JPH04300661A - Apparatus for treating fine particles in exhaust gas - Google Patents

Abstract

PURPOSE:To well ensure the collection of fine particles in exhaust gas without using high voltage. CONSTITUTION:A conductive adsorbing filter 3 collecting fine particles contained in combustion gas is provided to an exhaust gas passage through which combustion gas passes and a metal net 5 permitting the combustion gas containing fine particles to pass is provided to the exhaust gas passage 1 on the upstream side of the adsorbing filter 3. The metal net 5 is negatively charged by a DC power supply 7 and the adsorbing filter 3 is positively charged by said power supply 7 and the fine particles passing through the metal net 5 are negatively charged to be electrically attracted to the adsorbing filter 3 to be collected.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust particulate processing device that collects and processes exhaust particulates contained in combustion gas.

0002

[Prior Art] Generally, combustion gas, alcohol fuel, and biomass fuel are burned in internal combustion engines, gas turbines, industrial boilers, power generation boilers, water heaters, high-temperature gas furnaces, etc. that use fossil fuels such as oil and coal. If exhaust particulates such as soot and impurities (dust) contained in the combustion gas are released into the atmosphere as they are, it will cause environmental pollution, which is undesirable.

Conventionally, the amount of exhaust particulates such as soot and impurities released into the atmosphere has been strictly regulated for stationary combustion devices. Countermeasures for this regulation include the electrostatic precipitator method and the use of bag filters. Electrostatic precipitation uses corona discharge with high voltage (6,000 to 10,000 V) to charge exhaust particulates, and then electrically separates them from the exhaust gas using the action of an electric field (Coulomb force) and collects them. It is possible to collect exhaust particulates through electrostatic coagulation.

On the other hand, those using bag filters collect exhaust particulates when the exhaust gas passes through the bag filter installed in the exhaust passage, but recently, electrostatic charges have been placed on the upstream side of the bag filter. Another method is to use corona discharge to charge the soot and dust in the exhaust gas, which is then adsorbed and collected by a bag filter in the subsequent stage. A high voltage of about 4000 V/cm is applied to the corona discharge at this time.

[0005] In contrast to these stationary engines, it is inconvenient to install the above-mentioned high-voltage device and its power source in diesel engines and the like in mobile cars.
Moreover, since it is not economical, there is a method in which a ceramic filter is installed in the exhaust passage so as to be perpendicular to the exhaust flow, and the filter collects exhaust particulates. In this case, when the exhaust particulates contained in the exhaust gas pass through the gaps between carbon fibers and minute carbon particles in the filter, they are adsorbed or attached thereto, and when the collected exhaust particulates reach a predetermined amount, they are heated by an electric heater, etc. Developmental research is being conducted to regenerate filters by burning exhaust particulates (Japanese Patent Laid-Open No. 1983-1965).
(See Publication No. 113).

[0006]

[Problems to be Solved by the Invention] However, in the above-mentioned stationary electrostatic precipitator method and the method of generating corona discharge upstream of the bag filter, high voltage is used.
The equipment is large-scale, inconvenient to handle, and undesirable as it increases costs.Furthermore, although the bag filter itself provides stable dust collection performance, it suffers from pressure loss due to the accumulation of exhaust particulates, and short service life and replacement. There is a problem with maintenance such as work. In addition, ceramic filters require a large amount of power for the electric heater used during regeneration, and there is also the problem of poor fuel efficiency due to increased exhaust pressure, and exhaust particles are locally trapped. If the amount collected is too large, the combustion heat generated by the heater will be excessive and the filter life will be shortened, and if the amount is too small, combustion may not occur and regeneration may not be possible.

[0007] Accordingly, an object of the present invention is to ensure good collection of exhaust particulates without using high voltage.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an electrically conductive collection member for collecting exhaust particulates contained in the combustion gas in the exhaust passage through which the combustion gas passes. A conductive member through which the combustion gas containing the exhaust particulates can pass together with the exhaust particulates is provided in the exhaust passage on the upstream side of the collection member, and the conductive member and the collection member are charged with charges having mutually different polarities. A voltage applying means is provided.

