The utilisation of biomass as a fuel for electricity generation
is very dependant upon resource availability and proximity to electricity demand.
Those requirements are often met in conjunction with other services or industry such as sugar mills, paper mills and
land fill sites. In these situations, biomass can be very cost effective.
A good example of biomass generation in a local context is the 1 MW landfill gas fuelled generator at the Shoal
Bay dump in Darwin.
Answers to some frequently asked questions about
biomass energy can be found below:
What is it?
Biomass is simply plant-derived material. Biomass programs utilise plant material to produce green fuels, materials, chemicals and electricity. Biological products are being used to manufacture many consumer products currently made from petrochemicals. This web page however is mainly concerned with the use of biomass for the production of electricity. To learn more about some other types of biomass visit the US Department of Energy’s website.
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How can it be used?
Examples of biomass product used for electricity generation are ethanol, bio-diesel, woodchips, sugar cane stalks, weeds such as Mimosa Pigra, and paper-industry waste. The last three, along with any other type of combustible organic matter, can be used to fire or co-fire steam turbines for electricity generation. Co-firing means that the biomass products are substituted in place of some of the coal in a coal fired steam turbine.
Biodiesel is a biomass based diesel-like fuel that can be used in place of, and mixed with diesel as a fuel substitute. Under the right circumstances, ethanol can also be used as a fuel substitute for unleaded fuel. Alternatively, ethanol can be used as a fuel additive, mixed at around 10%, in standard unleaded vehicles. These fuel substitutes can be used in combustion driven generators to reduce greenhouse gas emissions, though at present there is little economic incentive to do so, in Australia, on a large scale.
Another biomass product used to generate electricity is landfill gas. Landfill gas can be used to directly run gas engines and Stirling engines and also to fire steam turbines. Municipal Solid Waste (MSW), which is comprised of up to 80% biomass, can also be used in co-fired systems.
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Where can it be used?
Unlike other sources of sustainable energy, some biomass products aren’t as restrained by climate and geology. Once processed, ethanol and biodiesel are liquid fuels and so can be used to power conventional engines, which are found just about everywhere. As a liquid fuel, they are also easy to store and transport.
Because unprocessed biomass has a low energy density, the refinery equipment needs to be located close to the biomass source. In many cases this means placing the biomass refinery near the actual growing biomass or near a location where the biomass products are brought to be processed for other purposes such as a sawmill, sugar mill or rubbish dump. The central elements required for economic biomass power generation is a large amount of organic matter, some capital to outlay for refining and/or generation equipment and any necessary approvals. The Northern Territory’s Power and Water Corporation has plans on the table for a trial biomass power generation plant using Mimosa Pigra as the fuel source.
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Why Biomass for electricity generation?
Because all products used for biomass generation are entirely sustainable, we reap all the benefits of sustainable energy. Biomass fuelled systems typically have near-zero net CO 2 emissions. This is because the CO 2 released by burning biomass products was recently absorbed from the atmosphere by the organic organism. The only emissions that are released and not re-captured are due to the harvesting & transportation of the biomass. Because coal and oil take millions of years to make, they are not considered renewable and the CO 2 released from burning them adds to the net short term (less than 1 million years) CO 2 emissions.
Burning municipal solid waste reduces the amount of space needed for landfill and also provides energy that would otherwise be thrown away. Landfill gas, which would otherwise escape and add to greenhouse gases in the atmosphere, is burnt cleanly to generate electricity.
In general, biomass products burn cleaner with fewer emissions of toxic gasses and other harmful chemicals compared to fossil fuels. Biomass generally produces less ash than its coal fired equivalent and the ash that is produced can be used to enrich soil for farming.
It is essential to only use biomass specifically grown for energy production rather than harvesting indigenous forests, as the social and environmental impact caused by deforestation contradict the suggestion of it being sustainable.
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How much does it cost?
The cost of biomass fuels can vary greatly. In the case of a sawmill, the cost of the fuel is actually negative, because by burning it the cost of transport and disposal is avoided. Having a landfill site provides gas at almost zero net cost after the initial installation, the gas only has to be tapped and run to a turbine or internal combustion engine. Some refineries must collect, transport then refine biomass before burning it. These would have the highest cost fuels but can be viable depending on location and the availability of coal or gas fired electricity.
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How does it work?
Most biomass products used in electricity generation are first converted to useable fuels, then burnt in either a conventional piston engine or an aero-derivative jet engine depending on fuel type or used to fire steam turbines.
There are five basic extraction techniques: Solid fuel, gasification, fermentation, anaerobic digestion and Pyrolysis. A brief outline of these techniques follows:
Solid fuel is the oldest form of biomass energy extraction, with millions of people for thousands of years using wood fires for cooking and heating. Solid fuel combustion is now used to fire steam turbines for electricity generation. As most biomass doesn’t come in solid fuel format already, some processing is required. Compacting biomass at high temperature and very high pressure is known as Briquetting or Pelleting. This process results in small bricks or pellets of high energy-density biomass that is easier, and more economical, to transport and store.
Gasification involves exposing a solid biomass to high temperatures with limited oxygen. The biomass will give off a number of gasses, including methane, nitrogen and hydrogen. The advantage of gasification is that it produces a cleaner, more convenient fuel.
The age-old technique of fermentation is used to make ethanol, the alcoholic component in beer, spirits and wines. This is then distilled to make it pure, and can be used as a fuel supplement in petrol or diesel or as a stand-alone fuel. Micro-organisms are being engineered to better turn non-sugar based biomass such as waste paper, wood pulp and wood fibre into methanol. Methanol is wood based alcohol. To find out more about ethanol, please visit the alternative fuels page.
Anaerobic (without oxygen) digestion produces biogas, a mixture of carbon monoxide and methane, through the decomposition of green or wet biomass by bacteria. This is how landfill gas and sewerage farm gas plants operate. Small-scale digesters also work on the same principle, with the main fuel source being animal manure. There are over five million of these operating in rural china and they provide sufficient gas for domestic heating and cooking needs.
Pyrolysis is similar to gasification but with less oxygen. The volatile matter is driven off the biomass, and can be harvested in advanced refineries, leaving behind charcoal, which has twice the energy density of the original material. This leads to savings in transportation and storage. The charcoal can also be used for chemistry and air filtration.
he manufacture of Biodiesel is a little more involved, but it can still be made by individuals. Biodiesel is generally made from used frying fat or oil but can also be made from unused oil derived from biomass. More information about biodiesel is available on our alternative fuels page.
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How can Novolta help?
Information on how we can help is located under the Services area of our website
Further information on biomass energy can be found through the Research Institute for Sustainable Energy or this Wikipedia article.