JPH0552360B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION The present invention relates to pelletized cellulosic fuel bound with a plastic binder and a process for making the same. Now that the quantities of coal, oil and natural gas products are decreasing, other energy sources are gaining attention. One energy source that is gaining attention is biomass materials such as wood, sugar cane husks, their by-products, agricultural residues, etc. For example, the use of wood chips compressed into pellets or blocks as a fuel source has to date only been accepted to a very limited extent. One reason for this is that compressed wood chips have a relatively low heating value.
Compressed wood chips also have a low burning rate. Some result in incomplete combustion, resulting in the formation of carbonaceous residue and low combustion efficiency. Furthermore, compressed wood chips are difficult to ignite. Another problem was the brittleness of compressed wood chips, which required special handling to prevent collapse and dust generation, and weathering had to be prevented. To overcome the problems of disintegration and weathering, inorganic binders such as cement and sodium silicate, and organic binders such as tar, pitch, longine, glue, wax, and fiber were mixed into the pellets. However, no binder has been found that completely solves the above problems, is also inexpensive, and does not reduce the heating value of wood. Attempts have been made to exploit the self-bonding properties of lignin in various types of wood to avoid the collapse problem. This method can be applied to some types of wood by heating the wood above the minimum plasticity temperature of lignin, 163°C, but it is not a method that can be applied to all types. However, such wood pellets do not have high mechanical strength. These high temperatures also significantly limit the useful life of pelletizing equipment and drive high BTU volatiles from the wood.
Some energy is lost due to heating requirements. Specific examples of known approaches include Stamicarbon UK Patent No. 901789, Masayoshi Japanese Patent Application No. 46-10282, and Hartman et al. US Patent No. 46-10282.
No. 3,947,255, Messman, US Pat. No. 3,843,336 and Gunnerman, US Pat. No. 4,015,951. Stamicarbon discloses a bulk fuel consisting of coal particles and an olefinically unsaturated hydrocarbon binder. Fuel particles are less than 3mm in size. The binder can be added to the coal particles by melting the binder and distributing it throughout the coal particles, by dissolving the binder and absorbing it into the coal particles, or by adding the binder to the coal particles by tar oil distillation and high temperature compression. This is achieved by coating with In the case of Stamicarbon, 1 to
A small amount of 2% plastic is used, and the moisture content is 5~5%.
It is 8%. The Masayoshi patent application discloses a fuel consisting of 9-66% thermoplastic material and a balance amount of wood flour or chips. In the case of Masayoshi, a thermoplastic material is melted and combined with wood flour or chitufu. Hartmann as a binder for bark
Use 2.5-40% plastic. This plastic obtains its binding effect by melting. Hartmann bark moisture is less than 7%. Messman discloses an artificial firewood consisting of thermoset resin, sawdust, wax and fuel oil. In the case of Messmann, the outside of the extruded firewood is coated with plastic, but the plastic content is high. Gunnerman uses fibrous materials, such as wood, with a moisture content of 16-28%. This material is compressed with a die, and the temperature of the pellet when it comes out of the die is 163 ~
The temperature should be 177℃ (325-350〓). The pellets are then dried. According to Gunnerman, the pellets obtained in this manner are secured by the interlocking of the protruding fiber particles and possibly by heat-softened lignin. The size of the individual particles does not exceed 85% of the pellet's smallest dimension. U.S. Application No. 943,393 to Iron Fraser Joneston discloses pellets comprised of cellulosic and thermoplastic materials. Johnston's pellets contain 1-10% thermoplastic material and the remainder is cellulose material. Moisture content is 5-15%. Both plastic and cellulose materials are 5 mesh.
Particles are small enough to pass through a screen. Johnstone discloses a unique bonding method between cellulose and plastic. Rather than melting or dissolving the plastic, it softens so that it penetrates between the fibers of the cellulosic material and forms a mechanical engagement between the materials upon extrusion. Johnstone pellets exhibit superior combustion properties than the individual components. Small plastic particles act as ignition sites, which release flammable gases,
It is thought that combustion of the cellulose material proceeds from this ignition site. That is, the combustible gas is combusted, promoting ignition and combustion of the cellulosic material. Cellulosic material separates the individual plastic particles so that each particle burns independently and prevents the charring phenomenon that accompanies the combustion of large plastic particles. In connection with the promotion of combustion in Johnstone pellets, the lignin component of cellulose materials such as wood emits higher combustion heat than cellulose during normal combustion, but this lignin is thermally decomposed and carbonized.
It is also known from other studies that combustion is not complete. Carbonized materials tend to burn slowly in solid-state combustion due to smoldering with a low heat release rate.
