Abstract:
An oil reclaiming system for plastic waste capable of producing oils and carbonized residues in a shorter period of time and at a higher yield and capable of providing oils and carbonized residues of higher qualities, wherein granite is disposed in a furnace.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates a plastic decomposition technique wherein plastic waste is introduced into a reacting furnace and decomposed by heating to be converted into reusable substances. 
         [0002]    Conventional processes for decomposing plastic waste is carried out by heating plastic waste in furnaces at high temperatures of 500 to 800° C. with added decomposition promoters such as sodium phthalate and sodium stearate. Breakage of polymer molecules of the plastic waste by such heating results in the generation of liquefied fat and oil components. The fat and oil components can then be fractionated and refined to give reusable oils and fats such as naphtha. 
         [0003]    When the plastic waste is decomposed at such high temperatures of 500 to 800° C. as described above, the cost for fuel and electric heating for maintaining such temperatures will disadvantageously increase. To cope with it, the present inventors have proposed in Patent Reference 1 measures by which plastic waste introduced into furnaces is heated at lower temperatures of 250 to 350° C. in such a way that the plastics may be roasted instead of being burned, to decompose them into fat and oil components which compose the plastics, and generated gases are removed and cooled in a cooler to be reduced into oils and fats. Specifically, a high efficiency of such an oil reclaiming process has been attained through the use of feldspar and mica paved in the furnaces. 
         [0004]    Patent Reference 1: Japanese Unexamined Patent 
       SUMMARY OF THE INVENTION 
       [0005]    When plastic waste is decomposed by an oil reclaiming system for plastic waste as claimed in Patent Reference 1 (batch type) the amount of oil collected per hour is 73 g/hr, as indicated in Experiment 4 see Table 1,  FIG. 11 , showing a value which is twice or more in comparison with that of Experiment 5 (refractory cement only, see Table 1,  FIG. 11 ) wherein no feldspar is contained in the furnace. In consideration of actual operation, however, it is desirable that a higher efficiency in oil reclaiming be achieved in a shorter period of time. In addition, it is also desirable that decomposed products (oils, carbonized residues) be more valuable for industrial use. As such, it is the object of the present invention to provide measures capable of producing oils and carbonized residues in a shorter period of time and at a higher yield and capable of providing oils and carbonized residues of higher qualities. 
         [0006]    The present invention (1) is an oil reclaiming system for plastic waste having a furnace for heating the plastic waste for decomposition, wherein granite is disposed in the furnace. The system typically includes a furnace having a heater along the outer periphery of its peripheral wall, the outer periphery of the heater being coated with a heat insulator, a feeder for charging plastic waste into the furnace, gas draw tubes for recovering a gas generated in the furnace through thermal decomposition of the charged plastic waste and a residue discharge device for recovering a residue produced by thermal decomposition of the charged plastic waste. 
         [0007]    The present invention (2) is the system according to the invention (1) wherein the granite is applied to the inner wall of the furnace. 
         [0008]    The present invention (3) is a process for reclaiming oils from plastic waste comprising a step of heating the plastic waste for decomposition, wherein the step for decomposition is carried out in the presence of granite. 
         [0009]    The present invention (4) is a process for producing oils using plastic waste as a raw material comprising a step of heating the plastic waste for decomposition, wherein the step for decomposition is carried out in the presence of granite. 
         [0010]    The present invention (5) is a process for producing carbonized residues using plastic waste as a raw material comprising a step of heating the plastic waste for decomposition, wherein the step for decomposition is carried out in the presence of granite. 
         [0011]    The mineral referred to as “granite” in Claims and Description is, for example, one containing 65% or more (for example, 65 to 70%) of silicon dioxide, mainly composed of quartz and feldspar and further containing one or more colored minerals (for example, biotite and amphibole). 
