Steam gasification characteristics of a pine-nut shell in a thermobalance and a fluidized bed reactor

Abstract

Pyrolysis kinetics of a pine nut shell in a thermo gravimetric analyzer (TGA) and the combustion and steam gasification kinetics of a pine nut shell's chars in a thermobalance reactor were determined. Also, the steam gasification characteristics of the pine nut shell were determined in a fluidized bed reactor. The maximum pyrolysis reaction rate is obtained at 360degreesC from the TGA and DTG studies. The activation energy and the pre-exponential factor of the char were determined from the Arrhenius plot based on the shrinking core model. The effects of the reaction temperature (350degreesC - 950degreesC) and the O-2 partial pressure on the combustion kinetics and that of the steam partial pressure (0.4 - 0.8atm) on the gasification kinetics were determined in a thermobalance reactor. In the combustion reaction, the activation energies and the pre-exponential factors are found to be 21.7 kcal mol(-1) at 61.9 s(-1) atm(-1) and 2.36 kcal/mol at 0.0029 s(-1) atm(-1) in the reaction control and the pore-diffusion control regimes, respectively. The reaction order is found to be 1.0 with respect to the O-2 Partial pressure at 750degreesC. In the steam gasification reaction, the activation energy and the pre-exponential factor are found to be 16.9 kcal mol(-1) at 0.0076 s(-1) atm(-1) and 2.67 kcal mol(-1) at 0.00036 s(-1) atm(-1) in the reaction control and the pore-diffusion control regimes, respectively. The reaction order is found to be 0.77 with respect to the H2O partial pressure at 750degreesC. The effects of the gas velocity (2U(mf) - 4U(mf)), reaction temperature (700degreesC - 850degreesC), steam/carbon ratio (0.56 - 1.12) and O-2/C ratio (0.16 - 0.32) on the gas composition, gas yield, cold gas efficiency and the calorific value of the product gas were determined in a fluidized bed reactor(10 cm-i.d. x 1.6m-high) with the feeding rate of the pine nut shell of 1 - 3 kg hr(-1). The carbon conversion, calorific value, cold gas efficiency and the total product gas yield increased with an increasing temperature. The hydrogen concentration increases with an increasing reaction temperature and the gas velocity and steam/carbon ratio as well as the hydrogen concentration decreases with an increasing O-2/C ratio in the fluidized bed reactor.