Abstract:
A thermal decomposition system is disclosed which can decompose wastes thermally in a continuous manner and which is therefore superior in its working efficiency. In the thermal decomposition system, wherein wastes to be treated are charged into a crucible and the crucible is heated while holding the interior thereof in vacuum to decompose the wastes thermally, both ends of a rotary furnace are supported rotatably by a frame, and drive units for rotating the rotary furnace are provided. The crucible, which is cylindrical, is installed in a central axis direction of the rotary furnace and a spiral groove is formed axially in an inner wall of the crucible. A heating device for heating the interior of the crucible is installed within the rotary furnace. Both opening ends of the crucible are connected to a feed box and a discharge box, respectively, which are supported by the frame. Shutter devices are installed in the feed box and the discharge box, respectively, to shut off the interior of the crucible from the exterior. The discharge box is connected to a suction device which evacuates the interior of the crucible and which causes gases produced during decomposition of the wastes to be discharged from the crucible by suction.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a thermal decomposition system for thermally decomposing ash discharged from incinerators, sludge, and wastes discharged from companies&#39; facilities, etc. Particularly, the invention is concerned with a thermal decomposition system capable of thermally decomposing even such industrial wastes as rubber and plastic products which produce poisonous gases during incineration. 
   2. Description of the Prior Art 
   Wastes discharged from homes and companies&#39; facilities have heretofore been classified mainly into combustible refuses capable of being incinerated, incombustible refuses incapable of being incinerated because of issuing of poisonous gases upon incineration, such as rubber and plastic products, resource refuses capable of being recycled such as paper, glass and aluminum products, and industrial wastes such as waste oils, concrete and metallic structures discharged from factories and facilities. These refuses and wastes are subjected to respective appropriate treatments and disposals. 
   Generally, combustible refuses are subjected to incineration, while incombustible refuse is buried in landfill spaces. As to resource refuses, they are classified according to the materials of paper, glass, aluminum, etc. and the thus-classified materials are subjected to crushing or melting for recycling. Further, industrial wastes are subjected to respective appropriate special processings. 
   However, as to some wastes, incineration is not accepted as is the case with rubber and plastic products even if they are combustible. Besides, those wastes issue smokes and gases due to, for example, incomplete combustion during incineration, exerting a bad influence on the environment. Moreover, in the conventional incinerators, wastes are incinerated by burning in air, so if a chlorine-containing waste is mixed therein, dioxin and chlorine compounds will be produced, thus giving rise to the problem that a bad influence is exerted on the environment. 
   Further, since ash from incineration and incombustible refuses incapable of being subjected to incineration are buried in landfill spaces, etc., it is necessary to ensure landfill spaces. Besides, offensive smells emitted from wastes and heavy metals contained in wastes exert a bad influence on the environment which surrounds the landfill space concerned. 
   The applicant in the present case has developed a thermal decomposition system wherein wastes to be treated are put into a hermetically sealed crucible, then the interior of the crucible is made vacuous and heating is conducted to thermally decompose the wastes, and obtained a patent for that system (Japanese Patent Publication No. 34902/95, U.S. Pat. No. 2,038,214). 
   In the said thermal decomposition system, a crucible which contains wastes to be incinerated is supported within a furnace body so as to give a clearance between an inner wall of the furnace body and an outer wall of the crucible except the supported portion of the crucible, a heating device for heating the crucible is mounted in the clearance between the inner wall of the furnace body and the outer wall of the crucible, an opening of the crucible is positioned inside an opening of the furnace body, an opening/closing lid for closing those openings at a time and a suction pipe for discharging gases produced during incineration of the materials to be treated from the interior of the crucible are provided, and further provided are a suction device connected to the suction pipe and a gas sorting/extracting device connected to the suction device. The interior of the crucible is closed with the opening/closing lid and is made vacuous, then in this vacuous state the wastes to be treated present in the interior of the crucible are heated, and gases produced from the wastes are withdrawn from the crucible by the suction device and are extracted by the gas sorting/extracting device. 
   However, according to the system being considered, wastes to be treated can be charged into the crucible only in a predetermined certain quantity, so the work comprising sealing the crucible interior hermetically, making it vacuous, heating, and withdrawal after the heating for a certain time, must be repeated for each predetermined quantity of wastes. Therefore, in the case where the volume of wastes to be treated is large, it is necessary that a series of operations be repeated many times, and thus much time and labor are required. 
