Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR PRODUCING FUEL PELLETS AND OTHER
LIGNOCELLULOSIC PRODUCTS WITH REDUCED
HEMICELLULOSE, ALKALI METAL AND CHLORINE CONTENTS
BACKGROUND
[0001]
Various embodiments disclosed herein are generally directed
to a method of producing lignocellulosic fiber masses suitable, among
other things for the manufacture of fuel pellets, in particular, from
feedstocks that, because of high contents of substances, are regarded as
deleterious to good combustion performance such as alkali metals and
chlorides.
[0002] The
high price of fossil fuels and the worldwide interest in
replacing fossil fuels by others based upon renewable resources, has led
to a dramatic increase in the demand for pelletized bionnasses that can be
burned in domestic stoves, and for products that can replace coal at
power stations.
[0003] The most widely-used procedures involve compressing
biomass in a pelletizing mill to make fuel pellets, which can be regarded
as being a more compact energy source than the raw material itself.
White pellets are made simply by compressing ground, dried biomass,
meaning that coarser materials need to be subjected to an energy
intensive size reduction step before pelletizing. The
pellets typically
contain about 10 /0 moisture and need to be stored under cover, as they
absorb water quickly and easily and lose their cohesiveness. They are
also liable to create dust during transport and storage and thus risk
causing a dust explosion.
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[0004] So-called black pellets are made by subjecting dried biomass
to medium pressure steam (steam explosion) or partial destructive
distillation (torrefaction) before pelletizing.
[0005] Each of these methods produce a fuel pellet having the bulk of
compounds of alkali metals, chlorine and sulfur present in the feed.
Furthermore, their resistance to water is variable; white pellets must be
stored under cover, while black pellets need to be stored under conditions
that minimize leaching. Therefore, a need exists to produce a fuel pellet
and other lignocellulosic products having reduced hemicellulose, alkali
metal and chlorine contents. The present disclosure is directed toward a
method of producing such a fuel pellet and/or other lignocellulosic
product.
DETAILED DESCRIPTION
[0006] The methods described herein can be used to manufacture
fuel pellets and other materials by steam treatment of biomass such as
wood chips, bagasse, straw and energy crops that may be difficult to
process without steam treatment and that may contain unacceptably high
levels of compounds of alkali metals, chlorine and sulfur, for use as fuel
pellets, with the additional possibility of avoiding an energy-demanding
and often difficult drying step before steam treatment. These pellets can
be stored under wet conditions for long periods of time with minimal loss
of energy content and durability. They have higher energy contents and
somewhat higher bulk densities than pellets made from the same feed by
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state-of-the-art methods and can be produced at lower temperatures,
thus reducing the cost of plant needed to make them.
[0007] The use of steam treatment is necessary in order to convert
the raw materials to a form that is more easily defibrillated and that can
be efficiently dewatered mechanically, e.g., in a filter press before drying.
[0008] The steam treated materials made in accordance with the
methods consist of two fractions: a water phase and a solid phase. The
water phase will contain water soluble materials, primarily carbohydrates
and minerals, primarily alkali metals and chlorides, plus some alkaline
earth metals and sulfates. This product is eminently suitable, as a
component in animal feed as a feedstock for fermentation or chemical
processing.
[0009] The solid fraction can, as described above, be used to
manufacture fuel pellets, but it can also be converted to fibrous materials
for cartons and coarse paper or, with the addition of vegetable oil and,
optionally, an acidic catalyst, as a component in wooden boards and
mouldings.
[0010] One particularly advantageous application for the methods of
this invention is the addition of an oil before or after steam treatment (or
both) enabling the dried residue to be used as a thermoplastic compound.
This is possible because the residue contains fewer substances such as
reducing sugars that can react with and crosslink the lignin.
[0011] Lignocellulose-based products with low contents of
hemicellulose, chlorine, sulfur, and alkali and alkaline earth metals are, in
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at least one embodiment, made by steam-treating an undried biomass,
and washing the steam treated material to remove water soluble
materials and, optionally, drying the residue.
[0012] In another embodiment, the lignocellulose-based products are
made by steam treating a biomass, which may contain up to 60% by
weight of moisture prior to steam treatment, defibrillating and washing
the steam treated material to remove water soluble materials and,
optionally, drying the residue.
[0013] In at least one embodiment, a vessel containing the biomass
is evacuated before the introduction of steam, such that the total free
oxygen content of the gas in the vessel into which the steam is injected is
less than 10 volume % and preferably not more than 3 volume %.
