Patent Publication Number: US-9897376-B2

Title: Drying method for processing material and horizontal rotary dryer

Description:
TECHNICAL FIELD 
     The present invention relates to a drying method for processing material and a horizontal rotary dryer improving a drying rate. 
     BACKGROUND ART 
     As a dryer which dries processing materials such as coals or ores, a steam tube dryer (which is referred to as “STD”, hereinafter), a coal-in-tube (Patent Document 1), a rotary kiln, and the like are often used. The aforementioned coals or ores are used as raw materials for iron making or refining, fuel for power generation, and the like, and since it is demanded to process a mass of the coals or ores in a stable manner, the above-described respective dryers have been employed as dryers which fulfill the demand. 
     The STD indirectly heats the processing materials, so that a thermal efficiency is high, and a processing amount per unit volume is also large. Further, it is also possible to increase a size of the STD, so that the STD fulfills the demand regarding mass processing. 
     The coal-in-tube also indirectly heats the processing materials, so that a thermal efficiency is high, and a processing amount per unit volume is also large, in a similar manner to the aforementioned STD. However, there is a disadvantageous point that a size thereof is difficult to be increased, when compared to the STD. For example, when an amount capable of being processed by one STD described above is tried to be processed by the coal-in-tube, a plurality of the coal-in-tubes are sometimes required. 
     The rotary kiln applies hot air to the processing materials to directly dry the processing materials, and thus it has a disadvantageous point that a heat efficiency is lower than that provided by the indirect heating. Further, there is also a disadvantageous point that an exhaust gas processing facility becomes very large. From the reasons as described above, the STD has precedence as the dryer which processes a mass of processing materials. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Publication of Utility Model Registration No. 2515070 
         Patent Document 2: Japanese Examined Patent Application Publication No. Sho 62-60632 
       
    
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     In recent years, the demand regarding the drying processing of mass of the processing materials is strong, and in order to meet the demand, a size of the dryer is becoming larger. When the increase in size of the STD is cited as an example, the STD whose shell diameter is 4 in and whose main body length is 30 in or longer is manufactured. 
     However, the increase in size of the dryer creates not only a problem such that an installation area has to be increased, but also problems in terms of manufacture and transportation. Concretely, a plate thickness of each member is increased to maintain strength, and weight of the main body of the aforementioned STD whose shell diameter is 4 in and whose main body length is 30 in, reaches 400 tons. Accordingly, there is a problem that it takes a lot of time until when the manufacture is completed. Further, there is also a problem that a special facility is required for the manufacture. 
     Further, in accordance with the increase in size, when a product is transported, a special vehicle capable of supporting weight of the product becomes required, and when a transportation route is narrow, the product has to be divided to be transported, and joined and assembled at a job site, and thus the construction work is very complicated, which is also a problem. 
     Accordingly, there was found out a task that, based on the fact that there is a limitation in the increase in size of the apparatus as described above, the aim should rather be to improve a drying rate of a processing material. 
     Therefore, the task of the present invention is to improve a drying rate of processing material dried by a dryer. 
     Further, the task of the present invention is to avoid the above-described problems in accordance with the increase in size of the apparatus to the utmost, by the present invention capable of increasing a drying processing amount per size (shell diameter) of the dryer. 
     Means for Solving the Problems 
     The present invention solving the above-described problems is as follows. 
     &lt;Invention Described in Claim  1 &gt; 
     A drying method for processing material using a horizontal rotary dryer provided with: a rotating shell having a feed port for processing material on one end side thereof and a discharge port for processing material on the other end side thereof, and capable of freely rotating around an axial center; and a group of heating tubes through which a heating medium passes, provided within the rotating shell, and configured in a manner that the processing material is lifted up in a rotational direction by the group of heating tubes in accordance with the rotation of the rotating shell, the drying method for processing material including drying, through indirect heating, the processing material by using the group of heating tubes in a process of feeding the processing material to the one end side of the rotating shell and discharging the processing material from the other end side of the rotating shell, in which the rotating shell is rotated to make a critical speed ratio α defined by the following expression 1 and expression 2 become 30 to less than 100% to dry the processing material,
 
 Vc= 2.21 D   1/2   Expression 1
 
α= V/Vc· 100  Expression 2
 
     wherein Vc indicates a critical speed (m/s), D indicates an inside diameter (in), α indicates the critical speed ratio (%) of the rotating shell, and V indicates a rotation speed (m/s). 
     (Operation and Effect) 
     Conventionally, operation has been conducted based on the following value without performing theoretical verification regarding a number of rotations of a rotating shell of STD. Specifically, when an inside diameter of the rotating shell is 4 in, operation has been conducted by setting an upper limit of a number of rotations to 2 to 4.5 rpm, when the inside diameter is 3 in, operation has been conducted by setting the upper limit of the number of rotations to 2 to 5 rpm, when the inside diameter is 2 in, operation has been conducted by setting the upper limit of the number of rotations to 2 to 6 rpm, and when the inside diameter is 1 in, operation has been conducted by setting the upper limit of the number of rotations to 3 to 10 rpm. 
     On the other hand, according to the findings of the present inventors, there is a problem that when a size of the STD (the inside diameter of the rotating shell) is changed, even if the STD is rotated with the same number of rotations, a drying rate of the processing material changes, and it is difficult to predict the rate. Particularly, as the STD becomes large, it becomes further difficult to predict the drying rate, so that a heat transfer area has been previously designed to be a large area, to thereby give a margin to drying performance. 
     Due to such reasons, it has been difficult, in the conventional example, to bring out desired drying performance when a scale-up is performed from a test machine to an actual machine. On the contrary, by using the drying method for processing material according to the present invention to decide the rotation speed, it becomes easy to bring out the desired drying performance when the scale-up is conducted. 
     Further, in the drying method for processing material of the present invention, by increasing the rotation speed of the dryer, the drying performance can be dramatically improved when compared to the conventional drying performance, and thus it becomes possible to perform mass processing of processing material. 
     &lt;Invention Described in Claim  2 &gt; 
     In the drying method for processing material described in claim  1 , the processing material is fed into the rotating shell to make a hold up ratio η of the processing material defined by the following expression 3 become 20 to 40%,
 
η= Ap/Af· 100  Expression 3
 
     wherein η indicates the hold up ratio (%), Ap indicates a cross-sectional area (m 2 ) occupied by the processing material with respect to a free cross-sectional area, and Af indicates a free cross-sectional area (m 2 ) as a result of subtracting a cross-sectional area of all of the heating tubes from the entire cross-sectional area of the rotating shell. 
     (Operation and Effect) 
     If the hold up ratio η is 20 to 40%, a processing amount per unit cross-sectional area becomes large, and besides, the drying rate also becomes fast. Further, since the upper limit of the hold up ratio η is not excessively large, good drying rate is provided. A more preferable hold up ratio η is 25 to 30%. Note that the entire cross-sectional area Af of the rotating shell indicates a cross-sectional area of the inside of the rotating shell at an arbitrary transverse section of the rotating shell, and does not include an area of a thick wall portion of the rotating shell. Specifically, the entire cross-sectional area Af indicates a cross-sectional area calculated based on an inside diameter of the rotating shell. 
     &lt;Invention Described in Claim  3 &gt; 
     In the drying method for processing material described in claim  1  or  2 , when the processing material is coal whose median diameter is 50 mm or less, the rotating shell with an inside diameter of 1 to 6 in is used, and the rotating shell is rotated to make the critical speed ratio α become 40 to less than 100% to dry the processing material. 
     (Operation and Effect) 
     When the processing material is coal, the critical speed ratio α of 40 to less than 100% is optimum from a viewpoint of processing amount and drying rate. A more preferable critical speed ratio α is 60 to 90%. 
     &lt;Invention Described in Claim  4 &gt; 
     In the drying method for processing material described in claim  1  or  2 , when the processing material is a resin-based material whose median diameter is 200 μm or less, the rotating shell with an inside diameter of 1 to 6 in is used, and the rotating shell is rotated to make the critical speed ratio α become 30 to 70% to dry the processing material. 
     (Operation and Effect) 
     When the processing material is the resin-based material with the median diameter of 200 μm or less, the critical speed ratio α of 30 to 70% is optimum from a viewpoint of processing amount and drying rate. A more preferable critical speed ratio α is 40 to 60%. 
     &lt;Invention Described in Claim  5 &gt; 
     In the drying method for processing material described in claim  1  or  2 , a plurality of the heating tubes are arranged in a radial manner or on concentric circles, and a separation distance between adjacent heating tubes is 80 to 150 mm. 
     (Operation and Effect) 
     The separation distance between the adjacent heating tubes relates to an amount by which the processing material is scooped up in accordance with the rotation of the rotating shell, and an amount by which the scooped-up processing material falls to return to a position between the heat transfer tubes, and besides, these amounts are associated with the rotation speed of the rotating shell as well, and it was found out that the separation distance of 80 to 150 mm is suitable. 
     &lt;Invention Described in Claim  6 &gt; 
     A horizontal rotary dryer, including: a rotating shell having a feed port for processing material on one end side thereof and a discharge port for processing material on the other end side thereof, and capable of freely rotating around an axial center; and a group of heating tubes through which a heating medium passes, provided within the rotating shell, configured in a manner that the processing material is lifted up in a rotational direction by the group of heating tubes in accordance with the rotation of the rotating shell, and drying, through indirect heating, the processing material by using the group of heating tubes in a process of feeding the processing material to the one end side of the rotating shell and discharging the processing material from the other end side of the rotating shell, in which the horizontal rotary dryer is configured to be able to operate to make a critical speed ratio α defined by the following expression 1 and expression 2 become 30 to less than 100%,
 
