From: John Seed

To: biochar@yahoogroups.com

Sent: Thursday, October 23, 2008 4:32 AM

Subject: Fw: [biochar] low cost/tech clean charcoal

 



 

----- Original Message -----

From: Paul Taylor

 

John:  The important goals are to produce char:

1. with good conversion quality of feedstock to char
2. cleanly in terms of ghg and visual and environmental pollution
3. efficiently in terms of utilization of waste heat
4. low tech, low cost, replicable design
5. others such as quality of char

As I see it the conversation with Sean seemed to be moving in divergent directions: you would like to consume the waste heat towards charring the feedstock, whereas Sean is concerned to get a clean burn such as in a TLUD.  Below I tried to recapture my original post aimed at clarifying that, and ended up thinking out loud.
-----------
In my understanding of method Sean was describing, TLUD, the primary air for pyrolysis is drawn in the bottom of the drum and supports pyrolysis which starts at the top of the drum and progresses downwards as the material is charred.  The air flow is limited to avoid burning char at or above the pyrolysis zone.  Ample secondary air is admitted at the top of the barrel to flame the off-gasses in the chimney.  In this method the energy for pyrolysis comes from the feedstock, and the off-gasses are fully flamed.  Energy from the secondary burning can be captured and utilized in any number of ways from simple hot water, hot tub, heating, drying or processing around the home or farm.  In a more high tech development they could be converted to electricity using thermoelectrics.  

This two stage process gives two burning zones of different temperatures with separate control over the limited O2 needed for charring and the ample O2 needed for flaming, but with some drop in efficiency of char output due to some C being used to drive pyrolysis.  In fact I understand conversion efficiency seems to be limited to about 20%.  Trying to combine the two functions can lead to compromise and loss of efficiency in other ways.  My earlier innovation was to draw off the off-gas and bring it into the bottom of the barrel. The fuel in the off-gasses would then burn at the pyrolysis front and save some C from the feedstock.  The problem is to recirculate the off-gas down past the drum (this could be via a jacket which warms the inner drum) and reinject it at the bottom with the right amount of fresh air to support pyrolysis.  The immediate concern is some of the off-gasses require a higher temperature to oxidize and I don’t know how one could preferentially vent and flame those.

An alternative would be to fully flame the off-gasses in the normal TLUD process but to exchange the heat produced into the kiln drum, example by clean burning the off-gasses below and around the drum.  This seems to be more or less what you are looking for, and moves in the direction of cooking the wood.  The simple version is a Folke Günther double drum kiln. In my preliminary understanding the process is initiated by building a fire in the outer drum, which then drives off wood gasses from wood in the inner drum through holes which feed the fire in the outer drum.  With enough air supply and a bit if canny design this should result in complete combustion, and limited extra fuel to initiate the reaction.  

I can think of an interesting idea involving a triplet of nested drums.  The inner drum, open at the top, contains the batch of feedstock. The intermediate drum, open at the bottom carries the off-gassing to the outer drum, open at the top.  The bottom of the outer drum has an air feed and it is mounted by a chimney.  Once pyrolysis is proceeding the off-gassing feeds a fire in the outer drum, which provides heat for the pyrolysis.  The problem is starting the pyrolysis.  If necessary one could use a two stage process so that the smaller primary stage would be started with less fuel and could ignite the secondary stage.  In fact the primary stage could be a TLUD since these are efficient to start and clean burning, and the secondary stage could be a perforated drum of feedstock in the “chimney” of the primary.  I think conversion efficiencies of 40% might be achieved in some version of this.

I am sure all this is part of the art for those skilled in it. I do see that with the grant, and some care in remaining flexible in our initial design, there could be considerable room for innovation.  In short I agree that we should pursue innovation in the area of low tech recycling of the flame off heat to the pyrolysis, since recycling it into hot water etc is a known art.