[0014] In at least one embodiment, the lignocellulose-based products
from biomass treated by injecting dry saturated or unsaturated steam at
a temperature of at least 300 F at a pressure of at least 52 psig and
preferably between 120 and 280 psig into a reactor containing the
biomass and maintaining the chosen pressure for between 1 and 30
minutes, the lower the steam pressure, the longer the residence time.
[0015] In at least one embodiment, the lignocellulose-based products
from biomass treated by injecting dry saturated or unsaturated steam
have a temperature of at least 150 C at a pressure of at least 60 psig and
between 120 and 240psig into a reactor containing the biomass and
maintaining the chosen pressure for between 3 and 30 minutes, the lower
the steam pressure, the longer the residence time.
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[0016] In another embodiment, up to 8% on biomass dry weight of
an organic substance capable of functioning as a swelling agent or solvent
for lignin during steam treatment and having a boiling point greater than
100 C such as a fatty acid, a triglyceride, glycerol or a glycol is included
in
the biomass prior to the introduction of steam.
[0017] In another embodiment, up to 5% on biomass dry weight of
an acidic catalyst such as nitric acid or acetic acid having a boiling point
of
less than 200 C may be added after evacuation of the vessel and prior to
the introduction of steam.
[0018] In another embodiment, hydrophobic lignocellulose-based
products, including fuel pellets with low chlorine and alkali metal contents,
made from steam processed materials as described herein are then
water-washed, in at least one embodiment, in a counter-current process
and the residue dried to less than 10% moisture by weight and in other
embodiments, less than 5% moisture by weight, adding to it between 3%
and 20% and between 5% and 8% by weight of an oil and then
subjecting the whole to compression, for example, in a conventional
molding or extrusion process.
[0019] In another embodiment, hydrophobic lignocellulose-based
products, including fuel pellets with low chlorine, hennicellulose and alkali
metal contents, made from steam processed materials as described
herein are then subjected to dewatering and optionally water-washed, in
at least one embodiment, in a counter-current process and the residue
dried to less than 10% moisture by weight and in other embodiments,
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less than 5% moisture by weight, then adding sufficient of one of the
above-mentioned lignin swelling agents or solvents to bring the total
content of the said agent to at least 2% and preferably between 2 and
8% by weight and then subjecting the whole to compression, for
example, in a conventional molding, pelletizing or extrusion process.
[0020] In
another embodiment, the oil can be added to the
dewatered filter cake prior to the final drying step, or immediately prior to
the subsequent conversion process or to the biomass itself before steam
treatment. In
one embodiment, hydrophobic molded or extruded
products, including fuel pellets, made as described herein, where the
lignin swelling agent is an oil of vegetable origin that contains at least
20% by weight unsaturated fatty acid compounds, e.g., canola oil, palm
oil, Jatropha oil, spent cooking oil, cottonseed oil, etc.
[0021] In
another embodiment, the raw material is in the form of
pellets, with or without the incorporation of at least 1% by weight of oil.
This is particularly beneficial when processing materials of low bulk
density, for example straw and bagasse.
[0022] In
one embodiment, fuel pellets are made with the inclusion
of up to 60 weight % of a brittle carbon source prior to pelletizing. The
brittle carbon source being, for example, ground coal, petroleum coke,
charcoal, or other thermally degraded biomass.
[0023]
Thermoplastic molding and extrusion compounds made as
described herein may contain at least 3% and not more than 25% by
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weight of an oil containing at least 20% unsaturates and having a boiling
point of at least 150 C at atmospheric pressure.
[0024] In order to further illustrate various embodiments of the
present invention, the following examples are given. However, it is to be
understood that the examples are for illustrative purposes only and are
not to be construed as limiting the scope of the subject invention.
Examples
Example 1 - Fuel pellets made without brittle additives in a pellet mill
Raw material:
100 parts by weight of chopped wheat straw or wheat straw pellets
0-5% by weight of an oil, preferably of vegetable origin, which can
be contained in the pellets
Processing in the reactor
The wheat straw or wheat straw pellets are transferred to the
reactor without drying. The whole is evacuated to -0.85 bar and allowed
to stand for 2 minutes. Dry saturated steam having a temperature of
200 C is introduced and the whole allowed to stand for 7 minutes once a
pressure of 14.5 bar is reached and maintained.
Water washing procedure
1. 0-stage washing
The moisture content of the steam treated material is adjusted to at
least 50% by weight and preferably between 60% and 70% by weight
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and compressed to remove as much moisture as possible, e.g. in a filter
or screw press. The resulting solid material can be dried to the desired
moisture content at once or the above process repeated as necessary
before the final material is dried as required.
