EP0018372A1

EP0018372A1 - Fuel pellets

Info

Publication number: EP0018372A1
Application number: EP79900410A
Authority: EP
Inventors: Ian Fraser Johnston
Original assignee: Individual
Current assignee: JOHNSTON, IAN FRASER
Priority date: 1978-04-26
Filing date: 1979-12-04
Publication date: 1980-11-12
Also published as: WO1979000988A1; AR223339A1; NO791383L; FI791339A

Abstract

Une boulette combustible comprend de 90 a 99% environ en poids de materiau cellulosique naturel et de 1 a 10% environ en poids de materiau thermoplastique polymere synthetique. La teneur en eau du materiau cellulosique est d'environ 5 a 25% en poids. Le materiau thermoplastique est generalement inferieur a 5 mesh. La maille du materiau thermoplastique synthetique est distribue dans toute la boulette combustible. Le materiau thermoplastique est solide a temperature ambiante et a une temperature de moulage par injection d'au moins 95 C. Une telle boulette combustible peut etre preparee dans un appareil a former les boulettes (70) ou la temperature de la boulette lorsqu'elle sort de la matrice est de 66 a 122 C environ.A combustible pellet comprises from about 90 to 99% by weight of natural cellulosic material and from about 1 to 10% by weight of synthetic polymeric thermoplastic material. The water content of the cellulosic material is about 5 to 25% by weight. The thermoplastic material is generally less than 5 mesh. The mesh of synthetic thermoplastic material is distributed throughout the fuel pellet. The thermoplastic material is solid at room temperature and at an injection molding temperature of at least 95 C. Such a combustible pellet can be prepared in a pelletizer (70) or the temperature of the pellet when it comes out of the matrix is from 66 to 122 C approximately.

Description

FUEL PELLETS

Background of the Invention

Due to diminishing quantities of coal, petroleum, and natural gas products, attention is being directed to other energy sources, including oil shale, solar energy, and nuclear energy. One source which is receiving considerable attention is biomass materials such as wood and its byproducts.

Recently, much attention has been directed to preparing briquets from wood waste.

Use of available pelletized wood waste as a fuel source has achieved only limited acceptance to date.

One reason for this is the relatively low heating value of pelletized wood as compared to coal. Other problems with use of available pelletized wood as a fuel source is that it has a slow burning rate and it exhibits incomplete burnout, resulting in formation of carbonaceous residues and low combustion efficiency. In addition, pelletized wood can be harder to ignite than coal and pelletized wood can be more fragile than coal, requiring special handling to avoid crumbling and to prevent weathering. To overcome the crumbling and weathering problems, inorganic binders such as cement and silicate of soda, and organic binders such as tar, pitch, rosin, glues, and fibers have been included in the pellets. However, no binder has been found which solves the above problems, and which also is inexpensive and does not reduce the heating value of the wood.

It has been attempted to use the self-binding characteristics of various species of wood due to lignin present to avoid the crumbling problem. This can be effected with some species of wood, but not all species, by heating the wood above its minimum plastic tempera¬ ture of 163°C. However, such high temperatures can severely limit the operating life of the pelletizing equipment and drive high BTU volatile components from the wood.

Therefore, there is a need for a fuel pellet which resists crumbling, is easily ignitable, burns fast and completely, and has a good heating value. There is also a need for a method for preparing the fuel pellet which does not require high pelletizing temperature.

Summary of the Invention

This invention provides a fuel pellet with the above features and a method for preparing the fuel pellet. The fuel pellet comprises from about 90 to about 99% by weight natural cellulosic material, and from about 1 to about 10% by weight synthetic polymeric thermoplastic material. The free moisture content of the cellulosic material is from about 5% to about 15%. The plastic is generally finer than 5 mesh. The thermoplastic material is chosen so it is solid at room temperature and has an injection molding temperature of at least 95°C. Preferably, the thermoplastic material is distributed throughout the pellet. The thermoplastic material serves to bind the pellet together, increase the heating value of the pellet, lubricate the pelletizing die, and improve the ignition and burning characteristics of the pellet. Fuel pellets of the present invention exhibit complete burnout, burn faster than pellets not containing thermoplastic material, and can have a heating value in excess of 5,005 K.Cal/Kg.

