Note: Descriptions are shown in the official language in which they were submitted.
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FIBREGLASS BIN AND WASTE INCINERATION METHOD
DESCRIPTION
Domain of the invention
The invention relates to melting and incineration of more or less toxic
metallic, organic and inorganic materials and waste, such as oxides, glass,
phosphates
and metals, in a furnace.
Prior art and problem that arises
Several methods are currently used to incinerate and/or vitrify mixes
of metallic, organic and inorganic waste in a continuous feed furnace. The
waste is firstly
ground and continuously delivered into the furnace. This solution has the
advantage of
continuous operation of the incinerator and it minimises the size of the
furnace and
treatment of gases. However, this solution requires prior grinding of the
waste that may
be difficult in practice.
A second solution consists of introducing unground waste in packets,
through a lock separating the internai atmosphere of the furnace from the
external
atmosphere. This second solution avoids grinding but it introduces a number of
risks and
problems, namely:
1) difficult manipulation of waste packets in the inlet lock with a risk of
melting or flow of organic materials in the lock subsequent to the temperature
rise
when the furnace side lock door is open;
2) risk of inflammation of organic materials in the lock and overheating
in this lock and its closing systems;
3) a risk of excessively fast combustion of the added waste packet as it
is introduced into the furnace. This requires oversizing of the oxidising gas
supply and of
the gas treatment installation;
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4) a risk of mechanical entrainment of flyash and toxic elements during
fast combustion of the waste packet.
In the current state of the art, the metal container containing the
waste can be used as a shuttle to bring waste into the furnace. In this case,
it can
gradually be cut in the furnace to limit the combustion rate, but it can no
longer be
recycled and it accounts for a non-negligible proportion of the final waste.
The cutting system, for example using a plasma torch installed in the
furnace is also complex and expensive. One alternative consists of placing the
waste
packet in a cardboard box that acts as a shuttle. This solution limits risks
in the lock but it
does not solve the problem of the combustion rate of the waste packet as soon
as the
cardboard box has burned.
Therefore the purpose of the invention is to avoid the above-
mentioned disadvantages related to the solutions described above by presenting
another method and another device for adding waste into the furnace.
Furthermore, with French patent application FR 2 293 769, an
installation intended for a radioactive waste conditioning press is known in
which a
receptacle is burned with its contents, and this receptacle is made from glass
fibre
among other materials.
Presentation of the invention
A first main objective of the invention is a basket that will contain
waste to be inserted into and incinerated in an incinerator.
According to the invention, this basket is composed of a glass fibre
envelope, among other materials. Ash from combustion may be melted in the
furnace,
within a molten glass bath. In this case, the basket formed particularly by
the glass fibre
envelope containing ash or combustion residues from the waste will be
dissolved in the
glass bath.
The first embodiments use a lightweight metal structure to increase
the stiffness of the basket. This metal structure is preferably composed of a
mesh.
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According to a first embodiment, said lightweight metal structure is
external and an internai envelope composed of glass fibre is located inside
the
lightweight metal structure.
ln a second embodiment, this envelope composed of glass fibres is
external and the lightweight metal structure is internai and therefore located
inside the
glass fibre envelope.
The glass fibres forming the envelope can also be woven, weaving
having a mesh size defining a porosity adapted to the type of waste so that
the pyrolysis
rate of this waste can be thermochemically controlled.
ln this case, it could be envisaged that the lightweight metal structure
could be composed of a mesh for which the wires are included in the fibre
weaving, thus
forming a single envelope.
A second main purpose of the invention is a method for vitrification of
waste in a waste vitrification incinerator.
According to the invention, it comprises at least two phases consisting
of:
-placing the waste to be incinerated in a glass fibre basket like that
defined above to be kept in it in a gas atmosphere above a molten glass bath;
and
-perform pyrolysis and a combustion for a duration longer than a
pyrolysis and combustion of waste without a basket (the incineration time is
multiplied
by a factor of three or even ten depending on the basket), so that complete
combustion
can be achieved without the presence of carbon monoxide in the incinerator
exhaust
gases.
Preferably, after complete combustion of the waste, the glass fibre
basket containing waste combustion residues is dissolved in the glass bath.
List of figures
The invention and its technical characteristics will be better
understood after reading the description that is accompanied by several
figures
representing the following respectively:
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-figure 1, a sectional view of a first embodiment of the basket
according to the invention;
-figure 2, a sectional view of a second embodiment of the basket
according to the invention;
-figure 3, a sectional view of a third embodiment of the basket
according to the invention;
-figure 4, a graph illustrating operation of the method according to the
invention; and
-figure 5, a sectional view of a fourth embodiment of the basket
according to the invention.
Detailed description of several embodiments of the invention
The concept according to the invention consists of putting the waste
packet to be incinerated into a basket composed largely of unwoven or more or
less
tightly woven glass fibre. The tightness of the glass fibre(s) makes it
possible to manage
contact between the contained waste and the hot and oxidising atmosphere
inside the
incinerator, weaving allowing variable thermal and gas exchanges. The basket
is
preferably stiffened by a lightweight metal structure.
The use of non-combustible glass fibre with a high melting point allows
mechanical transfer of the waste bag from the waste inlet lock to the
incineration zone,
thus preventing any loss of content of the basket during the transfer.
The principle of using the glass fibre for making the basket is that this
glass fibre surrounds the waste basket and thus delays its temperature rise.
This
prevents excessively fast fusion and/or pyrolysis of the organic waste,
particularly during
transfer from the inlet lock to the incinerator.
