Sintering Of Mixture Research Articles

The Sinter Mixture Moisture Control System Based on Fuzzy PID Controller

Because the sinter mixture moisture control system has time-varying, nonlinear and time-delay characteristics, it is difficult to establish its precise mathematical model. According to the defects that the conventional PID control in the fixed parameter is difficult to guarantee the system performance, this paper proposed the parameter self-tuning fuzzy PID controller which is used to the system. Based on the sintering furnace structural features and control performance requirements, the PID parameters are set by fuzzy logic reasoning. The actual operation results proved that the parameter self-tuning fuzzy PID controller improved more obviously the system performance than the original PID controller, and stabilized the sinter mixture moisture, and improved the sintering production condition and promoted the production capacity.

Effect of Oxygen Partial Pressure on the Formation Mechanisms of Complex Ca-rich Ferrites

The formation mechanisms of the complex Ca-rich ferrite iron ore sinter bonding phases SFCA and SFCA-I, during heating of a synthetic sinter mixture in the range 298–1 623 K and at pO2 = 0.21, 5 × 10 –3 and 1 × 10 –4 atm, were determined using in situ X-ray diffraction. SFCA and, in particular, SFCA-I are desirable bonding phases in iron ore sinter, and improved understanding of the effect of parameters such as pO2 on their formation may lead to improved ability to maximise their formation in industrial sintering processes. SFCA-I and SFCA were both observed to form at pO2 = 0.21 and 5 × 10 –3 atm, with the formation of SFCA-I preceding SFCA formation in each case, but via distinctly different mechanisms at each pO2. No SFCA-I was observed at pO2 = 1 × 10 –4 atm; instead, a Ca-rich phase designated CFAlSi, formed at 1 420 K. By 1 456 K, CFAlSi had decomposed to form melt and a small amount of SFCA. Such a low pO2 during heating of industrial sinter mixtures is, therefore, undesirable, since it would not result in the formation of an abundance of SFCA and SFCA-I bonding phases. In addition, CFA phase, which was determined by Webster et al. (Metall. Mater. Trans. B, 43(2012), 1344) to be a key precursor phase in the formation of SFCA at pO2 = 5 × 10 –3 atm, was also observed to form at pO2 = 0.21 and 1 × 10 –4 atm, with the amount decreasing with increasing pO2.

Optimization of Dolomite Usage in Iron Ore Sintering Process

To achieve the action mechanism and optimal usage of dolomite in the sintering process, solid reaction tests, fluidity tests, bonding strength tests and sinter pot tests were conducted, then microstructure and energy spectrum were analysed further. Reaction temperature of dolomite with calcium ferrite was lower than that with limonite iron ore about 155°C. Fluidity of bonding phase and strength of sinter using dolomite were lower than that using light burned dolomite and serpentine owing to the higher MgO content in the calcium ferrite and formation of secondary bonding phase. Action mechanism of dolomite in sintering process mainly included 4 steps, thermal decomposition, solid reaction, formation of primary bonding phase and formation of secondary bonding phase. Dolomite mainly played it’s role in the third step in which high viscosity CFM (calcium ferrite with MgO) and magnetite solid solution formed. Increasing the solid solubility of MgO in magnetite by mixing dolomite with magnetite concentrate before granulation, decreasing the dispersity of MgO in sinter mixture by increasing the particle size of dolomite appropriately, increasing the separation degree of MgO and CaO by light-burning the dolomite, and decreasing the reaction amount of MgO by using big particle size magnesia, all could decrease the content of MgO in calcium ferrite, thus showed good performance in sinter pot tests.

