JP2781398B2 - Powder flow measurement device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a granular material flow rate measuring device that measures the flow rate of a granular material by measuring the concentration of the granular material from the amount of transmitted light.

[Conventional technology]

In a pulverized coal boiler or the like, it is one of the indispensable factors to measure the flow rate of the granular material (for example, pulverized coal and ash) with high accuracy. The method of measuring the flow rate of the powder is
There are impact type, Coriolis type, differential pressure type, electromagnetic type, photoelectric type, etc. Among them, the photoelectric measuring method does not change the flow in the pipe compared to other methods, It is easy to measure without any problems.

Next, the principle of measuring the flow rate of the granular material by the photoelectric method (light transmission method) will be described.

In this light transmission type powder flow measurement method, when a light beam passes through a powder, the light is absorbed and scattered by the particles, and the concentration of the powder in the light path is measured by measuring the attenuated amount of transmitted light. The flow rate and the cross-sectional area are multiplied by this concentration, and the flow rate of the granular material is obtained.

In general, the amount of transmitted light has the following relationship according to Lambert-Beer's law.

I = I ₀ · exp (−C × X · S) where I _{0 is the} incident light amount, I is the transmitted light amount attenuated by absorption / scattering, and C is the absorption coefficient, which is the characteristic (spectral distribution) of the light source used. Etc.), the characteristics of the granular material (particle size,
Shape, etc.) and the characteristics of the equipment used. X: measured length, that is, length through which light passes, S: concentration of powder and granules. From the above equation, the granular material concentration S is Since the absorption coefficient C varies depending on many factors as described above, it cannot be specified. However, empirically, under certain conditions, the powder concentration S and the log (I ₀ / I) are linear. It has been confirmed that it is proportional to
₀ / I) (K is a coefficient). That be determined experimentally K, by measuring I and I _0, can be obtained granular material concentration. At present, a dust densitometer using the light transmission principle is widely used.

 FIG. 10 shows a schematic diagram of the photoelectric measuring device.

In the figure, reference numeral 1 denotes a powder / particle transport pipe, reference numerals 2 and 3 denote light-emitting and light-receiving elements mounted opposite the inner surface of the pipe wall of the transport pipe 1, reference numerals 4 and 4 denote air purging devices, and reference numeral 5 a light-receiving element 3
This is a signal processing unit that processes the signal obtained by photoelectrically converting the image data from the digital camera, and includes a smoothing circuit 10 and operation units 11 and 14. 13 is the operation unit
External signal input to 14.

At present, such a conventional apparatus lacks reliability as a flow rate / concentration measurement because an air purge or the like is performed in order to avoid the powder and particles from adhering to the light emitting element 2 and the light receiving element 3. . (Powder and Particle Measurement Handbook / Japan Powder Industry Association, p. 414) In addition, when the concentration of the powder changes greatly, it is difficult to accurately detect a high concentration condition. A specific example is shown in FIG. FIG. 7 shows the relationship between the C / A (pulverized coal / air) of the pulverized coal flow of the mill in the factory and the amount of transmitted light (converted to voltage) in the apparatus configuration as shown in FIG. There is a large difference in the amount of transmitted light between high density (during mill operation) and low density (during mill start / stop), so that a wide density range (← →) can be detected together with high density conditions (← →). Conventionally, the detection signal is logarithmically compressed by a long amplifier for measurement.

[Problems to be solved by the invention]

