Abstract:
A waste oil combustion apparatus can use various kinds of waste oils and burn the same efficiently, and permits effective utilization of the thermal energy resulting from the combustion thereof. The apparatus includes a bottomed cylindrical combustion furnace, a waste oil supply unit for supplying waste oil into the furnace, an auxiliary-fuel supply unit for supplying auxiliary fuel for burning the waste oil in the furnace, an ignition burner for heating the furnace inside and the waste oil and auxiliary fuel to ignite the fuels, an air supply unit for supplying air to the furnace, and a controller for controlling each of the igniting burner, waste oil supply unit, auxiliary-fuel supply unit and air supply unit to act at a predetermined time and operate for a predetermined time. The waste oil is spirally swirled inside the furnace under the action of air from the air supply unit.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present invention contains subject matter related to Japanese Patent Application JP 2007-52837 filed in the Japanese Patent Office on Mar. 2, 2007, the entire contents of which being incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to a combustion apparatus using waste oils such as discarded lubricant, engine oil or the like as main fuel. 
         [0003]    Recently, the regulations on the industrial wastes have been tightened more and more. Large costs have been required for disposal of the waste oils including discarded animal oils such as beef tallow, vegetable oils such as soy-beam oil or mineral oils such as lubricant, insulation oil, engine oil, etc. Under these circumstances, it has been proposed to utilize such waste oils as fuel for combustion apparatuses such as a boiler, burner, etc. 
         [0004]    However, used soy-beam oil, which is a vegetable oil, for example, has a high ignition point and is not easy to burn since it contains impurities in volume. To solve this problem, a combustion apparatus using waste oils as auxiliary fuel has been proposed in Japanese Published Unexamined Patent Application No. H08-334220 (Patent Document 1). In such combustion apparatuses using waste oils as fuel, impurities contained in the oil cause carbon sludge to adhere to the inner wall of the combustion furnace or chamber, which leads to hard work for removing the carbon sludge. 
         [0005]    The combustion apparatus disclosed in Patent Document 1 uses kerosene as main fuel and waste oil as auxiliary fuel. However, this apparatus should be able to burn waste oils more efficiently. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore desirable to overcome the above-mentioned drawbacks of the related art by providing a combustion apparatus using various waste oils each as main fuel and capable of efficiently burning the waste oil and utilizing the resultant heat energy effectively. 
         [0007]    According to an embodiment of the present invention, there is provided a waste oil combustion apparatus including a bottomed cylindrical combustion furnace, a waste oil supplying means for supplying a waste oil into the combustion furnace, an auxiliary-fuel supplying means for supplying an auxiliary fuel for burning the waste oil in the combustion furnace, an ignition means for heating the combustion furnace inside and the waste oil and auxiliary fuel to ignite the fuels, an air supplying means for supplying air to the combustion furnace, and a controller for controlling each of the ignition means, waste oil supplying means, auxiliary-fuel supplying means and air supplying means to act at a predetermined time and operate for a predetermined time. The waste oil supplying means supplies the waste oil in such a manner that the latter is spirally swirled inside the combustion furnace under the action of air supplied from the air supplying means. 
         [0008]    The combustion apparatus according to an embodiment of the present invention uses waste oils each as main fuel and is capable of burning the waste oils having been discarded as wastes in the past, which contributes to deployment of resources. According to the embodiment of the present invention, the waste oil supplying means supplies the waste oil in such a manner that the latter is spirally swirled inside the combustion furnace under the action of air supplied from the air supplying means, whereby the waste oil can be burned with an improved efficiency. 
         [0009]    The foregoing and other features and advantages of the present invention will become apparent from the following detailed description of embodiments of the present invention when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  is a schematic longitudinal-sectional view of a waste oil combustion apparatus according to an embodiment of the present invention; 
           [0011]      FIG. 2  is a perspective view, enlarged in scale, of a substantial part of the apparatus shown in  FIG. 1 ; 
           [0012]      FIG. 3  explains the flow of fuel and air from the fuel supply pipe in the intake pipe of the apparatus shown in  FIG. 1 , in which  FIG. 3A  is a cross-sectional view of the combustion furnace and  FIG. 3B  is a longitudinal-sectional view of the combustion furnace; 
           [0013]      FIG. 4  is a sectional view of the intake pipe; 
           [0014]      FIG. 5  shows a flow of operations made in the waste oil combustion apparatus shown in  FIG. 1 ; 
           [0015]      FIG. 6  is a perspective view of a rotary kiln connected to the waste oil combustion apparatus; 
           [0016]      FIG. 7  is a schematic sectional view taken along the axis of rotation of the rotary kiln shown in  FIG. 6 , connected to the waste oil combustion apparatus; 
           [0017]      FIG. 8  is a schematic sectional view taken perpendicularly to the axis of rotation of the rotary kiln connected to the waste oil combustion apparatus; and 
           [0018]      FIG. 9  schematically illustrates an inner casing of the rotary kiln connected to the waste oil combustion apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    The embodiments of the present invention will be described in detail below concerning the embodiment thereof with reference to the accompanying drawings. 
