Increase In Degree Of Reduction Research Articles

Evolution behavior and kinetic analysis of vacuum-extruded iron-rich dust briquette in blast furnace

The vacuum extrusion iron-rich dust briquette was prepared by vacuum extrusion of iron ore concentrates, blast furnace dust and Portland cement. The evolution behavior and kinetic analysis of briquette in blast furnace was studied by high temperature process interrupted experiment. The phase transformation, metallurgical strength, microstructure and three-dimensional structure of dust briquette during high temperature reduction process were analyzed by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy and micro computed tomography. It is found that the high temperature reduction process of briquette can be divided into six stages, and the mechanical strength of briquettes under reducing atmosphere decreases with the increase of reduction degree and metallization rate, from 4.58 KN at 100 °C to 0.52 KN at 1100 °C. As the temperature increases, the metal iron and porosity inside briquette gradually increase. The ratio of the volume of metallic iron at 700 °C, 900 °C and 1100 °C was 1.47%, 3.70% and 6.60%, and the porosity is 10.32%, 34.1% and 47.1%, respectively. Furthermore, the non-isothermal kinetic reduction process of briquette was analyzed, and the evolution mechanism was revealed. The reduction process of briquettes is mainly controlled by diffusion, and only in the fourth stage (510 °C–840 °C) is limited by the reduction reaction of magnetite and decomposition reaction of calcium carbonate. This paper provides a theoretical support for the efficient and economical recycling of dust in iron and steel enterprises.

Effect of reduction degree on cohesive zone and permeability of mixed burden

ABSTRACTLow-carbon operation, especially low-coke-rate operation, is very important for low CO2 emission in blast furnace ironmaking. Maintaining the permeability of the cohesive zone is required under low-coke operation of the blast furnace. The cohesive zone and permeability are determined by the softening and melting properties of the burden. In this study, the effect of reduction degree on the cohesive zone and permeability was investigated by using different reduction degree mixed burdens. The experimental results showed that as the reduction degree increased, the thickness of the cohesive zone decreased, the position of the cohesive zone moved downward, and the permeability of the mixed burden layer was significantly improved. The weight of the droplet and the carbon content of iron in the droplet decreased with the increase of reduction degree. The results of experiments provided an important guidance for improving the permeability of the mixed burden layer in low-coke operation of the blast furnace.

Thermodynamic analysis of reduction in copper slag by biomass molding compound based on phase equilibrium calculating model

Copper slag is a good valuable material resource with high iron content in the form of fayalite. Biomass as reduction reducer was proposed in this paper. For the basic research of the reduction in biomass, the biomass reducer was simplified as molding compound C, CO, H2 and CH4. The reactions of 2FeO·SiO2 with C, CO, H2 and CH4 could proceed spontaneously with the addition of CaO. The Gibbs free energy is decreased significantly by addition of CaO. The equilibrium compositions of products were calculated and analyzed combing with 19 basic reactions. Beginning temperature of C, CO, H2 and CH4 is 900, 623, 567 and 511 K, respectively The reduction degree of C, CH4, H2 and CO is 1, 0.851, 0.695 and 0.452, respectively, at 1773 K when the reducer addition ratio is 1.0 calculated by phase equilibrium calculating model. Direct reduction reaction of copper slag dominates at higher temperature, and temperature region of 700–1173 K is the transformational zone. Indirect reduction index curves are in the shape of reverse ‘S,’ and the higher temperature is in favor of indirect reduction in copper slag. There is a steady increase in reduction degree with the increase in reducer. Reduction reaction path of copper slag by C, CO, H2 and CH4 is established.

Effect of magnetic field on reduction of magnetite

The reduction behaviour of magnetite oxide by hydrogen below Curie temperature was investigated in the presence of external magnetic field by thermogravimetric analysis. The reduction rate of magnetite powder increased with increasing external magnetic field strength below Curie temperature of magnetite. In order to figure out the effect of external magnetic field on reduction of magnetite, two types of magnetite, powder and pellet, were studied. It was possible to enhance the reduction rate of magnetite powder, because the particles of magnetite in the presence of an external magnetic field exposed more surface to the reducing gas. The effects of reduction temperature, reducing agent, iron oxide type, particle size and specimen shape on the metallisation behaviour of magnetite were visually clarified below the Curie temperature under the influence of external magnetic field. Despite of the increase in reduction degree by applied magnetic field, the rate controlling step was not changed due to the formation of porous metallic iron layer that keeps the path for reducing agent to approach the unreduced iron oxide in the core of magnetite particle.

