April 1, 2010

OPG Charts Move from Coal to Biomass

Les Marshall, Chris Fralick, and Daryl Gaudry, Ontario Power Generation

In response to Ontario’s provincial regulatory mandates to phase out the use of coal by the end of 2014, Ontario Power Generation (OPG) is exploring its capability to employ biomass feedstocks to displace coal in some units within the OPG thermal fleet. The primary fuels employed during the respective trials at its Nanticoke and Atikokan Generating Stations have been agricultural by-products and commercial grade wood pellets. The Canadian utility has learned valuable lessons about fuel supply and logistics, and the technical challenges of safely handling and firing high levels of biomass.

As part of its strategy to reduce greenhouse gas emissions, the Ontario provincial government adopted a regulation in 2007 that will phase out the generation of electricity from coal in Ontario Power Generation’s (OPG) coal-fired generating stations by Dec. 31, 2014. The government has also identified interim targets that will limit carbon dioxide (CO₂) emissions from OPG’s coal-fired fleet to two-thirds below 2003 levels by 2011.

OPG has an installed capacity of 21,748 MW, consisting of a diversified generation mix in 2008 of 45% nuclear, 34% hydro, and 21% fossil-fueled electricity. OPG operates five fossil-fueled stations (four coal-fired and one gas/oil) with an installed capacity of 8,177 MW and co-owns two other gas-fired stations.

In 2007, OPG installed a direct injection system for agro-biomass with a capacity of 50 MWe at its 3,640-MW Nanticoke Generating Station (GS). However, much of the success of the current program has entailed the use of the dedicated mill concept, in which wood pellets are processed through the existing coal pulverizers, without coal, and are subsequently conveyed to the furnace with the existing firing systems.

In 2008, proof-of-concept testing was conducted at OPG’s Atikokan GS to assess the feasibility of operating the 227-MW lignite boiler with various percentages of biomass, specifically pelletized wood. The Atikokan program also employed the dedicated milling concept. This article discusses the lessons learned from the projects at both plants and what OPG’s future aspirations are as far as converting from coal to biomass as its major fuel source.

Regulatory Environment

At the federal level, the Canadian government has indicated an intention to regulate greenhouse gases on an intensity basis. It has also indicated that it will align with the U.S. system, which is likely to be a cap-and-trade system.

In February 2009, the Ontario government also announced its Green Energy Act (Bill 150), aimed at expanding renewable energy generation and strengthening the province’s commitment to energy conservation. The new procurement mechanism for new renewable energy will be delivered through a feed-in tariff, modeled after the successful policies of Germany and France.

Since 2005, OPG and, in particular, the Nanticoke GS, have been investigating the use of biomass as a coal offset option. However, as a result of the recent regulatory directive to phase out coal, the replacement of coal with biomass in some of its coal units has become the focus of OPG’s biomass program at its coal-fired generating stations.

Compared to some renewable energies such as wind and solar, biomass has the added benefit of being dispatchable, which means that it is capable of responding to the changing load demand when needed. Other benefits related to a large-scale biomass industry in Ontario are the synergies with agriculture and forestry sectors and the favorable economics of using existing provincial assets (the coal plants).

The guiding principles for OPG’s biomass testing program are as follows:

• OPG does not use food products fit for human consumption.

• OPG only uses biomass extracted using sustainable practices (as defined by the United Nations Framework Convention on Climate Change).

• OPG intends to maximize the use of existing assets.

Nanticoke’s Early Biomass Project

The Nanticoke Generating Station (Figure 1) is equipped with eight units, each with a nominal rating of 500 MW. The boilers are of the opposed-fired configuration, originally designed to fire a mid-sulfur bituminous coal. Currently, the Nanticoke boilers fire a furnace blend of 80% (by energy) Powder River Basin subbituminous coal with 20% low-sulfur eastern bituminous coal (see table). The units are equipped with five 10E10 ball-race pulverizers. All five mills are required for full load.

1. Leading the way. The Nanticoke Generating Station is located on the north shore of Lake Erie. Both it and its sister facility, the Atikokan Generating Station, are pioneering the use of biomass as a renewable energy source for their operations. Courtesy: Ontario Power Generation


A comparison of cofired fuels. Source: Ontario Power Generation

In 2005, Nanticoke was approached by the Ontario Ministry of Agriculture, Food and Rural Affairs and the Ontario Millers’ Association regarding the possibility of displacing some portion of its coal-fired generation with biomass. In 2006, Nanticoke conducted its first proof-of-concept biomass injection test using wheat shorts, a by-product of the milling of wheat to flour (see table). A single truckload of wheat shorts was brought to the site, and the integrated compressor on the truck was used to convey the biomass into the outlet pipes of a single pulverizer (mill 4E). This configuration was very rudimentary, but the results were encouraging enough to merit a series of follow-up tests in 2007, using a pair of blower trucks, each injecting wheat shorts into one of the two mill outlet lines of pulverizer 4E.

The initial test program provided the first results to OPG regarding the impact of biomass use on the firing systems and acid gas emissions. However, due to the nature of the truck unloading method (compartmentalized biomass, gravity fed to an onboard blower), it was difficult to control the biomass injection rate and avoid line pluggage. In addition, this mode of operation was limited in both capacity and duration. The need for a larger, engineered system was recognized in order to better demonstrate the potential of biomass at Nanticoke.