U.S. patent application number 13/056321 was filed with the patent office on 2011-07-28 for plasma method for disposing of waste material, and apparatus therefor.
This patent application is currently assigned to RE.CO 2 S.R.L.. Invention is credited to Mario Fabbri, Enrico Sonno.
Application Number | 20110180381 13/056321 |
Document ID | / |
Family ID | 40639724 |
Filed Date | 2011-07-28 |
United States Patent
Application |
20110180381 |
Kind Code |
A1 |
Fabbri; Mario ; et
al. |
July 28, 2011 |
PLASMA METHOD FOR DISPOSING OF WASTE MATERIAL, AND APPARATUS
THEREFOR
Abstract
A method and an apparatus based on a reactor vessel (201) that
is brought to a predetermined vacuum degree, in particular said
vacuum degree set between 2 and 6 absolute millibar, an to a high
temperature. A waste material is continuously introduced in the
vessel (202), in particular a solid waste material (5) is
introduced in such a way that a vacuum loss from the vessel (201)
is prevented. Owing to the high temperature, waste material (5)
forms a plasma that undergoes a molecular rearrangement, which
gives origin to a substantially liquid residue that is collected in
a bottom portion (204) of reactor (201), and to a gas (11). The gas
(11), which mainly comprises carbon monoxide, hydrogen, carbon
dioxide and steam, i.e. a typical syngas composition, is
continuously taken away from the vessel (201) through a duct (12),
and is sent to subsequent treatments to obtain a gas fuel that can
be burnt by devices such as a gas turbine, a motor or a boiler. The
high temperature in reactor (201) is maintained due to a current in
the form of electric discharges (20) that is established between
two electrodes (21,22) below the liquid head (7). The substantially
liquid residue is periodically discharged to maintain a liquid head
height (7) not exceeding a reference height value H*, in such a way
that air inlet into vacuum loss from the vessel (201) is
prevented.
Inventors: |
Fabbri; Mario; (Comacchio,
IT) ; Sonno; Enrico; (Ghezzano, IT) |
Assignee: |
RE.CO 2 S.R.L.
Pisa
IT
|
Family ID: |
40639724 |
Appl. No.: |
13/056321 |
Filed: |
August 10, 2009 |
PCT Filed: |
August 10, 2009 |
PCT NO: |
PCT/EP09/05791 |
371 Date: |
March 3, 2011 |
Current U.S.
Class: |
201/1 ; 201/19;
202/117; 202/118 |
Current CPC
Class: |
F23G 5/448 20130101;
B09C 1/06 20130101; F23G 5/444 20130101; F23G 2205/121 20130101;
F23G 2205/18 20130101; F23J 1/00 20130101; B09B 3/00 20130101; F23G
5/085 20130101 |
Class at
Publication: |
201/1 ; 201/19;
202/117; 202/118 |
International
Class: |
C10B 53/00 20060101
C10B053/00; C10B 7/00 20060101 C10B007/00; C10B 31/00 20060101
C10B031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2008 |
IT |
PI2008A000074 |
Claims
1. A method for transforming a waste material, said method
comprising the steps of: prearranging a vessel, said vessel having
a bottom part, an inlet duct that is associated to an inlet port,
and an outlet port; heating said vessel to a prefixed conversion
temperature; depressurizing said vessel to a prefixed vacuum
degree, and maintaining said prefixed vacuum degree, by suction
downstream of said outlet port; feeding said waste material into
said vessel through said inlet duct, said waste material being thus
heated to said conversion temperature, said conversion temperature
being such that said waste material turns into a ionized gas, in
particular a plasma, and into a substantially liquid residue, in
particular a lava, said liquid residue forming a predetermined
liquid head with respect to said bottom part, maintaining said
conversion temperature by causing electric discharges to occur in
said vessel, in particular below said head through said
substantially liquid residue, extracting said gas from said vessel
through said outlet port, extracting a part of said liquid residue
through said outlet port, such that said liquid head is maintained
between prefixed minimum and maximum levels, wherein: said steps of
feeding said waste material and extracting said gas are continuous,
said step of maintaining said prefixed vacuum degree is obtained by
said step of extracting said gas, and said step of feeding said
waste material into said vessel through said inlet duct is carried
out under vacuum conditions within said vessel.
2. A method according to claim 1, wherein said prefixed vacuum
degree is comprised between one and ten absolute millibar,
preferably between three and six absolute millibar.
3. A method according to claim 1, wherein said step of feeding said
waste material under vacuum conditions is selected from the group
comprised of: feeding a loose and substantially solid waste
material, forming a gas-tight plug within said duct by compressing
said waste material, said plug protruding into said conversion
vessel through said inlet port, feeding a waste material packaged
into rigid capsules, said capsules forming a gas-tight engagement
with said inlet duct while they are pushed towards said inlet port,
feeding a liquid or a gas, or a combination thereof, under said
head of liquid residues.
4. A method according to claim 1, wherein a step of determining the
level of said head is provided by ultrasonic analysis.
5. A method according to claim 1, wherein said step of extracting a
part of said liquid residue is carried out through an outlet hole
of said vessel through said bottom part, a step being provided of
eliminating a plug that is formed by a hardened amount of said
liquid residue at said outlet hole, in particular, said plug is
eliminated by withdrawing it to a prefixed extent into said vessel
such that it melts and opens said outlet hole, said plug restored
when said liquid head decreases down to a prefixed minimum
level.
