A DEVICE FOR CONVERTING A FUEL
The present invention relates in general to the
gasification of fuels comprising solid components.
More particularly, the invention relates to a device
5 for converting a fuel comprising solid components, known
as a solid fuel, into a gaseous fuel, said device
comprising:
• a pyrolysis zone for the pyrolyzing solid fuel,
comprising pyrolysis means that are capable of
10 decomposing said solid fuel into a pyrolysis gas and into
a solid pyrolysis residue, known as coke; and
• a combustion zone, which is distinct from the
pyrolysis zone, for burning said pyrolysis gas and
comprising combustion means.
15 Said gaseous fuel obtained with the aid of such a
device is an energetic gas, generally termed syngas,
which can be used to drive appropriate equipment such as
engines, turbines, or even fuel cells. However, syngas
often contains tars, and equipment suitable for being
20 supplied with syngas has a low threshold of tolerance to
tar. Beyond a corresponding tolerance threshold,
condensation of tar in such equipment causes rapid
deterioration of said equipment.
Specific gas treatment units exist that can be used
25 to reduce the quantity of tar remaining in the syngas.
However, such treatment units are bulky and expensive.
Devices known as staged gasification devices are
known in the art; they comprise a pyrolysis zone and a
distinct combustion zone. The gasifier from the Danish
30 manufacturer TK Energi AS is an example. A device of
that type can be used to reduce the tar content in the
syngas obtained because the pyrolysis and combustion
steps are partially separated out.
However, in such a known prior art device, a portion
35 of the solid fuel is burned in order to provide the heat
necessary for pyrolysis. Direct combustion of a solid of
that type results in a loss of the energy efficiency of
•
the device, as well as in the emission of polluting
gases, for example dioxins.
Further, said pyrolysis and combustion zones are
arranged for positioning end-to-end, and so the coke
5 obtained from pyrolysis of the fuel passes through the
combustion zone in order to form a reduction bed in the
reduction zone, which means that the device becomes very
bulky and the risk of polluting emissions is increased.
Finally, the arrangement of the pyrolysis and combustion
10 zones in such devices causes large energy losses in the
combustion zone, which is not beneficial to the pyrolysis
zone.
US2009/282738 discloses a device for converting a
solid fuel into a gaseous fuel, which device comprises a
15 pyrolysis zone and a combustion zone provided with
combustion means.
However, in the device of document US2009/282738,
the solid fuel is burned in the combustion zone and the
combustion gases then circulate in the pyrolysis zone.
20 Thus, the device of that document US2009/282738
generates the same problem as that proposed by the Danish
manufacturer TK Energi AS, which burns solid fuel to add
energy. Such combustion of solid fuel generates
polluting emissions and leads to a loss of energy
25 efficiency.
Further, the solution in that document US2009/282738
is not aimed at obtaining an energetic gas, but rather a
pyrolysis oil. It is then necessary to burn solid fuel
in the combustion zone throughout the operation of the
30 device in order to provide the additional heat required
to carry out the pyrolysis reaction.
Document WO02/40618 Al describes a device comprising
a central pyrolysis zone surrounded by a combustion zone.
Such a configuration can be used to transmit part of the
35 heat obtained from combustion to the pyrolysis zone, but
large losses of heat have been observed from the
combustion zone to the outside of the device. Thus, heat
recovery by the pyrolysis zone is not optimized.
The aim of the present invention is to propose a
device for converting a solid fuel into a gaseous fuel
5 that can be used to limit heat losses from the combustion
zone out -of the device and to improve heat recovery by
the pyrolysis zone.
Another aim of the present invention is to propose a
device for converting a solid fuel into a gaseous fuel,
10 known as syngas, wherein the quantity of impurities, in
particular tars, is reduced.
Another aim of the present invention is to propose a
device for converting a solid fuel into a gaseous fuel,
known as syngas, by means of which the emission of
15 pollutants, such as dioxins and metals, is reduced.
To this end, the invention provides a device for
converting a fuel comprising solid components, known as a
solid fuel, into a gaseous fuel, said device comprising:
• a pyrolysis zone for pyrolyzing solid fuel,
20 comprising pyrolysis means that are capable of
decomposing said solid fuel into a pyrolysis gas and into
a solid pyrolysis residue, known as coke;
• a combustion zone, which is distinct from the
pyrolysis zone, for burning said pyrolysis gas and
2 5 comprising combustion means; and
• gas circulation means for circulating gas in order
to circulate said pyrolysis gas from said pyrolysis zone
to the combustion zone;
the device being characterized in that said
30 combustion zone is surrounded by said pyrolysis zone.
