Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Apparatus for the conversion of waste material
'rhe invention relates to apparatus for the conversion of waste material
by means of pyrolysis which comprises a fire box in which a rotating --
kiln is provided,- which kiln has means for the introduction of waste
material in one end, and means for the discharge of pyrolyzed material
at the other end. MoreoverJ the kiln is provided with an outlet for the
gas produced in the pyrolysis process
British patent specification 919920 describes a pyrolysis retort internally
provided with a helical conveyor for the transport of the waste material.
The shaft of the conveyor is supported by bearings in the cover at the
front end of the retort and actli ated with a-chain drive. The refuse is
introduced in the retort from a hopper through a tube positioned parallel
to and above the retort, provided with a helical conveyor and a vertical
connecting tube. However, since the pitch of the conveyor is the same
over its entire length and the volume of the waste material is reduced
during its passagc through thc retort, the retort is not loaded uniformly,
so that its throughput is not optimal. Another disadvantage is that hard
fragments of refuse, such as metal and glass, may be jammed between
the conveyor and the retort, thus causing material damage to these
part s .
U.S. patent 3. 780. 676 describes a pyrolysis reactor having a rotatable
kiln which is placed in an inclined-position from the waste inlet to the
discharge end of the pyrolyzed residue. The waste is introduced into
the kiln by means of a conduit with a screw conveyor, fitted centrally
in the kiln. Also in this ayparatus there is no optimal utilization of the
kiln, because as a result of the reduction in volume of the waste
material during its passage, the loading of the kiln is not uniform.
The main objective of the present invention is to provide an apparatus
for the conversion of waste material by means of pyrolysis which
ensures an even and uniIorm loading of the kiln over its entire length
and whïch avoids the danger of damage as a result of jammed fragments
of refuse.
Accordingly, the invention relates to apparatus for the conversion of
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waste material by means of pyrolysls comprising a fire box
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in which~e~ externally heated substantially cylindrical
rotatable kiln is located, which kiln is provided with means
for the introduction of waste material and means for the
discharge of pyrolyzed material and pyrolysis gas, the kiln
being provided with an internal helical strip having a
central bore, the helix having a pitch which gradually
decreases in the direction of passage of solid material
through the kiln.
While the kiln is advantageously formed as a cylinder, other
geometrical forms are also possible, such as a truncated
cone, tapering towards the discharge end of the kiln. It is
also possible to use a kiln consisting of a cylindrical part,
and a tapering part.
The helical strip may be in the form of one continuous helix
the pitch of which decreases gradually in the direction of
the passage of the solid material through the kiln. However,
to simplify the construction of the kiln it may be desirable to
divide the helix into two or more independent sections, each
having a different pitch, the pitch in the second and following
sections being smaller than the pitch in the preceding section,
when mo~ing in the direction of the passage of solid material
through the kiln.
The helical strip may be a simple helix, or a compound helix,
having multiple independent windings round the same axis.
The profile of the strip may be square, trapezoid, serrated or
rounded.
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It is not necessary for the kiln to be provided with an
internal hellcal strip over its entire length. It is also
possible that either at the front or at the rear end or at
both ends the kiln is provided with a section, or sect'ons
which do not contain a helix. These sections, which are not
provided with a helical strip, may be cylindrical in shape,
having substantially the same diameter as the central part of
the kiln, or they may have theshape of a truncated cone, e.g.
tapering towards the discharge end of the kiln.
The kiln may be positioned horizontally, or slightly inclined.
In the embodiment in which the helical strip does not extend
over the entire length of the kiln, it is necessary to place
the kiln in an inclined
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pOsition so as to enable the discharge of pyrolyzed residue at its
lower en~d.
The main advantage of the apparatus according to the invention is -~
that as a result of the helical strip fitted to the interior of the kiln,
a steady and uniform passage of solid material through the kiln is
achieved, the decrease of the pitch of the helix in the direction of
the passage ensuring an even loading of the kiln over its entire
length. The reduction in volume of the waste material resulting
from the pyrolysis reaction is compensated by the reduction of the
pitch of the helical strip, so that substantially the same volume of
solid material is present in every unit volurne of the kiln, thus
ensuring optimal utilization of the kiln. The refuse is constantly
loosened as a result of the rotation of the kiln, and the action of the
helical strip, so that all the material is duly subjected to the action
of the high temperature.
The rate of introduction of the waste material is preferably so
adjusted that the volume of the kiln is loaded for not more than
abo.ut 15% with waste material. This limitation of the quantity of
waste material which can be processed prevents the clogging or
agglomeration of the material during its passage through the kiln.
The precise control of the residence time of the material in the kiln
results in a pyrolyzed residue which is completely free from organic
contaminants .
