APPARATUS FOR THE REGENERATION OF USED FOUNDRY SAND

Abstract: The invention relates to an apparatus for the thermal treatment of materials, and particularly for the regeneration of used foundry sand. The apparatus comprises a container which can rotate about a rotational axis and which has an inlet for an oxygen-containing gas. A burner is located in the container; the burner flame is directed onto the material introduced into the container for thermal treatment. The inlet for the oxygen-containing gas is formed by a porous plate. The porous plate is a sintered metal plate in a preferred embodiment.

Description: "Apparatus for the regeneration of used foundry sand" The invention relates to an apparatus for the thermal treatment of materials, and particularly for the regeneration of used foundry sand, with the features described in the preamble of Claim 1. An apparatus of this type is known from WO 91/08068. In the known apparatus a drum-shaped container is arranged with its rotational axis inclined slightly with respect to the vertical. The container is open at its upper end and equipped with an inlet for an oxygen-containing gas at its lower end; the inlet passes through the bottom wall from below on the rotational axis and projects from the bottom wall into the interior space of the container. In the interior space, the inlet is covered by a bell-shaped cap, which has openings arranged radially with respect to the rotational axis. In use, the known apparatus is filled with used foundry sand and made to rotate slowly around the inclined rotational axis. Oxygen is introduced from below into the organic binder-permeated sand and at the surface is ignited by an ignition flame. A flame front then sweeps uniformly through the sand from top to bottom until the entire hydrocarbon fraction has been burned. In actual practice it has become clear that the oxygen-containing gas forms preferred flow channels in the sand and thus does not reach all the binder resin particles. After the end of the burning process, a not inconsiderable fraction of the hydrocarbon remains in the regenerated sand. Thus, the goal of the invention is to further develop the known apparatus in order to achieve a more effective hydrocarbon combustion. This goal is achieved by an apparatus with the features described in Claim 1. The apparatus according to the present invention is characterized in that the inlet for oxygen-containing gas is constructed of a porous plate. The material introduced into the container for thermal treatment, for example, used foundry sand or oil-containing earth, will at least partially cover the porous plate. The oxygen-containing gas is introduced through the porous plate into the container in an area-wise regime and flows at least partly through the material introduced into the container. The formation of preferred channels for the spread of the gas is avoided by this distributed or area-wise introduction of the oxygen-containing gas, with the result that a more uniform formation of the flame front in the material is attained. Another advantage of this area-wise introduction of the oxygen-containing gas is that compaction of the material is avoided. The porous plate may be a sintered metal plate produced by powder metallurgy technology. These sintered metal plates are particularly durable. When the material intended for thermal treatment contains, for example, chlorinated hydrocarbons, solvent vapors, dioxins, or other toxic or at least harmful compounds, these substances must be combusted at approximately 1200iC For these high temperature ranges the plate preferably takes the form of a ceramic plate. In another preferred embodiment the inlet preferably takes the form of a porous cermet plate. Plates of this type combine the favorable characteristics of ceramics and metals. The inlet preferably resides at a distance from the wall of the container. This produces an intervening space between the wall of the container and the inlet, in which the oxygen-containing gas entering the intervening space can be distributed uniformly through the inlet into the interior space of the container. This feature generates an even more uniform distribution of the supplied gas. In a preferred embodiment of the apparatus the inlet lies in the plane of the wall of the container, preferably the bottom wall. Such an embodiment is preferred with apparatuses in which the container is constructed in the shape of a cylinder and the longitudinal axis of the container corresponds to the rotational axis wherein the rotational axis is slightly inclined with respect to the vertical. Placing the inlet in the plane of the bottom wall results in a desirable smooth-surfaced inner chamber. A uniform distribution of the gas flow is attained in an advantageous manner when the center of the inlet is located on the rotational axis. According to another implementation the container is constructed in such a manner that it can tilt about an essentially horizontal axis. This embodiment of the apparatus makes possible a simple emptying of the container. In another preferred implementation the apparatus is constructed in the form of a drum-shaped container whose rotational axis is slightly inclined with respect to the horizontal. In this connection, the configuration of the drum-shaped container can be described as quasi-horizontal. The advantage of such an apparatus resides in