JP2003080024A - Gas treating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas treating apparatus for purging harmful materials in a waste gas efficiently by plasma discharge without causing the lowering of energy efficiency, the increase of the size of the whole apparatus and the complication of its constitution. SOLUTION: This gas treating apparatus has a creeping discharge type plasma discharger 10 constructed by forming at least a discharge surface 11F in a discharge tube 11 from an adsorbing material provided with an action to adsorb NO (harmful material) to be purged and is constituted so that NO (harmful material) in the waste gas from a diesel engine which is a gas producing source is adsorbed to be captured on the discharge surface 11F of the discharge tube (discharge body) 11 and the captured NO is purged by the plasma discharge produced on the discharge surface 11F.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas treatment apparatus for purifying harmful substances such as nitrogen oxides contained in exhaust gas of an engine or the like. The present invention relates to a gas processing apparatus configured to capture harmful substances therein by an adsorbent and purify the captured harmful substances by plasma discharge. 2. Description of the Related Art Exhaust gas generated from a diesel engine or the like contains a large amount of harmful substances such as NO (nitrogen monoxide). Purification of these harmful substances prevents air pollution and the like. This is a major challenge. On the other hand, as a technique for purifying NO in exhaust gas, a technique for treating NO using plasma has been conventionally used, that is, an exhaust gas is caused to flow in a reaction vessel, a plasma discharge is generated in the reaction vessel, and a chemical change occurs. Techniques for purifying NO have been provided. Further, specific examples of the technology for treating NO using plasma include a method of decomposing / reducing NO into nitrogen and oxygen by plasma, and a method of oxidizing NO (NO ₂ ) by oxidizing radicals generated by plasma. Let this NO ₂
To reduce nitrogen to nitrogen and oxygen using a catalyst and a reducing agent. [0005] In the above-described method of decomposing / reducing NO into nitrogen and oxygen by plasma as described above, the concentration of NO contained in the exhaust gas is at most about several thousand ppm. Therefore, most of the energy of the plasma is consumed by components (nitrogen and the like) other than NO in the exhaust gas, and since the ratio effectively given to NO is extremely small, there is a disadvantage that the energy efficiency is extremely poor. there were. In the method of oxidizing NO with oxidizing radicals generated by plasma and reducing NO ₂ to nitrogen and oxygen using a catalyst and a reducing agent as described above, means for generating plasma (plasma discharger) In addition, since a catalyst and a reducing agent are required, there is an inconvenience that the entire apparatus becomes large and the configuration becomes complicated. As means for solving such inconveniences,
A configuration is conceivable in which harmful substances in the exhaust gas are collected at a predetermined location and plasma is generated at the predetermined location, so that plasma energy is intensively applied to the collected harmful substances. Here, as one of the plasma dischargers, there is a well-known dielectric pellet filling discharge type, in which a minute discharge (micro discharge) is generated near the surface of the dielectric pellet. . On the other hand, as a related technology of a plasma discharger,
Japanese Patent Application Laid-Open No. 2000-325735 (Japanese Patent Application No. 11-28508) discloses an adsorbent for plasma treatment in which a ferroelectric substance is disposed inside an adsorbent for adsorbing harmful substances in exhaust gas. Therefore, if the adsorbent for plasma treatment is a dielectric pellet of a plasma discharger, harmful substances in exhaust gas are adsorbed on the surface of the dielectric pellet, so that a discharge is generated on the surface of the dielectric pellet. By the generation, the energy of discharge can be effectively applied to the collected harmful substances. However, in the plasma discharge device of the dielectric pellet filling discharge type, although the largest discharge is generated in a portion where the dielectric pellets are in contact with each other, the above-mentioned portion is in the exhaust gas because the dielectric pellets are in contact with each other. It is difficult to adsorb harmful substances. That is, the harmful substances in the exhaust gas are as follows:
Since it is adsorbed to a portion other than the portion where the dielectric pellets come into contact with each other, in other words, to a portion having a low discharge energy, it is not possible to input sufficient discharge energy to the adsorbed harmful substances, thereby causing harmful effects in exhaust gas. It has been difficult to efficiently purify substances. In view of the above situation, the present invention provides a gas processing system capable of efficiently purifying harmful substances in exhaust gas by plasma discharge without lowering the energy efficiency, increasing the size of the entire apparatus and complicating the configuration. It is intended to provide a device. [0014] In order to achieve the above object, a gas treatment apparatus according to the present invention has a function of adsorbing a harmful substance to be purified on at least a discharge surface of a discharge body. Formed from an adsorbent with