         [0020]    As shown in  FIG. 1 , the waste oil combustion apparatus, generally indicated with a reference numeral  1 , includes an annular combustion cylinder  2 , a combustion furnace  3  provided inside the combustion cylinder  2 , an ignition burner  4  that heats the inside of the combustion furnace  3  to ignite the fuel and the like, a waste oil supply unit  5  to supply waste oil as main fuel into the combustion furnace  3 , a kerosene supply unit  6  to supply kerosene as auxiliary fuel into the combustion furnace  3 , an air supply unit  7  to supply air into the combustion cylinder  2 , a duct  8  to supply heat resulted from the combustion of the waste oil in the combustion furnace  3  to a heat exchanger or the like connected to the waste oil combustion apparatus  1  for effective utilization of the heat, and a controller  10  to control the operation of the entire apparatus. 
         [0021]    The combustion cylinder  2  is made of a heat resistant steel plate or the like. It includes a cylindrical annular portion  2   a , a top plate  2   b  that closes the upper end of the annular portion  2   a , and supporting members  2   c  provided near the lower end of the annular portion  2   a  to support the combustion furnace  3 . In the combustion cylinder  2 , the lower end of the annular portion  2   a  serves as a burning port. The duct  8  is connected to that lower end to supply the heat of combustion in the combustion furnace  3  inside the combustion cylinder  2  to the downstream. 
         [0022]    As shown in  FIG. 2 , the annular portion  2   a  of the combustion cylinder  2  is of a double structure being hollow to have an inner space  11  formed therein and to which water is supplied. The annular portion  2   a  has a water inlet  12  provided on the peripheral surface near the lower end of the annular portion  2   a  at which the latter is connected to the duct  8 , and the water inlet  12  communicates with the inner space  11 . The annular portion  2   a  has a water outlet  13  provided on the peripheral surface near the upper end at which a top plate  2   b  is provided, and the water outlet  13  communicates with the inner space  11 . Also, the annular portion  2   a  is connected at the water inlet  12  thereof to a water supply unit  14 . Water supplied from the water supply unit  14  is charged into the inner space II through the water inlet  12 , and it goes out of the inner space  11  through the water outlet  13 . In the annular portion  2   a , the water thus filled in the inner space  11  will serve as a coolant that cools the waste oil combustion apparatus  1 . The water supply unit  14  is of a well-known type, for example, a pump. 
         [0023]    The top plate  2   b  provided at the upper end of the annular portion  2   a  is a disc-shaped member that closes the upper end of the annular portion  2   a . It has an air inlet  15  connected to a blower  16  and through which air is supplied into the combustion cylinder  2 . The air inlet  15  is formed circular to blow air to between the combustion cylinder  3  and the annular portion  2   a  surrounding the former. 
         [0024]    The supporting members  2   c  support the combustion furnace  3  formed like a footman. More specifically, each of the supporting members  2   c  is formed from a bar-shaped member extending from near the lower end of the annular portion  2   a  of the combustion cylinder  2  toward the inside of the annular portion  2   a . The supporting member  2   c  is a little bent at the free end thereof toward the upper end of the annular portion  2   a . Also, the supporting member  2   c  is longitudinally hollow (as indicated with a reference numeral  2   d ) from one end thereof to the other, allowing air to pass through. The supporting member  2   c  is connected at one end thereto to an air blower  9  which is an air source. The air blower  9  is to supply air to the combustion furnace  3 . It blows air to the bottom of the combustion furnace  3  through the inner space  2   d  in the connected supporting member  2   c  to cool the combustion furnace  3 . 