In situ X-ray Diffraction Investigation of the Formation Mechanisms of Silico-Ferrite of Calcium and Aluminium-I-type (SFCA-I-type) Complex Calcium Ferrites

The formation mechanisms of the complex Ca-rich ferrite phase SFCA-I, an important bonding material in iron ore sinter, during heating of synthetic sinter mixtures in the temperature range 298–1 623 K in air and at pO2 = 5 × 10 –3 atm, were determined using in situ X-ray powder diffraction. In air, the initial formation of SFCA-I at ~1 438 K (depending on composition) was associated with reaction of precursor phases Fe2O3, CaO·Fe2O3, SiO2, amorphous Al-oxide and a CFA phase of approximate composition 71.7 mass% Fe2O3, 12.9 mass% CaO, 0.3 mass% SiO2 and 15.1 mass% Al2O3. At temperatures above ~1 453 K, the decomposition of another phase, γ -CFF, resulted in the formation of additional SFCA-I. At lower oxygen partial pressure the initial formation of SFCA-I occurred at similar temperatures and was associated with reaction between similar phases as its formation in air. However, the decomposition of γ -CFF did not result in the formation of additional SFCA-I, with the maximum SFCA-I concentration (25 mass%) lower than the values attained in air (54 and 34 mass%). Hence, more oxidising conditions appear to favour the formation of the desirable SFCA-I phase.

Improving Granulating and Sintering Performance by Pretreating Specularite Concentrates Through Mechanical Activation

In this paper, the pretreatment of specularite concentrates through roller press was present to improve the granulation of blends comprising some 10–30% specularite concentrates and enhance the sintering performance. It was shown that the content of +3 mm fractions of granulation mixture is elevated by 10% and the sinter mixture permeability is elevated by 35%. In the meantime, a sinter tumble index increasing from 62.00 to 64.13% was attainted with similar sinter productivity and at lower fuel rate. The mechanism of the pretreating concentrates process to improve sintering performance was demonstrated from mineralogy analysis that better permeability and improved reactivity which help to form more calcium ferrite and good microstructure of sinter, further proven by the better metallurgical performance of sinter.

Technology for Productivity Improvement of Sintering Based on Designing of Composite Granulation and Bed Structure of Sinter Mixture

Technology for Productivity Improvement of Sintering Based on Designing of Composite Granulation and Bed Structure of Sinter Mixture

Method and Technique of Grade Recovery and Cascade Utilization (GRUC) Based on Sintering and Cooling Integration

The key problems and causes of recovery and Utilization of sintering waste heat were analyzed firstly, on the basis of sintering and cooling integration , the method and technique of grade recovery and cascade utilization (GRUC) was put forward according to the first and second laws of thermodynamics. The waste heat was recovered in grades according to the quality firstly, and then different qualities of residual heat recovered were utilized in cascades. The higher temperature part of sinter cooling waste gas was used for power recovery, the medium temperature part was used for direct thermal utilizations, such as drying and preheating of sinter mixture, combustion supporting for ignition, hot air sintering and so on, and the lower temperature part was used for absorption refrigeration. Last, a 360m2 sintering machine of JTC was put forward as an example to validate economic feasibility of the process.

Analysis on Pb, Cd, Cr, As, Mn Emission and Control Technology of Typical Industries

The heavy metals including Pb, Cd, Cr, As and Mn emission characteristics of coal-fired power plant boilers, industrial boilers, lead and zinc smelters, cement kilns, and steel industries were studied in this paper. The removing effects of heavy metals by pollution control technology were analyzed. ICP-AES method was used to measure the contents of heavy metals in solid samples. In addition, M-29, the U.S. EPA isokinetic sampling method was used to sample heavy metals in the flue gas, and the sampled heavy metals were tested by ICP-AES-hydride generator system. For coal-fired boilers, heavy metal contents in descending order were Mn, Pb and Cd in the tested coal. The heavy metals’ emission concentrations of coal-fired industrial boilers were much higher than the heavy metals’ emission concentrations of power plants. For the lead and zinc smelters, Pb and its compounds in flue gas after cleaning can meet the emission standards. The heavy metal contents in the cement raw materials in descending order were Pb, Cr and Cd. For the sintering mixture, the heavy metal contents in descending order were Pb, Cr and Cd as well. The removal effects of heavy metals by existing pollutant control technologies in the various typical industries were also tested and analyzed in the paper. The research did in the paper made a scientific basis for controlling heavy metal emissions from typical industries.

