Pyrolysis of Almond Shells. Energy Applications of Fractions

The pyrolysis of almond shells residues were studied in nitrogen atmosphere in a laboratory fixed bed reactor. The influence of the temperature (300−800 °C) and the heating rate (5−20 K min^-1) on the composition and properties of the different fractions were analyzed. As the temperature was increased a decrease in the char yield and an increase in the gas yield was observed. The oil fraction yield passed through a maximum at temperatures between 400 and 500 °C. The decline at higher temperatures was likely due to the strong cracking, which increased the gas yield. The increase of the heating rate leads to a slight decrease of the char and oil yields and an increase of the gas yield. The production varied in the ranges between 21.5 and 47.3% for char, 31−51.5% for oil, and 11.4−47.5% for gas, with a maximum higher heating value of 29.0 MJ kg^-1, 14.1 MJ kg^-1, and 15.5 MJ N^-1 m^-3, respectively. The char had a high fixed-carbon content (>76%) as well as a high heating value, and therefore it could be used as solid fuel, precursor in the activated carbons manufacture (specific surface area BET until 121 m² g^-1), or to obtain category-A briquettes. Aliphatic and aromatic hydrocarbons and hydroxyl and carbonyl compounds were the majority components of the oil fraction, which suggests their use as a source of chemicals of industrial interest. Also, it can be used as liquid fuel. The gas composition was identified as hydrogen, carbon monoxide, methane, and carbon dioxide and can be used to heat the pyrolysis reactor or to generate heat/electricity in a gas-turbine/vapor-turbine combined cycle.