Woodfuel facts

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Treacodactyl
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Joined: 28 Oct 2004
Posts: 25795
Location: Jumping on the bandwagon of opportunism

Posted: Tue Dec 27, 05 4:34 pm Post subject: Woodfuel facts

While digging about for bio-fuel facts I've stumbled across this report which gives some numbers on "Small Scale Woodfuel Heating Equipment for Farms" but is also useful for homes:

https://www.forestresearch.gov.uk/pdf/TDB_TN1696.PDF/$FILE/TDB_TN1696.PDF

For example, if I've read a table correctly, a 30kWh energy requirement will need 41 tonnes a year of wood which can be met by 1.2 hectares of high yielding Short Rotation Forestry poplar on a 5 year cycle.

Other details about "Establishment and Maintenance of a Woodfuel Resource"

https://www.forestresearch.gov.uk/pdf/TDB_TN1796.PDF/$FILE/TDB_TN1796.PDF

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Wed Dec 28, 05 3:09 pm Post subject: Re: Woodfuel facts

Treacodactyl wrote:

... if I've read a table correctly, a 30kWh energy requirement will need 41 tonnes a year of wood which can be met by 1.2 hectares of high yielding Short Rotation Forestry poplar on a 5 year cycle.

Ummm, well.
30 kWh is their mistake. They say that a 30 kW (no h) woodburner will require perhaps 41 tonnes of seasoned wood a year (making assumptions about demand, seasoning {to 35% moisture content} and burning efficiency.)
Using their figures, 41 tonnes should supply about (41 x 11.5 x 277.8 = ) 131,000 kWh over the year - which comes out rather suspiciously close to 15 kW every hour 24/365, or flat out 50% of the time, (around the clock, all year). Has someone been making round number estimates?

Table 4 in TN 16/96 suggests 1.2 hectares needs to be cleared each year of the 5 year cycle since the column is headed "ha/yr", and the last sentance on Page 4 is "To provide a self sustaining supply the area must be multiplied by the rotation length in years to show total land requirement."
Thus the land requirement would be 6 ha of timber for a five year rotation.
And allowing for seasoning, one would have a six year wait before benefiting.
(Being a touch pedantic, it looks like 41/33 hecatares per year, ie 6.2 ha total for a five year rotation.)

I note from Table 1 that in the first 5 years a hectare of wood should produce about 33 tonnes of seasoned fuel, however after 10 years the same hectare would have produced 159 tonnes, so its put on 126 T in the second 5 years, almost 4x as much as was produced in the first 5 years. In the third 5 year period, 172 T is added.
It would appear that there is a considerable yield benefit from growing the trees bigger, ie harvesting when older than 5 years.
Thus, for a 10 year rotation, only 41/159 (ie 0.258) ha of mature trees need be cleared each year, a total requirement of 2.58 ha of woodland, about 42% of the requirement for a 5 year rotation. Just 1.86 ha would be needed if a 15 year rotation could be established.
Presumably the financial maths of the yield, and 'growing' a surplus, initially to allow a lengthening rotation, then to sell, are well established? (I'm surprised that the land requirement drops so slowly with the lengthening rotation...)

Now, in calculating the cost of the woodfuel, (as being rather cheap, much cheaper than even mains gas in 1996), I'm not sure that they are taking *any* account of the cost of the land - are they?

Treacodactyl
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Joined: 28 Oct 2004
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Posted: Wed Dec 28, 05 4:04 pm Post subject:
I missed the detail about multiplying up by the rotation years. It would also be good to see a scientific test of the energy in different types of wood as I've always understood poplar to not give off as much heat as ash & oak, an ash coppice example would be interesting. A 10 year cycle of high yielding poplar would require just over 7 acres which fits in with other numbers I've read.

SilentThunder

Joined: 08 Feb 2006
Posts: 3

Posted: Wed Feb 08, 06 1:58 pm Post subject: Wood Burning - Which woods provide good heat

Treacodactyl wrote:

It would also be good to see a scientific test of the energy in different types of wood as I've always understood poplar to not give off as much heat as ash & oak, an ash coppice example would be interesting.

I did some research a while ago on this very question, here's what I found.

One site said the following were the best for heat producing capability:
Hickory - 31 to 32 mm btu/cord
Oak - 30 to 31 mm btu/cord
Black Locust - 28 mm btu/cord
Beech - 27 mm btu/cord
Elms/Maples - 21 to 26 mm btu/cord

The other site gave these figures:
Species, Million Btu/Cord
Almond 24
Apple 24
Locust, Black 24
Madrone 24
Oak, Live 24
Oak, White 23

I hope that's of some use, if not, here's the links I gave for reference, perhaps they'll be useful in finding a better source of the information.
https://www.tdc.ca/wood.htm
https://forestry.about.com/cs/firewood/f/firewood_values.htm
https://www.ecofire.com/Wood.htm

There's also a very interesting poem from Tree Farm by John Estabrook about the qualities of the different woods, it's worth a read:

WOOD HEAT
Beech wood fires are bright and clear
If the logs are kept a year.
Chestnut's only good, they say
If for long it's laid away.
But ash wood new or ash wood old
Is fit for a queen with a crown of gold.

Birch and fir logs burn too fast,
Blaze up bright and do not last.
Is by the Irish said
Hawthorn bakes the sweetest bread.
Elm wood burns like churchyard mould -
E'en the very flames are cold;
But ash wood green and ash wood brown
Is fit for a queen with a golden crown.

Poplar gives a bitter smoke,
Fills your eyes and makes you choke.
Apple wood will scent your room
With an incense like perfume.
Oaken logs if dry and old
Keep away the winter cold.
But ash wood wet and ash wood dry
A king shall warm his slippers by.