         [0025]    The combustion furnace  3  is made of a heat resistant steel plate or the like to have the form of a bottomed cylinder. It is placed inside the combustion cylinder  2 . The combustion furnace  3  has formed therein near an open end  3   a  thereof an insertion hole  18  in which there is inserted a supply pipe assembly  17  through which waste oil, kerosene and air are supplied from the waste oil supply unit  5 , kerosene supply unit  6  and air supply unit  7 , respectively, to the combustion furnace  3 . The combustion furnace  3  has a bottom  3   b  on which there will be received the mist, not completely burned, of the fuels including the waste oil sprayed from the supply pipe assembly  17 . The fuels, including the waste oil on the bottom  3   b  of the combustion furnace  3 , are heated in the combustion furnace  3  for vaporization and burning. 
         [0026]    The ignition burner  4  is connected to the supply pipe assembly  17 . It uses kerosene, for example. The ignition burner  4  heats the inside of the combustion furnace  3  to ignite waste oil so that the waste oil combustion apparatus  1  can start combustion or other operation with only the waste oil. It should be noted that the ignition burner  4  is not limited to the above-mentioned type using kerosene but may be of a type using gas or the like. 
         [0027]    The waste oil supply unit  5  includes a first waste oil tank  19  in which waste oil is stored, a second waste oil tank  20  to which the waste oil is supplied from the first waste oil tank  19 , a heater  21  provided inside the second waste oil tank  20  to heat the waste oil in the second waste oil tank  20 , a waste oil supply pipe  22  through which the waste oil is supplied from the second waste oil tank  20  into the combustion furnace  3 , a waste oil pressure regulator  23  provided in the waste oil supply pipe  22  to regulate the pressure of the waste oil supplied from the second waste oil tank  20 , and a waste oil supply/stop valve  24  to supply or stop the waste oil to the combustion furnace  3 . 
         [0028]    The first waste oil tank  19  stores waste oil as main fuel for use with the waste oil combustion apparatus  1 . The second waste oil tank  20  is supplied with the waste oil from the first waste oil tank  19 . Using a liquid level adjuster (not shown) including a float and needle, the second waste oil tank  20  stores the waste oil supplied from the first waste oil tank  19  under a constant pressure. Inside the second waste oil tank  20 , there is provided a heater  21  that heats the waste oil in the tank to lower the viscosity of the waste oil. The heater  21  is of a well-known type, and its operation is controlled by the controller  10 . Water is supplied to the inner space  11  of the combustion cylinder  2  and given the heat of combustion in the combustion furnace  3 . The water thus heated is circulated through the water outlet  13  to the second waste oil tank  20  in which it further heats the waste oil being heated by the heater  21 . At this time, the controller  10  makes a selection between the heat exchange by the discharged hot water from the combustion cylinder  2  and the operation of the heater  21  in response to the operational status of the combustion furnace  3 . 
         [0029]    Note that for a lower viscosity of the waste oil in the second waste oil tank  20 , the latter may not be arranged to be supplied with the hot water from the combustion cylinder  2  as described above but may be provided in a position where it itself can be given the radiant heat from the combustion furnace  3 . 
         [0030]    The waste oil supply pipe  22  is connected to a fuel supply tube  29  (shown in  FIG. 4 ), which will further be described later, in the supply pipe assembly  17  to supply the waste oil from the second waste oil tank  20  to the combustion furnace  3 . The waste oil pressure regulator  23  is provided in the waste oil supply pipe  22  to regulate the pressure of the waste oil being supplied from the second waste oil tank  20  to the supply pipe assembly  17 . The waste oil pressure regulator  23  is controlled by the controller  10  to regulate the pressure of the waste oil being supplied. The waste oil supply/stop valve  24  is provided in the waste oil supply pipe  22  and downstream of the waste oil pressure regulator  23  to adjust the supply of the waste oil from the second waste oil tank  20 . Similarly to the waste oil pressure regulator  23 , the waste oil supply/stop valve  24  is operated (opened or closed) under the control of the controller  10 . 
         [0031]    Note that the waste oil pressure regulator  23  and waste oil supply/stop valve  24  may not be arranged separately from each other as above but they may be of an integral structure capable of adjusting the supply of the waste oil through the waste oil supply pipe  22  and regulating the pressure of the waste oil in the waste oil supply pipe  22 . 
