Pellets are biofuels made from compressed organic matter or biomass. Bio pellets can be made from any of the following categories of biomass: industrial waste and co-products, food waste, agricultural residues and energy crops. The most common type of bio pellet fuel, however, are wood pellets. Burning wood pellets are on the rise in Europe, but are wood pellets truly “clean”? And if not, what does Arundo donax offer as a feedstock for pellets?
The sad truth behind wood pellets
Up until about 2008 it was widely assumed – even in scientific papers – that burning wood pellets is carbon neutral, mainly because regrowth of vegetation was believed to recapture and store the carbon that is emitted to the air. However, as the Biomass Energy Resource Centre reported only two years later, the assumption of carbon neutrality
“Has shifted to a recognition that the carbon implications of biomass depend on how the fuel is harvested, from what forest types, what kinds of forest management are applied, and how biomass is used over time and across the landscape.”(BERC, 2010)
The wood pellets industry claims that what they use are tree branches and waste wood, environmental groups, however, disagree, saying there is strong evidence that vast amounts of valuable, untouched forest are being chopped down in states including North Carolina and Florida, US, to be then transported to Europe, replacing coal in power plants there.
In 2017, UK-based researchers found that burning wood is a “disaster” for climate change because older trees release large amounts of carbon when they are burned and are not always replaced with replanted forests. Even when trees are replaced, it can take up to a 100 years to cultivate a wooded area that takes up as much carbon as was previously released. Not to mention that the fuel burned in shipping wood pellets to Europe is also a significant source of GHG emissions.
Why choose Arundo donax as a feedstock for bio pellets?
One of the most important environmental arguments for its use is that giant reed is CO2 neutral and it is one of the most efficient alternative feedstock to biofuels. Its high biomass yields (50-80 dry tonnes per hectare, depending on climate and measured from the third year) and fast growth rate are also outstanding when compared to other plants. Giant reed also has the ability to adapt to a wide range of climates and environments, and thrives even on marginal lands and in water scarce regions.
Arundo donax is a sustainable alternative with an inexhaustible list of uses: biogas production, bioethanol production, paper production, forage feedstock and it can be useful as an alternative feedstock for the furniture industry. Once dried, giant reed can be processed using similar methods to wood based pellets and briquettes, thus no investment is required into new and unknown technologies – a low input and low cost way to produce bio pellets.
The table below presents characteristics of reeds belonging to the Poaceae family, just like Arundo donax. This study found the species of this family the most relevant in terms of renewable energy.
The values of giant reed as bio pellets
As for the heating value of giant reed, it equals to that of wood, more precisely it is 17-18 MJ/kg (dry matter value), and as perennial crops tend to contain higher concentrations of ash, the ash content of the giant reed is 4-6 % is higher than wood’s,consequently meaning that minor modifications of the furnaces to handle larger ash quantities could be required. According to Hungarian practice, the ash which accumulates in a biomass plant after burning Arundo donax is taken back to the plantation, to serve as a nutrient. This method helps enhancing the yields, and also the question of storing ash is solved – without having extra expenses.
As Croon (2014) pointed out, giant reed can be burned directly to produce heat, however it is more effective to chip or pulverize it before burning. In practice, the best is to convert the reed into thicker energy carriers, such as bio pellets or briquettes. Thanks to the relatively high melting temperature of giant reed (900-1000 ºC) its combustion is safe for furnaces.
Direct combustion of air-dry giant reed (9-12 % moisture), briquettes or pellets alone or in combination with coal (co-firing) is possible in power generation plants via standard steam cycles, where electricity is produced and waste heat remains. Bio pellets and briquettes are used for home heating and, increasingly in Europe and the United States, for domestic fireplaces as well.
Purchase giant reed for bio pellet production
For all the above mentioned reasons, investing into Arundo donax plantlets and plantation is worth it – for the environment as well as for the investor, as giant reed guarantees a faster payback return than, for example, wood.
If you are interested in purchasing Arundo donax, visit our website or get in touch with us at info@arundobioenergy.com!