6. A method according to claim 1, wherein said electric discharges
take place in a discharge region below said head close to a
plurality of conductive elements, in particular two electrodes, a
prefixed voltage being established and maintained between a pair of
said elements, wherein said discharges are produced with an
intensity and/or a frequency responsive to said voltage.
7. A method according to claim 6, wherein said voltage is adjusted
responsive to an inlet throughput of said waste material into said
vessel.
8. An apparatus for transforming a waste material, said apparatus
comprising: a vessel having a bottom part and an inlet duct that is
associated to an inlet port, a heating means for heating said
vessel to a prefixed conversion temperature, and maintaining said
vessel at said conversion temperature; a depressurizing means for
depressurizing said vessel to a prefixed vacuum degree, and
maintaining said prefixed vacuum degree; a waste feeding means for
feeding said waste material into said vessel through said inlet
duct, said waste material being thus heated to said conversion
temperature, said conversion temperature being such that said waste
material turns into a ionized gas or a plasma, and into a
substantially liquid residue, in particular a lava, said liquid
residue forming a liquid head with respect to said bottom part, a
gas extracting means for extracting said gas from said vessel a
liquid extracting means for extracting a part of said liquid
residue such that said head of said liquid residue is maintained
between prefixed minimum and maximum levels, characterized in that
said depressurizing means is adapted to maintain in use said
prefixed vacuum degree within said vessel during said gas
extracting, and that said waste feeding means is adapted to
continually feed in use said waste material into said vessel and to
create a gas-tight seal against air leakage together with said
waste material.
9. An apparatus according to claim 8, wherein said waste feeding
means is selected from the group comprised of a loose solid waste
feeding means for feeding a loose and substantially solid waste
material, said material forming a gas-tight plug within said duct
by compressing said waste material, said plug protruding into said
conversion vessel through said inlet port, a packed waste feeding
means for feeding rigid capsules containing a waste material, in
particular a solid waste material, said capsules forming a
gas-tight engagement with said inlet duct while being pushed
towards said inlet port, a liquid/gas waste feeding means for
feeding a liquid or a gas, or a combination thereof, below said
head of liquid residues.
10. An apparatus according to claim 9, wherein said loose solid
waste feeding means comprises a screw having a profile that is
suitable for engaging said inlet duct in such a way that said loose
solid material is compressed forming said gas-tight plug when it is
fed into said vessel through said inlet duct. said liquid/gas waste
feeding means comprises a duct that protrudes inside said vessel
and is arranged at a level below said head.
11. An apparatus according to claim 8, wherein said liquid
extracting means comprises: an outlet hole of said vessel, a plug
breaking means for breaking a plug that is formed by a hardened
amount of said liquid residue at said outlet hole, said means
selected from the group comprised of a drilling means that is
associated with breaking detection means, a screw that is arranged
inside an extraction duct, said outlet duct being arranged through
a wall of said vessel, said screw being kept in a first position
within said outlet duct by a plug that is formed by a solidified
amount of said residue, said screw adapted to assist said
extraction by rotating towards the inside of the vessel.
12. An apparatus according to claim 8, wherein said vessel
comprises: a plurality of conductive elements, in particular two
electrodes, a voltage maintaining means for maintaining a prefixed
voltage between a pair of said elements of said plurality of
elements, in order to generate said discharges in a region that in
use is submerged by said substantially liquid residue, said
discharges having an intensity and a frequency, said intensity and
frequency responsive to said voltage.
13. An apparatus according to claim 12, comprising: an inlet
throughput detecting means for detecting an inlet throughput of
said waste material in said vessel a voltage adjustment means for
arranging said voltage responsive to said throughput such that a
heat input associated with such discharges can be adjusted
responsive to said throughput by adjusting said voltage.
14. An apparatus according to claim 12, wherein said conductive
elements are consumable electrodes, each of said consumable
electrodes formed by a plurality of substantially linear elements,
each of said elements having ends, in particular screwed ends that
are adapted to engage with another adjacent element, wherein an
electrode restoring means is provided for restoring a consumed part
of said electrode, said electrode restoring means comprising: a
positioning seat, for positioning an electrode element close to an
electrode end, said extremity protruding out of said vessel an
electrode joining means for joining an end of said element to said
end of said electrode, an actuator for pushing said electrode
through said wall of said vessel, a gas-tight seal such that during
said progression air leakages into said vessel are hindered.
15. An apparatus according to claim 8, wherein a purification means
is provided to remove hydrogen sulphide from said extracted gas, in
particular a means for contacting said gas with a solution of
ferrous oxides and/or salts.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for disposing of a
waste material, which provides a transformation of the waste into a
plasma. The invention also refers to an apparatus for carrying out
the method.
[0002] The method and the apparatus are well suited for treating a
solid, liquid or gas waste material, which may contain an organic
and an inorganic part. In particular, the waste material may be a
municipal waste, a hospital or surgery waste, a harmful or infected
waste, a wastewater sludge, a metal workshop waste, a
slaughterhouse waste, a farm waste, a ground tires, etc.
BACKGROUND OF THE INVENTION
[0003] The need is felt of waste disposal techniques, which
overcome the well known drawbacks of traditional techniques, like
landfill and incineration, and possibly allow recovering
energy.