 Vc= 2.21 D   1/2   Expression 1
 
α= V/Vc· 100  Expression 2
 
     wherein Vc indicates a critical speed (m/s), D indicates an inside diameter (in) of the rotating shell, α indicates the critical speed ratio (%), and V indicates a rotation speed (m/s). 
     (Operation and Effect) 
     From a viewpoint of the apparatus, operation and effect similar to those of claim  1  are obtained. 
     &lt;Invention Described in Claim  7 &gt; 
     In the horizontal rotary dryer described in claim  6 , a plurality of the heating tubes are arranged in a radial manner or on concentric circles, and a separation distance between adjacent heating tubes is 80 to 150 mm. 
     (Operation and Effect) 
     From a viewpoint of the apparatus, operation and effect similar to those of claim  5  are obtained. 
     (Another Invention) 
     A drying rate evaluation method for processing material being a method in which a horizontal rotary dryer provided with: a rotating shell having a feed port for processing material on one end side thereof and a discharge port for processing material on the other end side thereof, and capable of freely rotating around an axial center; and a group of heating tubes through which a heating medium passes, provided within the rotating shell, and configured in a manner that the processing material is lifted up in a rotational direction by the group of heating tubes in accordance with the rotation of the rotating shell, is used, and a drying rate of the processing material when the processing material is dried, through indirect heating, by the group of heating tubes in a process of feeding the processing material to the one end side of the rotating shell and discharging the processing material from the other end side of the rotating shell, is evaluated, the drying rate evaluation method for processing material including evaluating the drying rate by using a critical speed ratio α defined by the following expression 1 and expression 2,
 
 Vc= 2.21 D   1/2   Expression 1
 
α= V/Vc· 100  Expression 2
 
     wherein Vc indicates a critical speed (m/s), D indicates an inside diameter (in) of the rotating shell, α indicates the critical speed ratio (%), and V indicates a rotation speed (m/s). 
     (Operation and Effect) 
     Operation and effect similar to those of claim  1  are obtained. Further, with the use of the evaluation method of the drying rate according to the present claim, it is possible to obtain a precise indirect heating horizontal rotary dryer at an actual machine level. 
     Effect of the Invention 
     As described above, according to the present invention, it is possible to improve the drying rate of the processing material dried by the dryer. Further, as a result of the improved drying rate, it is possible to increase the drying processing amount per size (shell diameter) of the dryer. Conversely, it is possible to reduce the size of the apparatus per processing amount. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of a horizontal rotary dryer according to the present invention; 
         FIG. 2  is a side view illustrating a screw feeder and a periphery thereof; 
         FIG. 3  is an enlarged view (side view) of the other end side of a rotating shell; 
         FIG. 4  is a side view of a horizontal rotary dryer (modified example) according to the present invention; 
         FIG. 5  is a sectional view taken along line X-X in  FIG. 4 ; 
         FIG. 6  is a side view illustrating a case where a feed system is one of chute type; 
         FIG. 7  is a side view illustrating a case where the feed system is one of vibration trough type; 
         FIG. 8  illustrates an example in which a shape of a transverse section of the rotating shell is set to a rectangular shape; 
         FIG. 9  is a side view illustrating a case where a jacket is provided on the outside of the rotating shell; 
         FIG. 10  is a side view illustrating a modified example of a discharge system for processed material; 
         FIG. 11  is a perspective view of a horizontal rotary dryer employing countercurrent flow; 
         FIGS. 12( a ) and 12( b )  are explanatory diagrams of a horizontal rotary dryer of a type employing a gas blowing pipe, in which  FIG. 12( a )  is a sectional view of the gas blowing pipe, and  FIG. 12( b )  is a perspective view in which the gas blowing pipe is arranged in the dryer; 
         FIG. 13  is an explanatory diagram illustrating a process of deriving a critical speed ratio; 
         FIG. 14  is a graph illustrating a relationship among a diameter of a rotating shell, a number of rotations, and a critical speed ratio; 
         FIG. 15  is a graph illustrating a relationship between the critical speed ratio and a drying rate when a diameter of the rotating shell is 320 mm; 
         FIG. 16  is a diagram obtained in a manner that a rotating shell is operated while arbitrarily changing the critical speed ratio and a diameter of the rotating shell, dispersion states of processing material in the inner part of the rotating shell are photographed, and the photographs are traced; 
         FIG. 17  is a graph illustrating a relationship between the critical speed ratio and the drying rate when the diameter of the rotating shell is changed; 
         FIG. 18  is a graph illustrating a relationship between the critical speed ratio and the drying rate when a hold up ratio is changed; 
         FIG. 19  is an explanatory diagram of a gap between heating tubes of the horizontal rotary dryer according to the present invention; 
         FIG. 20  is a graph illustrating a relationship between the critical speed ratio and the drying rate when a length of the gap between the heating tubes is changed (processing material:coal); 
         FIG. 21  is a graph illustrating a relationship between the critical speed ratio and the drying rate when the length of the gap between the heating tubes is changed (processing material:resin-based material); 
         FIG. 22  is a transverse sectional view illustrating an example of arrangement of the heating tubes of the horizontal rotary dryer according to the present invention; 
         FIG. 23  is an explanatory diagram regarding a method of deciding arrangement of the heating tubes; 
         FIG. 24  is a transverse sectional view illustrating an example of arrangement of the heating tubes of the horizontal rotary dryer according to the present invention; 
         FIG. 25  is a transverse sectional view illustrating an example of arrangement of the heating tubes of the horizontal rotary dryer according to the present invention; 
         FIG. 26  is a transverse sectional view illustrating a state where the number of heating tubes is increased based on  FIG. 22 ; 
         FIG. 27  is a transverse sectional view illustrating a state where the number of heating tubes is increased based on  FIG. 24 ; 
         FIG. 28  is a transverse sectional view illustrating a state where the number of heating tubes is increased based on  FIG. 25 ; 
         FIG. 29  is a transverse sectional view illustrating an example of arrangement of heating tubes of a conventional horizontal rotary dryer; and 
         FIG. 30  is a table which explains adhesive properties of materials to be processed. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, preferred embodiments of the present invention will be further described by using the drawings. Note that the following description and drawings merely illustrate one example of the embodiments of the present invention, and the contents of the present invention should not be construed as being limited to the embodiments. 
     (Gist of Invention) 
     Generally, a drying rate of a dryer can be represented as the following expression 4,
 
