[Stoves] Meat grinder fuels for TLUDs was Re: wheat husk pellets
Kevin
kchisholm at ca.inter.net
Thu Jun 13 21:31:06 CDT 2013
Dear Paul
Very interesting!!
Sawdust has an "R-Factor" of about 2 BTU-hr/ft^2- degF-inch. Would you recall the R-Factor for Rice Hulls?
Best wishes,
Kevin
----- Original Message -----
From: Paul Olivier
To: Discussion of biomass cooking stoves
Sent: Thursday, June 13, 2013 11:22 PM
Subject: Re: [Stoves] Meat grinder fuels for TLUDs was Re: wheat husk pellets
Tom,
Ten years ago I had worked a Carl Simpson of Riceland in Arkansas on the idea of using rice hulls as insulation. We found out that untreated rice hulls make an excellent insulation, and unlike cellulose insulation, chemicals do not have to be added to rice hulls to make them fire and fungi resistant. Untreated rice hulls passed all ASTM tests for insulation materials. Carl told me of piles of rice hulls that had been in place outdoors for over 20 years. Rice hulls do not decompose very easily. I do not know much about wheat hulls.
Paul Olivier
On Fri, Jun 14, 2013 at 4:39 AM, Tom Miles <tmiles at trmiles.com> wrote:
Fair enough. Wheat byproducts that I have worked with are usually either a granular or powdery meal. I don’t know how much hulls would break down biologically. Proabbly not much since they are used as a bulking agent for compost.
Tom
From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Legacy Mail
Sent: Thursday, June 13, 2013 2:18 PM
To: Discussion of biomass cooking stoves
Cc: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Meat grinder fuels for TLUDs was Re: wheat husk pellets
Tom, Paul,
the problem with running a fiberbound residue through, especially, an augur driven meat mincer type die, is that the process itself tends to shear the very fibers that do the binding. 1" dia x 1 long sausages are about as small as you can go from our experience .
Richard
Sent from my iPhone
On Jun 12, 2013, at 21:07, "Tom Miles" <tmiles at trmiles.com> wrote:
Paul,
The hulls would have to be incorporated into a meal that when dried would form into a ball or pellet shape by using something like a meat grinder. It might be possible to “ret” them with the coffee skins a la Bryant/Legacy. Then you would have something to form. I have always experienced a large quantity of fines with rice husks and straw. You could tie those up by combining them in a meal but you need something fibrous to hold them together.
Think of other uses for composted rice husks. I know someone who has made thousands of cubic yards of peat substitute by composting rice husks. So it is clearly possible to biologically “process” the husks to a beneficial form. Once you have composted the hulls why use them as fuel? They could be better as a soil amendment. The composting should generate biological binders that would give you a choice of densification methods. Pressing hulls through a metal die will just wear out the die. Probably not the first choice. I think there is a form of fuel or soil amendment that could be created. Meanwhile keep the day job and perfect your rice husk TLUD
Tom
From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Paul Olivier
Sent: Wednesday, June 12, 2013 7:38 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Meat grinder fuels for TLUDs was Re: wheat husk pellets
Tom's explanation still leaves me with a few questions.
Would the rice hull have to be ground into a powder to go through a meat grinder?
It takes a lot of energy and maintenance to grind up rice hulls.
With a conventional pellet machine, rice hulls do not have to be ground up.
What binder would be used with rice hulls?
Paul
On Thu, Jun 13, 2013 at 9:08 AM, Paul Anderson <psanders at ilstu.edu> wrote:
Stovers,
Tom gave a good explanation. His message is now in the Listserv Archives. But how can such content be made more available for future readers?
Paul
Paul S. Anderson, PhD aka "Dr TLUD"
Email: psanders at ilstu.edu Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
On 6/12/2013 4:24 AM, Tom Miles wrote:
Andrew,
Good explanation.
Think of two methods of forming fuels. One requires high heat and pressure.
The other requires water and biological or chemical degradation.
Heat, pressure and some moisture (10% MC) are required for densification to
pellets, briquettes or fire logs. A dry biomass is finely ground and pressed
through a metal die. There are two principal binding mechanisms. In one,
cellulose fibers pressed together with heat removes excess water and the
fibers are bonded to each other through what is called paper bonding, or
hydrogen bonding. It is like wetting two pieces of paper and letting them
dry out. They are difficult to pull apart. This is a chemical bond that is a
major bonding mechanism for most densification. When you break the pellet or
briquette it falls apart rather than snaps.
