Decarburization Rate Research Articles

Implementation of model predictive control in a programmable logic controller

The article is aimed at the development of modern automatic control systems, which should provide high-performance indicators in the conditions of variable operating modes of industrial equipment due to effective control structures and algorithms. The purpose of the study is to reduce the cost of the basic oxygen furnace steel, which is a consequence of the increase in the share of scrap metal due to the enhanced post-burning of CO to CO2 in the cavity, by optimal controlling the duty mode parameters using model-predictive control. The blowing mode of the basic oxygen furnace was considered as a technological object of control, and the problem of controlling blowing parameters in conditions of non-stationarity of the rate of metal decarburization was analyzed. The use of a model-predictive controller made it possible to improve the quality of control for the oxygen flow circuit by 39% and the maximum dynamic deviation of the CO2 content in the gases was reduced by 16.5% compared to the PID control. The implementation of a software-hardware control system using model-predictive control based on a programmable logic controller is considered.

Diffusion Behavior of Carbon and Silicon in the Process of Preparing Silicon Steel Using Solid-State Decarburization

In this study, we investigated the relationship between the decarburization effect of the solid-state decarburization method for preparing silicon steel and the atomic diffusion behavior in the matrix, focusing on 1 mm thick Fe-0.18 wt% C-Si (1.5, 3.5 wt%) alloy strips as the research object. Solid-state decarburization experiments were carried out in an Ar-H2O-H2 atmosphere, and the self-diffusion behavior of C and Si in Fe-C-Si alloy system was simulated by molecular dynamics. The results show that the molecular dynamics simulation results are consistent with the decarburization experimental results. When the temperature is lower than 800 °C, the atoms maintain a compact bcc structure, so the migration rate of carbon is low. When the temperature rises, the atoms move violently, resulting in the destruction of the crystal structure. Because the atomic arrangement tends towards a disordered structure, the migration rate of C is high and the diffusion coefficient increases. The experimental results showed that the decarburization rate was accelerated. At the same temperature, the diffusion activation energy Q = 48.7 kJ·mol−1 of carbon in an Fe-3.5 wt% Si-C alloy matrix can be calculated. The diffusion activation energy of carbon Q = 47.3 kJ·mol−1 was calculated using a molecular dynamics simulation. When the content of Si is 3.5 wt% and 1.5 wt%, the diffusion series of Si can be expressed as D3.5Si, Si = 8.54 × 10−10 exp(−33,089.7/RT) m2/s and D1.5Si, Si = 2.06 × 10−9 exp(−46,641.5/RT) m2/s, respectively. When the Si content is 3.5 wt%, the diffusion coefficient of Si is larger. After diffusion to the near surface, it combines with the remaining O to form a continuous strip of SiO2. When the Si content is 1.5 wt%, the diffusion coefficient of Si is small. The remaining O diffuses in the matrix and will oxidize when encountering Si; it cannot aggregate in a highly-dispersed distribution. The lattice transition from face centered cubic lattice austenite to body centered cubic lattice ferrite occurred in the matrix of the thin strip. The diffusion coefficient of C in ferrite is much larger than that in austenite. Therefore, the decarburization rate suddenly increases before decarburization stagnation. With the increase in Si content, the diffusion activation energy of C decreases, which promotes the decarburization effect.

Effect of Surface Oxide on Decarburization Reaction in the Austenitic Steel S304HCu

In the present work, the high-temperature decarburization of the austenitic stainless steel S304HCu in Ar–4%H2–xH2O at temperatures between 1000 and 1150 °C was investigated. The focus was on determining parameters that influence the decarburization rate during heat treatment. Thermogravimetric experiments were performed with simultaneous measurements of CO release from the sample using a mass spectrometer. The variation of the experimental parameters included the composition of the atmosphere during pre-oxidation and decarburization, the temperature and the sample thickness. The results indicate that the loss of carbon from the specimen occurs faster through reaction of Cr2O3 with C from the steel compared to the reaction of C at the steel surface with H2O, provided that in the former case CO can easily evaporate. The overall decarburization process is governed by competing reactions; the destruction of chromium oxide by C and the formation of oxide scale by water vapour. The relative rates of these two reactions determines whether decarburization will occur or whether formation of a protective oxide stops the release of CO, the latter being promoted at lower temperatures and high water vapour contents. A dense, sufficiently thick chromia scale retards the onset of decarburization but does eventually not stop the carbon loss. Indications were found that the destruction of a pre-formed chromia scale by carbon involves a two-step process whereby presence of hydrogen is important.

