[Stoves] Burning wet wood

Thu Jun 13 22:52:03 CDT 2013

See comments below.

On Fri, Jun 14, 2013 at 8:50 AM, Kevin <kchisholm at ca.inter.net> wrote:

> **
> Dear Paul
>
> In the TLUD Process, if there was no combustion of char, then all the
> phytolythic silica would remain within the char remaining, and would
> probably be a minimal health threat. However, the reality is that some of
> the char will get fully combusted, releasing the silica as quartz,
> cristobalite, or tridamite, depending on the particular local
> "thermo-metallurgical conditions."
>

If channeling occurs in a TLUD, then temperatures rise to the point that
cristobalite can form. When channeling occurs, total combustion takes place
and the sides of the reactor turn red hot. But before this happens, one
begins to see (in my type of TLUD) burner holes that do not support a
flame. With a small fan adjustment and shake of the gasifier, the problem
is gone.

Also another nice thing about pellets is that they are not so easily
subject to channeling. It is hard to create a channel in the midst of
pellets of a high bulk density.

> Thus, you may, or may not, have a significant health problem associated
> with the biochar produced from RH "Starting Fuel."
>

Unlikely, under normal operating conditions within a TLUD gasifier
operating on a uniform biomass.
But it is highly likely in a direct combustion stove.

So my point is that direct combustion of fine biomass is not ideal. If we
gasify or pyrolyze in the context of a top-lit updraft or a bottom-lit
downdraft we've got a better device. No CO2 is formed at a big distance
from the pot, and the formation of cristobalite is minimized. If we go one
step further and use pellets as a fuel, then a lot less particulate matter
is emitted.

The comment that a TLUD gasifier on rice hulls is a one-trick pony leaves
me mystified. What does one say about all of the forms of biomass that I
have tried in my TLUD other than rice hulls. I cite two prime examples:
coffee husks and tobacco stems, both of which are uniform in grain size.
And neither of these two products were pelletized.

But I am convinced that pelleting is the way to go:

   - less channeling and therefore less CO2 in the syngas,
   - less channeling and therefore less exposure of the reactor wall to
   truly intense heat,
   - less particulate matter in the syngas,
   - a much smaller, lighter and more mobile stove,
   - pellets are much easier to transport and store, especially important
   in an urban setting,
   - batch times of as long as 4.5 hours with a reactor height of only 75
   cm,
   - batch times as long as 1.5 hour with a reactor height of only 25 cm,
   - it might even be possible to do away with a fan on the shortest
   version of the pellet gasifier.
   - if we shorten the reactor height and do away with a fan, the price of
   the gasifier drops by more than 50%.
   - at the same time, this stove will produce biochar in pelleted form,
   which in Vietnam commands a significant price.
   - pelleting makes it possible to use a broad range of fine biomass fuels
   that would be very difficult to combust.

