ENERGY PELLET

Abstract

A high-energy water-resistant pellet of at least 75% biomass material such as torrefied wood, whole-tree (white) wood, agricultural waste, flax and the like. and the remainder a binder comprising from about 2% to about 20% by total weight of the pellet. The binder is a two-component systema plasticizer, such as tall oil pitch, rosin, fatty acid, vegetable oils, animal oils, corn protein and glycerinpreferably from 3% to about 20% of the binder, and lignin from about 80-97% of the binder.

Claims

1. A high-energy, water-resistant pellet comprising: (a) at least 75% biomass material; and (b) the remainder of said pellet being a two-component binder comprising from about 2% to about 20% by total weight of the pellet wherein said binder is a two-component system comprising a plasticizer, and the other component is lignin isolated from its source.

2. The high-energy water resistant pellet according to claim 1 wherein said high-energy water-resistant pellet comprises at least 85% biomass material and less than 10% by weight water.

3. The high-energy water resistant pellet according to claim 1 wherein said biomass material is selected from the group consisting of torrefied wood, whole-tree (white) wood, agricultural waste and flax.

4. The high-energy water resistant pellet according to claim 1 wherein said plastizer is selected from the group consisting of tall oil pitch, fatty acids, rosin, vegetable oil, animal oils, corn protein and glycerin.

5. The high-energy water resistant pellet according to claim 1 wherein said biomass material is flax.

6. The high-energy water resistant pellet according to claim 1 wherein said plastizer is glycerin.

7. The high-energy water resistant pellet according to claim 1 wherein said plasticizer is from about 3% to about 20% of said binder.

8. The high-energy water resistant pellet according to claim 1 wherein said lignin is from about 80% to about 97% of said binder.

9. The high-energy water resistant pellet according to claim 1 wherein high-energy water resistant pellets have a bulk density 40-45 lbs/ft.sup.3.

10. A high-energy, water-resistant pellet comprising: (a) at least 85% flax wood; and (b) the remainder of said pellet being a two-component binder comprising from about 2% to about 20% by total weight of the pellet, wherein one component of said binder is a plasticizer selected from the group consisting of tall oil pitch, fatty acids and rosin, vegetable oil, animal oils, corn protein and glycerin and the other component is lignin in an amount from about 80% to about 97% of said binder.

11. The high-energy, water-resistant pellet according to claim 10 wherein said plasticizer is glycerin.

12. A process for making an energy pellet from biomass material comprising: (a) preparing a binder by mixing from about 2% to about 20% total weight of said binder of lignin and the remainder of said binder being a plasticizer; (b) adding said binder to a biomass material to form a mixture of at least 75% of said biomass material; and the remainder of said mixture being said binder; and (c) compressing said mixture by extruding said mixture at a temperature at which said binder is in a molten state to form a pellet.

13. The process according to claim 12 wherein said plastizer is selected from the group consisting of tall oil pitch, fatty acids, rosin, vegetable oil, animal oils, corn protein and glycerin.

Description

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention now will be described more fully hereinafter in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather these embodiments are provided so that this disclosure will be through and complete and will fully convey the scope of the invention to those skilled in the art.

[0020] The energy pellets may be made from biomass material, such as torrefied wood, whole-tree (white) wood, agricultural waste, flax and the like. A preferred fuel pellet of the present invention is produced from torrefied wood having a moisture content of below 15% water, with the equilibria water content being about 10-15% water, that has been mixed with a binder and compressed by passing through an extruder, typically at a temperature at which the binder is in a molten state while the torrefied wood is compressed. Forming the pellets commonly involves hydraulic extrusion through a fuel pellet die. Of course, other suitable compression equipment known to those skilled in the art may be used. The temperature of the torrefied wood and binder in the extruder is above 100 C. but is not allowed to exceed 280 C. to avoid adverse exothermal torrefication conditions. Preferably the temperature is maintained between 100 C. and 165 C. Another preferred embodiment of the present invention uses flax. And yet another embodiment of the present invention uses whole-tree (white) wood. For use in this invention the white-wood is ground to a size that allows free-flow into the throat of the extruder.

[0021] The water-resistant high-energy pellet comprises at least 75% biomass material and preferably at least about 85% biomassmaterial, and the remainder a binder comprising from about 2% to about 25%, preferably about 3% to about 15%, by total weight of the pellet. The binder comprises of a plasticizer in an amount, preferably from 5% to about 20% by weight of the binder, and lignin from about 80% to about 97% by weight of the binder. The optimal ratio of the lignin to plasticizer will depend upon the characteristics of the biomass material, the lignin, and the plasticizer that are contained within the pellet. Those choices typically are made with economics being the primary factor.

[0022] Lignin, a by-product of the pulp and paper industry, of sufficiently low T.sub.g will flow and provide protective coverage within the pellet that is needed for water repellency but may not flow under the conditions of the pelletizer which operates at 105 C. and 40,000 psi. The individual characteristics of the lignin chosen may not be suitable without a plasticizer since its T.sub.g may be too high which inhibits its flow at the temperature of the pelletizer. Adding a plasticizer that itself is water resistant can provide the requisite T.sub.g allowing the binder to flow within the pelletizer yet solidify at ambient temperature. Again this ratio will be driven by performance and economics once the multiple large-volume lignin production facilities come on-line from papermaking operations and enzymatic conversion of biomass that will have lignin as a byproduct stream.

[0023] The plastizers contemplated for use in this invention are totally natural organics, preferably tall oil pitch, fatty acids, rosin, vegetable oils, animal oils, corn protein, glycerin and the like. The plastizer serves to plasticize the lignin while providing water repellency.

[0024] The preferred plastizer contemplated for use in this invention is a totally natural organic, such as glycerin. Glycerin comes from several sources such as vegetable oil. Glycerin isolated from vegetable oil processing provides a ready commercial source of natural plasticizers.

[0025] Tall oil pitch is another excellent binder, especially for fire logs. Tall oil pitch is currently commercially used for this application. The cost of TOP can be relatively high ($400-$600/ton). Tall oil pitch is the bottoms product from the first distillation column of a refinery that has tall oil as a feedstock and makes distilled rosins and fatty acids as products. The tall oil pitch may be used, or the spent tall oil pitch from which the valuable sterol fraction has been removed could be used.

[0026] Torrefied wood pellets have a bulk density (40-45 lbs/ft.sup.3), about twice that of non-pelletized torrefied wood (16-20 lbs/ft.sup.3), so making pellets dramatically reduces volume and subsequent transportation costs. Torrefied wood pellets have an energy density about the same as coal, 12,000 Btu/lb. Size-reduction characteristics of wood pelletshow they break down under mechanical forcesare much different than that of coal, which is a problem when large fractions of wood pellets are fed into existing pulverizing equipment used by all coal-burning power-generation equipment. However, size-reduction characteristics of torrefied wood pellets are very similar to those of coal. Thus the mechanical handling characteristics and energy density of torrefied wood pellets are very similar to coal, making those pellets much more acceptable as a direct substitute for coal.

[0027] As noted, one of the critical characteristics of the high-energy-content torrefied wood pellets of this invention is that they are water repellant. Another important property is pellet strength and attrition resistance, since dust creates not only worker health and safety issues but also dust severely reduces the bulk density of the pellets so that a ship loaded with pellets crossing an ocean carries a lower mass loading causing the shipping rates per ton to be higher. This densification effect is counter-intuitive because the dust particles separate the individual pellets thereby decreasing the bulk density instead of partitioning entirely in the interstitial areas of the bulk pellets.

[0028] Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.