The prior art described above has a problem in accurately measuring a high-concentration condition when the concentration of the granular material changes greatly.
Further, there is a problem that the attenuation of the amount of received light due to an abnormality in the optical system such as the adhesion of the powder or the like to the light emitting element 2 and the light receiving element 3 due to a defect of the air purging device 4 or the like, or the misalignment of the optical axis is regarded as the increase in the concentration of the powder or the particle. There was.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a granular material flow rate measuring device capable of detecting a granular material with high accuracy even in a region where the concentration of the granular material is high, and capable of monitoring an abnormal situation such as adhesion of the granular material or deviation of an optical axis. [Means for Solving the Problems] In order to achieve the above object, a first aspect of the present invention provides a light transmission type sensor including a light emitting element and a light receiving element in a flow path of a granular material, In a powder flow measuring device that measures the flow rate of a granular material from a change in the amount of transmitted light due to a change in concentration, a detection signal of the light receiving element is divided into an AC component intensity and a DC component intensity. And a first calculating means such as a calculating unit 9 described later, which calculates the granular material concentration from the AC component intensity when the DC component intensity is equal to or higher than a threshold value; If the intensity is less than the threshold, the concentration of the granular material is calculated from the DC component intensity.
And a third calculating means such as a calculating unit 14 to be described later, which calculates the granular material flow rate 9 based on the calculated value from the first calculating means or the second calculating means. It is characterized by having.

In order to achieve the above object, a second aspect of the present invention is to provide a light transmission type sensor including a light emitting element and a light receiving element in a flow path of a granular material, and to detect a change in transmitted light amount due to a change in concentration of the granular material. In a powder and particle flow rate measuring device for measuring a flow rate of a granular material, an AC / DC separation unit such as an AC / DC separation circuit 6 described below that divides a detection signal of the light receiving element into an AC component intensity and a DC component intensity; A first calculating means such as a calculating unit 9 described later, which calculates the concentration of the granular material from the intensity; and a second calculating unit calculating the concentration of the granular material from the DC component intensity, such as a calculating unit 11 described later. Means, a ratio of density values from the first calculating means and the second calculating means, and if the ratio is within a predetermined range (for example, in the range of 0.9 to 1.1), the optical system is normal, and the ratio is predetermined. It is determined that the optical system is abnormal if it is out of the range. Comparison judgment unit 17
And the like.

[Action]

The AC component of the transmitted light refers to flicker caused by the blocking of the optical path by the granular material. Figs. 8 and 9 show the relationship between the concentration (C / A) and the intensity of the DC and AC components of the transmitted light in the experiments conducted under the condition that the flow velocity and flow diameter distribution are constant and the distance between the light emitting element 2 and the light receiving element 3 is 13 mm. Is shown. When the C / A is low, the light from the light emitting element 2 is less likely to be blocked by the particles, so that the light receiving amount (DC component) received by the light receiving element 3 is large, and the optical path is less likely to be chopped. , The flicker (alternating current component) intensity is small. On the other hand, when the C / A rises, the light from the light emitting element 2 is often blocked by the particles, so that the amount of light received by the light receiving element 3 decreases and the number of times the optical path is chopped increases. , The intensity of the AC component increases. FIG. 8 and FIG. 9 are characteristic diagrams showing this tendency.
FIG. 8 is a diagram showing the relationship between the pulverized coal concentration (C / A) and the DC component intensity of the transmitted light, and FIG. 9 is a diagram showing the relationship between the pulverized coal concentration (C / A) and the AC component intensity of the transmitted light. is there.

As is clear from this figure, the DC component intensity shows a high value in the low density region, and decreases in the high density region.
On the other hand, the AC component intensity shows a high value in the high concentration region, and decreases in the low concentration region. The first aspect of the present invention utilizes the tendency of both, when the DC component intensity is equal to or higher than a predetermined threshold value, that is, in the case of a low concentration region, the DC component intensity indicating a high value is used. Is less than the threshold value, that is, in the case of a high concentration region, by using the AC component intensity indicating a high value to calculate each concentration, the flow rate measurement can be accurately performed over a wide range from the low concentration region to the high concentration region. it can.

If the optical system of the measuring device is normal, the density value calculated from the DC component intensity and the density value calculated from the AC component intensity should almost match. The second aspect of the present invention utilizes this fact to determine the ratio between the density value calculated from the DC component intensity and the density value calculated from the AC component intensity, and when the value is out of the predetermined range, the optical system By determining that an abnormality is present, a self-monitoring mechanism can be added to improve reliability.