The fuel pellet can be made by preparing a feed of particulate natural cellulosic material and particulate synthetic thermoplastic material. Substantially all of the thermoplastic material is -5 mesh, and preferably -10 mesh. The plastic and cellulosic materials are intimately combined by compressing the feed in a die.

Brief Description of the Drawings

FIGURE 1 llustrates in a perspective view a pellet representative of pellets prepared according to the present invention; and

FIGURES 2A and 2B illustrate a process embodying features of the process of the present invention. These two Figures are to be considered serially.

1 Detailed Description

With reference to Figure 1, there is shown a fuel pellet 10 prepared from cellulosic and thermoplastic materials. Fuel pellet 10, which is cylindrical in shape,

5. preferably has a minimum dimension of at least 4.75 m.m. and comprises from about 90 to about 99% by weight natural cellulosic material and from about 1 to about 10% by weight thermoplastic material.

The natural cellulosic material used to form the

10 pellets 10 can be particulate woody material such as sawdust, wood shavings, sander's dust, hog fuel, peat, and bark. Agricultural waste such as banana and papaya stalks, straw, bamboo, jute, bagasse, corn husks, corn cobs, cotton "gin trash", sisal, seed hulls, and peanut

15 hulls can also be used. Also, paper and cardboard can be included in the pellets. Combinations of the above natural cellulosic materials can also be used. Preferred natural cellulosic materials are those with low moisture content to minimize drying costs, and low contamination

20 levels to minimize pelletizer die wear. As used herein, the term "cellulosic material" includes lignin.

Particulate wood material preferably is used in the pellets because it has a higher heating value and lower moisture content than agricultural waste. Inclusion

25 of banana and/or papaya stalks in the pellets is desirable because banana and papaya latex are good binding agents and contribute to the cohesiveness of the pellets.

The synthetic thermoplastic material can be

30 practically any available synthetic thermoplastic such as, but not limited to, polystyrene, polyethylene, polypropylene, acrylonitrile-butadiene-styrene, acetal copolymer, acetal homopolymer, acrylic, polybutylene, and combinations thereof. Although thermoplastics

35 combinations thereof. Although thermoplastics containing a halogen such as polyvinylchloride can be used, for most applications these are to be avoided becaus of corrosion and emission problems associated with the combustion products of halogen-containing thermoplastics. It has been noted that for fast burning and ease of ignition of the fuel pellets, polypropylene and polyethylene are the preferred synthetic thermoplastic materials.

The term "synthetic thermoplastic materials" excludes naturally occurring thermoplastic materials and naturally occurring cellulosic materials. For ease of handling, the synthetic thermoplastic material must be solid at room temperature. Preferably the synthetic thermoplastic material has an injection molding temperature of at least 95°C. The minimum injection molding temperature of common thermoplastics as reported in Modern Plastics Encyclopedia, Vol. 49, McGraw-Hill, 1972-3 Edition, is presented in Table 1.

TABLE 1 Minimum Injection

Synthetic Thermoplastic Molding Temperature (°F.) Polystyrene 163°C. (325°F.)

Polyethylene 122°C. (250°F. )

Polypropylene 191°C. (375°F.) ABS 183°C. (360°F. )

Cellulosics 168°C. (335°F.)

Nylon 191°C. (360°F. )

Polyesters 132°C. (270°F.)

