JPH0250790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" This invention relates to a method of charging an electrostatic precipitator.

"Conventional technology" In a dry electrostatic precipitator, an uneven electric field is used to generate a corona discharge to create a charge, and a gas containing dust is flowed in, the dust is charged, and the dust is collected at a dust collection electrode, which removes the dust from the gas. are being collected. In this case, if the apparent electrical resistance of the dust collected on the dust collection electrode exceeds 10 ¹⁰ to 10 ¹¹ Ω-cm, the potential gradient within the dust layer collected on the dust collection electrode of the electrostatic precipitator becomes large. , causing dielectric breakdown within the dust layer. When dielectric breakdown occurs in the dust layer in this manner, positive ions are supplied from the dust layer, causing a so-called reverse ionization phenomenon.

When the reverse ionization phenomenon occurs, the negative ions that contribute to the dust collection effect are neutralized by the positive ions generated by the reverse ionization phenomenon, and most of the discharge current becomes a reactive current, significantly reducing the dust collection efficiency. I end up.

In order to prevent this drop in dust collection efficiency, measures may be taken to detect the occurrence of reverse ionization and increase the humidity in the gas of the electrostatic precipitator at an early stage to reduce the apparent electrical resistance. It has been conventional practice to prevent complete transition to a reverse ionization state by periodically stopping charging the electrostatic precipitator for a certain period of time.

However, both the method of increasing the humidity in the gas and the means of intermittent charging require the addition of a separate control device, resulting in a complicated device structure and difficulty in operation. Furthermore, since no quantitative conditions have been established regarding what kind of intermittent charging method should be used under what conditions, switching to the intermittent charging method may not necessarily be effective.

No matter what method is used, in order to operate the electrostatic precipitator with high dust collection efficiency, it is necessary to detect the reverse ionization phenomenon occurring in the dust collecting electrode of the electrostatic precipitator at an early stage.

Various methods have been proposed in the past in order to detect the reverse ionization phenomenon occurring in the dust collection electrode of an electrostatic precipitator without measuring the amount of dust contained in the gas.

These methods can be broadly divided into methods that use electrodes exclusively for detecting reverse ionization, and methods that detect based on the secondary voltage value and secondary current value of the electrostatic precipitator.
Among these, the method of detecting the reverse ionization phenomenon based on the secondary voltage value and secondary current value of the electrostatic precipitator is better in terms of detection accuracy and reliability than the method using a dedicated electrode for reverse ionization detection. It is widely used due to its excellent properties.

A typical method for detecting the reverse ionization phenomenon in an electrostatic precipitator based on the secondary voltage value and secondary current value is as shown in Japanese Patent Publication No. 58-55061 ``Reverse ionization detection method in electrostatic precipitator''. There is a method of calculating the rate of change of the secondary voltage and secondary current of an electrostatic precipitator and using these calculated values to detect the reverse ionization phenomenon of the electrostatic precipitator. On the other hand, a method has also been proposed in which the occurrence of back ionization is detected based on the waveform pattern of the secondary voltage and secondary current of the electrostatic precipitator to detect the reverse ionization phenomenon in the electrostatic precipitator.

"Problems to be Solved by the Invention" In the method of detecting the reverse ionization phenomenon of an electrostatic precipitator by calculating the rate of change of the secondary voltage and secondary current, the spark waveform that occurs in the secondary voltage and secondary current waveforms of the electrostatic precipitator is In order to prevent erroneous detection due to this erroneous calculation, it is necessary to add a complicated circuit for discriminating the spark waveform, making the detection method complicated.

On the other hand, in the method of detecting the reverse ionization phenomenon of an electrostatic precipitator based on the waveform pattern of the secondary voltage and secondary current of the electrostatic precipitator, the circuit configuration is complicated to recognize the pattern, and the detection operation is also complicated. is not desirable.

This invention detects the occurrence of a reverse ionization phenomenon based on the relationship curve between the secondary voltage and secondary current of an electrostatic precipitator, and simply changes the secondary voltage or secondary current in the charging method under predetermined conditions. The objective of this study is to propose a quantitative method that allows electrostatic precipitators to operate at optimal dust collection efficiency at all times.

"Structure of the Invention" This invention provides a first relationship curve showing the relationship between the operating secondary voltage and the operating secondary current in the normal charging operation state of the dry electrostatic precipitator, and the second relation curve in the reverse ionization operating state of the dry electrostatic precipitator. A second relationship curve showing the relationship between the secondary voltage and the secondary current is displayed on the same coordinate system. Straight lines representing at least three different secondary current values are drawn on the first and second curves displayed on the same coordinate system, and the relationship between each straight line and the first and second relationship curves is Find each intersection point.

