JP2607680B2 - Electric precipitator and operating method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is applicable to a high-speed flow having a main gas flow rate of 4 m / s or more.
The present invention relates to an electrostatic precipitator for collecting particulate matter such as dust, dust, mist, fume and the like with high efficiency.

[Prior art] An electrostatic precipitator is provided in a dust collecting space formed by a discharge electrode (high voltage side electrode) and a dust collecting electrode (earth side electrode).
Particulate matter such as dust, dust, mist, fume, etc., which is led along with the main gas, is charged by the corona current flowing between the electrodes, and at the same time, by the Coulomb force generated by the high electric field applied between the electrodes. It moves to the dust collecting electrode side and is collected, and is roughly classified into two types, a dry type electrostatic precipitator and a wet type electric precipitator.

A dry electrostatic precipitator is a collection of dried solid particulate matter, which is collected and deposited on a collecting electrode in a dry state, and the deposited layer is formed to a sufficient thickness. When growing, for example, by giving a mechanical impulse such as hammering a dust collecting electrode, the sedimentary layer is separated and dropped to discharge particulate matter into a hopper. For the purpose of preventing the particulate matter collected and deposited on the electrode from re-scattering, the main gas flow velocity in the dust collection space has conventionally been about v = 1m / s (0.5 to 2m / s) for general industrial use.
Is usually selected. In such a main gas flow velocity range, when the current density is increased, the trapping performance of the particulate matter increases up to a certain current value, but even if the current value is further increased, the performance does not increase. It is known that performance may be rather reduced before reaching the rated maximum current.

Fig. 9 shows the average current density i (mA / m ² ) in an electric precipitator (main gas flow velocity v1m / s) for collecting soot and dust generated from a coal-fired boiler, and the moving speed of Deutsch as a performance evaluation index. W (m / s) W (m / s) =-ln (1-η) / (F / Q) where η is the particulate matter collection efficiency of the electrostatic precipitator, F (m ² ) is the electric precipitator An example of the relationship between the dust collection area of the device and Q (m ³ / s): the flow rate of the processing gas of the electrostatic precipitator is shown. The W value shows a tendency to saturate near i = 0.1 mA / m ^2. When the value of i is further increased, the W value shows a decreasing tendency.

This amount of charge is increased to provide the particulate matter according to raise the i in the region of i0.1mA / m ^2, and since the electric field becomes stronger, the greater the Coulomb force acting on the particulate matter trapping performance In the area of i> 0.1 mA / m ² , the secondary flow due to ion wind increases with the increase of corona current, and the flow situation in the dust collection space is disturbed, and the dust is collected and deposited on the dust collection electrode. It is described that, although i is increased, the performance is no longer improved because the re-dispersion of the generated particulate matter is promoted.

Therefore, in a dry-type electrostatic precipitator, i = 0.15 mA / m in consideration of economy, power supply capacity, spark pressure resistance, etc.
^It is often set to about ² (about 0.1 to 0.2 mA / m2).

On the other hand, the wet-type electrostatic precipitator is a system in which water is applied to the surface of the dust collecting electrode to form a film, or water is sprayed into the dust collecting space, and the particulate matter collected on the dust collecting electrode is washed away with water. However, in the case of the wet type, since the re-scattering of trapped particulate matter is less than in the case of the dry type, the main gas flow rate is often set empirically to be higher than that of the dry type. Conventionally, v = 2 m / s (1
(About 3 m / s). When the current density is increased in such a main gas flow velocity range,
It is known that, unlike the case of the dry method, the current value is increased and the trapping performance of particulate matter is improved almost monotonously.

Figure 10 shows a wet-type electric precipitator (main gas flow rate of 1 m) installed after a flue gas desulfurization unit in a coal-fired boiler plant.
An example of the relationship between i (mA / m ² ) and W (m / s) at (/ s) is shown, but the W value increases almost monotonically as i increases.

When i exceeds about 0.5 mA / m ^2, the slope of the increase in the W value tends to decrease, but this is due to the improvement in the collection performance of the wet-type electrostatic precipitator, which is at the outlet of the wet-type electric precipitator. Since the concentration of particulate matter is extremely low, 1 mg / m ³ N or less, the measurement limit of this example (JIS Z8808) is exceeded, and the slope of the apparent increase in W value tends to decrease. it is conceivable that.

Therefore, in the wet electrostatic precipitator apparatus used in the conventional flow rate range, economy, power capacity, after taking into consideration also the spark breakdown voltage, etc., i = 0.5mA / m ² about (0.25~1mA / m ² approximately) It is usual to design so that a predetermined outlet particulate matter concentration is achieved at a setting.

