Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
Method and apparatus for high temperature heat treatment
of combustible material in particular waste
DESCRIPTION
Field of the invention
The present invention relates to an apparatus for
high temperature heat treatment of combustible material,
in particular industrial and municipal waste of any kind,
even toxic or noxious waste, for minimizing the
dangerousness of the combustion products. Furthermore, the
invention relates to a pyrolytic converter for recovering
the energy content of said waste.
Description of the prior art
It is well known that systems traditionally used for
waste disposal, in particular municipal solid waste,
provide either burying or burning the waste. Either
solution has problems of environmental impact. In case of
waste burying the risk is high of polluting for a very
long time the underlying ground water table owing to
percolates, whereas in case of burning, even if macro-
pollutants such as particulates and smoke can be retained,
the amount is high of micro-pollutants introduced in the
environment.
In the last years attempts have been made for
alternative systems. In particular, waste pyrolytic
processes have been proposed, i.e. heat treatments for
transformation of large molecules into simpler substances.
This transformation is made in an environment poor in
oxygen and at a high temperature enough to volatilize the
organic pollutants. More in detail, without oxygen, i.e.
in a reducing environment, pyrolysis causes the
thermochemical decomposition of the material. The process,
for its endothermic nature, causes the scission of the
complex molecules that form rubber, plastics, cellulosic
CONFIRMATION COPY
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components and other complex chemical components, turning
them into structurally simpler molecules.
This way, at the end of the pyrolytic process a gaseous
combustible mixture is obtained that can be used, for
example, for feeding a gas turbine and producing, then,
electric energy. More in detail, the combustion of the
waste causes a thermal decomposition and mineralisation of
the many organic substances contained in the waste and a
transformation of inorganic substances into more easily
separable species, which can be recovered or can be safely
disposed of, thus allowing a huge reduction of the weight
and of the volume of the waste (reaching up to 10% of the
starting volume).
The waste that can be treated in this type of plants
may be residues from paper, plastics, rubber converting
processes, tyres, as well as combustible material obtained
from biomass, such as wood and agriculture residues, and
even organic material such as waste of hospitals or
toxic/noxious industrial waste.
The substances emitted in the traditional combustion
processes are the following: dust, carbon monoxide,
sulphur dioxide, nitrogen oxides, hydrochloric or
hydrofluoric acid, heavy metals and chloride-organic
substances (dioxins and furans).
In particular, the presence of dioxins and furans in
the exhausted flue gas causes a strong environmental
impact of the existing processes. The production of
dioxins and furans occurs mainly owing to a not full
combustion of the waste products. For minimizing the
creation of these highly polluting substances, the
combustion process must provide: the supply of a
sufficient amount of oxygen, a high temperature and long
time of contact. Alternatively, the resulting dioxins and
the furans can be filtered with the aid of activated
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carbon (with very high costs of operation) or other
filtering systems.
However, the existing apparatus for burning waste, for
example of the type described in US 3759036 and US
4732092, is not always capable of avoiding the emission of
pollutants so that theyfall within the limits provided by
the environmental laws. In other cases, instead, it is
possible to fall within said limits only with the use of
structurally complicated and expensive apparatus, in
particular concerning the energy necessary for completing
the process.
Summary of the invention
It is a feature of the present invention to provide a
waste heat treatment method that provides a strong
reduction of the pollutants present in the flue gas with a
considerable energy saving with respect to the solutions
of prior art.
It is also a feature of the present invention to
provide a waste heat treatment method for conveying the
gas products within a burning apparatus even in the
presence of very high temperature.
It is also a feature of the present invention to
provide such a waste heat treatment method that allows to
obtain an optimal recovering of the energy content of said
waste.
It is, furthermore, a feature of the present invention
to provide a pyrolytic converter that carries out this
method.
