JP2003201824A - Coagulating method for particulates in exhaust gas, particulate removing method, and device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coagulating method for particulates of graphite, etc., contained in the exhaust gas which coagulates effectively and easily collects, using a cyclone, etc. <P>SOLUTION: The coagulating method for particulates contained in the exhaust gas and the particulate removing method work through the electrostatic coagulation process in which the particulates contained in the exhaust gas are charged electrostatically and coagulated in the forestream about the flowing direction of the exhaust gas from an internal combustion engine and the electrode plate coagulation process in which the particulates coagulated electrostatically between at least a pair of electrodes are allowed to flow down along the flow of the exhaust gas in the back stream in the electrostatic coagulation process, whereby the particulates are resputtered upon coagulating on one electrode to be made repetitively so that the particle size of the particulates or the diameter of each assembly thereof is enlarged. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for aggregating fine particles in an exhaust gas of an internal combustion engine, a method for removing fine particles, and an apparatus therefor. The present invention relates to a fine particle agglomeration method and a fine particle removal method suitable for aggregating and separating and removing fine particles such as graphite contained in engine exhaust gas.

[0002]

2. Description of the Related Art In recent years, exhaust gas regulations have been gradually tightened in many countries as environmental pollution caused by black smoke particles (PM) and nitrogen oxides (NOx) emitted from internal combustion engines has become serious. It was Among internal combustion engines, for example, a diesel engine has excellent fuel consumption performance and durability, and thus has a particularly important industrial position as a power source. From the environmental point of view, the amount of hydrocarbons (HC) and C0 contained in the exhaust gas is small, but on the other hand, PM which is a toxic substance suspected of being carcinogenic and NO which causes air pollution
A large amount of x is generated.

The use of a fine particle removal filter for exhaust gas is one of the effective techniques for reducing PM, and a method for collecting graphite fine particles using various filters has been developed. . At that time, when fine particles adhere to the inner surface of the filter, many methods of removing fine particles such as soot by a combustion reaction in the filter have been proposed in order to eliminate clogging in the internal flow path. However, the method of burning and removing fine particles such as soot has a problem that the load on the filter is large and the life of the filter is shortened due to deterioration or damage. Also,
In order to burn the fine particles accumulated in such a filter, a step of removing and regenerating the fine particles in the filter must be performed separately from the step of collecting the fine particles.
Therefore, it is difficult to remove fine particles from the exhaust gas continuously supplied, and it has been necessary to stop the flow of the exhaust gas and then perform regeneration by combustion. Therefore, there has been a long-felt demand for a method of efficiently collecting fine particles in exhaust gas that is continuously discharged.

[0004]

The fine particles in exhaust gas discharged from an internal combustion engine, for example, fine particles in diesel engine exhaust gas, are mainly carbon. Carbon particles are low resistance dusts, and their electric resistivity is about 10 ⁴ Ω · cm. On the other hand, the particle size of carbon particles (such as carbon black) that can be collected by a cyclone is about 10 μm. In the case of such a cyclone, when the particles are extremely small, the inertial force becomes small and the cyclone is carried on the gas stream, so that separation and recovery is difficult. Therefore, when the fine particles in the exhaust gas are collected using the cyclone, the particles to be collected must have a certain size or more. Therefore, as a pretreatment of the exhaust gas introduced into this cyclone, it is necessary to increase the particle size by aggregating fine particles having a small inertial force in the preceding stage. More specifically, when a cyclone is used, it is necessary to aggregate carbon particles discharged from the diesel engine to about 10 μm in the preceding stage.

In view of the above problems, the present inventors have considered
A method of effectively aggregating fine particles such as graphite contained in the exhaust gas into a particle size that can be efficiently recovered by a cyclone, etc., and further improving the processing efficiency of the entire particle purification system in the exhaust gas and We have earnestly studied to develop a method that can improve the operation efficiency. As a result, the present inventors have made it possible to efficiently separate and remove particles in the exhaust gas by increasing the particles in the exhaust gas with a unique particle aggregating system that combines electrostatic agglomeration and electrode plate agglomeration in the cyclone upstream. It has been found that the above problem can be solved by reducing the load on the wake filter and realizing long-term continuous operation. The present invention has been completed from this point of view.