It has been found difficult to pelletize a feed containing more than about 1.25% by weight high impact polystyrene. It was noted that pelletizer production rate decreased with such a feed and it was difficult to thoroughly disperse the high impact polystyrene in the pellets. Therefore, when the pellets include high impact polystyrene, it is preferred that feed to a

OM pelletizer contains only up to about 1.25% by weight high impact polystyrene. It is desirable to include polystyrene in the pelletizer feed because it has been found that polystyrene contributes greatly to the cohesiveness of the fuel pellets, such cohesiveness is important because it is undesirable for the pellets to break or disintegrate during handling and storage. Such breakage and disintegration can produce fines and dust, which can be a serious fire and explosion hazard. It is critical to the present invention that at least 1% by weight thermoplastic material be included in the fuel pellets. This is because fuel pellets containing thermoplastic material have many significant advantages compared to fuel pellets containing only cellulosic material. For example, inclusion of thermoplastic material in fuel pellets allows the fuel pellets to be formed easily in a pelletizer at temperatures lower than temperatures required for forming a fuel pellet with only cellulosic material. Thus, the thermoplastic material serves as a processing aid for forming pellets from the cellulosic material. In addition, the thermoplastic material has a higher heating value than the cellulosic material, and the resulting pellets have a correspondingly high heating value.

Another advantage of the presence of synthetic thermoplastic material in fuel pellets is that the thermoplastic material provides a substantially water-impervious coating, or sheath on the outside of the pellets, thereby both preventing uptake of moisture by the pellets and resisting weathering in storage. Because of the uniform distribution of the plastic within the pellets, there is plastic even at the ends of a cylindrical pellet. This also prevents uptake of water by the pellets. Furthermore, the hydrophobic nature of the plastic prevents water uptake.

A portion of the thermoplastic material can be in the fuel pellets in the form of discrete subparticles. The presence of discrete thermoplastic subparticles in fuel pellets results in easy ignition because the discrete subparticles provide an ignition situs.

Surprisingly, it has been found that the fuel pellets exhibit burning and ignition characteristics which are superior to the burning and ignition characteristics of either the cellulosic material and thermoplastic material which make up the fuel pellets. .For example, burning tests were conducted with (1) conventional fuel pellets made only with sawdust, (2) polypropylene, and (3) fuel pellets according to the present invention prepared with 91% by weight sawdust (different from the sawdust used for the all sawdust pellets) and 9% by weight polypropylene. The all sawdust fuel pellets burned at a rate equal to about 1/2 the rate of the fuel pellets of the present invention. The two types of fuel pellets were about the same size, but it should be noted that the all sawdust fuel pellets were denser than the sawdust/polypropylene fuel pellets, but this accounts for only part of the difference in burning rate. It has been noted that fuel pellets containing plastic burn faster than less dense conventional all wood pellets.

Therefore, in a boiler of a fixed size, the fuel pellets of the present invention can be used to generate heat and steam at a faster rate than conventional fuel pellets. In addition, the sawdust/polypropylene fuel pellets left practically no residue, while the conventional fuel pellets left a carbonaceous residue. Furthermore, the fuel pellets consisting only of thermoplastic material did not burn completely, but kept self-extinguishing. This was not a problem with the fuel pellets of the present invention. Therefore, fuel pellets prepared from cellulosic material and plastic material burn better than either the cellulosic material alone or the plastic material alone.

It is believed that thermoplastic material in fuel pellets acts as a binder for the cellulosic materials. Pellets containing at least 5% by weight thermoplastic material have been demonstrated to have sufficient toughness to withstand exposure to the shocks of transportation, storage, and stoking. When a pellet includes thermoplastic material, crumbling and excessive softening from weathering are avoided. Furthermore, thermoplastic materials typically have a higher heating value than cellulosic material. The pellets should contain at least 1% by weight of the thermoplastic material, and more preferably at least about 2.5% by weight, to obtain these advantages.

Preferably, the fuel pellets contain from about 1 to about 10% by weight thermoplastic material, and more preferably from about 2.5 to about 10% by weight thermoplastic material.

Materials other than natural cellulosic material and synthetic thermoplastic materials can be included in the pellets. For example, materials such as comminuted tires, thermosetting^' resins and/or petroleum distillation residue can be added to improve the heating value of the pellets.