These and other features are accomplished with one
exemplary method for high temperature heat treatment of
combustible material, in particular of waste, said heat
treatment being carried out between a pyrolysis chamber,
where said combustible material is heated in a reducing
environment, and a combustion chamber, where said
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combustible material is completely burnt by introducing a
current containing oxygen. The main feature of the method
is that in the pyrolysis chamber gas at high
temperature and vapour are inserted, said introduction
causing the production of semiwater gas. The gas at high
temperature is burnt gas drawn downstream of the
combustion chamber. The semiwater gas formed in -the
pyrolysis chamber, once reached the combustion chamber, is
burnt causing a considerable rise of the combustion
temperature. In other words, in the pyrolysis chamber the
combustible material is heated in a reducing environment
up to a determined temperature suitable for causing a
preliminary combustion, obtaining partially burnt material
and semiwater gas, comprising air gas and water gas. In
the combustion chamber, located downstream of the
pyrolysis chamber, the partially burnt material and the
.semiwater gas are then fed and subjected to a further
oxygenation/combustion with production of a gaseous
mixture at high temperature.
In particular, the production of semiwater gas in the
pyrolysis chamber is carried out sending a vapour jet and
a gas jet at high temperature on the burning material
which is arranged on a grid, and then the burning material
reaches the combustion chamber by moving the grid.
Advantageously, the semiwater gas reaches a predetermined
zone of the combustion chamber according to a path
different from that of the combustible material.
In particular, the gas at high temperature produced in
the combustion chamber can cross a post-combustion chamber
within which a further heating is effected by feeding a
further current containing oxygen with completion of the
combustion. Then, the burnt gas produced in the post-
combustion chamber, having a low oxygen content, is sent
to the pyrolysis chamber.
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In a preferred aspect of the method according to the
invention, the gas produced in one of the chambers is
transferred between a starting chamber and an arrival
chamber by a system comprising a conveying fluid current
5 that is supplied within a duct that connects the chambers
same. The said conveying fluid is fed into the duct direct
towards the arrival chamber at a suitable speed to cause a
suction of the gas inside. More in detail, both the high
speed of the conveying fluid and its expansion, which
occurs at the outlet arrival chamber, attract in the duct
the same gas to convey, i.e. the semiwater gas or the
burnt gas. The attraction, therefore, on one hand occurs
by entrainment and on the other hand by pressure
difference between the inlet and the outlet of the duct.
The above can be exploited both for conveying the
semiwater gas from the pyrolysis chamber to the combustion
chamber, both for conveying to the pyrolysis chamber the
gas at high temperature produced in the combustion
-chamber, or the burnt gas produced in the post-combustion
chamber.
In particular, for conveying the gas at high
temperature, or the burnt gas, to the pyrolysis chamber, in
the duct conveying water vapour is fed as conveying fluid.
This way, the water vapour used as conveying fluid can be
also used to obtain water gas in the pyrolysis chamber.
The conveyance of the semiwater gas from the pyrolysis
chamber to the combustion chamber is made by sending in
the duct variably oxygenated conveying gas as conveying
fluid. More in detail, according to the process conditions
it is possible to adjust the amount of oxygen supplied.
Advantageously, the burnt gas produced in the post-
combustion chamber before being conveyed to the pyrolysis
chamber is separated from possible solid particles giving
a vortical movement to the burnt gas, which separate from
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the solid particles by centrifugal acceleration. This can
be made, for example, forcing the burnt gas against the
walls of said post-combustion chamber which are suitable
for causing said vortical movement.
Advantageously, a preliminary ignition step is
provided suitable for heating the different chambers up to
a determined temperature. In particular, the step of
heating the pyrolysis chamber provides a preliminary
ignition step for bringing the pyrolysis chamber up to a
determined temperature necessary so that the reactions
take place for the creation of air gas and of water gas.