A dividing point is set for each straight line so that each straight line obtained by connecting the intersection points of the straight line indicating each secondary current value and the first and second curves is divided at a preset constant ratio. Desired. A determination curve indicating the relationship between the determined secondary voltage value and the determined secondary current value is drawn so as to pass through the division point obtained in this manner or to pass near the division point.

In this invention, the test secondary voltage value of the electrostatic precipitator during operation is read, and the secondary current value corresponding to the test secondary voltage value is determined to be the same as the test secondary voltage value obtained from the determination curve. The determined secondary current value corresponding to the secondary voltage value is compared. Through this comparison, if the secondary current value corresponding to the test secondary voltage value exceeds the judgment secondary current value obtained from the judgment curve, the secondary current value corresponding to the test secondary voltage value The electrostatic precipitator is charged by selecting the operating secondary voltage or operating secondary current so that the ratio of the determined secondary current values is equal to or less than a preset value.

"Example" Hereinafter, the present invention will be described in detail based on an example using the drawings.

A first relationship curve showing the relationship between the operating secondary voltage and the operating secondary current in the normal charging operating state of the dry electrostatic precipitator, and the relationship between the secondary voltage and the secondary current in the reverse ionizing operating state of the dry electrostatic precipitator. The second relationship curve shown in FIG. 1 is displayed on the same orthogonal coordinate system.

In general, dry electrostatic precipitators operate based on the physical and chemical properties of the incoming gas and the dust in the incoming gas, such as gas chemical composition, gas pressure, gas temperature, dust chemical composition, dust concentration, and dust particle size. The relationship curves obtained between the secondary voltage and the secondary current differ from each other in slope and shape.

Therefore, when a relationship curve between the secondary voltage and the secondary current during operation, which is obtained by using these factors as parameters, is obtained, a group of curves is obtained.

In the normal charging operation state of a dry electrostatic precipitator, for example, by determining the type of inflow gas and the dust contained therein, and using other physical conditions as parameters, the relationship between the operating secondary voltage V and the operating secondary current I is determined for each operating secondary. When the operating secondary current flowing with respect to the secondary voltage is measured and determined, the curve groups shown in Fig. 1 A ₀ , A ₁ , A ₂ . . . are obtained.

The group of curves obtained in this manner corresponds to the normal charging operation state, and another relationship curve group exists between the secondary voltage and the secondary current in the reverse ionization operation state. That is, when the operating state of the electrostatic precipitator shifts from this normal charging operating state to the reverse ionizing operating state, the relationship curve between the secondary voltage and the secondary current becomes A ₀ , A ₁ , A ₂ , A in FIG. _3. Transfer from the relational curve group obtained in ,... to another curve group.

In this invention, in order to obtain the determination curve described below,
The same electrostatic precipitator is used in a reverse ionization operation state in which reverse ionization actually occurs by determining the incoming gas and the type of dust contained in the gas in the same way as in the normal charging operation state, and changing other physical conditions. But let me drive,
At this time, the relationship curve between the secondary voltage and the secondary current is measured. The relationship between the secondary voltage and the secondary current obtained in this reverse ionization operating state is obtained as a group of curves as shown in B ₀ , B ₁ , B ₂ , and B ₃ in FIG.

In this invention, among a group of relationship curves between the operating secondary voltage and the operating secondary current obtained under normal charging operation conditions, the operating secondary voltage value is the smallest value for the same operating secondary current value. The relational curve A ₀ that takes the value is selected and displayed on the orthogonal coordinate system as the first relational curve A ₀ as shown in FIG.

Also, among the group of relational curves obtained in the reverse ionization operation state, the relational curve _B0 having the largest value of the secondary voltage value for the same secondary current value is selected as the second relational curve, As shown in FIG. 2, it is displayed on the same orthogonal coordinate system as the first relationship curve. Therefore, the first
And in order to select the second relational curves A ₀ and B ₀ ,
In general, electrostatic precipitators require a certain period of commissioning and adjustment.

On the orthogonal coordinate system created in this way, find the intersections between the straight lines indicating at least three different secondary current values and the first and second relationship curves, and find the intersections corresponding to the respective secondary current values. Each straight line obtained by connecting the lines is divided at a predetermined ratio to find each dividing point.

