Influences of carbonaceous materials on the quality of hematite ore pellets

Pellet in duration at high temperature for its hardening is an energy intensive process. Especially, for hematite ore pellet a very high in duration temperature (say 1325oC) is required to obtain the sufficient strength due to the absence of exothermic heat unlike magnetite ore. Therefore, in order to reduce the external energy requirement carbonaceous materials are added to supply in-situ energy on in duration. In the present study, different carbonaceous materials viz. Jhama coal, blast furnace flue dust, and coke powder have been added in pelletization of hematite ore fines to reduce the external energy requirement and to utilize the waste carbonaceous materials. It has been observed that green pellets’ properties are within acceptable limits which are not affected by the presence of the carbonaceous material. The cold compressive strength (CCS) of pellets increases with increasing in duration temperature. The furnace-cooled pellets show more strength than air-cooling. Blast Furnace flue dust added pellets show highest CCS among other carbonaceous material added in pellets which is 2515 N /pellet at 1280◦C. RI and RDI has also been influenced by the addition of other carbonaceous materials

Ash analyses of bio‑coal briquettes produced using blended binder

The behaviour of ash of fuel affects its thermal efficiency when in use. The ash analyses of bio-coal briquettes developed from lean grade coal and torrefied woody biomass have received limited intensive study. Therefore, the present study aims at analysing the ashes of briquette made from lean grade coal and torrefied woody biomass using blended coal tar pitch and molasses as the binder. Bio-coal briquettes were produced from coal and torrefied biomass in various hybrid ratios. Ashing of various briquettes was done in a muffle furnace at 850 °C for 3 h. Mineral phases of the ash were identified using an X-ray Diffractometer (XRD), while the mineral oxides were obtained using an X-ray Fluorescence Spectrometer. The AFT700 Furnace was used with its AFT700 software to evaluate the ash fusion temperatures of the ashes. The XRD patterns look similar, and quartz was found to be the dominant mineral phase present in the raw coal and bio-coal briquettes. The SiO2 (57–58%), Al2O3 (19–21%), and Fe2O3 (8–9%) were the major oxides observed in the ashes. The final fusion temperatures of the ashes range from 1300–1350 °C. The compositions of the ashes of the bio-coal briquettes are classifed as detrital minerals. It was concluded that the addition of torrefied biomass (≤10%)and blended binder (≤ 15%) to coal gave a negligible impact on the ashes of the resultant biocoal briquettes

Mitochondria-localized AMPK responds to local energetics and contributes to exercise and energetic stress-induced mitophagy

Mitochondria form a complex, interconnected reticulum that is maintained through coordination among biogenesis, dynamic fission, and fusion and mitophagy, which are initiated in response to various cues to maintain energetic homeostasis. These cellular events, which make up mitochondrial quality control, act with remarkable spatial precision, but what governs such spatial specificity is poorly understood. Herein, we demonstrate that specific isoforms of the cellular bioenergetic sensor, 5′ AMP-activated protein kinase (AMPKα1/α2/β2/γ1), are localized on the outer mitochondrial membrane, referred to as mitoAMPK, in various tissues in mice and humans. Activation of mitoAMPK varies across the reticulum in response to energetic stress, and inhibition of mitoAMPK activity attenuates exercise-induced mitophagy in skeletal muscle in vivo. Discovery of a mitochondrial pool of AMPK and its local importance for mitochondrial quality control underscores the complexity of sensing cellular energetics in vivo that has implications for targeting mitochondrial energetics for disease treatment

Effect of Heating Rate on Decomposition Temperature of Goethite Ore

The decomposition temperature is available for pure, synthetic, stoichiometric goethite and a particular type of goethite ore. The decomposition temperature depends on the size of grains, temperature, pressure, heating rate and so on. The decomposition temperature of goethite decides the drying and preheating temperature on induration stand during thermal hardening of the pellets. The induration steps are designed based on the thermal behavior of goethite. The goethite ores, because of their chemically combined moisture content, pose special problems. The generation of fines from iron ore due to internal pressure developed from the evaporation of moisture or phase transformation (28% increases in volume) has a harmful effect on induration of pellets and blast furnace performance. Such behavior of iron-bearing materials is evaluated by thermal degradation index. To avoid/control the cracking/breaking of goethite pellet on induration stand, we should be aware of phase transformation temperature and thermal behavior of goethite. Therefore, we can decide the thermal profile for the pelletization of the goethite ore. Therefore, this study is to find out the decomposition temperature of goethite with respect to the mineralogy of ores and heating rate

