Companion to the Discussion Paper:
Revisions to Forests Act Regulations
Affecting Forest and Wood Biomass Users
Revisions to Forests Act Regulations Affecting Forest and Wood Biomass Users • Discussion Paper
Conversion Factors and
Measurement of Biomass
Fuels for Nova Scotia
9
Conversion Factors and
Measurement of Biomass
Fuels for Nova Scotia
Companion to the Discussion Paper:
Revisions to Forests Act Regulations
Affecting Forest and Wood Biomass Users
Peter MacQuarrie
Director, Program Development
Kevin J. Hudson
Manager, Scaling and Forest Regulation Administration
Report FOR 2013-5
Nova Scotia Department of Natural Resources
ISBN: 978-1-55457-545-9
© Crown copyright, Province of Nova Scotia, 2013
July, 2013
Purpose
While various forms of wood biomass products have been bought and sold in
Nova Scotia for a very long time, the Registry of Buyers has not adopted and
published a set of conversion factors that is complete enough to meet the
needs of DNR, should the current (2013) Registration and Statistical Returns
Regulations under the Forests Act be amended to require more complete
reporting of all forms of such fuels.
The purpose of these conversions is to standardize statistical information
received from all buyers who report and to be able to describe the kinds,
amounts, and trends of withdrawals from our forests. We want to standardize
all amounts to a “net merchantable” solid wood volume basis, which will be
comparable to our forest inventory information and historical data sets.
Primary wood products are measured in either volume or mass units. It is the
general presumption of this paper that industrial biomass fuels will in almost all
instances be measured by mass (weight) as the basis for commercial trade and
the payment between suppliers and purchasers or service providers (loggers,
truckers, chippers, etc.).
This note describes and discusses some practices for conversion. The objective
of this note is to suggest an approach that, while not completely accurate, may
be considered sufficiently fair.
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Logs and Roundwood as Industrial Fuel
The Registry of Buyers has published conversion factors for log products for
both volume and mass measurements. They are published annually in the
annual buyer reports.1
It is the announced policy of government that it supports only the production
of primary biomass fuels made from tree stems. Therefore, the existing log
factors for pulpwood and firewood can be applied to what will become
biomass fuel, if it is delivered in log or roundwood form.
• For mixed softwood species, one green tonne of logs times
1.167 equals 1.167 cubic metres of solid wood
(1 t × 1.167 m3/t = 1.167 m3).
• For mixed hardwood species, one green tonne of logs times
0.963 equals 0.963 cubic metres of solid wood
(1 t × 0.963 m3/t = 0.963 m3).
Roadside Produced Fuel Chips
If the fuel has been chipped at roadside before delivery and measurement, the
Registry’s existing factors for roadside pulp chips should NOT be applied. When
making such pulp-quality chips, the tree stems are normally processed through
a flail to remove the limbs, foliage, and bark to improve chip quality. On an
intact tree stem, 17–20 per cent of the weight of small-diameter trees is bark.2
As much as 12 per cent of the bark may be removed during the logging and
forwarding process, reducing the bark content to 15–17 per cent of the
material entering the flail/chipper. The factors also differ from above because it
is possible to use a higher percentage of the total tree stem and recover some
stem volume not allowed for under the province’s forest inventory estimation
methods. Removal of the bark increases the factors, compared to whole logs.
1 DNR. 2012. Report on Primary Forest Products Acquired, Secondary Forest Products
Produced and Wood Acquisition Plan Program. DNR report 2012-1.
http://www.gov.ns.ca/natr/forestry/registry/annual/2012/2011AnnualReport.pdf
2 Kostiuk and Pfaff. 1997. Conversion Factors for Forest Products Industry in Eastern
Canada. FPInnovations, Special Publication SP523E, Tables 4.9 & 4.10.
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When intentionally making roadside pulp-quality chips, the buyer is normally
trying to reduce the bark content to less than 1 per cent, if possible, by
controlling the speed and severity of the flail stage. If using similar equipment
to process fuel grade stems or logs, the operator will want to retain all the bark
by retracting the flail.
Therefore, the existing roadside pulpwood chip conversion factors should not
be applied to roadside fuel chips. The regular roundwood factors should be
applied to roadside fuel chips made from tree stems. The same factors should
also be applied if the stems have been “ground” as opposed to “chipped.”
• For mixed softwood species, one green tonne of primary fuel
chips times 1.167 equals 1.167 cubic metres of solid wood
(1 t × 1.167 m3/t = 1.167 m3).