   SUMMARY OF THE INVENTION 
   The present invention has been accomplished in view of the above-mentioned point and it is an object of the invention to provide a thermal decomposition device capable of thermally decomposing a large volume of wastes in a continuous manner and thereby enhancing the working efficiency. 
   In the first aspect of the present invention there is provided an intermittent flow type thermal decomposition system for thermally decomposing wastes in the interior of a crucible while the interior of the crucible is held in vacuum, comprising the crucible which is formed in a cylindrical shape having an inlet and an outlet at both ends thereof and having a spiral groove formed in an inner wall thereof, a frame, a rotary furnace held rotatably by the frame, with the crucible being installed in the interior of the rotary furnace, a heating device disposed inside the rotary furnace and outside the crucible, a drive unit for rotating the rotary furnace, a feed box communicating with the inlet of the crucible and supported by the frame, a discharge box communicating with the outlet of the crucible and supported by the frame, a shutter device installed in said feed box for disconnecting said interior of the crucible from the exterior, a shutter device installed in said discharge box for disconnecting said interior of the crucible from the exterior, and a suction device connected with the discharge box to evacuate the interior of the crucible and discharge gases from the interior of the crucible by suction, the gases being produced when the wastes are decomposed thermally by the heating device. 
   In the second aspect of the present invention there is provided, in combination with the above first aspect, an intermittent flow type thermal decomposition system wherein a gas sorting/extracting device is connected to the suction device to sort and extract gasses produced during decomposition of the wastes. In the third aspect of the present invention there is provided, in combination with the above second aspect, an intermittent flow type thermal decomposition system wherein a heat treatment equipment is connected to the gas sorting/extracting device and a gas, if any, not extracted by the gas sorting/extracting device out of the gases produced during decomposition of the wastes is introduced into the said heat treatment equipment. In the fourth aspect of the present invention there is provided, in combination with the above first aspect, an intermittent flow type thermal decomposition system wherein the outlet of the crucible is positioned higher than the inlet of the crucible. In the fifth aspect of the present invention there is provided, in combination with the above first aspect, an intermittent flow type thermal decomposition system wherein the frame is mounted onto a base in a swingable relation to each other so that a tilt angle of the frame relative to the base can be changed freely. In the sixth aspect of the present invention there is provided, in combination with the above first aspect, an intermittent flow type thermal decomposition system wherein the shutter devices for shutting off the interior and exterior of the crucible from each other have each a double shut-off structure. In the seventh aspect of the present invention there is provided, in combination with the above first aspect, an intermittent flow type thermal decomposition system wherein the heating device is a far infrared radiation heating device capable of heating the wastes in the crucible to a temperature of not lower than 1200° C. In the eighth aspect of the present invention there is provided, in combination with the above first aspect, an intermittent flow type thermal decomposition system wherein a ring-like conductor is provided on an outer wall of the rotary furnace, the said conductor and the heating device disposed in the interior of the rotary furnace are connected with each other electrically, and a contact piece adapted to contact the ring-like conductor constantly during rotation of the rotary furnace is provided in the frame. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view of an intermittent flow type thermal decomposition system according to an embodiment of the present invention; 
       FIG. 2  is a sectional front view of a rotary furnace used in the embodiment; 
       FIG. 3  is a side view of the thermal decomposition system; 
       FIG. 4  is a sectional view of the rotary furnace with a frame removed; 
       FIG. 5  is a sectional view of a crucible used in the embodiment; 
       FIG. 6  is a sectional view of a rotary shutter used in the embodiment; 
       FIG. 7  is a plan view of the rotary shutter; 
       FIG. 8  is a front view of an auto-shutter used in the embodiment; and 
       FIG. 9  is a sectional view of a crucible used in another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described hereunder with reference to the accompanying drawings. 
