Tumble Strength Research Articles

Comparative study of pellets fired in pot grate and grate kiln pilot furnaces

The objective of this research is to study the quality of blast-furnace iron ore pellets with binary basicity 1 fired on a pilot scale using the two main firing processes that are presently in use in the world and comparing them. Currently, the great majority of pellet producers use the traveling grate process because of its higher production capacity. In this study, the physical and chemical qualities of the pellet feed, limestone, anthracite and bentonite were determined and the amount of additives for a blast furnace pellet with the defined basicity was calculated. The physical properties of the green and dried pellets were determined accordingly. Produced pellets, after being fired on a pilot scale using traveling grate and grate kiln, were subjected to chemical analysis and physical testing. No significant difference was observed in the metallurgical quality — that is, reducibility index (RI), reducing disintegration index (RDI) and swelling index (SWI) — of the pellets produced by both processes. However, a comparison of cold physical tests — tumble and cold compression strength — shows improved quality of the pellets fired using the grate kiln process.

Sintering behaviours of iron ore with flue gas circulation

ABSTRACTFlue gas circulation is an important method for energy conservation and pollutant emission reduction in iron ore sintering. In this paper the effects of flue gas recirculation ratio on sintering of different iron ores including haematite, magnetite and limonite were studied by illustrating the variation of sinter bed temperature, atmosphere and mineralisation characteristics of different types of iron ores induced by the circulation. It shows that the proper flue gas circulation ratios for haematite, magnetite and limonite are 37, 30 and 25%, respectively. For magnetite ore, preheating and high consumption of oxygen in combustion zone caused more silicate minerals and less acicular calcium ferrite, thereby lowering sinter tumbler strength. As for haematite ore, the rapid change of temperatures of combustion, melting and solidification zones leads to elevated combustion efficiency and increased formation of acicular calcium ferrite, which enhances the sinter strength. When using limonite ore as the main raw material, high oxygen consumption, lower maximum temperature of sintering bed, higher cooling rate and larger porosity of sinter are observed.

Gasification Reaction Characteristics between Biochar and CO2 as well as the Influence on Sintering Process

For achieving green production of iron ore sintering, it is significant to substitute biochar, which is a clean and renewable energy, for fossil fuels. In this paper, the gasification reaction between CO2 and biochar was investigated. The results showed the initial temperature and the final temperature of the gasification reaction between biochar and CO2 were lower, while the maximum weight loss rate and the biggest heat absorption value were much higher than those of coke breeze, which indicated gasification reaction between the biochar and CO2 occurred rapidly at lower temperature. The gasification activation energy of biochar was 131.10 kJ/mol, which was lower than that of the coke breeze by 56.26 kJ/mol. Therefore, biochar had a higher reactivity and easily reacted with CO2 to generate CO. As a result, when biochar replaced coke powder at equal heat condition in sintering process, the combustion efficiency of fuel decreased and was disadvantage to the mineralization of iron ores at high temperature. With the increase of substitute proportion, the sinter yield, tumble strength, and productivity were decreased. The proportion of biochar replacing coke breeze should not be higher than 40%. By reducing the heat replacement ratio of biochar, the yield and quality of sinter got improved.

Influence of adding Sewage Sludge instead of Coal Powder in the sintering process

Adding Sewage Sludge (SS) in sintering process may provide an alternative for disposal of SS. Therefore, the combustion characteristics of SS and Coal Powder (CP) mixed with the sinter were compared by Thermogravimetric Analysis (TGA) and the effects of adding SS on metallurgical properties of sinter were investigated by sintering pot tests in this paper. TGA results show that the combustion characteristics of SS (5%)-Sinter are better than CP (5%)-Sinter at the same heating rate. Besides, it is beneficial to decrease the ignition temperature by adding more SS into the sinter. The results of sintering pot tests indicate that increasing SS from 0% to 9% in the sintering process can increase the tumbler strength from 62% to 68% and the shatter strength from 63% to 67.4%, and reduce the abrasion index from 4.5% to 3.8%. In addition, the S content in the sinter from sintering pot tests, obtained via X-Ray Fluorescence, decreases from 0.223% to 0.197% and the P content increases from 0.201% to 0.276%; however, these changes are acceptable for the sinter. All these imply that SS is not only a good fuel for sintering, but that adding SS in the sintering process is appropriate as it could improve the metallurgical properties of the sinter to some extent. This will provide a good basis for the practical use of SS in the sintering process of the steel plant.

