OCR Text |
Show velocity of the combustion products leaving the first stage, velocity of the secondary air, pressure drop of the gases through the various components of the burner, and recirculation rates of the gases within the first and second stage zones. These design parameters are constrained by the size of the boiler or furnace openings, the distance between the openings, the depth of the wind box, and the acceptable size of the burner unit. Typical burner throat diameters are displayed in Figure 8. At 200 MMBtu/hr, a typical oil fired flare burner nozzle has a diameter of about 3.25 ft for a refractory lined throat and a diameter of 4.1 ft for a non-refractory lined throat. The typical distance between combustors in a large multi-burner industrial boiler using several 200 MMBtu/hr burners is about 8 ft. Thus the m a x i m um outside diameter of the VIStA burners would need to be less than 8 ft. Also, w e have assumed that the wind box for this size of boiler would be at least 5 ft deep. The heat release rate in the first stage and the velocities in both stages were maintained constant for the scale-up analysis. Initially, the heat release rate was assumed to be 1.2 MMBtu/hr/ft , which was the rate used to size the 3 MMBtu/hr pilot scale burner. However, Fluent model analysis predicted that increasing the heat release rate from 1.2 MMBtu/hr to about 2.7 MMBtu/hr/ft3 increased the overall N O x production from 2.3 p p m to only 2.8 ppm. Any additional increase in the heat release rate, however, showed a faster rise in N O x emissions. It was therefore, concluded that the original value of the heat release rate was too conservative. A revised heat release rate of 2.8 MMBtu/hr for the first stage was assumed, which increased the nominal rating of the pilot scale laboratory unit from 3 MMBtu/hr to 6.7 MMBtu/hr. 3 CO TJ o 250 200 150 100 50 I ! i i i i i i | H : i1 ! i i 1 ! j i i -\ 1 1 i mm 1 vatcaL VIStA Combustor / WMMMMMf- / / Typical Refractory / Lined I nroat -y Oil Fired . Flare Burner 1 l J / \ J 4 / f / S -*• i \j / ! / ' / / 1 / / Typical Non-Refractory ^ Lined Throat S Q )il Fired Flare Burner 0.5 1.5 2 2.5 Throat Diameter (ft) 3.5 Figure 8. Throat Diameter Available in Commercial Boilers 9 |