Steelmaking Converter Research Articles

A Novel Bottom Stirring Scheme to Improve BOF Performance through Mixing and Mass Transfer Modelling

In combined blown basic oxygen steelmaking converter bottom stirring plays an important role in mixing within the bath. Better mixing within the bath and improved mass transfer between slag and metal is believed to cause better dephosphorisation. Normally an equal amount of gas in passed from each tuyere in bottom stirring throughout the blow. Here a novel bottom stirring scheme has been proposed and investigated where different amount of gas was injected from different tuyeres in last 3 to 5 min of the blow. The investigation was carried out with respect to mixing and mass transfer in a scaled-down physical model having appropriate similarity with the actual steelmaking vessel. The scheme, differential flow bottom stirring, basically redistributes the total bottom gas flow in a manner so that a linear flow gradient is imposed across the bath. It was found that the differential flow bottom stirring scheme gives 30-35 % improvement in mixing compared to uniform flow through all the bottom tuyeres. The scheme also gave better mass transfer rates than the conventional stirring. A 30 % increase in the mass transfer rate was observed. Plant trials with the scheme were conducted to assess the impact on dephosphorisation within the practical BOF vessel. Improved BOF performance in terms of phosphorous removal was obtained in the plant trials. Comparatively lower turn-down phosphorous and improved phosphorous partition was achieved with a saving in bottom gas injection amount.

Evaluation of Bottom Stirring System in BOF Steelmaking Vessel Using Cold Model Study and Thermodynamic Analysis

Water model experiments have been carried out in a 1/6th scaled down model of the basic oxygen steelmaking (BOF) converter in order to optimize the bottom tuyere configuration of a new vessel bottom. The mixing time in the model was determined by conductivity measurement technique for ten different types of bottom tuyere configurations. Amongst the various bottom tuyere configurations, the one consisting of 8 tuyeres in a symmetric non-equiangular position was found to be the best with respect to mixing in the vessel. The same bottom tuyere configuration of the new vessel bottom was compared with the previous bottom tuyere configuration (6 tuyeres), and about 40% improvement in the mixing in the bath was observed with the new bottom tuyere configuration. After determining the best bottom tuyere configuration from water model, it was implemented in the actual steelmaking vessel at the LD1 shop of Tata Steel. Average phosphorus partition ratio improved by 10 to 12 points, and the average %Fetotal in the slag dropped by about 1–2%, and a record vessel life of more than 2000 heats was achieved in the first campaign itself with the new bottom tuyere configuration. Thermodynamic evaluation of dephosphorization in the BOF for different bottom stirring systems adopted by Tata Steel over a period of several years has been carried out using plant data of several heats. Gradual improvement in the approach to equilibrium due to improvement in the bottom stirring systems has been observed.

Exergy recovery from steelmaking off-gas by latent heat storage for methanol production

This paper proposes a new thermal energy recovery process of hot gas exhausted from the steelmaking converter by utilizing not only latent heat but also endothermic heat of reaction. The intermittently emitted LD gas was first transferred into continuous, constant-temperature heat source in the form of latent heat in the Phase Change Material (PCM) of copper. Then, the stored heat was supplied to Coke Oven Gas (COG) to induce endothermic reaction of steam reforming of methane. Methanol was finally produced from the obtained gas in the proposed system. A heat and material balance model predicted all operating data of the system and then exergy analysis based on the predicted data was conducted to validate the system theoretically. The results showed that the proposed system has a possibility to produce a large amount of methanol corresponding to 20% of total demand in Japan, with only 28% of exergy consumption in the conventional method.

Modelling of Nitrogen Intrusion into an AOD Converter at the Reduction Stage Caused by Suction Oscillation in the Ventilation Hood

