| OCR Text |
Show Effects of the surface emissivity on the surface temperature and radiant heat output were investigated using the same radiating surface at different excess air operation with or wi thout a coating, as shown in Figure 7. For the surface with higher emissivity (0.85) coating, the radiant heat output is about 20% higher than that with lower emissivi ty (0.35), while the surface temperature is lower, to about 4500 F, because of more heat loss from the surface. . l.J.. 0 Q) L. :J +J 0 L. Q) a. E .Q-) 3000~----------------------------------------,- 2000 <J-G- -0.- 0- - -0- --0 FIRING INTENSllY: 264 MBtu/h.ft.2 EMISSIVllY: 0 0.85 ~ 0.35 1000~----~--~----~----~--------~----~--~ 1.0 1.2 1.4 Stoichiometric Ratio 1.6 1.8 0.8 0.6 0.4 0.2 Figure 7. Effect of surface emissivity on radiant heat output. Q) -+-I 0 a::: ~ -+-I ~ :J a. " -+-I ~ :J , 0 -+-I C Ct.. 0 ~ -a 0 !) a::: Q Effect of firing intensity on radiant heat output is presented in Figure 8. The radiant heat flux is increased with the firing rate because of an increase in the surface temperature. However, the heat radiation rate to the overall heat input from combustion is decreased from 40% to 30% as firing intensity increases from 125 to 264 MBtu(h-ft2 , because more of the heat is carried off by the flue gas. Compared to an existing radiant burner working on the surface-combustion mode (22), the present burner provides approximately four times higher radiant heat flux because of higher surface temperature and higher firing intensity. EMISSIONS The major pollutant emissions, CO and NO/NOx , were measured in every test. It was found that CO emissions were too low to be accurately analyzed by the CO analyzer employed in the present testing because measuring range of the analyzer was 0 to 1000 ppm. In most tests, however, CO emissions were detected below 30 vppm (corrected to 0% 02). |
