A pilot-scale study of selective desulfurization via urea addition in iron ore sintering

The iron ore sintering process is the main source of SO_2 emissions in the iron and steel industry. In our previous research, we proposed a novel technology for reducing SO_2 emissions in the flue gas in the iron ore sintering process by adding urea at a given distance from the sintering grate bar. In this paper, a pilot-scale experiment was carried out in a commercial sintering plant. The results showed that, compared to the SO_2 concentration in flue gas without urea addition, the SO_2 concentration decreased substantially from 694.2 to 108.0 mg/m^3 when 0.10wt% urea was added. NH_3 decomposed by urea reacted with SO_2 to produce（NH_4）_2SO_4, decreasing the SO_2 concentration in the flue gas.

Influencing factor of sinter body strength and its effects on iron ore sintering indexes

Sinter body strength, which reflects the strength of sinter, plays an important role in the improvement of sinter. In this study, the sinter body strengths of iron ores were measured using a microsintering method. The relationship between the chemical composition and sinter body strength was discussed. Moreover, sinter-pot tests were performed. The effects of sinter body strength on the sintering indexes were then elucidated, and the bottom limit of sinter body strength of blending ores was confirmed. In the results, the compressive strengths（CSs） of iron ores are observed to decrease with the increasing of the contents of loss on ignition（LOI）, SiO 2, and Al2O3; however, LOI of less than 3wt% does not substantially influence the CSs of fine ores. In the case of similar mineral composition, the porosity, in particular, the ratio between the number of large pores and the total number of pores, strongly influences the sinter body strength. With an increase of the blending-ore CSs used in sinter-pot tests, the yield, productivity, and tumbler strength increase, and the solid fuel consumption decreases. The CSs of the blending ores only slightly affect the sintering time. The CS bottom limit of the blending ores is 310 N. When the CSs of the blending ores increase by 10%, the yield, productivity, and tumbler index increase by 1.9%, 2.8%, and 2.0%, respectively, and the solid fuel consumption decreases by 1.9%.

Influence of coke rate on thermal treatment of waste selective catalytic reduction(SCR)catalyst during iron ore sintering

Waste selective catalytic reduction(SCR)catalyst as a hazardous waste has a significant impact on the environment and human health.In present study,a novel technology for thermal treatment of waste SCR catalyst was proposed by adding it to sinter mix for iron ore sintering.The influences of coke rate on the flame front propagation,sinter microstructure,and sinter quality during sintering co-processing the waste SCR catalyst process were studied.In situ tests results indicated the maximum sintering bed temperature increased at higher coke rate,indicating more liquid phase generated and higher airflow resistance.The sintering time was longer and the calculated flame front speed dropped at higher coke rate.Sinter microstructure results found the coalescence and reshaping of bubbles were more fully with increasing coke rate.The porosity dropped from 35.28%to 25.66%,the pore average diameter of large pores decreased from 383.76μm to 311.43μm.With increasing coke rate,the sinter indexes of tumbler index,productivity,and yield,increased from 33.2%,9.2 t·m^(-2)·d^(-1),28.9%to 58.0%,36.0 t·m^(-2)·d^(-1),68.9%,respectively.Finally,a comprehensive index was introduced to systematically assess the influence of coke rate on sinter quality,which rose from 100 to 200 when coke rate was increased from 3.5%(mass)to 5.5%(mass).

Present situation and development of saving energy and reducing emission technology in iron ore sintering process

The energy consumption of iron ore sintering process is about 10%- 15%of the total of iron and steel industry.Therefore,it is of great significance to take effective measures to reduce the energy consumption in the iron ore sintering process to reduce the costs of sintering product and cut down the emissions of harmful gases,such as CO_2 and SO_2.In this study,the technology development of saving energy and reducing emission in iron ore sintering process was reviewed and discussed;some new directions and measures of saving energy were presented for the sintering process in the future.

