Patent Publication Number: US-2004050678-A1

Title: Plastic liquefying device

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to a plastic liquefying device for thermally decomposing plastic wastes to efficiently use the plastic wastes as reclaimed oil or the like.  
       BACKGROUND ART  
       [0002] Recently, one of the most serious issues in waste disposal problems to deal with ever-increasing wastes is how to dispose of plastic parts and plastic containers, which are utilized in a majority of industrial products such as electrical products, domestic house ware, automobiles, and PET (polyethylene telephthalate) bottles.  
       [0003] Since it is difficult to dispose of such plastic wastes by biodegrading (biological breakdown), which is commonly utilized to dispose of kitchen wastes, timber wastes or the like, the majority of such plastic wastes are generally incinerated. However, as is well known, when incinerating plastics, a large amount of funnel fume and poison gas are produced. Moreover, because of the high combustion temperature, there are problems such as the incinerator damage.  
       [0004] Therefore, recently an attempt has been made to collect these plastic wastes and recycle them as an important recycling resource. However, recycling plastic wastes entails onerous work such as collecting and separating plastic wastes by each type of plastic constituent, color, etc. As a result, the large amount of cost and labor is involved and the recycling plastic wastes does not meet its cost accounting.  
       [0005] The present inventors developed a novel plastic liquefying systems for efficiently disposing of the above-mentioned plastic wastes and recycling them as reclaimed oil or the like, and filed patent applications (Japanese Patent Application No. 2000-63335, etc.) for these systems.  
       [0006] As shown in FIG. 12, this plastic wastes liquefying device comprises mainly a gasifying furnace  1  for melting plastic wastes by way of heat from a gas burner  4 , etc. and generating pyrolytic gas by thermally decomposing, and a liquefying tank  2  for liquefying the pyrolytic gas which is generated in the gasifying furnace  1  after cooling and condensing. Specifically, after thermo-plastic wastes are melted and gasified into the pyrolytic gas including stylen-monomer and low monocular gravity polyethylene through a pyrolitical decomposition process in the gasifying furnace  1 . The pyrolitic gas is then contacted with cooling water to cause vapor-liquid contact, and is re-liquefied by being cooled and condensed in the liquefying tank  2 . Finally, the decomposed liquid is separated from the cooling water. The decomposed gas can be used as a material or the like for a new plastic product or fuel for a boiler, so that effective use of the decomposed liquid is achieved.  
       [0007] As shown in the drawings, the inlet of the gasifying furnace  1  is opened, and the plastic wastes can be loaded into the gasifying furnace  1 . The shutter  3  is closed. Then, the plastic wastes start melting and liquefying, and become fusion-liquid by the heat of the burner  4 . A part of the fusion liquid is sequentially and pyrolytically decomposed, then gasified. The pyrolytic gas flows into a gas line G through a gas outlet  5 , and reaches the liquefying tank  2 . This liquefying tank  2  integrally includes a jet scrubber  7 , a neutralization column  8 , etc. in a water tank  6  which stores the liquid. The pyrolytic gas reached to the liquefying tank  2 , is contacted with cooling water which belches up from the jet scrubber  7  having a cooling water circular line L 2  to cause vapor-liquid contact, and thus is rapidly cooled, condensed and liquefied. Then, the decomposed liquid resulting from the pyrolytic gas is temporarily stored into the water tank  6  together with the cooling water.  
       [0008] The above-mentioned blended liquid, which consists of the decomposed liquid and the cooling water, can be separated into the decomposed liquid and water at above and below respectively by specific gravity, after a certain time has elapsed. The decomposed liquid, which is separated into the upper side of the water tank, overflows a weir  9  positioned at the end of the water tank  6  and flows into an oil line L 1 . After removing solids by filtering through a filter  10 , reclaimed oil or the like made from decomposed oil can be collected into a recovery tank  12 . The water, which is stored in the lower side of the tank, can be pumped by a pump  11  out from the water tank  6  and re-sent into the jet scrubber  7  through a cooling water circular line L 2 . Afterwards, the water can be re-used as cooling water for cooling the high temperature pyrolytic gas which sequentially flows in.  
       [0009] The pyrolytic gas which has not been liquefied by the jet scrubber  7 , and detrimental constituents such as chlorine and bromine which cannot be liquefied by cooling, are sent to the neutralization column  8  in the form of gas. Then, the pyrolytic gas can be cooled and condensed again with the newly provided cooling water from a cooling water line L 4 , and be simultaneously neutralized by neutralizer supplied from a neutralization tank  13 . The process makes the pyrolytic gas harmless, and the harmless gas is retuned to the gasifying furnace  1  via a gas recovery line G 2 . Thus, the pyrolytic gas can be recycled as fuel gas, combustion air, etc. for the burner  4 . Also, the exhaust combustion gas which is emitted from the burner  4 , flows into an exhaust gas line G 1  through a jacket  16  which covers the gasifying furnace  1 , and is discharged into the atmosphere after being cleaned and filtered by a filter  14 . On the other hand, the superfluous cooling water which is stored in the water tank  6  of the liquefying tank  2  can be sequentially discharged through an exhaust line L 3 .  
       [0010] According to the above-described plastic liquefying device, it makes it possible to efficiently dispose of plastic wastes which were difficult to dispose of in the past. The plastic wastes can be recycled as burnable reclaimed oil, so that it promotes the economic and efficient recycling of plastic wastes. In regards to the above-mentioned process of recycling plastic wastes, it displays excellent effects such as the removal of the local area pollution, because in principal there is no possibility of any toxic gas leak. The reference numeral  15  denotes a hopper which facilitates the loading of plastic wastes into the device.  
       [0011] However, a few problems remain as described below, regarding the above-mentioned plastic liquefying device.  
