Devolatilisation characteristics of coal and biomass with respect to temperature and heating rate for HIsarna alternative ironmaking process

Abstract

Abstract HIsarna process offers a novel low CO2 emission alternative to the blast furnace for primary iron production. This new smelting ironmaking technology is flexible in raw material usage such as the substitution of biomass for coal as a reductant. Reduction is conducted through multiple mechanisms within the smelting vessel including gaseous reaction products from thermal decomposition of volatile matters reacting directly with iron oxide containing slags and injected iron ore. In this study, four coals with notable differences in volatile matter content along with two biomass samples sourced from wood and grass origins were investigated for the selection of suitable fuel mix. Thermogravimetric analysis (TGA) was used to measure the weight loss of the carbonaceous materials and a vertical tube furnace coupled with a quadrupole mass spectrometer (VTF-QMS) was employed for off-gas analysis during the devolatilisation. During TGA tests the samples were heated under a 99.9999% argon atmosphere to 1500\xa0°C at three different heating rates to investigate the kinetics of thermal decomposition for these materials. Through use of the Kissinger– Akahira–Sonuse model an average activation energy was determined as a function of the conversion degree. The furnace experiments were carried out under a 99.999% Ar atmosphere to a peak temperature of 1500\xa0°C, at a heating rate of 10\xa0°C/min. The wt% of reducing gases e.g. H2, CO, and hydrocarbons, and the temperature required for these gases to evolve was notably different for each materials, but the respective maximum peaks of evolution of these gases corresponded well to the maximum rate of mass loss. Furthermore, the off-gas analysis reveals torrefied grass contains large amount of water and carbon dioxide which will be released at very low temperature, therefore pre-treatment to the temperature of ~400\xa0°C is necessary to produce chars with similar properties to coal injected in HIsarna.