Fusibility of coal ash

The test method for determining the fusibility of coal ash (ASTM D-1857) covers the observation of the temperatures at which triangular pyramids (cones) prepared from coal and coke ash attain and pass through certain defined stages of fusing and flow when heated at a specified rate in controlled, mildly reducing, and where desired, oxidizing atmospheres. 

British Standard BS 1016, Part 15-1970. Fusibility of Coal Ash and Coke Ash. 

South African Bureau of Standards SABS Method 932. Fusibility of Coal Ash. 

Cubic Foot Weight of Crushed Bituminous Coal Drop Shatter Test for Coal Dustiness, Index of, of Coal and Coke Fusibility of Coal Ash... 

Slagging, fouling, and clinkering difficulties have been found to correlate not only with the composition of coal ash but also with the fusibility of the coal ash (ASTM D-1857 ISO 540) insofar as ash fusibility is related to composition. The critical temperature most commonly referenced in evaluation of the properties of coal ash is the softening temperature. 

ASTM D-1757. Standard Test Method for Sulfate Sulfur in Ash from Coal and Coke. ASTM D-1857. Standard Test Method for Fusibility of Coal and Coke Ash. 

Ash fusibility values are often specified in coal contracts because they are believed to be a measure of the tendency of coal ash to form clinkers. Softening... 

ASTM D-1857. Standard Test Method for Fusibility of Coal and Coke Ash. 

Fusibility ability of coal ash to soften and become fluid when heated according to prescribed conditions. See also Ash fusion temperatures. 

Hemispherical temperature in the fusibility of coal and coke ash, this is the temperature at which the cone has fused down to a hemispherical lump, at which point the height is one-half the width of the base (ASTM D-1857). 

FIGURE 16.17. Specimen profiles for ASTM standard for fusibility of coal and coke ash... 

The fusibility characteristics of coal ash will vary with its chemical constituents. Most low-rank coals produce an ash high in basic metals and low in iron content. Therefore, they have a higher softening temperature, and consequently, are less susceptible to slagging. The behavior of ash is extremely complex, and while some constituent melt below 1040°C (1900°F), as the calcium and sodium content of the ash increases, the rate of deposition increases on tube surfaces. The sodium oxide content, in particular, can have a catalytic effect on the rate of deposition, and investigations have shown that ash with a sodium content above 5% fouls at an accelerated rate. 

Coal Char Coal char is, generically, the nonagglomerated, non-fusible residue from the thermal treatment of coal however, it is more specifically the solid residue from low- or medium-temperature carbonization processes. Char is used as a fuel or a carbon source. Chars have compositions intermediate between those of coal and coke the volatile matter, sulfur content, and heating values of the chars are lower, and the ash content is higher, than those of the original coal. 

ISO 540. Determination of the Fusibility of Ash High-Temperature Tube Method. ISO 562. Determination of Volatile Matter in Hard Coal and Coke. 

In practice, types of burning equipment, rate of burning, temperature and thickness of the fire bed, distribution of ash-forming minerals in the coal, and viscosity of the molten ash may influence ash behavior more than do the laboratory-determined ash fusibility characteristics. The correlation of the laboratory test with the actual utilization of coal is only approximate, due to the relative homogeneity of the laboratory test sample compared to the heterogeneous mixture of ash that occurs when coal is burned. Conditions that exist during the combustion of coal are so complex that they are impossible to duplicate completely in a small-scale laboratory test. Therefore, the test should be considered only as an empirical one, and the data should be considered qualitative and should not be overinterpreted. 

Peoples Republic of China National Standard GE 219-74. Coal Ash Fusibility Determination Method. 

ISO. 2011 i. Coal and Coke—Determination of Fusibility of Ash (ISO 540). International Standards Organization, Geneva, Switzerland. 

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