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Show In addition to the derate recovery, cofiring at Dover Light & Power offers benefits of improved operability, particularly during upsets and problematic coal episodes, improved efficiency, and reduced emissions with availability of emission credits for S02 and NOx. COFIRING RETROFIT The Dover Light & Power Unit 4 was retrofit with Coen cofire burners during an outage in May-June 1995. The cofiring configuration selected is depicted on Figure 4. Opposed, staggered dual burners were specified to give better gas flame penetration through the combustion gases. The staggered configuration also induces a vortex motion which helps to break up channeling above the grate which can be a mechanism for unburned carbon and CO emissions. The burner swirl was counterclockwise for both front and rear burners. For the burner at the front wall, this effectively sweeps fines from the spreaders back toward the grate and the primary flame rather than short circuiting up the front wall and out the boiler. Near the rear of the boiler, where the majority of the stoker heat release occurs, the swirl entrains the combustion gases off the grate and directs the flame toward the center of the boiler away from the back wall. For this boiler, which is not designed with a nose below the superheate~, this motion should prevent carbon loss via quenching at the rear of the superheater. The Coen burner design is shown on Figure 5. Each burner has a design capacity of 37 MMBtu/hr. The burner was adapted from a fluidized bed warmup burner. It features a high pressure drop and small throat diameter for deep flame penetration into the stoker combustion gases. The 13-inch throat diameter for this application is more than a factor of 2 lower than conventional register burners which reduces installation costs and gives more latitude in positioning the burner around boiler obstructions. The burner also gives superior turndown and stability over a wide stoichiometry range. The capacity turndown is at least 10: 1, although a different gas spud may be desirable for sustained firing at one end of this spectrum. The stoichiometry stability gives the burner the capability to operate 11 |