Mathematical modeling and combustion characteristic evaluation of a flue gas recirculation iron ore sintering process

Flue gas recirculation sintering (FGRS) technology has been applied for two decades with the aim of reducing pollutant emissions. Compared with the conventional sintering (CS), the changes of input gas conditions may influence the bed combustion process greatly. Mathematical models have been developed to predict sintering behavior quantitatively, but few of the previous work focused on FGRS process. In this study, a multiphase theory-based mathematical model is established. This model considers nine kinds of major physicochemical reactions, in which six modes of gaseous reactions make it more comprehensive and accurate to model FGRS process. Heat transfer within/between different solid and gas phases are modeled in better manners. Geometric changes caused by reactive-factors are modeled in simple terms. Sub-models are available to simulate the effects of the temperature, gas supply, composition and content of recirculated gas on combustion characteristics in the sintering bed. Good agreements between simulated and measured results have been obtained from contrasting to six sinter pot tests based on FGRS technology. Four combustion parameters are selected to evaluate quantitatively the advantages and potential problems of FGRS technology. Results show that the flatter maximum temperature (MaxT) profile for FGRS compared with that for CS implies a stronger tumble strength of the sintered ore. The broader MaxT and combustion zone thickness (CZT) curve indicate a higher degree of melt fraction, together with a lower FFS and productivity. To better investigation, further parameter simulation and process optimization of FGRS technology is necessary.

Optimization of iron ore sintering process based on ELM model and multi-criteria evaluation

Optimization of iron ore sintering process is to maximize the productivity and the sinter ore quality while minimizing the energy consumption. However, these economic and technical criteria are sometimes contradictory and the improvement of one criterion generally leads to the deterioration of other criteria. This paper aims to seek the optimal manipulated parameters from the production data by considering this contraction. Several typical groups of manipulated parameters were firstly obtained by clustering the production data, and then one new artificial neural network model--online sequential extreme learning machine (OS-ELM) was established to predict FeO content and tumble strength of sinter ores for each group. Validation results showed that the OS-ELM model established possessed a higher accuracy than conventional BP (back propagation) model. Finally, a multi-criteria evaluation method--VIKOR was applied to obtain a set of compromise optimal solutions. Taking into account both economic and technical criteria, the final solutions acquired are instructive, and the optimal solution can directly reduce fuel consumption by about 0.5 kg per ton sinter ore without degrading sinter ore quality seriously.

Sintering behaviors and consolidation mechanism of high-chromium vanadium and titanium magnetite fines

To achieve high efficiency utilization of high-chromium vanadium–titanium magnetite (V–Ti–Cr) fines, an investigation of V–Ti–Cr fines was conducted using a sinter pot. The chemical composition, particle parameters, and granulation of V–Ti–Cr mixtures were analyzed, and the effects of sintering parameters on the sintering behaviors were investigated. The results indicated that the optimum quicklime dosage, mixture moisture, wetting time, and granulation time for V–Ti–Cr fines are 5wt%, 7.5wt%, 10 min, and 5–8 min, respectively. Meanwhile, the vertical sintering speed, yield, tumbler strength, and productivity gains were shown to be 21.28 mm/min, 60.50wt%, 58.26wt%, and 1.36 t·m−2·h−1, respectively. Furthermore, the consolidation mechanism of V–Ti–Cr fines was clarified, revealing that the consolidation of a V–Ti–Cr sinter requires an approximately 14vol% calcium ferrite liquid-state, an approximately 15vol% silicate liquid-state, a solid-state reaction, and the recrystallization of magnetite. Compared to an ordinary sinter, calcium ferrite content in a V–Ti–Cr sinter is lower, while the perovskite content is higher, possibly resulting in unsatisfactory sinter outcomes.

