Very fine sand is prepared in a well-defined and fully decompactified state by letting gas bubble through it. After turning off the gas stream, a steel ball is dropped on the sand. On impact of the ball, sand is blown away in all directions ("splash") and an impact crater forms. When this cavity collapses, a granular jet emerges and is driven straight into the air. A second jet goes downwards into the air bubble entrained during the process, thus pushing surface material deep into the ground. The air bubble rises slowly towards the surface, causing a granular eruption. In addition to the experiments and the discrete particle simulations we present a simple continuum theory to account for the void collapse leading to the formation of the upward and downward jets.

were determined from these images using a bubble detection algorithm. The particle velocity and voidage measurements were combined to calculate particle fluxes. Based on this quantity the numerical and experimental results were compared.

HIsarna is a new coal based smelting reduction process, which has the excellent features of using coal and fine hematite ore directly as raw materials instead of coke and pellet. In this context, the reduction kinetics of hematite ore fines in the smelting cyclone was studied in the laboratory scale. The gas-solid and gas-molten particle reduction behaviour were studied with a High-temperature Drop Tube Furnace (HDTF) and a combination of various characterization methods was used to track the kinetic behaviour such as chemical titration, optical microscope and Scanning Electron Microscope (SEM). A series of experiments with different reaction time (210-2 020 ms) has been conducted at different temperatures from 1 550 K to 1 750 K, thus enabling the kinetic study of the partially reduced hematite ore particles. It was found that a quantity of micro pores was formed during the reduction process mainly due to the loss of oxygen. The un-reacted shrinking core model could be used to describe both gas-solid particle reaction and gas-molten particle reaction.

In the smelting cyclone of HIsarna process, both thermal decomposition and gaseous reduction of iron ore contribute to the expected pre-reduction degree about 20%. However, the fine ore reduction and melting process in the smelting cyclone is extremely fast and it is very difficult to differentiate between the thermal decomposition and gaseous reduction. This study focused on the thermal decomposition mechanism of the fine iron ore under different conditions. Firstly, the theoretical evaluation has been conducted based on the thermodynamics, and then the laboratory investigation was conducted in three stages with three reactors: the TGA-DSC, the electrically heated horizontal tube furnace and the High-temperature Drop Tube Furnace (HDTF). According to the experimental results of the first two stages and the theoretical evaluation, it was found that the temperature of intensive thermal decomposition of Fe2O3 in the inert gas environment is in the range of 1 473-1 573 K, while the thermal decomposition of Fe3O4 could be sped up when the temperature is above 1 773 K in the inert gas. Temperature plays an important role in the thermal decomposition degree and reaction rate. Finally, it was found that the thermal decomposition of the individual iron ore particles took place very rapidly in the HDTF and no significant influence of the particle size and residence time (t ≤ 2 020 ms) on the equivalent reduction degree could be observed, when the particle diameter was smaller than 250 μm in the CO2 gas.

HIsarna is a new alternative ironmaking process of ULCOS program, which is under intensive development at EU. It uses coal and fine iron ore directly as raw materials instead of coke and pellet. In this context, the melting and pre-reduction behaviour of hematite ore in the smelting cyclone of HIsarna process was studied in the laboratory scale. The experimental study which used the typical reaction conditions of smelting cyclone in the pilot plant supplies a good reference to the HIsarna process and the results are helpful on determining the temperature range, gas composition and particle size in the smelting cyclone. All the experiments were performed in a High-temperature Drop Tube Furnace. The experimental temperature was varied from 1 550 K to1 750 K. A series of experiments have been conducted with different reaction time which was varied from 210 ms to 2 020 ms, thus enabling the characterization of partially reduced samples. It was found that the reduction degree increases with the increase of temperature and residence time, while decreases with the increase of particle size. The maximum reduction degree at the studied conditions is approximately in the range of 23-30%. Both solid sample and molten sample were obtained at the current experimental conditions. The completely gas-solid particle reduction took place at 1 550 K, 1 600 K for the residence time up to 2 020 ms. Fully molten particles can only be obtained at the temperature higher than 1 700 K.