CA1229229A - Fuel pellets - Google Patents
Fuel pelletsInfo
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- CA1229229A CA1229229A CA000447073A CA447073A CA1229229A CA 1229229 A CA1229229 A CA 1229229A CA 000447073 A CA000447073 A CA 000447073A CA 447073 A CA447073 A CA 447073A CA 1229229 A CA1229229 A CA 1229229A
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- fuel pellet
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Abstract
FUEL PELLETS
Abstract of the Disclosure A fuel pellet comprises from about 97 to about 99 per-cent by weight naturally occurring combustible material of which at least 50 percent is natural cellulosic material and from about 1 to about 3 percent by weight synthetic polymeric thermoplastic material. Any balance of the natur-ally occurring combustible material is filler and is prefer-ably selected form bark, stillage, byproducts of distilla-tion processes, and coal. If old bark, stillage, or byprod-ucts, such as tar and pitch, or coal are used, the amount of the material is limited to 30 percent. The free moisture content of the naturally occurring combustible material is from about 5 percent to about 15 percent by weight, with 10 to 13 being preferred and 10.5 to 11.5 percent being ideal.
Substantially all the thermoplastic material is finer than 30 mesh and coarser than 80 mesh. The cellulosic material is no greater than an order of magnitude coarser than the plastic particles and its minimum size is related to bonding requirements between it and the plastic; is is finer than 10 mesh and coarser than 40 mesh. The filler is finer than 10 mesh. The synthetic thermoplastic material is distributed throughout the fuel pellet as discrete particles, A sheath of plastic is on the outside of the pellet. The thermo-plastic material is solid at room temperature and has an injection molding temperature of about 95°C. or more. The fuel pellet is made in an extruder where the temperature of the pellet is controlled to assure softening of the plastic within the forming pellet without agglomeration.
Abstract of the Disclosure A fuel pellet comprises from about 97 to about 99 per-cent by weight naturally occurring combustible material of which at least 50 percent is natural cellulosic material and from about 1 to about 3 percent by weight synthetic polymeric thermoplastic material. Any balance of the natur-ally occurring combustible material is filler and is prefer-ably selected form bark, stillage, byproducts of distilla-tion processes, and coal. If old bark, stillage, or byprod-ucts, such as tar and pitch, or coal are used, the amount of the material is limited to 30 percent. The free moisture content of the naturally occurring combustible material is from about 5 percent to about 15 percent by weight, with 10 to 13 being preferred and 10.5 to 11.5 percent being ideal.
Substantially all the thermoplastic material is finer than 30 mesh and coarser than 80 mesh. The cellulosic material is no greater than an order of magnitude coarser than the plastic particles and its minimum size is related to bonding requirements between it and the plastic; is is finer than 10 mesh and coarser than 40 mesh. The filler is finer than 10 mesh. The synthetic thermoplastic material is distributed throughout the fuel pellet as discrete particles, A sheath of plastic is on the outside of the pellet. The thermo-plastic material is solid at room temperature and has an injection molding temperature of about 95°C. or more. The fuel pellet is made in an extruder where the temperature of the pellet is controlled to assure softening of the plastic within the forming pellet without agglomeration.
Description
1~:29~29 1~5 0 5: ERR --1--FUEL PULLETS
Background of the Invention The present invention relates to ~ellulosic fuels in the form of pellets bound with a plastic binder.
Due to diminishing quantities of coal, petroleum, end natural gas products, attention is being directed to other energy sources. One source which is receiving considerable attention is Bahamas materials such as wood, buggies, their byproducts, and agricultural residues.
use of compressed wood waste, poulticed or briquette, for example, as fuel oilers has achieved only limited acceptance to date. One reason for this is the relatively low realized seating value of compressed waste. Compressed wood wastes allusive a wow burning rate Some of these z5 wastesha~e exhibited incomplete burnout, resulting in the for-motion of carbonaceous residues and low combustion efficiency.
In addition, compressed wood can be hard to ignite. Another problem it in the frailty of compressed wood which leads to special handling to avoid crumbling, the creation of fines and 30 dust, nod the avoidance of weathering.
o overcome the crumbling and weathering problems, inorganic binders, such as cement and silicate ox soda, end organic binders, such as tar, pitch, rosin, glues, waxes end fibers, have been included in the pellets.
I
1 however, no binder has been found which completely olive s the above problems, end which also OR in expense and does not reduce the heaving value of the wood.
Attempts have teen ode to use the elf biding characteristics produced from lignin in various species of wood to avoid the crumbling problem. this can be done with some species of wood, but jot species, by heating the wood sloe the Signum plastic temperature for Logan of 163C. however, such a wood pellet still 10 does not have a high mechanical strength. ~urtherm~re, such high temperatures can severely limit the operating life of the poulticing equipment, drive sigh BTU volatile components from the wood, and lose Rome energy because ox the requirement of heating.
specific examples of prior art approaches include the disclosures of British patent specifications 901,789 to Stamicarbon, Japanese patent application 46-1028X of Masoyoshi, So patent 3,947255 Jo art man et I
US. Patent 3,843,336 to Mess man, end US. Patent 4,015,g51 I to Gunmen. Stamicarbon discloses a fuel briquette of coal particles end a binder of an olefinically unsaturated hydrocarbon. The fuel particles are smaller than 3 mm.
The bonding of the binder to the coal particles us by welting the binder to distribute it throughout the coal, 25 dissolving the winder to effect absorption on the coal, or effecting a spin of binder on the coal particles with a tar oil distillate end hot compression. Stamicarbon uses only n molest amount of plastic, one to two percent, and discloses a moisture content by from live to eight percent.
30 The Masayoshi patent application discloses a furl of 9 to 66 percent thermoplastic in balance of wood meal or chips. ~asayoshi melts the thermoplastic to combine it with the wood meal or chips. art man uses from 2.5 to 40 percent plastic as a binder for bark. The plastic is US melted to do its job. The moisture content of Hart man's Lo 1 bark is less thin OWE ~essman disallows an artificial foreplay log of thermo~et~ing resin, sawdust, Sax and fuel oil. ~essman effects a sheath of plus on the outside of an extradite, the log, end uses a high percent-age of plastic. Gunner man uses fibrous material, he examples wood, with moisture content of from 16 to 28%.
ye compresses the materiel with die such what the temperature of the pellet us it leaves the die it prom 325 to 350F. ~163 to 177C~, and then dries the 10 pellets. ye states that pellets mode by his process are held together by interlocking of broomed out, fibrous particles, end possibly heat softened lignin. The size of the individual particles is not mar Han By of the minimum dimension of the Delve s.
Another prior art product is attributed to Ian Fraser Johnston who invented a pellet of cellulosic material and thermoplastic. This pellet has from 1 to 10%
thermoplastic in a balance of cellulose twirl. That Material contains from 5 to 15% moisture Both the plastic 20 and cellul~sic material ore particles Hall enough to pass through 5 mesh screen. Johnston uses a unique bonding between the cellulosic cons fluent and the plastic. Instead : of melting or dissolving the plats he ovens it that upon extrusion interstitially penetrates the fixers of the 25 cellulosic material to produce a mechanical lock between pieces of the material. Johnston's pellets also burn better than the individual components alone. It is thought that the small plastic particles act us ignition sites which liberate combustible gases that progress from 30 the sites into the cellulosic material. err the combustible gases burn and enhance he ignition end turning of the cellulosic material. The cellulosic materiel separates the individual plastic particles and permits their burning independently of one another, voiding the charring attendant with the burning of larger plastic .. Jo I
Jo 1350~ -4-1 particles. In connection with the enhance combustion voted in the Johnston pellet, it is known from the work of others that in normal combustion a lignin ~ons~tuent of cellulosic materials like wood Howe a high heat of combustion relative to cellulose, but that lignin tends to pyrolyze to char end not burn completely. The char wends to burn slowly in solid phase combustion by smoldering with low Nate of heat release. The products of combustion of the lignin in this combustion domain ore high in combustible lo content. If the heat flux increases, the lignin can burn in flaming combustion, leaving 11t~le ash. [See Shafizadeh end Brad bury, Smoldering Combustion of Cellulosic materials, Journal of Thermal Insulation, Vol. 2 IJanua~y, 1979).) The combustion products of the Johnston fuel ore very low on lo carbonaceous ash content relative to a natural lignin con awning cellulosic material burned under the tame conditions. This has lead to the hypothesis what the particulate plastic creates combustion environment that competes the combustion of any lignin constituent of the cellulosic 20 material, liberating the considerable heat of combustion of lig~int no leaving very little carbonaceous ash.
: Summ~y_of the Invention This invention provides an improved fuel pellet of naturally 25 occurring combustible material including at least 50~ cellulosic material, and thermoplastic resin, and a process of its manufacture The pellet has excellent combustion characteristics even though only small amount of plastic us used. It has been found that by making the particulate particle size of the 30 plastic end cellulosic material small, less plastic can be used to get the tame combustion characteristics of pellet with more plastic, end these characteristics are excellent, giving high heat release and low carbonaceous ash residue. It has also been found that by observing a relationship between plastic 35 end cellulosic particle size, 8 good mechanical bond results between the plastic and fibers of the cellulosic material.
I I
1 on one form the present invention provides a oppressed fuel pellet that has from about 97 to about 99~ weight part curate naturally occurring combustible material, Dun from bout 1 to about 3% by weight particulate synthetic polymeric then-5 moplastic material. the naturally occurring combustible mate-fiat contains from 50 to around 100% natural cellulosic maze-fiat. Compression is preferably by a die, the fuel pellet be-coming an extradite. The plastic bridges between cellulosic particles and anchors to these particles by an intimate also-10 elation with their fibers. It is possible to include some filler material other than natural cellulosic materials, for example, bark, coal, village or tar-like residues from such processes as alcohol distillation. bark and village may be considered non-cellulosic here because they do not possess the 15 fibrous texture necessary or the ~;atis~actory bond produced by natural cellulosic materials.) If the material is somewhat fibrous, like young bark, a maximum of up to about 50~ part-curate non-cellulosic material can be used with the 1 to I
plastic, the balance being the particulate, natural cellulosic 20 material. Old bark it not fibrous, less can be used, say a maximum of 30% with 1 to I plastic, the balance being the natural cellulosic material.
Preferably, the pellet is substantially 97 Jo 99~ by weight particulate, natural, ~ellulosic material and from about 25 1 to about I by weight particulate, synthetic, polymeric then-plastic material. The use of substantially ~11 cellulosic material as the naturally occurring combustible material no-suits in a very strong pellet.
The plastic in the pullets homogeneous throughout, ox-30 crept on a preferred form where the lateral walls of the pellet it a continuous plastic sheath. The plastic in the pellet is also in particulate form. Importantly, the size of the plastic particles is such what substantially all of the plastic passes through a 30 U. S. standard mesh screen (-30) and it retained 35 on an 80 U. 5. standard mesh screen (+80). The particle size I
13505 h-1 of the cellulosic material bears a definite ~el~ionship Jo that of the Lucite so that the plastic woes not get too small selativ~ to the cellulosic material. The ~ellulosic material is idea 50 that substantially ~11 the material passes through a US. standard 10 mesh screen (-10) and is retained on a US. tankard 40 mesh screen ~+40~. This means that the cellulosic material has a characteristic dimension (diameter) no greater than an order of magnitude .
larger than a characteristic dimension ammeter) of the 10 plastic.
Any non-cellulosic filter should have a maximum particle size no greater than that of the cellulosic material The non-cellulosic material may be finer than the cellulosic.
