GB1576997A - Apparatus for the conversion of waste material by pyrolysis - Google Patents

Abstract

The device essentially consists of an externally heated, elongate, rotatable retort. This is associated at one end with a waste inlet and at the other end with a discharge for pyrolysed material and pyrolysis gas. The retort (2) is provided with an internal screw (25) having a central bore. Its pitch is smaller in the region of the discharge (4) for the pyrolysed residue than in the region of the waste inlet (3). This device ensures a uniform degree of filling of the retort over its entire length and precludes damage to the retort by jammed waste parts. <IMAGE>

Description

(54) APPARATUS FOR THE CONVERSION OF WASTE MATERIAL BY PYROLYSIS (71) We, ARCALON B.V. General Petroleum and Electric, of De Lairessestraat 131-135, Amsterdam, Holland, a limited liability company incorporated under the laws of the Netherlands, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The 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.

Moreover, 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 actuated 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 passage through the 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 parts.

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 apparatus 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 a substantially even and uniform loading of the kiln over its entire length and which avoids or reduces the danger of damage as a result of jammed fragments of refuse.

The invention provides apparatus for the conversion of waste material by means of pyrolysis comprising a fire box in which an elongated rotatable kiln is located, means for heating the kiln externally, which kiln is provided with means for the introduction of waste material into one end of said kiln and means for the discharge of pyrolyzed material and pyrolysis gas from the other end of said kiln, the kiln being provided with an internal helical strip with a central bore, the pitch of the helix near the discharge outlet for the pyrolyzed material being smaller than the pitch near the inlet for the waste material.

The elongated kiln is preferably a cylinder, but other geometrical forms are also possible, such as 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 moving 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 cross-sectional profile of the strip may be square, trapezoid, serrated or rounded.

It is not necessary for the kiln to be provided with an internal helical 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 sections 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 the shape 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 position so as to enable the discharge of pyrolyzed residue at its lower end.

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 volume 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 about 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.

A specific embodiment of the invention, with some possible modifications, will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates a perspective view of one embodiment of the apparatus, Figures 2,3, 4 and 5 illustrate some designs for a pyrolysis kiln which can be used in the apparatus as shown in Figure 1, and Figure 6 shows an enlarged detail of the helix.

The apparatus as shown in Figure 1 comprises a kiln 2 of substantially cylindrical shape, constructed of heat-conducting material, located in a slightly inclined position within the fire box 7 and provided with an inlet for waste material 3, a discharge outlet 4 for pyrolyzed material and a disengaging zone 5 in which the gas produced in the pyrolysis 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 2.

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 first 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.

Figure 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 P1 near the inlet opening 3 for the waste material is much greater 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 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 b1 near the inlet 3 to bn near the outlet 4. The kiln is provided with a ring gear 10 which is actuated 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 helix in this embodiment is of substantially the same geometry as the helix in figure 2.

Figure 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 4. 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.

Figure 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 P1 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, and the rectangular 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 of the refuse to be processed.

WHAT WE CLAIM IS: 1. Apparatus for the conversion of waste material by means of pyrolysis comprising a fire box in which an elongated rotatable kiln is located, means for heating the kiln externally, which kiln is provided with means for the introduction of waste material into one end of said kiln and means for the discharge of pyrolyzed material and pyrolysis gas from the other end of said kiln, and wherein the kiln is provided with an internal helical strip with a central bore, the pitch of the helix near the discharge outlet for the pyrolyzed mater ial being smaller than the pitch near the inlet for the waste material.

2. Apparatus according to claim 1 wherein the elongated kiln is substantially cylindrical.

3. Apparatus according to claim 1 or claim 2, wherein the pitch of the helix decreases gradually in the direction of the passage of solid material through the kiln.

4. Apparatus according to claim 1 or claim 2, wherein the helix in the kiln is subdivided into several sections, each having a different pitch, the pitch in the second and following sections being smaller than the pitch of the previous one, moving in the direction of the passage of solid material through the kiln.

5. Apparatus according to any one of the preceding claims, characterized in that the width of the helical strip decreases with the decrease of the pitch of the helix in the direction of the passage of solid material through the kiln.

6. Apparatus according to any one of the preceding claims, characterized in that the helix is a compound helix, having multiple independent windings around the same axis.

7. Apparatus according to any one of the preceding claims, characterized in that the cross-sectional profile of the helical strip is square, trapezoid, serrated or rounded.

8. Apparatus for the conversion of waste material by means of pyrolysis, substantially as described herein with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. reaction pass to the outlet 4 widens correspondingly from b1 near the inlet 3 to bn near the outlet 4. The kiln is provided with a ring gear 10 which is actuated 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 helix in this embodiment is of substantially the same geometry as the helix in figure 2. Figure 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 4. 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. Figure 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 P1 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, and the rectangular 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 of the refuse to be processed. WHAT WE CLAIM IS:

1. Apparatus for the conversion of waste material by means of pyrolysis comprising a fire box in which an elongated rotatable kiln is located, means for heating the kiln externally, which kiln is provided with means for the introduction of waste material into one end of said kiln and means for the discharge of pyrolyzed material and pyrolysis gas from the other end of said kiln, and wherein the kiln is provided with an internal helical strip with a central bore, the pitch of the helix near the discharge outlet for the pyrolyzed mater ial being smaller than the pitch near the inlet for the waste material.

2. Apparatus according to claim 1 wherein the elongated kiln is substantially cylindrical.

3. Apparatus according to claim 1 or claim 2, wherein the pitch of the helix decreases gradually in the direction of the passage of solid material through the kiln.

4. Apparatus according to claim 1 or claim 2, wherein the helix in the kiln is subdivided into several sections, each having a different pitch, the pitch in the second and following sections being smaller than the pitch of the previous one, moving in the direction of the passage of solid material through the kiln.

5. Apparatus according to any one of the preceding claims, characterized in that the width of the helical strip decreases with the decrease of the pitch of the helix in the direction of the passage of solid material through the kiln.

6. Apparatus according to any one of the preceding claims, characterized in that the helix is a compound helix, having multiple independent windings around the same axis.

7. Apparatus according to any one of the preceding claims, characterized in that the cross-sectional profile of the helical strip is square, trapezoid, serrated or rounded.

8. Apparatus for the conversion of waste material by means of pyrolysis, substantially as described herein with reference to the accompanying drawings.