Some AOD operators doubt that unusual high nitrogen content in low nitrogen grade stainless steel may come from the entrapped nitrogen of air through the gap between hood and AOD converter under some unsteady conditions. This paper modelled the unsteady condition caused by pressure jumping in the ventilation system of an AOD vessel in order to investigate the possible nitrogen intrusion inside the converter. Commercial CFD code, FLUENT6.1, was applied to study the gas flow field, thermal conditions and species transfer in the computing domain. The stainless steelmaking converters in AvestaPolarit's stainless steel plant in Finland, named AOD1 and AOD2, were simulated respectively. The modelling was carried out at the reduction stage of the AOD process, in which only argon is blown from the bottom tuyeres. The results show that most hot gas from the AOD converter escapes to the atmosphere as the local relative pressure in the ventilation hood jumps to a high value. The temperature inside the hood climbs suddenly when the suction ability of the ventilation system drops and the direction of the exhaust gas flow reverses. Because of different geometric location between hood and converter, the air can intrude further into AOD1 converter than into AOD2. Therefore, the high nitrogen fraction area also projects deeper inside AOD1. Although gas containing a high nitrogen fraction can be entrapped inside the converter due to a dramatic drop in suction ability in the ventilation system, the present research suggests that the area rich in nitrogen is so limited inside AOD that the mass fraction of nitrogen does not exceed 5% near the melt bath surface.

Heat Recovery of LDG by Utilizing Latent Heat and Reaction Heat for Producing Methanol.

This paper proposes a new heat recovery process of hot gas exhausted from the steelmaking converter by utilizing not only latent heat but also endothermic heat of reaction. The intermittently emitted LD gas was first transferred into continuous, constant-temperature heat source in the form of latent heat in the Phase Change Material (PCM) of copper. Then, the stored heat was supplied to Coke Oven Gas (COG) to induce endothermic reaction of methane steam reforming. Methanol was finally produced from the obtained gas in the proposed system. A heat and material balance model predicted all operating data of the system and then exergy analysis based on the predicted data was conducted to validate the system theoretically. The results showed that the proposed system has a possibility to produce a large amount of methanol corresponding to 20% of total demand in Japan, with only 28% of exergy consumption in the conventional method.

Splashing and Spitting Behaviour in the Combined Blown Steelmaking Converter.

The amount of iron droplets ejected in the BOF affects on metallic yield, refactory wear and the progress of decarburisation. The purpose of this study was to investigate the effect of lance height, lance nozzle angle, lance position, top gas flow rate, bottom blowing and foamy slag on splashing and spitting. A new cold model method for investigating the effects of above-mentioned parameters on the location and quantity of liquid splashed on the walls of the model was utilised. According to the model tests, reduction of the nozzle angle increased the total amount of splashing and spitting considerably. Consequently, reduced productivity due to an increase in metal losses, skulling of the cone and converter mouth and further increased time for skull removal is expected. Introduction of bottom blowing increased splashing significantly on lower parts of the vessel. Lance position has an effect on total amount of splashing when bottom blowing is used. The presence of even minor foam layer on water surface reduced the amount of total splashing significantly.

Physical Model Study of Selective Slag Splashing in the BOF.

Steelmaking converter vessels do not usually wear evenly. Often, the higher wear rate in the trunnion area determines the lining life of the vessel. On the other hand, major skull growth may occur in other parts. In order to ensure consistent BOF performance, maintaining the vessel geometry by selective slag coating is important. Since selective slag splashing is difficult to perform by conventional oxygen lance, the effect of e.g. plugging one or two lance nozzles on the amount and direction of splashing was investigated by physical model experiments. Furthermore, the model was used to predict the influence of lance height, lance position, bottom blowing configuration and liquid viscosity on splashing behaviour. Lowering the lance increased the rate of splashing to a certain lance height beyond which it decreased. Similar behaviour was found to apply also to the slag wash coating mechanism. At low lance distance, plugging one lance nozzle increased the amount of splashing on charge pad and trunnion areas and decreased on slag hole side. Generally, bottom blowing increased the amount of slag drops considerably. Positioning of bottom stirring plugs had a clear effect on the direction of splashes.