The Research of Fluxed Sinter Production with Sufficiently High Strength and Improved Technological Properties

This article is dedicated to utilization of substandard phosphorite fines and simultaneously producing of fluxed sinter. Optimal technological parameters of the sintering process of phosphate fines with addition of the substandard underoxidized nickel-cobalt-containing ore and the internal overburden of coal mining industry were established. The addition of the nickel-cobalt ore and internal overburden containing nickel, cobalt, silicon and aluminum in the charge composition permits to produce the fluxed sinter with improved technological properties, with acidity module 0.90-1.08, with the high impact, abrasion and compression strength. Decrease of the fines output (less than 6 mm) on 10-15% (relatively) in comparison with the existing (traditional) sintering technology is explained with a content of carbon (up to 50%) in the internal overburden and increase of eutectic liquid phase amount at the expense of fusible components of the nickel-cobalt ore. The result of this process is the fluxed sinter with sufficiently high strength and improved technological properties. At the subsequent electro thermal sublimation of phosphorus from the fluxed sinter with high strength properties the ferrophosphorus alloy forms which contains the alloying metals such as Ni, Co, Cr and others. These additions containing silicon and aluminum create an exothermic effect, which leads to decreasing of fuel and energy consumptions. The suggested technology allows to decrease a melting point of the charge on 100 °C due to presence of fusible compounds in the sintering mixture and to reduce the fuel and energy consumption for the sinter production. Found that the introduction of nickel-cobalt ore and internal overburden of coal industry in the sinter charge provides a fluxed sinter phosphorite with module of acidity 0.93-1.08 sufficiently high strength and improved technological properties, in addition, at subsequent electric sublimation of phosphorus from fluxed sinter the ferro alloy alloyed with nickel and cobalt is formed, which is a valuable raw material for the steel industry. According to the research it is assumed that the replacement of natural quartzite used as a flux to the nickel-cobalt-chromium containing ore and internal overburden, which include about 45% of silicon, as well as transition of nickel, cobalt and chromium ore into ferrophosphorous alloy with subsequent sales of its steel industry to a higher price will significantly improve the technical and economic indices of phosphorus production.

Silico-ferrite of Calcium and Aluminum (SFCA) Iron Ore Sinter Bonding Phases: New Insights into Their Formation During Heating and Cooling

The formation of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter phases during heating and cooling of synthetic iron ore sinter mixtures in the range 298 K to 1623 K (25 °C to 1350 °C) and at oxygen partial pressure of 5 × 10−3 atm has been characterized using in situ synchrotron X-ray diffraction. SFCA and SFCA-I are the key bonding phases in iron ore sinter, and an improved understanding of their formation mechanisms may lead to improved efficiency of industrial sintering processes. During heating, SFCA-I formation at 1327 K to 1392 K (1054 °C to 1119 °C) (depending on composition) was associated with the reaction of Fe2O3, 2CaO·Fe2O3, and SiO2. SFCA formation (1380 K to 1437 K [1107 °C to 1164 °C]) was associated with the reaction of CaO·Fe2O3, SiO2, and a phase with average composition 49.60, 9.09, 0.14, 7.93, and 32.15 wt pct Fe, Ca, Si, Al, and O, respectively. Increasing Al2O3 concentration in the starting sinter mixture increased the temperature range over which SFCA-I was stable before the formation of SFCA, and it stabilized SFCA to a higher temperature before it melted to form a Fe3O4 + melt phase assemblage (1486 K to 1581 K [1213 °C to 1308 °C]). During cooling, the first phase to crystallize from the melt (1452 K to 1561 K [1179 °C to 1288 °C]) was an Fe-rich phase, similar in composition to SFCA-I, and it had an average composition 58.88, 6.89, 0.82, 3.00, and 31.68 wt pct Fe, Ca, Si, Al, and O, respectively. At lower temperatures (1418 K to 1543 K [1145 °C to 1270 °C]), this phase reacted with melt to form SFCA. Increasing Al2O3 increased the temperature at which crystallization of the Fe-rich phase occurred, increased the temperature at which crystallization of SFCA occurred, and suppressed the formation of Fe2O3 (1358 K to 1418 K [1085 °C to 1145 °C]) to lower temperatures.