The small particle size of the plastic produces excellent 15 combustion of both the plastic and the naturally occurring combustible material. Combustion in the naturally occurring combustible material is enhanced by the liberation of combustible stases from the plastic. The tame mechanism enhances complete combustion of any lignin present. Combustion of the 20 plastic is also complete because the relatively high surface area of the plastic particles is maintained and he various plastic particles cannot agglomerate as they are tightly held within the cellulosic fibers, the plastic particle size can be too my no 25 the relation of that size to the cellulosic particle size must be observed for a good bond. If the plastic it seller than 80 mesh it no longer bridges satisfactorily between cellulosic particles. When the plastic particle size exceeds 30 mesh, good combustion and bonding are possible, but at 30 the cost of at least a greater amount of plastic. The order of magnitude difference in particle size must be observed a the limit of size difference because if the plastic becomes too Allah it will not be able to bridge the distance between individual cellulosic particles. The greater the
Background of the Invention The present invention relates to ~ellulosic fuels in the form of pellets bound with a plastic binder.
Due to diminishing quantities of coal, petroleum, end natural gas products, attention is being directed to other energy sources. One source which is receiving considerable attention is Bahamas materials such as wood, buggies, their byproducts, and agricultural residues.
use of compressed wood waste, poulticed or briquette, for example, as fuel oilers has achieved only limited acceptance to date. One reason for this is the relatively low realized seating value of compressed waste. Compressed wood wastes allusive a wow burning rate Some of these z5 wastesha~e exhibited incomplete burnout, resulting in the for-motion of carbonaceous residues and low combustion efficiency.
In addition, compressed wood can be hard to ignite. Another problem it in the frailty of compressed wood which leads to special handling to avoid crumbling, the creation of fines and 30 dust, nod the avoidance of weathering.
o overcome the crumbling and weathering problems, inorganic binders, such as cement and silicate ox soda, end organic binders, such as tar, pitch, rosin, glues, waxes end fibers, have been included in the pellets.
I
1 however, no binder has been found which completely olive s the above problems, end which also OR in expense and does not reduce the heaving value of the wood.
Attempts have teen ode to use the elf biding characteristics produced from lignin in various species of wood to avoid the crumbling problem. this can be done with some species of wood, but jot species, by heating the wood sloe the Signum plastic temperature for Logan of 163C. however, such a wood pellet still 10 does not have a high mechanical strength. ~urtherm~re, such high temperatures can severely limit the operating life of the poulticing equipment, drive sigh BTU volatile components from the wood, and lose Rome energy because ox the requirement of heating.
specific examples of prior art approaches include the disclosures of British patent specifications 901,789 to Stamicarbon, Japanese patent application 46-1028X of Masoyoshi, So patent 3,947255 Jo art man et I
US. Patent 3,843,336 to Mess man, end US. Patent 4,015,g51 I to Gunmen. Stamicarbon discloses a fuel briquette of coal particles end a binder of an olefinically unsaturated hydrocarbon. The fuel particles are smaller than 3 mm.
The bonding of the binder to the coal particles us by welting the binder to distribute it throughout the coal, 25 dissolving the winder to effect absorption on the coal, or effecting a spin of binder on the coal particles with a tar oil distillate end hot compression. Stamicarbon uses only n molest amount of plastic, one to two percent, and discloses a moisture content by from live to eight percent.
30 The Masayoshi patent application discloses a furl of 9 to 66 percent thermoplastic in balance of wood meal or chips. ~asayoshi melts the thermoplastic to combine it with the wood meal or chips. art man uses from 2.5 to 40 percent plastic as a binder for bark. The plastic is US melted to do its job. The moisture content of Hart man's Lo 1 bark is less thin OWE ~essman disallows an artificial foreplay log of thermo~et~ing resin, sawdust, Sax and fuel oil. ~essman effects a sheath of plus on the outside of an extradite, the log, end uses a high percent-age of plastic. Gunner man uses fibrous material, he examples wood, with moisture content of from 16 to 28%.
ye compresses the materiel with die such what the temperature of the pellet us it leaves the die it prom 325 to 350F. ~163 to 177C~, and then dries the 10 pellets. ye states that pellets mode by his process are held together by interlocking of broomed out, fibrous particles, end possibly heat softened lignin. The size of the individual particles is not mar Han By of the minimum dimension of the Delve s.
Another prior art product is attributed to Ian Fraser Johnston who invented a pellet of cellulosic material and thermoplastic. This pellet has from 1 to 10%
thermoplastic in a balance of cellulose twirl. That Material contains from 5 to 15% moisture Both the plastic 20 and cellul~sic material ore particles Hall enough to pass through 5 mesh screen. Johnston uses a unique bonding between the cellulosic cons fluent and the plastic. Instead : of melting or dissolving the plats he ovens it that upon extrusion interstitially penetrates the fixers of the 25 cellulosic material to produce a mechanical lock between pieces of the material. Johnston's pellets also burn better than the individual components alone. It is thought that the small plastic particles act us ignition sites which liberate combustible gases that progress from 30 the sites into the cellulosic material. err the combustible gases burn and enhance he ignition end turning of the cellulosic material. The cellulosic materiel separates the individual plastic particles and permits their burning independently of one another, voiding the charring attendant with the burning of larger plastic .. Jo I
Jo 1350~ -4-1 particles. In connection with the enhance combustion voted in the Johnston pellet, it is known from the work of others that in normal combustion a lignin ~ons~tuent of cellulosic materials like wood Howe a high heat of combustion relative to cellulose, but that lignin tends to pyrolyze to char end not burn completely. The char wends to burn slowly in solid phase combustion by smoldering with low Nate of heat release. The products of combustion of the lignin in this combustion domain ore high in combustible lo content. If the heat flux increases, the lignin can burn in flaming combustion, leaving 11t~le ash. [See Shafizadeh end Brad bury, Smoldering Combustion of Cellulosic materials, Journal of Thermal Insulation, Vol. 2 IJanua~y, 1979).) The combustion products of the Johnston fuel ore very low on lo carbonaceous ash content relative to a natural lignin con awning cellulosic material burned under the tame conditions. This has lead to the hypothesis what the particulate plastic creates combustion environment that competes the combustion of any lignin constituent of the cellulosic 20 material, liberating the considerable heat of combustion of lig~int no leaving very little carbonaceous ash.
: Summ~y_of the Invention This invention provides an improved fuel pellet of naturally 25 occurring combustible material including at least 50~ cellulosic material, and thermoplastic resin, and a process of its manufacture The pellet has excellent combustion characteristics even though only small amount of plastic us used. It has been found that by making the particulate particle size of the 30 plastic end cellulosic material small, less plastic can be used to get the tame combustion characteristics of pellet with more plastic, end these characteristics are excellent, giving high heat release and low carbonaceous ash residue. It has also been found that by observing a relationship between plastic 35 end cellulosic particle size, 8 good mechanical bond results between the plastic and fibers of the cellulosic material.
I I
1 on one form the present invention provides a oppressed fuel pellet that has from about 97 to about 99~ weight part curate naturally occurring combustible material, Dun from bout 1 to about 3% by weight particulate synthetic polymeric then-5 moplastic material. the naturally occurring combustible mate-fiat contains from 50 to around 100% natural cellulosic maze-fiat. Compression is preferably by a die, the fuel pellet be-coming an extradite. The plastic bridges between cellulosic particles and anchors to these particles by an intimate also-10 elation with their fibers. It is possible to include some filler material other than natural cellulosic materials, for example, bark, coal, village or tar-like residues from such processes as alcohol distillation. bark and village may be considered non-cellulosic here because they do not possess the 15 fibrous texture necessary or the ~;atis~actory bond produced by natural cellulosic materials.) If the material is somewhat fibrous, like young bark, a maximum of up to about 50~ part-curate non-cellulosic material can be used with the 1 to I
plastic, the balance being the particulate, natural cellulosic 20 material. Old bark it not fibrous, less can be used, say a maximum of 30% with 1 to I plastic, the balance being the natural cellulosic material.
Preferably, the pellet is substantially 97 Jo 99~ by weight particulate, natural, ~ellulosic material and from about 25 1 to about I by weight particulate, synthetic, polymeric then-plastic material. The use of substantially ~11 cellulosic material as the naturally occurring combustible material no-suits in a very strong pellet.
The plastic in the pullets homogeneous throughout, ox-30 crept on a preferred form where the lateral walls of the pellet it a continuous plastic sheath. The plastic in the pellet is also in particulate form. Importantly, the size of the plastic particles is such what substantially all of the plastic passes through a 30 U. S. standard mesh screen (-30) and it retained 35 on an 80 U. 5. standard mesh screen (+80). The particle size I
13505 h-1 of the cellulosic material bears a definite ~el~ionship Jo that of the Lucite so that the plastic woes not get too small selativ~ to the cellulosic material. The ~ellulosic material is idea 50 that substantially ~11 the material passes through a US. standard 10 mesh screen (-10) and is retained on a US. tankard 40 mesh screen ~+40~. This means that the cellulosic material has a characteristic dimension (diameter) no greater than an order of magnitude .
larger than a characteristic dimension ammeter) of the 10 plastic.
Any non-cellulosic filter should have a maximum particle size no greater than that of the cellulosic material The non-cellulosic material may be finer than the cellulosic.
The small particle size of the plastic produces excellent 15 combustion of both the plastic and the naturally occurring combustible material. Combustion in the naturally occurring combustible material is enhanced by the liberation of combustible stases from the plastic. The tame mechanism enhances complete combustion of any lignin present. Combustion of the 20 plastic is also complete because the relatively high surface area of the plastic particles is maintained and he various plastic particles cannot agglomerate as they are tightly held within the cellulosic fibers, the plastic particle size can be too my no 25 the relation of that size to the cellulosic particle size must be observed for a good bond. If the plastic it seller than 80 mesh it no longer bridges satisfactorily between cellulosic particles. When the plastic particle size exceeds 30 mesh, good combustion and bonding are possible, but at 30 the cost of at least a greater amount of plastic. The order of magnitude difference in particle size must be observed a the limit of size difference because if the plastic becomes too Allah it will not be able to bridge the distance between individual cellulosic particles. The greater the
2~2~
1 particle it the more plastic it required to produce a pellet vying Good strength. Also, if the pla~tlc particle size is zoo large, it Jill no soften during extrusion Jo form a thin piece that extents between pieces of rellulosic material. When the pellet is to be pulverized for air suspension burning, excessively issued plastic results in detached particles of plastic in the pulverized mixture, with a loss of the advantages what intimacy between the plastic end cellulosic material affords. The cellulosic material 10 con be too fine. If this material becomes smaller than 40 mesh it loses its fibrous quality and the interstitial bonding quality of the plastic end cellulosic twirl suffers. The free moisture content of the cellulosic material is from byway 5 to about 15~, with 10 to 13 being 15 preferred as measured prior to poulticing. Ideally he moisture content is even narrower, 10.5 to 11.5~ The moisture content aye poulticing end any drying is less, preferably about 8%. The thermoplastic material is chosen so it is solid at room temperature and has on injection molding 20 temperature of about 95C. or greater. Fuel pellets of the present invention exhibit complete burnout, burn faster than pellets nut containing thermoplastic material, end have Good structural integrity.
The range of plastic required, 1 to I is dictated 25 by both bonding end combustion requirements. If there is insufficient plastic, less than 1%, the advantageous individual ignition sites are lost and the strength of the pellet drops. A I plastic content may be required to wind some hard woods or where there is a high percentage of the non-I cellulosic component. In general, however, the less plastic the better because of cost. A preferred composition range is from 1 to I plastic.
