378 / 2018-07-31 11:27:04

Gasification Reactivity and Char Evolution during CO2 Gasification of Bio-char with Molten Salts

全体主题 > 生物质燃气

Molten salts (MS), as an efficient catalyst and high heat transfer media, can be used to promote char gasification. In this study, the CO2 gasification of bio-char (BC) from the cotton stalk pyrolysis was conducted in a fixed bed reactor with molten salts. The influence of the molten salt to bio-char ratio (MS/BC: 1, 5, 10) as well as the gasification temperature (750, 800, 850 ºC) on the reactivity of gasification were studied. Various analysis methods, i.e. X-ray diffraction, Raman, nitrogen iosthermal adsorption and scanning electron microscope, were performed to characterize the evolution of char structure at different carbon conversion rate. Results show that the reactivity of char was significantly increased with the introduction of the molten salts into gasification. Furthermore, at high MS addition (MS/BC of 5 and 10), the char gasification rate experienced a decrease after the carbon conversion reached 0.7, which might be attributed to the less contact between char and CO2 at the presence of MS. The activation energies of 193.04, 51.39 and 104.08 kJ/mol were obtained for the BC, MS1BC1 and MS10BC1, respectively. From the char characterization analysis, a good correlation between char structure and gasification reactivity can be concluded. With the increasing of carbon conversion, char structure became more ordered with aromatic crystallites, while the aromaticity was decreased with the MS, which was favorable for gasification. With the proceeding of gasification, the ratio of the small aromatic ring systems (with 3 to 5 rings) to the large aromatic ring systems (no less than 6 rings) gradually decreased. And the decrease was more apparant at the absence of MS, which was due to the prior consumption of small rings, while the presence of MS could promote the decomposition of lager rings into small ones. İn regarding to the porosity, it was found that the porous structure of chars firstly developed quickly, followed by a gradual collapse until the end of gasification. The percentage of meso- and macropores was significantly increased with the introduction of MS, and it was even higher at high carbon conversion rate.