JP6452062B2 - Powder flow rate measuring apparatus and powder flow rate measuring method - Google Patents

Description

  The present invention relates to a powder flow rate measuring apparatus and a powder flow rate measuring method, and more specifically, a capacitance type powder flow rate for measuring a powder flow rate by measuring a change in capacitance of the powder. The present invention relates to a measuring apparatus and a powder flow rate measuring method.

Conventionally, for example, as a means for measuring powder such as pulverized coal blown into a gasification furnace, a powder flow rate measuring device has been used. As a method for measuring the powder flow rate using the powder flow rate measuring device, for example, the density (t / m ³ ) and the flow velocity (m / s) of the powder are measured, and these are disconnected from the tube into which the powder is blown. There is a method of obtaining the flow rate (t / s) of the powder by multiplying the area (m ² ). Here, methods for measuring the density or flow velocity of the powder include a capacitance type in which the flow rate of the powder is measured by measuring a change in capacitance, and a powder in the tube from a transmission or reflection signal of microwaves. A microwave method for determining the density of the body is known.

  However, in the microwave type, since the microwave is passed through the sensor pipe (pipe), it is necessary to make the thickness thin, and the pressure of the carrier gas cannot be increased. Further, when the output of the microwave is increased, the object to be measured may have heat. Therefore, the microwave type is not suitable for use when the pressure in the pipe line is high like a coal gasifier. Therefore, a capacitance type is used as a method for measuring the density or flow velocity of powder when the pressure in a pipe such as a coal gasifier is high.

  FIG. 1 is a block diagram showing a capacitance measuring means 1 in a conventional capacitance type powder flow measuring device. The capacitance measuring means 1 includes an AC signal oscillator 2, an analog measurement sensor 3, an analog reference sensor 4, amplifiers 6 and 7, and a differential amplifier 8. The AC signal oscillator 2 is connected in parallel with a bridge circuit including a measurement sensor 3, a reference sensor 4, and resistors 5a to 5c. The measurement sensor 3 and the reference sensor 4 are connected to amplifiers 6 and 7, respectively, and the amplifiers 6 and 7 are connected to a differential amplifier 8. In addition, the capacitance measuring means 1 includes a powder data detection amplifier 9 connected to the differential amplifier 8 and an LPF 10 connected to the powder data detection amplifier 9.

  The conventional electrostatic capacity type powder flow rate measuring device accurately measures the electrostatic capacity by using, for example, a two-sensor system in which the electrostatic capacity measuring means 1 is provided at two locations upstream and downstream of the pipeline. . Specifically, using the average value of the capacitance measured by one or both of the two capacitance measuring means 1 as the density of the powder, from the correlation of the change in capacitance measured upstream and downstream The flow rate of the powder is obtained. In this case, the capacitance measuring means 1 uses a reference sensor 4 such as a reference capacitor in order to cancel a specific capacitance such as a pipe line when measuring the capacitance.

  However, in the conventional electrostatic capacitance type powder flow rate measuring device, the reference sensor 4 is installed separately from the measurement sensor 3 and separately piped to flow a carrier gas such as powder and air. There is a problem of increasing costs and cost. Furthermore, there is a case where there is not enough room for the installation of the reference sensor 4, and there is a problem that it is difficult to realize a compact apparatus.

  Further, the capacitance (specific capacitance) of the capacitance type measurement sensor is about pF, whereas the capacitance due to the powder is about several fF to several hundred fF. Therefore, there is a problem that when the gain of the AC amplifier is increased in order to accurately measure the capacitance of the powder, the amplifier is saturated.

  As a means for solving these problems, a technique is known in which a reference value setting calculation unit is provided for setting a reference value based on the capacitance indicated by the carrier gas before the powder flows through the pipeline, and a reference sensor is not required. (For example, Patent Document 1).

Japanese Patent No. 4762224

  However, in the technique of Patent Document 1 using an analog element, since the reference value setting calculation unit is provided instead of the reference sensor 4, there is a problem that the number of parts of the apparatus has not yet been reduced. Furthermore, in the technique of Patent Document 1, since the difference between the measured capacitance value and the set reference value is taken, if the reference value includes an error, the magnification of the subsequent differential amplifier or the like is usually 1000 times or more. Therefore, there is a problem that the error exceeds the allowable error.