 Q=Uoa×Aef×Tln   Expression 4
 
     wherein Q indicates a heat transfer amount (W), Uoa indicates an overall heat transfer coefficient (W/m 2 -K), Aef indicates an effective contact heat transfer area (m 2 ), and Tln indicates a temperature difference (° C.). 
     The drying rate is synonymous with the heat transfer amount Q, and in order to increase the heat transfer amount Q on the left side of the aforementioned expression 4, it is only required to take a measurement such that any one or all of the overall heat transfer coefficient Uoa, the effective contact heat transfer area Aef, and the temperature difference Tln on the right side of the expression 4 is/are increased. 
     The present inventor focused attention on the overall heat transfer coefficient Uoa and the effective contact heat transfer area Aef, and considered, in order to increase these, providing a faster relative contact speed between a heat transfer surface and the material to be dried W, and providing a larger effective contact heat transfer area between the heat transfer surface and the material to be dried W by improving dispersion of the processing material W. When various experiments and studies were actually conducted, it was possible to clearly confirm the effectiveness of the method of the present invention. 
     Besides, as a result of analyzing the high-speed rotation technique according to the present invention in detail, it was found out that the idea of the present invention can be applied also to a case where a diameter of a rotating shell  10  of a dryer is different. 
     (Processing Material W) 
     First, there is no limitation regarding a processing material W as a drying target, and as a concrete example of the processing material W, there can be cited coal, ore such as copper ore, iron powder, or zinc powder, a metallic material, terephthalic acid, a resin-based material such as polyethylene, polyacetal, or vinyl chloride, methionine, a processed food-based material such as gluten meal, soybean processed powder, corn fiber, or corn germ, an inorganic material such as gypsum, alumina, or soda ash, dehydrated sludge, or the like. 
     The processing material W is preferably one whose surface is not sticky and thus having a low adhesive property.  FIG. 30  illustrates a table cited from an explanatory diagram 5 on page 17 of an explanatory manual of Association of Powder Process Industry and Engineering, Japan Standard SAP 15-13, 2013. In the present invention, materials within a region surrounded by a dotted line in  FIG. 30 , which are, in detail, dried materials, materials in a pendular region, materials in a funicular region  1 , materials in a funicular region  2 , and materials in a capillary region, are preferably used as the processing material W. Slurry is not suitable for the processing material W in the present invention since it tends to have extremely high adhesive property. 
     (Median Diameter) 
     A median diameter of the present invention is defined by using the following method, for example. In detail, when a particle diameter of the processing material W is 500 micrometers or more, sieving is performed according to a method described in a coal testing method of JIS (Japan Industrial Standard) M 8801, a result of the sieving is represented by Rosin-Rammler distribution, and a particle diameter when a cumulative mass (oversize) corresponds to 50% is defined as a median diameter (D 50 ). Further, when the particle diameter of the processing material W is less than 500 micrometers, a particle size distribution is measured by using a laser diffraction type particle size distribution measuring apparatus (for example, SALD-3100, which is a product name manufactured by SHIMADZU CORPORATION), and a particle diameter when an accumulated volume corresponds to 50% is defined as a median diameter (D 50 ). 
     (Indirect Heating Horizontal Rotary Dryer) 
     Next, a horizontal rotary dryer according to the present invention (which is also referred to as “STD (abbreviated name of Steam Tube Dryer)”, hereinafter) will be described. The horizontal rotary dryer has a structure as exemplified in  FIG. 1 , in which a cylindrical rotating shell  10  is provided, the rotating shell  10  is installed so that its axial center slightly inclines with respect to a horizontal plane, and one end of the rotating shell  10  is positioned higher than the other end of the rotating shell  10 . At a position below the rotating shell  10 , two support units  20  and a motor unit  30  are installed so as to support the rotating shell  10 , and the rotating shell  10  is designed to be able to freely rotate around its axial center with the use of the motor unit  30 . The rotating shell  10  is designed to rotate in one direction. The direction can be arbitrarily determined, and, for example, as illustrated in  FIG. 5 , it is possible to make the rotating shell  10  rotate counterclockwise (in an arrow mark R direction) when looking at one end side (a feed port  41  side of processing material W) from the other end side (a discharge port side of processing material W). 
     Inside the rotating shell  10 , a large number of steam tubes (heating tubes)  11  each being a pipe made of metal, are attached to extend along the axial center of the rotating shell  10 , as heat transfer tubes for the material to be dried W. A plurality of the steam tubes  11  are arranged in a circumferential direction and in a radial direction, respectively, so as to form concentric circles around the axial center of the rotating shell  10 , for example. Forms of the arrangement will be described later in detail. Note that the heating tubes  11  are warmed when steam or the like being a heating medium flows through the inside of the heating tubes  11 . 
     Further, in the vicinity of the screw feeder  42 , there is provided a gas blowing unit (not illustrated) which blows air, inert gas, or the like as the carrier gas A into the rotating shell  10  from the feed port  41  which also serves as a gas blowing opening, and the carrier gas A blown by the gas blowing unit flows through the inner part of the rotating shell  10  toward the other end side of the rotating shell  10 . 
     As illustrated in  FIG. 1  and  FIG. 3 , on a peripheral wall on the other end side of the rotating shell  10 , a plurality of discharge ports  50  are penetrated to be formed. The plurality of discharge ports  50  are formed along the circumferential direction of the rotating shell  10 , and in the examples of  FIG. 1  and  FIG. 3 , the discharge ports  50  are formed by being separated from one another so as to make two lines. Further, all of the plurality of discharge ports  50  are formed in the same shape, but, they may also be formed in different shapes. 
     Further, on the other end side of the rotating shell  10 , a gas pipe  72  is provided, and a feed pipe  70  feeding steam into the steam tubes  11  and a drain pipe  71  are provided. 
     Modified Example 
     Note that as illustrated in  FIG. 4 , it is also possible to provide an agitating unit  65  that agitates the processing material W, at a position on the other end side of the rotating shell  10 . 
     Further, as illustrated in  FIG. 4  and  FIG. 5 , it is also possible that a classification hood  55  capable of discharging the processing material W and carrier gas A is provided to the rotating shell  10  so as to cover the other end side of the rotating shell  10  having the plurality of discharge ports  50 . The classification hood  55  is formed of thick metal, and it has, in a bottom surface, a fixed discharge port  57  from which the processing material W after being subjected to drying and classification, namely, the processed material E is discharged, and has, in a ceiling surface, a fixed exhaust gas opening  56  from which the carrier gas A is exhausted. 
     (Drying Process) 
     Next, a process of drying the processing material W in the horizontal rotary dryer will be described while referring to  FIG. 1  to  FIG. 3 . 
     The processing material W is fed into the screw feeder  42  from the feed port  41 , and by turning a screw  44  disposed inside the screw feeder  42  with the use of a not-illustrated driving unit, the processing material W is fed to the inside of the rotating shell  10 . The processing material W fed from the feed port  41  moves to the other end side of the rotating shell  10  while being dried by being brought into contact with the steam tubes (heating tubes)  11  heated by steam, and is discharged from discharge ports  50 . 
     On the other hand, the carrier gas A blown from the feed port  41  by the blowing unit provided on the one end side of the rotating shell  10  passes through the inside of the rotating shell  10 , and is exhausted to the outside of the rotating shell  10  from the discharge ports  50  which are also discharge ports for the processing material W. 
     Further, the steam fed into the heating tubes  11  from the feed pipe  70  is cooled in a process of flowing through the inside of the heating tubes  11 , when the processing material W and the heating tubes  11  are brought into contact with each other to perform heat exchange, and the steam is turned into liquid D to be discharged from the drain pipe  71 . 
     Modified Example 
     Next, description will be made also on a case where a horizontal rotary dryer provided with the agitating unit  65  and the classification hood  55  is used, while referring to  FIG. 4  and  FIG. 5 . In this case, a part of description overlapped with the above description will be omitted. 
     When the processing material W fed into the rotating shell  10  reaches the position at which the agitating unit  65  is provided, the processing material W is agitated by the agitating unit  65 , and subsequently lifted up by the lifters  60  which rotate in accordance with the rotation of the rotating shell  10 , as illustrated in  FIG. 5 . The lifted processing material W naturally falls down when the lifters  60  are positioned on the upper side of the rotating shell  10 , and at this time, fine particles C included in the processing material W are dispersed in the rotating shell  10  (so-called flight action). Note that the shape of the agitating unit  65  may employ a shape of plate projecting toward a center direction of the rotating shell  10 , or the like, so that the agitating unit  65  is structured to be able to lift up the processing material W in accordance with the rotation of the rotating shell  10 . For example, the agitating unit  65  may have a shape similar to that of the lifter  60 . 
     On the other hand, the carrier gas A blown from the feed port  41  by the blowing unit provided on the one end side of the rotating shell  10  passes through the inside of the rotating shell  10 , and is exhausted to the outside of the rotating shell  10  from the discharge ports  50  which also serve as outlets for the processing material W. At this time, the carrier gas A is exhausted from the discharge ports  50  while being accompanied by the fine particles C dispersed in the rotating shell  10  by the lifters  60 . The carrier gas A exhausted from the discharge ports  50  is exhausted from the classification hood  55  via the fixed exhaust gas opening  56 . 