       [0012] (1) After plastic wastes are loaded into the gasifying furnace  1 , the inlet of the gasifying furnace  1  is completely closed by a plate shutter  3 . As shown in FIG. 13A and FIG. 13B, the shutter  3  engages with rails  17  and  17  which are located at both sides of the shutter  3 , and can be horizontally moved to open and close along the rails  17  and  17  by a rack-and-pinion mechanism driven by a motor  18 . When the shutter  3  is closed, it is simply placed by its specific gravity on the sealing surface S of the inlet. Therefore, there would be a possibility that when the pressure in the gasifying furnace  1  is increased, the gas which is thermally decomposed may leak from the gap between the shutter  3  and the inlet, whereby the surrounding environment may be contaminated, the inner pressure may be lowered, and the amount of the thermally decomposed gas supplied may be decreased. Also, the plastic wastes and dirt may adhere to the sealing surface S of the inlet while loading the plastic wastes. Then the shutter  3  may not be closed completely, consequently leaving a gap between the shutter  3  and the inlet, and resulting in similar inconveniences.  
       [0013] (2) Also, if the solids (insolubles) such as dirt, metal scraps or timber are adhered to the plastic wastes which will be processed in the gasifying furnace  1 , these solids may accumulated or sticked to the bottom of the gasifying furnace  1  as residua, so that not only is the capacity of the furnace decreased but also the degree of heat conductivity may drastically deteriorate, because the accumulated solid may act as a heat insulant of the bottom of the furnace.  
       [0014] Therefore, regular removal of this accumulated solid is necessary, but this entails manual labor. Consequently, the device needs to be turned off and must be in a deactivated condition until the inside of the gasifying furnace  1  is cooled down completely. Then, workers have to remove the solid from the inlet with a scraper, a vacuum cleaner or the like, so that the work efficiency is drastically deteriorated and also the cleaning work is burdensome.  
       [0015] (3) In the liquefying tank  2 , the water and oil are separated by the specific gravity by way of an overflow system. For example, substances such as terephthalic acid, which is a constituent element of PET bottles, when heated, directly breaks down into condensation without liquefying, so that the substances accumulate into the bottom of water tank  6 , and this makes it difficult to collect them by the specific gravity separation. Thus, there is a limit on the types of plastic that can be dealt with. In addition, when the various kinds of mixed plastics are disposed, the process needs further labor work to separate the plastics depending upon the types of plastic before the disposal.  
       [0016] (4) Also, when plastic wastes such as injectors and catheters from medical institutions such as hospitals and clinics which may possibly contain infectious bacterial pathogen are disposed, it is necessary for such plastic wastes to be disposed after being submitted to sterilization for a given length of time under high pressure and high temperature. However, if the plastic wastes are disposed by the above-mentioned liquefying device in the same way as the normal plastic wastes disposal, in the initial process, the infectious bacterial pathogen which is adhered to the surface of these plastic wastes, is not sterilized completely and flows into the liquefying tank  2  together with the vapor. Consequently, the infectious bacterial pathogen may possibly contaminate the inside of the device or interfuse with the reclaimed oil.  
       DISCLOSURE OF THE INVENTION  
       [0017] One aspect of the present invention concerns a plastic liquefying device, which comprises a gasifying furnace for generating pyrolytic gas by heating and melting plastic wastes and a liquefying tank for liquefying the pyrolytic gas generated in the gasifying furnace and then separated. The gasifying furnace further includes a heating means provided at the bottom of the oven-shaped furnace body having an inlet at the top thereof for heating the inside of an oven-shaped furnace body, and an opening and closing mechanism positioned at the inlet for opening and closing the inlet. The opening and closing mechanism further includes a plate shutter which is larger than at least the opening area of the inlet and a locking means for securing the shutter to the sealing surface of the peripheral edge of the inlet.  
       [0018] Since the inlet for the plastic wastes can be hermetically closed, the lowering of the pressure inside the furnace due to gas leakage and the deterioration of the surrounding environment can be certainly prevented.  
       [0019] The shutter may include a sliding means for causing the shutter to move horizontally so as to open and close the inlet. For example, the sliding means can employ hydraulic cylinders, one end of which is connected to the shutter, and the other end is pivotably connected to the furnace body. Then, it is able to quickly open and close the inlet.  
       [0020] If the hydraulic cylinders which secure the shutter onto the sealing surface by way of pressure is employed as the above-mentioned locking means, the shutter can be completely closed.  
       [0021] If a purge gas header is provided at the peripheral edge of the inlet to spray purge gas onto the sealing surface of the inlet, thereby catching dust on the sealing surface, the sealing effect is prevented from being impaired.  
       [0022] If the bottom part of the furnace body has a corrugated shape defined by a plurality of canaliculate members which are placed parallel to each other, the superficial area of the bottom part of the furnace is enlarged. Then, the heat conductivity from the heating means to the furnace body can be enhanced, and an efficient melting process can be also promoted.  
       [0023] Each end of each of canaliculate members may merge to a discharge pipe, and also the canaliculate members and the discharge pipes may respectively include screw conveyers inside themselves. Then, the solids which have not been melted and have accumulated at the bottom of the furnace are easily discharged. Accordingly, the decrease of the furnace body capacity and the deterioration of the heat transmission can be avoided.  
       [0024] The heating means may include a gas burner. A jacket may be provided around the furnace for guiding the exhaust gas from the gas burner, and parting strips may be positioned spirally inside the jacket. The heat from the heating means is then efficiently transmitted to the furnace body, and the efficient melting is further promoted.  
       [0025] Another aspect of invention concerns a plastic liquefying device, which includes a gasifying furnace for generating pyrolytic gas by heating and melting plastic wastes and a liquefying tank for liquefying the pyrolytic gas generated in the gasifying furnace and then separating the pyrolytic gas. The gasifying furnace includes a vertical tube shape furnace body to receive infectious plastic wastes, a heating means for heating the furnace body from its surroundings to generate the pyrolytic gas by pyrolytically decomposing the infectious plastic wastes, and an agitator to agitate the inside of the furnace body. The top of the furnace body includes an inlet to receive the infectious plastic wastes, a lid to open and close the inlet and a gas outlet to discharge the pyrolytic gas. The gas outlet has an opening and closing valve which automatically opens and closes.  
