[Stoves] Between PM 2.5 and PM 10

[Crispin Pemberton-Pigott]

Dear Julien

 

I think it is important to emphasize that just because a TLUD burns really
cleanly, it is not necessary to use that method in order to a) burn just as
clean, b) to burn pellets, c) to make char if desired.

 

Despite the early raving about the high quality of TLUD emissions, this is
not always the case. TLUD are quite capable of produce high tar emissions
with poor combustion. Alternative designs like crossdraft and downdraft
stoves are quite capable of producing very low emissions. In all three
designs the critical factors are the same: heating of the fuel slowly to dry
it and create gases, a hot zone to break down the gases into mostly CO and
H2 and water vapour, a hot combustion zone with limited excess air, a heat
exchange zone where the completed burn passes to the pot (etc).

 

TLUD's are one way to get that nice set of features, if they are built
correctly. Many are not, but are still better than an open fire or a
dreadful 'box with a chimney'.

 

I appreciate the enthusiasm for the TLUD as an easy solution but it brings a
number of problems many users do not want to face: producing or using small
fuel particles (strong resistance to fuel preparation in Indonesia) and the
(almost) inability to be refuelled for continuous operation (4 hour burns
are common).

 

TLUD's are also very fuel dependent in terms of size, moisture, species and
the minimum power level to work properly. It is not a technology that solves
all our problems. Notice that Paul A and Paul are both very clear about how
to get wood or rice hulls or other fuels to 'burn properly' and that does
not make the fire controllable, it just makes it clean. Cooking absolutely
requires power control. A pyrolysis zone is inherently set against such
conditions. That is why TLUD coal stoves make such great space heating
appliances: continuous heat at constant power with at least some measure of
controllability. But they only cook at high power, basically.

 

Regards
Crispin

 

+++++++

 

Dear Crispin;

 

Thanks for your excellent response to the issue of untrafine particles and
the article by Just, Rogak and Kandlikar (2013).  That TLUDs have a strong
secondary gas fire is a very important distinction from many

other stove designs.   The ability of a stove to handle a variety of

fuel qualities is also an issue, because, as we all know, the rate of heat
production and the temperature of the flaming pyrolysis affects the nature
and temperature of gases entering the secondary gas fire.

We may find that in area of high human population density, pellet fuels are
way-and-above the best option for low-emissions of particulate matter.
Hopefully, there can be a market for biochar to offset the cost of pellets.
That were soil scientists (me) come in.

 

Speaking of pollution being relative, my parents lived in London, England
during 1930-1950.  A lot of coal was burned for heating and cooking.  The
particle emissions produced nuclei for water vapor to condense resulting in
the infamous London fog.  It was at times so dense that bus conductors had
to get off the bus and walk in front to show drivers the way.  The people of
London simply assumed that it was normal that your window curtains and the
white marble of buildings turned back.  When Londoners switched to using
more gas and electricity, the famous fog went away.

 

Julien.

 

--

Julien Winter

Cobourg, ON, CANADA

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20130610/4b6d9ac5/attachment.html>