A planned 50 MW Whole Tree Energy (WTETM) biomass-fired power plant
and previous pilot-scale and small-scale testing is described. Hybrid poplar trees are
planted and grown on land within 80 km of the power plant site. The time from planting
to harvest is five growing seasons, and the projected harvest yield is 56 dry t/ha. The
harvested trees are trucked to the power plant site and dried in a drying dome, which
utilizes waste heat from the power plant. The whole (not chipped) trees are then fed by
conveyor into a deep, fixed-bed furnace which provides heat for a high pressure steam
boiler-steam turbine-electrical generator. Flyash is removed from the stack gas with a wet
electrostatic precipitator, and the ash is pelletized and used as fertilizer for the trees.
Nitrogen oxides are controlled with extended over-fire air. A 50 MW power plant requires
18,400 ha of tree farms, which is about 1% of the land within a radius of 80 km. The
required land is leased for a 15 year period. The first WTETM power plant (50 MW) will be
built in St Peter, MN, with projected startup in mid-2004. The average present value of
electricity from a second 50 MW WTETM power plant is projected to be $0.049/kWh, and
for 150 MW MW WTETM power plant, $0.036/kWh (year 2000 basis, Federal tax credit for
closed loop biomass included).