As described above, the conventional electrostatic precipitator is based on the idea and principle of charging dust by corona discharge and collecting by Coulomb force using the electric field of the dust, and was determined empirically. Electrode spacing of about 100 to 200 mm, that is, utilizing the maximum voltage or current that can be charged by the device at the distance between the dust collection electrode and the discharge electrode, and in general industrial use, when the plant is in rated operation, Empirically, when the main gas flow rate is dry, 0.5 to 2 m / s,
In the case of a wet type, it is designed to be in a range of about 1 to 3 m / s.

In other words, the conventional electric precipitator is designed on the assumption that the gas flow rate is 0.5 to 2 m / s in the case of dry type and 1 to 3 m / s in the case of wet type. The current density at which dust collection saturates, i.e., 0 for dry type.
1mA / m ² ~0.2mA / m ² approximately, in the case of wet is 0.25 mA / m ²
The current density is set to about 1.0 mA / m ² , and a current density in a region higher than 1.0 mA / m ² is not employed because there is no empirical advantage in performance and power consumption increases.

Therefore, attention is paid to the behavior of the ion wind generated by corona discharge, and an operation method for setting the current value of the electrostatic precipitator in consideration of the relationship between the flow rate of the ion wind and the flow rate of the main gas, and an operation method thereof are realized. There has been no example of an apparatus in which the electrode spacing is narrowed in order to secure a current value to be set.

In some electrostatic precipitators used in air purifiers, etc., only the former charging section for the purpose of charging only particulate matter, and only the collection of particulate matter charged in the former stage are required. For the purpose, there is a method in which a two-stage type dust collecting method is adopted, which includes a latter-stage dust collector that gives only a high electric field without flowing a current. In this case, the latter-stage dust collector is separated by a unit gas amount. In general, the distance between the high-voltage side electrode and the ground side electrode is made to be a nano-spaced structure in order to reduce the size and the power supply capacity by increasing the dust collection area. The purpose of the narrow spacing is to obtain a high electric field strength at a relatively low voltage. Since corona discharge hardly occurs in this dust collecting portion, no ion wind is generated, and therefore, the narrow space is generated by corona discharge. Focusing on on-air non-na wax Spain sequencing was intended to secure and set the current in consideration of the relationship between the flow velocity of the main gas and the flow rate of the ionic wind.

FIG. 11 shows an example of a two-stage electric precipitator currently used in an air purifier. In FIG. 11, the high voltage side electrode 15 and the dust collecting electrode (earth side electrode) in the dust collecting part 14 are shown.
The spacing of 9 is usually narrow spacing of about 5 to 10 mm. However, since the electrodes are arranged in a parallel plate shape, corona discharge from the high voltage side electrode 15 hardly occurs. In addition, there is almost no ion wind caused by corona discharge. In FIG. 11, reference numeral 8 denotes a discharge electrode, 11 denotes a supporting insulator, 12 denotes a high-voltage power supply, and 13 denotes a charging unit.

[Problems to be Solved by the Invention] In the conventional general-purpose electric precipitator, the main gas flow rate in the dust collecting space is usually v = 1 m / s in the case of the dry type as described above.
(0.5-2m / s), v = 2m / s (1-3m / s)
s) Although the degree is selected with common sense, there is currently a strong demand for miniaturization of these electrostatic precipitators, that is, by setting the main gas flow velocity higher and reducing the main gas passage cross-sectional area of the electric precipitator. Accordingly, it is strongly desired to increase the amount of processing gas per unit volume of the dust collector.

In various plants for general industry, the gas flow velocity in the flue gas flue is about 15 m / s, which is the economic flow velocity, and it is usual to set this flow velocity. If the main gas flow velocity is increased to the same as the gas flow velocity in the flue, that is, to about 15 m / s, and high-efficiency dust collection is possible, make the main gas passage cross-sectional area of the electric precipitator equal to the flue cross-sectional area. Is possible, that is, it becomes possible to set and install an electrostatic precipitator in the exhaust gas flue.
A great cost reduction effect can be obtained.

In addition, by setting the main gas flow rate of the electrostatic precipitator equal to the main gas flow rate that is faster than the electric precipitator of the equipment disposed on the upstream side or the downstream side, the cross sectional area of the front and rear devices is reduced. By eliminating or restricting the flue between the equipment and the enlarged part of the flue, directly connecting or integrating the equipment and the electrostatic precipitator together with the downsizing of the electric precipitator by increasing the main gas flow velocity Can be expected to reduce total cost.

