Moisture content of wood chip?

MX7

Member
Location
cotswolds
What is the approx range of moisture contents of wood chip used in farm/ industrial wood furnaces that are used for indirectly heating greenhouses, warehouse , groups of estate domestic cottages/houses etc etc.
 

MX7

Member
Location
cotswolds
I visited a large tomato grower a while back and I was surprised when he told me the wood chip they used was about 35% moisture.
They are burning about 18 tonnes of wood chip per day,
 

renewablejohn

Member
Location
lancs
I visited a large tomato grower a while back and I was surprised when he told me the wood chip they used was about 35% moisture.
They are burning about 18 tonnes of wood chip per day,
For the same amount of heat you would probably use a quarter of that at 20% mc. Easy enough to dry woodchip in a glass house
 

Wisconsonian

Member
Trade
Nonsense. If everything else is up to snuff, then you might use a quarter LESS at 20% vs 35%. If it's running a medium pressure steam boiler, and the combustion relies on dry chip for efficiency, then it would could save half, but that's a stretch.

Commercial wood chip burners rarely pay to dry chip, the logistics doesn't pay. Burn it as ground.
"For wood chips with a moisture content (MC) of 45 percent, the maximum boiler efficiency with standard equipment is about 74 percent. If the same stand and equipment is burning dry wood (10 to 15 percent MC), the efficiency can be as high as 80 percent."
 

renewablejohn

Member
Location
lancs
Nonsense. If everything else is up to snuff, then you might use a quarter LESS at 20% vs 35%. If it's running a medium pressure steam boiler, and the combustion relies on dry chip for efficiency, then it would could save half, but that's a stretch.

Commercial wood chip burners rarely pay to dry chip, the logistics doesn't pay. Burn it as ground.
"For wood chips with a moisture content (MC) of 45 percent, the maximum boiler efficiency with standard equipment is about 74 percent. If the same stand and equipment is burning dry wood (10 to 15 percent MC), the efficiency can be as high as 80 percent."
Your confusing boiler efficiency with increase in calorific value. Its the substatially higher calorific value for low MC chip which is important not the fact that a boiler can burn wet woodchip.
 

Wisconsonian

Member
Trade
Yes, I'm confusing the concepts. But the numbers are on my side, there is not a four fold heat output increase from drying a KG of 35-40% chips down to 20%. Remember, a big part of the increase in heat output is per KG, which includes the water removed from the first sample, so there will be less weight in the dried sample.

I mention a boiler being able to burn wet woodchip, because efficiency can fall off fast if it's not capable of burning wet woodchip.
 

Old Tup

Member
If the chips are yellowish then they are wet….if they whitish then they are dry.
Wet is Bad …..Dry is Good.
Stack fresh cut softwood outside in an airy place for 12months, mid summer to mid summer…
Result dry chips.
 

renewablejohn

Member
Location
lancs
Yes, I'm confusing the concepts. But the numbers are on my side, there is not a four fold heat output increase from drying a KG of 35-40% chips down to 20%. Remember, a big part of the increase in heat output is per KG, which includes the water removed from the first sample, so there will be less weight in the dried sample.

I mention a boiler being able to burn wet woodchip, because efficiency can fall off fast if it's not capable of burning wet woodchip.
Thats part of the difference 18 tonnes @ 35% MC as opposed to 4.5 tonnes @ 20% moisture content. You then have the calorific value being a lot higher at 20% rather than 35% and finally the boiler efficiency being higher on 20% rather than 35% which is your 80% compared to 74% mainly due to higher temperature of combustion with 20% chip.
 

Bloders

Member
Location
Ruabon
Thats part of the difference 18 tonnes @ 35% MC as opposed to 4.5 tonnes @ 20% moisture content. You then have the calorific value being a lot higher at 20% rather than 35% and finally the boiler efficiency being higher on 20% rather than 35% which is your 80% compared to 74% mainly due to higher temperature of combustion with 20% chip.
are you sayimg that the energy out of 18 tonnes at 35% MC is the same as 4.5 tonnes at 20%?
seems a big difference to me
 

Bloders

Member
Location
Ruabon
It is a big difference. Design your own CHP plant and you soon learn this simple lesson.
Im not saying its not a big difference. I am saying i find those numbers hard to believe.
Can you back them up with some maths? If you design systems them as implied, I assume you have this info to hand to illustrate the point - thats my question.

