Combustion

Almost anything organic will burn, but low moisture-content biomass is best suited for combustion. Combustion refers to the rapid oxidation of the feedstock as it is exposed to high heat.  Most of todays biomass-powered plants are direct-fired systems, similar to fossil-fueled plants. The feedstock is burned in a boiler to produce high-pressure steam that is pumped into a turbine, over a series of blades that roate and power an electric generator. There are three general areas of combustion technology that are being used: Fixed-bed combustion, fluidised-bed combustion, and dust combustion.

Steam powered technologies have proven to be very dependable, but efficiency has at times been limited. Biomass power boilers typically are in the production range of 20-50 MW compared with coal-fired plants in the 100-1500 MW range. Small-capacity plants generally have lower efficiencies because the equipment needed to increase energy-efficiency is not economically viable (Brown 2003). The most economic near-term solution is co-firing furnaces with fossil and biomass feedstocks. Much of the existing power plant equipment can be used with little to no major modifications thus making this much more economically attractive than building new plants. Compared to the coal it might replace, biomass use reduces sulfur dioxide, nitrogen oxide, and other harmful air emissions resulting from combustion (Hustad et al. 1998).  

Many power plants have been burning or co-firing biomass for decades. Most recently the Dunkirk Power Station in New York has started producing energy from local willow plantations, assisting the regional forest products economy (Spaeth 2004). Advances in fluidized beds that promote full oxidation of the feedstock have seen energy efficiencies increase, but one of the largest impacts has been the adoption of pelletized biomass as a commodity fuel. Bixby Energy Systems has desinged a furnace especially for pellets with a 99.7 percent fuel combustion ratio, maximizing value at the same time as limiting emissions and ash residue. The UK-based Talbotts has been a world leader in the development of biomass generators, producing its first wood-fired system during the mid 1970s.