Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
Method and system for the conditioning of raw biomass
FIELD OF THE INVENTION
[0001] The present invention relates to biomass. More specifically, the
present
invention is concerned with a method and a system for conditioning of raw
biomass.
BACKGROUND OF THE INVENTION
[0002] Biomass material is increasingly used as a source of
thermal energy and to
produce bio-plastics and other renewable bio-products. For instance, some
residential, institutional
1 0 and industrial buildings have already been designed or converted to use
biomass pellets, instead of
fossil fuels, for heating and/or process use. Overall, a number of equipment,
including dryers, boilers,
and furnaces, continue to be converted to biomass use, instead of fossil
fuels. Moreover, recent
developments in the forestry field show that wood derivatives, such as
nanocrystalline cellulose, may
substitute fossil originating chemicals in the production of plastics, textile
and other products.
[0003] The biomass material used in these applications is typically sourced
from
waste streams in a number of industries, including the extraction and
transformation of wood and
agricultural products. In their raw form, biomass by-products usually have a
high moisture content
and a large particle size, making them ill-suited for direct use in modem
biomass applications.
[0004] In some cases, raw biomass by-products are used directly
in thermal
processes, using out-dated and conventional methods, such as moving grate or
fluidized bed
technologies, which implicates large-sized equipment. This approach results in
important energy
losses in the process, as well as high levels of flue gas emissions requiring
more elaborate emission
control systems.
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[0005] In order to tackle these limitations, conditioning
processes of the raw biomass
have been developed. The raw biomass is dried to a moisture content of 10% or
less, and is grinded
to a particulate size ranging from a few microns to a few millimetres,
depending on the application.
[0006] Typically, the biomass industry relies on a combination
of grinders and rotary
dryers to perform the above-described conditioning process. This solution is
problematic, because
the drying system itself relies on a burner which burns some of the dried
biomass, in order to provide
heating energy for the raw biomass; therefore, an emission control system is a
necessary addition to
this configuration. Moreover, there are overwhelming capital requirements
implicated in the
installation of rotary dryers and necessary auxiliary systems, as well as the
construction of large-
1 O sized building to house the entire system.
[0007] In general, ail types of dryers (including rotary dryers,
flash tube dryers, etc.)
rely on a thermal process which i) cannibalizes a portion of the dry biomass
production to feed a
burner that provides heating energy to raw biomass, ii) requires an emission
control system to treat
flue gases, and iii) implicates a capital requirement that is uneconomical for
small and medium plant
capacities.
[0008] Furthermore, the existing biomass drying and grinding
technologies that are
currently used to perform the conditioning process are unsteady, energy
inefficient and/or have a
limited dewatering capacity. In particular, these technologies commonly
exhaust vapour and heated
air from the drying chamber; in this manner, thermal energy is actually
evacuated and therefore
wasted from the process.
[0009] Some technologies recycle saturated air in the drying
chamber, which
effectively limits their ability to dewater raw biomass. As the recycled' air
becomes saturated with
moisture, it is unable to absorb further moisture. These technologies operate
at low temperature,
resulting in water condensation and, therefore, in a sticky biomass build-up
in the drying chamber
and in the single cyclone.
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[0010] There is therefore a need in the art for a method and a
system for conditioning
raw biomass.
SUMMARY OF THE INVENTION
[0011] More specifically, in accordance with the present
invention, there is provided a
biomass conditioning system, comprising a chamber, the chamber comprising: a
lower part adapted
to receive biomass, the lower part comprising grinding elements, cutting
elements and an air input,
an airflow from the air input and rotation of the elements creating an
uplifting vortex in the lower part;
and an upper part, the upper part comprising a partition comprising an inner
chamber generally
centered within an outer chamber, the outer chamber comprising a first outlet
and the inner chamber
comprising a second outlet; and a flange selectively connecting the lower part
with the inner chamber
and the lower part with the outer chamber; and an airflow loop, the airflow
loop comprising a source
of the input air in the lower part, a first exhaust connected to the first
outlet and a second exhaust
connected to the second outlet, the first exhaust evacuating air and biomass
particles from the inner
chamber, and the second exhaust evacuating mist and air from the outer
chamber; wherein the
flange diverts, from the uplifting vortex and under action of a vacuum created
between the air input
and the second outlet, a water particle flow to the first outlet of the outer
chamber and a biomass
particles flow towards the inner chamber; light biomass particles being
propelled up the inner
chamber to the second outlet.
