Tuyere Level Research Articles

“In situ” studies on cokes drilled from tuyere to deadman in a large-scale working blast furnace

The properties and deterioration of coke have a significant impact on the thermal efficiency, fuel consumption, and CO2 emissions of blast furnace. Coke sample drilling is one of the effective ways to investigate coke behaviors in a working blast furnace. However, previous coke sample drilling process involved compressed coke, which cannot accurately reflect the actual condition of coke in blast furnace. Therefore, “in situ” coke samples were drilled for three times from tuyere to deadman in their original positions within a large-scale working blast furnace in the present work. The results show that the coke particle size degradation reaches 85.36 % in the 0–5 m zone at the tuyere level. The proportion of coke size less than 3 mm increases sharply along the tuyere direction, and a new method of calculating the depth of the tuyere raceway zone is proposed for the first time. The study based on the grey relational analysis shows that the depth of the raceway is closely related to the blast volume and the blast kinetic energy. Main factors causing the degradation of coke in the tuyere level are fully revealed in different regions. It is suggested to reduce CaO and alkali metals brought in blast furnace in order to protect coke.

Development of softening and melting testing conditions simulating blast furnace operation with hydrogen injection

ABSTRACT Softening and Melting (S&M) experiments have evolved alongside the blast furnace as a crucial tool for burden characterisation and optimisation. Modern blast furnaces derive a base load of hydrogen from various sources. However, with hydrogen-enrichment of the blast furnace being considered to mitigate emissions, new S&M test conditions are required. In this study, a 2-D axisymmetric CFD model is used to simulate the internal conditions of a modern blast furnace operation, and a future operation with tuyere level hydrogen injection. The model results are used to guide the development of novel S&M test conditions, inclusive of H2, H2O, CO, CO2 and N2. The maximum hydrogen concentration under hydrogen enrichment was 20%, with the hydrogenous fraction of the gas primarily replacing nitrogen. A particular focus was given to the importance of including water vapour in the inlet gas, andits impact on reactions occurring in the S&M test.

Study of scull and lining in the hearth of blast furnace No. 2 of JSC EVRAZ ZSMK (Report 3)

Modern blast furnaces have operation life of 15-20 years. Such a duration of their operation to a great extent reached due to the resistance of lining of hearth and hearth bottom. To study the processes, effecting the rate of its erosion, a study of composition and structure of the scull on the lining of walls of a blast furnace hearth and hearth bottom was accomplished. For the study the No. 2 blast furnace of EVRAZ ZSMK was chosen after its stoppage for overhaul. Results of visual examination of the state of the lining of lower part of the hearth and hearth bottom presented. Macro-structure of the picked out samples presented, general view of lump samples and polished section briquettes shown. Mineral composition of the samples and chemical composition of their separate mineral phases studied. It was determined, that the samples density, picked out lower the iron notch, was considerably higher. By authors opinion, it is stipulated by the increase of metal phase content in the scull along the hearth height in the direction from tuyere level to the hearth bottom, as well as considerable change of the scull porosity along both the horizontal section and the hearth height. The porosity of the samples, picked out lower the iron notch, was not high - at the level of 2.73-3.73%. The gases (oxygen, nitrogen, hydrogen) contained in the BF melts, lead to the forming of scull porous structure of insignificant thickness in the upper horizons of the hearth and in the notch channel. It was determined, that a building-up of zinc can be observed on the hearth bottom, as well as its alloys with iron and lead. The samples macro-structure was clear laminated. The zinc in the sample exists in the form of two mineral phases: an oxide phase (zinc oxide) and a metal phase, often with iron contaminant and rarely - with iron and lead. The results obtained, apart from the studies carried out earlier on the scull and BF hearth lining state, will be base of a theoretical analysis of scull forming mechanism and lining properties change, effecting the blast furnaces campaign duration.

Coke Size Degradation and Its Reactivity Across the Tuyere Regions in a Large-Scale Blast Furnace of Hyundai Steel

It has been well recognized that coke samples can be effectively taken out of working blast furnaces using a drilling machine at the tuyere level. The core represents samples with different temperature profiles at various tuyere regions of a large blast furnace. The average coke size at the tuyere level is known to be about 50 pct smaller than the charged cokes. Using fixed bed reactor and XRD techniques, the cokes sampled were studied for CO2 reactivity and crystallinity, respectively. The apparent reaction rate of coke rapidly increases in the raceway zone, followed by a decrease as the samples are taken at deeper sites in the furnace where the Fe2O3 and CaO contents are high in the bosh and raceway zones in the high temperature regions. In this study, samples extracted at the tuyere level of a large blast furnace were examined to characterize the coke size degradation and the effect of coke graphitization on the reactivity and fines generation at various locations around the tuyere level.