• For mixed hardwood species, one green tonne of primary fuel
chips times 0.963 equals 0.963 cubic metres of solid wood
(1 t × 0.963 m3/t = 0.963 m3).
The government policy for biomass production will permit some whole-tree
chip production only if the material originates from a non-forestry activity such
as land clearing. In these instances, the bark, branches, and foliage may end up
in the total weight delivered but should be eliminated by the conversion factor
to adjust to the net merchantable volume basis. If the entire crowns of the trees
have been included in a load of fuel, it will be readily detected by visual
inspection and the presence of twigs, slivers, needles, and foliage.
• For mixed softwood species, one green tonne of whole-tree
chips times 0.817 equals 0.817 cubic metres of solid wood
(1 t × 0.817 m3/t = 0.817 m3).
• For mixed hardwood species, one green tonne of whole-tree
chips times 0.674 equals 0.674 cubic metres of solid wood
(1 t × 0.674 m3/t = 0.674 m3).
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Reporting Species Groups
Changes are proposed to regulations that anticipate more biomass fuels being
produced in future. While we can contemplate sampling and testing designs for
estimating the species proportions of mixed loads of either logs or chips (which
will have a high degree of variability), there will be little commercial interest for
suppliers to incur such costs. Buyers of more than 5,000 m3 of wood products
originating from private lands create a regulatory “required value” for providing
a silviculture program. The calculated value depends on the species
group acquired.
Using the fuel-chip factor above, acquiring a tonne of hardwood chips would
create a required value regulatory burden of $0.40/m3 (0.674 × $0.60).
Acquiring a tonne of softwood chips would create a required value of $2.45/m3
(0.817 × $3.00), six times more. The factors differ between hardwood and
softwood. The factors actually differ with each individual species, but the
difference between these two groups is more significant than the differences
within them. From a fuel-value perspective however, inter-species heat-value
differences (in Btus or kJ) become less significant when measured on a
common weight basis. It must be assumed that once the higher-value sawlog
and pulpwood portions have been used, there will be no economic or practical
motive for harvesters and truckers to physically segregate hardwood and
softwood stems that are fuel grade only.
Buyers will be required to use a deemed mixed species factor. How could such
a factor be established? In what follows, we discuss different aspects and
options for biomass conversion factors and measurements. This discussion
has informed our suggested conversion factors.
By Calculation
DNR has previously published measures of the amounts of biomass in our
forests, based on our current inventory.3 The average standing biomass on
a global per-hectare basis in tree stems as wood and bark is 28.20 oven dry
tonnes per hectare (odt/ha) of softwood and 24.63 odt/ha of hardwood.
Within the softwood group, “other” species, which have no sawlog or pulpwood
use, amounted to 0.03 odt/ha. Within the hardwood group, if one deems white
birch, trembling aspen, large tooth aspen, and “other” hardwoods as having
little sawlog or pulpwood demand, they amounted to 6.75 odt/ha. DNR has
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also published some stem-quality information in its conventional inventory
reports.4 From Townsend (2004), it is estimated that 1 per cent of softwood
stem volume and 3 per cent of hardwood stems were cull wood, unsuitable
for sawlog or pulpwood size or quality.
If one presumes that only the undesirable species in an average stand of trees,
plus the cull wood portions of all species stems, are recovered as fuel, then the
species ratio for such fuel would be estimated at 96 per cent hardwood and
4 per cent softwood; therefore, the Registrar would have to require that all
buyers convert mixed species primary chips annual reports on that (96/4) basis.
This would result in an effective required value regulatory burden of $0.482
per green tonne.
This same calculation should ideally be based on average values from
permanent sample plot (PSP) compilation that includes only those forest
stand types likely to be harvestable. Such an estimate has not been published.
This factor ignores other weaknesses in this method:
• The tree stems in the PSP system are classified based on the observable
external defects and shape. The system does not capture internal defects
such as soft rot or stain.
• The report cited (Townsend 2008) has included only the volume of living
trees, although the PSP system has collected information on the amount
of standing dead stems. If harvesters have the ability to sell dead wood
as biomass fuel, it will likely be harvested.
• The classification of stems into product groups does not consider whether
there is an actual market – sufficient to take any amount produced – for all
products. While white pine sawlogs might be easily sold in some counties,
they may be unwanted in others and would likely be sorted into a biomass
fuel pile as the most economic decision.
3 Townsend. 2008. Forest Biomass of Living Merchantable Trees in Nova Scotia. DNR
report FOR 2008-9.
