JP2018176123A - Method for manufacturing fine coal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably manufacturing fine coals by controlling drying conditions when pulverizing coals by a pulverization mill.SOLUTION: A method for manufacturing fine coals, in which firstly, a moisture value of a coal 6, which is inputted into a coal hopper 2, is determined, a moisture value of a coal to be supplied to a pulverization mill 1 is estimated from the determined moisture value, and a supply amount of coals from the coal hopper 2 to the pulverization mill 1 is determined by a load cell 10. A fuel gas amount of a gas burner 3 is feed-forward controlled based on the estimated moisture value and the supply coal amount, and on the other hand, a temperature of an exhaust gas discharged from the pulverization mill 1 is determined by a thermometer 11, and the fuel gas amount of the gas burner 3 is feedback-controlled so that the determined temperature of the exhaust gas falls within a prescribed temperature range.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing pulverized coal in which coal is pulverized by a pulverizing mill to produce pulverized coal.

  Pulverized coal is characterized in that it can be easily transported by an air flow transportation method and the flow rate can be easily controlled. Therefore, this pulverized coal is effectively used in various applications, such as blowing it from the tuyere of a blast furnace and using it as a fuel and a reducing agent, or using it as a fuel for a boiler or the like of a power plant.

  Conventionally, as a method for producing such pulverized coal, for example, a method as disclosed in Patent Document 1 is known. The disclosed technology relates to a control device and method of a coal crushing apparatus for producing pulverized coal to be supplied to a boiler or the like of a power plant, and hot air is sent to a crushing mill to which coal is supplied and obtained by the crushing mill. The proposed pulverized coal is dried using hot air, and then it is separated by gas-solid separation using a dust collector.

  In general, when it is intended to pulverize coal with such a pulverizer to obtain pulverized coal, it is important to make the moisture value of the manufactured pulverized coal equal to or less than a predetermined value. However, conventionally, there is no method for directly measuring the moisture value of the pulverized coal collected by the dust collector because of the configuration of the pulverizing apparatus, and even if the pulverized coal is periodically sampled to measure the moisture value, It takes time to determine the water content. Therefore, there is a problem that the moisture value of the pulverized coal actually measured can not be effectively used to control the temperature and amount of the hot air in the pulverizing apparatus.

  Therefore, in Patent Document 1, a control method of calculating the moisture value of pulverized coal to be discharged from various process values in a pulverizing mill for pulverizing coal, and correcting a mill temperature command value using this extracted moisture value of coal Is taken. Specifically, in order to suppress the insufficient drying of pulverized coal, the flow rates of combustion gas and air to the gas burner are changed so that the outlet temperature of the pulverizing mill (hereinafter referred to as mill outlet temperature) becomes constant. Control.

JP, 2014-117657, A

  Coal used for pulverized coal production generally has different moisture values depending on the brand. Therefore, the moisture value of coal supplied to the grinding mill usually fluctuates according to the change of the brand of coal and the change of the blending. In addition to that, when coal is piled in the open yard and crushed and dried, the water value differs between the top and the bottom of the pile piled in the yard, and the water value due to rainfall or sun drying In particular, when rainfall continues, a phenomenon such as a rapid change in water value is observed.

  5 (a) and 5 (b) respectively show one during rainfall and during fine weather when the flow rate of the fuel gas at the gas burner is subjected to PID control (feedback control) so as to keep the mill mill outlet temperature constant. An example of the trend of the mill outlet temperature for a day is shown. In fine weather (Fig. 5 (b)), control can be performed with a swing width of about 4 ° C against the target temperature set value of 93 ° C, but when it is raining (Fig. 5 (a)) It becomes large and has a fluctuation range of about 10 ° C at the maximum. This is considered to be because the feedback control for controlling the amount of fuel gas based on the mill outlet temperature could not sufficiently respond because the moisture value of the coal supplied from the coal hopper fluctuated significantly.

  In the method of manufacturing pulverized coal disclosed in Patent Document 1 which performs the same control, the moisture content of coal is calculated from various process values, and correction is performed using the moisture content of coal obtained by calculating the mill temperature command value. Is going. However, this method does not use the water value obtained by actually measuring the coal supplied to the grinding mill for correction. Moreover, in the case of this technology, the flow rate of the fuel gas in the gas burner is PID-controlled (feedback control) so as to keep the temperature at the milling mill outlet constant, so the moisture value of coal supplied to the milling mill rises sharply When this happens, there is a problem that the correction of the mill temperature command value based on the calculated moisture content of coal can not be made in time, and the mill outlet temperature will drop sharply.

