JPH0250788B2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to a charging method for an electrostatic precipitator, and particularly to a charging method for an electrostatic precipitator that selects and operates a charging method to increase dust collection efficiency. .

``Prior art'' In a dry type electrostatic precipitator, a voltage is applied between a discharge electrode and a dust collection electrode to cause a corona discharge and create an electric charge, and a gas containing dust is flowed in to charge the dust and collect the dust. Dust is electrostatically attached to the electrode. The dust contained in the gas and sent in this way is collected by the dry electrostatic precipitator.

In this case, the apparent electrical resistance value of the dust is 10 ¹⁰
When it exceeds ~10 ¹¹ Ω・cm, the potential gradient within the dust layer collected by the dust collecting electrode increases, causing dielectric breakdown within the dust layer and causing a reverse ionization phenomenon in which positive ions are supplied from the dust layer. may occur.
When such a reverse ionization phenomenon occurs, the negative ions that contribute to dust collection are neutralized by positive ions, so most of the discharge current becomes a reactive current, which significantly reduces the dust collection efficiency. Power consumption in the electrostatic precipitator also increases.

Figure 1 is a relationship curve between secondary voltage and secondary current, with the horizontal axis representing the secondary voltage V applied to the electrodes of the electrostatic precipitator and the vertical axis representing the secondary current I obtained at that time. Curve A in the figure is a relational curve obtained when only air flows through the electrostatic precipitator. The relationship curve between the secondary voltage and secondary current obtained by flowing the gas to be treated into the electrostatic precipitator from this state is shown in Figure 1.
As shown in Figure 2, there is a tendency for the secondary current to increase for the same secondary voltage compared to when only air is allowed to flow in. Furthermore, the relationship curve C shown in Figure 1 is a relationship curve between the secondary voltage and the secondary current when a reverse ionization phenomenon occurs in the electrostatic precipitator during operation. There is a tendency for the values to rapidly reach excessive values.

Generally, if a reverse ionization phenomenon occurs while an electrostatic precipitator is operated in the continuous charging mode, if the charging method of the secondary voltage between the discharge electrode and the collecting electrode is switched to the intermittent charging method, the electrostatic precipitator will It is known that it is possible to reduce power consumption and prevent a decrease in dust collection efficiency.

However, this is true when a significant reverse ionization phenomenon occurs in the electrostatic precipitator during operation, and the operation is carried out under complete reverse ionization conditions. If an intermittent charging method is adopted in a state where a significant reverse ionization phenomenon such as an excessive reactive current is not occurring, the dust collection efficiency of the electrostatic precipitator may be lower than when a continuous charging method is adopted. Conventionally, it has not been quantitatively understood under what operating conditions the intermittent charging method can improve dust collection efficiency and reduce power consumption.

Therefore, we constantly monitor the operation of the electrostatic precipitator and check the operating conditions in which the relationship between the secondary voltage and secondary current as shown by curve C in Figure 1 is clearly recognized.
It is possible to switch to the intermittent charging method for operation.
However, since the conditions for the switching cannot be quantitatively determined, it is difficult to quickly and accurately confirm the conditions for the occurrence of the reverse ionization phenomenon under which the charging method should be switched. In addition, the dust concentration on the outlet side of the electrostatic precipitator is continuously monitored, and it is possible to switch to the intermittent charging method based on changes in this concentration, but even in this case, it is difficult to understand the complete quantitative relationship. It is difficult and the detection process becomes complicated.

Conventionally, for this reason, even if the charging method of an electrostatic precipitator was switched to an intermittent charging method, by the time the charging method was switched, it had already been operating for a long time in a state with low dust collection efficiency, resulting in unnecessary power consumption. The charging method of the electrostatic precipitator may be switched to the intermittent charging method before the effectiveness of the electrostatic precipitator is not improved or a significant reverse ionization phenomenon that causes an excessive reactive current to flow occurs, resulting in a decrease in dust collection efficiency. It was hot.

"Problems to be Solved by the Invention" This invention quickly and accurately grasps that the reverse ionization phenomenon occurs under the conditions under which the charging method should be switched in the operation of a dry electrostatic precipitator, and allows the switching of the charging method to be carried out. It is an object of the present invention to provide a method for charging an electrostatic precipitator that allows charging to be carried out at appropriate operating times.

