JPS6094160A - Operation of electric dust collector - Google Patents

Abstract

PURPOSE:To prevent reduction of dust collecting efficiency and loss of electric power by operating apparent specific resistance of dust from measured temp. of dust-contg. gas and its humidity and selecting automatically the charging system by judging generation of back fire and condition thereof. CONSTITUTION:Relations between apparent specific resistance of dust to be collected, temp. and humidity of the dust-contg. gas are previously measured prior to operation. Numerical formulas obtd. from measurements are inputted to a storage part 15 of a microcomputer 12. Operation is started from this state and the temp. and humidity of the dust-contg. gas in the inside of a dust collecting part 7 are detected by respective sensor 8, 9; the values are inputted for substitution in an operation part 14 to operate the apparent specific resistance of the dust. Suitable charging system satisfying necessary charging characteristics stored in the storage part 16 is discriminated from obtd. results and control circuits 22-24 of control systems corresponding to each charging system are selected, and the operation is performed.

Description

[Detailed Description of the Invention] The present invention calculates the apparent resistivity value of dust by measuring the temperature and humidity of dust-containing gas, and determines the presence or absence of back corona and its state. The present invention relates to a method of operating an electrostatic precipitator that automatically selects a charging method based on the selected charging method.

Conventionally, the apparent resistivity of the dust that an electrostatic precipitator attempts to collect has been considered to be a factor that greatly influences the dust collection efficiency.Especially, the apparent resistivity of the dust It is well known that in a region exhibiting high resistance, a back corona is generated on the surface of the collecting m'rrLw, which significantly reduces the dust collecting efficiency.

By the way, theoretically and experimentally, a nokku corona occurs when the apparent resistivity of dust exceeds about 10Qcm, and furthermore, the apparent resistivity exceeds 1011Ωt1n.
If this happens, corona will be very likely to occur.

Normally, the dust collecting electrode absorbs all the anions from the discharge wire, but the bank corona absorbs all the anions from the dust collecting electrode, generates positive ions, and diffuses them into the dust collecting space. Therefore, when a negative corona occurs, the amount of dust charge decreases significantly, and the amount of positive charge due to cations and uncharged neutral dust increases. Since the force that attracts dust to the collecting electrode is buj, which follows Coulomb's law, dust collection cannot be carried out successfully in such a state. Moreover, the electricity will be consumed for the Nokutsuku Corona.

In the prior art, experimental methods for detecting the occurrence of back corona include detection of positive ions using an ion probe and methods of using luminescence associated with back corona as a detection element. However, when used in an actual dust collector, it is impossible to monitor the entire surface of the dust collector electrode plate, and if used for a long period of time, dust may adhere to the detection glove or mirror, etc., making maintenance difficult. It was difficult and impractical.

Because the occurrence of back corona could not be detected in this way,
It is necessary to measure the charging voltage waveform and the voltage/current characteristics of the dust collector before deciding whether to apply a control method to deal with phenomena such as frequent spark discharges or increases in corona discharge current due to the occurrence of back corona. However, there were drawbacks such as delays in countermeasures against back corona and inability to respond to changes in the state of back corona occurrence due to changes in gas conditions, etc.

The present invention focuses on the relationship between the apparent resistivity of dust, the presence or absence of back corona, and the state of back corona, and provides a new electrostatic precipitator that eliminates all of the above drawbacks. All driving instructions are provided.

The most significant effect that the apparent resistivity of dust has on the charging characteristics of a precipitator is the formation of bank corona. Back corona occurs when dust with apparently high resistivity is deposited on the dust collector plate, and the voltage applied to the deposited dust layer increases, causing partial dielectric breakdown within the dust layer1.
When dust, which has an apparently low fixed resistance, is deposited on the dust collecting electrode plate, the corona discharge characteristics change only slightly. When the apparent fixed resistance of the dust increases, corona ions are blocked by the electrical resistance of the dust layer, the voltage of the dust layer increases, and the voltage of the gas flow space decreases. As the apparent fixed resistance of the dust further increases, the voltage across the dust layer also increases, and eventually dielectric breakdown occurs locally within the dust layer.

This point is the starting point of bank corona. The conditions for starting the back corona can be expressed as follows:' [a=j*ρd≧Eds.

Here, Ed: electric field strength in the dust layer, j: current density, ρ
d: The apparent resistivity of dust is the upper resistivity value, Eds" dust layer 4iI breakdown electric field strength. Therefore, if the current density j is constant, back corona will occur more easily as the upper resistivity value ρd is larger. I understand.

The appearance of dust can be roughly classified as follows when all the effects of the above specific resistance value ρd on the charging characteristics are sorted out.

(1) Normally charged region [ρd〈1o10(Ωcrn)]・
...Region where no back corona occurs ■Region where spark discharge occurs frequently [ρd-1010~10" (Ωcr
Month n: Region where back corona occurs, spark discharge voltage decreases, and extremely intense spark discharge occurs (6) Region where corona discharge current increases [ρd>10” (9 cm)]…Back corona occurs The corona discharge current spreads over the entire surface of the dust layer of the dust collector plate, and the charging voltage decreases as the corona discharge current increases rapidly.In addition, the occurrence of spark discharge decreases.

As mentioned above, the charging characteristics of a dust collector vary depending on the value of the above specific resistance value ρd, so the appearance of dust can be determined by measuring the above specific resistance value ρd. It is possible to determine which region the characteristic is in.