       [0026] Accordingly, the furnace body can be hermetically sealed and the inside of the furnace body can be filled with high-pressure steam, so that the sterilization or removal of infectious bacterial pathogen which has adhered to plastic wastes can be completely undertaken.  
       [0027] Also, the above-mentioned furnace body may be made of a pressure vessel which includes hemispheric metal end covers respectively positioned at the top and bottom of the vertical tube-shaped metallic sack body. The opening and closing lid and gas outlet may also be provided at the top of the furnace body. Consequently, the inside pressure of the furnace body can be safely increased.  
       [0028] In addition, the above-mentioned agitator may include a drive shaft which is located at the shaft center part of the furnace body, a driving motor which rotates the drive shaft and a plurality of moving vanes which radially extend from the drive shaft. The moving vanes may revolve in contact with the bottom of the furnace body. So, when the plastic wastes are melted, an efficient pyrolytic decomposition can be conducted by agitating the inside of the furnace, and the deterioration of the heat transmission which can be caused by the solid or the like accumulated at the bottom of the furnace can be prevented.  
       [0029] If the bottom of the furnace further includes an outlet to discharge insolubles, the insolubles which have accumulated at the bottom of the furnace can be easily removed by driving the agitator. Accordingly, the cleaning of the inside of the furnace does not entail a large amount of labor and time.  
       [0030] Still another aspect of the present invention according to the present invention concerns a plastic liquefying device which comprises a gasifying furnace for generating pyrolytic gas by simultaneously melting various types of plastic wastes, and a liquefying tank for liquefying and separating the pyrolytic gas generated in the gasifying furnace. The bottom of the gasifying furnace is narrowed like a valley shape, which further includes a screw conveyer and a discharge opening for discharging insolubles at the bottom.  
       [0031] With this liquefying device, it is also easy to discharge insolubles, which have not been melted and have accumulated at the bottom of the surface, by driving the screw conveyer. Therefore, the decrease of the furnace body capacity and the deterioration of the heat transmission can be avoided.  
       [0032] The liquefying tank which may be a landscape water tank, may include a jet scrubber, which sprays cooling water onto the pyrolytic gas and condenses the pyrolytic gas, and a cleaning column, which cleans the exhaust gas. The bottom of the water tank may be narrowed like a funnel form. The bottom part may be connected to a drain line, and the middle part of the water tank is connected to an oil recovery line, so that the oil and water are separated, and the other substances of which specific gravity holds heavier than water can be certainly separated.  
       [0033] In addition, the drain line may include a neutralization tank for infusing the neutralizer. Therefore, the separated water can be efficiently neutralized. Consequently, the inconveniences such as acid corrosion of the pipes or the like caused by the acid water can be avoided. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0034]FIG. 1 is a longitudinal sectional view, which shows an embodiment of the gasifying furnace of the present invention;  
     [0035]FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1;  
     [0036]FIG. 3 is a cross-sectional view taken along the line Y-Y in FIG. 1;  
     [0037]FIG. 4 is a cross-sectional view taken along the line Y-Y in FIG. 1;  
     [0038]FIG. 5 is an enlarged partial view of the A part in FIG. 1;  
     [0039]FIG. 6 is an enlarged partial view of the A part in FIG. 1;  
     [0040]FIG. 7 is an enlarged partial view of the A part in FIG. 3;  
     [0041]FIG. 8 is an enlarged partial view of the B part in FIG. 3;  
     [0042]FIG. 9 is an enlarged partial view of the A part in FIG. 1;  
     [0043]FIG. 10 is a cross-sectional view taken along the line Z-Z in FIG. 1;  
     [0044]FIG. 11 is an enlarged partial view of the B part in FIG. 2;  
     [0045]FIG. 12 is a whole scheme diagram, which shows a conventional plastic liquefying device;  
     [0046]FIG. 13 is an enlarged partial view of the conventional plastic liquefying device&#39;s gasifying device;  
     [0047]FIG. 14 is a longitudinal sectional view, which shows another embodiment of the gasifying furnace in the present invention;  
     [0048]FIG. 15 is a cross-sectional view taken along the line A-A in FIG. 14;  
     [0049]FIG. 16 is a graph, which shows the relationship between the temperature and the pressure inside of the gasifying furnace shown in FIG. 14;  
     [0050]FIG. 17 is a whole scheme diagram, which shows an embodiment of the plastic liquefying device as it is in the present invention; and  
     [0051]FIG. 18 is a cross-sectional view taken along the line A-A in FIG. 17. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
     [0052] Hereinafter, the best mode of the present invention will be described in reference to the accompanying drawings.  
     [0053]FIG. 1 is a longitudinal sectional view, which shows an embodiment of gasifying furnace  19 , which is a part of the plastic liquefying device in the present invention. FIG. 2 is a cross-sectional view taken along the line X-X in FIG. 1.  
     [0054] As shown in the drawings, the gasifying furnace  19  comprises an oven-shaped furnace body including a plastic wastes inlet H, an opening and closing mechanism  21  for opening and closing the inlet H, and a heating means for heating the furnace body from its exterior. The furnace body has a structure which is covered with an insulative casing  23 .  
     [0055] The furnace body  20  is made of a metal such as hastelloy, stainless-steel or superalloy which has an excellent heat resistance, corrosion resistance, and heat conductivity effect. The plastic wastes which are loaded from the inlet H are melted by the heating means  22  and pyrolytically decomposed. The pyrolytic gas is supplied sequentially into the above-mentioned liquefying tank from a gas outlet  20   a.    