[0009]

[Operation] When a voltage applying means applies a negative charge to the conductive member and a positive charge to the collection member, for example, the exhaust particulates become negatively charged when passing through the conductive member together with the exhaust gas. When the negatively charged exhaust particles reach the positively charged collecting member at the subsequent stage, the exhaust particles are attracted and collected by the collecting member.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are explanatory diagrams showing the principle of the present invention. An exhaust passage 1 through which combustion gas passes is provided with a conductive adsorption filter 3 made of carbon fiber felt or the like, which is a collection member that collects exhaust particulates such as soot and dust in the exhaust gas. The conductive adsorption filter 3 uses coal and petroleum pitch-based, polyacrylonitrile (PAN)-based and phenol-based carbon fibers, as well as metal and non-ferrous metal fibers, and its shapes include raw cotton, felt, mat, and cloth. , yarn, sheet, chopped form, etc. Pitch-based carbon fibers are made from isotropic pitch, optically anisotropic mesophase pitch, and the like. The carbonization firing process is usually about 600 to 1500°C, so it is heat resistant, but it is particularly preferably about 800 to 1000°C, and in this case, straight or curly pitch-based carbon fibers are used. The specific gravity of carbon fiber is approximately 2.5, the wire diameter is 1 to 15 μm, and the bulk density is 20 to 1.
Approximately 20 kg/m3 is good.

As shown in FIG. 2, the exhaust passage 1 on the upstream side of the conductive adsorption filter 3 is provided with a wire mesh 5 as a conductive member through which the combustion gas containing the exhaust particles can pass together with the exhaust particles. It is provided. The wire mesh 5 and the conductive adsorption filter 3 are connected to a 12V or 24V DC power source 7, which serves as voltage application means for charging them with charges of mutually different polarities.

A soot tray 9 for receiving exhaust particulates is installed at the lower part of the exhaust passage 1 between the conductive adsorption filter 3 and the wire mesh 5, and a soot tray 9 near the conductive adsorption filter 3 is installed to receive the exhaust particulates. An electric heater 11 for combustion is provided. Since this electric heater 11 only burns the soot itself dropped into the soot tray 9, the supplied electric power may be small.

In the exhaust particulate processing apparatus having such a configuration, the DC power supply 7 applies a positive charge to the conductive adsorption filter 3 and applies a negative charge to the wire mesh 5. In this state, when combustion gas is generated on the upstream side of this device and the exhaust gas flows as shown by arrow A in the figure, the exhaust gas flows through the negatively charged wire mesh 5.
By passing through and coming into contact with this, electrically neutral exhaust particles such as soot and dust become negatively charged. When the negatively charged exhaust particles reach the positively charged conductive adsorption filter 3, the exhaust particles are electrically adsorbed and collected on the surface of the filter 3, and then become electrically neutral on the adhering surface. Return to

[0015] When the amount of collected exhaust particulates increases in this way and it becomes necessary to regenerate the conductive adsorption filter 3,
Contrary to the above, applying a negative charge to the conductive adsorption filter 3,
Give a positive charge to the wire mesh 5. As a result, the neutral exhaust particulates adhering to the conductive adsorption filter 3 are negatively charged, are attracted to the positively charged wire mesh 5, and are moved to the soot tray 9 near the conductive adsorption filter 3. to fall. The exhaust particles that have fallen onto the soot tray 9 are incinerated by the electric heater 11. In order to cause the soot adhering to the conductive suction filter 3 to fall onto the soot tray 9, the distance between the conductive suction filter 3 and the wire mesh 5 may be appropriately set according to the voltage of the power source 7.