4 Townsend. 2004. Nova Scotia Forest Inventory Based on Permanent Sample Plots
Measured between 1999 and 2003. DNR report FOR 2004-3.
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By Observation
The Registry of Buyers collects data from processing facilities within the
province. Data submitted to the Registry by two significant historical buyers
(NewPage and Brooklyn Energy) provides some evidence of species mix
contained in commercial deliveries of biomass type products. For the two
years 2010 and 2011, softwood was reported to make up 58 per cent of the
roundwood biomass they acquired as fuel. From observation at the NewPage
mill site, larch, white pine, poor-quality hemlock, recently dead white spruce
(beetle kill), and poor-quality balsam fir have contributed to the much higher
softwood content than inventory plot data would suggest.
At the Brooklyn Energy site, poor-quality white pine and hemlock made up
the vast majority of the softwood component. These species are generally
considered desirable species for sawlogs and pulp. The firewood market
also draws a high percentage of the hardwood species type away from the
biomass stream.
In 2012, biomass stockpile yard inventories acquired at Canso Strait under
the province’s Seven Point Plan also provide insight into the present and
actual species mix. Data from this source would indicate that a biomass
species type mix of 60 per cent hardwood and 40 per cent softwood has
been acquired. Therefore, an appropriate mixed species factor would be
(0.4 × 1.167) + (0.6 × 0.963) = 1.045 m3/t.
The Registrar could require that all buyers convert mixed species primary
chips annual reports on the basis that they contain 60 per cent hardwood
and 40 per cent softwood. This would result in an effective required value
regulatory burden of
(0.4 × 1.167 × $3.00) + (0.6 × 0.963 × $0.60) = $1.75 per green tonne,
or $1.67/m3.
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By Presumption
Commenters frequently speculate that firms would add trivial amounts of
hardwood to a softwood shipment, or vice versa, if it will be to their regulatory
advantage to do so. This suggests that we specify some tolerance. As part of
the province’s past forest inventory specifications for classifying forest stands,
it was the practice that a stand was considered “softwood” if less than 25 per
cent of the volume was hardwood species, “hardwood” if less than 25 per cent
was softwood, and “mixed species” if the proportion of softwood was more
than 25 per cent but less than 75 per cent. A conversion factor or a required
value for the mixed species group could be established based on an assumed
50/50 mix.
Sawmill Residues
The most common industrial wood fuel has been the residues from our
sawmills: bark, sawdust, shavings, chips, and chip fines. When one or more
portions of these materials are mixed together, it is commonly referred to as
hog fuel. On a green weight basis, all of the matter in the logs delivered to a
mill will be transformed into either lumber or one of these waste products.
So as to maximize sales revenue, mill operators strive to turn most of the log
into the highest-value good – lumber – and the least amount into low-value
goods or wastes such as sawdust. The actual ratios of the various components
differ between mills and can be affected by a number of factors, including
equipment used, relative prices of different sizes of lumber, size of logs, time
of year, and moisture content.
The moisture content of sawlogs when they enter the mill depends on how
quickly they are delivered from the forest or how long they were piled in the
log yard. Once processing starts, bark, sawdust, and pulp chips are produced
simultaneously. Mills have only limited storage capacity, and residues are
typically trucked to a buyer very soon, with little additional drying.
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Chips
Nova Scotia pulp and paper mills purchase only softwood chips for making
their products. To make the chips, sawmills must operate additional equipment
and incur additional costs. Pulp mills want their pulp chips to be as fresh as
possible and may deduct from the price if they get too dry (below 40 per cent
moisture content). In Nova Scotia there is a market for hardwood chips only to
make wood pellets or to be used as fuel.
Clean sawmill chips can be measured with the existing conversion factors the
Registry uses for roadside pulp chips:
• For mixed softwood species, one green tonne of sawmill chips
times 1.269 equals 1.269 cubic metres of solid wood
(1 t × 1.269 m3/t = 1.269 m3).
• For mixed hardwood species one green tonne of sawmill chips
times 1.070 equals 1.070 cubic metres of solid wood
(1 t × 1.070 m3/t = 1.070 m3).
Sawdust
Most of the sawdust in sawmills is generated from sawing roundlogs. Some
sawdust is recovered from the trim saws in planer mills, but that is a small
amount compared to the amount from primary breakdown. Sawdust will have
the same moisture content and wood density as pulp chips, so the conversion
factors can be the same:
• For mixed softwood species, one tonne of sawdust equals
1.269 cubic metres of solid wood.
