Iron Ore Sintering Bed Research Articles

Effect of raw material composition on combustion behavior of quasi‐particles in the iron ore sintering process

AbstractAs the basic unit of iron ore sintering bed, the combustion behavior of quasi‐particles significantly impacts the sintering process. Adding biomass char leads to the deterioration of sintering quality, which was originally for the reduction of carbon emission. In this study, the isothermal thermogravimetric platform was used to analyze the combustion behavior of quasi‐particles using different fuels and ores. The results show that the mass of quasi‐particles packed bed decreases rapidly with combustion, then rises slowly, and then tends to be stable. The quasi‐particle samples in the combustion process were quenched with liquid nitrogen, and the composition changes in the quasi‐particle combustion process were analyzed. The results show that the excessive mass loss is caused by the reduction of iron ore in the sintering atmosphere, which also means heat loss. Compared with the samples using coke, when the fuel is exhausted, the proportion of calcium ferrite in the samples using charcoal decreases by 10.94%, while the proportion of magnetite and FeO is 11.36% and 1.04% higher, respectively, which will further lead to the formation of calcium iron olivine and reduce the sinter strength. The addition of magnetic concentrate may help to reduce the heat loss caused by the reduction reactions, but it is necessary to optimize the sintering process.

Nitrogen monoxide reduction by carbon monoxide to combustion control with calcium ferrite redox in iron ore sintering

Steel industry nitrogen oxides (NOx) emission requirements are getting increasingly rigorous. Calcium ferrite around coal or coke fines controls the combustion of nitrogen monoxide (NO) reduction by carbon monoxide (CO) in an iron ore sintering bed. This control lacked mechanistic research. A hypothesis that it belongs to the redox mechanism. In an atmosphere of a combustion boundary layer with 13500 ppm CO and 450 ppm NO at 1000 °C, the transient-response method was used to investigate the effects of CO and NO on the calcium ferrite (CaFe2O4). The activity of CaFe2O4 and its reduction products in NO reduction was examined. The results show that CaFe2O4 features strong basic sites with NO storage capacity of 158.8 μmol/g⋅catalyst at high temperatures to promote the competitive adsorption of CO and NO. The CaFe2O4 reduction path by CO, which is not affected by NO, is CaFe2O4 → Fe-FeO- dicalcium ferrite(Ca2Fe2O5) → Fe-CaO. The reduced calcium ferrites have a catalytic effect of 100 % NO removal and display more pores. After CaFe2O4 reduction, the Fe-CaO oxidation path by NO is Fe-CaO → Fe3O4-Ca2Fe2O5 → CaFe2O4. Ca2Fe2O5 redox is also involved in the redox cycle that Ca2Fe2O5 → Fe-CaO by CO and then Fe-CaO → Ca2Fe2O5 by NO. A strategy of Fe-CaO around fuels is proposed to further improve the combustion control by expanding the reducing layer in the atmosphere and generating more Ca2Fe2O5.

Acceleration of Oxidation Reaction of Iron-bearing Materials Co-existed with Carbonaceous Materials in Iron Ore Sintering Bed

Acceleration of Oxidation Reaction of Iron-bearing Materials Co-existed with Carbonaceous Materials in Iron Ore Sintering Bed

Influence of Oxygen Partial Pressure on Oxidation Reaction of Iron-bearing Materials in Iron Ore Sintering Bed

Influence of Oxygen Partial Pressure on Oxidation Reaction of Iron-bearing Materials in Iron Ore Sintering Bed

Flame front progress in gas assisted iron ore sintering

The present paper is focused on the control of heat release and on the propagation of the flame front in an iron ore sinter bed. Small scale sinter experiments are performed in cylindrical packings of the sinter mix which are ignited at the bed surface and vertically passed by the suction gas. The heat front propagation is found to be closely linked to the consumption of the fuel mix in the sinter bed. Based on this findings, a dual fuel approach is explored whereas front propagation of the solid fuel combustion (coke breeze) is supported by pulsed injection of a secondary gaseous fuel. A non-stationary, one dimensional model is established to analyse the heat wave travelling in the sinter bed. The model setup describes a local thermal non-equilibrium between the sinter bed being defined as porous medium and the permeating gas. The model is based on the balance equations for the mass and heat transports caused by the solid and gaseous fuel combustion. Model calculations support the experimental findings and demonstrate that satisfying sinter peak temperature levels and locally focused energy release are ensured by combined solid fuel burnout and high temperature gas combustion. During some lab-scale sintering tests, coke breeze content was reduced in the sinter feed mixture, and secondary fuel gas was supplied in pulsed mode to compensate the missing energy demand. The flame front speed as well as properties related to the sinter quality such as the tumble and shatter strength were determined, with the later index showing more sensitive results. The investigations demonstrate that pulsed methane injection can increase the flame front speed compared to the pure coke case with 5.1 wt% coke. , the pulsed gaseous fuel combustion can nearly compensate the strength loss for a moderately coke reduced rawmix with a coke content of 3.5 wt%.

