Sinter Strand Research Articles

Exploring the Relationship Between Fe-rich SFCA and SFCA-III and Their Presence in Sinter Strand and Pot-grate Sinter

Exploring the Relationship Between Fe-rich SFCA and SFCA-III and Their Presence in Sinter Strand and Pot-grate Sinter

Variation in Iron Ore Sinter Mineralogy with Changes in Basicity

The target basicity of iron ore sinter is set by blast furnace slag composition requirements, and therefore varies with the proportion of acid burden such as lump iron ore and pellets. Increasing the lump proportion of the burden will increase the target sinter basicity. The mineralogy of sinter produced with a range of basicity between 1.0 and 3.0 was analysed using optical point counting under reflected light microscopy. Sinter from BlueScope Steel’s industrial sinter strand was analysed over a 30-year period, during which time a wide range of iron ore fines blends were utilised and several significant process modifications made. These data were compared with the mineralogy of sinters produced in a pilot-scale sinter pot, a laboratory-scale milli-pot, and small-scale sinter analogues. The mineralogy of the sinters from all scales followed a predictable trend with basicity, generally following the diagram proposed by Bagnall. At a basicity of 1.0, high temperatures were required to produce sinter with adequate strength, resulting in bonding phases dominated by magnetite and glass. Increasing basicity to 2.0 decreased the required sintering temperature and changed the mineralogy to a majority of hematite and SFCA. Further increases in basicity to 3.0 further decreased the required sintering temperature and increased the SFCA and dicalcium silicate content.

A STUDY ON THE EXAMINATION OF THE SINTER METALOGRAPHIC STRUCTURE

Sintering process is carried out domestic and imported iron ore powders, fluxes (limestone, dolomite etc.), coke dust, metallurgical recycling powders and slag forming agents. The purpose of the sintering process is to produce a charging material with suitable thermal, mechanical, physical and chemical properties that can be fed into the blast furnace. Nowadays, in order to obtain process and operating parameters that will work with the best sinter quality, extensive researches have been made by iron and steel industry. The sinter quality parameters followed by the sinter blend loaded on the sinter strand and then granulated were examined. In the sintering process, the temperature rises to 1450 oC, partially melting between the sinter grains and a series of reactions take place in the sinter matrix to be charged into the blast furnace to produce liquid crude iron. Many different approaches have been used to estimate sinter quality, to explain the effects of iron ore properties and process variables on sintering mechanisms, and to characterize sinter mineralogy of iron ore. We can obtain chemical analysis of the phases by scanning electron microscopy (SEM) technique, but full consistency with images is not always possible and especially SFCA (silico-ferrite of calcium and aluminium) and SFCA-I phases are difficult to distinguish from each other and future studies are required in this field. The mineralogy and microstructure of the sinter plays an important role in determining the physical and metallurgical properties of the iron ore sinter. Mineralogical characterization of sinter phases; it is a complementary tool to conventional physical and metallurgical tests applied to iron ore sinter to evaluate and estimate sinter quality. Measurement techniques used in this study; optical image analysis and X-ray diffraction (XRD), scanning electron microscopy (SEM), energy distribution spectroscopy (EDS), the results from raw data converted to autoquan format will be explained on the new studies on the interpretation of the Rietveld system. Depending on the measurement objectives of each technique, the quantification of the crystal phases, the relationship between the measurement results, the chemical composition of the phases and the relations between the minerals, as well as their advantages and disadvantages will be explained.

DEM study on size segregation and voidage distribution in green bed formed on iron ore sinter strand

The size segregation and voidage distribution down a green bed formed on an iron ore sinter strand were investigated experimentally and using Discrete Element Method (DEM). The simulated and experimental results showed that an increase in feed rate (from 6 kg/s/m to 18 kg/s/m) significantly decreased the level of vertical size segregation and the granule packing voidage of each bed sub-layer. With the increase in rill plate angle (from 45° to 65°), the level of vertical size segregation first decreased and, then, remained relatively constant. Furthermore, the results indicated that the voidage of each bed sub-layer generally increased with the increase in λ. In conclusion, enhancing the vertical size segregation down the green bed can generally improve the voidage of the green bed and thus increase the bed permeability.