Thanks.
Paul

>
> The additives I suggested for your consideration would be most aggressive
> toward the "exposed silica" that is most likely to be the hazard.
>
> Hope this helps. Any further questions, please let me know.
>
> Best wishes,
>
> Kevin
>
> ----- Original Message -----
> *From:* Paul Olivier <paul.olivier at esrla.com>
> *To:* Discussion of biomass cooking stoves<stoves at lists.bioenergylists.org>
> *Sent:* Thursday, June 13, 2013 10:28 PM
> *Subject:* Re: [Stoves] Burning wet wood
>
>   Kevin,
>
> But why directly combust biomass containing amorphous silica?
> Why not use it as fuel in a TLUD where the temperature is well below that
> needed for cristobalite formation.
> At normal TLUD temperatures, cristobalite is not formed.
> The silica remains amorphous and is found back in the biochar.
> If the biochar is incorporated into the soil, the silica can eventually be
> taken up by plants.
>  The silica came from the soil, and now it goes back to the soil.
> Simple. No?
>
> Paul Olivier
>
>
> On Fri, Jun 14, 2013 at 7:57 AM, Kevin <kchisholm at ca.inter.net> wrote:
>
>> **
>> Dear Paul
>>
>> To comment on your important question:
>> "How would cristobalite formation be avoided in a direct combustion unit
>> processing a biomass that has an appreciable content of amorphous silica?
>> ",
>> I would suggest for your consideration the possibility of adding alkaline
>> earths or metals to the rice husks, with a view to forming harmless
>> silicate compounds.
>>
>> 1: The first one I would try is Ca(OH)2, or "Hydrated lime". It might
>> have "binding characteristics" that would enable you to produce a pellet or
>> "Rice Hull Aggregate" if some sort, but on combustion, the CaO would
>> certainly react with the SiO2, to produce "Calcium Silicate" of some sort,
>> having the generalized formula "XCaO.YSiO2" This would tend to produce a pH
>> neutral ash. Or, it might also yield an ash with cementatious properties.
>>
>> 2: Another approach you might try is to add a Sodium or Calcium Bentonite
>> Clay to the RH fuel, firstly to act as a "binder/aggregator", and then to
>> act as a "Silica Getter" during combustion.
>>
>> 3: You might even try sodium carbonate, as a 'silica reactant. "
>>
>> 4: Iron Oxide has a strong affinity for silica also. If you have a 'high
>> iron clay", it might also be worth a try.
>>
>> Note that these are not necessarily "simple suggestions." Too much of the
>> alkalis may cause clinkering. Significant experimentation may be required.
>>
>> Best wishes,
>>
>> Kevin
>>
>>
>>
>>  ----- Original Message -----
>> *From:* Paul Olivier <paul.olivier at esrla.com>
>> *To:* Discussion of biomass cooking stoves<stoves at lists.bioenergylists.org>
>>  *Sent:* Thursday, June 13, 2013 9:21 PM
>> *Subject:* Re: [Stoves] Burning wet wood
>>
>>   Crispin,
>>
>> My point of departure is a top-lit, updraft gasifier that makes biochar.
>> Everything that I have written previously has to be understood in this
>> light. This could be contrasted with a direct combustion unit, but this was
>> not my point at all. But direct combustion units do not have a very great
>> appeal among the Vietnamese.
>>
>> I do not think that I could interest very many households in Vietnam to
>> switch from bottled gas to a biomass fuel if I were to ask them to directly
>> combust biomass in their kitchens. Most Vietnamese might not make a lot of
>> money per month, but they are sharp, intelligent and enterprising. They see
>> direct combustion units associated with poverty. They are not attracted to
>> handling a messy biomass of a low bulk density, and there is also a strong
>> social resistance even against handling loose rice hulls. This is
>> especially true in an urban setting.
>>
>> Rice is a major export item for Vietnam, and it is grown on over 80% of
>> the agricultural land in Vietnam. Therefore, Vietnam produces a lot of rice
>> hulls. In the highland areas where rice is not grown, we find coffee husks.
>> So for the Vietnamese, there are these two readily available fuels. We also
>> see rice hulls or coffee husks in many other Asian countries. Now let me
>> pose the following question to you.
>>
>> Do you think that you could build a small direct combustion unit that
>> would handle loose rice hulls and loose coffee husks as neatly and cleanly
>> as a TLUD? I have seen many people who try to burn these two waste
>> products, but there is always a lot of smoke. The coffee husk is especially
>> nasty to combust. When burned, it emits a strong, black, pungent smoke. I