     In the processing material W, heavy particles each having a large particle size fall down in the rotating shell  10 , and naturally fall down from the discharge ports  50  positioned on a lower side, without being discharged from the fixed exhaust gas opening  56  by the carrier gas A. The particles (processing material W) which have naturally fallen down are discharged as the processed material E to the outside from the fixed outlet  57 . 
     (Modified Example of Feed System) 
     A modified example of the horizontal rotary dryer according to the present invention will be described. 
     As a system of feeding the processing material W to the horizontal rotary dryer, there can be exemplified one of, other than the aforementioned screw type ( FIG. 2 ), a chute type ( FIG. 6 ) or a vibration trough type ( FIG. 7 ). In the chute type, a feed chute  46  is coupled to an intake box  45 , and the processing material W fed from the feed port  41  falls in the feed chute  46  to move to the inside of the rotating shell  10 . The intake box  45  is connected to the rotating shell  10  via a seal packing  47 , and it is structured in a manner that the rotating shell  10  rotates while maintaining sealing between the rotating shell  10  and the intake box  45 . In the vibration trough type, the intake box  45  has a trough shape (recessed cross-sectional shape), and a vibration motor  48  and a spring  49  are coupled to a lower end of the intake box  45 . The processing material W fed from the feed port  41  falls on the trough. Further, when the intake box  45  is vibrated by the vibration motor  48 , the processing material W moves to the inside of the rotating shell  10 . It is preferable that when the intake box  45  is attached, the intake box  45  is inclined downward toward the rotating shell  10  in order to allow the easy movement of the processing material W. 
     (Modified Example of Rotating Shell) 
     The cross-sectional shape of the rotating shell  10  may be set to a rectangular shape, other than a circular shape to be described later. As an example of the rectangular shape, the rotating shell  10  in a hexagonal shape is illustrated in  FIG. 8 . When the rectangular rotating shell  10  is rotated, the processing material W is raised by corner portions  15  of the rotating shell  10 , which realizes better mixing of the processing material W. Meanwhile, since the cross-sectional area of the rotating shell  10  becomes narrow when compared to a case where the circular rotating shell  10  is employed, there also exists a demerit such that the number of heating tubes  11  to be arranged is reduced. Note that the number of corner portions (number of sides) of the rectangular shape can be changed, and in more detail, the number of corner portions can be set to an arbitrary number of three or more. 
     As illustrated in  FIG. 9 , it is also possible to provide a jacket  12  surrounding the rotating shell  10 . In this case, a heating medium S is flowed between an outside wall of the rotating shell  10  and an inside wall of the jacket  12 , to thereby perform heating also from the outside of the rotating shell  10 . As a result of this, it is possible to increase the drying rate of the processing material W, when compared to a case where the jacket  12  is not provided. As an example of the heating medium S, there can be cited high temperature gas at 200° C. to 400° C., hot oil at 200° C. to 400° C., or the like. Other than the above, it is also possible to provide, instead of the jacket  12 , a plurality of trace pipes (not illustrated) so as to surround the rotating shell  10 . 
     (Modified Example of Discharge System) 
     As a system of discharging the processed material E from the horizontal rotary dryer, a configuration as illustrated in  FIG. 10  can also be employed. In such a configuration, the carrier gas A is sent to the inside a partition wall  23  from a carrier gas feed port  33  at an upper portion of a casing  80 . When the carrier gas A is reused gas, the carrier gas A contains powder dust and the like, but, since ribbon screws Z are arranged inside the partition wall  23 , namely, in a gas passage U 2 , the power dust and the like mixed in the gas are captured by the ribbon screws Z. The captured powder dust and the like are sent toward an opening  22  because of a transfer action of the ribbon screws Z, and discharged to the inside of the casing  80 . The discharged powder dust and the like freely fall to be discharged from the discharge port  32  at a lower portion of the casing. In contrast, gas as a result of removing the powder dust and the like from the carrier gas A is sent to the inside of the rotating shell  10  without being prevented by the ribbon screws Z. 
     Further, screw blades  24  also rotate in accordance with the rotation of the rotating shell  10 . Therefore, the dried material E as a result of drying the processing material W is sent, in a delivery passage U 1 , toward an opening  21  because of a transfer action of the screw blades  24 , and is discharged from the opening  21 . The discharged dried material E is discharged, by its own weight, from the discharge port  32  at the lower portion of the discharge casing. 
     On the other hand, a steam path (formed of an internal steam feed pipe  61  and an internal drain discharge pipe  62 ) penetrating through the casing  80  and extending to the inside of the partition wall  23 , is integrally provided with the rotating shell  10 . The internal steam feed pipe  61  is communicated with an entrance header portion for the heating tubes  11  of an end plate part  17 , and the internal drain discharge pipe  62  is communicated with an exit header portion for the heating tubes  11  of the end plate part  17 . Further, a steam feed pipe  70  and a drain discharge pipe  71  are connected to the internal steam feed pipe  61  and the internal drain discharge pipe  62 , respectively, via a rotary joint  63 . 
     (Modified Example of Gas Distribution System) 
     Each of the horizontal rotary dryers in  FIG. 1  and  FIG. 4  employs “cocurrent flow” in which the direction in which the processing material W moves and the direction in which the carrier gas A flows are the same. Other than the above, it is also possible to employ “countercurrent flow” in which the direction in which the processing material W moves and the direction in which the carrier gas A flows are opposite. 
     One example of a horizontal rotary dryer employing the “countercurrent flow” is illustrated in  FIG. 11 . This horizontal rotary dryer has a feed port  31  for the processing material W provided above a screw feeder  42 , and has a discharge port  32  for the processed material E provided at a lower end of a hood  35 . Further, the processing material W is fed from the feed port  31  to be moved from one end side to the other end side of the rotating shell  10 , the processing material W is heated to be dried by the heating tubes  11  through the movement process, and the dried processed material E is discharged from the discharge port  32 . Meanwhile, a feed port  33  for the carrier gas A is provided at an upper end of the hood  35 , and a discharge port  34  for the carrier gas A is provided above the screw feeder  42 . Further, the carrier gas A is fed from the feed port  33 , and flowed from the other end side to the one end side of the rotating shell  10 , the carrier gas conveys steam evaporated from the processing material W during a process of the flow, and the carrier gas A accompanied by the steam is discharged from the discharge port  34 . 
       10 , the carrier gas conveys steam evaporated from the processing material W during a process of the flow, and the carrier gas A accompanied by the steam is discharged from the discharge port  34 . 
     Other than the above, it is also possible to use a horizontal rotary dryer of a type employing a gas blowing pipe, as illustrated in  FIG. 12 . A gas blowing pipe  36  is provided inside the rotating shell  10  to extend in the axial direction, and rotates together with the rotating shell  10  and the heating tubes  11 . For example, the gas blowing pipe  36  can be provided between the plurality of heating tubes  11 ,  11 , or at a position further on the inner side relative to the heating tubes  11  positioned on the innermost side. Note that in  FIG. 12 , the illustration of the heating tubes  11  is omitted, for easier understanding of the gas blowing pipe  36 . On a wall surface of the gas blowing pipe  36 , a plurality of gas blowout openings  37  are opened. In the example of  FIG. 12 , the gas blowing openings  37  are provided in two lines in an axial direction, at upper portions of the gas blowing pipe  36 . 
     When the above-described dryer of the type employing the gas blowing pipe is operated, the carrier gas A is fed into the gas blowing pipe  36  from the other end side of the rotating shell  10 . The fed carrier gas A is blown out into the rotating shell  10  from the gas blowing openings  37 , and flows out from the one end side of the rotating shell  10  while being accompanied by the steam generated from the processing material W. Other than the above, it is also possible to employ a configuration in which the carrier gas A is fed into the gas blowing pipe  36  from the one end side of the rotating shell  10 , and the gas is exhausted from the other end side of the rotating shell  10 . 
     (Modified Example of Rotating Shell Supporting Structure) 
     Other than the above, the supporting structure of the rotating shell  10  may also employ, other than the aforementioned supporting structure in which two tire members  20 ,  20  are attached to the outer periphery of the rotating shell  10 , a structure in which bearings (not illustrated) are attached to outer peripheries of a screw casing  42  provided on one end side and the gas pipe  72  provided on the other end side, and the bearings are supported, or a supporting structure realized by combining the tire members  25  and the bearings. 
     (Rotation Speed) 
     In the present invention, the rotating shell  10  is rotated at a speed faster than that in the conventional horizontal rotary dryer, in order to increase the drying rate of the processing material W. A method of deciding the rotation speed will be described hereinafter. 
     (Process 1) 
     A processing load PL of the horizontal rotary dryer is decided. Concretely, the load PL is calculated based on a type of the processing material W, the water content (%), a targeted processing amount (kg/h), and the like. 
     (Process 2) 
     A small-sized horizontal rotary dryer is used as an experimental machine, to examine a drying rate Rd per unit load. 
     (Process 3) 
     A size of the rotating shell  10  is decided based on the drying rate Rd examined in the process 2. 
     (Process 4) 
     A number of rotations of the rotating shell  10  is decided. A conventional method of deciding the number of rotations uses, as an important criterion, a rotation speed of the rotating shell  10  (in the present invention, “rotation speed” is also referred to as “circumferential speed”), and concretely, the number of rotations has been decided by using the following expression 5. Note that a value of rotation speed V has been decided based on empirical rule within a range of about 0.1 to 1 [m/s].
 