Relationship Between Iron Ore Granulation Mechanisms, Granule Shapes, and Sinter Bed Permeability

ABSTRACTThe shape and size of granules are the basic factors that influence the packing structure and permeability of granular materials. This paper focuses on granulation mechanisms and the shapes (sphericities) of granules produced during the granulation of different feeds of iron ore for sinter production, using X-ray microtomography. Granule structures revealed that four mechanisms governed the formation of the granules namely autolayering, coalescence, adhesion of micropellets and two-stage layering. The addition of iron ore in the form of concentrate and micropellets to the sinter mixture enhances the mean sphericity of the granules while decreasing the sinter bed voidage and permeability.

Effect of concentrate and micropellet additions on iron ore sinter bed permeability

With the depletion of high-grade lump iron ore, concentrates have been identified as an alternative material for sinter making. In this study, the effect of concentrate and micropellet additions on the permeability of the sinter mixture was investigated. Permeability was measured on sinter mixtures containing 10–40% concentrate or micropellets at various moisture contents. The results confirmed that the addition of concentrates to the sinter mix decreases the maximum permeability of the sinter bed. Incorporation of micropellets into the sinter mix reduced the permeability less than concentrate addition. The maximum permeability of sinter mixes containing concentrate is reached at the same moisture content as the sinter mixture without concentrate addition. For sinter mixes containing micropellets, additional water must be added to obtain maximum permeability. Granule size, void fraction and angle of repose were also investigated to evaluate their effects on the permeability of the sinter bed.

Identifying major zones of an iron ore sintering bed

An unsteady, two-dimensional axisymmetric model is applied to simulate the iron ore sintering process. The present model consists of a wide range of chemical mechanisms in conjunction with detailed and complicated kinetic models. The temperature profile and gas species distribution throughout the bed are analyzed to identify chemical reactions taking place in different parts of the sintering bed. The study shows how simulation results of temperature and gas species variations throughout the bed can be analyzed in order to identify different zones of the sintering bed, based on the chemical reactions that control the process. Simulation results indicate that the sintering bed can be divided into four distinct zones with respect to the dominant chemical reactions taking place in the vertical direction of the bed. These zones are the flame front zone, preheating zone, dry zone and evaporation zone.

Modelling fuel combustion in iron ore sintering

In an iron ore sintering bed, the combustion behaviour of coke particles together with velocity of the flowing gas stream determines the temperature, width and speed of the traversing flame front. A bed heat treatment mathematical model was formulated in an earlier study to describe this complex relationship. An area of improvement in the model is the description of the coke combustion process, which is highly dependent on the resistances controlling the flow of gases to and from the coke particles. These vary for different coke particles because of the prior coarsening of the sinter mix by granulation. The characteristic structure of granules – nuclear particle with an adhering fines layer – indicates that gases have better access to finer coke particles. In this study, an available granulation model is integrated into the heat treatment model to provide a novel description of coke positioning within granules. In addition to this change, two endothermic reactions were introduced into the model. Using the previous and modified models, predicted bed temperature–time profiles as a function of position down the bed, were compared against embedded thermocouples results from seventeen laboratory sinter tests. Generally, the modified definition of coke combustion behaviour resulted in improved comparison with experimental results. In the sintering literature, studies have been reported on: the use of charcoal/biomass char to replace coke, the preferential placement of coke particles on the outside of granules, and varying the size distribution of the coke particles. Improving the access of gases to coke particles and decreasing coke size are comparable to using more reactive fuels. Combustion rate, efficiency and flame front properties are all influenced by fuel reactivity. Model predictions of changes in bed temperatures, flame front properties and sintering performance caused by fuel type, location and size are consistent with reported observations.

Process simulation of iron ore sintering bed with flue gas recirculation

Flue gas recirculation (FGR) has been incorporated into the sintering process with the aim of improving productivity while fulfilling tightened environmental regulations. The incorporation of FGR inevitably requires changes in the process equipment as well as incoming and outgoing gas conditions such as temperature, composition and flowrate. These changes may affect not only the reactions in the bed but also the factors related to the design and operation of the plant, which requires the checking of possible effects on gas conditions over the entire bed. The modelling approach proposed in this study for a sintering bed uses a flowsheet process simulator as the starting point for studying the effects of FGR on the sintering process. This paper is the first of two which will present comprehensive information on the modelling approach, and details of the modelling cases and the corresponding results will be described in the companion paper.

