DESCRIPTION Title of Invention HORIZONTAL ROTARY DRYER FOR COAL, COAL-FIRED BOILER SYSTEM, AND METHOD FOR OPERATING COAL-FIRED BOILER SYSTEM Technical Field [0001] The present invention relates to a horizontal rotary dryer for coal with a capability for use at a thermal power plant and the like, a coal-fired boiler system provided with the horizontal rotary dryer, and a method for operating the coal-fired boiler system. Background Art [0002] Plants and other facilities that use heat, such as a thermal power plant, a sugar mill, and a pulp mill, are provided with a boiler for heating water to generate steam, and these plants use coal as part or as whole of the fuel. As the coal for use in these plants, a coal having a high moisture content, such as brown coal and lignite and subbituminous coal, is used in some cases because of its inexpensiveness. The coal is pulverized by a pulverizer, such as a roller mill, and then combusted by a burner associated with the boiler. When the coal having a high moisture content is used as fuel without processing, however, part of the heat value is removed for the evaporation of the water contained in the coal. This is problematic in that it reduces the amount of steam generated 1 by the boiler. Hence, at present, the coal is predried by a dryer and then pulverized by a pulverizer before being used as fuel. In the case with the coal such as the brown coal and lignite and the subbituminous coal, its crumbling entailed by the drying generates fine powder. Because of this, the dried coal includes a large amount of dust coal. For example, when the brown coal and lignite with a moisture percentage at around 60% is dried until the moisture percentage is around 10%, the percentage of dust coal of a size equal to or smaller than 300 pim (fine particles) increases from just around 2% to around 10%. Hence, the release of the dust coal should be prevented during transportation and the like of the dried coal, posing a problem of poor handleability. In addition, the dust coal, which does not need to be pulverized, is also subjected to the pulverization by a pulverizer, posing another problem of poor pulverizing efficiency. In particular, when a roller mill or the like is used as the pulverizer, a large amount of dust coal may cause vibration, which leads to instability of operation. To solve these problems, there is a demand to feed the dried coal to a classifier to remove the dust coal from the dried coal before the pulverization by a pulverizer. [0003] As a dryer for coal, horizontal rotary dryers have been known, which are exemplified by a so-called steam tube dryer (STD) (for example, see Patent Literature 1). As illustrated in an example in Fig. 11, this steam tube dryer mainly includes a rotating shell 110, which rotates about its shaft center, and 2 a large number of heating tubes 111, which are positioned along the shaft center direction inside the rotating shell 110. A heating medium, such as steam, passes through the insides of the heating tubes 111. Coal is fed (charged) from one end side of the rotating shell 110 and transported to the other end side thereof as the rotating shell 110 rotates. In the process of the transportation, the coal is heated through contact with the heating tubes 111 to be dried. The dried coal is discharged through an outlet nozzle 112 placed at the other end side of the rotating shell 110. In addition, a carrier gas blowing nozzle 113 is placed at the one end side of the rotating shell 110. A carrier gas is, together with other gases such as steam generated inside the rotating shell 110, exhausted from an exhaust gas nozzle 122, which is in communication with the outlet nozzle 112 placed at the other end side of the rotating shell 110. This steam tube dryer is capable of drying coal in a stable manner, and it is extremely useful with a track record of numerous successful introductions. The conventional steam tube dryer, however, is unable to remove the dust coal from the dried coal. There is a demand, therefore, to provide a separate classifier even when the coal is predried using the conventional steam tube dryer, in order to avoid the problems caused by the dust coal. [0004] To address this demand, the use of, as a coal dryer, a horizontal rotary dryer having a classification function, which has been proposed by the applicant, is contemplated (see Patent 3 Literature 2). This horizontal rotary dryer is configured to remove dust coal from dried coal by discharging the dust coal together with exhaust gas. This horizontal rotary dryer can be used for drying the coal to be fed to a coke oven and for drying the coal to be used as fuel for a boiler. A degree of pulverization performed by a pulverizer is being changed at present in a manner dependent on a burning velocity of the coal, which varies in accordance with a type thereof, such as the brown coal and lignite and the subbituminous coal. For example, a comparison between the brown coal and lignite and the bituminous coal indicates that the brown coal and lignite has less fixed carbon and more volatile matter, and thus has a higher burning velocity, whereas the bituminous coal has more fixed carbon and less volatile matter, and thus has a lower burning velocity. The bituminous coal, therefore, needs to be pulverized into a smaller size than the brown coal and lignite. The horizontal rotary dryer removes the dust coal in order to prevent scattering of dust, depositing of carbon, and the like, but it is not intended to address the challenge of removing the dust coal of different sizes corresponding to the type of coal. Thus, for example, when the horizontal rotary dryer has been designed for the brown coal and lignite but is used for the subbituminous coal, it would remove the dust coal of a size larger than the pulverized coal. The removed dust coal can, of course, be used as fuel, but since it includes the dust coal of the size larger than the pulverized coal, it has to be pulverized by the pulverizer again. Conversely, when the dryer has been designed 4 for the subbituminous coal but is used for the brown coal and lignite, part of the dust coal of a size smaller than that of the pulverized coal cannot be removed from the dried coal. Hence, the dust coal that does not require the pulverizing would be subjected to the pulverization by the pulverizer, leading to a reduction in pulverizing efficiency. Citation List Patent Literature [0005] Patent Literature 1: JP 2004-44876 A Patent Literature 2: JP 2010-169324 A Summary of Invention Technical Problem [0006] A main challenge to be addressed by the present invention is to provide a horizontal rotary dryer for coal with a capability to remove different dust coal corresponding to the type of coal or the like, a coal-fired boiler system provided with the horizontal rotary dryer, and a method for operating the coal-fired boiler system. Solution to Problem [0007] Of the dust coal (fine particles) present in an upward flow, dust coal of a large size descends (falls) due to gravity, while dust coal of a small size is entrained in an upward flow and ascends. The inventors conducted various tests based on this understanding to find that the dust coal ascends and is 5 discharged through a (fixed) exhaust gas nozzle at ratios illustrated in Fig. 10 as the velocity of the upward flow is varied. In this diagram, the slip ratio of dust coal of a threshold size that falls or ascends with an upward flow velocity at ut changes as the upward flow velocity (u) is varied. The slip ratio refers to a ratio of dust coal discharged through the fixed exhaust gas nozzle, and at a higher slip ratio, more dust coal is removed. How