 N =( V× 60)/( D ×π)  Expression 5
 
     Here, N indicates the number of rotations (r.p.m.), V indicates the rotation speed (m/s), and D indicates an inside diameter (in) of the rotating shell  10 . 
     In the present invention, the number of rotations is decided based on, not the aforementioned expression 5, but a critical speed ratio, and concretely, the number of rotations is decided by using the following expression 6,
 
 N=V/Vc×Nc   Expression 6
 
     wherein N indicates the number of rotations (r.p.m.), V indicates the rotation speed (m/s), Vc indicates a critical speed (m/s), and Nc indicates a critical number of rotations (r.p.m.). 
     (Critical Speed, Critical Speed Ratio) 
     The “critical speed” and the “critical number of rotations” in the aforementioned expression 6 will be described in detail. When  FIG. 13  is referred to, the “critical speed” corresponds to a rotation speed at which gravity of the processing material W and centrifugal force acted on the processing material W are balanced in the horizontal rotary dryer, and theoretically indicates a rotation speed of the rotating shell  10  when the processing material W corotates with the rotating shell  10 . Note that no indicates a speed. Further, the “critical speed ratio” indicates a ratio of the actual rotation speed to the critical speed. 
     (Critical Speed) 
     The critical speed will be described in detail. At the critical speed, the gravity (mg) of the processing material W and the centrifugal force (mrω 2 ) are the same, so that the following expression 7 is satisfied,
 
 mg=mrω   2   Expression 7
 
     wherein in indicates mass (kg) of the processing material W, g indicates a gravitational acceleration (m/s 2 ), r indicates a radius (in) of the rotating shell  10 , and ω indicates an angular speed (rad/s). 
     Further, the following expression 8 can be derived from the aforementioned expression 7,
 
 g=r ( Vc/r ) 2   Expression 8
 
     wherein g indicates the gravitational acceleration (m/s 2 ), r indicates the radius (in) of the rotating shell  10 , and Vc indicates the critical speed (m/s). 
     Therefore, it is possible to derive the following expression 1 from the aforementioned expression 8, to thereby determine the critical speed (m/s),
 
 Vc =( rg ) 1/2 =( D/ 2· g ) 1/2 =2.21 D   1/2  
 
 Vc= 2.21 D   1/2   Expression 1
 
     wherein Vc indicates the critical speed (m/s), and D indicates the inside diameter (in) of the rotating shell  10 . 
     (Critical Speed Ratio) 
     Next, the critical speed ratio will be described. The critical speed ratio α indicates the ratio of the actual rotation speed V to the critical speed (Vc), and thus it can be represented by the following expression 2,
 
α= V/Vc· 100  Expression 2
 
     wherein α indicates the critical speed ratio (%), V indicates the rotation speed (m/s), and Vc indicates the critical speed (m/s). 
     (Critical Number of Rotations) 
     Note that the number of rotations of the rotating shell  10  at the critical speed is referred to as “critical number of rotations”, and can be determined through the following expression 9,
 
 Nc=Vc· 60/(π D )=2.21 D   1/2 ·60/(π D )=42.2/ D   1/2  
 
 Nc= 42.2/ D   1/2   Expression 9
 
     wherein Nc indicates the critical number of rotations (r.p.m.), Vc indicates the critical speed (m/s), and D indicates the inside diameter (in) of the rotating shell  10 . 
     (Scale-Up) 
       FIG. 14  illustrates a change in the critical speed ratio α (%) in which X-axis represents the inside diameter D (in) of the rotating shell  10 , and Y-axis represents the number of rotations N (r.p.m.). P 1  indicates a number of rotations of a conventional rotating shell  10 , and P 2  indicates a number of rotations of the rotating shell  10  of the present invention. According to  FIG. 14 , it can be clearly recognized, at a glance, that the operating condition of the present invention (critical speed ratio α=30 to less than 100%) is different from the operating condition of the conventional example. 
     Experimental Example 1 
     Three horizontal rotary dryers with different inside diameters were used to perform an experiment regarding a relationship between the critical speed ratio α (%) and the drying rate Rd. The diameters of the rotating shells  10  of the respective STDs are 320 mm, 900 mm, and 1830 mm. Further, a gap K between the heating tubes  11  arranged in each of the rotating shells  10  is 100 mm. 
     Coal (processing material W) was charged in each of the STDs in a batch manner. A charging amount of the coal with respect to the STD with the diameter of 320 mm is 4 kg, a charging amount of the coal with respect to the STD with the diameter of 900 mm is 50 kg, and a charging amount of the coal with respect to the STD with the diameter of 1830 mm is 250 kg. Further, the median diameter of the coal is 2.2 mm Note that a pressure of steam which is flowed in the heating tubes  11  arranged in each of the rotating shells  10  was set to 0.6 MPa (gage pressure). 
       FIG. 15  is a graph illustrating a relationship between the critical speed ratio and the drying rate when the diameter of the rotating shell  10  of the STD is 320 mm Values of the drying rate in  FIG. 15  are relative numeric values. In detail, a value of the drying rate when the diameter of the rotating shell  10  of the STD is 320 mm, and the critical speed ratio is 20% is defined as 1, and the values of the drying rate are represented by relative numeric values based on the value of 1. 
     Further, a diagram obtained in a manner that the rotating shell  10  was operated while arbitrarily changing the critical speed ratio and the diameter of the rotating shell  10 , dispersion states of the processing material W in the inner part of the rotating shell  10  were photographed, and the photographs were traced, is illustrated in  FIG. 16 . Specifically, a transparent plate was provided at a transverse section of each of the horizontal rotary dryers so that behavior of the processing material W could be visually recognized, the dispersion states of the processing material W in the inner part of the rotating shell  10  were photographed through this transparent plate, and the photographs were traced. Note that the rotational direction of the rotating shell  10  in  FIG. 16  is counterclockwise, in a similar manner to  FIG. 5 . 
     When the operation was performed by setting the critical speed ratio to 20%, the processing material W is subjected to kiln action in a region of right side of the rotating shell  10 . However, the processing material W remains, in an aggregated state, on an inside wall of the rotating shell  10 , and thus a movement amount thereof is small, so that the processing material W is not dispersed very much. This means that the heat transfer surface of the rotating shell  10  and the processing material W (coal) are not sufficiently brought into contact with each other. 
     On the other hand, when the inner part of the rotating shell  10  was checked at the time of performing operation by setting the critical speed ratio to 50%, it was confirmed that the processing material W was dispersed in a wide range in the rotating shell  10 . Further, when the operation was performed by increasing the critical speed ratio to 70%, and the inner part of the rotating shell  10  was checked, the processing material W was dispersed in a wider range. 
     Further, when the inner part of the rotating shell  10  was checked at the time of performing operation by setting the critical speed ratio to 100%, it was confirmed that, although a slight amount of the processing material W fell from the middle, almost all of the processing material W was subjected to corotation, and thus the heat transfer surface and the processing material W were not brought into contact with each other and no heat transfer was conducted. 
     Note that an arrow mark illustrated in the rotating shell  10  in  FIG. 16  indicates a direction in which the processing material W falls. 
     Actually, it was confirmed that the drying rate increases as the critical speed ratio increases, as illustrated in  FIG. 17 . Further, even if the diameter of the rotating shell  10  changes, there is no change in the upward tendency of the drying rate with respect to the critical speed ratio. Note that values of the drying rate in  FIG. 17  are relative numeric values. In detail, a value of the drying rate when the diameter of the rotating shell  10  of the STD is 320 mm, and the critical speed ratio is 20% is defined as 1, and the values of the drying rate are represented by relative numeric values based on the value of 1. 
     (Hold Up Ratio) 
     In the present invention, when the rotating shell  10  is rotated at a high speed, it is preferable to set the hold up ratio of the processing material W to 20 to 40%. The hold up ratio is preferably set to 25 to 30%. 
     Note that the hold up ratio can be determined by the following expression 3,
 