[0004] In particular, methods are known that provide heating a
waste material up to a temperature at which the organic part of the
waste material turns into a ionized gas, i.e. a plasma. In such
conditions, the most complex organic molecules are broken down into
lower molecular weight molecules, mainly carbon monoxide and
hydrogen. These form a mixture that can be fed to a boiler, a gas
turbine, or an endothermic motor to recover energy.
[0005] Waste materials may also contain a part that cannot be
turned into a gas. This part generally comprises metals, in
particular heavy metals, which at such a temperature are
transformed into a lava, i.e. into a liquid that hardens by
cooling, and gives origin to a glassy, hard, high-melting and not
leachable material. The lava provides a matrix that is able to
embed harmful compounds that may be present in the original waste
material; solidified lava can be also used as a construction
material.
[0006] WO2004/087840 relates to a two-stage process for disposing
of a waste material, and to an apparatus to carry out the process,
in which: [0007] in the first stage, a waste material is heated up
to a temperature at which a plasma is obtained from the waste, a
well as a liquid residue that comprises a molten metal, partially
treated waste material and a slag. This occurs preferably in a
furnace into which the waste material is dropped, and where the
plasma is maintained by the heat that is produced by an electric
current that circulates between the residue and two immersed
electrodes; [0008] after a rough solid separation, in the second
stage, the gas product is refined by further breaking residual
complex molecules; furthermore, carbonaceous particles, which may
have been formed in the first stage, are removed by contacting them
with a metered amount of an oxidizing agent like air and/or
steam.
[0009] Still in WO2004/087840, the steps are provided of quick
cooling and/or purifying the gas; these steps are carried out by
conventional methods and through a conventional equipment, in
particular, one or more filters. A prefixed vacuum degree is
created inside the furnace and throughout the gas circuit by means
of a fan; the vacuum is merely intended to prevent the gas from
leaking out of the furnace and the circuit through possible weak
couplings. A vacuum higher than what is required to this purpose
could not be used in the equipment according to the above mentioned
application, as confirmed by the square cross section of the
furnace, which is not adapted to work in deep vacuum
conditions.
[0010] Furthermore, the furnace described in WO2004/087840 is not
well suited for being steadily fed with solid waste material,
without appreciable vacuum loss and/or appreciable air inlet. In
fact, the feeding duct is just equipped with a "isolation valve",
i.e. an on-off valve, which cannot ensure a gas-tight seal.
Similarly, it is quite difficult to feed such a furnace with
hermetic, rigid capsules containing dangerous waste material, which
would not be safe to open before feeding the furnace, as in the
case of infected or harmful waste materials like hospital or
surgery waste materials, and the like.
[0011] The continuous or periodic removal of the molten residue
that is collected in the bottom part of the furnace is complicated
by the high temperature that is needed to maintain the liquid
state. Even if "holes for valves" are mentioned, the problem of the
lava hardening inside the valves remains unsolved.
[0012] Briefly, a solution is still to be found to the problems of:
[0013] continuously feeding a loose or packed substantially solid
waste material into a transformation vessel; without substantial
vacuum loss and/or air inlet; [0014] periodically removing the
liquid mass, in particular, without substantial loss of vacuum
and/or air inlet.
SUMMARY OF THE INVENTION
[0015] It is therefore a feature of the present invention to
provide a method and an apparatus for treating a waste material by
a transformation into a plasma, in which energy costs are lower
with respect to the prior art.
[0016] It is also a feature of the invention to provide such a
method and such an apparatus, which allows energy recovering.
[0017] It is also a feature of the invention to provide such a
method and such an apparatus, for obtaining useful products from
the transformed waste material.
[0018] It is, furthermore, a feature of the invention to provide
such a method and apparatus in which the waste material is
continuously fed to a vessel where the transformation takes place,
without substantial loss of vacuum and/or inlet of air along with
the fed material.
[0019] It is a particular feature of the invention to provide such
a method and apparatus that allow feeding a loose waste material or
rigid capsules containing a waste material into the vessel where
the transformation takes place.
[0020] It is, furthermore, an a feature of the invention to provide
such a method and such an apparatus that allow drawing away a part
of residual liquid from the vessel without stopping the treatment
and without substantial loss of vacuum and/or inlet of air.
[0021] It is still, an a feature of the invention to provide such a
method and such an apparatus that allow restoring portions of a
consumable electrode, without stopping the treatment and without
substantial loss of vacuum and/or inlet of air.
[0022] These and other objects are achieved through a method for
transforming a waste material, the method comprising the steps of:
[0023] prearranging a vessel, the vessel having a bottom part, an
inlet duct that is associated to an inlet port, and an outlet port;
[0024] heating the vessel to a prefixed conversion temperature;
[0025] depressurizing the vessel to a prefixed vacuum degree, and
maintaining the prefixed vacuum degree by suction downstream of the
outlet port; [0026] feeding the waste material into the vessel
through the inlet duct, the waste material being thus heated to the
conversion temperature, the conversion temperature being such that
the waste material turns into a ionized gas or a plasma, and into a
substantially liquid residue, in particular a lava, the liquid
residue forming a predetermined liquid head with respect to the
bottom part, [0027] maintaining the conversion temperature by
causing electric discharges to occur in the vessel, in particular
below the head through the substantially liquid residue, [0028]
extracting the gas from the vessel through the outlet port, [0029]
extracting a part of the liquid residue through the outlet port,
such that the liquid head is maintained between prefixed minimum
and maximum levels, wherein: [0030] the steps of feeding the waste
material and extracting the gas are continuous, [0031] the step of
maintaining the prefixed vacuum degree is obtained by the step of
extracting the gas, and [0032] the step of feeding the waste
material into the vessel through the inlet duct is carried out
under vacuum conditions within the vessel.