For example, as one of the main applications of the wet electrostatic precipitator, installed downstream of the flue gas desulfurization apparatus of the plant of the exhaust gas boiler, salts or dust dust and SO ₃ mist carryover from FGD In the case of collection, the outlet of the flue gas desulfurization device on the upstream side of the wet type electrostatic precipitator has a flow rate of 4 to 4 because a mechanical mist eliminator is attached to prevent carry-over of large particle size spray mist.
Since it is normal to be set to 6 m / s, if the wet type electrostatic precipitator can be set to the same main gas flow rate as the flue gas desulfurization unit outlet of 4 m / s or more, and high efficiency dust collection can be performed ,
Approximately half the cross-sectional area of conventional wet electrostatic precipitators
At the same time, the device can be directly connected to the flue gas desulfurization device or can be integrated with the flue gas desulfurization device, so that the total cost can be greatly reduced.

Also, in the case of a dry-type electrostatic precipitator, air heaters, upstream and downstream of the dry-type precipitator in general industrial processes are used.
Denitration equipment etc. are usually installed according to heat exchangers such as gas heaters or flow schemes, but the superficial velocity of the Jungstrom type air heater is about 10 m / s or less, and the superficial superficial velocity of the gas heater depends on the heat exchange method. Although it is different, considering that there are many 4 to 5 m / s and the superficial velocity of the denitration equipment is about 5 to 6 m / s, it is possible to collect dust with high main gas flow rate of 4 m / s or more If a dry-type electrostatic precipitator can be realized, the cross-sectional area of passage can be reduced to about 1/2 to 1/8 compared to the conventional dry-type precipitator, and at the same time, it should be directly connected to the front and rear heat exchangers or be integrated. It is possible,
Great cost reduction is possible in total. It is strongly desired to realize a high-efficiency electrostatic precipitator in a high-speed flow with a main gas flow velocity of about 4 m / s or more in both wet and dry systems.

However, in order to set the flow state and the charge state in the dust collecting space in the electrostatic precipitator so that the main gas flow velocity is increased and the trapping performance of the particulate matter is kept good, first, first, Main gas flow velocity v in high flow velocity range of 4m / s or more
To determine the average current density i so as to optimize the performance, in other words, select the optimum current density i for the main gas flow velocity v in the high flow velocity region of 4 m / s or more. Second, it is necessary to provide a biased index such as the following, and secondly, the current density i selected in the index can be realized even when the space charge is large. It is necessary to give the structure.

An object of the present invention is to provide an electric precipitator capable of solving the above-mentioned conventional problems.

[Means for Solving the Problems] Regardless of the state of the main gas flow velocity, re-dispersion and collection of trapped particulate matter by too strong ion wind while securing an appropriate corona current and electric field for dust collection. In order to maintain good dust collection performance without causing large turbulence in the flow in the dust space, it is necessary to set the ratio between the main gas flow velocity and the ion wind appropriately.

A dimensionless number, which is the ratio of the main gas flow velocity v to the ion wind velocity v _ion , is often referred to as an EHD number and is an important parameter in electrohydrodynamics (EHD). That is, EHD number N _ehd
= V _ion / v.

If the EHD number _Nehd is equal, it is possible to obtain a flow condition similar to the streamline pattern in the dust collection space, both numerical analysis and experimentally in streamline visualization, it has been confirmed, Recognized in the literature.

Therefore, by setting the ion wind velocity v _ion such that an EHD number _Nehd equivalent to the case where good dust collecting properties are known _empirically is obtained, the main gas flow velocity v4m / s In addition, good dust collection is ensured by ensuring an appropriate corona current and electric field for dust collection, and by preventing re-scattering of collected particulate matter and large disturbance of flow in the dust collection space due to ion wind. Performance can be maintained.

An electric precipitator according to the present invention as means for solving the problems is as follows.

(First Means) In a dry-type electrostatic precipitator according to the present invention, exhaust gas is caused to flow between a discharge electrode to which a high voltage is applied and a dust collection electrode, and corona discharge generated by the high voltage causes the exhaust gas in the exhaust gas. A dry electrostatic precipitator for charging particulate matter and collecting the charged particulate matter on a dust collection electrode by an electric field generated by the high voltage, wherein the electrostatic precipitator is a representative operating state of an exhaust gas generation source. , The gas flow cross section is such that the flow velocity v of the exhaust gas is 4 m / s or more, and the average current density i (mA / m ² ) of the corona discharge is set to 0.018 v ² ≦ i ≦ 0.69 v ² It has a control part.

(Second Means) In the wet-type electrostatic precipitator according to the present invention, the exhaust gas flows between the discharge electrode to which a high voltage is applied and the dust collection electrode, and the corona discharge generated by the high voltage causes the exhaust gas in the exhaust gas. In a wet electrostatic precipitator for charging particulate matter and collecting the charged particulate matter on a dust collecting electrode by an electric field generated by the high voltage, the electrostatic precipitator is a representative operating state of an exhaust gas generation source. And a control unit for setting the average current density i (mA / m ² ) of the corona discharge to 0.018 v ² ≦ i while having a gas passage cross-sectional area such that the exhaust gas flow velocity v becomes 4 m / s or more. It is characterized by the following.