The example shown in Figure 2 uses three types of secondary currents, and the first relational curve _A0 and the second relational curve
Straight lines corresponding to secondary currents i ₁ , i ₂ and i ₃ for B ₀
Subtract D ₁ , D ₂ and D ₃ to obtain the first and second relationship curves
Find the intersection points d ₁ , d ₂ , d ₃ and e ₁ , e ₂ , e ₃ with A ₀ and B ₀ . It is desirable that the secondary currents i ₁ , i ₂ , i ₃ be set at predetermined intervals in a region where both the first and second relationship curves A ₀ and B ₀ exist.

A straight line connecting the intersection points corresponding to each secondary current
Divide e ₁ d ₁ , e ₂ d ₂ , e ₃ d ₃ at a certain ratio and set the division points
Find c ₁ , c ₂ , c ₃ . In the example shown in Figure 2, e ₁ c ₁ / c ₁ d ₁ = e ₂ c ₂ / c ₂ d ₂ = e ₃ c ₃ / c ₃ d ₃ = 1, and a dividing point is placed at the midpoint of each straight line. is set. As a result of the inventors' studies, in setting the ratio for determining the above-mentioned dividing points c ₁ , c ₂ , c ₃ , e ₁ c ₁ /c ₁ d ₁ = e ₂ c ₂ /c ₂ d ₂ = e ₃ c ₃ /c ₃ d ₃ =n, n
It has been confirmed that desirable results can be obtained when the value of is set to about 1/5 to 5. Usually first and second relationship curves
If A ₀ and B ₀ can be selected in a state where they are closest to each other, a desirable result can be obtained by setting n≈1.

A determination curve that passes through or near these division points and indicates the relationship between the determined secondary voltage value and the determined secondary current value is determined.

In the example shown in FIG. 3, the determination curve C=f(V) is obtained by solving a quadratic equation as a quadratic curve passing through dividing points c ₁ , c ₂ , and c ₃ . Generally, by selecting four or more types of secondary current values, the determination curve C=f(V) can be obtained as a curve passing through the vicinity of these given dividing points by the least squares method.

The magnitude of the secondary current value corresponding to the secondary voltage value to be tested during operation of the electrostatic precipitator and the secondary current value corresponding to the secondary voltage value to be tested and the same secondary voltage value obtained from the determination curve C. Detects the occurrence of reverse ionization in a dry electrostatic precipitator.

For example, as shown in FIG. 3, it is assumed that the electrostatic precipitator is operated at an operating point indicated by D in the figure when the electrostatic precipitator is in operation when a state in which reverse ionization occurs is detected. In this case, the tested secondary voltage of the electrostatic precipitator is
Vd, and the secondary current corresponding to this secondary voltage is
Id. The determined secondary current value corresponding to the determined secondary voltage value Vd, which is the same as the tested secondary voltage Vd, is determined as f(Vd) on the determined curve C=f(V), where V=Vd.

In this invention, the secondary current value Id corresponding to the secondary voltage value Vd to be tested and the secondary current value f( Vd) is determined.

Id/f(Vd)≧1...(1) Id/f(Vd)<1...(2) In this invention, when the condition of equation (2) is satisfied, the operation is performed in a normally charged state. It is determined that the Figure 4 is a relationship curve with secondary current on the horizontal axis and I/f (V) on the vertical axis, and the straight line in Figure 4.
No indicates the boundary line corresponding to operation in this normal charging state. An operating state in which I/f(V) is less than or equal to this straight line _Np , for example, an operating state shown by the curve _Co, is determined to be a normal charge operating state.

When the condition of the previous equation (1) is obtained and it is detected that the state is not in the normal charging state, it is determined whether the electrostatic precipitator will completely shift to the reverse ionization state if it continues to operate in the current charging state. Make a judgment.

For this purpose, the secondary current value corresponding to the secondary voltage value to be tested is compared with the determined secondary current value corresponding to the determined secondary voltage value that is equal to the secondary voltage value to be tested and determined from the determination curve. . If the judgment secondary current value obtained in this way exceeds the predetermined ratio of the secondary current corresponding to the test secondary voltage value, the The operating secondary voltage or operating secondary current for the electrostatic precipitator is selected and controlled.

As a result of research by the inventors and actual measurements based on the research, it was confirmed that if I/f(V)<3, there is no need to change the current charging conditions.

Figures 4 and 5 show these relationships. The curve C _a in Figure 4 shows operation in a state where reverse ionization has occurred in the electrostatic precipitator, and the charging state is determined by the secondary current I. The operation is performed by increasing the secondary current from point B ₁ , which is ₁ , and the secondary current becomes I ₂
Until reaching the _B2 point, the dust collection efficiency η of the electrostatic precipitator gradually increases as shown by the curve Ka in FIG. However, when the secondary current value is further increased beyond the point _B2 , the dust collection efficiency η gradually decreases after the point _B2 , as shown by the curve Ka in FIG.

