[Stoves] Understanding TLUDs, MPF and more. (was Re: Bangladesh TLUD )

[Paul Anderson]

Scott,         (Third of 3 replies to about a dozen messages on this 
topic.  Not in any special order.  I thank everyone for their comments.)

Very nice explanation.   (a definition would probably be shorter). Only 
one suggested correction.   You wrote in first sentence:
> while producing combustible energy. 
Should be     while producing combustible gases.        When the gases 
burn then you have the release of energy.

The comments sent by Kirk Harris (in a later message) are also highly 
appropriate for some changes.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype:   paultlud    Phone: +1-309-452-7072
Website:  www.drtlud.com

On 12/10/2017 10:33 AM, Scott Zager wrote:
>
> Dear stovers:
>
> The recent discussion inspired me to amend a working definition I have 
> been writing for a glossary on biochar.  I was hoping that perhaps 
> more experienced stovers would be willing to review my definition of a 
> TLUD.  I would appreciate any comments for revision.  Thank you.
>
> P.S. I am trying to define a “Retort” next.
>
> *TLUD (top-lit, up-draft) Pyrolyzer*: TLUD gasifiers automatically 
> make char while producing combustible energy. A TLUD is basically a 
> canister filled with biomass to create a “fuel bed”.  TLUDs are either 
> batch-fed or continuously-fed, biomass gasifiers that are loaded with 
> a feedstock (biomass in the form of wood chips, pellets, briquettes, 
> etc.).  Air enters the canister through holes in a grate at the bottom 
> of the cylinder.  The fuel bed is ignited on top, burning some of the 
> volatile gases to generate the heat needed to gasify un-pyrolyzed 
> feedstock.  The ignition front travels down through the fuel by heat 
> radiating into the raw fuel, which dries it and initiates 
> thermochemical conversion of the feedstock into char and wood-gas. The 
> "ignition front" is actually a pyrolysis reaction within the canister 
> that moves through the feedstock, in what is called a "Migratory 
> Pyrolytic Front" (MPF).  The ignition front is maintained by air 
> (i.e., primary air) that enters the bottom of the cylinder.  Residual 
> char is left on top of the fuel bed as the MPF moves downward. The MPF 
> creates a draft for primary air, which can be also supplemented and 
> controlled by forced air pushed inward from fans. When the MPF reaches 
> the bottom of the cylinder, the smoke-producing reaction is complete, 
> and pyrolysis ends.  At this point the char is removed from the 
> cylinder.  If the char is not removed, it may burn slowly from the 
> bottom up unless the fire is snuffed out by the lack of oxygen. During 
> pyrolysis, volatile gasses in the form of white smoke (wood-gas) 
> dissipate upwards into a secondary combustion chamber where it is 
> consumed to produce heat and carbon dioxide (mostly). The gas flame in 
> the secondary chamber is supported by air (secondary air) entering 
> through side-holes or a gap near the top of the cylinder. The primary 
> and secondary air can move by natural draft, relying on the buoyancy 
> of hot gasses to push air through the system, or draft air can be 
> forced – and controlled – by using a variable-speed, small electric 
> fan to push the air.  The pyrolysis leaves behind char rather than ash 
> for two reasons: (1) as the  MPF moves downwards, it thermochemically 
> transforms new fuel at a rate faster than oxygen is supplied to 
> combust it, and (2) pyrolysis and the combustion of volatiles can 
> occur much faster than the combustion of char, which requires a higher 
> level of activation energy.^1 <#_ftn1> Continuously-fed TLUDs use 
> augers to maintain the MPF in a stationary position by supplying new 
> feedstock into the bottom of the cylinder while removing char through 
> an upward port into a quenching container that extinguishes any 
> reactions, cools the char and stores it.
>
>

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