[0006]

That is, the present invention provides a method for aggregating fine particles in exhaust gas, which includes an electrostatic aggregating step and an electrode plate aggregating step. Here, the electrostatic agglomeration (charge agglomeration) step is a step of electrostatically agglomerating fine particles contained in the exhaust gas from the internal combustion engine in a forward flow with respect to the flow direction of the exhaust gas, for example, a positive pulsed streamer discharge. Method or a high frequency barrier discharge method can be used. Further, the electrode plate aggregating step causes the particles to agglomerate on one electrode by flowing down the electrostatically agglomerated particles between at least a pair of electrodes along the flow of the exhaust gas in the downstream of the electrostatic aggregating step. This is a step of repeating the process of re-scattering and further increasing the particle size of the fine particles or the aggregate thereof.

Further, the present invention provides a method for removing fine particles in exhaust gas, which comprises the steps of the electrostatic coagulation step and the electrode plate coagulation step.
It is intended to provide a method further including a fine particle removing step of separating a fine particle component and a gas component contained in the exhaust gas by centrifugation using the exhaust gas as a swirling flow to collect the fine particle component. Furthermore, in the downstream of this fine particle removal step,
The method may further include a step of adsorbing and removing the fine particles by using a filter that captures and accumulates the unrecovered fine particles contained in the exhaust gas.

Further, according to the present invention, the ground electrode provided on the outer wall portion in the exhaust gas flow passage and the center provided in the central portion of the exhaust gas flow passage in the preceding stage with respect to the flow direction of the exhaust gas from the internal combustion engine. An apparatus for aggregating particulate matter in exhaust gas, comprising: an electrostatic aggregating unit provided with an electrode; and an electrode aggregating unit having at least a pair of electrode surfaces provided in an exhaust gas passage in a subsequent stage of the electrostatic aggregating unit. Is also provided. In such an apparatus, in the electrostatic coagulation unit, metal plates are provided as ground electrodes on opposing outer wall portions in the exhaust gas flow path, respectively, and a metal wire such as a tungsten wire is provided substantially parallel to the metal plate as a center electrode. There is an aspect in which the electrodes are arranged. Also, in the electrostatic coagulation section,
A cylindrical metal portion is provided on the outer periphery of the cylindrical exhaust gas flow passage as the ground electrode, and a metal wire made of a tungsten wire or a stainless steel bolt or an outer surface is uneven at the cylindrical central portion as the center electrode. There is also an aspect in which an electrode composed of the metal rod (for example, a bolt-shaped metal rod) is arranged.

On the other hand, in the electrode plate aggregating portion of the fine particle aggregating device, for example, at least a pair of electrode surfaces provided in the exhaust gas passage are arranged with two metal plates facing each other along the outer wall. The one metal plate is a ground electrode, and the other metal plate is a positive electrode. Similarly, in the electrode plate aggregating portion, at least a pair of electrode surfaces provided in the cylindrical exhaust gas passage form a ground electrode made of a cylindrical metal installed on the outer circumference and a coaxial circle with the cylindrical outer circumference. A preferred embodiment is a combination of the positive electrode and the positive electrode disposed therein. Further, in the particle agglomerating apparatus of the present invention, a plurality of the electrostatic aggregating portions and the electrode plate aggregating portions may be installed in parallel with the exhaust gas flow path.

According to the present invention, fine particles such as graphite contained in combustion exhaust gas can be effectively aggregated, and can be efficiently separated and collected by a cyclone or the like before being collected by a filter. Therefore, the load on the filter such as clogging of fine particles is reduced, and long-term continuous operation using the filter can be realized.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As a pre-stage for capturing and collecting graphite fine particles (soot component, PM) in exhaust gas by a porous filter, fine particles in exhaust gas are separated and collected by a centrifugal separator such as a cyclone. , Reduce the amount of fine particles.
In order to improve the ability of the cyclone to separate and collect fine particle components, it is necessary to aggregate the particles to about 10 μm. The present invention efficiently implements the aggregation of such fine particles. Hereinafter, specific embodiments of the method according to the present invention will be described with reference to the accompanying drawings.