Oxidizing agents such as sodium perchlorate and ammonium nitrate to facilitate combustion can also be included in the pellets. Also, binding agents in addition to thermoplastic materials can be used. Exemplary of such binding agents are paraffin slack wax, carnuba wax, and lignosulfonates, such as ammonium lignosulfonate, sodium lignosulfonate, calcium lignosulfonate, and magnesium lignosulfonate. Certain cellulosic materials can be added to the pellets as a pelletizing or processing aid. Preferred materials in this category are oil seeds and their products, which by their fatty acid content reduce wear on the dies of the pelletizing equipment. Exemplary of such materials which can be included are coconut husks, 'soy beans, peanuts, sunflower seeds, corn cake, pressing residuals, and the like.

As used herein, the term "pellet" refers to a discrete particle of any size or shape which contains both natural cellulosic material and synthetic thermoplastic material. The pellet need not be symmetrical, but it is preferred that pellet 10 be substantially symmetrical in shape, such as cylindrical, parallelepiped, or the like, having a diameter within the range of from about 4.75 m.m. to about 25.4 m.m. While it is most practical to form the pellets in a cylindrical shape, the pellets can be in any suitable symmetrical configuration such as the shape of a cube. The larger the diameter of the particles, the slower their burning rate. This is because of the fact that as the diameter increases, the surface area to volume ratio of the particles decreases. Depending upon the flame temperature and burning rate required in any given boiler, the optimum feed diameter for that boiler can vary within the range of about 4.75 m.m. to about 25.4 m.m.

It is necessary that the particulate cellulosic feed and particulate synthetic thermoplastic feed have a maximum particle size less than about 60% of the minimum dimension of the pellet to avoid crumbling of the pellet in storage. For example, if the pellet is cylindrical and has a diameter of 1/4 inch, then the cellulosic feed and thermoplastic feed should have a maximum particle size of about 3.82 m.m. (0.6 x 6.35), i.e. about 5 mesh.

OΛiP

^" The bulk density of the particles can vary in the range of from about 482 to about 643 kilograms per cubic meter. It has been found that pellets 25.4 m.m. long and 6.3 m.m. in diameter made from about 90% sawdust and about 10% polyethylene thermoplastic can have a bulk density of about 611 kilograms per cubic meter.

A process for preparing fuel pellets is shown schematically in Figures 2A and 2B. Cellulosic feed material, plastic feed particles, and plastic feed sheet are delivered by trucks (not shown) and stored in storage bins 20a, 20b, and 20c, respectively. Additional feed storage bins can be provided for segregating different types of feed. The feed, either before or after introduction into the feed bins, can be treated to separate foreign materials such as metallic impurities and soil. This can be done by means of such equipment as pneumatic conveyers, screen, magnets, and combinations thereof. Magnets conventionally are built into the equipment, described below, used for comminuting the feed materials. The feed from the cellulosic feed storage bin 20a is transferred via a belt conveyer 24a to a classifying device such as a vibrating screen 26 to separate oversize particles 28 from particles 30 which are suitable for direct feed to a pelletizing operation. The size of the holes in the screen depend upon the size of the pellets to be made, but in any case, the size of the holes is necessarily smaller than the minimum dimension of the pellets.