Occurrence and Behavior of Phosphorus‐Bearing Minerals in Metallurgical Coke

The behavior of phosphorus‐bearing minerals is characterized from coking coals to the feed coke and the blast furnace (BF) coke using scanning electron microscope and thermodynamic calculations. In coals, they are represented mostly by apatite (major phase, used for thermodynamic calculations), crandallite, gorceixite, goyazite, monazite and xenotime. Apatite fully transforms to Ca4P2O9 and Ca3P2O8 at coking temperatures. In the samples of BF coke, phosphorus‐bearing phases are 5–30 μm in size. In the case of a closed system (inside pieces of coke, no gas), phosphorus is presented in the BF in the form of Ca4P2O9 and Ca3P2O8 up to 1250 °C. Above this temperature, it is transformed to Fe3P (stable until 1495 °C). A further rise in temperature leads to the transformation of Fe3P to Fe2P (stable up to 1930 °C − tuyere level of the BF). In the case of an open system with intensive flow of BF gas, the formation of Fe3P from Ca4P2O9 and Ca3P2O8 starts at 1178 °C. The Fe2P appears near 1494–1495 °C, and after that it goes to a molten state.

Real-time indices focus on slag flowability and coke strength for blast furnace operation

It was well known that abnormal burden quality has a significant impact on the blast furnace (BF) permeability resulting in bad slag flowability and HM tapping, and the coke fines inside BF become much finer to reduce HM production and BF life when the coke strength is weak. Therefore, it is necessary to develop the real-time operation indices of the slag flowability and coke strength after reaction (CSR) in a lower part of BF. BF slag flowability was determined with liquidus temperature and viscosity from measured semi-synthetic slags (SiO2-Al2O3-CaO-MgO-TiO2), and the effects of MgO content, Al2O3 content and CaO/SiO2 on slag flowability are investigated according to the model equations derived from above measured data by using multiple-regression method. A real-time index combined with viscosity and liquidus temperature has been also designed to indicate appropriate slag flowability. In addition, a coke sampler was used to collect the coke samples at tuyere level to analyze the strength of BF bosh coke at various HM productivities. CSR quantitative target and its online index were obtained from the data of sampling coke properties, BF operation conditions and BF permeability to provide real-time reference for coke and HM production.

Reactions in the Tuyere Zone of Ironmaking Blast Furnace

A series of slags can be formed in the lower part of the ironmaking blast furnace that play important roles in smooth furnace operation, and in determining iron quality and productivity. The final slag tapped from the BF has been investigated extensively as it can be collected directly. Unfortunately, difficulties in accessing the interiors of the blast furnace limit the full understanding of other slags such as primary and bosh slags. In this study, different types of samples directly obtained from the tuyere zone of the blast furnace have been systematically analyzed and characterized using scanning electron microscopy (SEM), electron probe X-ray microanalysis (EPMA), and X-ray fluorescence (XRF), with focus on the characteristics of slags formed in the tuyere level. The samples were identified into three groups according to their morphological, mineralogical, and chemical properties: (1) tuyere slags originating from the reactions between ash and dripping slags; (2) bosh slags in the CaO-SiO2-Al2O3-MgO-FeO system, with a CaO/SiO2 weight ratio of around 1.50, and Al2O3 and MgO concentrations close to those of final slags; and (3) coke ash that did not react with bosh slags. These findings will provide useful information on the evaluation of slags inside the blast furnace and the reactions in the tuyere zone.