Combustion mechanism of benzene in iron ore sintering process:experimental and simulation

Benzene is a typical component of volatile organic compounds(VOCs)in the iron ore sintering flue gas.The combustion behavior of benzene directly affects the emission of VOCs in iron ore sintering process.The effects of temperature,benzene,and oxygen concentrations on the conversion ratio of benzene were investigated by experiments and numerical simulation.The experiments were carried out in a tube reactor at temperatures of 773-1098 K,benzene concentrations of 0.01-0.03 vol.%,and oxygen concentrations of 10-21 vol.%.The numerical simulation was performed with the plug flow model in the CHEMKIN program based on a kinetic model that consists of 132 chemical species and 772 elementary step-like reactions.The experimental results reveal that increasing the temperature and benzene concentration could signifi-cantly promote benzene combustion.It is attributed to the increase in the reaction rates of all steps in the pathway for forming CO_(2)and H_(2)O.In addition,due to the large equivalent ratio of oxygen to benzene,the conversion ratio of benzene remained constant at different oxygen concentrations.The simulation results were in good agreement with the experimental results and indicated that six elementary reactions dominated the formations of CO_(2)and H_(2)O.The oxidations of C_(6)H_(5)O,CO,and C_(5)H_(4)O intermediates to CO_(2)were the limiting steps in the reaction pathways.

Investigation on the evolution characteristics of bed porous structure during iron ore sintering

To better understand the evolution characteristics of bed porous structure during iron ore sintering,X-ray computed tomography scanning technology was used to analyze the pore parameters in different areas of the sintering bed.A pore skeleton structure model was established to study the characteristics of the airflow channels in different zones.The absolute permeability of different areas was calculated through simulation,and the corresponding streamline and pressure drop distribution were analyzed.The results show that the porosity of raw material zone,high-temperature zone,and sintered zone increases gradually,which are 37.69%,46.41%,and 55.57%,respectively.The absolute permeability calculation results of the raw material zone and sintered zones are 792.49μm^(2) and 20560.80μm^(2),while the tortuosity is 1.77 and 1.45,respectively.Compared with the raw material zone,the flow streamline in the sintered zone is thicker and denser,the airflow resistance and the pressure drop are minor.

Application status and comparison of dioxin removal technologies for iron ore sintering process

The emission of dioxins from the iron ore sintering process is the largest emission source of dioxins, and the reduction in dioxin emission from the iron ore sintering process to the environment is increasingly important. Three approaches to control the emission of dioxins were reviewed： source control, process control, and terminal control. Among them, two terminal control technologies, activated carbon adsorption and selective reduction technology, were discussed in detail. Following a comparison of the reduction technologies, the terminal control method was indicated as the key technology to achieve good control of dioxins during the sintering process. For the technical characteristics of the sintering process and flue gas, multiple methods should be collectively considered, and the most suitable method may be addition of inhibitors ＋ ultra-clean dust collection （electrostatic precipitation/bag filter） ＋ desulphurization ＋ selective catalytic reduction to sufficiently remove multiple pollutants, which provides a direction for the cooperative disposal of flue gas pollutants in future.

Effect of Ca-Fe oxides additives on NOx reduction in iron ore sintering

As the emission control regulations get stricter,the NO;reduction in the sintering process becomes an important environmental concern owing to its role in the formation of photochemical smog and acid rain.The NOxemissions from the sintering machine account for 48% of total amount from the iron and steel industry.Thus,it is essential to reduce NO;emissions from the sintering machine,for the achievement of clean production of sinter.Ca-Fe oxides,serving as the main binding phase in the sinter,are therefore used as additives into the sintering mixture to reduce NOxemissions.The results show that the NO;reduction ratio achieves 27.76% with 8% Ca-Fe oxides additives since the Ca-Fe oxides can advance the ignition and inhibit the nitrogen oxidation compared with the conventional condition.Meanwhile,the existence of Ca-Fe oxides was beneficial to the sinter quality since they were typical low melting point compounds.The optimal mass fraction of Ca-Fe oxides additives should be less than 8%since the permeability of sintering bed was significantly decreased with a further increase of the Ca-Fe oxides fines,inhibiting the mineralization reaction of sintering mixture.Additionally,the appropriate particle size can be obtained when mixing an equal amount of Ca-Fe oxides additives of-0.5 mm and 0.5-3.0 mm in size.