[0012] There is further provided a biomass conditioning method,
by separating water
particles from biomass particles in a chamber, using an airflow and a
centrifugal force, comprising
selectively directing the water particles to a first outlet of the chamber,
and the biomass particles,
depending on their weight, to a second outlet of the chamber.
[0013] Other objects, advantages and features of the present
invention will become
more apparent upon reading of the following non-restrictive description of
specific embodiments
thereof, given by way of example only with reference to the accompanying
drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In the appended drawings:
[0015] Figure 1 is a schematic representation of a conditioning
system according to
an embodiment of an aspect of the present invention;
[0016] Figure 2 is a schematic view of a pre-drying unit according to an
embodiment
of an aspect of the present invention; and
[0017] Figure 3 is a schematic view of a system according to an
embodiment of an
aspect of the present invention.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0018] A conditioning method and system will be described in relation to
the
illustrative embodiment of Figures 1 to 3.
[0019] As illustrated in Figure 1, biomass is accumulated in a
feeding hopper 2 and is
fed to the conditioning system using a conveyor 1, such as a screw conveyer
for example. The
hopper 2 is provided with an airlock valve 18 allowing the biomass onto the
conveyor 1, which
transports the biomass, typically as chunks of biomass, into a lower part of a
chamber 3.
[0020] The lower part of the chamber 3 comprises a vertical
shaft, upon which chains
6 and blades 5 are attached. Using a power transmission system 4 composed of
pulleys, a multi-belt
transmission (B) and a motor (M) for example, the shaft is spun at high speed,
for example 1200 rpm
and more, for example at 1500 rpm; thus forcing the chains 6 and blades 5 and
to spin at a required
speed for a grinding action on the biomass chunks by the chains 6, and a
cutting action on biomass
chinks, of a reduced size after grinding by the chains 6, by the blades 5. For
this purpose, variable
speed motors may be used.
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[0021] As the biomass falls onto the bottom of the chamber 3, it
is thus repeatedly
grinded and chopped by the chains 6 and blades 5 into biomass particles. The
biomass particles are
then propelled upwards by an uplifting airflow generated by the blades 5 and
by suction and vaccum
created by air blown a within the chamber 3 in the lower part thereof by a
blower 7, and returned
5 thereto as recycled air. As the biomass is broken down into particles,
the water content thereof is
released into this airflow, thus reducing the biomass' moisture content. A
portion of the superficial
water is phased in the form of mist and is absorbed by the airflow in the
exhaust 11.
[0022] In the upper level, the chamber 3 forms an outer cylinder
17 comprising an
inner cylinder 6 generally centered in the outer cylinder 17, creating a
cylindrical partition within the
upper level of chamber 3.
[0023] As the biomass particles and water particles rise from
the lower part of the
chamber 3, they are forced into a spiral circular motion, by the air input
which enters the chamber 3.
[0024] A flange 21 connects the lower part and the upper part of
the chamber 3. The
flange 21 is in the form of a torus and comprises a central orifice for
connecting the lower part of the
chamber 3 to the inner cylinder 16 and allowing the passage of biomass
particles from the lower part
to the inner cylinder 16, and lateral orifices at the extremities thereof for
connecting the lower part of
the chamber 3 to the outer cylinder 17 and allowing the passage of the water
particles from the lower
part to the outer cylinder 17. Along with the cylindrical partition within the
chamber 3, the flange 21
thus allows the diversion of the water particles flow toward the outer
cylinder 17 and exhaust 11, and
channelling the biomass particles flow towards the inner cylinder 16.
[0025] A cylindrical configuration of the chamber 3 is
described, but any rotational
symmetry configuration, such as an hexagonal configuration, may be used.