(Third Means) A dry-type electrostatic precipitator according to the present invention is characterized in that, in the first means, the shortest distance between the discharge electrode and the dust collection electrode is set to 80 mm or less.

(Fourth Means) The wet electrostatic precipitator according to the present invention is characterized in that, in the second means, the shortest distance between the discharge electrode and the dust collection electrode is set to 80 mm or less.

(Fifth Means) In the dry electrostatic precipitator according to the present invention, in the first means or the third means, the flow rate v of the exhaust gas is controlled by controlling the flow rate of the gas flowing through the equipment connected to the upstream side and / or the downstream side. It is characterized in that the gas passage cross-sectional area is determined so as to be the same as the flow velocity.

(Sixth Means) In the wet type electrostatic precipitator according to the present invention, in the second means or the fourth means, the flow rate v of the exhaust gas may be controlled by adjusting the flow rate v of the gas flowing through the equipment connected to the upstream side and / or the downstream side. It is characterized in that the gas passage cross-sectional area is determined so as to be the same as the flow velocity.

(Seventh Means) In the method for operating a dry-type electrostatic precipitator according to the present invention, exhaust gas flows between a discharge electrode to which a high voltage is applied and a dust collection electrode, and the corona discharge generated by the high voltage causes the exhaust gas to flow. The method for operating an electrostatic precipitator for charging particulate matter in exhaust gas and collecting the charged particulate matter on a dust collection electrode by an electric field generated by the high voltage, wherein the flow velocity v of the exhaust gas is set to 4 m / s or more. And the average current density i (mA / m ² ) of the corona discharge is set to 0.018 v ² ≦ i ≦ 0.69 v ² .

(Eighth Means) In the method of operating the wet electrostatic precipitator according to the present invention, the exhaust gas flows between the discharge electrode to which high voltage is applied and the dust collection electrode, and the corona discharge generated by the high voltage causes the exhaust gas to flow. The method for operating an electrostatic precipitator for charging particulate matter in exhaust gas and collecting the charged particulate matter on a dust collection electrode by an electric field generated by the high voltage, wherein the flow velocity v of the exhaust gas is set to 4 m / s or more. And the average current density i (mA / m ² ) of the corona discharge is set to 0.018v ² ≦ i.

[Operation] It is difficult to measure the ion wind v _ion in a place where the main gas flow velocity exists, and there is a practical inconvenience to use the ion wind speed v _ion as a parameter for specifying the EHD number as it is.

According to the result of experimentally measuring the ion wind speed in a field where the main gas flow velocity does not exist, the ion wind speed v _ion is substantially proportional to the square root of the planar current density i effective for dust collection generated by corona discharge. That is, when k is a proportional constant, However, the average current density i here is limited only to the current density generated by the corona current, and the apparently increased current density contributes to the ion wind regardless of corona discharge due to abnormal charging phenomenon called reverse ionization. Not included.

Therefore, the newly defined parameter Said to be substantially proportional to the parameter to the EHD number _{N ehd = v ion / v (} C is proportional to N _EHD). The parameter C is, for example, (mA) ^1/2 · s / m
It is a dimensional number with dimension ² .

Therefore, instead of the EHD number _Nehd , it is possible to specify a flow state corresponding to each main gas flow velocity using the parameter C, and furthermore, an appropriate current density i is directly determined for the main gas flow velocity v. In that respect, it is also highly practical.

Which is a typical numerical values in conventional dry electrostatic precipitator v = 1m / s, when the i = 0.15mA / m ^2, the parameter C = 0.3871 / 3 (mA) is ^1/2 · s / m ^2, When v = 2 m / s and i = 0.5 mA / m ² , which are typical numerical values in a conventional wet electrostatic precipitator, the parameter C is 0.3541 / 3 (mA) ^1/2 · s / m ² .

Therefore, regardless of the dry type or the wet type, the flow conditions under the conditions where good dust collecting properties are obtained empirically are almost the same, and the flow conditions are similar.

