Vaporization illite

Illite Vaporization. The clay mineral illite is frequently found as a mineral constituent of coal and is considered a major source of potassium vapor species in combustion systems. A "Beaver s Bend illite" sample was used (provided by the Morgantown Energy Technology Center) with the following composition for the major components, in vt.% Al203(26.0), Fe203(4.4), Si02(60.2),... 

Figure 4. Partial pressure data for K, Og, and SiO over illite. Key A, TMS method with Ng atmosphere , O, KMS under vacuum vaporization conditions and , Og with ticks indicating increasing (up) or decreasing (down) temperature...

Illite -H2O-H2 System. Vaporization of potassium from the highly acidic illite system, in neutral atmospheres, is expected to provide a relatively insignificant source of alkali in most coal combustion systems. However, in the presence of reactive combustion gases, such as H2O and H2, thermodynamic considerations predict a significant KOH partial pressure. In addition, an increase in the K-pressure should result from a reduction in the O2 pressure, in the presence of H2. However, KMS experiments did not indicate formation of KOH or additional K in the presence of H2 gas. Thus, thermodynamic equilibrium does not appear to have been established in this heterogeneous system, even though the temperatures were sufficiently high to have normally ensured a rapid approach to equilibrium. 

Quartz. The inherent silica retained in the char as quartz or silica released from kaolinite and illite at low temperatures (i.e., 950°C) is partially reduced to silica monoxide. Unlike silica, which boils at 2230°C, silica monoxide melts at 1420°C and boils at 2600°C [19]. The vapor pressure of silicon is low—in the range of temperatures experienced during combustion. Honig reports values ranging from... 

Typical results of specific surface area determinations on phyllosilicates by nitrogen gas/water vapor or nitrogen gas/CPB adsorption are listed in Table 1.7. For Mg-vermiculite and Na-montmorillonite, the measured adsorption specific surface area is close to that calculated from the unit cell dimensions and structural formula. For illitic mica, the area is about 14 per cent of the ideal crystallographic value, indicating that this mineral forms particles containing about seven phyllosilicate layers that cannot be penetrated by water vapor or CPB. 

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