Petrographic analysis and characterisation of a blast furnace coke and its wear mechanisms

Petrographic analysis of coke samples from the tuyere level of an operating blast furnace was carried out using a combination of advanced microscopy techniques including high resolution bireflectance and maximum reflectance measurements. A novel tribological approach was employed to investigate the wear mechanisms of the same cokes. The study showed that the wear mechanisms of coke are influenced by its microstructure and microtexture, as well as the strength and nature of the interfaces between the different coke textural constituents. The wear mechanisms of the cokes were found to vary with location from the tuyere entrance of the blast furnace and also differed to the feed coke. This is the first example of the application of petrographic analysis of cokes from an operating blast furnace to identify the difference in hardness and interaction strength of the distinct coke textural constituents. This research contributes towards improving understanding of the complex mechanisms of coke degradation in operating blast furnaces.

Development and Implementation of New Measuring and Monitoring Systems to Support BF Control

For optimal blast furnace control, suitable measurement and monitoring systems are required. This paper focuses on the development and implementation of three new measurement devices and methods at ROGESA in Dillingen: 1) sonic gas temperature measurement, 2) a camera-based monitoring system at tuyere level, and 3) EMF and strain gauge measurement to determine the liquid level in the hearth of the blast furnace. These measurement and monitoring systems have been installed and successfully tested in the recent years. The information obtained is used to optimize the furnace control for enhancing the BF performance.

Fractographic approach to metallurgical coke failure analysis. Part 3: Characterisation of fracture mechanisms in a blast furnace coke

Metallurgical coke samples across the tuyere level of an operating blast furnace were analysed using a fractographic approach to identify and quantify various coke failure mechanisms. Tuyere level cokes displayed different failure mechanisms compared to the feed coke, implying a strong influence of the blast furnace reaction environment on the modification of coke failure mechanisms. The conchoidal and brittle overload type failures were noted to have an effect on the propagation of transgranular and intergranular crack growth in the coke microstructure. Feed coke breakage behaviour was strongly influenced by existing fissures and conchoidal fracture, while the breakage of the deadman coke lumps was dominated by pore wall collapse through intergranular crack growth in combination with erosive wear.The porosity at the IMDC–RMDC interface in coke has been identified as a critical parameter contributing to coke failure at tuyere regions. This fractographic study demonstrates that the fracture faces show evidence of the varying failure mechanisms presented in the preceding manuscripts (Part 1 and Part 2), in addition to the erosive wear resulting from the blast furnace exposure. However, further studies are required to establish the association between the identified coke failure mechanisms and coke texture, which has implications for improving coke performance in a blast furnace.

Interfaces Between Coke, Slag, and Metal in the Tuyere Level of a Blast Furnace

An in-depth understanding about the reactions in the high-temperature zone of a blast furnace is significant to optimize both the current and future blast furnace process. The interfaces between coke, slag, and metal were observed using scanning electronic microscope with samples obtained from the tuyere level of a blast furnace. Two types of slag phases were identified, one originating from coke ash and the other from the bosh slag. Slag formed by coke ash was seen to cover the coke surface, which may hinder the reaction of coke with both gas and liquid iron. The reduction of FeO from the bosh slag (originated from the primary slag) occurs in the coke/slag interface with the reduced iron forming a metal layer surrounding the coke surface. The reduction of SiO2 occurs both in and outside the coke, and the reduced silicon reacts with iron to form iron silicide if the two species come into contact. Further study is proposed based on the results of this study.

Mineralogy and reactivity of cokes in a working blast furnace

Coke samples from tuyere level of a blast furnace were obtained through tuyere drilling. Mineral matter of tuyere level cokes was quantified using SIROQUANT and examined using scanning electron microscope. The apparent CO2 reaction rates were measured using a fixed bed reactor. About 50% of the total inorganic matter of tuyere cokes was found to occur as amorphous or glassy phase. At most of the tuyere level locations, Quartz and mullite contents of the feed coke decreased significantly or disappeared. Silicon carbide and gupeiite were found to be the most notable and common silicon and iron bearing minerals of cokes particularly in the raceway region while gehlenite and spinel were the typical calcium and magnesium bearing minerals respectively. Tuyere level cokes also indicated the presence of significantly high potassium levels as well as the graphite formation. The apparent reaction rate of tuyere level cokes is shown to increase up to ten times of the feed coke reaction rate, and is strongly related to the total amount of potassium species. The study highlights the strong influence of the raceway temperature, the alkali loading and the hot metal presence on the modification of the mineralogy and reactivity of tuyere level cokes with implications on coke selection criterion.

