OCR Text |
Show also is one of the most criticized slagging parameters. The criticisms come from two sources: (1) Persons who have found that it is not a good predictor of slagging (2) Researchers, who stress the difference between the nature of the ash fusion test and combustion of coal in a furnace. The ash fusion test is conducted slowly (over minutes and hours) and at slowly increasing temperatures; ash in a furnace rapidly heats to a high temperature and then is cooled in a few seconds, with possible condensation of volatilized species. Additionally, the reproducibility of ash softening temperature data is (3) stated to be 100 Fv , making ash softening temperatures low precision measurements. No specific ash softening temperatures are recommended as being slagging or non-slagging, but higher values indicate more difficult to melt ash and generally fewer slagging problems. Figure 4 shows the slagging data on an ash softening temperature/ unit area steam generation rate plot. The empirically drawn lines divide the area into three regions of varying degrees of slagging. Using ash softening temperature and the data available on this project, 69 percent of the data fell into the correct regions. Ash Fusion Temperature Range Another parameter used to evaluate coals for their slagging potential is based on ash fusion temperature and is calculated by taking the difference between the highest fluid temperature (usually for an oxidizing atmosphere) and the lowest initial deformation temperature (usually for a reducing atmosphere). This temperature difference is taken to be an indicator of the temperature range over which the ash is sticky. That is, the lowest initial deformation temperature is taken as the measure of initial melting, and the highest fluid temperature is a measure of complete melting. Within the intermediate temperature range, the ash is partially melted and tends to form sticky deposits. 1-8 |