  In addition, when a capacitance measuring digital device is used, it is difficult to accurately measure the flow velocity due to the limitation of the sampling time, and there is a problem that it can be used only for a system with a low flow velocity.

  The present invention has been made in view of the above points, and by reducing the number of parts by eliminating the need for a reference capacitor (reference value), it is possible to suppress a decrease in measurement accuracy due to an error in the reference value. An object of the present invention is to provide a powder flow rate measuring device and a powder flow rate measuring method that can be used.

  In order to achieve such an object, the present invention is characterized by having the following configuration.

Powder flow rate measuring apparatus of the present invention is a powder flow rate measuring apparatus of the electrostatic capacity type for measuring the powder flow rate by which the particles to measure the change in capacitance flows conduit, density Density determination capacitance measuring means for measuring a signal corresponding to the capacitance in the pipe using the determination AC voltage source, powder density calculation means for calculating the powder density from the measured signal, The first flow rate determination AC voltage source and the second flow rate determination AC voltage source having a frequency higher than that of the density determination AC voltage source are used to generate a predetermined electrostatic force from a signal corresponding to the capacitance in the pipe. powder flow rate based first and second flow rate determination capacitance measuring means for measuring and amplifying the change in the electrostatic Den'yo amount of powder to offset the capacitive component, the correlation between the variation of measurement And a powder flow rate calculation means for calculating the powder flow rate from the powder density and the powder flow rate. Characterized in that it obtain.

The powder flow rate measuring method of the present invention is a capacitance type powder flow rate measuring method for measuring a powder flow rate by measuring a change in capacitance in a pipeline through which powder flows. The step of measuring the capacitance in the pipe using the AC voltage source for density measurement, the step of calculating the powder density from the measured signal , and the first having a higher frequency than the AC voltage source for density measurement flow rate using a measuring alternating voltage source and the second flow rate determination AC voltage source, it is offset a predetermined electrostatic capacity of a signal corresponding to the capacitance in the conduit of the static Den'yo amount of powder A step of amplifying and measuring the change, a step of calculating the powder flow rate based on the measured correlation of each change, and a step of calculating the powder flow rate from the powder density and the powder flow rate And

  Here, the amount of offset need not be exactly equal to the intrinsic capacitance.

  As described above, according to the powder flow rate measuring device and the powder flow rate measuring method of the present invention, the number of parts is reduced by eliminating the need for a reference capacitor (reference value), and the measurement accuracy due to an error in the reference value. Can be suppressed.

It is a block diagram showing the electrostatic capacitance measurement means in the conventional powder flow rate measuring apparatus. It is a block diagram showing the pulverized coal supply system using the powder flowmeter which concerns on Embodiment 1 of this invention. It is a block diagram showing a mode that the powder flow rate measuring apparatus which concerns on Embodiment 1 of this invention was installed. It is a block diagram showing the detail of the powder flow rate measuring apparatus which concerns on Embodiment 1 of this invention. It is a graph which shows the method of measuring the flow rate of the conventional powder. It is a graph which shows the method of measuring the flow rate of the powder which concerns on Embodiment 1 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1]
FIG. 2 is a configuration diagram illustrating a pulverized coal supply system 21 using the powder flow rate measuring apparatus according to the first embodiment of the present invention. The pulverized coal supply system 21 of the present embodiment includes a pulverized coal bottle 22, a lock hopper 23, a load cell 24, a main powder flow meter 25, a branch powder flow meter 26, and a gasifier 27. I have.

  A lock hopper 23 is connected to the pulverized coal bin 22 via a main coal supply pipe 28, and a load cell 24 is installed in the lock hopper 23. The lock hopper 23 is connected to the gasifier 27 via a main coal supply pipe 28 and a plurality of branch coal supply pipes 29 branched in parallel from the main coal supply pipe 28. A main powder flow meter 25 is connected to a main coal supply pipe 28 between the lock hopper 23 and a branch coal supply pipe 29. A branch powder flow meter 26 is connected to each of the plurality of branch coal supply pipes 29.

