Pyrolysis furnace

Abstract

A pyrolysis furnace comprising an enclosure (E) defining a substantially cylindrical inner wall (E1) and comprising an entry airlock (I) and an exit airlock (O), and also an endless screw (V) rotated on itself inside the enclosure (E) between the entry airlock (I) and the exit airlock (O), the endless screw (V) comprising a central shaft (1) and rods (3) which extend radially toward the inner wall (E1) of the enclosure (E), the rods (3) being angularly offset so as to form at least one helical flight (3F) which extends spirally around the central shaft (E), the rods (3) are mounted on rings (2) engaged around the central shaft (1) with an angular offset, each ring (2) supporting at least one rod (3).

Description

Pyrolysis oven

[0001] The present invention relates to a pyrolysis furnace comprising an enclosure defining a substantially cylindrical inner wall and comprising an inlet airlock and an outlet airlock. The furnace also comprises a worm screw driven in rotation on itself inside the enclosure between the inlet airlock and the outlet airlock.

[0002] Such a furnace is known in particular from document FR2858570A1, which describes a pyrolysis furnace having an enclosure, in which the materials or waste to be treated are mixed with heated steel balls. The waste / ball mixture is conveyed by means of a worm screw, which is barely mentioned. The balls here have a function of hot crushing of the waste, while the worm screw only has a function of transporting the waste / ball mixture.

[0003] The disadvantage of this prior art furnace is that the steel balls must be heated outside the furnace, introduced through an inlet airlock, and recovered through an outlet airlock for reheating. This requires heavy equipment and considerable heat loss.

[0004] The object of the present invention is to remedy this drawback by eliminating the heated steel balls and by defining an endless screw which is both mixing and heating.

[0005] To achieve this, the present invention proposes that the worm screw comprises a central axis and rods which extend radially towards the inner wall of the enclosure, the rods being angularly offset so as to form at least one helical screw thread which extends in a spiral around the central axis.

[0006] Advantageously, the oven comprises at least one heating means, for example resistance and / or induction, for heating the rods.

[0007] The rods, in addition to their screw thread function to advance the waste into the enclosure, replace the steel balls, ensuring a waste crushing function. The rods can be heated from inside the central axis of rotation. The waste advances into the enclosure by passing partly through the heated rods, so as to bring the heat as close as possible to the waste, as do the steel balls of document FR2858570A1. With the rods of the invention, the heat remains inside the enclosure, resulting in minimal loss.

[0008] The term "rod" must be understood in its broadest sense and can be replaced by bar, tube, blade, fin, blade, and more generally by any element elongated in the radial direction.

[0009] In contrast to a conventional worm screw with one or more continuous screw threads in the form of a continuous helical web, the rods of the invention form one or more discrete screw threads, in that the rods are separate and spaced apart from each other, so that waste can partly circulate between the rods.

[0010] According to the invention, the rods are mounted on rings engaged around the central axis with an angular offset, each ring supporting at least one rod, and advantageously at least three rods, to form at least three nested screw threads. Advantageously, all the rings are identical and each support the same number of rods arranged in an identical manner. Advantageously, the rings each support several rods, so as to form several nested helical screw threads. Thus, the worm screw of the invention is made from a single type of element, namely a ring provided with one or more radial rods. The heating means mounted in the central axis heats the rings and the rods. These identical rings are engaged one behind the other on the central axis.The rings are angularly offset from each other by about 10 to 20°, preferably about 15°, so that there are about twenty-four rods per turn of the helical screw thread.

[0011] Advantageously, the central axis comprises an external surface which defines longitudinal flats, the rings being engaged one behind the other around the central axis, each ring comprising a central opening which defines longitudinal flats, the number of which corresponds to the number of longitudinal flats of the central axis. The angular offset is therefore facilitated.

[0012] According to another aspect of the invention, the pyrolysis furnace may comprise at least one helical sole mounted on the free ends of the rods of a helical thread, the helical sole being arranged close to the inner wall of the enclosure. The sole has the function of scraping the waste in the enclosure to advance it towards the outlet airlock. The sole does not come into direct contact with the inner wall of the enclosure: a gap of a few millimeters, or even centimeters, may be defined between them.