A second mechanism is lignin plastic flow, as Andrew describes below. The
lignin and part of the celluloses actually plasticize and flow. Under high
power magnification with a scanning electron microscope a portion of the
wood looks like solid plastic with no identifiable fibers. These pellets
snap when you break them.
Both mechanisms are at play in a densifier. Together these mechanisms make a
durable pellet or briquette. As Andrew points out they require power and an
extrusion process like a pellet mill.
A third mechanism that is used with mechanical densifiers is adding chemical
binders, starches, or even expanding clays. These were employed in the
older, low power cubers and briquetters to make animal feed. Molasses based
binders were added to help stick hay together in cubes and to add nitrogen
(protein) etc. They often added 30% to the cost of the feed. We used sodium
hydroxide to hydrolyze straw to make it pliable for making cubes. It had the
advantage of making the straw more digestable for the animals. This was fine
for using low quality feeds like straw in times of feed shortage but too
expensive when feed prices fell.
Wet methods of forming fuels are like the method described by Richard
Stanley. Using water, chemicals, or biological degradation the biomass is
softened and the surface become sticky. You make a pulp, meal, or dough. You
can then use a press, like a piston press (a la Bryant), a meat grinder, a
roller mill, or a cement mixer (Davis) to form the fuel into balls or
bricks. Then you dry it out. The sticking mechanisms include the paper
bonding, as described above, and adhesion by any number of sugars, starches,
etc. that are activated or released by the process. The dried fuel is not as
dense as a pellet or briquette but it is uniform, it stays together, and It
burns very well because for the form of the fuel.
When we worked with Ben Bryant in the 1970s and 1980s we tried a number of
simple wet pulping processes to make building products for both developed
and developing countries and fibers for erosion control. Some of his
products from this period are still made commercially. In the 1990s Ben
introduced me to Richard and how he was applying some of the same wet
forming principles to make bricks for fuel (and for growing seedlings). The
lesson is to learn and understand how natural fibers and fiber chemistry can
be used to an advantage. Sometimes a small percentage of long wet fibers can
be used to bind together dry fine particles.
Torrefaction. Think of torrefaction as roasting biomass fuel in the absence
of air. Biomass is heated first to dry it, then in the absence of air to
280C. At this temperature it is completely dry and some of the cellulose has
converted to gas. You lose about 30% of the weight and 10% of the heating
value. The fuel is in the same form that you started with but it is dry and
brittle. If you have a densifier then it takes less energy to pelletize it.
The pellets store well because they resist moisture. Torrefaction is used
primarily for preparing wood fuel for burning with coal in very large
utility boilers. There are several torrefaction projects in Europe and a few
in North America. A plant in Mississippi has shipped a couple of large barge
loads of torrefied wood to customers in Europe.
There was a project in Rwanda some years ago that used partial torrefaction
to prepare fuel bricks for domestic use. A professor from the US designed a
small torrefier and installed it in a refuse fuel operation run by a women's
coop. The torrefied biomass was formed into a brick using a fire log maker
like the Shimada machine. A USAID employee we contacted knew of the project
but did not know if it was still in operation. I haven't heard of any
similar projects at the small scale.
I hope that this long-winded explanation helps make these processes clear.
Tom
-----Original Message-----
From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
ajheggie at gmail.com
Sent: Wednesday, June 12, 2013 1:01 AM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Meat grinder fuels for TLUDs was Re: wheat husk
pellets
[Default] On Wed, 12 Jun 2013 12:53:02 +0700,Paul Olivier
<paul.olivier at esrla.com> wrote:
How does lignin soften to become a binding agent using a meat grinder?
This would be truly wonderful, if it were true.
It won't with a meat grinder, you will need some sort of binder, like
boiled starch or clay.
Lignin plastisises under high pressure and heat, the heat is normally
derived from the friction of the material passing through the die. At
these pressures the cell walls collapse and then the lignin re sets to
form a pellet that is denser than the wood it was made from. All these
systems use a lot of power and the expensive dies wear.
The Shimada press is the one that produces a hexagonal log with a hole
down the middle, often blackened on the outside from the heat from the
press walls.
Similarly rotary die extruders use pinch rollers to punch small
amounts of feed through the holes.
Have a look at:
http://www.fao.org/docrep/x5738e/x5738e0j.htm
AJH
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