Kinetic study of catalytic gasification of wood char impregnated with different alkali salts. (1st January 2017)

• Record Type: Journal Article
• Authors: Kirtania, Kawnish; Axelsson, Joel; Matsakas, Leonidas; Christakopoulos, Paul; Umeki, Kentaro; Furusjö, Erik
• Is Part Of: Energy. Volume 118(2017)
• Page Start: 1055
• Page End: 1065
• Publication Date: 2017-01-01
• Subjects: Alkali -- Gasification -- Catalytic -- Biomass -- Morphology -- Kinetics; Power resources -- Periodicals; Power (Mechanics) -- Periodicals; Energy consumption -- Periodicals; 333.7905
• DOI: 10.1016/j.energy.2016.10.134
• Languages: English
• ISSNs: 0360-5442

Abstract

Abstract: Different concentrations (0.1 and 1 M K + /Na + ) of salt solutions (K2 CO3, Na2 CO3, NaOH and NaCl) were used to impregnate alkali in sawdust. After devolatilization, char samples were gasified at different temperatures (750–900 °C) under CO2 in a macro-thermogravimetric analyzer for gasification kinetics. Morphologically, three classes of chars could be identified. Chars experiencing the highest catalytic influence were in Class-2 (0.5 M K2 CO3 and 1 M NaOH) with a swollen and molten surface. In contrast, Class-1 (wood char like) and Class-3 (with salt deposits) chars showed moderate and low catalytic effect on gasification reactivity respectively. It is believed to be related to char surface swelling and alkali salt used. At 850 °C or below, the reactivity increased linearly (Class-1 and Class-3 Char) with initial alkali content up to 2200 mmol alkali/kg of char (except for NaCl). The same reaction rate was maintained until 3600 mmol/kg of char of alkali loading (Class-2) and then decreased. However, no trend was observed at 900 °C due to drastic change in reactivity of the samples, probably due to alkali transformation. Among the salts, K2 CO3 (0.5 M) was found to be the most suitable for catalytic gasification due to its high catalytic activity in combination with relatively low carbon leaching. Highlights: Influence of biomass alkali impregnation on char gasification studied in TGA. Evaluation of kinetic modeling strategies for alkali catalyzed char gasification. Alkali impregnation increases char yield and influences char morphology. Alkali impregnation up to 2.2 mol/kg char increases gasification rate at ≤ 850 °C. At T = 900 °C alkali transformations lead to a distinctly different behavior.