Patent Publication Number: US-2022220019-A1

Title: System and method for treating oil sludge

Description:
TECHNICAL FIELD 
     The present invention relates to a system and a method for treating oil sludge. 
     BACKGROUND ART 
     Patent Document 1 discloses, for example, a method and a device for treating oil sludge in which oil and mineralized slag are obtained from oil sludge accumulated in an oilfield or the bottom of an oil tanker. 
     Patent Document 1 is to provide a method and a device for treating oil sludge, which easily obtains oil of good quality and mineralized and harmless slag from oil sludge by stirring water-added oil sludge in an electrolysis tank to accelerate liquefaction of the oil sludge while reducing separation burden of a separator. However, such method and device require a complicated and large-scale plant, and thus results in expensive installation costs. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         [Patent Document 1] JP H09-060848 A 
         [Patent Document 2] JP 4153685 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     The present invention was made in consideration of the above circumstances, an object of which is to obtain oil of good quality from oil sludge accumulated in an oilfield or a bottom of an oil tanker by a plant made by combining versatile apparatuses. Also, an object of the present invention is to improve the environment, especially to reduce air pollution, of the oilfield by returning residual matter (soil) generated by the present invention to the oilfield. 
     Means for Solving the Problem 
     The present invention provides an oil sludge treatment system that includes a reduced-pressure fermentation dryer configured to: store oil sludge in an airtight container; heat and stir the oil sludge under reduced pressure so that a temperature of the oil sludge is within a predetermined temperature range; decompose organic matter contained in the oil sludge using microorganisms while evaporating water; and obtain volume-reduced dried product. The oil sludge treatment system further includes: a filtration apparatus that filters oil from the dried product; and a cleaner that cleans, by steam, the dried product from which the oil has been filtered. 
     In the present invention, the reduced-pressure fermentation dryer removes water from the oil sludge, and the filtration apparatus filters oil from the obtained dried product, and furthermore the cleaner cleans such treated dried product. Therefore, it is possible to discharge residual matter in a harmless and clean state. Thus, by returning the residual matter to an original site, it is possible to improve the environment, especially to reduce air pollution, of the oilfield and the like. 
     In the present invention, the filtration apparatus preferably includes: a feeding hole provided in an upper part of a main body of the filtration apparatus; a discharge outlet provided in a front part of the main body, which has an opening smaller than an opening of the feeding hole; a large number of slits provided in a bottom part of the main body so as to penetrate the bottom part; a screw extruder rotatable in a direction from the feeding hole to the discharge outlet; and an oil collecting part that is provided under the bottom part of the main body so as to collect the oil and that includes an oil discharge port. With this configuration, the filtration apparatus can be compact in size, and furthermore can easily filter oil from the dried product. 
     In the present invention, the cleaner preferably includes: a plurality of steam discharge nozzles provided above a conveyor body that transports the dried product from which the oil has been filtered; a large number of slits provided in a bottom part of the conveyor body so as to penetrate the bottom part; and a waste liquid collecting part that is provided under the bottom part of the conveyor body so as to collect cleaning drainage and that includes a drainage port. With this configuration, the cleaner can be compact in size, and furthermore can easily clean the dried product from which the oil has been filtered. 
     In the present invention, it is preferable that the oil collected in the bottom part of the filtration apparatus is further fed into a fuel inlet of a boiler via an oil pipe connected to the oil discharge port. Also, it is preferable that steam generated in the boiler is supplied to a heating jacket of the reduced-pressure fermentation dryer and the steam discharge nozzles of the cleaner via respective steam pipes. With this configuration, since the filtered oil can be used as fuel for the boiler, it is possible to reduce costs for fuel to be used in the boiler. 
     Also in the present invention, it is preferable that the cleaning drainage collected in a lower part of the cleaner is fed into the reduced-pressure fermentation dryer via a waste liquid pipe connected to the drainage port of the waste liquid collecting part. With this configuration, the oil sludge can be treated by the cleaning drainage, thus there is no need to discharge the cleaning drainage of the cleaning liquid. 
     Furthermore, an oil sludge treatment method of the present invention includes: a reduced-pressure fermentation drying step of: storing oil sludge in an airtight container; heating and stirring the oil sludge under reduced pressure so that a temperature of the oil sludge is within a predetermined temperature range; decomposing organic matter contained in the oil sludge using microorganisms while evaporating water; and obtaining volume-reduced dried product; a filtration step of filtering oil from the dried product; and a cleaning step of cleaning, by steam, the dried product from which the oil has been filtered. By this oil sludge treatment method, it is possible to obtain the same effects as those obtained by the above-described oil sludge treatment system. 