the slip ratio changed (the shape of the curve) varied in a manner dependent on conditions such as the design of a classification hood and an internal configuration. When these conditions were kept unchanged, similar results were produced. This has led to a finding on the capability to control the ratio and the particle size distribution of fine powder to be removed by changing a flow velocity (u), which has resulted in the invention described below as a solution to the problems described above. [0008] [Aspect of the present invention described in claim 1] A horizontal rotary dryer for coal, the dryer including: a rotating shell having an inlet for a coal and a blowing nozzle for a carrier gas at one end side, and having discharge openings for a dried coal and an exhaust gas at another end side; a heating unit for heating the coal inside the rotating shell; and a classification hood covering the discharge openings, and having a fixed outlet nozzle for the dried coal at a bottom portion thereof and a fixed exhaust gas nozzle for the exhaust 6 gas at a top portion thereof, wherein an upward flow generating unit for generating an upward flow inside the classification hood and a flow velocity control unit for controlling a flow velocity of the upward flow are provided, and part or all of a dust coal in the dried coal is discharged by the upward flow through the fixed exhaust gas nozzle. [0009] (Main operational advantage) The upward flow generating unit, which generates the upward flow, and the flow velocity control unit, which controls the flow velocity of the upward flow, are provided inside the classification hood. This offers a capability to control the ratio and the particle size distribution of the dust coal discharged through the fixed exhaust gas nozzle, allowing different dust coal corresponding to the type of coal or the like to be removed. [0010] [Aspect of the present invention described in claim 2] A coal-fired boiler system, including: a coal dryer; a pulverizer for a dried coal that has been dried by the dryer; and a boiler configured to use, as a fuel, a pulverized coal that has been pulverized by the pulverizer, wherein a horizontal rotary dryer is used as the dryer, the horizontal rotary dryer including: 7 a rotating shell having an inlet for a coal and a blowing nozzle for a carrier gas at one end side, and having discharge openings for a dried coal and an exhaust gas at another end side; a heating unit for heating the coal inside the rotating shell; a classification hood covering the discharge openings, and having a fixed outlet nozzle for the dried coal at a bottom portion thereof and a fixed exhaust gas nozzle for the exhaust gas at a top portion thereof; an upward flow generating unit for generating an upward flow inside the classification hood; and a flow velocity control unit for controlling a flow velocity of the upward flow, and the horizontal rotary dryer discharging part or all of a dust coal in the dried coal by the upward flow through the fixed exhaust gas nozzle, and wherein the dried coal that has been discharged through the fixed outlet nozzle of the horizontal rotary dryer is pulverized by the pulverizer and then used as the fuel for the boiler, while the dust coal that has been discharged through the fixed exhaust gas nozzle of the horizontal rotary dryer is collected and used as the fuel for the boiler. [0011] (Main operational advantage) The upward flow generating unit, which generates the upward flow, and the flow velocity control unit, which controls 8 the flow velocity of the upward flow, are provided inside the classification hood, thereby offering a similar operational advantage to that of the aspect of the present invention described in claim 1. This can prevent the occurrence of problems that may be caused by the dust coal in association with the handleability and the pulverizing efficiency when the dried coal discharged through the fixed outlet nozzle is pulverized by a pulverizer. Furthermore, this can allow an appropriate type of dust coal corresponding to the type of coal to be discharged through the fixed exhaust gas nozzle, and thus, the dust coal, as discharged, can be collected to be used as fuel for the boiler without separate pulverization. [0012] [Aspect of the present invention described in claim 3] The coal-fired boiler system according to claim 2, wherein a distribution gas raising unit for raising a distribution gas from the bottom portion of the classification hood is provided as the upward flow generating unit, and at least one of the exhaust gas that has been discharged through the fixed exhaust gas nozzle and subjected to dust collection to collect the dust coal and the exhaust gas of the boiler is used as at least one of the carrier gas and the distribution gas. [0013] (Main operational advantage) The exhaust gas, which has been discharged through the fixed exhaust gas nozzle and subjected to the dust collection 9 to collect the dust coal, and/or the exhaust gas of the boiler is used as the carrier gas and/or the distribution gas, which offers excellent heat efficiency. Furthermore, these exhaust gases each have a low oxygen concentration, which can prevent a coal dust explosion. [0014] [Aspect of the present invention described in claim 4] A method for operating a coal-fired boiler system, the system including: a coal dryer; a pulverizer for a dried coal that has been dried by the dryer; and a boiler configured to use, as a fuel, a pulverized coal that has been pulverized by the pulverizer, the method including the steps of: using a horizontal rotary dryer as the dryer, the horizontal rotary dryer including: a rotating shell having an inlet for a coal and a blowing nozzle for a carrier gas at one end side, and having discharge openings for the dried coal and an exhaust gas at another end side; a heating unit for heating the coal inside the rotating shell; and a classification hood covering the discharge openings, and having a fixed outlet nozzle for the dried coal at a bottom portion thereof and a fixed exhaust gas nozzle for the exhaust gas at a top portion thereof, controlling a dust coal to be discharged, by controlling a flow velocity of an upward flow, when part or all of the dust 10 coal in the dried coal is discharged through the fixed exhaust gas nozzle by generating the upward flow in the classification hood, and using, as the fuel for the boiler, the dried coal that has been discharged through the fixed outlet nozzle of the horizontal rotary dryer and has been pulverized by the pulverizer, while using, as the fuel for the boiler, the dust coal that has been discharged through the fixed exhaust gas nozzle of the horizontal rotary dryer and has been collected. [0015] (Main operational advantage) The upward flow is generated in the classification hood to discharge part or all of the dust coal contained in the dried coal through the fixed exhaust gas nozzle. The dust coal to be discharged is controlled by controlling the flow velocity of the upward flow, which offers a similar operation advantage to that of the aspect of the present invention described in claim 2. Advantageous Effects of Invention [0016] The present invention provides a horizontal rotary dryer for coal with a capability to remove different dust coal corresponding to the type of coal or the like, a coal-fired boiler system provided with the horizontal rotary dryer, and a method for operating the coal-fired boiler system. Brief Description of Drawings 11 [0017] Fig. 1 is a system flow diagram of a coal-fired boiler system according to the present embodiment. Fig. 2 is a front view of a horizontal rotary dryer according to the