For convenience, the parameter C at each main gas flow rate is changed to a value C ′ = 1/3 (mA) ^1/2 of the parameter C under typical conditions.
・ Defining a new dimensionless parameter C _N = C / C ′ by s / m ² , Becomes Then, from equation (1), i = (1/9) (C _N v) ² (mA / m ² ) (2)

When this parameter C _N is within a certain range centered on C _N = 1 (no dimension) (3), the flow situation in the dust collection space is empirically similar to the case where the dust collection property is good. Becomes

In FIG. 7, for the main gas flow velocity v and the average current density i,
Shows the values of the parameters C _N in solid lines a representative operating conditions of the conventional dry electrostatic precipitator for general industrial v = 1 m
in the center of the ^{/s,i=0.1mA/m 2 v = 0.5~2m / s,} i = 0.1~0.2mA /
The range of about m ² is shown by a broken line. That is, the conditions of v and i in this circle can be considered as a range in which good dust collection performance can be obtained empirically.

As clear from FIG. 7, in the main gas flow velocity v is 4m / s or more high-speed flow, range parameters C _N of 0.4 to 2.5, (hence, the above equation (2), i = 0.018v ² ~ 0.69v ² m
A / m ² ), that is, by setting v and i in the hatched area in FIG. 7, the flow condition in the dust collecting space is empirically improved. Since it is almost similar to the case of the obtained conventional dry type electrostatic precipitator,
Again, it can be expected that good dust collection performance will be achieved.

In the region where C _N is 0.4 or less (i <0.018v ² mA / m ² ), the corona discharge current is small with respect to the main gas flow rate, so that the particulate matter is not sufficiently charged. Since the particles are weak and the electric field strength is low, the moving speed of the particulate matter is low, so that effective dust collection cannot be performed.

In contrary, C _N is 2.5 or more areas also (0.69 <area of i mA / m ^2), primary ions because the wind speed is too large with respect to the gas flow rate, the particulate matter trapped on a time collection electrode It is thought that the amount of re-scattering is large and the dust collection performance is reduced.

FIG. 7 also shows the operating range of the dust collecting portion of the conventional two-stage type electrostatic precipitator for air cleaning by a dashed line. Although there is a case of a high-speed flow of about v = 8 m / s, since the average current density i is extremely low, the operation range in the above-described hatched area does not touch.

In FIG. 8, each value of the parameter C _N is shown by a solid line with respect to the main gas flow velocity v and the average current density i, and the typical operating range of the conventional general-purpose wet electric precipitator for general industry is represented by v = 2m / s, i
= 0.5 mA / m ² is indicated by a broken line.

As described above in the section of the prior art, in the wet electrostatic precipitator, since there is almost no re-scattering of the trapped particulate matter, it is considered that the dust collecting performance is monotonously improved as the average current density i increases. The region indicated by the broken line in FIG. 8 can be considered as a range where good dust collection performance can be obtained empirically.

Eighth range of 0.4 or more parameters C _N even at high flow clear way the main gas flow velocity v is not less than 4m / s from the figure, (hence, the above equation ^{(2), 0.018v 2 <i mA / m} 2 By setting v and i in the shaded area in FIG. 8, the flow condition in the dust collecting space is empirically set to obtain good dust collecting performance. Since it is almost similar to the case of the wet electric precipitator of the type, it can be expected that good dust collecting performance is also achieved.

In the region where C _N is 0.4 or less, the charging of the particulate matter is insufficient due to the small corona discharge current relative to the main gas flow velocity, and the moving speed of the particulate matter is also weak due to weak ion wind and low electric field strength. Is too small to perform effective dust collection.

Conversely, C _N is large area for example C _N ion wind is relatively large with respect to the main gas flow rate was 2.5 larger area, there is little scattered again in the case of dry and Ili trapping particulate matter Therefore, good dust collection performance is achieved.

Taking the case of v = 6 m / s as an example, in order to obtain good dust collection performance, to realize C _N = 1, from the above equation (2), an average of about i = 4 mA / m ² The current density is required, which is almost one order of magnitude higher than the current density normally set in conventional dry and wet type electrostatic precipitators. It is necessary to secure in a stable charge state.

Generally, when the amount of particulate matter to be collected by an electrostatic precipitator is large or the particle size is fine, that is, when the specific surface area of the particulate matter per unit volume is large, a so-called space is used. Due to the charge effect, the corona current flowing between the discharge electrode and the dust collection electrode is suppressed.Therefore, at the interval between the discharge electrode and the dust collection electrode of about 80 to 200 mm, which is often used for general industry, the required corona current is collected. An average current density (i = 4 mA / m ² when v = 6 m / s) effective for dust may not be secured.

In this way, when the space charge is large and the corona current may be greatly suppressed, in order to secure a necessary current density, the interval between the discharge electrode and the dust collection electrode is, for example, 10 to 80 mm.
It is necessary to arrange (narrow spacing) to such an extent that the distance between the dust collection electrode and the discharge electrode is narrow spacing, so that the electrostatic precipitator formed by the particulate matter to be processed by the electric precipitator. Even in the case of the maximum space charge in the inside, it is stable without sparking and is effective against dust collection obtained by corona discharge defined by C _N = 1 for a predetermined main gas flow velocity v Average current density i can be secured.

