TITLE OF THE INVENTION

Fuel formed of Cellulosic and Biosolid Materials

CROSS-REFERENCE TO RELATED APPLICATIONS Not applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR

DEVELOPMENT

Not applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC Not applicable

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to the field of solid fuels, and more particularly to a cellulosic based preferably pelletized fuel and manufacturing process therefor utilizing a biosolid formed from bioslurry effluent derived from non- edible food residuals of fats, oils and grease (FOG) collected in sanitary sewer drainage (SSD).

Description of Related Art

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. This is somewhat ironic since the original source for energy in the United States and the rest of the world was wood. In fact, U.S. Pat. No. 43,1 12 issued on June 14, 1864 was directed to combining sawdust, tar, wood cuttings or chippings, water, and coal-tar to form an artificial fuel.

Much attention has previously been directed to preparing briquettes from wood waste. For example, L. H. Reineke wrote a U.S. Forest Research Note entitled "Briquettes from Wood Residue", in November, 1964 describing various techniques available for briquetting wood residue. In addition, U.S. Pat. Nos. 3,227,530, 3,635,684, 3,843,336, 4,015,951 and 4,043,764 describe techniques for briquetting cellulosic material.

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. Pelletized wood can have a heating value of less than 7,000 BTU's per pound, while coal generally has heating value in excess of 9,000 BTU's per pound. Therefore, the transportation and handling costs associated with available pelletized wood are higher per BTU than for coal.

Other problems with use of available pelletized wood as a fuel source are 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 affected with some species of wood, but not all species, by heating the wood above its minimum plastic temperature of 325. degree. F. as reported by Reineke in the above-mentioned U.S. Forest Service Research Note, and also as reported by Gunnerman in the above-mentioned U.S. Pat. No. 4,015,951. 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 was a need for a fuel pellet which resists crumbling, is easily ignitable, burns fast and completely, and has a heating value approaching that of coal; and there is also a need for a method for preparing the fuel pellet which does not require high pelletizing temperature.

In U.S. Patent 4,529,407 (incorporated herein by reference), I invented a fuel pellet with the above features and a method for preparing the fuel pellet. The fuel pellet, which preferably has a minimum dimension of at least 3/16 inch for ease of handling, comprises from about 50 to about 99% by weight natural cellulosic material, and from about 1 to about 50% by weight synthetic polymeric thermoplastic material. The thermoplastic material was chosen so it is solid at room temperature and has an injection molding temperature of at least 200. degree. F. The thermoplastic material serves to bind the pellet together, increases the heating value of the pellet, lubricates the pelletizing die, and improves the ignition and burning characteristics of the pellet. Fuel pellets of the '407 patent exhibit complete burnout, burn faster than pellets not containing thermoplastic material, and can have a heating value in excess of 9,000 BTU's per pound. Preferably, the thermoplastic material is uniformly distributed throughout the fuel pellet.

The '407 fuel pellet was made by preparing a feed comprising from about 50% to about 99% of particulate natural cellulosic material and from about 1 % to about 50% by weight of particulate synthetic thermoplastic material. The cellulosic material has a free moisture content of from about 5 to about 15% by weight, and preferably substantially all of the cellulosic material was -5 mesh. Substantially all of the thermoplastic material was -5 mesh, and preferably -10 mesh. The plastic and cellulosic materials are intimately combined by compressing the feed in a die.

The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those skilled in the art upon a reading of the specification and a study of the drawings.

The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative and not limiting in scope. In various embodiments one

or more of the above-described problems have been reduced or eliminated while other embodiments are directed to other improvements. In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions. BRIEF SUMMARY OF THE INVENTION

This invention is directed to A fuel pellet and method of forming a fuel pellet including a quantity of a natural particulate cellulosic material and a quantity of a particulate biosolid material from a dried bioslurry effluent derived substantially from fats, oils and grease (FOG) found in non-edible food residuals from sanitary sewer drainage (SSD) interceptor tanks. The biosolid material and the cellulosic material are substantially homogenous and solid at room temperature, preferably having a moisture content of from about 5% to about 15% by weight and at least substantially minus 5 mesh. A quantity of particulate synthetic polymeric thermoplastic fines material may be added for increased fuel content.

It is therefore an object of this invention to provide pellet fuel utilizing previously combustible cellulosic matter combined with biosolid material derived from non-combustible grease interceptors solids of fat, oils, and grease (FOG).

It is yet another object of this invention to provide an alternate means for disposing of the bioslurry of FOG and biomass non-edible food residuals in sanitary sewer drainage inclusive of "gray water" collected as a disposable byproduct from food preparation facilities.

Still another object of this invention is to build on the technology of my prior U.S. Patent 4,529,407 and the fuel pelletizing technology disclosed therein in formulating a new fuel pellet which combines with the FOG and other non-edible greasy food residuals collected from sanitary sewer drainages associated with food preparation facilities such as restaurants.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 illustrates in a perspective view a pellet representative of pellets prepared according to the teachings of U.S. Patent 4,529,407;

FIGS. 2A and 2B illustrate the process of the '407 patent and are to be considered serially.

