Abstract
This article explores the effects of SiO2/Al2O3 ratios (S/A) on sintering characteristics and provides guidance for alleviating ash depositions in a large-scale circulation fluidized bed. Five synthetic coal ash (SCA) samples with different S/As were treated in a muffle furnace for 12 h at different temperatures (from 773 K to 1373 K, in 100 K intervals). The morphological and chemical results of the volume shrinkage ratio (VSR), thermal deformation analysis by dilatometer (DIL), scanning electron microscope (SEM), X-ray photoelectron spectrometer (XPS), and X-ray diffraction (XRD) were combined to describe the sintering characteristics of different samples. The results showed that the sintering procedure mainly occurred in the third sintering stage when the temperature was over 1273 K, accompanied with significant decreases in the VSR curve. Excess SiO2 (S/A = 4.5) resulted in a porous structure while excess Al2O3 (S/A = 0.5) brought out large aggregations. The other three samples (S/A = 1.5, 2.5, 3.5) are made up of an amorphous compacted structure and are composed of low fusion temperature materials (e.g., augite and wadsleysite.). Sintering temperatures first dramatically decrease to a low level and then gradually rise to a high level as S/A increases, suggesting that Al2O3-enriched additives are more effective than SiO2enriched additives in alleviating depositions.
Highlights
Coal blending using coal slime or biomass in a large circulation fluidized bed (CFB, over 300 MW)is widely utilized for its environmental and economic benefits
The purpose of this paper is to investigate the effects of SiO2/Al2O3 ratios (S/A) on sintering characteristics through various experimental conditions conducted in a muffle furnace
Samples with various S/A ratios were treated in a muffle furnace at different temperatures
Summary
Coal blending using coal slime or biomass in a large circulation fluidized bed (CFB, over 300 MW)is widely utilized for its environmental and economic benefits. Ash deposition on the surface of the cyclone separator or the heat exchanger is an operational obstacle in combustion, which can adversely affect equipment performance. Previous studies have shown that ash fusion temperature (AFT) is a key factor in determining the progress of coal combustion, gasification, fluidization, and deposition [4]. Ash depositions formed at various ash fusion temperatures always differ in chemical composition. Researchers have established that ash deposition can be alleviated by changing chemical compositions through blending ash with proper additives [5,6,7,8,9]. It is important to investigate the relationship between ash fusion temperatures and chemical compositions in order to better understand the deposition mechanism and the necessary operational adjustments
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