Note: Descriptions are shown in the official language in which they were submitted.
CA 02771647 2012-02-21
DP 1384
Dieffenbacher GmbH + Co. KG
Heilbronnerstrasse 20
D-75031 EPPINGEN
Method and facility for producing pellets from biomass in a pelletizing press
for use as a fuel in
fireplaces
The invention relates to a method for producing pellets in a pelletizing press
for use as a fuel in
fireplaces according to the preamble of Claim 1.
Furthermore, the invention relates to a facility for producing pellets from
biomass in a pelletizing
press for use as a fuel in fireplaces according to the preamble of Claim 17.
The production of pellets, also referred to as granules, from fine material or
compacted and/or
molten material has already been known for some time. Briquette presses have
compacted
material between two rollers, either one or both having been constructed as
matrices, and molded
it into briquettes for combustion. In the plastic industry or the industry
which processes animal
food, pelletizing by means of extruders and perforated discs, optionally using
downstream
cutting devices, is also sufficiently known. The production of pellets for use
as a fuel in
fireplaces from preferably chopped biomass, such as wood, its wood chips,
sawdust, or the like,
is also already sufficiently known and is propagated in the field of renewable
energy sources as a
pioneering technology for climate protection, in particular in Europe. The
production process is
subject to certain norms, thus, the produced pellets must have a certain
abrasion resistance (for
pneumatic transport) and cannot release toxic or environmentally harmful
active ingredients in
the course of combustion. Low-quality pellets often contain foreign materials
(lubricants,
colorants,...).
During the facility planning for the production of pellets for use in
fireplaces, in particular in
large-scale industrial facilities, the cost factor due to the energy to be
applied is a problem in
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particular. The production of the pellets is advantageously to consume very
little energy, since it
typically does not originate from renewable energy sources (oil/gas
combustion, power plants). It
is also problematic to construct a large-scale facility from multiple
purchased individual plant
parts, in particular from niche producers, since each individual plant part
(heavy material
separator, drying device, grinding device, cyclone, or pelletizing press) can
rarely be integrated
cost-effectively and optimally in an overall facility. In previous facilities,
the chips were dried
very intensively, so that the chips could be heated using steam before the
pelletizing. The reason
for this is that the chips lose much of the temperature obtained through the
drying process during
the transport from the dryer up to the pelletizing, or in further devices for
the treatment of the
chips, but also in particular during the storage in a silo. For a rapid
production process, steam is
therefore used for preheating the chips before the pelletizing press, since
the condensing steam
not only causes dampening of the chips, but rather also a rapid temperature
increase of the chips.
However, known levels of moisture of the chips before the pelletizing are not
to be exceeded, 12
wt.-% moisture is typical, so that the chips must be dried to 8 to 10 wt.-% in
the case of a 2 to
4% increase of the chip moisture by the steam treatment. The excessive drying
of the chips and
the production of the steam requires a very large amount of energy. `
The object of the invention comprises providing a method and a facility, in
which biomass,
preferably wood mass in the form of chips, can be compressed into pellets in a
way which saves
energy in relation to the prior art and which is energetically cost-effective.
The achievement of the object for a method comprises the method heating and
drying biomass in
the course of the production in a dryer, the dried and heated biomass being
separated from the
dryer air, and the biomass being supplied to a pelletizing press,
the temperature of the biomass in a treatment area between the dryer and the
pelletizing press
being heated or substantially maintained using hot air and the treatment area
comprising at least
parts of the transport path and/or at least one further device for performing
at least one additional
method step, and the temperature of the hot air exceeding at least 65 C.
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The achievement of the object for a facility is that in the facility for
drying and heating the
biomass, a dryer having an airlock for separating the dryer air is arranged
before the pelletizing
press in the production direction,
at least one treatment area being arranged in the facility between the airlock
and the pelletizing
press and at least one transport means for transporting the biomass between
the dryer and the
pelletizing press and/or at least one device for performing at least one
further method step is
arranged in this treatment area, and at least one heating device for heating
and/or providing hot
air of essentially greater than 65 C is arranged associated with the treatment
area, the heating
device being operationally linked at least once with the transport means
and/or with a device for
performing further method steps for the supply of the hot air.
The method sequence according to the invention advantageously achieves high
savings
potentials in the power consumption in large-scale industrial facilities,
because the overall
production method is performed in an energetically optimized way and
energetically costly
temperature increases of the biomass to be treated are avoided or unnecessary
high-energy
method-measures are avoided, such as dampening the biomass using steam for the
temperature
increase, simultaneously increasing the biomass moisture by several percent,
and subsequently
drying the biomass to produce the required degree of dryness of the biomass
for the pelletizing.