2. Multistage washing
The steam treated biomass is removed from the reactor vessel and
transferred to a slurrying tank where the continuous phase can be the
final filtrate from the washing process. The whole is transferred to a
counter-current washing system, e.g., a series of filter presses. The
excess liquor from the first wash stage is removed for further treatment
and the washing process continued counter-currently such that the
residue in the final filtration step is washed with clean water. The final
filter cake is removed and dried as required.
Pellet manufacture in a pellet mill
The filter cake, is dried to a moisture content of more than 2% and
less than 1 5 % by weight and, in one embodiment between 4% and 8%
by weight either before or after the addition of oil, such that the total
amount of oil contained in the filter cake immediately prior to it being
converted to pellets is not less than 2% on dry matter and the whole
pelletized in a mill such that the surface temperature of the pellets is
..95 C and preferably between 105 C and 125 C.
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These pellets have the following properties:
Bulk density: 800-820kg/m3
Moisture content: <5%
Chlorine content (as chloride): <0.03%
K+Na content (as oxides): <0.2%
Water absorption after 24-hour immersion at 23 C: Less than 3%
Leaching loss after 24-hour immersion in water at 23 C: Less than
5%
Durability after 24-hour immersion in water: >90%
Energy content: .20g.J/kg
HGI: 25-35
Example 2- Fuel pellets made in an extruder
Raw materials:
100 parts by weight of chopped wheat straw or wheat straw pellets
0-5% by weight of an oil, preferably of vegetable origin, which can
be contained in the pellets
Processing in the reactor
The wheat straw or wheat straw pellets are transferred to the
reactor without drying. The whole is evacuated to -0.85 bar and allowed
to stand for 2 minutes. Dry saturated steam having a temperature of
200 C is introduced and the whole allowed to stand for 7 minutes once a
pressure of 14.5 bar is reached and maintained.
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Water washing procedure
1. 0-stage washing
The moisture content of the steam treated material is adjusted to at
least 50% by weight and preferably between 60% and 70% by weight
and compressed to remove as much moisture as possible, e.g., in a filter
or screw press. The resulting solid material can be dried to the desired
moisture content at once or the above process repeated as necessary
before the final material is dried as required.
2. Multistage washing
The steam treated biomass is removed from the reactor vessel and
transferred to a slurrying tank where the continuous phase can be the
final filtrate from the washing process. The whole is transferred to a
counter-current washing system, e.g., a series of filter presses. The
excess liquor from the first wash stage is removed for further treatment
and the washing process continued counter-currently such that the
residue in the final filtration step is washed with clean water. The final
filter cake is removed and dried as required.
Pellet manufacture
A sufficient quantity of oil is added to the filter cake, dried as per
1.1., to bring its total oil content to at least 4 weight % on dry matter and
preferably between 5% and 8% by weight on dry matter. The mixture of
oil and filter cake is processed in a pelletizing extruder such that the
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surface temperature of the pellets as they exit the die is not less than
90 C and preferably between 105 C and 125 C.
These pellets have the following properties:
Bulk density: 810-830kg/m3
Moisture content: <3%
Chlorine content (as chloride): <0.03%
K+Na content (as oxides): <0.2%
Water absorption after 24-hour immersion at 23 C: Less than 5%
Leaching loss after 24-hour immersion in water at 23 C: Less than
30/0
Durability after 24-hour immersion in water at 23 C: >93%
Energy content: 22g3/kg
HGI: 25-35
Example 3 - Fuel pellets made with a brittle additive
Raw materials
100 parts by weight of chopped wheat straw or wheat straw pellets
0-5% by weight of an oil, preferably of vegetable origin, which can
be contained in the pellets
Processing in the reactor
The wheat straw or wheat straw pellets are transferred to the
reactor without drying. The whole is evacuated to -0.85 bar and allowed
to stand for 2 minutes. Dry saturated steam having a temperature of
200 C is introduced and the whole allowed to stand for 7 minutes once a
pressure of 14.5 bar is reached and maintained.
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Water washing procedure
1. 0-stage washing
The moisture content of the steam treated material is adjusted to at
least 50% by weight and preferably between 60% and 70% by weight
and compressed to remove as much moisture as possible, e.g., in a filter
or screw press. The resulting solid material can be dried to the desired
moisture content at once or the above process repeated as necessary
before the final material is dried as required.
