Patent Publication Number: US-10758917-B2

Title: Coal pulverizing apparatus, control device and control method for same, and coal-fired power plant

Description:
TECHNICAL FIELD 
     The present disclosure relates to a coal pulverizing apparatus for pulverizing coal, a control device and a control method for controlling the same, and a coal-fired power plant. 
     BACKGROUND ART 
     For instance, a coal-fired power plant generates electric power by burning coal particles pulverized by a coal pulverizing apparatus with a furnace to produce a combustion gas, generating steam through heat exchange with the combustion gas, and driving a turbine by the steam. 
     The load of the coal-fired power plant is not always constant. The coal-fired power plant can be operated with the change in load. For instance, in a case where the coal-fired power plant is connected to a utility grid, it is desired to rapidly change the load of the coal-fired power plant in response to a demand of the utility grid, for stabilizing the utility grid frequency or other purposes. 
     In the coal-fired power plant, however, even if the amount of coal (raw material coal) supplied to the coal pulverizing apparatus is changed, there is a time lag (coal output delay) until the coal output, i.e., the amount of coal discharged from the coal pulverizing apparatus is changed. It is therefore difficult to rapidly change the load of the coal-fired power plant. 
     In this regard, Patent Document 1 discloses that the rotational speed of a table is determined based on a coal supply amount command value and a parameter related to the change in the load of a generator in order to overcome the coal output delay. 
     Patent Document 2 discloses a method for controlling a vertical mill, including changing the coal supply amount in accordance with an increase/decrease in load of the vertical mill and changing the rotational speed of a table to cover the lack or excess of the coal discharge amount due to the time delay between coal supply and coal discharge. 
     Patent Document 3 discloses that the coal supply amount and the rotational speed of a classifier are controlled in response to a load correction signal obtained based on dynamic characteristic of the coal discharge amount when the output command is changed followed by the change of parameters such as the moisture or the hardness of coal, a primary air flow rate, and the rotational speed of the classifier. 
     Patent Document 4 discloses a method for controlling a coal pulverizing apparatus, including subtracting an output demand signal from a signal obtained by inputting the output demand signal into a first-order lag operator to generate a correction signal, processing the correction signal by a limiter and an integrator, and adding a signal generated from a constant generator to generate a rotational speed command for a rotary separator (rotary classifier) in accordance with a load state. The constant generator is configured to set the rotational speed of the rotary separator (rotary classifier) to a fixed value. 
     Patent Document 5 discloses a method for controlling a coal pulverizing apparatus including a main operation circuit which calculates a command signal associated with the coal supply amount on the basis of detection data from a boiler or a generator, an additional control unit which calculates the deviation between a standard coal output pattern preset in the coal pulverizing apparatus and a current coal output pattern, in which a calculation result by the additional control unit is added to the main operation circuit as a correction signal. 
     Patent Document 6 discloses a pulverized coal supply system in which at least one manipulated value of a mill, a primary air conveying part, or a coal supply part is determined based on a coal output (coal discharge amount) determined based on driving conditions of the mill and output power necessary for a furnace. 
     Patent Document 7 discloses that even when the temperature of an outlet of a coal pulverizer is changed due to a control of the opening degree of a conveying-air-flow-rate adjustment damper at the change in load, a coal output temperature correction signal is determined based on the deviation between a detected temperature and a set temperature of the outlet of the coal pulverizer, and the coal output temperature correction signal is used for controlling the opening degree of the conveying-air-flow-rate adjustment damper to ensure the coal discharge amount in response to a coal discharge amount command signal. 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: JP2015-100740A 
     Patent Document 2: JPS63-62556A 
     Patent Document 3: JPH8-243429A 
     Patent Document 4: JPH4-334563A 
     Patent Document 5: JP2010-104939A 
     Patent Document 6: JP2012-7811A 
     Patent Document 7: JPH4-93511A 
     SUMMARY 
     Problems to be Solved 
     However, a higher load change rate is becoming necessary in the coal-fired power plant. The coal pulverizing apparatuses disclosed in Patent Documents 1 to 7 are insufficient to improve the coal output delay in some cases. 
     At least some embodiments of the present invention were made in view of the above problems. An object thereof is to provide a coal pulverizing apparatus, a control device and a control method for controlling the same, and a coal-fired power plant, whereby it is possible to improve the output delay of coal. 
     Solution to the Problems 
     (1) A control device for a coal pulverizing apparatus according to at least some embodiments of the present invention is used for a coal pulverizing apparatus including a rotatable table, a roller configured to pulverize a coal supplied from the table, a rotary classifier configured to classify a pulverized coal obtained by pulverizing the coal with the roller, and an air supply part configured to generate an air flow for guiding the pulverized coal toward the rotary classifier, the control device comprising: a first command value generation part configured to generate a command value of a first parameter including at least one of a rotational speed of the table, a pressing force of the roller to the table, or an air supply amount in the air supply part; and a second command value generation part configured to generate a command value of a second parameter including at least a rotational speed of the rotary classifier, the first command value generation part being configured to determine the command value of the first parameter, based on a first preceding signal determined in accordance with at least load information of a combustion device which burns the pulverized coal from the coal pulverizing apparatus, the second command value generation part being configured to determine the command value of the second parameter, based on a second preceding signal determined in accordance with at least the load information. 
     Herein, the load information of the combustion device may be information directly related to the load of the combustion device or may be information related to the load (e.g., the load of a steam turbine driven by steam generated by a boiler as the combustion device, or the load of a generator driven by the steam turbine) which indirectly indicates the load of the combustion device. 
     The coal (raw material coal) is supplied onto the table of the coal pulverizing apparatus. With rotation of the table, the coal on the table moves toward the outer periphery of the table and is pulverized with the roller. Pulverized coal particles obtained by pulverizing in the roller move toward the rotary classifier along with the air flow from the air supply part. In the rotary classifier, the pulverized coal particles are classified so that only fine particles of the pulverized coal particles pass through the rotary classifier and flow out of the coal pulverizing apparatus. In this way, various processes need to be followed inside the coal pulverizing apparatus, during a period between supply of the raw material coal and discharge of the coal. 
     Accordingly, there is a time lag (coal output delay) until the change of the supply amount of the raw material coal to the coal pulverizing apparatus leads to the change of the coal discharge amount from the coal pulverizing apparatus. 
     The coal output delay can be separated into: response delay in an upstream process between supply of the raw material coal to the table of the coal pulverizing apparatus and arrival of the pulverized coal to the inlet of the rotary classifier; and response delay in a downstream process between passage of the pulverized coal through the rotary classifier and discharge of the coal from the coal pulverizing apparatus. 
     In the above configuration (1), in the first command value generation part, the command value of the first parameter is determined based on the first preceding signal determined in accordance with the load information of the combustion device. 