FIG. 3 is a flow diagram of the process of manufacturing the new fuel pellet formulation of the present disclosure.

Exemplary embodiments are illustrated in reference figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered to be illustrative rather than limiting.

DETAILED DESCRIPTION OF THE INVENTION Prior Art

(A portion of the Detailed Description in U.S. Patent 4,529,407 is reproduced hereinbelow).

With reference to FIG. 1 , there is shown a fuel pellet 10 prepared from cellulosic material and thermoplastic material. Fuel pellet 10, which is cylindrical in shape, has a minimum dimension of at least 3/16 inch and comprises from about 50 to about 99% by weight natural cellulosic material and from about 1 to about 50% by weight thermoplastic material. As is more fully set forth below, these fuel pellets are easily ignitable, burn evenly, quickly and completely, resist weathering, and generally have a gross heating value in excess of 9,000 BTU's per pound, and can have a gross heating value in excess of 10,000 BTU's per pound.

The natural cellulosic material used to form the 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 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 these with low moisture content to minimize drying costs and low contamination levels to minimize pelletizer die wear. As used herein, the term "cellulosic material" includes lignin. Particulate woody material preferably is used in the pellets because it has a higher heating value and lower moisture content than agricultural waste.

Inclusion 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

practically any available synthetic thermoplastic such as, but not limited to, polystyrene, polyethylene, polypropylene, acrylonitrile-butadienestyrene, acetyl copolymer, acetyl homopolymer, acrylic, polybutylene, and combinations thereof. Although thermoplastics containing a halogen such as polyvinylchloride can be used, for most applications there are to be avoided, because 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 200 °F.

It is critical to the ('407) 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 in 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. Pellets of the present invention have been left out overnight in the rain and still

maintained their cohesiveness, while conventional wood pellets tend to disintegrate when wet. A portion of the thermoplastic material can be in the fuel pellets in the form of discrete subparticles, although it is preferred that the thermoplastic material be substantially uniformly distributed throughout the particles. The presence of discrete thermoplastic subparticles in fuel pellets results in easy ignition because the discrete subparticles provide an ignition situs.

Exemplary of such (cellulosic) 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 the pellet 10 be substantially symmetrical in shape such as cylindrical, parallel-piped or the like, having a diameter within the range of from about 3/16 inch to about 1 inch. 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. Pellets have been produced which are cylindrical in shape, such as the pellet shown in FIG. 1 , having a length of about 1 inch and a diameter of about 3/8 inch. For such a pellet, the "minimum dimension" of the pellet is the diameter, i.e. 3/8 inch.

A process for preparing fuel pellets is shown schematically in FIGS. 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 conveyors, screens, 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 conveyor 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. For example, if cylindrical pellets having a diameter of 3/16 inch are to be made, then the size of the holes in the screen is necessarily less than 3/16 of an inch. In the version of the process shown in FIG. 1 , the screen segregates particles greater than 1/8 inch in diameter, and passes these particles to a comminution device such as a hammer mill 32.

The particles 30 not requiring comminution and the comminuted particles 34 from the hammer mill 32 are collected on a belt conveyor 36 and passed via ducts 37 to two rotary dryers 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 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 (suspension-arc burner in Fig. 3) which supplies hot gas via ducts 41 to the dryers.

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 (FIG. 2A). The dried feed material is transferred by a storage bin tank feed conveyor 49 to one or more storage bins 52a or 52b (FIG. 2B). The different storage bins are used for storing different types of feed material. More storage bins than the two storage bins shown in FIG. 2A can be used. The storage bins 52a and 52b preferably are tumble 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 discharged 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 conveyor 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 from 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 -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 conveyor 62a, 62b, 62c, or 62d. The four conveyors 62a, 62b, 62c, and 62d are used to provide the proper weight ratios of the feed materials to a pellet mill 70. The four conveyors drop their feed onto a belt conveyor 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 such as a combination mill to obtain uniform mixing of the different types of feed material. The mixer discharges mixed feed onto a belt conveyor 67 which lifts the feed to a pellet mill feed bin 68. The feed is gravity fed from the bin 68 to a conveyor 69 which drops the feed into the pellet mill 70 in

which the pellets of the present invention, such as a pellet shown in FIG. 1 , are formed. Any suitable pelletizing machine can be used such as, for example, the one produced by the California Pellet Mill Company of San Francisco, Calif, or the mill produced by Koppers Sprout-Walden Company. 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 150° to about 250° F. 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 about 250° F., degradation and carbonization of the thermoplastic material can occur, and when the discharged pellets are at a temperature of less than about 150° F, the pellets can have insufficient cohesiveness. Preferably, the discharge temperature of the pellets is from about 190° to about 210° F. to produce pellets with excellent burning properties and good cohesion. As the discharge temperature of the pellets increases, their density increases. For example, pellets containing 5% by weight polyethylene and 95% by weight sawdust had a density of 31 pounds per cubic foot when discharged from a pelletizer at 190° F., and a density of 34 pounds per cubic foot when discharged from the pelletizer at a temperature of 199° F. 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.

