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The Mac Weekly - March 28, 2008
The Green Beat
By Anna Waugh, Associate News Editor
The Rock Tenn Community Advisory Panel meetings have yet to provide any conclusions to the problem of how to power the 100 year old Saint Paul paper recycling plant, and some members of the panel are beginning to worry that there will be no solution that will please everyone.
"It's becoming clearer and clearer that there is a fundamental conflict with the goals between an environmentally sound and a cheap [option, and they] may be mutually exclusive," said panel member and neighbor of the plant Tom Welna, who also works as the Director of Macalester's High Winds Fund.
There is pressure from the Saint Paul Port Authority to settle on a biomass burner which would use municipal and rural tree waste, corn stover, agricultural waste and other organic materials as fuel.
The Port Authority's interest in the power source comes from a desire to "tap some thermal energy from [the] proposed Rock Tenn power plant, pipe it underground and heat commercial buildings along University Avenue," wrote the president of the SPPA in a letter to RCAP.
Biomass in Minnesota is considered a renewable energy source according to the law, and this is one reason that the Port Authority has backed it. However, much of the tree waste that is used in other biomass burners, like District Energy's downtown Saint Paul plant, comes from trees from suburban construction, and sprawl is not renewable.
Another problem: Minnesota law allows biomass incinerators to burn a mixture that contains up to 30 percent refuse derived fuel, which is essentially garbage. Some amount of filtering can keep out the heaviest metals, but there is still a worry that unsorted batteries, computer parts and plastics will release harmful chemicals into the air if burned.
So if biomass is not the answer, what is a renewable resource with low carbon emissions, and is economically viable? After all, the plant employs 500 workers here in Saint Paul, but could ship off to cheaper Asian counterparts if threatened, so a solution is necessary.
Anaerobic digestion is an option that Welna suggested. This is a process that uses bacteria in the absence of oxygen to break down biodegradable material, and produces a biogas that can be used interchangeably with natural gas. This option would produce fewer air pollutants than a burner, less carbon dioxide and would be derived from a true renewable energy source.
The use of anaerobic digestion to produce gas for energy is not new - the first anaerobic digester was built by a leper colony in India in the late 1850s. Today, Germany and Denmark are leaders in anaerobic digestion technology, and some of the largest digester units can generate 2 MW of electricity. Digesters can run off of manure, organic industrial waste and source-separated municipal solid waste also known as compost.
Units can produce biogas anywhere and, after compression, feed it into existing natural gas lines. Leftover organic materials can be used as fertilizer.
From conservation improvements alone, Rock Tenn was able to find solutions that save about 25 percent of their need for power with payback periods of just two years. The RCAP panel, sponsored by Minnesota State Senator Ellen Anderson with $4 million granted from the MN Department of Commerce, is considering the options for the next 50 years and the long term costs and benefits.
Burning trees in a biomass incinerator to power a paper recycling plant is illogical. Why bother recycling at all? If Rock Tenn says it is able to put $200-$350 million on the table for a biomass burner, then it has the money to choose a different option.