OCR Text |
Show Type R coal nozzle arrangements with the existing air register design. The combustion trials generated the data necessary to assess RO-II burner performance. Flue gas O2 , NOx and CO concentrations were measured at each test condition , along with coal/primary air static pressure at the coal nozzle inlet. windbox and furnace static pressures, and total combustion air and primary air mass flows. Qualitative assessments of flame shape, length , and stability were also made throughout the development program. In addition, flyash samples were taken for subsequent carbon in ash analysis. Furnace horizontal exit gas temperatures were also quantified using suction pyrometry. The combustion test program parametrically evaluated a number of key RO-II design and operating variables. Some of the variables investigated included coal nozzle tip configurations, firing rate (MCR and reduced load), excess air level, coal/primary air velocity at the coal nozzle tip exit, pilot and main air damper position (pilot! main air flow split) and coal stream swirl. All laboratory trials were conducted with a Pennsylvania bituminous coal having 10% ash, with a fixed carbon to volatile ratio of 1.65 and a fuel nitrogen content of 1.5% by weight. Coal preparation for the laboratory tests was consistent with typical utility practice; the pulverized coal grind averaged 70.3% through 200 mesh (75 microns), with 0.6% remaining on a 50 mesh (300 microns) screen. The laboratory test furnace utilizes a dilute phase (1 .5 - 2.0 Ibs primary air/lbs coal) indirect coal feed system. A schematic of the feed system is shown in Figure 3. Figure 3 highlights the fact that a gravimetric feeder is employed to accurately quantify coal feed rate. The figure also illustrates the location of static pressure taps in the coal feed system. These pressures were documented throughout the test program for comparison to performance targets. COIiBUSTlON AIR INLET OUCT L COAL INLET STATIC PRESSURE MEASURED HERe 8' FLEXIBLE HOSE Figure 3: Coal Feed System Schematic • • PIPING Photo 3 shows the installed RO-II burner register as viewed from outside the furnace. Note the use of the tangential entry fuel nozzle inlet, characteristic of both the Type Rand RO-II burner designs. Photo 4 shows the installed RO-II from the furnace side and highlights the shadow vanes and divergent refractory quarl similar to typical field installations. Photo 3: Installed RO-II Burner Register as Viewed from OutSide the Furnace Photo 4: Installed RO-II Burner from the Furnace Side Note also in Photo 4 that there is refractory material on the furnace walls. The laboratory test furnace has atmospheric pressure water cooled walls. The furnace gas temperatures and heat release profile are adjusted by altering the refractory configuration depending upon test objectives. The refractory configuration selected for these trials was chosen to create a furnace thermal environment where relatively high levels of thermal NOx would be generated. In addition to refractory modifications, the test furnace was intentionally operated at a volumetric cubic heat release rate of 39,800 Btu/hr/ft3 . This volumetric heat release rate in effect far exceeded a typical coal-designed boilers volumetric heat re lease range of 9,000-16,000 Btu/hr/ft3. As a result of this (and combined with the refractory insulation thickness and pattern in the furnace) , measured furnace gas outlet temperatures (horizontal furnace outlet plane) were in the 2500 - 270QoF range, far exceeding typical boiler horizontal furnace gas outlet temperatures of 1900 - 2000°F. The implication of high temperature furnace operation during the RO-II laboratory trials is that NOx generated thermally via the Zeldovich mechanism (1) was projected to be conservatively higher than would be expected in subsequent field RO-II installations. Eleven different coal nozzle configurations were evaluated during the combustion trials. Baseline tests were 3 |