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Show - 6 - 2.3 Description of Sampling Probes Gas and solid samples were taken in the furnace experiments using a steam heated probe. Particles were collected in a sintered bronze filter at the back end of the probe and then the gas sample was drawn in a steam heated line to the gas analysis train. Water was condensed out of sample and the dry gas was analysed for NOx (Thermo Electron chemiluminescent analyzer), O2 (Servomex paramagnetic analyzer), CO and CO2 (Dnor infrared analyzers). The HCN and NH3 concentrations were co llected separately using the HCN/NH3 probe with specific trapper solutions injected into the probe tip. The analysis of HCN and NH3 were performed according to NEN 6489 and NEN 6472/6644 standards for measurement in waste water [9]. A detailed description of the probe operation is described in Reference 10. In the reburn zone experiments, all gas samples were collected using the HCN/NH3 probe. 3.0 Results of the Furnace Experiments Some general observations can be made concerning the test conditions in the furnace experiments. The NOx concentration exiting the precombustor was generally high for all tests (770-1000 ppm) and relatively insensitive to changes in operating conditions. This may have been due to the high mixing in the precombustor which caused rapid oxidation of the fuel nitrogen. The high NOx emissions may also be attributed to thermal NOx which could be significant in the precombustor due to high wall temperatures (1400-1600°C) and relatively low heat extraction (25% of the thermal input). The flow exiting the precombustor expanded rapidly to fill the volume between the chokes. The highest gas velocities were measured close to the choke walls with a weak recirculation zone in the middle of the reburn zone. The CO2 mixing tests indicated that the dispersion of the rebum stream into the primary combustion products could be significantly altered by changing the injection point. With the rebum guns positioned in-line with the furnace front wall, the CO2 was rapidly entrained into the external recirculation zone. With the guns positioned at 0.35 m axial distance, the CO2 mixed rapidly with the primary flow. This behaviour may be seen in the C02 concentration profiles measured at 0.6, 1.05 and 1.4 m axial distance, Figure 4. At 0.6 m axial distance, the position of the rebum jets was apparent from the high concentration of CO2. After 1.05 m, the CO2 was well dispersed and gas concentration varied from 0.5 % at the outside edge of the forward flow to 1.3 % at the centerline. With the rebum guns located at 0.7 m axial distance, the CO2 was injected into the weak internal recirculation zone and the mixing with the primary combustion products was poor. There was a large gradient in CO2 concentration measured at 1.05 m axial distance from 0.05% close to the choke walls to 4% along the centerline, Figure 5. At 1.4 m axial distance, the gradient was less with CO2 concentration increasing from 0.24 % around the outside of the forward flow to 3 % at the centerline. From these results, it was decided to vary only the gun position from 0.35 m to 0.7 m axial distance to obtain the low and high mixing conditions in the experiments. |