     Effect of the Invention 
     With the oil sludge treatment system and the oil sludge treatment method of the present invention, it is possible to remove a large amount of water from oil sludge by the reduced-pressure fermentation dryer. Also, it is possible to filter, by the filtration apparatus, oil from dried product obtained by the reduced-pressure fermentation dryer. Furthermore, it is possible to clean, by steam from the cleaner, the dried product from which the oil has been removed. Since the cleaning drainage is re-fed into the reduced-pressure fermentation dryer, the drainage step of discharging the cleaning drainage is not required. Moreover, since clean residual matter are generated from the dried product, it is possible to improve the environment, especially to reduce air pollution, of the oilfield by returning the residual matter to the oilfield. The residual matter can also be used as clean construction material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a schematic configuration of an oil sludge treatment system according to an embodiment of the present invention. 
         FIG. 2  is a front view illustrating a feeder and a reduced-pressure fermentation dryer in the oil sludge treatment system in  FIG. 1 . 
         FIG. 3  is a diagram schematically illustrating a conceptual configuration of the reduced-pressure fermentation dryer provided in the oil sludge treatment system in  FIG. 1 . 
         FIG. 4  is a cross-sectional view illustrating a schematic configuration of a filtration apparatus provided in the oil sludge treatment system in  FIG. 1 . 
         FIG. 5  is a perspective view illustrating a schematic configuration of a cleaner provided in the oil sludge treatment system in  FIG. 1 . 
         FIG. 6  is a cross-sectional view illustrating a schematic configuration of a boiler provided in the oil sludge treatment system in  FIG. 1 . 
     
    
    
     MEANS FOR CARRYING OUT THE INVENTION 
     Hereinafter, an embodiment of the present invention will be described with respect to the drawings.  FIG. 1  is a block diagram illustrating a schematic configuration of an oil sludge treatment system according to the embodiment of the present invention.  FIG. 2  is a front view illustrating a feeder and a reduced-pressure fermentation dryer of oil sludge.  FIG. 3  is a diagram schematically illustrating a conceptual configuration of the reduced-pressure fermentation dryer for fermenting and drying oil sludge under reduced pressure.  FIG. 4  is a cross-sectional view illustrating a schematic configuration of a filtration apparatus for filtering dried product after the oil sludge is subjected to reduced-pressure fermentation drying.  FIG. 5  is a perspective view illustrating a schematic configuration of a cleaner for cleaning the dried product.  FIG. 6  is a cross-sectional view illustrating a schematic configuration of a boiler for supplying steam to the reduced-pressure fermentation dryer and the cleaner. 
     As shown in  FIGS. 1 to 6 , an oil sludge treatment system (hereinafter also simply referred to as the “treatment system”)  1  includes: a feeder  2 ; a reduced-pressure fermentation dryer  3 ; a filtration apparatus  4 ; a cleaner  5 ; and a boiler  6 . In the treatment system  1 , for example, oil sludge accumulated in an oilfield or a bottom of an oil tanker is collected and stored in the feeder  2 . The stored oil sludge is fed into the reduced-pressure fermentation dryer  3  by the feeder  2 , and subjected to reduced-pressure fermentation drying in the reduced-pressure fermentation dryer  3 . Dried product obtained by reduced-pressure fermentation drying in the reduced-pressure fermentation dryer  3  is transported to the filtration apparatus  4 . Oil mixed with the dried product is removed by the filtration apparatus  4 . The dried product from which the oil has been removed is transported to the cleaner  5  so that the dried product not containing the oil is cleaned by the cleaner  5 . Thus, the dried product is discharged as clean residual matter. Since the residual matter does not contain impurities such as oil, it is possible to restore the environment to a state before extracting the oil by returning the residual matter to the original oilfield or the like. Thus, it is possible to sustain the natural environment. 
     Hereinafter, respective components included in the treatment system  1  are described in detail. 
     —Feeder— 
     The feeder  2  is to feed oil sludge stored in a hopper  23  (describer later) into a feeding hole  30   a  of the reduced-pressure fermentation dryer  3 . 
