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We get many requests from students for project
information. In this section we offer information suited to this
use, laid out in printable format.
The Kyoto Protocol || Raw
Materials || Pollution Control Technology
|| Water and Waste || LVL
process flowchart || MDF
process flowchart
The
Kyoto Protocol NPIL Environmental
Engineer Phil Wilson has been looking at what this means for NPIL
and where wood sits on greenhouse gas production, compared with
other products used for building, such as steel and concrete.
“This is a very complex issue but there are some useful points
to make,” says Phil. “In fact the forest based industries
are the ‘good guys’ in the way they contribute to reducing
the build up of CO2 in the atmosphere.”
What it’s all about? The
temperature of the Earth’s surface has risen over the past
100 years. There is strong evidence that most of this warming,
especially more recently, is a result of greenhouse gas emissions
caused by human activity. Greenhouse gases got their name because
they let the sun’s warmth through just like a greenhouse,
but don’t let the heat escape back into space. The effect
of this gradual warming is complex and is often referred to by
the more general term climate change.
The international community has come together to limit the growth
of greenhouse gas emissions, working through the United Nations
on an agreement called the Kyoto Protocol, finalised at the end
of 1997, and signed by New Zealand in 1998.
Where do greenhouse gases come from?
New Zealand’s main culprit in greenhouse gas emissions are
those harmless looking (but farty!) farm animals. Sheep and cattle
produce about 50% of our emissions. Methane is a potent greenhouse
gas, taking less gas to have the same effect as carbon dioxide.
Next up is transport, producing nitrous oxides from vehicle emissions.
Energy generation is third on the list. Although New Zealand has
a high level of hydro production, we also use coal and gas, which
put CO2 into the atmosphere. Industry accounts for only 10% of
the total amount of greenhouse gas produced in New Zealand.
Where NPIL fits in:
“At NPI our main contribution to greenhouse gas emissions
is through our use of electricity,” Phil says. “Even
though we might get our power from the Cobb Dam, we have to consider
our use as part of the national grid. We have to look at where
the country will get its next unit from – and that means
more burning of coal or gas.”
Over 70% of our energy requirements on site are for producing
heat: “We generate almost all of our own heat requirement
by burning wood waste,” Philip Wilson says. “This puts
us into a greenhouse gas neutral situation. Growing trees absorbs
CO2 so it’s what we call a ‘virtuous cycle’.”
In addition, carbon is stored in the wood products we produce
while they are used in buildings or furniture. This locks up carbon
in the urban environment.
Another plus is that by processing wood into profitable end products
we are encouraging more people to grow more trees. This is a better
land use in terms of climate change than farming sheep or cattle.
On the longer term: NPI
is watching the world situation closely. There will be down stream
effects as New Zealand moves to meet its commitments under the
Kyoto Protocol. If the Government puts a carbon tax on fossil
fuels, then the cost of electricity could go up, making it more
expensive to produce MDF in New Zealand than in a country like
Malaysia that is not a signatory to the Kyoto Protocol. The Government
may then have to look at tax relief to stop industry going offshore.
“Climate change is a huge problem to get to grips with, without
distorting the economy,” Philip Wilson says. “At NPIL
we can do our bit by ensuring we work efficiently, keep on using
bio-fuels, and staying up to date and having input on what Government
is doing.”
Why Wood?
In terms of energy required for production and the amount of emission
or effluents, wood stacks up well compared to other material.
Energy consumption to produce one tonne of:
- Material Energy
- Aluminium 70
- Steel 17
- Brick 3.1
- Concrete block 3.0
- Dry Lumber 1.0
Net carbon emissions in producing one
tonne of:
- Material kg carbon/tonne
- Aluminium 2,400
- Steel 1,090
- Brick 148
- Concrete block 2,810
- Dry Lumber -460
- MDF 100
This table, down to dry lumber, was developed
by the Department of Civil Engineering, University of Canterbury.
Philip Wilson says that timber gets a negative figure for carbon
emissions because while it’s growing it ties up carbon dioxide.
The figure for MDF is added to this chart, but if you took the
positive factor of tree growth into account as has been done for
lumber, and also the carbon stored in finished products like furnature
and houses it too would end up as a negative figure.
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Raw
materials
Wood: The
MDF (Medium Density Fibreboard) process at Nelson Pine Industries
Ltd (NPIL) uses up to 700,000 tonnes of wood per year, from the
residue of logging from renewable pine plantation forests LVL
uses an additional 200,000 cu per year of wood resource. It requires
a higher grade of log which is converted to an added value product.
Water: Every tonne of MDF made
requires about one tonne of water, very low compared with other
processes that use wood residues. For example, pulp and paper
production typically requires between 10 and 50 tonnes of water
per tonne of final product.