present embodiment. Fig. 3 is an enlarged view of the other end side of a rotating shell, with a classification hood omitted. Fig. 4 is a sectional view taken along line X-X of Fig. 2. Fig. 5 is an enlarged view of the classification hood. Fig. 6 is an enlarged view of a distribution gas raising unit. Fig. 7 is a diagram for describing the distribution gas raising unit. Fig. 8 is a diagram of a modification of the classification hood and the distribution gas raising unit. Fig. 9 is a diagram of a modification of the classification hood and the distribution gas raising unit. Fig. 10 is a graph of a relationship between flow velocity variation and slip ratio. Fig. 11 is a perspective view of a conventional steam tube dryer. Description of Embodiment [0018] Some embodiments according to the present invention will now be described. (Coal-fired boiler system) 12 Fig. 1 is a system flow diagram of a coal-fired boiler system according to the present embodiment. The coal-fired boiler system according to the present embodiment mainly includes a horizontal rotary dryer 100, a pulverizer 120 for dried coal C2 dried by the horizontal rotary dryer 100, and a boiler 130 to which pulverized coal C3 pulverized by the pulverizer 120 is fed as fuel. Here, the "pulverized coal" refers to dried coal that has been pulverized by a pulverizer, and the pulverized coal is not necessarily distinguished from "dust coal" to be described hereinafter because of a different particle size. [0019] The horizontal rotary dryer 100 mainly includes a rotating shell 10, a heating unit, and a classification hood 55. The rotating shell 10 has an inlet for coal Cl, including brown coal and lignite and subbituminous coal, and a blowing nozzle for a carrier gas G1 at one end side (the left side of the sheet plane), and discharge openings 50 (see Fig. 3) for the dried coal C2 and an exhaust gas G2 at the other end side (the right side of the sheet plane). The heating unit is for heating the coal Cl in the rotating shell 10. The classification hood 55 covers the discharge openings 50 for the dried coal C2 and the exhaust gas G2. The horizontal rotary dryer 100 will be described in detail hereinafter. [0020] The carrier gas G1 is blown (fed) into the rotating shell 10 by a blower 113, entrains steam and the like generated by 13 the heating of the coal Cl, and is exhausted from the rotating shell 10 as the exhaust gas. As the carrier gas G1, for example, any one or combination of an exhaust gas G3 of the boiler 130, an inert gas such as nitrogen, an exhaust gas G4 with dust coal C4 collected (removed), air, and the like can be used. Here, in order to prevent coal dust explosion in the horizontal rotary dryer 100, it is necessary to keep the oxygen concentration of the carrier gas G1 low (typically, 13% or lower, and preferably, 12% or lower). Thus, as the carrier gas G1, the exhaust gas G3 and/or the exhaust gas G4 is preferably used. The exhaust gases G3 and G4 each have a low oxygen concentration and a high temperature, and, hence, if used as the carrier gas G1, are not likely to hinder the heating of the coal Cl. Note that the oxygen concentration of the exhaust gas may be measured (monitored), and if the measurement exceeds a predetermined value, an inert gas may be added or increased to control the oxygen concentration. The illustrated example is an embodiment in which the exhaust gas G4 with the dust coal C4 collected is released from a chimney 160 into the atmosphere. [0021] The dried coal C2 dried in the rotating shell 10 is discharged from the rotating shell 10 into the classification hood 55. The dried coal C2 is, then, discharged through a fixed outlet nozzle 57 (see Fig. 2) provided at a bottom portion (a lower portion) of the classification hood 55 to the outside of the dryer to be transported by a transporting unit, such as a belt conveyor, to a feed hopper 121 of the pulverizer 120. Note 14 that, in the present embodiment, a distribution gas N raising unit 58 is provided as an upward flow generating unit for generating an upward flow in the classification hood 55. The distribution gas N raising unit 58 is configured to classify the dried coal C2 to obtain desired dust coal C4 to discharge the desired dust coal C4 through a fixed exhaust gas nozzle 56 (see Fig. 2) provided at a top portion (an upper portion) of the classification hood 55. Thus, the dried coal C2 transported to the feed hopper 121 does not include the dust coal C4, which offers excellent handleability. [0022] In the present embodiment, a distribution gas N is blown directly into the classification hood 55 and raised by the blower 113 used for blowing the carrier gas G1. A control valve 14 is provided in a flow path of the distribution gas N. By adjusting a degree of opening (opening) of the control valve 14, the flow velocity of the distribution gas N is controlled, and thereby the flow velocity of the upward flow in the classification hood 55 is controlled. As described above, in the present embodiment, the control valve 14 functions as a flow velocity control unit for controlling the flow velocity of the upward flow. Alternatively, a separate blower may be provided in addition to the blower 113 for the carrier gas G1, and this separate blower may work as the flow velocity control unit for the upward flow. In the case where the separate blower is provided in this manner, although an identical type of gas to or a different type of gas from that of the carrier gas G1 may 15 be used as the distribution gas N, the identical type of gas is preferably used from a viewpoint of stability of processing. [0023] The dust coal C4 that has been entrained in the upward flow and ascended to the top portion in the classification hood 55 is discharged, together with the exhaust gas G2, through the fixed exhaust gas nozzle 56 provided at the top portion of the classification hood 55 to be collected by a dust collector 140. The dust coal C4 collected by the dust collector 140 is transported to a dust coal hopper 150 for temporary storage. The dust coal C4 stored in the dust coal hopper 150 is fed to a burner 132 associated with the boiler 130 for combustion as appropriate. The dust coal C4 may be fed by, for example, air transportation. In the illustrated example, a flow of air Al (air flow) is generated by a blower 114 and this air flow transports the dust coal C4. [0024] Meanwhile, the dried coal C2 that has been transported to the feed hopper 121 for temporary storage is crushed by the pulverizer 120 into fine particles. The pulverized coal C3, thus pulverized, is fed to a burner 131 associated with the boiler 130 for combustion. In the present embodiment, the dust coal C4 has been removed from the dried coal C2, and, therefore, the pulverization by the pulverizer 120 is highly efficient. In addition, in the case where a roller mill is used as the pulverizer 120, vibration is less likely to be caused, so that the instability of the operation is less likely to be caused. 