Machines to produce woodchips from biomass of landscape conservation and maintenance work (LCMW)
Mostly, wood from landscape conservation work consists of bushes and has small dimensions. The processing of this biomass to woodchips is ideal because it allows the use as fuel in furnaces with mechanical auto feed. Woodchippers are available in different sizes and construction types.
Besides small, electrically operated garden devices woodchippers are used as attached or trailed machines on tractors from agriculture or forestry, as build-on aggregates on trucks, as self-propelled forestry machines or self-propelled chipping unities. Build-on machines are either powered by the engine of the carrier vehicle or an auxiliary engine. In total a trend towards large-scale chippers applied by contractors can be observed.
In Europe three construction types of woodchippers are available: the disc-chipper, drum-chipper and screw-chipper.
Disc-chippers work with 2 – 4 chipping knives which are arranged on a heavy and stable flywheel. Depending on the size and power of the machine the flywheel has a diameter of 600 to 1400 mm. Blades on the backside of the flywheel speed the woodchips up and carry them to the exhaust pipe. Because of the high oscillating weight, disc-chippers need less power to drive than drum-chippers and are thus often operated by tractors from agriculture or forestry.
Drum-chippers have 2 – 20 chipping knives which are arranged on a rotating drum with diameters ranging from 450 to 1120 mm. Compared to disc-chippers, drum-chippers have a relatively small oscillating weight and thus higher engine performance is needed. The infeed opening of the machine is defined by the dimension of the drum. A blower behind the drum transports the woodchips to the ejector. Hydraulic forced infeed for disc- and drum-chippers is also advantageous for smaller devices. Often, bigger machines are equipped with an infeed-table and additional pull-in belts, – chains or drums.
Screw-chippers work with a screw which has an increasing cross section. Their structure is simple and because the screw hauls the material autonomously into the machine, no forced infeed is needed. The size of the woodchips (60 – 80 mm) cannot be varied. The chippers strength lies in the small amount of fine material produced during the chipping process, also when material with a high amount of bark from landscape maintenance work or short-rotation plantation is used.
To haul the woodchips in every direction most chippers have a rotatable exhaust pipe. The feed in of the material is mostly done manually for small disc- or screw-chippers and with a build-on or attached crane for big drum-chippers.
The RH 25 by Jordan, a disc-chipper by the brand Jensen, can be combined with different attachments to remove deposited material from the ground. Either a “pick-up”, as known for the harvest of agricultural stalk material (straw, hay), or a more robust attachment with two vertical drums is mounted to the front of the woodchipper. These different pick-up aggregates can be exchanged in 30 minutes.
It is important to use sharp knives, sieve baskets and optimized settings when processing material from landscape conservation and maintenance work containing fine branches and bark. This way, high amounts of too big or too small fractions of woodchips are prevented.
In the German regions participating in greenGain, the counties Friesland and Rotenburg (Wümme), mostly drum-chippers applied by contractors are used for the processing of biomass obtained from landscape conversation and maintenance work.
Author: Carsten Brüggemann