• For mixed hardwood species, one tonne of sawdust equals
1.070 cubic metres of solid wood.
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Shavings
Most major softwood sawmills also operate dry kilns and planer mills. Lumber
is not planed until it has been dried. Grading rules require that to be considered
“dry,” lumber has reached moisture content of 19 per cent or less (dry weight
basis).5 This would be the approximate moisture content of the planer shavings
made from such lumber and is equal to 17 per cent moisture if expressed on
the green weight basis (Kostiuk & Pfaff 1997).
If one assumes pulp chips were produced at 42 per cent moisture content
and shavings at 17 per cent, it takes a larger volume of shavings to make a
tonne. The pulp chip conversion factor could be increased by 2.5 times
(42/17) to estimate a factor for shavings.
• For mixed softwood species, one tonne of shavings times
(1.269 × 2.5) equals 3.172 cubic metres of solid wood
(1 t × 1.269 m3/t × 2.5 = 3.172 m3).
• For mixed hardwood species one tonne of shavings times
(1.070 × 2.5) equals 2.675 cubic metres of solid wood
(1 t × 1.070 m3/t × 2.5 = 2.675 m3).
Hardwood sawmills may or may not operate kilns or planers. The drying and
dressing of hardwood might not occur until it has reached its next customer
and processed further.
Bark
While debarking equipment always removes some solid wood from a log, for
practical purposes it can be assumed to be none. If a fuel user is acquiring only
bark, it is deemed to contain no net merchantable solid wood.
• For mixed softwood species, one tonne of bark times
0.0 equals 0.0 cubic metres of solid wood.
• For mixed hardwood species, one tonne of bark times
0.0 equals 0.0 cubic metres of solid wood.
5 NLGA Standard Grading Rules for Canadian Lumber.
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Hog Fuel
The waste material handling systems typically mix together the different wood
wastes, in particular the bark, sawdust, and chip fines. The mix will likely not
contain shavings. Shavings are usually produced in a separate building at the
mill; they are sought-after for use on farms, and they are useful as fuel for the
mill’s own dry kiln.
Studies of actual sawmill component yields (Kostiuk & Pfaff 1997, Table 5-21)
imply that if all the bark and sawdust are mixed as hog fuel, the ratio is 50/50
for softwood, 58/42 for hardwood. Using the factors for bark and sawdust at
these proportions would suggest the following conversion factors:
• For mixed softwood species, one tonne of hog fuel times 1.269
times 50 per cent equals 0.634 cubic metres of solid wood
(1.269 m3 × 0.50 = 0.634 m3).
• For mixed hardwood species, one tonne of hog fuel times
1.070 times 42 per cent equals 0.449 cubic metres of solid
wood (1.070 m3 × 0.42 = 0.449 m3).
Species Content of Sawmill Residues
The nature of the products to be made and the equipment to economically
produce either hardwood or softwood lumber are significantly different. No
sawmills in the province are equipped to process both at the same facility.
Sawmill residues at the supplier’s location will be clearly observable as either
all softwood or all hardwood, and a buyer’s fuel purchase records can simply be
attributed to the name of the suppler mill if necessary. Physical separation or
tracking will be lost at the receiving facility, as fuels from different sources will
likely be mixed together.
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Tenure of Origin for Biomass Fuels
Buyers of biomass logs or roadside-produced fuel chips are in the same position
as any other registered buyer of primary forest products. If they have not
harvested the logs themselves, they can require that each seller declares the
origin of such logs and chips.
It is impractical to expect sawmills to track the origin of each load of delivered
hog fuel or other wood wastes. It is therefore suggested the Registry require
that the origin of sawmill chips or wastes is reported as sold to others or used
in-house in the same ratio as the roundlogs from which they were produced.
For example, if 15 per cent of their logs were Crown logs, then 15 per cent of
pulp chips and hog fuel should reported as Crown origin. These ratios differ for
each registered buyer and will change each year but are already being reported
to the Registry.
Summary of Suggested Conversion Factors
for Biomass Fuels
(green metric tonnes times factor equals cubic metres of solid wood)
Softwood
Hardwood
Logs and roundwood
1.167
0.963
Chips (stemwood from forestry)
1.269
1.070
Chips (whole-tree non-forestry)
0.817
0.674
Chips, sawmill
1.269
1.070
Sawdust
1.269
1.070
Shavings
3.172
2.675
Bark
0.000
0.000
Hog fuel (mixed bark and sawdust)
0.634
0.449
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