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Show In addition to the air register, the configuration of the coal pipe impeller and the pulverizer primary air to fuel ratio have significant effects on the flame quality. The B&W conical style impeller, used with the daisy chain cell burner, does not function well with the new Avon 9 registers. Also, the turbine blade or spinner type impeller can cause the flame to be skewed when the direction of spin is counter to the air register spin. Finally, accumulation of burner eyebrows and furnace wall slagging worsened considerably when the pulverizer primary air to fuel ratio is allowed to increase. This also increases CO levels measured in the lower furnace. In all three boilers tested (Avon 9, Eastlake 5 and Ashtabula 50 MW), the effect of the new burner was a noticeable and dramatic lowering of the fire in the furnace. This was noticed by the lack of flame tails in the upper furnace, lower FEGT, less slag on pendant surfaces and changes in heat absorption. A negative effect is that wall slag on the lower furnace walls increases and is an operating concern. Early Avon 9 Problems Early burner problems experienced after converting Avon 9 to the new burner were caused by three factors: ash blinding of the B&W conical impeller, coal nozzle movement damaging the air distribution vanes of the air register and a large windbox to furnace air leak allowing approximately 24% of the secondary air to bypass the combustion zone. The photos in Figure No. 9 show damage to Avon 9 burners that occurred during initial operation. The coal pipe movement problem and furnace air leak, once discovered, were readily solved. The impeller wastage and blinding problem required a lot more investigation and was eventually attributed to the stronger airflow in the central region of the new air register causing a reverse flow onto the impeller. Figure No. 10 illustrates how the wake created by the impeller is compressed in the new register, leading to a strong reverse flow back onto the impeller making it prone to blinding. It was concluded that this impeller is not compatible with the new air register. Impeller Studies The spinner or turbine bladed style impeller shown in the photo, Figure No.4, was substituted and tested in the 50 MW boiler with excellent results. This is a fabricated flat bladed impelLer with the blades at a 30° angle to the coal stream. This impeller was first installed in the Avon 9 burners, in a spin orientation counter to that of the register, so that the two flow streams opposed one another. This, in addition to the other corrections, made a big improvement in the character of the Avon 9 fire. The fire in the furnace was much lower and totally void of raw flame tails. Superheater pendant slagging was reduced and the furnace exit gas temperature was lowered approximately 100°F. However, on the negative side, lower furnace side wall slag and burner eyebrow formations were heavy and, at times, a runny slag flow would develop on the bottom slope. In addition, CO levels measured in the furnace just below the burners seemed higher than desirable. |