     This enables preceding change of the first parameter including at least one of the rotational speed of the table, the pressing force of the roller, or the air supply amount, in accordance with the load change of the combustion device, thus improving response delay in the upstream process between supply of the raw material coal to the table and arrival of the pulverized coal to the inlet of the rotary classifier. 
     On the other hand, in the second command value generation part, the command value of the second parameter is determined based on the second preceding signal determined in accordance with the load information of the combustion device. This enables preceding change of the second parameter including the rotational speed of the rotary classifier in accordance with the load change of the combustion device, thus improving response delay in the downstream process between passage of the pulverized coal through the rotary classifier and discharge of the coal from the coal pulverizing apparatus. 
     Thus, it is possible to improve both response delay in the upstream process and response delay in the downstream process, and it is possible to effectively reduce the coal output delay in the coal pulverizing apparatus as a whole. 
     When only the rotational speed of the rotary classifier, which is the second parameter, is adjusted by preceding control to rapidly change the coal discharge amount from the coal pulverizing apparatus, the classifying accuracy can decrease in the rotary classifier. 
     In this regard, in the above configuration (1), since preceding control is performed on not only the second parameter but also the first parameter, it is possible to improve the coal output delay while suppressing a reduction in classifying accuracy of the rotary classifier. 
     (2) In some embodiments, in the above configuration (1), the first command value generation part is configured to determine the first preceding signal, based on a change rate of the command value of the second parameter. 
     In the above configuration (2), since the first preceding signal is determined based on the change rate of the command value of the second parameter, it is possible to appropriately set the first control signal so as to achieve both the classifying accuracy and the improvement in coal output delay. 
     For instance, in a case where the change rate of the command value of the second parameter (rotational speed of the rotary classifier), which can affect the classifying accuracy, is large, the first preceding signal may be set to be a relatively large value, taken into consideration this condition. This makes it possible to achieve both the classifying accuracy and the improvement in coal output delay. 
     (3) In some embodiments, in the above configuration (2), the first command value generation part is configured to determine the first preceding signal so that a change rate of the first preceding signal is equal to or below a first rate limit determined based on the change rate of the command value of the second parameter. 
     In the above configuration (3), the first rate limit to limit the change rate of the first preceding signal is variable based on the change rate of the command value of the second parameter (rotational speed of the rotary classifier). Accordingly, it is possible to appropriately determine the first preceding signal, in accordance with the change rate of the command value of the second parameter (rotational speed of the rotary classifier) which can affect the classifying accuracy, and it is possible to achieve both the classifying accuracy and the improvement in coal output delay. 
     (4) In some embodiments, in any one of the above configurations (1) to (3), the second command value generation part is configured to determine the second preceding signal, based on a change rate of the command value of the first parameter. 
     In the above configuration (4), since the second preceding signal is determined based on the change rate of the command value of the first parameter, it is possible to appropriately set the second control signal so as to achieve both the classifying accuracy and the improvement in coal output delay. 
     For instance, in a case where the coal output delay is not sufficiently improved by preceding control of the first parameter, the second preceding signal may be determined taking into consideration this condition to sufficiently obtain achieve the effect of improving the coal output delay. 
     (5) In some embodiments, in the above configuration (4), the second command value generation part is configured to determine the second preceding signal so that a change rate of the second preceding signal is equal to or below a second rate limit determined based on the change rate of the command value of the first parameter. 
     In the above configuration (5), the second rate limit to limit the change rate of the second preceding signal is variable based on the change rate of the command value of the first parameter. Accordingly, even if the change rate of the command value of the first parameter is small and the coal output delay is not sufficiently improved by preceding control of the first parameter, an appropriate adjustment of the second rate limit effectively increases the coal output delay improvement effect owing to preceding control of the second parameter. Thus, it is possible to sufficiently control the coal output delay in the coal pulverizing apparatus as a whole. 
     (6) In some embodiments, in any one of the above configurations (1) to (5), the combustion device is a boiler for generating steam to be supplied to a steam turbine to drive a generator, and the load information of the combustion device includes at least one of a load, a load change rate, or a load change range of the generator. 
     In the above configuration (6), the first preceding signal and the second preceding signal are determined based on the load information such as the load, the load change rate, or the load change range of the generator, in the way as described in the above (1). Thus, it is possible to improve both response delay in the upstream process and response delay in the downstream process and thereby effectively improve the coal output delay, and it is possible to appropriately control the coal pulverizing apparatus in response to the load change of the generator. Furthermore, since preceding control is performed on not only the second parameter but also the first parameter, it is possible to improve the coal output delay in the coal pulverizing apparatus while suppressing a reduction in classifying accuracy of the rotary classifier. 
     (7) In some embodiments, in any one of the above configurations (1) to (6), the first command value generation part is configured to determine the first preceding signal in accordance with the load information and raw-material-coal characteristic information related to a characteristic of a raw material coal. 
     The coal output delay improvement effect with respect to a manipulated value of the first parameter is not the same when the raw material coal has a different characteristic. 
     In this regard, in the above configuration (7), since the first preceding signal is set taking into consideration not only the load information but also the raw-material-coal characteristic information, it is possible to appropriately perform preceding control of the first parameter in accordance with the characteristic of the raw material coal, and it is possible to effectively improve the coal output delay. 
     (8) In some embodiments, in any one of the above configurations (1) to (7), the second command value generation part is configured to determine the second preceding signal in accordance with the load information and raw-material-coal characteristic information related to a characteristic of a raw material coal. 
     The coal output delay improvement effect with respect to a manipulated value of the second parameter is not the same when the raw material coal has a different characteristic. 
     In this regard, in the above configuration (8), since the second preceding signal is set taking into consideration not only the load information but also the raw-material-coal characteristic information, it is possible to appropriately perform preceding control of the second parameter in accordance with the characteristic of the raw material coal, and it is possible to effectively improve the coal output delay. 
     (9) In some embodiments, in the above configuration (7) or (8), the raw-material-coal characteristic information includes a water content of the raw material coal. 
     According to findings by the present inventors, the water content of the raw material coal significantly affects the coal output delay improvement effect with respect to a manipulated value of each parameter. 
     In this regard, in the above configuration (9), since the water content of the raw material coal is used as the raw-material-coal characteristic information, it is possible to appropriately perform preceding control of the first parameter or the second parameter in accordance with the water content of the raw material coal, and it is possible to effectively improve the coal output delay. 
     (10) A coal pulverizing apparatus according to at least some embodiments of the present invention comprises: a rotatable table; a roller configured to pulverize a coal supplied from the table; an actuator configured to press the roller to the table; a rotary classifier configured to classify a pulverized coal obtained by pulverizing the coal with the roller; an air supply part configured to generate an air flow for guiding the pulverized coal toward the rotary classifier; and the control device with any one of the above configurations (1) to (9), configured to control the rotary classifier and at least one of the table, the actuator, or the air supply part. 