the corresponding simplification of the suspension of the container. In such an apparatus the inlet may, for example, be constructed in the vicinity of the burner, which is situated at one end of the container. This permits easy access to the burner. The inlet should extend at least over a partial section of the container. This apparatus is advantageously operated in countercurrent. To this end, the upper end of the container should have a flue gas opening through which the flue gas formed during combustion within the container can escape. The upper end should also be equipped with a loading opening through which the container can be loaded with the material to be thermally treated. A discharge opening should be provided at the lower end. During countercurrent operation, the flue gas flows opposite to the transport direction of the material. The hot flue gas will dry the material, thereby improving the energy balance. The flue gas opening is preferably constructed above the loading opening. Subject container can preferably oscillate about the rotational axis. The container can preferably move about the rotational axis to an angle of up to 180;. The oscillating motion of the container induces the circulation of the material present in the container, thereby promoting the thermal treatment of the material. This turning motion by the container results in transport of the material within the container from the loading opening to the discharge opening and thus supports the continuous operation of the apparatus. The oxygen-containing gas is preferably led to the inlet through movable feed lines. Movable feed lines make it possible to achieve sealing in a relatively simple manner. The feed line is preferably a flexible feed line, for example, a hose. The inlet can be supplied with the oxygen-containing gas through one or several feed lines. The use of several feed lines affords a more uniform gas distribution. The inlet may also be subdivided into individually separate sections with one feed line leading to each inlet section. A flow device can be provided in each feed line. The flow device can be a valve, preferably an electrically operated valve. Placing a flow device in the feed line makes it possible to make suitable adjustments in the flow velocity, pressure, and/or volumetric flow rate of the gas to the inlet. It may be advantageous to feed different volumes or gas pressures to individual subsections of the inlet. For example, it may be advantageous to supply higher quantities of gas to zones in which the fraction of untreated material is still relatively high. According to another advantageous implementation, the apparatus includes a cooler, which is inserted after the container. The material treated thermally in the container is introduced into the cooler, where the hot material is cooled. In a particularly energetically favorable tactic, the waste heat from the material is preferably used to preheat the combustion air for the burner in the container. The cooler is constructed as an air cooler for this purpose . The apparatus preferably includes an analytical device for determining the flue gas composition and, connected to said analytical device, a control device that controls the supply of oxygen-containing gas to the container. The flue gas composition can be analyzed continuously. The emission of, for example, NOx, can be optimized through the control device and the flue gas composition determined by the analytical device. In addition, a reduction in the carbon monoxide in the flue gas can be realized by an appropriate addition of oxygen. For this purpose, it is advantageous to connect the control device to the flow device. An improved thermal treatment of the material in the container is readily achieved when the inlet covers between 25% and 75% of the area of the bottom wall. The inlet preferably covers the largest possible area, and particularly the entire bottom wall. An improved combustion is readily generated when the inlet covers a circular area of the bottom wall of a cylindrical container which has a diameter of 100 mm to 300 mm. Other advantages and features of the invention are explained with reference to two exemplary embodiments. The figures in the drawings show the following: Figure 1 shows an apparatus according to the present invention in side view; Figure 2 shows an enlarged section of the apparatus according to Figure 1; Figure 3 shows a schematic representation of the structure of a second exemplary embodiment of an apparatus; Figure 4 shows the container of an apparatus according to Figure 3, in section; Figure 5 shows the container according to Figure 4, in side view from the left. Figure 1 shows, in side view, an apparatus 1 for the thermal treatment of, for example, used foundry sand. The apparatus 1 comprises a drum-shaped container 2, which is supported in a frame 3 so that it can rotate about a rotational axis 11. The frame 3 is, in turn, supported in a stand 4 by means of bearings 5, so that it can be tilted about a horizontal axis, which in Figure 1 is perpendicular to the plane of the drawing. The drum-shaped container 2 comprises a side wall 6 approximately in the shape of a cylinder wall and an approximately disk-shaped bottom wall 7. A connection 8 for an oxygen feed line 9 is provided on the bottom wall 7; this connection is located in the middle of bottom wall 7 in the area of the