Autothermal pyrolysis of wood chips in a rotary kiln pilot plant
Résumé
Today, renewable energy represents a significant interest to reduce the fossil fuels dependence and to rely on environmental technologies, especially biomass energy, due to the fact that it reduces CO2, NOx and SOx emissions in the atmosphere, as well as compared with fossil fuel, has a much shorter period of life cycle (from the growth of biomass to the final utilisation). While the traditional use of the biomass was the combustion, today different thermochemical processes exist to convert the biomass into bio-energy. In our case, the gasification seems to be an effective way to convert biomass (wood chips) into syngas with a step of pyrolysis prior to the gasification to obtain the charcoal. For this purpose, the "BIOH2" project was devoted to investigate this technology on two phases; the first step was focuses on the study of autothermal pyrolysis of wood chips in a rotary kiln, while the second phase will be dedicated to the biomass pyrogasification in a pilot plant in order to produce a synthesis gas. The final aim of the project is the construction of a pilot unit of biomass pyro-gasification (100 kg/h). In the current work, we studied the autothermal pyrolysis of various wood chips in a rotary kiln pilot plant of 30 kg/h in the presence of an excess air. Tests were carried out with three types of wood chips, comprising the white pine, maple and spruce and conducted at pyrolysis temperature without input of energy during the pyrolysis phase; the temperature has been stabilized at 450 °C (pyrolysis temperature) during the entire duration of the test. The pyrolysis gas analysis showed oxygen content of less than 3%, which indicates important oxygen consumption during the tests; the charcoal analysis showed a ratio of carbon of more than 75%. This will be used in a second step of gasification. A second phase of gasification will be performed in a new unit of 100kg/h a plant with two phases technology (autothermal pyrolysis with oxygen supply and an entrained flow gasifier) in order to obtain a synthesis gas.