[Stoves] Stoves Digest, Vol 17, Issue 35
Tom Miles
tmiles at trmiles.com
Wed Jan 25 14:43:20 CST 2012
Lloyd,
I just subscribed you to the gasification list so you should get a welcome
message. I have sponsored and hosted the gasification list since about 1996.
There are about 1200 members.
We maintain a website to support the list at:
http://www.gasifiers.bioenergylists.org/
Regards,
Tom
T R Miles Technical Consultants, Inc.
tmiles at trmiles.com
www.trmiles.com
From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Lloyd Helferty
Sent: Wednesday, January 25, 2012 12:03 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Stoves Digest, Vol 17, Issue 35
Tom,
I see a *new* list for the first time:
gasification at lists.bioenergylists.org
How do I join this list?
(Do I send <mailto:gasification-request at lists.bioenergylists.org>
"gasification-request at lists.bioenergylists.org " ??)
Regards,
Lloyd Helferty, Engineering Technologist
Principal, Biochar Consulting (Canada)
www.biochar-consulting.ca
48 Suncrest Blvd, Thornhill, ON, Canada
905-707-8754
**NEW CELL: 647-886-8754 NEW**
Skype: lloyd.helferty
Steering Committee coordinator
NEW Canadian Biochar Initiative (New CBI)
President, Co-founder & CBI Liaison, Biochar-Ontario
Advisory Committee Member, IBI
http://www.linkedin.com/groups?gid=1404717
http://www.facebook.com/group.php?gid=42237506675
http://groups.google.com/group/biochar-ontario
http://www.meetup.com/biocharontario/
http://grassrootsintelligence.blogspot.com
www.biochar.ca
Biochar Offsets Group: http://www.linkedin.com/groups?home=
<http://www.linkedin.com/groups?home=&gid=2446475> &gid=2446475
A nation that destroys its soil, destroys itself.
- Franklin D. Roosevelt
On 2012-01-25 12:20 PM, Tom Miles wrote:
Philip,
Thanks for the reference. It looks like the CarboConsult gasifier from South
Africa.
<http://www.carboconsult.com/> http://www.carboconsult.com/
<http://www.erc.uct.ac.za/jesa/jesa-currentabstracts.htm>
http://www.erc.uct.ac.za/jesa/jesa-currentabstracts.htm
Volume 22 No 4: December 2011
The technical pre-feasibility to use briquettes made from wood and
agricultural waste for gasification in a downdraft gasifier for electricity
generation
Pholoso Malatji, Ntshengedzeni Sampson Mamphweli and Martina Meincken
Biomass can be converted to energy through various thermochemical and
biological processes. Gasification is one of the thermochemical processes
that has recently gained popularity, because it achieves higher conversion
efficiencies than, for example, incinerators, boilers or furnaces. Fixed-bed
downdraft gasifiers are preferred for electricity generation, because they
produce very little tar, but on the other hand, they are limited with regard
to biomass properties, such as particle size, bulk density and moisture
content. Biomass material with a heterogeneous size is usually processed
into pellets or briquettes, which have to be mechanically strong enough to
be handled. Cohesive strength is provided by residual moisture and lignin
present in most biomass. However, the briquetting process becomes more
complicated if one wants to add agricultural waste products that do not
necessarily contain lignin as binders. The aim of this work was to process
wood chips, grape skins and chicken litter into briquettes that are
mechanically stable and have a sufficiently high energy content, as well as
adequate bulk density for gasification. The performance of these briquettes
in a downdraft gasifier was simulated with a program developed for wood,
which was modified to optimise the briquette yield. The results showed a
gasification performance comparable to solid pine wood, implying that the
blended briquettes could be used as fuel for a downdraft biomass gasifier.
Unfortunately, the briquettes proved too instable to experimentally verify
the performance in a gasifier. This paper describes the properties of the
briquettes as well as the gasification simulation results.
Tom
-----Original Message-----
From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Philip Lloyd
Sent: Tuesday, January 24, 2012 11:48 PM
To: stoves at lists.bioenergylists.org
Subject: Re: [Stoves] Stoves Digest, Vol 17, Issue 35
The latest edition of Journal of Energy in Southern Africa, Vol 22 No4
(November 2011) has an article on the use of biowaste briquettes in a
downdraft gasifier for electricity production (pp 2-7)
Prof Philip Lloyd
Energy Institute
Cape Peninsula University of Technology
PO Box 652, Cape Town 8000
Tel: +27 21 460 4216
Fax: +27 21 460 3828
Cell: 083 441 5247
-----Original Message-----
From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
stoves-request at lists.bioenergylists.org
Sent: 24 January 2012 07:45
To: stoves at lists.bioenergylists.org
Subject: Stoves Digest, Vol 17, Issue 35
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Today's Topics:
1. Re: The upside of Down feed (Alex English)
2. Re: The upside of Down feed (rongretlarson at comcast.net)
3. Re: [Ethos] ETHOS schedule (Choppalli Venkata Krishna)
4. Re: The upside of Down feed (Crispin Pemberton-Pigott)
5. Re: [Ethos] ETHOS schedule (Otto Formo)
6. Re: [Ethos] ETHOS schedule (Alex English)
7. Re: [Ethos] ETHOS schedule (Tom Miles)
8. Total Energy Wiki launched (Crispin Pemberton-Pigott)
9. Re: The upside of Down feed (rongretlarson at comcast.net)
10. Re: The upside of Down feed (Crispin Pemberton-Pigott)
----------------------------------------------------------------------
Message: 1
Date: Mon, 23 Jan 2012 20:45:36 -0500
From: Alex English <mailto:english at kingston.net> <english at kingston.net>
To: Discussion of biomass cooking stoves
<mailto:stoves at lists.bioenergylists.org>
<stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] The upside of Down feed
Dear Crispin,
On 22/01/2012 10:36 PM, Crispin Pemberton-Pigott wrote:
Dear Alex
This is interesting news. The grate looks great, and if there is a
pile of char that is maintained in front, we must conspire to burn it.
