Effect of calcium dispersion and graphitization during high-temperature pyrolysis of beech wood char on the gasification rate with CO2. (1st January 2021)

• Record Type: Journal Article
• Authors: Schneider, Christoph; Walker, Stella; Phounglamcheik, Aekjuthon; Umeki, Kentaro; Kolb, Thomas
• Is Part Of: Fuel. Volume 283(2021)
• Publication Date: 2021-01-01
• Subjects: Biomass char -- Pyrolysis -- Gasification -- Graphitization -- Ash dispersion; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2020.118826
• Languages: English
• ISSNs: 0016-2361

Abstract

Abstract: This paper presents thermal deactivation of beech wood chars during secondary pyrolysis in a drop-tube reactor. Pyrolysis temperature was varied between 1000 °C and 1600 °C at a constant residence time of 200 ms. The effect of pyrolysis conditions on initial conversion rate R 0 during gasification, graphitization of the carbon matrix and ash morphology was investigated. Gasification experiments for the determination of R 0 were conducted in a thermogravimetric analyzer using pure CO2 at 750 °C and isothermal conditions. A linear decrease in initial conversion rate R 0 was observed between 1000 °C and 1400 °C. However, a strong increase of R 0 at 1600 °C was encountered. Micropore surface area of the secondary chars showed no correlation with the initial conversion rate R 0 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 °C. Furthermore, CaO dispersion was analyzed quantitatively and qualitatively using temperature-programmed reaction at 300 °C as well as SEM/TEM. CaO dispersion D CaO decreases steadily between 1000 °C and 1400 °C whereas a strong increase can be observed at 1600 °C, which is in good accordance with the development of the initial conversion rate R 0 as a function of pyrolysis temperature. SEM/TEM images indicate the formation of a thin CaO layer at 1600 °C that is presumably responsible for the strong increase in initial conversion rate R 0 at this temperature. When excluding the catalytic activity of CaO via formation of the ratio R 0 D CaO −1, increasing graphitization degree has a linear negative influence on char reactivity at pyrolysis temperatures between 1000 °C and 1400 °C.