Biomass Feasibility Project Final Report - Xcel Energy

The result has been satisfactory, if not ideal. The boilers occasionally break down, and wood fuel
occasionally forms clumps on the grate which call for a blast of extra combustion air from
below. Slagging, however, has not been a problem.
The paper mill would like to see the boilers replaced eventually, but its immediate priority is a
system to dry and burn the 150 tons of mill sludge it sends each day to landfill. Longer term,
Stora Enso’s partnership with Minnesota Power could lead eventually to higher and better uses
of waste biomass.
Verso Paper, Sartell. A former owner of this mechanical mill, Champion, embarked in 1990 on an
ambitious program. It would lease or purchase 22,000 acres of farmland to raise hybrid poplars
that reach harvest size in ten years. Each year, one-tenth of the acreage would be planted. On
the eleventh year, the first tenth would be harvested and the hybrids would begin to
regenerate. The year after that, the second year’s planting would be harvested, and so on
through the ten-year cycle when the first stand again would be ready to harvest.
This plan was strategic for several reasons. Champion’s self-sufficiency in hardwood would
insulate it from the volatility of aspen prices. (Aspen is half the mill’s furnish. The other half is
softwoods which the mill would continue to purchase). By controlling more of its supply, the
corporation would raise its stock price, and waste from the hybrid harvests could become
biomass fuel.
That plan has been somewhat revised by successive changes of ownership. In 2000, Champion
sold the Sartell mill to International Paper (IP), which put the hybrid poplar program on hold. IP
then resold the mill in June, 2006, to CMP Holdings LLC, a holding company which purchased
three other mills to form a new paper company called Verso. The sale included the 12,000 acres
of hybrids that Champion had planted, and Verso will begin to harvest that next year.
The Sartell mill has a lot of room for more electric generation. Of its three boilers, the largest cofires
combinations of bark and wood waste, stoker coal, and dewatered paper mill sludge at 50-
60% moisture content. The second burns natural gas, and the third burns coal. The plant
consumes all its capacity of 22 MW.
Rock Tenn/The City of St. Paul/Ramsey County. Like Stora Enso in Duluth, Rock Tenn may enter
into a partnership between a paper mill and a municipality, but at this writing that is still in the
talking stages. A recycling paperboard mill with no wood residues to burn, Rock Tenn long has
bought process and power-generating steam through a pipe from Xcel Energy’s High Bridge
power plant. But that arrangement ends in mid-2007 when the Xcel Energy plant converts to
natural gas. Rock Tenn’s continued operation depends on finding a new steam source. For the
short term, it will get by with an existing oil-fired boiler. But expensive fuel oil is only a stopgap
until something more economical can installed.
For the long term, Rock-Tenn’s engineers considered first an on-site biomass power plant burning
agricultural wastes. The Minnesota Department of Employment and Economic Development
called on the Agricultural Utilization Research Institute to consult. But the high landed cost of
agricultural wastes, along with the logistical and permitting problems in using them in the center
of a large metropolitan area, made that idea unworkable.
Then discussions among company, state, city, Port Authority and county officials led to the idea
of an RDF gasification plant. The Green Institute recently completed a study investigating the
possibility of using biomass at the plant (Nelson, 2007).
Identifying Effective Biomass Strategies: Page 79
Quantifying Minnesota’s Resources and Evaluating Future Opportunities