16 The degree of pulverization of the dried coal C2 by the pulverizer 120 may be decided as appropriate on the basis of the type of coals, a burning velocity at the burner 131, and the like. For example, if the coal Cl is the brown coal and lignite, the burning velocity at the burner 131 is relatively high, and, thus, the degree of pulverization may be coarse. Conversely, if the coal Cl is the subbituminous coal, the burning velocity at the burner 131 is relatively low, and, thus, the degree of the pulverization should be fine. [0025] (Horizontal rotary dryer) The horizontal rotary dryer 100 will now be described in detail. Fig. 2 is a diagram of the horizontal rotary dryer (100) according to the present embodiment. The horizontal rotary dryer according to the present embodiment includes the cylindrical rotating shell 10. The rotating shell 10 has a length in the shaft center direction of, for example, 10 to 30 m. The rotating shell 10 is installed such that its shaft center is tilted relative to a horizontal plane to some extent, and thus, the one end side (the left side of the sheet plane) of the rotating shell 10 is located higher than the other end side (the right side of the sheet plane) thereof. Two support units 20 and a motor unit 30 are installed under the rotating shell 10 so as to support the rotating shell 10. The motor unit 30 enables the rotating shell 10 to rotate about the shaft center of the rotating shell 10. As illustrated in Fig. 4, the rotating 17 shell 10 is rotated in one direction. In the illustrated example, the rotating shell 10 is rotated in a counterclockwise direction (in an arrow R direction) . The speed of the rotation is not particularly limited, but the circumferential speed is typically below 1 m/s. [0026] A large number of steam tubes (heating tubes) 11 is attached inside the rotating shell 10 such that the steam tubes extend along the shaft center direction of the rotating shell 10. The steam tubes 11 are made with, for example, a metallic pipe, and allow a heating medium, such as steam, to flow through the insides thereof. A plurality of the steam tubes 11 may be each arranged, for example, in a circumferential direction and in a radial direction, concentrically with respect to the shaft center of the rotating shell 10. [0027] As illustrated in Fig. 3, a plurality of discharge openings 50 is formed through a peripheral wall of the rotating shell 10 at its other end. The dried coal C2 and the exhaust gas are discharged or exhausted through the plurality of discharge openings 50 from the rotating shell 10. The discharge openings 50 are located at an appropriate interval in the circumferential direction of the rotating shell 10 in rows along the circumferential direction. In the illustrated example, there are two rows, but alternatively, there may be one row, or three or more of rows. In addition, in the illustrated example, the discharge openings 50 each have a shape of an 18 identical rectangle, but alternatively, they may have different shapes from each other, or they may have a circle or another shape other than a rectangle. [0028] As illustrated in Fig. 4, a plurality of lifters 61 is provided inside the rotating shell 10 so as to extend from an inner wall of the rotating shell 10 toward the shaft center of the rotating shell 10. The plurality of lifters 61 is positioned in a plurality of rows, which is three rows in the illustrated example, spaced apart in the shaft center direction of the rotating shell 10 as illustrated in Fig. 2. As illustrated in Fig. 4, each lifter row 60 includes the plurality of lifters 61, which is four lifters in the illustrated example, spaced at a regular interval from each other. Each lifter 61 is formed with a thick metal, with an edge thereof in a shape of a hook bent toward a leading side in a rotational direction R of the rotating shell 10. The lifters 61 may extend to a length of, for example, 1/10 to 3/10 of an inner diameter D of the rotating shell 10. In addition, each lifter 61 is positioned such that the lifter 61 passes a leading-side end of one of the discharge openings 50 with respect to the rotational direction R of the rotating shell 10, the one discharge opening 50 being located at a trailing side, and that the lifter 61 extends from the proximity of a straight line in parallel with the shaft direction of the rotating shell 10. Hence, the discharge openings 50 do not exist in close proximity to the lifter 61 at the leading side, but the inner wall of the rotating shell 19 10 is present there. As illustrated in Fig. 2, the lifter rows 60 are positioned inside the rotating shell 10 between the discharge openings 50 and an inlet 41 to be described hereinafter. The lifter rows 60 do not exist in the rotating shell 10 at the other end side from the discharge openings 50. In addition, the lifter rows 60 are positioned toward the discharge openings 50 between the discharge openings 50 and the inlet 41. [0029] As illustrated in Fig. 2, an agitating unit 65 is installed toward the one end side of the rotating shell 10 from the lifter rows 60 inside the rotating shell 10. The agitating unit 65 is for agitating the coal Cl, which has been fed (charged) into the rotating shell 10. The agitating unit 65 is also spaced apart from one of the lifter rows 60, the one lifter row 60 being positioned closest to the one end side inside the rotating shell 10. As the agitating unit 65, for example, a publicly known stud type, a reversing blade, or the like may be used. In particular, the reversing blade is preferably used because of reasons including the effect of dust coal separation (dispersion) and the capability of increasing a filling factor of dried coal with bulk density and volume reduced due to the drying. [0030] As illustrated in Figs. 2 and 5, the rotating shell 10 is provided with the classification hood 55 such that the other end side of the rotating shell 10, where the plurality of 20 discharge openings 50 is located, is covered by the classification hood 55. The classification hood 55 is capable of discharging the dried coal C2 and the exhaust gas G2. The classification hood 55 is formed with a thick metal. As illustrated in Fig. 5, the classification hood 55 has the fixed outlet nozzle 57 in a bottom surface of a bottom portion (lower portion) 55d and the fixed exhaust gas nozzle 56 in a top surface of a top portion (upper portion) 55u. The fixed outlet nozzle 57 is for the dried coal C2 that has been dried and classified (with the dust coal C4 removed) , and the fixed exhaust gas nozzle 56 is for the exhaust gas G2. In addition, as illustrated in Fig. 4, the top portion 55u of the classification hood 55 is tapered down toward the fixed exhaust gas nozzle 56 in a width direction orthogonal to the shaft direction of the rotating shell 10. Similarly, the bottom portion 55d is tapered down in the width direction toward the fixed outlet nozzle 57. The fixed exhaust gas nozzle 56 and the fixed outlet nozzle 57 are located substantially in the middle of the classification hood 55 in a plan view. The inside of the classification hood 55 above the rotating shell 10 (a range marked with reference character L) is a settling region 90, which is a space filled with the exhaust gas and the distribution gas N from the rotating shell 10. In other words, the classification hood 55 is provided such that the settling region 90 is formed above the rotating shell 10. In addition, the classification hood 55 is fixed to a ground surface by means not shown so that the classification hood 55 is prevented from making a rotation 21 caused by the rotation of the rotating shell 10. [0031] The fixed exhaust gas nozzle 56 is open in upper and lower directions and connected to the dedusting unit 140 described above. The exhaust gas G2, including the carrier gas G1, the steam generated from the drying of the coal Cl, the distribution gas N, and the dust coal C4, is discharged through the fixed exhaust gas nozzle 56. The fixed outlet nozzle 57 is also open in the upper and lower directions and is connected to the feed hopper 121 of the pulverizer 120. The dried coal C2 with the dust coal C4 classified and removed is discharged through the fixed outlet nozzle 57. [0032] The horizontal rotary dryer 100 according to the present embodiment generates the upward flow inside the