Zone Of Furnace Research Articles

Effect of peripheral nonuniform distribution of furnace heat flux on thermo-hydraulic characteristics and design of riser downcomer circuit of natural circulation boiler

The usual practice of design of riser tubes of natural circulation boilers is with an assumption of uniform furnace heat flux. Using the uniform diameter of riser tubes inside the furnace zone is also very common. The effect of peripheral nonuniform distribution of furnace heat flux on thermo-hydraulic characteristics and design of the riser downcomer circuit of a natural circulation boiler is presented here for the first time. As the riser tubes are exposed under substantially high heat flux, the tubes containing water-steam mixture are vulnerable and susceptible to overheating, particularly at high flux zone. From systematic analysis, it is proposed that using different diameters and the number of riser tubes at various sections can overcome the early occurrence of tube dry-out. An appropriate two-phase flow model is developed with flow regime mapping, tube wall temperature calculation, and identification of possible dry-out. The peripheral nonuniform distribution of furnace heat flux is implemented analytically in the model by introducing a distribution parameter estimated from the actual furnace data. Results reveal that with an average heat flux of 150 kW/m2, the dry-out occurs near a riser tube height of 44 m for a typical 210 MW capacity boiler. However, considering the nonuniform heat flux variation, the dry-out appears near a height of 32 m and 73 m for higher and lower heat flux zone, respectively. The present analysis shows that the implementation of larger size and lower size diameter of riser tubes, respectively, in higher and lower heat flux regions has a 9.45 % cost-benefit compared to the usual design practice with a consideration of uniform diameter tube and heat flux. The present work concludes that instead of using uniform tube diameter with average heat flux assumption, the use of different diameter of tubes in different heat flux zone not only avoid the early onset of possible dry-out but also has a cost-benefit.

Advantages and risks of using ore-coal briquettes in blast furnaces

Reducing carbon consumption, and, consequently, CO2 emissions during iron smelting in blast furnaces is a priority for improving the technology of blast furnace smelting. In the literature, the question of the influence of the development of direct reduction of iron on the consumption of carbon as a source of reducing gas and a source of heat has been considered. In this case, the development of direct reduction in the lower zone of the furnace at temperatures above 900 °C is considered. However, direct (solid-phase) reduction can be implemented in the upper zone of a blast furnace when using ore-coal briquettes in the charge. It is shown that the solid-phase reduction reactions can proceed at temperatures above 700 °C in the upper zone of a blast furnace during the reduction of Fe3O4 and FeO. At the same time, the apparent heat capacity of the charge increases and the temperature of the top gas decreases, which is confirmed by data on the operation of blast furnaces of NLMK PJSC, which use ore-coal briquettes. The raw materials for the production of briquettes are iron ore concentrate, sludge, blast furnace dust, aspiration dust. A bentonite and a ce-ment are used as a binder. The briquettes contain 40‒42% iron and 10‒15% carbon. The theoretical analysis and statistical processing of data on the operation of blast furnaces led to the conclusion that the solid-phase reduction of iron oxides actively proceeds at temperatures below 900 °C. The results of experimental heats showed the use of briquettes allows to reduce the specific consumption of coke and the total carbon consumption of fuel. The prospects for the use of the briquettes are associated with an increase in their mechanical properties. The use of ore coal briquettes obtained from a concentrate with an iron content of 65‒68% will reduce the rate of fuel carbon and CO2 emissions.