[0033] This way, less energy is required to maintain a plasma torch
created by an electric arch in a vessel, provided that vacuum
conditions are maintained in the vessel, in such a way that the
current between the electrodes in intermittent, i.e. electric
discharges take place between the electrodes.
[0034] Advantageously, the prefixed vacuum degree is comprised
between one and ten absolute millibar, preferably between three and
six absolute millibar. This way, a surprising efficiency of the
electric discharge is obtained as compared to the costs for
maintaining the vacuum in the vessel.
[0035] In particular, the step of feeding the waste material under
vacuum conditions provides feeding a loose and substantially solid
waste material, forming a gas-tight plug within the duct by
compressing the waste material, the plug protruding into the
conversion vessel through the inlet port.
[0036] Alternatively, the step of feeding the waste material under
vacuum conditions provides feeding a waste material that is
packaged into rigid capsules, the capsules forming a gas-tight
engagement with the inlet duct while they are pushed towards the
inlet port.
[0037] Alternatively, but not exclusively, the step of feeding the
waste material under vacuum conditions provides feeding a liquid or
a gas, or a combination thereof, under the head of liquid
residues.
[0038] Preferably, a step of determining the level of the head is
provided by ultrasonic analysis.
[0039] Advantageously, the step of extracting a part of the liquid
residue is carried out through an outlet hole of the vessel through
the bottom part, a step being provided of eliminating a plug that
is formed by a hardened amount of the liquid residue at the outlet
hole, in particular, the plug is eliminated by withdrawing it to a
prefixed extent into the vessel such that it melts and opens the
outlet hole, the plug restored when the liquid head decreases down
to a prefixed minimum level.
[0040] Preferably the electric discharges take place in a discharge
region below the head close to a plurality of conductive elements,
in particular two electrodes, a prefixed voltage being established
and maintained between a pair of the elements, wherein the
electrical discharges are produced with an intensity and/or a
frequency responsive to the voltage.
[0041] Advantageously, the voltage is adjusted responsive to an
inlet throughput of the waste material into the vessel.
[0042] In particular, the conductive elements are consumable
electrodes; in this case, the method provides detecting the length
of the residual electrode and restoring a consumed portion of the
electrode, in such a way that the discharge zone maintains its
shape and its position while the electrodes are consumed.
Alternatively, the method can provide continuously restoring the
electrodes.
[0043] Preferably, the extraction step of the gas out of the
vessel, which takes place through the outlet port, is followed by
further gas treating steps.
[0044] In particular, a plasma purifying step can be provided, in
which the gas flows between a couple of electrodes that are
maintained at a predetermined voltage with respect to each other,
such that an electric discharge takes place and creates or
maintains a plasma torch, whereby harmful compounds are separated
from the gas and fall down in a liquid form.
[0045] In particular, a quick cooling or quenching step of the
outlet gas can be provided, such that the formation of harmful
substances is prevented, such as dioxins and furans.
[0046] In particular, one or more filtering steps and/or a washing
step of the gas can be provided to remove, in particular, hydrogen
sulfide. The gas filtering steps can be carried out by such a means
as a cyclone separator, and/or an electrostatic filter, or an
activated carbon filter. The gas washing step can be carried out by
means of solution of iron oxides or salts.
[0047] Advantageously, the plasma purifying, cooling, filtering and
washing steps are carried out in high vacuum conditions.
[0048] The above-mentioned objects are also achieved through an
apparatus for transforming a waste material, the apparatus
comprising: [0049] a vessel having a bottom part and an inlet duct
that is associated to an inlet port, [0050] a heating means for
heating the vessel to a prefixed conversion temperature, and
maintaining the vessel at the conversion temperature, [0051] a
depressurizing means for depressurizing the vessel to a prefixed
vacuum degree, and maintaining the prefixed vacuum degree, [0052] a
waste feeding means for feeding the waste material into the vessel
through the inlet duct, the waste material being thus heated to the
conversion temperature, the conversion temperature being such that
the waste material turns into a ionized gas or a plasma, and into a
substantially liquid residue, in particular a lava, the liquid
residue forming a liquid head with respect to the bottom part. The
apparatus comprises furthermore [0053] a gas extracting means for
extracting the gas from the vessel, [0054] a liquid extracting
means for extracting a part of the liquid residue such that the
head of the liquid residue is maintained between prefixed minimum
and maximum levels.
[0055] A main feature of the apparatus is that the depressurizing
means is adapted to maintain in use the prefixed vacuum degree
within the vessel during the gas extracting step, and that the
waste feeding means is adapted to continually feed in use the waste
material into the vessel and to create a gas-tight seal against air
leakage together with the waste material.
[0056] The waste feeding means can be a means for feeding a loose
and substantially solid waste material, the material forming a
gas-tight plug within the duct by compressing the waste material,
the plug protruding into the conversion vessel through the inlet
port.
