Gulf Power won a Sept. 11 air permit exemption from the Florida Department of Environmental Protection to allow a minimal amount of biomass, in the form of torrefied wood, to be test burned with the fuel used in one of the two front wall fired, dry bottom boilers (Units 1-2) at the little-used Scholz plant.
The proposal by this Southern Co. (NYSE: SO) subsidiary is to test burn about 500 tons over a two-week period. Torrefied wood is produced by heating wood chips in the absence of oxygen, which produces a more energy-dense, low-moisture product. The torrefied product is then pelletized which makes a dense fuel that is enough like coal that it can be pulverized and co-fired with coal.
The torrefied wood pellets will be transported to the plant by covered trucks. At the plant the pellets will be off-loaded and temporarily stored on the coal pile. The pellets will then be blended with coal, pulverized and combusted.
The objective of the torrefied wood test burn study includes:
- the determination of the maximum percentage of torrefied wood pellets that can be co-fired at the Scholz plant; and
- to determine the effect of co-firing torrefied wood on operations, emissions, controls and efficiency of the boiler.
The front wall fired, dry bottom boilers were originally built to combust coal and No. 2 fuel oil. The boilers are equipped with Buell Engineering Co. high efficiency (95%-99%) electrostatic precipitator for particulate emission control. Compared with coal and fuel oil, torrefied wood has lower sulfur, nitrogen and carbon content, as well as lower moisture. The torrefied wood product has about 80% of the heating value of coal and also has very low ash content.
“The biomass has been tested, burning 100% torrefied wood on other coal fired units and the data has shown nitrogen oxides (NOx) emissions were approximately 30% less and sulfur dioxide (SO2) emissions were approximately 75% less than when firing 100% coal,” the DEP noted. “The burning of 100% torrefied wood product also produced lower carbon dioxide (CO2) and mercury emissions compared to burning 100% coal.”
In Aug. 30 testimony filed at the Florida Public Service Commission as part of an annual fuel cost proceeding, Gulf Power said the two Scholz units are projected at capacity factors in 2013 of only 5.1% (Unit 1) and 4.3% (Unit 2). Unit 1 is projected at 11,116 tons of coal burn in 2013, and Unit 2 at 9,659 tons. This is a small (each unit is 46 MW net apiece), old plant that is usually only run to meet peak summer and winter power needs.