Then, the process is auto-fed. In fact, the production of
the gaseous mixture comprising the air gas and the water
gas is made sending an air jet and a vapour jet on the
burning material in the pyrolysis chamber when it has
achieved a measured temperature. When the air jet and
the vapour jet are sent on the burning material the
semiwater gas, i.e. air gas and water gas, is produced
according to known reactions. More in detail, the reaction
that causes the production of water gas is an endothermic
reaction and the required energy is supplied by the
reaction that causes the production of the air gas that is
instead an exothermic reaction. Sending then in the
pyrolysis chamber a suitable amount of vapour and of air,
according to the parameters of process used, in particular
responsive to the composition of the combustible material,
in particular municipal solid waste, in steady conditions
an auto-fed process is obtained.
Like for the pyrolysis chamber, also in the combustion
chamber a preliminary heating step is provided suitable
for bringing the combustion chamber same to a determined
temperature, in particular this step is made before
conveying the burnt gas to the pyrolysis chamber. This to
avoid conveying in the pyrolysis chamber gas with high
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content of oxygen that would be potentially dangerous
since it could give rise to explosions and backfire.
In particular, conveying in the pyrolysis chamber at
least one part of the burnt gas produced in the post-
combustion chamber is made only when the temperature in
the different chambers has achieved determined values.
This because until the temperature in the combustion
chamber has not achieved a determined value the amount of
oxygen is very high and then it is not possible sending
the mixture of gas to the pyrolysis chamber for not to
affect its correct operation.
Advantageously, a step is provided of feeding the
combustible material in the pyrolysis chamber by forcing
it through a tapered duct in order to reduce its volume.
'This avoids dangerous backfire, provides a semi-
combustion of the combustible material and assists a
measurement of its composition, in particular on the content
of carbon in order to adjust the flows and the temperature
in the different chambers of the apparatus.
Advantageously, downstream of the heat treatment of
the combustible material treatments are provided of
reduction of the waste material. In particular, a
treatment of neutralisation is provided, which exploits
the produced heat during the heat treatment of the
combustible material making inert substances from the ashes
deriving from the combustion. More in detail, the ashes
coming from the apparatus are superheated by jets of
semiwater gas and by air at high temperature for then
melting and flowing through a crucible having an opening,
an air or vapour jet transforming it into inert grains.
Or, the molten material can be fed to special moulds,
forming bricks for the building industry.
According to another aspect of the invention, an
apparatus for heat treatment of combustible material, in
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particular waste, comprises a pyrolysis chamber where the
combustible material is heated in a reducing environment
and a combustion chamber where the combustible material is
conveyed for being completely burnt, whose main feature is
that said pyrolysis chamber comprises means for feeding a
gas at high temperature drawn from the combustion chamber
and vapour, in order to make semiwater gas which, once
reached the combustion chamber, is burnt for causing a
considerable rise of the combustion temperature.
Means can be provided for conveying the semiwater gas
from the pyrolysis chamber to the combustion chamber
according to a path different from that of the combustible
material.
Advantageously, means are provided for connecting a
starting chamber to an arrival chamber, in particular for
conveying the semiwater gas from the pyrolysis chamber to
the combustion chamber or for conveying at least one part
of the burnt gas up to the pyrolysis chamber, comprising
at least one duct communicating with both the chambers
within which a conveying fluid current is fed, the said
conveying fluid being supplied to said duct at a suitable
speed to cause a suction inside, in particular of the
semiwater gas or the burnt gas.
Advantageously, downstream of the combustion chamber a
post-combustion chamber can be provided within which the
gaseous mixture is further heated at high temperature
obtaining burnt gas by feeding a current containing
oxygen, said further heating causing a full decomposition
of the part of the gaseous mixture not yet dissociated.
Advantageously, means are provided for feeding the
combustible material in the pyrolysis chamber comprising
means for forcing the passage through a tapered duct in
order to reduce its volume.