         [0012]    According to the present invention, since plastic waste may more efficiently be decomposed in a shorter period of time, such an effect is obtained that waste disposal may quickly be performed and decomposed products that are valuable for industrial use (oils, carbonized residues) may be obtained in a high yield. Also with respect to decomposed products, when they are processed at a low temperature (at 150° C.) for example, industrially useful components such as styrene and ethyl benzene (raw material for styrene) may be obtained in abundance. Also with respect to carbonized residues (cokes from decomposed plastic waste), components having no sulfur content, utilizable as an excellent coke source which may be used for ironmaking for producing non-fragile iron, may be obtained in abundance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is an elevation view of an oil reclaiming system as a whole (continuous operation type) according to the present invention as seen from the side wherein the direction of processing flow is from left to right in the drawing; 
           [0014]      FIG. 2  is an elevation view of the oil reclaiming system as a whole (continuous operation type) as seen from the side showing the upstream end of the processing flow (corresponding to a view as seen from the left in  FIG. 1 ); 
           [0015]      FIG. 3  is an elevation view of the oil reclaiming system as a whole (continuous operation type) as seen from the side showing the downstream end of the processing flow (corresponding to a view as seen from the right in  FIG. 1 ). 
           [0016]      FIG. 4  is a sectional view of the oil reclaiming system as a whole (continuous operation type) as seen from the side showing the direction of processing flow (from left to right in the drawing); 
           [0017]      FIG. 5  is a vertical section of a furnace of the oil reclaiming system (continuous operation type); 
           [0018]      FIG. 6  is a cross section of the furnace of the oil reclaiming system (continuous operation type); 
           [0019]      FIG. 7  is a perspective view of an oil reclaiming system as a whole (batch system) according to the present invention; 
           [0020]      FIG. 8  is a view showing the internal structure of a furnace of the oil reclaiming system (batch system); 
           [0021]      FIG. 9  is a view showing a cooling means of the oil reclaiming system (batch system); 
           [0022]      FIG. 10  is a view showing the manner in which a gas cooled and liquefied on the upper surface of the furnace is led to a reservoir in the oil reclaiming system (batch type); and 
           [0023]      FIGS. 11 and 12  show Table 1. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    First, with reference to  FIGS. 1 to 6 , an oil reclaiming system (continuous operation type) according to the invention will be described. As described above, in the oil reclaiming system of the invention granite is disposed in a furnace for heating plastic waste for decomposition. A preferred embodiment wherein a granite-containing layer is applied to the inner wall of a furnace (continuous operation type) is illustrated; however, any embodiment is within the scope of the invention as long as granite is present in a furnace. For example, embodiments are possible in which granite (or a ceramic which contains granite, or the like) is paved over the hearth (or on a plate, such as iron plate, placed over the hearth, or the like) of a furnace and/or granite may be allowed to mix into plastic waste. 
         [0025]    With reference to the drawings, the overall structure of the oil reclaiming system (continuous operation type) will be described in detail. As shown in  FIGS. 1-3 , the oil reclaiming system is composed of a furnace  1  having a cylindrical shape along the direction of processing, a feeder  2  for feeding plastic waste into the furnace  1 , a catalyst feeder  3  for feeding a sodium-based catalyst into the furnace  1 , gas draw tubes (ducts)  4  for extracting gases generated through decomposition by heating the plastic waste introduced into the furnace to lead the gas to a cooler  5  to be subsequently referred to, the cooler  5  for cooling the gas extracted through the gas draw tubes  4  and a residue discharge device  6  for discharging (receiving) carbonized residues mostly consisting of carbon produced in the furnace  1 . These components are accommodated and retained in a machine frame F. 