>> would insist that this direct combustion unit for rice hulls and coffee
>> husks not emit a whiff of visible smoke at any time during its entire
>> operation.
>>
>> Finally I must caution that the direct combustion of rice hulls is not
>> ideal, since the ash might easily contain cristobalite. How would
>> cristobalite formation be avoided in a direct combustion unit processing a
>> biomass that has an appreciable content of amorphous silica?
>>
>> Thanks.
>> Paul
>>
>>
>> On Thu, Jun 13, 2013 at 8:29 PM, Crispin Pemberton-Pigott <
>> crispinpigott at gmail.com> wrote:
>>
>>>  Dear Paul O****
>>>
>>> ****
>>>
>>> I am not sure why you think I am opposing the preparation of fuels. You
>>> have mentioned it perhaps a dozen times in your last message as if it is
>>> something I oppose. Because I have no idea why you think I oppose fuel
>>> preparation – an essential part of most combustion I will address this
>>> point.****
>>>
>>> ****
>>>
>>> Let me set the record straight so you do not waste any more time telling
>>> me that I oppose fuel preparation.****
>>>
>>> ****
>>>
>>> I fully agree that fuels need to be prepared. All fuels should be
>>> prepared in some way – either tree branches cut to length for transport or
>>> split to promote faster drying, chopping in certain cases or turning it
>>> into pellets or briquettes for certain applications.****
>>>
>>> ****
>>>
>>> I not only fully agree with coal preparation, I have researched the
>>> correct size that the raw coal should be in order to perform well in
>>> certain ultra-low emissions stoves. The answer is a 10 to 15 g pellet with
>>> well rounded edges so that it flows well under gravity without shaking or
>>> vibration. This can be done with high volatiles coal without adding any
>>> binder merely by getting the moisture and pressure of formation correct.
>>> This was researched in South Africa by Prof Horsfall (Shell Coal Chair,
>>> Wits Univ, JHB) and our fellow list member Prof Philip Lloyd. Briquetting
>>> raw coal is an excellent way to deal with the difficult of lowering
>>> emissions from very low priced stoves.****
>>>
>>> ****
>>>
>>> What does not work well at all, proven over and over, is making
>>> semi-coked briquettes and trying to promote that to households as a
>>> domestic fuel. This product, which is nearly useless for cooking, is
>>> promoted over and over as a ‘clean coal’ product. Time and again users find
>>> it is very hard to light, requires a much larger fire to remain alight,
>>> must be refuelled much sooner than unprocessed coal and is three times the
>>> price required the whole industry to be subsidised. It does not ‘burn
>>> cleaner’, it makes as much PM to light and makes more CO. To burn it
>>> correctly it has to be reduced to the same optimal size and manufactured
>>> with the volatiles intact so it can burn properly.****
>>>
>>> ****
>>>
>>> *>*If you say "dirty coal" to someone in the industry, they will
>>> understand exactly what you mean.****
>>>
>>> They will point to a coal their combustor cannot burn.****
>>>
>>> Obviously there are coals from the edge of the field that are very
>>> difficult to burn at all. In fact they call it ‘burned’ coal, meaning
>>> deteriorated. I was involved slightly in the exploration of the Transkei
>>> coal fields near MacClear in the early 80’s working with Heinemann whose
>>> PhD thesis describes the field well. The edges of the deposits will not
>>> burn in a domestic stove. That product is suited to >20 kW institutional
>>> stoves that are never turned off. In short, the device is tuned to the fuel.
>>> ****
>>>
>>> >Every body in the trade can tell you what a bad coal is, and they
>>> usually have a good idea of what is needed to prepare it into a good coal
>>> for a specific purpose. There are almost no coals coming out of the ground
>>> that must not be prepared.****
>>>
>>> ****
>>>
>>> I am ‘in the trade’ and I think there is far too much ‘old boy
>>> understanding’ of what a good or bad coal is. The best coal I have even
>>> worked with is from Nalaikh mine: 25% moisture, 50% volatiles, 0.2%
>>> Sulphur. This qualifies in the old school methods as a terrible, dirty, bad
>>> coal.****
>>>
>>> ****
>>>
>>> It is one of the cleanest burning fuels available – but not when put
>>> into a badly made copy of a Russian wood stove. It is really hard to
>>> produce clinkers with it (high ash fusion temperature) and is very easy to
>>> light. It will work in a TLUD or cross draft or downdraft stove and burn
