Thermal Reserve Zone Temperature Research Articles

Evaluation of Some Uncertainties in the Modeling of Blast Furnace Hydrogen Injection

While blast furnaces remain the dominant ironmaking technology, there is growing interest in using hydrogen to partially replace coke and pulverized coal to reduce CO2 emissions in this hard‐to‐decarbonize process. However, significant discrepancies in modeling the tuyere injection of hydrogen are noted in the literature, which can challenge the scale‐up from modeling predictions and pilot trials to actual blast furnace operations. To address this, the impact of uncertainties in the assumptions of the temperature in the thermal reserve zone and the ratio of H2 and CO utilization on the results of blast furnace process modeling are evaluated using a 1D steady‐state zonal model. The study indicates that variations in the assumed value of thermal reserve zone temperature significantly impact the estimation of optimal hydrogen injection rate, coke replacement ratio, and direct CO2 emissions reductions. In contrast, the same parameters are much less affected by the variations in the assumed value of the proportion between H2 and CO utilization ratios, which, however, affect the top gas composition. A need for further research to determine the range of the difference in temperatures of gas and solid in the thermal reserve zone tolerable for smooth blast furnace operation is highlighted.

A Numerical Study on the State of the Blast Furnace Thermal Reserve Zone under Different Starting Temperatures of Coke Solution Loss Reaction

As a measure to improve the blast furnace gas utilization efficiency during the iron making, decreasing the temperature of blast furnace thermal reserve zone (here called TRZ for short) by increasing the coke reactivity and therefore lowering the starting temperature of coke solution loss reaction (CSLR) has received much attention. However, this measure is proposed merely from a thermodynamic point of view by considering that the FeO reduction with CO is slightly exothermic. The effect of the CSLR starting temperature on the state of TRZ that also determines the kinetic conditions for indirect reduction has yet to be clarified. For this, a 1D kinetic model built previously is adopted in this paper to investigate how the TRZ state and gas utilization efficiency respond to the changes in the starting temperature of CSLR. The results show that with a decrease in the starting temperature, the height and average temperature of TRZ decrease, and the lower edge of TRZ shifts upwards. The gas utilization efficiency increases first and then decreases, thus leading to a critical starting temperature. Moreover, a lower critical temperature corresponds to a higher gas utilization efficiency. An increase in iron ore reducibility or top pressure can lower the critical temperature.

Evaluating the behavior of catalyst coated nut-coke in blast furnace conditions

For efficient blast furnace ironmaking, it is desired to have low reducing agent rate, primarily coke rate. Developing technology to improve reaction efficiency of the blast furnace is extremely important as it has the potential to allow a decrease in the reducing agent rate as well as CO2 emissions. The reaction efficiency of blast furnace can be improved by lowering the Thermal Reserve Zone (TRZ) temperature; which is also the starting temperature of coke gasification reaction. In present study, nut-coke has been coated with in-plant waste, consisting mainly of iron oxide and calcium oxide, as catalyst. There was a clear increase of 10 points in the reactivity of coated nut-coke. The coated nut-coke have been subjected to non-standard high temperature experiments simulating blast furnace conditions with reducing gas consisting of CO, CO2 and N2 to capture the effect of catalytic coating on the onset of gasification reaction. The high temperature experiments carried out advise the following: i) A drop of 100 °C in the reaction beginning temperature of catalyst coated nut-coke as compared to non-coated one ii) A typical calculation shows that the lowering of reaction beginning temperature corresponds to a potential carbon rate savings of about 2.5 kg/ton of hot metal (thm). Furthermore, in a trial conducted at blast furnace with charging catalyst coated nut-coke, it has been observed that the carbon rate during the trial period was 3 kg/thm lower than the base period. The findings of blast furnace trial agree with that of the experimental one.