         [0032]    The kerosene supply unit  6  includes a kerosene tank  25  in which kerosene as auxiliary fuel is stored, a kerosene supply pipe  26  to supply kerosene from the kerosene tank  25  into the combustion furnace  3 , a kerosene pressure regulator  27  provided in the kerosene supply pipe  26  to regulate the pressure of the kerosene supplied from the kerosene tank  25 , and a kerosene supply/stop valve  28  to supply or stop the kerosene to the combustion furnace  3 . 
         [0033]    The kerosene tank  25  stores kerosene as auxiliary fuel for the waste oil combustion apparatus  1 . The kerosene supply pipe  26  is connected to the fuel supply tube  29 , which will further be described later, in the supply pipe assembly  17  to supply the kerosene from the kerosene tank  25  to the combustion furnace  3 . The kerosene pressure regulator  27  is provided in the kerosene supply pipe  26  to regulate the pressure of the kerosene being supplied from the kerosene tank  25  to the supply pipe assembly  17 . The kerosene pressure regulator  27  is controlled by the controller  10  to regulate the pressure of the kerosene being supplied. The kerosene supply/stop valve  28  is provided in the kerosene supply pipe  26  and downstream of the kerosene pressure regulator  27  to adjust the supply of the kerosene from the kerosene tank  25 . Similarly to the kerosene pressure regulator  27 , the kerosene supply/stop valve  28  is operated (opened or closed) under the control of the controller  10 . 
         [0034]    Note that the kerosene pressure regulator  27  and kerosene supply/stop valve  28  may not be arranged separately from each other as above but they may be of an integral structure capable of adjusting the supply of the kerosene through the kerosene supply pipe  26  and regulating the pressure of the kerosene in the kerosene supply pipe  26 . 
         [0035]    As shown in  FIGS. 3 and 4 , the supply pipe assembly  17  includes a fuel supply pipe  29  to which the waste oil supply pipe  22  and kerosene supply pipe  26  are connected, an air supply pipe  30  having the fuel supply pipe  29  provided therein and which is supplied with air from the air supply unit  7 , and a heat shielding plate  31  provided to cover a portion, near the free end, of the air supply pipe  30 . The supply pipe assembly  17  is inserted in the insertion hole  18  provided near the open end of the combustion furnace  3  as shown in  FIG. 3  to supply fuel (waste oil and kerosene) and air into the combustion furnace  3 . 
         [0036]    The insertion hole  18  is to have the supply pipe assembly  17  inserted through it as above. It is formed so that the supply pipe assembly  17  is held tangentially to the inner circumference of the combustion furnace  3  as shown in  FIG. 3A  (cross-sectional view) and obliquely from above toward the bottom  3   b  of the combustion furnace  3  as will be seen in  FIG. 3B  (longitudinal-sectional view). This geometry is intended to swirl the fuel and air supplied from the supply pipe assembly  17  for efficient burning. 
         [0037]    The fuel supply pipe  29  is connected to the waste oil supply pipe  22  and kerosene supply tube  26  to supply waste oil and kerosene into the combustion furnace  3 . It is connected at one end thereof to the waste oil supply pipe  22  and kerosene supply pipe  26  to supply waste oil and kerosene as fuels into the combustion furnace  3 , and projected at the other end thereof into the combustion furnace  3 . 
         [0038]    The air supply pipe  30  is larger in inside diameter than the fuel supply pipe  29  and is laid coaxially with the latter. The air supply pipe  30  is connected at one end thereof to the air supply unit  7  and projected at the other end into the combustion furnace  3 . The air supply pipe  30  supplies air from the air supply unit  7  into the combustion furnace  3 . Also, the end, projected into the combustion furnace  3 , of the air supply pipe  30 , is deeper in the combustion furnace  3  than the corresponding end of the fuel supply pipe  29 . The free end, projected into the combustion furnace  3 , of the air supply pipe  30 , is somewhat reduced in inside diameter (as indicated with a reference numeral  30   a ). The smaller-diameter end  30   a  forms a Venturi tube that elevates the flow rate of supplied air to atomize waste oil etc. supplied from the fuel supply pipe  29  for spraying into the combustion furnace  3 . 