The Importance of Mixing Time in Intensely Stirred Metallurgical Reactors: Applied on Decarburization Reactions

In metallurgical converter processes, numerical modeling is a useful tool for understanding the complexity of the systems. In this paper, we present a practical model that couples fluid dynamics and chemical reactions to explore the impact of mixing time on decarburization. Using computational fluid dynamics (CFD), in this study, we investigate an arbitrary metallurgical reactor with continuous oxygen supply, focusing on the Fe–C–O system. The model employs local equilibrium, a turbulence limiter, and finite volume method for mass, momentum, and energy transfer. Tracer injection points in the gas plume’s rising region exhibit faster mixing, and a comparison of reaction cases reveals distinct decarburization rates based on oxygen injection distribution and the influence of turbulence on reactions. Overall, while mixing time matters, the results show that this system is primarily governed by thermodynamics and oxygen supply, and a 270% increase in mixing time increase had a small impact on the end carbon content.

Efficient decarburization modification of coal gasification fine ash by microwave field activation

The presence of residual carbon in coal gasification fine ash (CGFA) significantly impacts its subsequent processing and utilization. This paper proposes and investigates the use of microwave field heating to decarburize CGFA, exploiting its favorable microwave absorbing characteristics attributed to its composite structure comprising carbon, iron, and water. The experimental results demonstrate an 81% reduction in the required time and a 74% decrease in energy consumption (based on preliminary calculations) to achieve a decarburization rate of 95% compared to conventional thermal electric furnace calcination methods. The treated CGFA exhibits optimized mineral species, reduced electron binding energy, enhanced solubility, and increased heat release intensity during hydration, leading to improved reactivity of mineral phases in alkaline environments. Furthermore, when used as supplementary cementitious material, the activity index of CGFA shows a remarkable 21% increase in macroscopic performance testing.

Vibration and Audio Measurements in the Monitoring of Basic Oxygen Furnace Steelmaking

A basic oxygen furnace (BOF) is the main unit process for refining carbon steel. The aim of this work was to study the use of vibration and audio signal measurements to monitor, predict, and control the BOF process. Vibration and audio data from nearly 300 blows were collected and analyzed together with process variables. We could confirm high correlations between some of the process variables and vibration and audio measurements. Median filtered low-frequency (3–20 Hz) audio as well as X- and Z-direction acceleration root mean square (RMS) time series correlate with the off-gas temperature, although this is much more significant for the audio data. For Y-direction measurements (the upward direction) the correlation is negligible. The low-frequency audio and vibration data are likely related to the rate of decarburization. Median filtered mid-frequency (100–1000 Hz) audio as well as X-, Y-, and Z-direction acceleration RMS time series correlate with the lance height measurement during the interval 20–600 seconds from the beginning of oxygen blow. For the audio data, the correlation was high even without median filtering. We suggest that audio and vibration activity in this frequency range is possibly related to the formation of the metal–slag–gas foam and maybe even to slopping.

Performance of Mn-Ce-Fe/FA Catalysts on Selective Catalytic Reduction of NOX with CO under Different Atmospheres

Gas turbines produce a large amount of NOx and CO due to high temperatures and insufficient combustion. Through the selective catalytic reduction of NO with CO (CO-SCR) in a gas turbine, the activities of the Mn-Fe-Ce/FA catalyst using fly ash (FA) as a carrier under different atmospheres were studied. The catalysts prepared by calcining different active materials under different atmospheres were used to analyze their denitrification abilities and resistance to water vapor. The denitrification performance of the catalyst prepared under reducing atmosphere is about 30 percent higher than that of the catalyst prepared under air atmosphere, and the decarburization performance is about 40 percent higher. In the presence of oxygen, the denitrification rate and decarburization rate of the 1:1 ratio of the Mn-Ce catalyst reach 67.16% and 59.57%, respectively. In an oxygen-containing atmosphere, the catalyst prepared by replacing Ce with Fe shows better denitrification and decarburization performances, which are 78.56% and 78.39%, respectively. When the flue gas space velocity is 4000 h−1 and the carbon-nitrogen ratio is 1.6, the catalyst shows better performance. After the water vapor is introduced, the denitrification and decarbonization rates of the catalyst decrease by about 10% and 9%, respectively. After ceasing water vapor, it rebounds by about 8%, and the activity could not be fully restored. However, the catalyst still shows strong water resistance in general.

