Niagra Falls For Wood Power
Move over Niagara hydropower-there's a new generation of power in town.
In 2002, the New York state energy planning board's energy plan outlined a grim picture of dependence on imported fossil energy and an even darker image of the resulting environmental consequences, and warned of the eventual depletion of those supplies. Then Gov. George Pataki requested the exploration of developing an RPS. The state Public Service Commission agreed in 2004 to adopt such a standard, calling for a 25 percent increase in the percentage of renewable electricity consumed by New Yorkers by 2013. The 2004 base line already showed more than 19 percent of electricity consumed instate came from renewable resources-nuclear and hydro mostly. In adopting this RPS, the PSC designated the New York State Energy Research and Development Authority as the central procurement administrator.
USRG bought the facility in early 2007 and continued to operate the plant during the conversion. "It shut down for a month here and there, and in between those times it's run as a coal and TDF plant," Gardner says, adding that Feb. 1 is the target date for completion of the total conversion project.
Tweaking the Boiler
Wisconsin Public Service sold the small power plant to USRG because of the higher costs of Pennsylvania coal, and because the company had trouble with efficiency as the equipment was not maintained sufficiently, Gardner says. The plant, however, was equipped with a circulating fluidized bed (CFB) boiler, which makes a great conversion candidate for this type of project. Biomass industry veteran Andrew Grant was contracted by USRG to be project manager of the Niagara conversion. "Whenever you switch fuels-coal to wood-you affect the way the boiler runs," Grant says. "Essentially you have to redesign the boiler, and that's a major exercise." The CFB is flexible compared with coal or stoker units and allows combustion of fuels with varying properties. High ash-content fuels, even surpassing 60 percent, are routinely burned in CFBs, and the lower combustion temperatures associated with these boilers-1,600 degrees Fahrenheit compared with temperatures reaching 2,500 degrees in a coal or stoker unit-assists in keeping ash and alkalis from reaching their melting point. "This is vital," Grant says. While the CFB offers this inherent feedstock flexibility, there are limits on how much flue gas it can handle. "This affects flue gas velocities throughout the furnace and convection sections, and through the bag house and [induced draft] fan," Grant explains. "But we have addressed this by using a blend of waste wood and tire chips, keeping the resultant flue gas volume where we can handle it." More accurate metering of TDF from the existing day bins to the boiler, and new programmable logic controllers for on line blending and sampling of the fuels, were critical upgrades to the plant. The boiler was also outfitted with improved side-by-side fuel feed control and bed temperature monitoring, as well as updated combustion control loops. It just isn't feasible to burn 100 percent wood in the Niagara boiler. Because of wood's high moisture content, more energy is used to burn off that water, which results in a reduction in total peak output. "That's why TDF is used to enhance the [British thermal units] that go into the boiler," Gardner says. Seventy percent of the facility's feedstock by weight-an important caveat-is wood waste and 30 percent is TDF. "It's really like we have three fuels," Gardner says. "We have tire chips, green wood and dry wood." Dry wood is a better fuel than green wood, but it produces a lot more flue gas countered by the use of green wood and TDF. All three fuels are handled separately and blended at the point of use.
Even though by weight 70 percent of the Niagara Generating Facility's new feedstock will be biomass, TDF possesses more energy per equivalent mass basis than wood, which comes into play when the sale of renewable energy credits comes up. "To accurately account for the renewable portion of the power generation, we have to measure the mass flow of both fuel sources going in and then we have to do sampling and analysis of the samples in order to determine the Btu content over an average period," Gardner explains. If 100 units of electricity are produced but only 47 percent of the Btus fed into the boiler was from wood, then only 47 percent of that electricity is considered renewable and therefore eligible for credit as such.
Retrofitting the facility to accommodate the new fuel supply required new technical features on-site. Truck dumpers were added to receive the high volume of delivered wood. Disc screening and a magnetic separator were added, and new silos were built with hydraulic dischargers to segregate and feed dry biomass into the plant. For green wood storage, an open wood yard was needed with a stack-out conveyor and reclaimer. "This coal plant was built on a handkerchief-sized site, and even though we rented a little land from [a neighboring chemical factory] for our fuel storage, it's been very congested," Grant says. "It's probably been the tightest site I've ever worked on." The original site was five acres, but USRG is renting an acre from its neighbor.
"We have replaced most of the original fuel-feed system," Grant says. "In operation, the fuel yard staff manages the blending of fuels to the required composition while plant operators control the boiler operation to maximize the output." A new continuous emissions monitoring system was installed and the bag house was rebuilt. Gardner says nitrogen oxide and particulate matter emissions won't change much with the fuel switch-perhaps slight reductions in each-but sulfur dioxide reductions of 400 to 500 tons a year are expected. Some sulfur coming by way of the TDF will still be controlled with limestone in the boiler while selective noncatalytic reduction of nitrogen oxide will continue as before. Carbon dioxide emissions reductions will reach 160,000 tons per year with combustion of carbon-neutral wood.
Since the plant previously burned TDF, USRG walked into an established cache of rubber chip suppliers but has enhanced the "tenor" of those existing relationships, Gardner says. "We've reached out a little further to eastern New York and New Jersey, to access the tremendous amount of tires that are generated in that area." Relationships with wood suppliers, however, were developed from scratch. "There are tremendous resources in western New York, in terms of wood and waste wood, so we knew going in that there were towns and municipalities, and utility companies that manage rights of way for their lines and roads, which involves a lot of cutting and clearing," Gardner says. "They have to spend money to process and dispose of it, so for us to come in and take it off their hands for free allows them to realize a cost savings, and it provides us with a fuel that helps underpin our business." The distance limit of feedstock affordability is 80 miles, and USRG is talking with more than 20 towns and municipalities to hash out procurement arrangements; but the crux of wood waste comes from about 10 local utilities and tree trimmers. The feedstock is free, but transportation and processing increases the per-ton cost of wood from $5 to $15 dollars. In October 2006, a big snow and ice storm wreaked havoc in the Buffalo, N.Y., area, knocking down 30 percent of the trees. "There've been huge efforts through [the Federal Emergency Management Agency] and local contractors to dispose of that wood, which has been chipped and put into big piles that are just sitting around," Grant says. It's important to note that all of the wood consumed by the Niagara Generating Facility is "clean unadulterated waste wood," so there are no contaminants, paint, chemicals or treatments, keeping emissions within permitted allowances.
Ultimately several ingredients make such a conversion project viable: a plant (and boiler) able to accommodate the new fuel; modified permits to allow the combustion of wood, which is typically a nonissue due to the benefits of wood power compared with coal; an RPS to require the purchase of renewable power; and feedstock suppliers. The dynamics of this conversion project represent a tremendous amount of work, not because of the technologies needed but rather the overlapping complexities. "At the same time, this was an acquisition project, a development project, a construction project and an operating project," Gardner says, adding that the Niagara Generating Facility's conversion demonstrates a viable business model for the introduction of biomass in the United States. "There is no new technology here," Grant tells Biomass Magazine. "There are some major environmental benefits here and it's all done with established technology. I've worked on cellulosic ethanol biomass plants before and, although this project was complex in the managing of different permitting, design, construction and operations, the technical risk is very low with this established technology compared with trying to use biomass for gasification into liquid fuels, or something of that nature. Those are very promising processes, but they're still a long way out. What we have employed here today is based on 25-year-old technology and it works."
Ron Kotrba is a Biomass Magazine senior writer. Reach him at firstname.lastname@example.org or (701) 738-4962.