OCR Text |
Show in this region. W h e n water-ethanol-ammonium sulfate solution was atomized, NOx emission increased strongly with the atomization rate. This is because the amount of nitrogen fed into the combustion zone increases proportionally to the atomization rate. W h e n the circulating particles exists in the riser, the NOx emission is remarkably prohibited. Fig. 6 shows the effect of the particle hold up on the NOx conversion at the top of the riser. N O x conversion, XNOx is defined as following, *NOx=(^NOxjotal"^NOx,thermal)'CNOx max (1 ) where (CNOx,tota,-CNOx thermal) is fuel-NOx concentration in the flue gas and CN O x max is the concentration supposed that all nitrogen in the atomized liquid are converted NOx. It is confirmed that NOx conversion falls down from 0.7 to 0.4 by the circulating particles in this experiment. The reason of this N O x reduction is due to the cooling effect of the combustion gas by sensible heat of the particles as seen in Fig. 2. 2.3 Effect of SNCR using urea solution The experiment that urea is mixed into the model liquid has been carried out to observe the N O x reduction effect of urea simply. In this experiment ethanol (10 wt%)-ammonium sulfate (5 wt%)-urea (5 wt%) solution was atomized. The concentration of urea has been decided as the nitrogen containing in urea becomes more than that in ammonium sulfate. Fig. 7 shows the effect of the atomization rate on the NO emission. When urea is premixed in the model liquid, the N O concentration is higher than that in the case the liquid containing no urea. This result is caused because the reaction that the urea is converted into the N O proceeds since the urea is directly atomized into the center of the flame of the auxiliary fuel and passes through the region of the highest temperature in the riser. In the region beyond 2.1x10'7 m3/s in the atomization rate of ethanol-ammonium sulfate-urea solution, the N O concentration shows the tendency to begin falling. The fact can be explained by the temperature behavior in the flame. Temperature at the bottom of the riser significantly falls by the atomization rate of the liquid as shown in Fig. 8. Hence the NOx generation unsequently prohibited in atomization rate beyond 2.1 x10'7 m3/s. However the |