The combustion products of lignin in this combustion zone contain large amounts of combustible components. As the heat flow increases, lignin burns flamingly, leaving little ash (Smoldering Combustion of Cellulosic Materials, Journal of Thermal Injection, Vol. 2 (January 1979), Shafizadei and Bradbury). ”). The combustion products of Johnstone fuel have significantly lower carbonaceous ash compared to natural lignin-containing cellulosic materials burned under the same conditions. Therefore, it is thought that granular plastic completely burns the lignin component of the cellulose material, releases high lignin combustion heat, and creates a combustion environment that leaves almost no carbonaceous ash. SUMMARY OF THE INVENTION The present invention provides an improved fuel pellet comprising a naturally occurring combustible material containing at least 50% cellulosic material and a thermoplastic resin, and a method for making the same. Although this pellet uses a small amount of plastic,
Has excellent combustion characteristics. Experience has shown that by reducing the particle size of plastics and cellulosic materials, it is possible to use smaller amounts of plastic to obtain the same pellet combustion characteristics as larger amounts of plastic, but with a higher heat release. It was found to be an excellent product with low residual carbonaceous ash. It has also been found that by adjusting the particle size relationship between the plastic and the cellulose, an excellent mechanical bond between the plastic and the cellulose fibers can be obtained. In one embodiment, the present invention provides compressed fuel pellets comprising from about 97 to about 99 weight percent particulate naturally occurring combustible material and from about 1 to about 3 weight percent particulate synthetic polymeric thermoplastic material. Naturally produced combustible materials contain from 50 to about 100% natural cellulosic materials. Compression is preferably carried out using a die, and pellets are obtained as extrudates. The plastic is interposed between the cellulose particles and is bonded to the cellulose particles by working closely with the cellulose fibers. It is also possible to include fillers other than natural cellulosic materials, such as bark, coal, distillery waste, or tarry residues obtained from processes such as alcohol distillation. Bark and stillage liquors can be considered non-cellulosic here since they do not have the fibrous structure necessary for the full bond formed by natural cellulosic materials. If it is somewhat fibrous like young bark, 1~
A maximum of about 50% granular non-cellulosic material may be used with 3% plastic, with the remainder being granular natural cellulosic material. Since old bark is poor in fiber, it should be added in a small amount, ie at most 30%, and used together with 1 to 3% plastic, with the remainder being natural cellulose material. Preferably, the pellets consist of about 97 to about 99 weight percent particulate natural cellulosic material and about 1 to about 3 weight percent particulate synthetic polymeric thermoplastic material. The use of cellulosic materials, which are almost entirely naturally occurring combustible materials, results in extremely strong pellets. The plastic in the pellet is homogeneous throughout, except in the preferred embodiment where the side walls of the pellet are a continuous plastic coating. The plastic in pellets is also granular. An important condition is that the plastic particle size must be set so that substantially all of the plastic passes through a 30 US Standard mesh screen and is blocked by an 80 US Standard mesh screen (this particle size must be -30 US Standard mesh). (expressed as mesh to +80 US standard mesh). The particle size of the cellulose material also has a clear relationship with the plastic particle size, and is set so that the plastic does not become too small compared to the cellulose material. The size of the cellulosic material is set such that almost all of it passes through a 10 US mesh screen (-10) and is blocked by a 40 US mesh screen (+40). Therefore, the cellulosic material has a characteristic dimension (diameter) that is not more than one order of magnitude larger than the characteristic dimension (diameter) of the plastic. The particle size of the non-cellulosic filler should not be larger than that of the cellulosic material. Non-cellulosic materials may be finer than cellulosic materials. The small particle size of plastics facilitates the combustion of plastics and naturally occurring combustible materials. Combustion of naturally occurring combustible materials is facilitated by the release of combustible gases from the plastic. This same mechanism facilitates the complete combustion of lignin, if present. The combustion of plastics is also complete because the relatively large surface area of the plastic particles is maintained and the individual plastic particles are held tightly within the cellulose fibers and cannot agglomerate. Plastic particle size can become too small and the relationship of plastic particle size to cellulose particle size must be considered to obtain favorable bonding results. If the plastic particle size is less than 80 mesh, it is no longer possible to bridge cellulose particles satisfactorily. Plastic particle size is 30
If the mesh is larger, favorable combustion and bonding may be possible, but at least the amount of plastic must be increased. If the plastic particle size is too small, bridge bonding between individual cellulose particles will not be possible, so the order of the particle size difference must be maintained as the limit of the particle size difference. The larger the particle size, the
The amount of plastic required to obtain pellets with superior strength is increased. Also, if the plastic particle size is too large, it will not soften during extrusion and will not be able to form thin chips sandwiched between the cellulose. When pellets are pulverized and burned under air suspension, if the plastic particle size is too large, the plastic particles will separate in the powder mixture and the benefits of the close relationship between the plastic and the cellulose material will be lost. be exposed. It is also envisaged that the cellulose material may be excessively fine. When the cellulose material becomes smaller than 40 meshes, it loses its fibrous properties and the interstitial bond between the plastic and the cellulose material is impaired. The free water content of cellulose material before pelletizing is about 5 to about 15
%, preferably 10-13%. Furthermore, 10.5 to 11.5% is currently preferable. After pelleting and some drying, about 8% is preferred. The thermoplastic material is selected to be solid at room temperature and capable of injection molding at a temperature of about 95°C or higher. The fuel pellets of the present invention are completely combustible, have a higher burn rate, and have better structural integrity than pellets that do not contain thermoplastic materials. Plastic loadings are selected in the range of 1-3% depending on both bonding and combustion requirements.