  An object of the present invention is to propose a method for producing a stable pulverized coal by controlling drying conditions at the time of grinding of coal by a grinding mill.

  As a result of solving the above-mentioned problems of the prior art and earnestly researching to achieve the above object, the inventors have developed a novel method for producing pulverized coal described below. That is, according to the present invention, using a grinding mill equipped with a coal hopper, a gas burner and a dust collector, the coal supplied from the coal hopper is dried by high temperature gas from the gas burner and crushed by a grinding mill to obtain pulverized coal. In the method of producing pulverized coal obtained by forming and mixing the produced pulverized coal with the exhaust gas of high temperature gas and carrying it to a dust collector and separating the pulverized coal from the exhaust gas by the dust collector, first, coal fed to the coal hopper The water content of the coal is determined from the determined water content, the water content of the coal supplied to the grinding mill is estimated, and the amount of coal supply from the coal hopper to the grinding mill is determined, and the gas burner is Feed forward control of the amount of fuel gas, while the temperature of the exhaust gas discharged from the grinding mill is within a predetermined temperature range. Wherein the feedback control of the amount, is a manufacturing method of the pulverized coal.

In the method of producing pulverized coal according to the present invention configured as described above,
(1) The estimation of the moisture value of coal supplied to the grinding mill is based on the obtained moisture value of coal input to the coal hopper, tracking the movement of the coal input to the coal hopper within the coal hopper And by estimating the moisture value of the coal at the time of coal supply to the grinding mill,
Is considered to be a more preferable solution.

  In the method of producing pulverized coal according to the present invention, the moisture value of coal fed to the coal hopper is determined, and the moisture value of coal to be fed to the pulverizing mill is estimated from the determined moisture value, and the coal hopper to the pulverizing mill The feed amount is determined, and feedforward control is performed on the fuel gas amount of the gas burner based on the estimated moisture value and the feed amount, while the temperature of the exhaust gas discharged from the grinding mill is in a predetermined temperature range. Since the method of feedback control the amount of fuel gas in the burner, even if the moisture value of the coal supplied to the pulverizing mill increases or decreases, it is possible to suppress the rapid decrease of the mill outlet temperature and stably produce pulverized coal. be able to.

  Moreover, since the present invention is a method based on air flow transportation of pulverized coal, there is also an effect that adhesion to the pulverized coal transport piping can be suppressed, and a reduction in the amount of transportation can be suppressed.

It is a figure for demonstrating the structure of an example of the grinding mill which enforces the manufacturing method of the pulverized coal of this invention. It is a block diagram for demonstrating an example of the control method which considered the coal moisture value supplied to a crushing mill in the manufacturing method of the pulverized coal of this invention. In the manufacturing method of the pulverized coal of the present invention, it is a figure for explaining the tracking of the moisture value of the coal supplied from the coal hopper exit. (A)-(d) is a graph which respectively shows the effect of the control method which considered the coal moisture value supplied to a grinding mill in the manufacturing method of pulverized coal of this invention compared with a prior art example. (A), (b) is a graph which compares and shows the mill exit temperature in the time of fine weather and rainfall, respectively in the control method in the conventional manufacturing method of pulverized coal.

<About the grinding mill which carries out the present invention>
FIG. 1 is a figure for demonstrating the structure of an example of the grinding mill which enforces the manufacturing method of the pulverized coal of this invention. In the example shown in FIG. 1, the grinding mill 1 is provided with a coal hopper 2, a gas burner 3 and a dust collector 4. Further, 5 in the figure is a belt conveyor for transporting the coal 6, and 7 in the figure is a moisture meter for measuring the moisture value of the coal 6. Furthermore, 8 in the figure is a feeder which supplies coal 6 from the coal hopper 2 to the grinding mill 1. Furthermore, 9 in the figure is pulverized coal to be manufactured, 10 in the figure is a load cell, and 11 in the figure is a thermometer.

