[Stoves] Torrified Pellets

Sun May 24 14:13:42 CDT 2015

Dear Alex

The major reason to torrefy wood seems to be that it stops absorbing moisture (mostly) and it weighs less per MJ. The EU is importing a lot of pellets on this basis. The UK has a power station fired by them.

Regards

Crispin

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of alex english
Sent: Sunday, May 24, 2015 14:18
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Torrified Pellets

Torrified wood has most of it's volatiles.  I would expect the gases to have a higher CV and wider range of flame stability when used in a premix burner. Just guessing this has no relevance to cooking stoves.
Dean, what is the range, cat pee best to worst PM emissions, that you have measured from any and all tluds when burning dry wood pellets?
Alex

On 2015-05-24 1:53 PM, "Dean Still" <deankstill at gmail.com <mailto:deankstill at gmail.com> > wrote:

Dear Ronald,

Thanks for your helpful comments. Charcoal without remaining wood in it doesn't make smoke but, of course, wood really likes to smoke. With biomass the preparation including recipe, drying, pellet size, etc. makes a big difference in emissions when trying to get down to the very low levels needed to protect health. I'm making some torrified pellets and will report back after testing under the hood.

All Best,

Dean

On Sat, May 23, 2015 at 3:52 PM, Ronald Hongsermeier <rwhongser at web.de <mailto:rwhongser at web.de> > wrote:

Dear Dean,
I may seem like I'm harping here, but now that you've said a bit more, you've mentioned a couple of factors that I have noticed in my limited experience without a hood and therefore without concrete parametric analysis, but for which I can give some postulates.

1. The wood-gas stove in design mode depends on a uniform fuel "chunk-size" which promotes a level "pyrolysis" front(planar) migrating towards the bottom of the stove. If that plane is broken by dis-uniformity in the fuel or overly large gaps between the fuel pieces, you will get a spot drop in temperature along with glowing fuel which will migrate unevenly towards the bottom of the stove, breaking the pyrolysis front and sometimes dropping the mean temp inside the burning chamber such that the rising wood gas will no longer be close enough to critical temp that the onset of 2nd-ary air will ignite it.

2. 1. would be consistent with the bark observation. Bark generally has lots more minerals and less energy per unit mass. Did you/they assure dryness level of the bark? Were the pieces between (cross-section/10-20) of the stoves throat? Do you mean pellets from eucalyptus wood or when eucalyptus oil is poured on the fuel? Off the shelf kerosin burners here in germany are strictly regulated as to what you may or may not burn in them. If it is smoking it is either wrong fuel, design flaw or user error.

3. Pellets pack closely, so if they are smoking, usually the problem can be fixed by either turning up the fan a bit or putting some chimney length between the secondary air and the pan to increase the draw. (i.e., the primary air is probably not of sufficient pressure to deliver enough O2 to the pyrolysis front to keep it hot enough such that it will ignite upon contact with the secondary air.)

4. Because torrefied pellets are partially reacted, they may be somewhat less dense and especially because the ends will be cleaner, they may not resist airflow as much, which may help somewhat with 3. above. I would expect them to act very similar to dry pellets, except for the difference in density.

regards,
Ronald von Aftermidnighttimeforantibiotics (and bed)

On 23.05.2015 23:49, Dean Still wrote:

Dear Ron, 

We had three women interns here at the research center for a summer who found cleaner burning recipes for the TLUDs gathered from the surrounding forest. Some things like bark make smoke, etc.

Many pellets smoke when using eucalyptus, etc. Different mixtures of kerosene make more or less smoke in off the shelf stoves.

I'm wondering if torrified pellets will burn cleaner than normal pellets.

Best,

Dean

On Sat, May 23, 2015 at 1:28 PM, Ronald Hongsermeier <rwhongser at web.de <mailto:rwhongser at web.de> > wrote:

Hi Dean,
I remember that there was a proposed university program (W. Virginia or the Carolinas??) In view of the deaths(not _many_ but tragic) that have taken place due to off-loading of pellets at some European ports (CO in the hold) The torrefaction could lead to a more inert fuel. That's hopeful speculation on my part however. You would be transporting some less bound water and the energy density is better than regular pellets in addition to the lack of liquid or vapor H2O absorption issue mentioned before-- these would lend efficiencies in the logistics end of things and an even more uniform fuel than regular pellets, which tend to absorb quite a  bit of water here in the damp winter weather...
I have to admit that I'm a bit puzzled as to what you mean by cleaner fuel recipes. What specific pollutant are you interested in or are you talking about particulate?
If you aren't choking the burn by putting the pot too close, you should be getting a very clean burn with a TLUD?!?

regards,
Ron

On 23.05.2015 22:01, Dean Still wrote:

Hi Ronald, 

I'll keep looking. I think that we shouldn't forget cleaner fuel recipes as part of the solution. 

Best,

Dean

On Sat, May 23, 2015 at 12:33 PM, Ronald Hongsermeier <rwhongser at web.de <mailto:rwhongser at web.de> > wrote:

Hi Dean,
I did some searching around on the internet several years ago on this topic.
I'd like to try torrefied stuff as well, but I struck out at that time.
No idea where to find them.
The main advantage that I picked up on at that time was that they should be relatively inert as to picking up extra water after they were pelletized.
Cleaner burning than what?
clean burning is a control issue, not a fuel issue as far as I understand. If I understand the concept correctly, it's like using part of the large molecules initially broken out (cracked) by the heat in the reaction vessel to coat the surfaces of the remaining unpyrolized material. This should burn quite okay in a TLUD.

regards,
Ronald von Nasennebenhöhlenhölle (but I'm coming back)

On 23.05.2015 20:56, Dean Still wrote:

Hi All, 

I'd like to try torrified pellets in a TLUD under the emissions hood.

Any ideas on where to find them?

Or if it should be cleaner burning?

Best,

Dean

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