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To investigate the reduction behaviour of different reductants such as charcoal (CC), thermal coal (TC), and carbon black (CB) with HIsarna slag, a series of isothermal reduction experiments were performed in a vertical tube resistance furnace (VTF), coupled with a Quadrupole mass spectrometer (QMS) at 1450 °C, 1475 °C and 1500 °C. The results confirm that the highest overall reduction rate was achieved by CC, followed by TC and CB. The reduction mechanism between FeO containing molten slag and the selected carbonaceous materials is determined by studying the morphology of the water quenched samples at the intervals of 1.5, 3 and 5 minutes, using optical and scanning electron microscopes. The results reveal that the overall reaction is controlled by two main mechanisms: (1) nucleation and growth of CO bubbles, proceeded by the gaseous intermediates CO and CO2; and (2) diffusion of FeO in the molten slag. The initial reduction period in which chemical reaction control is dominant, can be described by the Avrami–Erofeev model, whereas the final period is described by the three-dimensional diffusion model. [ABSTRACT FROM AUTHOR]

To investigate the use of biomass in the novel HIsarna technology, the reduction of FeO in the slag by chars produced from thermal coal (TC), charcoal (CC), and Bana grass char (BGC) was studied. A drop tube furnace coupled with a quadrupole mass spectrometer (DTF-QMS) was employed to study the injection of chars into pre-melted slag in the temperature range between 1450 °C and 1525 °C. The reduction rate was calculated from evolved gases and the extent of FeO reduction was confirmed by wavelength-dispersive X-ray fluorescence (WDXRF). The FeO reduction proceeds through two stages, starting with a rapid reduction, which is dependent on the carbon type, and followed by gradual leveling off. The reduction rate with the charcoal char (CC) was the highest, over 60 pct reduction was achieved in the first 500 seconds at 1500 °C, while ~ 50 and 40 pct achieved with TC and BGC chars, respectively, for the same reaction time. The kinetic analysis suggests that the first and second stages of the reaction can be described by the second-order (F2) and three-dimensional diffusion (D3) models, respectively. The apparent activation energy values for the first stage were 290, 229 and 267 kJ/mol for reactions with TC, CC and BGC chars, while 265, 369, and 282 kJ/mol were obtained for the second stage. Based on the experimental data and kinetic results, it can be concluded that the first stage is controlled by chemical reactions on the carbon surface, and the second stage is influenced by a mixed-controlling mechanism. [ABSTRACT FROM AUTHOR]

• Effect of rapid devolatilization on carbonaceous materials investigated for the HIsarna alternative ironmaking process. • Chars produced under high temperature and rapid heating via drop tube furnace (DTF) • Explained the reactivity behaviour of chars from different carbon sources produced under rapid heating. • Revealed the effect of temperature on the physical structure for coal and biomass materials. • To measure the real-time structural changes via high temperature confocal scanning laser microscope (HT- CSLM) To evaluate the potential of using renewable biomass in the novel HIsarna technology, reactivity of thermal coal (TC), charcoal (CC), Bana grass char (BGC) before and after rapid devolatilization at 1500 °C in a drop tube furnace (DTF) was investigated. Thermogravimetric (TG) was used for CO 2 gasification study, and high temperature confocal scanning laser microscope (HT-CSLM), Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) were used to characterise the morphology of all three raw carbonaceous materials and their chars produced by rapid devolatilization. CC has fastest gasification reaction before and after rapid heat treatment, and BGC raw is more reactive than TC raw but BGC 1500 °C and TC 1500 °C have very similar gasification behaviour. The reactivity index of the rapidly devolatilized char is reduced to 84.21% (BGC), 92.11% (TC) and 94.23% (CC) compared to their raw materials. This shows that BGC is more severely affected by the rapid devolatilization, and this behaviour is likely to be governed by the high ash content which will melt and cause pore blockage during heat treatment. According to HT-CSLM results the average particle sizes decreased by 28%, 24% and 20 % for TC, CC and BGC respectively. While the SEM images shown that TC has gone through significant structural changes during the rapid devolatilization, but CC and BGC maintained their parent structural shapes. The BET results indicate that TC is non-porous, but both CC and BGC contain a large number of constricted micropores with significantly larger surface area. [ABSTRACT FROM AUTHOR]

• Rapid devolatilization of carbonaceous materials investigated for HIsarna technology. • Rapid heating via drop tube furnace with quadrupole mass spectrometer (DTF-QMS). • Explained the effect of temperature on variation of light gases in the rapid devolatilization. • Revealed the effect of temperature on the rate of carbon conversion for coal and charcoal. • R-factor obtained to give solid residual efficiency for different carbon sources. A drop-tube furnace coupled with quadrupole mass spectrometer (DTF-QMS) was employed to simulate rapid heating conditions that carbonaceous materials experience during HIsarna injection with the measurement of gas composition change as a result. A devolatilization study for thermal coal (TC) and charcoal (CC) samples was carried out at three temperatures of 1000, 1250 and 1500 °C under an initial high purity Ar gas environment. The volatiles released were measured online by QMS, while the char yield was determined directly by the weight of particles collected and the deficit was calculated by subtracting the gas yielded from the total weight loss. The study reveals that working temperature has a strong impact on the devolatilization rate, the maximum weight loss and the variation in gas species produced. Due to intensification in the carbon oxidation and secondary reactions at higher temperatures, there was an increase in the weight loss, which led to a greater yield of H 2 and CO but less yield of hydrocarbons, CO 2 and H 2 O. Despite lower volatile matter content in charcoal, the weight loss for charcoal (29%) was higher than that for thermal coal (23%) at 1500 °C. Although the amount of H 2 produced for both materials is similar, the amount of CO produced by charcoal is twice of that by thermal coal, and accounts for 79% of the total gas weight formed by charcoal. This suggests that a higher rate of carbon oxidation takes place through O 2 containing groups within the charcoal, which results in lower char efficiency. It was found that thermal coal produces a significant amount of tar, while a large number of particles in the form of soot/dust escaped from the bulk material during charcoal injection but no tar formation was observed. [ABSTRACT FROM AUTHOR]