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Show ~ eo o # o ,: ~ 40 E Q Q ...,..: 20 o : PILOT SCALE FOUR SINAXZIALO JETE CROSS FLOW JETS 6_ ~6 ~~.'. OUAC' Fig 12. Importance of reburning fuel mixing- natural gas reburning. The reduction was much higher when the natural gas was injected through a line source, consisting of 14 holes in a row. In the Limhamn boiler, the OFA port, main burners and secondary air port are arranged in a row, fig 2 c. During the trials, air was also supplied through the oil burners. Table 2 shows the distribution of air and momentum between the different openings From a mixing point of view the burner system can be regarded as a line source with 6 openings, capable to maintain better mixing than burners in one or two opposite walls. Table 2 Distribution of air and momentum through burner openings Baseline trial Airflow velocity jet momentum m3n/sek per cent mls N OFA 7.77 20.0 24 240 Upper oil burner 4.75 12.2 16 98 Upper coal burner 8.6 22.2 30 333 Lower oil burner 4.39 11.3 16 90 Lower coal burner 8.87 21.8 30 344 Secondary air port 4.84 12.5 23 144 Total 38.83 100.0 PRACTICAL EXPERIENCE After the fist heating season after the retrofit the boiler was inspected and no unsusual fouling was observed, neither on the tubes in the furnace, nor on the convection surfaces. There was only a dry dust that could be removed with the normas dust cleaning equipment. The baseline trials showed that the distribution of coal between the burners was unsymmetric. Therefore the temperature load on the four boiler walls was unsymmetric. Also the combustion was incomplete in the centre of the boiler furnace. The model experiments, however, indicated several possible remedies, and the boiler will be further rebuilt this summer. 9 |