In the present invention, atmospheric pressure non-equilibrium plasma is used, (1) electrostatic coagulation process in the discharge space by charging carbon fine particles, (2) repetition of coagulation and re-scattering on the dust collecting electrode. The particle size is increased by combining the electrode plate aggregating step by. The electrostatic aggregation step is performed by charging fine particles such as carbon in the presence of plasma under atmospheric pressure. Then, the agglomeration process on the electrode and the process of separating and re-scattering from the electrode plate surface by the shearing force of the gas flow are repeated. Enlarge. By combining these processes, fine particles such as carbon
It can be aggregated to 0 μm or more. In other words, in the case of low-resistance dust such as carbon particles, even if they are collected on the dust collecting electrode, they immediately lose their charge, so that the particles are separated and re-scattered by the gas flow. By repeating such electrode plate aggregation and re-scattering, the electrode is made to act as a so-called high-pass filter.

FIG. 1 and FIG. 2 show an example of the fine particle aggregating apparatus of the present invention. The apparatus of the present invention is composed of an electrostatic aggregating unit for charging fine particles in the former stage and an electrode aggregating unit in the latter stage. The shape is a rectangular parallelepiped type shown in FIG. 1, or
The concentric cylindrical shape type shown in FIG. 2 is preferably mentioned. Further, a structure in which these are arbitrarily combined is also possible. In the rectangular parallelepiped type, the metal plates 2 are respectively provided as the ground electrodes on the opposing outer wall portions in the exhaust gas passage in the electrostatic aggregation unit 10.
Is provided, and an electrode made of a tungsten wire 1 is arranged as a center electrode substantially parallel to the metal plate 2. In the electrode plate aggregating portion 11, a pair of electrode surfaces provided in the exhaust gas passage are arranged with two metal plates facing each other along the outer wall, and one metal plate 21 is provided.
Is a ground electrode, and the other metal plate 22 is a positive electrode. In the concentric cylindrical shape type, in the electrostatic aggregating portion 10, a cylindrical metal portion 31 is provided as a ground electrode on an outer wall portion which is an outer periphery in a cylindrical exhaust gas flow path, and a cylindrical central portion is provided as a center electrode. An electrode made of a tungsten wire 1 or a stainless steel bolt is arranged in the. In the electrode plate aggregating portion, the pair of electrode surfaces provided in the cylindrical exhaust gas flow passage form the ground electrode 41 in which the cylindrical metal is arranged on the outer wall portion which is the outer periphery, and the coaxial circle with the cylindrical outer wall portion. The positive electrode 42 is formed and disposed inside the positive electrode 42.

Next, the discharge method in the electrostatic aggregation step will be described. A streamer discharge, which is a type of corona discharge, can be used to generate an atmospheric pressure non-equilibrium plasma. As a first mode, a positive pulsed streamer discharge method can be mentioned. In this method, a positive bias voltage is applied in a pulsed manner to the linear electrode. This is DC
Compared to a streamer, discharge is not suppressed by space charge and efficiency is good, and in the case of a negative streamer, positive ions generated in the vicinity of the linear electrode suppress the progress of discharge and the discharge is less likely to spread. by. In addition, it is considered that the positive polarity can generate a large number of positively charged fine particles to increase the effect of the electrode plate aggregation in the latter stage. Furthermore, damage can be prevented by setting the pulse time before the all-way breakdown occurs and the counter electrode is damaged as the streamer progresses. In order to completely prevent damage, it is possible to cover the front surface of the opposing ground electrode with an insulator such as glass to form a barrier discharge.

In the case of the pulse streamer discharge method, for example, in the rectangular parallelepiped type apparatus shown in FIG. 1, metal plates 2 are provided on both sides in the exhaust gas flow path, and the central portions of the two metal plates are provided. Is provided with a center electrode such as a tungsten wire 1. A high voltage is applied between the metal plate and the center electrode. The pulse high voltage is generated by connecting a capacitor charged at a high voltage by a spark gap switch to a load. The shorter the voltage rise time, the larger the current and light emission intensity, and the wider the light emission region of discharge. To generate a pulse voltage with a short time width, there is a method that uses a pulse transmission circuit that combines a capacitor and an inductance and uses the transient phenomenon.To improve the pulse power transmission efficiency, the impedance between the power supply circuit and the load can be used. It is important to consider matching. In addition, pressurizing the spark gap switch is also effective for increasing the power transmission efficiency.

