The efficiency of kiln drying firewood?

[Big J]

13 minutes ago, Squaredy said:

I agree with you in principal Jonathon, but the biggest difference that kiln drying makes from a business perspective is time and space, which of course equals money.

 

If you are selling £50.000 worth of firewood per year and do not kiln dry you will have to have space to store around 1000 full IBC cages in a well ventilated building, with good access all round so you can get to the oldest ones first.  Plus of course you will need to tie up a lot of capital in logs and processing time, hoping that you will be able to make a profit in two years and more.

 

In principal though I agree it is a shame to force dry when nature will do it for you.  What would solve the problem is if kilns could be made more efficient, and recover their heat.  Most large kilns simply vent their hot air to the atmosphere - just like a tumble drier - such a waste, but we haven't yet invented a practical alternative.  I am aware of heat recovery systems, but they are not really effective as far as I know on the scale we are talking about.  

 

 

 

2 minutes ago, gdh said:

I don't agree with the new regulations but I don't see kiln drying as a problem. From a personal point of view there's no way we could do the amount and quality we do consistently without it.

 

Looking at it economically it makes sense as well - using less than 10% of your lowest grade timber is a very good trade off to ensure you never run out, can dry in any conditions and only need a fifth of the storage.

 

Air drying obviously has benefits to, they're just different techniques to get similar results, it depends on the individual business which works best.

 

I agree with both you both as regards business sense, but it still comes down to creating a huge pile of co2 because our customers won't dry timber themselves. Perhaps like unnecessary plastic packaging at supermarkets, if the punters can be persuaded that the kiln drying of firewood increases the environmental cost of their firewood consumption, they'd maybe consider drying their own logs. I'm pretty sure that they'd be more open to that if it was explained that kiln drying increases the co2 footprint of their logs by 8-15 times.

[SbTVF]

I agree with you in principal Jonathon, but the biggest difference that kiln drying makes from a business perspective is time and space, which of course equals money.
 
If you are selling £50.000 worth of firewood per year and do not kiln dry you will have to have space to store around 1000 full IBC cages in a well ventilated building, with good access all round so you can get to the oldest ones first.  Plus of course you will need to tie up a lot of capital in logs and processing time, hoping that you will be able to make a profit in two years and more.
 
In principal though I agree it is a shame to force dry when nature will do it for you.  What would solve the problem is if kilns could be made more efficient, and recover their heat.  Most large kilns simply vent their hot air to the atmosphere - just like a tumble drier - such a waste, but we haven't yet invented a practical alternative.  I am aware of heat recovery systems, but they are not really effective as far as I know on the scale we are talking about.  
 
 

We looked at heat recovery, it only really works when temperatures are below 6° I think and even then it only would recover 10% of the energy lost. I'd rather dry in summer, the kiln runs better, less cold air to heat up and dryer timber to dry in the first place. Just not far enough ahead yet to fully do that.

[openspaceman]

10 minutes ago, Squaredy said:

What would solve the problem is if kilns could be made more efficient, and recover their heat.  Most large kilns simply vent their hot air to the atmosphere - just like a tumble drier - such a waste, but we haven't yet invented a practical alternative.  I am aware of heat recovery systems, but they are not really effective as far as I know on the scale we are talking about.  

I don't see the definition of "efficiency" in the context, we used to use the same terminology as is used for heat pumps, coefficient of performance, and that measure was the amount of heat necessary to remove a kg of water from the wood.

 

@Squaredy is right about the waste and it is true of much of when we burn fuels which is why there have been combined heat and power schemes over the years to attempt to address this.

 

Most of our fossil fuelled electricity comes from combined cycle gas turbines, these use the waste heat from  the jet to boil water to turn a turbine, and manage to gain 50% more power from the heat.

 

We could do similarly with kilns in that the hot moist air leaving a kiln at, say 40C, could still be used in an underfloor heating system  but it's a question of increased capital cost verses cheap heat. Given that a furnace is going to put out 1200C+ there is lots of scope for cascading heat when you are drying wood at less than 100C but the added complexity costs.