Influences of Coal Tar Pitch on Metallurgical Properties of Iron Carbon Agglomerates

Utilization of iron carbon agglomerates (ICA) with high reactivity in blast furnace (BF) can reduce fuel ratio and carbon emission by decreasing the temperature of thermal reserve zone, which is considered to be an innovative technology for achieving low‐carbon ironmaking. Herein, the influences of coal tar pitch (CTP) as binder on the metallurgical properties of ICA are investigated. The results show that the compressive strength of ICA is first enhanced from 1639 to 3168 N and then reduced to 2243 N with the ratio of CTP increasing from 0% to 11%. Meanwhile, the drum strength () of ICA is accelerated from 67.3% to 80.5% and then leveled off. In addition, the reactivity of ICA is mitigated from 65.6% to 58.1% first and then increased to 68.8%, while the post‐reaction strength shows an inverse trend. When the ratio of CTP is 5–7%, the mechanical strength, reactivity, and post‐reaction of ICA are all at a relatively better levels. For the ICA with adding CTP, the mechanical strength is dependent on the microstructure, pore volume, and specific surface area, whereas the variation of reactivity and post‐reaction strength are relevant to the pore structure and carbon crystallites structure.

Reduced Carbon Consumption and CO2 Emission at the Blast Furnace by Use of Briquettes Containing Torrefied Sawdust

Lowering the carbon consumption and fossil CO2 emissions is a priority in blast furnace (BF) ironmaking. Renewable biomass is one option that can play an important role in future low-carbon ironmaking particularly in the countries rich in biomass resources. In this study, full-scale trials to investigate the impact of briquettes containing torrefied sawdust on the BF efficiency and process stability have been conducted. Briquettes containing 1.8% of torrefied pelletized sawdust (TPS), 86.2% of steel mill residues, and 12% cement with sufficient mechanical strength have been produced on industrial scale. The bio-briquettes were charged at two different rates: 37% ( ~ 39 kg/tHM) and 55% ( ~ 64 kg/tHM) bio-briquettes to the SSAB BF No. 4 in Oxelösund. The gas utilization was higher during bio-briquette-charging periods without change in pressure drop up to 55% bio-briquettes, indicating sustained shaft permeability. BF dust generation or properties did not change significantly. Measurements of the top gas composition using mass spectrometry did not indicate release of hydrocarbon from TPS in connection to the charging of bio-briquettes. Evaluation of process data has been carried out using a heat and mass balance model. The evaluation of operational data in the model indicated lowering of thermal reserve zone temperature by 45 °C and reduction in carbon consumption by ~ 10 kg/tHM when charging 55% bio-briquettes compared to the reference case. The total CO2 emission was reduced by about 33–40 kg/tHM when using 55% bio-briquettes.

Reduction Behavior of Self-Reducing Pellet (SRP) for Low Height Blast Furnace

One way to decrease the reducing agent rate in a blast furnace (BF) is the lowering of thermal reserve zone (TRZ) temperature by using self-reducing pellets (SRP). The lower strength requirement of raw materials for small BFs allows the charging of SRP. In the scope of the current study, the behavior of SRP under the TRZ simulated conditions has been investigated. Coal, charcoal, and coke breeze were used as embedded reducing agents. The reduction experiments have been performed under different iso- and non-isothermal scenarios. A Tammann furnace laboratory rig and a simultaneous Thermogravimetric/Differential Thermal Analysis (TG/DTA) experimental set were used for investigations. Mass loss, reduction degree, metallization degree, volume change, and reaction heat flow were examined. The results from experiments with TRZ condition show that embedded reducing agents, especially charcoal, promote iron oxide reduction in pellets. The crushing strengths of SRPs after both methods of hardening, fire-hardening and cement-bonded curing, and the reduction of cement-bonded SRP after curing have been investigated as well.