〔Example〕

FIG. 1 shows the configuration of a granular material flow rate measuring device according to an embodiment of the present invention.

1 includes a light-emitting element 2, a light-receiving element 3, a signal processing unit 5, and an air purging apparatus 4 mounted on the left and right sides of a transport pipe 1. The air purging device 4 is a blower for preventing powder and granules from adhering to the optical system.

Emitting element 2 and the light receiving element 3 is arranged a predetermined distance, the light emission quantity I ₀ is constant. The light receiving element 3 detects the amount of transmitted light corresponding to the concentration of the granular material, converts the amount of transmitted light into an electric signal, and then passes the signal through an AC / DC component value circuit 6 to divide it into an AC component e and a DC component E. If the DC component intensity E is equal to or greater than the threshold, 30 of the AC components e
11 KHz is passed through a filter circuit 7 that extracts
, And substitutes the signal into an empirical formula relating to the previously obtained AC component intensity and concentration to calculate in the calculation unit 9 to obtain the concentration of the granular material. On the other hand, when the DC component intensity E is less than the threshold, the DC component E is passed through the smoothing circuit 10 and the arithmetic unit 11 calculates the relationship between the DC component intensity and the concentration to obtain the concentration of the powder and granules. Then, the obtained concentration is switched by the switching circuit 12, and the switched concentration is multiplied by the flow rate and the cross-sectional area from the external signal 13, and the flow rate of the powder fluid is calculated by the calculation unit 14.

FIG. 2 shows the flow of the signal processing unit. If the DC component intensity E of the transmitted light of a specific threshold V ₁ lower than the high concentration region) (Y in step 2-1), and calculates the concentration S from the DC light E (step 2-2). In addition, the DC component intensity E of the transmitted light
There V ₁ or (in the case of the low concentration region (N in step 2-1),
The density S is calculated from the AC component intensity e (Step 2-
3). The product of the concentration S and the external signal 9 (flow velocity v, cross-sectional area A) is calculated (Step 2-4), and the flow rate Q of the granular material is obtained (Step 2-5). Then, output is performed in step 2-6.

By dividing a wide measurement area as described above, it is possible to accurately measure the signal during normal operation, which is particularly important for measurement, without logarithmic compression, and to match the low concentration state when starting and stopping the device. There is an effect that can be measured.

Another embodiment of the present invention is shown in FIG. This embodiment is the first
The apparatus configuration is such that an optical fiber is installed at at least one end of the combination of the light emitting element 2 and the light receiving element 3 of the powder flow measuring device shown in the figure as a light guide.

That is, for example, the optical fiber head 15 faces the position facing the light emitting element 2, and the light from the light emitting element 2 is guided to the signal processing unit 5 by the optical fiber 16.

As described above, since the detection signal can be transmitted by light when the optical fiber 16 is used, the signal processing unit can be separated from a poor measurement environment without the influence of noise.

FIG. 4 shows another embodiment of the present invention. The present embodiment relates to a signal processing unit 5 having an effect of detecting an abnormality occurring in an optical system of a measuring device by using both the DC and AC component outputs of the transmitted light amount. The apparatus has the same configuration as that of FIG. 1 or FIG. 3 except for the signal processing unit 5.

In the case of a powder flow meter that converts only the intensity of the DC or AC component of the transmitted light, if there is an abnormality in the optical system of the device (dust particles adhere to the light emitting / receiving element due to malfunction of the air purging device, deviation of the optical axis) ) May indicate a flow value that includes an error. FIG. 5 shows an example. In the case where the optical system is normal, the same powder / particle concentration a is calculated irrespective of whether the result of detection using either the AC component or the DC component is calculated. On the other hand, when an abnormality occurs in the optical system, both the AC and DC component intensities decrease, so that the calculation results from the two show greatly different values (b and c).

In the present embodiment, an abnormality in the measurement system can be detected by adding the comparison / determination unit 17 and the averaging circuit 18 using this characteristic, so that more reliable measurement can be performed. 19 is an abnormality determination signal.