A Method for Evaluating Coke Hot Strength

AbstractThe strength of coke is of major importance for efficient blast furnace operation. There are only a few studies related to compressive coke hot strength, possibly due to experimental difficulties. In this work, it has been demonstrated that the Gleeble thermomechanical simulator is suitable for evaluating coke hot strength and offers many benefits compared to purpose‐built devices reported in the literature. This finding could open coke hot strength research to a wider number of scientists. The compressive hot strength of coke was evaluated at 1000 and 1600°C by testing 50 samples at both temperatures. The yield strength and ultimate strength of the coke were, respectively, 46 and 20% lower at 1600°C than 1000°C. Stress–strain curves showed that the coke was brittle at 1000°C but partially plastic at 1600°C. The significantly lower coke strength at 1600°C could help explain the smaller coke lump size found near the tuyere level in quenched blast furnaces.

Fe-Si droplets associated with graphite on blast furnace coke

Fe-Si droplets on the surface of blast furnace (BF) coke from 25 to 50 cm at the tuyere level are mostly composed of Fe3Si, which has various shapes (round, elongated, and irregular) and penetration degrees into the BF coke matrix. The shapes and penetration degrees may depend on the saturation of molten iron by silicon during interaction with the coke matrix. The droplets are covered by a tiny shell of carbon. Graphite observed inside the droplets can be divided into two categories: well-formed tabular crystals with relatively large size and flakes with structures similar as those in cast iron. The textures of the droplets reflect composition, interaction with the coke matrix, and cooling conditions.

Multiobjective Optimization of Top Gas Recycling Conditions in the Blast Furnace by Genetic Algorithms

Limited natural resources and a growing concern about the potential effect of carbon dioxide emissions on the world's climate have triggered a search of ways to suppressing the emissions of CO2 in primary steelmaking. A possible future solution is to strip CO2 from the blast furnace top gas, feeding back the gas to the tuyere level. The work reported in this article explores states of an integrated steel plant that arise if both production costs and emissions are simultaneously minimized. This multiobjective problem is tackled by genetic algorithms using a predator–prey strategy for constructing the Pareto-frontier of nondominating solutions. Four alternative ways of treating the top gas recycling problem are explored, and the resulting solutions are analyzed with respect to the two objectives and to the internal states of the plant they correspond to. Conclusions are drawn concerning the solutions in terms of technical feasibility and complexity.

Assessment of the State of the Blast Furnace High Temperature Region by Tuyere Core Drilling

Tuyere core drillings give a unique opportunity to probe the blast furnace and detect changes in both physical and chemical conditions of its high-temperature region. In this paper the findings from drill cores taken from a blast furnace are used to characterize the internal state of the furnace hearth, quantified by an erosion model estimating the available hearth volume. The complex relation is studied by entertaining neural network models using different combinations of inputs consisting of the extent of the distinct tuyere-level zones (raceway, bird's nest, dead man, etc.) of the core samples. The resulting model can be used to gain knowledge of the relation between tuyere level conditions and hearth states, and to classify the findings from future core drillings. The results also throw light on possible reasons for thermal cycles observed in the hearth of the furnace studied.

Investigating the Fate of Injectant Coal in Blast Furnaces by Size-Exclusion Chromatography

The fate of injectant coal in blast furnaces has been investigated through characterizing samples collected from commercial-scale blast furnaces and laboratory-scale tests. Representative samples, including an injectant coal and the corresponding carryover dusts from a full-sized blast furnace, and a set of tuyere level core-drilled samples from another full-sized blast furnace, have been examined. The samples were extracted using 1-methyl-2-pyrrolidinone (NMP) as the solvent, and the extracts were then studied using size-exclusion chromatography (SEC). The carryover dust extracts were found to contain heavy carbonaceous materials of apparent mass ∼107−108 units, on the basis of polystyrene calibration. Similar materials were also found to be present in the NMP extracts of the core-drilled samples taken from the bosh, rear of bird's nest, and deadman regions of the furnace, at the tuyere level. In contrast, the feed coke did not give any extractable material. Controlled pyrolysis and combustion experiments, in an electrically heated wire-mesh reactor, suggest that the extent of injectant coal combustion in the raceway is limited by a very short exposure time to high temperatures and poor oxygen availability. These observations suggest that some coal char particles might escape from the raceway incompletely pyrolyzed. Unburned volatiles, particularly tars, may be further thermally altered, giving rise to the formation of high-molecular-weight (soot-like) materials.

