Publication Date:
2015-07-03
Description:
The aim of this work is to investigate the slow pyrolysis of olive stones in a rotary kiln as a means to increase the fuel properties and potential use of this renewable solid fuel. The pyrolysis process takes place primarily at temperatures between 300 and 500 °C resulting in the transformation of the solid biomass into a biochar, a pyrolysis liquid (up to 38.1 wt. %) and a non-condensable gas fraction (up to 35.4 wt. %). This thermal treatment has a positive influence in the fuel properties of the solid fraction in terms of increased C content (up to 75.9 wt. %), reduced O/C and H/C ratios (down to 0.28 and 0.03), reduced volatile matter and moisture content (down to 6.9 wt. % and below 1.0 wt. %, respectively), increased fixed carbon (up to 90.2 wt. %), increased Lower Heating Value (LHV o up to 37.1 MJ/kg) and energy density (26.7 GJ/m 3 ). The process also involved changes in the surface chemistry (increasingly hydrophobic nature) and textural properties of the solid (formation of cracks and internal voids, resulting in the development of a pore structure of up to 0.193 cm 3 /g and a surface area up to 507 m 2 /g). The condensable and gas fractions resulting from the pyrolysis process may also be used for their fuel properties. Thus, the pyrolysis liquid exhibited a high water content (62.5 wt. %), a mass density of 1.063 kg/m 3 , a viscosity of 1.33 cSt, and a Higher Heating Value (HHV o ) of 16.9 MJ/kg. The gas fraction resulting from the pyrolysis of olive stones contains high concentrations of combustible gases like CO and H 2 , and lower proportions of light hydrocarbons. The gas fraction exhibited HHV up to 6.83 MJ/Nm 3 due primarily to CO and H 2 , while the formation of light hydrocarbons was very limited. The energy distribution resulting from the pyrolysis of olive stone at 700 °C (following completion of the thermal degradation) is as follows: solid fraction 48.2%; oil fraction 11.0%; and gas fraction and energy losses (by difference) 40.8%.
Electronic ISSN:
1941-7012
Topics:
Energy, Environment Protection, Nuclear Power Engineering
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