     The feeder  2  includes: a cylinder body  20  of a transport conveyor that is inclined upward to the right in  FIG. 2 ; a screw extruder  21  provided inside of the cylinder body  20 ; an electric motor  22  provided at the lower part of the distal end of the cylinder body  20 ; the hopper  23  provided on the upper part of the base end of the cylinder body  20  so as to store oil sludge; and a connecting section  24  provided in the lower part of the distal end of the cylinder body  20  so as to be connected to the feeding hole  30   a  of a tank  30  (described later). The hopper  23  is supported by a frame  25  so as not to fall down due to the weight of the oil sludge. 
     When the electric motor  22  is driven, the screw extruder  21  is rotated and thus the oil sludge on the bottom of the hopper  23  is stably fed into the tank  30  via the cylinder body  20  of the transport conveyor and the connecting section  24 . 
     In addition, since the hopper  23  also stores cleaning drainage from the cleaner  5  (described later), the treatment system  1  is not required to have a waste water treatment device, and thus no harmful substances are discharged. 
     —Reduced-Pressure Fermentation Dryer— 
     The reduced-pressure fermentation dryer  3  is a publicly-known apparatus as described, for example, in Patent Document 2. The reduced-pressure fermentation dryer  3  is configured to: heat and stir organic waste as an object to be treated under reduced pressure so that the temperature of the organic waste is within a predetermined temperature range; decompose organic components of the organic waste using microorganisms while evaporating water; and obtain volume-reduced dried product. 
     More specifically, the water contained in oil of the oil sludge is trapped in the oil by organic components such as protein, and thus it does not evaporate easily. However, when the organic components are decomposed by microorganisms, the moisture is separated from the oil to be suspended moisture. Thus, by evaporating the suspended moisture, the volume-reduced dried product is obtained. 
     As schematically shown in  FIG. 3 , the reduced-pressure fermentation dryer  3  includes a substantially cylinder-shaped tank (pressure-resistant tank)  30  formed to have airtightness such that the pressure inside of the tank  30  is maintained equal to or lower than the atmospheric pressure. The tank  30  serves as an airtight container that stores the oil sludge supplied by the feeder  2 . A heating jacket  31  is provided on a peripheral wall part of the tank  30 . Steam for heating is supplied to the heating jacket  31  from the boiler. It is preferable that the temperature of the steam supplied from the boiler  6  is, for example, about 140° C. 
     In the tank  30 , a stirring shaft  32  is disposed so as to extend in the longitudinal direction (left and right direction in  FIG. 3 ) while it is surrounded by the heating jacket  31 . The stirring shaft  32  is rotated by an electric motor  32   a  at a predetermined rotational speed. The stirring shaft  32  includes a plurality of stirring blades  32   b  that is separated from each other in the shaft direction. By the stirring blades  32   b , the oil sludge is stirred, and then transported, after termination of the fermentation drying, toward the longitudinal direction of the tank  30 . 
     The feeding hole  30   a  is provided in the middle of an upper part of the tank  30  in the longitudinal direction, which is for the oil sludge supplied from the feeder  2 . The oil sludge that is fed through the feeding hole  30   a  is heated by the heating jacket  31  while stirred by the rotation of the stirring shaft  32 . After elapse of a predetermined period of time, the dried product after treatment is discharged from a discharge section  30   b  provided in a lower part of the tank  30 . In place of the electric motor  32   a , a hydraulic motor may be used. 
     On the upper part of the tank  30 , a guiding sections  30   c , which guide steam generated from the heated oil sludge to a condensing section  33 , are provided so as to protrude from the tank  30 . In this embodiment, two guiding sections  30   c  are provided, and these two guiding sections  30   c  are disposed one by one on both sides of the tank  30  in the longitudinal direction with the feeding hole  30   a  being interposed therebetween. The condensing section  33  includes a plurality of cooling tubes  33   b  held by a pair of heads  33   a . A cooling channel  38   a  is provided between the plurality of cooling tubes  33   b  and a cooling tower  38 . In this embodiment, the condensing section  33  extends in the longitudinal direction of the tank  30  so as to be parallel with the tank  30 . Also, the condensing section  33  is located behind the feeding hole  30   a  and the guiding sections  30   c.    
