Hammond Generating Station #1, Coosa, Georgia, USA
Power Plant Description:
Plant Hammond is located in Coosa, Georgia about 60 miles northeast of Atlanta. The power plant, owned by Southern Company/Georgia Power Company, has four boilers.
Boilers #1, #2 and #3 are front-fired pulverized coal boilers, with each boiler rated at 100 MWe and manufactured in 1954, 1954, and 1955 respectively by Babcock and Wilcox (B&W). The boilers each generate 725,000 pounds of steam per hour at 1,800 psig and 1000°F superheat and reheat.
Boiler #4 is a 500 MWe front-fired pulverized coal boiler manufactured in 1970 by Foster Wheeler Corporation. This boiler generates 3,626,000 pounds/hour of steam at 2,400 psig and 1000°F superheat and reheat.
All four boilers burn bituminous coal and have electrostatic precipitators for particulate control. Unit 4 is equipped with low NOx burners.
In 1992, there were a number of customers such as furniture manufacturers and others who were experiencing difficulty or costs in disposing of wood wastes. Plant Hammond personnel elected to determine if their coal-fired boilers could use the biomass material as fuel.
A study was conducted to consider the feasibility of blending sawdust and tree trimming waste with pulverized coal by blending the materials on the coal stockpile, co-milling the blend and then burning it in a utility-scale boiler. This resulted in selected short duration testing to evaluate the potential for co-milling as a means of producing biomass power in an existing pulverized coal unit (Boiler #1).
Fuel for this testing was initially intended to be stringy bark but some brief pilot work indicated that handling issues with that material were going to be difficult. A supply of tree trimming waste and aged sawdust was found and selected as a fuel.
The main objective of the study and subsequent cofiring testing was to determine the feasibility of burning sawdust and tree trimming waste in a pulverized coal boiler in order to lower overall fuel costs at the station.
Tree trimming waste was passed through a tub-grinder in order to achieve a minus 1/4” top size. The resultant fuel was mixed with waste sawdust from a furniture manufacturer in roughly equal parts. This mixture was then delivered to the Plant Hammond coal stockpile area where it was blended with the coal by bulldozers. An attempt was made to achieve 10-13% wood by weight by layering the sawdust and coal in approximate amounts to achieve the target percentage. The resultant wood/coal blend was then pushed into the reclaim hopper, where it travelled through the coal handling system to the bunker of Boiler #1. From the bunker, the blend passed through the coal feeders, the pulverisers and into the boiler.
The feasibility testing of cofiring with wood and coal by blending and comilling was performed on #1 Boiler in the summer of 1992. Three days of performance testing were conducted.
Boiler efficiency tests were conducted with and without biomass cofiring and control room data and plant emissions data were also recorded with and without biomass cofiring. A total of 140 tons wood was consumed during the test period.
The cofiring tests were conducted with 10% to 13% biomass by weight mixed with coal and compared with test results for 100% coal operation. With biomass cofiring, there was little, if any, NOx reduction for the duration of the testing, however the NOx levels did not increase. Boiler efficiency with the biomass-coal mixture showed a small reduction due to the fuel moisture, fuel hydrogen and unburned carbon losses.
Preparation of the tree trimming wastes may be a difficult cost factor to overcome but, once the minus 1/4” wood was delivered to the power plant, the material handled well when mixed with the coal and the blend passed through the coal feeders and pulverisers with little difficulty. Mill amps were somewhat increased with the presence of wood but the increase was not significant.
The results of the testing indicated that up to 13 % biomass by weight could be cofired successfully in pulverized coal boilers through co-milling.
Plant Hammond/ Georgia Power Company
Doug Boylan, Southern Company, 205-257-6917, email@example.com
Hammond Generating Station, P. O. Box 121, Coosa, GA 30129