Electric Arc Furnace Stirring: A Review

Thermodynamics and kinetics are affected by the stirring conditions. Higher‐stirring intensities promote conditions closer to equilibrium and increase the mass‐transfer coefficients. A major limitation of the conventional electric arc furnace (EAF) is the low velocities of liquid steel which result in very poor mixing conditions. The practical consequences are lower decarburization rates and lower melting rates. Herein, the forces that operate and promote the motion of liquid steel in a conventional EAF are reviewed in detail; buoyancy forces, momentum transfer by the oxygen jets, drag forces by CO bubbles are produced by decarburization and local electromagnetic forces at the electrode regions. It is shown in the short range and limited intensity of the previous forces. Bottom gas injection and electromagnetic stirring are the main methods that can induce forced convection in the EAF. The information available is summarized and analyzed to describe the results obtained at laboratory level and industrial scale using different stirring mechanisms. Finally, guidelines are provided in this review for further research on the basis of the limitations of the current results.

Preparation of Calcined Kaolin by Efficient Decarburization of Coal-Series Kaolinite in a Suspended Bed Reactor

The reaction process, mechanism, and kinetics of the decarbonation of coal-series kaolinite (CSK) were investigated using the thermal analysis (TG)–infrared spectrum analysis (IR) coupling method. A pilot test was performed using a suspended calcination system. Further, the carbon content, phase composition, whiteness, oil-absorbed value, and micromorphology of calcined kaolin were characterized. Results showed that the decarburization reaction of CSK was a two-step reaction that mainly occurred in the ranges of 593 °C–836 °C. The mechanism of the decarburization reaction was a phase-boundary reaction (unreacted-core shrinking model) with an activation energy of 214.56 kJ/mol. Calcination at 900 °C or 950 °C for ~3.3 s in a suspension reactor resulted in the decarburization rate of CSK becoming >99.9%. The whiteness of calcined kaolin was mainly positively associated with the decarburization rate, and increasing the calcination temperature aided in increasing the whiteness. The oil-absorbed value of calcined kaolin was positively correlated with the specific surface area. Insufficient or over-calcination decreased the oil-absorbed value of calcined kaolin products. The calcined kaolin product with a whiteness of 89.3% and an oil-absorbed value of 76.1 g/100 g was obtained via suspension calcination process, which meets the requirements of calcined kaolin for paper-making.

Compound purification of nickel base superalloy cutting waste through special cleaning agent attached to ultrasonic stirring

The GH4169 nickel-based superalloy is a type of alloy that exhibits excellent properties. It has high creep strength, fracture strength, as well as good corrosion resistance, fatigue resistance, and oxidation resistance under high-temperature conditions, allowing it to be widely used in the aerospace, nuclear reactor, and oil industries. However, it is challenging to process superalloys because of their high hardness and considerable processing wastes, such as cutting fluid. Many processing wastes cannot be directly used for remelting due to issues like surface stains. However, the production of GH4169 superalloys requires low carbon content for recycling, so the alloy scraps that meet the standard after pre-cleaning can be obtained. This study explores the ultrasonic cleaning effect of superalloy scraps with different liquid-solid ratios, cleaning times, and cleaning temperatures to obtain the optimal cleaning conditions of GH4169 superalloy scraps. The content of carbon in unwashed superalloy scraps is as high as 0.2%, far exceeding the carbon content of the alloy itself (0.015–0.036%). After ultrasonic cleaning at 60 °C for 30 min with a cleaning solution having a solid-liquid ratio of 1:2.5, the carbon content of the scraps decreased from over 0.2%–0.048%, and the decarburization rate reached above 77%. After remelting the cleaned scraps into alloy bars, the composition content and properties of the bars meet the production requirements. The cleaning mechanism is analyzed, and the cavitation effect, saponification, and emulsification mode in the ultrasonic cleaning process are explained. This paper positively promotes recycling GH4169 nickel-based superalloy waste to protect environmental resources.