  In the grinding mill 1 shown in FIG. 1, coal 6 which is a raw material is introduced into the coal hopper 2 by the belt conveyor 5. At that time, the moisture value of the coal 6 is measured by the moisture meter 7 in the middle of the belt conveyor 5. The moisture meter 7 is preferably a non-contact moisture meter such as an infrared moisture meter.

  The weight (the amount of coal supply) of the coal 6 input to the coal hopper 2 can be measured by the load cell 10 installed in the coal hopper 2. Further, the amount of coal supply may be measured by installing a conveyor scale on the belt conveyor 5 that transports the coal 6 to the coal hopper 2.

  At the lower part of the coal hopper 2, a coal feeder 8 is installed, and coal 6 is supplied from the coal hopper 2 to the grinding mill 1 via the coal feeder 8. As the coal feeder 8, an apparatus such as a chain conveyor or a screw conveyor that can adjust the supply amount of the coal 6 to the grinding mill 1 can be used. The high temperature gas is supplied from the gas burner 3 to the pulverizing mill 1, and the exhaust gas is sent to the dust collector 4 together with the dried pulverized coal 9, and the dust collector 4 separates and recovers the pulverized coal. Therefore, it is preferable to use a closed type coal feeder 8.

  In the grinding mill 1 where the use of a roller mill or the like is preferable, grinding of the supplied coal 6 is performed. At this time, the high temperature gas of the gas burner 3 is simultaneously supplied into the pulverizing mill 1. Therefore, the coal 6 is crushed and dried by being dried by the high-temperature gas while being crushed by the crushing mill 1. The pulverized coal 9 after drying is discharged upward from the inside of the grinding mill 1 in a state accompanied by the exhaust gas of the high temperature gas. The pulverized coal 9 and the exhaust gas are gas-solid separated by the dust collector 4, and the pulverized coal 9 is sent to a pulverized coal hopper installed below the dust collector 4. The exhaust gases are then dissipated to the atmosphere.

<About the control method of the present invention in a grinding mill>
In the method for producing pulverized coal according to the present invention, first, the moisture value of the coal 6 to be fed to the coal hopper 2 in the grinding mill is determined. Then, the moisture value of the coal supplied into the pulverizing mill 1 is estimated based on the determined moisture value. On the other hand, the amount of coal supplied from the coal hopper 2 to the crushing mill 1 is determined as the amount of coal supply by the load cell 10, and the amount of fuel gas of the gas burner 3 is feedforward controlled based on the estimated water value and the determined amount of coal supply. Do. At the same time, the temperature of the exhaust gas discharged from the pulverizing mill 1 is determined by the thermometer 11, and the amount of fuel gas of the gas burner 3 is feedback controlled so that the determined temperature of the exhaust gas falls within the predetermined range. .

  The feature of the present invention is to calculate the temperature of the exhaust gas discharged from the pulverizing mill 1 and add the amount of fuel gas of the gas burner 3 to feedback control so as to maintain the calculated temperature of the exhaust gas within a predetermined temperature range. The moisture value of the coal 6 fed to the coal hopper 2 is determined, the moisture value of the coal supplied to the pulverizing mill 1 is estimated from the determined moisture value, and the amount of coal supplied from the coal hopper 2 to the pulverizing mill 1 The point is that feedforward control is performed on the fuel gas amount of the gas burner 3 based on the estimated water content and the determined coal feed amount.

  In the present invention, as the moisture value of coal used for feed forward control, the data of the moisture value of coal 6 fed to the coal hopper 2 is not used as it is, but the coal 6 fed to the coal hopper 2 The moisture value is determined, and the moisture value obtained by estimating the moisture value of the coal supplied to the grinding mill 1 from the determined moisture value is used. The reason is that if the water content of the coal 6 just before being supplied to the grinding mill 1 can be measured, accurate control is possible. However, since the coal hopper 2, the coal feeder 8 and the grinding mill 1 are all sealed in structure, they can not be measured individually. Therefore, the water value of the coal 6 to be fed to the coal hopper 2 that can be actually measured is determined. And in this invention, the moisture value of coal supplied to the grinding mill 1 is estimated from the calculated | required moisture value, feedforward control is performed based on the estimated moisture value, and correction | amendment of a moisture value is tried.