Sintering of Iron Ores in a Millipot in Comparison with Tablet Testing and Industrial Process

To explore the feasibility of small-scale sintering pot testing, a ‘millipot’ facility (diameter of 53 mm and height of 400 mm) was established and used to examine the sintering performance of iron ores and other non-traditional ferrous materials. The sintering performance of a millipot was examined across a range of different operational conditions (coke rate and suction pressure) and compared with an industrial sinter strand operation. Tablet tests were also performed to assist in the design of the millipot experiments and identify conditions for achieving mineral composition similar to the industrial sinter. For the millipot experiments, the materials used need to be compacted to increase the bulk density, and a higher coke rate is required to compensate the high heat loss caused by wall effects. A higher suction pressure is also necessary to maintain an oxidizing atmosphere in the sinter bed. As expected, it was not possible to eliminate the wall effect, which resulted in more primary hematite at edges of the sintered column. However, the sintered material from the center of column simulates industrial sinter reasonably well. As such, millipot provides a practical way to evaluate the sintering process and material performance at laboratory scale, helping to bridge the gap between tablet sintering and large scale pot sintering, or full scale plant trial. The results of millipot testing can be used for designing larger scale experiments or commercial sintering trials.

The fingerprint nature of PCDD in iron ore sinter strand emissions, the effect of suppressants and alternative fuels, and the potential for comparison with the isomer profile of PCDF

It has been previously shown that the isomer profile of PCDF emissions from iron ore sinter plant only varies within limits even when suppressants or alternative fuels are added, to the extent that it can be said to have a 'fingerprint'. The isomer profiles of PCDD from tetra- to hexacholrodibenzo-p-dioxin from the same samples examined for PCDF emissions have been obtained, and show the same tendency for a 'fingerprint ' isomer distribution to occur. Occasional exceptionally high isomer abundances are observed, but these are uncommon. The potential for comparison of the abundances of PCDF and PCDD isomers with similar chlorination patterns to determine whether the same formation process is involved has been examined. It is found that co-elutions prevent extensive comparisons irrespective of whether the SP2331 or DB5ms column is used in the analyses for separation of isomers to provide the results used for comparisons, although they allow limited results to be obtained. It is suggested that analyses using the two chromatography columns to analyse the same sample in parallel could provide more resolution of the isomer profiles for use in comparisons. A pilot study using samples analysed using each column is limited because of detailed differences in the emissions profiles, but demonstrates that greater resolution is possible if the two columns are used to analyse one sample.

Assessment of particulate emissions from a sinter plant in steelmaking works in China.

In this paper, five particulate emission points from a sinter plant in China, including anthracite crusher, raw material blender, sinter strand, screener, and circular cooler, were selected for particle sampling. The particle size distribution, the toxic element content (As, Cd, Co, Cr, Cu, Ni, Pb, Ti, and Zn), and the morphology of the samples were determined by the gravimetric method, the ICP-OES, and the SEM-EDS, respectively. In addition, the gray relational analysis method was used to evaluate the rank of the particulate emission points in the sinter plant. The results show that the emission factor of PMTSP, PM10, and PM2.5 of the whole sintering process is 0.121, 0.075, and 0.039kg/t-sinter, respectively. Furthermore, the total toxic element emission factor is 5282.49mg/t-sinter. The sinter strand is the most important emitter and contributes 43.8% of PMTSP, 53.3% of PM10, 56.4% of PM2.5, and 81.1% of total toxic element in the sinter plant. Nevertheless, particles emitted from the post-sintering process are non-negligible and contribute 48.8% of PMTSP, 41.3% of PM10, 38.5% of PM2.5, and 15.5% of total toxic element in the sinter plant.

Integrated assessment of exergy, energy and carbon dioxide emissions in an iron and steel industrial network

Intensive energy consumption and high pollution emissions in the iron and steel industry have caused problems to the energy system, in the economy, and in the environment. Iron and steel industrial network as an example of energy conservation and emissions reduction, require better analysis and assessment. The present study comprehensively assesses an iron and steel industrial network and its environmental performance with respect to exergy, energy and CO2 emissions. The results show that the sinter strand needs to be greatly improved and the wet quenching process needs to be completely redesigned. The overall exergy efficiency and energy efficiency can be improved by adopting industrial symbiosis (IS) measures. We found that adjusting the energy structure to use renewable energy and recycling solid waste can greatly reduce CO2 emissions. Moreover, the maximum exergy losses occurred in the blast furnace with the maximum CO2 emissions. The iron making plant exerted a strong effect on the environment based on the equivalent CO2 emission potentials. Many performance indicators of the entire industrial network were also examined in this work. It can be seen that integrated evaluation of energy and CO2 emissions with exergy is necessary to help to mitigate adverse environmental impacts and more effectively fulfill the goals for energy conservation and emissions reduction.