~22~2Z~
1 the principles of the present invention permit the use of filler combustibles, such as bark, village, other products of distillation, end coal, with the cellulosic particul2ltes and plastics. . Old Mark generally is not fibrous, and therefore, 5 with it as well as with village end coal the locking motion-is of this invention dyes not apply. It Jan be bound, none-else, of there is enough cellulosic material to provide the anchor sites for the plastic. For coal, village and aid bark, up to about 30~ of the material with 67 Jo 69~ solely-lo sic material and 1 to I plastic produces a satisfactory prod-vat. For newer bark, bark that is fibrous, up to 50% bark can be used. The resulting formulation has up to So% bark, 1 to
1 particle it the more plastic it required to produce a pellet vying Good strength. Also, if the pla~tlc particle size is zoo large, it Jill no soften during extrusion Jo form a thin piece that extents between pieces of rellulosic material. When the pellet is to be pulverized for air suspension burning, excessively issued plastic results in detached particles of plastic in the pulverized mixture, with a loss of the advantages what intimacy between the plastic end cellulosic material affords. The cellulosic material 10 con be too fine. If this material becomes smaller than 40 mesh it loses its fibrous quality and the interstitial bonding quality of the plastic end cellulosic twirl suffers. The free moisture content of the cellulosic material is from byway 5 to about 15~, with 10 to 13 being 15 preferred as measured prior to poulticing. Ideally he moisture content is even narrower, 10.5 to 11.5~ The moisture content aye poulticing end any drying is less, preferably about 8%. The thermoplastic material is chosen so it is solid at room temperature and has on injection molding 20 temperature of about 95C. or greater. Fuel pellets of the present invention exhibit complete burnout, burn faster than pellets nut containing thermoplastic material, end have Good structural integrity.
The range of plastic required, 1 to I is dictated 25 by both bonding end combustion requirements. If there is insufficient plastic, less than 1%, the advantageous individual ignition sites are lost and the strength of the pellet drops. A I plastic content may be required to wind some hard woods or where there is a high percentage of the non-I cellulosic component. In general, however, the less plastic the better because of cost. A preferred composition range is from 1 to I plastic.
~22~2Z~
1 the principles of the present invention permit the use of filler combustibles, such as bark, village, other products of distillation, end coal, with the cellulosic particul2ltes and plastics. . Old Mark generally is not fibrous, and therefore, 5 with it as well as with village end coal the locking motion-is of this invention dyes not apply. It Jan be bound, none-else, of there is enough cellulosic material to provide the anchor sites for the plastic. For coal, village and aid bark, up to about 30~ of the material with 67 Jo 69~ solely-lo sic material and 1 to I plastic produces a satisfactory prod-vat. For newer bark, bark that is fibrous, up to 50% bark can be used. The resulting formulation has up to So% bark, 1 to
3% plastic and the balance cellulosic material. The moisture content of the product and the plastic particle size remain 15 unchanged.
In another aspect, Abe present invention includes on the pellet an alkali petal silicate selected from sodium silicate and potassium silicate. One to two percent ox the silicate by weight is preferred, but up to about 10% could be acceptable.
iota is believed that the alkali petal acts as a catalyst in promoting gaseous combustion. it is also believed that the silica crystals are thermal radiators and promote ignition by thermal radiation. The ability to produce intense infrared radiation, when heated, it an inherent property of silica 25 crystals The alkali metal silicate also promotes bonding, and the mechanical strength of the pellet, more densified pellet, and an enhanced hydrophobic sheath on the pellet.
The fuel pellet can be made by preparing a feed of par-ticulate natural cellulosic material, any of the filler, non-30 cellulosic material, and particulate synthetic the~moplasticmaterial. Substantially f the thermoplastic material is -30 U. S. standard mesh and +80 U. S. standard mesh. The eel-lulosic material is ~uhstantially all -10 U. JO standard mesh and +40 Us S. standard mesh. The filler is substantially all 35 -10 U. S. standard mesh. The plastic and cellulosic Metro-awls are intimately combined by compressing the feed in an 13505 -pa-1 extrusion die. Extrusion takes place under temperature end rate conditions where the plastic in the interior of the pot-let does not melt, but only often The plastic thus no-twins its particulate nature. Extrusion flattens the part-S curate plastic into thin pieces and forces these pieces intone intimate mechanical bond with the fibers of the cellulosic material.
US
~2Z~
1 Brief Description of he drawing The jingle Figure is a flow schematic of suitable facility to fabricate pellets in accordance with the preferred embodiment of the present invention.
US
1 e AYE cation of the Preferred my dominate The present invention provides both fuel pellet and a process for its manufacture. The pellet it characterized in its use of a small mount of plastic birder end its except 5 tonal mechanical strength and combustion char~cteri6tics.The pellet burns completely in either grate burning or in air suspension burning, the latter after pellet comminution.
In preferred form, the pellet is from bout 97 to bout 99~ cellul~sic material and from bout 1 to about I thermos 10 plastic. Preferably, the pellet is from Bout 98 to 99% eel-lulosic material and from About 1 to I thermoplastic. The thermoplastic is present in particulate form and acts us a binder between cellulosic particles. Gore peaceful, the pellet it formed in on extrusion process that maintains that integrity of individual plastic particles. That is, they do not fuse together to form one cohesive end continuous piece of material. The extrusion process deforms the plastic into thin pancake-like pieces or platelets (nut necessarily planar) and forces these pieces into intimate mechanical locks it ZOthe fibers of cellulosic host material. The plastic can be viewed as tendons holding the cellulosic gibers together. It is important that the plastic maintain its particulate quality.
The particulate quality assures good burning of not only the plastic, but also the cellulosic material.
the pellet can include naturally occurring filler mate-fiats of say, coal, village other products of distillation processes, bark, end tar-like substances. Bark has a high heat of combustion and is a plentiful product of the forest industry. Depending on the bark, it is more or less fibrous.
30 New bark can be relatively fibrous. Old bark canoe esstenti-ally free of fibers. Because of mechanical strength require mints, up to 50~ of the pellet can be new bark. When old bark it used, up to 30% of the pellet may be bark. on either vase, the plastic content remains 1 to I end the balance of the 35 pellet is natural cellulosic. Coal is not cellulosic at all, I
end it must be boy d between cellulc:)sic particles. Spillage is deified substance including Rome cellulose., The it-brows quzllity of cellulose what gives eye good bending kirk-'ceristics, however, if; largely lost in processing, and, there-5 fore, the material it a filler. distillation byproducts other Han spillage, such as molasses and pitch, may also be used with efficacy us {I Miller. These byproducts have been a dip-faculty problem in disposal The particulate quality of the plastic insures large 10 surface area for the plastic which leads to high combustion rites of the plastic The hot combustion gases prom the burn-no plastic particle ignite any filler and eye cellulosic ma-twirl round the particle and promote the total combustion of these. Cellulosic material derived from wood contains a con-15 siderable immunity of Lignin. Lignin does not burn as riddles cellulose. Quite often top lignin burns in solid state with a smoldering flame, leaving a substantially unburned residue in the form of char. this char has considerable fuel value. It also would c~stitute source it least of part-go curate pollution The particulate plastic creates combustion domain that assures complete burning of any lignin in the host cellulosic material. This is Jo whether the fuel it burned s pellet or whether it is commented or pulverized : end burned in air suspension. In the case of the latter, the 25 plastic remains in intimate contact with ~ellulosic particles when the size limitations to be described on the plastic are observed.
minimum mount of plastic may be used when the plastic is sufficiently fine to pass a 30 U. S. standard mesh screen, 30 but coarse enough not to pass an 80 I. S. standard mesh screen.
This size of particulate plastic is large enough to span ye-tweet cellulosic particles for the bonding junction. The size is desirably small to tare advantage of a large ~urface-to-volume ratio that produces easy ignition and rapid combustion that enhances lignin and cellulose combustion. This small ~22~2~
particle size also Sirius ~omple'ce combustion of the plastic As is well Nemo, when plastic gets too passive, god the ~urface-to-~olume ratio gets too low, the plastic tends to burn incompletely, leaving char. the plastic protocol size 5 is also us ficier-tly small Jo that it will soften to font thin platelets or pancakes in the pellet during extrusion. It has been found that when the plastic particle size YE; two 1 rye, the particles will not soften end form the thin lilts that bind the cellulosic particles together.
The particle size of the ~ellulosi~ material and any filler, Jay bar, bears a finite relationship Jo that of the plastic. The particle size should be sufficient to pass a 10 U. S. standard mesh screen. The ~ellulosic material should be sufficiently coarse to stay on top of a I U. S. standard 15 mesh screen. it thy s range of size, the characteristic dip mention of the cellulosic materials is tout on order of mug-nutted greater than corresponding characteristic dimension of the plastic material. If the cellulose particle size gets too large with respect to the particle size of the plastic, 20 the plastic cannot span the distance between individual cell-logic particles because it gets lost in thy fibers of the eel-lulosic material. Furthermore, excessively large cellulosic particles do not bury as well as smaller ones. If the plastic gets large with respect to the soliloquy material 9 where is 25 a waste of plastic, end one can encounter the combustion and the softening problems previously described. (Assuming what the softening problem can be overcome, and ignoring the pies-tic combustion problems that might occur, plastic particles larger than the limits jet out here will effect good bridge 30 between cellulosic particles If the cellulosic material is too fine, it loses its fibrous character. The result is a loss in mechanical strength because of a 10ss of the bonding mechanism between the plastic and the cellulosic material that relies upon the fibrous nature of the cellulosic material in 35 the interlocking mechanical bond.
13505 . -13~
1 Any filler must be he'd largely by the bond between the plastic end the cellulosic material. Jo the Lowry particles are too large, they interfere with the bonding mechanism between the plastic end the cellulosic twirl. Excessive large filler particles do not burn as readily either. the lower limit of filler ire is dictated by economics. There us no reason to make the filler particles very small, but if they ore ~lxeady, their fineness will not harm the result.
Coal dust is an example of fine filler that exists without 10 need for further size reduction.
The mount of plastic should be between bout 1 to bout 3% of the total fuel pellet. This amount of plastic in conjunction with the size and particulate limitations of the plastic and the size limitations of the cellulosic material 15 produces the good combustion and bonding characteristics with a minimum mount of plastic The inclusion of the 1 to I thermoplastic of a pellet as a binder can ye viewed in different light Without the thermoplastic, to sails-factorial pullout only the cellulosic material would 20 require considerably higher temperatures. It also assures that the plastic acts as lubricant in the pellet dies or rollers. It can effect a sheath on the outer surface of the pellet, which is helpful to make the pellet hydrophobic.
The referred range of plastic is between bout 1 to 25 bout 24 of the total fuel pellet. Usually this range 6atisf its the requirements of pellet strength and enhanced ignition. however, particularly with hard woods, and large amounts of filler, more plastic may be required as a winder.
The moisture content of the cellulosic material should be between about 5 to about 15%~ If there is inadequate or too much moisture the pellet tends to lose strength and can disintegrate in the rough and tumble of handling and transport. Too much moisture adversely affects the combs-lion qualities by lowering the flame temperature. It is preferred that the moisture content be held within 10 to 13~.
~2~2~2~
1 A moisture content of the cellulose of from 10.5 Jo 11.5~ is ideal This range is the optimum range for pellet ~tsength.
Moisture content is measured in the cellulosic material prior to ~elletizing. The ~elletizi~g may reduce the S moisture Jo some extent, 4 to I% by evaporation into air.
When the pellet is to be used for sir suspension turning, it may be desirable to reduce the moisture content to lower than the prescribed range after the pellet has been commented in order to enhance combustion characteristics.
10 Obviously, after the pellet has been commented into the small particles suitable for air suspension the moisture previously required for structural integrity of the pellet is no longer necessary. the process of commenting itself reduces the moisture content.
The thermoplastic ma trials have on injection molding temperature of close to about 95C. or higher. It can ye little lower than this. this limitation is necessary to avoid excessive plastic melting during the extrusion process.
If the plastic melts excessively, its particulate nature 20 it lost and the qualities associated with that characteristic are also lost. Some melting is permissible so long as the plastic particles do not agglomerate.
The cellulosic material may ye derived from any number of Bahamas sources. The most Common sources will be wood 25 waste, such as sawdust, wood shavings, end buggies Certain agricultural wastes also classify a cellulosic, us well as paper end cardboard. Wood end buggies materials are referred because they have a high teat of combustion and lower moisture content than agricultural wastes. They 30 are also preferred because of their abundance.
