Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
A PROCESS FOR M~KING FUEL PELLETS F~OM
ORGP~IIC FIBROUS ~ATFIRLAL
This invention relates to a process for making fuel pellets
frcm organic fibrous material and to fuel pellets thus obtained~
Such processes are already kncwn. Philippines patent 11922
for instance describes a process wherein the moisture content of
ccmminuted fibrous material, such as sawdust, is adjusted to
16-28%w and the material is pelletized at a temperature of
163-177C.
According to the process of the present invention a much
lower pelleti2ing te~erature can be applied.
Moreover it has been found that by bruising the fibrous
material in a crusher, preferably a roll crusher, the cuticles
of the material, if this is of the very wet type such as leaves,
are damaged which results in a reduction of the dryiny time of
80-85% compared with only cutting the material, such as leaves
into pieces.
Furthermore, this bruisiny results in considerable fibril-
lation, which has a favourable influence on the coherence forces
of the p~llets due to entanglement of the fibres.
Thus the present invention relates to a process for pro-
ducing fuel pellets from organic fibrous material, which ccm-
prises bruising the material to a maximum particle size of 5 x
the diameter of the holes of the die in ~he below-mentioned pel-
letizer, whereafter the material is dried to 20-10%w of water on
total material, optionally at least a pc~rt of the material is
chopped, and then pelletized in a die-pelletizer at a pellet
temperature of 70-135C, preferably 70-120C, more preferably
70-100C. ~le pellets may be Eurther dried in the field .
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If the organic fibrous material is of the very wet type,
such as pine-apple plant waste containing more than 70 %w of
water, the material is mechanically dewatered to 70 40 %w, pre-
ferably 60-40 %W, of water on total material at the same ti~
bruising the ~aterial -to said maximum particle size. This
mechanical dewatering is not necessary if the material has a
moisture content up to 70 -OW, e.g. 30-60 %w, such as certain
types of wood waste, e.g. mixtures of sawdust, bark fibres and
bark chips.
Preferably the bruising is carried out in such a way that
the particle size of the material shows some variation. The
s~aller particles then fill the voids between the larger par-
ticles, resulting in a lower pelletizing energy and a still
better entanglement of the fibres.
If desirable, water or steam may be used during the
pelletizing to facilitate the pellet-formation, e.g. 3-5 %w of
water or steam.
Suitable diameters of the holes of the die pelletizer are
in the range of from 5-30 mm.
The pellets preferably have a diameter of 10-20 mm, and
more preferably 13-18 mm, and an average length of e.g.
20-60 mm. Preferably the pelletizing is carried out in such a
way that some variation in the length is obtained, resulting in
a higher bulk density and therefor lcwer transport costs.
According to the invention the material may be mlxed with
other fine materials! e.g. coal or charcoal p~wder before
pelletizing and then pelletized. Also the material may be mlxed
with certain chemicals to prevent soot formation when burning
the pellets, or with hydrophobic ccmpounds to decrease n~isture
absorption of the pellets.
Furthermore the pellets may be treated with hot oil to
carbonize the outer skin thus decreasing the moisture sensivity,
making storage in wet surroudings possible.
m e present pellets may be used directly as industrial
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fuel, especially in boilers for electric power generation, as
well as for domestic purposes. They can also be used for thermal
gasification or the manuracture of liquid and solid fuels, e.g.
charcoal by carbonizing e.g. by heating in a closed burning
chamber.
The invention will in present Example 1 be elucidated ~or
pineapple plant waste and in Example 2 for maize waste~ The
present process is however also suitable for other cellulosic
wastes, such as described in Philippines patent 13155, in
partlcular those of a similar type.
EX~MPLE 1
Pineapple plant waste, e.g. from plantations, had a bulk
density of 200-300 kg/m3 and a water content of about 78 %w on
total material. The heating value was about 2-3 ~J/kg and the
size below about 500 mmO This material, viz. leaves, ste~ and
stumps, but predominantly leaves (65 %w~ was mechanically de-
watered by squeezing on one or more three-roll-crushers to about
56 ~w of water on total material, while by the bruising action of
the rolls the cuticles of the material, in particular of the
leaves, were damaged to facilitate the release of water. This
bruised material had an average length of about 35 mm, the
majority being shorter than 60 mm.
The resulting cake was loosened in a rotary chopper to
allcw for-effective drying.
The material was thermally dried to about 18 %w water on
total material, with hot air in a rotary cascading drier in
cocurrent flow with the combustion gases. ~ther driers, such as
a grate stoker, could also be used.
The dried material was classified and the fragments larger
3 than 65 mm were adequately chopped in a xotary chopper to a size
below 65 mm. me classified and the chopped material was pel-
letized in a three-roll die extrusion pelletizer at a pressure
of 7 kN/cm~, the holes of the die having a diameter of 13 mm and
a length of 65 mm. During this pelletizing, which WAS carried
out continuously, the friction and campaction in the die caused
, ,, ~'r
the temperature of the die and pellets to rise until a station-
ary condition settled after about 15 minutes at about 80C for
the dle and about 75C for the pellets.
The pellets had a diameter of 13 rnm an a length of 20-
60 mm.
The pellets were then cooled with a forced air flow to room
temperature, while being classified by a vibrating screen, and
transferred to a warehouse for despatch.
The pellets had sufficient strength to be handled by
mechanical conveyors. Their heating value was about 18 MJ/kg,
their water content about 14%w on total rnaterial, their density
1.1 g/cm3 and the bulk density was 675 kg/m3.
The output of the pellet mill was almost 50 kg pellets per
kilowatt hour electrical energy consumed by the pellet mill.
m e fines ex-screening may be recycled. The air ex-pellet
cooler may be used as secondary air in the furnace of the drier.
As fuel for firing this furnace mechanically dewatered
rnaterial, thermally dried material, or the pellets may e.g. be
used. The amount required will amount to about 20%w, of the
pineapple waste inta}ce.
EXAMPLE 2
Maize waste (stalls and leaves) with a water content of
62 %w on total material was squeezed and crushed to a water
content of 48 %w on total material. This product was dried in a
stove to 17 %w water on total material.
The length of the thus obtained straw feed stock before
densificatio~ ~as about 30-50 mm and the bu~c density 135 kg/m3.
Pellets were produced with various diameters, i.e. 8, 10 and 15
I~n. m e length over width ratio of the holes of the pelletizer
3 was chosen between seven and eight in those cases. This resulted
in an average pressure oE 11 kN/cm2 c~nd a material density of
about 1.2 g/cm3. The temperature of the die became in stationary
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operation 85C and that of the pellets 75C. The water content
of the cooled product was 13~w. The output of the pellet mill
was about 30 kg/kWh. The calorific value of the pellets was
19.8 ~/kg.