     With the above configuration (10), it is possible to improve both response delay in the upstream process and response delay in the downstream process by preceding control of the first parameter in the first command value generation part and preceding control of the second parameter in the second command value generation as described in the above (1). Thereby, it is possible to effectively reduce the coal output delay in the coal pulverizing apparatus as a whole. 
     Furthermore, since preceding control is performed on not only the second parameter but also the first parameter, it is possible to improve the coal output delay while suppressing a reduction in classifying accuracy of the rotary classifier. 
     (11) A coal-fired power plant according to at least some embodiments of the present invention comprises: the coal pulverizing apparatus with the above configuration (10); a boiler configured to burn the pulverized coal from the coal pulverizing apparatus to generate steam; a steam turbine configured to be driven by the steam generated from the boiler; and a generator configured to be driven by the steam turbine. 
     With the above configuration (11), it is possible to improve both response delay in the upstream process and response delay in the downstream process by preceding control of the first parameter in the first command value generation part and preceding control of the second parameter in the second command value generation as described in the above (1). Thereby, it is possible to effectively reduce the coal output delay in the coal pulverizing apparatus as a whole, and it is possible to rapidly change the load of the coal-fired power plant. 
     Furthermore, since preceding control is performed on not only the second parameter but also the first parameter, it is possible to improve the coal output delay while suppressing a reduction in classifying accuracy of the rotary classifier. 
     (12) A control method for a coal pulverizing apparatus according to at least some embodiments of the present invention is used for a coal pulverizing apparatus including a rotatable table, a roller configured to pulverize a coal supplied from the table, a rotary classifier configured to classify a pulverized coal obtained by pulverizing the coal with the roller, and an air supply part configured to generate an air flow for guiding the pulverized coal toward the rotary classifier, the control method comprising: a first command value generation step of generating a command value of a first parameter including at least one of a rotational speed of the table, a pressing force of the roller to the table, or an air supply amount in the air supply part; a second command value generation step of generating a command value of a second parameter including at least a rotational speed of the rotary classifier, the first command value generation step including determining the command value of the first parameter, based on a first preceding signal determined in accordance with at least load information of a combustion device which burns the pulverized coal from the coal pulverizing apparatus, the second command value generation step including determining the command value of the second parameter, based on a second preceding signal determined in accordance with at least the load information. 
     With the above method (12), it is possible to improve both response delay in the upstream process and response delay in the downstream process by preceding control of the first parameter and preceding control of the second parameter. Thereby, it is possible to effectively reduce the coal output delay in the coal pulverizing apparatus as a whole. 
     Furthermore, since preceding control is performed on not only the second parameter but also the first parameter, it is possible to improve the coal output delay while suppressing a reduction in classifying accuracy of the rotary classifier. 
     Advantageous Effects 
     According to at least one embodiment of the present invention, it is possible to improve the coal output delay in the coal pulverizing apparatus while suppressing a reduction in classifying accuracy of the rotary classifier. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a coal-fired power plant according to an embodiment. 
         FIG. 2  is a block configuration diagram of a control device according to an embodiment. 
         FIG. 3  is a block configuration diagram of a first preceding signal operation part according to an embodiment. 
         FIG. 4  is a block configuration diagram of a second preceding signal operation part according to an embodiment. 
         FIG. 5  is graphs showing the behavior of various parameters when the load of the coal-fired power plant is changed; (a) shows the change in the coal supply amount and coal discharge amount of the coal pulverizing apparatus; (b) shows the change in the command value of a first parameter; (c) shows the change in the command value of a second parameter; and (d) shows the change in the generator load. 
         FIG. 6  is a flowchart of a method for controlling a coal pulverizing apparatus according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention. 
       FIG. 1  is a schematic configuration diagram of a coal-fired power plant according to an embodiment. 
     As shown in  FIG. 1 , the coal-fired power plant  100  according to an embodiment includes a coal pulverizing apparatus  200 , a combustion device (boiler)  300 , and a control device  400 . 
     The coal pulverizing apparatus  200  includes a pulverizer  10  configured to pulverize coal (raw material coal), a rotary classifier  20  configured to classify fine particles of pulverized coal obtained by pulverizing the coal with the pulverizer  10 , and an air supply part  30  configured to generate an air flow which guides the pulverized coal from the pulverizer  10  toward the rotary classifier  20 . 
     In the illustrative embodiment shown in  FIG. 1 , the coal pulverizing apparatus  200  is a vertical pulverizing-and-classifying apparatus in which the rotary classifier  20  is disposed above the pulverizer  10  and the air supply part  30  is disposed around the pulverizer  10 . In this case, an upper end of a pulverizer housing  11  of the pulverizer  10  is connected to a lower end of a classifier housing  21  of the rotary classifier  20  so as to integrally form a housing of the entire coal pulverizing apparatus  200 . 
     In some embodiments, as shown in  FIG. 1 , the coal pulverizing apparatus  200  includes a supply tube  50  for supplying the coal (raw material coal) and a discharge tube  51  for discharging fine particles of the pulverized and classified coal to a furnace  301  of the combustion device  300  described later. The supply tube  50  is disposed at an upper portion of the coal pulverizing apparatus  200  and configured so that the raw material coal supplied from above the coal pulverizing apparatus  200  drops to a table  12  of the pulverizer  10  described later. The discharge tube  51  is disposed at an upper portion of the coal pulverizing apparatus  200  and configured to discharge the pulverized coal particles having passed through the rotary classifier  20  toward the furnace  301 . 
     The pulverizer  10  of the coal pulverizing apparatus  200  includes, as shown in  FIG. 1 , a rotatable table  12  and a roller  13  configured to press the raw material coal to the table  12  to pulverize the raw material coal. 
     The table  12  is driven by a table driving part  15  disposed below the table  12  and thereby rotates around a central axis C of the table  12 . The table driving part  15  may include a motor whose rotational speed is variably controlled in accordance with a table rotational speed command from the control device  400 . 
     On the other hand, the roller  13  is configured to rotate on the table  12  rotationally driven by the table driving part  15  while being pressed toward the table  12  by an actuator  16 . The actuator  16  may be for instance a hydraulic cylinder, and the pressing force of the roller  13  to the table  12  may be variably controlled in accordance with a roller pressing force command from the control device  400 . The roller  13  may include a plurality of rollers (e.g., three rollers) disposed in a radially outer region of the table  12  at an interval in a circumferential direction of the table  12 . 
     In the pulverizer  10  with the above configuration, the raw material coal drops from the supply tube  50  disposed above the table  12  to a radially inner region of the table  12  and then moves toward the outer periphery of the table  12  by a centrifugal force of the table  12 , so that the raw material coal is supplied to a gap between the table  12  and the roller  13 . Since the roller  13  is pressed toward the table  12  by the actuator  16 , the raw material coal supplied to the gap between the table  12  and the roller  13  is pulverized. Consequently, the pulverized coal is obtained. 