The design of the device of the invention, wherein
the pyrolysis zone surrounds the combustion zone, means
that losses of heat from the combustion zone to the
outside of the device are reduced, while heat recovery by
35 the pyrolysis zone is promoted, because of the transfer
of heat from the combustion zone to the pyrolysis zone
that encircles the combustion zone.
™ 4
Since the combustion zone is separate from the
pyrolysis zone, the solid fuel is not in contact with the
oxidizer such as air that injected into the combustion
zone, which means that the emission of pollutants can be
5 limited.
Because wood pyrolysis is carried out, preferably at
a temperature of about 500°C, metals and chlorine remain
in the coke obtained from the pyrolysis of wood, while
the pyrolysis gas is free from polluting elements.
10 Furthermore, the combustion of pyrolysis gas in the
absence of solid fuel in the combustion zone means that a
maximum quantity of tars can be cracked.
The communicating passage between the pyrolysis zone
and the combustion zone is formed in the upper portion of
15 the pyrolysis zone and the combustion zone. Thus, the
pyrolysis gas can pass from the pyrolysis zone into the
combustion zone, while the solids do not pass into the
combustion zone and remain in said pyrolysis zone before
passing, as is described in detail below, into the
20 reduction zone when they become sufficiently small
because of the pyrolysis.
Such a configuration for the combustion zone around
the pyrolysis zone means that the overall size of the
device can be reduced and advantage can be taken from the
25 transfer of the heat obtained by combustion from the
combustion zone to the pyrolysis zone by conduction
through the wall or walls separating the two zones, as is
described in detail below.
Furthermore, the zone of the device that is at a
30 very high temperature is confined to the combustion zone,
for example to the burner, thereby reducing the quantity
of materials that withstand high temperatures that need
to be used in the design of the device. This also helps
to reduce heat losses and thus to maximize the total
35 yield of the conversion process.
In accordance with an advantageous feature of the
invention, said combustion zone is housed coaxially in
said pyrolysis zone.
Said pyrolysis and combustion zones are defined
5 between two coaxial cylindrical walls with circular
sections such that the combustion zone forms a circular
zone centered in said annular space that defines the
pyrolysis zone.
In accordance with an advantageous feature of the
10 invention, said device comprises a reduction zone that
has a passage communicating with the pyrolysis zone to
collect coke obtained from pyrolysis of the solid fuel, a
station for receiving said coke, and a passage
communicating with the combustion zone for gas entering
15 said gas reduction zone obtained from the combustion of
pyrolysis gas in order to enrich said gas obtained from
the combustion of pyrolysis gas in at least hydrogen.
Advantageously, said gas-circulation means are also
configured to provide for circulating the gas that is
20 obtained from burning pyrolysis gas, from said combustion
zone to the reduction zone.
By means of such a configuration of the device, the
various gasification steps, namely pyrolysis, burning,
and reduction, are physically separated, which means that
25 each of these conversion steps can be optimized.
Preferably, said communicating passage comprises a
ramp dropping from the pyrolysis zone to the reduction
zone in order to collect coke in its receiving station
under gravity.
30 Advantageously, the ramp forms the base of the
pyrolysis zone and extends around the combustion zone to
form a cone to guide coke towards the reduction zone.
Since said pyrolysis zone is annular in shape and defined
between an outer peripheral wall and an inner peripheral
35 wall, said ramp co-operates with the inner peripheral
wall to define an outlet for the solid residue obtained
from pyrolysis of solid fuel, the outlet being of a
*
height that is smaller than the distance separating said
peripheral walls from each other.
In cross section, said annular-shaped pyrolysis zone
has an inner circumference and an outer circumference
5 that preferably are circular in shape; however, said
inner circumference and outer circumference of the
annular pyrolysis zone may have some other shape.
Advantageously, said device comprises fitter means
for filtering gas obtained from reducing the coke and
10 configured to filter said gas and re-inject the solid
particles, such as dust or ash contained in said gas,
into the reduction zone.
