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A Colossal Conversion

Xcel Energy is converting the last coal-fired boiler at Bay Front Power Plant in Ashland, Wis., to run solely on biomass. Through the implementation of a gasification technology, it will become the largest biomass-fired power plant in the Midwest.
By Anna Austin
Known as Lake Superior's hometown, Ashland, Wis., is near the head of Chequamegon Bay. Although small-just less than 9,000 people-the town will soon become home to a significant renewable energy landmark.

Two of the three boilers at Ashland's Bay Front Power Plant have been combusting woody biomass since 1979. For the past several years, Xcel Energy has been investigating the logistics of transforming Bay Front's third and final boiler to utilize a biomass gasification technology. The process involves conducting studies to determine project feasibility and the amount of sustainable woody biomass in the area, and gaining approval from groups such as Clean Wisconsin and Renew Wisconsin.

Upon completion, the plant will become the largest 100 percent biomass-fired power plant in the Midwestern U.S. Before construction can begin, however, Xcel Energy must gain
project approval from the Public Service Commission of Wisconsin.

Xcel Energy submitted an approval application to the PSCW in February 2009. The PSCW in turn announced a request for input from residents of Ashland and the surrounding communities. In order to elicit feedback, the PSCW mailed information about the project to libraries and local officials-city, village, township and country clerks as well as extension agents and foresters-in 17 northern Wisconsin counties in the upper third portion of the state.

Approval of the project is expected but still pending. As they await finalization of the application process, Xcel Energy continues to put together the final pieces of the project puzzle.

Sustainability First
In 2006, Xcel Energy funded a study with the Energy Center of Wisconsin to investigate the amount of biomass that could be removed from Wisconsin's forests to support energy projects and any associated environmental impacts.

Study conclusions were favorable, according to Xcel Energy Regulatory Policy Manager David Donovan. It was determined that area forests within a 50-mile radius of the Bay Front Power Plant could support additional biomass removal without adverse impacts to the local ecosystem, and dedicated biomass energy plantations could ultimately provide a portion of the plant's increased biomass needs.

"Results that came back indicated there is more than 850,000 tons of biomass available on an annual basis-that's if every acre that could be harvested was," Donovan tells Biomass Magazine. "On an annual basis, once the conversion is done, the entire plant-including the existing boilers-would require anywhere from 400,000 to 450,000 tons per year, based on how we are able to manage the dispatch of the boilers."

Though sustainability doesn't seem to be an issue, Donovan says the question of feedstock accessibility remains. "We believe that if we provide a market, the loggers will go out and access that material," he says. Xcel Energy won't send its own crews out or process any materials; rather they will pay suppliers to do it for them. "The key point is that we're not going to conduct any of the harvesting," Donovan points out. "We will contract existing logging companies, or even new ones that might come into the market. If there is an expansion of the forest products industry, such as a new saw mill sited nearby, we'll take their waste wood as well. We would take their bark and unusable materials."

Reiterating the company's emphasis on sustainability, Donovan says it's one of Xcel Energy's key principles. "We don't want anybody going out there to harvest and take every last twig off the site-we have to be concerned with the long-term characteristics of the site," he says. "We supported the Wisconsin Department of Natural Resources in the development of biomass harvesting guidelines (see Woody Biomass Harvesting Guidelines sidebar), and we are encouraging our loggers to use those. Based on that, and what the
Energy Center told us, we think there is more than an ample supply available for the facility."

Donovan says after the first study a follow-up study was done that evaluated forest service numbers from a haul area of approximately 100 miles. "Within that area, there was almost twice the available material," he says.

Boilers and Biomass
If Bay Front's previously converted boilers directly combust woody biomass, why did Xcel Energy decide to install a gasifier in the third? Donovan explains that boilers one and two are spreader stoker boilers, which more easily burn biomass, and still allow for the combustion of natural gas and coal. "Direct firing is more flexible," he says. "I can't say the efficiency is that great, but it's more flexible on the fuel side."

The third boiler is a cyclone boiler, which requires very specific fuel characteristic requirements, according to Donovan. "[The biomass] has to burn at a certain place in the boiler, otherwise the heat retention and heat exchanges are messed up," he says. "We did an internal study a few years back which showed that the retention time is not long enough if the fuel in the cyclones is biomass. It burns in the back half of the boiler and it doesn't allow us to capture the heat and energy in our exchange system."


Biomass Gasification System/SOURCE: XCEL ENERGY

The gasification technology mimics natural gas combustion characteristics, he says. The project's $58 million price tag covers the cost of the gasifier equipment and some minor changes to the boiler to maximize heat recovery, as well as new fuel handling equipment such as another hydraulic truck dumper and conveyer belts to move the fuel to its storage area.

According to Donovan, the power plant will not see a decrease in power production post-conversion. "Currently, boilers one and two produce approximately 20 megawatts (MW) of electricity from 100 percent biomass," he says. "Boiler number five, when burning 100 percent natural gas, it can produce about 32 MW; realistically about 28 MW on a consistent basis. With coal, we're at 20 MW, and when we convert to biomass, we'll replace that 20 MW."

Xcel Energy expects it will need an additional 40 trucks per day to deliver fuel to the plant, according to Donovan. "It really depends on how much material the trucks bring in, but we expect each to load 20 to 25 tons," he says.

Once delivered, the prepared biomass will be unloaded using Xcel Energy's existing systems to put it into a storage pile or directly into a storage bin for combustion. "Once it comes through the gate, it's very similar to how you'd handle coal or any other solid material," Donovan points out.

Cost Factors
Xcel Energy has projected biomass fuel costs to be cheaper than coal, if current prices can be maintained. "This plant is small, and it has specific fuel requirements," Donovan says. "We should be competitive with coal prices at that plant, and the analysis we've done so far is based on what it's going to cost us to make the conversion and what kind of a rate impact that will have on our electric customers."

Despite the cost benefits, Donovan admits the fuel procurement process has been long and arduous. "We have no rail access, and even if we did it is such a small plant; we couldn't get the economies of scale for fuel delivery with rail," he adds.

Biomass for the plant is trucked in from Duluth, Minn., Superior, Wis., or a freighter loads it to a storage dock, where Xcel Energy trucks it to the plant. "It's a very labor-intensive process," Donovan says.

Xcel Energy hopes to gain project approval from the PSCW in the fall, and has similar applications in Wisconsin and in North Dakota and Minnesota. "Because of the way our system operates, we share costs across a five-state jurisdiction," he explains. "In Xcel's northern territory, any investment made in Wisconsin is paid for by customers in North Dakota,
South Dakota, Michigan and Minnesota, and vice versa. We share all costs, and dispatch all of our generation resources as a system."

Engineering, design and construction work is expected to begin in 2010, so the new Bay Front Power Plant could be operational in late 2012. By this time, the plant will be less than five years away from its 100th birthday, and will venture into a new century of life with a clean slate.

Anna Austin is a Biomass Magazine associate editor. Reach her at aaustin@bbiinternational.com or (701) 738-4968.
 

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