Introduction to Biomass
This is an introduction to biomass as an energy source. Biomass is a fundamentally renewable source of energy in that it comes from living matter, and living matter can replace itself. Some applications of biomass technology are possible in the home. KCS will be publishing regular articles on the various types of usable biomass and their practical applications, of which there are many.
What do we mean by Biomass
In ecological terms it usually means the matter derived from living or recently living organisms and normally refers to plants (but does not necessarily exclude animal) matter. Animal matter however is usually too scarce and valuable to be burnt as fuel or composted. The world produces nearly 150 Billion tons of biomass a year
Biomass from timber
As a source of renewable energy biomass can be burnt either directly, typically in the form of wood, or indirectly, having first undergone thermal, chemical or biochemical conversion into various types of bio-fuel. We will looking regularly at developments in bio-fuels in future sustainability articles.
Sometimes fossil fuels like coal and oil are regarded as part of the biomass stock but for the purposes of renewable and sustainable energy they are not. Coal and oil are too remote from the present ecology and carbon cycle to be properly considered part of the renewable biomass stock. Fossil fuel deposits were laid down millions of years ago, and in the process removed carbon from the atmosphere at the time and stored it away in the form of fossilised biomass.
But for human intervention the carbon from this fossilised biomass would not have returned. The carbon contained in oil and coal which is released during burning is therefore, for all practical purposes, a new addition into the present atmosphere. Living and recently deceased biomass however is part of the present ecology of the surface of the planet.
Fossilised in the form of anthracite
Mankind has used energy derived from biomass ever since the discovery of how to make fire and continues to do so today. Biomass in the form of wood is still a primary source of energy for many societies.
Wood, an historic source
Wood ‘(Lignocellulosic’ biomass), is still the principle primary source of biomass energy. It comes in the form of dead tree matter, various by products of wood workings, and discarded pre used wood. It’s used either directly as fuel for burning or in the form of ‘black liquor’ a waste product from the wood processing industry. KCS will be returning to the subject of ‘Black Liquor’, an important but little discussed substance, in later articles.
In a secondary sense, biomass can be converted into biofuel and industrial chemicals. Biomass for use in
industry can be grown from an enormous variety of plants and tree species. KCS will be returning to the subject of biofuel at a later date.
Apart from wood, waste energy is the second largest source of energy from organic matter. Municipal and manufacturing waste and landfill gas are the main sources and organic matter have now reached the point of becoming (behind hydroelectric) the second largest renewable energy source in the US.
Plant biomass energy comes from crops grown specifically for use as fuel. The plant varieties are chosen for high energy output and low energy input per hectare. Wheat, for example in the UK yields 7.5–8 tons per hectare and can be used for liquid fuels. Straw yields about half as much and can be burned to generate electricity or to generate direct heat.
Plant biomass can be degraded through chemical processes to produce fuel and as a bio-fuel source plants offer a sustainable source of energy without adding carbon dioxide to the atmosphere.
Plant matter is convertible into other fuels such as bio-diesel, ethanol and methane gas. Rotting human waste and urban and agricultural rubbish all release methane gas.
Although it still has some way to go there is a great deal of research into biomass energy from naturally occurring and genetically engineered algae and the long term prospects seem promising with energy production rates up to ten times that of plants. The process would have the spin off benefit of leaving agricultural plants available for use as food. In recent years the demand for wheat for use as bio fuels has played a significant part in increased food prices.
Types of Biomass conversion
Thermal biomass conversion (dendrothermal energy) uses heat to convert biomass into energy and various chemicals. This is the process that occurs when wood is burned. Chemical biomass conversion converts the biomass into a variety of more transportable, often liquid, fuels. Biochemical biomass conversion uses bacterial and other microorganism enzymes to break down the organic matter.
Biochemical biomass conversion in the form of a microbial electrolysis cell can be used to make hydrogen from plant matter.
Wood Biomass plant
Anyone who has burnt wood will have noted that biomass is not free from pollutants. In some respects biomass burning processes are worse in terms of pollution than fossil fuels and some of the by products produced are carcinogenic. However the argument that biomass is a carbon neutral energy source does have some merit but is not quite as straightforward as it may appear.
When a tree’s carbon is released quickly into the atmosphere by burning it contributes more significantly to climate change than it would have done rotting over a period of decades and it takes many decades for a replanted forest area to recover its carbon storage capacity.
Current thinking holds that biomass crops are the best ecological bets. Perennial crops are much more efficient at taking carbon from the atmosphere than trees are and some may even sequester carbon. With some perennial crops the roots which are left after harvesting leave organic carbon in the soil. The plant has therefore taken carbon from the atmosphere which will not be returned in the burning process. The field in which the biomass crop is grown is therefore a net carbon sink.
From an ecological point of view the challenge is to ensure that the growing, harvesting and use of the biomass is carbon neutral and that the pollutants produced in the burning process do not outweigh the advantages of that carbon neutrality. And of course it must all be done cost effectively. At the moment biomass energy generation is somewhat (although not enormously) more expensive than nuclear power.
To date owing to the physical bulk associated with the inputs, biomass electricity generation has tended to be located where the plant material is available. This has had the advantage of reducing transport costs and has enabled a proper focus to be given to replanting. The carbon neutrality of biomass as an energy source depends entirely on replanting the areas from which the plant matter came.
KCS will be returning to this subject regularly in the form of articles concerning installations in the home. If you have any requests as to advice on a particular type of installation please let us know and we can bring it forward.