[0013] According to a practical embodiment, the helical screw thread comprises a first thread section separated from a second thread section by at least one thermally insulating ring, only the first thread section, extending from the inlet airlock, being heated by the heating means, which may in particular be resistance and / or induction. Thus, the materials or waste are crushed, advanced and heated in the first thread section and only crushed and advanced in the second thread section, before being extracted through the outlet airlock. Advantageously, the first thread section is provided with a thermally conductive helical sole, while the second thread section is provided with a thermally insulating helical sole. Advantageously, the pyrolysis furnace may comprise a pyrolysis gas outlet close to the thermally insulating ring.Thus, the pyrolysis gases are extracted from the enclosure after the first section of the net, while the waste (or its ashes) are conveyed without heating to the exit airlock.

[0014] The spirit of the invention lies in giving the worm screw an additional function of grinding, mixing, blending, stirring, kneading, etc. This function is fulfilled by the elongated elements which extend radially from the central axis, forming a discontinuous, interrupted, discrete screw thread, etc. Identical rings are particularly advantageous.

[0015] The invention will now be described in greater detail, with reference to the attached drawings, giving by way of non-limiting example, an embodiment of the invention.

[0016] In the figures:

[0017] This is a very schematic view of a pyrolysis installation which uses a pyrolysis furnace according to the invention,

[0018] This is an enlarged perspective view of part of the worm screw, and

[0019] This is a view of the pyrolysis furnace incorporating a worm screw according to a particular embodiment of the invention.

[0020] The picture shows a pyrolysis furnace F, which is integrated into a complete pyrolysis plant. The pyrolysis furnace F is the central element of the plant, which includes several accessories necessary for the operation of the pyrolysis furnace F.

[0021] Without going into detail, the pyrolysis furnace F comprises an enclosure E which defines an internal wall E1 of substantially cylindrical shape. The enclosure E is preferably provided with a layer of thermal insulation E2 to retain the heat inside the furnace F. The pyrolysis furnace F comprises an inlet airlock I for introducing the materials or waste to be treated and an outlet airlock O for extracting the pyrolysis residues. The enclosure E contains a worm screw S driven in rotation on itself inside the enclosure E between the inlet airlock I and the outlet airlock O. The pyrolysis furnace F also comprises a pyrolysis gas outlet G mounted on the enclosure E.

[0022] The worm screw S comprises a central axis 1 which passes through the enclosure E and even projects outside the enclosure E at a drive end 1e, which may be provided with a wheel W, driven in rotation by a motor M by means of a drive belt B. Thus, the worm screw S rotates on itself in the enclosure E to transport the materials or waste to be treated between the inlet airlock I and the outlet airlock O. The pyrolysis gas outlet G is positioned between the inlet airlock I and the outlet airlock O and makes it possible to recover the pyrolysis gases.

[0023] In the, it can be seen that the central axis 1 is provided internally with a heating means R, which can be in the form of a resistor, which is represented very schematically. Indeed, any suitable heating means can be used within the framework of the present invention.

[0024] Upstream of the inlet airlock I, the pyrolysis installation comprises a tank C, in which the materials or waste to be treated are stored. The tank C is equipped with an inlet C1 and a first conveyor screw C2 which feeds a second conveyor screw C3 which discharges the materials or waste to be treated into the inlet airlock I of the furnace F. This is only a non-limiting embodiment: the inlet airlock I can be fed by any suitable means. The advantage with this system of conveyor screws C2, C3 is that very little air enters the enclosure E.

[0025] Downstream of the outlet airlock O, the pyrolysis plant comprises a tank T, into which the residues or ash from the pyrolyzed materials or waste fall. The residues or ash are then evacuated from the tank by means of another conveyor screw T1 which discharges into an outlet hopper T2. The residues or ash stored in the tank form a plug, which prevents outside air from entering the enclosure E through the outlet airlock O.

[0026] Generally, the worm screw S is rotatably housed in the enclosure E. This worm screw S comprises three helical screw threads 3F, which spirally wind in an interlocking manner around the central axis 1. According to the invention, each helical screw thread 3F comprises rods 3, which extend radially towards the inner wall E1 of the enclosure E. The rods 3 are angularly offset so as to form the helical screw thread 3F. In other words, the helical screw thread 3F is not continuous, as is usually the case, but on the contrary discontinuous, since it is formed by the rods 3, which are separated from each other by an axial distance and an angle. The helical screw threads 3F also comprise rings 2 engaged around the central axis 1 and supporting the rods 3, as well as soles 4, which are fixed to the free ends of the rods 3, so as to be positioned close to the internal wall E1 of the enclosure E.