As a result of the inventors' studies, it was confirmed that when I/f (V) < 3, the secondary current does not increase beyond the operating conditions at point B ₂ in Figures 4 and 5. .
In the present invention, when it is confirmed that I/f(V)>3, the secondary voltage or secondary current of the electrostatic precipitator is controlled so that I/f(V)<3.

In order to perform this monitoring control automatically, a reverse ionization detection device whose configuration is shown in FIG. 6 is used.

That is, the output signal of the commercial AC power supply 11 is connected to the primary terminal of the transformer 13 via the thyristor 12. A secondary terminal of the transformer 13 is connected to a discharge electrode 15 via a rectifier 14. A dust collecting electrode 16 is provided opposite to this discharge electrode 15, and this dust collecting electrode 16 is grounded. A secondary current is drawn from the rectifier 14 by a current shunt 17. Similarly, from the rectifier 14 to the voltage shunt 1
The secondary voltage is derived by 8.

These secondary voltages and secondary currents are input to the computer system 19, and the determination calculations of the present invention are performed.

The output signal of the current shunt 17 is sent to the AD converter 21
The signal is converted into a digital signal by the averaging circuit 22, and then averaged by the averaging circuit 22. On the other hand, the output signal of the voltage shunt 18 is converted into a digital signal by the AD converter 23,
The signals are averaged by an averaging circuit 24. Using this average value, the determination current value f(V) is determined using the functional formula of the determination curve stored in the computer system 19.
is calculated by the first calculation circuit 25.

The output of the averaging circuit 22 and the output of the first arithmetic circuit 25 are input to the second arithmetic circuit 26, and a determination constant K=I/f(V) is calculated.

The determination constant K is determined by the determination circuit 27,
When it is confirmed that K<1, it is determined that the operating state is normal with no risk of shifting to a complete reverse ionization state, and the normality indicator 28 lights up. on the other hand,
When the determination circuit 27 confirms that K>1, it is determined that the operating state is likely to shift to a complete reverse ionization state, and the alarm 29 is activated.

At the same time, a drive signal is emitted from the driver 30,
For example, the secondary voltage is controlled so as to satisfy the condition K=I/f(V)<3.

In this control, a judgment curve is obtained in advance, and the supervisor uses this judgment curve to obtain a judgment current value from the secondary voltage and secondary current of the electrostatic precipitator currently in operation, and then calculates the I/f (V). It is determined whether the condition <3 is satisfied, and if I/f(V)>3, I/f(V
) may be 3 or less by manually controlling the secondary voltage or secondary current of the electrostatic precipitator during operation.

"Effects of the Invention" In this invention, the determination current obtained from the determination curve is compared with the secondary current I during operation, and the determination constant K=I/f(V) is used to determine whether a complete reverse ionization state is reached. If it is determined that there is a risk of transition, a simple operation of controlling the secondary voltage or secondary current so that the determination constant K is below a predetermined value can prevent complete transition to the reverse ionization state and It is possible to operate at the dust collection rate.

The relationship curve between the dust collection efficiency η and the secondary current I in FIG. 5 generally depends on the physical and chemical conditions of the gas and dust as well as the operating conditions of the electrostatic precipitator _. K changes as shown in _c .

However, as a result of research and actual measurements by the inventors, the condition I/f( It was confirmed that as long as control is performed to satisfy V)<3, the dust collection efficiency can be maximized under all operating conditions.

Control to satisfy the condition of I/f(V)<3 can be easily realized by controlling either the secondary voltage or the secondary current of the electrostatic precipitator.

The results obtained by applying this invention to a dry electrostatic precipitator with a processing capacity of 200,000 m ³ /H for treating exhaust gas generated from a dolomite firing kiln are as follows.

During operation of the electrostatic precipitator, the gas temperature is approximately 220℃ at the inlet side of the device, and the dust concentration is 6 to 128/ ^m3.
It was moderately hot.

Among the relationship curves between secondary voltage and secondary current in a normal charging state obtained by trial operation under these gas and dust conditions, curve F ₁ shows the maximum secondary current for the same secondary voltage. are displayed on orthogonal coordinates as shown in FIG.

On the other hand, among the relationship curves between secondary voltage and secondary current obtained by operating an electrostatic precipitator in a state where reverse ionization is occurring, curve F ₂ where the secondary current is the minimum with respect to the secondary voltage is selected. It is displayed on orthogonal coordinates as shown in FIG.