~22~2~
1 The the plastic material can ye practically any available synthetic thermoplastic, such as polystyrene, polyethylene, polypropylene, acrylonitrile-butadiene-styrenes Seattle copolymers, acutely homopolymer6, acrylics, polybutylene, and combinations of these. Polyvinyl chloride, however, should not be used because it contains a halogen that presents corrosion end emission difficulties upon combustion. If there is a preference of thermoplastic materials it would be or polypropylene end polyethylene 10 because these materials burn rapidly and ignite readily.
he minimum injection molding temperatures of common thermoplastics ore reported in Modern Plastics Encyclopedia, Vol. 49, ~cGraw-~ill, 1972-3 Eden, end aye presented in table 1.
pi minimum Iniec~on Synthetic Thermoplastic Molding Temperature (~F.3 polystyrene 163~C. ~325F.~
Polyethylene 1~2C. (250F.) Polypropylene l91~C. ~375~.) AS 183C. ~360~F.) Cellulosics 168C. (335F.) Nylon 191C. (360F.) Polyesters 132C. (270F.) sigh impact polystyrene presents difficulties in pellet-lying because it is Jo hard, it is difficult to pullout a feed having Gore than 1.25% by weight of such material.
It has been found that during the poulticing process some of the thermoplastic material at the surface of the pellets will be sufficiently heaved by the friction between the pallet end the extrusion dies to melt end form a thin sheet or coating on the lateral outside unlaces Do the pellets. This moating is hydrophobic and serves to prevent the absorption of moisture by the pellets Turing storage.
Iota contemplated that materials other than the cellulosic and thermoplastic materials can be included in the pellet for a particular application or processing : conditions. or example, oxidizing agents such as sodium per chlorate end ammonium nitrate might be added to facile-late combustion. Binding agents such as paraffin, slack wax, carnuba wax; end certain lignosulfanates, such as minim lignosulfanate, sodium lignosulfanate, calcium lignosul~anate, and magnesium lignosulfanate can be added.
Oil seeds and their products have a fatty acid content that can reduce wear in the poulticing die. Examples of such materials include coconut husks, Joy beans, peanuts, sunflower seeds, corn cake, pressing residuals, end ethanol plant village 1 Jo aid in the drying of cell~losic weed twirl dry Blake lime, that is, calcium carbonate, can be mined with the feed. Other discounts can be used. The calcium carbonate combines with water and feed material and allows the rapid release of isture from the feed in a dehydrator.
The calcium carbonate can be added in mounts from about 2 to about 104 by weight of the dry feed, with about 5% by weight significantly tiding in the drying process. The calcium carbonate is preferably removed as by dry classic 10 cation before poulticing.
In applications where there is an excessive amount offer water in the cellulosic feed material it is most economical Jo remove the water by mechanical processes, such as powered presses and tapered screw presses.
While it is presently preferred to pullout the pellets with a extrude, rocketing can also be attractive.
The bond in the pellet of this invention is a very good one. It it needs to be enhanced, as could be required with a high percentage of non-cellulosic material present J say 20 old bark, sodium or potassium silicate can be used. When such silicate is used, it h~rolizes acidic lignatious end cellulosic materials This results in a more compressible cellulosic coLlponent end a denser pellet. On dehydration, the silicate jets end acts as a cement; augmenting the 25 thermoplastic and knitting tile fibers tocJether. The thyme-plastic sheath is com~ol~n~ed on a more hydrophobic base and the pellet has enhanced weathering resistance. The silicate increases the ash content; jut will not materially affect performance in either air-sus~ension or grate turning.
30 The alkali silicate can be introduced in a blender upstream from an extrude or briquette. When just weather resistance is desired, it is also possible to add it, while the thermos plastic sheath is still hot nod the alkali silicate adhesion will take place. The amount of silicate my be on the order 35 of I by weight. The silicate has a high viscosity, which can be lowered by heating.
~z~z~
13505 -lo--1 the alkali metal silicate, such us waxer gloss, also thought to be a combustion enhance or combustion catalyst.
it has been observed that pellets with about I% by weight sodium silicate burn with greater intensity (at 8 faster rate) S than otherwise identical pellets without the silicate It is thought that the alkali metal acts as a catalyst for combs lion.
Solutions of sodium silicate are strongly alkaline end ore readily decomposed by acids with separation of ~ilicic 10 acid. Upon heaving, the latter is converted to silica. It us thought that ho tame processes take place in the mixture of sodium silicate and wood wastes, as the latter contain acidic substances. The resulting crystals of silica ore be-lived to promote ignition by intense radiation of infrared eta. The ability to produce intense infrared radiation, when heated, is an inherent property of silica chrysalis The preferred amount of the silicate is from 1 to 2% by White The combustion enhancement would be present with this amount of the silicate without excessive ash. The den-ossification, weatherproofing, end bonding qualities would also be good at these concentrations.
A pellet with the alkali metal silicate will have the following composition: from about 1 to about 3% by weight particulate, synthetic polymeric thermoplastic material, from I about 1 to about 10~ by weight of the alkali silicate, end from bout 87 to bout 98% naturally combustible material.
The naturally combustible material includes at least 50% net-rural cellulosic material with the balance being filler.
With wood wastes that have a high lignin content, it is Jo possible to make a fuel pellet with enhanced combustion pro-parties consisting of 1 to about 10% by weight of the alkali silicate and from bout 90 to 99~ naturally combustible ma-tonal.
I
~L2;2~
1~505 I
1 the jingle Figure owe schematically suitable plant for fabrication of pellets of the present ~nvent~on. Before getting into the-description, it ghoul be appreciated that there ore several Approaches to the manufacture of pellets.
In addition, the flow sheet ox the Figure voids inclusion of ..
detail which would be obvious to the artisan, such us certain storage hoppers, conveyors, and the like. The plant can also take advantage of waste material in the form of cellulosic and thermoplastic fines derived from the process inherent in the 10 flea material and resulting from pellet fines, to fuel energy consuming heaters, such us used in a dryer to dehydrate wet cellulosic feed materials.
referring to the Figure ~ellulosic feed material from any desired source us fed us stream 10 into an initial alas-15 sifter 12. An output stream 14 of the classifier containscellulosic feed materiel of -1~2 inch or -3/B inch mesh. That stream goes onto a conveyor 16 and feeds into to dehydrator 18.
A second stream 20 from the classifier feeds a primary hog 22 with ~1/2 inch or ~3/8 inch feud that muons the material 20 and discharges i as a stream 24 auto conveyor 16. The prim many hog functions to reduce the weed of stream 20 to -1~2 inch to -3/8 inch mesh Stream 24 combines with stream I on conveyor 16 end feeds into dehydrator 18.
A heater 26 supplies the heat energy for the dehydrator 25 In the dehydrator, the cellulosic feed material has its 40 to 60~ moisture convent dropped to from about 5 to bout 15~, preferably from about 3 to about 11%. seater 26 is fueled from a fuel bin 27.
The discharge stream from dehydrator 18 is indicated at 30 2B. It feeds a cyclone 30 where gas and solids separate. The was exits cyclone 30 us stream 32, end the oldies exit as a stream 34. A fraction of the gas can be recycled to heaver 26.
Stream 34 enters primary classifier 36. Those materials that are miner than 40 mesh leave the primary classifier 35 as a fine Bream 38. This stream is used as a source of 13505 ' I
energy to fuel heater 260 Coarse ~llulosic materiel leaves primary classifier 36 us Ryan 40 and it coDminuted in a hammer mill 42 to -10 to ~40 US. ~ndard mesh. the exit stream from hammer mill 42 is indicated us stream 44.
the primary stream exiting the primary classifier 36 is a stream 46 constituted of cellulosic material of -10 to ~40 US. standard mesh. This stream combines with stream 44 to form a stream 48 which is transported by air blowing to a high elevation level where it feeds a secondary cyclone 50 10 where again gas end solids sure separated, with the gas leaving the top as a stream 52 and the solids leaving the bottom as stream 54. Stream 52 Jay be recycled into fuel bin 27.
The solids enter secondary classifier US. In 15 secondary classifier 56 excessively fine material is classified end discharged as a stream I these fines are used as fuel in the plant, say in a boiler that provides steam. Stream 58 also includes silicates and carbonates, whose removal Improves pelletizer die life. Properly sized 20 material of from 10 to +40 mesh leaves secondary classifier I as a stream 60 and enters a holding bin 62 preliminarily to blending with granulated thermoplastic.
Thermoplastic preparation is done ~eparte from the cellul~sic material. It can oboe lye effect removal of 25 unwanted materials such as metals, glass, and polyvinyl-chloride by any of number ox techniques, including magnets, weight sensitive separators, and flotation.
The then~o~lastic enters a granulator 72 as a plastic Weed street I where it is ground. The granulated plastic 30 sasses as a stream 74 into a classifier 76. Excessively fine plastic leaves the classifier as a stream 78. This stream contains a plastic that sasses through an 80 So standard mesh screen. Excessively coarse material leaves classifier 76 in a stream 80 and is recycled back to US granulator 72 on a conveyor 73. This coarse material is I
1 coarser than Us S. standard mesh. The properly sized plastic of prom -30 to BY mesh leaves the c~ssifier 76 a stream 82 end combines with any additives from stream 84 as a stream 86 that goes to a bin 88.
yin 88 feeds B blender 90 us does bin 62. petering is effected by any number of well known techniques to effect the required 1 to I weight percent plastic feed with a balance of cellulosic material. Any sodium or potassium silicate can also ye added on blender 90.
The discharge prom blender 90 is a stream I that flows into conditioning chamber 94. A steam jacket 95 heats the cellulosic-plastic feed. the steam comes from a boiler fueled by cellulosio fines. The conditioning chamber has an exit stream 96 that supplies a pellet mill 98. Again the feed can 15 be metered in any number of known techniques. A high-speed mixer-convey~r moves the material through the conditioning chamber to a pellet mill chute.
The pellet mill must be capable of producing a pressure on an extrusion die that causes temperatures of the feed mate-20 fiat to increase so what the pellets have a temperature suffix client to oxen the plastic particulate material within the pellets to form the thin pancake-like platelet The pressure exerted by the die should ye adequate to force the plastic into the intimate relationship with the fibers of the cellulosic 25 material that is the characteristic of the mechanical lock of the plastic on the cellulose. It has teen wound that when the temperature of the exiting pellets it from about 66C to about 122C, the plastic is adequately malleable to deform under pressure. any temperature above this risks the possibility of I excessively molting the plastic in the pellet and can result on unacceptable agglomeration of the particulate plastic into particles that are too large. The preferred lower temperature is bout 88C. The surface of the extradite may be sufficiently heated, and preferably so, to produce localized melting of then-35 moplastic material on the surface. This material, when it I
1 hardens, forms a thin, continues eighth on the resulting pellet. As Already commented upon, this sheath frauds a ho-drophobic quality to the pellet. In addition, it lubricates the dies to increase their life and increase production gape city. The thermoplastic within the pellet, with the exception of this sheath, us substantially homogeneously distributed.
Prom the pellet mill, the pellets enter cooler I as a stream 100 .
From pellet cooler 99~ the pellets enter a classifier 101 10 by a stream 102. Fines and reject pellets are discharged from the classifier AS stream 1060 The reject pellets are put-versed and combined with waste fines from the other Claus-liens to form a mixture that is used as fuel for the dryer burner and toiler. A product stream 108 leaves for storage.
~L~22~
1 Example I
tests were conducted on c~mminuted fuel-pellets having 2% by weight thermoplastic end 98~ by weigh cellulosic material. The thermoplastic included polyethylene, polyp styrenes and polypropylene. jests were Lowe run oncomminuted fuel pellets end coal end just coal, The thermoplastic was between Cubs anti ally minus 30 mesh and plus 80 mesh. the cellulosic material was between tub-staunchly minus 10 mesh end substantially plus 40 mush.