     [0056] The opening and closing mechanism  21  includes a plate shutter  24  for opening and closing the plastic wastes inlet H and a locking means  25  for locking the shutter  24  by pressing the shutter  24  onto sealing surface S which is formed around the peripheral edge of the inlet H.  
     [0057] As shown in FIG. 3 and FIG. 4, the shutter  24  has a similar shape to the inlet H which opens in a rectangle shape. The shutter is made of a heat resistant rectangle plate, which is sufficiently larger than the aperture area of the inlet H. In addition, the both side of the shutter includes two pairs of wheels  26 ,  26 ,  26 ,  26  (4 wheels in total) (either one or two pairs). Since these wheels run along a pair of rails  27  and  27  which extend horizontally from both sides of the inlet H, the shutter is horizontally moved by a sliding motion to the inlet H. Also, both side ends of the shutter  24  integrally include brackets  28  and  28  which extend in an orthogonal direction to the shutter&#39;s movable direction, and the inlet H is opened and closed by sliding the shutter  24  in a horizontal direction by way of a sliding means, which includes a pair of hydraulic cylinders  29  and  29 . That is to say, both one end of each hydraulic cylinder  29  is fixed to a bracket  28  of the shutter  24  while the other side is fixed to the bracket  30  of an inlet casing  23   a . Consequently, as shown in FIG. 4, by simultaneously expanding and contracting the hydraulic cylinders  29  and  29  from brackets  30  and  30  which are starting points, the shutter  24  is controlled to be easily opened and closed.  
     [0058] As shown in FIG. 1 and FIG. 2, the locking means  25  includes totally four hydraulic cylinders  31  which each pair of which is provided at back and forth respectively and vertically supported on the upper part of the inlet casing  23   a , and channel shape presser claws  32 , which are provided at the each corner of shutter  24 . When the shutter  24  is closed, each presser claw  32  and each cylinder rod  33  of each hydraulic cylinder  31  are engaged with each other. Thus, the shutter  24  is secured by engaging the presser claws  32  to the piston rods  33  so that the inlet H is completely closed.  
     [0059] As shown in FIG. 5 to FIG. 8, each of cylinder rods  33 ,  33 ,  33 ,  33  includes circular plate shape collars  34 . After the presser claws  32  are fitted with piston rods  33 , the cylinder rods  33  are extended and their collar parts  34  forcibly press presser claws  32  down. Accordingly, the shutter  24  is pressed onto the sealing surface S at each of four collar parts. After closing the inlet H completely by the shutter  24 , pulling the cylinder rods  33  in an upper direction results in easy unlocking of the shutter  24  to resume a sliding.  
     [0060] When the shutter  24  is pressed forcibly down to the inlet H, and the rails  27  and  27  which support the shutter  24  are fixed, the vertical movement of the shutter  24  is limited by the wheels  26 . Therefore, as shown in FIG. 1 and FIG. 3, in the present embodiment, the rails  27  and  27  are divided into two parts in a longitudinal direction. As shown in FIG. 5 and other drawings, the divided rail segments  27   a  and  27   a  which are arranged at the side of the inlet H are supported by a coiled spring  35  to be able to move in a vertical direction. As shown in FIG. 6, the rail segments  27   a  and  27   a  is movable in the up and down directions with the shutter  24 , so that the vertical movement of the shutter  24  is not limited. In addition, as shown in FIG. 5, the end of rail segments  27   a  and  27   a  are connected with H-shape connecting beam  36 . The cylinder rods  33  may further include another collar part  37  connecting with the connecting beam  36 , so that the divided rails  27   a  and  27   a  are simultaneously movable with the vertical movement of the cylinder rods  33 .  
     [0061] As shown in FIG. 11, at the peripheral edge of the inlet H of the furnace body  20 , a purge gas header  38  is extends along the perimeter of the peripheral edge. By spraying the purge gas supplied from the purge gas tank or the like (not shown) onto the sealing surface of the inlet H through a slit which opens at the upper part of the purge gas tank, even if a part of plastic wastes and dirt are adhered or accumulated on the sealing surface H, it is possible to remove them from the sealing surface S by the pressure of the purge gas. A slit  39  includes a guide piece  40  to guide the purge gas into the direction of sealing surface H. The guide piece  40  is made of a flexible blade spring. When the shutter  24  is opened or closed, the guide piece  40  is easily deflected, so that there is no interference with the shutter  24 .  
     [0062] As shown in FIG. 1, FIG. 2 and FIG. 10, the bottom part of the furnace body  20  forms a corrugated shape by having a plurality of canaliculate shape members  20   b ,  20   b  . . . in parallel to each other. The each end of the canaliculate shape members  20   b ,  20   b  . . . includes a similar canaliculate shape discharge pipe  20 C to merge extending herefrom. The bottom area of the furnace body is larger than a flat plate bottom. In particular, it is about ½π rtimes larger than the flat plate bottom area.  
     [0063] Further, the inside of each of the canaliculate shape members  20   b ,  20   b  . . . and the discharge pipe  20   c  coaxially include rotatable screw conveyers  41 ,  41  . . . which extend in a longitudinal direction, so that the insolubles accumulated at the bottom of the furnace, such as dirt, metal scrape, a glass, or sludge, are forcibly scraped from the bottom wall of the furnace and discharged from the discharge opening  42  which is formed on the casing  23  through canaliculate member  20   b ,  20   b  . . . to the discharge pipe  20   c . The discharge opening  42  includes an opening and closing valve (not shown). Of course, the valve is closed while in operation in order not to leak any melting liquid or give off any pyrolytic gas from the discharge opening  42  to the outside.  