rotational axis. The oxygen feed line 9 is fed from an oxygen supply 10, which is known per se. Figure 2 shows in greater detail the area of the transition from the side wall to the bottom wall. The side wall 6 has a sandwich-type construction, with an outer shell 12, preferably made of stainless steel, an insulation layer 13 adjacent to the inside of the shell 12, and a refractory lining 14, which is attached on the inner side of the insulation layer 13. In the preferred exemplified embodiment the bottom wall 7 is fabricated in one piece with the shell 12 out of stainless steel and is essentially flat. A porous plate 15, preferably produced from a sintered metal, is situated parallel to the bottom wall 7 at a distance from the bottom wall. This creates a disk-shaped intermediate space between the bottom wall 7 and the plate 15. The connection 8 is situated in the center of the bottom wall 7 and points away from the interior space of the container. An oxygen-containing gas, and particularly pure oxygen, flows through the oxygen feed line 9 indicated in Figure 1 and through the connection 8 into the disk-shaped intermediate space between the bottom wall 7 and the plate 15. The plate 15 terminates the cylindrical interior space of the container, which is delimited radially by the inside wall of the refractory lining 14. This apparatus for the regeneration of used foundry sand functions in the following manner: The used, binder-permeated molding sand is introduced into container 2 of apparatus 1. The container 2 is then rotated about its vertical axis, which is slightly inclined with respect to the vertical, thus inducing a moderate tumbling action in the contents of the container 2. Oxygen is then supplied into the intermediate space under the plate 15 from the oxygen supply 10 through the oxygen feed line 9 and the connection 8. The porosity of the plate permits the oxygen to permeate through the plate and reach the introduced sand. The oxygen flows through the sand, which is undergoing moderate motion, and exits at its surface. At the surface of the sand the hydrocarbon-loaded sand is heated by an ignition flame (not shown) to such an extent that the hydrocarbons react exothermically with the through-flowing oxygen. The reaction heats the surrounding sand, and the area of the oxidation reaction spreads and migrates through the entire sand volume as a flame front, with the result that as oxygen is being supplied the hydrocarbons present are burned to form carbon monoxide and water. The reaction rate, and thus the evolution of heat and the velocity of the spreading flame front, can be controlled by adjusting the oxygen. After complete combustion of the hydrocarbons, the container 2 can be tilted about the horizontal axis and emptied. The porous plate 15 situated at the bottom of the container 2 causes the oxygen-containing gas to enter the sand from below along the axial direction over a large cross section. This achieves a uniform flow within the sand volume. In contrast, in the known apparatuses the oxygen enters the sand in a quasi-pointwise manner at the center of the bottom plate and is distributed from there in both axial and radial directions. Higher gas velocities occur as a result of the initially small cross section, which lead to the formation of preferred paths for dissemination of the oxygen in the sand volume. The sand is nonuniformly permeated by oxygen in the known apparatuses, with the result that regions still loaded with hydrocarbons can remain in the sand volume. Furthermore, locally high oxygen concentrations can lead to combustion of an explosive character. These problems are avoided in the apparatus according to the present invention by uniformly introducing the oxygen into the sand volume over a relatively large area. Figure 3 shows a second exemplified embodiment of an apparatus according to the present invention. This apparatus comprises a drum-shaped container 2. The container 2 is supported in such a manner that it can rotate about a rotational axis 11. The suspension of the container 2 is not depicted. The rotational axis 11 is slightly inclined with respect to the horizontal. A burner 27 is situated on the lower end 16 of the container 2. The upper end 19 has a loading opening 17, which communicates with a loading device. Used foundry sand, for example, is introduced into the container 2 through the loading device 18. For example, a screw conveyer (not shown) can be present in the loading device 18. A flue gas conduit 20, through which fumes flow out of the container 2, is situated on the upper end 19. The flue gas conduit 20 communicates with an opening 28 in the container 2. A discharge opening 21, through which the treated material is transported into a cooler 22, is constructed on the end 16 of the container 2 opposite the loading opening 17. The cooled material is then removed from the cooler 22. The container 2 is connected to oxygen feed lines 9a, 9b, 9c, each of which is connected to an oxygen supply 10 by a main conduit 23. A flow device 24a, 24b, 24c, which in this case is an electrically operated valve, is provided in each oxygen feed line 9a, 9b, 9c. Each valve is connected to a control device 25. The control device 25 is also connected to an analytical device 26 provided for determination of the flue gas composition. The control device 25 can optionally be connected to temperature sensors