10 The pellets were jade by an extrusion process. Percolate thermoplastic material was homogeneously present throughout the pellets. There was a thermoplastic sheath on each pellet.
the pellets were ~omminuted in a hammer mill and screen gloved with a 1~16 inch screen for the OK" pellet and a 15 1~32 inch screen for the ON" pellet. The commented pellets were transferred pneumatically trough a cyclone separator and ultimately transferred to a silo next to a test furnace.
Coal end 50% Cole pellet mixture were also tested.
The test furnace was a Coon Company horizontal 20 cylindrical suspension air heater. It had air cooled, refracting lined wall, internal Jan end wind box, end a rated heat input capacity of 4 million Btu~hr. the furnace had ; a pneumatically fed, pulverized fuel, air suspension burner with a five port infuser Fuel was fed prom the silo with a vibrating screw feeder end on air blower that pneumatically conveyed the fuel prom the feeder Jo the burner.
Al} tests were conducted with the furnace sully preheated to steady state temperatuxeO The best air and fuel feed I rates were determined by visual observation of the lame pa item .
~V~2~
13505 24~
Proximate Analysis Pellet Pellet Coal Straight I Ann No Coal 5 Moisture Content (%~ 4.81 4.21 3.85 4.30 Sulfur Content (~)0.010.01 1.51 2.08 Ash Content (%) 0.57 0.61 7.02 9.07 Volatile Matter (%)82.7884.6248.73 38.66 Fixed Carbon 11.4810.56 40.40 47.97 1 Heating Value (Btu/lb)8,1788,148 11,193 12,239 Firing Rate ~10 Btu/hr)3.48 2.42 3.58 3.20 Excess Air (%) 85 93 95 62 glue Gas Moisture content .10.0 10.3 5.6 8.4 Average Flue Gas Temperature (OF) 1887 1743 1732 1892 Average Furnace Temperature OF 2105 1995 lB66 2041 Average Flame temperature (OF) 2450 2350 2350 2450 Particular e Emission (GR/SCF) 0.16 0.12 0.97 1.47 ~lbs/hr) 1.6 1.0 9~7 11.9 : (lbs/10 But) 0.47 0.44 2.7 3.7 Unburned Carton In Plus Gas by White 0.19 0.22 S2 Emissions (lb/106Btu)<0.03~0.03 1.77 3.46 (Pam) ~15 ~15 ~40 1160 H2SO4Emissions(Ib/106Btu) ~.001~0.0010.00270.0042 (Pam) 2 1 5 9 NO Emissions ~lb/10 But) ~.15-0.250.35-0.39 0.24 0.81 Average Total Hydrocarbon pi I I c5 c5 Flue Gas Oxygen (I my volume) 9.8 10.5 10.6 8.3 Flue Gas Carbon Dioxide (I by volume) 10.3 8.4 10.1 11.2 Flue Gas Carbon Monoxide (% by volume) 0.002 0.003 0.005 0.005 ~3505 owe_ The pulverized fuel pellets exhibited complete burnout and very low emissions with a smoke-free tack in coal-type suspension burner. All emissions met current standards. The fuel pellets ridded to be pulverized in Henry mill to only minus 32 mesh. where is no need Jo grind the pellets a fine AS coal (normally 70% through 200 mesh), s30 that on economical homeowner mill can be used instead of a Gore expensive end more power-intensive coal grinder. the complete burnout of both the cellulosic content, as well as the ~henmoplas~ic additive 10 ox the pellet, was demonstrated my the low values of unburned carbon on the flash, 'eke low values for carbon monoxide and total hydrocarbons on the stack gas, nod the total absence oil em visible Miss in the stack gas. The extremely low value of sulfur in the pulverized fuel (0,. 01% sulfur it reflected in 15 the low values of sulfur dioxide (S02) Noah sulfuric acid SUE) in thy tack gas emissions (less than 0. 030 lb/lp6 TAO and less than 0.001 lb/106 BTU, respectively. The low ash content (0.6~) of the pulverized pellet is reflected in the low particulate emission- of 0.12 to 0.16 Grains/SC~. Jo solids separator of 20 any kind was used in these tests. ~hexefore, further reduce lion of these notions us feasible. A baseline run with straight pulverized coal ooze sulfur dioxide emissioals that ore two orders of magnitude and particulate emissions that are An order of magnitude higher Han the corresponding pulverized 25 pellet fuel emissions. the coal test showed an unburned car-bun on the flash amount of 20 to 30 times the corresponding value for pulverized pellet. A distinct amount of visible smoke was present in the stack gas when burning coal versus nhsolutely no visible smoke when burning the pulverized pellet.
A mixture of I pulverized coal and 50% pulverized pellet was burned successfully without any handling, feeding, or come bastion problems. Essentially complete burnout was obtained, end there was a considerable reduction in the amount of visible smoke relative to the straight coal run. The NO , ash, and 35 S2 emissions were considerably reduced relative to coal and I
1 were on between Jose for pure pulverized pellet end straight coal. Ash fusion temperatures for the pulverized fuel Pellet were higher than for just goal. The pulverized fuel pellet is, therefore, less likely to slag.
I
Seven tests were conducted to establish the computable-fly of burning fuel oil and pulverized pellets ~mult~neously end to compare gee performance of Jo. 6 fuel oil versus put-5 versed pellets. A special burner was used that injects astray of fuel oil within nun annuls of injected pulverized pellets. The pellets were commented through 1/16 inch screen.
The test results are given in Table IT Test No 1 was 10 a baseline test on 100% fuel oil. The test boiler had a gape-city of 60,000 lb/hr of steam end was operated a 75~ of gape-city, or it approximately ~5,000 lbthr of Tom end at 150 prig The percentage of pellet was then increased grad-ally until 85% pilotless owe 6 fuel oil. tests 2 and I
The ireful ~onfrol was manually operated to yield a clear tack exhaust appearance indicating complete combustion.
Tests were made for atmospheric emissions evaluation.
The percentage solid fuel was when reduced to 60~ for tests 4 end 5.
the unit was then switched back to ~11 oil operation for tests 6 end 7 at the tame percentage free oxygen in the tack gas us with the solid fuel.. Some unexpected phenomena were observed under these conditions. The fuel viol flame inside the furnace became much longer; the tack gases shows Rome 25 opacity due Jo toot formation; end the exhaust gas temperature increased over a hundred degrees Fahrenheit.
The excess sir was then increased just sufficiently to eliminate the opacity of the stack gas, and two more fuel oil-only tests were conducted under these new conditions. The Jo flame length was till longer than normal, nod the stack gas temperature was till over a hundred degrees byway normal.
The particulate emission test results ore shown in Table Rio together with other test data. The excess nor requirement for pulverized solid fuel pellets was lower than for No. 6 35 fuel oil under the same conditions. (Compare tests 2 end 3 with jests 6 and 7.) This phenomena shows that the combustion ~2~3Z~
1 rate of pulverized fuel pellets it foster Han the combustion rate of No 6 fuel oil. thus, normal oiled fir~bcx is sufficiently large to burn the pellets without modification.
under low excess air conditions, the tack gas temperature for s pulverized fuel pellets was over hundred degrees lower Han for the No. 6 fuel oil. compare tests 2 end 3 with tests 6 and 7.) This phenomenon indicates the potential for light-lye higher boiler efficiency by using the solid fuel in place ox the No. 6 fuel oil.
I
ox TUB I I
Set _ I C2~ _ Stack I Particulate ask.. I
So __ .. _. -.. _ t 12~ C02 1 0 9.5 0.1 399,0.124 7.0 2 OX, 2. 3 13.1 3580. lB3 13 . 2 03 Ye 2.3 13.6 3~30.142 10.7 I 60 2.0 14.1 363~ 1 1.7 14.2 35~0.167 13.1 56 0 I 12.2 ~8~~.076 8.1 7 7.6 12.~1 464 0.109 . _. _ _ _ _ :50 The present invention has bell described with reference to a preferred embodiment.. The spirit and ape of the append-Ed claims should not, however necessarily be l~mi Ed to the foregoing description.
In another aspect, Abe present invention includes on the pellet an alkali petal silicate selected from sodium silicate and potassium silicate. One to two percent ox the silicate by weight is preferred, but up to about 10% could be acceptable.
iota is believed that the alkali petal acts as a catalyst in promoting gaseous combustion. it is also believed that the silica crystals are thermal radiators and promote ignition by thermal radiation. The ability to produce intense infrared radiation, when heated, it an inherent property of silica 25 crystals The alkali metal silicate also promotes bonding, and the mechanical strength of the pellet, more densified pellet, and an enhanced hydrophobic sheath on the pellet.
The fuel pellet can be made by preparing a feed of par-ticulate natural cellulosic material, any of the filler, non-30 cellulosic material, and particulate synthetic the~moplasticmaterial. Substantially f the thermoplastic material is -30 U. S. standard mesh and +80 U. S. standard mesh. The eel-lulosic material is ~uhstantially all -10 U. JO standard mesh and +40 Us S. standard mesh. The filler is substantially all 35 -10 U. S. standard mesh. The plastic and cellulosic Metro-awls are intimately combined by compressing the feed in an 13505 -pa-1 extrusion die. Extrusion takes place under temperature end rate conditions where the plastic in the interior of the pot-let does not melt, but only often The plastic thus no-twins its particulate nature. Extrusion flattens the part-S curate plastic into thin pieces and forces these pieces intone intimate mechanical bond with the fibers of the cellulosic material.
US
~2Z~
1 Brief Description of he drawing The jingle Figure is a flow schematic of suitable facility to fabricate pellets in accordance with the preferred embodiment of the present invention.
US
1 e AYE cation of the Preferred my dominate The present invention provides both fuel pellet and a process for its manufacture. The pellet it characterized in its use of a small mount of plastic birder end its except 5 tonal mechanical strength and combustion char~cteri6tics.The pellet burns completely in either grate burning or in air suspension burning, the latter after pellet comminution.
In preferred form, the pellet is from bout 97 to bout 99~ cellul~sic material and from bout 1 to about I thermos 10 plastic. Preferably, the pellet is from Bout 98 to 99% eel-lulosic material and from About 1 to I thermoplastic. The thermoplastic is present in particulate form and acts us a binder between cellulosic particles. Gore peaceful, the pellet it formed in on extrusion process that maintains that integrity of individual plastic particles. That is, they do not fuse together to form one cohesive end continuous piece of material. The extrusion process deforms the plastic into thin pancake-like pieces or platelets (nut necessarily planar) and forces these pieces into intimate mechanical locks it ZOthe fibers of cellulosic host material. The plastic can be viewed as tendons holding the cellulosic gibers together. It is important that the plastic maintain its particulate quality.
The particulate quality assures good burning of not only the plastic, but also the cellulosic material.
the pellet can include naturally occurring filler mate-fiats of say, coal, village other products of distillation processes, bark, end tar-like substances. Bark has a high heat of combustion and is a plentiful product of the forest industry. Depending on the bark, it is more or less fibrous.
30 New bark can be relatively fibrous. Old bark canoe esstenti-ally free of fibers. Because of mechanical strength require mints, up to 50~ of the pellet can be new bark. When old bark it used, up to 30% of the pellet may be bark. on either vase, the plastic content remains 1 to I end the balance of the 35 pellet is natural cellulosic. Coal is not cellulosic at all, I
end it must be boy d between cellulc:)sic particles. Spillage is deified substance including Rome cellulose., The it-brows quzllity of cellulose what gives eye good bending kirk-'ceristics, however, if; largely lost in processing, and, there-5 fore, the material it a filler. distillation byproducts other Han spillage, such as molasses and pitch, may also be used with efficacy us {I Miller. These byproducts have been a dip-faculty problem in disposal The particulate quality of the plastic insures large 10 surface area for the plastic which leads to high combustion rites of the plastic The hot combustion gases prom the burn-no plastic particle ignite any filler and eye cellulosic ma-twirl round the particle and promote the total combustion of these. Cellulosic material derived from wood contains a con-15 siderable immunity of Lignin. Lignin does not burn as riddles cellulose. Quite often top lignin burns in solid state with a smoldering flame, leaving a substantially unburned residue in the form of char. this char has considerable fuel value. It also would c~stitute source it least of part-go curate pollution The particulate plastic creates combustion domain that assures complete burning of any lignin in the host cellulosic material. This is Jo whether the fuel it burned s pellet or whether it is commented or pulverized : end burned in air suspension. In the case of the latter, the 25 plastic remains in intimate contact with ~ellulosic particles when the size limitations to be described on the plastic are observed.
minimum mount of plastic may be used when the plastic is sufficiently fine to pass a 30 U. S. standard mesh screen, 30 but coarse enough not to pass an 80 I. S. standard mesh screen.
