Effect of calcium dispersion and graphitization during high-temperature pyrolysis of beech wood char on the gasification rate with CO2

FUEL

卷:283

Article

Schneider, Christoph¹  Walker, Stella¹  Phounglamcheik, Aekjuthon²  Umeki, Kentaro²  Kolb, Thomas^1,3 

[1] Karlsruhe Inst Technol, Engler Bunte Inst, Fuel Technol, EBI Ceb, Engler Bunte Ring 1, D-76131 Karlsruhe, Germany

[2] Lulea Univ Technol, Div Energy Sci, Dept Engn Sci & Math, S-97187 Lulea, Sweden

[3] Karlsruhe Inst Technol, Inst Tech Chem, ITC Vgt, Hermann von Helmholtz Pl 1, D-76344 Eggenstein Leopoldshafen, Germany

关键词: Biomass char;    Pyrolysis;    Gasification;    Graphitization;    Ash dispersion;   

DOI  :  10.1016/j.fuel.2020.118826

来源: Elsevier

【 摘 要 】

This paper presents thermal deactivation of beech wood chars during secondary pyrolysis in a drop-tube reactor. Pyrolysis temperature was varied between 1000 degrees C and 1600 degrees C at a constant residence time of 200 ms. The effect of pyrolysis conditions on initial conversion rate Ro during gasification, graphitization of the carbon matrix and ash morphology was investigated. Gasification experiments for the determination of R-o were conducted in a thermogravimetric analyzer using pure CO2 at 750 degrees C and isothermal conditions. A linear decrease in initial conversion rate R-o was observed between 1000 degrees C and 1400 degrees C. However, a strong increase of Ro at 1600 degrees C was encountered. Micropore surface area of the secondary chars showed no correlation with the initial conversion rate R-o during gasification with CO2. Graphitization of the carbon matrix was determined using X-ray diffraction and Raman spectroscopy suggesting the growth of aromatic clusters and graphite-like structures for increasing pyrolysis temperatures up to 1600 degrees C. Furthermore, CaO dispersion was analyzed quantitatively and qualitatively using temperature-programmed reaction at 300 degrees C as well as SEM/TEM. CaO dispersion D-CaO, decreases steadily between 1000 degrees C and 1400 degrees C whereas a strong increase can be observed at 1600 degrees C, which is in good accordance with the development of the initial conversion rate R-o as a function of pyrolysis temperature. SEM/TEM images indicate the formation of a thin CaO layer at 1600 degrees C that is presumably responsible for the strong increase in initial conversion rate Ro at this temperature. When excluding the catalytic activity of CaO via formation of the ratio R-o D-CaO(-1), increasing graphitization degree has a linear negative influence on char reactivity at pyrolysis temperatures between 1000 degrees C and 1400 degrees C.

【 授权许可】

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