[0057] Alternatively, the means for feeding the waste material can
provide a packed waste feeding means that is suitable for feeding
rigid capsules containing a waste material, in particular a solid
waste material, the capsules forming a gas-tight engagement with
the inlet duct while being pushed towards the inlet port.
[0058] Alternatively, but not exclusively, the means for feeding
the waste material can be a liquid/gas waste feeding means, or a
means for feeding a combination of liquid and gas waste material,
below the head of liquid residues.
[0059] In particular, the loose solid waste feeding means comprises
a screw having a profile that is suitable for engaging the inlet
duct in such a way that the loose solid material is compressed
forming a gas-tight plug when it is fed into the vessel through the
inlet duct, and the liquid/gas feeding means comprises a duct that
protrudes inside the vessel and is arranged at a level below the
head.
[0060] Preferably, the vessel is defined by walls that comprise:
[0061] an inner layer that is made of refractory bricks, which that
have respective engaging portions that are adapted to engage with
corresponding portions of adjacent refractory bricks; [0062] an
intermediate flexible layer made of a refractory material,
preferably made of aluminium oxide; [0063] an outer coil, or a
shell that is arranged about the intermediate layer of the wall, an
inner surface of the shell and an external surface of the
intermediate layer defining a jacket, the coil or the jacket being
adapted to receive a cooling fluid for cooling the wall and/or for
recovering heat from the vessel.
[0064] Advantageously, the liquid extracting means comprises:
[0065] an outlet hole of the vessel; [0066] a plug breaking means
for breaking a plug that is formed by a hardened amount of the
liquid residue at the outlet hole.
[0067] The liquid extracting means can comprise a drilling means
that is associated with a breaking detection means
[0068] Alternatively, but not exclusively, the liquid extracting
means can comprise a screw that is arranged inside an extraction
duct, the outlet duct being arranged through a wall of the vessel,
the screw being kept in a first position within the outlet duct by
a plug that is formed by a solidified amount of the residue, the
screw adapted to assist the extraction by rotating towards the
inside of the vessel.
[0069] Advantageously, the vessel comprises: [0070] a plurality of
conductive elements, in particular two electrodes; [0071] a voltage
maintaining means for maintaining a prefixed voltage between a pair
of the elements of the plurality of elements, in order to generate
the electrical discharges in a region that in use is submerged by
the substantially liquid residue, the electrical discharges having
an intensity and a frequency, the intensity and frequency
responsive to the voltage.
[0072] Advantageously, the apparatus comprises: [0073] an inlet
throughput detecting means for detecting an inlet throughput of the
waste material in the vessel; [0074] a voltage adjustment means for
arranging the voltage responsive to the throughput; such that a
heat input associated with such discharges can be adjusted
responsive to the throughput by adjusting the voltage.
[0075] The conductive elements can be consumable electrodes, each
of the consumable electrodes formed by a plurality of substantially
linear elements, each of the elements having ends, in particular
screwed ends that are adapted to engage with another adjacent
element, wherein an electrode restoring means is provided for
restoring a consumed part of the electrode, the electrode restoring
means comprising: [0076] a positioning seat, for positioning an
electrode element close to an electrode end, the electrode end
protruding out from the vessel, [0077] an electrode joining means
for joining an end of the element to the electrode end, [0078] an
actuator for pushing the electrode through the wall of the vessel,
[0079] a gas-tight seal such that during the electrode progression
air leakages into the vessel are hindered.
[0080] The gas extracting means is preferably connected to a high
temperature gas post-treating apparatus, as above described. This
is preferably a tubular vessel, which is so-called eductor, which
has a gas inlet port and a gas outlet port. A water or steam dosing
means is provided at the inlet port of the eductor, as well as a
couple of electrodes is provided between which a voltage is applied
that is suitable for changing a gas that is flowing between the
electrodes into a plasma. The outlet port of the eductor is
connected to a quick cooling means, for example to a heat
exchanger, which is suitable for quickly cooling down the gas, such
that the formation of such harmful substances as dioxins and furans
is prevented.
[0081] Preferably, a purification means is provided to remove
hydrogen sulphide from the extracted gas, in particular a means for
causing the gas to contact with a solution of ferrous oxides and/or
salts.
[0082] At the end of the gas circuit, a vacuum device is provided
for creating and maintaining suitable vacuum conditions inside the
vessel and the circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0083] The invention will now be made clearer with the following
description of an embodiment thereof, exemplifying but not
limitative, with reference to the attached drawings wherein:
[0084] FIG. 1 is a flow-sheet that shows the steps of the method
according to the invention;
[0085] FIG. 2 shows schematically a vessel where a transformation
of a waste material takes place;
[0086] FIG. 3 is a cross sectional view of a screw conveyor for
feeding the vessel of FIG. 2 with substantially loose or
conventionally packed waste material;
[0087] FIG. 4 is a cross sectional view of a feeding means for
waste material that is packed inside rigid capsules;
[0088] FIGS. 5' to 5'''' show the liquid extracting means according
to the invention, and the method for extracting a prefixed part of
the substantially liquid residual material from the vessel.
[0089] FIG. 6 is a shows schematically the device for restoring the
electrodes inside the vessel;
[0090] FIG. 7 shows schematically a vessel that is similar to the
vessel of FIG. 2, as well as a device for post-treating and
exploiting the fuel gas that is obtained from the vessel, including
gas combustion and exhaust gas cleaning.
DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS
[0091] With reference to the flow diagram of FIG. 1, a method 100
is described for transforming a waste material, according to the
invention. Method 100 comprises a step 110 of prearranging a
vessel, a step 111 of heating the vessel up to a conversion
temperature, which is normally set between 1600 and 2000.degree.
C., as well as a step 112 of depressurizing the vessel to an
absolute pressure, which is preferably set between 1 and 10
millibar, and most preferably about 4 millibar. Depressurizing step
112 is followed by a step 120 of introducing the waste material
into the vessel; step 120 is carried out in such a way that air is
prevented from entering into the vessel together with the waste
material, which would cause vacuum loss and combustion of a part of
the waste material. The conversion temperature is high enough to
cause and maintain a transformation step 130 of the waste material
into two fractions, a ionic gas 11, i.e. a plasma, and a
substantially liquid fraction 9 that is accumulated in a bottom
part 204 of vessel 201, forming a liquid head height H (FIG.
2).
[0092] The waste material can be a substantially solid and loose
material 5, which is continuously fed into vessel 201 in a compact
form, for instance by means of a converging screw conveyor 40 (FIG.
3) to prevent air from leaking into vessel 201 together with waste
material 5, which would cause vacuum loss. The method also provides
feeding into vessel 201 a waste material that is packed in rigid
capsules 51a-d (FIG. 4); in this case, a gas-tight engagement is
provided between capsules 51a-d and a plug conveyor 300 to prevent
air from entering into vessel 201. The method provides also feeding
a liquid and/or gas waste material 6, below liquid head height H
that accumulates in the bottom part 204 of vessel 201.
[0093] During transformation 130, heat is needed to maintain the
conversion temperature. The heat is supplied by electric discharges
20 that take place in substantially liquid residue 9 collected in
bottom part 204 of vessel 201.
[0094] Along with step 130, an extracting step 140 is provided for
extracting gas 11 from vessel 201, followed by a plasma-purifying
step 141, in which residual harmful compounds and impurities are
separated from gas 11, which is still maintained in the state of
plasma.
[0095] Step 141 is followed by a step 142 of quick cooling or
quenching gas 11, in order to prevent the formation of dioxins,
furans and other partially oxidized harmful substances, and by one
or more final purifying steps which may comprise one or more
filtering steps 143; a washing step 144 may also be provided to
remove such compounds as hydrogen sulphide from gas 11. Finally, a
step 145 may be provided of feeding purified gas 11 to a conversion
device, for example a boiler, in order to recover heat from the
process, or to a gas turbine or an endothermic motor, to obtain
electric energy.
[0096] Referring now to liquid residue 9, a step 150 is provided of
detecting liquid head height H (FIG. 2); the detected height value
is sent to a human operator or to an automatic control unit, not
shown, which carries out a step 151 of comparing detected head
height value H and a prefixed reference head height value H*. Step
151 enables to take a decision whether a step 152 of opening the
vessel must be actuated, in order to allow a subsequent step 153 of
extracting a part of substantially liquid residue 9 from vessel
201, in order to maintain or restore reference height value H*,
which is set between a prefixed minimum head height value and
maximum head height value.
[0097] Step 152 is preferably carried out by breaking or removing a
plug 26 of hardened liquid residue 9 through an outlet mouth 19 in
the wall 28 of bottom part 204 of vessel 201 (FIGS. 2, 5'); at the
end of step 153, a step 154 of blocking the outlet mouth or the
hole 19 of vessel 201 is carried out by spontaneous hardening of an
amount of substantially liquid residue 9 at outlet mouth 19, which
forms a new plug 26 (FIG. 5'''').
[0098] Step 150 can be carried out, for example, by means of an
ultrasonic level sensor 30 (FIG. 2).
[0099] Electric discharges 20, which allow heating and maintaining
the conversion temperature, take place below the head of the
substantially liquid residue, between two electrodes 67 and 68,
among which a predetermined voltage V is maintained. The intensity
and/or the frequency of electric discharges 20 depend/s upon
voltage V. The method provides furthermore, a step of adjusting
voltage V responsive to the feed rate of waste material 5 or 6, or
responsive to a parameter that is representative of the feed rate,
such as the speed of a screw 46 or of a plunger that causes the
introduction of waste material 5 into vessel 201.
[0100] The electrodes, in particular graphite electrodes, are
normally subjected to consumption during the process. For this
reason, a step 160 of detecting the length of residual electrode is
carried out along with step 130; for example, a length of the
portion of electrode that is immersed in the liquid, or the portion
present in vessel 201. The residual length value is sent to a human
operator or to an automatic control unit, not shown, which carries
out a step 161 of comparing residual length value E and a prefixed
residual length reference value E*. Step 161 enables to take a
decision whether a step 162 of adding an electrode element must be
performed, in such a way that reference value E* is restored, along
with a normal position of the electric discharge region. If two
electrodes are present, one of them is normally consumed more
quickly than the other, which is taken into account in step 162
still in order to maintain the shape and the position of the
electric discharge region.
[0101] FIG. 2 shows vessel 201 of an apparatus that carries out the
method 100. Vessel 201 is vertically arranged, and comprises a
middle cylindrical part 202, and two round end portions 203 and
204. The round shape of the end portions, associated with a
suitable wall thickness, allows creating high vacuum conditions
inside vessel 201, as provided by the method 100, without any risk
of implosion.