In the furnace (or incinerator), the content of the basket, namely the
waste, is heated progressively. This temperature rise leads to pyrolysis of
organic
materials. Pyrolysis gases escape from the basket to burn in the oxidising
atmosphere of
the furnace. The choice of the glass fibre envelope that partly forms the
basket, and its
porosity and the tightness of its weaving can slow heat transfers towards the
inside of
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the basket and gas transfers towards the outside. Thus, the size of the woven
mesh is
adapted to the type of waste. Therefore this can manage the pyrolysis and
combustion
rate of the waste contained in the basket. This thus minimises the size of gas
gusts
generated by sequential inlet of complete waste bags into the incinerator.
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Furthermore, the porosity of the glass fibre envelope forming the
basket with its more or less tight weaving, also helps to minimise losses of
ash and non-
volatile toxic elements contained in the gases inside the incinerator.
Therefore this
porosity can be adapted to the size of the solid toxic particles which must
not be
entrained in the gases.
With reference to figure 1, according to a first embodiment of the
basket according to the invention, the envelope 10 composed of glass fibre is
located
inside the lightweight metal structure 12. This lightweight metal structure is
welded to
the bottom of the basket that is advantageously composed of a drip pan 18
located
below the envelope 10. The mesh advantageously forming the lightweight metal
structure 12 is preferably cylindrical and is welded at the top to a metal
tube 16 that will
stiffen it. The function of the drip pan 18 forming the bottom of the basket
is to collect
any metal drops or other molten material drops if the waste contains this type
of
material with a low melting point that could, for example, melt prematurely in
the inlet
lock (in another type of embodiment the drip pan could be made of very tightly
woven
glass fibres that are made practically leak tight to liquids). In this
embodiment, the entire
basket is completed by a gripping handle 14 fixed on and above the metal tube
16.
In one example of this embodiment, the inside diameter of the
envelope 10 made of glass fibre is equal to about 500 mm and its height is
about
750 mm. In this case, the weight of the envelope is of the order of 1 kg for
glass fibre
woven at 45' with a mass per unit area equal to 600 g/m2. The drip pan 18 is
preferably
made of stainless steel and its thickness is of the order of one millimetre.
The mesh
forming the lightweight metal structure 12 is a stainless steel wire with a
diameter of
between 2 and 5 mm.
In this first embodiment, the large outside diameters for manipulations
of the basket in the lock and in the incineration zone are fixed by the
lightweight metal
structure 12 used.
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With reference to figure 2, the second embodiment according to the
disclosed invention uses a glass fibre envelope 20 located outside the
lightweight metal
structure 22. This lightweight metal structure is also composed of a
cylindrical mesh
welded at the top to a metal tube 26 above which there is a gripping handle
24. The
base of the assembly is preferably composed of a drip pan 28 that can be
installed inside
the glass fibre envelope 20. In this embodiment, this makes it easier to fill
the basket
with waste.
With reference to figure 5, the mesh wires forming the lightweight
metal structure 52 are integrated into the weaving of the glass fibre forming
the
envelope 50. The drip pan 58 can then be installed inside or outside the glass
fibre
envelope 50. In the embodiment shown, the glass fibres forming the envelope
pass
alternately on opposite sides of the mesh wires forming the lightweight metal
structure
52. This version is difficult to make, but it combines the advantages of the
two
previously disclosed embodiments.
With reference to figure 3, according to a third embodiment, the
basket comprises two glass fibre layers 30A and 30B placed one inside the
other. The
function of the outer layer 30A is to filter pyrolysis gases to remove dust.
The function of
the inner layer 30B is to contain waste with appropriate mechanical strength
properties.
Note that the function or the position of the two layers could also be
inverted. These
two layers 30A and 30B are preferably separate. The lightweight metal
structure 32 is
then located between these two layers 30A and 30B. These three elements 30A,
30B
and 32 may be attached to each other by stitching with glass fibres or metal
wire.
Therefore the incineration method according to the invention uses the
basket mentioned above to incinerate waste inside an incinerator for a
duration at least
fifteen minutes longer than for pyrolysis and combustion of waste without a
basket
(incineration time increased by a factor of three or even ten depending on the
basket).
The waste is thus placed above a molten glass bath above which there is a
combustion
zone in an atmosphere of oxygen diluted in argon and heated by arc plasma
transferred
between two electrodes.
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Figure 4 shows water, carbon dioxide and carbon monoxide contents in
outlet gases from the vitrification incinerator as a function of time. Water
is shown in
dashed Unes, carbon dioxide in thick lines and carbon monoxide in thin lines.
ut can be seen that if waste is sent directly to the surface of a molten
glass bath, at time denoted 16h45, the duration of pyrolysis and combustion is
very
short, in other words of the order of 3 minutes and the added oxygen is
insufficient to
guarantee complete combustion of the gust of pyrolysis gas. There is a
remaining
content of the order of 3 to 4% of carbon monoxide in the gas at the outlet
from the
reactor.
If a basket according to the invention is used, particularly together with
its glass fibre envelope, waste is kept suspended above a melting glass bath
at time
marked 15h42. Its combustion time is increased to 17 minutes until time marked
15h59.
This can give complete combustion without the presence of carbon monoxide in
the
reactor outlet gases.
This result is obtained with the glass fibre envelope acting to retard the
beginning of combustion 1, and delay pyrolysis / combustion. This results in
complete
combustion of waste without oversizing the installation, and particularly the
supply of
oxidising gas and gas treatment. It also very much minimises the presence of
combustion gases at the outlet from the installation.