Paul

On 10/22/08 2:18 AM, "John Seed" <johnseed1@ozemail.com.au> wrote:

Hi Paul, thats right, if you could usefully use the heat, then less of a problem flaring the gasses in the flue rather than using them to power the pyrolysis. I see this as "plan b" however, a fall back if we can't figure out a low tech way to reliably get enough oxygen to the pyrolysis exhaust gasses while they're still in a place to power the reaction. Do you agree?

for the Earth

John

----- Original Message -----
 
From:  Paul  Taylor <mailto:potaylor@bigpond.com>  
 
To: John Seed <mailto:johnseed1@ozemail.com.au>  
 
Sent: Tuesday, October 21, 2008 8:49  AM
 
Subject: Re: [biochar] low cost/tech  clean charcoal
 

John:  This recommendation comes back to the TLUD  stoves. A low tech addition to such a stove would be to use the heat generated  in the chimney for hot water, a welcome hot tub, home heating, farm process  heat, or - higher tech – refrigeration or using thermoelectrics to generate  electricity.  Does any of this fit with your chosen method?  In the  long run mainstream application it is easy to see how the excess energy can be  retrieved/used in one form or another, and it would be nice to illustrate a  low tech version of that from the beginning

Paul


On 10/20/08  1:57 PM, "Sean K. Barry" <sean.barry@juno.com>  wrote:

 

 


Hi John,
 
A  barrel with holes in the bottom of it, that is "cooked" (if you will allow  this description) over another open flame will have the gases from the  heated internal contents of the barrel ejecting out in the places where it  is easiest to get out.  This would be (possible, only) out through the  holes at the bottom.  Getting oxygen supplied, past the heating flames,  to the gases that are ejecting from the bottom of the barrel would be the  trick.  It will fan the flames of the heating fire and leave little  oxygen to combust the gases.  The off gases, too, being ejected this  way flow counter to the natural draught of the heat.
 
I would  suggest primary air inlet holes around the outside bottom of the barrel, a  chimney above a conical top for the barrel, and secondary air inlet holes  (with more cross-section area than the primary inlets) around the base of  the chimney, bottom of the cone top, or top outside rim of the barrel.   The draught will suck air in through both the primary inlet holes and  the secondary inlet holes (more through the secondary inlets).   Providing primary air to the pyrolizing biomass inside the barrel will  actually produce more solid charcoal byproduct, less liquids, and (depending  on the amount of primary air) more gases as reaction products.   Insulate the barrel (and chimney if you can) with refractory brick or  other high temperature insulation, then make sure that there are flames  inside the chimney and this will assure that most all of the flammable off  gases are being burned before they exit the chimney.
 
The main flaws in the type of design I suggest would be more complete combustion of  the raw biomass (meaning lower charcoal yield) and significant loss of what  might be otherwise useful energy in the form of lost heat (up the  chimney).
 
Regards,
 
SKB
 

----- Original Message -----  
 
From: John Seed <mailto:johnseed1@ozemail.com.au>   
 
To: biochar@yahoogroups.com  
 
Sent: Thursday, October 16, 2008 4:01   AM
 
Subject: Re: [biochar] low cost/tech   clean charcoal
 

 
 

   
Hi  Sean,

 
 
you wrote: <<The important  issue to achieve this performance (no or little  release of GHGs) is  to provide sufficient secondary air to mix with the off  gases  exiting from the pyrolysis reaction  vessel.>>

 
 
I'm wondering whether you could  do this with a  single 44 by surrounding it with brick or clay  insulation so that most of   the escaping heat goes up a chimney  and then somehow use that heat to  drive a fan pushing air under the  44 to make sure that there's enough oxygen  to burn all the gasses  exiting the drum there?

