Wood chips

Wood chips for energy production are made of whole logs (firewood), which are not accepted as paper wood or saw logs. There are several specifications of wood chips mainly depending on the size of the particles. In Europe is used Wood Chips Standard  EN 14961.

Very important is the moisture content of the wood chips. In Northern Europe moisture of the fresh cut wood chips is about 43-45%. After hot summer in September moisture may go down to 35-36%. After the winter in spring moisture may go up to 48-50%. Wood chips which has been laying long time at the open storage and been exposed to rain may have moisture content going up to 60%.

Chipping (cutting the wood by knives in pieces) may be done already at the forest road by mobile chippers, in this case wood chips may be directly going from the chipper into the trucks. Mobile chippers in the loading port may also prepare wood chips.

                       

                 

Another possibility is to make wood chips by mobile chippers  in the unloading port after transportation of the   fire logs by   a sea   vessel. It is also possible to chip the firewood directly in the power plant by huge   inbuilt chipping facilities. Less times the wood chips are reloaded the better it is from the   economical point of view. Transportation of logs by ship is also much more economical than the wood chips.

If we take a look at the energy content of the wood chips depending on the moisture content we will find that with moisture content about 45% the NCV of the chips will be 9,20 GJ per mt, in a case moisture content will be 60% NCV will be going much   lower – it will be only 6 GJ per mt.  With moisture content 38% NCV will be 10,29 GJ per mt. The high moisture   may create the situation when the vessel  is  fully loaded , but the total  energy amount  of the whole cargo carried by the ship   will be very low. In other words the cost of transportation will be much bigger than the value of the energy transported by the   ship  (vessel will mainly  carry over the sea water).Economic  result of such deal may be drastic.

 Another question besides the transportation of water is the carrying of air. Bulk density of the wood chips   is very low, only   about   280-350 kg per mt depending on the moisture content. The volume of the vessel has to be big enough to permit to load enough wood chips to get a   positive    economic   result.  Freight   cost   for wood chips transportation is paid on ‘’lumpsum’’ basis,   which means that the charterer have to pay the whole freight independently on   the quantity of the wood chips which will be loaded.

Economically good results may be obtained by using bigger vessels, also barges with high walls, which  allow to load more wood chips. Important is also trimming of the wood chips, which   is obtained by using bulldozers during the loading procedure. Trimming may increase the weight of the wood chips cargo by 15%.

             

In South Europe moisture content of the wood chips may go below 30%. Very dry chips may also create a problem. Energy content in the chips may be rather high, but the weight of the cargo loaded on a vessel   due to low bulk   density   will be so low that the total energy content of the cargo will be not    enough   to cover the transportation costs and to be profitable. It seems that there is   an    optimal   zone of moisture content and connected to it NCV and bulk density of the wood chips, which allows to get the best  economic  results  of the sea transportation. Moisture in these cases has to be around   38-40%. Moisture over   50% and below 30% may create economic problems.

Wood chips with higher moisture  content may be also interesting for the power plants  ,but in this case the cost of these chips per GJ  of energy  have to be lower ( so called ‘’ second quality’’).There is also a possibility to make wood chips of lower quality of so called ‘’ bush wood’’ which is similar to forest residue.

                                 

Wood chips which has been offered from Spain and made of Olive tree, Fruit trees, Citrus trees   turned out to be not acceptable for Northern European power plants because of the way they were prepared. There was a lot of long pieces   and leaves in the chips and they were not cut, but crushed.