Operating condition influences on PCDD/Fs emissions from sinter pot tests with hot flue gas recycling

This study was designed to clarify the influence of operating conditions on the formation and emissions of polychlorinated-p-dibenzodioxins and dibenzofurans (PCDD/Fs) from a sintering process with hot flue gas recycling. A pilot scale sinter pot with simulated flue gas recycling was developed, and four key operational parameters, including temperature, oxygen content of the simulated waste flue gas, the coke rate of the sintering mixture, and the quicklime quality, were selected for exploring PCDD/Fs formation. The results showed that the temperature of the recycled flue gas had a major affect on PCDD/Fs formation, and a high temperature could significantly increase their formation during sintering. A clear linear correlation between the temperature of recycling flue gas and PCDD/Fs emission (r = 0.93) was found. PCDD/Fs could be reduced to a certain extent by decreasing the level of oxygen in the recycled flue gas, while sintering quality was unchanged. The coke rate had no significant influence on the formation of PCDD/Fs, but the quality of quicklime used in the sintering mixture could affect not only the amount of PCDD/Fs emissions but also the sintering productivity. Compared with a benchmark sinter pot test, PCDD/Fs emissions markedly decreased with improvements to quicklime quality. However, the reduction in PCDD/Fs emissions realized by using high-quality quicklime was limited by the temperature of the inlet gas. The highest reduction achieved was 51% compared with conventional quicklime when the temperature of the inlet gas was 150°C.

Experimental investigation on the drying process of the sinter mixture

Achieving efficient recovery and utilization of waste heat during sintering is crucial for iron and steel plants. Previous studies on waste heat utilization have shown that steam and electricity are generated, after which the air and sinter mixture is preheated. However, few studies on the mechanisms of the drying process of the sinter mixture exist. This paper presents the results of an experimental investigation on the drying process that occurs during sintering. The results show that the drying process of the sinter mixture consists of three stages, namely, a short rising-rate stage, a long constant-rate stage, and a falling-rate stage. The moisture contents of specimens are 0.055–0.06 kg/kg in the first 5–7 min, and the critical moisture contents are approximately 0.023–0.03 kg/kg. The drying efficiency is mainly attributed to the temperature and the flow rate of the hot air, and the former one is more significant.

Improving the Granulating and Sintering Performance by Pretreating Concentrates Using Extrusion Machine

In this paper, the pretreatment of concentrates by extrusion machine was present to improve the granulation of blends comprising some 30% iron ore concentrates and enhance the sintering performance. It is shown that by pretreatment of fine concentrates through extrusion machine, the content of +3mm fractions of granulation mixture and sinter mixture permeability are elevated by 10% and 35%, respectively. In the meantime, an increase in sinter productivity from 1.51 to 1.62t.m-2.h-1 is attainted in pot tests with similar sinter tumble index and at lower coke rate. The mechanism of the pretreatment of concentrates process to improve sintering performance of fine iron ore concentrates was demonstrated by mineralogy that better permeability help form more calcium ferrite and good microstructure of sinter, further proven by the better metallurgical performance of sinter.

Sintering characteristics of fluxes and their structure optimization

Sintering characteristics of common fluxes and sintering blending ores, such as mineralization capacity, liquid generation capacity, consolidation strength, were examined to master the behavior and effect of fluxes in sintering. Based on fundamental studies, sinter pot tests were carried out to obtain the principles of optimizing the sinter flux structure. The results showed that strong mineralization capacity, liquid phase generation capacity, and consolidation strength were obtained as sintering blending ores combined with the calcareous flux, while relatively poor sintering characteristics were obtained as sintering blending ores combined with the magnesian flux. High reactive quicklime should be used as much as possible in the sintering mixture. It reached better sintering results while quicklime was used instead of limestone and its appropriate proportion in the sintering mixture was around 4wt%. On the premise of ensuring the MgO content, the dolomite amount should be decreased, and the substitution of quicklime for dolomite caused better sintering results. The granularity of serpentine should be refined with a proper size smaller than 2 mm. The application of the divided addition method brought the best sintering performance with 30wt% of quicklime and 70wt% of fuel.

