Radiant energy – Irradiation of objects or material – Ion or electron beam irradiation
Patent
1999-02-11
2000-04-25
Nguyen, Kiet T.
Radiant energy
Irradiation of objects or material
Ion or electron beam irradiation
H01J 3730
Patent
active
060547146
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an electron-beam irradiation apparatus for allowing electron beam generated in a vacuum container to pass through a window foil or window foils that partition the vacuum container from a process vessel and irradiating gas containing moisture or water (hereinafter referred to as "wet gas") such as flue gas in the process vessel with electron beam to thereby process or treat the gas, and more particularly to a structure of the above window foil.
DISCUSSION OF THE BACKGROUND
There has been known an electron-beam irradiation apparatus in which a filament is heated by causing electric current to flow therethrough to emit thermoelectrons which are then accelerated by applying a high voltage to produce electron beam in a vacuum container, and the produced electron beam passes through a window foil or window foils into a process vessel outside of the vacuum container to treat substance such as gas in the process vessel by irradiation of the electron beam. The electron-beam irradiation apparatus is used in a wide variety of fields including acceleration of chemical reaction of macromolecule, the sterilization of medical instruments, and many research and development activities. The electron-beam irradiation apparatus is also used to purify flue gas that is produced when fossil fuels such as coal and petroleum are combusted. Advantages offered by the use of electron beam as compared with X-rays and .gamma.-rays are that an electron-beam source may be of a large capacity and a large amount of substance may be processed or treated at one time.
It has been known to add an alkaline agent such as ammonia or lime to flue gas which contains harmful materials including sulfur oxides (SOx), nitrogen oxides (NOx), hydrogen chloride (HCl) and the like, and then irradiate the flue gas with electron beam to convert the harmful materials into particulates for removal and recovery, as disclosed in Japanese laid-open patent publication No. 52-140499. According to the disclosed process, ammonia (NH.sub.3) is added as the alkaline agent to the flue gas, and the flue gas is irradiated with electron beam to convert SOx into particles of ammonium sulfate and NOx into particles of ammonium nitrate, so that these particles can be recovered from the flue gas for use as fertilizer.
The electron beam generated in the vacuum container is taken out from the vacuum container by allowing the electron beam to pass through a thin metal film, i.e., a window foil that partitions the vacuum container of an electron beam accelerator from the process vessel. The window foil is required to be thick enough to withstand the pressure difference between pressure in the vacuum container and pressure in the process vessel. However, the window foil is required not to be excessively thick so that a large loss of energy of the electron beam is not caused when the electron beam passes through the window foil. Thus, the window foil having a thickness from ten to several tens of microns is practically used. If the flue gas to be treated by the electron beam contains pollutants of relatively low concentration, then only a primary window foil is placed between the vacuum container of the electron beam accelerator and the process vessel. However, if the flue gas contains a large amount of harmful materials including SOx, NOx, HCl and the like, as in flue gas discharged from a boiler, then a secondary window foil is added outwardly of the primary window foil such that the electron beam generated in the vacuum container passes through the primary and secondary window foils into the process vessel. In this case, a cooling chamber is defined between the primary and secondary window foils for allowing cooling gas such as cooling air to pass therethrough to cool the primary and secondary window foils. Owing to this structure, the flue gas is prevented from entering the vacuum container directly even when the secondary window foil directly contacting the flue gas is damaged.
Conventionall
REFERENCES:
patent: 5801387 (1998-09-01), Nablo et al.
Izutsu Masahiro
Ogure Naoaki
Ebara Corporation
Nguyen Kiet T.
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