According to the above-described exhaust particulate treatment device, the commercially available 100V or the 12 to 24V for automobiles can be used.
Since a low voltage power supply of V is used and there is no need to use a high voltage, the device is simplified and is advantageous in terms of handling, resulting in cost reduction. Furthermore, since the exhaust particulates begin to be electrically adsorbed on or near the surface of the conductive adsorption filter 3, if regeneration is performed in this state, the exhaust particulates will be less likely to enter the inside of the conductive adsorption filter 3.
It is possible to prevent an increase in exhaust pressure due to the accumulation of exhaust particulates, and to prevent a decrease in engine performance due to an increase in fuel consumption. In this way, it is difficult for exhaust particulates to enter the inside of the conductive adsorption filter 3, making it difficult for them to pass through there.
For this reason, the mesh of the conductive adsorption filter 3 itself may be made rough, or
The thickness in the exhaust flow direction can be made thinner, which also prevents the exhaust pressure from increasing. Furthermore, when regenerating the conductive adsorption filter 3, instead of burning the exhaust particulates adsorbed on the filter 3, a voltage of opposite polarity is applied between the conductive adsorption filter 3 and the wire mesh 5. Since the conductive adsorption filter 3 is detached and dropped, a decrease in the life of the conductive adsorption filter 3 is avoided, and the filter 3 is regenerated well.

Next, an example in which the present invention is applied to an automobile diesel engine is shown in FIG. An exhaust pipe 17 is connected to an exhaust manifold 15 connected to the engine body 13, and an exhaust particulate processing device 19 is provided in the middle of the exhaust pipe 17. The exhaust particulate processing device 19 has a filter box 21, which is made of carbon fiber felt as a collection member that divides the internal space of the filter box 21 into an upstream space 23 and a downstream space 25. A conductive filter 27 is housed. Filter 27 and filter box 21
An insulator 29 made of, for example, ceramic and having high heat resistance and high electrical resistance is interposed between the two. The cross-sectional area of the filter box 21 perpendicular to the exhaust flow is the same as that of the exhaust pipe 1.
7 in the same cross-sectional area to reduce the flow velocity of exhaust gas flowing out from the exhaust pipe 17 to the filter box 21.

An end of an upstream exhaust pipe 17a is inserted into and connected to the upstream space 23, and a downstream exhaust pipe 17b is connected to the downstream space 25 in communication. A wire mesh 31 as a conductive member is provided in the upstream exhaust pipe 17a located in the upstream space 23. An insulator 33 made of ceramic or the like is interposed between the wire mesh 31 and the upstream exhaust pipe 17a. Wire mesh 31 and the filter 27
is connected to a 12V or 24V DC power supply 35. A soot tray 37 is installed at the bottom of the filter box 21 between the filter 27 and the wire mesh 31.
An electric heater 39 is provided near the filter 27 of No. 7 to burn exhaust particulates.

FIG. 4 shows details of the vicinity of the area where the wire mesh 31 is provided. The wire mesh 31 is provided on the inner surface near both the upstream and downstream ends of the insulator 33, and a pair of conductive spacers 41 are interposed between the two wire meshes 31, 31 in contact with the wire meshes 31, 31. The negative electrode side of the power source 35 is connected to the spacer 41 .

With this configuration, the filter 27
while giving a positive charge to the wire mesh 31, giving a negative charge to the wire mesh 31,
In this state, when the electrically neutral exhaust particles in the exhaust gas pass through the wire mesh 31, they come into contact with the wire mesh 31 and are negatively charged. Here, two wire meshes 31 are arranged in series, so
Exhaust particles that could not be negatively charged by the upstream wire mesh 31 can also be negatively charged by the downstream wire mesh 31. The exhaust gas flows into the upstream space 23 together with the negatively charged exhaust particles, where they expand and the flow velocity decreases. In this state, the exhaust particles are electrically and efficiently adsorbed to the surface of the filter 27, and after adsorption, Return to neutral. Thereafter, the filter 27 and the wire mesh 31 are each charged with charges of opposite polarity to those described above, so that the exhaust particulates fall onto the soot tray 37 and are burned. In FIG. 5, a wire mesh 43 is attached to the filter box 21 immediately in front of the conductive filter 27 with an insulator 45 interposed therebetween. In this case, the wire mesh 43 is connected to the upstream exhaust pipe 1
7a, and the filter box 2 together with the filter 27.
1, the exhaust particulate treatment device can be made as a single unit, which is advantageous in terms of handling.

