Hydrogasification of Almond Shell Chars. Influence of Operating Variables and Kinetic Study

Abstract

The catalyzed hydrogasification of pyrolyzed almond shells was studied with the main objective of obtaining a gas with a high heating value (synthetic natural gas), as the major component of the gas is CH4 (with small amounts of CO). A kinetic study was also carried out using ideal models. Five experimental series were performed by varying particle size (0.4−2-mm diameter), initial sample weight (0.15−1 g), gas flow rate (150−300 cm3 min-1), temperature (700−900 °C), and hydrogen partial pressure (0.02−0.1 MPa). The range of particle size used in this work exerted little influence on the CH4 production. The hydrogasification rate was independent of the initial sample mass and hydrogen flow rate for values <0.25 g and >250 cm3 min-1, respectively. The particle size exerted a slight negative influence on the hydrogasification rate, whereas temperature and hydrogen partial pressure exerted positive effects. The optimum temperature for the process was found to lie in the range 800−850 °C, giving a production of gas of 1.86 Nm3/kg of converted char (where Nm3 indicates m3 at normal conditions, T = 0 °C and P = 1 atm) with a high heating value of 74 170 kJ/kg of converted char. The activation energy and reaction order with respect to hydrogen were found to be 103.1 kJ mol-1 and 1, respectively.