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Show "economizer" surfaces. Selective refractory lining over atmospheric pressure "waterwalls" allows the matching of the residence time/temperature history of large scale utility boilers, including the horizontal furnace outlet plane (HFOP) gas temperature. The BSF is fully instrumented to monitor the combustion process. Instruments for measuring coal feed rate, primary and individual secondary air mass flow rates, outlet emissions (02, CO2, CO, S02, NO, and NOx.), and convective pass heat flux distribution are tied into a combined DCS/data acquisition system to allow for control and logging of these and other important operational parameters. For the subject testing, the BSF was operated in a tangentially-frred mode with levels of separated overfrre air (SOFA). Prior laboratory test programs have shown that BSF test results can be reliably translated to the field for use in frring system design, and subsequent perfonnance prediction [3] . Perfonnance targets for the BSF combustion testing were consistent with those for the LEBS program; maximum NOx emissions of 0.1 pounds/MM Btu and carbon in the fly ash <5% for high sulfur, mid-western and eastern bituminous coals. In addition, the lower furnace heat absorption profiles and convective pass heat flux distribution were to remain similar to or improved over the existing system. The coal utilized during the BSF testing was the high sulfur, medium volatile, bituminous Viking coal from Montgomery, Indiana. Prior to the initiation of NO x control subsystem testing, the frring system for the BSF was modified to take advantage of current and previous R&D project fmdings. First, ABB CE' s Aerotip ™ coal nozzle tip design was utilized as the base from which the BSF coal nozzles were constructed. The AerotipTM design embodies improved aerodynamic features which support the test program need for a low NOx coal nozzle tip through its control over near field stoichiometry. In addition to the incorporation of an Aerotip ™ based coal nozzle tip, the main windboxes of the BSF were designed to accommodate a range of vertical and horizontal air and coal staging scenarios. The design of the secondary air nozzles was based on the need to maintain proper jet momenta, while having sufficient flexibility to test variations in vertical and horizontal air staging. In addition, excess coal nozzle capacity was incorporated to allow the testing of various coal staging scenarios, including two-comer coal frring. With this foundation, each of the "base" (i.e., benchmark) frring system designs tested in the BSF, including the TFS 2000™ frring system, was able to incorporate the results of the prior chemical kinetic modeling and small scale (FSBF) combustion testing with respect to main windbox vertical air staging. One goal of the BSF testing was to generate design data in support of achieving NOx emissions of 0.1 poundslMM Btu through in-furnace frring system modifications (i.e. , prior to any post combustion process NOx reduction system). Toward this end, various "conventional" global air staging techniques were tested in order to benchmark their NOx reduction potential on the test fuel. This work included investigations of close-coupled overfrre air (CCOF A), upper and lower (single) elevations of separated overfrre air (SOFA), and an implementation of TFS 2000™ technology. All of the various overfrre air configurations utilized the same main windbox arrangement, and all were perfonned with high fmeness (900/0 - 200 mesh) coal grind, which is consistent with TFS 2000™ firing system design standards. A summary of the results from testing various overfire air configurations with the test coal are given in Figure 1. As anticipated, the implementation of global air staging results in a significant reduction in furnace outlet NOx emissions. Beginning with NOx emissions of 0.52 poundslMM Btu with a typical "baseline" (post-NSPS) fir ing system arrangement, NOx reductions continued to a low of 0.13 poundslMM Btu for an "optimized" TFS 2000™ firing system arrangement (Note: similar 0.13 poundslMM Btu outlet NOx emissions were obtained with the upper SOFA only, but this was at slightly degraded carbon in the fly ash perfonnance). The "optimized" TFS 2000™ system incorporates improvements to the bulk stoichiometry history over the initial TFS 2000™ test, with identical main and overfrre air windbox configurations. In all, a 750/0 reduction in NOx from baseline levels was achieved with the "optimized" TFS 2000™ system. As expected, carbon in the fly ash increased as the global staging was increased, but remained below the limit of 50/0. |