η= Ap/Af· 100  Expression 3
 
     wherein η indicates the hold up ratio (%), Ap indicates a cross-sectional area (m 2 ) occupied by the processing material W with respect to a free cross-sectional area, and Af indicates a free cross-sectional area (m 2 ) as a result of subtracting a cross-sectional area of all of the heating tubes from the entire cross-sectional area of the rotating shell  10 . 
     Experimental Example 2 
     An experiment was conducted by charging coal (processing material W) into a STD with a diameter of 450 mm at 200 kg/h. The gap K between the heating tubes  11  arranged in the rotating shell  10  is 100 mm. Further, the median diameter of the coal is 2.2 mm Note that a pressure of steam which is flowed in the heating tubes  11  arranged in the rotating shell  10  was set to 0.6 MPa (gage pressure). 
       FIG. 18  is a graph illustrating the critical speed ratio and the drying rate when the hold up ratio is changed. Values of the drying rate in  FIG. 18  are relative numeric values. In detail, a value of the drying rate when the hold up ratio is 15% and the critical speed ratio is 20% is defined as 1, and the values of the drying rate are represented by relative numeric values based on the value of 1. When operation was performed by setting the hold up ratio of the processing material W to 15%, the contact area between the processing material W and the heating tubes  11  was small, so that the drying rate was not increased. On the other hand, when operation was performed by setting the hold up ratio of the processing material W to 25%, the contact area between the processing material W and the heating tubes  11  was increased, and the drying rate was increased. Further, when operation was performed by setting the hold up ratio of the processing material W to 35%, slip occurred at an upper layer of powder layer (layer of processing material W in powder form), and the number of processing material W which was not brought into contact with the heat transfer surface increased. As a result of this, when compared to the case where the operation was performed with the hold up ratio of 25%, the drying rate was not increased. However, the drying rate was faster than that when the operation was performed with the hold up ratio of 15%. Note that even if any one of the hold up ratios was employed, as the critical speed ratio was increased, the drying rate increased. 
     Through the above-described experiment, it was confirmed that it is preferable to employ the hold up ratio of 20 to 40% by which the drying rate of the processing material W significantly increases. 
     (Gap Between Heating Tubes  11 ) 
       FIG. 19  illustrates the gap K between the heating tubes  11 . In this example, the gap K is the same among four lines of concentric circles. For this reason, the diameter of the heating tube  11  is increased toward the outside. A distance between the adjacent heating tubes  11  (gap) K is preferably set to 80 to 150 mm. It is of course possible to perform appropriate modification such that the heating tubes  11  are set to have the same diameter, or the gap K is increased toward the outside, for example. Further, it is also possible to employ a later-described first arrangement form or second arrangement form. 
     Experimental Example 3 
     An experiment was conducted by charging 250 kg of coal (processing material W) into a STD with a diameter of 1830 mm in a batch manner. The median diameter of the coal is 2.2 mm Note that a pressure of steam which is flowed in the heating tubes  11  arranged in the rotating shell  10  was set to 0.6 MPa (gage pressure). 
       FIG. 20  is a graph illustrating the critical speed ratio and the drying rate. Values of the drying rate in  FIG. 20  are relative numeric values. In detail, a value of the drying rate when the gap K between the heating tubes  11  is 50 mm, and the critical speed ratio is 20%, is defined as 1, and the values of the drying rate are represented by relative numeric values based on the value of 1. 
     Further, the arrangement of the heating tubes  11  when creating the graph in  FIG. 20  was similar to that of  FIG. 19 . Specifically, the heating tubes  11  were arranged in a radial manner from a center of the rotating shell  10  toward the outside, and the diameters of the heating tubes  11  were gradually increased from the inside toward the outside. Accordingly, all of the gaps K between the heating tubes  11  positioned on the first column to the n-th column are set to be the same. For example, when the gap K between the heating tubes  11  is 50 mm, each of all of the gaps K between the heating tubes  11  positioned on the first column to the n-th column is 50 mm Note that this arrangement of the heating tubes  11  is similarly employed also in later-described  FIG. 21 . 
     When operation was performed by setting the gap K between the heating tubes  11  to 50 mm, an amount of the processing material W flowing through the gap K was small, and the processing material W was not mixed very much, resulting in that the drying rate was slow. Thereafter, as the gap K between the heating tubes  11  was increased to 80 mm, 100 mm, and 150 mm, the drying rate became gradually fast. It can be estimated that a part of the reason thereof is that the amount of the processing material W flowing through the gap K becomes gradually large, and thus the mixing of the processing material W favorably occurs. On the other hand, when operation was performed by setting the gap K between the heating tubes  11  to 200 mm, an amount of the processing material W flowing through the gap K was increased. However, when compared to the case where the length of the gap K was 150 mm, the contact area between the processing material W and the heating tubes  11  was not changed very much. As a result of this, the drying rate was not so different from the drying rate when the gap K was 150 mm Note that at any hold up ratio, as the critical speed ratio was increased, the drying rate increased. 
     Through the above-described experiment, it was confirmed that the distance (gap) between the adjacent heating tubes  11  is preferably set to 80 to 150 mm. 
     Experimental Example 4 (Resin-Based Material) 
     A resin-based material was charged into a STD with a diameter of 1830 mm in a batch manner. A charging amount of the resin-based material is 250 kg. Further, the median diameter of the resin-based material is 0.1 mm Further, a pressure of steam which is flowed in the heating tubes  11  in the rotating shell  10  was set to 0.45 MPa (gage pressure). 
       FIG. 21  is a graph illustrating a relationship between the critical speed ratio and the drying rate when the length of the gap K between the heating tubes  11  is changed by using the resin-based material as the processing material W. Values of the drying rate in  FIG. 21  are relative numeric values. In detail, a value of the drying rate when the gap K between the heating tubes  11  is 50 mm, and the critical speed ratio is 20% is defined as 1, and the values of the drying rate are represented by relative numeric values based on the value of 1. 
     As illustrated in  FIG. 21 , the drying rates form a shape of mountain in which peaks thereof appear when the critical speed ratio α is around 50%. Therefore, it can be understood that the critical speed ratio α of 30 to 70% is preferable. Further, when the gap K between the heating tubes  11  is gradually increased to 50 mm, 80 mm, and 100 mm, the drying rate also becomes gradually fast. 
     As can be predicted also from the above results, it is preferable to employ the critical speed ratio of 40 to 90%, although the optimum critical speed ratio differs depending on the type and the water content of the processing material W, the size of the dryer, and the like. 
     (Relationship Between Outside Diameter and Inside Diameter) 
     In the above-described respective descriptions and respective expressions, the inside diameter D of the rotating shell  10  is used, and the outside diameter is not used. However, it is also possible to use the outside diameter by correcting the above-described respective expressions. This point will be described hereinafter in detail. 
     In the above-described respective expressions, D indicates the inside diameter, and a correcting expression for using, not the inside diameter, but the outside diameter, will be described. When the outside diameter of the rotating shell  10  is set to Do, the plate thickness (wall thickness) of the rotating shell  10  is set to t, and the inside diameter is set to D, a relationship among these is represented by the following expression 10.
 
 D=Do −(2× t )  Expression 10
 
     Therefore, it is only required to substitute the right side in the expression 10 into D in the above-described respective expressions. For example, the expression regarding the critical speed ratio can be described as follows.
 
