The experimental design of mineral transformation and slagging characteristics analysis during the co-gasification of coal and sludge.

[Objective] Sludge production is abundant; however, its utilization rate remains low; co-gasification of sludge with coal is an important way to realize its resourcefulness and harmlessness. In industrial operations, gasification agents such as air and carbon dioxide primarily influence gasification, and the ash characteristics of the feedstock are crucial to ensure the long-term stable operation of the gasifier. The slagging characteristics of raw materials are closely related to their ash-melt properties, and the transformation of minerals is the essence of the change in the ash-melt properties. Currently, owing to the difference in the composition of raw materials, the evolutionary mechanism of the mineral transformation of the coal and sludge co-gasification process through the change in the sludge mixing ratio and the atmosphere on the mixing of the two remains unclear and lacks guidance for the change in the composition, which warrants further analysis. [Methods]In this paper, an experiment was designed for the mineral conversion and slagging characteristics analysis in the co-gasification process of coal and domestic sludge. The experiment involved the slagging characteristics of coal-sludge mixed samples, ash melting characteristics, and mineral conversion during co-gasification. Using anthracite and domestic sludge as raw materials, the two were mixed in different mass ratios. The characteristic temperature of ash melting was determined using an ash melting point tester. The basic-acid ratio, silica-aluminum ratio, and other evaluation criteria were used to evaluate the slagging characteristics. An oxidizing atmosphere and a weakly reducing atmosphere were employed as the environments for the co-gasification of coal and sludge, respectively. The high-temperature ash samples obtained from the co-gasification were characterized using X-ray diffractometry and Fourier transform infrared spectroscopy to analyze the changes in minerals. [Results] The experimental results revealed the following: 1) The characteristic temperature of coal ash melting remained higher. The characteristic temperature of ash melting decreased with increasing sludge mixing ratio. Among them, the melting characteristic temperature decreased most significantly when mixed with 20% sludge; 2) According to the discriminant indices such as alkaline-acid ratio, silica ratio, silica-aluminum ratio, and composite index, coal ash was associated with mild slagging, and domestic sludge ash belonged to severe slagging. After sludge mixing of over 50%, the mixed sample ash was associated with serious slagging; 3) The high content of mullite (Al₆Si₂O₁₃) in coal ash was the primary reason for its high ash melting point. The blending of sludge increased the alkaline oxides such as CaO and MgO in the mixed samples, and the mullite content decreased rapidly, transforming into eutectics with lower melting points such as anorthite (CaAl₂Si₂O₈). This was the main reason for the decrease in the melting temperature of the mixed ash sample; 4) Compared with the oxidizing atmosphere, the weak reducing atmosphere was more conducive to the formation of anorthite, and the coal could produce more anorthite by mixing a lower proportion of sludge. [Conclusions]Through this experiment, students can master the design method of mineral transformation and slagging characteristic experiment in the co-gasification process of coal and sludge mixed samples, which will help students to analyze and master the microscopic characterization methods and cultivate their innovative ability for the effective utilization of carbon-containing solid waste resources. [ABSTRACT FROM AUTHOR]