[Stoves] Saving the WBT

Fri Aug 16 23:02:16 CDT 2013

Ron,

One should look at a stove according to what it is designed to use as fuel.
Let us look, for example, at stoves that process rice hulls.

In a first instance, the stove might simply burn rice hulls. Here we are
talking about direct combustion where an air equivalency ratio situates
close to 1. Such a stove will produce a lot of CO2 and H2O as well as
relatively high levels of CO. The fuel for such a stove is rice hulls.

In a second instance, the air equivalency ratio might be 0.6, the process
temperature might be below 500 C, the moisture of the biomass might be 20%
or more, and too much secondary air might be applied to the combustion of a
dirty syngas containing a lot of CO2 and H2O. Since the production of CO
and H2 is suboptimal, it might make sense in this instance to burn the char
in order to maximize the production of energy. But unfortunately burning
the char has serious problems: a lot of CO is emitted by the stove, and
heat is generated far below the pot. If the char is burned within this
second stove, the fuel for such a stove is rice hulls.

In a third instance, the air equivalency ratio situates close to 0.3, the
process temperature rises above 800 C, the moisture content of the biomass
situates at 10%, and the supply of secondary air is kept low, but still
adequate, to achieve total combustion of the syngas. Here the production of
CO and H2 is optimized, the temperature of the syngas prior to combustion
at the burner reaches as high as 500 C, and not too much secondary air is
mixed in with the syngas. In this instance, up to 30% of the weight of the
rice hulls would still remain as biochar. But it would make no sense to
burn this biochar, since the production and combustion of the syngas were
optimized.

In measuring the performance of this third stove, we should not consider
rice hulls to be a fuel. This stove is designed to produce fuel from rice
hulls. The char produced is a by-product of a syngas-making process.
Therefore, the energy that remains within the char should be left out of
the equation in the calculation of the efficiency of this stove.

Propane (C3H8) is a by-product of natural gas processing and petroleum
refining. Likewise butane (C4H10) must be processed at a refinery. Propane
and butane can be mixed and burned in a stove. But in calculating the
efficiency of such a stove, no one takes into account the inefficiencies of
what takes place in the refining and bottling of these gases. Any
by-products created in the refining of propane and butane are left out of
the equation. Also one has to take into account the original hydrocarbons
from which propane and butane are derived, and the huge inefficiencies
associated with getting them out of the ground.

But unlike a propane/butane stove, a biochar-producing stove produces,
refines and burns gas all within the one process, and the by-product
created in this process, biochar, should be left out of the equation in
calculating stove efficiency.

But this biochar is not a worthless by-product. It sells for as much as
$500 per ton in the USA, and here where I live in Vietnam, it sells for up
to $400 per ton. Why would a poor farmer in Vietnam bother to buy biochar
and incorporate it into the soil season after season, if it did not have a
positive effect on plant growth? The sale of biochar just about always
covers the cost of buying and transporting the original biomass from which
it was derived. If this were not the case, those kiln operator in Vietnam
who simply make biochar while wasting all the gas would be out of business.

The many reasons why biochar sells for such high prices are explained in a
wonderful book by Lehmann and Joseph. A large number of scientists
contributed to this book and are cited within this book. They cannot be
dismissed as misguided in their understanding of the benefits of biochar.
Their science is as good as any science can get. And finally, if the
broader environmental concerns highlighted by the GACC relating to
greenhouse gas emissions are taken seriously, the burying of biochar into
the soil has an important contribution to make.

Many thanks.
Paul Olivier

On Sat, Aug 17, 2013 at 7:07 AM, Ronal W. Larson
<rongretlarson at comcast.net>wrote:

> Frank -  I am worried you haven't maybe been playing with TLUDs.  True?
>
> See below.
>
>
> On Aug 16, 2013, at 3:52 PM, Frank Shields <frank at compostlab.com> wrote:
>
> *Ron,*
> * *
> *I look forward to hearing Jim’s, or anyone else’s approach to the
> difficult problem of accounting for the energy. Whoever comes out with a
> method there will be another right around the corner. This is non-ending so
> there is no need to wait. My suggested approach is not a comparison – just
> a different way of looking at it. Hopefully one that will work without all
> the errors regarding calculating the remaining chars.*
>
>       [*RWL:    One measures, not calculates the "remaining chars".  Can
> be pretty accurate - especially with TLUDs.*
>
> **
> * *
> *I am thinking of a new approach where we do not need to handle char at
> all. I noticed when using the GEK and Tom Reeds TLUD that when fresh
> biomass ran out the secondary flame went out, or very poor flame. Just add
> more biomass and you are in business. *
>
>      *[RWL:  This is not normally done at all with TLUDs.  It is possible
> with BLDDs.*
>
>
> *Hot coals several inches below the pot did a poor job of heating the pot
> – so why even consider them? *
>
>       *[RWL:  Right.  One of the main purposes of TLUds is to stop the
> operation when the pyrolysis front hits the bottom.*
>
>
> *Its only the fresh tars that heat the pot and all that other energy just
> heats the stove body. Important to heat the stove body and aid in breaking
> the bonds to release lumps of tars and complex organics free to head to the
> secondary.  But IF (Big IF) they do not significantly heat the pot we can
> rule them out it saves that problem of all the difficult calculating. *
>
>      *[RWL:   If one purpose of the char was to make char, the
> measurement and calculating is relatively trivial.*
>
> * If you were to fill a rocket with char and blast air on the char would
> you get a secondary flame?*
>
>      *[RWL:  Yes.   This was demonstrated nicely at Stove camp by Kirk
> Harris, who had a special set of "intermediate" holes - so as to burn the
> chars nicely - from the top down.*
>
> * The stove body would get red hot but the pot only a few inches away
> would heat up slowly without the flames licking the bottom. Lots of useless
> heat.*
>
>     *[RWL:  Nope - Kirk had a nice flame.  His was a camping stove
> and not interested in producing char.  Very clever mod.*
>
> **
> * *
> *The question is can we take a block of wood and determine the weight
> fraction that will contribute to the secondary? And the fraction that sits
> and combusts in the stove body? I think the pipe will do that.*
> *   **[RWL:   It might do it if you could **reproduce all the stove
> operating temperature history.  Running at high power will expose the
> biomass/char to higher temps (and less char) than if the run was all at low
> power.]*
>
> *
> *
> *    Ron*
>
> * *
> *Something different to talk about.*
> * *
> *Thanks Ron for the reply.*
> * *
> *Regards*
> * *
> *Frank*
> *Frank Shields*
> *Control Laboratories; Inc.*
> *42 Hangar Way*
> *Watsonville, CA  95076*
> *(831) 724-5422 tel*
> *(831) 724-3188 fax*
> *frank at biocharlab.com*
> *www.controllabs.com*
> * *
> * *
> * *
> * *
> * *
> * *
> * *
> * *
> * *
> * *
> * *
> * *
> * *
> * *
> *From:* Stoves [mailto:stoves-bounces at lists.bioenergylists.org] *On
> Behalf Of *Ronal W. Larson
> *Sent:* Friday, August 16, 2013 1:27 PM
> *To:* Discussion of biomass cooking stoves
> *Subject:* Re: [Stoves] Saving the WBT****
> ** **
> Frank and list:****
> ** **
>     Abut 1.25 hours after yours was a message fem Jim Jeffords on a
> webinar.  He is obviously going to talk on Tuesday about how to handle
> remaining char when calculating efficiency.  It was not obvious to me how
> you are handling char in your example.  Could you give an example where the
> remaining char by weight was 25% of the input biomass weight.  Maybe 30%
> into the cook pot.   Or any numbers you want.  Then we can hopefully
> compare your approach with Jim's****
> ** **
> Ron****
> ** **
> ** **
> On Aug 16, 2013, at 12:12 PM, Frank Shields <frank at compostlab.com> wrote:*
> ***
>
>
> ****
> *Greetings Stovers,*****
> * *****
> *All this talk about the ocean water got me thinking about the Water
> Boiling Test.*****
> *I would like to suggest a new way of testing and reporting results:*****
> * *****
> *1)*  *Procedure*****
> *2)*  *Justification*****