   A frame  2  is supported on a base  1  through a horizontal shaft  1   a , and both ends of a cylindrical rotary furnace  3  are supported rotatably by the frame  2 . The reason why the frame  2  is supported centrally of the base  1  through the horizontal shaft  1   a  is that the rotary furnace  3  is to be tilted to discharge wastes automatically from the interior of a crucible which will be described later. Stationary discs  4  are fixed respectively to both ends of the frame  2 . The stationary discs  4  are opposed respectively to rotary discs  3   a  provided at both ends of the rotary furnace  3  in a rotatable state through bearings  4   a . The stationary discs  4  and the rotary discs  3   a  are attracted to each other magnetically. Centrally of each rotary disc  3   a  is formed a through hole  3   b , while centrally of each stationary disc  4  is formed a through hole  4   b.    
   On both sides of the frame  2  and at lower positions there are provided a plurality of rollers  5  in contact with an outer wall of the rotary furnace  3  on both sides and at lower positions of the furnace. The rollers  5  are rotated by drive units  5   a  respectively, thereby causing the rotary furnace  3  to rotate. To one stationary disc  4  is fixed a chamber-like feed box  6 , while to the other stationary disc  4  is fixed a chamber-like discharge box  7 . Feed hoppers  8  for the feed of wastes to be treated are installed on top of the feed box  6  and a rotary shutter  9  as a first shutter device is disposed in lower portions of the feed hoppers  8  (an upper portion of the feed box  6 ). Further, an auto-shutter  10  as a second shutter device is disposed within the feed box  6 . Also within the discharge box  7  is disposed an auto-shutter  11  as a first shutter device, and a rotary shutter  12  as a second shutter device is disposed in a lower portion within the discharge box  7 . 
   On an outer wall of the rotary furnace  3  are centrally provided a plurality of conductor rings  13  for power supply, while on both end sides of the outer wall of the rotary furnace  3  are provided a plurality of conductor rings  14  for temperature measurement. As shown in  FIG. 3 , the conductor rings  14  are supported on a plurality of support bases  14   a  which are provided at appropriate intervals on the outer wall of the rotary furnace  3 . In the thus-supported state the conductor rings  14  float from the outer wall of the rotary furnace  3 . The conductor rings  13  are also supported in the same way as the conductor rings  14 . Suspended from an upper portion of the frame  2  are contact pieces  15  and  16  which are respectively in contact with the conductor rings  13  and  14  constantly even when the rotary furnace  3  rotates. 
   As shown in  FIG. 2 , a cylindrical crucible  17  made of a material high in thermal conductivity and which material produces a far infrared ray is installed in the interior space of the cylindrical furnace  3 . The crucible  17  is rotated together with the rotary furnace  3 . A central axis of the cylindrical crucible  17  is aligned with a rotational central axis of the rotary furnace  3 . As shown in  FIG. 5 , the cylindrical crucible  17  has a hollow portion  17   a  for receiving wastes to be treated therein, as well as an inlet  17   b  and an outlet  17   c  as openings formed at both ends of the crucible. In an inner wall of the hollow portion  17   a  is formed a spiral groove  17   d . Both ends of the crucible  17  are supported by the rotary discs  3   a . The inlet  17   b  of the hollow portion  17   a  is in communication with the feed box  6  through the through hole  3   b  of the rotary disc  3   a  located on the inlet  17   b  side and further through the through hole  4   b  of the stationary disc  4  located on the same side. On the other hand, the outlet  17   c  of the hollow portion  17   a  is in communication with the discharge box  7  through the through hole  3   b  of the rotary disc  3   a  located on the outlet  17   c  side and further through the through hole  4   b  of the stationary disc  4  located on the same side. A suction pipe  18  is provided in the discharge box  7 , and to an end of the suction pipe  18  opposite to the discharge box  7  side is connected a suction device  32  for evacuating the interior of the hollow portion  17   a  of the crucible  17  and for the suction of gases issued during decomposition of the wastes. To the suction device  32  is connected a gas sorting/extracting device  33  for sorting and extracting the issued gases. Further, to the gas sorting/extracting device  33  is connected a heat treatment equipment  34  for heating a gas, if any, which has not selectively been extracted by the gas sorting/extracting device  33 . 
