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Show IFRFDocNoK70/y/113 -13- AFRC Spring IJmuiden, April 1997 meeting 1997 800 700 600 o S? 500 cr> 2* "° 400 >" E 5. - 300 oK z 200 100 0 0 25 50 75 100 125 150 High velocity air gun position [ m m ] Figure 3.10 The Effect of High Velocity Air on NOx The figure shows the baseline type I flame (without HVA and gun position 60 mm) and the N O x levels attained with a H V A of 185 m/s. It is clearly shown that it is possible to reduce N O x levels with the H V A provided that the H V A does not penetrate too far forward of the coal gun. 4. CONCLUSIONS The firing of pulverised fuel, as rebum fuel, through the centre of an IFRF pulverised coal burner, in combination with appropriate local stoichiometrics resulted in reductions of N O x by as much as 80 %. The burner operating principle was not affected by the fuel bound nitrogen content of the solid fuel, but was critical to the volatile matter content and burner injection modes. For the cases where natural gas was used as rebum fuel, and using a similar burner setup, N O x levels were shown to be lower than those achieved when reburning with solid fuel. When fuel staging with dried sewage sludge, a major consideration particularly for air or fuel staging is the high ash content of the fuel (-46 % ) which can cause severe slagging and fouling of the air and gas injectors. However, provided that the quantity of sewage fired is a small fraction of the total fuel input, the burning of sewage sludge with pulverised coal for electricity generation appears to be practicably possible. Fuel staging with bluff bodies has shown that NOx can be reduced depending on the initial burner condition and type of bluff body used. The introduction of an additional high velocity air stream between the secondary and tertiary air has shown that substantial reductions in N O x can be achieved relative to the baseline burner. - • - 180m/s H VA J , I . I . I i L |