Utilising of the oiled rolling mills scale in iron ore sintering process

Up to 5% of steel is lost with the scale at hot rolling operation. This waste contains 69–72% of iron in the form of oxides. However, its recycling is confronted with presence of up to 20% of oil and 10% of water. E.g. when the oiled scale is introduced as an additive to the iron ore sintering mixture, incomplete combustion of liberated oil at heating during sintering process creates problems for gas cleaning and may even lead to damage of the equipment. A possibility to improve combustion of the scale's oil at the sintering process by preparation of a mixture with peat was shown in the laboratory experiments. Industrial trials demonstrate possibility to increase the oil combustion degree at sintering 2.7 times as much. Consumption of the oiled scale was increased from zero to 12.8 kg (in a form of scale–peat blend) per ton of sinter, which allows for closing the loop of this waste at the integrated steelmaking factory.

Iron ore sinter porosity characterisation with application of 3D X-ray tomography

X-ray tomography has been applied for the estimation of iron ore sinter porosity. Procedures to distinguish open and closed pores and to estimate the volume and the equivalent diameter of each pore were developed, providing the possibility to calculate the amount of porosity considering open and closed pores separately. The effect of the sinter mixture composition on the porosity parameters was investigated, and a comparison with a mercury intrusion measurement is also presented. Reducibility tests were performed for the samples, the porosity of which had been previously identified by tomography. The fact that samples with a premeasured porosity could be analysed with other characterisation methods opens new possibilities to understand the effect of the porosity on the properties of the sinter.

Application of 3D X-ray tomography to investigation of structure of sinter mixture granules

X-ray tomography was applied to the investigation of the structure of sinter mixture granules. Different components such as ore, concentrate, coke breeze and limestone were identified and their sizes and spatial distribution estimated. Classification of the granule structure by the thickness of the adhering fines layer in a proportion to the whole granule radius has been estimated. Excessive amount of fines (concentrate) in a mixture leads to the increasing presence of granules with an adhering fines layer thicker than a half of the granule radius. Abnormal structures of granules have been observed in some cases such as microgranules embedded in the adhering layer of bigger granules, granules formed as the result of two or more granules coalescence or granules formed without a nucleus particle with a structure similar to pellets.

Granule Design for the Sintering with Less Amount of Liquid Phase Formation

In order to clarify the conditions to produce a dense and large pellet required from the MEBIOS method, some basic sintering experiments were conducted. Consequently, the pellet having a sufficient strength as a blast furnace burden was able to be produced by selecting the composition of the pellet and the temperature so that the liquid phase ratio in the CaO–Fe2O3–SiO2 system was about 40 mass%. Moreover, it was confirmed by the sintering pot experiment using X-ray CT that a void was formed around the pellet when this pellet was placed in the sintering mixture. The crushing strength of the pellet collected from the sinter cake was low. However, increasing of the basicity of the pellet and extension of the retention time at high temperature were effective for improving the crushing strength of the pellet.

Analysis of Raw Material Flow with Axial Direction in Continuous Drum Mixer for Sintering Process

The granulation process is known to be important to achieve high productivity in sinter process because the granulation of sinter mixture is connected with permeability of sinter bed. Past studies on the granulation in the drum mixer for sintering process mostly used the batch type drum mixer, hence their studies were on the raw material behavior for cross-section of the drum mixer. In contrast there were few reported on the raw material behavior for a drum axial and a residence time in a continuous type drum mixer. The raw material flows and the residence times have been investigated experimentally by using a continuous type drum mixer, and results were compared to those by the theory predicts suggested by Saeman. In addition, the effects of the ring dam fitted to the discharge end on the residence time and granulation improvement were investigated. As a result, with the drum set at the low angle, the observed residence times were shorter than the theory predicts. This is due to the level of the raw material tapering off as it reaches the discharge end. Thus, by newly considering angle ψ between the raw material surface and the drum mixer, the residence time was accurately estimated. Also, with the drum set the low angle, the ring dam fitted to the discharge end prevented any tapering, resulting in the longer residence time and greatly improved granulation.

Investigation of wear resistance of a hard alloy modified by nanoaddititives

The effect of additions of nanostructured tungsten carbide powder into a sinter mixture with compaction of sintered hard alloy VK8 on its tribological properties has been studied. Physicomechanical properties of the material obtained have been estimated. The produced hard alloy shows elevated wear resistance to abrasive wearing.