classification hood 55 and controls the flow velocity of the upward flow in order to control the particle size distribution and the amount of the dust coal C4 discharged through the fixed exhaust gas nozzle 56. By adjusting a spacing distance L between the top of the rotating shell 10 and the fixed exhaust gas nozzle 56, however, the particle size distribution and the amount described above can be controlled more suitably. More specifically, when the spacing distance L is short, an overall slip ratio increases, but the ratio of the increase is larger for the dust coal C4 with a relatively large diameter. Hence, when the spacing distance L is short, the dust coal C4 discharged through the fixed exhaust gas nozzle 56 has a particle size 22 distribution with larger values for large diameters. Conversely, when the spacing distance L is long, the overall slip ratio decreases, but the ratio of the decrease is larger for the dust coal C4 with a relatively small diameter. Hence, when the spacing distance L is long, the dust coal C4 discharged through the fixed exhaust gas nozzle 56 has a particle size distribution with smaller values for small diameters. In view of these circumstances, the spacing distance L relative to the inner diameter D of the rotating shell 10 can be L > 0.3D, and preferably, 0.8D < L < 4.OD, and more preferably, 1.OD < L < 2.5D. In addition, from a viewpoint of adjusting the particle size distribution of the dust coal C4 discharged through the fixed exhaust gas nozzle 56, as illustrated in an enlarged view in Fig. 4, one or more baffle plates 91 are preferably attached to an inner wall surface 55a of the classification hood 55, and preferably to the inner wall surface 55a of the classification hood 55 forming the settling region 90. The dust coal with a large diameter that has collided with the baffle plate 91 falls and is discharged smoothly through the fixed outlet nozzle 57. Conversely, the dust coal with a small diameter that has collided with the baffle plate 91 falls temporarily, but part of the dust coal ascends again by the upward flow. Thus, the dust coal C4 discharged through the fixed exhaust gas nozzle 56 has a particle size distribution with small values for large diameters. [0033] As illustrated in Fig. 5, the classification hood 55 is 23 expanded at the settling region 90 in the shaft direction of the rotating shell 10. The expansion of the classification hood 55 at the settling region 90 in the shaft direction reduces the ratio of collision between the mutual dust coal particles and between the dust coal and the classification hood 55 (especially at wall materials 55A and 55B at both ends of the classification hood 55 in the axial direction) , which allows more accurate control of the particle size distribution of the dust coal C4. Here, the expansion in the shaft direction refers to an expansion relative to a connection portion with the rotating shell 10. [0034] The settling region 90 does not have to be expanded in the shaft direction throughout its length in the upper and lower directions. The dust coal and the like in the proximity of the rotating shell 10 have just been discharged through the discharge openings 50 from the rotating shell 10 and hence they have not spread in a plane. Thus, the settling region 90 in the proximity of the rotating shell 10 can be left unexpanded in the shaft direction as in the illustrated example. In addition, the top portion 55u of the classification hood 55 is preferably tapered down toward the fixed exhaust gas nozzle 56 in the shaft direction of the rotating shell 10 as in the illustrated example. The degree of the expansion of the classification hood 55, with a length of the connection portion with the rotating shell 10 in the shaft direction being Z1 and a length of the expanded portion in the shaft direction being 24 Z2, is preferably 1.5Z1 < Z2 < 6Z1, and more preferably, 2Z1 < Z2 <4Z1. Note that the settling region 90 may be expanded in the width direction as illustrated in Figs. 8 and 9, or it may be expanded both in the width direction and in the shaft direction although not shown. A manner in which the settling region 90 is expanded may be decided as appropriate in consideration of surrounding equipment and the like. Note that the expansion in the shaft direction offers an advantage of a reduced installation space for the entire horizontal rotary dryer. [0035] In the settling region 90, as illustrated in Figs. 4 and 5, a plurality of supports (62 and 63) is provided between the wall material 55A at the one side in the axial direction and the wall material 55B at the other side in the axial direction of the classification hood 55. The expansion of the classification hood 55 in the shaft direction may lead to a reduction in strength. By providing the plurality of supports (62 and 63) between the wall material 55A at the one side in the axial direction and the wall material 55B at the other side in the axial direction, the strength of the classification hood 55 is maintained. Here, the supports (62 and 63) may be also provided between the wall material 55A at the one side and the wall material 55B at the other side in an unexpanded portion of the classification hood 55 in the axial direction as in the illustrated example. [0036] 25 The supports for maintaining the strength of the classification hood 55 may be constituted only by a bar component, a pipe material, or the like in a straight shape, but in the present embodiment, the supports are each constituted by a pipe material 62 and an umbrella component 63 positioned on the pipe material 62. The umbrella component 63 has an umbrella shape with a middle in a width direction protruded upward, and is positioned so as to extend along an extending direction of the pipe material 62. The presence of the umbrella component 63 prevents the dried coal C2 from depositing on the pipe material 62. The umbrella component 63 may, but it does not have to, have a function of maintaining the strength of the classification hood 55. [0037] As described above, the top portion 55u of the classification hood 55 is tapered down in the width direction toward the fixed exhaust gas nozzle 56. In this case, the supports (62 and 63) are preferably not located under the fixed exhaust gas nozzle 56 as illustrated in Fig. 4. The tapering of the upper portion 55u of the classification hood 55 in the width direction toward the fixed exhaust gas nozzle 56 generates a flow (an upward flow) Si along the tapered wall material as illustrated in Fig. 4. The dust coal C4 is entrained in this flow S1. Hence, the ascending dust coal C4 does not collide with the top surface of the classification hood 55 to descend, which allows more accurate control of the particle size distribution of the dust coal C4. In addition to the generation 26 of the flow Si along the wall material, a flow S2 is mainly generated in the classification hood 55 to ascend vertically in the middle of the classification hood 55, and the dust coal C4 is also entrained in the flow S2. Thus, when the plurality of supports (62 and 63) is not located under the fixed exhaust gas nozzle 56, the dust coal C4, entrained in the flow S2 ascending in the middle vertically, does not collide with the supports (62 and 63) to descend, which allows more accurate control of the particle size distribution of the dust coal C4. [0038] As illustrated in Fig. 4, the distribution gas N raising unit 58 is provided as the upward flow generating unit inside the classification hood 55 in the flow path of the dried coal C2, by free fall and the like, reaching the fixed outlet nozzle 57 from the discharge openings 50 of the rotating shell 10. By raising the distribution gas N, an upward flow is generated. In particular, when this raising is performed in the flow path of the dried coal C2, the dust coal that has descended from the discharge openings 50 together with the dried coal C2 is raised for certainty, which allows more accurate control of the particle size distribution of the dust coal C4. Moreover, when the raising of the distribution gas N is performed in the flow path of the dried coal C2 reaching the fixed outlet nozzle 57, the dried coal C2 is discharged through the fixed outlet nozzle 57 at the bottom surface of the classification hood 55 to the outside smoothly, which eliminates consideration for guiding the dried coal C2 to the fixed outlet nozzle 57. 