In FIG. 6, a conductive filter 49 is provided at the downstream side of a filter box 47 with an insulator 50 interposed therebetween. This filter 49 has a cup shape consisting of a downstream end surface 49a and a cylindrical portion 49b, and the insulator 50 also has the same shape as the filter 49. The downstream end of the upstream exhaust pipe 51 faces a space 53 within the filter 49 in the filter box 47, and the upstream end of the downstream exhaust pipe 55 also faces this space 53. In the portion upstream of the space 53 of the upstream exhaust pipe 51 in the filter box 47,
A wire mesh 57 is interposed as a conductive member. wire mesh 5
7 is clamped and fixed between flanges 61 and 61 via a pair of insulators 59 and 59 made of ceramic, and its outer peripheral portion is also exposed inside the filter box 47 . A ceramic insulator 63 is interposed between the downstream exhaust pipe 55 and the filter 49.

According to this configuration, the DC power supply 35 charges the filter 49 with a positive charge and the wire mesh 57 with a negative charge. In this state, when exhaust gas flows into the upstream exhaust pipe 51, the exhaust gas passes through and comes into contact with the negatively charged wire mesh 57, so that electrically neutral exhaust particles such as soot and dust are removed from the negatively charged wire mesh 57. is charged with electricity. When the negatively charged exhaust particles reach the space 53 within the filter 49, they are electrically adsorbed to the positively charged filter 49 and return to electrical neutrality on the adhering surface.

[0023] The amount of collected exhaust particulates increases, and the filter 49
When it becomes necessary to regenerate the filter 49, contrary to the above
is charged with a negative charge, and the wire mesh 57 is charged with a positive charge. As a result, the neutral exhaust particles adhering to the filter 49 are negatively charged, and the wire mesh 57 is positively charged.
The soot is attracted to the outer periphery of the soot and moves, and falls into the soot tray 37. The exhaust particles that have fallen onto the soot tray 37 are incinerated by the electric heater 39.

In this case, the exhaust gas flows from the exhaust upstream pipe 51 into the filter box 47 and then flows into the exhaust downstream pipe 55 without passing through the filter 49, so that pressure loss can be kept low. The exhaust pressure is also lower than that when exhaust gas passes through the filter 49, resulting in less fuel consumption and improved engine output. In addition, the upstream exhaust pipe 51
Since the exhaust gas flowing through the filter box 47 once flows out and expands, an exhaust silencing effect can also be obtained.

FIG. 7 shows a filter box 63 in which a conductive filter 65 is arranged perpendicularly to the exhaust flow in consideration of its bulk density, so that the interior of the filter box 63 is divided into an upstream space 67 and a downstream space. It is divided into a space 69. Reference numeral 64 is an insulator. An upstream exhaust pipe 51 similar to that shown in FIG. 6 faces the upstream space 67, and a downstream exhaust pipe 55 faces the downstream space 69. In this example, in addition to obtaining the exhaust silencing effect as in FIG.
6, the exhaust pressure is higher than that in FIG. 6, but the effect of removing exhaust particulates is improved.

FIG. 8 shows a filter box 71 in which a plurality of conductive filters 73 are installed downstream of the wire mesh 43 in parallel to the exhaust flow. By providing the filter 73 in parallel with the exhaust flow, the exhaust pressure can be kept low as in the example of FIG.

Next, FIG. 9 shows test results when the present invention was applied to a 500cc single-cylinder four-stroke diesel engine (direct injection type). Figure 9 shows the relationship between the rate of change (%) of the soot concentration in the exhaust gas at the inlet and outlet of the filter box and the engine output (PS) at an engine speed of 2,600 rpm with different applied voltages. It is something. here,
The solid line shows the concentration change rate when 0V is applied, the broken line shows 12V, the one-dot chain line shows 24V, and the two-dot chain line shows the concentration change rate when 50V is applied. Furthermore, the filter box format shown in FIG. 6 was used. According to this, when voltages of 12V, 24V, and 50V are applied, the concentration change at the filter box outlet relative to the filter box entrance is larger than when no voltage is applied and a filter is simply installed, and the soot is more It can be seen that much has been removed.