  High-pressure nitrogen gas 30 is supplied into the coal supply pipes 28 and 29 and circulates toward the gasification furnace 27. The pulverized coal in the coal supply pipes 28 and 29 is gasified by the high-pressure nitrogen gas. It is conveyed toward.

  The pulverized coal bin 22 stores pulverized coal. The lock hopper 23 temporarily stores pulverized coal and cuts it into a predetermined amount. The load cell 24 measures the weight of the lock hopper 23 and the weight of the pulverized coal inside thereof. The main powder flow meter 25 and the branch powder flow meter 26 are examples of a powder flow rate measuring apparatus, and measure the flow rate of the powder flowing through the main tube or the branch pipe. The gasifier 27 gasifies the pulverized coal supplied into the gasifier.

  Next, the operation | movement which blows in the pulverized coal of the pulverized coal supply system 21 of this embodiment is demonstrated.

  First, the pulverized coal in the pulverized coal bottle 22 is temporarily stored in the lock hopper 23 through the main coal supply pipe 28, cut into a predetermined amount therefrom, and further, the main coal supply pipe 28. It is distributed to each coal supply pipe 29 of the branch pipe. The distributed pulverized coal is blown into the gasification furnace 27 through each coal supply pipe 26 of the branch pipe. Further, the measured value by the load cell 24 and the measured value by the main powder flow meter 25 or the branch powder flow meter 26 are compared to adjust the flow rate of powder in the main pipe or branch pipe.

  FIG. 3 is a configuration diagram illustrating a state in which the main powder flow meter 25 according to the first embodiment of the present invention is installed. The powder flow meter 26 of the branch pipe can be configured similarly. The main powder flow meter 25 includes a density measurement sensor electrode 33 and two flow velocity measurement sensor electrodes 35 and 36 connected to a sensor pipe (pipe) 31. The density measurement sensor electrode 33 is provided between the two flow velocity measurement sensor electrodes 35 and 36. The density measurement sensor electrode 33 connected to the sensor pipe 31 and the two flow velocity measurement sensor electrodes 35 and 36 are covered with a cast iron shield 37, and the density measurement sensor electrode 33 is covered with the cast iron shield 37. A control BOX 39 for controlling the two flow velocity measuring sensor electrodes 35 and 36 is connected. The control BOX 39 and each sensor are connected by two lead wires.

  In the present embodiment, the sensor pipe 31 is made of a reinforced resin such as glass epoxy, the inner diameter is φ13.0 mm, and the outer diameter is φ16.5 mm. Further, the density measuring sensor electrode 33 and the two flow velocity measuring sensor electrodes 35 and 36 are made of a good conductor such as a copper foil, and each lead wire attached to the electrode has a diameter of a single Junflon wire of φ0.6 to 0.8 mm.

  In the main powder flow meter 25 of the present embodiment, the pulverized coal as the object to be measured passes through the inside of the sensor pipe (pipe) 31. The sensor electrode 33 for density measurement and the sensor electrodes 35 and 36 for flow velocity measurement are opposed to each other with the sensor pipe 31 interposed therebetween, and a carrier signal voltage generated by an oscillator is applied to the sensor pipe 31 via each lead wire. An alternating current generated by the carrier signal voltage flows through each lead wire, and this alternating current is amplitude-modulated in accordance with a change in capacitance due to a change in the flow rate of pulverized coal. The alternating current amplitude-modulated according to the electrostatic capacity is taken into the control BOX 39 through each lead wire. As will be described in detail with reference to FIG. 4, a density determination capacitance measuring unit, two flow rate determination capacitance measuring units, and a control unit are mounted inside the control BOX 39. The operation of the main powder flow meter 25 of this embodiment will be described in detail with reference to FIG.