Calculation Model of Using Appropriate High Reactivity Coke in Blast Furnace

AbstractThe technology of using high reactivity coke in iron‐making process by blast furnace has been verified to promote the reduction of iron ore in the thermal reserve zone through theoretical analysis combined with experimental research. However, the absence of relative calculation model makes it difficult to determine the coke saving ability quantitatively and supply substantial guidance for industry. In present study, thermal reserve zone and high temperature zone are taken as investigation objects and a calculation model has been established to study the influences of high reactivity coke on reduction of iron oxide, shaft efficiency, and fuel rate. Combined with calculation model, the industrial practice is analyzed by concluding a new important index namely the proportion of high reactivity coke taking Boudouard reaction in the blast furnace (PCTBR for short). The results show that, introduction of high reactivity coke could reduce the temperature of the thermal reserve zone and promote the exothermic indirect reduction of FeO. The high reactivity coke reduces direct reduction, and decreases the heat consumption of high temperature zone by allocating the direct reduction region reasonably as well, which leads to a lower fuel rate. The fuel rate has been reduced by 16.84 kg tHM−1 when the high reactivity coke amount participating Boudouard reaction is 40 kg tHM−1. The PCTBR of WuJing coke and Ca‐rich coke is around 7.8%.

ウスタイトの還元速度に及ぼす熱保存帯温度低下の影響

ウスタイトの還元速度に及ぼす熱保存帯温度低下の影響

試験高炉による焼結鉱，コークス品質評価

The use of high reactivity coke is proposed to realize low reducing agent rate blast furnace operation. The reducing agent rate was reduced by use of high reactivity coke in an actual blast furnace. The reduction of reducing agent rate is caused by the improvement of the reaction efficiency due to the decrease of the thermal reserve zone temperature. On the other hand, it is suggested that sinter reducibility will affect on the effect of the high reactivity coke. Therefore, in this paper, the quality of high reducibility sinter and the effectiveness of high reactivity coke coexistence of high reducibility sinter were verified by the experimental blast furnace and following results were obtained.1) The top gas utilization was improved and the reducing agent rate was reduced by use of high reducibility sinter.2) The permeability was improved by use of high reducibility sinter. The improvement of permeability will be expected in actual blast furnaces.3)The top gas utilization was improved by use of high reactivity coke. The improvement was caused by the improvement of reaction efficiency due to the decrease of the thermal reserve zone temperature.4) The degradation of coke was decreased due to the decrease of the amount of reaction.5) The high reactivity coke works effectively when high reducibility sinter co-exists.

フェロコークスによる高炉内低温度域でのガス化，還元反応の促進

Iron-coke having various amount of M.Fe were produced in laboratory scale and the influence of M.Fe content in Iron-coke on reaction behavior under the condition simulating blast furnace has been investigated. Cold strength of Iron-coke products was decreased with an increase of mixing ratio of iron ore mostly due to a prevention of dilatation of coal particles by iron ore, resulting in weak bonding of coal particles. Nevertheless formed Iron-coke with iron ore in the fraction up to 30% would have enough strength for use in blast furnace as nut coke. Both CRI and JIS-reactivity were enhanced by increasing ratio of mixed iron ore, confirming the catalysis effect of M.Fe. The temperature at which carbon consumption started was lowered with an increase of T.Fe in coke. Formed Iron-coke containing 43% of T.Fe started reaction consuming its carbon at lower temperature than conventional coke by 150°C. Furthermore, consumed carbon ratio was improved by M.Fe installation to coke due to increasing gasification. Process evaluation with using Iron-coke in blast furnace was performed by BIS test. It was revealed that using formed Iron-coke having 43% of T.Fe for blast furnace resulted in an increase of shaft efficiency by 6.8%. It was found that to lower the reducing agent rate in blast furnace by decreasing the temperature of thermal reserve zone, lowering the beginning temperature of coke reaction was effective. Usage of Iron-coke having M.Fe catalyst within coke matrix is one of the methods.