> *3)*  *Calculations*****
> * *****
> *Procedure: We take some oven dried wood and place in a pipe. Add both
> end caps, loosen one, weigh and place in an oven at ~450c. Then cool and
> weigh. The loss in weight is the volatile fraction of the fuel. This is the
> fraction that provides the energy to boil water. We determine the energy of
> this fraction and that is the energy of the fuel. Keeping track of the fuel
> weight we use we determine the total usable volatile-energy.*****
> * *****
> *We put the pot of water on the stove, measure the temperature of the
> water, start the fire and monitor the water temperature. We keep the fire
> going until the water is at ‘simmer’ then keep steady for 30 min. Adding no
> more fuel we then we manipulate the fire to keep the secondary burn going
> as long as possible. Soon as the secondary burn goes out we pull the pot
> off and measure the area under the temperature plot for energy that went
> into the pot. Energy in the pot / volatile-energy X 100 is the
> efficiency(?).*****
> * *****
> *Justification: When you are boiling water it is only good as long as the
> secondary burn is going. When that goes out, even with a glowing stove
> below, the water heating process slows way down because, as I learned in
> Stove Camp, we need the heat forced hitting the bottom of the pot to stick
> to it, go through the pot and heat the water.*****
> * *****
> *Biomass fuel has two types of energy; 1) the tars (C-H-O) that create
> the secondary burn and 2) the chars (C-C) that only heat the stove body.
> Important for the chars to heat the stove body but there is more than
> enough with a good insulated stove and all that extra heat is wasted – not
> used to heat the pot. When biomass is heated between 300c to 450c tars of
> massive C-H-O structures go to the secondary burn and ALL C > CO2, and all
> H > H2O releasing massive energy just at the pot bottom. The C-C bonds
> (chars) left need to go C (solid) – CO volatile) forms releasing energy
> only in the stove body. The CO (volatile) goes to the secondary burn
> (adding to the energy of the tars) to go CO > CO2 releasing a relatively
> small amount of energy. Under the best of conditions all the C goes to CO
> (not CO2) in the stove body but this is such a small amount of energy
> compared to the tars providing ALL their energy to heat the pot I suggest
> we can ignore (or estimate) the CO > CO2 added energy.*****
> * *****
> *This being the case if we use only the volatile fraction as the total
> energy then once the secondary burn stops all the rest of the material in
> the stove body can be ignored.*****
> * *****
> *Calculations: A block of 100 g dried wood contains 44g C, 50g O and 6g
> H. Let’s say 22g C goes to the secondary as tars to heat the pot and 22g C
> left behind to heat the stove. This can be determined (if needed) in the
> lab measuring C and H in the biomass and C and H in the char left. The
> weight loss in the pipe contains 28.2 % carbon and 7.7 % hydrogen for the
> starting energy value figuring all H and all O are included in the tar
> fraction.*****
> * *****
> *Now we need to use Bond Energy (I need help) to determine the energy
> value we give for all the tar carbon going all the way to CO2 and the
> hydrogen going all the way to H2O. We sum the Bond Energies in the tars as
> the Total Energy of the fuel. Add to it (ignore or estimate) the Bond
> Energy of the CO to CO2 in the chars.*****
> * *****
> *Bond Energies:*****
> *C - - O = 360 kj/mol*****
> *H - - O = 366 kj/mol*****
> *What is C>CO2 and H>H2O?*****
> * *****
> *I realize if one has H2 and O2 that nothing happens until you provide
> enough energy (light a match) to break the H-H and O-O bonds to re-create
> H2O in an explosion. In this stove case there might be enough of the extra
> heat in the stove body to break apart the tars into C and H and O so we can
> just calculate them going completely to their end components.  *****
> * *****
> *Regards*****
> * *****
> *Frank*****
> * *****
> * *****
> *     *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> *  *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> * *****
> *Frank Shields*****
> *Control Laboratories; Inc.*****
> *42 Hangar Way*****
> *Watsonville, CA  95076*****
> *(831) 724-5422 tel*****
> *(831) 724-3188 fax*****
> *frank at compostlab.com*****
> *www.compostlab.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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