[0102] For the introduction of solid waste material 5, a gas-tight
introduction means 10 is provided that prevents air or gas passage
from a storage place, not shown, of waste material 5, into vessel
201. Gas-tight introduction means 10 is selected according to the
nature of solid waste material 5, as shown in FIGS. 3 and 4,
respectively referring to a loose waste material, and to a waste
material that is packed in rigid capsules 51a-e.
[0103] For the introduction a solid or liquid waste material 6, a
duct 13 is provided, which has an outlet end preferably below a
normal head of substantially liquid residue 9 that is contained in
vessel 201. Along duct 13 a flow meter is provided, which produces
a gas/liquid flow rate signal that is used by a control unit 23 to
adjust voltage V between electrodes 66 and 67.
[0104] Due to the exposition to the conversion temperature and to
the substantial absence of oxygen in vessel 201, waste materials 5
and 6 undergo a molecular rearrangement, by which a gas 11 is
formed, as well as a substantially liquid residue 9, which is
collected in the bottom part 204 of vessel 201. Substantially
liquid residue 9 comprises a lava that derives mainly from an
inorganic portion of waste materials 5 and 6, and that has a very
high specific weight, normally about ten with respect to water
specific weight. By hardening, residue 9 forms a glassy, hard,
high-melting and not leachable material that is able to embed
harmful compounds that may be present in the original waste
material in particular, heavy metals.
[0105] Gas 11 evolves from waste material 5 while falling down
inside vessel 201, and from substantially liquid residue 9. Gas 11
derives from an organic portion of waste materials 5 and 6, and
contains mainly carbon monoxide, hydrogen, together with minor
amounts of carbon dioxide and water. Gas 11 is therefore adapted to
be used as a fuel in a conversion device, to recover energy from
the process. On the other hand, gas 11 may contain solid
particulate, comprising mainly inorganic materials like metals, as
well as carbon that formed in the vessel due to the high
temperature to which the organic portion of waste material 5 and 6
is exposed. Gas 11 is continuously extracted through a duct 12, and
is sent to a sequence of purifying devices (FIG. 7) to obtain a
gas, such as a syngas, that is suitable to be burnt in an energy
conversion device like a boiler, a gas turbine, or an endothermic
motor.
[0106] The conversion temperature in vessel 201 is ensured by the
heat that is produced during electric discharge 20. For causing
such discharge, a voltage V is applied between electrodes 21 and 22
by a voltage generating means 23. Voltage generating means 23
receives a feed rate signals 24 from a feed rate measuring device
26 and a flow rate signal 25 from a flow rate measuring device 27;
signals 25 and 26 are respectively related to solid waste material
5 feed rate and to liquid/gas waste material 6 flow rate, and are
used by generating means 23 to adjust voltage V, and therefore
frequency and/or intensity of discharge 20. This way, the heat that
is produced by discharge 20 is appropriate to treat the amount of
waste material 5 and 6 that is currently introduced in vessel
201.
[0107] Walls 28 of vessel 201 comprise a first layer that is made
of bricks (not shown) that have respective engaging portions that
are adapted to engage with corresponding portions of a plurality of
bricks. The bricks are made of a refractory material, for example
aluminium oxide. Walls 28 comprise furthermore a refractory
flexible second layer. Outside the second layer a coil or a jacket
is provided, which allows a cooling fluid to lap the outer face of
the second layer, in order to limit the temperature of the wall and
possibly to recover heat.
[0108] An ultrasonic level sensor 30 that emits ultrasonic pulses
31 is provided to detect head height H; such sensor is connected to
a control unit 32 with a display 33 where current value of head
height H can be read.
[0109] FIG. 3 shows a screw conveyor 300 for introducing a loose
substantially solid waste material 5 into vessel 201, for example a
municipal waste or a ground tire material. Screw conveyor 300
comprises: [0110] a hopper 38 with a vertical axis 39, [0111] an
introduction duct 40 that is arranged below hopper 38, in which a
recess 41 is made that extends between an end 42 that communicates
with hopper 38 through passage 43 and an end 44, opposite to end
42, which communicates with vessel 201 through an inlet port 56.
Recess 41 is convergent towards end 44 according to a predetermined
conical shape. [0112] a screw 46 that is pivotally arranged within
recess 41 and passage 43, with a helical profile 49 whose outer
diameter decreases according to the conical shape of recess 41.
[0113] This way, waste material 5, periodically or continuously
renewed in hopper 38 by a hopper feeding means, not shown, is
continuously conveyed by screw 46 through recess 41 into vessel
201. While being conveyed, waste material 5 is shrunk and compacted
along recess 41 and, at the same time, it is heated by contacting
hot wall of duct 40, up to provide a compact and crumbly mass that
prevents air from leaking into vessel 201 through hopper 38 and
recess 41, even if end 44 is at a pressure less than atmospheric
pressure. Once inlet port 56 has been achieved, the mass of waste
material 5 falls down inside vessel 201 and disintegrates. Screw 46
is conventionally supported, for instance by a ball bearing 48,
which is located in the wall behind duct 40.