Enhancement of Low-temperature Gasification and Reduction by Using Iron-coke in Laboratory Scale Tests

Iron-coke having various amount of M.Fe were produced in laboratory scale and the influence of M.Fe content in Iron-coke on reaction behavior under the condition simulating blast furnace has been investigated. Cold strength of Iron-coke products was decreased with an increase of mixing ratio of iron ore mostly due to a prevention of dilatation of coal particles by iron ore, resulting in weak bonding of coal particles. Nevertheless formed Iron-coke with iron ore in the fraction up to 30% would have enough strength for use in blast furnace as nut coke. Both CRI and JIS-reactivity were enhanced by increasing ratio of mixed iron ore, confirming the catalysis effect of M.Fe. The temperature at which carbon consumption started was lowered with an increase of T.Fe in coke. Formed Iron-coke containing 43% of T.Fe started reaction consuming its carbon at lower temperature than conventional coke by 150°C. Furthermore, consumed carbon ratio was improved by M.Fe installation to coke due to increasing gasification. Process evaluation with using Iron-coke in blast furnace was performed by BIS test. It was revealed that using formed Iron-coke having 43% of T.Fe for blast furnace resulted in an increase of shaft efficiency by 6.8%. It was found that to lower the reducing agent rate in blast furnace by decreasing the temperature of thermal reserve zone, lowering the beginning temperature of coke reaction was effective. Usage of Iron-coke having M.Fe catalyst within coke matrix is one of the methods.

Enhancement of Reduction Rate of Iron Ore by Utilizing Iron Ore/Carbon Composite Consisting of Fine Iron Ore Particles and Highly Thermoplastic Carbon Material

Decreasing the thermal reserve zone temperature is believed to increase the energy efficiency of blast furnace iron-making. To do so, either the direct reduction reaction rate or the coke gasification reaction rate must be significantly increased below 1000°C in CO-lean atmosphere. An iron ore/carbon composite (IOC) has been proposed as a new raw material that can enhance the reduction rate of iron ore. In this paper the possibility of the reduction rate enhancement was examined by preparing a kind of ideal IOC sample consisting of nano-sized Fe2O3 particles (10–70 nm in diameter) and a carbon material prepared from a thermoplastic resin. The nano-sized Fe2O3 particles in the IOC sample were surprisingly reduced to Fe in a few minutes at as low as 650°C in an inert atmosphere. This was realized by increasing the interfacial area between the Fe2O3 particles and carbon and by establishing intimate contact between the two. The carbon in the IOC sample was also completely gasified in less than 10 minutes at as low as 750°C in a CO2 atmosphere. The dramatic enhancement of the gasification rate was found to be realized by the enhancement of one of the direct reduction reactions, the reaction between Fe3O4 particles and carbon, by the aid of in-situ XRD measurement. This suggested that the enhancement of both the reduction reaction rate and the gasification reaction rate is realized by the same mechanism. These new findings will give a clue for designing IOC samples applicable to the blast furnace iron-making.

Influence of Mixing Coal Composite Iron Ore Hot Briquettes on Blast Furnace Simulated Reaction Behavior in a Packed Mixed Bed

For iron making processes which need decreasing CO2 exhaust, coal composite iron ore hot briquette (CCB) is promising. This agglomerate contains coal with iron ore by utilizing the thermal plasticity of coal, where, carbonaceous material and iron ore are closely adjoined at the micro level, and which enables reactions to proceed from lower temperatures and finish earlier.In this study, we assumed mixed charging of CCB in ore bed aiming at improvements of permeability and gas utilization and performed high temperature reaction tests under load simulating blast furnace conditions using mixed samples consisted of iron ore mini pellet and briquette.As a result, gasification and reduction in mixed bed were accelerated around 910°C to 1000°C. This reaction acceleration was presumed to derive from mutual acceleration between gasification in briquette and indirect reduction in pellet. However, if the residual carbon in briquette is consumed completely by gasification, reduction is possibly delayed through the deterioration of permeability by sintering of pellet and briquette.It was also found that increase of reduction gas flow rate prevented the residual carbon in briquette from being consumed and accelerated reduction by sustaining the role of briquette as a spacer. And it was found that lowering thermal reserve zone temperature aggravated reducibility of pellet and delayed reduction of mixed bed. Moreover, it was found that shrinkage behavior of the bed had strong relation to amount of residual carbon in briquette and reduction behavior of pellet.

