When it is completed, later this summer, the UK’s Drax Power Station biomass facility will become the largest dedicated cofiring project of its kind in the world. As U.S. coal-fired generators come under increasing pressure to cut emissions and take advantage of incentives to promote power generation from renewables, Drax offers an example of what is possible.
Although there currently is no federal law in the U.S. related to the use of renewables, many states have renewable portfolio standards to drive the use of renewables in power generation. These policies, which may be mandatory or voluntary, require or encourage electricity producers within a given state to generate a specified share of their electricity supply from renewable resources such as wind, solar, or biomass.
In areas that have forest products or agricultural waste, biomass can be the most economical of the various renewable sources. Accordingly, utilities operating within such states are showing tremendous interest in how to take advantage of this renewable resource.
While building dedicated biomass-fired plants is an option, an attractive alternative is cofiring biomass with coal in large coal-fired plants. Cofiring is not only more efficient than burning biomass in small, dedicated plants, it also offers the generator greater fuel flexibility while reducing emissions of SOx, NOx, and other pollutants. (Also see “OPG Charts Move from Coal to Biomass,” April 2010; “Biomass Cofiring: Another Way to Clean Your Coal,” July 2009; and “PSNH’s Northern Wood Power Project Repowers Coal-Fired Plant with New Fluidized-Bed Combustor,” August 2007.)
Burning Biomass with Coal
There are three main methods of introducing biomass into a coal-fired utility boiler. In the co-milling method, biomass can be added to coal before it is milled and then passed through the existing milling system. Using an existing coal-milling system, however, limits the quantity and type of biomass that can be fired. A typical limit is 5% cofiring (by heat input basis) or less.
Alternatively, the biomass can be gasified to produce low-calorific-value gas, which can then be fired in either a boiler or combustion turbine. However, this can be a complex and relatively expensive process when used upstream of an existing conventional utility boiler.
Another method is to use a dedicated cofiring system, where the biomass is processed and milled separately from the coal. This technique offers the best CO2 abatement versus cost ratio of all cofiring solutions. It also increases the proportion of biomass that can be fired to more than 10% by mass. Importantly, the technology also lends itself particularly well to existing coal-fired power plants. As a retrofit project, a relatively quick installation and short tie-in time is possible, often using the existing grid connection as well as road and rail links.
Alstom has been involved with biomass power generation for almost two decades and much longer in the pulp and paper industry in the U.S. However, its first utility-scale cofiring retrofit project was carried out in the Netherlands. In 2004, Alstom successfully designed, installed, and commissioned a dedicated cofiring system on the 640-MWe tangential coal-fired boiler at Essent Energy’s Amer 8 Power Station in the Netherlands. This dedicated biomass-firing system was designed to fire up to 14% biomass on a heat input basis.
In 2006, Alstom designed, installed, and commissioned a dedicated biomass-firing system for two 500-MW coal-fired boilers at Fiddler’s Ferry Power Station in the UK. This was the UK’s first dedicated cofiring project, enabling the cofiring of biomass at up to 20% on a thermal heat input basis. The success of Amer 8, together with its fossil fuel–firing expertise, and success at Fiddler’s Ferry led to Alstom being awarded the contract for the Drax Power Station.
Large-Scale Cofiring
At 4,000 MW, Drax is the UK’s largest coal-fired power station. The plant, which supplies 7% to 8% of the country’s power requirements, consumes about 10 million metric tons (mt) per year of coal, making it a major source of CO2 emissions. As such, Drax is the most important dedicated cofiring project to date in terms of its scale and carbon emissions reduction potential (Figure 1).
 |
| 1. Cofiring central. The 4,000-MW Drax Power Station is the largest coal-fired power plant in the UK. Drax expects to produce up to 10% of its electricity from cofiring biomass once the plant modifications are completed mid-year. Courtesy: Alstom Power |
Drax operates in baseload mode for six months of the year and operates flexibly through the summer months. In winter, about 250,000 mt of coal arrive at the plant each week. With this quantity of coal being consumed, Drax Power Ltd. finds managing the carbon emissions from the plant to be one of its biggest challenges.
Drax Power Station produces around 22 million mt/year of CO2 and emits 815 kg of CO2/MWh compared to an industry average of 950 kg of CO2/MWh. However, the CO2 issue remains important in the European Union.
Drax Power Ltd. set for itself a very aggressive target of producing 12.5% of its output from renewables by mid-2010. This has the potential to save over 2.5 million mt of CO2 each year. Part of these plans is Drax’s approximately £80 million ($150 million) investment to expand its biomass cofiring capability. Once completed, it will be the largest dedicated cofiring project in the world. The plant will burn a variety of biomass, such as peanut husks, straw, wood, and energy crops.
Email
Comments
Print
Reuse