2. Multistage washing
The steam treated biomass is removed from the reactor vessel and
transferred to a slurrying tank where the continuous phase can be the
final filtrate from the washing process. The whole is transferred to a
counter-current washing system, e.g., a series of filter presses. The
excess liquor from the first wash stage is removed for further treatment
and the washing process continued counter-currently such that the
residue in the final filtration step is washed with clean water. The final
filter cake is removed and dried as required.
Pellet manufacture
At least 3 weight % on dry matter of an oil and at least 10 /0 finely
ground bituminous coal are added to the filter cake and the whole
thoroughly mixed.
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The whole is then transferred to a pellet mill and pelletized through
a pellet die such that the surface temperature of the pellets as they exit
the die is not less than 90 C and preferably between 105 C and 120 C.
These pellets have the following properties:
Bulk density: 810-820kg/m3
Moisture content: <2%
Chlorine content (as chloride): <0.03%
K--Na content (as oxides): <0.2%
Water absorption after 24-hour immersion at 23 C: Less than 8%
Leaching loss after 24-hour immersion in water at 23 C: Less than
6%
Durability after 24-hour immersion in water at 23 C: >90%
Energy content: 30gJ/kg
HGI: 30-45
Example 4 - The use of granulated materials made in accordance with the
methods as disclosed herein as thermoplastic moulding and extrusion
compounds
State-of-the-art steam-treated biomass used in the manufacture of
so-called black pellets has the property of beginning to crosslink or
thermosetting once subjected to the temperatures and pressures that
typify pelletizing, whether in an extruder or a pellet mill. This is also the
case when pellets containing vegetable oils are made from this type of
biomass.
Most unexpectedly, this is not the case when materials made in
accordance with this invention are processed and these materials have
the exceptional property of being fully remeltable in the sense that they
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behave as thermoplastics rather than thermosets. This makes it possible
to envisage their use as alternatives to conventional, fossil fuel based
thermoplastics with all that this implies in terms of reducing petroleum
consumption and the emission of greenhouse gases.
Unlike conventional thermoplastics, these products are also fully
biologically degradable.
Raw material:
100 parts by weight of fresh, birch-wood "microchips" (in at least
one embodiment, the chips having at least 30% moisture content by
weight).
Processing in the reactor
The wood-chips are transferred to the reactor without drying. The
whole is evacuated to -0.85 bar and allowed to stand for 2 minutes. Dry
saturated steam having a temperature of 210 C is introduced and the
whole allowed to stand for 5 minutes once a pressure of 18 bar is reached
and maintained.
Water washing procedure
1. 0-stage washing
The moisture content of the steam treated material is adjusted to at
least 50% by weight and preferably between 60 and 70% by weight and
compressed to remove as much moisture as possible, e.g., in a filter or
screw press. The resulting solid material can be dried to the desired
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moisture content at once or the above process repeated as necessary
before the final material is dried as required.
2. Multistage washing
The steam treated biomass is removed from the reactor vessel and
transferred to a slurrying tank where the continuous phase can be the
final filtrate from the washing process. The whole is transferred to a
counter-current washing system, e.g., a series of filter presses. The
excess liquor from the first wash stage is removed for further treatment
and the washing process continued counter-currently such that the
residue in the final filtration step is washed with clean water. The final
filter cake is removed and dried as required.
Granulate manufacture
Up to 15 weight % on dry matter of Jatropha oil is added to the
filter cake and the whole thoroughly mixed. This is conveyed to
granulating extruder equipped with cooling, volatile venting and die and a
cutting device and to produce a plastic granulate whose size is suitable for
subsequent use in a(n injection) moulding machine or extruder. The
material is processed such that its temperature in the extruder's mixing
zone is maintained at least 120 C and preferably between 140 C and
160 C and granulate made.
At least one embodiment of the method as disclosed can also be
adapted to make a finished product such as a board, extruded profile or
moulded part directly from the raw material itself, by processing it in an
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extruder having a die with the required profile or a suitably equipped
injection moulding machine.
Example 5 - Fuel pellets made without brittle additives in a pellet mill
Raw material:
100 parts by weight of chopped miscanthus
Processing in the reactor
The miscanthus is transferred to the reactor without drying. The
whole is evacuated to -0.85 bar and allowed to stand for 2 minutes. Dry
saturated steam having a temperature of 200 C is introduced and the
whole allowed to stand for 7 minutes once a pressure of 14.5 bar is
reached and maintained.
Water washing procedure
The steam-treated biomass is removed from the reactor vessel and
transferred to a slurrying tank where the continuous phase is the final
filtrate from the washing process. The whole is transferred to a counter-
current washing system, e.g., a series of filter presses. The excess liquor
from the first wash stage is removed for further treatment and the
washing process continued counter-currently such that the residue in the
final filtration step is washed with clean water. The final filter cake is
removed and dried to 5% moisture content by weight.