Gas-phase and particle-phase PCDD/F congener distributions in the flue gas from an iron ore sintering plant

The activated carbon injection-circulating fluidized bed（ACI-CFB）-bag filter coupling technique was studied in an iron ore sintering plant. For comparison, the removal efficiencies under the conditions without or with ACI technology were both evaluated. It was found that the polychlorinated dibenzo-p-dioxins and dibenzofuran（PCDD/F） removal efficiency for total international toxic equivalence quantity（I-TEQ） concentration was improved from 91.61% to 97.36% when ACI was employed, revealing that ACI was very conducive to further controlling the PCDD/F emissions. Detailed congener distributions of PCDD/Fs in the gas-phase and particle-phase of the Inlet and Outlet samples were determined. Additionally, the PCDD/F distribution for the Fly ash-with ACI sample of was also studied.

Three-dimensional structure and micro-mechanical properties of iron ore sinter

A new analysis method based on serial sectioning and three-dimensional（3 D）reconstruction was developed to characterize the mineral microstructure of iron ore sinter.Through the 3 Dreconstruction of two types of iron ore sinters,the morphology and distribution of minerals in three-dimensional space were analyzed,and the volume fraction of minerals in a 3 Dimage was calculated based on their pixel points.In addition,the microhardness of minerals was measured with a Vickers hardness tester.Notably,different mineral compositions and distributions are obtained in these two sinters.The calcium ferrite in Sinter 1 is dendritic with many interconnected pores,and these grains are crisscrossed and interwoven;the calcium ferrite in Sinter 2 is strip shaped and interweaves with magnetite,silicate and columnar pores.The calculated mineral contents based on a two-dimensional region are clearly different among various layers.Quantitative analysis shows that Sinter 1 contains a greater amount of calcium ferrite and hematite,whereas Sinter 2 contains more magnetite and silicate.The microhardness of minerals from highest to lowest is hematite,calcium ferrite,magnetite and silicate.Thus,Sinter 1 has a greater tumbler strength than Sinter 2.

An efficient method for iron ore sintering with high-bed layer:double-layer sintering

Poor permeability and low sintering productivity restrict the development of high-bed sintering.An efficient method of the double-layer sintering process(DLSP)was proposed to achieve high-bed sintering and solve the aforementioned problems.Theoretical calculation and sintering pot experiments were implemented to investigate the double-layer sintering process.Traditional sintering process and DLSP were compared in terms of sintering indices,metallurgical properties and morphology characterization.Under the condition of traditional sintering process,DLSP successfully realized fast velocity and highly productive sintering of 1000-mm high bed.After the sintering bed is charged and ignited twice,the air permeability of the bed has been greatly improved.Sintering time is shortened significantly by simultaneous sintering of the upper and lower feed layers.Under the condition of bed height proportion of 350/650 mm and pre-sintering time of 20 min,the yield,tumbler strength,productivity and solid fuel consumption are 69.96%,65.87%,1.71 t(m^(2)h)^(-1)and 56.71 kg/t,respectively.Magnetite,hematite,calcium ferrite and complex calcium ferrite are the main phases of DLSP products.The metallurgical properties of DSLP products meet the requirement of ironmaking.It indicates that DLSP is an effective method to solve the disadvantages of bad permeability and low sintering productivity in high-bed sintering.

Research progress on multiscale structural characteristics and characterization methods of iron ore sinter

At present,blast furnace ironmaking is still the main process for producing molten iron,and sinters are the main raw material for blast furnace ironmaking.A sinter with good metallurgical performance can not only ensure smooth operation of the blast furnace but also reduce the blast furnace fuel ratio and increase the molten iron production.Structure is the most important factor affecting the metallurgical properties of the sinter.Thus,the research progress of sinter pore and mineral phase structures was reviewed and the mechanism by which they influence sinter properties was expounded.Multiscale characterization methods for the sinter and their advantages and disadvantages were introduced,and the future research direction of sinter was discussed.