[0114] FIG. 4 shows a plug conveyor 400 for introducing into vessel
201 capsules 51a-d in which a waste material is sealed, in
particular a harmful waste material like a hospital or surgery
waste, and which would not be safe to open before feeding into
vessel 201. Plug conveyor 400 comprises an introduction duct 52
that has a preferably cylindrical duct 53 with an inlet end 54 that
receives capsules 51a-e, and an outlet end 55, opposite to end 54,
which communicates with an inlet port 56 of vessel 201. Capsules
51a-e have preferably a central cylindrical portion, whose outer
dimensions allow moving the capsules through duct 53 under the
action of a force 57, and provide a gas-tight seal that prevents
air inlet into vessel 52 together with waste material. In general,
when a capsule 51a-e enters into vessel 201 through outlet end 55,
there is at least one capsule that forms the gas-tight seal at
inlet end 54 of introduction duct 52; in the example of FIG. 4
there are two further following capsules 51c-d that form the
gas-tight seal.
[0115] FIGS. 5' to 5'''' show an accumulation/extraction cycle of
substantially liquid residue 9 in bottom part 204 of vessel 201. In
particular, a screw conveyor 16 is arranged within an outlet duct
15, which is in turn arranged through a hole 19 of a wall 28 of
vessel 201; screw conveyor 16 (FIG. 5') is kept in a prefixed
position within outlet duct 15 by a plug 26 formed by an amount of
substantially liquid residue 9, which has been naturally hardened
due to the exposition to room temperature outside vessel 201. Screw
conveyor 16 is actuated by an electromechanical actuator, not
shown, and is adapted (FIG. 5'') to break plug 26 by a rotation
according to a prefixed direction 17; by rotating screw conveyor 16
in a direction 17' opposite to direction 17 (FIG. 5''') it is
possible to assist extracting substantially liquid residue 9 from
vessel 201. Once the head has fallen to a height value H.sub.1,
(FIG. 5''''), which is no longer enough to allow outflow of residue
9 through hole 19 and duct 15, plug 26 is naturally restored by the
hardening of an amount of substantially liquid residue 9 that
remains inside duct 15. Head H.sub.1 is a head at which hydrostatic
pressure of substantially liquid residue above duct 15 equals
atmospheric pressure external to vessel 201, the internal absolute
pressure of vessel 201 being negligible with respect to atmospheric
pressure.
[0116] Electrodes 21 and 22 are preferably made of graphite, and
are therefore consumed during transformation of waste material. In
order to periodically restore the appropriate length of electrodes
20 and 21 without undesired air inlet and/or frequent treatment
stops, each electrode is formed by modules 59/60, as shown in FIG.
6, which have screw threaded portions 68 for reciprocal engagement.
and vessel 201 comprises an electrode restoring means 36, for
restoring electrodes 21 and 22. Electrode restoring means 36
comprises a seat 63 for positioning a screw threaded module 60, in
which module 60 can be rotated, and a means 61 for joining module
60 with modulus 59; electrode restoring means 36 comprises
furthermore two couples of counter rotating wheels 58 for causing
electrodes 21 or 22 to advance through wall 28 into vessel 201, and
a gas-tight seal 64, which is engaged by electrode 21 or 22 during
the movement towards inside vessel 201. In particular, wheels 58
can be operated automatically according to a program means residing
in a control unit 35 (FIG. 2), which is suitable to set two
different advancing speeds for electrodes 21 and 22, to maintain
the relative position of zone 66 and 67 of electrodes 21 and 22
where electric discharges 20 take place.
[0117] With reference to FIG. 7, the gas extracting means 202 are
connected to a post-treatment apparatus, which comprises a tubular
vessel 210, called the eductor, which has an inlet port 211 and an
outlet port 212. At the inlet port 212 a means 213 is provided for
dosing water and/or steam in the gas flow, as well as two
electrodes 214, among which a voltage V1 is applied suitable for
changing the flow of gas 11 into a plasma torch, or to maintain the
plasma state of gas 11. Outlet port 212 of eductor 210 is connected
to a heat exchanger 220, which is suitable for quickly cooling or
quenching gas 11, in order to prevent the formation of such harmful
compounds as dioxins and furans. Heat exchanger 220 is followed by
an absorber 230 where gas 11 comes into contact with an aqueous
solution of ferrous oxide and/or ferrous salts, in order to remove,
in particular, hydrogen sulphide H.sub.2S.
[0118] After exchanger 220, conventional gas/solid separation means
240 are provided such as a cyclone separator, an electrostatic
filter or an activated carbon filter. Once purified, gas 11 is
sucked by a compressor or a vacuum pump 250 adapted to create a
predetermined vacuum degree in vessel 201 and in the circuit
engaged by gas 11. Gas 11 is then fed to a combustion chamber 260
of an energy converting device, for example a boiler to recover
thermal energy or a gas turbine, or an endothermic motor to produce
electric energy. Exhaust gas that flows out of the combustion
chamber 260 is treated in a further eductor 270, preferably
equipped with a gas diffuser 280 to diffuse the gas that is
released to atmosphere.
[0119] The foregoing description of specific embodiments will so
fully reveal the invention according to the conceptual point of
view, so that others, by applying current knowledge, will be able
to modify and/or adapt for various applications such embodiments
without further research and without parting from the invention,
and it is therefore to be understood that such adaptations and
modifications will have to be considered as equivalent to the
specific embodiments. The means and the materials to realise the
different functions described herein could have a different nature
without, for this reason, departing from the field of the
invention. It is to be understood that the phraseology or
terminology employed herein is for the purpose of description and
not of limitation.
* * * * *