   In the interior of the rotary furnace  3  is installed a heating device  19  for heating the wastes introduced into the crucible  17 . The heating device  19  is a far infrared radiation heating device capable of heating at a temperature in the range from room temperature to 1200° C. or higher. As shown in  FIGS. 2 and 4 , the heating device  19  is spaced from an outer wall of the crucible  17  and extends throughout the overall length from one end to the opposite end of the crucible. The heating device  19  is supplied with electric power from the conductor rings  13 . 
     FIG. 6  is a sectional view showing the configuration of the rotary shutter  9  installed in the feed box  6  and  FIG. 7  is a plan view thereof. The rotary shutter  9  is made up of a shielding disc  20  disposed in the upper portion of the feed box  6  and having a large number of through holes  21  formed concentrically on the shielding disc  20  and a rotary disc  22  superimposed on the shielding disc  20 , the rotary disc  22  being rotatable about a shaft  23  and having a through hole  24 . As the rotary disc  22  is rotated by drive means (not shown), the through hole  24  comes into registration with one of the through holes  22  intermittently, allowing the wastes to pass therethrough. The rotary shutter  12  in the discharge box  7  also has the same configuration as the rotary shutter  9 . 
     FIG. 8  illustrates the configuration of the auto-shutter  10  installed in the feed box  6 . The auto-shutter  10  is composed of an upper shutter  26  located in an upper portion within a vertical passage  25  of a square section and a lower shutter  27  located in a lower portion of the passage  25 . The upper shutter  26  is supported at an upper end thereof pivotably by a hinge  28  secured to an inner wall of the passage  25 . When a free end of the upper shutter  26  on the side opposite to its hinged  28  side is raised, the passage  25  is closed, while when the free end is lowered, the passage  25  is opened. The lower shutter  27  is supported at a lower end thereof pivotably by a hinge  29  secured to the inner wall of the passage  25 . When a free end of the lower shutter  27  is lowered, the free end of the upper shutter  26  is lifted, whereby the passage  25  is closed with both upper and lower shutters  26 ,  27 . Therefore, if the free end of the lower shutter  27  is lifted into abutment against an inner wall of the passage located on the opposite side, i.e., the hinge side, the upper shutter  26  also lowers at its lower portion and is superimposed on the inside of the lower shutter  27 , whereby the passage  25  is opened, allowing the wastes to drop. The lower shutter  27  is connected to a piston  31  of a cylinder  30  disposed outside the passage  25  and is interlocked with motions of the piston  31 . Also as to the auto-shutter  11  disposed in the discharge box  7 , it has the same configuration as the auto-shutter  10 . 
   The wastes when introduced into the feed hoppers  8  are conveyed to the feed box  6  continuously by the rotary shutter  9 . When the wastes accumulate within the feed box  6 , the auto-shutter  10  opens, so that the wastes enter the hollow portion  17   a  of the crucible  17  installed centrally of the rotary furnace  3 . Thereafter, the rotary shutter  9  and the auto-shutter  10  are closed and the suction device  32  is operated to evacuate the interior of the crucible  17 . Then, the heating device  19  is operated to heat the crucible  17  to about 1200° C. and the rollers  5  are actuated by the drive units  5   a  to rotate the rotary furnace  3 , whereby the wastes present within the crucible  17  are heated and decomposed with an ultra-high heat energy of an electromagnetic wave (far infrared radiation) in vacuum. As a result, the wastes in the crucible  17  move, while being thermally decomposed, from the inlet  17   b  side to the outlet  17   c  side of the crucible  17  along the spiral groove  17   d  formed in the inner periphery of the crucible which is rotating. At the same time, gases produced by the thermal decomposition are withdrawn from the interior of the crucible by the suction pipe  18 . Therefore, the interior of the crucible  17  is held in vacuum by suction with the suction pipe  18 . 
   The gases sucked by the suction device  32  reach the gas sorting/extracting device  33 , in which the gases are sorted and extracted. The gases thus extracted are, for example, liquefied for disposal or re-utilized. A gas, if any, which has not been extracted by the gas sorting/extracting device  33  enters the heat treatment equipment  34 , in which a portion of the gas is decomposed at a high temperature and the other portion is made harmless through a clean filter (not shown) and is then released to the exterior. 