Influence of addition of carbon on Pelletization of Hematite Ore Fines

Energy consumption for the production of hematite ore pellet is much greater than that of magnetite ore pellet due to the absence of exothermic heat of reaction and diffusion bonding. To reduce the energy consumption in induration several investigators have mixed varieties of carbonaceous materials in pellet blend to supply in-situ energy. Carbon via Indian coal has been used for this purpose. This coal has hardly any metallurgical use. However, it is found in a large quantity in India. Its use in pellet mix may reduce the energy consumption and induration temperature. Therefore, it is used in Acidic pellets as well as in basic pellets (basicity=0.3). It has been found that the CCS of carbon added pellets decreases with increase in wt % C in the pellet. The reduction degradation index (RDI) has been found to be minimum at 2% of carbon addition

An Improved process for preparation of iron oxide pellets using sodium Lignosulphonate containing wastes and copper smelting slag replacing bentonite

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Effect of Cooling Rate on Cold Compressive Strength of Carbon-Burdened Hematite Pellets

The pelletization of iron ore fines involves mainly two steps, (i) green ball production (ii) induration of green pellets. The induration of green pellets is the thermal treatment of pellets wherein drying, preheating, firing and cooling stages occur. The carbonaceous materials are admixed in pellets mix to lower the energy requirement and induration temperature of hematite ore pellets. Some extent of iron oxides is always reduced to lower iron oxide during induration process due to the presence of the coke in pelletization mixture. For the better quality of pellets, reduced iron oxide in pellets should re-oxidized into hematite phase. The degree of pellets re-oxidation depends on induration conditions and furnace atmosphere on induration stand for the given type of iron ore. The firing and cooling of pellets can control the phase formation and quality of the pellets. The FeO or Fe3O4 content in final pellets should be as low as possible for good cold compressive strength of the pellets. The extent of formation of FeO (Fe3O4) in final pellets mainly depends on induration parameters and atmospheric condition of the induration furnace. Therefore, we have studied the effect of cooling rate on CCS of the carbon burned pellets. The CCS of furnace-cooled pellets (annealing) is more than that of air-cooling (normalizing) and water-cooling (quenching) pellets because of more recrystallization bond, diffusion bond and uniform distribution of phases in the final products of furnace cooled pellets. CCS of the furnace, air and water-cooled pellets at 1280 ◦C /10 min are 235, 140 and 35 kg/pellet, respectively. However, the only furnace cooled pellets displayed acceptable strength for blast furnace operation at 1280 ◦C /10 min

Effect of an organic binder and copper slag on pelletization of hematite ore eliminating bentonite

