OCR Text |
Show -11- 3 range 0.4 to 0.5 MW/m , thus simulating the conditions in oil fired boilers. The work was extended ultimately in CWS2, to encompass a study of the effect of slurry composition upon combustion characteristics. To allow this, seven slurries were tested all with coal concentrations of about 70% by weight but with variation in coal volatile matter concentration - 18.7% to 37.5% on a dry ash free basis - and the manufacturing process. The latter was achieved through the purchase of slurries from four different manufacturers but it must be pointed out, that it simply was intended to gain experience of the possible variations in combustion characteristics that might be experienced. All four manufacturers produced slurries from high volatile bituminous coals but not with coal samples from the same source. Further, information could not be made available of the details of the manufacturing processes. The results of these investigations have been summarised in reference 14, where it was noted that good atomization is certainly the first step in achieving a stable CWS flame without gas support and with a high burnout. Both the slurry type and the atomizer design are important in achieving a fine particle size distribution in the spray. Once a combination a slurry type and atomizer design has been found which produces a suitable spray, then other slurry, burner and furnace parameters, such as coal particle size, coal type, combustion air temperature etc., become important. In these experiments, Y-jet or T-jet type atomizers - see figure 11 - were found to produce the best atomization and also allow the spray to be directed into the optimum region of the burner flow pattern. The amount of atomization air required to achieve flame stability and a good final burnout varied from 12% with the best slurry to 25% with the worst. The slurry characteristics, which relate to a slurry's "atomizability" are not clear from these experiments. There is no |