         [0039]    The heat shielding plate  31  covers the near free-end portion of the air supply pipe  30  to shield heat from the combustion furnace  3  in order to prevent the air supply pipe  30  from being overheated. The heat shielding plate  31  has an ignition hole  32  through which flame is taken in from the ignition burner  4 . 
         [0040]    The ignition hole  32  is provided in such a position near the end portion, inside the combustion furnace  3 , of the heat shielding plate  31  that fuel from the fuel supply pipe  29  can be ignited by the flame from the ignition burner  4 . 
         [0041]    The air supply unit  7  is a blower connected to the air supply pipe  30  to supply combustion air into the combustion furnace  3  and to atomize waste oil from the fuel supply pipe  29  for spraying into the combustion furnace  3 . 
         [0042]    The duct  8  is to supply the heat of combustion developed in the combustion furnace  3  to a drying equipment which is located downstream of the waste oil combustion apparatus  1 . The duct  8  is annular and generally equal in diameter to the combustion cylinder  2 . It is bent for one and other ends thereof to form an angle of about 90 degrees between them. As shown, the duct  8  is of a double structure being hollow to have an inner space  33  formed therein as in the combustion cylinder  2  and to which water is supplied. 
         [0043]    The duct  8  is connected at one end thereof to the bottom of the combustion cylinder  2  and at the other end to a rotary kiln  41  which will be described in detail later. Further, the duct  8  has a water inlet  34  provided at the peripheral surface thereof near the end at which it is connected to the rotary kiln  41  and which communicates with the inner space  33 , and a water outlet  35  provided at the peripheral surface thereof near the end at which it is connected to the combustion cylinder  2  and which communicates with the inner space  33 . The duct  8  is connected at the water inlet  34  thereof to a water supply unit  36  so that water is taken into the inner space  33  and discharged from the water outlet  35 . The water thus filled in the inner space  33  of the duct  8  serves as a coolant to cool the waste oil combustion apparatus  1 . The water supply unit  36  is of a well-known type, for example, a pump. 
         [0044]    Note that the water supply unit  36  that supplies water to the inner space  33  of the duct  8  may not be provided separately from the water supply unit  14  that supplies water to the inner space  11  of the combustion cylinder  2  as above but a single water supply unit may be used to supply water to the inner spaces  33  and  11 . 
         [0045]    The controller  10  is to control the operation of the entire waste oil combustion apparatus  1 . More specifically, the controller  10  controls the supply rate and pressure of water oil from the waste oil supply unit  5 , those of kerosene from the kerosene supply unit  6 , and supply rate etc. of air from the air supply unit  7 . The controller  10  includes a CPU (central processing unit), a memory and a timer, which are connected to each other via a bus or the like. The memory in the controller  10  has stored therein an operation timing program for each unit. The timer in the controller  10  counts a start time of each operation. CPU in the controller  10  counts a time count supplied from the timer, and controls the operation of each unit according to a corresponding program evoked from the memory. The controller  10  is connected to the ignition burner  4 , waste oil supply unit  5 , kerosene supply unit  6 , air supply unit  7 , air blower  9 , water supply units  14  and  36 , blower  16 , etc. and controls outputs from these units. 
         [0046]    Next, the operation for combustion of waste oil in the waste oil combustion apparatus  1  constructed as having been explained above will be explained with reference to  FIG. 5 . As shown, in step S 1 , the user turns on the power supply to -the waste oil combustion apparatus  1 . In step S 2 , the controller  10  puts, into operation, the ignition burner  4 , waste oil supply unit  5 , kerosene supply unit  6 , air supply unit  7  and blower  16 . Then, waste oil, kerosene and air supplied to the combustion furnace  3  are burned while being swirled down spirally along the inner surface of the combustion furnace  3  toward the bottom  3   b  and then swirled up from the bottom  3   b  toward the open end of the combustion furnace  3  as shown in FIG  3 . 
         [0047]    In step S 3  the controller  10  determines whether a predetermined time, for example, five minutes, has elapsed after each unit is put into operation in step S 2 . If the controller  10  has decided in step S 3  that the predetermined time has not elapsed, it will repeat the operation in step S 3 . In case the controller  10  has decided that the predetermined time has elapsed, it will go to step S 4 . Each unit is operated for the predetermined time in step S 3  in order to heat the inside the combustion furnace  3  by the ignition burner  4  to produce an atmosphere for easy combustion of the waste oil. 
