Norwegian senior scientist Øyvind Skreiberg is transforming the chopped-off branches and tops of felled spruce trees into a fine powder that is then pressed into high-energy pellets. The transformation is made using a process called torrefaction, a sort of extreme sauna for timber and vegetation.
Norway possesses major unexploited energy resources of waste wood in the form of the branches and tops – known in their Norwegian acronym as GROT. There is an abundance of waste wood to see when we walk in the forest after the lumberjacks have been there. When the logging machinery moves on, what it usually leaves behind are piles of branches and tops.
Skreiberg is leading a team at Norway’s SINTEF Energy Research where samples of the logging waste regularly arrive to be transformed into fuel.
In the raw form in which the biomass arrives at the laboratory, it is regarded as a problematic and therefore low-value fuel.
But when the scientists and technicians have finished processing it, they are left with a valuable source of heat – ready for use in industrial heating furnaces that are currently fuelled with wood pellets or chips, and for Norway’s domestic pellet stoves.
Woody Biomass and Torrefied Wood Biomass Sample.
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Skreiberg said referring to the photo above, “This is what the raw material looks like when it comes to us!” The fistful of fragments of wood with an admixture of spruce needles looks just like the sort of debris that litters the pavement around the Christmas tree stands on Christmas Eve. This is chopped-up GROT from spruce logging.
“Cheap fuel, and Norwegian logging sites are full of it. But it is a poor-quality fuel, because it is so variable in composition,” said Skreiberg.
If the GROT is tipped into the furnace, the woody component of the mixture may burn in one instant, bark and needles in the next. “This mixture means that the efficiency and characteristics of the combustion process are extremely variable. In the worst case, they can destroy a combustion chamber,” says Skreiberg. Then he opens his other hand as seen above and shows the evidence that the problem is capable of being solved.
On the right Skreiberg holds a fine-grained brownish-black mass, which he has taken from the steel apparatus that stands behind him. This is a laboratory reactor, in which the chopped-up GROT has been subjected to torrefaction.
On its way through the highly insulated steel cylinders of the laboratory rig, the raw material has been heated to 275°C. The heat treatment has broken down the fibrous structure of the biomass.
According to Skreiberg, this has two benefits. “In the first place, the torrefied material can easily be crushed into the powder that you can see here, which can be stirred around to form a homogeneous, and therefore combustion-friendly, mass. Secondly, this powder can be pressed into pellets with a high-energy content per unit of weight and volume; in other words, it is also a transport and storage friendly fuel. Pellets of torrefied biomass can withstand getting wet, just like coal, and are very stable under storage.”
The catch is the energy industry will not act until the price is right.
Skreiberg explains, “This technique improves a biofuel that is cheap but problematic in terms of combustion technology, and makes it much easier to handle. There is already a market price for GROT, which is well below that of wood chips. We hope that the method will be competitive, precisely because of the low price of the raw material and the reduced transport costs that the saving in weight and volume make possible.”
The energy cost to do the torrefaction is quite low. Skreiberg said, “The volatile components that are released as gases from the raw material are combusted, to maintain the ideal process temperature, and as much as 90 per cent of the energy in the raw material is retained by the torrefied material.”
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Norway is energy blessed. As well as North Sea oil, the GROT left lying on Norwegian logging sites contains enough energy to provide between five and six Terawatt hours (TWh) of energy a year. That’s equivalent to the heat from five to six million 1000 Watt heaters, each switched on for 1000 hours (nearly 42 days).
The Norwegian team isn’t alone; a race to develop torrefied material for fuels is under way in both Europe and North America, driven by a desire for a new timber-based fuel that can be burned alongside coal in thermal power stations.
Skreiberg believes that torrefied GROT will find a place in the Norwegian energy supply system, as fuel for both households and industrial heating furnaces. But what does the energy sector think?
The SINTEF press release quotes Morten Fossum, business development manager in Statkraft Varme who answers that it is impossible to predict the future of this energy source until it is clear what the cost of producing the fuel will be. “Everything is a matter of price. If this fuel is cheap enough, it would be suitable for small and medium-sized combustion plants that use dry fuel,” he said.
The Norwegians are also looking ahead. Fossum does not hide the fact that the quality of Norwegian GROT is poorer than it is in Sweden, where it is used as fuel much more than in Norway. He believes that the difference is largely due to the way in which the raw material is harvested and treated. “If large-scale harvesting of GROT gets under way in Norway, this will mean that nutrients are also being removed from forest soil. In that case, we ought to look at the possibility of bringing its ash back to the forest. But at present, that is not permitted in Norway,” he said.
By. Brian Westenhaus
Source: Making Waste Wood Into Fuel