Investigation of slagging characteristics and anti-slagging applications for Indonesian coal gasification

Abstract

The phase diagram characteristics of Indonesian coal ash were studied with thermodynamic equilibrium calculations and the Na2O-Al2O3-SiO2 ternary system. Baikuang coal was selected as the blended coal, and the blending ratio was optimized. Gasification experiments were carried out in a horizontal tube furnace system; the microstructure, mineral crystalline phases and chemical compositions of residues were analyzed; and the retention ratios of sodium and potassium were calculated. The particles underwent three stages, namely, (1) internal crushing and quick pore growth, (2) the formation of dense layers on the surface, and (3) the coverage and blockage of pores. These three stages corresponded to the release of the internal gas phases, the formation of silicates and aluminosilicates, and the low-temperature co-melting with other metallic elements (Ca, Mg, Fe), respectively. The main crystalline phases in the residues were converted from SiO2 to NaAlSiO4. During the reaction, the chemical form of Na changed from H2O-soluble to insoluble and HCl-soluble. The gasification temperature had a pronounced effect on the sodium conversion rate and the conversion degree, and the retention ratio of sodium and potassium was significantly reduced as the temperature was increased. After coal blending, the slagging tendency was significantly alleviated, the peak of NaAlSiO4 decreased, and the crystal phase of mullite (3Al2O3·2SiO2) was determined. In addition, the sodium content in the ash was remarkably reduced. Adjusting the coal ash components by coal blending was an effective way to alleviate or even avoid slagging of Indonesian coal, and a mixing ratio of 25% was optimal.