CHARAKTERISTICS OF FINE-GRID IRON-BEARING MATERIALS (DUSTS, SLUDGES, MILL-SCALE SLUDGES)

As a result of manufacturing processes, steelworks plants produce large amounts of waste materials. Currently in modern steelworks the most of waste is utilized in the same steelworks and passed to external customers or it is reused as a feed for other technological processes. Fine-grained metallurgical waste materials are used to production of granules because of the high contents of iron and other valuable elements. Granulation of iron-bearing waste materials increases permeability of blend and performance of the sinter strand. Dosing of material in the form of granules to an average sinter mix may be accomplished in a more controlled manner than is the case for bulk material. Due to recycling carried out by adding granulated wastes to blast furnace charge or to sintering process the cost of production of steel is reduced. This procedure allows metallurgical sector on the delivery of measurable economic, technological and environmental benefits. In this work the chemical composition, grain size and the possibility of using fine-grained iron-bearing wastes are presented.

Removal Mechanism of Zn, Pb and Alkalis from Metallurgical Dusts in Direct Reduction Process

The high-temperature tube furnace was applied to simulate the rotary hearth furnace (RHF) for the direct reduction of zinc-bearing dusts from steel plants. The removal mechanism of Zn, Pb and alkalis from cold bonded briquettes made by mixing metallurgical wastes, such as dust from bag house filter, OG sludge, fine converter ash and dust from the third electric field precipitator of the sinter strand, in various proportions was investigated. More than 70% of metallization rate, more than 95% of zinc removal rate, 80% of lead removal, as well as more than 80% of K and Na removal rates were achieved for the briquettes kept at 1473–1603 K for 15 min during the direct reduction process respectively. The soot generated in the direct reduction process was studied by chromatography, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results suggested that the main phases of the soot were ZnO, KCl, NaCl and 4ZnO · ZnCl2 · 5H2O. Furthermore, the content of Zn reached 64.2%, which could be used as secondary resources for zinc making. It was concluded that KCl and NaCl in secondary dust resulted from the volatilization from the briquettes, whilst ZnO and PbO were produced by the oxidation of Zn or lead vapour from briquettes by direct reduction.

Understanding Coalescence in Iron Ore Sintering Using Two Bench-scale Techniques

With the formation of melt, the structure of a sintering bed transforms because of material coalescence. The drivers of coalescence were studied using two bench-scale techniques. Analogue sinter mixes of varying the basicity and gangue levels were taken to high temperatures using thermomechanical analysis (TMA) and in an ash fusion test (AFT). In TMA, the penetration of a piston into the sinter mix as melt was generated provided information on the deformation, shrinkage, densification and flow of the sample as a function of temperature. Projected sample shapes in the AFT were used to determine sample density and densification level. A computer model FactSage and reported equations were used to provide estimates of melt volume and viscosity. Trends indicated by the TMA and AFT results were similar and large changes in results were only obtained with significant melt generation. Differences in results between the samples could not always be explained because varying the composition of the sinter mix altered the porosity of the sample. Increasing sample porosity meant that the generated melts were not as connected and more work is required to achieve the same level of densification. On a sinter strand, coalescence occurs under a normal load and this effect is simulated in the TMA. However, the excessive flow of melt from the crucible and chemical reactions means that TMA results are unreliable at temperatures greater than 1300°C. For this reason, the AFT is the preferred technique to understand the factors that cause material coalescence on a sinter strand.

Three dimensional mathematical model of the iron ore sintering process based on multiphase theory

In the integrated steel industries the sintering process plays an important role furnishing raw material to the blast furnace. In this work, a computational simulation of the sinter process is developed that is able to predict the most important phenomena within the sintering bed. The model is based on the multi phase concept with multiple components described by conservation equations of each component coupled with the momentum, chemical reactions and heat transfer. The model validation was carried out comparing the model predictions with averaged industrial data and local temperature measurements within the sinter strand. The model predictions presented good agreement with the averaged values measured on the industrial sinter process.

Mathematical modelling of iron ore sintering process using genetic algorithm

A mathematical model of the iron ore sintering process in a fixed sinter bed and optimisation of the process parameters using real valued genetic algorithm is described. The mathematical model is formulated based on mass and energy balances in gas and solid phases, which are represented by simple partial differential equations. The model has a number of process controlling parameters, which are optimised using a heuristic optimisation tool, genetic algorithm. Predictions of temperatures at different bed heights are found to be in reasonable agreement with the experimental data obtained in a laboratory scale pot sintering machine. The model could be used as a potential tool to predict temperature and progress of fire line in industrial sinter strand after being tuned sufficiently with plant trials.