         [0048]    Next, in step S 4 , the controller  10  controls the kerosene supply unit  6  to stop the supply of kerosene and the ignition burner  4 , to stop the operation. At this time, the controller  10  controls the waste oil supply unit  5  and air supply unit  7  to keep operating. 
         [0049]    Thus, in the waste oil combustion apparatus  1 , waste oil and air are supplied from the waste oil supply unit  5  and air supply unit  7 , respectively, into the combustion furnace  3  so that only the waste oil will be burned as fuel. At this time, the waste oil, kerosene and air supplied from the supply pipe assembly  17  into the combustion furnace  3  of the waste oil combustion apparatus  1  are swirled down along the inner surface of the combustion furnace  3  toward the bottom  3   b  of the furnace  3  and then swirled up from the bottom  3   b , which will assure efficient and stable combustion of the waste oil. Also, since the waste oil combustion apparatus  1  is so arranged that after elapse of the predetermined time, supply of the kerosene is stopped for combustion of the waste oil alone. Thus, it is possible to limit the consumption of the kerosene. Further in the waste oil combustion apparatus  1 , the blower  16  blows air into the space between the combustion cylinder  2  and combustion furnace  3  from the upper end toward lower end of the combustion cylinder  2  to guide the heat of combustion and flame in the combustion furnace  3  into the duct  8  (as indicated with a reference symbol A in  FIG. 1 ). 
         [0050]    In the waste oil combustion apparatus  1 , with the fuels and air being supplied into the combustion furnace  3  from the supply pipe assembly  17  provided at a predetermined angle in relation to the combustion furnace  3 , the waste oil can be burned more efficiently and positively. Also, since during operation of the waste oil combustion apparatus  1 , namely, during combustion of the waste oil, the combustion furnace  3 , combustion cylinder  2 , duct  8 , etc. are cooled while the air blower  9  and water supply units  14  and  36  are in operation, the durability of the entire apparatus is much improved. Further, since the controller  10  of the waste oil combustion apparatus  1  can lower the viscosity of the waste oil by controlling the operation of the heater  21  of the waste oil supply unit  5 , it is possible to assure efficient and positive combustion of the waste oil. 
         [0051]    Moreover in the waste oil combustion apparatus  1 , since it is possible to burn the waste oil efficiently and stably, the heat of combustion can be utilized for various purposes. 
         [0052]    For one of such purposes, the rotary kiln  41  may be connected to the downstream of the waste oil combustion apparatus  1  having been explained above, namely, to the end of the duct  8  to build a drying system for metal chips resulted from machining. This drying system can effectively utilize waste oil to dry the metal chips for recycling. 
         [0053]    The rotary kiln connected to the waste oil combustion apparatus  1  will be explained below with reference to the accompanying drawings. In the rotary kiln  41 , metal chips  44  resulted from machining, fed from on a belt conveyor  42  into a feeding hopper  43 , are guided by means of a spiral conveyor  45  into a rotary kiln body  51 , and then heated with hot air introduced into an outer casing  56  of the rotary kiln body  51  from an end of the latter opposite to the feeding hopper  43  of the rotary kiln body  51 , as shown in  FIG. 6 . The rotary kiln  41  includes a support base  52 , a rotary kiln body  51  supported on the support base  52  by means of support rollers  53  provided on the support base  52 , and a motor  54  to rotate the rotary kiln body  51 . 
         [0054]    The support base  52  is made of a heat resistant steel plate or the like. The plurality of support rollers  53 , motor  54 , etc. are fixed in place on the top of the support base  52 . It supports the rotary kiln body  51  on contact with the support rollers  53 . 
         [0055]    The support rollers  53  on the support base  52  are to support the rotary kiln body  51  rotatably. For example, four support rollers  53  may be provided on the support base  52 . 
         [0056]    The rotary kiln body  51  rotatably supported on the support rollers  53  is of a double structure including the outer casing  56  and an inner casing  55  provided in the outer casing  56  as shown in  FIGS. 6 to 8 . 
         [0057]    The inner casing  55  of the rotary kiln body  51  is made of heat resistant steel or the like to be generally cylindrical. At one end  55   a  of the inner casing  55 , there is provided the spiral conveyor  45  into which metal chips  44  to be dried are put. The inner casing  55  is supplied at the other end  55   b  thereof with the heat of combustion from the waste oil combustion apparatus  1 . Also, the inner casing  55  has provided on the inner surface  55   c  thereof a plurality of first feed vanes  57  that move the metal chips  44  fed from the spiral conveyor  45  in a direction from the one end  55   a  to the other end  55   b  as shown in  FIGS. 7 to 9 . 
