As the availability of wood fuels in Europe is limited, and also because we should adapt to a more economical attitude in the way we are treating our forests, high yield energy crops give an important contribution to biomass based energy production. It is high time we focused on the investigation of the best possible utilisation of perennial energy crops, like Arundo donax, which could be sustainably developed in rural areas and marginal lands of Europe.
Eco pellets: the shift from wood to alternative fuels
A public concern arose two years ago, when British researchers claimed that burning wood could have disastrous consequences in terms of climate change, as older trees release large amounts of carbon when they are burned and are not always substituted with replanted forests. Even when trees are replaced, it can take up to a hundred 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 from point A to point B is also a significant source of greenhouse gas emissions.
Of course, a shift from wood-based pellets to eco pellets (that is, non-wood pellets), cannot be expected to happen overnight. One possibility for this transition would be to blend the energy crops with wood fuels.
By blending with wood, also the HCl, SO2, NOX (oxides of nitrogen) and particles emissions are expected to decrease due to the dilution effects achieved. What is more, burning giant reed is CO2 neutral.
This approach is probably the best way to introduce these new crops into the market.
When dried, Arundo donax can be treated using similar devices to wood based pellets and briquettes, meaning no investment is required into new and unfamiliar machineries. Using giant reed as a feedstock is a low input and low cost way to produce eco pellets.
Eco pellets: giant reed compared to other crops
Arundo donax offers competitive advantage over other biomass crops, as it yields about 50-80 tonnes of biomass per year. Evidently, the yield is also dependent on the climate, the soil quality and the applied cultivation technology and its intensity – but given the right ecotype of Arundo and a well-working cultivation know-how, the yields can be further maximised.
A study in 2014 pointed out that although giant reed can be burned directly to produce heat, it is more effective to chip or pulverize it before burning. In practice, the best is to convert the reed into denser energy carriers, such as eco pellets or briquettes.
Thanks to the relatively high melting temperature of giant reed (900-1000 ºC) its combustion is safe for furnaces.
The high heating value of giant reed ranges between 17-20 MJ per kilogram, a value, which is similar to other energy crops such as poplar, Miscanthus or switchgrass. Arundo donax has high ash (4-6%) and silicon content, such as switchgrass, and these elements accumulate mainly in the leaves. It is worth mentioning that 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.
In the experiment of Nassi o Di Nasso et al. (2010) it was confirmed that biomass and heating value of giant reed can be largely improved with the application of appropriate agronomy techniques (for example autumn-winter harvest and convenient fertilization).
In agronomy, environment and economic researches of Nassi o Di Nasso et al. and Angelini et al. (2009) compared the productivity and efficiency of giant reed production and utilization to Miscanthus, short-rotation poplar or annual agricultural crops (sugar-beet, durum wheat, sorghum, sunflower). From the energy production of plants, energy input of cultivation of Arundo donax and Miscanthus were close to equal per hectare (13 GJ).
The maximum annual net energy yield can be reached with producing giant reed (about 600 GJ), the values of Miscanthus (~450 GJ), poplar (~300 GJ) or agricultural crops (~110 GJ) are far more less.
If you are interested in reading more about the usage of Arundo donax, visit our website. Whilst you here, why don’t you try out Arundo and send us an email at info@arundobioenergy.com.