The invention will now be demonstrated with reference to the
accompanying drawings in which:
Figure 1 illustrates a perspective view of one embodiment of the
apparatus, and
Figures 2, 3, ~ and 5 illustrate some designs for a pyrolysis kiln
which can be used in the apparaLus as shown in Figure 1.
Figure 6 shows an enlarged detail of the heli~.
The apparatus as sho~,vn in Figure 1 comprises a kiln 2 of substantially
cylindrical shape, constructed of heat-conducting matcrial, located in
a slightly inclined position within the fire boY 7 and provided with an
inlet for waste material 3, a discharge outlet ~ for pyrolyY,ed material
and a disengaging zone 5 in which the gas procluced in the pyrolysis
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reaction is separated from the pyrolyzed residue. The kiln 2 is
rotatably supported by bearings 6 outside the fire box 7. The kiln 2
defines the pyrolysis zone 8. The heating zone 9 is defined by the
interior of the fire box 7 and the exterior of the shell of the kiln Z.
The kiln 2 is provided with a ring gear 10 which is actuated by a
driven gear 11 connected to a power source 12. The means for the
introduction of waste material into the kiln comprise a hopper 13
for the waste material 14, the hopper being provided with screw
conveyor driven by a power source. The screw conveyor serves to
introduce waste material in desired quantities for the hopper 13 into
the kiln^ 2. The burner assembly 15 located in the fire box 7 is
provided with a irst fuel inlet 16 provided with a valve 17 for the
supply of fuel gas from an external source and a second fuel inlet 18
for pyrolysis gas. Moreover, burner 15 is connected to a blower 20
driven by a power source 19. The hot combustion gases are removed
from the heating zone 9 through a conduit 21.
The disengaging zone 5 develops into two conduits. The conduit 22
which extends downwardly from zone 5 serves to discharge pyrolyzed
residue from the apparatus. The conduit 23, which extends upwardly
from zone 5 serves to discharge the gases produced in the pyrolysis
process from the apparatus. From this conduit 23 a lateral conduit 24
leads to the fuel inlet 18 for the burner 15.
To achieve a controlled passage of the waste material through the kiln 2,
the interior of the kiln is provided with an internal helix or helical strip,
the pitch of the helix decreasing continuously or in degrees when moving
from the waste inlet 3 to the outlet 4 for the discharge of pyrolyzed
residue .
~igure 2 illustrates a pyrolysis kiln for use in the apparatus according
to the invention, in which the internal helical strip has a gradually
decreasing pitch. As will be seen from the drawing the pitch Pl near
the inlet opening 3 for the waste material is much smaller than the
pitch Pn near the discharge outlet 4 for the pyrolyzed residue. At the
same time the width of the helical strip is also decreasing in the
direction of passage of the material through the kiln from dl at the inlet
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to dn at the outlet. The central bore through which the gases which
evolve in the pyrolysis reaction pass to the outlet 4 widens
correspondingly from bi near the inlet 3 to bn near the outlet 4.
The kiln is provided with a ring gear 10 which is actu ated by a
driven gear (not shown).
Figure 3 illustrates a pyrolysis kiln having a shell in the form of
a truncated cone, tapering in the direction of the passage of the
material through the kiln. The kiln in this embodiment is of
substantially the same geometry as the helix in figure 2.
~igure 4 demonstrates a pyrolysis kiln comprising a cylindrical
section 26, provided with a helical strip with gradually decreasing -
pitch, and a section 27 in the form of a truncated cone, tapering
towards the outlet opening ~. Obviously, in order to ensure the
passage of the material through the tapering section 27 it is
necessary that the kiln is located in an inclined position in the fire
box .
_i~ure 5 illustrates a pyrolysis kiln of cylindrical design, consisting
of three sections 28, 29 and 30. Within each of these sections the
pitch of the helix is constant, but the pitch Pl in the first section 28
is larger than the pitch P2 in the second section 29. Likewise, the
pitch P2 in the second section 29 is Larger than the pitch P3 in the
third section 30. The width of the helical strip is also larger in the
first section 28 than in the second section 29. However, in this
embodiment the width in the third section 30 is the same as the
width in the second section of the kiln.
Figure 6 shows on a somewhat enlarged scale as compared with
figures 2, 3, 4 and 5, the geometry of the internal helix, ancl the rect-
angular profile of the metal strip.
Obviously the invention is not restricted to the particular embodiment
illustrated in the figures. Moreover, the geometry and the number of
windings of the helix as well as the dimensions of both the kiln and the
helix can vary from case to case in relation to the desired throughput
of the apparatus and the composition Or the refuse to be processed.
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