Numerical Analysis of Natural Gas Injection in Shougang Jingtang Blast Furnace

A static model of blast furnace operation of natural gas (NG) injection was developed. The effect of NG injection on the raceway adiabatic flame temperature, the amount and composition of bosh gas, the direct reduction degree and fuel ratio were studied. The results showed that under no thermal compensation, the heat loss of the whole blast furnace increases, which means the heat surplus of the whole furnace is sufficient. However, the heat in the high-temperature zone of the blast furnace is insufficient, showing the characteristics of “cold at bottom and hot at the top”. Based on the comparison of heat loss in the high-temperature zone after NG injection with the reference condition, if the heat loss is consistent with the reference case, the suitable NG injection volumes are 17.3, 34.6, 52 and 69.3 m3/t when the coal ratio is reduced by 20, 40, 60 and 80 kg/t, respectively. With the increase of the suitable NG injection volumes, the adiabatic flame temperature gradually decreases, the amount of bosh gas slightly increases, and the overall fuel ratio reduces gradually. The effect of other thermal compensation operations, such as increasing blast temperature and addition of oxygen on the NG injection, were also investigated. The findings of this work can be used as a theoretical basis to guide plant operations for NG injection in blast furnaces.

Smart Design of Cz-Ge Crystal Growth Furnace and Process

The aim of this study was to evaluate the potential of the machine learning technique of decision trees to understand the relationships among furnace design, process parameters, crystal quality, and yield in the case of the Czochralski growth of germanium. The ultimate goal was to provide the range of optimal values of 13 input parameters and the ranking of their importance in relation to their impact on three output parameters relevant to process economy and crystal quality. Training data were provided by CFD modelling. The variety of data was ensured by the Design of Experiments method. The results showed that the process parameters, particularly the pulling rate, had a substantially greater impact on the crystal quality and yield than the design parameters of the furnace hot zone. Of the latter, only the crucible size, the axial position of the side heater, and the material properties of the radiation shield were relevant.

Comparing different syngas for blast furnace ironmaking by using the extended operating line methodology

This paper assesses the injection of different syngas in air-blown blast furnaces, oxygen blast furnaces, and advanced oxygen blast furnaces. The selected types of syngas come from biomass gasification, plastic gasification, CO2 electrolysis, and reverse water–gas shift reaction. An Aspen Plus model, based on the new extended operating line methodology, was used for the simulation. This methodology is a generalization of the conventional Rist diagram, to extend its application to cases in which the injected gases have large contents of CO2 and H2O, and also to cases in which injections take place at the middle or upper zone of the blast furnace. The base cases were elaborated and validated with data from literature, with a discrepancy below 3.5%. A total of 7 key performance indicators were defined for the study (mass flow of syngas, coke replacement ratio, gas utilization, percentage of direct reduction, blast furnace gas temperature, flame temperature, and net CO2 emissions). In practice, the amount of syngas that can be injected is limited to 92 – 264 kgsyngas/tHM because of the drop in the flame temperature. The lowest net CO2 emissions are achieved in oxygen blast furnace with injection of syngas from reverse water–gas shift reaction.

Slag mode regulation in electric arc furnace based on electrical parameters control during melting oxidation period

The results of observation of steelmaking oxidation stage at EAF-135 were analyzed with automated control system of the electrical characteristics. There are three main zones in the furnace working space, which differ by the aggregate state of the materials in them: arc discharge, melt and foamed slag. The distribution data of electric power over the furnace zones is given. There is active powers asymmetry of the arcs under single electrodes affected by asymmetry of the short network. It is shown that the main factors impacting the melt and slag resistances are oxygen blow and electrode movement. The authors studied the influence of magnesia flux feeds on the melt resistance. These feeds correspond to a sharp increase and a subsequent gradual decrease in resistance, and the time for assimilation of additives does not exceed one minute. The average electrical parameters of the working space zones are given for the EAF-135 at single heats. A comparison was made of the nature of change in the arc discharge power and the change in the melt temperature. The profiles match of changes in these characteristics to an increase in the arc power corresponds to increase in the melt temperature. An attempt to correlate FeO content in the slag with the arc power did not give a positive result. However, this methodology should be tested under conditions of steel refining in a ladle-furnace unit. It is noted that the parameter control at changing of the electrical parameters of the arc and slag zones due to the overwhelming influence of intense oxygen blast, melt mixing and electrode displacement does not meet the reliability criterion.