A second mode is a high frequency barrier discharge system of about 50 Hz. In this case, since the fine particles pass through the bulk plasma and are charged positively and negatively, electrostatic aggregation in the space is accelerated. On the other hand, in the latter-stage electrode plate aggregation, since the dust is collected by both electrode plates, it is considered that the effect of repeating the electrode plate aggregation is different from that in the case of the positive polarity pulse streamer.

In the case of the high frequency barrier discharge method, for example, in a rectangular parallelepiped type apparatus as shown in FIG. 1, metal plates 2 are provided on both sides in the exhaust gas flow path, and tungsten is provided in the central portion. A center electrode such as the wire 1 is provided. A high voltage is applied during this period, and a plate made of an insulating material such as glass is placed between them. Further, in the concentric cylinder type device as shown in FIG. 2, a central electrode such as the tungsten wire 1 is provided in the central portion of the exhaust gas passage, and an insulating material such as glass surrounds the outer periphery thereof. Further, an electrode 31 is provided on the outer circumference thereof.

In the case of the positive streamer discharge method, the fine particles contained in the exhaust gas are positively charged when passing through the discharge part. Many positive ions existing in the streamer are trapped on the surface of the fine particles, and most of them become fine particles having a positive charge. These fine particles agglomerate mainly due to electrostatic aggregation (heteroaggregation) due to the difference in the amount of electric charge, but the potential barrier is lowered while they have the same charge. Also, it is considered that some of them are negatively charged due to electron attachment.
Electrostatic aggregation with them also occurs. On the other hand, in the case of high frequency barrier discharge, the passing particles are charged in both positive and negative polarities.
Negatively charged ones are due to electron attachment, and positively charged ones are due to secondary electron emission or positive ion collision charge. When the particle size is about 10 nm, a phenomenon that changes like positive and negative polarities like a flip-flop appears, which is considered to be a factor for rapid aggregation of particles to 100 nm to 1 μm. From this, it is possible that the high frequency barrier discharge method has a larger particle size of the fine particles in the rear portion of the charging / aggregating portion. In the case of using any of these methods, the fine particles that have undergone electrostatic agglomeration in the front part are sent to the electrode plate agglomeration part in the latter part, and about 10
The diameter is further increased so that the particle diameter becomes μm or more.

Next, the electrode plate aggregating step will be described. FIG. 3 schematically shows the aggregation process of fine particles. By passing the fine particles that have passed through the electrostatic aggregating part through the electrode plate aggregating part,
The particles increase in size due to cumulative electrode plate aggregation. As described above, low resistance dust such as carbon particles easily re-disperses in the dust collector, and the dust collection performance of particles having a large particle size deteriorates. It is considered that this is due to repetition of electrode plate aggregation and scattering as shown in FIG. The fine particles that have been positively charged in the streamer discharge are collected by the ground electrode. The positively charged fine particles that fly one after another are deposited on the ground electrode and are aggregated there.
When the separation force resulting from the gas flow exceeds the adhesion force with the electrode plate, the fine particles grown on the electrode plate return to the gas flow and re-scatter. At this time, the re-scattered particles are charged with the same polarity as the ground electrode by electrostatic induction, and are then collected on the positive electrode by the electric field between the electrode plates. Particles on the positive electrode also aggregate on the electrode plate,
It is also peeled off and collected by the ground electrode. By repeating this operation, the particle size of the particles becomes large, and eventually the particles are discharged out of the system together with the gas flow. When the high frequency barrier discharge is used in the former stage, fine particles are collected in both the positive polarity and the ground electrode in the latter dust collecting section. In this case as well, in principle, the same aggregation and scattering of the electrode plates as described above are repeated. In this way, by combining the two-stage aggregating action of the electrostatic aggregating step and the electrode plate aggregating step described above, only carbon particles having a particle size that can be collected by a cyclone in the latter stage or the like are released to the downstream of the aggregator. It becomes possible.