     The temperature of the cooling water increases by heat exchange with the high temperature steam during flowing through the cooling tubes  33   b  of the condensing section  33 . Then, as schematically indicated by the arrows in  FIG. 3 , the cooling water flows into a water receiving tank  38   b  of the cooling tower  38  via the cooling channel  38   a . The cooling tower  38  is provided with: a drawing pump  38   c  that draws the cooling water from the water receiving tank  38   b ; and a nozzle  38   d  that sprays the drawn cooling water. The cooling water sprayed from the nozzle  83   d  flows downward through a downward flowing section  38   e  with being blown by a fan  38   f , which lowers the temperature of the cooling water. Thus, the cooling water flows again into the water receiving tank  38   b.    
     The cooling water cooled by the cooling tower  38  is transported by a cooling pump  38   g  and is sent to the condensing section  33  via the cooling channel  38   a  so as to pass through again the plurality of cooling tubes  33   b . Then, after the temperature of the cooling water increases by heat exchange with the steam generated in the tank  30  as described above, the cooling water once again flows through the cooling channel  38   a  so as to flow into the water receiving tank  38   b  of the cooling tower  38 . That is, the cooling water circulates through the cooling channel  38   a  between the condensing section  33  and the cooling tower  38 . Also in this embodiment, the cooling water cooled by the cooling tower  38  is supplied to the condensing section  33  as described later. Thus, the cooling water circulates between the condensing section  33  and the cooling tower  38 . 
     Apart from the circulating cooling water as described above, steam-condensed water also flows into the cooling tower  38 , which is generated by the heated oil sludge and condensed in the condensing section  33 . Although it is not shown in the drawings, the condensed water generated by heat exchange with the high temperature steam is accumulated in a lower part of the condensing section  33 . Also, a vacuum pump  36  is connected to the condensing section  33  via a communication passage  35  so as to reduce the pressure in the tank  30 . 
     Thus, when the vacuum pump  36  operates, air and condensed water are drawn from the condensing section  33  via the communication passage  35 , and furthermore air and steam in the tank  30  are drawn via a communication passage  34  and the guiding section  30   c . Accordingly, the condensed water is drawn from the condensing section  33  by the vacuum pump  36 , and guided from the vacuum pump  36  to the water receiving tank  38   b  of the cooling tower  38  via a water conduit. 
     Thus, the condensed water introduced in the water receiving tank  38   b  of the cooling tower  38  is mixed with the cooling water. The mixed cooling water is drawn, as described above, by the drawing pump  38   c  so as to be sprayed by the nozzle  38   d . After being sprayed, the cooling water flows downward through the downward flowing section  38   e  while being cooled. Since the condensed water contains the same microorganisms as those added to the oil sludge in the tank  30 , an odor component or the like contained in the condensed water has been decomposed. Thus, the odor is not emitted outside. 
     —Operations of Reduced-Pressure Fermentation Dryer— 
     Here, operations of the above-configured reduced-pressure fermentation dryer  3  are described. The oil sludge stored in the tank  30  is heated by steam for heating supplied to the heating jacket  31  while being stirred by the rotation of the stirring shaft  32 . The organic matter stored in the tank  30  is heated from the outside by the heating jacket  31  surrounding the inside of the tank  30  as well as heated from the inside by the stirring shaft  32  and the like. Thus, the temperature of the organic matter is effectively increased while the organic matter is stirred by the stirring shaft  32 . Furthermore, since the pressure in the tank  30  is reduced due to operations of the vacuum pump  36 , the boiling point is reduced in the tank  30  and thus the water evaporates at the temperature range in which decomposition of the organic components of the oil sludge is accelerated by the microorganisms. 
     It is preferable that the reduced-pressure fermentation drying step by the reduced-pressure fermentation dryer  3  takes, for example, 2 hours as one step (one cycle). First, the organic components of the organic matter are decomposed for 30 minutes in the fermentation step. When the inside of the tank  30  is decompressed to −0.06 to −0.07 MPa (gauge pressure, hereinafter this unit name is omitted), the water temperature inside of the tank  30  is maintained at 76 to 69° C. (saturated steam temperature). As a result, the fermentation and the decomposition of the organic matter is mainly promoted by the microorganisms described below. 
     Next, the fermenting organic matter is dried for 1.5 hours. For this purpose, the inside of the tank  30  is further decompressed to −0.09 to −0.10 MPa, thus the water temperature inside of the tank  30  is maintained at 46 to 42° C. (saturated steam temperature). As a result, the drying of the oil sludge is sufficiently promoted in the drying step. As to the microorganisms added to the oil sludge in the tank  30  at the time of drying treatment, it is preferable to use complex effective microorganisms, which are cultured in advance using a plurality of kinds of native microorganisms as a base, as described in Patent Document 2. That is, groups of so-called SHIMOSE 1, SHIMOSE 2 and SHIMOSE 3 have the majority of the colony. 