   The wastes present within the crucible  17  reach the outlet  17   c  along the spiral groove  17   d  while being thermally decomposed. By being heated for a certain time, the wastes are decomposed into ash, which ash is then introduced into the discharge box  7 . The auto-shutter  11  is opened, allowing the ash thus introduced into the discharge box  7  to drop, and is then closed once. Thereafter, the rotary shutter  12  is opened to discharge the ash to the exterior from the discharge box  7 . Thus, the ash is discharged to the exterior by opening and closing the double shutter structure in the discharge box  7 . The ash thus discharged can be re-utilized as a product such as a ceramic product by cooling it into a solid matter with use of a suitable method. 
   Thus, the wastes to be treated are introduced into the crucible  17  by intermittent opening and closing of the auto-shutter  10  and are discharged from the discharge box  7  by intermittent opening and closing of the auto-shutter  11 . At this time, the interior of the crucible  17  is opened temporarily by the auto-shutter  10  in the feed box  6  and the auto-shutter  11  in the discharge box  7 , but except this time the auto-shutters  10  and  11  are closed to seal the interior of the crucible  17  hermetically and the crucible interior is made vacuous by the suction device  32 . 
   The retention time of the wastes in the crucible  17  is about 20 to 40 minutes and 3 to 10 kg of wastes per minute can be treated. In this way wastes are introduced into the crucible  17  intermittently and ash is discharged from the discharge box  7  also intermittently. Thus, the wastes are thermally decomposed intermittently but in a continuous manner. 
   In  FIGS. 1 and 2  the crucible  17  is in a horizontal state, while  FIG. 9  illustrates a tilted state of the crucible  17  (rotary furnace  3 ). In  FIG. 9 , the outlet  17   c  of the crucible  17  is relatively higher than the inlet  17   b  of the crucible (a tilt angle relative to the horizontal plane is set at θ). The reverse may also be adopted in the invention. As shown in  FIG. 9 , the crucible  17  is tilted so that the wastes present therein rise as they move within the crucible. This is advantageous in that the thermally decomposed ash can be raised to a high position, e.g., a drying position, automatically. Heretofore, a lift has been required for lifting the ash up to a high position for drying, but by tilting the crucible  17  (rotary furnace  3 ) the use of such a lift is not required. With the crucible  17  (rotary furnace  3 ) tilted, the amount (decomposition volume) of wastes advancing through the interior of the crucible  17  can be adjusted by changing the rotational speed of the roller  5  rotated by the drive units  5   a . Even without causing the crucible  17  (rotary furnace  3 ) to tilt, a proper thermal decomposition can be done if the rotational speed of the rollers  5  is changed by the drive units  5   a  according to the type of wastes to be treated. 
   According to the present invention, as set forth above, since the interior of the crucible which is held in vacuum is heated to about 120° C. to decompose wastes thermally, dioxin, etc. can be decomposed. Since the wastes which have entered the crucible are conveyed from the inlet side to the outlet side of the crucible successively along the spiral groove in the crucible with rotation of the rotary furnace, the wastes can be decomposed thermally while being passed intermittently through the crucible. Thus, in comparison with the conventional batch process involving repetition of wastes feed into the crucible, a large volume of wastes can be subjected to a thermal decomposition treatment continuously and hence it is possible to enhance the working efficiency. 
   Gases sucked out from the crucible are sorted and extracted by the gas sorting/extracting device and extracted gases are collected. Even if there is any gas not extracted by the gas sorting/extracting device, the gas is introduced into the heat treatment equipment connected to the gas sorting/extracting device and is thermally decomposed therein, whereby the release of harmful gas and offensive smell to the exterior is prevented. 
   Moreover, by tilting the crucible so that the wastes present therein rise as they move through the interior of the crucible, ash resulting from thermal decomposition can be conveyed automatically to a high position for drying, thus making it possible to omit the use of a lift for lifting such ash to a high drying position. Further, the decomposition volume of wastes advancing through the interior of the crucible can be adjusted by changing the rotational speed of the crucible with use of drive units. Ash resulting from thermal decomposition of the wastes is solidified and can be re-utilized thereby. Additionally, since the thermal decomposition of wastes is performed under rotation of the rotary furnace, the wastes can be decomposed uniformly. By providing pantograph-like conductor rings on the outer wall of the rotary furnace, electric power can be supplied from the frame to the interior of the rotary furnace stably even during rotation of the same furnace.