SYNOPSIS Ammasi. A Traditionally, bentonite is used as the most common binder in iron ore pelletization from the very beginning. It gives good bonding property to green and dry pellets at ambient as well as elevated temperature. However, bentonite contains around 60% silica and 18 % alumina that proportionally increase the alumina and silica content in pellet and increases slag volume and energy consumption in downstream process of blast furnace iron making. An organic binder may be used for replacement of bentonite as it hardly contain alumina and silica and does not leave any significant residue after burning at high temperature during induration of pellet. Many researchers have studied on it and found that several organic binders such as dextrin, starch, molasses, cellulose, peridur, polyacrylamide etc. provide sufficient green and dry compressive strength, drop strength. However, most of these are failed to provide strength at high temperature due to the poor thermal stability (burning or evaporation) during induration of iron ore pellets. Furthermore, Fe3O4 in magnetite pellet is oxidized during induration and provides exothermic heat to the pellet. This reaction helps in forming diffusion bond and supplying internal heat to the pellet for bond formation at 1050-1250 ºC. But, the hematite pellet does not contain lower iron oxides due to which it requires higher induration temperature (1300ºC) and consumes higher energy than magnetite pellet. The required induration temperature can be lowered if the diffusion bond formation is enhanced or some low melting compound is added in pellet for slag bond formation. In present study, the feasibility of a suitable organic material for bond formation in green and dry pellet has been investigated. The Na-Lignosulphonate (NLS), a byproduct of paper mill has been used for this purpose. Since organic binder does not provide strength at high temperature (700-900°C), the low melting (1200ºC) Cu-smelting slag has been used to form bond at relatively lower temperature, where organic binder loses its strength. The Cu-smelting slag enhances slag bonding at relatively lower temperature and can reduce the induration temperature as it contains a significant amount of FeO with some silica (fayalite) and magnetite. Moreover, FeO in copper slag is oxidized at elevated temperature during heating in induration strand. This oxidation enhances diffusion bonding and recrystallization of secondary hematite. Thus, during induration, NLS can provide cold bonding at the low temperature region and Cu-smelting slag may enhance diffusion bonding and slag bonding at the higher temperature region, when NLS evaporates / burns and loses its bonding property. The combined effects of these two materials may help eliminating bentonite completely in developing blast furnace (BF) quality pellets. Therefore, the objectives of the present study are; • Feasibility study for use of NLS as binder and Cu-smelting slag to enhance the strength at elevated temperature and lowering the induration temperature of hematite pellet without bentonite. • Development of good quality hematite pellet in combination of Na-lignosulphonate and Cu-smelting slag replacing bentonite and reducing induration temperature. The study was carried out in laboratory scale taking Noamundi iron ore fines with varying amount of NLS (0.3, 0.5, 0.7 and 1 wt%) as a binder and constant amount of copper slag (1.0 wt %) and basicity (0.3) to optimize the binder content. The characterizations of green balls were done to measure the green pellet property such as green compressive strength (GCS), dry compressive strength (DCS) and drop numbers. The Green balls were indurated at 1200,1225,1250,1275 and 1300°C for 15min. Then, characterizations of indurated pellets were performed to measure their property such as cold compressive strength (CCS), reducibility index (RI), reduction degradation index (RDI), swelling index (SI), apparent porosity (AP) and phase formation (used X-ray diffraction (XRD) and optical microscope). In order to optimize the copper slag content, the pellets were prepared with varying amount of copper slag (0.5, 1.0, 1.5, 2.0& 3.0 wt %) and constant amount of sodium lignosulfonate (0.5%) as optimized. After studying green properties, the pellets were indurated and characterized for CCS, RI, RDI, SI, AP and phase identification as above. The properties of the developed pellet with optimum amount of NLS and copper smelting slag was compared with usual bentonite pellets of identical basicity. The heat of exothermic reaction of FeO and Fe2O3 with copper slag in pellet has been calculated by thermodynamics software ‘Factsage6.4’. The possible phase formation with the flux composition used in pellet at varying temperature near induration has been estimated by the equilibrium module of ‘Factsage6.4’ and it was compared with the phases identified by X-ray diffraction techniques. The microstructures of indurated pellets were analysed using optical microscope. It has been observed that only 0.5% NLS can provide very good green properties (1.8 kg GCS, 4.5kg DCS and 22 drop numbers) to the pellets which are beyond the acceptable limit in plant (1.2 kg, 2.2 kg and 6 Nos, respectively). At 0.3% level of NLS, drop number deteriorates drastically and also with increasing to 0.7% NLS, the GCS deteriorates slightly. Therefore, 0.5% NLS may be considered as optimum percentage. From the properties of indurated pellet, it has been found that 0.5% of only NLS bonded pellet shows comparable strength properties with 0.5% bentonite bonded pellet. However, only NLS bonded pellet shows very high RDI (27%). The evaporation or burning of NLS may be the primary reason behind this. Thus, use of only NLS would not be acceptable. The varying amount of copper smelting slag has been added with 0.5% NLS and found to improve CCS to a great extent. RI has been improved and RDI and swelling has been decreased. 1.0% copper smelting slag addition with 0.5% NLS has been found to be optimum. The developed pellet with this composition shows around 300 kg/pellet strength at induration temperature of only 1250°C. However, the pellet of similar basicity with 0.5% bentonite shows 300 kg/ pellet CCS at induration temperature of 1300°C; i.e. the induration temperature requirement for the developed pellet is 50 °C lower than the usual bentonite bonded pellet. The developed pellet (0.5%NLS+1% Cu-slag added) also shows better RI (80%), almost similar RDI (18%) and swelling (10%) to the usual bentonite pellet. The above properties may be well acceptable in plants. Phase identification of both developed pellets and bentonite bonded pellet through XRD shows mainly Fe2O3, CaAl2Si2O8 phases which are in agreement with the estimation through Factsage. Thus, the present work developed a process of pellet preparation wherein, CCS and reducibility of pellet is superior than bentonite bonded pellet and other properties are also comparable. The bentonite has been eliminated completely by using NLS and copper smelting slag and induration temperature has been lowered by 50°C that may provide a considerable energy and cost saving

Reaction Mechanism of In-situ Carbon in Hematite Ore Pellet during Induration

Carbon is used in the hematite ore pellet as a partial heat source for induration. Apart from this, it has several other roles in the pellet. To achieve the maximum benefit of carbon in pellet quality improvement and energy reduction, a detailed study on the mechanism of C reaction in hematite pellets is required. Although some investigators have reported improvement in pellet properties on using carbon, its detailed analysis is still lacking. For this, the study on the reaction mechanism during induration is essential, which has not been done so far. To alleviate the above knowledge gap, the reaction mechanism of in-situ carbon has been studied through thermodynamic analysis and experimentation in this work. The possibility of evolving carbon monoxide and carbon dioxide during the burning of carbon at the initial stage has been analyzed from the thermodynamic study. The produced carbon monoxide gas may partially reduce the iron oxides in the pellet. This in-situ reduced iron oxide may be beneficial in the sintering of pellets. The possibility of reduction of ferric oxide in pellets followed by its re-oxidation in the final stage has been studied thermodynamically and experimentally. This study helps to understand the mechanism of in-situ carbon reaction during induration and its role in improving the quality of pellets and reducing energy consumption. It is found that the use of carbon enhances diffusion bonding in acidic pellets and both diffusion and slag bonding in basic pellets. The use of 1.5% carbon reduces the induration temperature by 50 K