     [0064] Each end of rotation axis of the screw conveyers  41 , 41  . . . which are provided in the canaliculate shape members  20   b ,  20   b  . . . penetrates casing  23  and extends to the outside respectively. Each end of the axis of the screw conveyers  41  further includes pulleys  43 ,  43  . . . respectively. By connecting each pulley  43  to a scraping motor  44  which is fixed to the outside of the casing, with a belt  45 , the screw conveyers  41 , 41  . . . can be rotated simultaneously in the same direction.  
     [0065] The end of rotation axis of the screw conveyer  41  which is located in the side of the discharge pipe  20   c , also penetrates the casing  23  and extends to the outside. The screw conveyer is rotated by connecting the pulley  46  located at the end of the screw conveyer to a discharge motor  47  with a belt  48 .  
     [0066] As shown in FIG. 11, reinforcing plates  49 , 49  . . . which are band plate shapes, and extend in an elongated direction are provided among the canaliculate shape members  20   b ,  20   b  . . . . A metal heat gauge  50  is embedded in the reinforcing plate  49 . The strength of the bottom furnace is maintained by these reinforcing plates  49 ,  49  . . . . The temperature of the bottom furnace can be measured at any time by the metal heat gauge  50 . In addition, the temperature information read on the metal heat gauge  50  is input into the control unit which controls output from a gas burner which will be described hereinbelow.  
     [0067] As shown in FIG. 1 and FIG. 2, a heating means  22  for heating the furnace body  20  includes a combustion chamber  51  which is located at the bottom of the furnace body  20 , a gas burner  52  which is provided in the combustion chamber  51  and a jacket  53  which covers around the furnace body  20  while maintaining a certain distance from it. The furnace body  20  can be heated from its bottom part by combustion gas generated in the combustion chamber  51  by the gas burner  52 . The exhaust combustion gas is guided into the jacket  53  which is communicated with the combustion chamber  51  and further guided to the outside from an exhaust gas exit  54  which is located at the top part of the jacket  53 . Because of this structure, the furnace body  20  can be heated from its lateral side and its surroundings.  
     [0068] The present embodiment further includes parting strips  55  which spirally separate the inside of the jacket  53 . The high temperature exhaust combustion gas which is guided into the jacket  53  is not directly flown into the gas exit  54 , but the gas is spirally flown around the furnace body  20  by the parting strips  55 . Consequently, it makes it possible to cause the longest contact between the high temperature exhaust combustion gas and the furnace body  20 . As shown in FIG. 1 and FIG. 2, the reference numeral  56  denotes a maintenance hatch for opening and closing the combustion chamber, and the reference numeral  57  denotes its opening and closing lid. The reference numerals  58  and  58  denote supporting legs for the furnace body. The reference numeral  59  denotes a hopper to facilitate the loading of the plastic wastes. The reference numeral  60  denotes a view port for checking the inside of the combustion chamber  51 .  
     [0069] In the gasifying furnace  19  of the present invention which has the above-described structure, the shutter  24  which closes the inlet H of the furnace body  20  is closed in such as that the shutter  24  is pressed to the sealing surface S of the inlet H by way of hydraulic cylinders  31 , presser claws  32  and the like. Therefore, even if the inside of the pressure of the furnace body  20  is raised during its operation, the gap between the shutter  24  and the sealing surface S can not be compromised. Accordingly, inconveniences such as contaminating the surrounding environment because of harmful pyrolytic gas leaks can certainly be prevented.  
     [0070] In addition, the peripheral edge of the inlet H includes a purge gas header  38 . When the shutter  24  is closed, the high pressure purge gas is sprayed onto the sealing surface S from the purge gas header  38  in order to certainly remove the part of the plastic wastes and dirt from the sealing surface, which may be attached when the plastic wastes are placed. Therefore, it is certainly avoided to compromise the gap on the sealing surface because of the attachment of the dirt, or the like.  
     [0071] The surface of the bottom of the furnace body  20  is enlarged by forming a corrugated surface at the bottom of the furnace body  20  with a plurality of canaliculate shape members  20   b , so that the contact surface between the high temperature generated combustion gas and the bottom of the furnace is enlarged. Consequently, the heating efficiency of the furnace body  20  is improved and efficient melting or pyrolytic decomposition can be achieved. Moreover, the screw conveyers  41  are provided in the canaliculate shape member  20   b  or the like, so that solids, sludge, or the like which has accumulated or attached to the bottom of the furnace are scraped from the bottom of the furnace and are easily removed. Accordingly, there is no need to remove them by hand, which was previously burdensome work in the conventional device. Also, the removal can be done even when the furnace body maintains a high temperature, so that the down time of the furnace body is curtailed and a high operating rate can be maintained.  
     [0072] The metal heat gauge  50  for measuring the temperature of the bottom of the surface is provided at the bottom of the furnace, so that it is possible to accurately measure the temperature of the whole furnace body  20  together with a conventional furnace body heat gauge. For example, when the temperature gap between the temperature of the bottom of the furnace measured by the metal heat gauge  50  and the temperature of the inside of the furnace body  20  measured by the furnace body heat gauge is small, it can be determined that the gasifying process has not finished and the operation should be maintained. On the other hand, when the temperature gap exceeds a predetermined value, it can be determined that the gasifying process has finished.  
     [0073] In the operating method of the plastic wastes furnace according to the present embodiment, it is necessary to add some water at the same time or about the time when the plastic wastes are loaded at its initial operation stage, which is same as in the above-mentioned conventional device. However, because of the corrugated shape of the furnace bottom, the contact surface between the loaded plastic wastes and the bottom of the furnace (furnace wall) is decreased. Consequently, in the initial operation stage, there is a possibility that the heat transmission (melting) cannot be performed under the best conditions. For example, if a small amount of high boiling oil such as reclaimed oil is added with the water, following the water evaporation, the high boiling oil evaporation could be carried out. Accordingly, even if the contact surface between the plastic wastes and the heat transmission surface (furnace wall) is small, the heat transmission can be efficiently carried out, and effective melting can be accomplished.  