In the comminution device, the feed cellulosic material is comminuted to a desired particle size. As used herein, the term "comminution" refers to any physical act of size reduction, including, but not limited to chopping, crushing, and grinding by suitable machinery. There are at least three types of machines useful for reducing the size of wood. Veneer and comparable fine scrap can be reduced to chips in a hammer ill, in which rotating bars of various designs break up the material by impact. A disk chipper can be used for solid scrap and round wood of various sizes. This chipper has knives set in radial slots. A knife hog is similar in action to the chipper, but the knives are set in the sloping surfaces of a V-shaped drum. The knife is suitable for solid wood and for scraps that may be somewhat smaller than the disk chipper can handle. Exemplary of the operation of the hammermill 32 is comminuting cellulosic feed for making cylindrical pellets having a diameter of 9.5 m.m. and cylindrical pellets having a diameter of 6.35 m.m. For pellets having a diameter of 9.5 m.m., preferably, all of the particles are -5 mesh, and at least 50% of the particles are -10 mesh. If the pellets have a diameter of 6.35 m.m., then preferably all of the cellulosic material is comminuted to -10 mesh. Preferably, the comminuting equipment is operated so that substantially all of the particulate cellulosic material has a particle size greater than about 30 mesh. This is to avoid the presence of fines and dust in the feed to the pelletizer, and the explosion hazard associated with such small particles of cellulosic material. The particles 30 not requiring comminution and the comminuted particles 34 from the hammermill 32 are collected on a belt conveyer 36 and passed via ducts 37 to two rotary driers 38 in parallel to reduce the moisture content of the cellulosic material. To develop the necessary strength and hardness in the pellets, it is essential that the free moisture content of the cellulosic material be reduced to less than about 15% by weight. By "free moisture" there is meant moisture which can be removed by evaporation at normal temperatures and does not include any bound water such as chemically

BU

O bound water that might be present in the feed material. Various types of dryers such as steam-heater plates, and dry steam pipes over which the feed is cascaded can be used to bring the feed to the desired moisture content. Flash dryers using a short exposure to hot gases can be used. The heat from drying can be provided by burning the fuel pellets and/or fines produced by this process in a heater 40 which supplies hot gas via ducts 41 to the dryers. When the free moisture content of the cellulosic material is reduced to less than about 5% by weight, the pellets upon discharge from the pelletizer burst and demonstrate a "Christmas tree" effect. These pellets are unsatisfactory because they tend to form fines in storage and handling. This problem can be overcome by introducing steam, as necessary, at the pelletizer. In summary then, preferably the dryers reduce the moisture content of the feed to about 5% to about 15% by weight, the same as required for feed to the pelletizer. For high production rates from a pelletizer, and for production of pellets which exhibit excellent cohesiveness and high strength, preferably the free moisture content of the feed to the pelletizer is from about 8% to about 12% by weight, and most preferably about 10% by weight.

To aid in drying the cellulosic feed material, dry slaked lime, i.e. calcium carbonate, can be combined with the dryer feed. The calcium carbonate combines with water of the feed material and then releases moisture more easily in the dryer, thereby aiding more rapid drying of the feed material. Use of calcium carbonate in an amount of from about 2 to about 10% by weight of the feed, and preferably in an amount of about 5% by weight, significantly aids in the drying process. The preferred grade of calcium carbonate is a fine grade having a particle size of less than 100 mesh. When this drying technique is used, the product fuel pellets contain at least 1% by weight calcium.