[0027] We can now refer to the to describe the worm screw S in more detail. We see that the central axis 1 defines a hollow interior 11, in which the heating means R is housed (shown schematically in the): only the connection cables 1R of the heating means R are shown in the. The central axis 1 comprises an external surface 12 which defines longitudinal flats 12a. For example, twenty-four flats 12a can be provided, corresponding to the number of rods 3 per turn of the thread.

[0028] The rings 2 are engaged one behind the other around the central axis 1. Each ring 2 comprises a central opening 21 which defines longitudinal flats 21a, the number of which corresponds to the number of longitudinal flats 12a of the central axis 1. Thus, the rings can be engaged around the central axis 1 with angular offsets of 15°, which makes it possible to create the helical screw thread(s) 3F. Each ring also defines an external wall 22, on which the rods 3 are mounted. More precisely, the rods 3 comprise anchoring ends 31 fixed to the external wall 22 of the ring 2, for example by welding or screwing. The rings 2 also define opposite flat faces 23, which are in mutual contact. The rods 3 also comprise free ends 32, on which the soles 4 are mounted, for example by welding.The rods 3 and the soles 4 together define helical screw threads 3F, which extend in a spiral around the central axis 1. The angular and axial offset of the rods 3 comes from the angular offset of rings 2 around the central axis 1, which is made possible by the longitudinal flats 12a and 21a.

[0029] By way of non-limiting example, the rods 3 can be angularly offset by approximately 10 to 20°, advantageously by approximately 15°, so that there are approximately twenty-four rods 3 per complete turn of the helical screw thread 3F. In the figures, there are three nested helical screw threads 3F: each ring 2 therefore supports three rods 3, which extend radially and are offset by 120°. Without departing from the scope of the invention, it is also possible to provide only one or two, or on the contrary more than three.

[0030] The rings 2, the rods 3 and the soles 4 are made of thermally conductive material, such as a metal, and preferably stainless steel.

[0031] The worm screw S of the invention performs several functions. The first basic function is to transport or push the materials or waste into the enclosure E between the inlet I and outlet O airlocks. The second function is to heat the materials or waste, which come into contact with the rings 2, the rods 3 and the soles 4. Indeed, the heating means housed in the central axis 1 of course heats the central axis 1, but also and above all the rings 2, the rods 3 and the soles 4. The third function is to crush or knead the materials or waste: part of the materials or waste is pushed by the rods 3 and the soles 4 and another part passes through the rods 3. In the end, the materials or waste are heated uniformly thanks to the kneading, so that a maximum of pyrolysis gas is extracted from them.

[0032] Referring to the, a particular embodiment for the worm screw is seen. However, the overall design remains the same as for the worm screw of Figures 1 and 2, with a central axis 1, rings 2, rods 3 and soles 4. The major difference lies in the fact that the worm screw S' of the is divided into two parts, namely a first heating part and a second non-heating part. In more detail, the first heating part comprises a first series of rings 2a and the second non-heating part comprises a second series of rings 2b. The first series of rings 2a extends substantially from the inlet airlock I to the pyrolysis gas outlet G and the second series of rings 2b extends substantially from the pyrolysis gas outlet G to the outlet airlock O. The heating means comprises an inductive coil R', integrated into the enclosure E, around its internal wall E1 and below the insulation E2.The inductive coil R' extends only over the first series of rings 2a. The rings 2 of the first and second series of rings 2a and 2b are preferably identical. The first and second series of rings 2a and 2b are separated by at least one thermally insulating ring 2i, so that the heat, communicated to the first series of rings 2a by the inductive coil R', does not propagate to the second series of rings 2b. Preferably, the thermally insulating ring 2i is without a rod.

[0033] The rods 3, mounted on the rings 2 of the first and second series of rings 2a and 2b, are preferably identical and in the same number per ring 2, for example three rods 3 per ring. A single model of ring 2 with rods 3 is therefore used for the two series of rings 2a and 2b. Alternatively, it is also possible to produce the second series of rings 2b with a thermally insulating material and to provide thermally insulating rods.