>>> clean enough to take the PM out of the ambient air. Show me a power station
>>> running ‘clean good coal’ that will do that. The stoves being promoted had
>>> lower CO per MJ than a new Eskom power station, lower PM and of course a
>>> much greater system efficiency than using electricity.****
>>>
>>> ****
>>>
>>> >But, Crispin, just about all coal must be prepared. Also there is
>>> extensive blending going on. Combustors generally are not designed to
>>> handle everything.****
>>>
>>> ****
>>>
>>> That is correct – combustors are designed to handle particular fuels.
>>> Fuels are prepared for particular combustors. We all know this. When fuels
>>> are not matched to the stove or vice versa, it is not true that the fuels
>>> are ‘dirty’. That is my point. In the wrong stove, biomass is a ‘dirty
>>> smoky fuel’. At a ProBEC conference once there was a lady who was just dead
>>> set against anyone burning wood because it was ‘a smoky fuel’.  It did not
>>> occur to her that there were more options than an open fire.****
>>>
>>> ****
>>>
>>> >Yes, but please do not tell me the South Africans do not do extensive
>>> coal preparation. ****
>>>
>>> ****
>>>
>>> That is why I said nothing about that. I am not sure where you are
>>> coming from. Coal is always prepared, usually by sizing.****
>>>
>>> ****
>>>
>>> >Yes, there are power stations designed to burn coal of a 40% ash. But
>>> often they have little choice in doing so. ****
>>>
>>> ****
>>>
>>> Correct. They design burners to go with the fuel. Until then, the fuel
>>> is ‘bad’ – is that correct? Then it becomes ‘good’?****
>>>
>>> ****
>>>
>>>   >>Imagine trying to design a biomass stove that was tuned to each
>>> type of fuel that happened to be available…oh wait…that is exactly what is
>>> happening on this list! What a surprise, again. Is that not exactly what
>>> you are doing?****
>>>
>>>  >Not at all. That is precisely what I am opposing. ****
>>>
>>> ****
>>>
>>> What exactly are you opposing? It is not at all clear. Are you opposing
>>> stoves that can burn unprocessed fuels? Are you opposing stoves that only
>>> burn one fuel?****
>>>
>>> ****
>>>
>>> >Crispin, I challenge you to put coconut powder or fine sawdust into
>>> the best TLUD that you can design. ****
>>>
>>> ****
>>>
>>> Why would I try to burn fine sawdust in a TLUD? There is nothing magical
>>> about a TLUD. There are plenty of bad TLUD’s. Fine sawdust burns perfectly
>>> well in a blown burner and there is a very fine ceramics factory in Malawi
>>> that uses such a burner – two of them actually. Just because a fuel doesn’t
>>> burn well in a TLUD does not mean the fuel is ‘bad’ or ‘dirty’.****
>>>
>>> ****
>>>
>>> >Then tell me if air is going to flow up through this fine biomass in a
>>> uniform manner. ****
>>>
>>> ****
>>>
>>> It is not going to, that is why a TLUD is not suitable for burning that
>>> fuel. Use something more appropriate.****
>>>
>>> ****
>>>
>>> >Tell me that there will be minimal CO2 present in the outgoing syngas.
>>> ****
>>>
>>> ****
>>>
>>> Why should we have to produce syngas? Is this based on the idea that
>>> only a TLUD gasifier can burn cleanly??****
>>>
>>> ****
>>>
>>> >Also the device you design has to be small and easy to use. It cannot
>>> occupy an entire corner of your kitchen, and no part of it should be
>>> situated outdoors. Go for it.****
>>>
>>> ****
>>>
>>> That’s silly. I will choose my own design criteria, thank you very much.
>>> The challenge is to burn a fuel properly in a way convenient to the user.
>>> ****
>>>
>>> ****
>>>
>>> >However, if we pelletize the coconut dusk or the wood shaving, air
>>> flows up through it in a uniform manner, and we have an incredibly simple
>>> reactor that weighs less than 1.2 kg. It can be in continuous operation for
>>> up to 1.5 hours.****
>>>
>>> ****
>>>
>>> That is one solution. Go for it. See if people want to buy it. If they
>>> do, you have a winner. If it tests well, I will promote it. Testing will
>>> include user acceptance, emissions and durability, cost and controllability.
>>> ****
>>>
>>> ****
>>>
>>> >Ok, then show me a TLUD operating on loose coconut dust or fine
>>> sawdust. ****
>>>
>>> ****
>>>
>>> Why would I bother trying to burn in in a TLUD? They are batch loaded.
>>> They are hard to control, they can’t really be turned off.  A TLUD is very
>>> finicky about the fuel – in fact the fuel can be considered a significant
>>> part of the stove. Fuel preparation is so onerous that when we tried late
>>> last year to talk about ‘improved stoves’ in Central Java, the group of