     [0074]FIG. 14 is a longitudinal sectional view which shows an embodiment of another gasifying furnace  60  for gasifying the infectious plastic wastes which especially have a possibility of the attachment of the infectious bacteria pathogen in injectors or the like compared with the above-mentioned plastic wastes. FIG. 15 is a cross-sectional view taken along the line A-A in FIG. 14.  
     [0075] As shown in the drawings, the gasifying furnace  60  mainly includes an elongated tube shape furnace body  61  for pyrolitically decomposing infectious plastic wastes and generating pyrolytic gas, a heating means  62  for heating the furnace body  61  from its bottom and an agitating means  63  for mixing the inside of the furnace body  61 .  
     [0076] The furnace body  61  is made of a metal such as hastelloy, stainless-steel or superalloy which has an excellent heat resistance, corrosion resistance, and heat conductivity effect. The furnace body  61  is a pressure vessel, in which top and bottom of a longitudinal tube shape sack body  64  respectively include hemispheric end covers  65  and  66 . An inlet  67  for the placement of the plastic wastes is provided at the top end cover  65 . Moreover, the inlet  67  can be opened and closed by the flanged type opening and closing lid  68 . The inlet  67  is connected to the feed water pipe  69  for feeding water to promote melting in the initial stage. The feed water pipe  69  can be opened and closed by a magnetic valve V.  
     [0077] A gas outlet  70  is provided at the upper part of the sack body  64 , and pyrolytic gas which is generated by the furnace body  61  can be guided into the above-mentioned liquefying tank  2 . Moreover, the gas outlet  70  also includes an automatic opening and closing valve  71  and the gas outlet  70  can be automatically opened and closed by a predetermined condition which is mentioned below.  
     [0078] The bottom end cover  66  of the furnace body  61  includes an insoluble vent  72  for removing insolubles such as sand or metal pieces, which have accumulated at the furnace bottom, as needed.  
     [0079] The heating means  62  includes a combustion chamber  73  located at the bottom of the furnace body and jacket  74  which covers the surrounding area of the furnace body  61  from the combustion chamber  73 . A heating device  75  located in the combustion chamber  73 , such as a gas burner, an oil burner or an electrical heater, directly heats the furnace body  61  from its bottom. When the gas burner, the oil burner or the like which utilizes fossil fuel is employed as the heating device  75 , the high temperature of combustion gas generated in the combustion chamber  73  is guided into the exhaust gas outlet  76  through jacket  74 . Accordingly, the furnace body can be heated evenly over its entire body.  
     [0080] An agitator  63  located in the furnace body  61  includes a drive shaft  77  which is positioned in the shaft center part of the furnace body  61 , a driving motor  78  which is installed at the upper part of the drive shaft  77  to rotatably drive the drive shaft  77 , and a plurality of moving vanes  79 ,  79 ,  79 ,  79  which radially extend from the bottom part of the drive shaft  77 , to efficiently melt the infectious plastic wastes loaded in the inside of the furnace body  61  by mixing and heating the wastes evenly. As shown in FIG. 2, the tips of the moving vanes  79 ,  79 ,  79 ,  79  are curved toward the down stream side of the rotative direction, and the bottoms of the moving vanes  79  are normally in contact with the bottom of the furnace. When the moving vanes revolve and slide on the bottom surface like scraper, the attachment and accumulation of stickum, insolubles or the like to the bottom of the furnace can be prevented.  
     [0081] One example of the operation method for the gasifying furnace  60 , which has the above-mentioned structure of is described below.  
     [0082] Firstly, as shown in FIG. 14, after an inlet  67  positioned at the top of the furnace body  61  is opened, infectious plastic wastes and a small amount of water are loaded into the inside of the furnace body  61 . Then, an automatic opening and closing valve  71  of a gas outlet  70  and a valve V of the water feed pipe  69  are closed. In other words, the furnace body  61  is hermetically closed, and the furnace body  61  can be heated by the heating means  62  with driving an agitator  63 .  
     [0083] In the furnace body  61 , firstly water which has a lower boiling point starts evaporating by the heating mentioned above. Following to the evaporation, the pressure and the temperature inside the furnace body are gradually raised, as shown in FIG. 16. The heating means  62  is adjusted as needed to keep the pressure or temperature which eradicates infectious bacterial pathogen, for example, as shown in FIG. 16, the saturation pressure can be established at 121° C. water temperature, and the condition is maintained for a predetermined time of period, twenty minutes, for example. Then, the infectious bacterial pathogen which is attached to the plastic wastes is completely eradicated by steam sterilization un der pressure. Therefore, there is no possibility that the infectious bacterial pathogen flows into the liquefying tank  2  together with pyrolytic gas.  
     [0084] Thus, after meeting the condition in which the infectious bacterial pathogen is completely sterilized, as shown in FIG. 16, the inside pressure of the furnace body  61  can be decreased by gradually opening the automatic opening and closing valve  71  of the gas outlet  70 . At the same time, the inside temperature is raised by increasing the energy output of the heating means. In the furnace body  61 , following the evaporation of the water which has placed at the first stage of the operation, plastic wastes start melting. Also, the temperature is increased, and when the temperature reaches the gasifying temperature, for example 380° C., the melt liquid is pyrolitically decomposed and gasified. The pyrolytic gas is sequentially guided into the liquefying tank  2 , and then the oily water separation, which is conducted in the same way as the conventional process, is undertaken. Such reclaimed oil or the like can be effectively utilized.  
     [0085] In the gasifying furnace  60  according to the present embodiment, it is possible that the furnace body  61  can be hermetically closed with high pressure and under high temperature for a certain period of time, so that the infectious plastic wastes such as injectors or catheters for infectious disease, in which the infectious bacterial pathogen is attached, can be pyrolitically decomposed of safely and surely.  