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Pellet manufacture
6 weight % on dry matter of Jatropha oil added to the filter cake
and the whole thoroughly mixed. The mixture of oil and filter cake is
pelletized in a mill through a die with a compression ratio of 6, so that the
surface temperature of the pellets is .95 C and preferably between 105 C
and 125 C.
These pellets have the following properties:
Bulk density: 800-820kg/m3
Moisture content: <2%
Chlorine content (as chloride): <0.03 /o
K+Na content (as oxides): <0.2%
Water absorption after 24-hour immersion at 23 C: Less than 3%
Leaching loss after 24-hour immersion in water at 23 C: Less than
2%
Durability after 24-hour immersion in water: >98%
Energy content: 23gJ/kg
HGI: 25-30
Example 6- Fuel pellets made in an extruder
Raw materials:
100 parts by weight of chopped miscanthus.
Processing in the reactor
The nniscanthus is transferred to the reactor without drying. The
whole is evacuated to -0.85 bar and allowed to stand for 2 minutes. Dry
saturated steam having a temperature of 200 C is introduced and the
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whole allowed to stand for 7 minutes once a pressure of 14.5 bar is
reached and maintained.
Water washing procedure
The steam treated biomass is removed from the reactor vessel and
transferred to a slurrying tank where the continuous phase is the final
filtrate from the washing process. The whole is transferred to a counter-
current washing system, e.g., a series of filter presses. The excess liquor
from the first wash stage is removed for further treatment and the
washing process continued counter-currently such that the residue in the
final filtration step is washed with clean water. The final filter cake is
removed and dried to 5% moisture content.
Pellet manufacture
9 weight % on dry matter of Jatropha oil added to the filter cake
and the whole thoroughly mixed. The mixture of oil and filter cake is
processed in a pelletizing extruder such that the surface temperature of
the pellets is 95 C and preferably between 105 C and 125 C.
These pellets have the following properties:
Bulk density: 810-830kg/m3
Moisture content: <1%
Chlorine content (as chloride): <0.03%
K+Na content (as oxides): <0.2%
Water absorption after 24-hour immersion at 23 C: Less than 2%
Leaching loss after 24-hour immersion in water at 23 C: Less than
30/0
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Durability after 24-hour immersion in water at 23 C: >98%
Energy content: 24gJ/kg
HGI: 25-30
Example 7 - Fuel pellets made with a brittle additive
Raw materials
100 parts by weight of chopped miscanthus.
Processing in the reactor
The miscanthus is transferred to the reactor without drying. The
whole is evacuated to -0.85 bar and allowed to stand for 2 minutes. Dry
saturated steam having a temperature of 200 C is introduced and the
whole allowed to stand for 7 minutes once a pressure of 14.5 bar is
reached and maintained.
Water washing procedure
The steam treated biomass is removed from the reactor vessel and
transferred to a slurrying tank where the continuous phase is the final
filtrate from the washing process. The whole is transferred to a counter-
current washing system, e.g., a series of filter presses. The excess liquor
from the first wash stage is removed for further treatment and the
washing process continued counter-currently such that the residue in the
final filtration step is washed with clean water. The final filter cake is
removed and dried to 5% moisture content by weight.
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Pellet manufacture
9 weight % on dry matter of Jatropha oil and 30% by weight finely
ground petroleum coke are added to the filter cake and the whole
thoroughly mixed.
The whole is then transferred to a pellet mill and pelletized through
a pellet die having a compression ratio of 5, making sure that the surface
temperature of the pellets thus made is not less than 95 C and preferably
between 105 C and 120 C.
These pellets have the following properties:
Bulk density: 830-850kg/m3
Moisture content: <2%
Chlorine content (as chloride): <0.03%
K+Na content (as oxides): <0.2%
Water absorption after 24-hour immersion at 23 C: Less than 4%
Leaching loss after 24-hour immersion in water at 23 C: Less than
4%
Durability after 24-hour immersion in water at 23 C: >96%
Energy content: 30gJ/kg
HGI: 38-45
From the above description, it is clear that the present invention is
well adapted to carry out the objects and to attain the advantages
mentioned herein as well as those inherent in the invention. While
presently preferred embodiments of the invention have been described for
purposes of this disclosure, it will be understood that numerous changes
may be made which will readily suggest themselves to those skilled in the
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art and which are accomplished within the spirit of the invention
disclosed.
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