[Stoves] Adding fuel to TLUD ..... was Re: A review of chronological development in cookstove assessment methods: Challenges and way forward

[Paul Anderson]

Dear Crispin,

Please check my publication in /Boiling Point/, 2007 (eight years ago), 
available at my website in Quick Picks or directly at

http://www.drtlud.com/wp-content/uploads/2012/08/BP53-Anderson-14.pdf

It discusses both TLUD and AVUD methods.  The AVUD method is the basis 
of the Chip Energy Biomass Furnace (in the range of 200,000 BTU or 50 kW 
thermal).   And I have made AVUD functional in as small as a gallon 
container (4 liters).  And several hundred of the Chip Energy Biomass 
Grill were made and sold (with a plancha top).

Contrary to what you wrote about the system that you mention:
1.  The new fuel on top cannot be piled on in large quantities. Reason:  
The heat that rises up to the new fuel will first dry the fuel, and then 
torrify and eventually pyrolyze.   too much fuel to be dried at one time 
results in high moisture in the gases, capable of making them 
non-combustible until getting to torrification temperatures.

2.  Therefore, some degree of frequent fuel feeding is needed. Works 
great while the user is happy sitting there feeding occasionally.   OR 
if the user has the money to pay for automatic feeding.

[Now that pellets are obtained so easily in so many places, I should 
probably return my attention to this type of unit plus some small 
automatic fuel feeder.   Related to the Chip Energy Biomass Grill. 
Anyone interested in this should write to me directly off-line at 
psanders at ilstu.edu ]

3.  In the AVUD processes, there is not any upward MPF (migratory 
pyrolytic front) because the pyrolyzed fuel keeps collapsing onto the 
lower char bed and air-inlet/grate.   Also, any primary air entering is 
into a bed of hot char where the O2 will be consumed, leaving nothing of 
O2 to go up to the pyrolytic front, therefore no flaming (glowing) 
pyrolysis as is found in TLUD stoves.   Instead, AVUD has retort style 
pyrolysis unless the char is being removed and the fuel is getting low 
enough to receive some of the O2, which is the case in the Chip Energy 
Biomass Furnace, which is a wonderful char maker and can run 24/7 for 
days and days.

4.  This is BB gasification, which is Bottom Burning.   It is not 
related to being LIT at the top or at the bottom.   It is Bottom 
BURNING.   [Anything that is Bottom LIT is by definition also Bottom 
Burning, so that is why I dislike the insinuation that BLUD (which is 
BBUD with static location of burning) is anything like a TLUD technology.]

Bottom BURNING is the case of virtually all gasifiers until Tom Reed and 
Paal Wendelbo built TLUDs that are LIT a the top.   But the pyrolysis 
does NOT STAY at the top.   It eventually gets to the bottom and becomes 
BB (and without any further MPF activity).   And the combustion 
processes transition over from MPF to BB Bottom Burning.

5.  You put Chakrabarti's paper at your website.
http://www.newdawnengineering.com/website/library/Papers+Articles/Chakrabarti,%20H/BIOMASS%20GASIFICATION%20Hirendra%202013.pdf
You are welcome to put mine from Boiling Point 2007 there also. People 
correctly listen to and read what you provide, and we all want what you 
write and say to be as accurate as possible.

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 11/27/2015 3:41 PM, Crispin Pemberton-Pigott wrote:
> Dear Paul
>
> There is another way to operate the TLUD which is what the 
> aforementioned Hirendra Chakbarti's company makes.
>
> Start the stove in the regular manner.
> When the pyrolytic front is well established‎ start loading fuel on 
> top but not a thin layer - lots.
>
> The MPF burns to the bottom and the ignited bottom of the net fuel 
> burns upwards. For a short time it has two fronts.
>
> The bottom burns out and the char and turns all to ash. The upper MPF 
> moves upwards without flaming. New fuel is added on top to keep the 
> front buried in the pile.
>
> After some time the bottom is opened on the side and ash withdrawn‎, 
> dropping the pile with the MPF somewhere above the ash and under the 
> raw fuel. More fuel is dumped in top.
>
> This produces gas which is very wet. The gas is drawn off by a pipe 
> and cooled to remove the water.
>
> The process is continuous. It can be controlled by means of the 
> primary air flow. There is no secondary air as the combustion is 
> elsewhere. In a stable operating condition it is a BLUD gasifier that 
> can be operated continuously.
>
> It is the inversion of the Cambodian rice hull gasifiers I described a 
> couple of years ago. Those feed the fuel in from the bottom and take 
> the rice hull char off the top with the gas going up, and the MPF 
> going down. ‎It also runs continuously.  Both can be fueled episodically.
>
> Regards
> Crispin thinking this BLUD approach has not been tried within this 
> group of experimenters.
>
>
> On 11/27/2015 12:10 PM, Ronal W. Larson wrote:
>> 4.  Here is an idea that I wonder if you (anyone) has tried. (I haven’t)
>> a.  Start a TLUD in the normal way -  maximum primary air may be best 
>>  (since mostly we want high power only at the beginning).
>> b.  As soon as the pyrolysis front is clearly well established - then 
>> add a “thin” layer of the same (?) combustibles on the top.
>> c.  There should be no ignition at the bottom of the new layer, as 
>> there is no oxygen there.   But new pyrolysis should occur - so 
>> increased power.   The top of the new added layer could ignite, if 
>> there is plenty of secondary air there.
>> The down side of this is that you probably need to control the 
>> secondary air so that you don’t have too much latterm  Most os us 
>> never do this.  But there could be some inherent control of the 
>> secondary (that secondary follows primary naturally)..
>>
> This has been done many many times.   It is a way to extend the 
> duration of the TLUD operation.   You are correct that causes an 
> increase in the pyrolytic gas creation but does not increase secondary 
> air (except through increase of draft from more burning gases).   It 
> is a good way to put soot on the bottom of the pot.   Note that this 
> is anoxic pyrolysis via the heat, with no small flames (glowing 
> pyrolysis) present as is found in the MPF (migratory pyrolytic front).
>
> Actually two conditions are possible.
> 1.  As you describe, while the MPF is also functional and descending.
> 2.  After the MPF reaches the bottom (and stops because it transitions 
> into char-burning at the bottom).  This is how people make their unit 
> become "continuous" (at least until it chokes up with too much char or 
> ash).   But it requires the very frequent attention to the feeding of 
> the fuel, thereby losing one of the desired aspects of TLUD batch 
> operation (consistent flame without needing to add more fuel during 
> the batch time of the MPF).
>
> Therefore, what you describe certainly has been and is frequently 
> done.  Actually, I did that in the testing in 2005 that won the Cat 
> Pee award at Aprovecho.   Then I did not understand it fully.   
> Trickle feeding of fuel into TLUD stoves does work, has pros and cons, 
> and is likely to be done by some individuals with or without their 
> understanding of why or how it works and its limitations.
>
> Paul
>
>
>
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