A plasma discharger of a creeping discharge type is provided, and a harmful substance to be subjected to a purification treatment in exhaust gas from a gas generation source is adsorbed and captured on the discharge surface of the discharger in the plasma discharger, The captured harmful substance is purified by plasma discharge generated on the discharge surface. According to the above configuration, the harmful substances in the exhaust gas are adsorbed and trapped on the discharge surface of the discharge body in the plasma discharger. Therefore, when the plasma is generated on the discharge surface, the trapped harmful substances are removed. The energy of the plasma is intensively applied to the substance. [0016] Thereby, the energy efficiency is remarkably improved as compared with the conventional method of decomposing / reducing harmful substances in exhaust gas by plasma, and after harmful substances are oxidized by oxidizing radicals generated by plasma. In contrast to the conventional method of reducing using a catalyst and a reducing agent, a catalyst and a reducing agent are not required, so that an increase in the size of the entire apparatus and a complicated configuration are not caused. Further, according to the above structure, a creeping discharge type plasma discharger, that is, a plasma discharger in which plasma discharge is generated over the entire discharge surface of the discharge body, is employed, so that the discharge surface of the discharge body is adsorbed. Regarding the harmful substance captured as a result, it is possible to input a sufficient discharge energy to each harmful substance regardless of where it is adsorbed on the discharge surface. Therefore, according to the gas treatment apparatus of the present invention, the harmful substances in the exhaust gas can be efficiently purified by the plasma discharge without lowering the energy efficiency, enlarging the whole apparatus and complicating the configuration. can do. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing embodiments. FIG. 1 shows an embodiment in which a gas treatment device according to the present invention is applied to a device for treating NO (nitrogen monoxide) in exhaust gas generated from a diesel engine mounted on a construction machine such as a power shovel. I have. An exhaust pipe 2 extending from a diesel engine 1 serving as a gas generating source is provided with a gas processing device 3 described later, and a muffler 4 is attached to a rear end of the exhaust pipe 2. The gas processing apparatus 3 includes a chamber 3C interposed in the exhaust pipe 2 and a plasma discharger 10 housed and installed in the chamber 3C. After being introduced into the chamber 3C from the exhaust pipe 2 through the inlet 3i as shown by the arrow I and purified by the plasma discharger 10 as described later, the exhaust pipe 2 at the rear through the outlet 3o as shown by the arrow O Going to be exhausted. As shown in FIGS. 2 and 3, the plasma discharge device 10 constituting the gas processing apparatus 3 is a surface discharge type plasma discharge device, and is a cylindrical discharge tube (discharge tube) made of an electrically insulating material. ), A ground electrode 12 provided on the outer periphery of the discharge tube 11, and a high-voltage electrode 13 provided on the inner periphery of the discharge tube 11. Here, the discharge tube 11 is made of activated carbon, silica gel, alumina ceramic, or activated carbon having a function of adsorbing harmful substances to be purified, that is, NO (nitrogen monoxide), in the exhaust gas from the diesel engine 1. It is formed from an adsorbent such as zeolite. That is, since the discharge tube 11 is formed of the above-described adsorbent, the inner peripheral surface of the discharge tube 11, that is, the discharge surface 11F where the plasma discharge occurs as described later, becomes the adsorbent as described above. Will be constituted by The discharge tube is formed of a general electric insulating material such as ceramic or glass material, and the inner peripheral surface of the discharge tube is coated or coated with an adsorbent such as activated carbon, silica gel, alumina ceramic, zeolite or the like. so,
The discharge surface of the discharge tube can be made of the adsorbent. The ground electrode 12 of the plasma discharger 10 surrounds the entire outer peripheral surface of the discharge tube 11, while the high voltage electrode 13 of the plasma discharger 10
Of the inner peripheral surface of the discharge tube 11
Four high-voltage electrodes 13, 13... Are attached to the discharge surface 11F at equal intervals. When a high voltage is applied to the high voltage electrodes 13, 13,..., A plasma discharge is generated along the inner peripheral surface / discharge surface 11F of the discharge tube 11. Here, the ground electrode 12 and the ground electrode 12 are formed so that the plasma discharge is generated only in the vicinity of the discharge surface 11F of the discharge tube 11, in other words, in order to suppress the generation of the plasma discharge in the central space of the discharge tube 11 and reduce the energy loss. The shape, size, and interval of the voltage electrode 13, the mode of applying a high voltage, and the like are appropriately set. The layout of the above-described ground electrode 12 and high-voltage electrode 13, such as the shape, size, and spacing, is not limited to the above-described embodiment.
