HE Chong;BAI Jin;GUO Jing;LU Hao;HUANG Lei;

• 1:College of Environmental Science and Engineering
• 2:Taiyuan University of Technology
• 3:State Key Laboratory of Coal Conversion
• 4:Institute of Coal Chemistry

Abstract：

Alkali metals(potassium and sodium) in biomass are easy to be released into the gas phase during gasification, causing corrosion, ash deposition, slagging and other problems in the gasifier, seriously affecting the long-term operation of the gasifier. In this study, the effect of kaolin addition on the release behavior of alkali elements during straw gasification was explored in the aspects of the distribution of alkali elements, phase evolution behavior, slag structure, and the Gibbs free energy of alkali element capture by slag, via thermodynamic modelling. The results indicate that K and Na are mainly in the form of the K-Mg silicate and feldspar, respectively, while sodium exists in feldspar, and the increase of temperature promotes the release of alkali metal in ash to gas phase. The released content of alkali elements increases with the gasification temperature. In addition, the mineral species and slag structure are the key factors governing the release behavior of alkali elements at low temperature and high temperature, respectively. The addition of kaolin at 800 ℃ promotes the transformation of potassium fixing minerals from potassium magnesium silicate to leucite in the ash, and the transformation of sodium fixing minerals from sodium calcium silicate to nepheline, reducing the release behavior of alkali metals. At high temperature, the addition of kaolin decreases the depolymerization parameter G value of slag, leading to the conversion of the structure unit Si-Si-O-O to Si-Al-O-O. The resulted Si-Al-O-O is the key structure unit of capturing alkali elements in the slag by forming the structure unit Si-KAl-O-O and Si-NaAl-O-O, and this process is driven by the charge compensation effect. Furthermore, the kaolin addition decreases the ΔG of the reaction of slag capture alkali elements at 1 400-1 600 ℃, which enhances the ability of alkali metal fixation of slag and inhibits the alkali element release. In contrast to Na, the ΔG of the K capture reaction by slag is higher, indicating that the K is easier to be released than Na during biomass gasification.

Key Words： biomass gasification;alkali elements;kaolin;slag structure;Gibss free energy

Abstract:

Keywords:

Foundation: 国家自然科学基金资助项目(22108190)

Authors: HE Chong;BAI Jin;GUO Jing;LU Hao;HUANG Lei;

DOI: 10.13226/j.issn.1006-6772.RE22090901

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