紧卷罩式退火的温度场模拟

紧卷罩式退火炉在钢板生产中广泛使用，该炉包括以Ｎ２和Ｈ２混合气体为保护气体的传统罩式炉和以１００％Ｈ２作为保护气体的全氢罩式炉。模拟罩式退火温度场对确定和优化钢板的退火制度、预报钢板的机械性能极为重要。本文介绍了影响罩式退火炉效率的因素，并着重论述了钢卷罩式退火的温度场模拟的原理及实现手段。     

JPMA development awards

Abstract

The challenges in controlling carbon potential during sintering of steel powder have been discussed in many experimental and theoretical studies. The main issues lie within the complex thermodynamics and kinetics of processing atmosphere chemistry in continuous sintering furnaces. Although many models have been proposed to address the problem, these have rarely come to reality and entered industry practice. The purpose of this article is to summarise these discussions and investigate the interaction of the atmosphere constituents with the sintered compact within a sintering furnace. An important aim is to provide the PM industry with a fresh understanding of furnace operations and to provide recommendations to improve the control of furnace conditions. A case study is given of an existing furnace installation using Sinterflex technology which allows continuous monitoring and/or control of the furnace atmosphere. The reduction of oxides and carbon potentials to optimise the production parameters is described.     

Decreased gas consumption of a fluidized bed furnace

The feasibility of utilizing a closed circulatory system to generate gases for a fluidized bed furnace was investigated with the primary concentrations of both economizing on the raw materials used for producing furnace atmospheres and decreasing the air pollution caused by exhaust gases. Air humidified with water vapor was first introduced into a charcoal furnace for causing a reaction with hot charcoal to form a carburizing atmosphere. This atmosphere was then introduced into a fluidized bed furnace to carburize steels. The exhaust gases from the fluidized bed furnace were recycled by repassing them through the hot charcoal layer in the charcoal furnace with a gas pump. The charcoal furnace and the fluidized bed furnace formed a closed circulatory system during the carburization of steels. Experiments were performed with various parameters of this system, including content of water vapor in the humid air, temperature of the charcoal, rate of recirculation of the atmosphere,etc. The effect of each parameter on the carburizing behavior in the fluidized bed furnace was investigated on the basis of the rate of carburization and the carbon potential of the atmosphere. The feasibility of applying this system to a fluidized bed furnace was assessed from the aspects of the fluidization of A1₂O₃ powder, the result of carburizing steel, and the rate of consumption of charcoal. The closed system employed in generating atmosphere was demonstrated by the experimental results to have enabled the fluidized bed furnace to operate normally and to have significantly decreased both the consumption rate of charcoal and the environmental pollution.     

bdGas carburizing of steel with furnace atmospheres formedin situ from methane and air and from butane and air

Carburizing experiments were conducted at 927°C (1700°F) and 843°C (1550°F) using furnace atmospheres formed from methane and air and from butane and air introduced directly into the carburizing furnace. Gas flow rates were low to promote equilibration of the reaction products within the furnace. The air flow rate was held constant while the methane or butane flow was automatically regulated to maintain a constant oxygen potential, as measured by a zirconia oxygen sensor, within the furnace. In comparing the results of these experiments with earlier results obtained using propane and air, several differences were noted: (a) The methane content of the furnace atmosphere, measured by infrared analysis, was about twice as great when methane was the feed gas rather than propane or butane. This was true despite the fact that the mean residence time of the gas within the furnace was greater in the methane experiments. Methane appears to be less effective than propane or butane in reducing the CO₂ and H₂O contents to the levels required for carburizing. (b) There was a greater tendency for the CO content of the furnace atmosphere to decrease at high carbon potentials when methane is used instead of propane or butane. The decrease in CO content is due to hydrogen dilution caused by sooting in the furnace vestibule. These differences in behavior make propane or butane better suited than methane forin situ generation of carburizing atmospheres. However, there is no difference in the amount of carburizing occurring at a specified carbon potential when methane, propane, or butane are used as the feed gas in this process. J.A.Pieprzak, formerly a member of the Engineering and Research Staff     

Gas carburizing of steel with furnace atmospheres formedIn Situ from propane and air: Part III. Control of furnace atmosphere composition with a zirconia oxygen sensor

Gas carburizing experiments were conducted in a batch-type sealed-quench furnace using furnace atmospheres produced by the reaction of propane and air within the furnace. The air-propane ratio of the inlet gases was automatically controlled to maintain a constant oxygen potential, as measured by a zirconia oxygen sensor, within the furnace. The results of carburizing trials at 843 and 927 °C are described. The effect of inlet gas flow rate on furnace atmosphere composition and the amount of carburizing is illustrated.     

