Investigation of chemical composition and morphology of ash deposition in syngas cooler of an industrialized two-stage entrained-flow coal gasifier

The migration process of minerals and ash deposition in an entrained-flow coal gasifier with a capacity of 2000 t/d were investigated through twelve ash samples collected from various positions of gasification unit, including slagging, fly ash, filter cake, as well as ash deposits in the bottom layer, middle layer, core layer of the syngas convective cooler, respectively. The Na–Ca–Al–Si eutectics, KCl, and a large amount of FeS were clearly detected in the ash fouling samples. The occurrence modes of ash chemical element were also analyzed. Experimental results showed that sodium compounds tended to migrate from sodium chloride into aluminosilicate after the generation of chlorides, except potassium chloride. The low-melting eutectic, Na2O–SiO2–FeO with melting temperature below 800 °C, was determined in the ash deposit layers. The sticky magnetic spherical particles detected in the samples were distinguished into iron-oxygen-sulfur eutectics with high iron content and aluminosilicates associated with low iron content. With the combined effects of alkali metal reaction with chlorine/sulfur, low-melting eutectics, and magnetic spherical particles, the ash accumulation phenomenon appeared in the syngas cooler, which was dominated by the low-melting eutectics and magnetic substances. An effective operational measure strictly controlling the syngas temperature was applied to alleviate the ash deposition.