OCR Text |
Show balance was not established. With one ellipsoidal radiometer, it took abut 30 minutes to measure total radiative heat flux at six axial positions along the furnace sequentially. The furnace temperature increased about 15 K during the total radiative heat flux measurement. To examine the effect of temperature increase on total radiative heat flux, heat flux measurement was conducted reversely from the opposite inspection window closest to the flue. The results showed that the maximum difference between two measurements was less than 3 % , suggesting the influence of temperature increase on total radiative heat flux to be practically negligible. The total radiative heat flux was thus measured from the burner side in all the experiments. The PSA system is expected to be a standard oxygen generator because of its low cost of oxygen production. The oxygen produced by the regular P S A contains about 5 % of nitrogen. Since a few percent of nitrogen greatly affects N O x emission, the effect of nitrogen content in the oxidant was tested. The effect of nitrogen content in the fuel was also tested to investigate N O x emission characteristics with the natural gas supplied in Europe and the U S . which contains several percent of nitrogen. In these experiments, natural gas and oxygen were doped with nitrogen and the air respectively. It should be noted that the resulting injection velocity increased marginally, by maximum 15%, with the increase of nitrogen content in the natural gas and oxygen. 3.4 NOx emission from the oxy-fuel combustion Theoretically, the concentrations of C O , and N O x in the flue should be 1 0 0 % and 0 respectively if ether the fuel or the oxidant contains no molecular nitrogen as was in this experiment. The measured concentration of C 0 2 in the flue, however, was around 9 5 % and substantial N O x emission was observed even though the furnace pressure was kept positive at +10 to +50 Pa in all the experiments. The source of nitrogen is generally believed to be due to the in-leaking of ambient air into the furnace. The estimated volume of leaking air was 0.88 m3/h from the exhaust gas analysis. Should all of this in-leaking air was contained in the fuel, the nitrogen content in the fuel would be 2.9%. The nitrogen content in the oxidant would be 1.2% if contained in the oxidant. Taking into account of the nitrogen contained in the in-leaking air, the equilibrium NO concentration is 793 p p m (at 0 % 02, dry basis) at 1673 K that is the furnace temperature in the experiment. The equilibrium N O increases substantially to 1580 p p m at 1873 K, more appropriate for actual glass melting furnaces. It is therefore very important to prevent the air in-leakage into the furnace to achieve low N O x emission in the glass melter. 5 |