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 conveyor 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.

THE PRESENT INVENTION

Building upon the teaching of my '407 patent, and generally utilizing the manufacturing process previously described, a use for a previously discarded food preparation facility byproducts in the form of non-combustible combinations of grease interceptors solids of fat, oils and grease (FOG) and non-edible food residuals in sanitary sewer drainage (SSD, known as "gray water") is now incorporated into the fuel pellet of the present invention. These non-combustible previously discarded food preparation facility byproducts are now being collected in subsystems of restaurants designed for this purpose. The collected byproducts are then drained into storage interceptor tanks for timely pick up and removal by mobile tankers to a pretreatment facility where overflow gray water is recycled to EPA standards.

Until now, the reuse opportunities for this otherwise non-combustible bioslurry which is collected by grease removal devices (GRD) interceptor water systems have overlooked the fact that the FOG is a carbon rich effluent resource when properly dewatered and treated when combined particulate cellulose under the teachings of this disclosure. In addition to obtaining the resultant FOG which has a commercially acceptable level of BTU energy, particularly when supplemented by particulate plastic fines, this invention has many additional side benefits related to avoiding landfill disposal thereof, self adhesive pellet binding, lubrication and extended life of pellet mill dies used to extrude the finished product, and the resultant higher manufacturing capacity and improved economics provided thereby.

Referring now to Figure 3, a multi-facet process plant is there shown in flow diagram format at numeral 100. The origin of the bioslurry begins in the food preparation kitchen at 102 wherein a wash up macerator 104 deposits the effluent discharge at 106 into interceptor tank grease pit trap system at 108. The gray water overflow at 110 is then distributed to a sanitary drainage system at 112. From there, the bioslurry may be either disposed of into a sewer at 112 or recycled at 114.

In the present invention 100, the fats, oils and grease (FOG) in the bioslurry are pumped at 116 into a mobile tanker 120 or, alternatively, into a condenser settlement tank 118 for water/solids separation for disposal at 122 or transported into a receiving tanker discharge at 124 ready for pretreatment operations at 130.

Pretreatment operations at 130 include a mixer/macerator blender 132 which receives the partially dewatered FOG biosolids from 124 also received into the blender 132 is cellulosic particulate from silo 134 which has been processed as previously described in Figures 2A and 2B previously described and received from conveyor 49 also shown in Figure 2B. This blending of the raw material from 124 and the prepared cellulosic particulate from silo 134 within the blender 132 also serves to additionally dewater the fuel being prepared within the blender 132 down to about 50% moisture by weight or greater for further processing.

This blended mixture of cellulosic particulate and partially processed FOG is then fed into a screw press 136 or alternately into a rotary sieve dewatering drum and knife scraper 138 for further dewatering. Thereafter, the dewatered and concentrated slurry cake of near-combustible material is then discharged in the form of a biocake of semi-dry solids at 140. This biocake material having a moisture content in the range of about 25% by weight is then fed into a rotary drum dryer 144 which further dries the fuel mixture down to a moisture content in the range of up to 15%. Once dried, the fuel material is then shipped at 142 in particlized form ready for use as a fuel or fed into a sieve/screen/pulverize stage at 146 which properly adjusts the overall size of the material to specification, preferably the size of about minus 5 mesh size and no greater for the purpose of pelletizing. Note also that the fuel being shipped at 152 has a maximum particle size of about minus 5 mesh to be used in a suspension arc burner.

The properly pulverized, sized and dried fuel material is then fed into a densification press or pelletizer 150 or alternately to a storage silo 148 for conveyance into the pelletizer 150 at a later time. The pelletized fuel is then fed into a rotary cooler 154 using ambient air to cool the pelletized fuel, then into a storage silo 156 ready for shipment at 158.

To enhance the energy content of the pelletized fuel, particulate plastic fines at 160 may be introduced into the pulverizing stage at 146. As previously described, the BTU content may increase to an average up to 14,000 BTUs from the original maximum of 7,000 BTUs of the cellulosic material. Particulate biomass material at 162 may also be introduced into the pulverizing stage at 146 to help further dry and add to the energy content of the pelletized fuel. This biomass material at 162 may include sawdust, bark, wood shavings, sand or dust, hog fuel, peat and agricultural waste such as stalks, straw, bamboo, jute, bagasse, corn husks, cob cotton, gin trash, sisal, seed hulls and peanut hulls as well as paper, and cardboard, all having been previously particlized to size of an overall negative 5 mesh maximum.

To provide additional energy for the rotary drum drier 144, the fines recycle energy step at 164 gathered from the pulverizing stage 146 may be recycled into the suspension burner 166 which delivers this drying heat into the rotary drum drier 144 for additional drying efficiency of the fuel particulate.

To repeat, while pelletizing of this new fuel source is preferred, other forms of the prepared particulate cellulosic/biosolid fuel are envisioned within the scope of this invention.

While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permeations and additions and subcombinations thereof. It is therefore intended that the following appended claims and claims hereinafter introduced are interpreted to include all such modifications, permeations, additions and subcombinations that are within their true spirit and scope.