     The air supply part  30  includes an air intake port  31  provided in the pulverizer housing  11 , an air chamber  33  which is an annular space located below the table  12  so as to communicate with the air intake port  31 , a fan  34  for supplying air to the air chamber  33  via the air intake port  31 , and an air discharge port  32  configured to discharge an air flow upward from the air chamber  33 . 
     The air discharge port  32  may be a flow path formed between throat vanes arranged in a circumferential direction at a distance on a radially outer side of the table  12 . 
     The air supply part  30  may further include a damper  35  for adjusting the air supply amount from the fan  34 . In this case, the opening degree of the damper  35  may be controlled so that the air supply amount in the air supply part  30  is adjusted in accordance with an air supply amount command from the control device  400 . 
     The air supply part  30  with the above configuration allows air taken from the air discharge port  32  into the air chamber  33  to be discharged upward via the air discharge port  32 , consequently forming an upward air flow (see arrow “a” in  FIG. 1 ) inside the housing ( 11 ,  21 ) of the coal pulverizing apparatus  200 . 
     In this context, particles having a large particle size deviate from the air flow “a” due to gravity, drop downward and return to the table  12 , and are pulverized again. 
     The rotary classifier  20  is disposed above the pulverizer  10  and configured to classify the pulverized coal particles accompanying the air flow “a” formed by the air supply part  30 . 
     In some embodiments, as shown in  FIG. 1 , the rotary classifier  20  includes an annular rotational portion  22  for classifying the pulverized coal particles. The annular rotational portion  22  is rotatably provided around a rotational axis O along a vertical direction in an inner space of the classifier housing  21 . The annular rotational portion  22  includes a plurality of rotary fins arranged in a circumferential direction at a distance and allowing the pulverized coal particles to pass through a gap between adjacent rotary fins. 
     The pulverized coal is classified in the annular rotational portion  22  according to the following principle. 
     The rotation of the annular rotational portion  22  imparts rotation to the pulverized coal flowing toward the rotary classifier  20  accompanying the air flow “a”. As a result, a centrifugal force directed radially outward due to the centrifugal field formed by the annular rotational portion  22 , as well as a drag due to the velocity component of the air flow directed radially inward, are applied to the pulverized coal particles accompanying the air flow. A particle size with equilibrium of the centrifugal force and the drag is called a theoretical classification size. Coarse particles having a greater particle size than the theoretical classification size have a stronger centrifugal force than a drag caused by the velocity component of the air flow and are thrown outside the annular rotational portion  22 . On the other hand, fine particles having a smaller particle size than the theoretical classification size are subjected to a stronger drag from the air flow than the centrifugal force and thus pass through the annular rotational portion  22  along with the air flow. In this way, in the annular rotational portion  22 , the pulverized coal particles conveyed by the air flow are classified into coarse particles and fine particles. 
     In some embodiments, the rotary classifier  20  includes a classifier driving part  24  for rotating the annular rotational portion  22  around the rotational axis O. 
     The classifier driving part  24  may include a motor whose rotational speed is variably controlled in accordance with a classifier rotational speed command from the control device  400 . 
     As shown in  FIG. 1 , the rotary classifier  20  may include an annular stationary portion  23  disposed on a radially outer side of the annular rotational portion  22 , inside the classifier housing  21 . The annular stationary portion  23  has a plurality of stationary fins arranged in a height direction at a distance and allowing the air flow “a” to pass through a gap between adjacent stationary fins. The annular stationary portion  23  is configured to guide the air flow “a” flowing from the radially outer side. 
     Further, as shown in  FIG. 1 , the rotary classifier  20  may further include a hopper  25  disposed below the annular rotational portion  22  and configured to recover the coarse particles which have not pass through the annular rotational portion  22  to the table  12  of the pulverizer  10 . 
     The pulverized coal produced in the coal pulverizing apparatus  200  with the above configuration is supplied to the combustion device  300 . 
     The combustion device (boiler)  300  includes a furnace  301  for burning the fine particles of coal discharged from the coal pulverizing apparatus  200  with a burner  302  to produce a combustion gas. A heat exchanger  303  is disposed inside the furnace  301 . In the heat exchanger  303 , steam is generated by heat exchange with the combustion gas inside the furnace  301 . 
     The steam generated by the combustion device (boiler)  300  is supplied to a steam turbine  310  of the coal-fired power plant  100 . The steam turbine  310  is driven by the steam supplied from the combustion device (boiler)  300 . To a rotational shaft of the steam turbine  310 , a shaft of a generator  320  is connected, so that the generator  320  is driven by the steam turbine  310  to generate electric power. 
     The steam discharged from the steam turbine  310  is recovered by a condenser  330 . Condensed water obtained by the condenser  330  is supplied to the heat exchanger  303  again through a water supply pump  340 . 
     In the coal-fired power plant  100  with the above configuration, the control device  400  controls each part of the coal pulverizing apparatus  200 , such as the table driving part  15 , the actuator  16 , the damper  35 , and the classifier driving part  24 . 
     The coal pulverizing apparatus  200  includes some measurement tools to check the state of the coal pulverizing apparatus  200 , for instance, including at least one of an inlet air flow rate meter  111 , an inlet air thermometer  112 , an outlet air thermometer  113 , a coal supply amount meter  114 , a coal supply thermometer  115 , a furnace differential pressure gauge  116 , or an outlet pressure gauge  117 . Further, a wattmeter (not shown) is disposed to measure the output power of the generator  320 . Load information (e.g., load change range, load change rate, load) of the combustion device  300  (coal-fired power plant  100 ) can be thus acquired. 
     In this case, measurement results of these various tools may be sent to the control device  400  and used for controlling each part of the coal pulverizing apparatus  200  by the control device  400 . 
     Next, with reference to  FIGS. 2 to 4 , the control device  400  will be described in detail. 
       FIG. 2  is a block configuration diagram of the control device according to an embodiment.  FIG. 3  is a block configuration diagram of a first preceding signal operation part  520 A of the control device  400 .  FIG. 4  is a block configuration diagram of a second preceding signal operation part  620  of the control device  400 . 
     In some embodiments, the control device  400  includes a first command value generation part  500  for generating a command value of a first parameter including at least one of the rotational speed of the table  12 , the pressing force of the roller  13  to the table  12 , or the air supply amount in the air supply part  30 , and a second command value generation part  600  for generating a command value of a second parameter including at least the rotational speed of the rotary classifier  20 . 
     In the illustrative embodiment shown in  FIG. 2 , the first command value generation part  500  is configured to generate a command value of each of three first parameters including the rotational speed of the table  12 , the pressing force of the roller  13  to the table  12 , and the air supply amount in the air supply part  30 . In another embodiment, the first command value generation part  500  is configured to generate a command value of only a part of the three first parameters. 