This size of particulate plastic is large enough to span ye-tweet cellulosic particles for the bonding junction. The size is desirably small to tare advantage of a large ~urface-to-volume ratio that produces easy ignition and rapid combustion that enhances lignin and cellulose combustion. This small ~22~2~
particle size also Sirius ~omple'ce combustion of the plastic As is well Nemo, when plastic gets too passive, god the ~urface-to-~olume ratio gets too low, the plastic tends to burn incompletely, leaving char. the plastic protocol size 5 is also us ficier-tly small Jo that it will soften to font thin platelets or pancakes in the pellet during extrusion. It has been found that when the plastic particle size YE; two 1 rye, the particles will not soften end form the thin lilts that bind the cellulosic particles together.
The particle size of the ~ellulosi~ material and any filler, Jay bar, bears a finite relationship Jo that of the plastic. The particle size should be sufficient to pass a 10 U. S. standard mesh screen. The ~ellulosic material should be sufficiently coarse to stay on top of a I U. S. standard 15 mesh screen. it thy s range of size, the characteristic dip mention of the cellulosic materials is tout on order of mug-nutted greater than corresponding characteristic dimension of the plastic material. If the cellulose particle size gets too large with respect to the particle size of the plastic, 20 the plastic cannot span the distance between individual cell-logic particles because it gets lost in thy fibers of the eel-lulosic material. Furthermore, excessively large cellulosic particles do not bury as well as smaller ones. If the plastic gets large with respect to the soliloquy material 9 where is 25 a waste of plastic, end one can encounter the combustion and the softening problems previously described. (Assuming what the softening problem can be overcome, and ignoring the pies-tic combustion problems that might occur, plastic particles larger than the limits jet out here will effect good bridge 30 between cellulosic particles If the cellulosic material is too fine, it loses its fibrous character. The result is a loss in mechanical strength because of a 10ss of the bonding mechanism between the plastic and the cellulosic material that relies upon the fibrous nature of the cellulosic material in 35 the interlocking mechanical bond.
13505 . -13~
1 Any filler must be he'd largely by the bond between the plastic end the cellulosic material. Jo the Lowry particles are too large, they interfere with the bonding mechanism between the plastic end the cellulosic twirl. Excessive large filler particles do not burn as readily either. the lower limit of filler ire is dictated by economics. There us no reason to make the filler particles very small, but if they ore ~lxeady, their fineness will not harm the result.
Coal dust is an example of fine filler that exists without 10 need for further size reduction.
The mount of plastic should be between bout 1 to bout 3% of the total fuel pellet. This amount of plastic in conjunction with the size and particulate limitations of the plastic and the size limitations of the cellulosic material 15 produces the good combustion and bonding characteristics with a minimum mount of plastic The inclusion of the 1 to I thermoplastic of a pellet as a binder can ye viewed in different light Without the thermoplastic, to sails-factorial pullout only the cellulosic material would 20 require considerably higher temperatures. It also assures that the plastic acts as lubricant in the pellet dies or rollers. It can effect a sheath on the outer surface of the pellet, which is helpful to make the pellet hydrophobic.
The referred range of plastic is between bout 1 to 25 bout 24 of the total fuel pellet. Usually this range 6atisf its the requirements of pellet strength and enhanced ignition. however, particularly with hard woods, and large amounts of filler, more plastic may be required as a winder.
The moisture content of the cellulosic material should be between about 5 to about 15%~ If there is inadequate or too much moisture the pellet tends to lose strength and can disintegrate in the rough and tumble of handling and transport. Too much moisture adversely affects the combs-lion qualities by lowering the flame temperature. It is preferred that the moisture content be held within 10 to 13~.
~2~2~2~
1 A moisture content of the cellulose of from 10.5 Jo 11.5~ is ideal This range is the optimum range for pellet ~tsength.
Moisture content is measured in the cellulosic material prior to ~elletizing. The ~elletizi~g may reduce the S moisture Jo some extent, 4 to I% by evaporation into air.
When the pellet is to be used for sir suspension turning, it may be desirable to reduce the moisture content to lower than the prescribed range after the pellet has been commented in order to enhance combustion characteristics.
10 Obviously, after the pellet has been commented into the small particles suitable for air suspension the moisture previously required for structural integrity of the pellet is no longer necessary. the process of commenting itself reduces the moisture content.
The thermoplastic ma trials have on injection molding temperature of close to about 95C. or higher. It can ye little lower than this. this limitation is necessary to avoid excessive plastic melting during the extrusion process.
If the plastic melts excessively, its particulate nature 20 it lost and the qualities associated with that characteristic are also lost. Some melting is permissible so long as the plastic particles do not agglomerate.
The cellulosic material may ye derived from any number of Bahamas sources. The most Common sources will be wood 25 waste, such as sawdust, wood shavings, end buggies Certain agricultural wastes also classify a cellulosic, us well as paper end cardboard. Wood end buggies materials are referred because they have a high teat of combustion and lower moisture content than agricultural wastes. They 30 are also preferred because of their abundance.
~22~2~
1 The the plastic material can ye practically any available synthetic thermoplastic, such as polystyrene, polyethylene, polypropylene, acrylonitrile-butadiene-styrenes Seattle copolymers, acutely homopolymer6, acrylics, polybutylene, and combinations of these. Polyvinyl chloride, however, should not be used because it contains a halogen that presents corrosion end emission difficulties upon combustion. If there is a preference of thermoplastic materials it would be or polypropylene end polyethylene 10 because these materials burn rapidly and ignite readily.
he minimum injection molding temperatures of common thermoplastics ore reported in Modern Plastics Encyclopedia, Vol. 49, ~cGraw-~ill, 1972-3 Eden, end aye presented in table 1.
pi minimum Iniec~on Synthetic Thermoplastic Molding Temperature (~F.3 polystyrene 163~C. ~325F.~
Polyethylene 1~2C. (250F.) Polypropylene l91~C. ~375~.) AS 183C. ~360~F.) Cellulosics 168C. (335F.) Nylon 191C. (360F.) Polyesters 132C. (270F.) sigh impact polystyrene presents difficulties in pellet-lying because it is Jo hard, it is difficult to pullout a feed having Gore than 1.25% by weight of such material.
It has been found that during the poulticing process some of the thermoplastic material at the surface of the pellets will be sufficiently heaved by the friction between the pallet end the extrusion dies to melt end form a thin sheet or coating on the lateral outside unlaces Do the pellets. This moating is hydrophobic and serves to prevent the absorption of moisture by the pellets Turing storage.
Iota contemplated that materials other than the cellulosic and thermoplastic materials can be included in the pellet for a particular application or processing : conditions. or example, oxidizing agents such as sodium per chlorate end ammonium nitrate might be added to facile-late combustion. Binding agents such as paraffin, slack wax, carnuba wax; end certain lignosulfanates, such as minim lignosulfanate, sodium lignosulfanate, calcium lignosul~anate, and magnesium lignosulfanate can be added.
Oil seeds and their products have a fatty acid content that can reduce wear in the poulticing die. Examples of such materials include coconut husks, Joy beans, peanuts, sunflower seeds, corn cake, pressing residuals, end ethanol plant village 1 Jo aid in the drying of cell~losic weed twirl dry Blake lime, that is, calcium carbonate, can be mined with the feed. Other discounts can be used. The calcium carbonate combines with water and feed material and allows the rapid release of isture from the feed in a dehydrator.
The calcium carbonate can be added in mounts from about 2 to about 104 by weight of the dry feed, with about 5% by weight significantly tiding in the drying process. The calcium carbonate is preferably removed as by dry classic 10 cation before poulticing.
In applications where there is an excessive amount offer water in the cellulosic feed material it is most economical Jo remove the water by mechanical processes, such as powered presses and tapered screw presses.
While it is presently preferred to pullout the pellets with a extrude, rocketing can also be attractive.
The bond in the pellet of this invention is a very good one. It it needs to be enhanced, as could be required with a high percentage of non-cellulosic material present J say 20 old bark, sodium or potassium silicate can be used. When such silicate is used, it h~rolizes acidic lignatious end cellulosic materials This results in a more compressible cellulosic coLlponent end a denser pellet. On dehydration, the silicate jets end acts as a cement; augmenting the 25 thermoplastic and knitting tile fibers tocJether. The thyme-plastic sheath is com~ol~n~ed on a more hydrophobic base and the pellet has enhanced weathering resistance. The silicate increases the ash content; jut will not materially affect performance in either air-sus~ension or grate turning.
30 The alkali silicate can be introduced in a blender upstream from an extrude or briquette. When just weather resistance is desired, it is also possible to add it, while the thermos plastic sheath is still hot nod the alkali silicate adhesion will take place. The amount of silicate my be on the order 35 of I by weight. The silicate has a high viscosity, which can be lowered by heating.
~z~z~
13505 -lo--1 the alkali metal silicate, such us waxer gloss, also thought to be a combustion enhance or combustion catalyst.
it has been observed that pellets with about I% by weight sodium silicate burn with greater intensity (at 8 faster rate) S than otherwise identical pellets without the silicate It is thought that the alkali metal acts as a catalyst for combs lion.
Solutions of sodium silicate are strongly alkaline end ore readily decomposed by acids with separation of ~ilicic 10 acid. Upon heaving, the latter is converted to silica. It us thought that ho tame processes take place in the mixture of sodium silicate and wood wastes, as the latter contain acidic substances. The resulting crystals of silica ore be-lived to promote ignition by intense radiation of infrared eta. The ability to produce intense infrared radiation, when heated, is an inherent property of silica chrysalis The preferred amount of the silicate is from 1 to 2% by White The combustion enhancement would be present with this amount of the silicate without excessive ash. The den-ossification, weatherproofing, end bonding qualities would also be good at these concentrations.
A pellet with the alkali metal silicate will have the following composition: from about 1 to about 3% by weight particulate, synthetic polymeric thermoplastic material, from I about 1 to about 10~ by weight of the alkali silicate, end from bout 87 to bout 98% naturally combustible material.
The naturally combustible material includes at least 50% net-rural cellulosic material with the balance being filler.
With wood wastes that have a high lignin content, it is Jo possible to make a fuel pellet with enhanced combustion pro-parties consisting of 1 to about 10% by weight of the alkali silicate and from bout 90 to 99~ naturally combustible ma-tonal.
I
~L2;2~
1~505 I
1 the jingle Figure owe schematically suitable plant for fabrication of pellets of the present ~nvent~on. Before getting into the-description, it ghoul be appreciated that there ore several Approaches to the manufacture of pellets.
In addition, the flow sheet ox the Figure voids inclusion of ..
detail which would be obvious to the artisan, such us certain storage hoppers, conveyors, and the like. The plant can also take advantage of waste material in the form of cellulosic and thermoplastic fines derived from the process inherent in the 10 flea material and resulting from pellet fines, to fuel energy consuming heaters, such us used in a dryer to dehydrate wet cellulosic feed materials.
referring to the Figure ~ellulosic feed material from any desired source us fed us stream 10 into an initial alas-15 sifter 12. An output stream 14 of the classifier containscellulosic feed materiel of -1~2 inch or -3/B inch mesh. That stream goes onto a conveyor 16 and feeds into to dehydrator 18.