Multiple Cycle LES Simulations of a Direct Injection Natural Gas Engine

In this work the flow field evolution, mixture formation and combustion process in an engine with methane Direct Injection (DI) is investigated using Large Eddy Simulations. The supersonic methane injection is modeled according to Muller et al. (2013) and combustion by a level set approach. The flame propagation showed to be dependent on the grid resolution. Higher grid resolutions have two opposing effects: first the fraction of unresolved turbulence is reduced, which decrease the flame speed and second flame wrinkling is increased resulting in faster flame propagation. For the observed setup the wrinkling effect was stronger. The average in-cylinder pressure traces as well as the cyclic variability thereof were compared to experimental data and very good agreement was found. During the supersonic gaseous injection the turbulence level in the cylinder is significantly increased, which dissipates quickly and thus has only a minor effect on the flame propagation. The introduced momentum showed a larger impact, since it enhances the tumble motion resulting in increased turbulence levels as the tumble decays shortly before ignition. During DI the cyclic differences in the tumble motion are preserved, but the impact on the average tumble level results in changing relative differences of the cyclic turbulence levels at ignition timing. Thus an injection direction supporting the tumble flows is expected to reduce the Cycle-to-Cycle Variations (CCV), while a reduction of the tumble strength could increase the CCV level. Compared to the fluctuations in the turbulence levels, the cyclic variability of the equivalence ratio at the injection location with DI showed a minor effect on the simulated CCVs.

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), SiO2, 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%.

Vanadium–titanium magnetite ore blend optimization for sinter strength based on iron ore basic sintering characteristics

Vanadium titanium magnetite (V–Ti) ore is one kind of important polymetallic minerals in China and the mainstream route of comprehensive utilization process is blast furnace (BF)→basic oxygen furnace (BOF). V–Ti sinter is one of the main burdens employed for BF and poor tumbler strength (TI) limits its efficiency. In order to optimize the V–Ti blends for sinter TI, the basic sintering characteristics (BSCs) of 5 kinds of V–Ti ores, 2 ordinary ores and 3 groups of optimization V–Ti blends were studied. In addition, the sinter pot tests were conducted to obtain the TI of the produced sinter. The influencing factors on assimilation temperature (AT), the relations between the 4 characteristics of BSCs, and the factors influencing the V–Ti sinter TI were analyzed. The results showed that the BSCs of 5 kinds of V–Ti ores DB, HW, YT, JL and FH were good except liquid phase fluidity characteristic index (LF). The key reason why V–Ti sinter had a poor TI was the low LF, which caused the sinter with a large-pore structure. Therefore, the matching ores for optimization V–Ti blends should have a high LF. In addition, self-strength of the bonding phase (BS) and crystal intensity (CI) had an important impact on TI when the melt formed was sufficient and meanwhile the melt had a high LF. Moreover, the proper AT was the prior factor for the melt generation. In addition, the optimization V–Ti blends had good BSCs. The sinter TI with 7% NF ore addition could meet the production requirements for its TI was higher than 65%. Totally, the method of V–Ti magnetite ore blend optimization for sinter strength based on iron ore basic sintering characteristics was useful.