     In some embodiments, as shown in  FIG. 2 , the first command value generation part  500  includes a basic command value calculation part  510  ( 510 A to  510 C) for calculating a basic command value of the first parameter in accordance with a coal supply amount command, which sets the amount of coal supplied to the coal pulverizing apparatus  200 , and a first preceding signal operation part  520  ( 520 A to  520 C) for calculating a first preceding signal determined in accordance with the load information of the combustion device  300 . The basic command value calculation part  510  ( 510 A to  510 C) may include a function which increases the basic command value of the first parameter with an increase in the coal supply amount command. The coal supply amount command may be determined based on the load of the combustion device  300  (=the load of the generator  320 ). 
     In the illustrative embodiment shown in  FIG. 2 , an adder  530  ( 530 A to  530 C) calculates the sum of the basic command value of the first parameter obtained by the basic command value calculation part  510  ( 510 A to  510 C) and the first preceding signal obtained by the first preceding signal operation part  520  ( 520 A to  520 C), and the command value of the first parameter is generated based on an output signal from the adder  530 . 
     As shown in  FIG. 2 , the output signal from the adder  530  ( 530 A) may be subjected to limit processing by a first limit (upper limit)  540  and a second limit (lower limit)  550  to limit the command value of the first parameter within a desired range. 
     In this case, the first limit  540  may limit the command value of the first parameter to be equal to or below an upper limit value, based on an output signal from a function  542  configured to variably set the upper limit value of the command value of the first parameter, in accordance with the water content of the raw material coal. The water content of the raw material coal may be calculated through estimation based on measurement results of the aforementioned various measurement tools ( 111  to  117 ). 
     Similarly, the second limit  550  may limit the command value of the first parameter to be equal to or higher than a lower limit value, based on an output signal from a function  552  configured to variably set the lower limit value of the command value of the first parameter, in accordance with the mill differential pressure (differential pressure between upstream and downstream of the coal pulverizing apparatus  200 ). 
     Although in the example shown in  FIG. 2 , limit processing by the first limit  540  and the second limit  550  is performed only on the table rotational speed command, in other embodiments, limit processing by the first limit  540  and the second limit  550  may also be performed on other first parameters (air supply amount command or roller pressing force command). 
     Additionally, as shown in  FIG. 2 , a limit  560  may be provided to limit the command value of the first parameter within a range specified by a fixed upper limit value and a fixed lower limit value. The limit  560  is configured to perform limit processing on the output signal from the adder  530  ( 530 B,  530 C) to limit the command value of the first parameter within the specified range. 
     Although in the illustrative embodiment shown in  FIG. 2 , limit processing by the limit  560  is applied only to the air supply amount command and the roller pressing force command, in other embodiments, limit processing by the limit  560  may also be performed on the table rotational speed command, instead of the first limit  540  and the second limit  550 . 
     Further, as shown in  FIG. 2 , the control device  400  may include a change rate operator  580  ( 580 A to  580 C) for calculating the change rate (change speed) of the command value of the first parameter generated by the first command value generation part  500 . The change rate of the command value of the first parameter obtained by the change rate operator  580  may be used for calculating a second preceding signal in a second preceding signal operation part  620  described later (see input signals to functions  880 ,  882 ,  884  in  FIG. 4 ). 
     As shown in  FIG. 3 , the first preceding signal operation part  520  ( 520 A) of the first command value generation part  500  is configured to determine the first preceding signal, in accordance with the load information of the combustion device  300  (or the coal-fired power plant  100  including the same). 
     Although  FIG. 3  shows a configuration of the first preceding signal operation part  520 A for obtaining the first preceding signal used for calculating the command value of the table rotational speed, which is an example of the first parameter, first preceding signals for other first parameters (air supply amount or roller pressing force) may also be calculated by first preceding signal operation parts ( 520 B,  520 C) having the same configuration as the first preceding signal operation part  520 A shown in  FIG. 3 . 
     More specifically, the first preceding signal operation part  520  ( 520 A) may include a first reference preceding signal calculation part  700  for obtaining a reference value (first reference preceding signal) of the first preceding signal, based on the coal supply amount command value, and an operation coefficient calculation part  710  ( 710 A to  710 C) for obtaining an operation coefficient (correction coefficient) by which the first reference preceding signal is multiplied, in accordance with the load information of the combustion device  300  (coal-fired power plant  100 ). 
     The first reference preceding signal calculated in the first reference preceding signal calculation part  700  and the operation coefficient calculated in the operation coefficient calculation part  710  ( 710 A to  710 C) are input into a multiplier  750  and multiplied together, so that the first preceding signal is determined based on the product calculated by the multiplier  750 . 
     The first reference preceding signal calculation part  700  may include a function which increases the first reference preceding signal with an increase in the coal supply amount command. 
     On the other hand, the load information considered when the operation coefficient calculation part  710  ( 710 A to  710 C) calculates the operation coefficient may be at least one of the load, the load change rate, or the load change range of the combustion device  300 . In this case, the operation coefficient calculation part  710  ( 710 A to  710 C) may include a function which increases the operation coefficient with an increase in the load information such as the load, the load change rate, or the load change range of the combustion device  300 . 
     In some embodiments, as shown in  FIG. 3 , the first preceding signal operation part  520  ( 520 A) is configured to calculate the first preceding signal, based on raw-material-coal characteristic information related to the characteristic of the raw material coal, in addition to the load information. 
     In the illustrative embodiment shown in  FIG. 3 , the first preceding signal operation part  520  ( 520 A) further include an operation coefficient calculation part  740  for calculating an operation coefficient in accordance with the water content of the raw material coal, which is an example of the raw-material-coal characteristic information. The operation coefficient obtained by the operation coefficient calculation part  740  is input to the multiplier  750 . Thus, since the first preceding signal is set taking into consideration not only the load information but also the raw-material-coal characteristic information, it is possible to appropriately perform preceding control of the first parameter in accordance with the characteristic of the raw material coal, and it is possible to effectively improve the coal output delay. 
     In some embodiments, as shown in  FIG. 3 , the first preceding signal operation part  520  ( 520 A) is configured to determine the first preceding signal, based on the change rate of the command value of the second parameter. 
     In the illustrative embodiment shown in  FIG. 3 , the first preceding signal operation part  520  ( 520 A) includes rate limits ( 760 ,  770 ) for limiting the change rate of the first preceding signal to be equal to or below a threshold (=first rate limit) determined based on the change rate of the command value of the second parameter (=classifier rotational speed command change rate). The rate limit  760  is adapted to limit a positive change rate (=increase rate) of the first preceding signal to be equal to or below a threshold. On the other hand, the rate limit  770  is adapted to limit a negative change rate (=decrease rate) of the first preceding signal to be equal to or below a threshold. 