 

 

[openspaceman]

10 minutes ago, Big J said:

if the punters can be persuaded that the kiln drying of firewood increases the environmental cost of their firewood consumption, they'd maybe consider drying their own logs

More likely it will put them off buying logs

[Big J]

3 minutes ago, openspaceman said:

More likely it will put them off buying logs

Possibly, or possibly not if they realised how much cheaper it would be. 

[gdh]

24 minutes ago, Big J said:

 

 

I agree with both you both as regards business sense, but it still comes down to creating a huge pile of co2 because our customers won't dry timber themselves. Perhaps like unnecessary plastic packaging at supermarkets, if the punters can be persuaded that the kiln drying of firewood increases the environmental cost of their firewood consumption, they'd maybe consider drying their own logs. I'm pretty sure that they'd be more open to that if it was explained that kiln drying increases the co2 footprint of their logs by 8-15 times. 

Is the 8-15 times figure just an example or from somewhere? Electric use is the only big increase I can think of over air drying. Our electric bill is about £4k for 1200 tons by the way if you want to back work it.

 

It would be nice if everyone dried their own wood but in reality most don't have the space so I can't see it happening myself, I've never had any success selling fresh.

 

On a side note kiln dried (or any very dry wood) is a lot lighter to transport so we're able to deliver bigger loads in the pickup now.

[Big J]

6 hours ago, gdh said:

Is the 8-15 times figure just an example or from somewhere? Electric use is the only big increase I can think of over air drying. Our electric bill is about £4k for 1200 tons by the way if you want to back work it.

 

It would be nice if everyone dried their own wood but in reality most don't have the space so I can't see it happening myself, I've never had any success selling fresh.

 

On a side note kiln dried (or any very dry wood) is a lot lighter to transport so we're able to deliver bigger loads in the pickup now.

I worked out the carbon cost for the supply chain up to the timber arriving into the firewood retailers yard, then made the assumption that that cost would be replicated again for processing, handling and delivery of the logs. 

 

I then worked out the co2 output from burning the required quantity of wood to run the kiln and added it to the process cost up to that point. Your system running at about 10% is the best case I've heard of, and would represent a 7-8 times increase in the co2 output, per cubic metre when compared to air dried.

[Squaredy]

10 minutes ago, Big J said:

I worked out the carbon cost for the supply chain up to the timber arriving into the firewood retailers yard, then made the assumption that that cost would be replicated again for processing, handling and delivery of the logs. 

 

I then worked out the co2 output from burning the required quantity of wood to run the kiln and added it to the process cost up to that point. Your system running at about 10% is the best case I've heard of, and would represent a 7-8 times increase in the co2 output, per cubic metre when compared to air dried.

One more factor to remember.  Man made climate change is caused by burning fossil fuels not wood.  The most important factor is whether the wood fuel is sustainably sourced.  If it is then what is the problem?

 

 More of a concern is if we are burning wood from unknown sources and possibly causing deforestation.  In the UK this is unlikely but if the wood comes from overseas much more difficult to track.

[doobin]

7 minutes ago, Squaredy said:

One more factor to remember.  Man made climate change is caused by burning fossil fuels not wood.  The most important factor is whether the wood fuel is sustainably sourced.  If it is then what is the problem?

 

 More of a concern is if we are burning wood from unknown sources and possibly causing deforestation.  In the UK this is unlikely but if the wood comes from overseas much more difficult to track.

Lack of efficiency. If we're wasting five tons drying twenty five tons (or whatever Big J worked out), then that's five tons that has to be replaced by fossil fuels to meet total energy demand.

 

Mind you, if you go too far down the efficiency route then the logical soloution is central CHP plants in a town running on woodchip. Which they do a lot in Europe I believe.

 

Logs in the UK are a luxury product, that's all there really is to it. As for RHI- fucking criminal. There's a reason the NI government collapsed over it.

[openspaceman]

1 hour ago, doobin said:

Logs in the UK are a luxury product, that's all there really is to it

Too right mate