     [0086] After all the plastic wastes loaded inside the gasifying furnace  60  has pyrolitically decomposed, the same disposal process can be repeated by butch processing. However, in cases of metal pieces such as injector needles or insolubles (solid) such as dirt which have gradually accumulated inside the furnace body during pyrolytic decomposition, the insolubles disposal exit  72  at the bottom of the furnace body  61  can be opened, and the insolubles can be easily removed by revolving the moving vanes  79  of the agitating means  63 . Accordingly, disadvantages such as the deterioration of the heat transmission and the decrement of the furnace capacity, which are caused by the attachment and accumulation of the insolubles at the furnace bottom, are easily eliminated.  
     [0087]FIG. 17 and FIG. 18 show other embodiments of the plastic liquefying device according to the present invention.  
     [0088] As shown in the drawings, this plastic liquefying device mainly comprises a gasifying furnace  80  for melting plastic wastes, generating pyrolytic gas and a liquefying tank  81  for condensing and separating the pyrolytic gas which is generated in the gasifying furnace  80 , similar to the conventional device.  
     [0089] Firstly, as shown in FIG. 1 and FIG. 2, the gasifying furnace  80  comprises a heating means  83  for heating a furnace body  82  from its exterior. The heating means is located in the furnace body  82  having an inlet H at its upper part. The variety of mixed plastic wastes (which are limited to the thermoplastics) which are loaded from the inlet H, are melted by the heating means  83 , and gasified. The pyrolytic gas is guided into the liquefying tank  81  through a gas line G 1  from a gas outlet  84 .  
     [0090] A closure lid  85  is connected to the end of the inlet H located at the furnace body  82  by way of hinges. The closure lid  85  is arbitrarily opened and closed by an opening and closing member  86  such as a motor cylinder, which is positioned between the bottom surface of the closure lid and the wall of the inside furnace body  82 .  
     [0091] The bottom of the furnace body  82  curves into a valley shape toward its center. A screw conveyer  87  which extends in a horizontal direction is provided at the bottom part of the valley shape. As shown in FIG. 2, the screw conveyer  87  integrally includes a spiral screw  89  around a rotation axis  88  which extends along an elongated direction of the bottom part of the valley shape. One end of the rotation axis  88  penetrates the furnace body  82  and connects to a driving motor  90  which is located outside, so that the axis of rotation  88  revolves in both directions by the driving motor  90 . The other end of the rotation axis  88  includes a discharge opening  91 . The discharge opening  91 , which can be opened and closed, is closed by an exhaust lid  92 .  
     [0092] As shown in FIG. 1, the heating means  83  for heating furnace body  82  includes three flat shape heaters  93 ,  94 ,  95 . The flat shape heater  94  is located at the bottom of the furnace body  22 , and the flat shape heaters  93  and  95  are located at the both sides of the bottom part, and independently operate.  
     [0093] The liquefying tank  81  liquefies the pyrolytic gas which is guided from the gas line G 1  and stores the pyrolytic gas temporarily. A landscape tank  96  includes a jet scrubber  97  which sprays cooling water onto the pyrolytic gas guided from the gas line G 1  and condenses it, and a cleaning column  98  which cleans and exhausts unliquefied gas which has not liquefied by the jet scrubber  97 .  
     [0094] The bottom of the water tank  96  narrows into a funnel-like shape. The rock bottom part is connected to a drain line L 1  through a valve V 1  and the middle part is connected to an oil recovery line L 2  through a valve V 2 .  
     [0095] This drain line L 1  includes a strainer  99  and a circulating pump  100 . The drain line L 1  extracts water from the water tank  96 , circulates the water to the above-mentioned jet scrubber  97  and the cleaning column  98 , and also returns a part of the water to the above-mentioned gasifying furnace  80  through a return line L 3 . In addition, the return line L 3  and its branch part include lines L 1 , L 3 , a scrubber line L 4  and magnetic valves V 3 , V 4 , V 5 , V 6  which respectively open and close the cleaning column line L 5 .  
     [0096] Also, the drain line L 1  is connected to a neutralization tank  101  via a branch line L 6  and a valve V 7 , and the water extracted from tank  96  is neutralized by injecting the neutralizer. A cooling water line L 9  and valve V 9  branch off from the scrubber line L 4 , and cooling water (tap water) is supplied to the jet scrubber  97 . Furthermore, the oil recovery line L 2  includes a reclaimed oil tank  102 , and the reclaimed oil, which was separated in the water tank  96 , is extracted from the oil recovery line L 2  and stored.  
     [0097] A cleaning column  98  includes an upper spray nozzle  104 , a demister  105 , a lower spray nozzle  106  and a baffle plate  107  in orders from the top in the vertical column body  103 . The pyrolytic gas, which has not been liquefied by the lavation (tap water, etc.) that flows from a cleaning column line L 5  and a cooling water line L 10 , is cleaned and then sent to the exhaust line L 7 . Also, the exhaust line L 7  includes a pre-heater  108  and a catalytic deodorizer  109 , so that the gas is pre-heated and deodorized, and then is released to the atmosphere.  
     [0098] In the drawings, the reference numeral  110  denotes a level meter for measuring liquid level in the water tank and the reference numeral  111  denotes a translucent liquid level meter for checking the condition of the oily-water separation from the outside. Also, the reference numeral  112  denotes a heat insulating material for preventing the gas line G 1  which extends between the gasifying furnace  80  and the liquefying tank  81  from cooling down.  
     [0099] Next, the operation of the plastic liquefying device according to the present embodiment, which has above-mentioned structure, that is to say, the disposal process of the plastic wastes is described hereinafter.  
     [0100] Firstly, in the disposal process of plastic wastes, before loading the plastic wastes into the gasifying furnace  80 , a small amount of water is put into the furnace body  82  of the gasifying furnace  80 . Then the opening and closing lid  85  is closed, and the furnace body  82  is heated with a condition in which the inside furnace body  82  is hermetically closed. In this initial stage, there is no need to operate all flat shape heaters  93 ,  94 ,  95  of the heating means  83 , so that only one of the heaters, for example, the bottom part heater  94  is operated.  