The narrowing of the electrodes widens the range of the average current density that can be charged and ensures a large corona discharge current, as described in FIGS. 12 and 13.

FIG. 12 shows a model of a cylindrical electric precipitator.

Figure 13 shows the charging characteristics of the air load when the electrode Supeishingu D ₀ in Figure 12 as a parameter.

As shown in FIG. 13, the smaller the electrode spacing D _0, that is, the narrower the spacing, the greater the slope of the characteristic curve of the average current density i with respect to the average electric field intensity E, and the average electric field at the spark generation point is increased. Since the intensity shifts to the high electric field side, it is clear that the maximum average current density, that is, the average current density at the spark generation point can be increased, and a larger corona discharge current can be secured.

[Example] FIG. 1 shows a flow diagram of an example which demonstrates that high-efficiency dry-type dust collection is possible with a high-speed flow of main gas flow velocity v = 4 m / s or more by the method described above. FIG. 2 shows a detailed view of the electric dust collecting apparatus.

In FIG. 1, normal temperature air (a) sucked from the left side
From the particulate matter supply device 1 to the particulate matter supply hole 2
The particulate matter supplied via the above is dispersed and supplied.

The main gas formed as a result is the main body of the electrostatic precipitator 4
The main gas (b) is discharged to the outside of the system after passing through the suction blower 7 after being subjected to dust collection processing in the electrostatic precipitator 4.

The dust collection efficiency of the electrostatic precipitator 4 is obtained by measuring the particulate matter concentration at the inlet particulate matter measuring seat 3 and the outlet particulate matter measuring seat 5, respectively, and the flow rate of the main gas is the orifice flow rate. It is measured by a total of 6.

As shown in FIG. 2, the main body of the electrostatic precipitator 4 includes a discharge electrode 8, a dust collecting electrode 9, and a main body casing 10 of an insulator. The dust collecting electrode 9 is reliably grounded and grounded, the dust collecting electrode 9 and the discharge electrode 8 are electrically insulated, and a high voltage is applied to the discharge electrode 8 supported by the supporting insulator 11 by the high voltage power supply 12. A high electric field is formed between the applied discharge electrode 8 and the dust collection electrode 9.

The shape of the discharge electrode 8 has sharp barb-like projections as shown in FIG. 3, and the electrode spacing between the tip of the barb of the discharge electrode 8 and the surface of the dust collecting electrode 9 is D ₀ = 40 mm, which is a narrow space. As a result, a sufficiently large corona discharge current can flow under the conditions of the supplied particulate matter in the present embodiment described later.

The barb shape of the discharge electrode shown in FIG. 3 is an example actually used in this embodiment, and the barb shape (height,
The width), the pitch, and the like are not limited as long as the required corona discharge current can be achieved according to the conditions of the particulate matter to be treated, that is, the parameter C _N = 1 (C _N > 0.4). Can be arbitrarily selected, and the fourth
FIG. 4 (A) shows a pipe-shaped support with spike-shaped protrusions, FIG. 4 (B) shows a flat bar-shaped end with sharp edges, and FIG. It is also possible to select the shown thin wire or the like.

The electrode spacing can also be arbitrarily selected depending on the conditions of the particulate matter to be treated, as long as a corona discharge current required to achieve C _N = 1 (C _N > 0.4) can be obtained. A narrow spacing of 80 mm or less is required.

The suction blower 9 is selected so that the main gas flow velocity v in the electrostatic precipitator 4 is variable in the range of 1 to 8 m / s, and the particulate matter supply device 1 is solid dust at room temperature. Fly ash (10 kinds of fly ash of JIS Z8901), the main gas flow rate v in the electrostatic precipitator 4 is 1 to
When taking each value of 8m / s, select a device that can adjust the fly ash concentration Si at the inlet of the electrostatic precipitator 4 to 500mg / m ³ and can evenly distribute the fly ash in the flowing normal temperature air. Have been.

FIG. 5 is an example of typical results obtained with the apparatus shown in FIGS. 1 and 2.

The horizontal axis in FIG. 5 indicates the main gas flow velocity v in the dust collection space of the electric dust collector of FIG. 2, and each measured value when v is changed in the range of 1 to 8 m / s and The calculated values are shown on the vertical axis. At this time, the fly ash concentration Si at the entrance of the electrostatic precipitator is constant at 500 mg / m ³ . As the main gas flow velocity v increases, the gas amount Q to be processed by the electric precipitator increases linearly.

