[Stoves] Tuning of secondary air in TLUD stoves (no longer is Re: Cuber and size of densifying machines.
Paul Anderson
psanders at ilstu.edu
Thu Mar 6 17:22:58 CST 2014
Dean,
My comments here are about tuning of TLUD stoves.
I view the "tuning of the combustion" as being done mainly with the
secondary air. The primary air is mainly for the "turn-down of the
combusiton" (that is, the quantity of gases that are to be produced.)
Control of secondary air in NATURAL DRAFT TLUD stoves is rare to
non-existent. Usually the objective is to just have low emissions, and
to get that seems to mean having plenty of secondary, often in excess
(which can result in lower efficiencies, but we are discussing the
emissions issues.)
In the FA (Forced Air or Fan Assisted) stoves, "tuning of the secondary
air for combustion" is really great!! and is not yet well studied.
Examples/comments:
1. Reed's Woodgas Campstove (TLUD-FA) has a carefully determined number
and diameter of hole sizes, with a set balance for primary and secondary
air. Two speeds for the fan, but no change in the ratio of P and S
air. But the unit comes with 3 small screws and instructions that say
that when operating the unit at higher elevations (such as 5000 feet or
more above sea level), then use the screws to block off some of the 11
primary air holes. Great that such impact has been noted, but not
great that nothing more has been done about that "tuning" issue.
2. With the exception of the Rua/HOS TLUD-FA from Hanoi, the Rice Hull
TLUD-FA designs by Belonio (and by those he has influenced) all use a
special burner head that seems to be very well tuned. (Alexis and I
spoke at ETHOS and Aprovecho Open House about variations that can still
be considered.) It is notable that those stoves have FA for only
Primary air. Therefore, there is no way to change the secondary air
supply, that is being drawn in by natural convective forces.
********** IMO, the reason it is working so well is that the stove is
designed specifically for rice hull fuel. And as a stove made for use
with a SPECIFIC fuel, it can be manufactured with a single specific
burner head. (that is along the same lines as the burner heads on LPG
and natural gas stoves where tuning is not needed.)
*********** Alexis says that his stoves can also burn other dry biomass
fuels. I am sure that they can, but I am not sure that the existing
combustion head is optimal for the other fuels. This is another research
topic to examine, and it will require testing under an emissions hood to
see what the impacts will be.
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 3/6/2014 3:57 PM, Dean Still wrote:
> Hi Paul,
>
> I think that the denser pellets might not maintain the flame as easily
> as the .56g small pellets described by Tom. I wonder if for clean
> emissions the TLUD has to be tuned to burn the fuel even if the tuning
> is easily accomplished by adjusting primary and secondary air.
>
> Best,
>
> Dean
>
>
> On Thu, Mar 6, 2014 at 11:35 AM, Paul Anderson <psanders at ilstu.edu
> <mailto:psanders at ilstu.edu>> wrote:
>
> Stovers,
>
> Crispin wrote, in agreement with Dean, and I have added the
> emphasis on Crispin's words:
>> The air flow through the pellets strongly affects the way they
>> burn*/_if the device is constructed such that the fuel
>> contributes a significant element of air control._/*
> Simply, stove devices should NOT be constructed for a specific
> fuel UNLESS that fuel is specified and can be supplied. The
> issue is just like using an incorrect grade of gasoline in your
> automobile. LEADED gas will not burn like unleaded. Super
> premium is different from regular. And pellet sizes are
> different from each other (assuming that the pellet materials were
> also the same, which might or might not have been the case in what
> Dean has mentioned.)
>
> Most of the TLUD stoves that have been tested have not been the
> ones with serious control of the primary air supply. Hence the
> problem that Dean mentions.
>
> I do not know of any tests of emissions from different pellet
> sizes that have been conducted in TLUD stoves that have serious
> control of primary air. One more research topic to add to the
> list of things to do.
>
> Personal comment: I have had my hand involved with the
> development of the "Champion Family" of TLUD stoves:
> 1. Champion TLUD that won the first Cat Pee Award at Aprovecho
> Stove Camp 2005. We just had a blocker on the primary air inlet.
>
> 2. Champion by Servals (India): Still with a rather rudimentary
> control of primary air (a disk into a cone).
>
> 3. Mwoto (for BEIA project by CREEC in Uganda): It has a
> slider control of primary air directly on the fuel cylinder, but
> we had not perfected it then and did not make much of an issue
> about closing off the primary air through tiny gaps such as at the
> ends the strips that hold the slider in place..
>
> 4. Quad (by Awamu in Uganda): We made a better slider door and
> placed it onto a "snout" for primary air. But we did not seal
> with great care. Also, the tab-and-slot construction left tiny
> air leaks that proved to be too much uncontrolled air. This was
> discovered at the July 2013 Stove Camp at Aprovecho where we
> progressively sealed better and better the stoves being tested.
> The best sealed stove won one of the Cat Pee Awards. That was
> seven months ago, and we have stopped production of the Quad stove
> with tab-and-slot construction (and have sealed better the
> existing units.)
>
> 5. Troika Bingwa (by Awamu in Uganda): This stove is just
> getting out to the users. It has a tightly sealed fuel chamber
> with a slider over the primary air entry.
>
> Note: Do not underestimate the impact of even a very very very
> small leak of primary air if you expect to have turn-down of a
> TLUD stove.
>
> Of all the other TLUD stoves, most have no attempt to control the
> primary air. The unit by Prof. Nurhuda does seem to have
> excellent primary air control (but I do not have one of those
> stoves, and there are additional issues to be considered.)
>
> I hope that these comments are useful for everyone dealing with
> natural draft TLUD stoves. Comments pro or con are most welcome.
>
> Paul
>
> Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
> Email:psanders at ilstu.edu <mailto:psanders at ilstu.edu>
> Skype: paultlud Phone:+1-309-452-7072 <tel:%2B1-309-452-7072>
> Website:www.drtlud.com <http://www.drtlud.com>
>
> On 3/6/2014 11:38 AM, Crispin Pembert-Pigott wrote:
>>
>> Dear Friends
>>
>> I agree with Dean on this score. The air flow through the pellets
>> strongly affects the way they burn if the device is constructed
>> such that the fuel contributes a significant element of air control.
>>
>> These devices
>>
>>
>> Are 'cubers' in that they are producing densified lumps that can
>> be put into a stove. But they will work best in a large stove
>> such as is used in China for space heating and cooking. The
>> input material is straw and other stover.
>>
>> The mechanism is an eccentric roller running inside a perforated
>> cage at maybe 60-100 RPM. As Tom notes, power consumption is
>> about 110 kW.
>>
>> So far I don't think the product is economically viable as there
>> is a subsidy involved. What we need is a breakthrough technology
>> that will make densified fuel without the need for heat.
>>
>> Regards
>>
>> Crispin
>>
>> **
>>
>> Hi Paul,
>>
>> I have seen the very small pellets sold for heating stoves in the
>> US burn very cleanly. Larger sized pellets did not burn as cleanly.
>>
>> Best,
>>
>> Dean
>>
>>
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