Southern Co releases report on co-firing tests

Southern Company has released a report detailing a series of tests conducted on co-firing green wood chips from whole and from approximately needle free pine trees. The purpose of the project was to "determine what level of processing of whole trees is required to successfully co-fire the chips in a boiler, and to evaluate the benefits and costs of wood processing compared with the effect of the fuel on the power plant." The tests were performed at Plant Gadsden in Gadsden, Alabama. From the report, summary results are as follows:

• Green wood chips were successfully co-fired in blends with coal between 8% and 15%
  wood by weight. Of the input fuel energy, 2.8% and 5.5% was from wood, and represented about 2.0 MW to 3.8 MW biomass power.
  
• Sulfur emissions were reduced, and particulates were no higher with co-firing. At normal operating condition, carbon monoxide emissions were unchanged. The measured impact on NOx emissions was small.
  
• With 10% co-firing, boiler efficiency was about the same as coal alone, while there was a slight reduction in efficiency with 15% wood.
  
• Higher moisture losses due to high wood moisture were offset or nearly offset by reduced dry gas losses up the stack.
  
• High moisture of the wood coal mixtures resulted in low mill temperatures and high mill bowl under pressures. This caused a 5% load derate when co-firing 15%.
  
• The coal-wood mixtures had much lower fuel energy to volume ratio than the baseline coal. The issues appear to have been related to the installation of new automatic controls. Stability issues were corrected in subsequent tests by tuning the fuel-steam pressure automatic controls.

The project was initiated by Southern Company & Alabama Power, USDA Forest Service, Forest Based Economic Development Services, University of Alabama, and Auburn University.

The full report can be found here.