[0026] The shape of the chamber 3 allows using centrifugai force
to separate water
from the biomass particles. Given that water particles have a higher density
than dry/fine biomass
particles, and that the centrifugai force is proportional to the weight of the
particles, the dry/fine
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biomass particles rotate closer to the center of the chamber 3 than the water
particles, which rotate
closer to the lateral walls of the chamber 3. The cylindrical partition within
the chamber 3 allows the
diversion of the water particle flow toward the exhaust 11 of the outer
cylinder 17, and of the biomass
particle flow towards the inner cylinder 16.
[0027] As the biomass particles reach the level of the flange 21 in the
chamber 3,
they are sucked in by the inlet of the inner cylinder 16 through the central
orifice of the flange 21.
Since the particles rotate on average at the same speed and depending on the
equilibrium between
the centrifugai force and the forces related to the motion of the vortex air,
the heavier biomass
particles tend to rotate further from the center of rotation, thus hitting the
inner walls of the inner
cylinder 16 and falling back down to the lower part of the chamber 3 through
the central orifice of the
flange 21, where they are subjected again to the grinding, chopping and
dewatering operation
described hereinabove, until they are sufficiently light to be propelled up to
the top of the inner
cylinder 16 by the conveying air.
[0028] A sizer 8 is positioned at the top of the inner cylinder
16. The biomass
particles enter the sizer 8, which sorts the biomass particles by size: only
those biomass particles
that are sufficiently small are allowed through the sizer 8, whereas the
balance of the particles is
returned to the bottom of the chamber 3 through the central aperture in the
flange.
[0029] Therefore, by forcing the biomass particles into the
inner cylinder 16 and into
the sizer 8, only the biomass particles with a sufficiently small moisture
content and particle size are
allowed to exit the chamber 3, in a flow of air/biomass particles conveyed
towards a multi-cyclone 9,
in which the biomass powder can be separated from the conveying airflow, and
collected, at the
bottom of the multi-cyclone 9, through an airlock valve 15 fro example.
[0030] Given that the temperature of the exhaust air is higher
than that of ambient air,
energy can be recovered by recycling the conveying airflow used to transport
the biomass particles
to the multi-cyclone 9. To that effect, a blower 7 sucking air from the top of
the multi-cyclone 9 may
be used to send the conveying air back to the chamber 3 at the lower part
thereof. At the same time,
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heated ambient air (see amblent air blower 13) is used to make-up the balance
in airflow required for
injection into the chamber 3 at the lower part thereof, in replacement to the
exhaust.
[0031] Back inside the chamber 3, as the water particles airflow
reaches higher levels
in the outer cylinder 17, it is exhausted out and into a heat exchanger 10,
using an exhaust fan 11.
Given that the temperature of the exhaust airflow is higher than that of
amblent air, the system is able
to recuperate an important part of the energy it uses by exchanging the energy
of the exhaust airflow
onto ambient air. This mechanism also prevents the reintroduction of a
moisture-saturated airflow
into the chamber 3 and therefore helps increase the dewatering capacity of the
injected air into the
system.
[0032] Using a blower 13, ambient air is sent to the heat exchanger 10,
where it
receives energy from its hot side, i.e. form the exhaust air/mist (from blower
11). The heated air may
be directed into an electrical duct heater 12, in order to control its
temperature and humidity to a
desired level, before reuniting with the flow of recycled air made to enter
the chamber 3.
Alternatively, a heat pump could also be used to increase the temperature of
the input air. In addition
and when available, it is also possible to inject heat from an externat source
20 into the duct heater
12. The heater 12 is only activated if the incoming aies temperature is
inferior to the temperature
inside the chamber 3; in this case, it is activated so as to heat the make-up
air to the temperature of
the chamber 3. Typically, the air made to enter the lower part of the chamber
3 has a temperature
between about 50 and about 70 C, for example of about 70 C, for efficient
moisture absorption.
[0033] The combination of heated ambient air and recycled air is made to
enter the
chamber 3 in the lower part of the chamber 3. Using a tangentiel air input at
a downward angle may
ease creating a vortex in the lower part of the chamber 3. Given its
temperature, the hot airflow
facilitates the system's drying and sorting operations. The hot airflow into
the system is controlled by
a control panel so as to ensure that temperature inside the chamber 3 remains
within an operational
range, typically between 50 C and 70 C. As the temperature inside the chamber
3 is maintained
below water boiling point, the drying of the biomass is achieved mainly in the
liquid phase, as a mist,
evacuated from the chamber 3 by an outlet on an upper level of the outer
cylinder 17 as described
hereinabove.