27 [0039] The distribution gas N raising unit 58 is not particularly limited by a specific embodiment. For example, the raising unit 58 may be formed with a distribution plate, constituted by a net material and the like, and a unit for raising the distribution gas N through mesh of the net material. In the present embodiment, the distribution gas N raising unit 58 is provided with a pipe material 58A. As illustrated in Figs. 6 and 7, the pipe material 58A extends across the flow path of the dried coal C2 reaching the fixed outlet nozzle 57 and has holes 58Ac in a peripheral wall thereof. The raising unit 58 is configured to raise the distribution gas N from the holes 58Ac formed in the pipe material 58A. When the distribution gas N raising unit 58 is constituted by the pipe material 58A that extends across the flow path of the dried coal C2 reaching the fixed outlet nozzle 57, as described above, the consideration for guiding the dried coal C2 to the fixed outlet nozzle 57 is eliminated. In addition, by raising the distribution gas N from the holes 58Ac formed in the peripheral wall of the pipe material 58A, a raising effect is exerted with certainty on the dust coal in the dried coal C2. [0040] In the present embodiment, each hole 58Ac formed in the peripheral wall of the pipe material 58A has a circular shape. In addition, in the present embodiment, a plurality of holes 58Ac is formed at an appropriate interval in the extending direction of the pipe material 58A. In addition, each hole 58Ac 28 is formed such that the distribution gas N is raised obliquely upward as illustrated in Fig. 7(a). [0041] A plurality of pipe materials 58A is preferably arranged in the proximity of the fixed outlet nozzle 57 in parallel with the shaft direction of the rotating shell 10 as in the illustrated example. In this embodiment, the distribution gas N impinges on the dried coal C2 that is in the process of descending between the pipe materials 58A adjacent to each other, so that the dust coal is raised by the distribution gas N. Meanwhile, the dried coal C2 keeps descending between the pipe materials 58A to be discharged through the fixed outlet nozzle 57. Note that the dust coal raised by the distribution gas N rises inside the classification hood 55. Part of the dust coal C4 is discharged through the fixed exhaust gas nozzle 56 in relation to the velocity of the rising (the velocity of the upward flow). [0042] In the present embodiment, by controlling the flow velocity of the distribution gas N raised from each hole 58Ac, the flow velocity of the upward flow is controlled. Here, the flow velocity of the distribution gas N is controlled to control the flow velocity of the upward flow in the classification hood 55, but the flow velocity of the upward flow varies typically in correspondence with a portion such as the bottom portion and the top portion. Accordingly, it is recommended that, to determine the flow velocity of the upward flow, a flow velocity 29 at the settling region 90, in particular, at a middle portion (which is a portion in the middle when the spacing distance L is divided into three portions) of the settling region 90 in the upper and lower directions is used as a reference. The dust coal is classified at the settling region 90, and thus, the flow velocity of the upward flow at the settling region 90 is preferably used as the reference. In addition, when a lower end of the settling region 90 in the upper and lower directions is used as the reference, the slip ratio tends to be lower than intended. When an upper end of the settling region 90 in the upper and lower directions is used as the reference, the slip ratio tends to be higher than intended. Thus, the middle portion of the settling region 90 in the upper and lower directions is preferably used as the reference to determine the flow velocity. [0043] Alternatively, a group of pipe materials, constituted by a plurality of pipe materials 58A, may be provided in a plurality of tiers that are spaced apart in the upper and lower directions. In addition, as described in the present embodiment, an umbrella component 58B may be positioned above each pipe material 58A. The umbrella component 58B has an umbrella shape with a middle in a width direction protruded upward and extends along the extending direction of the pipe material 58A. The presence of the umbrella component 58B prevents the dried coal C2 from depositing on the pipe material 58A with more certainty. [0044] 30 As illustrated in Figs. 1 and 2, a feed pipe 70, which feeds steam J1 into the steam tubes (heating tubes) 11, and a drain pipe 71 are placed at the other end side of the rotating shell 10. Drain water D discharged through the drain pipe 71 can be conveyed to a heat exchanger 115 to be used for heating the air Al, which is used to transport the dust coal C4. In addition, as the steam to be fed to the steam tubes 11, steam J2 generated by the boiler 130, extracted steam of a steam turbine that uses the steam J2, and the like can be used. [0045] At the one end side of the rotating shell 10, a screw feeder 42, which includes a screw therein and has a cylindrical shape, is inserted to be installed in the rotating shell 10. The screw feeder 42 is provided, at its one end, with a driving unit 43, such as a motor, to turn the screw placed in the screw feeder 42. In addition, the screw feeder 42 has, at its upper portion, the inlet 41 for the coal Cl. The inlet 41 and the inside of the screw feeder 42 are in communication with each other. [0046] The coal Cl, which is to be dried, is fed from the inlet 41 into the screw feeder 42. The screw installed inside the screw feeder 42 is turned by the driving unit 43 to feed the coal Cl into the rotating shell 10. The carrier gas G1 is also blown in from the inlet 41 or another inlet now shown. The carrier gas G1, which has been blown in, flows through the inside of the rotating shell 10 toward the other end side of the rotating shell 10. 