Since my post about pyrolyzing biomass stoves, I’ve been trying to understand how the Lucia Stove works. A lot of the pyrolyzing stoves are “TLUDs” (Top Lit Updraft). My understanding was that TLUDs really only work well in batch mode, while the Lucia Stove promises that more fuel can be added during a burn run. Unfortunately the WorldStove site and YouTube Videos contain just enough information to confuse me, so I went digging around the Stoves Mailing list and finally found what I was looking for, in an explanation by Nat Mulcahy to some questions posed by Clement Davis.
I’m reproducing it here to make it easier to find in the future. I’ve also cleaned up some of the formatting.
nataniele at aim.com
Wed Feb 11 09:42:31 CST 2009
Thanks for the great questions. I’ll do my best to answer them all; if you are like me the more I learn about anything the more I want to ask, so please do not hesitate to ask if more question arise.
I’ll try to answer in order:
1. “Please explain ‘coaxial gasification'”
Coaxial Gasification differs from stratified gasification normally found in Imbert, TLUD (Tom and Paul), or Downdraft type gasifiers. In traditional gasifiers, either from top to bottom or bottom to top you find a series of layers (the order of which vary based on design) but usually include Fuel, Flaming Combustion (Reed) or Combustion, Drying, Pyrolisis, Reduction, Oxidation, and Ash. These are the “solid components”, and then there are the gaseous zones which also vary from gasifier to gasifier. In the case of Kelly or Cross Draft, the zones at times could be defined as partial spheres but still have the various components.
The layering in a LuciaStove differs in that the same elements are present but that they are arranged in a coaxial fashion. Combustion occurs in a much reduced form, and only on the outer most perimeter of the top of the combustion chamber. The Pyrolysis zone occurs in a central vertical column (which because of a series of controlled vortexes, also acts as the filter and cyclone) and all the rest happens in a very thin outer cylindrical shell just below the combustion ring.
The primary advantages of the LuciaStove in Coaxial Gasification mode are: improved emissions, more surplus gas can be produced per unit of feedstock, fuel can be added at any time, does not have to be a closed chamber, adjustable flame, more complete combustion of fuel, and can deal with changing fuel size and type during operation with no adjustments.
In the Pyrolytic Mode of operation there is only combustion of the feedstock during the first 40 seconds or so of operation, after that any feedstock in the chamber or added to the chamber is simply pyrolysed by the heated inert gases, and the char produced never gets a chance to combust.
The Primary Advantages of the LuciaStove in Pyrolytic mode are: Controlled char production with out the need for quenching, controllable char qualities (Ph, pore size, etc), even lower emissions because the char is used as a filter.
2. “Is the stove drawing gas from the combustion chamber into the gap to meet the incoming 2nd air?”
Yes, the lower part of the chamber is designed in such a way that gases are extracted and no air can enter the combustion chamber if not from the top.
3. “Can you confirm the type of blower used to provide the forced air (cfm+watts)?”
The LuciaStove can work with almost any blower or fan and in some applications it works without a fan. The cfm is not as critical so long as pressure differences are maintained. All fans have both flow vs pressure curve and the pressure point is a critical parameter for the function of the LuciaStove.
4. “Is the blower the muffin fan from an old computer?”
While the LuciaStove if often built using muffin fans, the blower used in the demonstration was a cross flow or tangential fan used in our pellet stove, wood stove, and fireplace insert applications.
5. “During the demonstration was the Luciastove running in gasification, pyrolysis or coaxial mode?”
During the demonstration at ETHOS, the LuciaStove was running in Coaxial Gasification mode.
6. Is there a need to “change parts” to make this stove run in different modes?
No, there is not a need to change parts. All LuciaStoves can function in either mode; it takes some practice which is why we offer training classes for groups that do humanitarian work.
7. “Was there any fuel added during the run?”
Boy howdy was there, a veritable cornucopia of feedstock options to the delight or any pyromaniac or stover! Thanks to Paul and Charlie we had all sorts of nifty different things to toss in, including, bark, wood chunks, pellets, small branches, even snow-soaked pellet mash as we ran out of fuel the top notch stuff.
8. “Was there any smoke during startup or refuelling?”
Yes, during start up, it takes about 40 seconds for the LuciaStove to become “smokeless” after that, an experienced operator can maintain indefinite smokeless operation.
Thanks for the super questions and a special thanks to Mark, Angie and Andy for putting together such a wonderful conference.
Thus endeth the lesson.