<Concrete control method>
Hereinafter, a specific control method in the method for producing pulverized coal of the present invention will be described.
FIG. 2 is a block diagram for explaining an example of a control method in consideration of a coal moisture value supplied to a grinding mill in the method for producing pulverized coal according to the present invention. In FIG. 2, the amount of coal supplied from the coal 6 supplied to the grinding mill 1 and the water content of the coal 6 estimated based on the actually measured water value of the coal 6 charged to the coal hopper 2 The fuel gas flow rate to be corrected for drying is determined (feed forward control), while the target value of the mill outlet temperature of the exhaust gas from the grinding mill 1 is set by the temperature setting device, in contrast to the actual mill outlet temperature Is measured, and PID control (feedback control) is performed to make the difference 0. This makes it possible to determine the target fuel gas flow rate supplied to the gas. In addition, the actual fuel gas flow rate is measured by a flow meter, and the opening degree of the fuel gas flow control valve is controlled so that this matches the target fuel gas flow rate.

  By performing such control, even if the coal supply amount of coal 6 supplied to the pulverizing mill 1 is the same, when the water value of the coal 6 changes, the change of the fuel gas amount according to this is feed forward The required fuel gas correction can then be made before the mill outlet temperature changes.

  In this point, conventionally, since the moisture value of coal 6 was not measured, it is not possible to accurately control the change of the required fuel gas amount due to the difference in moisture value even with the same amount of coal feeding, and the dry state in the grinding mill Was unstable. That is, conventionally, since the fuel gas flow rate was corrected after detecting that the mill outlet temperature has changed, a time lag has necessarily occurred. In this respect, the application of the present invention makes it possible to correct the fuel gas flow rate at the time of coal supply, and to minimize the change in the drying condition in the grinding mill.

<About estimation method by tracking of moisture value of coal>
As described above, it is desirable to measure the moisture value of the coal 6 between the feeding machine 8 supplied from the coal hopper 2 to the grinding mill 1 to the grinding mill 1. However, since this part needs to be in a sealed structure as described above, it is difficult to continuously measure the moisture value accurately at such a part. Therefore, in the present invention, the coal 6 input to the coal hopper 2 is sequentially measured for each predetermined amount, and the process of moving the predetermined amount of coal 6 in the coal hopper 2 is tracked, and the supply from the coal hopper 2 is performed. The water value at the time of being supplied to the grinding mill 1 through the coal machine 8 is estimated, and the estimated value of the water is used for feedforward control.

  FIG. 3 is a view for explaining tracking of a moisture value of coal supplied from a coal hopper outlet in the method for producing pulverized coal of the present invention. Hereinafter, with reference to FIG. 3, the method of determining the moisture value of coal 6 to be fed to the coal hopper 2 in the present invention and estimating the moisture value of coal supplied to the grinding mill 1 from the determined moisture value will be described. Do.

  As shown in FIG. 3, the coal 6 which has been fed into the coal hopper 2 by a predetermined amount sequentially deposits from the lower part of the coal hopper 2 as coal having a moisture value of a, b, c. Here, when the coal 6 is supplied to the grinding mill 1 by the coal feeder 8 from the lower part of the coal hopper 2, the water value of the coal 6 supplied first is a, and the water value of the next coal is Is b, and so on. However, it is expected that the coal 6 fed into the coal hopper 2 will not deposit in a flat layer form as shown in FIG. 3 but will deposit in a chevron shape with a peak at the feeding position. On the other hand, it is conceivable that the coal 6 directly above the feeder 8 also descends and is discharged by funnel flow from the lower part of the coal hopper 2 by the feeder 8. Therefore, the moisture value M of the coal 6 discharged from the coal hopper 2 can be calculated as shown in the following formula (1).

  In addition, what multiplied the coefficient to the moisture value for n pieces of coal 6 of the predetermined amount which has moved to the lower part of the coal hopper 2 at the time is considered as an estimated moisture value.

  Here, the above-mentioned predetermined amount can be appropriately set according to the size of the coal hopper 2 but may be set to about 2 to 8% of the capacity of the coal hopper 2. For example, if the capacity of the coal hopper 2 is 20 t, it is about 400 kg to 1.6 t. In addition, the value of n is about 3 to 8, that is, the predetermined amount of coal moved to the lowermost part of the coal hopper 2 is taken as the first piece, and thereafter to the predetermined amount of coal up to the n th The sum of the values obtained by multiplying the coal moisture value of the predetermined amount by the coefficients ka to kn is calculated and estimated as the moisture value M of the coal 6 currently supplied from the coal hopper 2 to the grinding mill 1. At this time, the coefficients are given such that the sum of the coefficients from ka to kn is 1.