  FIG. 4 is a configuration diagram showing details of the powder flow meter 25 according to the first embodiment of the present invention. The powder flow meter 26 of the branch pipe can be configured similarly. In the powder flow meter 25 according to the first embodiment of the present invention, a density determination capacitance measuring means 43 is connected to a sensor pipe (pipe) 41, and the density determination capacitance measuring means 43 is further connected to the pipe 41. Two capacitance measuring means 45 and 46 for determining the flow velocity are connected to each other. The portion of the pipeline 41 to which the sensor of each measuring means is connected is covered with an electromagnetic shield 47 to electromagnetically shield each sensor from the outside air, thereby reducing the influence on the capacitance due to the humidity of the outside air. Yes. A control means 49 is connected to each of the density determination capacitance measuring means 43 and the two flow velocity determination capacitance measurement means 45 and 46.

  The density determination capacitance measuring means 43 is provided with a density measurement sensor (electrode) 51 and a capacitance measuring device 52 connected to each other. The density measuring sensor (electrode) 51 is composed of a pair of electrodes disposed to face the outer surface of the conduit 41. In the present embodiment, a belt-like shape is used. The capacitance measuring device 52 uses, for example, a digital 24-bit type capacitance measuring device manufactured by Analog Devices.

  The flow rate determination capacitance measuring means 45 includes a flow rate measurement sensor (electrode) 53, an AC amplifier (AC amplifier) 54 that is an AC amplifier, a rectifier 55, a low-pass filter (LPF) 56, and a DC amplifier. A certain DC amplifier (DC amplifier) 57 and an analog-digital converter (AD converter) 58 are connected in series. Further, the flow velocity determination capacitance measuring means 45 includes an oscillator 59. Although not shown in the figure, the output of the oscillator 59 is connected to the electrode 53. The flow velocity determining capacitance measuring means 46 also includes the same components as the flow velocity determining capacitance measuring means 45. Each of the flow rate measuring sensors (electrodes) 53 of the capacitance measuring means 45 and 46 for determining the flow rate is composed of a pair of electrodes installed facing the upstream and downstream outer surfaces through which the powder of the pipe 41 flows, In the present embodiment, a strip shape is used. In addition, the shape of each electrode 51 and 53 can be made into the shape of a spiral or the shape of a comb, for example. When the electrode is shaped like a comb, the tip of the electrode is sharpened because the effective area of the electrode is reduced due to the skin effect when the carrier frequency is increased, so that the skin effect is less likely to occur.

  Here, if an AC voltage is applied to each sensor with an oscillation source having the same frequency, the sensors are subject to interference with each other, which may cause an error in measuring the capacitance. Therefore, conventionally, the density measuring sensor (electrode) 51 and each flow velocity measuring sensor (electrode) 53 must be separated and installed in the pipe 41, and as a result, the total length of the powder flow meter 25 is long. It was. However, in this embodiment, since the frequency of the AC voltage oscillation source differs between the density measurement sensor 51 and each flow velocity measurement sensor 53, the density measurement sensor 51 and each flow velocity measurement sensor 53 have almost no interference. You do n’t have to.

  Accordingly, each flow velocity measuring sensor 53 can be installed upstream and downstream of the pipe 41 with the density measuring sensor 51 interposed therebetween, thereby ensuring the distance between the respective flow velocity measuring sensors 53 and the powder flow rate. The total 25 can be made compact.

  The AC amplifier 54 arbitrarily sets the gain value within a predetermined range. The rectifier 55 rectifies the amplitude-modulated carrier signal, and the LPF 56 has a predetermined cutoff frequency. The DC amplifier 57 arbitrarily sets an offset value and a gain value within a predetermined range. The AD converter 58 converts the output value of the DC amplifier 57 into a digital value and transmits it to the control means 49.

  The oscillator 59 generates a carrier having a predetermined frequency (1 MHz or more). Further, the oscillator 59 can amplitude-modulate the carrier signal by a change in capacitance due to a change in powder density. Here, in order to improve the accuracy of the flow velocity measurement, it is important to increase the frequency of the carrier signal to about 1 MHz. However, when the frequency is increased, there is a problem that the detection effect per electrode area decreases due to the skin effect. Therefore, in this embodiment, high measurement accuracy is not necessary for the flow rate determination and it is not necessary to amplify the flow rate greatly. Therefore, the gain of the AC amplifier 54 that amplifies the amplitude-modulated wave is set to a low value. In this embodiment, the detection effect per electrode area is maximized by making the electrode shape, for example, a comb tooth shape.

