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Show type. For each boiler type, the furnace volumes and heat release rates vary greatly and influence the choice of low NO firing modifications. x CONCENTRIC CLUSTERED TANGENTIAL FIRING SYSTEM (CCTFS) ABB C-E has developed a new NO emissions control system called the x Concentric Clustered Tangential Firing System (CCTFS). Like earlier ABB C-E firing systems, CCTFS is designed to control the availability of oxygen to the fuel throughout the combustion process. CCTFS (Figure 1) is a "deeply staged'.' combustion technique that employs multiple elevations of overfire air (OFA) to minimize the available O 2 in the primary combustion zone. OFA is introduced at the top of the main fuel admission assembly windbox as close-coupled OFA, and at a higher elevation as separated OFA. The two levels of OFA, together with variable injection angle and velocity, permit tailoring of the mixing rates of OFA and furnace gases to maximize NO reduction for a given boiler and fuel. Since the main x windbox height does not change in most retrofit applications, pressure part and other structural modifications are minimized. The CCTFS design also utilizes the patented Concentric Firing System (CFS) principle of directing the auxiliary air away from the fuel toward the waterwalls (3). This system may serve to protect the waterwalls from the near-reducing atmosphere inherent when bulk furnace combustion staging techniques are employed. In certain cases, concentric firing has demonstrated an ability to control furnace outlet temperature as well. In addition, CCTFS incorporates a new concept of clustered coal nozzles which maximize the separation of the fuel and air in the early stages of combustion. The combination of these features (OFA, CFS, and clustered nozzles) allows the firing system to achieve very low NO emissions with x minimal impact on boiler performance. CCTFS was developed by ABB C-E on the basis of large 15 MWt (50 MBtufhr) pilot scale testing at the Boiler Simulation Facility located at ABB C-E's Kreisinger Development Laboratory in Windsor, Connecticut, USA (Figures 2 and 3). The BSF replicates the aerodynamic and thermal conditions of a 3 |