Thermogravimetric investigation of four fuels

The KRAV project focuses on small-scale CHP plants running on biomass, included low quality biomass fuels. In order to be more cost efficient, it is a need to be able to burn low quality fuels in small-scale CHP plants. Four fuels (wood pellets, demolition wood, coffee waste and glossy paper) were investigated in this report, with TGA-MS technique. Two atmospheres were used, the combustion experiments were carried out in argon with 21 vol% oxygen and the pyrolysis experiments were carried out in pure argon. Three different heating rates (5, 20 and 100 K/min) were used, to investigate the influence of the heating rate on the fuel conversion. Coffee waste releases volatiles at the lowest temperature, but the release is slowest in this case, followed by wood and demolition wood, and glossy paper releases volatiles at the highest temperature. The volatiles release temperature is not affected by the presence of oxygen but increases slightly with increasing heating rate. The volatiles release is followed by the char conversion process at higher temperatures, and this process is slow. The process is faster in the presence of oxygen. When oxygen is not available in the reactive gas, the char does not convert completely. The char conversion rate decreases with increasing heating rate and the portion of unconverted char in the ash increases. In the combustion experiments, coffee waste ignites at 5 K/min heating rate, all fuels ignite at 20 K/min heating rate and none at 100 K/min heating rate. The results derived in these TGA experiments will together with planned accompanying macro-TGA experiments provide useful fundamental knowledge about the characteristics of the fuels.