Some of the water is used for washing the wood chips to remove
any dirt, sand or stones that could cause wear on the refining
process, and also to ensure the board is clean.
The other major use of water is to make steam used to heat and
soften the chips before they are ground up into fibre.
NPIL is continuing to find ways to reduce the amount of water
required in the process. In the last 10 years total water consumption
has been reduced to a third of the original amount, while at the
same time the amount of board made has trebled.
Energy: About
70% of the energy used on the site is generated by burning wood
waste. This comes from:
- bark taken off in
the debarking and chipping operation
- sawdust from trim
and sizing saws
- sander dust from board
sanding
- board offcuts from the panel sizing saws
The other 30% of the
energy comes from electricity supplied via Network Tasman.
Resin:
Resin to glue the fibres together into board is supplied by two
resin companies. Dynea has a resin plant next door to NPIL and
pumps the resin to tanks on site via a pipeline. Orica manufactures
resin for NPIL at its resin plants in Christchurch and Tauranga.
Both resin manufacturers have worked closely with NPIL to develop
environmentally friendly resins.
These minimise environmental effects when the resins are used
to make board and also minimise the emissions from the board when
it is used. GoldenEdge MDF can now be made with emission levels
similar to natural wood.
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Pollution
Control Technology
Furnaces: Most
of the energy required for MDF production and veneer drying is
obtained by burning wood residues, such as the bark removed from
logs at the chipmill. The furnaces used are very clean burning
because of the dry fuel and high temperatures used for burning.
The hot gas is also cleaned as it goes through a multicyclone,
which takes out any ash. The hot chimney gas coming out of the
MDF furnace is clean enough to be used directly for drying the
wood fibre in our MDF drying system.
All of the fuel used for the furnaces comes from a renewable source
(trees) thus the emissions do not contribute additional CO2 to
the atmosphere. CO2 is one of the gases thought to cause global
warming.
Dust Control:
The MDF process involves conveying dry wood fibre and also sander
dust. Special attention is paid to preventing dust or fibre escaping
from the process. Specially-designed cyclones are used for separating
the fibre from transport air. These are fitted with special blockage
detectors that will shut down the process if a fibre discharge
is likely to happen. On the sander dust systems special bag filters
are used to separate out all the dust and purify the air used
for conveying prior to release into the environment.
Waste Water Treatment:
Water used for washing chips and other process wash water is treated
to remove solids before it leaves the site. A flotation clarifier
uses tiny dispersed air bubbles to float coagulated solids to
the surface of the clarifier where they are skimmed off. The solids
are then thickened up in a big screw press. These solids are then
burned with other wood waste in the furnaces. This minimises requirements
for land fill disposal. The treated water is then pumped to the
Bells Island treatment plant for further biological treatment
prior to discharge.
Noise:
Significant attention has been given to minimise the amount of
noise generated by the plant. Although the plant runs 24 hours
a day, the chipping operation is designed to allow all the chip
required for production to be made during daytime.
Most of the noisier equipment is housed in specially designed
noise enclosures. Many of the process vents have noise attenuators
or silencers attached to them to reduce fan noise.
Formaldehyde:
From Nelson Pine Industries' early days in the mid 1980s, research
carried out in conjunction with resin suppliers has resulted in
significant reductions in formaldehyde levels of GoldenEdge Medium
Density Fibreboard. Production for special markets is made to
low fuming levels similar to the formaldehyde levels found in
natural wood products.
Formaldehyde has from time to time created controversy in the
production of MDF and particle-board. This substance does not
occur just in the urea formaldehyde resins used in the manufacture
of MDF- there are many other sources including car exhausts, open
fires and indoor furnishings.
When the third line was installed in 1997, as part of the process
of gaining Resource Consent, consultants 'modelled' the effects
of an additional line on the ambient air conditions down wind
of the plant. The computer modelling work showed that there would
be very little impact from the new line.
Careful siting of the discharge stacks - in the right place and
at the right height - disperses discharges in such a way that
there is no increase to maximum downwind concentrations, beyond
the boundary, to the amount produced from two lines.
The drier cyclones with their highly visible plumes of water-saturated
air are the most visible discharge from the NPIL plant. However,
because they are so high and produce a high volume at very high
temperatures, the material goes up and is dispersed. It takes
unusual weather conditions before you will see the plume from
the cyclones heading for the ground.
In fact the main source of discharge containing formaldehyde is
the exhaust from the presses. In the design of Line 3 the vents
were spread out and some stacks elevated to avoid situations where
the plumes from any two vents overlapped. The worst-case scenario
in results from the modelling had these overlaps occurring only
in certain weather conditions. Even in these cases, predicted
formaldehyde concentrations were lower than the 70 micrograms
per normal cubic metre allowed by the Resource Consent already
granted for Lines 1 and 2. This level is lower than measurements
taken inside in the Tasman District Council chambers.
