Biofuel potential of Rushes

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Biofuel potential of Rushes
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Scope

• Potential of rush as a biofuel
• Determine calorific value
• Compare with available alternatives

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Juncus effusus

• Juncus family - Approx. 300 spp worldwide
• J effusus habitats are diverse
• moist areas at forest margins,
• wet grasslands,
• wetland margins
• lake shores
• river banks
• wet meadows
• Some bog

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Soft Rush

• Moderate amount of research on Juncus spp in
  Ireland
• Slightly surprising given label as agricultural
  weed
• Might suggest that issues concerning soft rushes
  are minimal or have been solved

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In Ireland

• Broad distribution in Ireland
• In many areas, with poorer soils, some fields
  almost completely covered
• Some work to reclaim peat soils for agricultural
  use in Mayo in 2001 but soft rush invaded and
  became dominant

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Biology

• Hab prefs previously covered
• Rhizome permits vegetative growth producing new
  shoots and also reproduces by flowering

www.irishwildflowers.ie
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Biology

• Rhizome grows at about 2cm per year
• Can send adventitious roots up to 50cm below
  surface, commonly 20cm
• Growth of roots and shoots accelerates from March
  onwards flowers June/July/August

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Growth

Growth reaches a maximum in the summer and is
generally positively correlated with seasonal
climatic factors, and negatively correlated with
standing - dead biomass parameters
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Growth

• Produces very high numbers of seeds - estimated
  at 4 milion per square metre
• But seeds represent tiny fraction of biomass
  produced annually (0.27)
• Soil seedbank remains viable and provides for
  events such as flooding

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Control

• Undesirable aspects of soft rush growth not a
  recent problem.
• Classified as a weed as it is unpalatable to
  stock and low feed value It is well known as an
  agricultural
• Soft rush is quite resilient, not normally eaten
  by stock, but they will at high densities
• Soft rush resistant to grazing pressure,
  trampling and annual cutting

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Control

• Hydrologic conditions that favour the development
  of rush stands will not change with control
  methods such as
• Cutting
• Herbicides
• Grazing
• Common to drain and cut or cut and spray

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Effects of cutting

• Research in 1939 - two cuts in two consecutive
  years produced an 80 reduction in shoot numbers
• This work also stated that it was important to
  have first cut in July before and after was
  less effective at control
• Work in 1936 suggested that rushes seemed to be
  most susceptible to weakening if cut shortly
  after mid - summer.
• Others noted that some rush species do not
  flourish at sites where hay is cut annually
  fields cut for hay year after year.
• Trials in 1964 found that mowing repeatedly 46
  times per year was required to control the
  rushes but would not eliminate them.

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Effects of cutting

• 1995 work suggested that cutting to half their
  height had no effect
• Cutting to ground level twice a year over two
  years effective at controlling them
• Most control methods in use in Ireland involve
  herbicides in combination with cutting or
  drainage depending on land use

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Energy Content

• Determined moisture content
• 5 size classes of rush
• 20 30 cm
• 30 40 cm
• 40 50 cm
• 50 60 cm
• gt60cm

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Moisture content
Length class Number of rushes Mean length Wet mass(g) Dry Mass Moisture
20-30cm 12 25.46 4.35 3.01 30.72
30-40cm 16 33.93 10.73 7.48 30.32
40-50cm 34 45.1 28.89 20.23 29.99
50-60cm 23 53.26 26.79 18.83 29.72
60-70cm 15 64.1 21.67 14.79 31.75
Rushes had approx 30 moisture content when
harvested
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Moisture content

• Also looked at some commercial products
• MACE wood briquettes approx 25
• NCF wood logs approx 15
• Turf 16 - 35
• Peat briquettes 10
• Kiln dried wood
  9
• Miscanthus 9 - 20
• Strogs 12

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Energy content

• Used bomb calorimeter
• Calibrated with standard material
• Determines energy content by ability to heat
  known mass of distilled water when substance is
  combusted in presence of oxygen

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Energy Content
Fuel MJ/Kg 
 Coal  27.1 - 33
 Straw Briquettes  16
Miscanthus 18
Turf 14-18
briquettes 17
gt60cm rush 17
50-60cm rush 18.7
NCF wood logs 19
Mace wood briquettes 19
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Summary to date

• High moisture content but relatively easy to dry
• Obviously dont have to get moisture to zero
• Very low ash content on combustion
• Very low density when dry
• Energy content comparable to currently available
  products
• Perhaps consider them as an addition

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Main source

• Forest Ecosystem Research Group Report Number 69