For this purpose, the biomass is advantageously heated by means of hot air
after the dryer along
its transport path and/or in further devices for performing further method
steps. The further
devices are referred to hereafter as the treatment area (between dryer and
pelletizing press). The
corresponding transport paths and/or the devices are advantageously to be
sufficiently insulated
in relation to the surroundings or the lower temperature.
A hot steam dryer or a flash dryer is preferably used for the basic drying
method. However, a
drum dryer is particularly preferred because of the high exit temperature
and/or the high
throughput quantity. A drum dryer or flash dryer or a hot steam dryer can
typically have a
temperature of the biomass which is 10 higher than the typical belt dryers.
A treatment area, in which the dried biomass is prepared for the pelletizing
press, is preferably
established in an advantageous manner between the dryer and the pelletizing
press. Required or
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advisable preparations can be, for example, conduction through a heavy
material separator, a
grinding device, a classification device, a water spraying device, a dosing
device for the
pelletizing press, transport devices, or the like. In all of these devices,
the temperature of the
biomass is typically significantly reduced, but particularly in start-up
operation of the facility, of
course. Typical facilities have a steaming device before the pelletizing press
for this purpose,
which elevates the biomass to a temperature at which it can be pelletized
again in an
energetically costly manner. However, the steaming normally also increases the
moisture content
of the biomass, so that in anticipation a dryer must dry the biomass more
intensively below this
increased moisture content. The present invention particularly advantageously
has the property
that this special energy expenditure no longer must be completed twice, in
particular through a
special design of the treatment area between dryer and pelletizing press. It
is sufficient, in order
to make the pelletizing in the pelletizing press easier, to apply water to the
biomass before the
pelletizing press, preferably to spray it with water. The water is to be
preheated in this context, of
course, and is preferably to have a temperature greater than 60 C. The biomass
is preferably
transported using hot air and/or introduced into or guided through the
treatment devices as
needed. In addition to the optimum temperature control of the machine elements
which come
into contact with the biomass, maintaining the temperature or increasing the
temperature of the
biomass is possible. A plurality of measuring and regulating devices is
preferably located in the
facility, in order to set the temperature control and the control or
regulation of the hot air supply
or the temperature of the hot air in an energetically optimal manner. The goal
is to transport the
biomass at a temperature of substantially greater than 65 C into the
pelletizing press, without
changing the essential temperature level of the biomass after the dryer, whose
exit temperature is
preferably greater than 60 C, downward in the direction of a typical ambient
temperature. This
measure is to be supported in particular by insulation of the corresponding
devices in the
treatment area and/or heating devices of the devices themselves.
In a particularly preferred embodiment, a hot air circulation is provided as
the treatment area,
which comprises at least one device for achieving a method step (for example,
grinding, sorting,
classification, heating), a heating device for the hot air, and a cyclone for
separating the hot air
from the biomass. Known facility requirements, such as control and regulating
devices, fresh air
supply, hot air purification, or the like will be added by a person skilled in
the art in accordance
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with the facility requirements or specifications, where necessary or
advisable, in particular in the
course of overall energetic economy.
In the course of energetic optimization, it can be advisable or even necessary
to use a hot air-
water steam mixture instead of hot air, which allows a better heat transfer,
in particular during
heating of the biomass. In this case, of course, application or spraying of
water before the
pelletizing press can be omitted or it is throttled accordingly.
Moreover, the water is heated to a temperature of greater than 65 C,
preferably greater than
80 C, particularly preferably 90 C before or during the supply to the biomass.
In a preferred
embodiment, the applied water can alternatively or additionally be heated on
the biomass by
means of radiant energy. Microwave emitters are preferably arranged for this
purpose, which
heat the water or the biomass during the transport between the water spraying
and the pelletizing
press. The temperature of the hot air is particularly preferably set using a
heating device, the
heating device using fresh air as the supply air and/or preheated air from at
least one hot air
return line and/or preheated air from a heat exchanger or directly from the
waste heat of a pellet
cooler after the pelletizing press. In the treatment area between the dryer,
preferably a drum
dryer having an airlock device for separating the dryer air from the biomass,
and the pelletizing
press, multiple method steps may be necessary in order to prepare or condition
the biomass for
the pelletizing. Safety aspects for the pelletizing press itself from metal,
rocks, or the like are
also to be considered. For this purpose, for example, a heavy material
separator for separating
heavy material and/or a grinding device for chopping the biomass and/or a
cyclone for separating
the hot air from the biomass would be necessary before the pelletizing press.