Effect of Size Distribution of Coke Breeze on Sintering Performance

Coke breeze is added as fuel in sintering process. The size distribution of coke breeze is one of the important factors, which plays an important role in achieving proper sintering process. Therefore, the effects of size distribution of coke breeze on sintering performance are investigated. Experimental results show that, in practical production, we should adjust the size distribution of coke breeze according to the different production strategy (aimed for best strength or highest productivity, or others). For example, aimed for sinter with maximum tumble strength, the size distribution of coke breeze should be 57.20% of −1 mm, 25.63% of 1–3 mm, 11.17% of 3–5 mm, and 6.00% of +5 mm. Then the tumble strength of sinter increases about 1.48%, production yield increases about 1.7%. Similarly, aimed for sinter with maximum productivity, the size distribution of coke breeze should be 47.22% of −1 mm, 23.10% of 1–3 mm, 28.68% of 3–5 mm, and 1.00% of +5 mm. For this case, the productivity increases 0.1 t m−2 h−1, the sintering speed increases 0.7 mm min−1, and the production yield increases 0.4%. There are two reasons for that sinter B (optimized by maximum tumble strength) has better sintering performances, they are as follows: (i) the effect of coke breeze size on the sintering temperature profile and (ii) pores distribution. The research results of present work could give a scientific guide to reasonably utilize fuel resources in practical sintering process.

Laboratory iron ore sintering studies. 3. Critical heat transfer period

The generation of sufficient melt of appropriate properties is essential for the transformation of a blended sinter mix bed into a bed composed of large discrete sinter particles. For a chosen sinter mix, melt properties are determined by the quantity of heat transferred from the moving flame front and the chemical properties of the bed. Temperature-time profiles from embedded thermocouples are used to assess the transferred heat. From considerations of melt initiation and solidification temperatures, a critical sintering reaction area in the profiles is defined. The area is about three times the flame front area as it includes high temperature regions outside the front. It represents the total amount of heat available to the material in the partially molten state. Reasonable correlations are obtained between this area and the tumble strength of the sinter product. Temperature–time profiles are quite variable and strong correlations cannot be expected.

IRON ORE SINTERING PART 2. QUALITY INDICES AND PRODUCTIVITY

Sinter plants have to process mineral mixes in order to obtain sinter of a suitable composition and quality to be loaded into the blast furnace. For this purpose a series of parameters need to be taken into account, such as the nature and composition of each component of the mineral mix and the conditions of the manufacturing process. Sinter is subjected to in-depth characterisation in terms of chemical and granulometric analysis, determination of the mineral phases in its structure and of quality indices such as reducibility, low temperature degradation, reduction degradation, and tumbler strength. It is also important to operate sinter plants with high productivity and to ensure a uniform sinter composition and quality so as to facilitate the steady state operation of the blast furnace.

Changing Bed Bulk Density and other Process Conditions during Iron Ore Sintering

Iron ore sintering blends in the Asia-Pacific contain significant levels of Australian ores which are lower in bulk density compared to Brazilian ores. This study explores the impact of further decreasing the bulk density of a fairly typical ore blend. This was done by introducing small amounts of a very porous ore into the blend. Measured decreases in bulk density were up to 3%. All the sinter quality parameters could be maintained or improved without the need to increase coke rate. Changes in sinter density results were not significant, indicating that the changes in bed bulk density did not have a significant effect on sinter porosity. The study was then extended to include a comparable blend and two hematite blends of higher bulk density. Decreasing green bed bulk density, bed shrinkage and sinter density did not have a detrimental effect on sinter tumble strength. The associated increase in porosity with the measured changes in sinter density is estimated to be up to 10%. Results showed that sinter density values obtained for the low bulk density mixes at increased coke addition were still lower than equivalent values for the hematite mixes. As expected flame front speed was dependent on post-ignition airflow rate and both these parameters influence sinter strength. Many blends studied have binders and results indicated that their inclusion into sinter mixes gave increased post-ignition airflow values.

Simulation of the combined effect of production factors on metallurgical sinter mechanical strength

Problems are considered for choice of properties for evaluating sinter quality, and also choice of structure and creation of a simulation model for calculating mechanical cold (tumble) strength index using a selection of models describing the effect of individual features of the process.