In accordance with an advantageous feature of the
invention, said combustion means include an inlet for
15 oxidizer, preferably air, and means for initiating the
reaction between the oxidizer and the pyrolysis gas.
In an embodiment of the invention, said combustion
zone and said pyrolysis zone include a common separating
wall. Advantageously, at least part of said reduction
20 zone is located below said combustion zone and/or below
said pyrolysis zone.
In accordance with an advantageous feature of the
invention, at least part of said reduction zone is
located between said combustion zone and said pyrolysis
25 zone, surrounding the combustion zone.
In other words, the reduction zone separates said
combustion zone from said pyrolysis zone. In particular,
the combustion zone is surrounded by the reduction zone
that is itself surrounded by the pyrolysis zone such that
30 the reduction zone is defined between a wall that defines
the inner peripheral circumference of the pyrolysis zone
and a peripheral wall that defines the combustion zone.
Preferably, said device comprises a zone for
circulating the gas obtained from reducing the coke and
35 configured to allow said gas to circulate around the
pyrolysis zone in order to transmit at least some of its
heat to the pyrolysis zone by conduction via a wall of
said pyrolysis zone, preferably the outer peripheral
wall.
Thus, the pyrolysis zone is heated both by the
combustion zone and by the gas circulating in the
5 circulation zone that surrounds the pyrolysis zone in
order to enhance energy recovery via the pyrolysis zone.
Advantageously, said device comprises solid fuel
drying means communicating with the inlet to the
pyrolysis zone in order to dry the solid fuel prior to
10 introducing it into said pyrolysis zone.
In accordance with an advantageous feature of the
invention, said device comprises means for injecting
steam into the reduction zone, preferably steam obtained
from the drying means when they are present.
15 Preferably, since the device has an outer wall, at
least a portion of the outer wall comprises thermal
insulation means.
The invention also provides a method of converting a
fuel comprising solid components, termed a solid fuel,
20 into a gaseous fuel, with the aid of a device as
described above, the method being characterized in that
it comprises the following steps:
a) pyrolyzing solid fuel in the pyrolysis zone in
order to decompose said solid fuel into a pyrolysis gas
25 and into a solid pyrolysis residue known as coke;
b) burning, preferably partially burning, said
pyrolysis gas in said combustion zone.
In accordance with an advantageous feature of the
invention, in order to initiate said conversion, the
30 combustion zone is pre-heated, preferably using a burner,
and once said conversion has been initiated, pre-heating
is reduced, and preferably halted.
In accordance with an advantageous feature of the
invention, said process also comprises the following
35 additional step:
c) reducing the gas obtained from partially burning
pyrolysis gas, preferably in order to enrich said gas in
hydrogen.
Advantageously, said reduction of the gas obtained
5 from partially burning pyrolysis gas is carried out by
means of a reaction between said gas and the coke
obtained from solid fuel pyrolysis.
Preferably, the gas obtained from reduction
circulates around the pyrolysis zone in order to transmit
10 at least a portion of its heat to the pyrolysis zone.
Advantageously, said solid fuel is fed, preferably
after drying, into the pyrolysis zone and is absent from
the combustion zone.
The invention can be better understood from the
15 following description of embodiments, made with reference
to the accompanying drawings in which:
• Figure 1 is a view of a conversion device of the
invention, in accordance with a first embodiment;
• Figure 2 is a view of a conversion device of the
20 invention, in accordance with a second embodiment;
• Figure 3 is a view of a conversion device of the
invention, in accordance with a third embodiment.
Referring to the figures and as noted above, the
invention provides a device for converting a fuel
25 comprising solid components, known as a solid fuel, into
a gaseous fuel, known as syngas. Such a device is also
known as a gasifier.
Gasification is a technique for the thermochemical
conversion of solid fuel into a fuel gas, known as
30 syngas, primarily comprising H2 and CO.
It should be noted that the term "solid" as used
encompasses solids per se, for example pieces of wood,
but also granules, or fine elements such as sawdust.
Various types of solid organic materials may be used
35 to form the solid fuel to be transformed into a gaseous
fuel. In the example detailed below, the solid fuel used
is wood.
The device comprises a solid fuel pyrolysis zone 2
comprising pyrolysis means that can be used to decompose
said solid fuel into a pyrolysis gas and into a solid
pyrolysis residue known as coke.
