OCR Text |
Show 1 1 In the case with heavy fuel oil a minimum of the NOx emissions exists at the same air ratio for the 0.1 MW double cone burner and the 9 MW system. Although there is an increase in emissions on the fuel rich side, the minimum is rather flat in the large scale tests compared with the lab experiments. Therefore, it can be concluded that the premix combustion is only partially achieved in this scale. The video pictures support this assumption, because the flame could be seen partly inside of the conical flame holder. IV.2. Influence of the total excess air ratio The influence of the overall excess air ratio and/or the secondary excess air ratio in the flame tube, which determines directly the residual oxygen content, was independent of the fuel quality, the air preheat and the load. Therefore this dependence is presented here only for oil no.2 (see fig. 9). 80~--------------------------------------------~ 70 N o 60 o~ C'? E 50 Q. Q. - 40 CD C o 30 CD CD E 20 w , 0 opt. primary air excess ratio 85% load recirculation rate 35% • , r\ .. '. \. \ .\ " , ~ • NOx [ppm] • CO [ppm] - - -CO [ppm] '----~---- o +-------r-------r-----~------_+--~~~------~ 1.05 1.1 1.2 1.25 1.3 Influence of the total excess air ratio in the 2nd Stage (determined from mass flow measurements) The NOx-emissions are only slightly reduced with decreasing total excess air ratio, but the CO - emissions rise suddenly below Atot < 1.1. However, no soot production was connected with this CO rise! |