diffraction(XRD),inductively coupled plasma-optical emission sp... 相似文献
17.
Jia Gong Y.M. Jiang B. Deng C. Zhong D.M. Sun J. Li 《Metallurgical and Materials Transactions A》2009,40(11):2511-2513
The oxidation behavior of Fe-16Cr steels in N2-12 vol pct H2O was studied at 850 °C. The oxide scale was compact and had excellent adhesion to the substrate; moreover, there were three
layers of different compositions existing in the scale. To gain an insight into the transport mechanism, two-stage oxidation
was carried out in N2-12 vol pct H216O and followed in N2-12 vol pct H218O gas mixtures. The oxygen isotope profiles in oxide scales were determined by secondary ion mass spectrometry. The results
showed that oxidation in water vapor proceeded by outward chromium transport, especially, the oxidation involved inward transport
of water molecules. 相似文献
18.
The Pourbaix diagrams of the systems SO42??SO32??H2O and iron hydroxide (oxide)–H2O are refined. The E(pH) dependence of the sulfitization of iron(III) hydroxide is refined with allowance for the regions of predominant phase constituents of the systems. The potential E–pH electrochemical equilibrium diagrams of the systems Fe(OH)3–H2SO4–SO32?–H2O, FeOOH–H2SO4–SO32?–H2O, and Fe2O3–H2SO4–SO32?–H2O are plotted. These diagrams can be considered as a thermodynamic basis for the sulfite conversion of the ferrous cake of copper–nickel production. 相似文献
19.
《中国稀土学报(英文版)》2023,41(7):1022-1030
In this work, V/Ce–Ti catalysts were modified with different kinds of transition metals (Cu, Fe, Co, Mn) by sol–gel and impregnation methods. The NH3 oxidation performance of them was tested to select the most active catalyst in NH3-selective catalytic oxidation (NH3–SCO). The effect of NO, SO2 and H2O was also investigated. The experimental results indicate that 1% Cu–V/Ce–Ti catalyst exhibits the most significant ability to remove slip ammonia discharged from coal-fired plants and its NH3 conversion efficiency reaches 90% at 300 °C. In addition, 97% NOx can be removed when NO is introduced in the gas. Cu–V/Ce–Ti catalyst also obtains good resistance to H2O and SO2. Based on the characterization experiment, the introduced Cu and V are highly dispersed on Ce–Ti catalyst and they can increase the redox properties and the number of acidic sites. Besides, the redox cycles among Cu, V and Ce species on Cu–V/Ce–Ti catalyst surface are conducive to generating more active oxygen and promoting the oxidation capacity of the catalyst. 相似文献
20.
A series of MnMgA10 samples with different amounts of Ce doping were facilely prepared using coprecipitation method and their catalytic soot combustion activity was evaluated by temperature programmed oxidation reaction (TPO). The methods of X-ray diffraction (XRD), Brumauer-Emmett-Teller (BET), H2-TPR, NO-TPO and in situ 1R were used to characterize the physio- chemical properties of these samples. Dopant Ce improved the soot combustion performance of MnMgA10 catalyst due to the en- hanced redox ability. Introduction of NOx led to the further increase of catalytic soot oxidation activity on these samples. Over Ce-containing samples, the catalytic activity was slightly decreased as the amount of dopant Ce increased in 02. Diftbrently, in NO+O2, a certain amount of dopant Ce was much more favorable and excess amount of Ce resulted in a sharp drop of the catalytic soot combustion activity. Both NO: and nitrates were found to have great contributions to the effects of NOx on the soot combustion activity of Ce-doped catalysts. More NO2 was generated as dopant Ce increased. When appropriate amount of Ce was introduced, the as-formed NO2 was stored as bridging bidentate nitrate on Mn-Ce site, which was confirmed to have higher reactivity with soot than nitrite or monodentate nitrate on Mn and/or Ce sites. Overall, Mno.sMg2.sCeo.lAlo.90 was considered as the most potential catalyst for soot combustion. 相似文献