Experimental Study on Decarburization and Chromium Retention in Stainless Steel Smelting with CO2 as Alternative to N2

Reusing CO2 as a secondary resource in the steel industry is one of the research hotspots in recent years. Herein, O2–N2 and O2–CO2 are injected into Fe–C–Cr melt at 1823 K to study the effect of CO2 (as an alternative to N2) on decarburization and chromium loss in the argon–oxygen decarburization (AOD) stainless steel smelting process. The results show a higher decarburization rate and lower chromium loss with O2–CO2 injection compared with O2–N2 injection. CO2 injection helps oxidatively remove a part of carbon (C) in the melt. Simultaneously, the increase in CO partial pressure reduces the loss of Cr by CO2 oxidation to a measurable extent. In the middle–late stage of smelting, the corresponding content of C and Cr is relatively consistent with the trend of thermodynamic analysis. From the view of kinetics, CO2 injection increases the gas–metal interface area to improve the Cr formation rate in the melt, improving decarburization and chromium retention with the substitution of CO2 for N2. The research results herein provide a new direction for the development of the AOD process in the future and put forward a way of CO2 resource utilization.

Theoretical analysis and experimental study of the application of CO2 in the smelting of 410S stainless steel

The use of CO2 as a blown gas in the smelting process of 410S stainless steel is investigated and compared with the use of N2. The experimental smelting of a Fe–C–Cr melt with CO2 replacing N2 in different proportions shows the effect of CO2 on decarburization and chromium oxidation. The results show that the decarburization rate increases with increasing CO2 proportion. When the replacement ratio was less than 75%, the oxidation loss rate of Cr decreased with increasing replacement ratio. When CO2 completely replaces N2, the C content in the liquid melt is relatively low, causing an increase in CO partial pressure from the blown CO2, resulting in increased oxidation loss of Cr. An industrial test using a 70-t stainless steel smelting furnace verifies that when [%C]> 0.1, the use of CO2 as a blown gas results in excellent decarburization and chromium retention performance, and the Fe-Si reductant consumption decreases with reduction in chromium oxidation loss in molten steel. Blown CO2 induces a temperature drop in the molten steel that cannot be ignored for stainless steel smelting. This study provides a reliable foundation for the application of CO2 in stainless steel smelting.

Contribution of Hot-Spot Zone in Decarburization of BOF Steel-Making: Fundamental Analysis Based upon the FactSage-Macro Program

An improved computational model to describe the decarburization process in basic oxygen furnaces for steel making is presented in this work. A dynamic model was thus developed to calculate the decarburization rate and its breakup as a contribution coming from the hot-spot zone (under jet impact) and emulsion zone (by droplet and slag reactions). In this work, multiple interconnected equilibrium/adiabatic stoichiometric-reactor-based approaches are used to describe the overall basic oxygen steel-making process. The macroprogramming facility of FactSage™ software was used to understand the thermodynamics and kinetics of basic oxygen steel-making processes. The temperature, compositions, and volumes of various phases are estimated with the use of this model. Hot-spot temperatures in the range from 2000 to 3000 °C as a benchmark was considered for calculations. The major contribution of decarburization was established to come from hot-spot reactions in the major part of the blow, except in the last part when emulsion phase reactions govern it. This development represents an original contribution to our understanding of the BOF steel-making process.

Mathematical model for the forced oxygen blowing decarburization process of ultra-low carbon steel during RH treatment

A new mathematical model for the RH forced oxygen blowing decarburization process which takes the influence of post combustion on decarburization into account is established. Decarburization reactions are considered to take place at four reaction sites. The simulated results of carbon and oxygen contents show relatively good agreement with the experimental data under different oxygen flow rates. At the rapid decarburization stage including the O2 blowing process, 66.1% of the total decarburization amount is removed. By using the forced oxygen blowing decarburization process, the decarburization rate in the bulk steel is improved most significantly. Additionally, the effects of oxygen flow rates on carbon, oxygen and total decarburization rate are evaluated in detail. At 1500 m3 · h−1, the oxygen content is adequate to completely remove carbon of molten steel in the vacuum vessel during the O2 blowing. Combining with the analysis of oxygen flow rates on the decarburization rate at each site, 1500 m3 · h−1 is chosen as the critical oxygen flow rate to achieve the best decarburization performance. The influences of other parameters including initial carbon and oxygen contents and oxygen utilization rate on decarburization are also investigated.