According to an exemplary embodiment of the invention
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the means for forcing the motion of the combustible
material in the feeding duct comprise a conical track
system. In particular, the feeding means are associated to
means for measuring at least one parameter of process in
the pyrolysis chamber. This adjusts the feeding speed of
the combustible material in the pyrolysis chamber
according to the variation of the parameters of process,
in particular of the temperature in the pyrolysis chamber.
Advantageously, in each chamber ignition means are
provided suitable for giving the starting energy necessary
for activating the heat treatment of the combustible
material.
In particular, in the apparatus directional elements
can be arranged of refractory material suitable for
deflecting a flow of gas to determined zones of the
apparatus, said directional elements being arranged
between the different chambers of the apparatus.
Advantageously, in each chamber of the apparatus
directional elements are provided of the gas flow obtained
during the heat treatment of the combustible material. In
particular, the directional elements of the gas flow are
diaphragms suitably shaped of refractory material that
define the different chambers of the apparatus.
In each chamber of the apparatus, furthermore, ducts
are provided for introducing hot air.
Brief description of the drawings
Further characteristics and the advantages of the method
and apparatus for high temperature heat treatment of
combustible material, in particular waste, according to
the present invention will be made clearer with the
following description of an exemplary embodiment thereof
exemplifying but not limitative, with reference to the
attached drawings wherein:
- figure 1 shows diagrammatically a first exemplary
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embodiment of an apparatus for high temperature heat
treatment of combustible material, in particular waste,
according to the present invention;
- figure 2 shows diagrammatically an alternative
5 exemplary embodiment of the apparatus of figure 1;
- figure 3 shows a simplified block diagram of the
method for heat treatment of waste operated by the
apparatus for figures 1 and 2.
Description of a preferred exemplary embodiment
10 In figure 1 a first exemplary embodiment is
diagrammatically shown of an apparatus 1, according to the
present invention, for high temperature heat treatment of
combustible material, in particular municipal solid waste
(waste products), or combustible waste of a desired
nature, provided that it is a solid and not explosive
waste. It comprises a pyrolysis chamber 41, where the
material 85 to treat is heated in a reducing environment,
up to a temperature suitable for making a first molecular
break of the substances in it present, and a combustion
chamber 42 within which a full combustion is achieved of
the combustible material by introducing a predetermined
flow of oxygen 8. The full combustion of the combustible
material is carried out only in combustion chamber 42 of
the apparatus 1 and produces, in particular, gas at high
temperature that is directed back to pyrolysis chamber 41
in order to remarkably raise the temperature of
pyrolysis. In addition to this water vapour 86, through a
duct 6, and air 87, through a duct 7, are added into
pyrolysis chamber 41 to produce semiwater gas that is
then burnt in combustion chamber 42 by feeding a current
8 of a fluid containing oxygen to raise the combustion
temperature in order to carry out the process at a
temperature that assures the molecular break of the
totality of the toxic substances. According to the
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invention a part of the burnt gas 88 produced by the
combustion of the burning material 85 in combustion
chamber 42 is sent to pyrolysis chamber 41 through a
duct 80 by introducing a conveying fluid 81. The
current of burnt gas 82 that reaches pyrolysis chamber
41 crosses the burning material to cause the
production of the semiwater gas.
In figure 2 an alternative exemplary embodiment is
diagrammatically shown of the apparatus 1 of figure 1.
The substantial difference with the previous exemplary
embodiment is the presence of a post-combustion chamber
43 downstream of combustion chamber 42. In both cases a
preliminary step is always provided of feeding the waste
subject to heat treatment in pyrolysis chamber 41
through a tapered duct 20, block 101 of figure 3. In
duct 20 the waste is preheated up to a temperature of
about 300 C exploiting the heat produced in
pyrolysis chamber 41, and that may be assisted with the
use of a electrical resistance, not shown in the figure,
arranged along the duct same. The feeding of the waste
through duct 20 is effected by a system of toothed
tracks 55 that at the same time compress and push
forward the waste that in pyrolysis chamber 41 roll on a
first hot deflector 61 and then fall on a
movable grid 50 arranged inclined in pyrolysis chamber
41.
