TG-FTIR and kinetics of devolatilization of Sulcis coal

摘要

The N_2-pyrolysis of low-rank Sulcis coal was investigated by thermogravimetric techniques (TG/DTG) in the temperature range ambient to 1000 ℃ under dynamic heating conditions (50, 75, and 100 ℃ min~(-1) heating rates). Little differences in the mass losses with heating rates were observed. From thermogravimetric analysis it was established that coal pyrolysis consisted of three main stages: water evaporation; devolatilization of thermally labile and more stable volatiles; and char formation. The evolved gas (EGA) by Fourier transform infrared spectrometry (FTIR) coupled to the thermobalance under 100 ℃min~(-1) heating rate was conducted for the identification of the gaseous species and their evolution profiles during coal thermal degradation. The temperatures of maximum rate of release of H_2O, CO_2, CO, COS, C_2 H_4, as well volatile fragments originating from breaking of covalent bonds such as alkyl and ether groups, were in agreement with the temperature of maximum mass-loss rate around 466 ℃. Meanwhile the maximum releasing rates of SO_2, CH_4, and NH_3 took place at 330, 575, and 690 ℃. respectively. An increase of CO emission intensity at 770 ℃ was indicating in situ gasification with CO_2 -bearing product of freshly formed char. The kinetic processing of non-isothermal TG data was performed by isoconversional method. In the coal conversion regions α = 5-40% the apparent activation energies were almost constant suggesting a single-step reaction path. The calculated average £ value was 189 kJ mol~(-1). A kinetic compensation effect existed between £ and In A: the linear dependence provided an average pre-exponential factor A_0 value of 2 × 10~(11) min~(-1). With further increase of conversion degree a complex £ dependence on α was evident as the coal thermal degradation process underwent a multi-step reactions.