5 The device also comprises a combustion zone 3 for
burning said pyrolysis gas, which combustion zone is
distinct from the pyrolysis zone 2 and comprises
combustion means 31, 32, 33 that can be used to carry out
partial combustion of pyrolysis gas in order to oxidize
10 the tars and the other hydrocarbons contained in said
pyrolysis gas.
The device has a path 23 for passing pyrolysis gas
to the combustion zone 3. Said pyrolysis means are
formed by the wall or walls that define the pyrolysis
15 zone, which walls can be used to transmit heat into the
pyrolysis zone without any specific addition of oxygen.
As is described in detail below, this heat source
principally derives either directly or indirectly from
the heat released by the combustion zone.
20 Characteristically for the invention, said
combustion zone 3 is surrounded by said pyrolysis zone 2.
Said pyrolysis zone 2 extends around the combustion zone
3 over at least 180°. Preferably, said pyrolysis zone 2
extends around the combustion zone 3 over 360° in order
25 to completely surround it like a belt.
Said pyrolysis zone comprises an inlet 21 for the
supply of solid fuel, configured so that the solid fuel
is fed into the pyrolysis zone via an upturned V-shaped
dome 230, part of which extends over the pyrolysis zone 2
30 and part of which extends over the combustion zone 3
without entering the combustion zone.
In the example shown in Figures 1 and 2, said path
23 for passing pyrolysis gas to the combustion zone 3 is
formed by the opening in the upper portion of the
35 combustion zone 3 that communicates with the upper
portion of the pyrolysis zone 2, and guide means formed
by the upturned V-shaped dome 230 in order to guide the
^ 10
pyrolysis gas from the upper portion of the pyrolysis
zone 2 to the combustion zone 3.
In particular, said device is provided with gascirculation
means for circulating gas 11 in order to
5 circulate the pyrolysis gas from said pyrolysis zone 2 to
»
the combustion zone 3. More generally, said gascirculation
means are configured to allow the gas present
in the device to circulate from the pyrolysis zone 2 to
the outlet 52 from said device.
10 In the example shown in Figure 3, in which the
pyrolysis zone is separated from the combustion zone by
the reduction zone 4 as is described in detail below, one
or more ducts 23 are provided in order to pass pyrolysis
gas from the pyrolysis zone 2 to the combustion zone 3.
15 Said combustion means 31, 32, 33 of the combustion
zone 3 comprise an inlet 31 for oxidizer, preferably air,
and means 32, 33 for initiating the reaction between the
oxidizer and the pyrolysis gas. Said initiating means
are formed by a burner 33 and an inlet 32 for fuel,
20 preferably propane, which is different from the pyrolysis
gas, in order to form a high temperature air flame along
with the oxidizer fed via the inlet 31, preferably at a
temperature of at least 1000°C, in order to provide the
heat necessary for pyrolysis and to initiate partial
25 burning of the pyrolysis gas. After initiating partial
burning of the pyrolysis gas, i.e. during normal
operation of the gasifier, the flow rate of the incoming
fuel 32 can be reduced or even halted.
As described in detail below and shown in Figures 2
30 and 3, the device may be equipped with means 6 for drying
the solid fuel in order to obtain a dry solid fuel and
water in the vapor state.
Pyrolysis enables solid fuel to be converted, in the
absence of oxygen in the combustion zone, into a gas
35 known as pyrolysis gas and into a solid residue known as
coke. The pyrolysis gas includes tars, which are a
mixture of hydrocarbons with high condensation
m n
temperatures, higher than that of benzene. As described
in detail below, the tars are produced during pyrolysis
and then oxidized and cracked thermally during the
partial burning stage in the combustion zone, and finally
5 they are catalytically cracked in the reduction zone with
the coke.
The combustion zone 3 can be used to partially
oxidize the pyrolysis gas (tars and other hydrocarbons)
in order to produce molecules of CO2 and H2O. The heat
10 released by the partial oxidation of the pyrolysis gas in
the combustion zone 3 is transferred directly or
indirectly to the solid fuel present in the pyrolysis
zone 2 and to the coke present in the reduction zone 4.
The pyrolysis gas combustion means thus form at
15 least a portion of said pyrolysis means. In other words,
the heat obtained from partially burning pyrolysis gas is
recovered at least in part by the pyrolysis zone 2 such
that the pyrolysis reaction is self-maintaining once
partial burning of the pyrolysis gas has been initiated.
