Kiln Heat Exchanger Advice

[hawthornheavyhorses]

Hi All,

 

Not been on here for a while, but hoping someone might be able to give me some advice.  I'm building a kiln from a small insulated container.  I have a heat source and fans, but am looking for a suitable heat exchanger for venting.

 

Is anyone able to point me in the direction of one that would be suitable for this sort of application?

 

Many thanks,

 

Matt

[Squaredy]

Most timber drying kilns I believe are of the heat vent design, which means they simply vent the hot air to the atmosphere.

 

Very wasteful I know, but when I looked into heat recovery in my kiln it would not have been financially viable to add retrospectively.  My kiln is out of use now, but when I did use it the hot wet air simply vented to the outside and cold fresh air was drawn in.

[hawthornheavyhorses]

 

15 hours ago, Squaredy said:

Most timber drying kilns I believe are of the heat vent design, which means they simply vent the hot air to the atmosphere.

 

Very wasteful I know, but when I looked into heat recovery in my kiln it would not have been financially viable to add retrospectively.  My kiln is out of use now, but when I did use it the hot wet air simply vented to the outside and cold fresh air was drawn in.

That's what I was going to do originally, but have read some promising things about heat recovery units, so might be worth the longer term investment if I can find one that is suitable.  Our firewood has always been produced/marketed as sustainably as possible, so this would also help keep those credentials.  Just need something that can cope with higher temperatures than a bog standard domestic unit. 

[openspaceman]

14 hours ago, Squaredy said:

Most timber drying kilns I believe are of the heat vent design, which means they simply vent the hot air to the atmosphere.

 

Very wasteful I know, but when I looked into heat recovery in my kiln it would not have been financially viable to add retrospectively.  My kiln is out of use now, but when I did use it the hot wet air simply vented to the outside and cold fresh air was drawn in.

That's right, all the time heat is cheap the extra capital cost is prohibitive unless done very cheaply. Also the higher the temperature of the kiln the more worthwhile it becomes,

 

Have a look at the simple plate heat exchangers that are in discarded condensing tumble driers. The thing about these is they recoup some of the latent energy in the warm saturated air which is significantly more than the energy in the hot air itself.

 

The trouble is the massflows of fresh air and exhaust vapour don't match so unless the kiln is hot and you have something you can use the lower grade heat for.. .

 

What may work would be the kiln inside a poly tunnel full of wood waiting to go into the kiln, so a modicum of dying from the larger massflow of the condenser heat exchanger is usable

[Woodworks]

On 04/10/2021 at 13:45, hawthornheavyhorses said:

Hi All,

 

Not been on here for a while, but hoping someone might be able to give me some advice.  I'm building a kiln from a small insulated container.  I have a heat source and fans, but am looking for a suitable heat exchanger for venting.

 

Is anyone able to point me in the direction of one that would be suitable for this sort of application?

 

Many thanks,

 

Matt

Some of the Pressvess retort users have a heat exchanger taking heat from the exhaust gases to dry wood. Think it is made be Pressvess 

[muttley9050]

 
That's what I was going to do originally, but have read some promising things about heat recovery units, so might be worth the longer term investment if I can find one that is suitable.  Our firewood has always been produced/marketed as sustainably as possible, so this would also help keep those credentials.  Just need something that can cope with higher temperatures than a bog standard domestic unit. 

In order to keep your firewood production and marketing "as sustainable as possible"
Air drying would be a better choice, most kilns are anything but.

[WINTERBOURNE]

If of interest we supply a wood gasification hot air blower that is often linked up for kiln drying.

Product like this obviate the need for a plate heat exchanger as with the use of spiral ducting it is the movement of hot air on a dry system.

There is a customer of ours who installed a 60Kw wood gasification hot air blower who has put some videos of this on YouTube for those interested.

 

Guy Winterbourne

Eco Angus Ltd

[Squaredy]

9 hours ago, WINTERBOURNE said:

If of interest we supply a wood gasification hot air blower that is often linked up for kiln drying.

Product like this obviate the need for a plate heat exchanger as with the use of spiral ducting it is the movement of hot air on a dry system.

There is a customer of ours who installed a 60Kw wood gasification hot air blower who has put some videos of this on YouTube for those interested.

 

Guy Winterbourne

Eco Angus Ltd

I don't get it. 

 

If you don't vent the hot wet air that will come off the logs how do you expect to remove any moisture?  Unless your customer has powerful dehumidifiers in the kiln which it doesn't look as if there are.

 

So if he vents the hot wet air he will lose a huge amount of heat, hence the question about heat exchangers.

 

[WINTERBOURNE]

This product must have seasoned wood less than 20% moisture content as it is a wood gasification log boiler.

You will only get the good gases being burnt off in the secondary burn chamber with dry wood.

If you burn wet wood you dry steam out of the wood, get a smoky burn and end up with pitch inside the heat exchanger tubes. 

Those customers use a small proportion of the dry wood produced from the kiln as the fuel for the boiler to dry all the wood in the kiln itself from one batch to another.

The airflow temperature is typically 120°C for kiln drying.

Our installer has fitted a number of these for kiln drying and there is lots of information on their web site about this product and application see   

Home | Emberair

WWW.EMBERAIR.CO.UK

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Hot Air Space and Process Heating | Ember air | United Kingdom

 

I hope that explains.

☺

Edited October 6, 2021 by WINTERBOURNE

[muttley9050]

This product must have seasoned wood less than 20% moisture content as it is a wood gasification log boiler.
You will only get the good gases being burnt off in the secondary burn chamber with dry wood.
If you burn wet wood you dry steam out of the wood, get a smoky burn and end up with pitch inside the heat exchanger tubes. 
Those customers use a small proportion of the dry wood produced from the kiln as the fuel for the boiler to dry all the wood in the kiln itself from one batch to another.
I hope that explains.
[emoji5]

I think you missed his point.