Analytical and Thermal Evaluation of Carbon Particles Recovered at the Cyclone of a Downdraft Biomass Gasification System

Gasification of biomass gives off syngas that is contaminated mostly by carbon particulates and tars. The degree of contamination is attributed to factors such as gasification process, type of gasifier and type of biomass material. Downdraft gasifier minimizes the production of tar to a tolerable limit for engine applications; however, carbon particles still pose a challenge particularly with the integration of a heat exchanger for the purpose of heat recovery from the product gas. The presence of carbon particles in the syngas does influence the heat recovery process and materials used in the recovery. Hence, there is need for the characterization of these carbon particles to ascertain their chemical compositions, thermal properties and morphological features. This study was aimed at evaluating the characteristic features of carbon particles recovered from the syngas stream during gas cleaning at the cyclone. The elemental analysis of the carbon particle samples was performed using energy dispersive X-ray spectroscopy. An electron beam from scanning electron microscopy was passed through the sample surface at a magnification of 1000× and an accelerating voltage of 15 kV to determine the morphological features of the carbon particles. Their thermal properties were investigated using a thermogravimetric analyzer at a heating rate of 10°C/min. A weight loss of approximately 5.4 wt % was recorded at the maximum temperature of 900 °C. Silicon, oxygen and carbon were found to be the dominating elements in the carbon particulate.