An intelligent control system based on prediction of the burn-through point for the sintering process of an iron and steel plant

This paper concerns an intelligent control system based on prediction of the burn-through point (BTP) of the sintering process of an iron and steel plant. The system has a two-level hierarchical configuration: intelligent-control level and basic-automation level. At the intelligent-control level, first, a BTP prediction model is derived using an intelligent, integrated modeling method based on grey theory and back-propagation neural networks. Next, a hybrid fuzzy-predictive controller for the BTP is established using fuzzy control, predictive control, and a flexible switching control strategy. Finally, an intelligent coordinating control algorithm based on the satisfactory solution principle is employed to coordinate BTP control and bunker-level control. Then, a satisfactory sinter strand velocity is obtained and used as the target value. The basic-automation level regulates the speed of the motor driving the strand so as to make the strand velocity track the target value. The results of actual runs show that the system adequately suppresses the variation in BTP, increases the quantity and quality of sintering agglomerate, and ensures process safety.

Assessment of Exposure to PCDD/F, PCB, and PAH at a Basic Oxygen Steelmaking (BOS) and an Iron Ore Sintering Plant in the UK

An assessment was carried out at a UK integrated steelworks to investigate the exposure of workers via inhalation to dioxins [polychlorinated dibenzo-p-dioxins (PCDD/F)], polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAH) including benzo[a]pyrene (B[a]P). Investigations focused on a basic oxygen steelmaking (BOS) plant and an iron ore sintering plant. The highest concentrations of PCDD/F and dioxin-like PCB were found at the BOS vessels and sinter strand area at the BOS and sinter plant, respectively. A risk assessment was carried out by comparing the daily intake of PCDD/F and PCB via inhalation with the recommended tolerable daily intake (TDI) proposed by the World Health Organisation (WHO). For the most exposed category of worker in this study (i.e. sinter plant workers inside the strand area), the estimated daily intake via inhalation was estimated to be 0.25 pg WHO-toxic equivalent concentrations (TEQ) kg(-1) body weight (bw). Considering that the average UK adult exposure to PCDD/F from the diet is 1.8 pg WHO-TEQ kg(-1) bw day(-1), the results indicated that the estimated daily intake of PCDD/F and PCB via inhalation for sinter plant workers would not result in the recommended range of the TDI (1-4 pg WHO-TEQ kg(-1) bw day(-1)) being exceeded. Cancer risks for a 40-year occupational exposure period were determined by multiplying the estimated intake by the inhalation cancer potency factor for 2,3,7,8-tetrachlorodibenzo-p-dioxin. For the most exposed category of worker, cancer risks from exposure to PCDD/F and PCB ranged from 2.5 × 10(-6) to 5.2 × 10(-5). Under most regulatory programmes, excess cancer risks between 1.0 × 10(-6) and 1.0 × 10(-4) indicate an acceptable range of cancer risk, suggesting a limited risk from PCDD/F and PCB exposure for workers in the sinter plant. With regard to PAH, B[a]P concentrations were typically <10 ng m(-3) at all locations at both the sinter plant and the BOS plant. In several cases, particularly at the sinter plant, B[a]P concentrations were well below or only marginally above the target value of 1 ng m(-3) specified in ambient air by the European Commission in the fourth 'Daughter' Directive of the Air Quality Framework Directive suggesting a very low risk of exposure for workers. For PAH, excess cancer risks ranged from 2.4 × 10(-6) to 7.3 × 10(-6) for BOS plant workers and from for 5.3 × 10(-7) to 1.5 × 10(-5) for sinter plant workers, well within the acceptable range proposed by the US EPA.

Coordinating fuzzy control of the sintering process

Abstract The sintering process is an important step in the iron and steel making process and features strong complexity, nonlinearity and large time-delay. This paper presents a coordinating control method that two fuzzy controllers are designed to control the burning through point (BTP) and the bunker-level. First, the BTP control is the main control task with the sinter strand speed as the control variable, and a predictive fuzzy control scheme is developed where an intermediate process model is used to perform on-line controller design to meet a closed-loop performance specification that is associated with desired process output. Then, a fuzzy controller is designed to control the charging bunker-level via adjusting the strand speed. The two fuzzy controllers are proposed for these two closed-loops and it is shown that the satisfactory response of the closed-loop system can be achieved by handling the strand speed. Results of simulation and actual running illustrate the performance of the proposed method.

