OCR Text |
Show NOx Design Procedure The following factors were considered in the design of the burner for control of NOx emissions: 1. Firing density, 2. Staging ratio, 3. Flue gas recirculation rate, 4. Spray angle, 5. Fuel nitrogen level. The firing density of a 2.5 MW burner in the ERL test furnace is low. This gives a thermal NOx emission level of about 52 ppm, and only 25% NOx reduction from the baseline value would be required to meet the desired 30 ppm NOx emi ss ion 1 eve 1 when fi ri ng on natura 1 gas. Thi s 1 eve 1 of NOx reduction can be achieved either using flue gas recirculation or air staging to give a 0.8 primary zone stoichiometry. The firing density with the heavy fuel oil, at a 2.5 MW input, would be the same as with the natural gas fuel and consequently the baseline thermal NOx emissions from the oil would also be about 51 ppm. However with the heavy fuel oil, NOx will also be formed from fuel nitrogen resulting in an overall baseline NOx emission level of about 150 ppm. The thermal NOx component with the heavy fuel oil fan be reduced using either flue gas recirculation or air staging, while the fuel NOx component can also be reduced using staging or varying the spray angle. BURNER DESIGN The main burner dimensions were based on the flame stability analysis. NOx control was achieved using a combination of staging, flue gas recirculation and nozzle design. Swirl was generated using an axial vane swir1er positioned in the throat section. The blades were curved to generate the desired swirl with a minimum pressure drop. -10- |