     Here, SHIMOSE 1 has the accession number FERM BP-7504 (internationally deposited with the Patent Microorganisms Depository of the National Institute of Advanced Industrial Science and Technology and the National Institute of Bioscience and Human-Technology of the Ministry of Economy, Trade and Industry (1-1-3 Higashi, Tsukuba, Ibaraki, Japan) on Mar. 14, 2003). Also, SHIMOSE 2 has the accession number FERM BP-7505 (internationally deposited in the same manner as SHIMOSE 1), which is microorganism belonging to the genus  Pichiafarinosa  having salt tolerance. SHIMOSE 3 has the accession number FERM BP-7506 (internationally deposited in the same manner as SHIMOSE 1), which is microorganism belonging to the genus  Staphylococcus.    
     Here, the procedures of the reduced-pressure fermentation drying step of the organic matter by the reduced-pressure fermentation dryer  3  are described. First, the oil sludge containing organic matter is fed into the reduced-pressure fermentation dryer  3 . At this time, the lid of the feeding hole  30   a  of the tank  30  of the reduced-pressure fermentation dryer  3  is opened to feed the oil sludge stored in the hopper  23  through the feeding hole  30   a  by feeder  2 . Then, the lid of the feeding hole  30   a  is closed so that the inside of the tank  30  is kept at the atmospheric pressure. 
     Next, after adding the prescribed microorganisms to the oil sludge in the tank  30 , the tank  30  is sealed by closing an atmosphere opening valve. Then, the inside of the tank  30  is heated under reduced pressure so as to promote fermentation and drying of the organic components of the oil sludge in the tank  30 . Specifically, the inside of the tank  30  is heated by steam for heating that is supplied from the boiler  6 . 
     The inside of the tank  30  is thus heated by the steam for heating while the stirring shaft  32  is rotated at a predetermined rotational speed (for example, about 8 rpm). Furthermore, the pressure in the tank  30  is reduced by operating the vacuum pump  36 . Thus, the temperature inside of the tank  30  is optimized for microbial activity. As a result, decomposition of the organic components contained in the oil sludge is effectively promoted by the microorganisms. Here, the rotational speed (8 rpm) of the stirring shaft  32  is shown as an example, and any other rotational speed may be adopted to the extent that the organic components of the oil sludge can be decomposed. 
     When a predetermined period of time (for example, about 2 hours) is elapsed in the state in which the temperature and the pressure in the tank  30  are maintained, the operations of the vacuum pump  36  and the boiler  6  are stopped so that the pressure inside of the tank  30  becomes the atmospheric pressure. Furthermore, the stirring shaft  32  is reversely rotated and the lid of the discharge section  30   b  of the tank  30  is opened so as to discharge the dried product from the tank  30 . At this time, the volume of the dried product that is discharged from the tank  30  has been reduced. 
     —Filtration Apparatus— 
     The dried product discharged from the discharge port  30   b  of the reduced-pressure fermentation dryer  3  is fed into the filtration apparatus  4 . As schematically shown in  FIG. 4 , the filtration apparatus  4  is configured such that the dried product fed from an inlet nozzle  41  is transported to an outlet chute  43  by a worm screw  42  rotated by, for example, an electric motor  42   a . In the process of the transport of the dried product, the gap between the worm screw  42  and a cylinder-shaped wall part  44  becomes gradually narrower. Thus, as the dried product is conveyed toward the outlet, the dried product is more filtered. Specifically, in the wall part  44  provided on the outer periphery side of the worm screw  42 , a number of slits (openings)  45  are formed in a penetrating manner such that oil is filtered by the slits  45 . The oil filtered by the slits  45  is collected in a collecting part  46 , and after that, it is discharged from a discharge port  47  to the outside. The dried product transported to the end part of the worm screw  42  is also compressed by being sandwiched between the worm screw  42  and an outlet side plate  48 . By adjusting the position of the outlet side plate  48  by a hydraulic cylinder  49 , the dried product with a predetermined deoiling rate is discharged from the outlet chute  43 . 
