Seward Generating Station #12, Pennsylvania, USA

Power Plant Description:

Seward Station is located in western Pennsylvania about 70 miles east of Pittsburgh.  The station was originally owned by GPU, Inc. and was recently acquired by Reliant Energy.  Seward Station has three boilers: # 12, #14 and #15. 

Boiler #12, is a front-fired pulverized coal boiler with a steaming capacity of 330,000 lb/hr, that was manufactured in 1949 by Babcock & Wilcox.  It has two horizontal rows of three burners with each row being fed by a ball and race mill. 

Boiler #14 is a twin to #12 except it has been modified with low NOx burners. 

Boiler #15 is a 147 MWe (gross) Combustion Engineering (CE) tangentially-fired pulverized coal boiler built in 1957.  This boiler has four CE Raymond bowl pulverisers.  Each pulveriser supplies one level of the furnace on four corners.

Project Description/Objectives:

This project consisted of cofiring sawdust with pulverized coal in a 32 MWe wall-fired pulverized coal boiler (#12) by utilizing separate injection of the wood at a rate of approximately two tons per hour (up to 10 percent on a heat basis) for an extended period of time.

The objectives of the Seward test program were to: quantify the impacts of cofiring wood waste with pulverized coal by separate injection with respect to boiler efficiency, flame stability, operability, and the formation of airborne emissions including SO2, NOx and opacity; demonstrate that the cofiring technology can be applied to wall-fired pulverized coal boilers at moderate percentages; evaluate the economics of cofiring to improve the capacity factor of the unit; and provide a basis for evaluating the infrastructure needed to deliver biomass to Seward Station.

Project Design:

The overall system design, developed by Foster Wheeler, was to deliver raw sawdust from the sawmills by walking-bed trailer.  The receiving system is also a walking bed which delivers the sawdust to a trommel screen where the sawdust is screened to minus 1/4” x 0.  The trommel screen is capable of screening 20-30 tons of sawdust per hour.  The oversized material is reground and reintroduced to the trommel.  The properly sized sawdust is then conveyed to a silo for storage.  From the silo, the fuel is delivered by screw and paddle conveyors to a surge bin.  From this bin, the sawdust is metered by a weighbelt feeder. The metered sawdust is then picked up by two separate sets of screw conveyors and rotary air lock feeders.  From the airlock feeders, the sawdust drops into two separate three inch diameter delivery tubes being supplied with air from two separate blowers.  The delivery tubes then transport the sawdust to the burner front and into the boiler past inverted cone distributors which are inserted into the center of the two center coal burners.

Project History/Status:

Parametric testing was performed on #12 Boiler in December, 1996 and July, 1997 to prove the concept.  Installation of a continuous system was completed in March, 1999.  Initial testing began in April, 1999 and was suspended shortly thereafter due to unit unavailability during the ozone season. 

Additional testing was to resume upon unit availability in the late Fall or early Winter but, due to the high cost of the unit, the dispatch rate was so poor that the test program was suspended.  It was hoped that the test equipment could be used on the larger boiler but that unit was involved in another long term test and wasn’t available.  A new host site for the test program has been found.  Testing will resume at the new location in 2001.

These tests evaluated biomass cofiring up to 10 percent by heat of wood wastes with various moisture and ash contents and with varying fuel volatility.  Fuel moisture ranged from 13 percent to over 50 percent and ash contents ranged from less than one percent to 5 percent.  The biomass fuels varied from kiln dried sawdust to over two-year old sawdust that had begun the process of devolatilization.

Results/Conclusions:

The optimum cofiring percentage for this boiler is 10 to 12 percent by weight.   Under these conditions, the boiler efficiency loss was about 0.5 percent.  Only slight impacts on opacity and unburned carbon were experienced.  Carbon monoxide emissions always were below 20 ppmv, indicating no problem with combustion completeness.  Impacts on SO2, NOx, and CO2 emissions were favourable.  Sulphur dioxide emissions were reduced as a function of the cofiring percentage expressed on a heat input basis. NOx emissions were reduced on the order of 10% to 12%.  Fossil CO2 emissions were also reduced as a function of biomass substitution for coal on a heat input basis, adjusting for efficiency losses. The cofiring tests at Seward Generating Station have been sufficiently favourable to support pursuing a long term demonstration of this cofiring technology at a new location.

Project Partners:

­          GPU Genco/Reliant Energy

­          EPRI

­          United States Department of Energy (USDOE) – Energy Efficiency & Renewable Energy (EERE)

­          United States Department of Energy (USDOE) – Federal Energy Technology Center (FETC)

­          Upgraded Coal Interest Group (UCIG)

­          Biomass Interest Group (BIG).

Contacts:

­          David Tillman, Foster Wheeler Development Corp., 908-713-3181, david_tillman@fwc.com

­          Joseph Battista, Cofiring Alternatives, 814-471-6689, jbattista@lenzlink.net

­          Richard Imler, Reliant Energy – Seward Station, 814-446-7100

­          Seward Station, RD-2, Box 405, New Florence, PA 15944, 814-446-5641