The electrical resistance logP of the dust from the electrostatic precipitator is plotted on the horizontal axis, and the secondary voltage or secondary current is plotted on the vertical axis.
When the relationship between these is shown, a relationship curve shown in FIG. 2 is obtained. In the figure, D is called a normal discharge region, E is called a corona discharge suppression region, and F is called a reverse ionization region. Previously, it was thought that intermittent charging could improve the dust collection efficiency of an electrostatic precipitator only in the reverse ionization region F, but as a result of research by the inventors, the predetermined judgment conditions were satisfied even in regions other than the reverse ionization region F. We have found that it is possible to improve the dust collection efficiency of an electrostatic precipitator by doing so.

This invention solves the above-mentioned problem, and by checking whether the specific judgment conditions given by this invention are satisfied, continuous charging and intermittent charging of the dry electrostatic precipitator can be switched in accordance with the judgment conditions. It is possible to operate with optimum dust collection efficiency at all times.

"Structure of the Invention" In this invention, during the operation of a dry electrostatic precipitator, the charging method of the voltage that charges the discharge electrode for a predetermined judgment operation time is currently selected from the continuous charging method and the intermittent charging method with a charging rate γ. Switch to a charging method that does not. PW(C)γ obtained from the power consumption element value PW(C) in the continuous charging method before and after this switching
and the power consumption element value PW(I) in the intermittent charging method are compared.

If it is determined by this comparison that PW(I)<PW(C)・γ, the continuous charging method is selected, and PW(I)>
When it is determined that PW(C)・γ, the intermittent charging method is selected, the electrostatic precipitator is charged, and the electrostatic precipitator continues to operate.

``Example'' Hereinafter, a method for charging an electrostatic precipitator according to the present invention will be described in detail based on an example using the drawings.

FIG. 4 shows an example of a circuit used to carry out the method of charging an electrostatic precipitator according to the present invention, in which an output signal from a commercial AC power source 11 is applied to the primary side of a transformer 13 via a thyristor 12. The secondary side of the transformer 13 is connected to a discharge electrode 15 via a rectifier 14, and this discharge electrode 15 is connected to the dust collection electrode 1 of an electrostatic precipitator.
6, and the dust collecting electrode 16 is grounded.

A secondary voltmeter 17 and a secondary ammeter 18 are connected to the secondary side of the transformer 13, respectively, so that the secondary voltage and secondary current can be detected. Further, a wattmeter 19 is connected to the output terminal of the commercial AC power supply 11. On the other hand, the output of the intermittent charge control circuit 20 is applied to the thyristor control circuit 21, and the output of the thyristor control circuit 21 is applied to the control terminal 22 of the thyristor 12.

The output signal of the commercial AC power supply 11 is boosted to 20 to 100 KV by the transformer 13, and this boosted output signal is charged between the discharge electrode 15 and the dust collection electrode 16 to induce corona discharge.

The electrostatic precipitator used in this invention is configured to be able to switch between continuous charging mode and intermittent charging mode, and the switching is performed by an intermittent charging control circuit 20, a thyristor control circuit 21, and a thyristor 12, as will be described later. .

FIGS. 3a and 3b are diagrams respectively showing the voltage waveform and current waveform during intermittent charging in the charging method of the electrostatic precipitator of the present invention, where the horizontal axis is the time axis, and the intermittent charging is performed every cycle time T. .

That is, the secondary voltage V is charged between the discharge electrode 15 and the dust collection electrode during the charging time _t1 from the start point of the period time T,
Thereafter, charging of the secondary voltage V is stopped during a charging pause time _t2 . The period time T and the charging time _t1 of the secondary voltage are selected depending on the physical and chemical conditions of the processing gas and dust flowing into the electrostatic precipitator, such as gas composition, gas pressure, gas temperature, and dust particle size. In the intermittent charging method, intermittent charging is performed every cycle time T. In this case, the average secondary voltage and average secondary current during the charging time are charging time t ₁
represents the average secondary voltage and average secondary current in
The charge rate γ is expressed as γ=t ₁ /t ₁ +t ₂ , and in a continuously charged state, γ=1.

From the intermittent charging control circuit ₂₀ in FIG.
1 is given. The output signal of the thyristor control circuit 21 is applied to the control terminal 22 to control the thyristor 12, and a secondary voltage signal as shown in FIG. 3a is obtained from the secondary side of the transformer 13 via the rectifier 14. , this secondary voltage signal is applied to the discharge electrode 15 of the electrostatic precipitator.

