G. San Miguel

Slow pyrolysis of olive stones in a rotary kiln: Chemical and energy characterization of solid, gas, and condensable products

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 (LHVo up to 37.1 MJ/kg) and energy density (26.7 GJ/m3). The process also involved changes in the surface chemistry (increasingly hydrophobic nature) and textural properties of the solid (formation of cracks and internal vo...

Biomass pyrolysis kinetics through thermogravimetric analysis

Abstract The objective of this work is to produce a semi-empiric kinetic model for the pyrolysis of five biomass feedstocks widely generated in the Mediterranean area. These include olive stone, pine wood, paulownia wood, cardoon and vine shoots. The biomass samples were characterized for their elemental composition. Thermogravimetric analyses (TG/DTG) were conducted under inert atmospheric conditions. The experimental results were fitted in order to determine the kinetics parameters in terms of reaction order ( n ), specific rate constant ( k ) and activation energy ( E a ) for each considered reaction.

Environmental and economic analysis of power generation in a thermophilic biogas plant

This paper investigates the environmental and economic performance of the power production from biogas using Life Cycle Assessment, Life Cycle Costing and Cost Benefit Analysis methodologies. The analysis is based on a commercial thermophilic biogas plant located in Spain where is installed a Combined Heat and Power system that produces electricity that is sold to the grid. Power generation has been assumed as the only function of the biogas system, expanding the system boundaries to include the additional function related to the end-of-life management of the biowastes. Thus environmental burdens from the conventional management of residues were calculated separately and subtracted. The base scenario involves using agri-food waste, sewage sludge and pig/cow manure as substrates. This situation is compared against an alternative scenario where the production of synthetic fertilizer is surrogated by the digestate. The results have shown that the most impacting activities in all impacts categories of power production are primarily attributable to the operation and maintenance of the biogas plant except for water resource depletion and climate change. The avoided emissions associated with the conventional management of pig/cow manure more than offset GHG emissions of the biogas system resulting in a negative impact value of -73.9gCO2eq/kWh in the base case scenario. The normalized results show that local impact categories such as primarily human toxicity, fresh water ecotoxicity and particulate matter are the most significantly affected by the biogas system while global impact categories as climate change and ozone depletion are less severely affected. The operation and maintenance phase is also shown to be the largest contributor after the life cycle cost analysis, followed by the construction and dismantling of the biogas plant and the profitability of the project is primarily related to the income obtained from the management of the biowastes used as substrates.