located in the container 2. The container 2 can oscillate around its rotational axis 11, and in this case the container 2 can rotate 180; about the rotational axis. The swiveling process leads to a rocking motion by the container 2, with the result that material introduced into the container 2 through the loading opening 17 reaches the lower region of the container 2 and is there removed from the container 2 through the discharge opening 21. The side wall 6 of the container 2 has a sandwich-type construction, with an outer shell 12, an insulation layer 13 adjacent to the inner side of the shell 12, and a refractory lining 14 attached on the inner side of the insulation layer 13. A porous plate 15 is located in the area of the burner. The apparatuses described above can be used for the regeneration of used foundry sand. They can also be used, for example, for the treatment of soil contaminated with oil products. LIST OF REFERENCE NUMBERS 1 Apparatus 2 Container 3 Frame 4 Stand 5 Bearing 6 Side wall 7 Bottom wall 8 Connection 9a,b,c Oxygen feed line 10 Oxygen supply 11 Rotational axis 12 Shell 13 Insulation layer 14 Lining 15 Plate 16 End 17 Loading opening 18 Loading device 19 End 20 Flue gas conduit 21 Discharge opening 22 Cooler 23 Main conduit 24a,b,c Valve 25 Control device 26 Analytical device 27 Burner 28 Flue gas discharge opening

Claims: CLAIMS 1. Apparatus for the thermal treatment of materials, in particular for the regeneration of used foundry sand, having a container (2) which can rotate about a rotational axis (11) , an inlet for an oxygen-containing gas, and at least one burner (27) located in the container (2) , characterized in that the inlet is constructed of a porous plate (15) . 2. Apparatus according to Claim 1, characterized in that the plate (15) is a sintered metal plate. 3. Apparatus according to Claim 1, characterized in that the plate (15) is a ceramic plate. 4. Apparatus according to Claim 1, characterized in that the plate (15) is a cermet plate. 5. Apparatus according to one of Claims 1 to 4 , characterized in that the plate (15) is located at a distance from the wall of the container (6) . 6. Apparatus according to Claim 5, characterized in that the inlet lies in the plane of the container wall (6) , preferably the bottom wall (7) . 7. Apparatus according to one of Claims 1 to 6, characterized in that the center of the inlet is located on the rotational axis (11) . 8. Apparatus according to one of Claims l to 6, characterized in that the container (2) can be tilted about an essentially horizontal axis. 9. Apparatus according to one of Claims 1 to 4, characterized in that the container (2) is constructed in the shape of a drum, whose rotational axis (11) is slightly inclined with respect to the horizontal, the burner (27) is located on the lower end (16) of the container (2) , and the inlet is formed over at least a partial section of the container (2) . 10. Apparatus according to Claim 9, characterized in that the inlet extends from the burner (27) in the direction of the rotational axis (11) . 11. Apparatus according to Claim 9 or 10, characterized in that a discharge opening (21) is provided on the lower end (16) and the upper end (19) has a flue gas opening (28) and a loading opening (17) . 12. Apparatus according to Claim 11, characterized in that the flue gas opening (28) is constructed above the loading opening (17) . 13. Apparatus according to one of Claims 9 to 10, characterized in that the container (2) can move in an oscillating manner about the rotational axis (11) . 14. Apparatus according to Claim 13, characterized in that the container (2) can move over an angle of up to 180; about the rotational axis (11) . 15. Apparatus according to one of Claims 9 to 14, characterized in that the inlet is connected to at least one movable feed line (9a, 9b, 9c) . 16. Apparatus according to Claim 15, characterized in that the feed line(s) is (are) constructed in a flexible manner. 17. Apparatus according to Claim 15 or 16, characterized in that a flow device (24a, 24b, 24c) is located in each feed line (9a, 9b, 9c) . 18. Apparatus according to Claim 17, characterized in that the flow device (24a, 24b, 24c) is a valve, preferably an electrically operated valve. 19. Apparatus according to one of Claims 9 to 18, characterized in that a cooler (22) is inserted after the container (2) . 20. Apparatus according to Claim 19, characterized in that the cooler (22) is inserted directly after the container (2) . 21. Apparatus according to Claim 19 or 20, characterized in that the cooler (22) is an air cooler. 22. Apparatus according to one of Claims 1 to 21, containing an analytical device (26) for the determination of the flue gas composition and a control device (25) , connected to the analytical device (26) , which controls the supply of the oxygen-containing gas into the container (2) . 23. Apparatus according to Claims 17 or 18 and 22, characterized in that the control device (25) is connected to each flow device (24a, 24b, 24c) . 24. Apparatus according to one of Claims 1 to 23, characterized in that the inlet covers between 25% and 75% of the area of the container bottom wall.

Inventors: LEGIRET THIERRY, LEGIRET, THIERRY
Applicants: AIR LIQUIDE, LEGIRET THIERRY, L'AIR LIQUIDE, SOCIETE ANONYME POUR L'ETUDE ET L'E, LEGIRET, THIERRY
Application year: 1996
Main classification: B22C5
IPC codes: B22C5