Influence of O2 Content in Circulating Flue Gas on Iron Ore Sintering

Circulating flue gas can reduce the emission of flue gas, and furthermore, it can reuse the waste heat effectively in the sintering process. Compared with conventional sintering, O2 that gets through the sintering bed decreases because of substituting circulating gas for air. The influences of O2 content on sintering process are studied through simulating the flue gas circulation sintering with artificial gas. It shows that, with the reducing of O2 content in circulating gas, the combustion speed of fuel decreases and incomplete combustion degree increases, which makes the flame front fall behind the heat front and reduces the heat utilization efficiency of fuel. The ultimate result is that the temperature of sintering bed decreases and the liquid phase reduces. In addition, the reducing atmosphere is strengthened because of flue gas circulation, which makes the magnetite increase yet calcium ferrite reduce gradually. Because the content of calcium ferrite with good strength reduces, the sinter yield and tumble strength decrease. To ensure the sinter index, the favorable O2 content of circulating flue gas is no less than 15%.

Lower fuel consumption model and air-flow segregation feeding system for sintering

In order to utilize the spontaneous accumulation of heat (SAH) reasonably and obtain the high quality sinter with low energy consumption, a lower fuel consumption modeling based on raw materials of a certain steel works was built. An air-flow segregation feeding (ASF) experimental equipment was designed to simulate strand feeding process and calculate the lower fuel consumption quantity. Compared with baseline test, the ASF experimental equipment was adopted. The results of sinter pot tests show that the solid fuel consumption is lower than that in baseline test, which is decreased by 5.8%. Meanwhile, other sinter indexes, such as pan yeild, tumbler strength and strand productivity are improved. The mineralogical examination indicates that the mineral compositions and micostructures are improved in sinter.

Fundamental Research of Sintering Process on Improving the Tumbler Strength of Low SiO<sub>2</sub> Sinter

In the laboratory condition, a series of experiments were carried out in a sintering pot in order to improve the tumbler strength of low SiO2 sinter. The results shows that the content of SiO2 is decreased from 4.4wt% to 3.9wt% when the ratio of serpentine is decreased from 2.2wt% to 1.0wt%, as a result, the tumbler strength and the reduction degradation index of sinter all fall down. When the ratio of serpentine is further decreased, all kinds of sintering indexes fall down rapidly. If the basicity of sinter is increased from 1.75 to 1.85, and 5wt% iron concentrate is added in sintering mixture, the content of SiO2 can be decreased to 3.9wt%~4.0wt%, meanwhile, the tumbler strength of sinter is the same as that of the reference sinter with 4.4wt% SiO2. When Niuman iron ore, Hainan iron ore and Hamosili iron ore are used as the hearth layer instead of sinter, and the basicity of sinter is increased to 1.85, the tumbler strength of sinter with 3.9wt%~4.0wt%SiO2 is the same as that of the reference sinter with 4.4wt% SiO2.

Sintering Pot Test on Improving TiO<sub>2</sub>-Containing Ore’s Allocated Proportion

The effects of different TiO2-containing ore’s allocated proportion on quality, mineral structure and sintering process of Xuan steel sinter were studied in this paper. The results showed that the increasing of the TiO2-containing ore’s allocated proportion was disadvantageous to the sinter sample’s anti-compressive strength, and the yield and tumbler strength of sinter were decreased although the velocity of sintering was improved. The tumbler strength decreased from 68.67% to 63.33%, and the main reason is that the content of perovskite increases and the content of calcium ferrite decreases with the increasing of TiO2-content in the sinter. The TiO2-content in the sinter should be controlled less than 1.3% considering effect of TiO2-content on sintering process, burdening and iron making of blast furnace in all.

Experimental Study on Lump Iron Ores as Sintering Hearth Layer

In the laboratory condition, a series of experiments were carried out in a sintering pot when Hamersley, Niuman and Hainan lump iron ore were used as sintering hearth layer instead of the recycled sinter. The results show that the sintering productivity is increased by 1.3%, 2.6 % and 13.2 %, and the fuel consumption is decreased by 4.4%, 2.0 % and 6.6 %, respectively. Meanwhile, the tumbler strength and the reduction disintegration index of sinter are also improved. During sintering experiments, the crack of two lump iron ores used as hearth layer didn’t happen. Through using the new technology, the combined water and the sulfur impurity were effectively decreased in the sintering products. Furthermore, the micro-porosity of the sintering products was found to increase, which will contribute to improve the metallurgical properties of sinter.