OCR Text |
Show regard. The low volatile matter content of the Chinese "X" coal portends lesser combustion performance in terms of flame stability and burnout relative to the other coals. 2.2 COAL WATER MIXTURES Coal water mixtures were formulated from the three coals described previously. The results for five CWM types, Table 4, are presented in this paper. These were made from the three coals, described above, using three particle size distributions as discussed further below. Coal content was held constant, near 70 percent, to elucidate the PSD and coal type effects. Within the constraints of these objectives, the additive package was adjusted to achieve the desired rheological properties which were established considering the practical requirements of storage stability, pumping ease and atomization quality. All of these slurries have a yield point and are protected against biological degradation to ensure a minimum of 60 days stability in storage. This is evidenced by their relatively high low shear viscosity.^ ' r^eir I 2 ) viscosity drops to less than 3000 cp in the pumping shear rate rangeK ' of 110 sec" as shown in Table 4. Atomization quality is affected by many variables; the apparent (3) -1 viscosity at high shear ratesv/ of about 3000 sec has been found to be an important factor. An intensive study in which about 50 slurries were tested led to a good correlation between slurry composition, high shear rheology and, in turn, atomization quality. Having established the slurry requirements for fine atomization, as reported in a following section, the slurry compositions for combustion testing listed in Table 4 were chosen. ^1'Brookfield viscometer "D" spindle, 30 rpm * 'Haake Rotovisco viscometer t 3) 1 'Burre11 rheometer KVB72-P327 D1 94 |