Henson Center Fiure Burner System; Was: Re: [Stoves] improving charcoal stoves

[Kevin Chisholm]

Dear Paul

----- Original Message ----- 
From: "Paul S. Anderson" <psanders at ilstu.edu>
To: "Dean Still" <dstill at epud.net>
Cc: "'Stoves-List'" <stoves at listserv.repp.org>
Sent: Monday, May 29, 2006 2:35 AM
Subject: Re: [Stoves] improving charcoal stoves


> Dean and all, (especially Tom Reed who is asked for comments below)
>
> Dean's comments, questions and concerns make a lot of sense.  Here are 
> some
> thoughts:
>
> 1.  From what I have seen of charcoal cooking in American backyard cooking 
> and
> around the world, flame (the burning of the CO and any lingering 
> hydrocarbons)
> is not sought, and seems to be intentionally avoided.  I doubt that 
> devices or
> methods to burn the CO from a typical charcoal cookfire will be found or, 
> if
> found, be acceptable for cooking practices.

The Henson Centerfire Burner System is a new and innovative burning 
technique that Lanny discovered. It potentially opens the door for burning 
the CO evolved from charcoal burning. If burning the CO is more important 
than "present acceptable cooking practise", then it can potentially solve 
the CO problem. If cooks and stove designers don't want to change and make 
use of the new combustion tool that Lanny presented to the List, then they 
would appear to be saying "We don't want any changes from what we are doing 
now." The classic charcoal barbeque gives a highly desired cooking effect, 
and if this desired cooking effect is of paramount importance, then CO, and 
particulate matter considerations are of minor concern. Stick with the 
conventional barbeque, in this case.
>
> 2.  Successful clean burning of charcoal IS accomplished during the final
> (post-pyrolysis) stage of using Reed's WoodGas CampStove, the first of the
> T-LUD devices.  In that device, there is forced air both for primary and
> secondary combustion.  Tom can get a nice blue flame in that situation 
> where
> there is only char fuel, and no raw biomass.  Reasons are (I believe) that 
> the
> forced primary air will assure a goodly supply of combustible gases 
> (including
> some H2 and maybe methane as well as CO), and the forced secondary air 
> assures
> mixing of new (with O2) air into those hot and highly combustible gases.

The key to the T-LUD seems to be "forced air". The wonderful thing with the 
Henson Center Fire Burner System is that it introduces primary and secondary 
air to the combustion front with the least possible pressure drop. There is 
virtually zero pressure drop through the fuel bed. This inherently means 
that the Henson Center Fire Burner System has the potential for complete 
combustion with the least possible requirement for external draft 
assistance, from fan or stack height effects.
>
> 3.  The day I first met Tom Reed (about April or May 2001), he had a 
> prototype
> IDD (now called T-LUD) gasifier stove that had a feature that is not in 
> the
> commercially produced WoodGas CampStove.

Just for the record, Lanny presented his observations on the discovery of 
the Henson Center Fire Burner System to he Stoves List on 12 May, 2006. 
There is a lot of work to be done to fully understand the concept, and to 
find ways to make best use of the phenomenon.

 That early stove had a little cover
> or slider or "door-like" control so that Tom could direct a different 
> amount of
> the total air to the primary or to the secondary pathways, depending on 
> whether
> the stove was in the pyrolysis stage or in the char-burning stage.  Tom 
> said
> that the ratio of primary to secondary air was almost inverted between the 
> two
> stages.  Tom can give the exact numbers for the units of air, but I think 
> it
> was 1 primary to 5 secondary during pyrolysis stage and 4 primary to 1
> secondary during the charcoal burning stage.  5 x 4 = 20, so there are 
> some
> serious changes going on.

Lanny probably hasn't had time yet to find ways to optimize methods for 
controlling the primary and secondary air flows.
>
> And a question for Tom:  Is the primary to secondary air ratio during the 
> char
> burning stage different if (A) there is modest air flow yielding simple 
> char
> burning to make CO2 and H2O down near the level of the char bed, or if (B)
> there is more forceful air flow resulting in active gasification that 
> makes CO
> and H2 come from the char bed and available for subsequent combustion? 
> (See #5
> below for more explanation about char combustion vs char gasification with
> close-coupled combustion.)

It will be very interesting to see Lanny's future results from work such as 
this. The Hensen Center Fire Burner System is quite different from the T-LUD 
and other previous burning systems, in that it does not require flow of air 
streams through the fuel bed.
>
> 4.  Lanny's experiments (central open core with charcoal around, right?)

The essence of the Henson Center Fire Burner system is the empty central 
core up through a surrounding bed of fuel. Its operation is not confiuned to 
the use of charcoal fuel.

> reminded me of Richard Stanley's holey briquettes, of which I have made 
> and
> burned many.  I think a key to success is that an appropriate amount of 
> air was
> constrained to a small, fast rising column of air with "fanning impact" on 
> the
> char closest to the air.  That is how the holey briquettes do such a great 
> job
> of burning vigorously, but not all at once.