     In this way, the dried product from which the oil has been removed by the filtration apparatus  4  is sent from the outlet chute  43  to the cleaner  5 . Also, the oil filtered by the filtration apparatus  4  is transported to a fuel inlet  61   a  of the boiler  6  via an oil pipe  40 . Thus, the boiler  6  is combusted using the oil to generate steam. The generated steam is supplied to the heating jacket  31  of the reduced-pressure fermentation dryer  3  via a steam pipe  71 , a steam control device  92  and a steam pipe  70 . Accordingly, the tank  30  can be heated to ferment and dry the organic components of the oil sludge at an appropriate temperature. 
     In addition to the above, the surplus oil in the boiler  6  is stored in an oil tank  40   b  by appropriately opening and closing a valve  40   a  disposed in the middle of the oil pipe  40 . Moreover, the oil stored in the tank  40   b  can be sold, and the money obtained by selling the oil can be used as working capital to drive the system. 
     —Cleaner— 
     The cleaner  5  is to remove impurities contained in the dried product transported from the filtration apparatus  4  by steam cleaning and thus to obtain clean residual matter  50  (soil). By returning this residual matter to the oilfield, the environment of the oilfield can be restored to its original state. 
     The cleaner  5  includes: a conveyor body  51 , in a bottom surface of which are provided a number of slits (having the size of 1 to 5 mm)  51   a  in a penetrating manner; and a vibration motor  52  that vibrates the conveyor body  51 . Also, the cleaner  5  is supported by a lower base  54  via a plurality of (for example, four) coil springs  53 . The conveyor body  51  is provided in a state being inclined diagonally downward, and an upper side thereof is opened. Above the conveyor body  51 , a plurality of steam discharge nozzles  55  is provided. 
     The steam discharge nozzles  55  are connected to the steam control device  92  via a steam pipe  72 . Thus, the steam generated in the boiler  6  is sent to the steam discharge nozzles  55  in a state in which its discharge pressure is appropriately controlled by the steam control device  92 . 
     In this way, the cleaner  5  is supported by the coil springs  53  in a floating state with respect to the lower base  54 . Thus, the dried product in the conveyor body  51  is vibrated and transported forward by vibration of the conveyor body  51  caused by driving the vibration motor  52 . On the way of the transport, the steam is sprayed to the dried product from the steam discharge nozzles  55  provided above. Thus, impurities contained in the dried product are filtered together with water droplets by the various number of slits  51   a  to be collected in a waste liquid collecting part  56  provided in the lower part of the conveyor body  51 . From a drainage port  57  of the waste liquid collecting part  56 , cleaning drainage flows through a waste liquid pipe  58  to be stored in the hopper  23  of the feeder  2 . Therefore, in the cleaning step, the oil sludge can be treated without discharging drainage containing pollutants. 
     Also, it is possible to treat oil sludge accumulated in the bottom of an oil tanker in the same manner as described above. Thus, the oil sludge can be removed from the bottom of the oil tanker, and furthermore oil can be generated from the oil sludge without discharging drainage containing pollutants. 
     —Boiler  6 — 
     The boiler  6  includes: a combustion furnace  60 ; a burner  61  disposed on the right side of the combustion furnace  60  in  FIG. 6 ; and a heat exchanger  62  disposed in the combustion furnace  60 . 
     First, the configuration of the combustion furnace  60  is described. The combustion furnace  60  includes three thick walls (a front wall  60   a , a back wall  60   b  and a bottom wall  60   c ). A large-volume internal space of the combustion furnace  60  is constituted of these three walls, left and right side walls  60   d  and  60   e , and a roof wall  60   f . Thus, the internal space has a rectangle shape viewed from the side. The height of the back wall  60   b  is about a half the height of the front wall  60   a . Behind the back wall  60   b  (on the left side in  FIG. 6 ), a second back wall  60   g  is disposed. The second back wall  60   g  extends to the same height of the upper end of the front wall  60   a . The lower end of the second back wall  60   g  is connected to the upper end of the back wall  60   b  via a second bottom wall  60   h . Thus, a small-volume internal space is formed above the second bottom wall  60   h . The small-volume internal space and the large-volume internal space constitute a combustion chamber  60 F in the combustion furnace  60 . For the sake of explanation, in the combustion chamber  60 F, the internal space above the bottom wall  60   c  is hereinafter referred to as a “first combustion chamber  601 F” while the internal space above the second bottom wall  60   h  is hereinafter referred to as a “second combustion chamber  602 F”. The walls  60   a  to  60   h  are made of, for example, refractory bricks or insulating material resisting a high temperature of approximately 1000° C. 