20 The solid fuel is not in direct contact with the
oxidizer injected into the combustion zone 3, thereby
reducing the emission of any pollutants such as dioxins
or metals.
In particular, each of the combustion and pyrolysis
25 zones is cylindrical, with a circular section for the
combustion zone 3 and an annular section for the
pyrolysis zone 2. Said combustion zone 3 is mounted
coaxially in said pyrolysis zone 2.
In the example shown in Figures 1 and 2, partial
30 oxidation of pyrolysis gas releases heat that is
transferred, via the peripheral wall 320 separating the
pyrolysis zone 2 from the combustion zone 3, to the solid
fuel present in the pyrolysis zone 2. In particular, in
the example shown in Figures 1 and 2, the peripheral wall
35 320 separates the two zones, the pyrolysis zone 2 and the
combustion zone 3, by defining the inner circumference of
^ 12
the annular pyrolysis zone 2 and the outer circumference
of the circular combustion zone 3.
Said device also includes a reduction zone 4 that
has a passage 42 communicating with the pyrolysis zone 2
5 to collect coke obtained from pyrolysis of the solid
fuel, and a receiving station 44 for said coke in order
to form a reduction bed. Said reduction zone also
includes a passage 43 communicating with the combustion
zone 3 to allow combustion products, in particular CO,
10 CO2, CH4, H2O and H2, obtained from partially burning the
pyrolysis gases, to enter into said reduction zone 4 in
order to enrich the gas obtained from partially burning
the pyrolysis gas, at least in H2.
To this end, said means 11 for circulating gas are
15 also configured in order to ensure that the gas obtained
from the combustion of pyrolysis gas is circulated from
said combustion zone to the reduction zone.
Said circulation means 11 may be formed by a turbine
disposed at or in the vicinity of the outlet 52 from the
20 device in order to force the circulation of gas from the
pyrolysis zone 2 to the outlet 52 of the device, passing
via the combustion zone 3, and the other treatment zones
such as the reduction zone 4; preferably, as described in
detail below, the gas-circulation zone 5 extends around
25 the reduction zone 4.
The syngas thus obtained also contains CO. The
communicating passage 42 is configured so that it does
not pass through the combustion zone 3 in order to avoid
reacting coke with the high temperature oxidizer of the
30 combustion zone 3.
Thus, pyrolysis with the device of the invention
enables tars to be released from the solid fuel, which
tars then pass through the very hot combustion zone, then
through the bed of coke. This results in the tars
35 cracking, and so not only is tar eliminated per se, but
also the composition of the final gas is improved and the
quantity of gas produced is increased.
^ 13
In the example shown in Figures 1 and 2, the
reduction bed formed by the coke is preferably very deep,
not only so as to react with the gas obtained from the
combustion zone in order to promote the production of H2
5 and CO, but also to act as a filter in order, as far as
possible, to eliminate tars and particles remaining in
said gas in order to obtain a clean gas.
In the example shown in Figure 3, the heat released
by the combustion zone 3 is transmitted to the pyrolysis
10 zone 2 via the facing peripheral walls of the reduction
zone 4, which are common both to the combustion zone 3
and the pyrolysis zone 2.
Relative to the center of the combustion zone, the
communicating passage 43 is located remote from the
15 communicating passage 23 between the pyrolysis zone 2 and
the combustion zone 3 in order to recover the gas
obtained from partially burning the pyrolysis gas, i.e.
after oxidation of the tars and the other hydrocarbons.
In the example shown in Figures 1 and 2, said
20 reduction zone 4 is located below the level of said
combustion zone 3 and of said pyrolysis zone 2. In
addition, said reduction zone 4 is located vertically
below said combustion zone 3 so as to allow the CO2 and
H2O products obtained from partially burning the pyrolysis
25 gas to react with the bed of coke located in said station
44.
The receiving station 44 is preferably defined by a
screen that holds the coke and allows ash obtained from
reducing the coke to pass through and be recovered in an
30 ash pan 45 located below the screen then evacuated via a
duct 46.
Advantageously, the device is provided with means
for reducing the pressure in the reduction zone 4 in
order to ensure that gas obtained from partially burning
35 pyrolysis gas circulates through the bed of coke present
in the reduction zone 4.
