[Stoves] Insulation and stove life

Fri Jun 14 19:09:40 CDT 2013

Kevin,

You write: *Rice Hulls are very interesting. While they have a high
percentage of highly siliceous ash, complete combustion could potentially
make the ash available in a hazardous manner.  In Paul O's case, where he
is interested in char making, I would guess that most of the siliceous
components would remain embedded within the char particles, in a safe and
non-hazardous manner. However, some ash particles would be liberated in
that some of the char would be burned in the pyrolysis process.*

If, in a TLUD, air does not flow up the reactor in a uniform manner,
channeling occurs, and zones that are incredibly hot are created. If the
biomass contains amorphous silica, some of this silica will surely be
converted into cristobalite at such high temperatures. When this mixture of
biochar and ash containing cristobalite is removed from the reactor and
handled, it would be so easy for the operator to breathe this deadly
mixture.

The possibility of channeling is minimized if the biomass is thoroughly
uniform. Also in the design of the stove, one has to be careful that the
fan is not too powerful. Turning up a powerful fan a bit too high will
cause channeling.

Also rice hulls from most mills that I have seen in Vietnam are not
properly dedusted. Consequently there is always some particulate matter in
the syngas. This particulate matter might also contain cristobalite.

One simple way to solve these two problems is to use a pelleted fuel. Here
the flow of air will be perfectly uniform. The pellet is relatively heavy
and is not easily displaced within the reactor by a powerful fan. Also the
pellet does not have much dust associated with it.

So as you see, I have been working for several years on a unit to gasify
loose rice hulls. But in the last few weeks I have begun to have serious
doubts about the safety of such an apparatus. I feel strongly that the rice
hull should be pelleted if it is to be used safely within a stove.

Also please do not think about directly combusting any form of biomass that
contains appreciable amounts of amorphous silica. For example, burning rice
hull pellets is not a very good idea. And yet sadly, this is what is
happening to most rice hull pellets in Vietnam. Imagine the poor workers
who handle this ash.

Thanks.
Paul Olivier

On Sat, Jun 15, 2013 at 1:01 AM, Kevin <kchisholm at ca.inter.net> wrote:

> **
> Dear Crispin
>
> Thanks very much for your helpful comments.
>
> Clearly, a chimney that vents products of combustion outside the Living
> Space is advantageous, compared to a stove system that vents into the
> Living Space.
>
> I was aware of the great importance of the size of the Particulate Matter.
> Basically, "big dirt particles" are not nearly as bad as are fine particles
> that can lodge deep in the lungs. Clearly also, "more bad-sized particles",
> with "bad type composition", are worse than fewer "safer sized particles",
> of "relatively neutral composition.
>
> The only way to "digitize the generalities" is with a scientifically sound
> test program that identifies and then measures the relevant parameters.
> Once numbers have been attached to the relevant parameters, then it is
> relatively easy to determine whether or not a given stove system is "safe"
> or "hazardous."
>
> Rice Hulls are very interesting. While they have a high percentage of
> highly siliceous ash, complete combustion could potentially make the ash
> available in a hazardous manner.  In Paul O's case, where he is interested
> in char making, I would guess that most of the siliceous components would
> remain embedded within the char particles, in a safe and non-hazardous
> manner. However, some ash particles would be liberated in that some of the
> char would be burned in the pyrolysis process.
>
> Best wishes,
>
> Kevin
>
> ----- Original Message -----
>
> *From:* Crispin Pemberton-Pigott <crispinpigott at gmail.com>
> *To:* 'Discussion of biomass cooking stoves'<stoves at lists.bioenergylists.org>
> *Sent:* Friday, June 14, 2013 10:51 AM
> *Subject:* Re: [Stoves] Insulation and stove life
>
>  Dear Kevin****
>
> ** **
>
> I would like to add that using a fan will in all likelihood create much
> more flyash than without one. The advantage of a chimney is that the tends
> to suck the ash up the chimney, whereas a fan tends to blow it up from
> below into whatever outlet it can find. The difference in the room will be
> large, obviously.****
>
> ** **
>
> Secondly the size of the PM matters a lot. If the pyrolysis process
> releases very fine siliceous matter with a gentle push from a fan, that
> material can easily rise through the fuel bed.****
>
> ** **
>
> So we should be investigating size, total mass, chemical composition and
> whether the stove draws it from the stove and room or pushes it up from
> below.****
>
> ** **
>
> Maybe it is of no consequence at all, maybe it is a hazard.****
>
> ** **
>
> Regards
> Crispin****
>
> ** **
>
> ** **
>
> ** **
>
> Dear Rebecca****
>
>  ****
>
> Firstly, I am concerned about the "Cristobalite Link" below, in that it
> seems to overlap "silica", "cristobalite", and other forms of quartz. See:
> http://www.quartzpage.de/gen_mod.html showing how various forms of quartz
> exist at various temperatures.****
>
> Note that "cristobalite" is one specific crystalline phase of quartz.****
>
>  ****
>
> Secondly, what is important is the "respirable" dust that is actually
> respired. ****
>
>  ****
>
> It is well known that respiring "silica dust" can cause "Silicosis". It is
> well known that "Small Particulate Matter emissions" from virtually any
> poor stove can cause serious health problems. Hence, the effort to design
> "stove systems" that minimize "Small Particulate Matter Emissions" into the
> living space, where they can potentially be respired.****
>
>  ****
>
> Rice Hull Ash, even at 90% silica in the ash pit, is not a problem, in
> that it is in the ash pit, where it is not respired. On the other hand, an
> "apparently superior fuel" that only had say 25% silica content in the ash
> pit would be vastly more hazardous, if it vented 10 or 100 times as much
> ash into the living space, in respirable form.****
>
>  ****
>
> This is where competent and meaningful stove design and testing comes into
> play. ****
>
>  ****
>
> As has been said many times, "It is not so much the fuel, but the stove
> system design, that is good or bad."****
>
>  ****
>
> Best wishes,****
>
>  ****
>
> Kevin****
>
>  ****
>
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-- 
Paul A. Olivier PhD
26/5 Phu Dong Thien Vuong
Dalat
Vietnam

Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
http://www.esrla.com/
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