Combined blowing with three ‐ hole lance in a sidewall blowing converter

Traditionally, in stainless steelmaking converters, oxygen has been blown by a one‐hole lance (1 HL) and sidewall tuyères. In order to reduce the tap‐to‐tap time, the multi‐hole lance has been used for oxygen blowing. The aim of this work was to develop blowing practise for a multi‐hole lance to reduce the tap‐to‐tap time and minimise metal splashing and spitting in the sidewall blowing converter (chromium converter). In the chromium converter the chemical energy of liquid ferrochrome (which contains 4 % silicon and 7 % carbon) is utilised for scrap melting by oxidising the silicon and the part of carbon.The research has been made by a dynamically scaled water model and full‐scale converter. Used parameters were the gas flowrate from sidewall tuyères and lance, lance height, charge weight and position of multi‐hole lance. Splashing has been measured during blowing from walls (splashing) and mouth of the converter model (spitting). The model tests indicated less splashing and spitting by the three‐hole lance (3 HL) than traditional 1 HL. The 1 HL caused strong skulling of the converter cone. By 3 HL blowing the position of the lance has a remarkable effect on the direction and the amount of splashing and lance life. Because of hot metal‐slag splashes, the life time of the 3 HL was halved by position 1 (compared to 1 HL). With the lance position 2 the splashing decreased by approx. 50% in model tests and lance life time increased by ~ 50% (compared to 1 HL) in the full‐scale converter. The model agreed well with the full‐scale converter. According to the process tests, the nominal productivity of the chromium converter has increased 15 % and depending on the refining practise and the silicon content of ferrochromium the lining life has increased 20 ‐ 30 %. In the future the multi‐hole lance will be tested in the AOD vessel.

Numerical modelling of processes of upper blow-down and carbon monoxide reburning in a steel-making converter

Numerical modelling of processes of upper blow-down and carbon monoxide reburning in a steel-making converter

Dynamic Model of Slag Foaming in Oxygen Steelmaking Converters.

The foaming and emulsification of steelmaking slags can be analyzed in terms of an emulsion number which is defined as the ratio of the velocity of gas bubbles and that of metal droplets present in slag at any given stage of the blow. An improved procedure is suggested to evaluate the viscosity of gas-slag foam at high gas void fractions. The calculated velocity of gas bubbles in foaming slags is verified using the experimental results reported in literature. A critical comparison is also made with the other approaches available in the literature. It is shown that the emulsion number is directly related to foaming conditions. A dynamic model of slag foaming is developed on the basis of the bubble and droplet velocities, changing slag composition and temperature and the continuous reduction of iron oxide content of slag during the main blow period. Combined effects of lance nozzle design and blowing regime on slag foaming are discussed.

Characterization of Slag-Metal Droplet-Gas Emulsion in Oxygen Steelmaking Converters.

Metal droplets of various sizes are ejected from the jet impact zone in oxygen steel making converters. The residence time of these droplets in the surrounding gas-slag mixture is calculated for different operating conditions in top blown converters. A new dimensionless emulsion number, En, based on the ratio of the residence time of the metal droplets to the residence time of gas bubbles in liquid slag is proposed. This emulsion number is found to be strongly dependent on the ratio of lance height to the throat diameter of De Laval nozzle. The blowing regimes followed in three plants are analyzed in terms of emulsion number. The reduction of FeO in slag by dissolved carbon in metal droplets also depends upon emulsion number and, in turn, decides the lance height chosen at various stages of the blow as well as lime dissolution, slag formation and slopping. The emulsion number can be used as an effective tool to control slag formation behaviour.

The Recycling of Linz-Donawitz (Ld) Converter Slag By Use as a Liming Agent On Pasture Land

Slag is a major by-product of the basic oxygen steelmaking converter process (BOS). Methods are being developed to make use of this by-product and large quantities are now employed in agriculture and in the production of aggregates in several European Community (EC) countries. However, a great deal of slag is still either simply discarded or discharged in landfills. This paper reports the effects over a 3-year period on both soil and crops, of the application of Linz-Donawitz (LD) converter slag on pasture land. Comparative studies were performed using different quantities of low phosphorus LD converter slag and fertilizer on land sown with Dactylis glomerata, Trifolium repens and Lolium perenne. The results showed an increase in soil pH and in the availability of Ca and Mg in the soil exchange complex. Aluminium content was reduced. When LD converter slag and fertilizer were applied together, plants were seen to contain the greatest concentrations of nutrients and greater yields were obtained. © 1995 ISWA

The recycling of Linz-Donawitz (LD) converter slag by use as a liming agent on pasture land

Slag is a major by-product of the basic oxygen steelmaking converter process (BOS). Methods are being developed to make use of this by-product and large quantities are now employed in agriculture and in the production of aggregates in several European Community (EC) countries. However, a great deal of slag is still either simply discarded or discharged in landfills. This paper reports the effects over a 3-year period on both soil and crops, of the application of Linz-Donawitz (LD) converter slag on pasture land. Comparative studies were performed using different quantities of low phosphorus LD converter slag and fertilizer on land sown with Dactylis glomerata, Trifolium repens and Lolium perenne. The results showed an increase in soil pH and in the availability of Ca and Mg in the soil exchange complex. Aluminium content was reduced. When LD converter slag and fertilizer were applied together, plants were seen to contain the greatest concentrations of nutrients and greater yields were obtained.