Below 1% plastic, the advantage of providing individual ignition sites is lost and pellet strength is reduced. If a moderately hard wood is to be engaged, or if there is a high content of non-cellulosic components, 3% plastic may be required.
However, from a cost perspective, it is generally better to have a lower plastic content. The preferred range is 1-2%. The principle of the present invention is to enable the use of combustible materials as fillers, such as bark, stillage liquor, other distillation by-products, coal, etc., together with cellulose particles and plastics. Old bark is generally not fibrous and, like distillery liquor and coal, is irrelevant to the binding mechanism of the present invention. However, bonding of the non-fibrous fillers is also possible if a sufficient amount of cellulosic material is present to provide a plastic anchorage site. If coal, distillery waste, old bark, etc. account for approximately 30% of the total, cellulose materials account for 67-69%,
A satisfactory product can be obtained with a plastic content of 1-3%. Up to 50% of new fibrous bark can be used. In this case, the composition is 50% bark, 1-3% plastic, and the remainder cellulose material. The moisture content and plastic particle size of the product remain unchanged. In another embodiment of the invention, the pellets contain an alkali metal silicate selected from sodium silicate and potassium silicate. Silicates are preferably present at 1-2% by weight, but up to about 10% are acceptable. It is believed that alkali metals act as catalysts that promote gas combustion. In addition, silica crystal is considered to act as a thermal radiator and promote ignition by thermal radiation.
A unique property of silica crystals is that they emit strong infrared rays when heated. The alkali metal silicates also promote the binding effect, the mechanical strength of the pellets, the densification of the pellets, and the strengthening of the hydrophobic coating of the pellets. Combustion pellets can be produced by preparing a feedstock consisting of particulate natural cellulosic material, optionally non-cellulosic filler, and particulate synthetic thermoplastic material. Almost all thermoplastic materials have a particle size of -30 US mesh to +80 US mesh. Almost all fills are of -10 US mesh particle size. The plastic and cellulosic material are tightly bonded by compressing the feedstock in an extrusion mold. In extrusion molding, the plastic inside the pellet does not melt,
It is carried out under temperature and speed conditions that only cause softening. Therefore, the plastic remains granular.
As a result of extrusion, the particulate plastic is flattened and mechanically bonded tightly to the cellulosic fibers. [Detailed Description] Hereinafter, the present invention will be further described in detail based on the accompanying drawings. The present invention provides fuel pellets and methods for making the same. The pellets are characterized by the use of a small amount of plastic binder and its unique mechanical strength and combustion properties. The pellets burn completely either when burned on a grate or after being crushed and then burned under air suspension. In a preferred embodiment, the pellets are about 97 to about 99
% cellulosic material and about 1 to about 3% thermoplastic material, but about 98 to 99% cellulosic material and about 1 to about 3%
A composition with 2% thermoplastic material is preferred.
Specifically, the pellets are formed in an extrusion process that maintains the integrity of the individual plastic particles.
That is, the plastic particles do not fuse together into a single continuous plastic mass. The extrusion process transforms the plastic into a thin (not necessarily flat) pancake and mechanically bonds this flat body tightly with the fibers of the cellulosic base material. The plastic can be thought of as acting as a tendon that holds the cellulose fibers together. The plastic must maintain its granularity. This granularity promotes combustion not only of plastics but also of cellulosic materials. The pellets may contain naturally occurring fillers such as coal, stillage, other distillation products, bark, tarry substances, and the like. The bark has a high heat of combustion and is abundantly available as a forestry product. The fibrous nature of bark varies depending on its type; new bark is relatively fibrous, while older bark contains almost no fibers. Due to mechanical strength requirements, new bark can account for up to 50% of the pellet, while old bark can only account for up to 30%. In both cases, the plastic content is 1
It remains unchanged at ~3%, with the remainder being natural cellulose.
Coal is completely non-cellulosic and must be bound between cellulose particles. Distillery waste is a modified material containing some cellulose. However, it is only a filler, since the fibrous nature of cellulose, which gives it favorable binding properties, is significantly lost during processing. Distillation by-products other than distillation waste, such as molasses and pitch, can also be effectively used as fillers. Conventionally, these by-products have been difficult to dispose of. Granular plastics have a larger surface area, which increases the rate at which they burn.