About Electrical Properties of Chromite Pellets – Effect of Reduction Degree

Chromite pellets are used in the production of ferrochrome. Pellets are typically one part of the feed material mixture of a submerged arc furnace (SAF). The electrical behavior of the feed material in a SAF is of great interest due to its effects on the function and productivity of the furnace. In this paper electrical behavior as a function of reduction degree of chromite pellets was studied. Reduction degree was defined for all industrial pellets by placing the pellets at 1500 °C, in CO atmosphere for different durations. Pellet slices were measured for electrical conductivity at room temperature. It was observed that increase in reduction degree decreased the electrical conductivity measured at room temperature.

Reduction of Ilmenite with Coal in the Presence of Nitrogen

In this study, the carbothermal reduction of ilmenite with coal was investigated in laboratory-scale experiments. Reactions were performed in nitrogen atmospheres in the temperature range of 1,225–1,325°C with a residence time of 6 h. The solid reaction products obtained in the investigation were characterised by ICP-EOS and LECO analysers, X-ray diffraction, and scanning electron microscope (SEM). The results show that temperature increase leads to an increase of reduction degree for constant bed depth but the reduction degree decreases with increase of bed depth. The reduction degree of 42.2% was obtained with a bed depth of 25 mm, at 1,350°C after 6 h of residence time. The reaction started with the reduction of ilmenite to titania, followed by the reduction of titania to suboxides. Titania was reduced to Ti3O5, which was later converted to titanium nitride or titanium oxycarbonitride depending on element reactivity and temperature. It was found that Ti2O3 does not appear as an intermediate reaction product due to its instability.

Mathematical modeling of the reduction process of iron ore particles in two stages of twin-fluidized beds connected in series

A mathematical model is presented to describe the reduction process of iron ore particles in two stages of twin-fluidized beds (TFBs) connected in series: prereduction and final reduction stages. Main features of the model are the inclusion of particle degradation phenomenon to account for its effect on reduction of iron oxides and reduction kinetics for multiparticles having a wide size distribution. It was found that about 90 pct of overall particle degradation occurs in the prereduction stage mainly due to thermal stress and volume expansion. The reduction degree of particles larger than 1 mm decreased fast with increasing particle size in both the prereduction and final reduction stages. However, the particles sized between 0.2 and 1 mm showed mild increase in reduction degree, and steep increase for the fines smaller than 0.2 mm. The reduction degree was also gradually decreased with increasing the gas oxidation degree of feed gas in both the prereduction and final reduction stages. It was found that to obtain a desired reduction degree, it is of great importance to control the bed temperature in stage I rather than in stage II. The optimum range of residence time was 15 to 20 minutes in the prereduction stage and 30 to 35 minutes in the final reduction stage.

Respiratory Rate as a Regulatory Factor in the Biosynthesis of the Denitrification Pathway of the Bacterium Paracoccus denitrificans

The decrease in the electron flow of the aerobic respiratory chain of the bacterium Paracoccus denitrificans, owing to either the drop in the saturation of terminal oxidases by oxygen or to the inhibition of the rate of respiration by azide or nitrite, resulted in the synthesis of dissimilatory nitrate reductase and nitrite reductase. The dependence of the resulting activities of the two enzymes (after a three-hour adaptation) on the initial value of the parameter Vmax/kLa (oxidase activity of the volume unit of the culture divided by the volumetric oxygen transfer coefficient) or on the concentrations of the inhibitors had a similar form, characterized by the appearance of a maximum. The increasing parts of the obtained curves reflect the synthesis of enzymes, probably initiated by the increase in the intracellular degree of reduction, the subsequent drop being evidently in connection with the lack of metabolic energy for biosynthesis. The possible mechanisms of the effect of nitrogenous terminal accepto...