Ash fusibility

Coal ash (Chapter 3) is the noncombustible residue that remains after all the combustible material has been burned. It is a complex mixture that results from 

Initial deformation temperature (IT) temperature at which the first rounding of the apex of the cone occurs 

Softening temperature (ST) temperature at which the cone has fused down to a spherical lump in which the height is equal to the width of the base 

Fluid temperature (FT) temperature at which the fused mass has spread out in a nearly flat layer with a maximum height of Jf, inches. 

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Ash Fusibility. A molded cone of ash is heated in a mildly reducing atmosphere and observed using an optical pyrometer during heating. The initial deformation temperature is reached when the cone tip becomes rounded the softening temperature is evidenced when the height of the cone is equal to twice its width the hemispherical temperature occurs when the cone becomes a hemispherical lump and the fluid temperature is reached when no lump remains (D1857) (18). 

Other important chemical and physical tests performed to characterize coal include (I) Heating value (Btu content) (2) sulfur forms (31 ash fusibility temperatures (4) ash analysis (5) trace elements (6) free swelling index and (7) hardgrove grindability. 

Page 19k A little borax or phosphorus salt is sometimes added, in order to make the ash fusible. 

Ash fusibility Qualitative observation of temperature at which ash passes through defined stages of fusing and flow... 

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. 

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... 

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. 

Standard tests consisted of proximate, ultimate, higher heating value, ash composition, ash fusibility temperatures, Hardgrove grindability, and screen analyses. Special bench scale characterization tests consisted of micro-proximate analysis and micro-ultimate analysis (C, H, N) micro-proximate and micro-ultimate analyses were performed on particulate samples collected from varying stages of combustion in the DTFS and CMHF. In addition, selected samples of SRC and chars from partial combustion or pyrolysis of the SRC were submitted for Thermo-Gravimetric analyses. 

ASTM measurements such as ash fusibility (D1857) have formed the basis for traditional ash behavior predictive techniques. These bench-scale tests provide relative information on a fuel which is used in a comparative fashion with similar data on fuels of known behavior. Unfortunately, these commonly used tests do not always provide sufficient information to permit accurate comparison. 

State Standard of the UUS GOST 2057-82. Methods of Determining Ash Fusibility. 

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

Multiple correlations for ash composition and ash fusibility are discussed in the Coal Conversion Systems Technical Data Book (part lA, U.S. Dept, of Energy, 1984). 

Sulfur forms Ash properties Elemental analysis Mineralogical analysis Trace element analysis Ash fusibility... 

The ash fusibility temperatures are used to predict whether the ash will perform properly in the process for which the coal was chosen. 

Instrumental methods are now becoming accepted as alternative techniques, provided they are shown to give equivalent results to the conventional test. These methods can allow a greater throughput of samples, with less operator dependence than conventional techniques, and often generate useful data that were not previously available. In fact, there are some instrumental companies, i.e., LECO Corporation, devoted almost exclusively to the development and sale of apparatus for chemical analysis - immediate analysis, elemental analysis, sulfur determination -calorific value, ash fusibility, and other technical tests of coals. 

The chemical analyses of ash for major elements and a test in ash fusibility temperature give guidelines on coal utilization, defining the suitability of coal for different combustion or conversion systems. Analysis for minor elements is gaining impetus as greater interest is taken in the environmental consequences of coal uses. Typical ranges of concentration for major, minor, and trace elements are summarized in Table 4. 

ASH FUSIBILITY. The determination of ash fusion temperatures (initial deformation, softening, hemispherical, and fluid) is a laboratory procedure, developed in standardized form (ASTM Standard D 1857). 

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