         [0026]    Next, the structure of the furnace  1  of the present invention will be described in detail. First, with reference to  FIGS. 4 to 6 , a granite-containing layer formed over the inner surface of the furnace  1  will be described in detail. The base structure of the furnace  1  is made of a peripheral wall  10  formed in a cylindrical shape along the direction of processing and side walls  11  closing the peripheral wall  10  at the front and the back (closing the axially opposite ends). The inner surface of this horizontally oriented cylindrical furnace  1  (the inner surface composed of the peripheral wall  10  and the side walls  11 ,  11 ) is provided in whole or in part with a granite-containing layer m. The granite-containing layer m is not limited as long as it contains granite, examples which include shaped articles of granite itself (for example, panels), ceramics containing ground granite (for example, ceramics made of ground granite, refractory cement and water that are admixed and calcined, such as panels) and castables containing ground granite. More specifically, an embodiment in which a ceramic of natural granite formed into a panel is attached to the surface of the inner wall of the furnace and an embodiment in which ground natural granite is kneaded with a refractory cement and water to cause it to be mortared to the surface of the inner wall (the mortared material will be calcined by the heat of operation of the furnace to form a granite-containing layer as a ceramic) may be mentioned. The granite-containing layer may be formed anywhere on the inner surface. It is however more effective to form it over the surface of the inner wall than over the hearth. Although, in this embodiment, a cylindrical furnace is illustrated, in the case of other shapes, positioning of a granite-containing layer will be determined appropriately according to such shapes. For example, in the case of a furnace as a U-shaped tube having a flat top and a peripheral wall having a U-shaped cross section (one end of which is provided with a feed port for plastic waste and the other end of which is provided with a discharge port), a granite-containing layer is formed in whole or in part over the upper side, the peripheral wall, the side wall with the feed port and the side wall with the discharge port. 
         [0027]    As apparent from the results of Examples to be subsequently referred to, the granite-containing layer is preferably embodied as containing granite as coarsely ground pieces having a size of a pebble (Experiment 6 of EXAMPLES). In such an embodiment, the amount of oil collected per hour is much higher in comparison with an embodiment where granite is present as a plate (Experiment 1 of EXAMPLE) or as powder (Experiment 3 of EXAMPLE) and, in addition, cracks may be prevented from occurring in calcined ceramic panels. When the ground pieces are provided over the inner wall (especially, over the wall surface which is subjected to the influence of gravity), a refractory cement or the like should be used to secure the ground pieces to the wall. Also, when the ground pieces are placed at locations where no influence of gravity is exerted, such as on the hearth, they may merely be placed such as by being paved. 
         [0028]    Next, other constituent features in relation to the internal structure of the furnace  1  will be described. Since constituent features other than the granite-containing layer described above are not characteristic of the present invention, embodiments in which some of the features to be described below are different or absent and embodiments in which other constituent features are added are still within the scope of the present invention as long as such embodiments possess the characteristics of the present invention mentioned above. 
         [0029]    First, as shown in  FIGS. 1 to 3 , the furnace  1  is secured to the machine frame F by supports  1   a . A rotation axis  12  is rotatably hung across the machine frame F in such a manner that it penetrates the furnace  1  horizontally through its bore along the axial center. Further, as shown in  FIG. 4 , this rotation axis  12  is provided with a spiral agitator  13  on its peripheral surface. The agitator  13  is rotated by operation of a motor M 1  attached to one end of the rotation axis  12 , which rotates the rotation axis  12 . 
         [0030]    Next, the furnace  1  has, on its outside, an electric heater a wound around the outer peripheral surface (tubular peripheral wall  10 ) of the furnace  1  for maintaining the temperature inside the furnace  1  at a predetermined temperature and has further, on its outer periphery, a heat insulator b wound in a multilayered manner. In this embodiment, such a heating means is adopted in view of facilitating and ensuring temperature control of the furnace. Any form of heating may however be used as long as it can preset the working temperature inside such an oil reclaiming system to or within predetermined values or ranges (for example, a burner may be used in Examples). 