Simulation of tuyere–raceway system in blast furnace

A uniform distribution of the blast is an important prerequisite of a balanced blast furnace operation, because the blast is the main source of the hot gases that are needed to preheat, reduce and melt iron ores. The supply of hot gas from the raceways is not necessarily uniform along the furnace periphery, but depends on flow resistances encountered on the individual bustle main tuyere–raceway–raceway boundary routes. A model for this system has been developed in order to study and analyse the effects of changes in tuyere parameters and boundary conditions. Variables such as the total blast volume, blast pressure, tuyere diameter and the combustion degree of injected reductants in the tuyeres can be studied. An online version of the model has also been developed to track how the conditions on the tuyere level change with time in operating blast furnaces.

Numerical Analysis of Static Holdup of Fine Particles in Blast Furnace

With increased in pulverized coal injection rate into blast furnace, the importance of understanding flow characteristics of powders within packed bed increases because more unburned char and coke fragments would be generated, it would be deteriorate permeability in the blast furnace. Although flow characteristics of dynamic or total holdup of powders in packed beds is found in several reports, 3-6) behavior of powders in blast furnace using separate treatment of dynamic and static holdup has yet to be reported. In this study the behavior of static powders was examined through numerical simulation using the “four fluid model”, 3) which included the formulation of static powders behavior. The model results were compared with two dimensional temperature distributions measured in the furnace for three different pulverized coal injections (PCI) rates (100, 200 and 250 kg/thm) for validated. The model was applied to quantitative analysis of static powders holdup in the blast furnace operation with high-rate pulverized coal injection. The higher amount of static powders holdup was found mostly in the center lower deadman, above and below the tuyere level, and in upper shaft, for PCI rate 100 kg/thm, 150 kg/thm, 200 kg/thm and 225 kg/thm respectively. The lower amount of static powders holdup was found in the raceway region throughout the surface of deadman.

Assessing the internal state of the raceway/dead man part of the blast furnace at low coke rate : Negro, P. et al. European Commission, [Report] EUR, 2002, 1–309

The principal aims of this project were to study the blast furnace hearth and raceway behaviours in case of low coke and high coal rates operations. The different partners of this project have used their own possibilitiesand devices installed on several industrial blast furnaces. Using the tuyere coke sampling devices, it has been established that : - with coal injection rates ranging from 50 to 200 kg/thm, significant differences were apparent in the drill core structures. In the cases of lower coal injection rates, the drill cores incorporated lower levels of coke fines and iron/slag and were much less compacted than those achieved in cases of high coal injection rates. With high coal injection, the fines content increases just behind the bird nest ; - with high coal injection the raceway length becomes lower showing that the permeability of the dead man boundary becomes also lower ; - the fines sampled along the coal along the tuyere radius when using different coke qualities did not show any accumulation of unburnt coal in the dead man or at the outer shell of the dead man. However, the fines are made of three carbon phases with different level of organisation as graphite and coke. The graphite content in the fines was higher with high coal injection rates, near the raceway and in the smaller fraction. Nevertheless, the origin of the graphite fines is till now uncertain ; - the study of the unburnt char by sampling dust and gas at different positions along the height at the wall and the radius at the top of the furnace when using different coke qualities showed very different results : - the Coke contents in dust rise in the blast furnace from top to bottom in accordance with the increasing thermochemical demand on the coke, when using feed coke with low CSR values. In the case of using coke with high CSR values there is no increase in the Cake content in the dust, i.e. this coke shows a lower degradation mainly in the lower part of the furnace. This has been also confirmed by calculation of the coke degradation inside the blast furnace issued from coke core borings results. More over, hot strength measurements on coke from the tuyere level show higher values with higher CSR values of feed coke in the raceway, in the transition zone and in the dead man. This fact is of great importance because the stress on coke is not finished in the tuyere level ; - in the case of centre coke charging operations, the maximum C c o a l contents in the dust appear in the lower furnace area and in the upper shaft. Both maximum contents are attributable to transverse flows from the furnace centre, where the highest concentrations of unburnt coal particles are measured. The trials with feed coke with a higher hot strength show lower C c o a l contents in the dust despite of higher coal rates. This means a more uniform gas flow when charging cokes with high CSR values.