 
 
for the Earth

 
 
John

 
 
 
 
 

----- Original Message -----  
 
From: Sean K.  Barry <mailto:sean.barry@juno.com>   
 
To: biochar@yahoogroups.com  
 
Sent: Thursday, October 16, 2008 12:55   AM
 
Subject: Re: [biochar] low cost/tech   clean charcoal
 

 
 

   
 
Hi John,
 
 
 
I  appreciate your concern.  However, I think that you doing useful   experiments using biochar in your garden may be worth making some  charcoal  however you see fit to do it.  Folke's barrel within  a barrel retort is  one possibility.  It may or may not  entirely burn the off gases.   I can't say that I really know  that it does or doesn't either way, without  testing this somehow.   I just understand the desired  performance.
 
 
 
The important issue to  achieve this performance (no or little release  of GHGs) is to  provide sufficient secondary air to mix with the off gases  exiting  from the pyrolysis reaction vessel.  This would be something   like several larger holes around the top of the outside barrel,  more and  larger holes than at the  bottom.
 
 
 
TLUD stoves also have large  secondary air entry vents at the base of  the chimney.  THe  draught created in the chimney serves to "suck in"  this secondary  air.  It also pulls air in the bottom holes.  This  is  why you would want smaller and fewer holes at the bottom than at the top   (or base of the  chimney).
 
 
 
Pyrolysis reactions go  through different "energy input vs output"  phases during the rise  in temperature.  From ambient temperature up to  about  250-300C, the reaction is said to be endothermic.  This means it   needs a continuous input of heat from an external source in order  to  continue its rise in temperature.  Once the pyrolysis  reaction has  begun to expel gases, the reaction becomes  exothermic.  It generates  enough heat to be self sustaining,  even without the application of external  heat.  The only  input need is a limited oxygen supply, not heat.   If too much  oxygen is supplied, then the biomass will burst into flames and   combustion will be occurring.  Really, it is just more  complete  combustion and more heat is  generated.
 
 
 
As the fuel in the biomass  "burns" during combustion, gases, liquids,  and solids are all  being expelled from the feedstock very vigorously.   Things  are literally exploding off the surfaces that are engulfed in   flames.  Where the temperatures are high enough and there is  sufficient  oxygen that has not already been consumed, then fuel  combines with oxygen  and generates more heat.  But,  throughout this vigorous production of  energy and expelling of  matter, some things fly through places without  enough oxygen or  without enough heat and they do not combust.  This is  the  smoke, the tars, and the gases.  Even large roaring fires don't   burn everything.  It there is smoke then there is fire, but  the smoke  is evidence that some things have not burned.  It  there is heat, but no  smoke, then there is still fire, and it is  more complete combustion.
 
 
 
The same is  true of gases, liquids, and solids exiting from a pyrolysis   reactor.  More fuels exit, too, because the oxygen supply is  being  limited.  Oxygen is supplied just enough to sustain the  reaction,  but there is no explosive combustion occurring.   So, gases once vented  from the reactor need two things to be  "completely combusted", more oxygen  and enough heat to ignite the  combustion.  If the oxygen near the  bottom is being limited,  then that cannot be the secondary source of  oxygen.  A true  second input of oxygen is required and it cannot go to  the  pyrolyzing biomass inside the reactor vessel.  It has to mix with   the escaping producer gas.  Then this mixture needs to be   ignited.  If there is no flame above the reactor or in the  chimney  above the reactor, if there is "blue smoke", then the  gases, vaporized  liquids, and particulate solids are being  "liberated" without being  consumed.  This is when Methane-CH4  can be  vented.
 
 
 
Regards,
 
 
 
SKB
 
 

----- Original Message -----  
 
From: John Seed <mailto:johnseed1@ozemail.com.au>   
 
To: biochar@yahoogroups.com   
 
Sent: Wednesday, October 15, 2008   3:29 AM
 
Subject: Re: [biochar] low cost/tech   clean charcoal
 

 
 

   
Hi Sean, thanks for the further   clarification.

 
 
I'd like to make  some  biochar to start  conducting trials in my garden and orchard. However, I  don't  want to do so if this means releasing methane.

