<div dir="ltr"><div><div><div><div>Tom's explanation still leaves me with a few questions.<br></div>Would the rice hull have to be ground into a powder to go through a meat grinder?<br></div>It takes a lot of energy and maintenance to grind up rice hulls.<br>
</div>With a conventional pellet machine, rice hulls do not have to be ground up.<br></div><div>What binder would be used with rice hulls?<br></div><div><br></div>Paul<br></div><div class="gmail_extra"><br><br><div class="gmail_quote">
On Thu, Jun 13, 2013 at 9:08 AM, Paul Anderson <span dir="ltr"><<a href="mailto:psanders@ilstu.edu" target="_blank">psanders@ilstu.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Stovers,<br>
<br>
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?<div class="im HOEnZb"><br>
<br>
Paul<br>
<br>
Paul S. Anderson, PhD aka "Dr TLUD"<br>
Email: <a href="mailto:psanders@ilstu.edu" target="_blank">psanders@ilstu.edu</a> Skype: paultlud Phone: +1-309-452-7072<br>
Website: <a href="http://www.drtlud.com" target="_blank">www.drtlud.com</a><br>
<br></div><div class="HOEnZb"><div class="h5">
On 6/12/2013 4:24 AM, Tom Miles wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Andrew,<br>
<br>
Good explanation.<br>
<br>
Think of two methods of forming fuels. One requires high heat and pressure.<br>
The other requires water and biological or chemical degradation.<br>
<br>
Heat, pressure and some moisture (10% MC) are required for densification to<br>
pellets, briquettes or fire logs. A dry biomass is finely ground and pressed<br>
through a metal die. There are two principal binding mechanisms. In one,<br>
cellulose fibers pressed together with heat removes excess water and the<br>
fibers are bonded to each other through what is called paper bonding, or<br>
hydrogen bonding. It is like wetting two pieces of paper and letting them<br>
dry out. They are difficult to pull apart. This is a chemical bond that is a<br>
major bonding mechanism for most densification. When you break the pellet or<br>
briquette it falls apart rather than snaps.<br>
A second mechanism is lignin plastic flow, as Andrew describes below. The<br>
lignin and part of the celluloses actually plasticize and flow. Under high<br>
power magnification with a scanning electron microscope a portion of the<br>
wood looks like solid plastic with no identifiable fibers. These pellets<br>
snap when you break them.<br>
<br>
Both mechanisms are at play in a densifier. Together these mechanisms make a<br>
durable pellet or briquette. As Andrew points out they require power and an<br>
extrusion process like a pellet mill.<br>
<br>
A third mechanism that is used with mechanical densifiers is adding chemical<br>
binders, starches, or even expanding clays. These were employed in the<br>
older, low power cubers and briquetters to make animal feed. Molasses based<br>
binders were added to help stick hay together in cubes and to add nitrogen<br>
(protein) etc. They often added 30% to the cost of the feed. We used sodium<br>
hydroxide to hydrolyze straw to make it pliable for making cubes. It had the<br>
advantage of making the straw more digestable for the animals. This was fine<br>
for using low quality feeds like straw in times of feed shortage but too<br>
expensive when feed prices fell.<br>
<br>
Wet methods of forming fuels are like the method described by Richard<br>
Stanley. Using water, chemicals, or biological degradation the biomass is<br>
softened and the surface become sticky. You make a pulp, meal, or dough. You<br>
can then use a press, like a piston press (a la Bryant), a meat grinder, a<br>
roller mill, or a cement mixer (Davis) to form the fuel into balls or<br>
bricks. Then you dry it out. The sticking mechanisms include the paper<br>
bonding, as described above, and adhesion by any number of sugars, starches,<br>
etc. that are activated or released by the process. The dried fuel is not as<br>
dense as a pellet or briquette but it is uniform, it stays together, and It<br>