         [0031]    Next, the feeder  2  is composed of a hopper  20  for introducing plastic waste, a transport cylinder  22  in communication with a bottom opening  21  of the feeder  20 , a screw-like conveyor  23  hung inside the transport cylinder  22  and a motor M 2  for driving the conveyor  23 . Further, the forward end of this transport cylinder  22  is in communication with a connector cylinder  24  for introducing plastic waste, which is in communication with a feed port  15  provided at one end (to the left in  FIG. 4 ) of the furnace  1 . The plastic waste introduced into the hopper  20  is forcibly fed toward the forward end of the transport cylinder  22  (to the right in  FIG. 4 ) by operation of the conveyor  23  being driven by the motor M 2 . The plastic waste forcibly fed to the forward end of the transport cylinder  22  passes through the connector cylinder  24  connected to the forward end to be introduced through the feed port  15  into the furnace  1 . In the feeder  2 , a delivery mechanism  25  as a rotating valve is provided at the forward end of the conveyor  23  for forcibly feeding the plastic waste, in order to prevent gases generated by the thermal decomposition of the plastic waste fed in the furnace  1  from backflowing and outflowing due to the pressure. Materials, constructions and the like of the feeder  2  are appropriately determined so that the plastic waste, wet after being washed with water, may be fed into the furnace  1 . 
         [0032]    Next, the catalyst feeder  3  is composed of a hopper  30  for introducing catalyst, a metering mechanism  31  for separating and feeding a predetermined amount from the catalyst introduced into the hopper  30  and a transport cylinder  32  for guiding the predetermined amount of catalyst. The lower end of the transport cylinder  32  is communication with an intermediate portion of the transport cylinder  22  along the direction of transport. Consequently, the plastic waste from the feeder  2  is mixed with the predetermined amount of catalyst, before being charged into the furnace  1 . 
         [0033]    Next, the gas draw tubes  4  are positioned slightly rearward from the center of the furnace  1 , as shown in  FIG. 4 . Also, as shown in  FIG. 5 , the gas draw tubes  4  are provided via connector ports  40  which are in communication with the bore of the furnace  1  at both sides of the furnace  1  in relation to the axial direction of the furnace  1  through an angle of approximately 30° in relation the vertical center line X passing through the axial center of the peripheral wall  10 . Consequently, gases (gases generated from plastic waste), water vapors and the like accumulated at the upper portion of the furnace  1  will efficiently be led to the cooler  5  to be subsequently referred to. 
         [0034]    Next, the cooler  5  is composed of an airtightly formed cooling box  50 , a radiator-like heat exchanger  51  disposed in the box, a cooling water tank  52  for storing cooling water, which is circulated in the heat exchanger  15 , cooled in a refrigerator and a pump P 1  for circulating the cooling water in the tank  52 . A tray-like receiver  53  is disposed in the cooling box  50  and below the heat exchanger  51  for receiving oil and fat components condensed and reclaimed by cooling. An oil discharge tube  54  is connected via a valve V 1  to the bottom of the receiver  53  for discharging the stored oil and fat components, to which a recovery tank t 1  is further connected. The receiver  53  also stores water condensed from the water vapor, which is generated from the water fed into the furnace, led into the cooling box  50  via the gas draw tubes  4  along with the gas  1  (NaCl produced by reaction of decomposition of vinyl chloride with the sodium-based catalyst), in addition to the reclaimed oil and fat components. The water and the oil and fat components will separate into two layers, the water layer sedimenting as the lower layer. The salt water passes through a water discharge tube  55  connected via a valve V 2  to the bottom surface of the receiver  53  to be stored in a salt water tank t 2  connected at the bottom end of the tube. Separation into two layers does not have to be carried out in the system and, instead, a mixture liquid can be discharged and then separated into two layers. 
