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 <[email protected]> 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: [email protected] 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@lists.**bioenergylists.org<[email protected]>] >> On Behalf Of >> [email protected] >> 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 >> <[email protected]> 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 >> >> ______________________________**_________________ >> Stoves mailing list >> >> to Send a Message to the list, use the email address >> [email protected].**org <[email protected]> >> >> to UNSUBSCRIBE or Change your List Settings use the web page >> http://lists.bioenergylists.**org/mailman/listinfo/stoves_** >> lists.bioenergylists<http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists> >> .org >> >> for more Biomass Cooking Stoves, News and Information see our web site: >> http://stoves.bioenergylists.**org/ <http://stoves.bioenergylists.org/> >> >> >> >> ______________________________**_________________ >> Stoves mailing list >> >> to Send a Message to the list, use the email address >> [email protected].**org <[email protected]> >> >> to UNSUBSCRIBE or Change your List Settings use the web page >> http://lists.bioenergylists.**org/mailman/listinfo/stoves_** >> lists.bioenergylists.org<http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org> >> >> for more Biomass Cooking Stoves, News and Information see our web site: >> http://stoves.bioenergylists.**org/ <http://stoves.bioenergylists.org/> >> >> > > ______________________________**_________________ > Stoves mailing list > > to Send a Message to the list, use the email address > [email protected].**org <[email protected]> > > to UNSUBSCRIBE or Change your List Settings use the web page > http://lists.bioenergylists.**org/mailman/listinfo/stoves_** > lists.bioenergylists.org<http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org> > > for more Biomass Cooking Stoves, News and Information see our web site: > http://stoves.bioenergylists.**org/ <http://stoves.bioenergylists.org/> > > -- 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 http://www.esrla.com/
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