I assumed its along the lines of
1 tonne of wood chip at 35% contains x Joules
1 tonne at 20% contains Y

I appreciate that if the chip is dryer, you get the compound effect of
a) more "wood" per tonne, and
b) when its burnt, then less energy is used in evaoprationg off the moisture trapped in the wood, so that the net result is the energy avaialble (which i assume is the same whether wet or dry per molecule* of wood) is used to heat the water in this example, giving what appears to be higher efficiency.

*i dont know how the calorific content of wood is measured other than by weight.

thanks
 

renewablejohn

Member
Location
lancs
Im not saying its not a big difference. I am saying i find those numbers hard to believe.
Can you back them up with some maths? If you design systems them as implied, I assume you have this info to hand to illustrate the point - thats my question.

I assumed its along the lines of
1 tonne of wood chip at 35% contains x Joules
1 tonne at 20% contains Y

I appreciate that if the chip is dryer, you get the compound effect of
a) more "wood" per tonne, and
b) when its burnt, then less energy is used in evaoprationg off the moisture trapped in the wood, so that the net result is the energy avaialble (which i assume is the same whether wet or dry per molecule* of wood) is used to heat the water in this example, giving what appears to be higher efficiency.

*i dont know how the calorific content of wood is measured other than by weight.

thanks
Really not as simple as that. Its like comparing an open fire with a log stove. Put 35% moisture logs on an open fire it will smolder and probably go out. Put it in a log stove and it will probably burn but badly. Put it in a gasification log stove and it will still burn badly as you cannot get to gasification temperature with wet wood it needs to be 20% or less.
 

Bloders

Member
Location
Ruabon
Really not as simple as that. Its like comparing an open fire with a log stove. Put 35% moisture logs on an open fire it will smolder and probably go out. Put it in a log stove and it will probably burn but badly. Put it in a gasification log stove and it will still burn badly as you cannot get to gasification temperature with wet wood it needs to be 20% or less.
ok, now im starting to understand. Interesting.
What is the gasification temp of wood?

As a side point, we have a Glenfarrow boiler, and i installed a temp probe to measure the flue temp - would this be a similar temperature, or on a gasification boiler, do you recover the exhuast heat somehow. I try and run our boiler as low a temp as possible over a longer period, thinking (maybe rightly, maybe wrongly) that less heat is going up the chimney and therefore it will be more efficient?
 
ok, now im starting to understand. Interesting.
What is the gasification temp of wood?

As a side point, we have a Glenfarrow boiler, and i installed a temp probe to measure the flue temp - would this be a similar temperature, or on a gasification boiler, do you recover the exhuast heat somehow. I try and run our boiler as low a temp as possible over a longer period, thinking (maybe rightly, maybe wrongly) that less heat is going up the chimney and therefore it will be more efficient?

You need a Buffer tank.

Burn hard and fast, get most efficiency then and less crap in tubes.
 

renewablejohn

Member
Location
lancs
ok, now im starting to understand. Interesting.
What is the gasification temp of wood?

As a side point, we have a Glenfarrow boiler, and i installed a temp probe to measure the flue temp - would this be a similar temperature, or on a gasification boiler, do you recover the exhuast heat somehow. I try and run our boiler as low a temp as possible over a longer period, thinking (maybe rightly, maybe wrongly) that less heat is going up the chimney and therefore it will be more efficient?
As stated above running hard for a shorter time is more efficient then idle over a long period.

This explains simply how a gasification boiler works and how high moisture content is the enemy.

 

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Man fined £300 for bonfire-related waste offences

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Written by William Kellett from Agriland

court-640x360.jpg
A man has pleaded guilty at Newtownards Magistrates’ Court to waste offences relating to a bonfire next to the electrical sub-station on the Circular Road in Newtownards, Co. Down.

Gareth Gill (51) of Abbot’s Walk, Newtownards pleaded guilty to two charges under the Waste and Contaminated Land (Northern Ireland) Order 1997, for which he was fined £150 each and ordered to pay a £15 offender’s levy

On June 25, 2018, PSNI officers went to Gill’s yard, where they found a large amount of waste consisting of scrap wood, pallets, carpet and underlay.

Discussion with Northern Ireland Environment Agency (NIEA) officers confirmed the site...
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