If the power consumption element value during continuous charging is PW(C), the power consumption element value during intermittent charging is PW(I), and the charging rate is γ, then the average secondary voltage during charging time t ₁ is V, and the average secondary voltage is The following equations are obtained by setting the current to I.

PW(C)=V・I ……(1) PW(I)=V・I・γ ……(2) The inventors operated the electrostatic precipitator at various charge rates and found the benefits in each case. As a result of conducting research on the relationship between power consumption, power consumption element value, and dust collection efficiency, conducting actual measurements, and proceeding with analysis, we found that the power consumption element value is proportional to the power consumption, and the dust collection efficiency η and charging rate γ and Fig. 5 a, b, c.
It turns out that there are three states shown in the following. The dust collection efficiency η in this case is defined by the ratio of the dust content in the gas measured at the inlet and outlet sides of the electrostatic precipitator.

Figure 5 a, b, and c show the electrostatic precipitator when the charging rate γ is set to 0.25 and when γ is continuously charged.
The dust collection efficiency η was measured for each case by operating with the setting set to 1.0. Figure 5a shows that when operating in the continuous charging mode, the charging rate is
The dust collection efficiency η is higher than that in the case of intermittent charging mode operation at a charging rate of 0.25, and in Figure 5b, the case of continuous charging mode operation is higher than that in the case of intermittent charging mode operation at a charging rate of 0.25. Dust collection efficiency η is low. Further, in FIG. 5c, the dust collection efficiency does not change between the continuous charging method and the intermittent charging method at a charging rate of 0.25.

The inventor believes that this is because the discharge state is subtly affected by the electric resistance value of dust near the boundaries of the normal discharge region D, corona discharge suppression region E, and reverse ionization region F in Figure 2. This has been clarified as a result of actual measurements and analysis of actual measurement data.

On the other hand, Figure 6 shows the relationship between the power consumption element value and the charging rate actually measured by the inventors, and the power consumption element value PW is determined by the average secondary voltage and average secondary current during operation in a continuous charging state γ = 1.0. By measuring =V·I, points P shown in FIGS. 6a to 6c are obtained. Next, a straight line is created by connecting this point P to the origin of the coordinate system. These straight lines represent the theoretical VIγ that can be realized by maintaining the continuous charging conditions as they are. In other words, if the electrostatic precipitator that is currently operating in the continuous charging method is switched to the intermittent charging method, the power consumption element value PW at this time can theoretically be reduced.
should lie on these straight lines. Power consumption element value PW (I) obtained by switching an actually operating electrostatic precipitator to an intermittent charging method with a charging rate of 0.25
are points S in FIG. 6a, b, and c, respectively.

Figure 6a shows that the power consumption element value η when operating in the intermittent charging method with a charging rate of 0.25 is less than or equal to the value obtained by multiplying the power consumption element value when operating in the continuous charging method with a charging rate of 1.0 by the charging rate. This is the case. b is charge rate 0.25
This is a case where the power consumption element value during operation in the intermittent charging method is larger than the value obtained by multiplying the power consumption element value during operation in the continuous charging method with a charging rate of 1.0 by the charging rate, and C is the charging This is a case where the power consumption element value during operation in the intermittent charging method with a charging rate of 0.25 is approximately equal to the value obtained by multiplying the power consumption element value during operation in the continuous charging method with a charging rate of 1.0 by the charging rate.

The results of the inventor's research and actual measurements based on the research,
Corresponding to each state of Fig. 6 a, b, c,
It was confirmed that there is a certain relationship between the dust collection efficiency of the electrostatic precipitator obtained when operating with the continuous charging method and when operating with the intermittent charging method. In other words, the dust collection efficiency η of the electrostatic precipitator obtained when operating with each charging method
It is clear that a, b, and c in both figures correspond to each other between Fig. 5 showing the power consumption element values during operation with each charging method and Fig. 6 showing the power consumption element values during operation with each charging method. Ta. According to the inventors, the charge rate is 0.1 to
It has been confirmed that this correspondence condition is satisfied within the range of 0.5.

Therefore, according to the present invention, while an electrostatic precipitator is in operation, the theoretical power consumption element value when operating in the intermittent charging method and the intermittent charging method are obtained based on the power consumption element value during operation in the continuous charging method. By comparing the actual power consumption element values obtained during operation, it is possible to determine which charging method has better dust collection efficiency. Therefore, based on this determination result, the charging method of the electrostatic precipitator currently in operation can be switched to a charging method that provides high dust collection efficiency.