Gas carburizing of steel with furnace atmospheres formedIn Situ from propane and air: Part II. Analysis of the characteristics of gas flow in a batch-type sealed quench furnace

Gas flow dynamics in a batch-type sealed quench carburizing furnace were studied for operations utilizing low inlet gas flow rates. By analyzing the rate of change of furnace atmosphere composition when a sudden change is made in the inlet gas composition, it is shown that a significant amount of gas circulation occurs between the hot furnace chamber and the unheated vestibule. This circulation has the effect of increasing the mean residence time of gases within the furnace. A long mean residence time is advantageous for carburizing when the inlet gases consist of an airJhydrocarbon blend rather than prereacted endothermic gas.     

Numerical Evaluation of Blast Furnace Performance under Top Gas Recycling and Lower Temperature Operation

The new process of top gas recycling by hot reducing gas (HRG) injection has been developed in this study in order to overcome the disadvantageous problems under the lower temperature operation, to enhance the utilization of top gas carbon and to reduce carbon dioxide emission of blast furnaces. Numerical evaluation of blast furnace top gas recirculation together with lower‐temperature operation was performed by means of a multi‐fluid blast furnace model. The simulation results show that, (1) under the lower temperature operation, the shaft injection, or simultaneous shaft and tuyere injection of hot reducing gas is effective to increase the heat supply and to enrich the reduction atmosphere in the shaft zone, to improve the reduction of iron burdens, and enhance the efficiency of the shaft zone. (2) If top gas is recirculated by HRG on the basis of lower temperature operation, a highly efficient low‐carbon blast furnace is obtained. The productivity of the furnace shows a remarkable increase and the total reducing agent rate shows a considerable decrease. Furthermore, the top gas carbon utilization is enhanced and the carbon dioxide emission rate is lowered. (3) Generally, shaft efficiency, carbon emission and heat efficiency under simultaneous tuyere and shaft injection are comparatively better than in the other two methods of single injection.     

数学模型在宝钢高炉操作中的应用

论述了炉况判断GO-STOP模型、TC指数和炉温预报模型、软熔带模型、煤气流分布判断和布料控制模型的原理、建模方法及其在宝钢大型高炉生产操作中的应用情况。宝钢高炉生产不仅采用先进的自动化装备,而且从 1号高炉建设起即先后引进了8个先进的数学模型指导高炉操作。通过长期学习、消化,特别是近几年来对模型的改造和完善,并融人现代智能模型技术,大大提高了模型的精度和应用效果,这些模型为宝钢大型高炉实现长期稳定顺行、主要技术经济指标达到世界先进水平发挥了重要作用。     

Calculating the blast-furnace profile

A mathematical model is developed for calculating the height and outline of the working space in a blast furnace from the batch surface to the axis of the air tuyere, on the basis of data regarding the density, acceleration of the batch flux, and pressure difference of the gas. The optimal working height of blast furnaces in smelting titanomagnetite sinter and pellets is 10.1–21.8 m. For larger furnace height, relatively immobile refractory batch is formed in the bosh and periodically slips to the hearth, with impairment of the furnace’s thermal state. The calculated values obtained provide guidelines in the design and reconstruction of shaft furnaces.     

Calculation of gas release from DC and AC arc furnaces in a foundry

A procedure for the calculation of gas release from arc furnaces is presented. The procedure is based on the stoichiometric ratios of the oxidation of carbon in liquid iron during the oxidation heat period and the oxidation of iron from a steel charge by oxygen in the period of solid charge melting during the gas exchange of the furnace cavity with the external atmosphere.     

Gas carburizing of steel with furnace atmospheres formedIn Situ from propane and air: Part I. The effect of air-propane ratio on furnace atmosphere composition and the amount of carburizing

Gas carburizing experiments were conducted in a batch-type sealed quenched furnace at 843 and 927 °C using furnace atmospheres produced by reacting propane and air within the furnace chamber. With low, constant gas flow rates it is shown that the amount of carburizing varies regularly with air-propane ratio. Furnace atmosphere composition was monitored as a function of temperature and air-propane ratio and compared with the composition expected at thermodynamic equilibrium.     