         [0058]    The first feed vanes  57  are provided intermittently on the inner surface  55   c  of the inner casing  55  to project inwardly of the latter and depict a virtual spiral extending from the one end  55   a  toward the other end  55   b . The first feed vanes  57  are fixed obliquely in a direction in which rotation of the inner casing  55  converts circumferential motion into axial motion The inner casing  55  is rotated along with the outer casing  56 , so that the first feed vanes  57  move the metal chips  44  put in the inner casing  55  in a direction from the one end  55   a  to the other end  55   b  while shaking them The first feed vanes  57  are intermittently disposed in order to forward the heat of combustion supplied from the waste oil combustion apparatus  1  in a direction toward the one end  55   a  of the inner casing  55 . 
         [0059]    The outer casing  56  having the inner casing  55  provided therein made of a heat resistant steel plate or the like to be generally cylindrical. The outer casing  56  is large enough in diameter to house the inner casing  55 , and provided concentrically with the inner casing  55 . One end  56   a  of the outer casing  56  is opposite to the one end  56   a . As shown in  FIG. 2 , the outer casing  56  has provided on the inner surface  56   c  thereof a plurality of second feed vanes  58  that take in the heat of combustion from the waste oil combustion apparatus  1  and move, to the other end  56   b  of the outer casing  56 , the metal chips  44  which are to be passed from the other end  55   b  of the inner casing  55  to the other end  56   b  of the outer casing  56 . 
         [0060]    The second feed vanes  58  are provided intermittently on the inner surface  56   c  of the outer casing  56  to project inwardly of the latter and depict a virtual spiral extending from the one end  56   a  toward the other end  56   b . The second feed vanes  58  are fixed obliquely in a direction in which rotation of the outer casing  56  converts circumferential motion into axial motion The second feed vanes  58  are directed crosswise in relation to the first feed vanes  57 . The outer casing  56  is rotated along with the inner casing  55  to move, by the second feed vanes  58 , the metal chips  44  transferred from the inner casing  55  in a direction from the other end  56   b  to the one end  56   a  while shaking them. Similarly to the first feed vanes  57 , the second feed vanes  58  are intermittently disposed in order to forward the heat of combustion supplied from the waste oil combustion apparatus  1  in a direction toward the one end  56   a  of the outer casing  56 . The outer casing  56  further has provided on the outer surface  56   d  thereof rings  59  which are received on the support rollers  53 , and a transmission member  61  that transmits the driving force from the motor  54  to the rotary kiln body  51  through a change belt  60 . 
         [0061]    The rings  59  are positioned on the outer surface  56   d  of the outer casing  56  for engagement on the support rollers  53 . The transmission member  61  is annular to extend over the outer surface  56   d  of the outer casing  56 , and positioned to face the motor  54 . It is a kind of rack, for example, which is in mesh with the chain belt  60 . 
         [0062]    The rotary kiln body  51 , having the double structure including the inner and outer casings  55  and  56  as above, is coupled by a coupling member  62  to each other to be concentric with each other. The coupling member  62  is to couple the inner and outer casings  55  and  56  securely to each other at the one end  55   a , for example, of the inner casing  55 , whereby rotation of the outer casing  56  by the motor  54  leads to similar rotation of the inner casing  55 . In the rotary kiln body  51 , since the direction of the first feed vanes  57  spirally provided in the inner casing  55  is different from that of the second feed vanes  58  also spirally provided in the outer casing  56 , the metal chips  44  in the inner casing  55  and those in the outer casing  56  can be moved in different directions with the inner and outer casings  55  and  56  being rotated in the same direction 
         [0063]    Note that the coupling member  62  may not be provided in a limited place such as the one end  55   a  of the inner casing  55  but may take any form or may be provided in more than one place so long as it can securely couple the inner and outer casings  55  and  56  to each other so that they are concentric with each other. 
