Biomass is an energy resource that does not receive as much media attention as wind and solar, but it is definitely an important part of the renewable energy repertoire.
Biomass is biological material derived from plants or animals that makes a sustainable and renewable energy source.
It can be used directly as a fuel source or it can be converted into biofuel. In this column, I’ll deal with biomass as a solid fuel being used directly as an energy source.
Fossil fuels — coal, natural gas and oil — come from previously live plant material that has been compressed for millions of years but are in no way renewable, at least not by human effort. Those fossilized plants sequestered carbon, and a lot of it.
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Biomass, past and present, is essentially hydrocarbons, which contain primarily the elements carbon, hydrogen, and oxygen. This means they give off water and carbon dioxide when they experience combustion or decomposition.
The carbon dioxide is problematic.
We add dramatic amounts of carbon dioxide to the atmosphere when we burn fossil fuel. The CO2 acts as a greenhouse gas, trapping heat at the earth’s surface and creating a warming effect.
Biomass is assumed to come from currently growing plant material, which will be replaced by similar plant material when it is harvested.
The theory is the biomass will release carbon dioxide when it is burned, but the replacement plants will absorb carbon dioxide as part of the photosynthetic process. As a result, carbon dioxide amounts in the atmosphere will remain neutral.
The use of biomass is not new. Those living in the bush simply call it cordwood.
Using virgin wood that could be used for other purposes such as house framing material is considered to be an unacceptable practice, but using products that would otherwise be waste is considered a wise use of biomass material.
Wood, whether it be chopped wood, wood chips, pressed fire logs or pellets, is definitely the most commonly known biomass, but straw bales can be used as biomass energy.
Straw is not truly waste, given its value to the soil, but burning in a boiler is more productive than burning it in the field, which is not only wasteful but also creates air pollution and breathing problems.
Animal waste is also used in biomass energy production. In some cases, perennial and high production crops such as switchgrass and sugar cane, or trees such as poplar, willow and eucalyptus, are specifically grown for use as biomass.
Food waste also makes a good source of biomass combustion, although composting is an obvious alternative. Food waste can produce methane if disposed of in the landfill, which is a far more potent greenhouse gas.
Industrial waste is also used as a biomass fuel.
Grain can be used as a direct fuel in boilers for space heating, although burning grain has the same image challenge as ethanol: they both use a crop or land that could be used to feed humans and livestock.
One of the great benefits of fossil fuels is the extreme concentration of energy. Burning a given amount of natural gas, coal, or oil produces so much more energy than burning the same amount of biomass. This means that biomass is most economical when used closer to its source, which mitigates the environmental cost of transportation.
Small farmers in China have long used biomass to feed animals. They use the animal waste in digesters to produce methane and then burn the methane for cooking.
Some areas with cheap surplus grain use grain-burning heaters.
Forests yield usable byproducts, while cities’ concentrated populations produce prodigious amounts of garbage.
In Africa, rural residents collect dried animal dung for direct burning for cooking.
While the use of biomass for energy has been considered to be theoretically carbon-storage neutral, more recent scientific work suggests that sequestering carbon in a mature forest is greater than removing the forest to burn it and replanting the area.
So while biomass may be a significant improvement over fossil fuel, it is not entirely benign.
Burning biomass can also produce carbon monoxide and release other elements such as heavy metals that are part of plant material.
The burning of biomass by individuals often results in incomplete combustion, giving rise to a variety of combustion byproducts, including black carbon, which is worse than carbon dioxide.
Biomass industrial plants can often work with much greater efficiencies, both extracting more energy and using exhaust filtration to produce fewer pollutants.
Large biomass plants are not seen in Canada, but major operations in other parts of the world, particularly in Europe, use forest byproducts to simultaneously produce electricity and steam used for processing, known as co-generation.
Some plants produce enough electricity for tens of thousands of households, which would otherwise have to be provided by some other energy source, most likely fossil fuel.
Biomass is likely less noticeable in this part of the world because fossil fuel is still plentiful and relatively inexpensive. We will see a greater emphasis on biomass as an energy source when the price of fossil fuel rises.
In the meantime, for many of us the closest we will get to using biomass is when we light a fire at summer camp. And you thought that was just wood.
