End of an Era
With the close of 2014, Ontario will make history by becoming the first jurisdiction in North America—and one of the first in the world— to drop coal power from its energy portfolio.
Pulling off such a feat hasn’t proved to be too difficult, evidenced by a quicker-than-planned transition. By the end of this year, the province will have shut down or converted 17 of its 19 coal units, leaving a full year for the remaining two to power down.
One plant that has already burned its last pieces of coal is Ontario Power Generation’s Atikokan Generating Station, a 211-MW coal plant that’s being converted from low-sulphur lignite coal to wood pellets. Located in northwestern Ontario’s Atikokan, a small, scenic town dubbed “the canoeing capital of the world,” over 150 construction personnel are currently working on the site of AGS. That number is expected to reach 250 by midsummer, with jobs in construction, technical work and administration.
While work on the $170 million project began last September, research of and plans to utilize biomass fuel span many years back.
Back in the 1970s, Ontario Hydro—Ontario Power Generation’s predecessor—conducted preliminary investigations of biomass potential that included successful test burns of waste grain material at a number of OPG’s coal-fired stations, AGS among them. AGS began operations in 1985 and today employs about 85 people.
In 2006, the provincial government allocated $4 million to build the Atikokan Biomass Research Center, and after a great deal of research and test burns over the next few years—as well as the passage of a province-wide law that required the cessation of coal use at all power stations by Dec. 31, 2014—the project began to gain momentum and make sense to stakeholders and the community.
Finally, a major milestone was reached in 2010, when the Ontario Minister of Energy announced the official conversion, and directed the Ontario Power Authority to negotiate a Power Purchase Agreement with Ontario Power Generation for biomass-generated electricity from AGS. Even further research was done then, including sustainability and safe handling and storage analyses, engineering concept studies and combustion and ash studies.
Initially, the converted plant will cover peak demand, outages and weather-related needs, but using biomass will retain the plant’s capability of producing at full load of 205 MW. The conversion to biomass will cost less than building a new natural gas plant. While the cost of powering with wood pellets will be more expensive than coal, the plant will be able to meet the no-coal provincial mandate at minimal costs.
While AGS isn’t the largest biomass conversion completed or ongoing, it is certainly notable—conversion of a lignite coal generating station to biomass has never been completed on such a scale. “Therefore, the technical solutions determined for this plant are very leading edge,” says AGS Station Manager Brent Boyko. “Components were chosen based on well-established industry success; however, the overall integration for this application is the first of its kind.”
It’s actually far more challenging to retrofit a plant than to open a new one, according to Boyko. At AGS, that includes overhauling the fuel handling facilities, installing 15 new burners and installing a new controls system.
Slipform construction of the storage silos began the week of May 1, according to Darcey Bailey, ABC project engineering manager. Slipforming is the use of a continuous, cast-in-place method that relies on the quick-setting and high-strength properties of concrete to create a structure with no joints. “The silos progressed very well,” Bailey says. “The work was continuous—24 hours a day, for nine to 10 days straight. The final height of the concrete is 43 meters (142 feet). Both silos were poured together, and the forms are joined with a solid bridge.”
Completed May 11, 2,750 cubic meters of concrete—over 300 truckloads—were cast in the silos project, supported by over 200 metric tons of rebar. Now that the silo skeletons are erected, the walls of which are about one-half meter thick, work has begun to link them into the fuel transfer system into the plant. They will have a combined storage capacity of 10,000 metric tons.
AGS has agreements in place with two northwestern Ontario pellet suppliers. Fuel supply contracts were recently signed with Atikokan Renewable Fuels, which was recently acquired by Rentech Inc., and Resolute Forest Products, each for 45,000 metric tons annually, for 10 years. The fuel has been sourced and will be processed in northwestern Ontario, and both companies include aboriginal involvement. Transportation contracts from the source to the station are also in place, according to Chris Fralick, plant manager for OPG's Northwest Thermal, which runs AGS and Thunder Bay Station.
Once on site, the pellets will be received from self-unloading, rear discharge trucks—about five deliveries each day— and a new receiving system will transport the pellets to large storage silos via conveyor belt and a bucket elevator.
“When needed for production, the pellets will be delivered to the plant on a first-in, first-out basis from the silos, via new conveyor belts and a second bucket elevator,” Bailey explains. “Once inside the powerhouse, the pellets are pulverized in the existing system and fed into the boiler much the same way the coal was previously.”
Structural steel for the truck receiving and transfer tower is complete, the shell of which is about six stories high. Work on repurposing the coal-handling facilities inside the plant has also begun, and still to come are furnace and combustion system modifications, which will begin this year.
All 15 of AGS’s burners are being replaced with Doosan Mark IV biomass burners. The plant utilizes a wall-fired, pulverized-fuel, radiant-heat Babcock & Wilcox boiler designed for lignite coal fuel, an ideal candidate for fuel conversion, due to the similar heat content of lignite coal and wood pellets.
On the back end, new ash transport systems are being installed.
Major equipment has been ordered and is arriving steadily, Bailey says, and work on the replacement of the controls system will begin soon.
Besides the many construction workers on site, Atikokan Generating Station staff members are involved with the work going on.
Besides working directly with AGS staff, contractors have islands set up throughout the station where they are able to work independently.
AGS employees serve as contract monitors and administrators and work closely with contractors on quality control, says Bailey. “Their knowledge and familiarity of the plant and its operations are vital as the work progresses.” Therefore, all staff will be involved in commissioning and will be trained on process modifications prior to startup.
Commissioning and in-service for AGS is planned for mid-2014, and further out on the horizon, OPG plans to continue to explore options for its other power stations. Advanced pellets have shown considerable promise, as they can be handled much like coal, but more research has to be done before they might be considered a viable option. “We have tested advanced biomass pellets at some of our other stations,” Fralick adds. “While they show great promise, we are not quite at the point where they can be used in a commercial environment, but our testing of these materials continues.”
Meanwhile, Ontario will finish the course it set out on six years ago. While biomass won’t be the right option for every plant, AGS is a successful example of preserving time, money and air quality by utilizing an abundant, clean and renewable resource.
Author: Anna Simet
Managing Editor, Biomass Magazine