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

Paul Anderson psanders at ilstu.edu
Fri Nov 27 20:13:11 CST 2015


Crispin,

For maybe 150 years engineers have been able to make LARGE gasifier 
systems work quite well.  20 kW is quite large in comparison to the 
cookstove needs.

Without some external verification, let's agree to differ as to whether 
(and how) a migratory pyrolytic front can move upward is such a 
device.   It can move up somewhat, but if it is to be a continuous 
process, it cannot reach the top and stay there.   So, the system 
requires that the fuel load be occasionally or progressively moved 
downward.
> "Air &  biomass move in counter current direction as shown in fig-1."
And that means that the pyrolysis zone stays close to one location, and 
that is easiest and most likely at or near the bottom.   I have no 
access to his technology, so I cannot confirm that what you say is correct.

Bottom LIT is not the issue.   It is Bottom BURNING.    Note that 
Top-LIT is significant BECAUSE THE PYROLYSIS FRONT MOVES AWAY FROM THE 
TOP, AND DOES NOT STAY THERE.   I have written (see "Micro-gasification 
Terminology..." at my website) that I should have named it "MPF 
gasifier" to capture in the name the fundamental difference from all 
other gasifiers.   TLUD is Top-LIT and the front moves downward and is 
not burning at the top of the pyrolyzed fuel now-char.    Bottom-lit is 
ignited at the bottom and the fire that makes the heat for pyrolysis 
stays at the bottom, being bottom BURNING.

Look at his Figure 1 again.   At the bottom is oxidation.   Where the 
heat is generated for driving the pyrolysis, which is occurring higher 
up.   But that is anoxic pyrolysis (without oxygen).   In the TLUD, 
there is oxic pyrolysis (glowing or "flaming" pyrolysis), and THAT is 
the layer that moves.   And THAT is the layer that requires that O2 can 
reach it from below.   But in Figure 1, the O2 is consumed in the 
oxidation zone at the bottom.

So, in some ways, we are discussing two quite different processes, but 
both are forms of pyrolysis.

Tongue in cheek:  Maybe I should have called it Migratory OXIC Pyrolytic 
Front, or shortened to MOPF.   That would be more precise.   But then 
the other systems should need to put in the "AP" for "Anoxic Pyrolysis" 
to show that they are different from the MPF of TLUD technology.

For clarity, please note:   AP (Anoxic Pyrolysis) occurs where a 
quantity of biomass becomes heated.   Commonly this is in large piles of 
wood in traditional charcoal making, or inside of a barrel that is being 
heated in a retort.   Basically all of the biomass is being warmed at 
the same time.   Therefore, much heat is needed to bring the whole 
quantity up to zero moisture  and then torrification and then pyrolysis 
temperatures.   Adam retorts send off plumes of basically steam at the 
start, and then later have massive amounts of pyrolytic gases coming off.

In contrast, OP (Oxic Pyrolysis) occurs where a small quantity (actually 
a rather thin layer) of biomass becomes heated because small amounts of 
combustible gases are burned in a pyrolytic zone or front.   The OP 
process cannot remain in that position because it will soon burn off all 
of the combustible gases and then the oxygen would be in contact with 
the hot carbon (char) that was created, and that would be 
char-gasification, not pyrolysis.   So the front moves downward just a 
small distance, in relation to the incoming flow of air with O2.  The 
MOPF is quite thin but is very distinct.

Well, wrestling with this terminology has helped me for future 
discussions about different types of gasfiers.

By the way, to all readers:  This is discussion is about gasification AS 
IT OCCURS IN VARIOUS TYPES OF GASIFIERS.   Applying these comments (such 
as up-draft and down-draft) to common burning such as a bonfire or a 
simple (early style) rocket stove would be out of context.   Gasifiers 
are based on _controls _of drying, torrification, pyrolysis, 
char-gasification, and combustion of combustible gases.   Common burning 
has all of those processes intermingled and not as controlled.  Control 
is what makes gasifiers so successful for clean combustion.   The need 
for control also is what adds costs and operational issues to gasifiers 
versus 3-stone fires or simple "combusition-in-a-container stoves."

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 6:38 PM, Crispin Pemberton-Pigott wrote:
> Dear Paul
>
> Are you saying the system described by Hirendra can't be made to work? 
> It doesn't make a gas that can be burned without getting the water 
> out, agreed. The gas has a high energy content.
>
> From the link:
>
> "TYPES OF GASIFIERS:  Generally, gasifiers are of four types.  i) 
> Updraft- in which the biomass is fed from the top & air at particular 
> BST is pushed from the bottom. The gaseous products are drawn from the 
> top of the gasifier for cooling & cleaning. Air &  biomass move in 
> counter current direction as shown in fig-1."
>
> The sketch shows the position of the pyrolysis layer and it is not at 
> the top, and it is covered by fuel, and you can buy one.
>
> The fuel is indeed placed on top in large quantities, it does not need 
> to be added frequently (we can quibble about the meaning of 
> 'frequent') and the MPF moves upward.
>
> So, what to say? I described it, Hirendra makes them, and it is 
> described in the paper, though he was not describing his own product 
> in detail.
>
> I find it interesting that you were not able to get the system to work 
> except as you describe below. Do you think it is because of the small 
> size? He gives as a lower limit 20 kW though when discussing the 
> system with me he did not indicate why. As indicated in my message the 
> gas is very wet and requires drying. You note that it was too wet to 
> burn directly which confirms this need when operated with the MPF in 
> the middle of the fuel pile and you changed the fueling behaviour to 
> maintaining a thin layer on top. That is a different approach, in my 
> view. If it is maintained continuously, how is the moisture level 
> different? Hirendra's paper mentions that the BLUD method can deal 
> with a 'higher fuel moisture level'.
>
> On reflection I don't see why it should not be bottom lit in which 
> case it is correctly described as a bottom-lit up-draft device.
>
> For those with an interest, Anton Soedjarno ‎in Yogyakarta makes a 
> fluidised bed gasifier which is also fed from the top through a 
> trapdoor with quite large fuel particles: 1/2 to 1/4 of an oil palm 
> 'empty fruit bunch' (OPEFB).  This approach greatly reduces the need 
> for dealing with the tars contained in the UD gas. Anton says it 
> doesn't make tars, actually, and it is burned directly in an engine. 
> The pyrolysis zone heat is used to create steam in a parallel chamber 
> to drive the process which is a pretty cool idea. The reactor is quite 
> tall.
>
> Regards
> Crispin
>
>
> 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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