FIG. 10 shows the relationship between the soot concentration (%) at the outlet of the filter box and the applied voltage (V) when the engine is started. According to this, the soot concentration was 89% when a filter was simply installed, but it significantly decreased to 72% when a voltage of 12V was applied.
As the voltage increases to 0V, the soot concentration gradually decreases to 68% and 65%. Note that the soot concentration at the entrance of the filter box at this time was 96%. As is clear from these test results, exhaust particulates can be effectively removed by giving them a negative charge and causing them to be adsorbed by a positively charged filter.

In the above embodiment, a negative charge is given to the exhaust particulates when they pass through the wire mesh, but on the contrary, a positive charge is given to the wire mesh so that the exhaust particulates are given a positive charge at this time. , a negative charge may be applied to the filter, and after the exhaust particles adhere to the filter, a negative charge may be applied to the wire mesh and a positive charge may be applied to the filter. Although the explanation is given using a diesel engine as a specific example, the explanation is not limited to this, but includes gas turbines that use fossil fuels such as oil and coal, industrial boilers, power generation boilers, water heaters, high-temperature gas furnaces, alcohol The present invention may be applied to systems that burn fuel and biomass fuel.

[0030]

As explained above, according to the present invention, a conductive member through which combustion gas can pass is provided upstream of a conductive collection member provided in the exhaust passage for collecting exhaust particulates. , a voltage is applied between the collection member and the conductive member to charge the exhaust particles passing through the charged conductive member, so that they are electrically attracted to the downstream collection member and collected. Therefore, only a low voltage can be used, and the device can be simplified, which is advantageous in terms of handling, and cost reduction can be achieved. In addition, since the exhaust particulates adsorbed to the collection member start adhering from the surface of the collection member, it is difficult for them to enter the inside of the collection member, and in this state, the polarity opposite to the above is formed between the collection member and the conductive member. If the exhaust particulates are caused to fall by being charged with an electric charge, the increase in exhaust pressure can be minimized, and the collection member can be regenerated well without reducing its life.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the principle of an exhaust particulate treatment device of the present invention.

FIG. 2 is a sectional view taken along line BB in FIG. 1;

FIG. 3 is an overall configuration diagram showing a first embodiment of the present invention.

FIG. 4 is an enlarged cross-sectional view of the wire mesh portion of FIG. 3;

FIG. 5 is a sectional view of an exhaust particulate treatment device showing a second embodiment of the present invention.

FIG. 6 is a cross-sectional view of an exhaust particulate treatment device showing a third embodiment of the present invention.

FIG. 7 is a sectional view of an exhaust particulate treatment device showing a fourth embodiment of the present invention.

FIG. 8 is a sectional view of an exhaust particulate treatment device showing a fifth embodiment of the present invention.

FIG. 9 is an explanatory diagram showing test results of the present invention, showing the rate of change in concentration at the outlet of the filter box with respect to the inlet of the filter box, depending on the engine output.

FIG. 10 is an explanatory diagram showing the test results of the present invention, showing the soot concentration according to the applied voltage.

[Explanation of symbols]

1 Exhaust passage 3 Conductive adsorption filter (collection member) 5 Wire mesh (conductive member) 7 DC power supply (voltage application means)

Claims (1)

[Claims] 1. A conductive collection member for collecting exhaust particulates contained in the combustion gas is provided in an exhaust passage through which combustion gas passes, and the exhaust particulates are collected in an exhaust passage upstream of the collection member. An exhaust particulate processing device comprising: a conductive member through which combustion gases contained therein can pass together with the exhaust particulates; and voltage application means for charging the conductive member and the collection member with charges of different polarities. .