The kinetics and mechanism of the combustion of the carbon in biochar from oak, as studied in an electrically heated, fluidised bed of sand
Year: 2024
Type: article
Abstract: The oxidation of small particles (size 200 μm) of char from oak has been studied, by adding a small batch of them to an electrically heated bed of inert, silica sand, fluidised by mixtures of O 2 and N 2 . The concentrations of CO, CO 2 , and O 2 , in the off-gases from the bed were continuously monitored, enabling the rate of combustion and also the fraction, X , of the carbon oxidised in each particle to be measured throughout combustion at different, well-controlled temperatures. The rate of oxidation declined as (1 – X ) during burnout , b e c a u s e t h e O 2 freely contacted the carbon in these tiny particles, whose oxidation was kinetically controlled at 700 °C and below. In fact, these tiny char particles burned in the fluidised bed at 500–700 °C in Zone 1 according to S 0 (1 – X )( k 5 C O2 + k 6 ) per g of char. This matches Hurt and Calo’s three-step mechanism, whereby a porous char burns at a rate controlled by two reactions, one first-order in O 2 , the other zeroth-order in O 2 . Reactions (V) and (VI) were found to be, respectively, k 5 = 1.7 × 10 3 exp (−139 ± 18 kJ mole −1 /R T ) m s −1 and k 6 = 1.5 exp (−92 ± 20 kJ mole −1 /R T ) mole s −1 m −2 . Reaction (V), between O 2 and a surface complex containing oxygen, became faster as X increased, if the temperature exceeded 600 °C; catalysis by potassium was suspected as providing this extra reactive boost.
Source: Fuel
Authors: E.J. McMurchie, J. Olatunji, K.Y. Kwong, E.J. Marek, A.N. Hayhurst
Language: English
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,200
OpenAlex ID: W4401988129