The separation of
the hot air from the biomass can be necessary in order to increase the overall
energetic economy
of the facility. This is particularly advantageous if, in the treatment area,
the hot air is guided via
the heating device in an essentially closed circuit. This circuit offers
substantial advantages in a
control and regulating aspect. Of course, the circuit can also be expanded via
an optional silo
and/or the pelletizing press itself, so that after the pelletizing press,
preferably in the pellet dryer,
the still warm hot air is preferably guided via a heat exchanger via a hot air
return line or a heat
reclamation unit back to the heating device. The hot air in the circuit of the
treatment area is to
be regularly exchanged and/or filtered at least in parts, the corresponding
exhaust air being
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guided in accordance with the environmental regulations, if needed via an
exhaust air
purification device, for example, a wet electrostatic precipitator (WESP)
and/or a regenerative
thermal oxidizer (RTO).
The teaching of the invention fundamentally states that the cooling of the
biomass between the
drying in the dryer and the pelletizing is to be reduced as much as possible
or even prevented.
Depending on the facility type or method type, heating of the biomass can even
be provided, in
particular if the biomass must still be stored in a silo before the
pelletizing press, in order to
ensure proper distribution or shaking of the biomass into one or more
pelletizing presses.
Depending on the definition, the storage and the discharge from the silo can
also be considered
as a method step associated with the treatment area. The biomass is preferably
to reach the
pelletizing press at a temperature of greater than 65 C, and the hot air in
the treatment area is to
be set accordingly. Further suggestions on the design or regulation of the
temperature of the
biomass are dependent on the devices used for performing the method steps in
the treatment area
and the employed biomass itself, of course. The possibility for insulating the
respective devices
or the transport paths is also partially a matter of design by the designer of
the facility and
therefore cannot be described in the specific case for a person skilled in the
art. However, the
biomass is also preferably at least surrounded with hot air or correspondingly
pneumatically
transported during the transport.
To support the specification that the biomass reaches the pelletizing press at
65 C, it can be
necessary for the biomass to leave the drum dryer at least at a temperature T1
of substantially
greater than 65 C. Subsequently, the biomass is to be transported in a further
method step by
means of hot air through at least one heavy material separator and/or guided
through a grinding
device and chopped. For possibly necessary heating of the biomass, it can be
necessary to
increase the temperature of the hot air, in particular using hot air of a
temperature of 70 to 80 C,
and to transport the biomass through at least one heavy material separator and
simultaneously
heat it and/or guide it through a grinding device, chop it, and heat it
therein. Alternatively or in
combination with the previous method steps, it would further be advantageous
to apply hot air to
the biomass, in particular hot air at a temperature greater than 65 C, in at
least one silo and/or in
a discharge device associated with the silo. To save energy, it can also be
necessary for the
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biomass to be separated from the hot air in a cyclone in a further method step
after the grinding
device and/or a heavy material separator, insufficiently chopped parts of the
biomass being
returned to the grinding device and/or the separated hot air being supplied
via a hot air return line
to the heating device. It is energetically advisable, depending on the
starting temperature of the
dryer, to heat the hot air for the transport means, the heavy material
separator, the grinding
device, the silo, and/or the cyclone to at least the temperature of the
biomass.
Further advantageous measures and designs of the subject matter of the
invention are disclosed
in the subclaims and the following description of the drawing.
The biomass 1 which is used and produced partially consists of chips or
shreds, which arise in
sawmills and other fabrication locations as a waste product, and which are
delivered on trucks. In
the case of large-scale industrial pellet production, it is necessary to make
use of a felled stock of
trees, which is chopped by means of so-called chopping facilities into chips
or shreds. After a
first preparation, optionally even mechanical dewatering, these are introduced
into a dryer 2. In
the case of large-scale industrial pellet production, drum dryers are
preferably provided, which
are distinguished by large throughput quantities and uniform exit temperature
T1 of the biomass
1. A dryer 2 in the drum embodiment preferably has dryer supply air 11 applied
thereto, which is
preferably guided in a circuit and is separated from the biomass 1 by a dryer
cyclone 10 for this
purpose after the dryer 2. The dryer air is typically strongly loaded with
dust and even loaded
with pollutants because of the drying and is regularly replaced either
completely or in parts, in
the case of a circuit application of the dryer supply air 11 (dashed line).
The moist dryer air,
which is enriched with dust, is typically first pre-purified in an exhaust air
purification facility
12, before it can be discharged as exhaust air 25 to the environment.
The biomass 1 exits from the dryer cyclone 10 via an airlock 13, typically a
rotary airlock, at a
temperature T1 in the treatment area 23, and has a temperature T4/T4' after
the treatment area 23.