  This coefficient can be determined as appropriate depending on the size and shape of the coal hopper 2 and the position and shape of the opening to be discharged to the coal feeder 8, but for convenience, charging of the coal 6 to the coal hopper 2 and feeding can be performed offline. It is possible to discharge from the coal machine 8 and measure the moisture value of the discharged coal 6 to determine it from the moisture value of the input coal and the moisture value of the discharged coal.

<About the effect of the present invention>
FIGS. 4 (a) to 4 (d) are graphs showing the effects of the control method in consideration of the moisture content of coal supplied to the pulverizing mill in the method of producing pulverized coal according to the present invention in comparison with the prior art. In the graphs shown in each of FIGS. 4 (a) to 4 (d), the change in the data for one day when control of the mill outlet temperature using coal moisture value is not performed according to the prior example is shown in the left half. The change in one day's data is shown in the right half when control of the mill outlet temperature is performed in consideration of the coal moisture value according to the example. In the present embodiment, as shown in FIG. 4D, the amount of coal feeding supplied to the grinding mill 1 is assumed to be constant throughout the day.

  From FIGS. 4 (a) to 4 (d), when control of the grinding mill outlet temperature using coal moisture value is not performed according to the prior art, only control (feedback control) to change the M gas flow rate based on the grinding mill outlet temperature Therefore, the change in the M gas flow rate controlled as shown in FIG. 4C does not follow the change in the amount of coal moisture actually measured as shown in FIG. 4A, as shown in FIG. 4B. It can be seen that the temperature at the outlet of the grinding mill fluctuates significantly due to the fluctuation of the moisture content of the coal. On the other hand, when control of the grinding mill outlet temperature in consideration of the coal moisture value is carried out according to the example of the present invention, control of changing the M gas flow rate based on the grinding mill outlet temperature together with control based on fluctuation of the coal moisture value (feed forward control) In order to carry out (feedback control), the change in the M gas flow rate controlled as shown in FIG. 4C follows the change in the amount of coal moisture actually measured shown in FIG. As shown in), it can be seen that the temperature at the outlet of the grinding mill does not significantly fluctuate due to the fluctuation of the moisture content of the coal.

  According to the method of the present invention for producing pulverized coal, even when the moisture value of coal supplied to the pulverizing mill increases or decreases, the rapid reduction of the mill outlet temperature can be suppressed, and the pulverized coal can be stably produced. The pulverized coal produced according to the present invention can be applied to various applications such as blowing from the tuyere of a blast furnace to be used as a fuel and a reducing agent, or used as a fuel in a boiler or the like of a power plant.

Reference Signs List 1 grinding mill 2 coal hopper 3 gas burner 4 dust collector 5 belt conveyor 6 coal 7 moisture meter 8 coal feeder 9 pulverized coal 10 load cell 11 thermometer

Claims (2)

The coal supplied from the coal hopper is dried by the high temperature gas from the gas burner using a grinding mill equipped with a coal hopper, a gas burner and a dust collector, and pulverized by a grinding mill to produce pulverized coal, and the pulverized powder produced In a method of producing pulverized coal, coal is carried along with exhaust gas of high temperature gas and carried to a dust collector, and pulverized coal is separated from exhaust gas by the dust collector,
First, the moisture value of coal fed into the coal hopper is determined, the moisture value of coal supplied to the pulverizing mill is estimated from the determined moisture value, and the amount of coal supply from the coal hopper to the pulverizing mill is determined, and the estimated moisture Feed-forward controls the amount of fuel gas in the gas burner based on the value and amount of coal supply, and feedback controls the amount of fuel gas in the gas burner so that the temperature of the exhaust gas discharged from the grinding mill falls within a predetermined temperature range A method of producing pulverized coal characterized by   The estimation of the moisture value of the coal supplied to the grinding mill is based on the moisture value of the coal input to the coal hopper, tracking movement in the coal hopper of the coal input to the coal hopper, and crushing The method for producing pulverized coal according to claim 1, wherein the method is carried out by estimating the moisture value of coal at the time of coal supply to the mill.

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