Hot combustion gases from the burning plastic particles ignite the filler and cellulosic materials surrounding the plastic particles, promoting their overall combustion. Cellulosic material obtained from wood contains large amounts of lignin. Lignin does not burn as easily as cellulose. In many cases, lignin burns in its solid state, producing a smoky flame and leaving a charcoal-like, largely unburned residue. This charcoal material has considerable fuel value. Conventionally, this would also cause at least particulate contamination. Granular plastics create a combustion zone that completely burns out the lignin in the primary cellulosic material. This is the same whether the fuel is burned as pellets or the fuel is pulverized and then burned using air suspension. In the latter case, the plastic will remain bound to the cellulose particles as long as the particle size conditions described above for the plastic are observed. If the plastic has a particle size that will pass through a 30 US Standard mesh screen but not an 80 US Standard mesh screen, then the minimum amount of plastic may be added. Plastics of this particle size can act as a bond between cellulose particles. Particle size provides a large surface for easy ignition/
It must be small enough to take advantage of the volume ratio and high combustion rate that promotes the combustion of lignin and cellulosic materials. This small particle size also ensures complete combustion of the plastic. As is known, if the plastic particle size is too large and the surface area/volume ratio is too small, the plastic will tend to burn incompletely leaving behind a charcoal-like material. The plastic particle size must be small enough to soften during extrusion to form thin plates or pancakes inside the pellet. It has been found that if the plastic particle size is too large, the particles will not soften and form lamellae that bind the cellulose particles. Particles of cellulosic materials and fillers, such as bark, have a clear relationship to plastic particle size. The particle size must be sufficient to pass through a 10 American Standard mesh screen. However, cellulose material
Must be coarse enough to remain on top of the 40 American Standard mesh screen. With such a particle size range, the characteristic dimensions of the cellulosic material are approximately one order of magnitude larger than the corresponding characteristic dimensions of the plastic material. If the cellulose particle size is too large relative to the plastic particle size, the plastic will become entangled in the fibers of the cellulosic material and will not be able to span between individual cellulose particles. Also, cellulose particles that are too large will not burn as well as smaller particles. The large size of plastic relative to cellulosic material leads to plastic wastage and the combustion and softening problems already mentioned. If softening problems can be overcome and potential plastic combustion problems are ignored, plastic particles larger than the limits set here are effective in linking cellulose particles. If the cellulosic material is too fine, it loses its fibrous nature. As a result, mechanical strength is lost because the bonding mechanism between the plastic and the cellulose material, which relies on the fibrous nature of the cellulose material in mechanical bonding through engagement, is lost. If a filler is added, this filler is retained primarily by the bond between the plastic and the cellulosic material. If the filler particles are too large, they will interfere with the bonding mechanism between the plastic and the cellulosic material. Excessively large filler particles are difficult to burn. The lower limit of the filler particle size is determined by economics. There is no reason to make the filler particles extremely small, but if they are already very small, such fineness will not adversely affect the results. Coal dust is an example of a naturally occurring fine filler that does not require particularly small particle size. The amount of plastic should be about 1% to about 3% of the total amount of fuel pellets. Using this amount of plastic while adhering to plastic and cellulose particle size limits will provide favorable burn and bonding properties with a minimum amount of plastic. 1~ of pellets as a binding material
The effectiveness of adding 3% of thermoplastic material can be considered from various aspects. If no thermoplastic material is added, significantly higher temperatures are required to pelletize the cellulosic material alone. The addition of this thermoplastic material allows the plastic to act as a lubricant in pellet molds or rollers. Thermoplastic materials are also effective in rendering the pellets hydrophobic by coating the outer surface of the pellets. The preferred amount of plastic added is about 1% to about 2% of the total amount of fuel pellets. However, especially when using hard wood and large amounts of filler, large amounts of plastic may be required as a bonding material. The moisture content of the cellulosic material is about 5% to about 15%.
If the moisture content is too high or too low, the pellets may lose strength and disintegrate during handling or transportation. Excessive moisture content lowers the flame temperature and negatively affects the quality of combustion. Preferably, the moisture content is maintained in the range of 10-13%. Ideally, the moisture content of the cellulose material is 10.5 to 11.5%, and this range is most preferable in terms of pellet strength. Moisture content is measured on the cellulose material before pelletizing. Pelletization can reduce it to 4-8% due to evaporation into the air. When pellets are used for air suspension combustion, it is preferable to reduce the moisture content after crushing the pellets to below the above range in order to improve combustion characteristics. Naturally, if the pellets are crushed into fine particles suitable for air suspension combustion,
Moisture content required for pellet structural integrity is no longer necessary. The milling process itself reduces the moisture content. The injection molding temperature of the thermoplastic material is about 95°C or higher. It may be slightly lower than this. This restriction is necessary to avoid excessive melting of the plastic during the extrusion process. When a plastic melts too much, it loses its particulate nature and properties based on its particulate character. Some melting is allowed as long as the plastic does not clump. Cellulosic materials can be obtained from a variety of biomass sources. The most common sources are wood chips such as sawdust, planer shavings, and sugar cane husks. Wood and sugarcane husks are preferable because they have a high combustion heat and have a lower moisture content than agricultural waste.