31 [0047] An operation of the horizontal rotary dryer (100) will now be described. To dry the coal Cl with the horizontal rotary dryer according to the present embodiment, the coal Cl is fed into the inlet 41 as illustrated in Fig. 2. The coal Cl fed from the inlet 41 is fed by the screw feeder 42 into the rotating shell 10 and, while heated to be dried by contacting the steam tubes 11 heated by the steam J1, the coal Cl is moved to the other end side of the rotating shell 10. [0048] Upon reaching a location where the agitating unit 65 is present, the coal Cl (the dried coal C2) is agitated by the agitating unit 65. Subsequently, as illustrated in Fig. 4, the coal Cl (the dried coal C2) is lifted by each lifter 61 turning due to the rotation of the rotating shell 10. When the lifter 61 is located at an upper side of the rotating shell 10, the lifted coal Cl (the dried coal C2) falls naturally. During the fall, the dust coal included in the coal Cl (the dried coal C2) is dispersed (a so-called flight action) inside the rotating shell 10. [0049] The carrier gas G1, which has been blown in from the inlet 41 or another inlet, not shown, placed at the one end side of the rotating shell 10, passes through the rotating shell 10. The carrier gas G1 is then exhausted, together with the steam and the like, as the exhaust gas through the discharge openings 32 50, which also serve as the discharge openings for the dried coal C2, to the outside of the rotating shell 10. During the exhausting, the exhaust gas entrains the dust coal, which has been dispersed by the lifters 61 in the rotating shell 10, and is exhausted through the discharge openings 50. The exhaust gas, which has been exhausted through the discharge openings 50, entrains part of the dust coal and is exhausted through the fixed exhaust gas nozzle 56 from the classification hood 55. In addition, the distribution gas N is raised to be fed toward the upper part of the classification hood 55 by the distribution gas N raising unit 58 so that the upward flow is formed. The flow rate of the distribution gas N is typically made smaller than the flow rate of the exhaust gas exhausted through the discharge openings 50. Here, the exhaust gas is exhausted through the discharge openings 50 at a flow velocity of, for example, 5 to 10 m/s. The flow velocity is adjusted as appropriate according to the area of the discharge openings 50 and the blowing amount of the carrier gas G1. [0050] The dried coal C2 falls within the rotating shell 10 and, without being entrained by the exhaust gas, falls naturally through the discharge openings 50 located at a lower side. Furthermore, the dried coal C2, which has been naturally fallen, is not raised by the distribution gas N and passes between the pipe materials 58A to be discharged through the fixed outlet nozzle 57. Of the dust coal included in the dried coal C2, the dust coal that has a relatively large diameter is entrained by 33 the exhaust gas or accompanied by the dried coal C2 to be discharged through the discharge openings 50. However, the large-diameter dust coal is not transported by the upward flow to the fixed exhaust gas nozzle 56 because of a heavy weight thereof, but falls downward to be discharged together with the dried coal C2 through the fixed outlet nozzle 57. Conversely, of the dust coal included in the dried coal C2, the dust coal that has a relatively small diameter is entrained by the exhaust gas or accompanied by the dried coal C2 to be discharged through the discharge openings 50. The small-diameter dust coal is then transported by the upward flow to the fixed exhaust gas nozzle 56 to be discharged together with the exhaust gas G2 through the fixed exhaust gas nozzle 56. [0051] An operational advantage of the horizontal rotary dryer (100) will now be described. As described for the horizontal rotary dryer according to the present embodiment, the lifters 61 are placed inside the rotating shell 10. These lifters 61 allow the dust coal, contained in the coal Cl (the dried coal C2), to disperse in a space inside the rotating shell 10. This allows the dust coal to be entrained in the exhaust gas, which reduces a likelihood that the dust coal is discharged together with the dried coal C2 through the discharge openings 50 and then discharged through the fixed outlet nozzle 57. Hence, the particle size distribution of the dust coal C4 can be controlled more accurately. 34 [0052] In addition, each lifter 61 is positioned such that the lifter 61 passes a leading-side end of one of the discharge openings 50 with respect to the rotational direction R of the rotating shell 10, the one discharge opening 50 being located at a trailing side, and that the lifter 61 extends from the proximity of a straight line in parallel with the shaft center direction of the rotating shell 10. This causes the dried coal C2 on the lifter 61 to be located at a trailing side of the discharge openings 50. Hence, the dried coal C2 on the lifter 61 is prevented from entering through the discharge openings 50 directly, which reduces a likelihood that the dried coal C2 with the dust coal mixed in is discharged through the discharge openings 50. [0053] The lifter rows 60 are located intermittently in the shaft center direction of the rotating shell 10. This allows the coal Cl (the dried coal C2), while moving inside the rotating shell 10, to pass a portion with the lifters 61 present and a portion with the lifters 61 not present alternately. Hence, the coal Cl (the dried coal C2) is lifted more than once, thereby improving lifting efficiency. [0054] In addition, the lifters 61 are located intermittently so as to be spaced from each other at a regular interval in the circumferential direction of the rotating shell 10. This allows the coal Cl (the dried coal C2) to be lifted efficiently. 35 Specifically, the lifters 61 that extend from the inner wall of the rotating shell 10 toward the shaft center to lift the coal Cl (the dried coal C2) as the rotating shell 10 is rotated are placed at an interval in the circumferential direction. This allows the exhaust gas to pass through the coal Cl (the dried coal C2) while the coal Cl is falling from the lifters 61, which can cause the exhaust gas to entrain a large amount of the dust coal, reducing a likelihood that the dust coal as mixed in the dried coal C2 is discharged. Furthermore, the lifters 61 increase the contact efficiency between the coal Cl and the steam tubes 11, which brings about a secondary advantage of the improvement of drying efficiency. [0055] In the present embodiment, a positional relationship is such that each lifter 61 included in at least one of the lifter rows 60, which is located at the other end side (a downstream side), has a base end thereof at a location in the vicinity of the leading-side edge of one of the discharge openings 50 with respect to the rotational direction R of the rotating shell 10, and each lifter 61 extends from the inner wall of the rotating shell 10 toward the shaft center. Hence, a large amount of the coal Cl (the dried coal C2) can be held for the lifting between each lifter 61 and a subsequent one of the discharge openings 50 at the leading side in the rotational direction of the rotating shell 10. As a result, in comparison with a kiln action, the coal Cl (the dried coal C2) is agitated more finely, reducing a likelihood that the dust coal as mixed in the dried coal C2 36 is discharged. [0056] Furthermore, in the present embodiment, each lifter 61 extends from the base end toward the shaft center of the rotating shell 10, and is formed such that the extending edge thereof is bent toward the leading side with respect to the rotational direction R of the rotating shell 10. Hence, a larger amount of the coal Cl (the dried coal C2) can be held for the lifting between each lifter 61 and a subsequent one of the discharge openings 50 at the leading side in the rotational direction of the rotating shell 10. As a result, the coal Cl (the dried coal C2) is agitated with more certainty, reducing a likelihood that the dust coal as mixed in the dried coal C2 is discharged. [0057] The agitating unit 65, which is for agitating the coal Cl (the dried coal C2) fed into the rotating shell 10, is installed toward the one end side of the rotating shell 10 from the lifter rows 60. This allows the coal Cl (the dried coal C2) to be agitated before the coal Cl (the dried coal C2) is lifted by the lifters 61, thereby sorting out the dust coal contained in the coal Cl (the dried coal C2). As a result, the dispersion efficiency of the dust coal by the lifters 61 is