 
 
The descriptions I've seen of  Top-Lift-Updraft (such  as at http://terrapreta.bioenergylists.org/taxonomy/term/89  ) appear  to ensure that there is enough oxygen to burn the  methane etc but at the  cost of wasting the heat as these gases  burn in the chimney.  

 
 
What I like about burning these gasses  beneath   the drum in which the charcoal is being made, (if I   understand this correctly) is that if the drum is well  insulated, the  burning gasses could provide enough heat to drive  the whole process (once  burning wood has heated the drum and  contents sufficiently to begin  expelling the gasses in the first  place). So, less fuel would need to be  burned to drive the  pyrolysis and less CO2 produced.

 
 
However, as you say, you'd need to design the  thing  so that there was always enough oxygen being sucked into the space   below the drum to ensure that all the gasses  combusted.

 
 
Problem is, how would you know that there  were no  uncombusted gasses escaping without expensive testing   equipment?

 
 
Of course if you had a way of utilising the  heat  coming out from the Top-Lift-Updraft stove  because you were   cooking and charcoal was just a byproduct  or some other  way of  making the heat do some work, that might give an  efficient  solution.

 
 
John Seed

 
 
 

----- Original Message -----  
 
From: Sean  K. Barry <mailto:sean.barry@juno.com>   
 
To: biochar@yahoogroups.com   
 
Sent: Wednesday, October 15, 2008   1:16 AM
 
Subject: Re: [biochar] low   cost/tech clean  charcoal
 

 
 

   
 
Hi  John,

 
 
See my comments to this post  below.

 
 
 

Thanks so much  for that clear reply concerning the chemistry of  pyrolysis  
Sean.  SKB: You're welcome.  I hope it  was  not too technical or confusing.

If I make charcoal   using a sealed 44 gallon drum with holes in the bottom to  
allow the  gasses to escape but little oxygen to enter and  a fire underneath,  
then will all the escaping methane  necessarily be consumed?   SKB: This is kind of hard to  answer.  It depends greatly  upon the amount of oxygen  available and the amount of fuel be vented  from the 44 gallon  drum.  Secondary combustion is not complete if  there is  not sufficient oxygen.  When you say there is a fire   underneath, there is consumption of oxygen occurring right  there where  the holes are.  I suppose that if you see  jets of flame shooting  out of the holes in the bottom of the  drum that you could assume that at  least some of the offgas is  also being consumed.  But, if there is  not enough oxygen  left after the fire below consumes the oxygen, then  some of  the fuel gases (H2, CO, CH4) will exit hot and leave the area   where ignition is still possible before there is sufficient  oxygen for  it to burn.  


If you think  about a fire made of wood, there are times when  there are lots  of flame, but right in the middle of the flame there  still  sits some unburned wood.  That is fuel, too, like the gases   H2, CO, and CH4.  That wood "sitting" inside the flames  just has  not burned yet.  There is not enough oxygen  there yet to burn  it.   In fact, sometimes over a  campfire, for instance, you  can shove a dry stick right into a  flame and pull it back out, over and  over again, roasting  marshmellows.  It doesn't burn.  This is  basically  because inside the flame, there is not enough oxygen or enough   time at the ignition temperature, or both, for consumption to   occur.

You wrote that <<Pyrolytic reactions  do not  emit Sulfur Oxides-SOx, Nitrogen
Oxides-NOx  (specifically NO, NO2,  NO3), nor Nitrous Oxide-N2O. The only  of
these which is a GHG is  N2O. The temperatures of  pyrolysis, 400C to 600C,
are just not hot  enough to form  these compounds>>

Given that there's no way  to  control the temperature using this method and
that the   temperature is going to rise above 600C, will N2O be   produced?
SKB: N2O is produced via a completely other   pathway, involving the nitrification/de-nitrification cycle in  soil  amended with nitrogen fertilizers.  Temperatures for  NOx are still  higher than what can be achieved with low oxygen  flow and at atmospheric  pressure, like that occurring in the  kind of pyrolysis reaction you are  using.  If the  pressures were substantially higher or the  temperatures like  those inside the flame front of a gasoline burn at  11:1  compression inside an internal combustion engine (I'm guessing   here, but maybe 1500C+, then concern over generating NOx might  be  warranted.