Mechanisms of dust generation in a stainless steelmaking converter

The four possible mechanisms of dust formation in converter steelmaking are evaporation of metal, ejection of slag, ejection of metal and entrainment of solids. In order to describe the relation between process operation and dust formation and take appropriate measures to minimize the quantity of dust, more detailed information is needed on the amounts contributed by the different dust generation mechanisms. For their determination, dust samples were taken from the off‐gas during refining of five austenitic heats in a modified 80‐t AOD converter. On the basis of dust, metal and slag analyses and process and product gas flow rates, the contributions of the different dust generation mechanisms were quantitatively determined for blowing step I (pure oxygen blowing) and reduction step R (pure argon blowing). The predominant mechanism is ejection of metal and slag droplets by bursting of bubbles at the bath surface. Dust formation via the vapour phase in AOD steelmaking is of less importance than previously expected, the relative amount is only about 3 %. During the addition of fluxes through the converter mouth, the entrainment of solids plays a role, too.

コークスベッドの活用による転炉内100%スクラップ溶解法

コークスベッドの活用による転炉内100%スクラップ溶解法

Mathematical model for computer simulation and control of steelmaking

A dynamic model for computer simulation and control of steelmaking has been developed. It is essentially based on multicomponent mixed transport control theory with the incorporation of energy balance calculations. The model is applicable to both steelmaking in electric furnaces as well as in oxygen steelmaking converters. The adjustable parameters of the model for simulation of oxygen steelmaking are gas evolution rate (Gco). oxygen flux factor (Fo) and emulsification factor (EM). These simulation parameters, when combined with on‐line measurement of off‐gas composition and temperature, enable complete dynamic control of the process. The model developed is applied, as an example, to an industrially produced heat in a top blown oxygen steelmaking converter and the results of simulation are discussed.

Reaction mechanism of coal hydrogenation 4. Effect of catalyst type

Japanese Taiheiyo coal was hydrogenated in naphthalene or tetralin under 10 MPa hydrogen using three types of catalyst of varying activities: stabilized nickel, iron dust (from steel-making converter) plus sulphur and cobalt-molybdenum on alumina support. In naphthalene, conversion (calculated from the pyridineinsoluble residue) and hydrogen consumption decreased with catalyst activity, in the order: Ni 〉 Fe 〉 Co-Mo 〉 no catalyst. In tetralin, conversion and hydrogen consumption was in the same order as in naphthalene, and the ratio of the amount of hydrogen consumed from gaseous hydrogen to that transferred from tetralin also had a similar tendency. This result supports the finding that the catalyst accelerates the direct hydrogenation of coal by gaseous hydrogen.

製鋼用各種転炉内におけるスラグと溶鋼中の成分の化学ポテンシャル

製鋼用各種転炉内におけるスラグと溶鋼中の成分の化学ポテンシャル

The Iron and Steel Industry of the Lipetsk Industrial Node

AbstractThe Lipetsk iron and steel industry, in existence since 1899, began a major expansion program in the middle 1950's, designed to make it one of the principal steel producers of the Soviet Union. The status of the expansion program as of 1969–70 is analyzed in detail, including a rundown of ore, flux and coke sources. The use of sintered ore from near-by deposits of the Kursk Magnetic Anomaly, high-temperature oxygen-enriched air blasts in the blast furnaces, large-capacity blast furnaces and steelmaking oxygen converters are expected to reduce the costs of production below existing levels in the Soviet iron and steel industry and to foster an efficient operation based on modern, automated equipment. (See also Shabad, Basic Industrial Resources of the USSR, pp. 98–101; maps, pp. 40, 96; News Notes, Soviet Geography, February 1970, p. 143; June 1972, pp. 409–410; June 1973, p. 407.)