OCR Text |
Show 7 From the fuel analysis (composition and moisture content) a calculation of flame temperature versus equivalence ratio can be made for the conditions of adiabatic heat release, and also the present case of a well stirred reactor with significant heat transfer. For ease of calculation, the nondissociated temperatures are shown, which means that the no heat loss case is higher than would be measured, but does not affect the calculation of the furnace temperatures with heat loss, since these are in the range where dissociation is not significant. For the existing design, Figure 3 presents these idealized calculations showing both the adiabatic case and the actual design case with significant heat loss. With the intended heat extraction from the furnace to the turbine cycle, and at equivalence ratios of from 1.2 to 1.5, temperature of the "well stirred reactor" will range from 2350° F to 2150° F. Following the calculation of temperature, an equilibrium NOx calculation can be made at the temperatures, and excess O2 represented by the fuel composition and equivalence ratio. Without heat loss, very high equilibrium NOx theoretically could exist, and even with heat loss equilibrium values of around 500 ppm could exist if formed. These values are shown in Figure 4. To determine actual thermal NOx, rates of formation need to be calculated and applied to the residence time in the furnace. These values are shown in Figure 5, for the heat loss case, and even at the lowest equivalence ratio formation rates of less than 1 ppm per second are calculated from the standard Zeldovich mechanism. However, it should be noted that if well stirred conditions do not occur throughout the radiant furnace , formation rates of localized areas could approach 3000 ppm/sec. Fuel nitrogen originated NOx represents another source of NOx emissions. In this case, the process conditions are not so favorable and the current literature suggests conversion ratios of from 18% to 55 % of the fuel nitrogen to nitrogen oxides. At .11 % nitrogen in the fuel , 100% conversion would be 320 ppm, and optimistically a 20% conversion will occur, but still result in emissions of 64 ppm (.08 lbs/million Btu of higher heating value), or about .4 lbs per hour. This is still an area of concern, and will be monitored during the startup tests. |