For curves F ₁ and F ₂ in Fig. 7, secondary current value I = 30,
Draw straight lines of 60, 120 and 180 mA, and intersect with the respective curves F ₁ and F ₂ at A ₁ , A ₂ , A ₃ , A ₄ and B ₁ , B ₂ ,
Find B ₃ and B ₄ . Next, find the points _{C 1 ,} C ₂ , C 3 and C _{4 that bisect A 1 B 1 , A 2 B 2 , A 3 B 3 and A 4 B 4 and subtract the quadratic curve passing through} these areas _. The following equation is obtained by calculating by the square method.

I=1.53925V ² −151.373V+3749.06 (1) The determination curve shown by equation (1) is curve C in FIG.

In this case, the maximum allowable value of the determination constant K is set to 3. While the electrostatic precipitator was in operation, the secondary voltage and secondary current were determined to be 51 kV and 160 mA, respectively. The determination current for the same determination voltage as this secondary voltage of 51kV is calculated from the determination curve as 35mA.
is obtained.

When the determination constant is calculated from these, it is found that K=I/f(V)=160/35=4.57, which confirms that it exceeds the maximum allowable value of 3. Based on this judgment result, the secondary voltage of the electrostatic precipitator is lowered and when it reaches 49kV, the secondary current becomes 32mA, the corresponding judgment current is 27mA, and the judgment constant is K = I / f ( V) = 32/27 = 1.18, and it was confirmed that the device was in normal operating condition. From then on, it became possible to operate with high dust collection efficiency in this charged state.

As explained in detail above, according to the present invention, the secondary voltage and secondary current during operation are measured, the secondary current corresponding to the determination voltage equal to the secondary voltage is determined, and the determination constant is determined from these. A simple method is to control the secondary voltage or secondary current so that the determination constant is less than or equal to a predetermined value. With a simple operation, it is possible to perform an operation in which there is no risk of shifting to a reverse ionization operation state and in which the maximum dust collection rate can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram showing the first and second relationship curves, Figure 2 is a diagram showing a method for creating a determination curve based on the first and second relationship curves, and Figure 3 is a diagram showing a method for creating a determination curve based on the first and second relationship curves. FIG. 4 is a diagram showing the relationship between the secondary current and the determination constant I/f (V) in a reverse ionization occurrence state and a normal charging state. FIG. 5 is a diagram showing the relationship between secondary current and dust collection efficiency in a state where reverse ionization occurs, FIG. 6 is a diagram showing the configuration of a reverse ionization generator used in an embodiment of the present invention, and FIG. It is a figure which shows the creation method of the determination curve in the Example to which the invention is applied. A ₀ : first relational curve, B ₀ : second relational curve,
C ₁ , C ₂ , C ₃ : Division point, C: Judgment curve, η: Dust collection efficiency, 11: Commercial AC power supply, 12: Thyristor,
13: transformer, 14: rectifier, 15: discharge electrode,
16: Dust collection electrode, 17: Current shunt, 18: Voltage shunt, 19: Computer system, 2
1, 23: AD converter, 22, 24: averaging circuit, 25: arithmetic circuit, 26: first arithmetic circuit, 2
8: Normal indicator, 29: Alarm, 30: Driver.

Claims (1)

[Claims] 1 A first relationship curve showing the relationship between the operating secondary voltage and the operating secondary current in the normal operating state of the dry electrostatic precipitator, and the relationship between the secondary voltage and the secondary current in the reverse ionization operating state of the dry electrostatic precipitator. and a second relationship curve shown on the same coordinate system, and on this coordinate system, find the intersections of the straight lines showing at least three different secondary current values and the first and second relationship curves, respectively. , each straight line obtained by connecting the intersection points corresponding to each secondary current value is divided at a predetermined ratio to find each dividing point, passing through or near these dividing points, A determination curve showing the relationship between the determined secondary voltage value and the determined secondary current value is obtained, and a secondary current value corresponding to the tested secondary voltage value during operation of the dry electrostatic precipitator is obtained from the determined curve. If the judgment secondary current value corresponding to the same judgment secondary voltage value as the test secondary voltage value is exceeded, the judgment secondary current value for the secondary current value corresponding to the test secondary voltage value is exceeded. A method for charging an electrostatic precipitator, characterized in that the dry electrostatic precipitator is charged by controlling an operating secondary voltage or an operating secondary current so that the ratio is equal to or less than a preset value.