In other words, while operating an electrostatic precipitator using the continuous charging method,
The operation is switched to the intermittent charging method for a short time, and the power consumption element values PW(C) and PW(I) in each charging method are measured before and after the switching. Next, PW(C)γ is determined from the power consumption element value obtained during operation in the continuous charging method, and this is compared with the power consumption element value obtained during operation in the intermittent charging method.
Is PW(I)<PW(C)γ or PW(I)>PW(C)
Determine whether it is γ.

As a result, if the judgment result of PW(I)<PW(C)γ is obtained and it is judged that the state corresponds to Fig. 6a, in this case, the continuous charging method is recommended as shown in Fig. 5a. Since this results in high dust collection efficiency, the conventional operating state, ie, the continuous charging method, is used.

If the judgment result is PW(I)>PW(C)γ, and it is judged that the state corresponds to Fig. 6b, then according to Fig. 5b, the intermittent charging method has better dust collection efficiency. Therefore, the intermittent charging method is used. In this case, the switching state performed for comparing the power consumption element values is maintained as it is, and the electrostatic precipitator is operated.

If the judgment result is PW(I) = PW(C)・γ, depending on the processing gas conditions and operating conditions of the electrostatic precipitator, intermittent charging method may have better dust collection efficiency, or continuous charging method may result. There are some cases where dust collection efficiency is better when operating at In this case, during the trial run of the electrostatic precipitator, it is necessary to determine which charging method will yield higher dust collection efficiency when PW(I) = PW(C), depending on the processing gas conditions and operating conditions of the electrostatic precipitator. The settings are made in advance to correspond to each other.

Therefore, if PW(I) = PW(C) is obtained as a result of the determination, it is necessary to decide whether to operate the electrostatic precipitator in the continuous charging method or the intermittent charging method in accordance with the preset conditions. The charging method is determined and the operation is performed using that charging method.

In this way, the charging method during operation of the electrostatic precipitator is switched during operation for a determined operation time, and the power consumption element value when operating with different charging methods before and after switching, that is, when operating with continuous charging method and intermittent charging method. Find PW(I) obtained from these and
PW(C)γ is compared to determine which charging method will result in higher dust collection efficiency, and the selected charging method is operated. In this case, if the intermittent charging method is used, the charging rate used in the measurement at the time of the determination operation is used.

The interval between the determination operations performed by changing the charging method is determined depending on the processing gas conditions and the operating conditions of the electrostatic precipitator. According to research by the inventors and actual measurements based on the research, it has been confirmed that it is sufficient to perform the determination operation every 1 to 2 hours when the processing gas conditions and the operating conditions of the electrostatic precipitator do not change much. However, if the processing gas conditions fluctuate drastically, it is necessary to perform the determination operation every 10 to 30 minutes.

Also, change the charging method and calculate the power consumption element value.
The determination operation time for performing the determination operation based on this requires at least one second until the charging state becomes stable, and several seconds are required if the charging method is frequently switched. If this judgment operation time is too long, the dust collection efficiency of the electrostatic precipitator may decrease during this judgment operation, so it is necessary to avoid a judgment operation time of 10 seconds or more.

The value of charge rate γ used in the determination operation is 0.1 to 0.5. When the charge rate γ is γ<0.1, it is often not possible to maintain the dust collection efficiency at an optimum state, and when γ>0.5, the energy saving effect may not be obtained. Furthermore, in the hysteresis curve of a high-voltage transformer, the minimum unit that can be handled in order to avoid one-sided saturation is a half cycle, but in this invention, the charging time t ₁ and the charging pause time t ₂ are defined as one AC cycle or an integral multiple thereof. It is possible to treat it as a unit.

The switching operation of the above charging method in this invention,
Calculation of power consumption element values by measuring secondary voltage and secondary current, calculation from power consumption element values in continuous charging method
Calculation of PW(C)γ, PW obtained before and after switching
Operations such as a comparison operation between (I) and PW(C)γ and selection of a charging method based on a determination based on the result of the comparison operation can be performed using a microcomputer system.

For example, the actual operating conditions in which the present invention was applied 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 were as follows.

In this case, the gas temperature was approximately 220° C. on the inlet side, and the dust concentration was 6 to 12 g/m ³ . The secondary voltage and secondary current when operating in the continuous charging method with γ = 1.0 are 54.2 KV and 266 mA, respectively, and in this case
PW(C)=14.4VA.