On the other hand, the conventional dry electric precipitator (v1m /
s) i = 0.1 mA, which is a typical average current density condition
/ m ² constant, the dust collection efficiency η sharply decreases as the main gas flow velocity v increases, and η = 50% when v = 4 m / s or more.
The performance drops below.

On the other hand, i is set so that the parameter C _N = 1 according to each flow velocity.
When the main gas velocity v was increased, the dust collection efficiency η showed a tendency to increase, and when v = 4 m / s or more, η was almost 90%. That is, the parameters
By setting the average current density i so that C _N = 1, a high-efficiency collector can be obtained even at a high speed flow of v 4 m / s, even in a dry-type electrostatic precipitator, which is generally apt to cause re-dispersion of particulate matter. It was confirmed that dust was possible.

In addition, as in the apparatus shown in FIGS. 1 and 2, the provision of the narrow electrode spacing and the provision of a barbed discharge electrode enables a large corona discharge current to be secured. The representative results obtained are shown in FIG.

The horizontal axis of Figure 6 shows the parameters C _N, the average current density i
The vertical axis represents the Deutsch moving speed W (m / s) as a performance evaluation index. The particulate matter used at this time was dioctyl phthalate (13 type A aerosol of JIS Z8901), and the aerosol concentration Si at the entrance of the electrostatic precipitator was
30 mg / m ³ constant, the main gas flow velocity v is 6 m / s constant, gas temperature 50
℃, water content saturation conditions.

In FIG. 6, by increasing the average current density i, that is, as the parameter C _N is increased,
The tendency was confirmed that the W value increased linearly.

This tendency is due to the conventional wet type electrostatic precipitator (v1m /
s), the same tendency as in FIG. 10. If the average current density i corresponding to the main gas flow velocity can be secured, high-efficiency wet-type dust collection can be achieved even at a high-speed flow of v4 m / s. In the case of a dust apparatus, since the collected particulate matter does not re-scatter, higher performance is obtained as the average current density increases and the ion wind speed increases. And it was confirmed that, unlike the case of the dry type, for example, even in the region of C _N > 2.5, highly efficient dust collection was obtained.

Next, a control method and a control unit of the device of the present invention will be described.

(1) Control of average current density i of corona discharge Parameters such as average current and average voltage are controlled by a high-voltage power supply.
In the control circuit in the controller 12, because it is electrically grasped as a control parameter, knowing the average current i _m, average current density i it is a value obtained by dividing by the dust collecting area
Is uniquely determined.

Control algorithm of the high-voltage power supply 12, the case - but is set by by-case, for example, control such to control the average current density i constant, the average current i _m is grasped as one control parameter, it is possible to control the average current density i by controlling the average current i _m.

(2) Control of gas flow velocity v The device of the present invention is a dust collector (auxiliary machine) mainly installed downstream of an exhaust gas generation source (main plant) such as a power plant. Since the entire amount of generated exhaust gas is processed by the present apparatus, if the gas passage cross-sectional area of the present apparatus is determined, the gas flow velocity v in the present apparatus is uniquely determined according to the amount of gas generated by the main engine.

In designing the present apparatus, the gas passage cross-sectional area of the present apparatus is determined so that the gas flow velocity v is 4 m / s or more in a typical operating state such as the maximum or rated value of the main engine exhaust gas.

(3) The control unit is a control device of the high voltage power supply 12, and controls the average electric field intensity E and the average current density i applied from the high voltage power supply 12 to the electrostatic precipitator.

As shown in FIG. 13, the average electric field intensity E and the average current density i
Although the parameters such as the spacing conditions of the electrodes and the conditions such as the composition of the gas are used as parameters, the relationship between the average electric field intensity E and the average current density i is a one-to-one monotonic increase. The average current density i is controlled by changing the electric field strength E (that is, the applied voltage E).
(Note that, in order to show an image in which the high-voltage power supply 12 shown in FIGS. 2, 3, 11, and 12 is variable in voltage, an oblique arrow is drawn on a mark of the DC electric wire.) [Effect of the Invention] Is configured as described above, and has the following effects.

(1) As described in claim 1 or 2, by setting the flow velocity of the exhaust gas and the average current of corona discharge, it is possible to collect a large amount of exhaust gas with high efficiency.

(2) As described in claim 3 or 4, by setting the shortest distance between the discharge electrode and the dust collection electrode to 80 mm or less, the required average current density can be ensured even when the space charge is large. it can.