Said passage 42 providing for communication of the
pyrolysis zone 2 with the reduction zone 4 comprises a
ramp dropping from the pyrolysis zone 2 to the reduction
zone 4 in order to allow coke to collect under gravity in
5 its receiving station 44. Said ramp 42 forms the bottom
wall of the pyrolysis zone.
In cooperation with the inner peripheral wall of the
pyrolysis zone, said ramp 42 defines an outlet for
evacuating solid fuel residue after pyrolysis, having a
10 size that is smaller than the distance separating the
inner and outer peripheral walls of the pyrolysis zone 2.
Thus, the solid fuel is evacuated from the pyrolysis zone
by the ramp 42 towards the reduction zone 4 only after
said solid fuel has been pyrolyzed, i.e. in the form of a
15 solid residue of said fuel, with dimensions smaller than
the dimensions of the as yet non-pyrolyzed solid fuel.
The ramp 42 extends about the axis of the pyrolysis
zone 2 (which is aligned with the axis of the combustion
zone 3) and also extends from the pyrolysis zone 2 to a
20 zone located between the combustion zone 3 and the
reduction zone 4 at right angles to the combustion zone
3, to form a flow cross section from the combustion zone
3 to the reduction zone 4 that is smaller in size than
the dimensions of the section of the combustion zone 3.
25 The ramp 42 thus forms a flow restriction that
increases the turbulence in the gas flows between the
combustion zone 3 and the reduction zone 4 and promotes
local oxidizer/pyrolysis gas mixing in the combustion
zone 3. Furthermore, such a flow restriction may be used
30 to improve local oxidizer/pyrolysis gas mixing on a
macroscopic scale so as to limit the risk of relatively
cold zones being present, over or through which the tars
could pass without being cracked.
Said device also comprises a zone 5 for circulating
35 gas obtained from reducing coke and configured to allow
said gas to circulate around the pyrolysis zone 2 in
order to transmit at least some of its heat to the
pyrolysis zone 2 by conduction via the outer peripheral
wall of said pyrolysis zone 2.
Said gas-circulation zone 5 is defined between the
outer peripheral wall of the pyrolysis zone 2 and another
5 peripheral wall, for example the outer peripheral wall of
the device, which other wall surrounds said outer
peripheral wall of the pyrolysis zone 2 at a distance
therefrom.
Said circulation zone 5 includes a passage 51
10 communicating with the reduction zone 4 and a gas outlet
52 allowing gas to be recovered in order to drive
appropriate equipment.
In the example shown in Figure 3, said device
comprises filter means 40 for filtering the gas obtained
15 from coke reduction, and for re-injecting the solid
particles contained in said gas into the reduction zone
4.
Said recirculation means 40 comprise an inlet 41 for
gas opening into said reduction zone 4, a cyclone 49, an
20 outlet 47 for re-injecting solid particles, such as dust
or ash, into said reduction zone 4, and an outlet 48 for
filtered gas communicating with the circulation zone 5
that extends around the pyrolysis zone 2.
Advantageously, the organic matter used as a solid
25 fuel in the device of the invention has a moisture
content of less than 50% (based on the dry content). The
following fuels in particular may be mentioned:
• wood and uncontaminated derivatives thereof, such
as sawdust, logs, or bark;
30 • poultry litter;
• wood containing additives;
• green waste;
• an organic fraction of household refuse;
• a plastics fraction of household refuse;
35 • plastics;
• tires.
* 16
As shown in Figures 2 and 3, the device of the
invention may comprise means 6 for drying the solid fuel
communicating with the inlet 21 of the pyrolysis zone 2,
in order to dry the solid fuel prior to introducing it
5 into said pyrolysis zone 2.
As shown in Figures 2 and 3, said device may be
provided with means 61 for injecting steam into the
reduction zone 4, preferably steam obtained from the
drying means 6. Other gases may also be injected via a
10 duct 62 into the reduction zone 4.
The device has an outer wall 10, so at least a
portion of the outer wall of the device includes thermal
insulation means. In particular, said outer wall of the
device may be covered with a layer of thermal insulation.
15 The device as described above can be used to carry
out a method of converting a solid fuel into gas as
follows. This method is described below for a conversion
device corresponding to the device shown in Figure 1.