It is also preferable because it is available in abundance. The thermoplastic material can actually be any synthetic thermoplastic material, such as polystyrene, polyethylene, polypropylene, acrylontolyl-butadiene-styrene, acetyl copolymers, acetyl homopolymers, acrylics, polybutylene, and combinations thereof. . However, polyvinyl chloride should not be used because it is associated with corrosion problems and combustion emissions problems. Thermoplastic materials such as polypropylene and polyethylene, which have a high burning rate and are easily ignited, are preferred. The minimum injection molding temperatures for widely used thermoplastic materials are reported in the Modern Plastics Encyclopedia, published by McGraw-Hill, Volume 49, 1972-3 edition, and are shown in Table 1 below. It is.

[Table] High impact polystyrene is extremely hard, 1.25% by weight
The above content makes it difficult to pelletize the feedstock, which poses difficulties in the pelletizing process. For some thermoplastic materials, during the pelletizing process, the friction of the extruder mold heats and melts the thermoplastic material on the surface of the pellet, resulting in the formation of a thin sheet or coating on the outside surface of the pellet. This coating is hydrophobic and prevents the pellets from absorbing moisture during storage. Materials other than cellulosic and thermoplastic materials may be added to the pellets depending on the particular application or processing conditions. For example, oxidizing agents such as sodium perchlorate or ammonium nitrate may be added to facilitate combustion. Paraffin, sludge wax, and carnauba wax, as well as some lignosulfanates, such as ammonium lignosulfanate, sodium lignosulfanate, calcium lignosulfanate, and magnesium lignosulfanate. Can be added as a binder. Oilseeds and their products contain resin acid components that can reduce wear in pellet molds. Examples of such materials include coconut husks, soybeans, peanuts, sunflower seeds, corn cakes, milling residues,
Examples include ethanol distillation waste liquid. Anhydrous slaked lime, ie, calcium carbonate, may be added to the feed to aid in drying the cellulosic feed. Other desiccant agents may also be used.
Calcium carbonate combines with water and feedstock, allowing rapid dewatering from the feedstock in a dehydrator. Calcium carbonate may be added in an amount of from about 2 to about 10% by weight of the dry feed, with additions of about 5% significantly accelerating layer processing.
Preferably, the calcium carbonate is removed prior to pelletizing, for example by dry screening. In applications where the free water content in the cellulosic feed is excessively high, power presses and taper
It is economical to dewater by a mechanical process such as a screw press. Although it is currently preferred to use an extruder to form pellets, pressure forming is also noteworthy. The binding effect in the pellets of the present invention is extremely excellent. If a high binding effect is desired due to the high content of non-cellulosic materials such as old bark, sodium or potassium silicates may be used. The use of such silicates hydrolyzes acidic wood cellulosic materials. As a result, the compressibility of the cellulose component increases,
High density pellets are obtained. Upon completion of dewatering, the silicate hardens and acts as a cement, reinforcing the heated plastic material and binding the fibers together. The relatively high hydrophobicity of thermoplastic materials results in pellets that are resistant to the effects of ambient air. Silicates increase ash content but have no significant effect in either air suspension or grate combustion. The alkali silicate may be introduced into a mixer placed upstream of the extruder or press. If only air resistance is desired, the alkali silicate may be added while the thermoplastic coating is still hot and adhesion of the alkali silicate occurs. The amount of silicate may be about 1% by weight. Silicates have high viscosity, but this viscosity can be reduced by heating. Alkali metal silicates such as water glass are also considered combustion promoters or combustion catalysts. Approximately 4
% sodium silicate was observed to burn much more strongly (at higher burn rates) than identical pellets except that they contained no silicate. It is believed that the alkali metal acts as a combustion catalyst. Sodium silicate solution is strongly alkaline;
Easily decomposed by acid to separate silicic acid.
When heated, silicic acid is converted to silica. This same process is believed to occur in a mixture of sodium silicate and wood chips containing acidic substances. The resulting silica crystals are thought to promote ignition through intense infrared radiation. A unique property of silica crystals is that they emit strong infrared rays when heated. The preferred amount of silicate is 1-2
Weight%. This amount of silicate promotes combustion without significantly increasing the ash content. Densification, air resistance, and bonding properties are also improved at this addition concentration. The composition of the pellet containing the alkali metal silicate is as follows. That is, from about 1% to about 3% by weight particulate synthetic polymeric thermoplastic material, from about 1% to about 10% alkali silicate, and from about 87% to about 98% natural combustible material. Natural combustible material contains at least 50% natural cellulosic material, the remainder being filler. With high lignin content wood chips, highly combustible fuel pellets can be produced comprising from about 1% to about 10% by weight alkali silicate and from about 90% to 99% natural combustible material. The accompanying drawings schematically represent a suitable plant for producing the pellets of the invention. Before getting into the description of this plant, it should be noted that there are several approaches to pellet production. Additionally, the illustrated flow sheet omits details obvious to those skilled in the art, such as storage hoppers and conveyors. The plant uses fine powder of cellulosic and thermoplastic materials inherent in the feedstock obtained from the manufacturing process and obtained from the pellet details, for example as fuel for heaters used in dryers for dewatering wet cellulosic feedstock. You can also use it. In the drawing, cellulosic feedstock obtained from any source is fed as stream 10 to an initial screener 12 . The output stream 14 of the sorter 12 contains a -1/2 inch or -3/8 inch mesh cellulose feed. This stream is fed by conveyor 16 to dehydrator 18 . The second stream 20 from the sorter 12 is sent with a +1/2 inch or +3/8 inch feed to the primary shredder 22 where it is shredded and discharged as stream 24 onto the conveyor 16. The primary shredder 22 feeds the stream 20 -
Reduce to 1/2 inch to -3/8 inch mesh. Stream 24 joins stream 14 on conveyor 16 and is sent to dehydrator 18. Heater 26 supplies thermal energy to dehydrator 18 . In the dehydrator 18, the moisture content of the cellulose feedstock is between 40% and 60%, preferably between about 5% and about 15%, preferably about 8%.
