OCR Text |
Show temperature rather than using softening temperature for bituminous coals (Figure 3). Corey20 showed that the correlation of the critical viscosity temperature (Tcv) and softening temperature was reasonably good (Figure 4)-not unexpected as both represent the transition from Bingham plastic flow to Newtonian flow as the last solid substance goes into solution. Duzy15>21 correlated softening temperature with the percentage of basic constituents (Fe203 + CaO + MgO + Na20 + K20) or lignitic ash and identified that the minimum in softening temperature occurred at a value of 40 percent basic constituents. To improve the correlation, Duzy proposed the dolomite ratio: DR • CaO + MgO/Fe203 + CaO + MgO + Na20 + K20 (1) Sondreal and Ellman applied Duzy's correlation to lignite and bituminous coals. The dolomite ratio acknowledges that CaO and MgO behave differently from other basic oxides. For 1ignitic-type ash, calcium and magnesium cause an increase in softening temperature; iron, sodium, and potassium cause a decrease. Sondreal and Ellman15 developed a lignite ratio consisting of weighted proportions of constituents that contribute to lowering the ash fusion temperature to those that contribute to raising the lignitic ash fusion temperature: LR = 1.74(Na20) + K20 + 0.73(SiO2) + 0.39(Fe203)/l.40(CaO) + MgO (2) A close correlation with little scatter was obtained for a small number of coal samples. As the input data increased, the correlation degenerated. The correlation did not fit bituminous coals very well at all. 1-18 |