Reaction behavior of Formed Iron Coke and Its Effect on Decreasing Thermal Reserve Zone Temperature in Blast Furnace

Usage of highly reactive coke in order to decrease the thermal reserve zone temperature in blast furnaces is promising to increase reaction efficiency in blast furnaces and to decrease the reducing agent rate. We focused on the catalytic effect of iron and succeeded in producing highly reactive formed iron coke with high iron content. In this paper the reaction behavior of formed iron coke when mixed with conventional coke and in the presence of alkali was investigated and the following results were obtained. When the mixture of iron coke and conventional coke is heated in a reaction gas, iron coke selectively and preferentially reacts near the thermal reserve zone temperature (900°C), which causes a decrease in the thermal reserve zone temperature, while conventional coke barely reacts and is protected from degradation. It was also confirmed that the catalytic activity of Fe and that of K is independent of each other and that in the presence of alkali, the reaction beginning temperature of iron coke is lower than that of conventional coke. These results show that the use of formed iron coke could decrease the thermal reserve zone temperature in an actual blast furnace where coke reactivity is promoted by condensed alkali vapor.

Conceptual design and simulation analysis of thermal behaviors of TGR blast furnace and oxygen blast furnace

Extensive use of carbon based fuel is the main inducement for global warming and more extreme weather. Reducing carbon dioxide emission and enhancing energy use is a common subject in steel industry. In the integrated steel plant, decreasing carbon dioxide emission must consider energy balance in the whole iron and steel works, and secondary energy must be actively utilized. As promising blast-furnaces, top gas recovery blast furnace (TGR-BF) and oxygen blast furnace have been investigated. In this paper, conceptual TGR blast furnace and oxygen blast furnace are proposed. Base on the idea of blast furnace gas de-CO2 circulating as reducing agent and the idea of pure oxygen blast decreasing the thermal reserve zone temperature, process modeling is conducted with ASPEN Plus. It is shown that the developed model reasonably describes the energy balance and mass balance feature of the furnace, and provides basic thermodynamic condition for furnaces. The effects of changes in different operation conditions are studied by sensitivity analysis and reference data from simulation.

Effect of Coke Reactivity on Blast Furnace Operation and Coke Reaction Behavior

Recent years various trials to improve operation efficiency of blast furnace by combining the decrease in operation temperature and the increase in reaction rates. An increase in coke reactivity is one of the approaches to decrease thermal reserve zone temperature in blast furnace. Although the mechanism to improve the efficiency by increasing the reactivity is explained by the static models like the Rist diagram, these models are incapable of estimating the temperature decrease by the reactivity increase. In this study numerical simulations of blast furnace operation using a mathematical model based on the kinetic theories were performed. In the simulations, descending motions of burden materials were tracked and the reaction behaviors of coke particles along the trajectories were discussed in details through the method of chemical reaction engineering. The results showed that the increase in the coke reactivity lowers the temperature of upper part of the furnace. In the studied range of the reactivity, the reaction scheme of the solution loss reaction in thermal reserve zone varied from uniform reaction to surface reaction with increase in reactivity. Although the coke consumption by the solution loss reaction increases, the solution loss reaction in the central part of the coke particle is suppressed by the increase in coke chemical reactivity.

Reaction Behavior of Formed Iron Coke and Its Effect of Decreasing Thermal Reserve Zone Temperature in Blast Furnace

Usage of highly reactive coke in order to decrease thermal reserve zone temperature in blast furnace is considered promising to increase reaction efficiency in blast furnace and to decrease reducing agent rate. We focused attention on the catalytic effect of iron and succeeded in producing highly reactive formed iron coke with high iron content. In this paper the reaction behavior of formed iron coke when mixed with conventional coke and in the presence of alkali was investigated and the following results were obtained. It was shown that when the mixture of iron coke and conventional coke is heated in a reaction gas, iron coke selectively and preferentially reacts near the thermal reserve zone temperature (900°C), which causes a decrease in thermal reserve zone temperature, while conventional coke reacts little and is protected from degradation. It was also confirmed that catalytic activity of Fe and that of K is independent each other and that in the presence of alkali, the reaction beginning temperature of iron coke is lower than that of conventional coke. These results show that the use of formed iron coke could decrease thermal reserve zone temperature in an actual blast furnace where coke reactivity is promoted by condensed alkali vapor.