         [0064]    The spiral conveyor  45  to feed the to-be-dried metal chips  44  to the one end  55   a  of the inner casing  55  is generally cylindrical. It has provided therein a vane  63  that moves the supplied metal chips  44 . The spiral conveyor  45  has connected thereto a motor  64  that rotates the vane  63 . The spiral conveyor  45  has the feeding hopper  43  installed at one end  45   a  thereof, and is inserted at the other end  45   b  thereof in the one end  55   a  of the inner casing  55 . The vane  63  of the spiral conveyor  45  extends spirally to move the metal chips  44  from the one end  45   a  toward the other end  45   b.    
         [0065]    Note that the spiral conveyor  45  may not be constructed as above but may be of any structure so long as it can move the metal chips  44  into the inner casing  55 . 
         [0066]    The feeding hopper  43  installed to the spiral conveyor  45  is to feed the metal chips  44  to the spiral conveyor  45 . The feeding hopper  43  has, for example, a vibrator etc. (not shown) and feeds a predetermined amount of the metal chips  44  to the spiral conveyor  45  under the effect of vibration given by the vibrator. 
         [0067]    The rotary kiln  41  further has a blower  65  for cooling the surface of the rotary kiln body  51 , that is, the outer surface  56   d  of the outer casing  56 , and a blower  66  for cooling the metal ships  44  already dried and going to be discharged from the rotary kiln body  51  at the one end  56   a  of the outer casing  56  while forwarding the heat of combustion from the waste oil combustion apparatus  1  into the rotary kiln body  51 . The rotary kiln  41  also has provided at the one end  56   a  of the outer casing  56  a duct  67  which guides air from the blower  66 . 
         [0068]    In the rotary kiln  41  constructed as above, the motor  54  is driven to rotate the rotary kiln body  51  and take in the heat of combustion from the waste oil combustion apparatus  1  into the rotary kiln body  51  from the other end  56   b  of the outer casing  56 . In this condition, the metal chips  44  are fed by the spiral conveyor  45  from the one end  55   a  of the inner casing  55 , and shaken and moved by the first feed vanes  57  from the one end  55   a  to the other end  55   b  while being heated. At the other end  55   b  of the inner casing  55 , the metal chips  44  take a position near the waste oil combustion apparatus  1  which is a heat source, and thus dried and transferred to the other end  56   b  of the outer casing  56 . Further, the metal chips  44  are shaken and moved by the second feed vanes  58  from the other end  56   b  to one end  56   a  of the outer casing  56 . That is, they are moved away from the waste oil combustion apparatus  1  which is the heat source, while gradually releasing the heat. Finally, the metal chips  44  thus heated and dried are discharged from the one end  56   a  of the outer casing  56 . 
         [0069]    In the above rotary kiln  41 , since the metal chips  44  are dried in both forward and backward ways, the rotary kiln body  51  can be designed shorter in whole length. Therefore, the rotary kiln  41  can be formed smaller. The reduction in whole length of the rotary kiln body  51  of the rotary kiln  41  permits to have the waste oil combustion apparatus  1  operate with a lower output. Further, in the rotary kiln  41 , since the first and second feed vanes  57  and  58  are provided intermittently to depict a virtual spiral, arrival of the heat of combustion from the waste oil combustion apparatus  1  at the one ends  55   a  and  56   a  of the inner and outer casings  55  and  56 , respectively, can be controlled appropriately to prevent the temperature from being sharply elevated in a position near the other end  55   b.    
         [0070]    Moreover, since the inner and outer casings  55  and  56  of the rotary kiln  41  are coupled to each other by the coupling member  62 , they can be rotated by a single motor  54 , which contributes to power saving. 
         [0071]    Also, a drying apparatus including the waste oil combustion apparatus  1  and rotary kiln  41  connected to each can use waste oil as main fuel to dry the metal chips  44 . Namely, the embodiment of the present invention permits more effective use of resources and space saving. 
         [0072]    Note that the first and second feed vanes  57  and  58  are not limited to the aforementioned ones but the feed vanes may be designed to have a variable tilt angle, height, etc. in the axial direction for moving the metal chips axially at a variable speed corresponding to the uniform rotation of the rotary kiln body  51 . More specifically, the first feed vanes  57  are designed to have an increased height and tilt angle at the one end  55   a  for moving the metal chips  44  toward the other end  55   b  at an increased speed, while having a decreased height and tilt angle at the other end  55   b  for having the metal chips  44  stay for a longer time to be long exposed to the heat of combustion from the waste oil combustion apparatus  1 . 
         [0073]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.