Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1999-03-25
2001-12-11
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S366000, C313S433000, C313S440000
Reexamination Certificate
active
06329769
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electron beam irradiation device and method and, more specifically, to an electron beam irradiation device and an electron beam irradiation method which are utilized for removing harmful constituents contained in exhaust gas discharged from, for example, a steam power station.
It is considered that greenhouse effect, acid rain and other effects due to air pollution, which have become the problems throughout the world, originate from constituents such as SOx, NOx, etc., which are included in combustion exhaust gas exhausted from, for example, a thermal power station, etc. One method, which is practiced, for removing harmful constituents such as SOx, NOx, etc., is to irradiate an electron beam on the combustion exhaust gas, thereby carrying out desulfurization and denitration (removal of harmful constituents such as SOx, NOx, etc.).
FIG. 1
shows an example of an electron beam generation device which is used for the above application. The combustion exhaust gas processing device mainly comprises: a power supply
10
which generates a high DC voltage; an electron beam irradiation device
11
which irradiates an electron beam on the combustion exhaust gas; and a flow path
19
for the combustion exhaust gas which is placed along an irradiation window
15
which is an exit for the electron beam irradiated by the device
11
. The electron beam, which is emitted from the irradiation window
15
to the outside, irradiates molecules of oxygen (O
2
), steam (H
2
O), etc., in the combustion exhaust gas, wherein the irradiation window
15
comprises, for example, a thin film of titanium, etc. By receiving the irradiation, these molecules become free radicals such as OH, O, HO
2
, etc., which have very strong oxidative power. These free radicals oxidize harmful constituents such as SOx, NOx, etc., and form intermediate products such as sulfuric acid, nitric acid, etc. These intermediate products chemically react with ammonia gas (NH
3
) which is injected in advance, and become ammonium sulfate and ammonium nitrate. The ammonium sulfate and ammonium nitrate are recovered as materials for fertilizer. By using such an exhaust gas processing system, it becomes possible to remove harmful constituents such as SOx, NOx, etc., from the combustion exhaust gas, and recover byproducts such as ammonium sulfate and ammonium nitrate which can be used as materials of fertilizer.
The electron beam generation device
11
mainly comprises: a thermoelectron generation source
12
such as a thermoelectron filament, etc.; an accelerating tube
13
for accelerating electrons emitted from the thermoelectron generation source
12
; a focusing electromagnet
16
for applying a magnetic field to a high energy electron beam formed by the accelerating tube, thereby controlling the beam diameter of the electron beam; and a scanning electromagnet
17
for applying a magnetic field to the electron beam, of which beam diameter is controlled, thereby deflecting the electron beam. These elements are contained within enclosing elements
18
a
and
18
b
and are held in a high vacuum atmosphere. The thus formed high energy electron beam is deflected and scanned by the magnetic field applied by the scanning electromagnet
17
, and emitted from the irradiation window
15
to a predetermined area of the flow path
19
of the exhaust gas.
FIG.
2
(
a
) is a drawing which shows deflecting and converging of a beam which is formed by a conventional focusing electromagnet and a scanning electromagnet. For example, thermoelectrons generated by a thermoelectron generation source
12
such as a filament, etc., are accelerated and converged by a high voltage of, for example, about 1 MV at the accelerating tube
13
and becomes a high speed electron beam. Then, to enlarge or reduce the beam diameter, the beam diameter is controlled by the focusing electromagnet
16
for converging to a beam of a constant diameter. In this construction, the focusing electromagnet
16
is an electromagnet which comprises a ring-shape coil which is placed around the main axis. By the focusing electromagnet, a magnetic field is formed symmetrically with respect to the axis in the direction of the beam axis, and the beam diameter is controlled in accordance with the magnitude and direction of the magnetic field. For the above purpose, a direct electric current I
O
, as shown in FIG.
3
(
b
), is supplied to the electromagnet.
The electron beam, of which beam diameter is controlled by the focusing electromagnet
16
, is scanned toward x and y directions by the scanning electromagnet
17
. In this construction, the scanning electromagnet
17
is an electromagnet which comprises two sets of magnetic poles capable of deflecting an electron beam to x and y directions. By controlling the magnitude and direction of the electric current which is supplied to the coil of the electromagnet, the deflection angles in the x and y directions are controlled, the electron beam is scanned and the irradiated location of the electron beam is controlled. To this end, a sinusoidal AC current I
S,
as shown in FIG.
3
(
a
), is supplied to the electromagnet coil. As a result, to the irradiation window
15
, an electron beam is scanned in the left and right directions in FIG.
2
(
b
) as shown therein. It should be noted that, in FIG.
2
(
a
), the scan in the vertical direction is abbreviated for convenience of explanation.
SUMMARY OF THE INVENTION
However, when an electron beam is scanned in the x direction by using the scanning electromagnet
17
, if the angle of deviation near the maximum scanning points A and B is large, such a problem has arose that the outgoing angle of the electron beam is made different in accordance with the incident angle thereof due to the deflection effect of the magnetic field created by the electromagnet and that the electron beam converges to a focal point due to an effect like a convex lens. In other words, it is expected to obtain a uniform beam pattern as is shown by a broken line in FIG.
2
(
b
), but, actually, the irradiation of the beam is particularly concentrated on the maximum scanning points A and B which are located at the left and right sides of the hatched region in the figure. When the electron beam is concentrated on the places near the maximum scanning positions A and B as mentioned above, the energy density of these places is increased and, as a result, such a problem has arose that the irradiation window may be damaged. Also, some regions which is not irradiated by the electron beam are formed at the places near the maximum scanning positions A and B. As a result, removal of the harmful constituents from combustion exhaust gas cannot be done sufficiently.
The present invention has been made to solve the above problems. An object of the present invention is to provide an electron beam irradiation device capable of avoiding the problem of convergence of the electron beam at the maximum scanning points, and constantly and wholly obtain an irradiated region of uniform energy density.
An electron beam irradiation device according to the present invention comprises: an electron beam source; an accelerating tube for accelerating electrons emitted from said electron beam source, a focusing electromagnet for applying a magnetic field to a high energy electron beam, which is formed by said accelerating tube, thereby controlling a beam diameter of the electron beam; and an electromagnet for applying a magnetic field to said electron beam to deflect and scan the electron beam of which beam diameter is controlled; the electron beam irradiation device characterized in that an electric current component which is synchronized with an electric current of said scanning electromagnet is superimposed on an electric current of said focusing electromagnet, thereby controlling the electric current of said focusing electromagnet in such a manner that said beam diameter becomes maximum at said maximum points of said scan.
According to the present invention, by superimposing, on an DC electric
Armstrong Westerman Hattori McLeland & Naughton LLP
Ebara Corporation
Lee Wilson
Vu David
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