[Stoves] Cuber and size of densifying machines. (no longer Re: The wood and char and fuel "debate" )
Tom Miles
tmiles at trmiles.com
Thu Mar 6 12:01:40 CST 2014
Dean, Paul,
Back to fundamentals: fuel and air. The advantage of pellets is the ability
to control air and fuel in a small, contained firepot. You have dry fuel
with a very high surface area that is also very dense. You can develop a
very hot concentrated flame and provide enough air for complete burnout in a
small volume. All pellet appliances in the US are designed to burn small
pellets. The "firepot" works very well with the 6 mm (1/4 inch) pellets. For
a larger pellet or cube you need a different arrangement for air
distribution and a refractory tube to maintain high temperature to burn out
the gases. Actually as Paul suggests a TLUD might be much better for cubes
or large pellets.
Density takes energy. Commercial wood pellets are 560 kg/m3 (35 lb/ft3). We
often dry the wood to less than 5% MC, add moisture back to the surface to
about 8% MC and then we use abundant and cheap energy to smash the wood
though the steel die to make it stick and flow together. In the process we
cook off about 3% MC. Cold they will snap when you break them. You'll notice
that when they burn they are slow to break apart. If the biomass is not dry
you will not get the integrity of the pellet, cube or briquette. You need to
be at 10% MC or less. Open air drying usually only gets you to about 15-20%
MC unless you have very dry air.
Cubes, bricks and briquettes are often 256-384 kg/m3 (16-24 lb/ft3). It
takes slightly less energy to make cubes but you need about the same
installed power (~50-75 kWh/ton) to make them. The bonding mechanism is more
"stick" than "flow" so they break apart more easily. Low density cubes and
briquettes can expand rapidly when heated, so you need a burner that will
allow for that expansion and that will supply air through the pile. The
large air spaces can create good radiative heat transfer so you can get a
nice glowing charcoal effect in a gasifier or combustor. Manual presses
probably produce cubes or briquettes that are only 128-160 kg/m3 (8-10
lb/ft3). The bonding is primarily by "sticking" so they break apart easily
unless they are formed and dried like the holey briquettes.
We just need to match the stove to the fuel.
Tom
From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
Dean Still
Sent: Thursday, March 06, 2014 9:16 AM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Cuber and size of densifying machines. (no longer Re:
The wood and char and fuel "debate" )
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
On Thu, Mar 6, 2014 at 7:02 AM, Paul Anderson <psanders at ilstu.edu> wrote:
Dear Stovers and other Friends,
I am in agreement with Bjarne. It appears (yet still to be totally proven)
that the larger diameter (such as 60 mm = 2.3 inches) densified biomass is
probably a better way to proceed into larger production with mechanization
in the developing societies.
Note that "densified" is with higher compression (including the crushing of
cell structures and the "melting" of lignin that gives the glossy outer
coating on DENSIFIED pellets and "processed logs" or densified briquettes).
Note: IMO, the term "briquette" is used differently by various people who
do not distinguish between the high-density and the low-density briquettes
and the processes to make them.
Similarly, there can be high and low density "pucks" or disks or wedges.
Maybe HD and LD can be used to distinguish between the two main types.
For example, LD briquettes and pucks are made with manual presses and jacks
for lifting vehicles. These LD processed fuels can also be great as fuel
(especially for TLUD gasifiers) if that is what the budget and circumstances
allow for production. Bjarne and I are NOT commenting against the LD
precessed fuels. We are commenting about the HD processed fuels, and are
stating that the larger (60mm) diameter fuels are probably the more
practical (lower cost and less maintenance) way to make HD processed biomass
fuels. Clearly pellets (HD and about 6 to 8 mm diameter) have an
important role and are commercially viable, but that is in the context of
developed and affluent societies.
As I have commented before, when the HD processed biomass "log" is extruded
by a ram press (not by an auger), the log is essentially a series of disks
that are jammed together. The disks come out hot and slide along a cooking
rack perhaps 5 meters long. And while still hot (meaning closer to the
press), they can be gently tapped and they will break apart into very clean
disks measuring about 60 mm diameter and 10 to 15 mm thick. If the fuel
user needs smaller pieces at the time to cooking the meal, the disks can be
easily broken by hand or hit with a rock or piece of log to become halves
and quarters. For Awamu in Uganda, two different makers of HD "logs" have
provided us with disks when requested.
Also stated in earlier messages, inside a TLUD gasifier, the disks can be
place vertically (on edge) and have a superior air flow than if they are
placed horizontally.
Comments in support or contrary would be greatly appreciated.
Paul
Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
Email: psanders at ilstu.edu
Skype: paultlud Phone: +1-309-452-7072 <tel:%2B1-309-452-7072>
Website: www.drtlud.com
On 3/6/2014 1:32 AM, Bjarne Laustsen wrote:
To Paul and others
Fuel supply can be big business but it does not need to be.
We have been making pellets for gasification stoves.
The pellets in itself work very well if they are in sizes from 6 mm or 8 mm
in diameter, they have been burning very good in our gasification stoves.
The problems in relation with pellets for gasification stoves are how to
find good and sustainable pellet presses for producing the pellets.
The slides from the presentation from Crane Wang MUYANG illustrate this very
well. Because the pellet press they shows are big and expensive equipments
that will do a good job, however they are outside the financial reach of
most of us.
