Effect of atmosphere reaction and heating rate on the devolatilization of a Colombian sub-bituminous coal

Effects of pyrolysis atmosphere on the porous structure and reactivity of chars from middle and high rank coals

“…Figure 3 shows the DTG curves obtained from the mass loss tests under N 2 and CO 2 -atmosphere in both coals (See Figure 3a, c and e to SA coal and Figure 3b, d and f to HVBC coal). For both coal rank and independently of the heating rate, it was found that at higher heating rates, there is a greater mass loss rate, as reported by other studies (Niksa, Heyd, Russel, & Saville, 1985;Strezov, Lucas, Evans, & Strezov, 2004;Valdés et al, 2016). DTG profiles clearly show the presence of the devolatilization steps in N 2 and CO 2 for SA and HVBC samples.…”

“…These results can be explained through the greater diffusive type restrictions that volatiles have in the presence of CO 2 (Molina & Shaddix, 2007;Valdés et al, 2016), which implies a minor interaction between the CO 2 -atmosphere and char (less occurrence of secondary processes between CO 2 and char at low temperatures). Therefore, a reduction in the values of the Ea and reaction rate can be expected.…”

“…This can be explained by the reactive effects of the atmosphere on some of the volatile species which are released and the development of porous structure (Yin & Yan, 2016). Also, the high temperature (above 600 °C) favors the occurrence of the CO 2 -gasification reaction (Su et al, 2015;Valdés et al, 2016;Xu et al, 2016); which provided a slightly higher reaction rate when the coals were pyrolyzed under a CO 2 -atmosphere compared to N 2 (see Figure 4c and d).…”

“…Then, for chars obtained from the pyrolysis of both coal samples and both reaction environments with particle size distributions between 45 and 38 mm, (Figure 2b) combustibility tests were implemented. The measurements were performed under non-isothermal conditions following the same procedure described by the FWO method (Flynn-Wall-Ozawa) (Ozawa, 1965;Flynn & Wall, 1966) as described by Valdés, Marrugo, Chejne, Román, & Montoya (2016). A particle bed height of less than 2 mm was fixed, which corresponded to 10mg of sample in the crucible placed in the TGA.…”

“…The analyses of mass loss and mass loss rate were used to calculate the activation energy, describing the thermal devolatilization mechanism of both coals during the pyrolysis processes with different conversion rate (a), using a method for various heating rates (more methodological details can be consulted in Valdés et al (2016)). The results presented in Figure 4 suggest that since the porous structure of both coals is similar (See Figure 1), the physicochemical composition and the reaction environments are responsible for the variations in the devolatilization kinetic rates.…”