The feeding system above described causes a
considerable reduction of the volume of the waste and
reduces the possibility of backfire from pyrolysis chamber
41, making also easier both the steps of semi-combustion of
the waste same and a satisfactory measure of the content of
carbon in the introduced waste. The content of carbon in
the introduced waste is strictly linked to the nature of
the waste treated and is a parameter of process of primary
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importance, on the basis of which the gas flows introduced
in the apparatus are then adjusted.
In pyrolysis chamber 41 and behind combustion
chamber 42 ignition means are arranged, for example
methane gas burners 25, for bringing the temperature in
the chamber to a determined temperature beyond which the
system practically is auto-fed and does not require other
supply of energy from the outside. Once achieved the
determined temperature, in fact, the burner 25 can be
deactivated, since the material present in the pyrolysis
chamber continues burning for the heat transmitted for
conductivity from the combustion chamber. In steady
conditions the temperature in the pyrolysis chamber is
about 800-900 C and allows to gasify a large part of the
material deposited on grid 50, block 102 of figure 2.
Once achieved a determined temperature in
pyrolysis chamber 41 an compressed air jet 11 and a
water vapour jet are directed onto the material at high
temperature to create a semiwater gas comprising water
gas and air gas, as previously said, according to known
reactions. In particular, the reaction that causes the
production of the air gas is an exothermic reaction
i.e. it occurs with release of a certain amount of
energy, which is used for the reaction that produces
water gas, which is instead an endothermic reaction,
i.e. it occurs with absorption of energy. On this basis
the system can be said as completely auto-fed.
The semiwater gas produced as above has a heating
power that even if not comparable to that of
traditional fuel, is in any case high enough because when
burning it an amount can be obtained of energy to cause a
further remarkable rise of the temperature. In order to
exploit the potentiality of the semiwater gas versus
energy, the gas is in part transferred from pyrolysis
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chamber 41, where it has been just produced, to combustion
chamber 42. The semiwater gas can be conveyed, for
example, through a duct 21 in which a conveying fluid
passes and connecting pyrolysis chamber 41 with
combustion chamber 42. More in detail, into duct 21 a
conveying fluid current is fed at a suitable speed to
cause a suction of the semiwater gas inside, also owing
to the expansion of the conveying fluid same that occurs
when it reaches combustion chamber 42. In particular, in
duct 21 two channels are arranged, a first channel fed
with air with a variable oxygen content according to the
process needs, and the second channel fed with a current
of vapour. This exemplary embodiment avoids the use of
fans or other propelling systems to convey the
semiwater gas, with a considerable energy saving and
reduction of maintenance costs. The vapour is
superheated in a way not shown using the heat of the
burnt gas.
From the pyrolysis chamber the partially burnt
material present on grid 50 burns in low oxygenated
conditions and forms a "brazier" that is repeatedly
transferred to combustion chamber 42, block 103. This is
made by grid 50 that is moved in the direction indicated
by the arrows in the figure. At the two sides of the waste
feeding tapered duct two ducts are provided that end in
combustion chamber 42 with two spray nozzles each, one for
compressed air and one for oxygen, oriented towards the
rear part that carry the gas formed in the high part of
pyrolysis chamber 41. In pyrolysis chamber 41 sensors can
be arranged for measuring parameters of process such as
temperature, pressure and carbon content or the amount of
unburnt hydrocarbons on the basis of which are the inlet
flows are adjusted.
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In the combustion chamber 42 an almost complete
combustion of the combustible material is achieved, in
part entrained by the gas flow and in part displaced by
grid 50. The combustible material under heat treatment is
hit by jets of extremely hot air, which burning completes
the combustion of the waste, that was already carbonized
in pyrolysis chamber 41.
