OCR Text |
Show IFRFDocNoK70/y/113 -3- AFRC Spring IJmuiden, April 1997 meeting 1997 Elemental Analysis (wt %) Carbon Hydrogen Nitrogen Oxygen Sulphur Proximate Analysis (wt %) Ash Volatiles Fixed Carbon H20 Lower Calorific Value (MJ/kg) Polish Coal 80.07 4.77 1.27 6.81 0.68 6.4 32.0 61.56 6.5 31.46 Douglas Prem. 2 S. Africa 69.04 4.16 1.72 10.11 0.66 14.4 29.8 53.3 8.13 27.57 Friedrich Heinrich Germany 82.24 4.63 1.72 4.29 1.24 7.5 25.6 63.4 8.5 32.05 Table 3. Fuel Properties - Fuel staging with Coal Blend The suitability of coal for fuel staging or reburning depends on coal type, and in particular the fuel volatility, nitrogen content and nitrogen reactivity although no conelation has been found for low rank coals [10]. Fuel volatility has an impact on the availability of fuel in the reburn zone, and the evolution of radical species. A high volatile coal with low nitrogen content has, in theory, the ability to maximise overall N O x reduction levels. Fuel nitrogen has been shown to increase the level of reactive nitrogen in the reburn and therefore has an adverse effect on the coals ability to reduce NOx. 2.3 Facility Used For Internal Fuel Staging With Natural Gas Or Coal The burner, with the three idealised flame combustion zones, Figure 2.1 was developed using concept ideas tried in previous experimental programmes [3, 4]. The burner quarl profile was designed to fit a third order polynomial with a zero inlet and outlet angle, and a quarl expansion ratio of 2 as the imposed boundary condition. The shape has been used and modeled in other experiments since it provides a controlled vortex expansion and cylindrical flow of the secondary/tertiary air stream at the quarl outlet. Figure 2.1 Schematic of the burner used for internal fuel staging |