     [0101] The water placed into the inside of the furnace body  82  evaporates into steam by the heat, and then flows into the liquefying tank  81  through the gas line G 1  from the gas outlet  84 . Furthermore, the steam flows into the drain line L 1 , the oil recovery line L 2 , and the exhaust line L 7 , etc. from the liquefying tank  81 . Accordingly, the steam expels all the air inside the device.  
     [0102] Thus, when the inside of the device is replaced with steam, the valve V 1  of the drain line L 1  connected to the liquefying tank  81  and the valve V 2  of the oil recovery line are closed. Then, the opening and closing lid  85  of the gasifying furnace  80  is opened again, and the plastic wastes to be disposed are loaded into the furnace body  82  from the inlet H. After the furnace body  82  is hermetically closed by closing the lid  85  again, the furnace body  82  is heated by the heating means  83 .  
     [0103] After melting and liquefying the plastic wastes which are loaded in the furnace body  82  by the heating means, the pyrolytic gas which is sequentially and pyrolitically decomposed, flows from the gas outlet  84  to the gas line G 1 , then reaches the jet scrubber  97  of the liquefying tank  81 . At this time, as shown in FIG. 18, the opening and closing lid  85  is secured to the furnace body  82  by bolts B or the like, so that the inside of the furnace body is hermetically closed. Accordingly, the pyrolytic gas leak is completely prevented and the above-mentioned infectious plastic wastes such as injectors are safely disposed of.  
     [0104] After that, the pyrolytic gas which has reached the jet scrubber  97 , is contacted with cooling water supplied from the drain line L 1  and the branch line L 4  to cause a vapor-liquid contact, and then the pyrolitic gas is rapidly cooled down and liquefied into reclaimed oil. The reclaimed oil is sequentially stored into the water tank  96  together with the cooling water. When the screw conveyer  97  is revolved, and the inside of the furnace is agitated, the melting process of plastic wastes in the gasifying furnace  80  is efficiently accomplished. Also, the pyrolytic gas is cooled down by way of the jet scrubber  97 , so that terephtalic acids or the like which directly solidifies from the gas, is not clogged. Thus, it is possible to maintain the efficient gas circulation. If the jet scrubber is substituted by for example, a fin-tube heat exchanger, such terephtalic acid which directly solidifies from the gas, is generated inside the tube, and may cause blockages by the accumulation of the solid. Even if the gas is solidified around the exit, the solid can be blown off by the jet water of the jet scrubber  97 . Thus, disadvantages such as blockage are not caused.  
     [0105] On the other hand, un-liquefied gas (pyrolytic gas), which could not be liquefied by the jet scrubber  97 , passes though the upper space of the water tank  96  as it is and after being cleaned by the cleaning column  98  and also deodorized and purified by the exhaust gas line L 7 , the pyrolytic gas exhausts into the atmosphere.  
     [0106] Thus, when all the plastic wastes loaded into the gasifying furnace  80  have been gasified into the pyrolytic gas and have flown into the liquefying tank  81 , the heating of the furnace body  82  is stopped. At this time, however, if the loaded plastic wastes include insolubles such as dirt, metal pieces or timber pieces, they accumulate at the furnace bottom, and cause the decrement of the furnace cap acity and the deterioration of the heat transmission from the heating means  83 . Accordingly, when such insolules are accumulated to some degree, as shown in FIG. 18, a lid  92  of a discharge opening  91  at the furnace bottom and the screw conveyer  87  are driven. Accordingly, the accumulated insolubles are carried to the discharge opening  91  and easily disposed of through the discharge opening  91 . Thus, the furnace body cleaning which is done by workers at the conventional device is no longer needed.  
     [0107] The mixed liquid of cooling water and reclaimed oil, which is stored in the water tank  96  of the liquefying tank  81 , is separated by its own specific gravity after setting for a while. In other words, the reclaimed oil which has a light specific gravity can be collected to the liquid surface, and water which has a heavy specific gravity is collected at the bottom part. Firstly, the valve V 2  of the reclaimed oil line L 2  is opened, and the reclaimed oil at the upper part flows into the reclaimed oil tank  102 , so that only reclaimed oil can be efficiently collected by the separate collection. After a certain amount of the reclaimed oil has been removed, the water can be extracted from the bottom through the drain line L 1 , which are then recycled as cooling water for the next process. However, as illustrated, if any substances such as solid terephtalic acid which specific gravity is heavier than that of water or oil is contained, it is accumulated in layers at the bottom of the tank. Therefore, when recycling the water in the water tank, the constituents which have heavier specific gravity, need to be previously extracted by the exhaust oil line L 8  which branches off from the upper part of the drain line L 1 . Then, only the substances which have a heavier specific gravity can be collected. Also, the water in the water tank can be recycled as cooling water for the water used at the initial operation and also as cooling water for the jet scrubber  97  as was mentioned above. Therefore, the effective utilization of the resource can be accomplished. If the extracted water includes chlorine or the like, it may incur acid corrosion of the pipes in each line. Therefore, the water is neutralized by adding an adequate dose of the neutralizer such as caustic soda. The water can be then recycled.  
     [0108] When the collection of the reclaimed oil is completed, new plastic wastes can be added, and the process, such as the above-mentioned heating and gasifying decomposition is carried out by batch processing. Thus, regardless of its composition, the majority of the plastic wastes can be efficiently disposed of and the effective utilization of resources can be accomplished.  
     [0109] The present embodiment employs the electrical flat shaped heaters  93 ,  94 ,  95  as the heating means  83  of the gasifying furnace  80 . However, a gas burner or the like may be alternatively used.