     Thus, the rate limits ( 760 ,  770 ) limit the change rate of the first preceding signal equal to or below a threshold which is variable depending on the change rate of the command value of the second parameter (=classifier rotational speed command change rate). Accordingly, it is possible to appropriately determine the first preceding signal, in accordance with the change rate of the command value of the second parameter (rotational speed of the rotary classifier  20 ) which can affect the classifying accuracy, and it is possible to achieve both the classifying accuracy and the improvement in coal output delay. 
     In the example shown in  FIG. 3 , the first preceding signal operation part  520  ( 520 A) includes a function  780  which outputs a value in accordance with the change rate of the command value of the second parameter (=classifier rotational speed command change rate) and a function ( 782 ,  784 ) which outputs a value in accordance with the change rate of the first parameter (in case of the example in  FIG. 3 , air supply amount command change rate and roller pressing force command change rate) other than the first parameter (in case of the example in  FIG. 3 , table rotational speed) related to an operand in the first preceding signal operation part  520  ( 520 A). The adder  786  provides the sum of respective outputs from the functions ( 780 ,  782 ,  784 ). The operation result of the adder  786  is multiplied by gain K 1 , K 2  to obtain the threshold used for limit processing in each rate limit ( 760 ,  770 ). 
     Referring to  FIG. 2  again, the second command value generation part  600  will be described. 
     In some embodiments, as shown in  FIG. 2 , the second command value generation part  600  includes a basic command value calculation part  610  for calculating a basic command value of the second parameter in accordance with the coal supply amount command, and a second preceding signal operation part  620  for calculating a second preceding signal determined in accordance with the load information of the combustion device  300 . The basic command value calculation part  610  may include a function which increases the basic command value of the second parameter with an increase in the coal supply amount command. 
     In the illustrative embodiment shown in  FIG. 2 , an adder  630  calculates the sum of the basic command value of the second parameter obtained by the basic command value calculation part  610  and the second preceding signal obtained by the second preceding signal operation part  620 , and the command value of the second parameter is generated based on an output signal from the adder  630 . 
     Additionally, in the illustrative embodiment shown in  FIG. 2 , a limit  640  may be provided to limit the command value of the second parameter within a range specified by a fixed upper limit value and a fixed lower limit value. The limit  640  is configured to perform limit processing on the output signal from the adder  630  to limit the command value of the second parameter within the specified range. 
     In other embodiments, the output signal from the adder  630  may be subjected to limit processing by a similar configuration to the first limit (upper limit)  540  and the second limit (lower limit)  550  as shown in  FIG. 2 , instead of the limit  640 , to limit the command value of the second parameter within a desired range. In this case, the first limit  540  may limit the command value of the second parameter to be equal to or below an upper limit value, based on an output signal from a function  542  configured to variably set the upper limit value of the command value of the second parameter, in accordance with the water content of the raw material coal. Similarly, the second limit  550  may limit the command value of the second parameter to be equal to or higher than a lower limit value, based on an output signal from a function  552  configured to variably set the lower limit value of the command value of the second parameter, in accordance with the mill differential pressure (differential pressure between upstream and downstream of the coal pulverizing apparatus  200 ). 
     Further, as shown in  FIG. 2 , the control device  400  may include a change rate operator  680  for calculating the change rate (change speed) of the command value of the second parameter generated by the second command value generation part  600 . 
     The change rate of the command value of the second parameter obtained by the change rate operator  680  may be used for calculating the first preceding signal in the first preceding signal operation part  520  as described above (see an input signal to the function  780  in  FIG. 3 ). 
     As shown in  FIG. 4 , the second preceding signal operation part  620  of the second command value generation part  600  is configured to determine the second preceding signal, in accordance with the load information of the combustion device  300  (or the coal-fired power plant  100  including the same). 
     More specifically, the second preceding signal operation part  620  may include a second reference preceding signal calculation part  800  for obtaining a reference value (second reference preceding signal) of the second preceding signal, based on the coal supply amount command value, and an operation coefficient calculation part  810  ( 810 A to  810 C) for obtaining an operation coefficient (correction coefficient) by which the second reference preceding signal is multiplied, in accordance with the load information of the combustion device  300  (coal-fired power plant  100 ). 
     The second reference preceding signal calculated in the second reference preceding signal calculation part  800  and the operation coefficient calculated in the operation coefficient calculation part  810  ( 810 A to  810 C) are input into a multiplier  850  and multiplied together, so that the second preceding signal is determined based on a product calculated by the multiplier  850 . 
     The second reference preceding signal calculation part  800  may include a function which increases the second reference preceding signal with an increase in the coal supply amount command. 
     On the other hand, the load information considered when the operation coefficient calculation part  810  ( 810 A to  810 C) calculates the operation coefficient may be at least one of the load, the load change rate, or the load change range of the combustion device  300 . In this case, when the load information is the load change rate of the combustion device  300 , the operation coefficient calculation part  810 A may include a function which decreases the operation coefficient with an increase in the load change rate of the combustion device  300 . By contrast, when the load information is the load change range or the load of the combustion device  300 , the operation coefficient calculation part  810  ( 810 A to  810 C) may include a function which increases the operation coefficient with an increase in the load change rate of the combustion device  300 . 
     In some embodiments, as shown in  FIG. 4 , the second preceding signal operation part  620  is configured to calculate the second preceding signal, based on raw-material-coal characteristic information related to the characteristic of the raw material coal, in addition to the load information. 
     In the illustrative embodiment shown in  FIG. 4 , the second preceding signal operation part  620  further include an operation coefficient calculation part  840  for calculating the operation coefficient in accordance with the water content of the raw material coal, which is an example of the raw-material-coal characteristic information. The operation coefficient obtained by the operation coefficient calculation part  840  is input to the multiplier  850 . Thus, since the second preceding signal is set taking into consideration not only the load information but also the raw-material-coal characteristic information, it is possible to appropriately perform preceding control of the second parameter in accordance with the characteristic of the raw material coal, and it is possible to effectively improve the coal output delay. 
     In some embodiments, as shown in  FIG. 4 , the second preceding signal operation part  620  is configured to determine the second preceding signal, based on the change rate of the command value of the first parameter. 
     In the illustrative embodiment shown in  FIG. 4 , the second preceding signal operation part  620  includes rate limits ( 860 ,  870 ) for limiting the change rate of the second preceding signal to be equal to or below a threshold (=second rate limit) determined based on the change rate of the command value of the first parameter (=table rotational speed command change rate, roller pressing force command change rate, air supply amount command change rate). The rate limit  860  is adapted to limit a positive change rate (=increase rate) of the second preceding signal to be equal to or below a threshold. On the other hand, the rate limit  870  is adapted to limit a negative change rate (=decrease rate) of the second preceding signal to be equal to or below a threshold. 
