Tampa Electric applied recently at the Florida Department of Environmental Protection for an air permit change that would allow it to make alternations to the coal-fired Big Bend Unit 3 to alleviate boiler slagging problems caused by add-on emissions controls built there in recent years.
This emission unit has routinely experienced slagging issues and lower steam temperatures and the new emissions controls have exacerbated these issues, Tampa Electric told the DEP in a March 23 letter that accompanied the application. Tampa is a unit of TECO Energy (NYSE: TE).
“This project consists of a physical modification and routine maintenance,” it added. “The physical modifications involve adding additional boiler surface area to increase the outlet steam temperatures of the High Temperature Superheater and High Temperature Reheater. The routine maintenance includes the replacement of the High Temperature Superheater (HTSH), High Temperature Reheater (HTR), Economizer, Radiant Super Heater (RSH) and nose arch.”
Big Bend Unit 3 is a wet bottom steam boiler rated at 4,115 mmBtu per hour. The boiler was originally designed as a pressurized furnace and was subsequently converted to balanced draft system as part of a 2000 clean-air consent decree with the federal government that mandated selective catalytic reduction (SCR) installation.
The boiler was originally designed to operate up to 4,115 mmBtu per hour. This project targets a nominal heat input condition of around 4,052 mmBtu per hour. This is within 1% of the original design heat input using the same calculation metric.
“The nose arch and RSH in the boiler will be extended to control and minimize slagging and erosion in the upper furnace area and at the superheater,” the letter noted. “This modification reduces slagging by reducing the peak flue gas temperature in the furnace exit plane and at the HTSH. It is necessary to extend the nose arch if the surface modification in the high temperature superheater is performed, so the high temperature superheater surface does not extend over the nose arch and increase slagging potential.”
Also, Tampa separately applied in March at the DEP for a permit on a coal bypass system at Big Bend. “Tampa Electric Company (TEC) intends to install an emergency by-pass conveyance system (J3 bypass conveyors),” said the filing. “The system will serve as a backup system conveyance system should one or more of the existing conveyors fail. The system is expected to operate continuously up to 7 days while the existing conveyors are being repaired.”