It decreases to ~11%. The heater 26 is the fuel container 2
Fuel is supplied from 7. The discharge stream from dehydrator 18 is indicated at 28. This discharge stream is sent to cyclone 30 where gas and solids are separated. Gas is discharged from cyclone 30 as stream 32 and solids are discharged as stream 34. A portion of the gas may be recycled to heater 26. Stream 34 enters a primary sorter 36. Material finer than 40 mesh is discharged from the primary sorter as a trickle 38. This trickle 38 is used as an energy source for the heater 26. Coarse cellulosic material is discharged from primary screener 36 as stream 40 and is processed in hammer mill 42 from -10 to +
Milled to 40 US standard mesh. The discharge stream from hammer mill 42 is illustrated as stream 44. The primary flow discharged from the primary sorter 36 is -10~
Stream 46 is comprised of cellulosic material of +40 US standard mesh. This stream 46 joins stream 44 to form stream 48, which is carried to a high level position under the action of a blower and fed into a secondary cyclone 50, where gas and solids are again separated and the gas is transferred to the top of the cyclone. The solids are discharged as stream 52 from the cyclone bottom and the solids are discharged as stream 54 from the cyclone bottom. flow 5
2 may be recycled to the fuel container 27. The solids flow into a secondary sorter 56. In this secondary sorting machine 56, excessively fine materials are sorted out,
It is discharged as stream 58. This fine powder is used as fuel for plants, for example boilers that provide steam. Stream 58 also contains silicates and carbonates, the removal of which increases the useful life of the pellet mold. Appropriately sized material from -10 to +40 meshes exits the secondary screener as stream 60 and enters holding vessel 62 before being mixed with the granulated thermoplastic material. Processing of the thermoplastic material is done separately from the cellulosic material. This method clearly uses metal, glass,
Various methods are effective for removing undesirable materials, such as polyvinyl chloride, etc., including magnets, weight-sensing separators, and flotation. The thermoplastic material enters a granulator 72 as a plastic feed stream 70 and is pulverized. The granulated plastic enters a sorter 76 as stream 74. Excessively fine plastics are discharged from the sorter 76 as stream 78. This stream contains plastics with a particle size that passes through an 80 US Standard mesh screen. Excessively coarse materials flow 8
0 from the sorter 76 and transferred to the conveyor 73.
and is recycled to the granulator 72. This coarse material is 30
Rougher than American standard mesh. Appropriately sized plastics ranging from -30 to +80 mesh exit the sorter 76 as stream 82, combine with additives from stream 84, and pass as stream 86 to holding vessel 88. Holding container 83 supplies material to mixer 90 in the same manner as holding container 62. Plastic is 1~
3% by weight, the balance being cellulosic material, by any known technique. Sodium or potassium silicate may also be added to the mixer 90. The discharge stream 92 from the mixer 90 flows into the conditioning chamber 9
4. A steam jacket 95 heats the cellulose/plastic feedstock. Steam is supplied from a boiler fueled by fine cellulose powder. Discharge flow 96 from conditioning chamber 94
flows into pellet mill 98. Here too, the feed material can be metered in any desired manner. A high speed mixer conveyor conveys the material through conditioning chamber 94 to the pellet mill chute. Pellet mill 98 generates pressure within the extruder to increase the feed temperature so that the pellet temperature reaches a temperature at which the plastic granules within the pellet soften to form thin pancake-like platelets. It must be possible to do so. The pressure applied by the mold must be sufficient to mechanically engage the plastic with the cellulosic fibers. Experience has shown that pellet temperatures during processing of about 66 DEG C. to about 122 DEG C. provide sufficient malleability for the plastic to deform under pressure.