     Thus, the rate limits ( 860 ,  870 ) limit the change rate of the second preceding signal equal to or below a threshold which is variable depending on the change rate of the command value of the first parameter (=table rotational speed command change rate, roller pressing force command change rate, air supply amount command change rate). Accordingly, even if the change rate of the command value of the first parameter is small and the coal output delay is not sufficiently improved by preceding control of the first parameter, an appropriate adjustment of the second rate limit effectively increases the coal output delay improvement effect owing to preceding control of the second parameter. Thus, it is possible to sufficiently control the coal output delay in the coal pulverizing apparatus  200  as a whole. 
     In the example shown in  FIG. 4 , the second preceding signal operation part  620  includes functions ( 880 ,  882 ,  884 ) which output values in accordance with the change rates of the command values of the first parameters (=table rotational speed command change rate, roller pressing force command change rate, air supply amount command change rate). The adder  886  provides the sum of respective outputs from the functions ( 880 ,  882 ,  884 ). The operation result of the adder  886  is multiplied by gain K 1 , K 2  to obtain the threshold used for limit processing in each rate limit ( 860 ,  870 ). 
     According to some embodiments described above, in the first preceding signal operation part  520  ( 520 A to  520 C) of the first command value generation part  500 , the first preceding signal is determined in accordance with the load information of the combustion device  300 , and the command value of the first parameter is determined based on the first preceding signal. This enables preceding change of the first parameter including at least one of the rotational speed of the table  12 , the pressing force of the roller  13 , or the air supply amount in the air supply part  30 , in accordance with the load change of the combustion device  300 , thus improving response delay in the upstream process between supply of the raw material coal to the table  12  and arrival of the pulverized coal to the inlet of the rotary classifier  20 . 
     On the other hand, in the second preceding signal operation part  620  of the second command value generation part  600 , the command value of the second parameter is determined based on the second preceding signal determined in accordance with the load information of the combustion device  300 . This enables preceding change of the second parameter including the rotational speed of the rotary classifier  20  in accordance with the load change of the combustion device  300 , thus improving response delay in the downstream process between passage of the pulverized coal through the rotary classifier  20  and discharge of the coal from the coal pulverizing apparatus  200 . 
     Thus, it is possible to improve both response delay in the upstream process and response delay in the downstream process, and it is possible to effectively reduce the coal output delay in the coal pulverizing apparatus  200  as a whole. 
     When only the rotational speed of the rotary classifier  20 , which is the second parameter, is adjusted by preceding control to rapidly change the coal discharge amount from the coal pulverizing apparatus  200 , the classifying accuracy can decrease in the rotary classifier  20 . 
     In this regard, according to the above-described embodiment, since preceding control is performed on not only the second parameter but also the first parameter, it is possible to improve the coal output delay while suppressing a reduction in classifying accuracy of the rotary classifier  20 . 
       FIG. 5  is graphs showing the behavior of various parameters when the load of the coal-fired power plant  100  is changed;  FIG. 5( a )  shows the change in the coal supply amount and coal discharge amount of the coal pulverizing apparatus  200 ;  FIG. 5( b )  shows the change in the command value of the first parameter;  FIG. 5( c )  shows the change in the command value of the second parameter; and  FIG. 5( d )  shows the change in the load of the generator  320 . 
     In each of  FIGS. 5( a ) to 5( d ) , temporal change of the parameters when preceding control by the first preceding signal and the second preceding signal is not performed is shown on the left side; temporal change of the parameters when preceding control by the first preceding signal and the second preceding signal is performed is shown in the middle; temporal change of the parameters when the load change range is large is shown on the right side. 
     As shown in  FIGS. 5( b ) and 5( c ) , in the case where preceding control by the first preceding signal and the second preceding signal is not performed, the command values of the first parameter and the second parameter themselves are respectively the basic command values ( 900 ,  950 ) calculated in accordance with the coal supply amount command in the basic command value calculation parts ( 510 ,  610 ) shown in  FIG. 2 . 
     Consequently, as shown in  FIG. 5( a ) , even if the coal supply amount to the coal pulverizing apparatus  200  is increased with an increase in the load command value of the generator  320 , the coal discharge amount from the coal pulverizing apparatus  200  is only gently increased. The reason is that even if the command value of the first parameter (=table rotational speed command, roller pressing force command, air supply amount command) and the command value of the second parameter (=classifier rotational speed command) are changed with the increase in the coal supply amount, the coal discharge amount from the coal pulverizing apparatus  200  does not rapidly follow the change, due to the coal output delay. Thus, response delay occurs in the coal discharge amount from the coal pulverizing apparatus  200 , which causes response delay of the load of the generator  320  in response to the load command value, as shown in  FIG. 5( d ) . 
     By contrast, as described in the above embodiment, in the case where preceding control by the first preceding signal and the second preceding signal is performed, the first preceding signal and the second preceding signal determined in accordance with the load information are added to the basic command values ( 900 ,  950 ) to generate a command value  910  of the first parameter and a command value  960  of the second parameter. 
     Consequently, as shown in  FIG. 5( a ) , when the coal supply amount to the coal pulverizing apparatus  200  is increased with an increase in the load command value of the generator  320 , response delay (coal output delay) of the coal discharge amount from the coal pulverizing apparatus  200  is reduced. Thus, since response delay of the coal discharge amount from the coal pulverizing apparatus  200  is reduced, response delay of the load of the generator  320  in response to the load command value is also reduced, as shown in  FIG. 5( d ) . 
     Similarly, in the case where the load change range is large, when preceding control by the first preceding signal and the second preceding signal are performed, the first preceding signal and the second preceding signal determined in accordance with the load information are added to the basic command values ( 930 ,  970 ) to generate a command value  940  of the first parameter and a command value  980  of the second parameter. 
     Consequently, as shown in  FIG. 5( a ) , when the coal supply amount to the coal pulverizing apparatus  200  is increased with an increase in the load command value of the generator  320 , response delay (coal output delay) of the coal discharge amount from the coal pulverizing apparatus  200  is reduced. Thus, since response delay of the coal discharge amount from the coal pulverizing apparatus  200  is reduced, response delay of the load of the generator  320  in response to the load command value is also reduced, as shown in  FIG. 5( d ) . 
     Next, with reference to  FIG. 6 , a control method for the coal pulverizing apparatus  200  according to some embodiments will be described.  FIG. 6  is a flowchart of the control method for the coal pulverizing apparatus  200  according to an embodiment. 
     As shown in  FIG. 6 , first, load information of the combustion device  300  (coal-fired power plant  100 ) is acquired (step S 10 ). The load information may be at least one of the load, the load change rate, or the load change range of the combustion device  300 . 
     Then, a first preceding signal used for calculating a command value of a first parameter is calculated in accordance with the load information of the combustion device  300  acquired in step S 10  (step S 12 ). The first parameter includes at least one of the rotational speed of the table  12 , the pressing force of the roller  13  to the table  12 , or the air supply amount in the air supply part  30 , as described above. 