(3) As described in claim 5 or 6, by setting the flow rate of the exhaust gas to the flow rate of the gas flowing in the equipment connected to the upstream side and / or the downstream side, it is directly connected to and integrated with the upstream / downstream equipment. Therefore, downsizing and total cost reduction can be realized.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a flow scheme according to one embodiment of the present invention, FIG. 2 is a detailed view of a dry dust collecting apparatus main body according to one embodiment of the present invention, and FIG. 3 is one embodiment of the present invention. Fig. 4 is a detailed view of a discharge electrode in another embodiment of the present invention, and Fig. 5 is a performance diagram of a dry electrostatic precipitator according to one embodiment of the present invention. Evaluation diagram, FIG. 6 is a performance evaluation diagram of a wet electrostatic precipitator according to another embodiment of the present invention, FIG. 7 is a diagram showing an average current density setting range in the dry electroprecipitator of the present invention, FIG. The figure shows the average current density setting range in the wet electrostatic precipitator of the present invention, FIG. 9 is a performance evaluation diagram of the conventional dry electroprecipitator, and FIG. 10 is the performance evaluation of the conventional wet electrostatic precipitator. FIG. 11 is a diagram showing the configuration of a conventional two-stage electrostatic precipitator for air cleaning. FIG. 2 is a conceptual diagram of a cylindrical electrostatic precipitator model, and FIG. 13 is a charging characteristic diagram of the cylindrical electric precipitator model. (Explanation of reference numerals) 1 ... particulate matter supply device, 2 ... particulate matter supply hole, 3 ... inlet particulate matter concentration measuring seat, 4 ... electric precipitator main body, 5 ... outlet particulate matter Concentration measuring seat 6 Orifice flow meter 7 Suction blower 8 Discharge electrode 9 Dust collecting electrode 10 Body casing 11 Support insulator 12 High voltage power supply 13 ... Charging part, 14 ... Dust collecting part, 15 ... High voltage side electrode, 16 ... Control part.

Claims (8)

(57) [Claims] An exhaust gas flows between a discharge electrode to which a high voltage is applied and a dust collecting electrode, and the particulate matter in the exhaust gas is charged by corona discharge generated by the high voltage. In a dry electrostatic precipitator that collects on a dust collection electrode by an electric field generated by the high voltage, the electric precipitator has a flow rate v of exhaust gas of 4 m / s or more in a typical operation state of an exhaust gas generation source. A dry electric collector having a gas passage cross-section such that the control section sets an average current density i (mA / m ² ) of the corona discharge to 0.018 v ² ≦ i ≦ 0.69 v ^2. Dust equipment. 2. Exhaust gas is caused to flow between a discharge electrode to which a high voltage is applied and a dust collecting electrode, and the particulate matter in the exhaust gas is charged by corona discharge generated by the high voltage. In a wet electrostatic precipitator that collects on a dust collecting electrode by an electric field generated by the high voltage, the electric precipitator has a flow rate v of exhaust gas of 4 m / s or more in a typical operation state of an exhaust gas generation source. A dry electrostatic precipitator having a gas passage cross section and a control unit for setting an average current density i (mA / m ² ) of the corona discharge to 0.018 v ² ≦ i. 3. The dry electrostatic precipitator according to claim 1, wherein the shortest distance between the discharge electrode and the dust collecting electrode is set to 80 mm or less. 4. The wet electrostatic precipitator according to claim 2, wherein the shortest distance between the discharge electrode and the dust collecting electrode is set to 80 mm or less. 5. The gas passage cross-sectional area is determined so that the flow velocity v of the exhaust gas is the same as the flow velocity of the gas flowing in the equipment connected upstream and / or downstream. The dry type electrostatic precipitator according to claim 1 or 3. 6. The gas passage cross-sectional area is determined so that the flow velocity v of the exhaust gas is the same as the flow velocity of the gas flowing in the equipment connected upstream and / or downstream. The wet electrostatic precipitator according to claim 2 or 4. 7. An exhaust gas flows between a discharge electrode to which a high voltage is applied and a dust collection electrode, and charges the particulate matter in the exhaust gas by corona discharge generated by the high voltage. In the method of operating a dry electrostatic precipitator that collects on a dust collecting electrode by an electric field generated by the high voltage, the flow velocity v of the exhaust gas is set to be 4 m / s or more, and the average current density of the corona discharge is set. A method for operating a dry electrostatic precipitator, wherein i (mA / m ² ) is set to 0.018 v ² ≦ i ≦ 0.69 v ² . 8. An exhaust gas is caused to flow between a discharge electrode to which a high voltage is applied and a dust collection electrode, and the particulate matter in the exhaust gas is charged by corona discharge generated by the high voltage, and the charged particulate matter is discharged. In the method of operating a wet electrostatic precipitator that collects on a dust collecting electrode by an electric field generated by the high voltage, the flow velocity v of the exhaust gas is set to be 4 m / s or more, and the average current density of the corona discharge is set. A method for operating a wet electrostatic precipitator, wherein i (mA / m ² ) is set to 0.018 v ² ≦ i.