At least one device for performing a method step, which can comprise sorting,
classification,
grinding, separation of heavy materials, and much more, is located in the
treatment area 23. The
transport of the biomass I between the dryer 2 and the pelletizing press 8 is
also considered to be
a method step in this context, as is the storage in a silo 6, although the
latter is not thus shown in
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the overview drawing. The overview drawing primarily shows a simplified
facility having a
method step between the dryer 2 and the pelletizing press 8. The method
sequence is read as
follows on the basis of the continuous method arrows. After the airlock 13,
the biomass I is
transported at a temperature Ti into a grinding device 4, hot air of a
temperature T2 from the
heating device 15 is applied thereto in the grinding device 4, the biomass I
subsequently has a
temperature T3, which preferably at least corresponds to the temperature T, or
is even higher,
and is transferred with the hot air into the cyclone 5. The cyclone 5
separates the hot air at a
temperature T6 from the biomass I and transfers the hot air back into the
heating device 15 for
reheating to the temperature T2, if necessary. After the cyclone 5, the
biomass 1 is discharged via
an airlock 13, preferably a rotary airlock, from the treatment area 23 and
supplied at a
temperature T4, which is greater than 60 C, preferably greater than 65 C, to a
pelletizing press 8.
After pelletizing of the biomass I to form pellets 9, these pellets are stored
in a pellet cooler 17
or guided through and cooled. The waste heat 18 at a temperature T7can be
supplied back to the
heating device 15 via an optional heat exchanger 19 at a temperature T8, in
order to maintain or
even heat the temperature T1 of the biomass 1 after the dryer 2. The latter
possibility is an
expansion of the circuit of the hot air of the treatment area 23, which can be
used alternatively or
in combination. The circuit has a corresponding required fresh air supply and
the hot air in the
circuit is regularly purified in parts or completely, preferably before or in
the area of the heating
device 15, in an exhaust air purification device (not shown), and exhausted as
exhaust air 25 to
the environment.
In an alternative exemplary embodiment, if a silo 6 is used to store the
biomass 1 having an
associated discharge device 7, the temperature T4 can or even should be
increased, so that heat
losses of the biomass I during the storage and the discharge from the silo 6
can be compensated
for, and the temperature T5 of the biomass before the pelletizing press 8, in
conjunction with an
optional water introduction by a spraying device 22, corresponds to the
specifications and is
preferably greater than 60 C, more preferably greater than 65 C.
In a further alternative exemplary embodiment, the biomass can pass through a
screen 24,
preferably designed as a flat screen, in the treatment area 23 or as shown in
the drawing. It is also
advantageous here if the entrained air is heated as the hot air and has at
least the temperature of
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the biomass 1 or even greater. The screen 24 is preferably used for the
purpose of screening out
sand or fine dust. Similarly as during the use of a silo 6, the biomass can
also have a temperature
T4" beforehand and a temperature T5' thereafter, the temperature T5'
preferably being greater than
60 C, particularly preferably greater than 65 C.
In an optional embodiment of the treatment area 23, which is shown by double-
dot-dash lines,
the hot air can already be supplied, immediately after the biomass 1 is
transferred out of the
airlock 13 of the dryer cyclone 10, to the biomass as transport air or as
ambient air having a
temperature T2 of the biomass 1 on the path to the grinding device 4. The
alternatives shown by
dashed lines comprise further possible additional possible applications of the
hot air, also in
combination with multiple method steps. One of these steps is the additional
arrangement of a
heavy material separator 3 between the dryer 2 and the billing device 4. The
biomass is
correspondingly first supplied to a heavy material separator in order to
separate out rocks or
large clumps of the biomass 1, preferably those having harmful properties for
the following
devices. However, a heavy material separator in particular requires a large
quantity of air for
swirling the biomass and correspondingly cools down the biomass if the hot air
is not preheated.
The teaching of the invention has a particularly advantageous effect here and
supplies the
biomass 1 to the heavy material separator already having ambient air to which
hot air is applied
and/or causes the air swirling in the heavy material separator 3 by means of
supplied hot air from
the heating device 15. Fresh air as the supply air 14 and/or regenerated
heat/air having a
temperature T8 from the pellet cooler 17 and/or, via a hot-air return line 21,
hot air from the
cyclone 5 for heating and setting the hot air to the temperature T2 is
supplied to the heating
device 15. The hot air used in the treatment area should and can be regularly
replaced with fresh
air or can be partially or regularly filtered by means of a round filter 16.
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List of reference numerals: DP 1384
1 biomass
2 dryer
3 heavy material separator
4 grinding device
cyclone
6 silo
7 discharge device
8 pelletizing press
9 pellets
dryer cyclone
11 dryer supply air
12 exhaust air purification device
13 airlock
14 supply air
heating device
16 round filter
17 pellet cooler
18 waste heat
19 heat exchanger
fresh air
21 hot air return line
22 water spraying device
23 treatment area
24 screen
exhaust air
T, temperature of biomass after dryer (before preparation area)
T2 temperature of hot air for biomass
T3 temperature of hot air/biomass
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T4 temperature of biomass after preparation area
T5 temperature of biomass after storage in silo
T6 temperature of hot air after cyclone 16
T7 temperature of air waste heat (air) from pellet cooler
T8 temperature of air after heat exchanger 19
11