     The first preceding signal may be calculated using the first preceding signal operation part  520  shown in  FIG. 3 . In this case, a reference value of the first preceding signal (first reference preceding signal) may be obtained by the first reference preceding signal calculation part  700  in accordance with the coal supply amount command value, an operation coefficient (correction coefficient) may be obtained by the operation coefficient calculation part  710  ( 710 A to  710 C) in accordance with the load information of the combustion device  300  (coal-fired power plant  100 ), and the first preceding signal may be determined based on a product of the first reference preceding signal and the operation coefficient. In this operation, the first preceding signal may be determined taking into consideration raw-material-coal characteristic information related to the characteristic of the raw material coal, in addition to the load information of the combustion device  300 . More specifically, an operation coefficient in accordance with the water content of the raw material coal, which is an example of the raw-material-coal characteristic information, may be calculated by the operation coefficient calculation part  740 , and the first preceding signal may be determined based on a product of the first reference preceding signal, the operation coefficient obtained by the operation coefficient calculation part  710  ( 710 A to  710 C), and the operation coefficient obtained by the operation coefficient calculation part  740 . Further, when the first preceding signal is determined in the first preceding signal operation part  520 , the change rate of a command value of a second parameter may be taken into consideration. More specifically, the change rate of the first preceding signal may be limited by the rate limits ( 760 ,  770 ) to be equal to or below a threshold (=first rate limit) which is determined based on the change rate of the command value of the second parameter (=classifier rotational speed command change rate). 
     Then, a command value of the first parameter is generated based on the first preceding signal obtained in step S 12  (step S 14 ). 
     More specifically, a basic command value of the first parameter is calculated by the basic command value calculation part  510  ( 510 A to  510 C), in accordance with a coal supply amount command, which sets the amount of coal supplied to the coal pulverizing apparatus  200 , and the first preceding signal obtained in step S 12  is added to the basic command value to calculate the command value of the first parameter. 
     Further, a second preceding signal used for calculating the command value of the second parameter is calculated in accordance with the load information of the combustion device  300  acquired in step S 10  (step S 16 ). The second parameter includes the rotational speed of the rotary classifier  20 , as described above. 
     The second preceding signal may be calculated using the second preceding signal operation part  620  shown in  FIG. 4 . In this case, a reference value of the second preceding signal (second reference preceding signal) may be obtained by the second reference preceding signal calculation part  800  in accordance with the coal supply amount command value, an operation coefficient (correction coefficient) may be obtained by the operation coefficient calculation part  810  ( 810 A to  810 C) in accordance with the load information of the combustion device  300  (coal-fired power plant  100 ), and the second preceding signal may be determined based on a product of the second reference preceding signal and the operation coefficient. In this operation, the second preceding signal may be determined taking into consideration raw-material-coal characteristic information related to the characteristic of the raw material coal, in addition to the load information of the combustion device  300 . More specifically, an operation coefficient in accordance with the water content of the raw material coal, which is an example of the raw-material-coal characteristic information, may be calculated by the operation coefficient calculation part  840 , and the second preceding signal may be determined based on a product of the second reference preceding signal, the operation coefficient obtained by the operation coefficient calculation part  810  ( 810 A to  810 C), and the operation coefficient obtained by the operation coefficient calculation part  840 . Further, when the second preceding signal is determined in the second preceding signal operation part  620 , the change rate of the command value of the first parameter may be taken into consideration. More specifically, the change rate of the second preceding signal may be limited by the rate limits ( 860 ,  870 ) to be equal to or below a threshold (=second rate limit) which is determined based on the change rate of the command value of the first parameter (=table rotational speed command change rate, roller pressing force command change rate, air supply amount command change rate). 
     Then, the command value of the second parameter is generated based on the second preceding signal obtained in step S 16  (step S 18 ). 
     More specifically, a basic command value of the second parameter is calculated by the basic command value calculation part  610 , in accordance with the coal supply amount command, which sets the amount of coal supplied to the coal pulverizing apparatus  200 , and the second preceding signal obtained in step S 16  is added to the basic command value to calculate the command value of the second parameter. 
     Then, each part of the coal pulverizing apparatus  200  is controlled based on the command value of the first parameter obtained in step S 14  and the command value of the second parameter obtained in step S 18  (step S 20 ). 
     More specifically, in accordance with the command value of the first parameter, at least one of the table driving part  15 , the actuator  16 , or the damper  35  of the coal pulverizing apparatus  200  is controlled. Similarly, in accordance with the command value of the second parameter, the classifier driving part  24  of the coal pulverizing apparatus  200  is controlled. 
     According to the method shown in  FIG. 6 , it is possible to improve both response delay in the upstream process and response delay in the downstream process by preceding control of the first parameter and preceding control of the second parameter. Thus, it is possible to reduce the coal output delay in the coal pulverizing apparatus  200  as a whole. 
     Furthermore, since preceding control is performed on not only the second parameter but also the first parameter, it is possible to improve the coal output delay in the coal pulverizing apparatus while suppressing a reduction in classifying accuracy of the rotary classifier  20 . 
     Embodiments of the present invention were described in detail above, but the present invention is not limited thereto, and various amendments and modifications may be implemented. 
     REFERENCE SIGNS LIST 
     
         
           10  Pulverizer 
           11  Pulverizer housing 
           12  Table 
           13  Roller 
           15  Table driving part 
           16  Actuator 
           20  Rotary classifier 
           21  Classifier housing 
           22  Annular rotational portion 
           23  Annular stationary portion 
           24  Classifier driving part 
           25  Hopper 
           30  Air supply part 
           31  Air intake port 
           32  Air discharge port 
           33  Air chamber 
           34  Fan 
           35  Damper 
           50  Supply tube 
           51  Discharge tube 
           100  Coal-fired power plant 
           111  Inlet air flow rate meter 
           112  Inlet air thermometer 
           113  Outlet air thermometer 
           114  Coal supply amount meter 
           115  Coal supply thermometer 
           116  Furnace differential pressure gauge 
           117  Outlet pressure gauge 
           200  Coal pulverizing apparatus 
           300  Combustion device 
           301  Furnace 
           302  Burner 
           303  Heat exchanger 
           310  Steam turbine 
           320  Generator 
           330  Condenser 
           340  Water supply pump 
           400  Control device 
           500  First command value generation part 
           510  Basic command value calculation part 
           520  First preceding signal operation part 
           600  Second command value generation part 
           610  Basic command value calculation part 
           620  Second preceding signal operation part 
           700  First reference preceding signal calculation part 
           710  ( 710 A to  710 C) Operation coefficient calculation part 
           800  Second reference preceding signal calculation part 
           810  ( 810 A to  810 C) Operation coefficient calculation part