OCR Text |
Show condition are collected on a glass fiber filter and analyzed for loss on ignition (LOI). Flue gas and fly ash sampling locations are shown in Figure 1. Burner Hardware A full-size, 100 MBtu/hr, unstaged, DRB-XCL ® 10w-NOx PC burner [4] was used for testing. Figure 2 shows the standard burner components schematically. A conical diffuser disperses the PC-laden primary air into a fuel-lean core surrounded by a fuel-rich mixture. The dispersed fuel exits through a flame stabilizer which accelerates ignition and devolatilization. Evolving nitrogenous species, hydrocarbon radicals, char, and other combustible intermediates in the primary combustion zone reduce NOx to molecular nitrogen by homogeneous and heterogeneous reactions. Swirl is imparted on the secondary air by fIXed and adjustable spin vanes as it passes through two concentric annuli surrounding the coal nozzle. The air separation vane partitions the inner and outer secondary air zones at the burner exit. In some commercial installations, the flame stabilizer is replaced with a conical impeller inside the coal nozzle. Conical impellers consist of concentric hollow cones which deflect the coal particles radially outward into the path of swirling secondary air. Although this modification reduces the flame length and LOI, it raises NOx emissions. Besides the standard burner, a number of swirlers and impellers were installed in the coal nozzle and tested sequentially with the goal of reducing LOI while maintaining low NOx emissions. PRIMARY AIR AND PULVERIZED COAL SECONDARY AIR BURNER QUARL ---- FlAME 14-l-.....L. ........... __ ----n----,.-~--___il/ STABIUZER SUDE DAMPER IF====:;" jI;;;~-__ -. ____ AIR SEPARAnON VANE ADJUSTABLE VANES Figure 2. DRB-XCL ® low-NOx PC burner - Standard configuration. 5 |