I would suggest that there are totally different mechanisms at play. 
Richard's holey briquettes are an excellent way to increase the effective 
surface of the fuel, to promote easy drying, and to promote combustion, but 
they make use of air flows through the fuel bed. The Henson Center Fire 
Burner System has most of the air flow, primary and secondary, outside the 
fuel bed.

  Main difference is that Lanny's
> charcoal had some air spaces among the char pieces while Richard's 
> briquettes
> are solid (except for the central hole) and have raw biomass.   And I 
> suspect
> that Lanny's char could shift and fall some as the pieces get smaller, but
> Richard's had to drop off the ash from the central hole while the rest of 
> the
> briquette stayed in place, but with an ever increasing diameter of the 
> central
> air shaft.

Richard's Holey Briquette System, and the Henson Center Fire System are 
totally different. In the Henson Center Fire Burner System, products of 
combustion can leave the system without being compelled to contact unburned 
fuel, and/or without having to provide for draft loss because of extra 
pressure drop requirements resulting from gas flow through the fuel bed.
>
> 5.  Increased natural draft through a constricted channel acts like forced 
> air
> as in Reed's WoodGas unit.  And that is also similar to the use of a tin 
> can to
> hold the charcoal together when lighting a barbeque, and similar to a 
> forge with
> a bellows to push air onto the hot charcoal.

In the Henson Center Fire Burner System, there is no need for forced draft, 
and the gases do not flow through the fuel bed. Big differences.

  In all cases, a
> respectable amount
> of air hits a relatively small area of charcoal, resulting in 
> significantly
> increased heat of the char, giving exothermic combustion to yield CO2 + 
> H20, or
> gasification (some endothermic reactions also) to yield CO and H2.

In the Henson Center Fire Burner System, products of combustion from one 
level are not forced through the fuel bed at another level. There is a very 
much reduced tendancy for these "endothermic back reactions", and a much 
greater potential for "exothermic complete reactions."
>
> 6.  The gasification process of char works best (perhaps even requires) 
> when
> there is a layer of char (carbon) above the hot zones, so that the CO2 can 
> be
> changed (reduced) into CO.  (It is more complicated than that, but I am 
> not one
> to quote the full equations.)

If you already have the CO burned to CO2, why would you want to convert it 
back to CO and then go to the trouble of re-burning it??

Therefore, a thin layer of large diameter
> charcoal in the bottom of a typical charcoal grill is NOT going to 
> generate the
> quality combustible gases that are made in the Reed T-LUD gasifier (with 
> many
> layers of smaller diameter charcoal), or the Hanson stack of charcoal
> lumps/briquettes.

Combustion mechanisms in a charcoal grille, the Reed T-LUD and the Henson 
Center Fire Burner System are very different.

> the char,
> with the stack being sufficiently SMALL in cross-section so that the
> appropriate amount of air (which will determine the combustion rate) is 
> not
> spread thinly, but is concentrated onto a relatively small amount of the 
> char. HOWEVER, with this heat coming out of a relatively small exit, it is 
> not
> condusive to grilling a burger or skewers of anticuchos (Andean meat 
> cooking
> done on charcoal embers), and could give a hot spot on the bottom of a 
> pot.

The Henson Center Fire Burner System Concept is 17 days old, as we speak. 
Imagine what Lanny could do with a few months of work on his concept. Would 
you perhaps know where Lanny could get some Grant Money so that he could 
devote more time to this work?
>
> Personally, I would prefer to NOT have a better charcoal stove because 
> that
> would encourage people to use and therefore make more charcoal, which is 
> very
> wasteful of the pyrolysis gas-energy, causes polluting, and drives 
> deforesting
> to get large chunks of wood to make charcoal.

A lot of people use charcoal as their "accepted cooking practise." The 
Henson Center Fire Burner System seems to work equally well on both charcoal 
and raw biomass feed.

  On the other hand, if a T-LUD
> stove was used to make the charcoal, the picture of the negative impacts
> changes dramatically.  But even then, why use charcoal stoves if a good 
> T-LUD
> could let urban dwellers use dry biomass without the energy wastes, the
> polluting, and deforesting (because T-LUDs use small pieces of wood from
> sustainable forest practices, or non-wood biomass fuels.)

The "Big Picture Issue" is cooking, and the best way to get the job done. 
The Henson Center Fire Burner System seems capable of using charcoal, wood 
chips, twigs, forest trash, grasses, and waste biomass of all forms, BUT 
with no need for forced draft, and with reduced need for natural draft, 
because gases do not have to flow through the fuel bed.

 In that "ideal
> world" [  ;-)  ], the char produced by the T-LUD could be permanently
> sequestered in the soil (soil building) and CDM carbon credits could be 
> paid
> for the Carbon not sent back to the atmosphere.     NOTE:  If you want to 
> reply
> to THIS paragraph, please change the Subject line of your message to 
> "T-LUD
> stove claims" or some other clear Subject line.

In that this is the Stoves List, discussions on producing charcoal for 
burial are perhaps better conducted elsewhere.
>
> But I will help you make a better charcoal burning stove.
>
What do you think of ther potential for the Henson Center Fire Burner System 
to make a better charcoal burning stove?

Best wishes,

Kevin