FIG. 6 shows a flow of abnormality determination. This should be determined in a low concentration region (0.1 or less for C / A) where the relationship between the AC and DC component intensities of transmitted light has been confirmed. The densities S and S 'are calculated from the DC and AC component intensities of the transmitted light (steps 6-1 and 6-2) (steps 6-3 and 6-4), and the ratio of S to S' is other than 0.9 to 1.1. If so (N in step 6-5), it is determined that an abnormality has occurred in the optical system, and the optical system is determined to be abnormal (step 6-6). If the ratio of S to S 'is within 0.9 to 1.1 (Y in step 6-5), the detection signal is regarded as normal, and the average of S and S' is taken as the powder concentration (step 6-7). Take the product of the flow rate v and the cross-sectional area A from Step 13 (Step 6).
-8) to calculate the flow rate (step 6-9).

〔The invention's effect〕

As described above, according to the present invention, the measurement area is divided into the high-density area and the low-density area, and the measurement is performed. There is an effect that the measurement can be performed with high accuracy and the measurement can also be performed when the apparatus is started and stopped (low concentration).

In addition, since the validity of the received light signal can be determined from the system based on the correlation between the DC and AC component intensities of the transmitted light with respect to the granular material concentration, highly reliable measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a granular material flow rate measuring device according to the present invention, FIG. 2 is a flowchart of a calculation unit, FIG. 3 is a block diagram of a device according to another embodiment, and FIG. FIG. 5 is a circuit diagram of a signal processing unit for judging abnormality, FIG. 5 is a diagram showing a relationship between the concentration of powder and granules and the concentration of DC and AC components of transmitted light, FIG. 6 is a flowchart of optical system abnormality judgment, and FIG. Fig. 8 shows the relationship between A and the amount of transmitted light. Fig. 8 shows C / A.
FIG. 9 is a diagram showing the relationship between C / A and the intensity of the AC component of the transmitted light, and FIG. 10 is a diagram showing the configuration of a conventional apparatus. 1 ... Transport tube, 2 ... Light emitting element, 3 ... Light receiving element, 5 ...
... Signal processing unit, 6 ... AC / DC separation circuit, 7 ... Filter circuit, 8 ... Rectifier circuit, 9 ... Operation unit, 10 ... Smoothing circuit,
11… Calculator, 12… Switching circuit, 13… External signal,
14… Calculator, 17… Comparative judgment unit, 18… Average circuit, 19
... Abnormality determination signal, E... DC component, e... AC component.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-81216 (JP, A) JP-A-57-124255 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01F 1/74

Claims (2)

(57) [Claims] An optical transmission sensor comprising a light emitting element and a light receiving element is provided in a flow path of a granular material, and a flow rate of the granular material is measured from a change in the amount of transmitted light due to a change in concentration of the granular material. In the granular material flow measuring device, AC / DC separating means for dividing a detection signal of the light receiving element into an AC component intensity and a DC component intensity; A second calculating means for calculating the concentration of the granular material from the DC component strength when the DC component strength is less than a threshold value; and the first calculating means or the second calculating means. A third calculating means for calculating the flow rate of the granular material based on the calculated value from the calculating means. 2. A powder which is provided with a light transmission type sensor comprising a light emitting element and a light receiving element in a flow path of a granular material, and measures a flow rate of the granular material from a change in transmitted light amount due to a change in concentration of the granular material. In the granular material flow measuring device, an AC / DC separation unit that divides a detection signal of the light receiving element into a DC component intensity of an AC component intensity; a first arithmetic unit that calculates a powder / particle concentration from the AC component intensity; A second calculating means for calculating the concentration of the granular material from the strength; and a ratio of the density values from the first calculating means and the second calculating means. If the ratio is within a predetermined range, the optical system is normal. ,
A comparison and determination means for determining that the optical system is abnormal when the ratio is out of a predetermined range.