Hydrogen on softening-melting and slag forming behavior under the operation of blast furnace with iron coke charging

The effect on the slag formation behavior in the softening melting zone of a hydrogen-rich blast furnace is investigated by charging iron coke to the iron ore and controlling different volume fractions of hydrogen. The reduction mechanism of iron coke to iron ore under hydrogen-rich conditions is expounded that iron coke and hydrogen increase the concentration of CO around iron ore and promote its further reduction. The participation of iron coke and hydrogen promotes that FeO is reduced to Fe in iron ore, which prompts the production of high melting point substances in slag. The melting point of slag iron increases the melting start temperature. Hydrogen and iron coke promote the carburization of dripping iron so that molten iron drips quickly, which narrows the melting drop interval. From the perspective of the maximum pressure difference and the comprehensive permeability S value, the blast furnace permeability will be improved.

Experimental and numerical study of the effect of water injection into the reaction zone of a flameless combustion furnace

The effect of water injection on the stability and emissions of a flameless combustion regime was evaluated. Flameless combustion operation was studied without self-regeneration, with self-regeneration, and with combustion air oxygen enrichment. For each case, increasing water flows were injected until the combustion regime was unstable. The evaluation criteria were temperature uniformity and pollutant emissions of species such as carbon monoxide and nitrogen oxide. Ansys Fluent 2020 software was used to perform the different simulations, while the experimental evaluations were carried out in a laboratory-scale furnace operating with Natural Gas at a thermal power of 30 kW, based on high heating value. Flameless combustion without self-regeneration was found to become unstable when the injected water mass to fuel mass ratio (m factor) was >2.5, while self-regeneration and combustion air oxygen enrichment increased the maximum operable m factor to 4.3 and 5, respectively.

Hot repair of blast furnace lining – a way to reduce its carbon footprint

The experience of JSC "Tulachermet" in the restoration of the refractory lining of blast furnaces with unshaped refractory materials by the shotcreting method is presented. Using this method of restoring a refractory lining can significantly reduce the cost and duration of repairs and use it more often when critical, especially with respect to coke consumption and the carbon footprint of the unit, values of lining erosion and thermal loads on the blast furnace cooling system are reached. Practical experience has shown the need to use different refractory materials for different zones of the furnace. The state of the refractory lining before the restoration repair is shown. The technology of restoration repair is described, the grades of refractory concretes and the thickness of the lining by furnace zones are indicated. An assessment of greenhouse gas emissions, specific coke consumption and furnace productivity after the repair was carried out. A model of rational decision-making on the restoration of the furnace lining is proposed, depending on the thermal loads on the blast furnace cooling system.

Situational optimization of the work of the thermal department, taking into account the ordering instability

The task of optimizing the functioning of the thermal department consists in determining such a plan for the operation of a complex of roller furnaces, which guarantees the fulfillment of the received orders for heat-treated steel wire and corresponds to the maximum profit for a given planning interval. To solve this problem, it is necessary to identify the situational and normative models of the performance of the control object, which is implemented by the authors on the proposed clock approach. In order to build models, preliminary comprehensive studies of the production process in the thermal department of the steel wire shop were carried out. The article considers the tact method for constructing a normative model for the functioning of the thermal department, reflecting the multi-mode operation of roller furnaces, which is used to substantiate the situational standards for the productivity of the department, which includes several units. The features of the organization of material flows are revealed; the structure of the technological process of heat treatment has been determined, a rigid connection has been established in the operation of the zones of the roller furnace. Formula-algorithmic normative situational models of the thermal department functioning have been formed, technically possible and standard values of operation cycles, furnace productivity and the department as a whole have been calculated. A tact method is proposed for calculating the standard productivity of a roller furnace, based on the decomposition of the control object (thermal department) and production operations. Variants of the efficient operation of the department are considered, taking into account changes in demand for hardware products, changes in the range of wire, the number of simultaneously operating furnaces, their technological modes and loading. As an illustration, three options for changing the demand for heat-treated wire are considered, for which the optimal modes of use of heat-treating furnaces have been determined.

