OCR Text |
Show pilot-scale baseline NOx emissions within the range of these commercial boilers. Both programs were structured to investigate the consequences of the 10w-NOx combustion retrofit. The main categories are shown in Table 1, but other considerations included flame length change and increased combustion air pressure drop. Tasks were structured to cover these consequences in detail. Extensive physical flow modeling and numerical flow and combustion modeling were utilized in both projects. Before discussing the test results, a review of the test facilities used and literature regarding limitations of pilot-scale testing will be addressed. Pilot and Intermediate-Scale Facilities The B& W pilot facility used was originally designed to directly fire pulverized coal using an MPS-32 mill with multiple burners. Figures 3 and 4 show some details. The unit has a water jacket with internal insulation. It measures 18 feet high by 4.5 feet wide by 6 feet deep. The vertical orientation was chosen to provide more realistic flow patterns (than existing tunnel furnace) to better simulate utility boilers. This design proved especially advantageous for the cell and cyclone development programs. This is because both retrofit technologies require combustion gases from lower zones of the furnace to be reacted further along: at the air throat for the low-NO cell burner and at the reburn burner for the cyclone reburning technology. " In its original design, the pilot unit was called the Combustion and Fuels Preparation Facility (CFPF). The low-NO" cell burner papers refer to it by that name. The unit was originally designed following partial modeling criteria(10) to duplicate utility boiler furnace gas temperatures and residence times from the burner to the superheater area. Gas velocity is considerably less than in a full-scale boiler and the refractory-lined walls are hotter. Characterization testing using single and multiple B&W dual register burners showed NO" and unburned combustibles levels very similar to field data (450 ppm V NO" and less than 0.1 % Btu combustibles loss). The 6-million Btulhr cell burner pilot-scale project utilized two burners in an over/under mode (see Figure 4). Following the cell burner pilot-scale testing, the facility was extensively modified by replacing the back end with a convective pass which duplicates the time/ temperature history of utility boiler flue gases. Thus, time/temperature history duplicates a utility boiler from burner to air heater. An arch was added for more realistic upper furnace air flow and the lower furnace was replaced with a section to simulate that of a single wallfired cyclone boiler. A geometrically-scaled B&W cyclone furnace completed the changeover. The unit has been referred to as the Small Boiler Simulator (SBS) ever since (1985). More complete descriptions of auxiliary equipment can be found in the references previously cited. Figure 5 shows the SBS in cyclone firing mode. Characterization of the unit in cyclone mode showed excellent agreement with typical field data as shown in Table 2. The U.S. EPA Large Water Simulator (LWS), operated by Energy and Environmenal Research Corporation, was used for intermediate-scale testing in the 10w-NOx cell burner development program. It is capable of firing I 50-million Btu/hr. A schematic of the test 3 |