James Montgomery, Associate Editor, RenewableEnergyWorld.com
September 12, 2013 | 9 Comments
Toronto, Ontario, Canada -- North America's biggest 100-percent biomass plant is a former coal plant under conversion about a two-hour drive west from Thunder Bay, Ontario. The facility burned its last load of coal and powered down one year ago, but it's all abuzz with activity now. I got an up-close look at the upgrades in-progress as part of a tour of renewable energy companies, groups, and facilities sponsored by the Ontario Ministry of Economic Development, Trade and Employment (MEDTE).
Ontario Power Generation's (OPG) Atikokan Generating Station opened in 1985, the newest of OPG's thermal fleet, a single-unit site with a little more than 200 MW output. In tandem with Ontario's decree to eliminate coal-fired electricity generation (Regulation 496/07), Atikokan is converting to biomass with wood pellets. The conversion is about halfway through completion and the company anticipates the plant coming back online in mid-2014.
Atikokan cost nearly $800 million to build back in the 80s when it first opened as a coal plant. Shortening its operating lifetime to just 27 years was a tough economic pill to swallow, noted Darcey Bailey, engineering manager for the Atikokan biomass conversion who also grew up in the town. For an extra $170 million investment they're guaranteed another 10 years and likely much more, which he noted was "an easy case to make."
OPG's predecessor, Ontario Hydro, had looked into biomass options back in the 1970s, starting with waste grain material. In 2007 a government-funded $4 million Biomass Research Center was established at Atikokan following several workshops around the province (Nanticoke, Lambton, and Thunder Bay generating stations all are affected by the no-coal ruling). Testing in 2008 further looked at potential biomass efficiency vs. coal; environmental approvals were crafted, and community/stakeholder support galvanized, starting in 2010. A separate sustainability analysis showed that biomass conversion across four coal plant sites could be done sustainably, and specifically that local forest-based biomass could support the Atikokan site. Agricultural-based biomass such as wheat, which was part of Ontario Hydro's early evaluations, is deemed more feasible for the southern part of the province where those sources are abundant.
Atikokan's Conversion, Up-Close
One of the major decisions in the biomass redesign was to scrap the coal handling system. The new system is entirely automated, all run from the control center; trucks unload themselves, undesirable material is automatically sorted, with rejection capabilities at the silo, even if the pellets are deemed too warm. Trucks will take 15 minutes to unload: 10 trucks a day, 35 tonnes per truck, five days a week, totaling 90,000 tonnes/year. Even though Atikokan used a rail system for its coal, it's not a feasible option; the amount of material that will be needed to power the biomass plant would equate to roughly just nine
rail carsunit trains in an entire year, trucks make far better sense over the short distances from suppliers (see below).
View of the Atikokan plant from the gatehouse. Credit: MEDTE
The boiler at Atikokan was built extra-large to fire high-moisture lignite coal, so it will easily process the wood pellet feedstock "as far as chemistry will allow us to burn it," said Bailey. The only modification to the boilers has been adding 15 new burners, because the old NOx ones were deemed not able to have a sustainable flame over full load. All but three of the new burners have been installed.
Pulverizers which previously reduced chunks of coal into a fine powder now will render pellets down to fibers. An additional inner skin in the pulverizers will reduce the internal volume, increasing airflow to process the larger biomass fiber particles.
Foundations for the two 5,000-tonne storage silos were completed in early spring and quickly erected in about 10 days. More recently, conveyer bridges were connected between the silos. Inside the silos is more design work: a spiral chute will soft-handle the pellets, rows of explosion panels were opened up, and inert-gas fire suppression injection systems are going in. Individually, there's a laundry list of safety measures that are recognized industry best-practices -- positive isolation on the bins and feeders, explosion suppression systems on the mills, temperature monitoring in storage, regular cleaning to mitigate dust -- but having them wrapped all together in a single system is new to such a scaled-up biomass conversion, explained Brent Boyko, Atikokan's director of business development.
The first new explosion suppression system being hauled up to a pulverizer. Its function is to inject sodium bicarbonate, i.e. baking soda, into the chamber. Credit: MEDTE
Feedstock supply will come from a 200-km radius, with two suppliers splitting the business: Resolute Forest Products with pelletized sawdust from a sawmill in Thunder Bay, and Rentech which is converting an old particle board plant to handle un-merchantable hardwood that's already been harvested. The boilers were built extra-tall to handle coal but actually will work exceptionally well to incinerate pellets, he noted. They are expecting at most 3 percent ash by volume, but more likely it will be less than one percent. Compare that to the previous coal operation which had up to 25 percent ash. The little ash that remains will be recycled to agricultural soil or sent back to the harvesters for forest reincorporation. "This is a green operation," Bailey said, "we want to be as green as possible."
The controls system has been entirely revamped from what were cutting-edge late-1970s analog systems to a brand-new digital system. It's "almost a one-button startup process," Bailey noted, and allows more capabilities for data monitoring, archival, compiling spreadsheets during operation, etc. The room-sized ABB motor -- dwarfed, though, inside a cavernous bay inside Atikokan -- has been refurbished to an 80,000 ohms output, taking advantage of the rare opportunity of year-plus downtime.
Notice the black tinge on some of the pipes? That's residue from a coal chute a few floors above,
from which material once was dropped back down to floor-level to be carted away. Credit: MEDTE