Numerical Study on Combustion Behavior of Semi-Coke in Blast Furnace Blowpipe-Tuyere-Combustion Zone

Injecting low-cost semi-coke is critical to reducing blast furnace production costs. The combustion behavior of the co-injection of semi-coke and undersized coke powder is still rarely studied. In this work, a three-dimensional CFD mathematical model was established to simulate the gas velocity, temperature, composition distribution and burnout of semi-coke during the combustion of pulverized semi-coke. The influence of mass fraction of semi-coke on the composition and burnout in the combustion zone of blast furnace was also studied. The results show that the maximum concentrations of CO and H2 in the combustion zone are 36% and 8%, respectively. With the decrease of the semi-coke ratio in the blended coal, the fixed carbon content and the calorific value of the blended coal increase, but the burnout of the blended coal reduces. When bituminous coal is single injected, the burnout reaches 70%, which is higher than that of semi-coke. In actual production, for the semi-coke and coke powder injecting into the blast furnace, a proportion of bituminous coal can be appropriately added to improve the burnout rate of the coal blends and increase the H2 content in reducing gas.

Increasing the Energy Efficiency of Blast-Furnace Smelting by Choosing Rational Parameters for Loading a Multicomponent Charge

The purpose of this study was to develop a calculation tool for researchers and technologists - metallurgists, providing the ability to quickly assess the distribution of charge materials in a blast furnace when it is loaded with a multicomponent charge. The goal is achieved by analyzing and summarizing the multidimensional matrix of values for the content of the charge components in the annular zones of the blast furnace, obtained using a mathematical model of its loading under various modes, changing the content of pellets in the charge and the moment the pellets are unloaded onto the main conveyor. The most important results of the studies carried out are the substantiation of the possibility of obtaining and applying calculated dependencies to determine the characteristics of the distribution of charge components with an accuracy acceptable for technological practice, as well as the established relationship between the content of the component in the charge and the value of the set point for the start of unloading it onto the conveyor with the content of this component in the annular zones of the top. Estimated composition of mixtures of charge materials formed in different zones of a blast furnace makes it possible to predict the properties of melts formed from them and to correct them in order to achieve the required level of energy efficiency in melting a multicomponent charge by promptly choosing rational parameters of the loading mode.

On-line detecting the tuyere coke size and temperature distribution of raceway zone in a working blast furnace

Developing the new injection energy including full oxygen, hydrogen and natural gas injection in raceway zone of blast furnace is one of the effective and feasible measures to reducing the carbon emission and satisfying the carbon neutral plan. While the tuyere combustion condition under all-coke smelting model of blast furnace could supplying a direct manner to observing how the new energy affecting the coke combustion and temperature variety process during raceway process. In this paper, the tuyere coke particle sizes and raceway temperature distribution, as the representative parameters of raceway combustion, are online detected at the same time in a working 2500 m3 blast furnace under the all-coke smelting model by machine vision, Fully Convolutional Networks (FCN), and colorimetric thermometry method (CTM). The results showed the same ranges compared to research of coke sampling and average temperature in tuyere zone. And the calculation of coke belt length (CBL) in raceway zone by empirical model were modified to evaluate the coke combustion and size decaying under all-coke smelting model. Which could not only benefit to study the coke cracking and formation mechanism in the raceway zone in a blast furnace after the new energy injection, but also provide a new method to online detect particle size and temperature distribution at the same time in complex environment by deep learning and machine vision methods.

