Steam-Powered Window Plant
Popular window maker Andersen Corp. is commissioning its new steam plant in Bayport, Minn., powered exclusively by the wood waste generated from the manufacturing of 6 million windows and doors a year.
The window maker's plant came on line this spring, producing all the steam needed to manufacture 6 million wooden doors and windows a year. "The Bayport plant is Andersen's mother ship," says Dan Kinrichs, Andersen facilities engineer. Andersen's other plants across North America are mostly assembly facilities that don't require steam like the Bayport plant. Since the 1980s, Andersen's Bayport facility purchased a portion of its steam from a thermal facility owned by NRG Energy Inc., which was on the site of a neighboring power plant. By 2005, 60 percent of Andersen's steam was being piped in from its neighbor, with the remainder generated in-house by Andersen's increasingly antiquated wood-fed boiler system. Susan Roeder, Andersen's manager of community relations and public affairs, says the business simply outgrew its capacity to generate enough of its own steam, which led to an increasing dependence on its supplier.
Fueled by sawdust, shavings and wood fines (all byproducts of wood processing) from its own manufacturing process, Andersen's new facility is self-sufficient and modern. By all measures the project has been a smashing success, which is phenomenal considering the inflexible schedule project leaders faced. They were given less than two years to have this plant running full steam ahead by April 2007, when Andersen's long-time steam supply would no longer be available. Amidst all of this, Stevens says he dealt with the stress just fine. "I went from looking like I was 25 [years old] to looking 45, but I dealt with it just fine," he laughs. The pressure was intense as the window maker set out to determine the best solution to address a projected steam deficiency.
Identifying the Right Financial, Environmental Solution
Luckily for Andersen, some employees were already investigating options for steam before the company's steam supply contract was up-well before the news hit that its current contract with NRG would not be up for renewal. Kirk Hogberg, manager of energy and environmental management for Andersen, says he and his team eventually learned NRG's steam plant would no longer be running after April 2007 due to emissions reductions targeted at the Alan S. King power plant, on which NRG's facility was located. "One way for them to reduce their environmental impact was to stop making and selling steam," Hogberg says. "The mood here when we found out was that it was a good thing we started having discussions when we did."
Many different proposals for steam replacement were considered, requiring an interdisciplinary approach. "The decision involved personnel from a wide range within our company," Kinrichs says. "Some of the key criteria we looked at ranged from return on investment, environmental impact and redundancy on the system. We received seven or eight proposals, each with different options." Andersen finally selected a package and TKDA, a St. Paul-based engineering firm, was awarded the contract in July 2005 for an April 2007 completion date. "We approached them with an Andersen-owned concept-a unique project that met their steam needs and provided a good return on investment," says Charles Lederer, TKDA project manager and senior engineering specialist. Pioneer Power was selected to be general contractor. The design-build package consisted of a $22 million steam generation facility to be entirely owned by Andersen featuring all new, state-of-the-art equipment accompanied by a unique and energy-saving addendum within the design.
The heart of Andersen's new facility is the wood fuel feeding it, and the burners and steam-generating boilers turning that wood into energy and steam. Different waste wood streams result in differently sized wood particles like shavings, chips or fines. Depending on the particle sizes within a particular waste stream, the material is either run through a hammermill or an initial grinder to pulverize the wood and make it into a more consistent size. All the woody material is turned into wood flour after it leaves the second grinder. It's stored in what Kinrichs calls the north brown silo and ready for use. "The wood flour is pumped from the north brown silo to the day bin, which holds a half a day's worth of storage," Kinrichs says. Two augers transport the wood flour from the day bin into the plant.
The wood flour is blown from the augers into Cohen wood-scroll burners firing three boilers made by C-B Nebraska Boiler. Each boiler is capable of producing 40,000 pounds of steam an hour. Lederer says all the equipment from the wall of the plant-where the material is fed inside-to the burners was supplied by Cohen. "We wanted the burner operations and the fuel feed system to be matched up-it's a keystone piece of the plant," Lederer says. According to Stevens, the boilers and burners had to be matched up by August 2006. "That was a big task," he says. An economizer is positioned after the boilers, which reduces the temperature of the flue gas. From there, an electrostatic precipitator (ESP) collects particulate matter from the waste gas stream. The ESP conveys an electrical charge to the particles and initiates their collection upon metal plates inside the precipitator, after which the collected particulate matter is dispensed into a hopper for removal. The use of an ESP rather than a bag house offers advantages such as reduced energy consumption, improved performance and a longer life for the system. Because the burners and boilers had to be matched up so quickly and the ESP system had a six-month lead time, Pioneer Power was forced to negotiate the purchase of the ESP before the final specs on the burner-boiler system were configured, Stevens says. After the exhaust gases pass through the ESP, a draft fan carries the gases up the emissions stack where the continuous emissions monitoring system grabs a final analysis of the gases before they are released into the atmosphere. Because the wood from Andersen's waste stream is made into such a fine, clean flour that contains no paint or contaminants, the resulting ash content from burning it is extremely low-two-tenths of one percent of what goes in comes out as ash.
Andersen's Bayport operation produces lots of fine particles derived from cutting wood or from the exhaust stream just detailed, all of which must eventually be exhausted from the plant. This necessitates a massive exodus of air jettisoned from the complex with every passing minute. "There's a lot of venting going on," Stevens tells Biomass Magazine. "There's an air deficit of about 600,000 cubic feet per minute (cfm)." Hogberg elaborates, "With all of our different dust collecting and manufacturing operations in Bayport, there's a lot of exhaust. In the winter there's a big negative air pressure inside the facility, so TKDA came up with the idea for a warm water recovery system." While NRG's thermal facility on-site of the local power plant couldn't provide steam to Andersen anymore, the power plant had been releasing warm water (up to 65 degrees Fahrenheit) from its turbines into the river. Part of TKDA's design proposal included the utilization of this warm water from its neighbor to run through four large makeup air-handling units each capable of ingesting 750 gallons of temperate water per minute for a total of 3,000 gallons per minute. The warm water is used to temper the oftentimes sub-zero air from Minnesota winters that rushes into the negative air-pressure environment inside the plant. With a 600,000 cfm deficit inside the plant, the makeup air handling units utilizing warm water discharged from the power plant puts 400,000 cfm of temperate air back into the plant, thereby reducing the amount of steam Andersen needs to generate. "The warm-water recovery system eliminates the need for an additional boiler," Roeder says. Approximately 360,000 million British thermal units (MMBtu) of energy are needed to produce all of the steam Andersen consumes in a year; the warm-water recovery system recovers 50,000 MMBtu annually, which amounts to one-seventh of the total energy needed to produce all of its steam requirements. Now that Andersen's new plant is running, 98 percent of the wood funneled through its Bayport plant is either resident in the wooden door and window products it sells, or is consumed to generate process steam for the manufacture of those very same products.
Identifying the final adjustments needed to effectively address those last remaining comissioning issues is ongoing as inefficiencies from suboptimal combustion in the burners are being investigated. Also, the unavoidably rushed purchase of the ESP before the specifications for the boilers and burners were fully configured has culminated in an inordinate loading of particulates in the ESP. But these are all said to be part of the normal routine when dialing into the optimal performance of any new design.
Ron Kotrba is a Biomass Magazine senior staff writer. Reach him at firstname.lastname@example.org or (701) 746-8385.