Comparison of rapid and slow sintered pulverised fuel ash

This study has investigated the properties of sintered PFA using conventional (20 °C/min) and rapid heating rates. Rapid heating was achieved by directly placing pressed PFA samples into a furnace preset at the sintering temperature. Slow sintered PFA samples show an increase in shrinkage and fired density and a reduction in water absorption as the sintering temperature increases, with maximum density obtained at around 1250 °C. At higher temperatures samples show a bloating effect associated with the enlargement of closed porosity. This peak in density is not observed in rapidly sintered PFA. Rapid sintering at temperatures between 1150 °C and 1300 °C resulted in constant values of shrinkage (6.5%), fired density (1.4 g/cm 3) and water absorption (15%). During rapid sintering the residual carbon in the PFA is present in the sample at the sintering temperature whereas conventional sintering removes the carbon at lower temperatures before sintering occurs. Rapid sintering also retains significant carbon in the core of the sintered sample. This carbon is believed to act as rigid inclusions that inhibit PFA sintering, limiting shrinkage and densification. Rapid sintering is associated with black coring which is also characteristic in lightweight aggregate manufactured from PFA sintered on a sinter strand. The rapid heating rate experienced by PFA pellets on a sinter strand and the associated inhibition of sintering by carbon is essential for producing sintered PFA products with properties appropriate for use as lightweight aggregate.

Factors Influencing Particulate Emissions during Iron Ore Sintering

Controlling particulate emission from a sinter strand is important to minimizing its impact on the environment. Several factors influencing particulate emission from an iron ore sinter strand were investigated in the current work using a laboratory scale sinter pot. A blend fairly typical of that currently used in the Asia Pacific region, as well as another containing 30 mass% Marra Mamba ore that could represent a future ore blend were used. It was established that most of the particulates emitted were less than 1.18 mm and were mostly from the calcination and dried zones of the bed. In addition, most particulates were released from the bed after the wet zone in the bed had ceased to exist. This work suggests mix moisture and coke rate had a significant impact on particulate emissions. Increasing moisture from 5.5 to 9.0 mass% decreased particulate emission while increasing coke content from 5.5 to 7.5 mass% increased particulate emission. Therefore when altering the ore blend changes in mix moisture and coke rate may also need to be accounted for when evaluating the impact on particulate emission. It was also found that particulate emission could be decreased by decreasing sintering suction just before burn-through.

PCDD/F and “Dioxin-like” PCB emissions from iron ore sintering plants in the UK

Investigations have been carried out at the three Corus UK sinter plants over the period 2002–2004 to characterise the emissions of both 2,3,7,8-PCDD/Fs and WHO-12 PCBs, to estimate annual mass releases of these organic micro-pollutants using the I-TEF and WHO-TEF schemes, and to investigate the formation of PCBs in the iron ore sintering process. Results showed that the sintering of iron ore produces a characteristic WHO-12 PCB and PCDD/F congener pattern that is substantially the same for all UK sinter plants. With regard to WHO-12 PCBs, the most abundant congeners were typically PCBs 118 (6–9 ng N m −3), 105 (2–4 ng N m −3) and 77 (2–3 ng N m −3). All other WHO-12 PCBs were also detected at concentrations around 1 ng N m −3. All sinter plants investigated exhibited very similar TEQ concentrations. WHO-12 PCB emissions were in the range 0.042–0.111 ng WHO-TEQ N m −3, whereas PCDD/F emissions ranged from 0.39 to 1.62 ng WHO-TEQ N m −3. PCDF congeners were the main contributors to the overall TEQ in sintering emissions (ca. 85%). Amongst WHO-12 PCBs, PCB 126 was the only noteworthy contributor to total TEQ (ca. 5–7%), a similar contribution to that from PCDDs. Based on the measurements that Corus UK has undertaken at these three sinter plants, annual mass releases of WHO-12 PCBs and PCDD/Fs have been calculated. For UK sinter plants, a total mass release of 29.5 g WHO-TEQ per annum [WHO-12 PCBs + PCDD/Fs] has been estimated, representing 9% of the total PCDD/F emissions to the UK atmosphere. Measurements were also carried out at a UK sinter plant to determine the windleg emission profile of WHO-12 PCBs. Results showed that WHO-12 PCBs were formed in the same regions of the sinter strand as 2,3,7,8-PCDD/Fs, indicating that there was a strong correlation between the formation of WHO-12 PCBs and PCDD/Fs in the iron ore sintering process.

Influence of nature and particle size distribution on granulation of iron ore mixtures used in a sinter strand

The ore mixture granulation process is described and the granulation fitness of a series of iron ores forming part of the mixture is studied. Good granulation and control of the maximum sintering temperature makes it possible to achieve the optimum sinter structure, formed by a hematite nucleus surrounded by a lattice of acicular ferrites. The granulation fitness of ore mixtures used to manufacture a series of sinters in a pilot plant are also determined. It is verified that sinters with an optimum structure have been obtained. A series of iron ores are classified using the granulation index (G index). The evolution of the G index of ore mixtures used in ACERALIA during recent years is considered and it is verified how improvement of the G index increases productivity and decreases coke consumption in the sinter strand.