It is believed that to make good pellets with bark, it is necessary to first comminute the bark, then dry the comminuted bark and then comminute the dried bark one more time before feeding to the pelletizer. This is because raw bark is usually available only as large particles which are difficult to dry efficiently. Water can be removed from the feed material upstream of the dryers when the feed material contains gross quantities of water. For example, water can be removed from peat, bark, or sawdust with presses that operate on the roller or clothes-wringer principle. Screw presses, using tapered screws, are also useful for dewatering of bark. The drying operation can be run as a batch operation to avoid the expense of duplicating drying, cooling and conveying equipment for different cellulosic feed materials. The gases and water evolved in the dryers 38 are withdrawn from the dryers via lines 42 into two cyclones 44 in parallel, one for each dryer, by an exhaust fan 46. The discharge from the fan 46 can be passed to a dust collector (not shown) or passed directly to the atmosphere. Particulate matter withdrawn via line 42 is separated in the cyclones 44 and dropped into a fines bin 47. The particulate matter in bin 47 is fed by a rotary valve 48 to a fines bin 77 (Figure 2A). The dried feed material is transferred by a storage bin tank feed conveyer 49 to one or more storage bins 52a or 52b (Figure 2B). The different storage bins are used for storing different types of feed material. More storage bins than the two storage bins shown in Figure 2A can be used. The storage bins 52a and 52b preferably are tumbled bins to avoid compaction of the feed material and to maintain dehydration of the feed. A rotary cooler (not shown) using ambient air to cool the material dis¬ charged by the dryer can be used if required to avoid caking of the feed material in storage. The plastic feed is passed from the plastic feed bins 20b and 20c via belt conveyers 24b and 24c, respectively, to comminution devices such as granulators 56a and 56b, respectively. The smaller the particle size of the thermoplastic feed, the stronger the fuel pellets and the more even and uniform their burning characteristics, and the less plastic required in the fuel pellets. In addition, when the pellets are to be pulverized before burning, it is important that the plastic be comminuted to a small size so that each- particle resulting f om the pulverization contains both plastic and cellulosic material. Therefore, the granulators are operated so that substantially all of the particulate thermoplastic material is minus 5 mesh. Preferably, the bulk, i.e. at least 50% by weight of the particulate thermoplastic material is minus 10 mesh, and more preferably substantially all is minus 10 mesh. It is believed that optimumly substantially all of the plastic is -20 mesh. The comminuted plastic feed discharged by the granulators 56a and 56b passes to belts 57a and 57b, respectively, for transport to plastic feed storage bins 52c and 52d, respectively. More than two plastic storage bins can be used if required.

Each of the storage bins has associated with it a weigh belt conveyer 62a, 62b, 62c, or 62d. The four conveyers 62a, 62b, 62c, and 62d are used to provide the proper weight ratios of the feed materials to a pellet mill 70. The four conveyers drop their feed onto a belt conveyer 64 which carries it to a chamber 65 for preheating of the feed with dry steam, if desired. From the chamber 65 the feed passes into a mixer 66

OMPI W1P0 such as a combination mill to obtain uniform mixing of the different types of feed material. The mixer discharges mixed feed onto a belt conveyer 67 which lifts the feed to a pellet mill feed bin 68. The feed is gravity fed from the bin 68 to a conveyer 69 which drops the feed into the pellet mill 70 in which the pellets of the present invention, such as a pellet shown in Figure 1, are formed. Any suitable pelletizing machin can be used. In this apparatus, the material is fed into a hopper and pressed into dies having the desired configuration and shape.

The pellet mill must be capable of producing a pressure in the die during compression which causes the temperature of the feed material to increase so that the pellets have a temperature of from about 66°C. to about 122°C. where they are discharged from the pellet mill, i.e. where the pressure is released. When the discharged pellets are at a temperature in excess of abou 122°C. , degradation and carbonization of the thermoplastic material can occur, and when the discharged pellets are at a temperature of less than about 66°C. , the pellets can have insufficient cohesiveness. Preferably, the discharge temperature of the pellets is from about 88 to about 123°C. to produce pellets with excellent burning properties and good cohesion. As the discharge temperature of the pellets increases, their density increases.

Supplemental heat and moisture for the pellet mill 70 can be provided by steam 71 which can be generated in a boiler 72 fueled by pellets produced by this process or reject fines. The steam can be used for drying the feed in the dryers 38.

Pellet mills can produce a high pressure at the impact point of the rollers to produce the desired temperature during pelletizing. A portion of the thermoplastic material forms a surface skin on the pellet at these temperatures. This skin protects the pellets from shattering and from significant changes in moisture content. Before introducing the feed to the pelletizer, it can be combined with a binding agent such as an aqueous solution of sodium silicate. For example, the material can be sprayed with about 5% by weight based on the total feed of 40 Bau e alkali stabilized sodium silicate solution added to the mixer 66. During the drying step, the moisture content needs to be adjusted to compensate for the water added by spraying with the silicate solution. It is believed that destabilized alkali sodium silicate solubilizes lignin of the cellulosic feed and the lignin then polymerizes, resulting in a stronger pellet.

