Characterization of gas/particle flows with respect to staged-air ratio for a down-fired 600 MWe supercritical utility boiler with multiple injection and multiple staging: A lab-scale study

To achieve significant reductions in particularly high NOx emissions and to eliminate severely asymmetric combustion found in down-fired boilers, a multiple-injection and multiple-staging combustion technology was developed in our previous study. Representing great progress in this area, one of two newly-designed down-fired 600 MWe supercritical utility boilers using this technology had a recent trial run before its 168-h test. By phase-Doppler anemometry measurements within a cold 1:40-scaled model of the furnace, gas/particle flow characteristics were compared among various staged-air ratio settings (i.e., 20%, 25%, 30%, and 35%) to establish an appropriate staged-air ratio range for boiler operation. Meanwhile, to validate this first industrial application of the newly developed technology, industrial-size measurements were made at a 550 MWe load during the trial run. Experimental gas/particle flow results uncovered that at the highest setting, a severely asymmetric gas/particle flow field developed in the furnace. For the two lower settings, an essentially symmetric gas/particle flow field appeared. Moreover, gas/particle flow-field symmetries at the 30% setting were generally acceptable. Consequently, a staged-air ratio range of 20-30% is recommended for the boiler. As expected, industrial-size data revealed that excellent furnace performance, characterized by symmetric combustion and low levels of carbon in fly ash (5.1%) and NOx emissions (822 mg/m(3) at 6% O-2), appeared within the boiler. This was despite combustion optimization and a present lack of industrial-size data at full load. (C) 2013 Elsevier Masson SAS. All rights reserved.