The gasifier is pre-heated with the aid of a burner
20 33 by supplying an oxidizer 31, air in this example, and
a fuel 32, preferably propane 32 or, for example, syngas
or another fuel gas. The gasifier may also be pre-heated
by a flow of hot gas obtained from the exhaust gas or any
other heat source.
25 Once the temperature of the pyrolysis zone of the
gasifier is above the startup temperature, for example
500°C, the solid fuel stored in the storage zone 9 is fed
into the pyrolysis zone 2. The wood is decomposed to
produce a pyrolysis gas and a carbonaceous residue
30 forming the coke.
The pyrolysis gas then passes into a combustion zone
3 and is partially burned with the injected air 31. The
flow rate of the injected propane 32 is gradually reduced
as the pyrolysis gas production increases until finally,
35 continuous supply is stopped. In other words, the
propane functions to ignite and pre-heat.
^ 17
The coke obtained from pyrolysis slides along the
ramp 42 under gravity and falls over the screen 44 to
form a reduction bed.
The gas obtained from partially burning pyrolysis
5 gas in the combustion zone 3 passes into the reduction
zone 4 to react with the coke in order to enrich the gas
that is produced in H2 and CO.
Said device may be provided with a double wall, for
example the zone 5 shown in Figures 1 to 3, heated by an
10 external means, such as another heat source, combustion
of a portion of the syngas, the exhaust gases from an
engine, a turbine or a boiler, in order to reduce the
startup time of the process and improve its operation.
Pre-heating the air injected at 31 into the
15 combustion zone 3 may be carried out by recovering the
heat from the gases produced and/or the heat released by
the device and/or from any other source of heat.
The method described above may function with a gas
31 other than air in order to form the oxidizer injected
20 into the combustion zone 3: pure oxygen, or air enriched
in oxygen.
Preferably, the hot zone does not include any
mechanisms, not even any mechanism for conveying the
fuel, so technical complications are avoided.
25 By means of such a design of the device of the
invention, solid fuel is never burned directly, nor is it
brought into contact with the oxidizer injected into the
combustion zone. As a result, the essential part of any
pollutants (chlorine, metals) remains in the solid state
30 in the ash or in the particle filter. Thus, emissions of
dioxins and gaseous metals are greatly reduced compared
with a conventional combustion method.
The device of the invention forms a gasifier that is
simple to use and inexpensive. In fact, the conversion
35 of solid fuel into gaseous fuel with such a device in
accordance with the invention is simple to carry out,
efficient, environmentally-friendly, and relatively
* 18
inexpensive as regards extracting value from a solid
fuel.
Furthermore, the solid fuel pyrolysis can be used to
generate a pyrolysis gas that requires only a small
5 quantity of oxygen to be injected for oxidation purposes,
which means that the production of polluting compounds
such as dioxins is limited. Such a device can also be
used to further reduce polluting emissions.
As noted above, the syngas obtained by converting
10 solid fuel may be used in a reliable and efficient manner
in a variety of applications: boiler, internal combustion
engine, turbine, fuel cell, or even small scale cogeneration,
etc.

W 19
CLAIMS
1. A device for converting a fuel comprising solid
components, known as a solid fuel, into a gaseous fuel,
said device comprising:
5 'a pyrolysis zone (2) for pyrolyzing solid fuel,
comprising pyrolysis means that are capable of
decomposing said solid fuel into a pyrolysis gas and into
a solid pyrolysis residue, known as coke;
• a combustion zone (3), which is distinct from the
10 pyrolysis zone (2), for burning said pyrolysis gas and
comprising combustion means (31, 32, 33);
• a path (23) for passing pyrolysis gas to the
combustion zone (3); and
• gas-circulation means for circulating gas in order
15 to circulate said pyrolysis gas from said pyrolysis zone
(2) to the combustion zone (3);
the device being characterized in that said
combustion zone (3) is surrounded by said pyrolysis zone
(2) .
20
2. A device according to claim 1, characterized in that
said combustion zone (3) is housed coaxially in said
pyrolysis zone (2).