Process simulation of iron ore sintering bed with flue gas recirculation

As issues of productivity, quality control, energy efficiency and environmental regulation become ever more important in the iron ore sintering process, controlling combustion inside the sinter bed is attracting renewed interest in terms of flue gas recirculation (FGR) and oxygen or gaseous fuel enriched combustion. The application of combustion control schemes inevitably brings changes to incoming and outgoing gas conditions as well as to plant configuration. The objective of this study is to build a process model of a sintering bed using a flowsheet process simulator and to obtain information on material flows for various process configurations and operating conditions. The process modelling was designed to quantify the heat and mass flow in each of the bed segments, which could then be integrated to represent the overall material and energy flow of the entire bed. Variations in incoming and outgoing gas conditions were compared among different configurations of recirculation using the model.

Effective utilization of operating condition in production of sintered ore

Combustion of solid fuel supplies heat in an iron ore sintering bed and the quality and productivity of the processes are highly dependent on the variation of operational parameters. To set the optimized operation modes through the application of various ideas, a numerical model can be employed prior to the conceptual designing of the actual plant. In this study, the effects of oxygen enrichment, increment of bed height, waste gas recirculation, as well as supplementary gaseous fuel combustion are investigated by employing a previously developed unsteady one-dimensional model of an iron ore sintering bed. Through the simulation, temperature distribution can be observed and used as the key data for the evaluation of the combustion efficiency. Flame front speed and sintering time, which represent propagation speed of the combustion zone, are also employed for quantification of the simulation. Through the parametric studies with numerical analysis, preliminary information about the detailed situation in the bed can be obtained.

Theoretical Characterization of Steady-state Heat Wave Propagating in Iron Ore Sintering Bed

Knowledge of heat wave is a key to control the iron ore sintering process. To enhance the knowledge, numerical integration of differential equations for gas and solid is prevailing; this report, otherwise, used an analytical method and introduced several solutions by the assumption that the heat wave descended in steady state and that gas and solid temperatures coincided. The solutions correlated characters of heat wave with operational factors in a simple and explicit manner like:1) Heat behind speed (UB) was a function of gas velocity (ug) as UB=(cgug)/(csρs);2) Solid maximum temperature (TP) comprised an adiabatic temperature increase due to coke combustion (θc) and a heat convection due to downdraft necessary for solid temperature to heat up to coke ignition (θig) as TP=θc+θig;3) Heat front speed (UF) correlated with UB (=ν) and the terms for coke combustion heat generation (θc) and ignition temperature (θig) as UF=ν·(1+θc/θig).

Combustion characteristics in an iron ore sintering bed—evaluation of fuel substitution

In an iron ore sintering bed, combustion of solid fuel supplies heat needed for sintering of fine particles and determines the quality of the sintered ores and the productivity of the process. Coke has been widely used as an ideal fuel for this process, but recent attempts to partially replace coke with a less expensive fuel have been considered effective in the real applications. This paper reports simulation results of mathematical modeling of bed combustion as well as experimental observation from scale-downed pot tests. Combustion characteristics of the solid fuel bed are also described and fuel substitution from coke to anthracite coal is evaluated. A numerical model of the 1-D unsteady level considers the processes in the bed of particles: drying, devolatilization, char reactions, gaseous reactions, heat transfer, and geometrical changes of the bed material. The model can treat the solid material as multiple solid phases whose contents include fine particles of iron ore, limestone, coke, and coal. Quantitative parameters are newly defined for characterization of the bed combustion. These include flame front speed, sintering time, duration time in the combustion zone, combustion zone thickness, melting zone thickness, and maximum temperature. Relationships between these parameters and the mechanism of combustion propagation are also investigated. The results show quantitatively that temperature profiles, combustion propagation, and thickness of the combustion zone in the bed are dominated by combustion-related operating parameters. This description is applied to case studies for various coke contents, air supply rates, and fuel characteristics. It is shown that the different reactivity of anthracite in comparison with coke can significantly affect the bed combustion in terms of combustion propagation and the quality of the sintered ores in the upper part of the bed.

