Stump Harvesting for Biofuel

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Stump Harvesting for Biofuel

• FEG Symposium 2009
• Jack Barnes
• Biomass Manager
• Scottish Woodlands Ltd.
• University of Cumbria
• Newton Rigg
• 9th September 2009

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Introduction- Why Stumps

• Scottish Government Targets
• 50 Renewable energy by 2020
• To substitute SRW and fossil fuels with an
  additional source of fibre.
• Two companies based in south Scotland working
  together to provide AW Jenkinson with 120 000
  tonnes of forest residue chip per annum for
  supply to the Eon Plant.

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What Next?

• A source of non roundwood forest derived chip was
  required.
• Two pairs of stump shears were acquired by Dick
  Bros and a further four sets were purchased by
  SWL with SBSS grant assistance.
• These were mounted on 360 excavators.

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Stump Shears
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Stump Removal

• A protocol was developed for stump removal
• UPM Tilhill, Euroforest and Scottish Woodlands
  came together with the Forestry Commission to
  produce the industry protocol and operating
  procedure. This is the Stump Harvesting
  Operational Control document.
• Forest Research launched the finished document in
  April 2009.

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The excavator mounted shears lift the stumps and
present them for cleaning alongside the brash mat.
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The excavator mounted cleaner lifts the stumps
and drops them onto the Grid to clean them before
presenting for extraction to roadside.
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A modified forwarder extracts the split stumps
after a weathering period.
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The modified forwarder has a solid tray in the
base that can be tilted to remove soil, a rear
headboard and extra bolsters.
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Following a further weathering period and
possibly a secondary cleaning, which reduces the
soil from 20-30 to around 10 to 15, the
stumps are transported to the processing facility
at Lockerbie.
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There has been a change in the haulage system to
use dedicated self loading wagons specifically
designed to haul stumps.
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Yet more pics
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The processing facility

• This is an independent operation set up by a
  large local harvesting contractor with the
  assistance of SBSS grant aid.

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The stumps are initially put through the
cleaner.
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and then through the shredder..
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to produce the hogfuel chips.
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These are then collected from the processing
facility for use at the power plant.
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Site Selection

• It is vital that correct sites are selected for
  de-stumping. There are many factors determining
  this selection including
• Soil type
• Distance from the processing facility
• Available stacking / storage space for stumps
• Restocking timelines
• Access restrictions
• Slope
• Environmental Factors, e.g. archaeology, riparian
  zones
• Size of site (minimum of approx 6ha)

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De-stumped Site

• If the correct sites are selected then it is
  possible to leave a site that will need minimal
  works to allow restocking.
• It is important to remember that some brash mats
  and stumps will remain, only about 60 of the
  site is de-stumped on average.
• Some additional drainage will still be required
  on most sites.

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De-stumped and awaiting extraction.
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Diagram of a Working Site
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Potential Benefits to the Grower

• There should be some saving in ground preparation
  costs, depending on the site requirements post
  de-stumping.
• Further work into these costs is currently being
  undertaken.
• Easier access across the site for restocking,
  establishment operations and also sporting uses.
• Potentially reduced Hylobius activity due to
  removal of breeding sites.
• Possibly faster establishment due to increased
  site cultivation.

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Potential Site issues post De-stumping.

• Higher weed growth, de-stumping operations tend
  to favour better site types.
• Potential soil erosion, following the protocol
  should minimise this, (max allowable slope is
  20)
• Possible larger carbon release than other ground
  preparation operations. Limited data at present,
  and we do not know the long term effects. The
  big picture approach needs to be taken. More
  mineral soils have less of a carbon issue.
• Embodied carbon in the operation, lots of large
  plant required to produce the fibre.

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Current Position

• The south Scotland project has de-stumped a total
  of 500 ha since January 08, yielding
  approximately 100t per ha.
• In 2008 we delivered 59 000 tonnes on the
  contract, of which 22 000 tonnes came from forest
  residue chips.
• In 2009 to date we have delivered 61 000 tonnes
  on the contract, of which 14 000 tonnes came from
  forest residue chips.

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In Conclusion

• Stump harvesting is producing a useful additional
  fibre source.
• The Industry has developed standard protocols for
  methods of operating and site selection.
• Soil has been a major issue but operating
  developments have already reduced this by 50.
• Specialist transport units have been developed
  and the processing infrastructure is in position
  to handle significant volumes.