Decarburisation of Fe-C alloy strips by gas–solid reaction in Ar-CO-CO2

The gas–solid reaction decarburisation of cast iron strips is a direct steel production method with low production costs. In this study, the decarburisation kinetics of Fe-C alloy strips in an Ar-CO-CO2 atmosphere were investigated. Fe-C alloy strips with 4.2 wt.% C and different thicknesses (1, 1.5, and 2 mm) were used for the decarburisation experiments under temperatures of 1293, 1353, and 1413 K. The results indicate that, under appropriate mixed gas conditions, rapid decarburisation can be achieved. With an increase in the decarburisation temperature, the decarburisation rate increases significantly. Under the same decarburisation temperature and time, thinner Fe-C alloy strips exhibit a better decarburisation effect. The decarburisation process includes three rate-limiting stages, namely gas and surface reaction, carbon diffusion, and cementite decomposition. The microstructure of the decarburised strips comprises a complete decarburised layer and a partial decarburised layer, and the thickness of the complete decarburised layer increases with decarburisation time. The decarburisation of the Fe-C alloy strip is an apparent first-order reaction with an activation energy of 124.7 kJ ∙ mol−1, and the activation energy for the growth of the complete decarburised layer is 132.3 kJ ∙ mol−1. The results of this study can help develop more efficient and cost-effective steel production methods.

A model predictive controller of the blowing mode during basic oxygen furnance process

Today in Ukraine and the world, the problem of energy saving and reducing the cost of smelted steel is state of art. Metallurgical enterprises are developing in conditions of fierce competition, the main reason is that Ukrainian products are extremely energy-intensive due to the depreciation of fixed assets and outdated technological processes. The basic oxygen furnace process is a process of producing steel from liquid cast iron with the addition of steel scrap to the converter and blowing oxygen from above through a water-cooling lance. Nowadays, the production of steel by BOF process is the most popular in the world and is becoming increasingly common. The main disadvantage of the basic oxygen furnace is the need to provide the initial amount of heat (in the form of liquid cast iron) and as a consequence - restrictions on the processing of scrap metal. Reducing the cost of basic oxygen furnace steel is achieved by increasing the share of scrap metal by increasing the degree of afterburning of CO to CO2 in the cavity of the converter, by optimal control of the parameters of the blast mode using model-predictive control. The principle of model-predictive control is based on a mathematical model of the plant. This approach minimizes the functional that characterizes the quality of the process. The linear-quadratic functional was chosen. A forecasting model is proposed taking into account the constraint on changing the position of the lance and the pneumatic oxygen supply valve. It was found that the change in the rate of decarburization of the metal depends on the distance of the lance to the level of the quiet bath and affects the degree of afterburning of CO to CO2. The decarburization process is non-stationary, described by a first-order inertial model, the transfer coefficient and time constant of which depends on the melting period and the duration of the purge. The mathematical model of the blast mode of oxygen-converter melting has been improved, taking into account the influence of the blast intensity on the decarburization process of the bath, which allowed to increase the accuracy and quality of blast control in terms of changing oxygen flow during purging. The simulation results of the automatic control system show that the model-predictive regulator provides the required level of carbon dioxide in the converter gases when the flow rate of oxygen for purge changes.