Effect of Prior Austenite Grain-Size on the Annealing Twin Density and Hardness in the Austenitic Stainless Steel

The present study examined the effect of prior austenite grain size on twin density and hardness of austenitic stainless steels (ASS). The 253 MA and 316L ASS were subjected to multi-pass cold rolling to reduce thickness up to 2.3 mm. Subsequently, the rolled steels were heat treated at 1100°C at 0, 900, 1800, 2700, and 3600 seconds in a tubular furnace in a hydrogen atmosphere. At the end of the annealing time, the rolled steel was quenched in the cooled zone of the tubular furnace until it reached room temperature in a hydrogen atmosphere. Then, microstructure observation of ASS was done to identify the austenitic grain size and annealing twin, and a hardness test was performed using the micro-Vickers hardness scale. The line intercept method was used to measure the changes in 253 MA and 316L austenitic grain sizes. ImageJ software was used to measure grain size and twin length. The results showed that austenite grains of both steels grew normally; 253 MA ASS had a lower SFE and K value than 316L ASS, which indicated that 253 MA ASS had sluggish grain growth, smaller grains, more easily formed annealing twins, and higher twin density. The Hall–Petch coefficient, K’, of 253 MA ASS was higher than 316L ASS, which resulted in a higher hardness value. The Sellars, Pande and Hall-Petch models were shown to predict austenite grain sizes, twin density, and hardness in 253 MA and 316L ASS.

РОЗРАХУНОК ЕЛЕКТРОТЕПЛОВИХ ПРОЦЕСІВ В ІНДУКЦІЙНІЙ КАНАЛЬНІЙ ПЕЧІ В УСТАЛЕНОМУ РЕЖИМІ НА ОСНОВІ ТЕОРІЇ ТЕПЛОВИХ КІЛ

Based on the theory of thermal circuits, a computer model of an induction channel furnace has been developed, which is used to obtain industrial copper wire rods in the mode of continuous casting. The model allows calculating the established electrothermal processes considering the flows of cold and molten metal in its core. In the developed thermal model, it is proposed to consider the convection fluxes of heat in the metal using controlled current sources. The temperature distribution in the active zone of the channel furnace is calculated, and the influence of the mass flow of metal at the inlet and outlet of the furnace on the non-uniformity of temperature distribution in the active zone is shown. The obtained results allow determining the required electric power of the furnace at different values ​​of the flow rate of the metal that moves continuously through its core while heating to a given temperature. The developed model is relatively easy to implement, using the Matlab/Simulink package, and allows online to estimate the melt temperature in different zones depending on the electric power consumed by the furnace and the metal consumption at the outlet of the furnace, as well as to determine rational modes of its operation. Ref. 7, fig. 4.

Research of thermal energy processes during silicon carbide production in the resistance furnace

Thegoal. Silicon carbide is one of the most essential artificial inorganic materials widely used to produce abrasive instruments, high-temperature heaters, fireclay ceramics, and metallurgy. The most amount of silicon carbide produces in the resistance furnaces. One of the issues of the silicon carbide production process is the lack of supervisory of thermal state in the furnace working space, which does not always allow for select rational electrical modes and accordingly get the material of appropriate quality. One of the methods to solve this issue is computer modeling the thermal state of the resistance furnace. Therefore, the goal of this research is the development of a computer model of the thermal state in the reaction zone of the resistance furnace, that further allows the development of technological recommendations concerning modes of conducting the process of obtaining silicon carbide. In addition, the development of a mathematical model of the dynamics of the thermal state of the resistance furnace opens up new opportunities for improving the existing automated control systems, which is very important from the point of view of the implementation of the Industry 4.0 paradigm at the enterprises of the mining and metallurgical complex of Ukraine. Methodology. The thermophysical model of the silicon carbide production process in the resistance furnace was developed. By finite difference method, the dynamics of the thermal state of the reaction zone in the furnace are computed. Resultsandscientificnovelty. Zones of the existence of products of carbothermic reduction of silica due to the heat generated when an electric current is passed through the furnace core are sized up by results of modeling, and the temperature front of the progress of the reductive reactions was detected. Practical value. The developed model allows for evaluating the influence of supplied power dynamics on the reduction products size zones, obtaining the analytical dependences of changes in the thermal state of the reaction furnace zone, and thereafter developing the technological recommendations concerning silicon carbide production process performance and improvements for the furnace automated control system. The structure of control of the thermal modes of the resistance furnace and the control computer complex based on Siemens technology is proposed.