To directly measure the apparent resistivity of dust, a high voltage is applied to a needle-like electrode and a flat electrode, and the apparent resistivity of dust is calculated from the current flowing through it. Although there are methods, it is difficult to install it in an actual dust collector and measure it continuously.

Based on the above, in the present invention, the apparent resistance of dust is not measured directly by the specific resistance value, but the apparent resistance of dust is determined by focusing on the fact that the specific resistance value is greatly affected by temperature and humidity. By measuring this as a parameter, the apparent resistivity of the dust is calculated, and the occurrence and state of back corona is automatically determined to select the charging method.

An embodiment of the present invention will be explained using FIG. 1 and FIG. 2. In Fig. 1, 1.1' is an AC input terminal, 2 is a circuit breaker, 6 is a main control element such as a Zyristor or a saturable reactor, 4 is a current limiting reactor, 5 is a high voltage transformer, 6
is a high voltage rectifier, 7 is a dust collector, 8.9 Fi sensor, 10 is a temperature-voltage signal converter, 11 is a humidity-voltage signal converter,
12 is a microcomputer consisting of an interface circuit 16, an arithmetic unit 14, a storage unit 15, 16, etc.; 17;
18 is a drive circuit, and 18 is a control section consisting of electronic switches 19-21 and control circuits 22-24.

Prior to operation of the electrostatic precipitator having such a configuration, first the second
As shown in the figure, the relationship between the apparent resistivity ρd of the dust to be collected and the temperature Tg and humidity Wg of the dust-containing gas is measured in advance. From the measurement results, the apparent resistance of the dust is determined by the function ρd of the above specific resistance value ρd=temperature Tg and humidity.
This formula is expressed as f(1g2wg) and input into the storage unit 15 of the entire microcomputer-2. When the dust collector starts full operation, the temperature T and humidity wg of the dust-containing gas inside the dust collector 7 are detected by the respective sensors 8 and 9, and the temperature-voltage signal converter 10 and the humidity-voltage signal converter 1 are detected.
1 to each standardized voltage and input it to the interface circuit 16 of the microcomputer 2. The formula ρd=f(Tg, Wg
) are substituted with the measured values Tg and Wg, and the calculation unit 14 calculates the apparent specific resistance value ρd of the dust. The apparent value obtained as a result is input in advance to the storage unit 16 from the upper specific resistance value ρd.
Classification of charging characteristics according to the value of Ωα It is determined which category of the month it corresponds to.As a result, the drive circuit 17
One of the electronic switches 19 to 21 is driven by
One of the control circuits 22 to 24 based on a control method corresponding to each of the six charging characteristics is selected, and the selected control circuit is able to complete the operation. The control circuit 22 for the "normal charging region" uses a conventionally commonly adopted control method using spark frequency control or spark tracking control, and the control circuit 23 for the "frequent spark discharge region" has a basic control function of controlling the number of sparks. The control method is the same as the spark tracking control and the spark tracking control, but the temporary pause time after spark detection and the 9-hour start-up time during recharging are set shorter. Further, the control circuit 24 for the "corona discharge current increase region" uses a voltage waveform control method that changes the phase angle of the thyristor on a cycle-by-cycle basis and controls the peak value of the charging voltage to be completely high.

As described above, in this example, the appearance of dust can be detected by a microcomputer by measuring the temperature Tg and humidity of the dust-containing gas, which have a large influence on the specific resistance value. By determining the specific resistance value ρdti of the dust, determining whether the dust condition is in the back corona generation area, and what the back corona condition is, and automatically selecting the control method, it is possible to always apply the optimal load tar. Can be done.

As described above, in the present invention, by measuring the temperature and humidity of the dust-containing gas, the apparent specific resistance of the dust is calculated, and the presence or absence of back corona generation and its state are determined. Since the charging method is automatically selected, it is possible to prevent a significant drop in dust collection efficiency due to back corona and power loss due to an increase in corona discharge current due to back corona. In particular, it is very effective if implemented as a counter-ionization countermeasure for electrostatic precipitators in equipment where the furnace is frequently operated or stopped, or in equipment where gas conditions tend to fluctuate.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a circuit for explaining one embodiment of the method of operating an electrostatic precipitator according to the present invention, and Fig. 2 shows the apparent specific resistance of dust, temperature, and humidity. FIG. 1.1'...AC input terminal 2...Circuit breaker 6.
...Main control element 4...Current limiting reactor 5...High voltage transformer 6...High voltage rectifier 7...Dust collector 8,9.
... Sensor 10 ... Temperature-voltage signal converter 11 ... Humidity-voltage signal converter 12 ... Microcomputer 16 ... Interface circuit 14 ... Arithmetic unit 1
5.16...Storage unit 17...Drive circuit 18...
Control unit 19-21...Electronic switch 22-24...
・Control circuit patent applicant Origin Electric Co., Ltd.

Claims (1)

[Claims] The appearance of dust is determined by the relationship between the above specific resistance value and the temperature and humidity of the dust-containing gas. Calculate all the specific resistance values of , determine which category of the above categories the apparent resistance value of the dust falls under based on the magnitude of the specific resistance value, and use the control method that is most suitable for the applicable category. A method of operating an electrostatic precipitator, which is characterized by operating an electrostatic precipitator.