[Stoves] Meat grinder fuels for TLUDs was Re: wheat husk pellets

Wed Jun 12 21:08:14 CDT 2013

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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