     Next, the configuration of the burner  61  is described. The burner  61  combusts fuel that is the oil obtained by filtering, using the filtration apparatus  4 , the volume-reduced dried product treated by the fermentation dryer  3 . 
     The burner  61  includes: the fuel inlet  61   a ; a combustor body  61   b  that generates mixed gas from the oil and a large amount of air supplied from an air supply port (not shown); and a combustor pipe  61   c  that combusts the mixture. The burner  61  generates swirling flame F in the first combustion chamber  601 F, and combustion is consecutively continued in the second combustion chamber  602 F. Thus, exhaust gas is generated and discharged to a discharge path  60   j.    
     The heat exchanger  62  provided in the boiler  6  heats the water using combustion energy generated by the combustion of the fuel in the first combustion chamber  601 F and the second combustion chamber  602 F so as to generate hot temperature steam. The steam for heating generated by the heat exchanger  62  is supplied to the steam control device  92  via the steam pipe  71 , and furthermore supplied from this steam control device  92  to the reduced-pressure fermentation dryer  3  (e.g. the heating jacket  31  of the tank  30 ). 
     More specifically, the heat exchanger  62  includes: a number of water tubes  62   a ; a steam-water drum  62   b ; and a water drum  62   c.    
     The water flows through the various number of water tubes  62   a , and evaporates by receiving the combustion energy of the fuel in the first combustion chamber  601 F and the second combustion chamber  602 F. 
     The steam-water drum  62   b  is a drum having a circular cross-section into which steam flows. The steam is generated by evaporation of the water that passes through the plurality of water tubes  62   a . The steam-water drum  62   b  is located at a center position between the left side wall  60   d  and the right side wall  60   e , and furthermore disposed so as to cover the first combustion chamber  601 F and the second combustion chamber  602 F. As shown in  FIG. 6 , the lower half of the steam-water drum  62   b  is located in the first combustion chamber  601 F and the second combustion chamber  602 F, and the upper half thereof is located above the roof wall  61   f . A steam port  62   c  is opened in the middle part of the steam-water drum  62   b  in the front and back direction. The steam accumulated in the steam-water drum  62   b  is supplied from the steam port  62   d  to the steam control device  92  via the steam pipe  71 . Water inlets  62   e  are respectively formed on both front and bask sides of the steam port  62   d . The water from the water inlets  62   e  is supplied to the water drum  62   c  via the steam-water drum  62   b  and the water tubes  62   a.    
     The steam accumulated in the steam-water drum  62   b  of the boiler  6  is supplied from the steam port  62   d  to the steam control device  92  via the steam pipe  71 . After that, the steam is supplied to a steam electric generator  91  so that the steam electric generator  91  generates electricity by the supplied steam. 
     The steam electric generator  91  is constituted, for example, of a steam turbine generator that generates electricity by the supplied steam. Part of the electric power obtained by the electric generation is supplied to the reduced-pressure fermentation dryer  3  so as to be used as drive power of the reduced-pressure fermentation dryer  3 . Thus, the costs for driving the reduced-pressure fermentation dryer  3  can be reduced. Also, the remaining part of the generated electric power is supplied to an electric power company. Thus, the money obtained by selling the electric power can be used as working capital to drive the system. 
     The boiler  6  has a configuration burning the oil obtained by filtration by the filtration apparatus  4  in the oil sludge treatment system  1 . However, the boiler  6  may be applied to a boiler for combusting another substance. 
     The foregoing embodiment is to be considered in all respects as illustrative and not limiting. The technical scope of the invention is indicated by the appended claims rather than by the foregoing embodiment, and all modifications and changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein. 
     INDUSTRIAL APPLICABILITY 
     The present invention is suitably applied to a system and a method for treating oil sludge by the reduced-pressure fermentation dryer. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1  Oil sludge treatment system 
           2  Feeder 
           3  Reduced-pressure fermentation dryer 
           4  Filtration apparatus 
           40  Oil pipe 
           41  Feeding hole 
           41  Screw extruder 
           42  Discharge outlet 
           43  Slit 
           46  Oil collecting part 
           5  Cleaner 
           51  Conveyor body 
           55  Steam discharge nozzle 
           56  Waste liquid collecting part 
           57  Waste liquid pipe 
           6  Boiler 
           60  Combustion furnace 
           61  Burner 
           62  Heat exchanger