What is more, monthly monitoring reveals that the actual discharge
from the plant is consistently lower than what would be expected
from the models. Tests are taken at the end of every month, in
the mid afternoon when there is a consistent sea breeze. Data
built up from this monitoring indicates the actual level of formaldehyde
down wind of the plant is only 20 to 30 micrograms per cubic metre.
In fact the test levels often show no difference upwind and downwind
of the plant. This is not surprising as the modelling looks at
the worst case scenario in weather terms: overcast conditions
with low wind speeds, which bring the gases to ground. In fact
the prevailing wind disperses gases in a way which renders them
harmless.
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Water
and Waste
Nelson Pine Industries is part of a cluster
of industrial users of the water and waste services provided by
Nelson's two district councils. Both water supply and effluent treatment
benefit from economies of scale in a council provided service.
Water:
In total the big three industries use about 1.6 million cubic
metres of water per year, broken down as follows:
>> NPIL 350,000 m3/year
>> ENZA Foods 450,000 m3/year
>> Nelson Bays Meat Producers 2800,000 m3/year
This adds up to 2% of the total water right allocation for the
Waimea Catchment or about as much as is allocated to irrigate
90ha (about two dairy farms).
Good water quality is important for all the industries involved.
For both meat and apple processing there are strict MAF guidelines
that require the water to be chlorinated. At NPIL, water used
for raising steam must be very clean to prevent boiler fouling
and corrosion.
All three industrial users have taken steps to reduce water use.
At NPIL, by changing from hydraulic debarking to mechanical debarking
and other water saving and re-use measures, the plant has gone
from using 7.5 m3 of water per m3 of board to 1.1 m3 of water
per m3 of board.
Effluent:
In the mid '80's, Nelson Pine Industries Ltd, the freezing works
and the apple processing plant along with Richmond and Stoke domestic
services, were separately treating effluent to varying degrees
and discharging into the Waimea Estuary. Councils and industries
came up with a plan for a combined scheme to pump all the effluent
to Bells Island for treatment in large oxidation ponds. This was
set up in 1985 and more recently upgraded, bringing the total
cost of the scheme to over $20million. A 1998 Cawthron Institute
report indicates the estuary is in good health downstream from
the outfall; and there are also good results in tree growth from
the application in forestry areas of bio-solid generated as a
by-product of the treatment process.
Effluent Treatment : Chipwashing, motor cooling water, washdown
water from the cleaning yards and stormwater all contribute to
the waste water produced on site at Nelson Pine Industries. When
Line 3 was installed in 1997, the amount of effluent produced
increased by around 50%. To deal with this increase the liquid
waste treatment system was upgraded. Previously all liquid waste
ran into a settling pond to remove solids and was then pumped
away to the Bells Island sewage treatment plant.
To find the best way to treat the effluent, laboratory studies
were done to look at methods of separating the solids from the
waste. These were followed by pilot trials of equipment manufactured
for this job. These trials showed that a flotation clarifier would
improve effluent quality at much lower operating costs than the
previous system.
All liquid effluent, mainly from the chipwashing stage of production,
is now pumped to the effluent treatment plant. The first step
in the process is the addition of a polymer to clump the solids
together, giving the waste water a curdled appearance. It is then
aerated by two machines like giant milk-shake makers, which float
the solids to the surface. The water then flows through the flotation
clarifier, where the sludge is skimmed from the top and fed into
the screw press where the solids are de-watered and later burnt
in the furnacesbark burner. A bottom scraper moves across the
floor of the tank to remove any sand, small pieces of gravel or
chips that have come through the chip wash. The liquid effluent
is then pumped via the sewer system to Bells Island. To help protect
the pipeline from erosion, caustic soda is added by a small pump
to neutralise any wood acids present.
Water Purity:
Water used on site at NPIL to raise steam is treated to ensure
it is as pure as possible. Steam is an important part of the MDF
production process, used to cook the wood chips and refine them
into wood pulp.
The big steam generator bundles are heated by hot oil, and evaporate
5,000 litres of water into steam every hour, for each line. They
are just like the coil on an electric jug - if the water was not
treated they would clog up with scale and slow down the rate of
heat transfer.
Salt is used to soften water and remove the calcium and magnesium
which would create scale on the heat transfer surfaces. Close
to 50 tonnes of salt per year is trucked over from Grassmere for
this use. Balancing chemicals are added and lab tests done to
ensure the water enters the steam making process in a pure state.
LVL Process: Download
the LVL process flowchart
MDF Process: Download
the MDF process flowchart
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