 Vc= 2.21 D   1/2  
 
 Vc= 2.21×( Do− 2× t ) 1/2   Expression 1
 
     Note that as a reference, a general numeric value of the wall thickness t of the rotating shell  10  of the STD or the like will be described. As the size of the rotating shell  10  becomes large, the wall thickness t tends to increase in order to maintain strength of the rotating shell, and actually, the wall thickness t is designed to have approximately the following numeric value. When the inside diameter D of the rotating shell  10  is 0.3 to 6 in, the wall thickness t becomes 3 to 100 mm. 
     &lt;Regarding Heating Tube&gt; 
     Although the size and the arrangement of the heating tubes  11  can be appropriately selected in the present invention, in order to increase mainly the contact efficiency to thereby increase the drying rate in the process of realizing the high-speed rotation aimed by the present inventors, it was found out that measurements to be described next are effective. 
     (Arrangement of Heating Tubes) 
     Conventionally, the heating tubes  11  have been arranged in a radial manner in the rotating shell  10 , as illustrated in  FIG. 29 . In the rotating shell  10 , the processing material W (granular material) enters gaps between the plurality of heating tubes  11  moved to a lower part of the rotating shell  10 , and lifted up in the rotational direction by the plurality of heating tubes  11  in accordance with the rotation of the rotating shell  10 . The processing material W lifted up to its repose angle starts to fall mainly at a point of time of exceeding the repose angle, and is subjected to falling motion. In more detail, the processing material W falls, like a snowslide, from portions between the plurality of heating tubes  11  at upper positions exceeding the limit of the repose angle, and collides with the heating tubes  11  positioned at the lower part of the rotating shell  10 . 
     The fallen processing material W enters again the gaps between the plurality of heating tubes  11 ,  11  at the lower part of the rotating shell  10 . It was clarified that, since an angle at which the processing material W falls and an angle at which the processing material W enters the gap between the heating tubes  11 ,  11  are different, the processing material W does not immediately enter the gap between the heating tubes  11 ,  11 , and remains on the outside of the heating tubes  11 ,  11  (center side of the rotating shell  10 ), resulting in that the contact efficiency between the processing material W and the heating tube  11  is poor. If the contact efficiency is poor, there was a problem that the drying rate of the processing material W is lowered. 
     Further, since the direction in which the processing material W falls and the direction in which the processing material W enters between the plurality of heating tubes  11 ,  11  are different, there was a problem that the fallen processing material W collides with the heating tubes  11 ,  11  on the innermost column (column on the side closest to the center of the rotating shell  10 ), and kinetic energy once becomes zero (kinetic energy is reset). 
     The present invention improved the arrangement of the heating tubes  11  in order to solve the above-described problems. 
     Specifically, in the horizontal rotary dryer provided with: the rotating shell  10  having the feed port for processing material W on one end side thereof and the discharge port for processing material W on the other end side thereof, and capable of freely rotating around the axial center; and the large number of heating tubes  11 ,  11  . . . through which the heating medium passes, provided within the rotating shell  10 , and heating and drying the processing material W by using the heating tubes  11 ,  11  . . . in the process of feeding the processing material W to the one end side of the rotating shell  10  and discharging the processing material W from the other end side of the rotating shell  10 , the arrangement of the heating tubes  11 ,  11  . . . desirably employs the following arrangement forms. 
     The group of the heating tubes  11 ,  11  . . . is arranged substantially in a concentric form around the center of the rotating shell  10 , and a connecting line connecting from a core of a first reference heating tube S 1  on the center-side circle to a core of a second reference heating tube S 2 , is selected from one of the following (1) and (2) arrangement forms, and an arrangement form as a result of combining these (1) and (2) arrangement forms. 
     &lt;With Reference to  FIG. 24 : Form in Shape of Diagonal Straight Line&gt; 
     (1) First arrangement form in which cores of the respective heating tubes  11 ,  11  . . . are positioned on a straight line L 1  directly connecting the core of the first reference heating tube S 1  and the core of the second reference heating tube S 2 , and further, the core of the second reference heating tube S 2  is positioned rearward in the rotational direction of the rotating shell  10  with respect to a radial line J 1  passing through the core of the first reference heating tube S 1 . 
     &lt;With Reference to  FIG. 22 : Form in Shape of Curved Line&gt; 
     (2) Second arrangement form in which cores of the respective heating tubes  11 ,  11  . . . are positioned on a curved line L 2  connecting the core of the first reference heating tube S 1  and the core of the second reference heating tube S 2 , and positioned further on the rear side in the rotational direction of the rotating shell  10  as they direct toward the core of the second reference heating tube S 2 , and further, the core of the second reference heating tube S 2  is positioned rearward in the rotational direction of the rotating shell  10  with respect to a radial line J 1  passing through the core of the first reference heating tube S 1 . 
     Specifically, as illustrated in  FIG. 22  and  FIG. 24 , the heating tubes  11 ,  11  . . . are arranged in the concentric form around a center F of the rotating shell  10 , and are arranged on respective concentric circles including a concentric circle r 1  being a center-side circle on which the first reference heating tube S 1  is positioned, a concentric circle r 2  on which the second reference heating tube S 2  is positioned, and a concentric circle r 3  on which the outermost heating tubes  11  positioned on the outermost side of the rotating shell  10  is positioned. 
     The core of the first reference heating tube S 1  (refer to  FIG. 22  and  FIG. 24 ) corresponds to a core of the heating tube  11  (center of the heating tube) which is arbitrarily selected from a column of the group of the heating tubes  11  positioned on the side closest to the center of the rotating shell  10  (“column  1 ”: refer to  FIG. 23 ). 
     Further, the core of the second reference heating tube S 2  indicates a core of the heating tube S 2  (center of the heating tube  11 ) on a desired column number, in “columns” of the plurality of heating tubes  11 ,  11  . . . (refer to  FIG. 23 ), counted from the heating tube  11  positioned on the side closest to the center of the rotating shell  10  (the first reference heating tube S 1 ) toward the outside along the same “row”. 
     A position of the core of the second reference heating tube S 2  can be appropriately selected in accordance with a flow behavior of the processing material W (this flow behavior depends on a factor derived from physical properties (shape, size, viscosity, type of material, and the like) of the processing material W, a factor derived from operating conditions of the dryer, and the like). 
     At this time, an arrangement ratio ε=h 2  (from the concentric circle r 2  on which the second reference heating tube S 2  is positioned to the concentric circle r 1  on which the first reference (innermost) heating tube S 1  is positioned)/h 1  (from an inner surface of the rotating shell to the concentric circle r 1  on which the first reference (innermost) heating tube S 1  is positioned), is desirably set to greater than ½. 
     Further, in the present invention, at least a section from the first reference heating tube S 1  to the second reference heating tube S 2  desirably employs arrangement of heating tubes of the aforementioned first arrangement form or second arrangement form. 
     Further, the present invention also includes a case where the position of the core of the second reference heating tube S 2  is on the concentric circle r 3  on which the outermost heating tubes  11  are positioned. 
     As described above, the region which employs the first arrangement form or the second arrangement form can be appropriately selected, and in the example illustrated in  FIG. 24 , the total number of columns of the heating tubes  11  is seven, and the core of the second reference heating tube S 2  is positioned on the fourth column. 
       FIG. 24  illustrates the example of the first arrangement form, and  FIG. 22  and  FIG. 23  illustrate the example of the second arrangement form. 
       FIG. 24  illustrates the example in which all of the seven columns employ the first arrangement form. Specifically, the cores of the respective heating tubes  11 ,  11  . . . are positioned on the straight line L 1  directly connecting the core of the first reference heating tube S 1  and the core of the second reference heating tube S 2 , and further, the core of the second reference heating tube S 2  is positioned rearward in the rotational direction of the rotating shell  10  with respect to the radial line J 1  passing through the core of the first reference heating tube S 1 . 
       FIG. 22  and  FIG. 23  illustrate the example in which all of nine columns employ the second arrangement form. Specifically, the cores of the respective heating tubes  11 ,  11  . . . are positioned on the curved line L 2  connecting the core of the first reference heating tube S 1  and the core of the second reference heating tube S 2 , and positioned further on the rear side in the rotational direction of the rotating shell  10  as they direct toward the core of the second reference heating tube S 2 , and further, the core of the second reference heating tube S 2  is positioned rearward in the rotational direction of the rotating shell  10  with respect to the radial line J 1  passing through the core of the first reference heating tube S 1 . 
     Note that in  FIG. 22  and  FIG. 24 , a line passing through the core of the first reference heating tube S 1  and a line passing through the core of the second reference heating tube S 2 , by setting the center point F of the rotating shell  10  as a starting point, are indicated as the radial line J 1  and a radial line J 2 , respectively. The respective distances of h 1  and h 2  described above may be determined from a distance on the radial line J 2 . 
     (Another Arrangement in Shape of Curved Line or Straight Line of Heating Tubes) 