improved. Here, the agitating unit 65 and the lifters 61 may be excluded, but providing the agitating unit 65 and the lifters 61 reduces a likelihood that the dust coal as mixed in the dried coal C2 is discharged, offering a more preferred dryer. [0058] 37 The discharge openings 50, which are placed on the peripheral wall of the rotating shell 10 and move in the circumferential direction due to the rotation of the rotating shell 10, the fixed outlet nozzle 57, which is placed at the bottom portion of the classification hood 55 installed so as to cover the discharge openings 50 and is fixed in place to be immobilized, and the fixed exhaust gas nozzle 56, which is placed at the top portion of the classification hood 55 are offered in combination. This allows classification to be performed by the upward flow in the settling region 90 between the discharge openings 50 and the fixed exhaust gas nozzle 56. In other words, the desired dust coal C4 is entrained by the exhaust gas G2 to be discharged through the fixed exhaust gas nozzle 56, and the rest is allowed to fall toward the fixed outlet nozzle 57 to be discharged, so that the classification can be achieved. [0059] The inside of the classification hood 55 above the rotating shell 10 is the settling region 90, which is a space filled with the exhaust gas and the like. This allows the dust coal with a relatively large diameter entrained in the exhaust gas to fall by inertia in the settling region 90 to be discharged through the fixed outlet nozzle 57. [0060] The distribution gas N raising unit 58 is placed in the flow path of the dried coal C2 reaching the fixed outlet nozzle 57. This allows the dust coal falling together with the dried 38 coal C2 toward the fixed outlet nozzle 57 to ascend toward the fixed exhaust gas nozzle 56. As a result, the removing efficiency of the dust coal is improved. [0061] In the present embodiment, the number of the lifters 61 in each lifter row 60 may be other than four and is not particularly limited. In order to maintain a lifting capacity, however, the number of the lifters 61 is preferably four to six. In addition, although the number of the discharge openings 50 in one row is not particularly limited, the number is preferably 10 to 17 in consideration of a reduction in pressure loss, the dispersion of the dust coal, and a mechanical strength of the rotating shell 10. [0062] [Modification 1] A modification of the horizontal rotary dryer (100) will now be described with an emphasis on differences from the embodiment described above. Fig. 8 is a diagram of a classification hood 55 according to the present embodiment. The classification hood 55 according to the present embodiment is also installed at one end side of a rotating shell 10 so as to cover discharge openings 50. This classification hood 55 is also fixed to a ground surface by means not shown so that the classification hood 55 does not make a turn caused by the turning of the rotating shell 10. Note that the classification hood 55 according to the present embodiment has a top portion 55u wider than a middle 39 portion 55c to some extent. The inside of the top portion 55u is a settling region 90, which is a space filled with the exhaust gas and the like. In addition, a bottom portion 55d is tapered down below the rotating shell 10 in the width direction toward a fixed outlet nozzle 57. [0063] A distribution gas N raising unit 58 is provided as the upward flow generating unit at the bottom portion 55d of the classification hood 55 according to the present embodiment. This distribution gas N raising unit 58 is formed with a distribution plate 58a which includes an upper portion constituted by a fine-mesh net. This distribution plate 58a is positioned on a floor surface of the bottom portion 55d and tilted down toward the fixed outlet nozzle 57 to form a chute. This raising unit 58 is also fed with, for example, a distribution gas N similarly to the foregoing embodiment. The fed distribution gas N passes through the distribution plate 58a to be raised inside the classification hood 55. In the present embodiment, the distribution plate 58a is tilted, which thereby allows the dried coal C2 to fall promptly toward the fixed outlet nozzle 57 in comparison with a horizontal distribution plate 58a. Note that, in the embodiment described above, the fixed outlet nozzle 57 is formed in a substantially entire region of the bottom surface of the bottom portion 55d is, whereas, in the present embodiment, the fixed outlet nozzle 57 is formed only in a middle portion of a bottom surface of the bottom portion 55d in order to position the distribution 40 plate 58a. Hence, the dried coal C2 may deposit on the bottom surface, which makes the foregoing embodiment more preferred in this viewpoint. In addition, in the present embodiment, the distribution gas N raising unit 58, which is the upward flow generating unit, is not placed in the flow path of the dried coal C2 reaching the fixed outlet nozzle 57 from the discharge openings 50 of the rotating shell 10. Hence, the distribution gas N may not directly act on the dried coal C2, which also makes the foregoing embodiment more preferred in this viewpoint. [0064] [Modification 2] Fig. 9 is a diagram of a classification hood 55 according to another embodiment. In the classification hood 55 according to the present embodiment, the location of a distribution gas N raising unit 58, which is the upward flow generating unit, and the location of a fixed outlet nozzle 57 are different from those in the embodiments described above. The fixed outlet nozzle 57 is not opened downward, but opened sideward. The distribution gas N raising unit 58 is positioned alongside of the fixed outlet nozzle 57 to allow a distribution plate 58a, constituting the raising unit 58, to be placed horizontally. This embodiment is effective in the case where there is no space below the classification hood 55. [0065] (Others) In the exemplary embodiments described above, the classification hood 55 is provided with one upward flow 41 generating unit (58) . Alternatively, the number of upward flow generating units (58) provided may be two, three, four, or more. In the case where a plurality of upward flow generating units (58) is provided, the upward flow generating units (58) are preferably positioned separately, for example, at a top portion 55u, a middle portion 55c, and a bottom portion 55d of a classification hood 55. In addition, the approach to the generation of the upward flow is not limited by the raising of the distribution gas N. A suction process (a negative pressure) may be used from above, if possible. [0066] In addition, the application of the coal-fired boiler system according to the present embodiments is not particularly limited. The coal-fired boiler system may be used in, for example, a plant using heat, such as a thermal power plant, a sugar mill, and a pulp mill. The coal-fired boiler system may be applied as appropriate to facilities that can use the steam J2 generated by heating water W at the boiler 130. Industrial Applicability [0067] The present invention is applicable as a horizontal rotary dryer for coal with a capability for use at a thermal power plant or the like, and as a coal-fired boiler system provided with the horizontal rotary dryer. Reference Signs List [0068] 10 Rotating shell 42 11 Steam tube (heating tube) 41 Inlet 50 Discharge opening 55 Classification hood 56 Fixed exhaust gas nozzle 57 Fixed outlet nozzle 58 Raising unit 61 Lifter 65 Agitating unit 100 Horizontal rotary dryer 120 Pulverizer 130 Boiler Cl Coal C2 Dried coal C3 Pulverized coal C4 Dust coal G1 Carrier gas N Distribution gas 43