Cause of white smoke from stack?

[Knowitallnot]

125 kpph water tube boiler with scr (19% aqueous nh3) and co catalyst burning ulsd (15 ppm sulfur) getting white/brown (not blue) smoke at low loads (25% fire rate). Clears up at when firing rate is raised. Exceptionally long stack, 50% is horizontal, CO is zero, Nox is 9 ppm, nh3 is 4 ppm, O2 is 6%. Any ideas?

 

[whammett]

Fuel may be off spec and your not burning everything. Have you tried increasing O2?

"Scientists dream about doing great things. Engineers do them." -James Michener

 

[Knowitallnot]

Yes, O2 was increased and condition (opacity - white smoke) worsened.

Lowered O2 and condition got better but CO started to form (O2 is down around 3% at 100% fire with decimal CO)) Decreased nh3 injection, condition worsened. Stack temp. is around 290 F. Thanks

 

[25362]

I wonder whether the following link would be helpful:

www.alentecinc.com/papers/AMMONIA/-AMMONIA_FCG.pdf

 

[Knowitallnot]

Very helpful. Thank you.