Analysis on Non‐Uniform Gas Flow in Blast Furnace Based on DEM‐CFD Combined Model

Blast furnace technology is currently aiming at low reducing agent operation so as to decrease CO₂ emissions. At the same time, the inner volume of blast furnaces has frequently been enlarged so as to increase production rate in some countries, including Japan. Operating conditions designed for low reducing agent in a large blast furnace tend to cause unfavorable phenomena such as slipping of the burden and gas channeling due to the decrease in coke rate. Mathematical models help to clarify the in‐furnace phenomena under these situations. From the above backgrounds, a new model has been developed that combines Discrete Element Method with Computational Fluid Dynamics (DEM‐CFD) to simulate precisely the gas flow and solid motion in a blast furnace. The present study aimed to develop a three‐dimensional mathematical model based on DEM‐CFD for simultaneous analysis of gas and solid flow in the whole blast furnace. The unbalanced gas flow in the case of clogging of the particular tuyere was analyzed to clarify the circumferential unevenness in the lower part of the blast furnace. Based on the combined DEM with CFD model, the non‐uniform gas flow in the lower part of the blast furnace was precisely evaluated.     

Raw Material Strength in a Blast Furnace at Operating Temperature

This paper presents simulative tests in a continuous hot model of the lumpish zone in a blast furnace. Samples after reaction were analysed in compression tests and a relationship between reaction degree and temperature in a blast furnace was derived. Compression strengths of coke, pellets and sinter with different reaction degrees were measured at relevant temperatures using a high temperature compression testing machine with adjustable atmosphere. Based on the results, the regulation of strength variability and the mechanism of breakage of raw materials in blast furnaces were researched. As an effect of the increases of temperature and carbon loss rate, the strength of coke had a negative linear relationship with the temperature in the indirect reduction zone in a blast furnace. The carbon loss rate of coke in the stock column of a blast furnace is about 36% and the strength can be decreased by more than 90%. A practical way to save coke strength is to reduce the carbon loss rate. The strength of pellets was decreased by about 60% to 70% in the lumpish zone. If the original strength of pellets was higher than 2000 N, the high temperature strength roughly kept at a coordinative level over 1000 N and was sufficient to avoid damage in the blast furnace. Due to the reduction of hematite and disappearance of calcium ferrite, the strength of sinter showed a strong decline when the reduction degree reached 10%. The value at the top of the cohesive zone was only about 15% of that on the charging bank. Powder from sinter was easily produced at these two places.     

晋南钢铁高炉喷吹富氢气体工业化实践

 钢铁工业是中国制造业中碳排放量最高的行业,碳排放占全国碳排放总量的15%左右。高炉是钢铁工业碳消耗量最大的工序,碳消耗占钢铁流程总碳消耗的70%以上,减少高炉冶炼碳消耗是降低钢铁工业碳排放的最有效措施。高炉喷吹富氢气体不但可以提高冶炼效率,减少污染物排放,而且可以减少焦炭或煤粉消耗,从源头上降低高炉冶炼碳消耗,从而减少碳排放。以山西晋南钢铁两座1 860 m3高炉风口喷吹富氢气体工业化生产数据为例,详细研究了高炉喷吹富氢气体对燃料比、风口理论燃烧温度、炉腹煤气量、H₂利用率以及CO₂排放量的影响。结果表明,喷吹富氢气体可以显著降低高炉固体燃料消耗,在吨铁富氢气体喷吹量为65 m3条件下,富氢气体与固体燃料的置换比为0.49 kg/m3;风口喷吹富氢气体降低了风口理论燃烧温度,吨铁每喷吹1 m3富氢气体,风口理论燃烧温度降低约1.5 ℃,高炉鼓风量和炉腹煤气量都少量降低;喷吹富氢气体以后,炉内H₂的利用率平均为37.3%,CO的利用率约为43.2%;吨铁CO₂排放量可以降低80 kg左右,高炉CO₂排放降低了5.6%,取得了较好的经济、环境和减污降碳效果。     

连续退火炉气氛双挡板隔离装置设计分析

高牌号无取向、取向硅钢连续退火炉需要一种隔离炉膛两边气氛的装置。设计这种装置可以实现硅钢二次结晶退火工艺需要的干湿气氛隔离要求,防止相邻炉段的炉膛气氛互相串通,污染炉膛气氛,影响带钢质量。     

