Influence of structure of burned pellets on strength and destruction in static compression tests

The burned pellets must retain the strength from the time they come off the roasting machine until they are loaded into the blast furnace. One indicator of the strength of burned pellets is the compressive strength, i.e., the maximum applied load at which the iron-ore pellet completely collapses. The paper studies the character of destruction of burned iron-ore titanomagnetite pellets of fraction 10 - 16 mm in the static compression test according to the Russian State Standard 24765-81. It is shown that the main type of destruction during the test is the emergence and development of plane cracks passing through the center of the magnetite core, where the maximum radial tensile stresses act or in the immediate vicinity. In some cases, the trajectory of one of the destructive cracks deviates from the above plane and envelopes the magnetite core. Obviously, this is due to the presence of a second area of tensile stress concentration at the boundary of the magnetite core and the hematite shell, formed during cooling of the pellets, due to differences in their mechanical and thermophysical properties. As a result, the final structure of pellets is characterized by the presence of two zones -peripheral hematite and central magnetite. The role of the relative size of the magnetite core on the compressive strength of burned pellets has been determined. It was established that the strength characteristics of the pellet increase with a decrease in relative size of the magnetite core. During the process of magnetite complete oxidation (when the whole volume of the pellet consists of hematite), the maximum level of the pellets compressive strength can be: the maximum destructive force - 3300 N, destructive energy - 0.55 J, mass destructive energy - 0.18 J/g.

PRODUCTION OF IRON ORE PELLETS BY UTILIZATION OF SUNFLOWER HUSKS

Steel production is the most dynamic industry and one of the key sectors for the development of the global economy. The growing production of iron ore increases the need for its beneficiation and granulating for subsequent use in the production of iron and steel. As a result, the number of CO2 emissions and harmful substances increases, which negatively affects both society and the environment. It is important to study the use of biomass for the production of iron ore pellets. Lignocellulosic biomass is a renewable and sustainable source of heat and energy that can mitigate climate change. The efficiency of using sunflower husks on the combined machine “straight grate - rotary kiln - annular cooler” to partially replace natural gas in the production of iron ore pellets has been studied. The influences of alternative fuel use on technological indicators of the process and quality of iron ore pellets have been analyzed. It was found that the combustion of sunflower husks generates enough heat to obtain iron ore pellets with good strength. The main indicators of the quality of iron ore pellets remain at the same level as the iron ore pellet quality when using natural gas.

Estimation of Iron Ore Pellet Softening in a Blast Furnace with Computational Thermodynamics

In blast furnaces it is desirable for the burden to hold a lumpy packed structure at as high a temperature as possible. The computational thermodynamic software FactSage (version 7.2, Thermfact/CRCT, Montreal, Canada and GTT-Technologies, Aachen, Germany) was used here to study the softening behavior of blast furnace pellets. The effects of the main slag-forming components (SiO2, MgO, CaO and Al2O3) on liquid formation were estimated by altering the chemical composition of a commercial acid pellet. The phase equilibria for five-component FeO-SiO2-CaO-MgO-Al2O3 systems with constant contents for three slag-forming components were computed case by case and the results were used to estimate the formation of liquid phases. The main findings of this work suggested several practical means for the postponement of liquid formation at higher temperatures: (1) reducing the SiO2 content; (2) increasing the MgO content; (3) reducing the Al2O3 content; and (4) choosing suitable CaO contents for the pellets. Additionally, the olivine phase (mainly the fayalitic type) and its dissolution into the slag determined the amount of the first-formed slag, which formed quickly after the onset of softening. This had an important effect on the acid pellets, in which the amount of the first-formed slag varied between 10 and 40 wt.%, depending on the pellets’ SiO2 content.

Metallurgical properties of iron ore pellet when using lime powder instead of bentonite

This paper reported effects of lime powder and bentonite binder using in iron ore pelletization on metallurgical properties of pellets as green strength, compressive strength and degree of reduction. The investigated pellets contain 0, 1 and 2 mass % of lime powder and 2, 1 and 0 mass % of bentonite, respectively. Green balls were dried (105 °c for 24 hours) then heated at 1200 °c for 30 minutes. The reductibility of fired pellets was examined at different temperatures of 900, 1000 and 1100 °c with various holding time (45, 90 and 120 minutes). The results showed that the combination of 1 mass % of bentonite and 1 mass % of lime powder in the pellet gave the most apropriate metallurgical properties of pellets as green strength, porosity and degree of reduction. This material charging ratio can be recommended for application in manufacturing of the pellet.

Use of Lebedinsky Mining and Processing Works Overburden Chalkstone for Iron-Ore Pellet Fluxing

Mine rocks generated abundantly in the course of iron-ore deposit development and containing high quality overburden chalkstone are mainly stored in dump pits. This relates to the Lebedinsky Mining and Processing Works as well. This results in certain environmental issues. Therefore the work provides the investigation results in some measure allowing the defined problem solution through complete replacement of limestone used for iron-ore pellet fluxing by the overburden chalkstone. This required a whole set of experiments. Derivatographic investigation was carried out on the overburden chalkstone samples of the Lebedisky Mining and Processing Works and allowed defining of the studied sample temperature and heating time impact on production of chalkstone with varying decarbonization process extent. Activity of the lime produced from the chalkstone was evaluated through determination of the total content of active calcium and magnesium oxides in it. In the course of the experiments the temperature and time impact on the liming process was defined. To justify the potential of the overburden chalkstone use as an additive for iron-ore pellet fluxing and their production with sufficiently high strength properties ensured, as well as of the complete replacement of the limestone used for these purposes, the experiments with the briquettes were carried out. At that the briquette composition complied with that of the fluxed iron-ore pellets. The briquette strength properties with chalkstone additives versus the firing temperature and degree were studies, as well as physicochemical processes occurring in the samples at their heat treatment. As a result of the investigation it was determined that the chalkstone additive use in the pellet fluxing contributes to their significant strength increase. The obtained results are of certain interest for the specialists dealing with iron ore material preparation for metallurgical conversion and allow development of pellet heat treatment conditions ensuring their high metallurgical performance.

Analysis of the factors affecting the iron ore pellet FEO index using data mining technique

One of the most critical factors affecting iron pellet quality is the reduction in FeO (Iron Oxide) index in the final product. This study aims to predict factors affecting the FeO (Iron Oxide) of iron pellets and find out the contribution of each factor to reduce the pellets FeO (the ideal amount is between 0.4 to 0.6) using data mining tech­niques. When the FeO index's value is in the optimal range, the quality and price of pellets are higher. The data used in this study was collected from the pelletizing plant of Gol-E-Gohar in Sirjan, Iran, and the decision tree and regression algorithms are used in this analysis. Forty-five factors that can affect the FeO (Iron Oxide) index of the final product were studied, showing that the Magnesium Oxide and Airflow of the inlet fan of the indurating machine had the greatest impact on the FeO (Iron Oxide) of iron pellets.