From the pellet mill, the formed pellets are cooled in a cooler 72 by ambient air supplied by a blower 73, and transferred to a screen 74 for separation of any fines 75 which are carried by a conveyer 76 to a fines storage bin 77. The fines are transferred from the storage bin 77 by a rotary valve 78 and a blower 79 for feed to the boiler 72 used to generate steam for the pellet mill. The product pellets 80 can be sent to storage, bagged, or transferred to trucks or railroad cars for shipment.

Claims

WHAT IS CLAIMED IS:

1. A fuel pellet comprising from about 90 to about 99 percent by weight natural cellulosic material and from about 1 to about 10 percent by weight synthetic polymeric thermoplastic material, the synthetic thermoplastic material being distributed throughout the fuel pellet, the thermoplastic material being solid at room temperature and having an injection molding temperature of at least 95°C. , the free moisture content of the cellulosic material being from about 5 to about 15% by weight.

2. The fuel pellet of Claim 1 wherein the thermoplastic material comprises polypropylene.

3. The fuel pellet of Claim 1 wherein the thermoplastic material is selected from the group consisting of polystyrene, polyethylene, polypropylene, acrylonitrile-butadiene-styrene, acetal copolymer, acetal homopolymer, acrylic, polybutylene, and combinations thereof.

4. The fuel pellet of Claim 3 comprising up to about 1.25 percent by weight polystyrene.

5. The fuel pellet of any of the preceding claims including at least about one percent by weight calcium.

6. The fuel pellet of any of the preceding claims wherein the cellulosic material includes one or more of banana stalks or papaya stalks.

7. The fuel pellet of any of the preceding claims wherein the cellulosic material includes oil seeds, products of oil seeds, or both.

8. The fuel pellet of any of the preceding claims having a minimum dimension of about 4.75 m.m..

9. The fuel pellet of any of the preceding claims wherein the cellulosic material includes at least one member selected from the class consisting of peat and bagasse.

^B 10. The fuel pellet of any of the preceding claims wherein the thermoplastic material is present in an amount of from about 2.5 percent to about 10 percent by weight. 11. A fuel pellet of any of the preceding claims wherein the synthetic thermoplastic material covers the pellet to present a substantially hydrophobic surface.

12. A method for preparing a fuel pellet from particulate natural cellulosic material and particulate synthetic polymeric thermoplastic material comprising the steps of: a) providing particulate natural cellulosic material having a free moisture content of from about 5 to about 15 percent by weight, and substantially all of the particulate cellulosic material being minus 5 mesh; b) providing particulate synthetic polymeric thermoplastic material which is solid at room temperature and has an injection molding temperature of at least 90°C. , substantially all of the particulate thermoplastic material being minus 5 mesh; c) preparing a feed comprising from about 90 percent to about 99 percent by weight of the particulate cellulosic material and from about 1 percent to about 10 percent by weight of the particulate thermoplastic material; and d) compressing the feed in a die at a pressure whereby the temperature of the resulting pellet as it emerges from the die is from about 66°C. to about 122°C.

13. The method of Claim 12 in which the temperature of the pellet as it emerges from the die is from about

88°C. to about 123°C. 14. The method of any preceding Claim 12 and 33 in which particulate thermoplastic material is selected from the group consisting of polystyrene, polyethylene, polypropylene, acrylonitrile-butadiene-styrene, acetal copolymer, acetal homopolymer, acrylic, polybutylene, and combinations thereof.

15. The method of any preceding Claim 12 through

14 in which the particulate thermoplastic material includes polystyrene and the die eed comprises up to about 1.25 percent by weight of polystyrene.

16. The method of any preceding Claim 12 through

15 in which the particulate cellulosic material comprises banana stalks, papaya stalks, or both.