We have experiences with some of the smaller and cheaper pellets mills, and
they are not able to produce pellets in a sustainable way. They are designed
for feed pellet production, and they aretherefore not able to produce fuel
pellets in an economical way.
I have noted that in China they are mainly working with pellets for fuel
production while in India they are working with briquettes.
For me to see the cuber will still be an to expensive solution.
The solution for us will be to use the Indian type of mechanical piston
briquette presses that can make briquettes with diameter of 60 mm and get
attached a puck cutter on that so the briquettes are cut out in pucks. Such
pucks will be a good fuel for gasification stoves. And the equipment is
reasonable in price so it is possible for many to finance such a solution.
These briquette presses can work with most types of agricultural residues,
so we at the same can shift to using renewable biomass for cooking and in
this way also contribute to reducing the deforestation.
Bjarne Laustsen
On 3/5/2014 10:47 PM, Paul Anderson wrote:
Stovers,
Slide #9 of the presentation at the site given below is interesting. Those
cubes should work very well in gasifiers of many different sizes.
I was impressed by the other slides that show the very large sizes of the
pelletizers and cubers. If supply of raw materials is sufficient, large
machines seem so much more appropriate than 100 or 1000 small units. Fuel
supply is BIG business.
Paul
Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
Email: psanders at ilstu.edu
Skype: paultlud Phone: +1-309-452-7072 <tel:%2B1-309-452-7072>
Website: www.drtlud.com
On 3/5/2014 9:58 AM, Energies Naturals C.B. wrote:
Hello Michael,
.....
We saw some examples of cubers in a Beijing(?) stove exposition some time
ago.
Also check this:
http://www.novator.se/bioint/BPUA12Pres/10_BPUA12_Crane_Wang_MUYANG.pdf
Hope this helps
Rolf
On Wed, 26 Feb 2014 10:36:47 -0600
Michael Mahowald <mailto:memahowald at hotmail.com> <memahowald at hotmail.com>
wrote:
You are absolutely correct Paul !
Deforestation happens all over the world with the lack of fire wood.
There simply is not enough dry sources of trees or waste from them even for
TLUD's to keep even poor consumers interested in them.
We know vetiver grass has the highest photosynthetic activity of any plant,
making it the most renewable energy source on the planet. We just have to
densify the grass into pellets at a cost that people can afford. The only
way we can do this is to eliminate the cost of diesel fuel to run the
generator to make the pellets.
We are planning on using a downdraft gasifier for gas to accomplish this.
We just have to perfect this process and size it for a portable pelleting
plant that can be taken to the fields they grow it.
When we perfect this it will be capable to work everywhere in the world that
needs clean cook stoves.
If you want to see what we are doing check out
http://haitireconstruction.ning.com/page/grass-energy
and http://haitireconstruction.ning.com/page/sustainable-path-on-how-to
Michael E. MahowaldPresident
Haiti Reconstruction International952-220-6814
Date: Tue, 25 Feb 2014 20:43:31 -0600
From: psanders at ilstu.edu
To: stoves at lists.bioenergylists.org; biochar at yahoogroups.com
Subject: [Stoves] The wood and char and fuel "debate" (was a long time ago
called Re: Request for technology proposals - Clean Stove Initiative,
Indonesia)
Dear Crispin, Ron and all,
It is interesting reading the back and forth between Ron and
Crispin. I emphasize two paragraphs from Crispin,
On 2/24/2014 10:10 AM, Crispin Pembert-Pigott wrote:
There
is no dispute between us whatsoever as to the energy
consumption: the energy remaining in the char represents
energy not liberated from the fuel consumed.
The
important question is not what we want, but what the
customer of the test result wants. They are not asking how
much energy was used when cooking, they asked how much fuel
was consumed. The answer is of course different if there is
char remaining and that char is not 'fuel' to the same stove
for the next fire.
For the vast majority of "customers" (including
governments that
want to reduce or reverse deforestation), the important question is
"how much wood is burned." The interests are highly related to
WOOD, specifically related to TREES, not even counting sawdust that
goes into pellets.
So, because TLUD stoves are VERY GOOD at burning NON-wood biomass,
the wood saved can be 100%. And we still get the char.
Concerning fuel and wood and non-wood and char and other such
measurements, the real problems can come from rankings and Tiers and
o
ther reports that could give excellent stoves some poor results
because the "authorities" are defining fuel as being exclusively
wood, as in trees and woodlands that need to be protected.
If we could get past that "imposed intellectual construct" of fuel
being wood, we could make more progress about some types of biomass
stoves being even better than good for the environment.
Rest assured that the advocates of alcohol and kerosene and other
NON-biomass fuels are pointing out that their stoves help minimize
deforestation/enviromental degradation.
Biomass that is NOT WOOD needs to be recognized as being favorable
for saving trees, and credit given to the stoves that can use those
non-wood biomass fuels.
AND that recognition and credit needs to be EXPLICITLY STATED IN THE
REPORTS ABOUT FUEL CONSUMPTION.
In some ways, this is all just another discussion about why the
reported results of any stove testing need much explanation (which
is usually not provided) and why the results are so easy to ignore
as being poorly related to the realities of people and their stoves
and their fuels.
I hope we can do better in the future.
Paul
(still another week to go on my vacation trip to Brazil,
so I probably will not be sending replies.)
Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
Email: psanders at ilstu.edu
Skype: paultlud Phone: +1-309-452-7072 <tel:%2B1-309-452-7072>
Website: www.drtlud.com
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