Mechanism of kaolinite’s influence on sodium release characteristics of high-sodium coal under oxy-steam combustion conditions

Abstract

Oxy-steam combustion technology with high steam concentration is one of Oxy-fuel combustion. In terms of the distinct physicochemical properties of steam, the high steam concentration substantially affected the combustion by changing the heat capacity, radiation and gasification. This work aims to numerically investigate characteristics of Na under Oxy-steam atmosphere, mainly related to temperature, steam concentration, particle size and modification methods of kaolinite. Results indicated that the high temperature promoted the release of Na: compared with 750 °C, the Na content in ash at 950 °C has dropped by more than 27%. With the increase of particle size, the Na content increased obviously: when the particles increased from 0.25 ~ 0.27 mm to 1.7 ~ 4.75 mm, Na content increased by about 14%. Furthermore, steam enhanced pore structure of the particles, promoted the release of Na inside the coal. Compared with the steam concentration of 45%, the Na content at 70% was reduced by about 10%. The sequence of adsorption for Na was: KAc-kao > C-kao > R-kao > H-kao. KAc-kao has significantly increased the W-soluble and Insolubel content, about 27% and 65% respectively. Monte Carlo simulation results indicated that temperature showed significant influence on NaCl adsorption by KAc-Kao: temperature had obvious influence on adsorption. Concentration of steam exhibited negligible to NaCl adsorption. When the distance between layers was less than 9.8 Å, NaCl couldn’t enter the kaolinite’s layer. In the range of 11.5 Å to 13.3 Å, NaCl could enter and form adsorption. In synergy with experimental results discussed hereinbefore, some interesting points of NaCl behaviors in Kaolinite were obtained.