17. The method of any preceding Claim 12 through 16 in which the step of providing particulate cellulosic material comprises combining particulate cellulosic material having a free moisture content greater than 55 percent by weight with calcium carbonate, and then drying the particulate cellulosic material to the prescribed free moisture content.

18. The method of Claim 1 in which the particulate cellulosic material is combined with an amount of calcium carbonate equal to about 2 to about 10 percent by weight of the particulate cellulosic material. 19. The method of Claim 17 in which the particulate cellulosic material is combined with an amount of calcium carbonate equal to about 5 percent by weight of the cellulosic material.

20. The method of any preceding Claim 12 through 19 in which the particulate cellulosic material includes oil seeds, products of oil seeds, or both, for lubricatio of the die. 21. The method of any preceding Claim 12 through 20 in which the step of preparing a die feed comprises preparing a die feed including from about 2.5 to about 10 percent by weight of the particulate thermoplastic material.

22. The method of any preceding Claim 12 through

15 in which the particulate cellulosic material comprises peat.

23. The method of any preceding Claim 12 through 15 in which the particulate cellulosic material comprises bagasse.

24. The method of any preceding Claim 12 through

23 including the step of combining the cellulosic material with alkali stabilized sodium silicate. 25. The method of any preceding Claim 12 through

24 in which the particulate cellulosic material has a free moisture content of from about 8 to about 12 percent by weight.

26. The method of any preceding Claim 12 through ^' 25 in which the bulk of the particulate thermoplastic material is minus 10 mesh.

27. The method of any preceding Claim 12 through

25 in which substantially all of the particulate thermoplastic material is minus 10 mesh.

AMENDED CLAIMS

(received by the International Bureau on 2 October 1979 (02.

10.79)) 10. The fuel pellet of any of the preceding claims wherein the thermoplastic material is present in an amount of from about 2.5 percent to about 10 percent by weight.

11. A fuel pellet of any of the preceding claims wherein the synthetic thermoplastic material sheaths the pellet to present a substantially hydrophobic surface.

12. A method for preparing a fuel pellet from particulate natural cellulosic material and particulate synthetic polymeric thermoplastic material comprising the steps of: a) providing particulate natural cellulosic material having a free moisture content of from about 5 about 15 percent by weight, and substantially all of the particulate cellulosic material being minus 5 mesh; b) providing particulate synthetic polymeric thermoplastic material which is solid at room temperatur and has an injection molding temperature of at least 90°C. , substantially all of the particulate thermoplasti material being minus 5 mesh; c) preparing a feed comprising from about 90 percent to about 99 percent by weight of the particulate cellulosic material and from about 1 percent to about 10 percent by weight of the particulate thermoplastic material; and d) compressing the feed in a die at a pressur whereby the temperature of the resulting pellet as it emerges from the die is from about 66°C. to about 122°C.

13. The method of Claim 12 in which the temperatur of the pellet as it emerges from the die is from about

88°C. to about 123°C.

14. The method of any preceding Claim 12 and 13 in which particulate thermoplastic material is selected from the group consisting of polystyrene, polyethylene, polypropylene, acrylonitrile-butadiene-styrene, acetal copolymer, acetal homopolymer, acrylic, polybutylene, and combinations thereof.

15. The method of any preceding Claim 12 through

14 in which the particulate thermoplastic material includes polystyrene and the die feed, comprises up to about 1.25 percent by weight of polystyrene.

16. The method of any preceding Claim 12 through

.

18. The method of Claim12 in which the particulate cellulosic material is combined with an amount of calcium carbonate equal to about 2 to about 10 percent by weight of the particulate cellulosic material.

19. The method of Claim 17 in which the particulate_ cellulosic material is combined with an amount of calcium carbonate equal to "about 5 percent by weight of the cellulosic material. x

20. The method of any preceding Claim 12 through 19 in which the particulate cellulosic material includes oil seeds, products of oil seeds, or both, for lubrication of the die.