Not so fast. I rather like the idea of a naturally formed biochar venturi:)
To review, it is a crossdraft fire with all the advantages inherent in
it: refuellable and lots of room for flames.
If the char builds up in front of the hopper but self-limits (i.e.
burns away) then it has to be eaten by the passing flame and available
O2. That being so, I see a couple of options. One is to admit air
through some small holes (1.6, 2.0mm) drilled under the early part of
the pile (on the grate side of the pile). That will bleed air under
the char which is a good way to burn it. Another is to change the
shape of the pipe in that area to allow ash to drop. I presume at the
moment the ash is blown into the larger chamber of the stove.
I see the odd spark or glowing particle fly into the stove. This is what you
see in most pellet stoves which do tend to have relatively low PM emissions.
In part that has to do with the way the size of the particles in the pellet
('sawdust' is really tiny wood chips) and how they tend to hold together.
When the hopper does runs out of fuel the added air flow literally blows
whole charred pellets into the stove. A chimney draft is nothing to sneeze
at, so to speak.
It is highly likely you have a fairly large PM10 number compared with
the same fuel burned in a pile in that larger chamber because of
lofted ash.
I am really pleased to hear that the flow is so reliable. I have some
really short fat pellets here which are probably going to feed well
because they are nearly marbles. Probably made with one of those
trochoid, concentric-ring pellet formers.
As for the fire rising into the hopper, that is not going to happen if
the air velocity is high enough. Conditions we have observed it is
when the velocity is quite low. If the heat is enough, a rising
current of heated air and gas circulates in the fuel immediately above
the burning layer and the fire works its way up. That can only happen
if a) there is some air (especially from above) or b) the fuel is
volatile enough to run an air-free charring burn in the present of
enough heat.
The advantage of coal, even with a highly volatiles one like the
lignite from Nalaikh mine, it is still less volatile than wood. The
talk of torrefied pellets intrigues me for that reason. It is more
likely to behave like slow roasting coal. Very controllable. There are
small coal pellets, say 16mm diameter which might feed well too.
Is there any reason you can think of that the hopper, feed tube and
burning chamber should be round?
No.
If you pass by the house I can show you a stove body that your burner
will directly attach to with several novel features. It won't be shown
until March and sort of solves the 'rest of a stove' for you. I am
pretty sure you will like it. It /might/ address the PM10 issue, or
not, and solves the heat extraction issues for cooking and heating.
I have some Kanthal wire here which we are recommending for grate
material. It will work well for you and will hardly get hot at all. If
some small bits of fuel drop through (being ahead of the grate) a
pocket can be provided underneath to let them smoulder, feeding CO and
C and H2 into the beginning of the fire. No problem.
The arrangement is made similarly on the SeTAR BLDD5 with the
smoulderings fed into the flaming portion of the pipe. The reason I
mention a wire grate is it is cheap and easy to make. But like the
layered flats too. It should be possible to punch that in a single
stroke with the right tool.
How deep is the fuel in the hopper?
40 cm. I have materials to go up to 100cm, and I could take it up to near
the ceiling with some stove pipe, though I might have to counter balance the
stove:)
I tried a number of things with hopper shape and decided there is a
general rule about bridging which is the following: if the hopper
tapers inwards the point of burning, there is an upper limit to the
height of the fuel for each degree of narrowing. I tried shoulders too
and they are OK further up (for example, within 1 hopper width of the
top of the fuel pile). On all cases, if the fuel is compressed by
pushing down on it or by stacking lots of fuel up, bridging occurs
just above the beginning of the taper.
These pellets are highly resistant to bridging. On the other hand I have
seen chips defy gravity:)
The solution is agitation or a non-tapering hopper bottom.
This is bound to be affected by the surface smoothness of the fuel
particle. If the pellets are shiny and hard that has to be a help
avoid bridging, right? I am impressed that you are able to keep it
feeding so well with such a significant narrowing.
It is difficult to measure but the pellet flow is in fact air (wind)
assisted. However they are more bullet than sail. Small dry wood chips are
sails and if they make it down through the hopper, they blow right out of
the tube.
To you think it is necessary to tilt the flame tube downwards at all?
If the char pushed ahead it would be burned by the continuous heat of
the flame. Using wood, I can report that I have seen flames reaching
more than 24 inches along the tube so you may get better combustion
efficiency by lengthening the one you have.
Yes, a view of the flame is useful for understanding the process but is not
ideal for combustion.
Thanks for an interesting (tiny) burner idea. If you bring it here I
have some 5mm switchgrass pellets I have had difficulty burning it
anything yet. Maybe...
I suspect the ash would bung it up, but maybe...not.
Alex
<snip>
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