While the electrostatic precipitator was operating in the continuous charging mode, when the charging method was changed to the intermittent charging mode with γ = 0.25 for 3 seconds, the secondary voltage and secondary current were 50.4 KV and 421.7 mA, respectively. Ta. In this case, PW(I)=50.4×421.7×0.25=5.31VA, and PW(C)×γ=14.4×0.25=3.6VA. Comparing the two, it was found that PW(I)>PW(C)γ, so from then on, operation was performed using an intermittent charging method with a charging rate γ=0.25.

The secondary voltage and secondary current obtained while operating a similar electrostatic precipitator with intermittent charging method of γ = 0.25 are
It was 55KV and 256mA. In this case PW(I)=55
×256 × 0.25 = 3.52 VA, and when operating in a continuous charging mode with γ = 1.0 for 3 seconds, the secondary voltage and secondary current were 56 KV and 225 mA, respectively.

In this case, PW(C)=18.2VA, and PW(C)γ=
18.2×0.25=4.55 was obtained, and PW(C)γ before and after switching
When compared with PW(I), PW(I)<PW(C)×γ, so from then on, the electrostatic precipitator is operated in a continuous charging mode.

"Effects of the Invention" According to this invention, it is possible to quantitatively understand the occurrence of a remarkable reverse ionization phenomenon that requires switching of the charging method in a dry electrostatic precipitator during operation, and to determine whether the operation with any charging method will result in high dust collection. It is possible to determine whether efficiency can be achieved and operate the electrostatic precipitator in a state with high dust collection efficiency.

This determination operation is as simple as switching the charging method of the electrostatic precipitator to a different method than the one currently in operation for a short period of time during operation, and comparing and calculating the values obtained based on the power consumption element values before and after switching. This determination operation immediately determines which charging method has the best dust collection effect.
By selecting a charging method based on this determination result, it is possible to perform operation using a charging method that provides a good dust collection effect, and the power consumption can also be reduced.

As explained in detail above, according to the present invention, an operating electrostatic precipitator is caused to perform a judgment operation by changing its charging method, and a charging method with excellent dust collection efficiency is selected based on the judgment operation. Thus, it is possible to provide a charging method for an electrostatic precipitator that allows the electrostatic precipitator to be operated under conditions of high dust collection efficiency and low power consumption.

[Brief explanation of drawings]

Figure 1 shows the relationship curve between secondary voltage and secondary current during operation in an electrostatic precipitator, where A is the relationship curve obtained when only air is flowing, and B is the relationship curve obtained when gas is flowing. The obtained relational curve, C is the relational curve obtained in the state where the reverse ionization phenomenon occurs, Fig. 2 is a diagram showing the relation between the electrical resistance value of dust and the secondary voltage and secondary current in an electrostatic precipitator, Fig. 3a, b
are diagrams showing the secondary voltage waveform and secondary current waveform during intermittent charging of the electrostatic precipitator, respectively. FIG. 4 is a block diagram showing an example of the control circuit used for carrying out this invention. FIG. 5 a, b, and c are FIGS. 6A, 6B, and 6C are diagrams showing the relationship between the charging rate and the dust collection efficiency, and FIGS. 6A, 6B, and 6C are diagrams showing the relationship between the charging rate and the power consumption element value. 11: Commercial AC power supply, 12: Thyristor, 1
3: Transformer, 14: Rectifier, 15: Discharge electrode, 1
6: dust collection electrode, 17: secondary voltmeter, 18: secondary ammeter, 19: wattmeter, 20: intermittent charging control circuit,
21: Thyristor control circuit, T: cycle time, t ₁ :
Charging time, _t2 : Charging pause time, γ: Charging rate, PW
(C): Power consumption element value during continuous charging, PW (I): Power consumption element value during intermittent charging.

Claims (1)

[Claims] 1. During operation of the dry electrostatic precipitator, switch the charging method of the voltage applied between the discharge electrode and the dust collecting electrode to the charging method that is currently not being charged, either the continuous charging method or the intermittent charging method with a charging rate γ, and switch this. Power consumption element value PW(C) in continuous charging method before and after
Compare PW(C)・γ obtained from PW(I) with the power consumption element value PW(I) in the intermittent charging method,
For (C) and γ, select the continuous charging method, and PW (I)>
In PW(C)/γ, an intermittent charging method with a charging rate γ is selected to charge the dry electrostatic precipitator and continue its operation.