A second stream 20 from the classifier feeds a primary hog 22 with ~1/2 inch or ~3/8 inch feud that muons the material 20 and discharges i as a stream 24 auto conveyor 16. The prim many hog functions to reduce the weed of stream 20 to -1~2 inch to -3/8 inch mesh Stream 24 combines with stream I on conveyor 16 end feeds into dehydrator 18.
A heater 26 supplies the heat energy for the dehydrator 25 In the dehydrator, the cellulosic feed material has its 40 to 60~ moisture convent dropped to from about 5 to bout 15~, preferably from about 3 to about 11%. seater 26 is fueled from a fuel bin 27.
The discharge stream from dehydrator 18 is indicated at 30 2B. It feeds a cyclone 30 where gas and solids separate. The was exits cyclone 30 us stream 32, end the oldies exit as a stream 34. A fraction of the gas can be recycled to heaver 26.
Stream 34 enters primary classifier 36. Those materials that are miner than 40 mesh leave the primary classifier 35 as a fine Bream 38. This stream is used as a source of 13505 ' I
energy to fuel heater 260 Coarse ~llulosic materiel leaves primary classifier 36 us Ryan 40 and it coDminuted in a hammer mill 42 to -10 to ~40 US. ~ndard mesh. the exit stream from hammer mill 42 is indicated us stream 44.
the primary stream exiting the primary classifier 36 is a stream 46 constituted of cellulosic material of -10 to ~40 US. standard mesh. This stream combines with stream 44 to form a stream 48 which is transported by air blowing to a high elevation level where it feeds a secondary cyclone 50 10 where again gas end solids sure separated, with the gas leaving the top as a stream 52 and the solids leaving the bottom as stream 54. Stream 52 Jay be recycled into fuel bin 27.
The solids enter secondary classifier US. In 15 secondary classifier 56 excessively fine material is classified end discharged as a stream I these fines are used as fuel in the plant, say in a boiler that provides steam. Stream 58 also includes silicates and carbonates, whose removal Improves pelletizer die life. Properly sized 20 material of from 10 to +40 mesh leaves secondary classifier I as a stream 60 and enters a holding bin 62 preliminarily to blending with granulated thermoplastic.
Thermoplastic preparation is done ~eparte from the cellul~sic material. It can oboe lye effect removal of 25 unwanted materials such as metals, glass, and polyvinyl-chloride by any of number ox techniques, including magnets, weight sensitive separators, and flotation.
The then~o~lastic enters a granulator 72 as a plastic Weed street I where it is ground. The granulated plastic 30 sasses as a stream 74 into a classifier 76. Excessively fine plastic leaves the classifier as a stream 78. This stream contains a plastic that sasses through an 80 So standard mesh screen. Excessively coarse material leaves classifier 76 in a stream 80 and is recycled back to US granulator 72 on a conveyor 73. This coarse material is I
1 coarser than Us S. standard mesh. The properly sized plastic of prom -30 to BY mesh leaves the c~ssifier 76 a stream 82 end combines with any additives from stream 84 as a stream 86 that goes to a bin 88.
yin 88 feeds B blender 90 us does bin 62. petering is effected by any number of well known techniques to effect the required 1 to I weight percent plastic feed with a balance of cellulosic material. Any sodium or potassium silicate can also ye added on blender 90.
The discharge prom blender 90 is a stream I that flows into conditioning chamber 94. A steam jacket 95 heats the cellulosic-plastic feed. the steam comes from a boiler fueled by cellulosio fines. The conditioning chamber has an exit stream 96 that supplies a pellet mill 98. Again the feed can 15 be metered in any number of known techniques. A high-speed mixer-convey~r moves the material through the conditioning chamber to a pellet mill chute.
The pellet mill must be capable of producing a pressure on an extrusion die that causes temperatures of the feed mate-20 fiat to increase so what the pellets have a temperature suffix client to oxen the plastic particulate material within the pellets to form the thin pancake-like platelet The pressure exerted by the die should ye adequate to force the plastic into the intimate relationship with the fibers of the cellulosic 25 material that is the characteristic of the mechanical lock of the plastic on the cellulose. It has teen wound that when the temperature of the exiting pellets it from about 66C to about 122C, the plastic is adequately malleable to deform under pressure. any temperature above this risks the possibility of I excessively molting the plastic in the pellet and can result on unacceptable agglomeration of the particulate plastic into particles that are too large. The preferred lower temperature is bout 88C. The surface of the extradite may be sufficiently heated, and preferably so, to produce localized melting of then-35 moplastic material on the surface. This material, when it I
1 hardens, forms a thin, continues eighth on the resulting pellet. As Already commented upon, this sheath frauds a ho-drophobic quality to the pellet. In addition, it lubricates the dies to increase their life and increase production gape city. The thermoplastic within the pellet, with the exception of this sheath, us substantially homogeneously distributed.
Prom the pellet mill, the pellets enter cooler I as a stream 100 .
From pellet cooler 99~ the pellets enter a classifier 101 10 by a stream 102. Fines and reject pellets are discharged from the classifier AS stream 1060 The reject pellets are put-versed and combined with waste fines from the other Claus-liens to form a mixture that is used as fuel for the dryer burner and toiler. A product stream 108 leaves for storage.
~L~22~
1 Example I
tests were conducted on c~mminuted fuel-pellets having 2% by weight thermoplastic end 98~ by weigh cellulosic material. The thermoplastic included polyethylene, polyp styrenes and polypropylene. jests were Lowe run oncomminuted fuel pellets end coal end just coal, The thermoplastic was between Cubs anti ally minus 30 mesh and plus 80 mesh. the cellulosic material was between tub-staunchly minus 10 mesh end substantially plus 40 mush.
10 The pellets were jade by an extrusion process. Percolate thermoplastic material was homogeneously present throughout the pellets. There was a thermoplastic sheath on each pellet.
the pellets were ~omminuted in a hammer mill and screen gloved with a 1~16 inch screen for the OK" pellet and a 15 1~32 inch screen for the ON" pellet. The commented pellets were transferred pneumatically trough a cyclone separator and ultimately transferred to a silo next to a test furnace.
Coal end 50% Cole pellet mixture were also tested.
The test furnace was a Coon Company horizontal 20 cylindrical suspension air heater. It had air cooled, refracting lined wall, internal Jan end wind box, end a rated heat input capacity of 4 million Btu~hr. the furnace had ; a pneumatically fed, pulverized fuel, air suspension burner with a five port infuser Fuel was fed prom the silo with a vibrating screw feeder end on air blower that pneumatically conveyed the fuel prom the feeder Jo the burner.
Al} tests were conducted with the furnace sully preheated to steady state temperatuxeO The best air and fuel feed I rates were determined by visual observation of the lame pa item .
~V~2~
13505 24~
Proximate Analysis Pellet Pellet Coal Straight I Ann No Coal 5 Moisture Content (%~ 4.81 4.21 3.85 4.30 Sulfur Content (~)0.010.01 1.51 2.08 Ash Content (%) 0.57 0.61 7.02 9.07 Volatile Matter (%)82.7884.6248.73 38.66 Fixed Carbon 11.4810.56 40.40 47.97 1 Heating Value (Btu/lb)8,1788,148 11,193 12,239 Firing Rate ~10 Btu/hr)3.48 2.42 3.58 3.20 Excess Air (%) 85 93 95 62 glue Gas Moisture content .10.0 10.3 5.6 8.4 Average Flue Gas Temperature (OF) 1887 1743 1732 1892 Average Furnace Temperature OF 2105 1995 lB66 2041 Average Flame temperature (OF) 2450 2350 2350 2450 Particular e Emission (GR/SCF) 0.16 0.12 0.97 1.47 ~lbs/hr) 1.6 1.0 9~7 11.9 : (lbs/10 But) 0.47 0.44 2.7 3.7 Unburned Carton In Plus Gas by White 0.19 0.22 S2 Emissions (lb/106Btu)<0.03~0.03 1.77 3.46 (Pam) ~15 ~15 ~40 1160 H2SO4Emissions(Ib/106Btu) ~.001~0.0010.00270.0042 (Pam) 2 1 5 9 NO Emissions ~lb/10 But) ~.15-0.250.35-0.39 0.24 0.81 Average Total Hydrocarbon pi I I c5 c5 Flue Gas Oxygen (I my volume) 9.8 10.5 10.6 8.3 Flue Gas Carbon Dioxide (I by volume) 10.3 8.4 10.1 11.2 Flue Gas Carbon Monoxide (% by volume) 0.002 0.003 0.005 0.005 ~3505 owe_ The pulverized fuel pellets exhibited complete burnout and very low emissions with a smoke-free tack in coal-type suspension burner. All emissions met current standards. The fuel pellets ridded to be pulverized in Henry mill to only minus 32 mesh. where is no need Jo grind the pellets a fine AS coal (normally 70% through 200 mesh), s30 that on economical homeowner mill can be used instead of a Gore expensive end more power-intensive coal grinder. the complete burnout of both the cellulosic content, as well as the ~henmoplas~ic additive 10 ox the pellet, was demonstrated my the low values of unburned carbon on the flash, 'eke low values for carbon monoxide and total hydrocarbons on the stack gas, nod the total absence oil em visible Miss in the stack gas. The extremely low value of sulfur in the pulverized fuel (0,. 01% sulfur it reflected in 15 the low values of sulfur dioxide (S02) Noah sulfuric acid SUE) in thy tack gas emissions (less than 0. 030 lb/lp6 TAO and less than 0.001 lb/106 BTU, respectively. The low ash content (0.6~) of the pulverized pellet is reflected in the low particulate emission- of 0.12 to 0.16 Grains/SC~. Jo solids separator of 20 any kind was used in these tests. ~hexefore, further reduce lion of these notions us feasible. A baseline run with straight pulverized coal ooze sulfur dioxide emissioals that ore two orders of magnitude and particulate emissions that are An order of magnitude higher Han the corresponding pulverized 25 pellet fuel emissions. the coal test showed an unburned car-bun on the flash amount of 20 to 30 times the corresponding value for pulverized pellet. A distinct amount of visible smoke was present in the stack gas when burning coal versus nhsolutely no visible smoke when burning the pulverized pellet.
A mixture of I pulverized coal and 50% pulverized pellet was burned successfully without any handling, feeding, or come bastion problems. Essentially complete burnout was obtained, end there was a considerable reduction in the amount of visible smoke relative to the straight coal run. The NO , ash, and 35 S2 emissions were considerably reduced relative to coal and I
1 were on between Jose for pure pulverized pellet end straight coal. Ash fusion temperatures for the pulverized fuel Pellet were higher than for just goal. The pulverized fuel pellet is, therefore, less likely to slag.
I
Seven tests were conducted to establish the computable-fly of burning fuel oil and pulverized pellets ~mult~neously end to compare gee performance of Jo. 6 fuel oil versus put-5 versed pellets. A special burner was used that injects astray of fuel oil within nun annuls of injected pulverized pellets. The pellets were commented through 1/16 inch screen.
The test results are given in Table IT Test No 1 was 10 a baseline test on 100% fuel oil. The test boiler had a gape-city of 60,000 lb/hr of steam end was operated a 75~ of gape-city, or it approximately ~5,000 lbthr of Tom end at 150 prig The percentage of pellet was then increased grad-ally until 85% pilotless owe 6 fuel oil. tests 2 and I
The ireful ~onfrol was manually operated to yield a clear tack exhaust appearance indicating complete combustion.
Tests were made for atmospheric emissions evaluation.
The percentage solid fuel was when reduced to 60~ for tests 4 end 5.
the unit was then switched back to ~11 oil operation for tests 6 end 7 at the tame percentage free oxygen in the tack gas us with the solid fuel.. Some unexpected phenomena were observed under these conditions. The fuel viol flame inside the furnace became much longer; the tack gases shows Rome 25 opacity due Jo toot formation; end the exhaust gas temperature increased over a hundred degrees Fahrenheit.
