OCR Text |
Show at firing rates of 4 X 106 to 5.5 X 106 Btujh but higher at 2.2 X 106 Btu(h . This is probably caused by the loss in swirl and internal recirculation at very low firing rates because of the very low inj ection velocities. The commercial burner can be designed to maintain the primary air/ natural gas inj ection velocities to minimize this effect. The second configuration involved moving the refractory orifice to enhance the internal recirculation. This resulted in a lower NOx emission level than that of the first configuration; however, the CO level was somewhat higher. For firing rates of 4 X 106 to 5.5 X 106 Btujh, a NOx level of 10 ppm required about 55% excess air with the first configuration and produced a little over 10 ppm co. A similar NOx level with the second configuration required only 45% excess air but produced 30 ppm co. As discussed earlier, similar NOx reductions should be possible with FGR or another diluent, but these are not the preferred techniques and will be further evaluated and developed only · if combustion air staging is found to provide insufficient NOx reduction. HEAT FLUX AND BOILER THERMAL EFFICIENCY The heat flux data acquired during the 200-hp burner tests have not been fully reduced and compared with data for conventional burners. As a result, these are not presented here. However, at comparable excess air levels, or with comparable levels of diluent addition, cyclonic burners should provide higher heat fluxes than those from conventional burners due to the significantly higher convective heat transfer rates that result with this type of swirling combustion. Similarly, the thermal efficiency of the boiler is expected to be higher with the cyclonic burner. The extent of these increases would be determined in the next phase of the program using a commercial prototype burner. TOTAL HYDROCARBON EMISSIONS The THC emissions were not measured for the 40-hp burner, but for the 200-hp burner, THC levels were measured for each test. For all the test data presented, the THC emission levels were below 2 ppm. NO. 2 OIL FIRING The capability for backup No.2 oil firing was tested on the 40-hp burner. With a single stage, NOx emissions at the low excess air levels were relatively similar to those with natural gas, whereas CO emissions were somewhat higher. The effect of excess air was not tested because it was not expected to be effective; however, one test was carried out with combustion air staging and showed about 50% higher NOx compared wi th the level with natural gas at the same primary stoichiometric ratio of 0.94. |