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[0034] The action of the exhaust fan 11 creates a negative
pressure inside the
chamber 3; which reduces the quantity of thermal energy required to evaporate
the biomass' surface
water particles, and increases the release of water particles that are trapped
in biomass particles.
[0035] A control system may be designed to ensure that the
system works efficiently.
This control system is used to control the temperature of the recycled/ambient
air combination
entering the chamber 3, as well as the operating pressure inside the chamber
3. The operating
pressure inside the chamber is kept negative.
[0036] A temperature sensor may be located between the heat
exchanger 10 and the
electrical heater 12 so as to monitor the temperature of the amblent air at
the outlet of the heat
exchanger 10. Another temperature sensor may monitor the temperature inside
the chamber 3.
When the temperature measurement of the amblent air sensor is significantly
lower than that of the
chamber sensor, the electrical heater may be activated; otherwise, the
electrical heater 12 remains in
off-mode.
[0037] The pressure inside the chamber 3 may be monitored, using
a pressure
sensor directly con nected to the exhaust fan 11. If the pressure inside the
chamber 3 becomes too
high, the speed of the exhaust fan 11 is increased until the pressure inside
the chamber 3 returns to
its desired level.
[0038] When the biomass has a very high moisture content, i. e.
with a moisture
content of more than 50% by weight for example, such as sludge from a sewage
treatment plant,
which can have moisture content as high as 80% for example, the biomass may be
sticky. In order to
ease processing by the conditioning system of the present invention as
described hereinabove in
relation to Figure 1, a pre-drying unit 100, as illustrated in Figure 2 for
example, may be used to
lower the moisture content of the biomass before the biomass enters the
conditioning system, using
a feeding conveyer 300 as shown in Figure 3 for example.
[0039] The biomass enters the pre-drying unit 100 through a hopper 104
located at
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the top of a drying chamber 108. An airlock 112 underneath the hopper 104,
controlled by a variable
frequency drive, allows controlling the flow of biomass entering the drying
chamber 108. When the
airlock 112 is opened, the biomass falls within the drying chamber 108 on
conveyor unit, shown in
Figure 2 as a series of variable speed conveyors 116a, 116b, 116c arranged in
cascade. Guides 120
are located on the inner side walls of the drying chamber 108 ensure that the
biomass falls on the
conveyors 116a, 116b, 116c and flot beside it. Radiant heaters 122, such as
halogen heating
elements, are provided above each conveyor 116a, 116b, 116c to provide the
biomass with radiant
heat, to reduce its moisture content. The length and number of the radiant
heaters 122, as well as
the speed of the conveyors 116a, 116b, 116c are selected to maximize the drop
in moisture of the
biomass, i.e. depending on the nature and moisture content of the biomass.
[0040] Temperatures of the biomass and in the drying chamber 108
are monitored so
that they do not exceed a temperature that may damage the conveyors 116a,
116b, 116c, by
controlling operation of the radiant heaters 122 and evacuation of air from
the drying chamber 108.
[0041] The vapor or mist generated within the drying chamber 108
is evacuated to an
exhaust 138 therefrom by a blower 128 such as an induce fan located on the top
of the drying
chamber 108. The blower 128 may be a vacuum blower, and used to create a
vacuum, i.e. a
negative pressure in the drying chamber 108. Creating a vacuum in the drying
chamber 108 allows
reducing the input of thermal energy needed to separate the water from the
biomass, based on the
principle that water evaporates at lower temperature at high altitude than at
sea level, due to the
pressure of the air, which is much lower at high altitude than at sea level.
Thus, creating a vacuum in
the drying chamber 108 allows lowering the evaporation temperature of the
water inside the drying
chamber 108. Moreover, a vacuum enhances the physically removal of water from
the wet biomass,
by using the air removed from the drying chamber 108 as a pneumatic conveyor
to convey the fine
droplets of water located on the wet biomass to the outside of the drying
chamber 108.