  The control means 49 includes powder density calculation means 61, flow velocity calculation means 62, flow rate calculation means 63, offset value setting means 64, and gain setting means 65. The powder density calculation means 61 inputs the measurement value from the capacitance measuring device 52 of the density determination capacitance measurement means 43 and outputs the calculated value to the flow rate calculation means 63. The flow velocity calculation means 62 receives the measurement values from the AD converters 58 of the flow velocity determination capacitance measuring means 45 and 46 and outputs the calculated values to the flow rate calculation means 63. Specifically, the flow velocity calculation means 62 determines that the powder reaches the downstream flow velocity measurement sensor (electrode) 53 from the upstream flow velocity measurement sensor (electrode) 53 from the correlation between the upstream and downstream capacitance changes. The time is calculated. The flow rate calculation means 63 calculates the flow rate by multiplying the measurement results of the density and flow velocity. The offset value setting means 64 is connected to the DC amplifier 57 of each of the flow rate determination capacitance measuring means 45 and 46, and appropriately sets the offset value. In the present embodiment, the offset value is set to a value approximately equal to the intrinsic capacitance of the pipeline 41. The gain setting means 65 is connected to the AC amplifier 54 and the DC amplifier 57 of each of the flow velocity determination capacitance measuring means 45 and 46, and appropriately sets the gain value. The offset value setting means 64 and the gain setting means 65 can automatically set the offset value and gain of the DC amplifier 57 and the gain of the AC amplifier 54.

  In the present embodiment, the density measuring sensor 51 is installed between the two flow velocity measuring sensors 53 of the pipe line 41, but the density measuring sensor 51 is provided outside the flow velocity measuring sensors 53. Can also be installed.

  Next, the operation of the main powder flow meter 25 of the present embodiment will be described.

  First, a method of measuring the capacitance proportional to the density of the powder by the density determination capacitance measuring means 43 will be described. When powder such as pulverized coal is blown into the pipe 41 together with the nitrogen gas 30, the density measuring sensor 51 uses the pipe 41 and the powder as an interelectrode substance, and the intrinsic capacitance and powder of the pipe 41. The total value of the electrostatic capacitance is detected. The capacitance measuring device 52 directly measures the total value of the detected inherent capacitance of the pipeline 41 and the capacitance of the powder, and outputs the total value to the powder density calculating means 61 of the control means 49. By directly measuring the total value, installation of a reference capacitor for comparison can be eliminated. As a result, the number of parts can be greatly reduced.

  Next, a method for measuring the flow rate by the flow rate determination capacitance measuring means 45 and 46 will be described. The flow rate determination capacitance measuring means 45 and 46 measure the capacitance of the powder with a flow rate measurement sensor (electrode) 53 installed upstream and downstream of the density measurement sensor 51, and the correlation between the two electrodes is obtained from the correlation. Measure the transit time of the powder.

  First, the oscillator 59 generates a carrier signal for detecting a change in capacitance. When a carrier signal voltage generated between the electrodes of the flow velocity measuring sensor 53 is applied, an alternating current flows through the flow velocity measuring sensor 53. When a powder such as pulverized coal is blown into the pipe 41 together with the nitrogen gas 30 after the voltage is applied, the flow velocity measuring sensor 53 is connected between the electrodes of the flow velocity measuring sensor 53 according to the change in the density of the powder. The dielectric constant changes and the capacitance of the powder changes. As a result, the amplitude of the alternating current flowing through the flow velocity measuring sensor 53 changes according to the change in capacitance of the powder. As described above, by amplitude-modulating the carrier signal according to the change in the electrostatic capacity of the powder due to the change in the powder density, a signal corresponding to the density of the powder can be measured.

