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Show The burner configuration used, shown schematically in fig. 4 comprised a continuously variable swirl generator in the combustion air supply and a refractory quarl. The swirl level defined as the ratio of the axial flow of angular and linear momenta normalized by the radius at the burner throat, could be varied over the range 0.1 - 0.84. For the work reported here, two quarl designs were employed. The first for the nominal 4 MW burner,was a divergent refractory quarl with a half angle of 25° and a length to throat diameter ratio of unity. This setup had been used in the past for the firing of a variety of fuels LluD a n d i t s characteristics were well known. In this instance, fired at 4.5 MW with ambient temperature air, the throat velocity of the combustion air at 5% excess air was 32 m/s which was considered to be representative of industrial burners for oil or coal firing. A second burner/quarl was designed for the nominal 2 MW firing rate. This was based on the design of the 4 MW nominal burner and scaled down such that the throat velocity was maintained constant for similar conditions of combustion air temperature and excess air. A second factor in the design of the smaller burner was an objective to maintain constant, the average residence time of the combustion air in the quarl. Therefore the length to throat diameter ratio of this quarl was 1.16. Full details of IFRF work concerning the scaling of burners if given elsewhere QllJ-Two basic types of fuel atomizer were employed as shown in fig. 5. These were Y-jet and internal mix atomisers, each incorporating six holes. The experimental atomisers were nitrided in order to allow them to withstand coal-in-oil fuel atomization for a sufficiently long period of operation to execute the work but evaluation of abrasion characteristics was beyond the scope of investigation. The atomising medium used was steam. In the first experiments, only ambient temperature combustion air was used. However in the later work, the effect of increasing the combustion air preheat was studied. Here a preheat of 200 °C was chosen to be representative of oil-fired water-tube boiler operation and this was achieved by means of an independantly fired combustion air preheater. Experimental methods The experimental procedure utilized was to "optimise" coal-in-oil fuel flames on the basis of visual observations of stability, flame form and minimization of post-flame tail sparklet emission in conjunction with measurements of exhaust solids loading. Temperature and composition of the exhaust gas were also determined and solids analysis made subsequent to the experiments were also used in the assessment of combustion performance. Optimization was effected by variation of excess air, atomizing steam flow rate, atomizer included angle,combustion air swirl level and burner gun position. Several heavy fuel oil flames were examined simi larly. 15-6 |