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

Wed Jun 12 21:37:44 CDT 2013

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<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<http://www.fao.org/docrep/x5738e/x5738e0j.htm>
>>
>>
>> AJH
>>
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-- 
Paul A. Olivier PhD
26/5 Phu Dong Thien Vuong
Dalat
Vietnam

Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
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