  The AC amplifier 54 amplifies the carrier signal that has been amplitude-modulated in order to increase the detection accuracy. At this time, in order to improve the measurement accuracy and accurately measure the powder density, since the change in the capacitance of the powder is small, it is necessary to greatly amplify the modulated component. However, since the intrinsic capacitance of the conduit 41 is larger than that of the powder, the AC amplifier 54 is saturated immediately when the gain is increased to amplify the modulated component. However, for measuring the flow velocity, it is only necessary to know the correlation between changes in capacitance, so that high measurement accuracy is not necessary. Therefore, since it is not necessary to increase the gain, the gain setting means 65 sets the amplification gain to a low value so that the AC amplifier 54 is not saturated.

  Here, when detecting for density determination, if the gain is increased by the AC amplifier 54 and the resolution (change amount) is not increased, the resolution is not increased even if the gain is increased by the DC amplifier 57 after passing through the LPF 56. The noise component is amplified without increasing. On the other hand, when detecting for obtaining the flow velocity, it is only necessary to calculate the time difference between the values (waveforms) detected upstream and downstream, so there is no need to increase the resolution so much. Therefore, in this embodiment, there is no need to increase the gain of the AC amplifier 54. Thus, saturation of the AC amplifier 54 can be prevented by setting the gain of the AC amplifier 54 to a low value. This eliminates the need for a reference capacitor for comparison.

  The rectifier 55 rectifies the amplified signal. The LPF 56 removes the high frequency component due to the carrier signal from the rectified signal, and extracts only the component whose capacitance changes in proportion to the density of the powder.

  Thereafter, the offset value setting means 64 sets the offset value to a value approximately equal to the intrinsic capacitance of the pipeline 41 so that the DC amplifier 57 does not saturate, and the DC amplifier 57 calculates the change in the extracted capacitance. Amplify with proper gain. The AD converter 58 converts the analog output of the DC amplifier 57 into a digital value and transmits the digital value to the flow velocity calculation means 62 of the control means 49.

  Measurement of the change in electrostatic capacitance of the powder in the flow rate measurement method of the present embodiment will be further described with reference to FIG.

  Next, a method for measuring the powder flow rate by the control means 49 will be described. The powder density calculating means 61 removes the intrinsic capacitance of the pipeline 41 from the total value of the measured intrinsic capacitance of the pipeline 41 and the capacitance of the powder, and electrostatic capacity proportional to the density of the powder. The capacity is obtained, and the powder density is calculated by an internal table based on this capacitance. Based on the transmitted digital value, the flow velocity calculation means 62 takes time until the powder reaches the downstream flow velocity measurement sensor 53 from the upstream flow velocity measurement sensor 53 due to the correlation between the upstream and downstream capacitance changes. And the flow rate of the powder is calculated by dividing the distance between the two sensors. The flow rate calculation means 63 calculates the powder flow rate by multiplying the calculated powder density, the calculated powder flow velocity, and the cross-sectional area of the pipe 41.

  The measurement of the change in capacitance of the powder in the flow rate measurement method of the present embodiment described above will be described in comparison with the conventional measurement.

  5 (a) to 5 (d) are graphs showing the measured values of the electrostatic capacity of the conventional powder flow rate. Conventionally, in FIG. 5 (a), the total value of the capacitance of the conduit and the powder due to the change in the density of the powder between the electrodes of the sensor for measuring the flow velocity by the upstream sensor for measuring the flow velocity ( A value obtained by subtracting a reference value B corresponding to the inherent capacitance of the pipeline from the measured value A) is measured by a bridge circuit. In FIG. 5B, the gain is increased as much as possible by an amplifier, and the value obtained by subtracting the reference value B from the measured value A is amplified. In FIG. 5C, the amplified signal is rectified by a rectifier circuit. In FIG.5 (d), the high frequency component by a carrier signal is removed from the rectified signal by LPF, and the change in electrostatic capacitance of the powder is extracted. In the same manner as described above, the change in electrostatic capacity of the powder is measured by the downstream flow rate measuring sensor. Calculate the passage time of the powder between the two electrodes based on the correlation between the measured capacitance changes of the upstream and downstream powders, and divide the distance between the two electrodes by the calculated passage time. Is calculated.