         [0035]    The residue discharge device  6  is composed of a discharge tube  61  connected to a residue discharge outlet  14  provided at the other end of the furnace  1 , a valve shutter-like residue draw mechanism  60  operable to hermetically seal the residue discharge outlet  14  to the outside and forcibly feed residues fed thereto and a residue draw bin  62  connected downstream along the direction of feed. The residue draw mechanism  60  functions to sequentially feed residues into the residue draw bin  62  by being driven by a motor M 3  (not shown). The residue draw bin  62  has its outer periphery surrounded by a cooler  63  consisting of water jackets. The cooling water in the cooling water tank  52  mentioned above is circulated in the cooler  63  by a pump P 2 . Consequently, carbonized residues recovered in the residue draw bin  62  is cooled and airtightly retained so that dust explosion due to synergistic action with heat while the residues are in contact with the air may be prevented. The residue draw bin  62  for recovering residues is further provided with a draw outlet  64  at the bottom for discharging the cooled residues. The draw outlet  64  also has a shutter  65  installed in an openable/closable manner for preventing outflow from the residue draw bin  62 . A conveyor  66  is provided at the draw outlet  64  for drawing out the cooled residues when the shutter  65  is open. 
         [0036]    Next, a method of operating the oil reclaiming system (continuous type) according to this embodiment is illustrated by way of example. First, the hopper  20  is loaded with chopped plastic waste. The plastics may be loaded as wet after being washed with water but without being drained or dried. The catalyst feeder  3  is loaded with a sodium-based catalyst (such as sodium hydroxide and sodium bicarbonate) for decomposing chlorine compounds produced when vinyl chloride contained in the plastic waste is decomposed. The temperatures of the furnace in which the plastic waste in the hopper and the sodium-based catalyst is loaded are not particularly limited, with the upper limit preferably at or below 500° C., and are preset in the range of 150 to 400° C., for example. 
         [0037]    Next, with reference to  FIGS. 7 to 10 , an oil reclaiming system according to another embodiment (batch system) will be described. Description of features that are identical to those of the continuous type will be omitted. First, as shown in  FIG. 7 , the oil reclaiming system is composed of an approximately rectangular furnace  101 , a burner  102  for heating inside the furnace, a heat transfer piping  103  connected to the burner  102  and penetrating the interior of the furnace  101 , a thermal insulator  104  for preventing the heat transfer piping  103  from being cooled up to where the tube is introduced into the furnace  101 , a cooling water tank  106  connected with a water pump, in which cooling water to be fed to a cooling means (to be subsequently referred to) for cooling and liquefying gases generated in the furnace  101  is stored, a reservoir  107  provided immediately below the furnace  101 , a manipulator  109  for allowing temperature control and the like of the furnace  101  and a frame  110  for housing the mentioned components. As shown, a refrigerator  108  for cooling the reservoir  107  by a cooling gas may further be included. 
         [0038]    Next, with reference to  FIG. 8 , the structure of the furnace  101  according to this embodiment will be described. The furnace  101  has the heat transfer piping  103  disposed therein in such a manner that it may form a U shape. Burned air from the burner  102  is introduced into the heat transfer piping  103 . As a result of the heat of the burned air being transferred through the heat transfer piping  103  into the furnace  101 , the furnace  101  is heated from inside. Decomposition temperatures inside the furnace  101  are controlled through adjustment of the combustion at the burner  102 . 
         [0039]    Next, with reference to  FIG. 9 , the structure of the cooling means according to this embodiment will be described.  FIG. 9  is a partial section of the furnace  101 . The furnace is provided with coolers  112  mounted on top and on both sides, in which cooling water pipings  112   a  are embedded. The furnace  101  has a dual structure in the vicinity of the coolers  112 . Specifically, the furnace  101  has inner walls  101   a  on top and on both sides for building space for gases generated from decomposition to be introduced (gas introduction space  101   b ). The inner walls  101   a  on both sides are provided with introduction slits  101   a - 1  for introducing gases generated in the furnace  101  into the gas introduction space  101   b . In such configuration, a gas G generated from decomposition will be led through the introduction slits  101   a - 1  into the gas introduction space  101   b  and contacted with the coolers  112  to be cooled and liquefied, as shown. The liquid L will then fall down with its own gravity and to be stored in the reservoir  107  mentioned above, as indicated by the arrows in the drawing. The reservoir  107  is also equipped with a similar cooler. In a case where the gas is led to the reservoir  107  without being liquefied, therefore, cooling on the basis of a similar mechanism will be carried out in the reservoir  107 . As an example,  FIG. 10  shows the manner in which a gas cooled and liquefied on the upper surface of the furnace  101  is led to the reservoir  107 . 