You wrote <<The most  significant  problems creating "non-clean" GHG emissions  
from a pyrolysis  reaction done in a low cost/low tech  reactor/kiln would be
to NOT  BURN (or FLARE) any  Methane-CH4 exiting from the reactor or to be so   
inefficient as to release more carbon in the "producer  gas" (as CO,  CO2, or
CH4) than is left in the charcoal  by-product. The main  reason not releasing
Methane-CH4 is  that it is such a potent GHG. It  is 23 times more potent  
than CO2 in the  atmosphere.>>

Assuming that  the methane necessarily  flares in the woodfire beneath the 44,  
what would be any other  factors that might make this  process <<be so
inefficient as to  release more  carbon in the "producer gas" (as CO, CO2, or
CH4) than  is  left in the charcoal by-product.>>  SKB: I  think  it is difficult to determine that the Methane necessarily flares   in the woodfire beneath.  Have you heard of the terms  "rich" and  "lean" with regard to how an internal combustion  engine is  running?  "Rich" means there is more oxygen  being supplied to the  combustion zone than is required to  completely burn the fuel.   "Lean" means the opposite, so  some fuel exits the engine unburnt.   Many modern engines  in automobiles have what are called Lambda sensors  (or oxygen  sensors)  These device sense the amount of oxygen left  in  that exhaust stream that is exiting the engine.  If there is   excess oxygen, then the air/fuel ratio (the lambda) can be  adjusted  up.  If there is more oxygen, then the air/fuel  ratio can be  adjusted down.  This way the engine can  automatically regulate the  efficiency of the combustion  process.


With your "sealed"  44 gallon drum  that only has holes  in the bottom of it, there is no draught  and no independent secondary  air entry point.  All of the  oxygen that is used for the fir below,  the flaming pyrolyis  within, and the consumption of the exiting offgases  enters  from below the barrel.  Unless you have this barrel elevated   and are blowing air or oxygen directly at the bottom, then I  suspect  there is not sufficient oxygen coming in to consume  all of the wood in  the fire below plus the exiting off gases.   However, I am not there  to measure the gas inflows and  outflows.

I guess I'm  wondering if there's any way  to make this low tech method so
that I  can feel assured  that what I'm doing is greenhouse friendly?   SKB: The  short answer would be I don't know.  Low tech  might be  workable if the design of the reactor/kiln , with air in flows   and gas out flows are all known or well understood.  Some  make  claims that Top-Lit-Updraft (TLUD), or stratified  air-blown, downdraft  reactors "work better".  But "work  better" is a subjective term,  work better at producing gas is  not the same thing as work better at not  emitting GHGs.   Work better at generating usable heat is not the  same  thing as work better at producing more charcoal.  I suppose it   is possible that some people with excellent educations and  experience at  thermodynamis and the biochemistry of wood  combustion could specify as  design for a low-tech solution for  a kiln that produces a high yield of  charcoal and vents little  or no GHGs, but I do not know of one which has  been proven.   The techniques for analysis and/or the equipment   required to sufficiently analyze any particular design are  likely not  entirely LOW-EXPENSE/LOW-TECH.


I  read a lot about this particular topic from people who  maybe  could know this stuff, People like Tom Reed and Aqua Das from the   Biomass Energy Foundation (see woodgas.com).  But,  honetsly, I  can't say that I know enough about this yet to  beable to say what kind  of kiln/reactor/retort design will do  what you are asking.   I'm still just learning and  struggling with how to do this   myself.


Regards,


SKB


 
 



thanks

John
 
 


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