>>> women immediately, loudly and without prompting, told us firmly that we
>>> should *not* bring to them any stove that required extensive fuel
>>> preparation, “especially chopping wood into small pieces”. They were simply
>>> *not* willing to do that, they said.****
>>>
>>> ****
>>>
>>> It seems someone had been there before us.****
>>>
>>> ****
>>>
>>> >There should be relatively little CO2 in the syngas****
>>>
>>> ****
>>>
>>> Why make syngas? Why not just burn the fuel? This gasifier thing is
>>> getting out of hand. We are not trying to supply town gas we are trying to
>>> cook. If you don’t separate the fire from the fuel many problems are
>>> eliminated. Close-coupled semi-gasifiers avoid all sorts of problems for
>>> this reason.****
>>>
>>> ****
>>>
>>> >It should also make a uniform biochar. ****
>>>
>>> ****
>>>
>>> What on earth for? Having collected all the fuel and dried it, with
>>> effort, and handled it into the stove, why would I not burn it? The
>>> economic argument about char in the soil may well be shown, in future, to
>>> be valid. Until then it is arm waving. If char helps soil, make a reactor
>>> that is smokeless and make it at scale. Cheaply, locally, and apply it
>>> without transporting to the kitchen and back. In your special
>>> circumstances, which are hardly universal, you have a local market – go for
>>> it. Don’t advertise it for people for whom it is completely inappropriate.
>>> ****
>>>
>>> ****
>>>
>>>   >>We do not focus enough on how to design good stoves and hope that
>>> preparing the fuel will compensate for our collective ignorance. ****
>>>
>>>  >No, but we can make things infinitely complicated and expensive if we
>>> do not prepare fuels correctly. ****
>>>
>>> ****
>>>
>>> So, prepare the fuels. Nothing wrong with that if people are willing to
>>> do it.****
>>>
>>> ****
>>>
>>> >Ok, then put Mongolian coal, of a 30% moisture content and of all
>>> shapes and sizes, into a TLUD, and tell me if you are going to get a
>>> beautiful flame with no CO2 formation in the synas. ****
>>>
>>> ****
>>>
>>> You are mixing two things: a decent burn and gas production. No
>>> Mongolian is trying to make syngas in a TLUD. I doubt they know what the
>>> term ‘TLUD’ means, 99% of the TLUD users. It is just a stove. It burns “Mongolian
>>> coal, of a 30% moisture content and of all shapes and sizes” and they
>>> do it hundreds of thousands of times a day. Emissions are down more than
>>> 90% against the baseline. If they would prepare the fuel into small round
>>> briquettes, PM would drop another order of magnitude. Is there any other
>>> project that has a) as many TLUD’s promoted? As much reduction in the local
>>> environmental PM? As much an advance over the baseline? As little
>>> attention? ****
>>>
>>> ****
>>>
>>> >The TLUD works superbly on both rice hulls and coffee husk because
>>> these materials are uniform and generally do not require preparation. When
>>> hulled, coffee cherries and rice hulls are at a 12% moisture, and air flows
>>> up through them within the reactor in a uniform manner. ****
>>>
>>> So what you are saying is that when the fuel is perfectly prepared, it
>>> happens to work well with a particular type or types of TLUD. How is this
>>> going to assist us all? We cannot prepare all the fuels available so they
>>> will suit a certain burning technology. The technology is much easier to
>>> change than 99% of the fuels.****
>>>
>>> >I venture to say the TLUD will work well on most types of irregular
>>> biomass provided they are properly prepared. This measn that the one stove
>>> could handle almost any type of properly prepared biomass.****
>>>
>>> An approach specifically and heartily rejected by our target audience.
>>> They are drowning in biomass and they are not interested in a) paying for
>>> fuel and b) preparing it to fit what someone happens to be making as a
>>> combustor. Far easier to change the combustor. Develop once. Buy once,
>>> problem solved. ****
>>>
>>> That is my point.****
>>>
>>> Regards
>>> Crispin****
>>>
>>> ****
>>>
>>> _______________________________________________
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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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>
>
> --
> 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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-- 
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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