         [0040]    Next, a method of operating the oil reclaiming system (batch system) according to this embodiment is illustrated by way of example. First, chopped plastic waste is placed in the furnace  101  at a predetermined location (for example, on an iron plate placed on the heat transfer piping  103 ). The plastics may be introduced as wet after being washed with water but without being drained or dried. The plastic waste is mixed with a sodium-based catalyst (such as sodium hydroxide and sodium bicarbonate) for decomposing chlorine compounds produced when vinyl chloride contained in the plastic waste is decomposed. The temperatures of the furnace in which the plastic waste and the sodium-based catalyst are introduced are not particularly limited, with the upper limit preferably at or below 500° C., and are preset in the range of 120 to 350° C., for example. 
       EXAMPLES 
       [0041]    The present invention will be illustrated in more detail with reference to Examples. In Examples, a batch-type oil reclaiming system as shown in  FIG. 6  and other drawings was used. Chopped plastic waste was placed on an iron plate disposed on the heat transfer piping  103 . For Experiments 1 and 2, a granite plate was applied to the iron plate, for Experiment 3, a refractory cement was applied to the iron plate which was then calcined and for Experiment 6, ground granite was applied to the iron plate. 
       1. Experimentation 
       [0042]    Experiment 1 (Example 1): natural granite plate plus moisture added
 
Experiment 2 (Example 2): natural granite plate (no moisture added)
 
Experiment 3 (Example 3): powdery granite in mixture with refractory cement plus moisture added
 
Experiment 4 (Comparative Example 1): ground feldspar (Patent Reference 1) (pebbles) plus moisture added
 
Experiment 5 (Comparative Example 2): refractory cement plus moisture added
 
Experiment 6 (Example 4): ground granite (pebbles) plus moisture added
 
       2. Conditions and Results 
       [0043]    The conditions and results of Experiments are shown in Table 1 ( FIGS. 11 and 12 ). Most noteworthy data are the amount of oil collected per hour as calculated by dividing the total amount of oil collected by the net processing time in hour and the amount of residue of plastic waste which was not decomposed into oil. The results of Experiments in the light of such remarks are summarized as follows. 
         [0044]    (1) The granite plate (Experiment 1), the powdery granite in mixture with refractory cement (Experiment 3) and the ground granite (Experiment 6) with moisture added provide 100 g or more of oil collected per hour and enable constant oil reclaiming for plastic waste. 
         [0045]    (2) With no moisture added (Experiment 2), the amount of oil collected per hour is slightly less at 92 g, showing a relatively small influence of moisture added. 
         [0046]    (3) Use of feldspar (Experiment 4) provides a smaller amount of oil collected per hour in comparison with the use of granite and, in particular, provides 50% or less of the amount of oil collected per hour in comparison with the use of ground granite (Experiment 6) comparable to the form of feldspar (ground). It has thereby been proven that granite is far effective than feldspar in oil reclaiming capability for plastic waste. 
         [0047]    (4) Use of refractory cement without granite (Experiment 5) provides a very small amount of oil collected per hour of 34 g, with residues containing undecomposed plastic waste, showing an extremely poor oil reclaiming capability for plastic waste. 
         [0048]    Based on the results, it has been verified that granite has an excellent capability in oil reclaiming for plastic waste. Furthermore, it was found that, as indicated by the results of analysis for components of collected oils, useful components can be obtained by virtue of processing at a low temperature of 150° C.