profile than a bag house offers advantages such as reduced energy con- tem.” While NRG’s thermal facility on-site of the local power sumption, improved performance and a longer life for the sys- plant couldn’t provide steam to Andersen anymore, the power tem. Because the burners and boilers had to be matched up so plant had been releasing warm water (up to 65 degrees quickly and the ESP system had a six-month lead time, Pioneer Fahrenheit) from its turbines into the river. Part of TKDA’s Power was forced to negotiate the purchase of the ESP before design proposal included the utilization of this warm water the final specs on the burner-boiler system were configured, from its neighbor to run through four large makeup air-handling Stevens says. After the exhaust gases pass through the ESP, a units each capable of ingesting 750 gallons of temperate water draft fan carries the gases up the per minute for a total of 3,000 galemissions stack where the continulons per minute. The warm water is ous emissions monitoring system used to temper the oftentimes subgrabs a final analysis of the gases zero air from Minnesota winters that Now that Andersen’s new plant is before they are released into the rushes into the negative air-pressure running, 98 percent of the wood atmosphere. Because the wood environment inside the plant. With a funneled through its Bayport plant is from Andersen’s waste stream is 600,000 cfm deficit inside the plant, either resident in the wooden door made into such a fine, clean flour the makeup air handling units utilizand window products it sells, or is that contains no paint or contamiing warm water discharged from the consumed to generate process steam power plant puts 400,000 cfm of nants, the resulting ash content for the manufacture of those very from burning it is extremely low— temperate air back into the plant, same products. two-tenths of one percent of what thereby reducing the amount of goes in comes out as ash. steam Andersen needs to generate. Andersen’s Bayport operation “The warm-water recovery system produces lots of fine particles eliminates the need for an additional derived from cutting wood or from the exhaust stream just boiler,” Roeder says. Approximately 360,000 million British detailed, all of which must eventually be exhausted from the thermal units (MMBtu) of energy are needed to produce all of plant. This necessitates a massive exodus of air jettisoned from the steam Andersen consumes in a year; the warm-water recovthe complex with every passing minute. “There’s a lot of vent- ery system recovers 50,000 MMBtu annually, which amounts to ing going on,” Stevens tells Biomass Magazine. “There’s an air one-seventh of the total energy needed to produce all of its deficit of about 600,000 cubic feet per minute (cfm).” Hogberg steam requirements. Now that Andersen’s new plant is running, elaborates, “With all of our different dust collecting and manu- 98 percent of the wood funneled through its Bayport plant is facturing operations in Bayport, there’s a lot of exhaust. In the either resident in the wooden door and window products it sells, winter there’s a big negative air pressure inside the facility, so or is consumed to generate process steam for the manufacture TKDA came up with the idea for a warm water recovery sys- of those very same products.
30 BIOMASS MAGAZINE 10|2007