Effect of Char Preparation Conditions on Gasification in a Carbon Dioxide Atmosphere

Abstract

Pyrolysis conditions have a substantial impact on the properties of the resulting char and, consequently, on the kinetics of the gasification process. The aim of this study was to determine the impact of coal pyrolysis on the gasification stage. By applying the thermogravimetric method, kinetic analyses of CO 2 gasification of chars derived from Polish "Janina" coal were conducted. Gasification examinations were performed for chars prepared earlier in an argon atmosphere at various heating rates, which, after cooling, were subjected to CO 2 gasification (indirect char gasification). Examinations were also carried out in the case of chars formed during heating of coal samples in a CO 2 atmosphere (direct char gasification). Samples of chars were gasified in non-isothermal conditions of up to 1100 °C under 0.1 MPa pressure at various heating rates. The char gasification reaction order with CO 2 was determined with the use of the Coats−Redfern method, and it can be assumed that it is a first-order reaction. The activation energy and pre-exponential factor were calculated using two first-order models: Coats−Redfern method and Senum−Yang method. The results were subsequently compared to kinetic parameters calculated on the basis of the modelfree isoconversional method combined with the model-dependent Coats−Redfern method. Despite the differences in values of kinetic parameters obtained from the use of a given model, all results confirmed that the method of char preparation has an influence on the gasification stage and direct char gasification is more favorable. Activation energy obtained from the use of models based on the first-order reaction ranged between 275 and 296 kJ/mol for direct gasification of chars, while the chars gasified indirectly between 307 and 342 kJ/mol, depending upon the heating rate that was used. The model-free isoconversional method confirmed these results. The values for chars gasified directly amounted to E a = 257−277 kJ/mol, and the values for indirect char gasification obtained by the pyrolysis process at heating rates of 3, 10, and 20 K/min amounted to E a = 280−291, 287−309, and 289−305 kJ/mol, respectively.

Effect of pyrolysis temperature on pine sawdust chars and their gasification reactivity mechanism with CO2

“…Liu et al studied the gasification mechanism of low‐rank coal by using distributed activation energy model. Czerski et al studied the effect of pyrolysis conditions on char gasification at CO 2 atmosphere with the CR method and the Senum–Yang method. Compared with the isothermal thermogravimetric analysis, the nonisothermal thermogravimetric method is more appropriate for the research on the gasification process because it has many advantageous characteristics of the smaller experiments, shorter test duration, and more measured data .…”

Effect of Pyrolysis Atmosphere on the Gasification of Waste Tire Char

“…In the authors' previous work [21], a greater reactivity of the char from coal obtained in an atmosphere of carbon dioxide than in an atmosphere of argon was observed, but the heating rate during pyrolysis in the range between 3-20 K/min did not affect the course of gasification. In turn, the paper [22] shows that, during direct gasification of coals, they are more reactive than chars prepared from the parent coal and, thus, the gasification of coals progresses much faster and, consequently, with a higher formation rate of gaseous products.…”

The Effect of Temperature-Pressure Conditions on the RDF Gasification in the Atmosphere of Steam and Carbon Dioxide

“…It is also worth emphasising that most research on the gasification process is carried out on chars obtained from parent material; therefore, they do not include the pyrolysis process. On the other hand, pyrolysis plays a crucial role-it affects the composition and quantity of gaseous products and determines the properties of the resulting char [24]. Therefore, when examining the gasification process, in addition to the gasification reactions, the pyrolysis stage should be taken into account.…”