The gas produced by the combustion of the material
arranged on grid 50 in combustion chamber 42 move
upwards and in the higher part of chamber 42 mix with
the air and the semiwater gas flowing from
pyrolysis chamber 41 and that are burning at high
temperature (1200-1400 C).
In combustion chamber 42 a further air flow is
supplied at high temperature through a duct 11. The
warm air exits at a diaphragm 62 that divides
combustion chamber 42 from a third chamber, or post-
c-ombustion chamber 43, crossing combustion chamber 42
in the centre and oxygenating the remaining partially
burnt waste in addition to lateral semiwater gas
flows. This way, the temperature is further raised up
to about 1600 C that provides a substantially total
dissociation of the molecules present.
The burnt gas comes then to a third chamber, or post-
combustion chamber, in which they are further oxygenated by
extremely hot air coming from a duct 12. In the last part of
this post-combustion chamber, immediately behind another flow-
deflecting diaphragm 63, which, as the other two diaphragms,
is made of special refractory material, before that the "flue
gas" reaches a vapour generating heat exchanger, two
opposite and oblique vapour jets slightly cool the gas and
create a vertical current for causing the loss of solid
particles and for increasing the heat exchange coefficient
within the heat exchanger. In this zone of the plant a part of
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burnt gas is drawn back for being conveyed to the
pyrolysis chamber by means of water vapour. This can be
made, for example, by a duct 80 in which the vapour is
inserted at high pressure and at a high speed through a
5 inlet 81. The high speed of the vapour and the expansion
that is achieved at the outlet 83 when entering pyrolysis
chamber 41 attracts the burnt gas produced in the post-
combustion chamber 43 into duct 80 causing their
conveyance through it, using the same system as above
10 described for conveying the semiwater gas from pyrolysis
chamber 41 to combustion chamber 42.
The apparatus 1 for heat treatment of waste can be
coupled to systems of reduction of polluting residues.
In particular, the burnt gas coming from the post-
15 combustion chamber 43 still hot and containing residue
particles, can be "washed" and cooled further in a
scrubber, block 107. In the first part of the scrubber
any solid or gaseous substances which escaped from
dissociation in post-burner 43 are precipitated and
captured. In the second part of the scrubber, the same
reactions are repeated as in the first part, but with
addition of water and basic reactants, in order to
eliminate any residue acid substances. In the scrubber
sludge is formed that is then put in the heat treatment
cycle for being inertized.
Finally, the gas can conveyed through a
biofilter before being released in the atmosphere, in
order to provide to a complete removal of toxic and
noxious substances. The action of the biofilter
begins with a saturation of the gas, by water vapour,
to pass then to the first layer, comprising lignite
and organic carbon, in which colonies of specially
selected bacteria live. From here the gas passes
through second layer, comprising peat, also this
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containing colonies of specially selected bacteria,
different from the previous and that selectively attack
other products; in a third and last layer, formed by chips
and saw dust of wood, other bacteria are present that
together with a catalyst attack any residue possible
molecules of furans or dioxins.
Similarly, a system of reduction of any solid
residues produced by the apparatus 1 is provided, i.e.
the ashes, blocks 104 and 106. The high temperature
reached in the apparatus 1, allows melting the ashes
that are gathered in reservoir 71 located at
combustion chamber 42. The ashes already at high
temperature, are superheated by jets of water gas and
of very hot air, and are conveyed in a crucible with a
hole the centre, from which the molten material flows
and falls, entrained by a jet of compressed air or
vapour, into cold water, creating inert pellets.
Alternatively, the molten material is supplied into
moulds forming bricks, for example self-locking for
pavements or garden pathways. The hardness of the
bricks can be adjusted with the addition to the
ashes of silica and soda.
The foregoing description of a specific embodiment
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 an embodiment 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 embodiment. 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
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understood that the phraseology or terminology employed
herein is for the purpose of description and not of
limitation.