In the downstream of the electrostatic aggregation process and the electrode plate aggregation process,
Usually, a fine particle removing step is performed in which an exhaust gas containing agglomerated fine particles is used as a swirling flow to separate a fine particle component and a gas component contained in the exhaust gas by centrifugation and to collect the fine particle component. This step of removing fine particles can be suitably performed by, for example, a cyclone dust collector. The cyclone used here is a type of centrifugal separator, in which the fine particles in the exhaust gas rotate inside the conical shape, while the heavy particle components accumulate underneath the cyclone due to gravity, while the light components (gas etc.) It is discharged from the pipe to the outside. In the electrostatic aggregating apparatus described above, there is a distance between the electrode that applies a dischargeable voltage and the ground electrode based on the magnitude of the applied voltage that is obtained. That is, since the gas of the electrostatic condensing device flows, the cross-sectional area of the opening is determined by the distance. Also, in the downstream electrode plate agglomerator, the electric field strength between the electrodes is determined by the magnitude of the applied voltage to obtain the fine particles, and the re-dispersion distance of the fine particles is changed. In this case, the distance between the electrodes, that is, the cross-sectional area of the opening of the device may be specified. In such a case, it is preferable to use a multi-cylinder type fine particle agglomerating device in order to prevent unnecessary pressure loss even at a desired gas flow rate. In the multi-cylinder type fine particle aggregating apparatus, the electrostatic aggregating section and the electrode plate aggregating section may be bundled and installed in plural in parallel with the gas flow path, and the cross-sectional area of the gas flow path may be set to a desired size. Specifically, for example, as shown in FIG. 4, the fine particle agglomeration portion 10 having a rectangular cross section is used.
An example is a multi-cylinder type fine particle agglomeration device 201 in which four 1s are bundled into a four-cylinder type.

Further, in the downstream of the step of removing fine particles, usually, a filter for completely capturing and accumulating unrecovered fine particles contained in the exhaust gas is used, and a step of further adsorbing and removing fine particles is performed. That is, even by the combination of the electrostatic aggregating step and the electrode plate aggregating step, the particles which remain as fine particles without being agglomerated cannot be separated and removed by a cyclone or the like and flow into the downstream. In this step, a filter is used to adsorb and remove uncollected fine particles in the exhaust gas.

As the material of the filter, for example, cordierite, silica, alumina or the like is used. In the present invention, since fine particles having a certain size or more are removed before the cyclone, it is preferable to use a filter having a pore size of, for example, about 50 μm to 200 μm. Partial fine particles can be removed. In addition, a filter having two or more different pore diameters may be combined and used in this filter section from the viewpoint of more completely capturing the graphite fine particles. When a filter is used in combination, larger particles are trapped in the former stage, and smaller particles with different sizes are gradually trapped in the latter stage, so that rapid clogging in the filter section can be made less likely to occur. The shape of the filter is not particularly limited, and can be arbitrarily determined according to the shape of the exhaust gas passage in each device,
For example, a cylindrical filter or the like can be used.

[0023]

According to the method of the present invention, it is possible to efficiently agglomerate fine particles such as graphite contained in the exhaust gas of an internal combustion engine, and by increasing the particle size to about 10 μm or more, Fine particles can be effectively separated and collected by a separation device such as a cyclone provided downstream. When a filter is installed in the downstream of the cyclone, effective particulate removal is performed in the preceding stage, so the load on the filter such as blockage due to particulates is greatly reduced, and the filter is used. It is possible to realize continuous operation for a long time.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a rectangular parallelepiped device which is an example of a particle aggregating device of the present invention.

FIG. 2 is a perspective view showing a concentric cylindrical device configuration which is an example of a particle aggregating device of the present invention.

FIG. 3 is a schematic diagram sequentially showing (a) discharge in the electrostatic aggregation step, (b) electrostatic aggregation, and (c) electrode plate aggregation in the present invention.

FIG. 4 is a perspective view showing a multi-cylinder type fine particle aggregating apparatus which is an example of the fine particle aggregating apparatus of the present invention.