Interface reaction between alloys and submerged entry nozzle controlled by an electric current pulse

To solve the limitations of clogging and erosion of the submerged entry nozzle (SEN) for the production of high-quality special steel, the chemical reactivity between different alloys and the SEN and the interface reaction between alloys and the SEN controlled by an electric current pulse (ECP) were examined in this study. Results revealed that the chemical reactivity between different alloys and the SEN is different. For example, the reactivity between rare-earth metal and the SEN was strong, while that between Al and the SEN was extremely weak. At the same time, some differences between the clogging and interface reaction by ECP control were observed. Typically, at the positive electrode of the SEN, when a stable and dense clogging layer is formed, the internal SEN was effectively protected. However, at the negative electrode of the SEN, the decarburization rate of the SEN was accelerated by ECP, probably leading to a vicious circle of accelerated clogging and erosion of the SEN. Therefore, in the future, issues of clogging, erosion, infiltration, and decarbonization between active alloys and the SEN in the casting process may be solved and regulated by using the positive electric field of ECP. Meanwhile, the gain effect of ECP also helped to promote the homogenization of molten steel.

Thermodynamic and experimental study on CO2 injection in RH decarburization process of ultra-low carbon steel

In this work, carbon dioxide (CO2) was investigated as a lifting gas in the Ruhrstahl–Heraeus (RH) decarburization process of ultra-low carbon steel. The main challenge was to determine whether the local carburization reaction leads to the carburization of molten steel with ultra-low carbon content. Thermodynamic analysis of the reaction of the Fe-C-O melt with CO2 demonstrated that compared with traditional Ar injection, the decarburization rate can be improved during the early stage of the decarburization process. This occurs because oxygen that is present not only in molten steel but also produced by CO2 dissociation can react with dissolved carbon to remove the carbon from molten steel. However, it is difficult to determine whether the decarburization rate can be influenced during the later stage by injecting CO2. This is because the carburization reaction at the surface of CO2 bubbles in the up-snorkel and the decarburization reaction at other reaction sites can occur simultaneously. Industrial test results demonstrated that compared with Ar injection, the decarburization rate was not significantly affected by CO2 injection at the early stage, whereas it was reduced during the middle and later stages. Nevertheless, the average carbon content in molten steel after the RH treatment with CO2 injection was only 2.6 ppm higher compared with that in Ar injection. Therefore, Ar can potentially be replaced by CO2 in the RH decarburization process of ultra-low carbon steel based on economic and environmental considerations.

Nature of dust and smoke generation during gas-oxygen blasting in converter bath

The article presents the study of the nature of dust and smoke generation during gas-oxygen blasting of a converter bath. The main reasons causing metal waste have been determined. Influence of the process main parameters on metal loss has been studied during dust removal and evaporation of iron in the reaction zone. The authors have estimated the process of metal pulverization due to CO bubbles floating, determined by the rate of their rise to the bath surface. Specifics of temperature regime of the reaction zone and heat balance have been determined when adding fuel to the oxygen flow. Adding fuel to oxygen makes it possible to increase heat input into the bath, while reducing the rate of decarburization. This enables reduction of dust discharge during rupture and crush of metal films by gas bubbles. The effect of combustion products oxygen use on metal impurities oxidation is considered. By the example of blasting carbon and alloyed steel for mill rolls, it has been shown that the degrees of CO2 and H2O decomposition in the bath are the main qualities of gas-oxygen blasting. These indicators determine the oxidizing and heating properties of the blast. Assessment of change in total, consumed heat and its losses with exhaust gases, depending on degree of the oxygen flow dilution with natural gas (methane), has been carried out. Under these conditions, use of submersible combustion torches with change in their oxidizing ability makes it possible to solve various technological tasks, including provision of an effective way to reduce dust emission in converter process.

Effect of smelting temperature and CO2 gas flow rate on decarburization kinetics between CO2 gas and liquid Fe-C alloy

ABSTRACT The effect of smelting temperature and CO2 flow rate to decarburization kinetics between CO2 and liquid Fe-C alloy were investigated. The decarburization rate caused by CO2 increases with smelting temperature. Compared with low carbon condition (near 0.45 wt pct), the effect of temperature on decarburization rate is more significant under high carbon condition (near 3.5 wt pct). At high carbon content, the decarburization rate increases linearly with CO2 flow rate. And a CO2 decarburization kinetics model considering the influence of bubble diameter, bubble generation frequency, rising velocity and rate controlling step was established. When CO2 transfer in gas phase boundary layer is rate controlling step, the calculated data are in good agreement with the experimental data. It was also found that the effect of CO2 flow rate on the decarburization rate was mainly affected by the reaction surface area, but less on gas phase mass transfer coefficient in current experimental situations.