Digital transformation of pyrometallurgical technologies: State, scientifc problems and prospects of development

The article considers an overview and critical analysis of the digitalization of the leading Russian ferrous metallurgy enterprises in accordance with the Industry 4.0 development concept. It provides for the creation of digital twins of pyrometallurgical technologies, the widespread use of machine vision and artifcial intelligence. The examples of domestic industrial systems using the technologies of machine (technical) vision in production cycle, digital assistants (twins) of metallurgical units and their sets are presented. With regard to blast­furnace production, technical vision systems used to control processes in the upper and lower zones of blast furnace are considered. A promising area is the integration of technical vision and decision support systems, including algorithms and software modules for implementation of deterministic mathematical models of individual phenomena of blast furnace smelting. They are based on fundamental physical concepts of blast­furnace smelting processes. One of the main directions of digital transformation of pyrometallurgical technologies is creation of intelligent control systems for technological process in metallurgy in real time. When formulating and solving problems, it is required not only to study the characteristics describing the effect of change in melting conditions on technical and economic indicators of the operation of individual furnaces, but also a detailed analysis for mathematical description of external and internal constraints. The authors present the examples of subsystems for control of heat losses in a blast furnace, predicting the parameters of tuyere hearths and controlling distribution of blast parameters around the perimeter of a blast furnace, an automated system for analyzing and predicting production situations in a blast furnace. Creation of such systems was carried out on the basis of modern principles and technologies for the development of appropriate mathematical, algorithmic and software support.

Edge defect-assisted synthesis of chemical vapor deposited bilayer molybdenum disulfide

The synthesis of two-dimensional molybdenum disulfide (MoS2) has invoked much research interest in recent years. In this work, chemical vapor deposition (CVD) was employed to grow a novel molybdenum disulfide. The synthesis reaction was operated in an inert gas environment, with the sulfur precursor placed in the upstream zone of a double zone tube furnace, and the molybdenum trioxide (MoO3) precursor placed in a small tube in the downstream zone. A piece of glass was used as the substrate, which was placed beside the small tube. We intentionally built a high concentration of molybdenum precursor above the substrate. The specific morphology hinged highly on the concentration of molybdenum. Abundant molybdenum atoms adsorbed on the edges of the bottom MoS2 and formed defects, which promoted the nucleation of the top layer MoS2 and preferentially grew from the edges. This result provides an innovative method to controllably synthesize novel bilayer molybdenum disulfide by a one-step method of chemical vapor deposition.

Empirical Study of Foundry Efficiency Improvement Based on Data-Driven Techniques

In this paper, a data-driven approach was applied to improve a furnace zone of a foundry in Taiwan. Improvements are based on the historical production records, order-scheduling, and labor-scheduling data. To resolve the bottleneck provided by the company, historical data were analyzed, and the existence of large variance in the process was found. Statistical analysis was performed to identify the primal factors causing the variance, and suggestions were made and implemented to the production line. As a result, daily production increased steadily to more than 30 pots of molten metal, while the original production was 20–30 pots of molten metal and are not controllable. Such significant improvement was mainly made by standardizing the input and reducing the variance of processes. The average cycle time of each pot of molten metal was reduced from 219 min to 135 min. Our suggested improvements also reduced the foundry’s electricity consumption cost by almost $240,000NT per month. In summary, data analysis can help traditional industries in identifying the main factors causing the bottleneck.

The influence of ash-content pulverized coal particles on their burning characteristics in tuyere hearth

Effect of ash content in coal dust on the burning characteristics in tuyere zone of blast furnace is studied. The ash is considered as an individual fraction in addition to two fractions of coal dust. It is shown, that the variation of pulverized coal fractional composition allows increase of carbon monoxide yield and fuel particles burnout. The presence of ash results in oxygen zone extension and increase of coke residue burnout. At the same time the total coal dust burnout is lower than that of low-ash coal. Fine pulverized coal combustion is characterized by increased production of carbon monoxide and reduction of carbon dioxide percentage.