It goes without saying that various modes can be adopted as long as an effective plasma discharge can be generated along the inner peripheral surface / discharge surface 11F. Hereinafter, the manner in which NO (nitrogen monoxide) is purified in the gas processing apparatus 3 having the above-described configuration will be described in detail step by step with reference to FIG. In the gas processing apparatus 3 described above, the plasma discharger 10 operates to generate plasma discharge when the diesel engine is operating, as a matter of course. When the exhaust gas from the diesel engine 1 (see FIG. 1) flows into the discharge tube 11 of the plasma discharger 10 in the above-described gas processing device 3, as shown in FIG. Is adsorbed and captured by the inner peripheral surface / discharge surface 11F of the discharge tube 11 made of an adsorbent. N captured on the discharge surface 11F of the discharge tube 11
As shown in FIG. 4B, the O molecules collide with high-energy electrons of the plasma discharge generated along the discharge surface 11F, in other words, the high-energy electrons of the plasma discharge are injected into the NO molecules. , N molecules and O molecules. At this time, NO molecules in the exhaust gas are discharged into the discharge tube 1
1 discharge surface 11F, the discharge surface 11F
The energy of the plasma discharge generated in F is intensively injected into the trapped NO molecules. Also, a surface discharge type plasma discharger 1
At 0, since a plasma discharge is generated over the entire area of the discharge surface 11F of the discharge tube 11, any NO molecules adsorbed at various places on the discharge surface 11F are:
Sufficient discharge energy is input. As shown in FIG. 4B, the NO molecules decomposed by the plasma discharge produce harmless O molecules as shown in FIG.
₂ (oxygen) and N ₂ (nitrogen)
0, the chamber 3 of the gas processing apparatus 3 shown in FIG.
C is discharged to the exhaust pipe 2. As described above, according to the gas treatment apparatus 3 having the above-described configuration (see FIG. 1), the discharge of the exhaust gas by the plasma discharge can be performed without lowering the energy efficiency, increasing the size of the entire apparatus, and complicating the configuration. Harmful substances can be efficiently purified. FIGS. 5 and 6 show another embodiment of the plasma discharger constituting the gas processing apparatus according to the present invention. The structure of a gas processing apparatus (not shown) having the plasma discharger of FIGS. 5 and 6 as an element is basically different from that of the gas processing apparatus 3 shown in FIG. Absent. As shown in FIGS. 5 and 6, the plasma discharge device 20 is a surface discharge type plasma discharge device, and has a large number of exhaust gas passages 21A, 2A extending in the axial direction.
, And electrodes 22, 22... Provided inside each exhaust gas channel 21 </ b> A. The discharge body 21 is a cylinder body made of an electrically insulating material and a rectangular cylindrical exhaust gas passage 21A is arranged in a matrix. The discharge body 21 is a diesel engine 1 (see FIG. 1), is formed of an adsorbent such as activated carbon, silica gel, alumina ceramic, or zeolite having a function of adsorbing harmful substances to be purified, ie, NO (nitrogen monoxide). That is, since the discharge body 21 is formed of the above-described adsorbent, the inner peripheral surface of each exhaust gas passage 21A, in other words, the discharge surface 21F where plasma discharge occurs as described later, is adsorbed as described above. It will be composed of materials. The shape of the discharge body 21 is not limited to the cylindrical body shown in the embodiment, but may be various shapes such as an elliptical cylinder or a prism according to various conditions such as an installation mode. It is needless to say that can also be adopted. Further, a discharge body having a honeycomb structure is formed of a general electric insulating material such as ceramic or glass material, and activated carbon, silica gel, alumina ceramic, zeolite, or the like is formed on the inner peripheral surface of each exhaust gas passage in the discharge body. It is also possible to apply or coat the above adsorbent, and to configure the discharge surface of the discharge body with the above adsorbent. The electrodes 22, 2 in the plasma discharger 20
Are mounted at two diagonal corners along the axial direction of the exhaust gas passage 21A, and are installed in the same manner in all the exhaust gas passages 21A. Have been. The two exhaust gas passages 21A are provided in each exhaust gas passage 21A.