Observation of Behavior of Dioxins and Some Relating Elements in Iron Ore Sintering Bed by Quenching Pot Test

Understanding of the formation mechanism of dioxins in the sintering bed is of importance in developing countermeasures to reduce the emission of dioxins from sintering plants. This research has clarified the behavior and the possible mechanism of dioxin formation and the relation to Cl and Cu components in the sintering bed by conducting a series of quenching tests utilizing sintering pots.The progress of flame front was quenched by terminating the air supply, then introducing N2 gas in the reverse direction when the sintering process progressed halfway through the test pots, specifically to the position of the thermocouples. The primary specimens were obtained from the raw mixture zone situated beneath the combustion interface for chemical analysis.Concentrations of dioxins, Cl and Cu were found at the depth of 10-20 mm beneath the combustion interface in raw mixture zone. This was considered to be the site of dioxin synthesis. Slight increase of dioxins in the wet zone was related to dioxin vaporizing from the site of the synthesis, then to be trapped in this zone. Significant amounts of dioxins escaping into the outlet gas at and after burn through point could be explained by both the releasing of trapped dioxins and the acceleration of the synthesizing process attributable to the increased concentration of Cl and Cu.

Effect of Fuel Characteristics on the Thermal Processes in an Iron Ore Sintering Bed

Coke in an iron ore sintering process is being replaced in part by powdered anthracite; less expensive fuel. In this study, influence of the different fuel characteristics on the thermal condition in the sintering bed has been investigated using a mathematical model. Numerical simulation along with experiments in a lab-scale sintering pot has been performed. The mathematical model is based on the assumption that the sintering bed can be treated as homogeneous medium, through which a reacting flow passes. Temperature distribution and flue gas composition are predicted for various kinds of solid fuel and various particle sizes of anthracite. The simulation results show that propagation of combustion zone is faster in the case of using coke than the case of using anthracite. Results also show that the reactivity of the anthracite can be improved by decreasing the size of fuel particles.

Unsteady one-dimensional model for a bed combustion of solid fuels

A transient one-dimensional combustion model of a solid fuel bed that can be applied to various types of combustors employing the solid bed is suggested. Configuration of solid beds can be characterized by combinations of solid and gas flow directions, ignition methods, and dominant reactions. These features can be reflected numerically to the boundary and initial conditions of the model, while the governing mechanism in each type of bed is similar. The mechanism is expressed as forms of conservation equations for the solid and the gas phase. Solid-gas reactions, gaseous reactions, heat transfer, geometrical changes of the particles, and physical properties are modelled and reflected to each term of the governing equations. Simulation results are shown for two cases: a packed bed combustor and an iron ore sintering bed. Two cases have distinctively different bed configurations and ignition methods. The propagation rates of the combustion zone are quantitatively discussed in terms of the flame propagation speed. Future development of the model is discussed for possible application to more complicated simulation cases.

Mathematical model of thermal processes in an iron ore sintering bed

An unsteady one-dimensional model of an iron ore sintering bed with multiple solid phases was proposed. The proposed model confers a phase on each solid material. The present model was established with a series of conservation equations in the form of a partial differential equation for each solid phase and gas phase. Coke combustion, limestone decomposition, gaseous reaction, heat transfers in/between each phase, and geometric changes of the solid particles are reflected by each term of the governing equations. Simulation results are compared with the limited experimental data set of sintering pot tests. Parametric studies for various initial water contents and coke diameters have also been performed. The simulation results predict the experimental results well and show physically reasonable trends for various parameters.

제선 설비의 열공정 해석 모델링 접근 방법

Thermo-fluid characteristics in coke oven, sintering machine and blast furnace in Iron-making facility are key processes related to the quality and productivity of the pig Iron Solid material in the processes usually forms a bed in a gas flow For simulation of the processes by mathematical model, the solid beds are Idealized to be a continuum and a reacting solid flow In the gas flow Governing equations in the Conn of partial differential equations for the solid material can be constructed based on flus assumption, Iron ore sintering bed is simulated and limited amount of parametric study have been performed. The results have a good agreement with the experimental results or physical phenomena, which shows the validity and applicability of the model.<br/>

Modeling of Combustion and Heat Transfer in an Iron Ore Sintering Bed with Considerations of Multiple Solid Phases

The iron ore sintering was characterized as a relatively uniform process of solid material, coke combustion, various modes of heat transfer, and the complicated physical changes of solid particles. The sintering bed was modeled as an unsteady one-dimensional process of the solid materials with multiple solid phases, which confers a phase on each kind of solid material. Each solid phase had a specific particle size and compositions. Drying, condensation, coke combustion, limestone decomposition, generation of the macroscopic internal pore and shrinking of the bed were considered. Complicated modes of heat transfer including conduction, convection and radiation were considered. Numerical simulations of the condition in the iron ore sintering bed were carried out for various parameters: coke contents and air suction rates, along with some other parameters of the model. Calculation results were compared with the results of the sintering pot test. The temperature profiles and gas compositions showed a good agreement with the experimental data.