Carburizing performance and kinetics of carbon sources in blast furnace hearth

It is of great significance to improve the carbon saturation of molten iron which weakens the erosion of sidewall carbon bricks, so as to realize the hearth longevity. Carburizing properties of various carbon sources in molten iron by static method was systematically investigated. The apparent reaction rate constant K of samples was calculated. The results show that the carburizing properties of different carbon sources from strong to weak are NMA carbon brick > carbon rod > pulverized coal > coke > 9RDN carbon brick. The carburizing performance of carbon sources decreases with the increase in its graphitization degree. Ash has a negative effect on the carburizing performance of carbon sources, but ash in the form of agglomerated large particles cannot weaken the carburizing performance of carbon sources. The Al2O3 phase can obviously degrade the carburizing performance of carbon sources. The 9RDN carbon bricks with low carburizing properties can be adapted to more complex furnace conditions. The carburizing properties of pulverized coal and coke are relatively weak. When the pulverized coal and coke powder formed in the tuyere raceway enter the hearth, the porosity of the deadman will be reduced, resulting in hearth inactivity and frequent fluctuation of furnace condition, and it is not conducive to the carburization of the deadman. Therefore, it is necessary to properly improve the coke particle size and increase the air volume for weakening the negative effects of unburned coal powder and coke powder on the longevity of the hearth sidewall carbon bricks.     

Energy aspects of a lead blast furnace

The energy effects accompanying the processing of the feed material to a lead blast furnace are considered in terms of a reversible model. Relative to this model the efficiencies of operating furnaces are found to be in the range 18 to 35 pct. The effects of the effluent gas CO₂/CO ratio and temperature and oxygen enrichment of the blast air in the thermodynamic efficiency are quantified. Improvements in efficiency achieved in industrial furnaces as a result of oxygen enrichment of the blast air are substantially greater than those predicted. Mass and enthalpy balances on an industrial lead blast furnace are presented from which it is estimated that approximately 9 pct of the carbon charged to the furnace is lost due to the solution loss reaction in the upper regions of the furnace. David R.Morris, currently on sabbatical leave, University of Cambridge, Cambridge, United Kingdom.     

Power increase of plasma heating systems by CO2 addition into the furnace atmosphere: Investigations in view of the plasma ladle furnace

For certain steel grades the treatment in conventional ladle furnaces equipped with graphite electrodes may not be advisable because of the risk of carbon pick-up. In these cases metallic plasma torch systems operated with argon as plasma gas may be preferable. However, the maximum active power available from a 3 torch AC argon plasma system is at present limited to about 4 MW. Tests were carried out with 200 kg heats in a pilot furnace equipped with 2 AC argon plasma torches to investigate the arc voltage increase by adding CO₂ to the furnace atmosphere. With 20% CO₂, the voltage of a 30 cm arc was raised from 100 to 173 V. The transfer rate of oxygen from the CO₂ in the atmosphere via the plasma arc to the steel melt was measured by means of steel and off-gas analyses. After formation of a slag layer, about 10% of the oxygen supply injected into the furnace as CO₂ was transferred to the melt. The measured values concerning power increase and oxygen transfer were extrapolated to ladle capacities of 50 to 150 t and 3-torch 12 kA AC plasma heating systems. In a furnace atmosphere containing 60% CO₂, the active power available from a plasma system would be 10 MW as compared to 3.5 MW in pure argon. The oxygen transfer rates proved to be relatively small due to the low gas flow rates of such systems and to the low mass transfer efficiency. The addition of 40% CO₂ would raise the power to heat 110 t of steel at a heating rate of 3 K/min, while the oxygen level would increase within 30 min by less than 10 ppm. The specific CO₂ demand would in that case be 0.12 m³(STP)/t.     

THE IMPORTANCE OF ATMOSPHERE CONTROL IN HARD-METAL PRODUCTION

Abstract

The furnace atmospheres used in the manufacture of hard-metal from the pressed compact to the sintered component are discussed.

The very fine size (0·5–8·0 μm) of the powder particles makes the compacts particularly prone to react with furnace atmospheres. All these reactions affect the carbon content of the alloys, which must be controlled within extremely close limits to ensure good quality.

The removal of pressing lubricant, presintering, and final sintering all involve heating the components to temperatures at which reactions with the furnace atmosphere can occur. Both hydrogen and vacuum furnaces are used and care is required to maintain a quality of atmosphere that will not lead to a deleterious change in carbon content.