[0042] The outlet of the vacuum blower 128 may be connected to an ac
cyclone 132
for recuperating biomass particles that may be carried by the air sucked out
from the drying chamber
108 before the exhaust 138. The exhaust 138 of the drying system 100,
evacuating air sucked out
from the drying chamber 108, may be coupled with the air exhausted by the
conditioning system of
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the present invention as described hereinabove in relation to Figure 1 (see
exhaust fan 11).
[0043] lnstead of a conveyor unit comprising a series of
variable speed conveyors
116a, 116b, 116c in a staggered arrangement for compactness of the conveyor
unit as illustrated
shown in Figure 2, the conveyor unit may comprise a long straight conveyor if
more space is
5 available on the ground for example.
[0044] The number of radiant heaters 122, the conveying length
and the speed of the
conveyors, in relation to the condition of the biomass at the input of the
dryer system 100 and of the
required biomass conditions at the outlet 142 for feeding to the conditioning
system of the present
invention as described hereinabove in relation to Figure 1.
10 [0045] The present system and allow conditioning raw biomass powder
into a dry fine
powder while recuperating an important part of the energy that is evacuated in
the form of exhaust
vapour and heated air.
[0046] The biomass may originate from wood, such as waste or by-
product of the
forestry industry, or from other sources, such as agricultural and animal
waste, or pulp and paper and
wastewater sludge. If necessary and as a preparative measure, the raw biomass
may be shredded to
a size of a few inches, upstream of the system.
[0047] The resulting biomass powder may be used in a wide range
of modem
biomass applications, including for example the production of wood pellets and
logs and bio-fuels in
general, the production of heat using dust burners or the pyrolysis process,
the production of
nanocrystaline cellulose, the methanation process etc.
[0048] In a nutshell, the system delivers mechanical energy to
the raw biomass,
using blades and chains/or bars that are spun by an electric motor; the blades
also acting as an
internai fan generating an internai flow. Due to the important airflow
generated within the system,
light biomass particles become airborne while heavier biomass particles are
forced back into the
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blades and chains to continue the dewatering/size reduction process.
Furthermore, some of the
thermal energy contained in the system's outgoing airflows is recuperated
through the exhaust heat
recovery system, whereas the moisture is prevented from re-entering the
system. In addition, the
moisture absorption capacity in the chamber is optimised
[0049] The exhaust system is designed to create a vacuum, i.e. a negative
pressure,
in the chamber, which, given the temperature of operation in the chamber,
facilitates the partial
evaporation of moisture and hence increases the dewatering capacity of the
system.
[0050] Generally stated, the process comprises feeding raw
biomass to the lower part
of the chamber of the system, in which the biomass is crushed by repeated
impact with blades and
chains; injection of a dry, hot tangential airflow from the heat recovery
system into the system;
separation of water particles, light biomass particles and heavy biomass
particles using the
centrifugai force; separation of oversized biomass particles using a rotating
size selecting device,
referred to as the sizer; high efficiency separation of biomass particles from
its conveying airflow
using a multi-cyclone; recycling this conveying airflow into the system;
recovery of thermal energy
from the exhaust by ambient air using a heat exchanger; secondary heating of
make-up air in an
electrical duct heater; and injection of make-up air into the system.
[0051] The present method and system promote the use of
conditioned biomass in
the form of a dry/fine powder in biomass-to-energy applications in order to
achieve important gains in
process efficiency as well as important reductions in overall capital,
operation and maintenance
costs.
[0052] The present method and system allow a simultaneous
grinding and drying
operation on the raw biomass, yielding a dry/fine powder in an efficient
manner. The present method
and system allow conditioning raw biomass while achieving higher energy
efficiency and dewatering
capacity. As people in the art will appreciate, the present method and system
allow end-users to
condition biomass more economically, eliminate the need for additional
equipment in thermal
processes, and render modem biomass applications more viable and economical.
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[0053] The
scope of the daims should flot be limited by the embodiments set forth in
the examples, but should be given the broadest interpretation consistent with
the description as a
whole.