     Other than the above, in another preferred embodiment of the present invention, it is also possible to employ an arrangement in which the gap between the adjacent heating tubes  11  is increased from the center side toward the outside on the concentric circles around the rotation axis of the rotating shell  10 .  FIG. 22  to  FIG. 24  illustrate examples in which the gap between the adjacent heating tubes  11  is gradually increased from the center side toward the outside. 
     Further, as the curved line L 2  connecting the core of the first reference heating tube S 1  and the core of the second reference heating tube S 2 , it is possible to employ a cycloid (line drawn by a particle when the particle falls at the fastest speed), the Cornu&#39;s spiral (line drawn by a particle when the particle smoothly falls), a logarithmic curve, an arc line, a line approximated to these lines, or the like. 
       FIG. 28  illustrates an example of form in which inside parts of the heating tubes  11 ,  11  . . . are arranged in a shape of curved line in accordance with the second arrangement form, and outside parts of the heating tubes  11 ,  11  . . . are arranged along a radial direction. 
       FIG. 25  illustrates an example of form in which inside parts of the heating tubes  11 ,  11  . . . are arranged in a shape of curved line in accordance with the second arrangement form, and outside parts of the heating tubes  11 ,  11  . . . are arranged along a radial direction. 
       FIG. 27  illustrates an example in which the heating tubes  11 ,  11  . . . are arranged in a shape of diagonal straight line in accordance with the first arrangement form, in which regarding the outside parts, rows of heating tubes  11 ,  11  . . . arranged in a shape of diagonal straight line are interposed from positions on an intermediate concentric circle toward the outermost concentric circle. 
     On the other hand, as can be estimated based on these examples, it is also possible to arrange the heating tubes by combining the first arrangement form and the second arrangement form, although a concrete example thereof is not illustrated in the drawing. 
     Regarding all of the columns, when the first arrangement form and the second arrangement form are not employed, but, these arrangement forms are employed up to the middle of the columns, it is also desirable that the arrangement ratio ε=h 2  (from the concentric circle r 2  on which the second reference heating tube S 2  is positioned to the concentric circle r 1  on which the first reference (innermost) heating tube S 1  is positioned)/h 1  (from the inner surface of the rotating shell to the concentric circle r 1  on which the first reference (innermost) heating tube S 1  is positioned), is set to greater than ½. 
     (Operation and Effect) 
     By arranging the heating tubes  11  in the shape of curved line or diagonal straight line as described above, the direction in which the processing material W falls and the direction in which the processing material W enters between the plurality of heating tubes  11  are approximated, resulting in that the fallen processing material W enters the gap between the plurality of heating tubes  11 ,  11  without greatly changing its moving direction. The processing material W which enters the gap between the heating tubes  11 ,  11  flows from the inside toward the outside of the rotating shell  10 , and reaches a shell wall of the rotating shell  10 . By selecting the arrangement of the heating tubes  11 , the processing material W immediately enters the gap between the heating tubes  11  and does not remain on the outside of the heating tubes  11  (center side of the rotating shell  10 ), so that the contact between the processing material W and the heating tubes  11  becomes good, which enables to improve the drying efficiency. Further, the contact area between the processing material W and the heating tubes  11  increases, and the contact time between the both also increases, and also from that point, it is possible to improve the drying efficiency. 
     Further, since the processing material W smoothly enters the gap between the heating tubes  11 ,  11 , impact received by the heating tube  11  from the processing material W becomes small. For this reason, when compared to a case where the heating tubes  11  are arranged in the conventional manner, the diameter of the heating tube  11  can be reduced, and the number of heating tubes  11  can be increased. As a result of this, the heat transfer area of the heating tubes  11  is increased as a whole, which enables to improve the drying efficiency. 
     Other than the above, in the conventional device, crush of the processing material W (granular material) has occurred due to collision between the fallen processing material W and the heating tube  11 , but, according to the above-described preferred embodiments, it is possible to prevent or suppress the crush. As a result of this, the particle size distribution of the final product (dried product) is stabilized, and at the same time, fine powder is reduced, which enables to reduce the load on the exhaust gas processing facility. 
     Note that the diameter and the wall thickness of each of the heating tubes  11 ,  11  . . . can be appropriately selected. 
     (Number of Heating Tubes  11 ) 
     Although it is possible that all of the numbers of heating tubes  11  on the respective concentric circles are set to be the same, when the heating tubes  11  are provided in a shape of straight line, the number of heating tubes  11  from the outermost periphery to the vicinity of the middle of the rotating shell  10  is preferably set to be larger than the number of heating tubes  11  from the vicinity of the middle to the innermost periphery of the rotating shell  10 , as illustrated in  FIG. 27 . By increasing the number of heating tubes  11  from the vicinity of the middle to the outermost periphery of the rotating shell  10  as described above, the distance between the adjacent heating tubes  11 ,  11  can be set to approximately the same from the innermost periphery to the outermost periphery. Further, by increasing the number of heating tubes  11 , the heat transfer area of the heating tubes  11  increases, which enables to improve the drying efficiency of the processing material W moved to the outer peripheral side of the rotating shell  10 . 
     (Diameter of Heating Tube  11 ) 
     Although all of the heating tubes  11  may have the same diameter, it is also possible to design such that, as illustrated in  FIG. 23 , the diameter is gradually increased from the inner peripheral side toward the outer peripheral side of the rotating shell  10 . By changing the diameters of the heating tubes  11  as described above, the distance between the adjacent heating tubes  11  can be set to approximately the same from the inner periphery to the outer periphery. By increasing the diameters of the heating tubes  11  as described above, the heat transfer area of the heating tubes  11  increases, which enables to improve the drying efficiency of the processing material W moved to the outer peripheral side of the rotating shell  10 . 
     (Method of Deciding Arrangement of Heating Tubes  11 ) 
     A method of deciding the arrangement of the heating tubes  11  will be described with reference to  FIG. 23 . Note that the arrangement of the heating tubes  11  is represented by “rows and columns”, in which the arrangement in a radial direction of the rotating shell  10  (direction from the center side toward the outside of the rotating shell  10 ) is represented by the “column”, and the arrangement in a circumferential direction of the rotating shell  10  is represented by the “row”. 
     By changing a distance between adjacent rows (distance between row  1  and row  2 , for example), and a distance between adjacent columns (distance between column  1  and column  2 , for example), it is possible to change dispersibility and flowability of the processing material W. 
     For example, when the heating tube  11  to which hatching is applied in  FIG. 23  (referred to as “reference heating tube  11 ”, hereinafter) is set as a reference, as a distance between rows, there can be considered, other than a distance between the heating tube  11  of (1) and the reference heating tube  11 , and a distance between the heating tube  11  of (5) and the reference heating tube  11 , a distance between the heating tube  11  of (2) and the reference heating tube  11 , a distance between the heating tube  11  of (8) and the reference heating tube  11 , a distance between the heating tube  11  of (4) and the reference heating tube  11 , and a distance between the heating tube  11  of (6) and the reference heating tube  11 , and each of these distances is set to have the above-described certain value or greater. Further, as a distance between columns, there can be considered a distance between the heating tube  11  of (3) and the reference heating tube  11 , and a distance between the heating tube  11  of (7) and the reference heating tube  11 , and each of these distances is also set to have the above-described certain value or greater. Note that the distance between the adjacent heating tubes  11  is preferably set to 80 to 150 mm. 
     As described above, the distance between rows and the distance between columns become restriction conditions at the time of deciding the arrangement of the heating tubes  11 . Various variations are tested while changing the diameters of the heating tubes  11 , the number of rows, and the number of columns so that the heat transfer area becomes as large as possible and the flowability is improved, while complying with the restriction conditions, and as a result of this, the arrangement with which the heat transfer area becomes the largest and the flowability is improved is adopted, and a product is designed. Note that as a result of actually studying the arrangement of the heating tubes  11 , when a curvature of the row was gradually increased, by gradually decreasing the diameters of the heating tubes  11  and gradually increasing the number of columns, it was possible to realize the largest heat transfer area. On the contrary, when the curvature of the row was gradually decreased, by gradually increasing the diameters of the heating tubes  11  and gradually decreasing the number of columns, it was possible to realize the largest heat transfer area. 
     EXPLANATION OF NUMERALS AND SYMBOLS 
     
         
         
           
               10  rotating shell 
               11  steam tube (heating tube) 
               41  feed port 
               50  discharge port 
               55  classification hood 
               56  fixed exhaust gas opening 
               57  fixed discharge port 
               60  lifter 
               65  agitating unit 
             A carrier gas 
             E processed material 
             W processing material