Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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
13505 -2-
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
13505 -3-
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
13505 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~
13505 -7-
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~
13505 -8-
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~
13505 -9-
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
13505 -10-
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
13505
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~
13505 -12
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~
13505 -14-
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~
13505 -15-
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
13505 -16-
1 ALLAH 1
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
13505 -17-
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
13505 -21-
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
13505 -22-
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~
13505 -23-
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~
1 FUEL TYPE TABLE I
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
135 0 5 - 6-
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
13505 -27-
1 EXAMPLE II
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~
13505 I
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.
15
I
ox
13505
--29
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
13505 --30-
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.