Oak logs will warm you well,
If they're warm and dry.
Larch logs of pine wood smell
But sparks will fly.
Beech logs for Christmas time;
Yew logs heat well.
Scotch logs it's a crime
For anyone to sell.
Birch logs will burn too fast,
Chestnut scarce at all.
Hawthorn logs are good to last,
If cut in the fall.
Holly logs will burn like wax,
You should burn them green.
Elm logs like smouldering flax;
No flames to be seen.
Pear logs and apple logs,
They will scent your room.
Cherry logs across the dogs
Smell like flowers in bloom.
But ash logs all smooth and gray,
Burn them green or old,
Buy up all that come you way,
They're worth their weight in gold.

from Tree Farm by John Estabrook

tahir

Joined: 28 Oct 2004
Posts: 45676
Location: Essex

Posted: Wed Feb 08, 06 2:00 pm Post subject:
Great post, thanks. What's a cord?

sean
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Joined: 28 Oct 2004
Posts: 42219
Location: North Devon

Posted: Wed Feb 08, 06 2:30 pm Post subject:
128 cubic feet.

Treacodactyl
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Joined: 28 Oct 2004
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Location: Jumping on the bandwagon of opportunism

Posted: Wed Feb 08, 06 2:48 pm Post subject:

Thanks for the poem SilentThunder, I often come across it in my travels. Thanks also for the info, I'll check the links out tonight. I have now received the info pack the forestry commission sells for �10 and it has some useful basic info in with lists of extra reading and links.

What I now need to look into, if they exist in this country, are large domestic/small commercial wood-fired boilers which can generate electricity. I can then get data and try and work out the cost of buying and installing the boiler, running costs and costs of land to grow the timber. I can then try and calculate the possible income from selling the electricity and finally see if the idea has any mileage in it or if it's un-workable!

SilentThunder

Joined: 08 Feb 2006
Posts: 3

Posted: Wed Feb 08, 06 3:11 pm Post subject:
no probs, thought some of that info might be useful

tahir

Joined: 28 Oct 2004
Posts: 45676
Location: Essex

Posted: Wed Feb 08, 06 3:18 pm Post subject:

Treacodactyl wrote:

TWhat I now need to look into, if they exist in this country, are large domestic/small commercial wood-fired boilers which can generate electricity.

Dunno about that, wood fired stirling engine by the sounds of it, maybe Dougal could help you build one?

Blue Peter

Joined: 21 Mar 2005
Posts: 2400
Location: Milton Keynes

Posted: Wed Feb 08, 06 3:49 pm Post subject:

Treacodactyl wrote:

If you look for posts by the guy BillHook on this thread (and also the whole powerswitch forum):

https://www.powerswitch.org.uk/forum/about821.html&postdays=0&postorder=asc&start=15

you'll see that he is keen on producing methanol from wood. It might be worth looking into,

Peter.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Wed Feb 08, 06 5:04 pm Post subject:

Treacodactyl wrote:

What I now need to look into, if they exist in this country, are large domestic/small commercial wood-fired boilers which can generate electricity.

They used to be called "steam engines"...
I think you'd likely generate much more heat than electricity.

Treacodactyl
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Joined: 28 Oct 2004
Posts: 25795
Location: Jumping on the bandwagon of opportunism

Posted: Wed Feb 08, 06 5:27 pm Post subject:

dougal wrote:

Treacodactyl wrote:

What I now need to look into, if they exist in this country, are large domestic/small commercial wood-fired boilers which can generate electricity.

They used to be called "steam engines"...
I think you'd likely generate much more heat than electricity.

There are details in the FC folder I've been sent, I'll add some comments tonight.

Treacodactyl
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Joined: 28 Oct 2004
Posts: 25795
Location: Jumping on the bandwagon of opportunism

Posted: Wed Feb 08, 06 9:26 pm Post subject:

Based on the details from the Forest Research department from the FC and other sites I come up with the following idea. Wood can make a liquid fuel by pyrolysis and gas by gasification but both seem quite complicated technologies. Simple but modern combustion where the wood is burnt efficiently with minimal emissions and used to produce steam is used for most wood fuelled electricity plants and seems the ideal method for a small scale plant. Yes there is a large amount of spare heat in such a system but I think this will fit in with what we want to do as well.

So, a form of CHP plant that can heat a house (or some others in a community) and some greenhouses which can then be used to produce out of season fruit and veg looks like a reasonable idea to investigate further.

Treacodactyl
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Joined: 28 Oct 2004
Posts: 25795
Location: Jumping on the bandwagon of opportunism

Posted: Wed Feb 08, 06 9:31 pm Post subject:

tahir wrote:

Treacodactyl wrote:

TWhat I now need to look into, if they exist in this country, are large domestic/small commercial wood-fired boilers which can generate electricity.

Dunno about that, wood fired stirling engine by the sounds of it, maybe Dougal could help you build one?

The commercial plants just use the old fashioned steam turbines and I'm sure some small scale boilers must exist it's just tracking them down. If I can get some facts and figures then I can work out if the idea might suit us and possibly look at other more efficient technologies.

thos

Joined: 08 Mar 2005
Posts: 1139
Location: Jauche, Duchy of Brabant (Bourgogne-ci) and Charolles, Duchy of Burgundy (Bourgogne-�a)

Posted: Thu Feb 09, 06 8:35 am Post subject:
The Forestry Commission paper seems quite disturbing. It advocates monoculture with spraying and rabbit-protection - just the thing we're trying to get away from.

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