The roundwood chip supply chain uses the standard method of harvesting products from forests in Ireland. In the standard flow of wood from the forest, the logs that are produced and stacked along the road are usually transported to saw mills and pulp mills, but in the case of this supply chain, the small pulpwood (circa 3 m in length and has a small end diameter of a minimum of 7 cm) is chipped and transported to the end-user for use as a fuel. The other larger logs continue to the mills as usual.
Forest harvesters are used to perform a combined line and selection thinning. Typically between 30% - 40% of the crop is removed, depending on the silvicultural prescription of the thinning. The harvester cuts, fells, delimbs, and crosscuts the trees into specified lengths depending on the size of the trees. Small sawlog is usually prioritised, which has a 2.5 m length, and a minimum small end diameter of 14 cm. Small sawlog can be cut from the lower sections of the larger trees in the forest. Pulpwood is cut from the remaining portions of the trees where possible. Pulpwood typically has dimensions of 3 m in length, and a minimum top diameter of 7 cm. These products (or assortments) are stacked separately at right angles to the extraction rack. The tree top and branches are used as a brash mat underneath the machines, and are not recovered from the site.
Shortly after harvesting, a forwarder machine travels into the forest and picks up the small stacks of logs with a crane. The logs are loaded onto a bunk on the back of the forwarder. Once the bunk is full, the forwarder travels to a stacking area beside the forest road. The assortments are piled separately into large stacks.
The small sawlog assortments are transported to the mill by timber truck. The pulpwood, which is to be chipped into a fuel, is either:
Transporting to a terminal allows the wood fuel supplier to have a stock pile of wood at one location, which is beneficial if the the chipper is contracted in to work (i.e. not owned by the wood fuel supplier). The down side to transporting to a terminal is the extra cost in transport. It may also be more appealing to transport to a terminal if supplying to small and medium end users, such as hotels, who will not have a large intake capacity. Whereas, if supplying to a large industrial end-user who can accept all the wood being supplied to it, transporting to a terminal may have no benefit at all.
During storage, stacks may be covered to enhance drying of the logs. Covering material may be plastic sheeting, however this does cause a refuse disposal need at the end of the storage period. Alternative covering material is available which is made out of a waxed paper, which can be chipped with the logs and simply incorporated into the woodchip.
The logs are chipped into woodchip after seasoning either at the forest roadside, or at the terminal. Chipping machines for roundwood logs can be tractor trailer mounted or truck mounted. They are usually self powered, but also can be powered by PTO. The logs are fed into the chipper with a crane that can either be powered by the tractor / chipper, or they can be powered by the chipper themselves.
During chipping, the woodchip is blown directly from the chipper into road transport vehicles (tractor and trailer, truck with curtain side trailer). The chip is then transported to the end-user.