[0034] Advantageously, the first series of rings 2a is provided with a thermally conductive helical sole 4c, while the second series of rings 2b is provided with a thermally insulating helical sole 4i. Preferably, the two soles 4c and 4i are not joined, but separated from each other at the thermally insulating ring 2i.

[0035] Thus, this worm screw S' comprises two sections of helical screw threads, namely a first section of heated thread 3Fc with one or more thermally conductive soles 4c and a second section of unheated thread 3Fi with one or more thermally insulating soles 4i, the two sections of threads 3Fc and 3Fi being separated by at least one thermally insulating ring 2i.

[0036] With this auger S', the materials or waste to be treated are heated only in the first thread section 3Fc, at the end of which the pyrolysis gases are extracted through the outlet G. Then, the materials or waste, already at least in the form of ash, are conveyed to the outlet airlock O through the second insulating unheated thread section 3Fi. In this way, a significant energy saving is achieved for heating the auger S'.

[0037] Without departing from the scope of the invention, the heating means can be of any type. We have seen that it can be by resistance integrated into the central axis or by induction integrated into the wall thickness of the enclosure E. The two heating means by resistance and by induction can even be implemented cumulatively.

[0038] The invention provides a pyrolysis furnace whose rod-driven screw conveys, heats, and crushes the materials to be processed. Mounting the rods on angularly offset rings significantly simplifies the manufacture and assembly of the screw.

Claims

Pyrolysis furnace comprising an enclosure (E) defining a substantially cylindrical inner wall (E1) and comprising an inlet airlock (I) and an outlet airlock (O), as well as a worm screw (S; S') driven in rotation on itself inside the enclosure (E) between the inlet airlock (I) and the outlet airlock (O), the worm screw (S; S') comprising a central axis (1) and rods (3) which extend radially towards the inner wall (E1) of the enclosure (E), the rods (3) being angularly offset so as to form at least one helical screw thread (3F; 3Fc, 3Fi) which extends in a spiral around the central axis (E), characterized in that the rods (3) are mounted on rings (2) engaged around the central axis (1) with an angular offset, each ring (2) supporting at least one rod (3), advantageously at least three rods (3). Pyrolysis oven according to claim 1, in which all the rings (2) are identical and each support the same number of rods (3) arranged in an identical manner. Pyrolysis oven according to claim 1 or 2, in which the rings (2) each support several rods (3), so as to form several nested helical screw threads (3F; 3Fc, 3Fi). Pyrolysis oven according to any one of the preceding claims, in which the central axis (1) comprises an external surface (12) which defines longitudinal flats (12a), the rings (2) being engaged one behind the other around the central axis (1), each ring (2) comprising a central opening (21) which defines longitudinal flats (21a), the number of which corresponds to the number of longitudinal flats (12a) of the central axis (1). Pyrolysis oven according to any one of the preceding claims, in which the rings (2) define opposite planar faces (23), which are in mutual contact. Pyrolysis oven according to any one of the preceding claims, comprising at least one heating means (R; R') for heating the rods (3). Pyrolysis oven according to claims 6, wherein the heating means (R) mounted in the central axis (1) heats the rings (2) and the rods (3). Pyrolysis furnace according to any one of the preceding claims, wherein the rings (2) are angularly offset from each other by about 10 to 20°, advantageously by about 15°, so that there are about twenty-four rods (3) per turn of the helical screw thread (3F; 3Fc, 3Fi). Pyrolysis oven according to any one of the preceding claims, comprising at least one helical sole (4; 4c, 4i) mounted on the free ends (32) of the rods (3) of a helical thread (3F; 3Fc, 3Fi), the helical sole (4; 4c, 4i) being arranged close to the internal wall (E1) of the enclosure (E). Pyrolysis furnace according to any one of the preceding claims, wherein the helical screw thread comprises a first thread section (3Fc) separated from a second thread section (3Fi) by at least one thermally insulating ring (2i), only the first thread section (3Fc), extending from the inlet airlock (I), being heated by the heating means (R'). Pyrolysis furnace according to claim 10, wherein the first thread section (3Fc) is provided with a thermally conductive helical sole (4c), while the second thread section (3Fi) is provided with a thermally insulating helical sole (4i). Pyrolysis furnace according to claim 10 or 11, comprising a pyrolysis gas outlet (G) close to the thermally insulating ring (2i).* * *

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