At higher temperatures, the plastic in the pellets may melt excessively and the particulate plastic may agglomerate into particles that are too large. The preferred lower temperature limit is about 88°C. It is preferable to heat the surface of the extruded body to such a preferred temperature to locally melt the thermoplastic material on the surface. In its cured state, the thermoplastic material forms a thin continuous coating on the pellet surface. As already mentioned, this coating imparts hydrophobic properties to the pellets. Furthermore, it lubricates the mold, extending its useful life and contributing to improved productivity. Except for this coating, the thermoplastic material within the pellet is approximately uniformly distributed. pellets
Pellets from the mill 98 enter a cooler 99 as a stream 100. Flowing from the pellet cooler 99, the pellets enter the sorter 101 as 102. Fines and reject pellets are discharged from the sorter 101 as stream 106. The defective pellets are crushed and mixed with waste fines from other separators and used as fuel for drying burners and boilers. Product flow 10
8 from the pellet cooler and stored. [Description of Examples] Examples of the present invention are shown below. Example 1 Tests were conducted on ground fuel pellets consisting of 2% by weight thermoplastic material and 98% by weight cellulosic material. Polyethylene, polystyrene and polypropylene were used as thermoplastic materials. Tests were also conducted on crushed fuel pellets and coal, and on coal alone. The thermoplastic material particle size was approximately -30 mesh to +80 mesh. Cellulose material particle size is approximately -10 mesh to approximately +40
It was a mess. The pellets were formed by extrusion. The particulate thermoplastic material was uniformly distributed throughout the pellet. A coating of thermoplastic material was formed on the surface of each pellet. The pellets were ground in a hammer mill and sieved through a 1/16 inch screen for the "K" pellets and a 1/32 inch screen for the "N" pellets. The ground pellets were pneumatically fed to a Cyclelon separator and finally to a silo adjacent to the test furnace. Coal and a 50% coal/50% pellet mixture were also tested. A horizontal cylindrical suspension air heater manufactured by Cohen was used as the test furnace. The test furnace is equipped with an air-cooled refractory wall, an internal fan and a wind box, and has a rated heat input capacity of 1.01×10 ⁴ Kcal/hr.
(4000000Btu/hr). The test furnace also includes an air suspension burner with five diffusion ports that is pneumatically supplied with powdered fuel. Fuel is supplied from the silo by means of a vibrating screw feeder, from which the fuel is conveyed pneumatically by a blower to the burner. All tests were conducted with the furnace completely preheated to a constant temperature. The optimal air/fuel supply rate was determined while visually observing the flame pattern. Table 2 shows the results.
It was shown to.

【table】

[Table] The crushed fuel pellets were completely combusted and emissions at the smokeless exhaust of the coal suspension burner were at extremely low levels. None of the emissions exceeded current standards. It was sufficient to grind the fuel pellets to -32 mesh in a hammer mill. Since the pellets do not need to be crushed to the same level as coal (usually 70% passes through 200 meshes), an economical hammer mill can be used instead of an expensive and energy-consuming coal crusher. The fact that not only the cellulose content but also the thermoplastic additives are completely combusted is due to the low amount of unburned carbon contained in the fly ash, the low amount of carbon monoxide and hydrocarbons contained in the flue gas, and the low amount of carbon monoxide and hydrocarbons contained in the flue gas. This was evidenced by the absence of any visible smoke in the gas. The extremely low sulfur content (0.01% sulfur) in the crushed pellets directly contributes to the SO ₂ and
H ₂ SO ₄ levels were found to be low (less than 0.030 lb/10 ⁶ BTU and 0.001 lb/
¹⁰⁶ BTU or less). Low ash content of crushed pellets (0.6
%) resulted in particulate emissions as low as 0.12-0.16 grains/SCF ( ^ft3 ). No solids separator of any kind was used in this test. It should therefore be possible to further reduce these emissions. In the standard test using pulverized coal, the amount of SO ₂ released was two orders of magnitude higher and the amount of granular emissions was one order of magnitude higher than that of the corresponding crushed pellets. In addition, in coal tests, the amount of unburned carbon in fly ash was 20 to 30 times that in crushed pellets. When burning coal, a large amount of visible smoke is produced in the flue gas, whereas in the case of crushed pellets, there is no visible smoke at all. The 50% pulverized coal/50% ground air suspension mixture was able to burn smoothly without any handling, feeding, or combustion problems. Almost complete combustion was achieved, and the amount of visible smoke was significantly reduced compared to the case of coal alone. NOx, ash, and SO ₂ emissions were significantly lower than with coal alone, and were intermediate between those with crushed pellets and coal alone. The ash melting point for crushed pellets was higher than for coal alone. Therefore, the crushed pellets are less likely to form slags. Example 2 Seven tests were conducted to evaluate the compatibility of fuel oil and pulverized pellets when burned simultaneously and to compare the performance of No. 6 fuel oil and pulverized pellets. A special burner was used to spray fuel oil into the annularly injected crushed pellets. The pellets were sized using a 1/16 inch screen. The test results are shown in Table 3. Test No. 1 is a standard test using 100% fuel oil. The test boiler has a steam capacity of 27,215 Kg/hr (60,000 lbs/hr), but 75% of this capacity, or approximately 20,412 Kg/hr
(45000 lbs/hr) and 10.5Kg/cm ² G
(150 psig). The pellet percentage was then gradually increased until it was 85% pellets/15% No. 6 fuel oil (Tests 2 and 3). The air/fuel ratio was manually controlled to obtain clear flue gas indicating complete combustion. Airborne emission measurements were also tested. The solid fuel percentage was then reduced to 60% in tests 4 and 5. In tests 6 and 7, the equipment was switched to 100% fuel oil and the % free oxygen in the flue gas was set the same as for solid fuel. Under these conditions, an unexpected phenomenon was observed. That is, the fuel oil flame in the furnace becomes significantly longer, the flue gas becomes slightly opaque due to soot formation, and the exhaust temperature decreases to 56°C (100°C).