The polarity of the electrode 22 differs between the exhaust gas channels 21A adjacent vertically and horizontally. This gives (+)
The electrode 22 on the negative side and the electrode 22 on the (−) side sandwich the wall defining the adjacent exhaust gas flow path 21A, and when a high voltage is applied to the electrodes 22, 22,. A plasma discharge is generated along the inner peripheral surface / discharge surface 21F of each exhaust gas channel 21A. Here, in the gas processing apparatus having the above-described plasma discharger 20 as an element, the diesel engine 1
The manner in which NO (nitrogen monoxide) in the exhaust gas from the exhaust gas (see FIG. 1) is purified is the same as that of the gas processing apparatus including the plasma discharger 10 shown in FIGS. Description is omitted. In the gas processing apparatus including the plasma discharger 20 as described above, the energy efficiency is lowered and the entire apparatus is reduced as in the gas processing apparatus including the plasma discharger 10 shown in FIGS. The harmful substances in the exhaust gas can be efficiently purified by the plasma discharge without increasing the size and complicating the configuration. In each of the above-mentioned embodiments, the discharge tube / discharger in the plasma discharger is made of activated carbon, silica gel, alumina ceramic, or silica having a function of adsorbing NO (nitrogen monoxide) to be purified. Although it is formed from an adsorbent such as zeolite, it goes without saying that an appropriate adsorbent other than the above-described adsorbent may be employed depending on the target of the purification treatment. Further, in each of the above-described embodiments, a gas processing apparatus for purifying NO (nitrogen monoxide) in exhaust gas generated from a diesel engine mounted on a construction machine such as a power shovel has been described. Various harmful substances in exhaust gas generated from vehicle diesel engines and various internal combustion engines, or exhaust gas generated from various combustion devices
Of course, as a device for purifying various harmful substances in (combustion gas), and further various harmful substances discharged from various devices, the gas processing device according to the present invention can be applied very effectively. is there.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and (b) are a conceptual diagram of a diesel engine and a conceptual diagram of a gas processing device showing an embodiment of a gas processing device according to the present invention. FIG. 2 is an external perspective view showing a plasma discharger in the gas processing apparatus of FIG. FIGS. 3A and 3B are a longitudinal sectional view and a transverse sectional view showing the plasma discharge device of FIG. 2; 4 (a), (b), and (c) are conceptual diagrams sequentially showing the manner in which harmful substances are purified in the plasma discharger of FIG. FIG. 5 is an external perspective view showing another embodiment of the plasma discharger in the gas processing apparatus according to the present invention. 6 (a) and (b) are a longitudinal sectional view and a main part transverse sectional view showing the plasma discharge device of FIG. 5; [Description of Signs] 1 ... Diesel engine (gas generation source), 2 ... Exhaust pipe, 3 ... Gas processing device, 3C ... Chamber, 3i ... Inlet, 3o ... Outlet, 10 ... Plasma discharger, 11 ... Discharge tube (Discharge body), 11F: discharge surface, 12: ground electrode, 13: high-voltage electrode, 20: plasma discharger, 21: discharge body, 21A: exhaust gas channel, 21F: discharge surface, 22: electrode.

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Claims (1)

Claims 1. At least a discharge surface of a discharge body,
Equipped with a creeping discharge type plasma discharger formed of an adsorbent having an action of adsorbing harmful substances to be purified, and harmful substances to be subjected to purification in exhaust gas from a gas generation source Wherein the gas discharge device is configured to adsorb and capture the harmful substance on the discharge surface of the discharge body in the plasma discharger and purify the captured harmful substance by plasma discharge generated on the discharge surface. .