Study of coal pyrolysis by thermo-gravimetric analysis (TGA) and concentration measurements of the evolved species

Abstract

Mass losses of coal and the mole fractions of evolved species were measured during coal pyrolysis using a thermo-gravimetric analyzer and a real-time gas analyzer, respectively. Coal samples from Shin-Wha, China were pyrolyzed using a lab-scale furnace in a nitrogen atmosphere under non-isothermal conditions at heating rates of 5, 10, 20, and 30 °C/min until the furnace wall temperature reached 900 °C. Using a non-isothermal kinetic method based on a first-order model, experimental data from the thermo-gravimetric analysis (TGA) and real-time gas analysis (GA) were interpreted using a single model and a parallel model, respectively. Using the TGA data, the activation energy E and pre-exponential factor A were 130 kJ/mol and 3.19E + 07 min −1, respectively. Using both TGA and GA data, the calculated activation energies for CO {1}, CO {2}, H 2{1}, H 2{2}, total gaseous hydrocarbon(THC), and the liquids (tar and water) were 67.0, 204.2, 72.0, 43.8, 78.7, and 97.0 kJ/mol, respectively, where subscripts {1} and {2} refer to the first and second peaks of GA data. The yield of the liquids was obtained by subtracting the total gaseous mass from the derived thermo-gravimetric (DTG) data. The yields of the total gases, liquids, and char ranged from 20 to 30%, 10 to 15%, and 62 to 64%, respectively. The thermal lag effect and the promotion of lighter species by the slower heating rate were observed using the TGA and the GA, respectively. The cold gas efficiency ( CGE) ranged from 0.37 to 0.52. Slower heating conditions enabled extended residence time for volatiles within the particles, and thus promoted the generation of lighter species. The Brunauer, Emmett, and Teller (BET) surface increased (5–10 °C/min) as the heating rate increased, reached a maximum, and then decreased (10–30 °C/min).