OCR Text |
Show Furnace temperatures are measured using a suction pyrometer. Temperature gradients were about -300 K/s. Flue gas was sampled at different locations and analyzed by the CEM system. In all experiments the initial Stoichiometric Ratio in the main combustion zone was SRI =!.1. Ammonia was added to the main fuel to provide an initial NO concentration of 530-600 ppm. The rebuming fuel was injected at 1600-1700 K at two injection rates, 10 and 20% of heat input, providing stoichiometries in the reburning zone SR2=0.99 and 0.90. Ammonia and urea were injected in the form of aqueous solutions with different Nitrogen Stoichiometric Ratios (NSR); ammonia was also injected in gas form. NSR is a molar ratio of N-agent to the NO concentration at the time of injection. N-agents were injected with a delay time, 0 - 1.0 s, after injection of the reburning fuel. Sodium salts were diluted in N-agent solutions. Sodium carbonate, sodium formate, and sodium gluconate were tested. Since the process was not particularly sensitive to the type of sodium salt, most experiments were conducted with sodium carbonate. Concentration of N~C03 was varied from o to 120 ppm Na in flue gas. OFA was injected at different locations to provide a final stoichiometry SR3= 1.15. BENCH SCALE CIT RESULTS The initial NO concentration in the CIT tests was about 600 ppm. Figures 4 and 5 compare two different hybrid reburn/SNCR processes: reburn + SNCR (i.e. injection of the rebuming fuel, OFA, and then, N-agent) and AR-Lean (i.e. injection of the rebuming fuel and OFA with N-agent. Reburn+SNCR with 20% reburning fuel achieves 73-84% NO control. AR-Lean requires only 10% rebuming fuel and demonstrates 75-82% NO control. Temperature resolution in these experiments is relatively low, and performance can be perhaps higher at the optimum N-agent injection temperature. Previous EER data [7] shows that AR-Lean can achieve up to 85% NO control. Figures 6 and 7 demonstrate efficiency of the AR-Rich process, i.e. injection of the rebuming fuel, delayed injection of a N-agent, with or without sodium carbonate, in the rebuming zone, and then OFA Only 15 ppm N~C03 (30 ppm Na) substantially improve periormance of the process to 88% NO control. Figure 8 illustrates that injection of ammonia at two locations results in above 90% NOx control. In these experirrents, 10% reburning fuel was injected at about 1620 K. The fITst NH3 was injected in the reburning zone, with or witho_ut 15 ppm sodium carbonate, at three different locations: 1620 4 |