25 3. A device according to either preceding claim,
characterized in that said device comprises a reduction
zone (4) that has a passage (42) communicating with the
pyrolysis zone (2) to collect coke obtained from
pyrolysis of the solid fuel, a station (44) for receiving
30 said coke, and a passage (43) communicating with the
combustion zone (3) for gas entering said gas reduction
zone (4) obtained from the combustion of pyrolysis gas in
order to enrich said gas obtained from the combustion of
pyrolysis gas in at least hydrogen.
35
4. A device according to claim 3, characterized in that
said communicating passage (42) comprises a ramp dropping
^ 20
from the pyrolysis zone (2) to the reduction zone (4) in
order to collect coke in its receiving station (44) under
gravity; and in that said pyrolysis zone (2) is annular
in shape and defined between an outer peripheral wall and
5 an inner peripheral wall, said ramp (42)co-operating with
the inner peripheral wall to define an outlet for the
solid residue obtained from pyrolysis of solid fuel, the
outlet being of a height that is smaller than the
distance separating said peripheral walls from each
10 other.
5. A device according to claim 3 or claim 4,
characterized in that said device comprises filter means
(40) for filtering the gas obtained from reducing the
15 coke and configured to filter said gas and re-inject the
solid particles, such as dust or ash contained in said
gas, into the reduction zone (4).
6. A device according to any one of claims 3 to 5,
20 characterized in that at least part of said reduction
zone (4) is located below said combustion zone (3) and/or
below said pyrolysis zone (2) .
7. A device according to any one of claims 3 to 6,
25 characterized in that said device comprises a zone (5)
for circulating the gas obtained from reducing the coke
and configured to allow said gas to circulate around the
pyrolysis zone (2) in order to transmit at least some of
its heat to the pyrolysis zone (2) by conduction via a
30 wall of said pyrolysis zone (2), preferably the outer
peripheral wall.
8. A device according to any one of claims 3 to 7,
characterized in that said device comprises means (61)
35 for injecting steam into the reduction zone (4).
^ 21
9. A device according to any one of claims 3 to 8,
characterized in that at least part of said reduction
zone (4) is located between said combustion zone (3) and
said pyrolysis zone (2), surrounding the combustion zone
5 (3) .
10. A device according to any one of claims 1 to 8,
characterized in that said combustion zone (3) and said
pyrolysis zone (2) include a common separating wall
10 (320) .
11. A device according to any preceding claim,
characterized in that said combustion means (31, 32, 33)
comprise an inlet (31) for oxidizer, preferably air, and
15 means (32, 33) for initiating the reaction between the
oxidizer and the pyrolysis gas.
12. A device according to any preceding claim,
characterized in that said device comprises means (6) for
20 drying solid fuel communicating with the inlet (21) to
the pyrolysis zone (2) in order to dry the solid fuel
prior to introducing it into said pyrolysis zone (2).
13. A device according to any preceding claim,
25 characterized in that, since the device has an outer
wall, at least a portion of the outer wall of the device
comprises thermal insulation means.
14. A method of converting a fuel comprising solid
30 components, termed a solid fuel, into a gaseous fuel,
with the aid of a device according to any preceding
claim, the method being characterized in that it
comprises the following steps:
a) pyrolyzing solid fuel in the pyrolysis zone in
35 order to decompose said solid fuel into a pyrolysis gas
and into a solid pyrolysis residue known as coke;
• 22
b) burning, preferably partially burning, said
pyrolysis gas in said combustion zone.
15. A method according to claim 14, characterized in that
5 in order to initiate said conversion, the combustion zone
(3) is pre-heated, preferably using a burner (33), and
once said conversion has been initiated, pre-heating is
reduced, and preferably halted.
10 16. A method according to claim 14 or claim 15,
characterized in that said process also comprises the
following additional step:
c) reducing the gas obtained from partially burning
pyrolysis gas, preferably in order to enrich said gas in
15 hydrogen.
17. A method according to claim 16, characterized in that
said reduction of the gas obtained from partially burning
pyrolysis gas is carried out by means of a reaction
20 between said gas and the coke obtained from solid fuel
pyrolysis.
18. A method according to claim 17 or claim 16,
characterized in that the gas obtained from reduction
25 circulates around the pyrolysis zone (2) in order to
transmit at least a portion of its heat to the pyrolysis
zone (2).
19. A method according to any one of claims 14 to 18,
30 characterized in that said solid fuel is fed, preferably
after drying, into the pyrolysis zone (2) and is absent
from the combustion zone (3).