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Gasification reactivity of char with CO 2 at elevated temperatures: the effect of heating rate during pyrolysis
Author(s) -
Liu Hao,
Zhu He,
Yan Liye,
Huang Yongjun,
Kato Shigeru,
Kojima Toshinori
Publication year - 2011
Publication title -
asia‐pacific journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.348
H-Index - 35
eISSN - 1932-2143
pISSN - 1932-2135
DOI - 10.1002/apj.483
Subject(s) - char , pyrolysis , reactivity (psychology) , chemical engineering , wood gas generator , chemistry , volume (thermodynamics) , coal , reaction rate , fluidized bed , materials science , integrated gasification combined cycle , waste management , syngas , organic chemistry , thermodynamics , catalysis , medicine , physics , alternative medicine , engineering , pathology
ABSTRACT Integrated coal gasification combined cycle (IGCC) technology is being promoted to make better use of energy resources, and an entrained‐flow gasifier is a key item of equipment in the process due to its high gasification efficiency, smooth discharge of molten ash, etc. The temperature and heating rate under entrained‐flow gasification conditions are very high, and these two parameters can influence the gasification reactivity of a char with CO 2 . Therefore, the clarification of characteristics and mechanisms of char gasification under conditions close to entrained‐flow gasification is very important. To obtain a valid kinetics of char gasification, it is necessary to clarify the effect of heating rate during pyrolysis on char reactivity. The effect of heating rate during pyrolysis on the gasification reactivity of three types of chars in CO 2 was investigated experimentally at elevated temperatures in a novel fluidized bed. It was shown that even at elevated temperatures, the heating rate has significant influence on the char reactivity during gasification. A higher heating rate during pyrolysis leads to higher char reactivity of gasification, however it has only limited effect on the activation energy of char gasification with CO 2 . The char reactivity is closely related to its specific surface area and pore volume. The high reactivity of a char derived from pyrolysis at a high heating rate is most likely due to its enhanced porous structure as a result of the rapid release of volatile matter at a high heating rate. The effect of heating rate during pyrolysis on char reactivity is pronounced at low temperatures, and is very different for various coal types, i.e. very pronounced for a low‐rank coal. The gasification reactivity of a char is related to both the char pore structure and temperature, which suggests that even at elevated temperatures the gasification of a char with CO 2 is controlled by both chemical reaction and diffusion inside the particles. Our results demonstrate that it is necessary to derive the gasification kinetics of a char at a high heating rate to obtain valid kinetic equations for an entrained‐flow gasifier. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.