OCR Text |
Show IFRFDocNoK70/y/113 IJmuiden, April 1997 -7- AFRC Spring meeting 1997 levels of -100 ppm. N O x levels with internal fuel staging at this Rff are - 3 0% higher and in fact shows very little difference from reburning with an Rff of 20%. 3.1.2 Reburning coal with coal Effect of coal properties on N O x The following results show the effect of coal properties with the burner fired in unstaged and staged conditions. In Figure 3.3, the numbers in the brackets next to the unstaged conditions, refer to the flue gas temperature. Rff=30% : So" SA=1.1 : TA=0.56 3^ •o O 2 1000 800 600 400 200 - [1234°C) I1248=C] (1031°C] a Polish • unstaged A Klein Kopje • unstaged • Et Cerejon - unstaged other conditions are fuel and/or air staged Primary fuel Pol Pol Pol KK KK KK ElCn El Cn El Cn Rebum fuel Pol KK KK Pol ElCn Pol Figure 3.3 Effect of coal properties on N O ; Figure 3.3, displays the results from cases where 30 % of the total fuel input was injected through the centre of the burner as rebum fuel. Results with 15 % of the fuel injected as reburn fuel are very similar. In the unstaged condition, the Polish coal had the highest level of NOx. With the input condition and with a similar flue gas temperature, N O x emissions for the Klein Kopje coal were approximately 20 % lower. For the staged conditions, irrespective of the coal type used as primary or rebum fuel, N O x emissions were within the range 385 to 660 ppm @ 3 % 02. For all conditions shown, the secondary and tertiary air swirl numbers were kept constant at 1.1 and 0.56 respectively. Overall the best performance was achieved when the high volatile coal was used as primary and rebum fuel i.e the cases of Polish/Polish and El Cerejon/El Cerejon. In all cases where Klein Kopje was used as primary and rebum fuel or used in combination with one of the other coals, there was a noticeable increase in N O x concentrations. This is consistent with other test cases where a medium/low volatile coal was added to a high volatile coal. In these test cases, it was shown that there are |