OCR Text |
Show Flue gas samples were withdrawn using a water cooled and water quenched probe. The Staging sample was passed through a refrigerated 1800 FUa! Rich SR = 0.62 Rebuming FUel Rich SR = 0.68 knock out pot, through in-line continuous ~ 1600 ~ monitors for O2, CO, CO2 and NOx analysis, ~ woo ~ and then to gas chromatographs. The ~ 1200 chromatograph that was used for H2, CH4, ~H6 and ~H2 analysis was outfitted with dual molecular sieve and Porapak T columns, and thermal conductivity and flame ionization detectors. Argon was used as a carrier gas. The analysis for N20 was by gas chromatograph, equipped with Porapak Q column and an electron capture detector. A mixture of 5% CH4 and Argon was used as a carrier gas. HCN was partly captured by the metered quench water and partly dissolved in 0.1 molar NaOH aqueous solution in a bubbler. After sulfur precipitation, the aqueous samples were analyzed for HCN using an ion specific electrode. NH3 was captured by the quenched water and analyzed using a gas specific electrode. Aqueous concentrations of HCN and NH3 were converted to ppm values in the combustion flue gas. Temperature measurements were made using an uncoated '3;. to U ~ 0.5 > E 600 aa.. en .!? 400 ~ a. Vl z 200 X .. o 0 o 0 • O~~~~~ ~~~~~ 0.0 0.5 to 1.5 0.0 0.5 to 1.5 2.0 Residence Tme. s Residence Time, s Figure 2: Typical Profiles in the Fuel Rich Zones of Air Staging (Left) and Reburning (Right) Configurations. Primary flame is bituminous coal/air. type R thermocouple, corrected for radiation losses. Residence times were calculated from measured concentrations, temperatures and calculated molar gas rates. Compositions of the coals are given by Bose et al.(1988). RESULTS The reburning experiments were conducted under reburn zone stoichiometric ratios ranging from 0.68 to 0.9. The primary fuel was either bituminous coal or natural gas doped with NH3• The experimental data are presented as time resolved measurements of species and temperatures in the fuel rich zone. The results of 12 air staged combustion experiments were extracted from the work of Bose(1989) and covered a wide range of stoichiometries (0.6-0.8) and temperatures. The profiles shown on Figure 2 are typical of fuel rich regimes in air staging and reburning configurations, with time zero starting at the inlet to the fuel rich zone. Fuel rich zone temperatures in reburning are usually lower than those in an air staging configuration. Furthermore, hydrocarbon concentrations in the rebum zone are much higher than those in the fuel rich zone of air staging, due to the introduction of a secondary fuel. An examination of CH4 profiles in Figure 2 suggests that, under certain conditions, the exclusion of hydrocarbon reactions can be justified in describing the inter-conversion of nitrogenous species in the fuel rich zone of air staging, where measured values of CH4 can be lower than 3 |