| OCR Text |
Show OVERALL PERFORMANCE COMPARISON AND CONCLUSIONS Overall heat transfer performance data predicted for all cases· is listed in Table 4. Note, that the fuel heat input cited in this table, is calculated with the lower calorific value. Table 1 confirms the known fact, that overall heat transfer efficiency of the 02-firing system is improved ~olflpared to conventional air combustion. For the 02-firing systems studied, this increase is achieved without significant increase in maximum flame temperatures and maximum refractory temperatures. Although the air flames are wider than the O2 jet flames, the discrepancy in size of the O2 flames is offset by much higher mixing and recirculation rates induced by the 02-burners. It is also obvious from Table 4, that positioning and angling of the 02-burners can influence overall performance to a certain degree. Lowering the burners (Case 3) slightly increases heat transfer efficiency to the glass surface. A somewhat stronger improvement is achieved when the burners are angled towards the glass surface. In this case, heat transfer efficiency is increased by 0.5 percentage points compared to the baseline O2 case with horizontal burner orientation. The study also showed, that there is certainly an impact of the glass surface thermal properties on heat transfer in the combustion space itself. A darker glass will likely tend to smooth out local inhomogeneities. of net heat fluxes to the glass by increase of glass surface or near surface temperatures, thus reducing the effect of the firing system or of the burner placement on heat flux distribution. Although some of the absolute predictions made in the present study may be inaccurate due to simplifications of the current a~proach, there is little doubt that the general trends concluded from this study are realistic. This is due to the dominance of radiation on overall heat transfer in the high temperature glass furnace, and the fact that radiative exchange is treated very accurately by the current model. ACKNOWLEDGEMENT This work was jointly funded by the U. S. Department of Energy and Union Carbide Industrial Gases Inc. under Contract No. DE-FC07-88ID12833. The authors would like to express appreciation to Mr. J. Keller of EG&G and Mr. R. N. Chappell of the U. S. Department of Energy for their support and advice. 16 |
