| OCR Text |
Show Further at entry the coal:air jet is not swirling (coal + primary air mass -0.3), at the same velocity as gas; hence, the tangential velocity of the whole air and coal must be reduced approximately to a factor of 0.7. Combining the effects of reduction in tangential velocity and the radius of injection, it can be shown using the scaling group that the time to travel to the wall t is increased by a factor of two. Correspondingly, the transi-w tion size (size below which impact time is shorter than burning time) will be increased to about 30 ym. This is given in Figure 5 as C3 D3. 6.0 SUMMARY The low ash rejection with Illinois No. 6 coal is the result of finer particle size in the feed compared to the size of Polish coals. From the analysis; it is shown that in order to maximize slag deposition on the cyclone walls the feed must have negligible mass in the size range below 30 ym. A secondary effect of low ash rejection at the walls is a nonuniform and insufficient thickness of the slag layer. A consequence of this may be to further reduce slag rejection as the thin, low slag layer may not be effective in capturing large impinging char particles. Coal injector position does not significantly affect the time to reach wall for a position up to about 70 percent of the radius of the cyclone; but, the location at which the secondary gas input is introduced into the cyclone affects the impact time significantly. When air is staged so as to maintain a fuel rich environment as long as possible the slag capture efficiency is improved. Acknowledgment The authors wish to acknowledge the support of Mr. Dwight Shelor of the MHD Division of the Fossil Energy Branch of DOE as well as the cooperation of their Polish colleagues, Prof. W. Brzozowski, G. Dul, T. Kozlowski, Z. Rybacki and M. Zielinski in providing the experimental data. The first author wishes to thank Prof. Hopkins, head of the Department of Mechanical Engineering, Texas A and M University for providing travel and partial research support. -26- ^i7AVCO EVERETT |