〓) It has become over. Therefore, the amount of excess air was increased until the flue gas became clear, and two further tests using only fuel oil were carried out under these new conditions. The flame length was still longer than normal, and the flue gas temperature was still more than 56°C (100°C) higher than normal. The results of the particulate emissions test are shown in Table 3 along with other test data. The surplus air demand for the crushed pellets was lower than for No. 6 fuel oil under the same conditions (compare Tests 2 and 3 with Tests 6 and 7). This phenomenon indicates that the combustion rate of the crushed pellets is faster than that of No. 6 fuel oil. That is, a normal fuel oil firebox can be used as is for pellet combustion without any modification. Under low surplus air conditions, the flue gas temperature of the crushed pellets is more than 56°C (100°C) lower than for No. 6 fuel oil (compare Tests 2 and 3 with Tests 6 and 7).
This phenomenon suggests that the boiler efficiency can be slightly increased by using solid fuel instead of No. 6 fuel oil.

[Table] Although the present invention has been described in terms of preferred embodiments, the spirit and scope of the invention is not necessarily limited to the above description.

[Brief explanation of drawings]

The accompanying drawing is a flow sheet illustrating a method of making pellets in accordance with a preferred embodiment of the present invention.

Claims (1)

[Scope of Claims] 1. About 97% to about 99% by weight of a granular natural combustible material; and about 1.
~3% by weight of a granular synthetic polymeric thermoplastic material, wherein the natural combustible material consists of at least 50% natural cellulosic material and a balance amount of filler, and the synthetic polymeric thermoplastic material is discontinuous. distributed throughout the fuel pellet as particles, exhibiting a solid form at room temperature of approximately -30 US standard mesh to approximately +80 US standard mesh, the injection molding temperature of which is at least about 95°C; by having a free water content of 15% by weight, having a particle size of about -10 US mesh to about +40 US mesh, and having a synthetic polymeric thermoplastic material interposed between and bonded to the cellulose particles. A fuel pellet characterized in that it binds cellulosic material and the filler has a particle size of at least -10 US standard mesh. 2. Claim 1 consisting of one or more materials, such as distillation waste (an ethanol distillation by-product), coal, and old bark or 50% new bark, with fillers of about 30% or less Fuel pellets as described in Section. 3. The fuel pellet of claim 1, wherein the free water content of the cellulosic material is from about 10 to about 13% by weight. 4. A fuel pellet comprising from about 97% to about 99% by weight of granular natural cellulosic material and from about 1% to about 3% by weight of granular synthetic polymeric thermoplastic material, the synthetic polymeric thermoplastic material being disposed within the fuel pellet as discrete particles. a solid that is uniformly distributed and has a particle size of about -30 US mesh to about +80 US mesh at room temperature, the injection molding temperature of which is at least about 95°C, and at least about 5% to about 15% by weight of cellulosic material; of free water content, particle size from about -10 US mesh to about +40 US mesh, and a synthetic polymeric thermoplastic material interposed between and bonded to the cellulose particles. A fuel pellet characterized in that cellulosic material is bound by a bond. 5. The fuel pellet of claim 4, wherein the free water content of the cellulosic material is from about 10 to about 13% by weight. 6 The free water content of cellulose material is approximately 10.5 to approximately
11.5% by weight of fuel pellets according to claim 4. 7. A process for producing fuel pellets from a particulate naturally occurring combustible material and a particulate synthetic polymeric thermoplastic material, comprising: (a) having a free water content of at least about 5 to about 15% by weight -10; providing a granular naturally occurring combustible material comprising a natural cellulosic material having a particle size of from U.S. mesh to +40 U.S. mesh and 50% or less by weight of filler consisting of at least -10 U.S. mesh granular material; b) provide a particulate synthetic polymeric thermoplastic material that is solid at room temperature, has an injection molding temperature of at least about 95°C, and has a weight of about -30 US Standard mesh to +80 US Standard mesh; (d) substantially all of the thermoplastic material within the pellet remains granular and dissolves A method for producing fuel pellets, characterized in that it comprises the step of compressing the feed material at a pressure and temperature such that it does not soften but becomes intercalated between the cellulose particles and fixed within the fibers of the cellulose particles. 8. The method for producing fuel pellets according to claim 7, wherein the compression step is carried out by extrusion molding. 9. A method of making fuel pellets as claimed in claim 8, including the step of forming a substantially hydrophobic thermoplastic coating on the pellet surface during extrusion.