  6 (a) to 6 (d) are graphs showing measured values of the flow rate of the powder according to Embodiment 1 of the present invention. In the main powder flow meter 25 according to this embodiment, the density of the powder between the electrodes of the flow velocity measuring sensor 53 is changed by the upstream flow velocity measuring sensor 53 in FIG. The total value of the capacitance of the pipe line 41 and the powder is measured, and the measured total value is amplified with a low gain that does not saturate the AC amplifier 54. In FIG. 6B, the rectifier 55 rectifies the amplified signal and removes a high-frequency component due to the carrier signal from the rectified signal by the LPF 56. In FIG. 6C, the DC amplifier 57 applies the offset from the intrinsic capacitance of the pipeline 41 to the value from which the high frequency component by the carrier signal has been removed, so that the pipeline from the measured total value (measured value A). Forty-one specific capacitance (reference value B) is canceled and only the change in capacitance of the powder is extracted. In FIG. 6D, the DC amplifier 57 amplifies the extracted change in capacitance with an appropriate gain so as to facilitate measurement. In the same manner as described above, the change in electrostatic capacitance of the powder is measured by the downstream flow rate measurement sensor 53. Calculate the passage time of the powder between the two electrodes based on the correlation between the measured capacitance changes of the upstream and downstream powders, and divide the distance between the two electrodes by the calculated passage time. Is calculated.

  Here, in the conventional method for measuring the density of powder using an analog method, the electrostatic capacitance due to the powder may be as small as fF and the intrinsic capacitance may be as large as pF. In this case, there is a problem that if the gain of the AC amplifier is increased in order to accurately measure the electrostatic capacitance due to the powder, the AC amplifier is saturated and a surge is generated. In order to solve this problem, conventionally, as shown in FIG. 1, a “reference capacitor” for amplifying only the electrostatic capacitance due to powder after subtracting the intrinsic electrostatic capacitance by a bridge circuit or a differential amplifier. It was necessary to use (reference value). For this reason, an increase in the number of parts of the apparatus and a measurement error due to the reference capacitor are problems.

  On the other hand, in this embodiment, the latest digital device for capacitance measurement is used to directly measure the capacitance in the pipeline including the intrinsic capacitance, and the reference capacitor is not required. Thereby, the number of parts of an apparatus can be reduced and the fall of the measurement precision by the difference | error of a reference value can be suppressed.

  Further, in the conventional capacitance method, there is a problem similar to the above because the capacitance obtained by subtracting the intrinsic capacitance using a reference capacitor is measured even when the flow velocity is measured. However, if only the flow rate is measured, only the change in capacitance needs to be measured, so the gain of the AC amplifier may be small, and there is no need to subtract the specific capacitance using a reference capacitor. .

  Therefore, in this embodiment, after the offset of the AC amplifier is reduced to the extent that it is not saturated by the DC amplifier after the AC signal is rectified and passed through the LPF by reducing the gain of the AC amplifier and suppressing the saturation of the amplifier. By amplifying, only the change in capacitance is amplified while suppressing the saturation of the amplifier.

  As a result, according to the configuration and operation of the powder flow meter 25 of the present embodiment, the number of parts is reduced by eliminating the need for a reference capacitor (reference value), and a decrease in measurement accuracy due to an error in the reference value is suppressed. can do.

DESCRIPTION OF SYMBOLS 1 Capacitance measuring means 2 Oscillator 3 Measuring sensor 4 Reference sensor 5a-5c Resistance 6, 7 Amplifier 8 Differential amplifier 9 Powder data detection amplifier 10 LPF (low-pass filter)
21 Pulverized Coal Supply System 22 Pulverized Coal Bottle 23 Lock Hopper 24 Load Cell 25, 26 Powder Flowmeter 27 Gasifier 28, 29 Coal Supply Pipe 30 Nitrogen Gas 31 Sensor Pipe (Pipe)
33 Sensor electrode for density measurement 35, 36 Sensor electrode for flow velocity measurement 37 Shield made of cast iron 39 Control BOX
41 Sensor pipe (pipe)
43 Capacitance measurement means for density determination 45, 46 Capacitance measurement means for flow velocity determination 47 Electromagnetic shield 49 Control means 51 Density measurement sensor (electrode)
52 Capacitance measuring device 53 Flow rate measuring sensor (electrode)
54 AC amplifier 55 Rectifier 56 LPF (low pass filter)
57 DC amplifier 58 AD converter (analog / digital converter)
59 Oscillator 61 Powder density calculating means 62 Flow velocity calculating means 63 Flow rate calculating means 64 Offset value setting means 65 Gain setting means 66 Powder flow rate

