OCR Text |
Show promoters. In AR, the N-agent is injected along with the overlire air (OFA) in the fuel-lean gas (ARLean). However, the N-agent can also be injected into the reburning zone (AR-Rich). This allows two stages of N-agent injection for deeper NOx control (Multiple Injection AR - MIAR). Both Nagents can be injected with promoters which considerably enhance the NOx control from N-agent injection. The promoters are water soluble inorganic salts [8] which can be added to aqueous nitrogen agents. Experimental data on different SGAR systems were obtained in 30 and 300 kW combustors. These data and kinetic modeling results are presented below. The results demonstrate that NO reduction is enhanced ifN-agents are injected into the reburning zone with a delay time after injection of the reburning fuel. Furthennore, the presence of sodium compounds, such as sodium carbonate, promote the effect of both "lean" and "rich" N-agents. Above 90% NOx control was achieved by injections of 10% rebuming fuel, N-agents (ammonia or urea) and only 15 ppm N~C03 in comparison with about 50% NOx reduction by 10% rebuming alone. Kinetic modeling qualitatively describes the chemical processes responsible for NOx reduction. Figure 1 presents general schematic of the SGAR process. It includes injection of aN-agent into the reburning zone, and then, injection of OFA with the second N-agent Each N-agent can be injected with or without promoter. EXPERIMENTAL Most of experiments were conducted in a 30 kW Controlled Temperature Tower (CTT). Some tests were also perlonned in a 300 kW Boiler Simulator Facility (BSF). Both facilities used natural gas as main and reburning fuels. The CIT is a vertically downfired combustor (Figure 2) with a 20 cm inside diaIreter and 3.5 m height. The facility is equipped with several ports to allow introduction of sampling and injection probes. The BSF (Figure 3) is a downfrred combustor consisting of a vertical radiant furnace and a horizontal convective pass. The radiant furnace is a refractory lined cylinder with a 56 cm inside di.arreter and 6.7 m height. It is equipped with numerous ports to allow introduction of sampling and injection probes. Both facilities are equipped with movable water cooled heat exchangers (to allow control of the residence time-temperature history) and continuous emissions monitoring (CEM) systems with personal computer based data acquisition systems. Each CEM system includes a chemiluminescent NO/NOx analyzer, infrared CO and CO2 analyzers, a flame ionization total hydrocarbon analyzer, a paramagnetic O2 analyzer, and infrared N20 analyzer. 3 |