The excess sir was then increased just sufficiently to eliminate the opacity of the stack gas, and two more fuel oil-only tests were conducted under these new conditions. The Jo flame length was till longer than normal, nod the stack gas temperature was till over a hundred degrees byway normal.
The particulate emission test results ore shown in Table Rio together with other test data. The excess nor requirement for pulverized solid fuel pellets was lower than for No. 6 35 fuel oil under the same conditions. (Compare tests 2 end 3 with jests 6 and 7.) This phenomena shows that the combustion ~2~3Z~
1 rate of pulverized fuel pellets it foster Han the combustion rate of No 6 fuel oil. thus, normal oiled fir~bcx is sufficiently large to burn the pellets without modification.
under low excess air conditions, the tack gas temperature for s pulverized fuel pellets was over hundred degrees lower Han for the No. 6 fuel oil. compare tests 2 end 3 with tests 6 and 7.) This phenomenon indicates the potential for light-lye higher boiler efficiency by using the solid fuel in place ox the No. 6 fuel oil.
I
ox TUB I I
Set _ I C2~ _ Stack I Particulate ask.. I
So __ .. _. -.. _ t 12~ C02 1 0 9.5 0.1 399,0.124 7.0 2 OX, 2. 3 13.1 3580. lB3 13 . 2 03 Ye 2.3 13.6 3~30.142 10.7 I 60 2.0 14.1 363~ 1 1.7 14.2 35~0.167 13.1 56 0 I 12.2 ~8~~.076 8.1 7 7.6 12.~1 464 0.109 . _. _ _ _ _ :50 The present invention has bell described with reference to a preferred embodiment.. The spirit and ape of the append-Ed claims should not, however necessarily be l~mi Ed to the foregoing description.
Claims (31)
1. A fuel pellet comprising from about 97 to about 99 percent by weight particulate naturally combustible material, and from about 1 to about 3 percent by weight particulate, synthetic polymeric thermoplastic material, the naturally combustible material comprising at least 50 percent natural cellulosic material with any balance being a filler, the synthetic thermoplastic material being distributed as discrete particles throughout the interior of the fuel pellet, solid at room temperature, between substantially minus 20 U.S. standard mesh and substantially plus 80 U.S. standard mesh, and having an injection molding termperature of at least about 95°C., the cellulosic material having a free moisture content of from about 5 to 15 percent by weight, and being between substantially minus 10 U.S. standard mesh and substantially 40 U.S. standard mesh, the plastic binding the cellulosic material together with a mechanical bond by bridging between cellulosic particles and anchoring to the particles, any filler being at least minus 10 U.S. standard mesh.
2. The fuel pellet claimed in claim 1, wherein the filler comprises up to about 30 percent of one or more members of the class consisting of stillage (byproducts of ethanol distillation processes), coal, and old bark, or 50 percent new bark.
3. The fuel pellet claimed in claim 1, wherein the free moisture content of the cellulosic material is from about 10 to about 13 percent by weight.
4. A fuel pellet comprising from about 97 to about 99 percent by weight particulate natural cellulosic material, and from about 1 to about 3 percent by weight particulate, synthetic polymeric thermoplastic material, the synthetic thermoplastic material being distributed as discrete particles throughout the interior of the fuel pellet, solid at room temperature, between substantially minus 30 U.S. standard mesh and plus 80 U.S.
standard mesh, and having an injection molding temperature of at least about 95 degrees C., the cellulosic material having a free moisture content of from about 5 to about 15% by weight, and being between substantially minus 10 U.S. standard mesh and substantially 40 U.S. standard mesh, the plastic binding the cellulosic material together with a mechanical bond by bridging between cellulosic particles and anchoring to the particles.
standard mesh, and having an injection molding temperature of at least about 95 degrees C., the cellulosic material having a free moisture content of from about 5 to about 15% by weight, and being between substantially minus 10 U.S. standard mesh and substantially 40 U.S. standard mesh, the plastic binding the cellulosic material together with a mechanical bond by bridging between cellulosic particles and anchoring to the particles.
5. The fuel pellet claimed in claim 4, wherein the free moisture content of the cellulosic material is from about 10 to about 13 percent by weight.
6. The fuel pellet claimed in claim 4, wherein the free moisture content of the cellulosic material is from about 10.5 to about 11.5 percent by weight.
7. 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.
8. The fuel pellet claimed in claim 1 including a sheath of the thermoplastic material on the lateral surface of the pellet.
9. The fuel pellet claimed in claim 1 including up to about one percent by weight of an alkali silicate selected from the class consisting of sodium silicate and potassium silicate.
10. The fuel pellet claimed in claim 1 wherein the filler comprises bark.
11. The fuel pellet claimed in claim 1 wherein the filler comprises up to about 50 percent new bark.
12. The fuel pellet claimed in claim 1 wherein the filler comprises up to about 30 percent old bark.
13. The fuel pellet claimed in claim 1 wherein the filler comprises up to about 30 percent of one or more members of the class consisting of stillage, and byproducts of ethanol distillation processes, coal and bark.
14. The fuel pellet claimed in claim 1 wherein the free moisture content of the cellulosic material is from about 10.5 to about 11.5 percent.
15. The fuel pellet claimed in claim 1 wherein the pellet is an extrudate.
16. The fuel pellet claimed in claim 1 wherein the pellet is a briquette.
17. The fuel pellet claimed in claim 5 wherein the thermoplastic material is selected from the group consisting of polystyrene, polyethylene, polypropylene, acrylonitrile-butadiene-sytrene, acetal copolymer acetal homopolymer, acrylic, polybutylene, and combinations thereof.
18. A fuel pellet comprising from about 87 to about 98 percent by weight particulate naturally combustible material from about 1 to about 3 percent by weight particulate, synthetic polymeric thermoplastic material, and from about 1 to about 10% by weight of an alkali silicate selected from the class consisting of sodium silicate and potassium silicate, the naturally combustible material comprising at least 50 percent natural cellulosic material with any balance being a filler, the synthetic thermoplastic material being distributed as discrete particles throughout the interior of the fuel pellet, solid at room temperature, and having an injection molding temeprature of at least about 95 degrees C., the cellulosic material having a free moisture content of from about 5 to 15 percent by weight, the plastic binding the cellulosic material together with a mechanical bond by bridging between cellulosic particles and anchoring to the particles.
19. The fuel pellet claimed in claim 18 wherein the alkali silicate is present in from about 1 to about 2% by weight.
20. The fuel pellet claimed in claim 19 wherein the synthetic thermoplastic material is between substantially 30 U.S. standard mesh and substantially plus 80 U.S. standard mesh, the cellulosic material being between substantially minus 10 U.S. standard mesh and 40 U.S. standard mesh, and any filler being at least minus 10 U.S. standard mesh.
21. A method for preparing a fuel pellet from particulate naturally occurring combustible material and particulate systhetic polymeric thermoplastic material comprising the steps of:
(a) providing particulate naturally occurring combustible material including as a constituent at least natural cellulosic material having a free moisture content of from about 5 to about 15 percent by weight, and being between minus 10 U.S.
standard mesh and plus 40 U.S. standard mesh and a filler of up to 50% by weight of a particulate material that is at least minus 10 U.S. standard mesh;
(b) providing particulate synthetic polymeric thermoplastic material that is solid at room temperature, has an injection molding temperature of at least about 95 degrees C, and being between substantially minus 30 U.S. standard mesh and plus 80 U.S. standard mesh;
(c) preparing a homogeneous feed comprising from about 97 to about 99 percent by weight of the particulate naturally occurring combustible material and from about 1 to about 3 percent by weight of the particulate thermoplastic material; and (d) compressing the feed at a pressure and a temperature whereby substantially all the thermoplastic material within the pellet remains particulate and unmelted but softens and bridges between cellulosic particles and anchors within the fibers of the cellulosic particles.
(a) providing particulate naturally occurring combustible material including as a constituent at least natural cellulosic material having a free moisture content of from about 5 to about 15 percent by weight, and being between minus 10 U.S.
standard mesh and plus 40 U.S. standard mesh and a filler of up to 50% by weight of a particulate material that is at least minus 10 U.S. standard mesh;
(b) providing particulate synthetic polymeric thermoplastic material that is solid at room temperature, has an injection molding temperature of at least about 95 degrees C, and being between substantially minus 30 U.S. standard mesh and plus 80 U.S. standard mesh;
(c) preparing a homogeneous feed comprising from about 97 to about 99 percent by weight of the particulate naturally occurring combustible material and from about 1 to about 3 percent by weight of the particulate thermoplastic material; and (d) compressing the feed at a pressure and a temperature whereby substantially all the thermoplastic material within the pellet remains particulate and unmelted but softens and bridges between cellulosic particles and anchors within the fibers of the cellulosic particles.
22. The method claimed in claim 21, wherein the compression step is by extrusion.
23. The method of claim 22 including the step of forming a substantially hydrophobic sheath of the thermoplastic on the pellet during the extrusion.
24. The method of claim 22 wherein the free moisture content of the cellulosic material before extrusion is from about 10 to about 13 percent.
25. The method of claim 21 wherein the naturally occurring combustible material comprises essentially the natural cellulosic material.
26. The method of claim 25 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.
27. The method of claim 21 including the steps of drying naturally occurring material by combining it with an amount of calcium carbonate equal to about 2 to about 10 percent by weight of the naturally occurring material and then removing the calcium carbonate before the compression step.
28. The method claimed in claim 21 including the steps of softening the cellulosic material by adding between about 1 to about 10 percent by weight of an alkali silicate selected from one or more members of the class consisting of sodium silicate and potassium silicate before the compression step, and strenthening the pellet with such silicate by drying.
29 The method of claim 23 in which the particulate cellulosic material includes oil seeds, products of oil seeds, or both, for librication of the die.
30. The method claimed in claim 21 wherein the filler is selected from one or more members of the class consisting of coal, bark, stillage, and byproducts of ethanol distillation processes, and is present in no more than about 30 percent by weight.
31. The method claimed in claim 21 wherein the filler is new bark.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000447073A CA1229229A (en) | 1984-02-09 | 1984-02-09 | Fuel pellets |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000447073A CA1229229A (en) | 1984-02-09 | 1984-02-09 | Fuel pellets |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1229229A true CA1229229A (en) | 1987-11-17 |
Family
ID=4127147
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000447073A Expired CA1229229A (en) | 1984-02-09 | 1984-02-09 | Fuel pellets |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1229229A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10662387B2 (en) | 2017-06-13 | 2020-05-26 | Arr-Maz Products, L.P. | Additive used in the production of wood pellets |
| CN111475931A (en) * | 2020-03-20 | 2020-07-31 | 岭东核电有限公司 | PCI rapid analysis method and device based on neural network, electronic equipment and storage medium |
| US10858606B2 (en) | 2017-06-13 | 2020-12-08 | Arr-Maz Products, L.P. | Structured composite wood pellets for dust/fines mitigation and method of producing them |
-
1984
- 1984-02-09 CA CA000447073A patent/CA1229229A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10662387B2 (en) | 2017-06-13 | 2020-05-26 | Arr-Maz Products, L.P. | Additive used in the production of wood pellets |
| US10858606B2 (en) | 2017-06-13 | 2020-12-08 | Arr-Maz Products, L.P. | Structured composite wood pellets for dust/fines mitigation and method of producing them |
| CN111475931A (en) * | 2020-03-20 | 2020-07-31 | 岭东核电有限公司 | PCI rapid analysis method and device based on neural network, electronic equipment and storage medium |
| CN111475931B (en) * | 2020-03-20 | 2023-06-13 | 岭东核电有限公司 | PCI rapid analysis method and device based on neural network, electronic equipment and storage medium |
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