Ore-blending optimization for Canadian iron concentrate during iron ore sintering based on high-temperature characteristics of fines and nuclei

Canadian iron concentrate(CIC)can elevate the ferrous grade and lower the contents of gangue components and harmful elements in the sinter.To understand high-temperature characteristics of CIC and typical iron ore,the formation of the melt was calculated mainly through FactSage 7.2,and melt fluidity(MF)test for iron ore fines and penetration characteristic test of CIC melt into iron ore nuclei were carried out via micro-sintering method.The results show that hematite,calcium ferrites,dicalcium silicate,and magnetite take part in the formation of the melt in N2.The formation temperature of the liquid for CIC is higher than that for hematite/limonite ore.The MF of CIC is lower than that of hematite/limonite ore fines.The MF of hematite/limonite ore fines is dominated by the liquid amount and melt viscosity.The penetration depth(PD)of CIC melt into limonite ore nuclei is smaller than that into hematite ore nuclei.The PD is related to the reaction ability of the nuclei with the melt.Based on above results,sinter pot tests were conducted.The result shows that in the base ore blends including two hematite ores and two limonite ores,adding CIC deteriorates the sintering indexes.Increasing the proportion of high-MF and small-PD hematite ore can significantly improve the sintering indexes.10 mass%is a suit-able proportion for adding CIC in ore blends.

Evaluation of granule structure and strength properties of green packed beds in iron ore sintering using high-resolution X-ray tomography and uniaxial compression testing

The strength properties of green sinter beds,including the Young’s modulus and maximum bed strain,were evaluated using uniaxial compression tests.The green-sinter-bed samples were scanned using X-ray computed tomography(XCT),and the geometry characteristics of the granules were quantified by XCT image analysis.The orthogonal array method was applied to determine the concomitant effects of the moisture,hydrated lime,and concentrate contents on the bed strength characteristics.Less bed strain was observed when the granules had a thin adhering layer and increased interlock contacts,which had a great capacity to resist the applied load collectively.The optimal combination for decreasing the bed maximum strain was 5.8%moisture,2%hydrated lime,and 0%concentrate.The moisture and concentrate contents were the most significant factors determining the green bed strength.Increasing the moisture and concentrate contents produced granules with a thicker and more deformable adhering layer,resulting in a more compact bed.The addition of hydrated lime inhibited rearrangement,deformation,and fracture of the granules in green sinter bed during compression.

Model of Iron Ore Sintering Based on Melt and Mineral Formation

A model of iron ore sintering was built with consideration of fuel combustion, catalysis of sinter mixture as well as formation of melt and mineral, which was verified via sintering pot tests and showed a good fit to the experi- mental results. The effect of bed depth on temperature was reflected by the residence time in high-temperature zone, rather than the top value of the temperature, which was weakened by melt formation as well as hematite decomposi- tion. Moreover, the effect of bed depth, fuel content and distribution on sintering process was different, which was reflected by temperature profiles and the rule of calcium ferrite formation. The formation of melt as well as magnetite was a process which was decided by kinetic factors, while the formation of calcium ferrite was related to fuel blend- ing conditions, which is determined by thermodynamics when the fuel ratio inside sinter granules is low or fuel con- tent is high, otherwise, it is determined by kinetics.

Detection of the assimilation characteristics of iron ores: Dynamic resistance measurements

Resistance in iron ore undergoes a sharp change of up to several orders of magnitude when the sintered solid phase changes to liquid phase.In view of the insufficiency of existing assimilation detection methods,a timing-of-assimilation reaction is proposed,which was judged by continuously detecting the changes in resistance at the reaction interface.Effects of pole position and additional amounts of iron ore on assimilation reaction timing were investigated.The results showed that the suitable depth of pole groove was about 2 mm,and there was no obvious impact when the distance of the poles changed from 4 to 6 mm,or the amount of iron ore changed from 0.4 to 0.6 g.The temperature of sudden change of resistance in the temperature-resistant image was considered to be the lowest assimilation temperature of iron ore.The accuracy of this resistance method was clarified by X-ray diffraction,optical microscope,and scanning electron microscope/energy dispersive spectrometer(SEM/EDS)analyses.