Reaction Model and Reduction Behavior of Carbon Iron Ore Composite in Blast Furnace

Decreasing the carbon dioxide emission from steel industries is an important issue. It is considered that due to the high reactivity of carbon iron ore composite, it can control the thermal reserve zone temperature and decrease the consumption of reducing agents in blast furnace. In the present study, a reaction model of the carbon iron ore composite based on a lumped system is proposed to analyze the reduction behavior in the blast furnace. This model is composed of several reaction steps between carbon, iron ore, and gas phase. The carbon solution loss reaction rate of the small particles of reducing agents is determined by the thermogravimetric method. It is found that the gasification of reducing agents is the rate-determining step in the reduction of the carbon iron ore composite. Accordingly, the particle size and reactivity of reducing agents such as coke have an influence on the reduction rate of the carbon iron ore composite. The influence of the gas composition in the atmosphere around the composite on the reduction is analyzed by using the reaction model. Moreover, the reduction behavior of the carbon iron ore composite in the blast furnace is quantitatively examined by comparison of reduction degree and gas composition change in order to investigate the reduction mechanism of reducing agents.

Improvement of Reactivity of Carbon Iron Ore Composite with Biomass Char for Blast Furnace

Enhancement of reactivity of the burden in the blast furnace can decrease the reducing agent of blast furnace. Besides high reactivity coke, the carbon iron ore composite is considered to be a typical high reactivity burden that can control the thermal reserve zone temperature. Since the reactivity of biomass char is much higher than that of coke, the use of carbon iron ore composite with biomass char will be favorable for decreasing the reducing agent. In the present study the reaction and reducing behavior of the carbon iron ore composite with biomass char were investigated. The gasification rate of biomass char was measured in CO2 atmosphere, and the reaction rate equation of that was derived. The microscopic structure change of biomass during carbonization was experimentally analyzed. According to the experimental results, the reduction of the composite begins at about 550°C in an inert gas atmosphere, and it is much lower than the composite with coke. Analysis of the reaction of carbon iron ore composite was carried out with the reaction model of the carbon iron ore composite based on a lumped system, in which the reaction rate of biomass char and iron ore were installed. The reaction model shows that the biomass char can improve the reduction behavior of the carbon iron ore composite especially in the lower temperature region. Moreover, the influence of gas atmosphere and the optimum structure of the composite were investigated by the model calculation to estimate the optimum condition of the composite in the blast furnace.

Post-reaction Strength of Catalyst-added Highly Reactive Coke

The development of production and utilization technology for highly reactive coke is significant in order to improve blast furnace reaction efficiency. In this report, the post-reaction strength of catalyst-added highly reactive coke was investigated. The reaction between coke and CO2 was stopped at a weight loss of 20% and the reaction temperature was adjusted so that the reaction lasted for a constant period. In this experimental condition, the reaction temperature of highly reactive coke was lower than that of normal coke, which corresponds to the decrease in the thermal reserve zone temperature in a blast furnace. First, a decrease in reaction temperature made the reaction of the catalyst added coke more homogeneous, which increased the post-reaction strength of the highly reactive coke produced by the post-addition of catalyst to coke method; however, it decreased that of the highly reactive coke produced by the pre-addition of catalyst to coke method. Secondly, the post-reaction strength of catalyst-added highly reactive coke produced by the post-addition of catalyst to coke method became equal to or greater than that of normal coke. The types of catalysts and the catalyst adding method affect the porosity distribution in the coke after reaction and hence the post-reaction strength of coke to a great extent. Suitable selection of catalysts and its addition method to coke leads to highly reactive coke with post-reaction strength greater than that of normal coke. Catalyst-added highly reactive coke is a promising material to improve blast furnace reaction efficiency.