burns very well because for the form of the fuel.<br>
<br>
When we worked with Ben Bryant in the 1970s and 1980s we tried a number of<br>
simple wet pulping processes to make building products for both developed<br>
and developing countries and fibers for erosion control. Some of his<br>
products from this period are still made commercially. In the 1990s Ben<br>
introduced me to Richard and how he was applying some of the same wet<br>
forming principles to make bricks for fuel (and for growing seedlings). The<br>
lesson is to learn and understand how natural fibers and fiber chemistry can<br>
be used to an advantage. Sometimes a small percentage of long wet fibers can<br>
be used to bind together dry fine particles.<br>
<br>
Torrefaction. Think of torrefaction as roasting biomass fuel in the absence<br>
of air. Biomass is heated first to dry it, then in the absence of air to<br>
280C. At this temperature it is completely dry and some of the cellulose has<br>
converted to gas. You lose about 30% of the weight and 10% of the heating<br>
value. The fuel is in the same form that you started with but it is dry and<br>
brittle. If you have a densifier then it takes less energy to pelletize it.<br>
The pellets store well because they resist moisture. Torrefaction is used<br>
primarily for preparing wood fuel for burning with coal in very large<br>
utility boilers. There are several torrefaction projects in Europe and a few<br>
in North America. A plant in Mississippi has shipped a couple of large barge<br>
loads of torrefied wood to customers in Europe.<br>
<br>
There was a project in Rwanda some years ago that used partial torrefaction<br>
to prepare fuel bricks for domestic use. A professor from the US designed a<br>
small torrefier and installed it in a refuse fuel operation run by a women's<br>
coop. The torrefied biomass was formed into a brick using a fire log maker<br>
like the Shimada machine. A USAID employee we contacted knew of the project<br>
but did not know if it was still in operation. I haven't heard of any<br>
similar projects at the small scale.<br>
<br>
I hope that this long-winded explanation helps make these processes clear.<br>
<br>
Tom<br>
<br>
<br>
<br>
<br>
-----Original Message-----<br>
From: Stoves [mailto:<a href="mailto:stoves-bounces@lists.bioenergylists.org" target="_blank">stoves-bounces@lists.<u></u>bioenergylists.org</a>] On Behalf Of<br>
<a href="mailto:ajheggie@gmail.com" target="_blank">ajheggie@gmail.com</a><br>
Sent: Wednesday, June 12, 2013 1:01 AM<br>
To: Discussion of biomass cooking stoves<br>
Subject: Re: [Stoves] Meat grinder fuels for TLUDs was Re: wheat husk<br>
pellets<br>
<br>
[Default] On Wed, 12 Jun 2013 12:53:02 +0700,Paul Olivier<br>
<<a href="mailto:paul.olivier@esrla.com" target="_blank">paul.olivier@esrla.com</a>> wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
How does lignin soften to become a binding agent using a meat grinder?<br>
This would be truly wonderful, if it were true.<br>
</blockquote>
It won't with a meat grinder, you will need some sort of binder, like<br>
boiled starch or clay.<br>
<br>
Lignin plastisises under high pressure and heat, the heat is normally<br>
derived from the friction of the material passing through the die. At<br>
these pressures the cell walls collapse and then the lignin re sets to<br>
form a pellet that is denser than the wood it was made from. All these<br>
systems use a lot of power and the expensive dies wear.<br>
<br>
The Shimada press is the one that produces a hexagonal log with a hole<br>
down the middle, often blackened on the outside from the heat from the<br>
press walls.<br>
<br>
Similarly rotary die extruders use pinch rollers to punch small<br>
amounts of feed through the holes.<br>
<br>
<br>
Have a look at:<br>
<br>
<a href="http://www.fao.org/docrep/x5738e/x5738e0j.htm" target="_blank">http://www.fao.org/docrep/<u></u>x5738e/x5738e0j.htm</a><br>
<br>
<br>
AJH<br>
<br>
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