[Explanation of symbols] 1 Tungsten wire 2 Metal plate (electrode) 3 DC power supply 4 DC pulse 10 Electrostatic agglomeration part 11 Electrode plate aggregation part 101 Single cylinder type fine particle aggregating device (fine particle aggregating section) 201 Multi-cylinder type fine particle aggregator

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01J 19/08 B01J 19/08 E (72) Inventor Kenji Muta 1-8 Kochiura, Kanazawa-ku, Kanagawa Prefecture Mitsubishi Heavy Industries (72) Inventor, Toshiaki Monaka 1-chome, 8-chome, Koura, Kanazawa-ku, Kanagawa Prefecture CA25 CA47 DA02 EC21 EE02 EE04 EE07 EE12 FA05 FB02

Claims (11)

[Claims] 1. An electrostatic aggregating step of electrostatically aggregating fine particles contained in the exhaust gas in a forward flow with respect to a flow direction of an exhaust gas from an internal combustion engine, and a downstream flow of the electrostatic aggregating step, Particles that are electrostatically aggregated between at least a pair of electrodes are allowed to flow down along the flow of the exhaust gas, and the particles are repeatedly aggregated on one electrode and then re-dispersed to obtain a particle size of the particles or an aggregate thereof. A method of aggregating fine particles in exhaust gas, which comprises increasing the diameter of the electrode plate. 2. The method for aggregating fine particles in exhaust gas according to claim 1, wherein a positive pulsed streamer discharge method is used in the electrostatic aggregating step. 3. The method for aggregating fine particles in exhaust gas according to claim 1, wherein a high frequency barrier discharge method is used in the electrostatic aggregating step. 4. The electrostatic coagulation process and the electrode plate coagulation process according to claim 1, wherein the exhaust gas is swirled to separate a fine particle component and a gas component contained in the exhaust gas by centrifugal separation. A method for removing fine particles in exhaust gas, further comprising: a fine particle removing step of collecting fine particle components. 5. The step of adsorbing and removing fine particles using a filter for capturing and accumulating unrecovered fine particles contained in the exhaust gas, in the downstream of the fine particle removing step according to claim 4. A method for removing fine particles in exhaust gas, comprising: 6. A ground electrode provided on an outer wall portion in an exhaust gas flow passage, and a center electrode provided in a central portion of the exhaust gas flow passage in a front stage with respect to a flow direction of exhaust gas from an internal combustion engine. Particle agglomeration in exhaust gas, comprising: an electrostatic aggregating section; and an electrode aggregating section provided at the rear of the electrostatic aggregating section, the electrode plate aggregating section having at least a pair of electrode surfaces provided in the exhaust gas passage. apparatus. 7. In the electrostatic aggregating portion, metal plates are provided as the ground electrodes on opposing outer wall portions in the exhaust gas passage, respectively, and the center electrode is formed of a metal wire substantially parallel to the metal plates. 7. The apparatus for aggregating fine particles in exhaust gas according to claim 6, wherein an electrode is provided. 8. In the electrostatic aggregating portion, a cylindrical metal portion is provided on the outer periphery of a cylindrical exhaust gas passage as the ground electrode, and a metal wire or a metal wire is provided on the cylindrical central portion as the center electrode. The apparatus for aggregating fine particles in exhaust gas according to claim 6, wherein an electrode made of a metal rod having an uneven surface is arranged. 9. In the electrode plate aggregating portion, two metal plates are arranged as at least the pair of electrode surfaces so as to face each other along an outer wall, and one metal plate is a ground electrode and the other metal plate is disposed. The device for aggregating particles in exhaust gas according to claim 6, wherein the plate is a positive electrode. 10. In the electrode plate aggregating portion, at least a pair of electrode surfaces provided in a cylindrical exhaust gas flow path have a grounding electrode made of a cylindrical metal installed on the outer circumference, and a coaxial circle with the cylindrical outer circumference. 7. A positive electrode which is formed inside and is arranged therein.
The apparatus for aggregating fine particles in exhaust gas according to [4]. 11. The electrostatic aggregating portion and the electrode plate aggregating portion,
7. The apparatus for aggregating particles in exhaust gas according to claim 6, wherein a plurality of particles are installed in parallel with the exhaust gas passage.