Reduction of NO_(x)emission based on optimized proportions of mill scale and coke breeze in sintering process

Reducing NO_(x) emission of iron ore sintering process in a cost effective manner is a challenge for the iron and steel industry at present.Effects of the proportion of mill scale and coke breeze on the NO_(x) emission,strength of sinter,and sinter indexes were studied by com-bustion and sinter pot tests.Results showed that the peak value of NO concentration,total of NO emission,and fuel-N conversion rate gradu-ally decreased as the proportions of the mill scale increased because NO was reduced to N_(2) by Fe_(3)O_(4),FeO,and Fe in the mill scale.The strength of sinter reached the highest value at 8.0wt%mill scale due to the formation of minerals with low melting point.The fuel-N conver-sion rate slightly fluctuated and total NO_(x) emission significantly decreased with the decreased proportions of coke breeze because CO forma-tion and content of N element in the sintered mixture decreased.However,the sinter strength also decreased due to the decrease in the amount of the melting minerals.Furthermore,results of the sinter pot tests indicated that NO_(x) emission decreased.The sinter indexes performed well when the proportions of mill scale and coke breeze were 8.0wt%and 3.70wt%respectively in the sintered mixture.

Effects of Temperature and Atmosphere on Sintering Process of Iron Ores

The relationship of time to minerals composition in sinters is investigated by mineragraphy are claritied observation and component analysis, and the effects of temperature and atmosphere on mineralization process. Results are obtained as follows. The initial melt forms below the eutectic temperature of CaO·Fe2O3 and CaO·2Fe2O3, which is complex substance containing Ca, Fe, Si and Al, rather than the binary calcium ferrite melt. Minerals composition of binding phase is related to local content of silica in melt, which is influenced by temperature. Appearance of the melt promotes the transition from hematite to magnetite, which then alters the mechanism of calcium ferrite formation. Before the formation of magnetite, the contents of Fe and Ca within the multiple calcium ferrite decrease with temperature, but in the case of magnetite presence, the content of Fe increases solely with increase of temperature and decrease of oxygen potential. Temperature and atmosphere determine minerals composition together, and bring influence on sintering process in different ways. It can be deduced that temperature affects kinetics of the mineralization process, but atmosphere just plays a role in thermodynamics.

Strengthening granulation behavior of specularite concentrates based on matching of characteristics of iron ores in sintering process

Specularite concentrates have advantages of high ferrous grade, less harmful impurities and low price. However, the small size and poor granulation behavior of specularite concentrates consequently deteriorate the permeability of sinter bed and reduce the productivity of sinter, resulting in un-effective utilization in sintering process. The granulation experiments were carried out when specularite concentrates matched with five kinds of fine or coarse ores, and the effects of surface property and wettability of fine or coarse ores on granulation behavior of specularite concentrates were investigated. Then, the optimized ore blending recipes were proposed to strengthen the granulation behavior of specularite concentrates. The results indicated that the growth index increased with increasing the specific surface area of fine ores and had a positive linear correlation with the circularity degree of coarse ores, whereas negative correlations exist between the growth index and the contact angle of fine or coarse ores. Compared with the concentrates, the growth index increased by approximately 22% scheme of blended ores containing 15 mass% specularite in the case of using Ore-A and Ore-E with greater surface property and higher wettability to replace all of Ore-B and half of Ore-D, respectively. Furthermore, the vertical sintering speed and the productivity of sinter improved by approximately 23% and 20%, respectively.

Influence of oxygen-rich hot air composite gas medium on sintering performance and function mechanism

Hot air sintering technology is used to improve the quality and production efficiency of sintered ore.However,the current thick layer condition highlights the disadvantage of the low oxygen potential of the hot air sintering layer.Therefore,it is considered to use oxygen enrichment sintering to improve the environment of hot air sintering.Traditional sintering,hot air sintering,and oxygen-rich hot air sintering were compared through sintering cup experiments,and the influence of hot air and oxygen-rich hot air on sintering indexes was clarified.Hot air reduced the vertical sintering velocity,while improved the yield and tumbler index.Oxygen-rich hot air sintering contributed to improving the vertical sintering velocity while ensuring the quality of sintered ore,thus comprehensively improving production efficiency.Under the action of hot air,the highest temperature of the sintering layer increased and the high-temperature holding time was prolonged.After oxygen enrichment,the combustion efficiency of fuels in the upper layer of materials was promoted,which optimized heat distribution in the middle and lower layers of materials and increased the content of calcium ferrite in the sintered ore,thus strengthening the sintering process.