Claims (7)

A capacitance type powder flow measuring device for measuring a powder flow rate by measuring a change in capacitance in a pipeline through which powder flows,
A density determination capacitance measuring means for measuring a signal corresponding to the capacitance in the pipe using the density determination AC voltage source;
Powder density calculating means for calculating the powder density from the measured signal;
Using a first flow rate determination AC voltage source and a second flow rate determination AC voltage source having a frequency higher than that of the density determination AC voltage source, a predetermined signal is obtained from a signal corresponding to the capacitance in the pipe. First and second flow rate determination capacitance measuring means for offsetting the capacitance component to amplify and measure the change in capacitance of the powder;
Powder flow rate calculating means for calculating a powder flow rate based on the correlation of the measured changes,
A powder flow rate measuring device comprising: a powder flow rate calculating means for calculating a powder flow rate from the powder density and the powder flow rate. The first and second flow rate determination capacitance measuring means include a rectifier, an LPF, and a DC amplifier,
The signal corresponding to the electrostatic capacity in the pipe is rectified to remove high frequency components and then input to the DC amplifier,
The DC amplifier has an offset unit and a DC amplification unit,
2. The powder flow rate measuring apparatus according to claim 1, wherein the signal input to the DC amplifier is DC amplified after removing the predetermined capacitance by the offset unit. The density determination capacitance measuring means includes a pair of density measurement electrodes connected to the density determination AC voltage source installed on the outer surface of the conduit, and the pair of density measurement electrodes To directly measure the capacitance in the pipeline,
Each of the first and second flow rate determination capacitance measuring means is connected to the first flow rate determination AC voltage source installed on the outer surface of the pipe. A pair of electrodes and a second pair of electrodes for measuring the flow velocity connected to the second AC voltage source for determining the second flow velocity,
3. The powder flow rate measuring device according to claim 1, wherein the pair of electrodes for density measurement is installed between the pair of electrodes for measuring the first and second flow velocities. 4. . Each of the first and second flow rate determination capacitance measuring means includes a DC amplifier that amplifies a change in capacitance of the powder,
4. The DC amplifier includes an element capable of digitally setting an offset value and a gain value, and the offset value and the gain value are automatically set by a control unit. The powder flow rate measuring apparatus according to 1.   2. Each of the first and second flow rate determination capacitance measuring means includes an oscillator that generates a carrier signal having a predetermined frequency, and the frequency of the carrier signal is 1 MHz or more. 5. The powder flow rate measuring device according to any one of items 4 to 4.   4. The powder flow rate measuring apparatus according to claim 3, wherein the pair of electrodes for density measurement and the pair of electrodes for measuring the first and second flow velocities are comb teeth. . A capacitance type powder flow rate measuring method for measuring a powder flow rate by measuring a change in capacitance in a pipeline through which powder flows,
Using a density measuring AC voltage source to measure a signal according to the capacitance in the conduit;
Calculating a powder density from the measured signal;
Using a first flow rate measurement AC voltage source and a second flow rate determination AC voltage source having a frequency higher than that of the density measurement AC voltage source, a predetermined signal is obtained from a signal corresponding to the capacitance in the pipe. Amplifying and measuring a change in capacitance of the powder by offsetting the capacitance; and
Calculating a powder flow rate based on the correlation of each measured change;
Powder flow rate measuring method characterized by having a step of computing a powder flow rate from said powder flow rate as the powder density.

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