Radiant energy – Irradiation of objects or material – Ion or electron beam irradiation
Reexamination Certificate
2002-01-24
2004-02-24
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Ion or electron beam irradiation
C250S492230, C250S492100
Reexamination Certificate
active
06696693
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electron beam irradiation apparatus and method, and more particularly to electron beam irradiation apparatus and method which are employed for irradiating combustion exhaust gas discharged from thermal power stations or the like with an electron beam to remove toxic components from the exhaust gas.
BACKGROUND ART
As economy develops, more and more energy is demanded. Amidst the continuous growth of energy demand, energy source is still dependent on fossil fuels such as coal and petroleum. However, the harmful products or pollutants generated by burning of fossil fuels are responsible for global pollution. It is considered that a global issue of the global warming and the acid rain caused by air pollution is attributed to components such as SOx and NOx which are contained in combustion exhaust gas discharged from thermal power stations or the like. As a method for removing toxic components such as SOx and NOx, there has been used a method of irradiating combustion exhaust gas with an electron beam for desulfurization and denitration (i.e. removing toxic components such as SOx and NOx).
In a flue gas treatment system for treating the combustion exhaust gas by employing an electrom beam, molecules such as oxygen (O
2
) and water vapor (H
2
O) in the combustion exhaust gas are irradiated with the electron beam emitted from an irradiation window comprising a thin film made of Ti or the like to form radicals such as OH, O, and HO
2
having high oxidizing strength. These radicals oxidize toxic components such as SOx and NOx to produce sulfuric acid and nitric acid as intermediate products. These intermediate products react with ammonia gas (NH
3
) previously injected into the exhaust gas to produce ammonium sulfate and ammonium nitrate which are recovered as materials for fertilizer. Therefore, such a system for treating exhaust gas can remove toxic components such as SOx and NOx from the combustion exhaust gas and simultaneously recover ammonium sulfate and ammonium nitrate as useful by-products used for materials for fertilizer.
FIG. 3
shows an electron beam irradiation apparatus used for the above flue gas treatment system according to an example.
The electron beam irradiation apparatus
11
mainly comprises a thermoelectron generator
12
comprising a filament or the like, an accelerating tube
13
for accelerating electrons emitted from the thermoelectron generator
12
, a focusing electromagnet
16
for controlling a diameter of the electron beam by applying the magnetic field to the high-energy electron beam formed in the accelerating tube
13
, and scanning electromagnets
17
,
18
for deflecting the electron beam in x and y directions by applying the magnetic field to the electron beam whose diameter has been controlled by the focusing electromagnet
16
. The x direction is a horizontal direction shown in
FIG. 3
, and the y direction is a direction perpendicular to the x direction and also perpendicular to the sheet surface of
FIG. 3. A
surrounding comprising a container
19
and an irradiation window
20
is provided, and the interior of the surrounding is kept under high vacuum condition in the range of 1.33×10
−3
to 1.33×10
−4
Pa (10
−5
to 10
−6
Torr). The high-energy electron beam formed by the accelerating tube
13
is deflected and scanned by the scanning electromagnets
17
,
18
which apply the magnetic field to the electron beam, and emitted through the irradiation window
20
into a certain range of an exhaust gas passage (not shown in
FIG. 3
) located at the outside.
Thermoelectrons generated by the thermoelectron generator
12
comprising a filament or the like are accelerated by high-voltage of about 800 kV, for example, in the accelerating tube
13
to cause a high-speed electron beam to be formed. Then, a beam diameter of the electron beam is controlled by the focusing electromagnet
16
to thus form a linear electron beam, having substantially the same diameter in a travelling direction in an example shown in
FIG. 3
, which is then directed toward the magnetic field formed by the scanning electromagnets
17
,
18
. The focusing electromagnet
16
comprises an electromagnet having a ring-shaped coil disposed around an axis of the electromagnet, and forms a magnetic field which is symmetric with respect to the axis of the electron beam. The beam diameter of the electron beam is controlled by magnitude and direction of the magnetic field. In other words, focusing of the electron beam is controlled by magnitude and direction of the magnetic field. Therefore, direct current I
0
is supplied to the coil of the electromagnet, and the degree of convergence or divergence of the electron beam is adjusted by magnitude of the direct current I
0
.
The electron beam whose diameter has been controlled by the focusing electromagnet
16
is scanned in the x and y directions by the scanning electromagnets
17
,
18
. The scanning electromagnet
17
comprises an electromagnet having a pair of poles for deflecting the electron beam in the y direction, and the scanning electromagnet
18
comprises an electromagnet having a pair of poles for deflecting the electron beam in the x direction. By controlling magnitude and direction of current supplied to the coils of the scanning electromagnets
17
,
18
, angles of deflection in the x and y directions are controlled, and hence the electron beam is scanned and the irradiation position of the electron beam is controlled. In an example, the electron beam is scanned in the y direction (latitudinal direction) using rectangular wave in the scanning electromagnet
17
, and the electron beam is scanned in the x direction (longitudinal direction) using sine wave in the scanning electromagnet
18
.
However, when the electron beam is scanned in the x direction by the scanning electromagnet
18
, if the angle of deflection is large in the vicinity of maximum scanning positions A, B corresponding to both scanning ends, the electron beam is deflected by the magnetic field produced by the electromagnet, so that an angle of outgoing electron beam differs according to an angle of incidence of the electron beam. Therefore, the electron beam converges at the irradiation window portions A, B corresponding to the maximum scanning positions A, B due to a lens effect created by a convex lens or the like. Specifically, as shown in the irradiation window portions A, B and C of
FIG. 3
, while the beam diameter is about 10 cm, for example, at the central position C, the beam diameter is about 5 cm, for example, at the maximum scanning positions A, B corresponding to both scanning ends. Thus, the irradiation area of the electron beam is remarkably converged at the maximum scanning positions A, B. The irradiation window
20
comprises a thin film made of titanium (Ti), and hence if the electron beam converges at the maximum scanning positions A, B or thereabouts, then energy density of the electron beam is increased thereat, causing damage to the irradiation window.
Further, areas where irradiation of the electron beam is not made are formed at the maximum scanning positions A, B or thereabouts, and hence toxic components in the combustion exhaust gas cannot be sufficiently removed.
DISCLOSURE OF INVENTION
It is therefore an object of the present invention to provide electron beam irradiation apparatus and method which can prevent an electron beam from being converged at a maximum scanning position and can stably obtain an irradiation area having a uniform energy density where irradiation of the electron beam is uniformly performed.
According to an aspect of the present invention, there is provided an electron beam irradiation apparatus, comprising: an electron beam source for emitting electrons; an accelerating tube for accelerating the electrons emitted from the electron beam source; a focusing electromagnet for controlling a diameter of an electron beam by applying a magnetic field to an electron beam having a high energy formed in the accelerating tube; an elect
Ebara Corporation
Lee John R.
Quash Anthony
Westerman Hattori Daniels & Adrian LLP
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