Electric heating – Metal heating – By arc
Reexamination Certificate
2000-12-12
2003-09-02
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121520, C219S121500, C315S111510
Reexamination Certificate
active
06614000
ABSTRACT:
BACKGROUND ART
1. TECHNICAL FIELD
The present invention relates to an organic halogen compound decomposition device which utilizes a plasma, a decomposition method for organic halogen compounds using the device, and an operation control method for the above decomposition device. In particular the invention relates to an organic halogen compound decomposition device which uses microwaves to generate a plasma, a microwave plasma torch and a plasma ignition method suitable for use in the decomposition device, and an operation control method for the above decomposition device.
2. BACKGROUND ART
Organic halogen compounds such as freon, trichloromethane and halon, which incorporate elements such as fluorine, chlorine and bromine within the molecule, are used in large quantities for a variety of uses such as refrigerants, solvents and fire extinguishing agents, and are extremely important in industry.
However, these compounds display high volatility, and if discharged untreated into the environment, such as into the atmosphere, soil, or water, can have undesirable effects on the environment such as the generation of carcinogenic substances or the destruction of the ozone layer. Consequently from an environmental conservation viewpoint, it is necessary to treat the compounds to render them harmless.
Conventional treatment methods for organic halogen compounds typically utilize thermal decomposition reactions at high temperatures. These treatment methods can be further roughly classified into incineration methods and plasma methods.
In incineration methods, organic halogen compounds are incinerated together with typical waste products such as plastics. In contrast, in plasma methods, the organic halogen compound is reacted with steam within a plasma, and decomposed to carbon dioxide, hydrogen chloride and hydrogen fluoride. In recent years, operation control methods have been developed for organic halogen compound decomposition devices which utilize the above plasma methods and which utilize microwaves to generate the plasma.
Decomposition devices used in such decomposition methods comprise an exhaust gas treatment tank containing an alkali solution, a reaction tube in which the open lower end section thereof is immersed in the alkali solution, a cylindrical waveguide which extends in a vertical direction above the reaction tube, a discharge tube disposed inside the cylindrical waveguide in which the bottom end thereof interconnects with the reaction tube, a square waveguide in which one end thereof is connected to the cylindrical waveguide, and a microwave transmitter which is installed at the other end of the square waveguide.
In this type of decomposition device, freon gas and steam are supplied to the discharge tube, while microwaves generated by the microwave transmitter are transmitted to the cylindrical waveguide via the square waveguide. Then, a discharge is produced within the microwave electric field formed inside the cylindrical waveguide, and the freon gas is decomposed by a thermal plasma within the reaction tube. The product gases produced by this decomposition reaction are then neutralized by passage through the alkali solution, and any remaining gases such as carbon dioxide are expelled through an exhaust duct.
However, in the above plasma type organic halogen compound decomposition device, prior to the formation of the plasma, it is first necessary to ignite the gas in a stable and reliable manner enabling a simple formation of the plasma. Furthermore, in terms of the operation of the device following ignition, maintenance of a good plasma form and maintenance of a stable decomposition reaction are important factors.
Moreover, in the above plasma type organic halogen compound decomposition device, because the freon gas or the like needs to be in a plasma state, the device needs to be controlled so that the freon gas is converted to a plasma in a stable and reliable manner. Furthermore, because the substances generated on decomposition of the freon gas are toxic, safety must also be ensured in the control of the device.
The present invention takes the above factors into consideration, with an object of providing a microwave plasma torch and an organic halogen compound decomposition device for which a stable and reliable ignition is possible prior to plasma formation, and moreover for which good plasma form, and stable operation, can be maintained following ignition.
Furthermore, another object of the present invention is to provide a plasma ignition method which enables a stable and reliable ignition prior to the plasma formation, and an organic halogen compound decomposition method which utilizes this ignition method.
Moreover, another object of the present invention is to provide an operation control method for an organic halogen compound decomposition device in which an organic halogen compound such as a freon gas can be converted to a plasma in a stable and reliable manner. In addition, another object of the present invention is to provide an operation control method for an organic halogen compound decomposition device which enables an improvement in safety of the organic halogen compound decomposition devices.
DISCLOSURE OF THE INVENTION
In order to resolve the above problems, the following construction was employed in the present invention.
A microwave plasma torch of the present invention comprises a cylindrical waveguide made up of an outer conductor and an inner conductor, and a dual construction discharge tube made up of an inner tube and an outer tube which is provided inside the cylindrical waveguide and on an identical axis, wherein a probe antenna formed from an extension of the inner conductor is positioned so as to encircle the discharge tube, and the tip of the inner tube is positioned further inwards than the tip of the probe antenna.
According to this microwave plasma torch, the helical gas flow flowing out from between the inner tube and outer tube forms a stagnation point directly below the inner tube. Consequently, the gas flow stagnation point can be easily ignited, making a stable and reliable ignition possible. Furthermore, because the tip of the inner tube is positioned further inwards than the tip of the probe antenna, the inner tube tip section is separated from the energy intensive section of the plasma, and is less likely to be subjected to heating effects.
Moreover, because a distance L is provided between the inner tube tip and the probe antenna tip, with the inner tube being positioned further inwards, the inner tube tip is separated from the energy intensive section of the plasma, and is less likely to be subjected to heating effects. Consequently, thermal deformation of the inner tube can be prevented, and by providing a stable gas flow, a stable decomposition reaction can be maintained.
Furthermore, an organic halogen compound decomposition device of the present invention comprises an exhaust gas treatment tank containing a treatment solution for neutralization treatment of the decomposition products from the organic halogen compound, a reaction tube in which the open lower end section thereof is immersed in the treatment solution of the exhaust gas treatment tank, and a microwave plasma torch, and the microwave plasma torch further comprises a cylindrical waveguide made up of an outer conductor and an inner conductor, which extends in a vertical direction above the reaction tube, and a dual construction discharge tube made up of an inner tube and an outer tube which is provided inside the cylindrical waveguide and on an identical axis, wherein a probe antenna formed from an extension of the inner conductor is positioned so as to encircle the discharge tube, and the tip of the inner tube is positioned further inwards than the tip of the probe antenna.
This organic halogen compound decomposition device employs a plasma torch which has excellent ignition properties and which is able to maintain a stable decomposition reaction, and so at the beginning of operation, a stable and reliable ignition is possible. Moreover, a good plasma form
Bessho Masahiro
Hattori Toshio
Tsubaki Yasuhiro
Mitsubishi Heavy Industries Ltd.
Paschall Mark
Scully Scott Murphy & Presser
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