OCR Text |
Show without utilizing either selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR). The emissions targets established for the laboratory development program apply to a wide range of coals, from medium-volatile bituminous through lignite, recognizing that absolute emissions values will vary with coal type. A comprehensive laboratory program was used to develop the TFS 2000™ system. Physical flow, computational modeling, fundamental combustion experiments, and extensive pilot-scale testing up to 15 M W t (50 x 106 Btu/hr) were performed. Introduction Large, central pulverized coal-fired power stations are expected to play an important role in worldwide power generation throughout the 1990s and into the twenty-first century. These stations will be designed for: • Maximum cycle efficiency • Multiple-fuel flexibility • Cycling • Maximum availability • Least capital cost • Minimum maintenance cost • Lowest possible emissions that meet or exceed federal, state, and local rules This paper addresses reduction in combustion-generated emissions via an improved firing system design. Tangential Firing Historically, tangential firing (Figure 1) has demonstrated inherently low N Ox production for large, coal-fired units (Figure 2)1. Lower N O x emissions result from the staging that occurs with the physical separation of the coal and air streams emanating from the corner windboxes (Figure 3). The flames produced at each fuel nozzle are stabilized through global heat- and mass-transfer processes. A single rotating flame envelope ("fireball"), centrally located in the furnace, provides gradual but thorough and uniform fuel-air mixing throughout the entire furnace.2 Figure 1: Tangential Firing Flame Pattern Al'\ 3 11-10 |