Radiant energy – Irradiation of objects or material – Ion or electron beam irradiation
Reexamination Certificate
2000-06-02
2002-06-25
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Ion or electron beam irradiation
C250S311000, C250S306000, C250S492200
Reexamination Certificate
active
06410929
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron beam irradiation apparatus which is 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, and more particularly to an arrangement of a power supply for applying a high voltage to an electron accelerator incorporated in the electron beam irradiation apparatus.
2. Description of the Related Art
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).
FIG. 3
is a schematic view showing an electron beam irradiation apparatus for conducting the above method. An apparatus for treating combustion exhaust gas shown in
FIG. 3
mainly comprises a power supply
10
for generating a high DC voltage from a commercial AC power supply, an electron accelerator
11
for accelerating electrons emitted from an electron beam source by applying a high voltage to the electrons and for irradiating a target with the electrons, and a combustion exhaust gas passage
19
disposed along an irradiation window
15
serving as an irradiation outlet of the electron beam from the electron accelerator
11
. 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 the irradiation window
15
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.
The electron accelerator
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 radius of the electron beam by applying the magnetic field to the high-energy electron beam formed in the accelerating tube
13
, and a scanning electromagnet
17
for deflecting the electron beam by applying the magnetic field to the electron beam whose radius is controlled by the focusing electromagnet
16
. The accelerating tube
13
is housed in a container
18
b
and the interior of the accelerating tube
13
is kept under high vacuum condition. The high-energy electron beam formed by the accelerating tube
13
is deflected and scanned by the scanning electromagnet
17
which applies the magnetic field to the electron beam, and emitted through the irradiation window
15
into a certain range of the exhaust gas passage
19
.
FIG. 4
is a schematic view showing an arrangement of a conventional power supply incorporated in the electron beam irradiation apparatus shown in FIG.
3
. The power supply
10
has input terminals
21
connected to the commercial AC power supply of a high voltage, e.g. 3300 V. This commercial AC voltage of 3300 V is applied to the input terminals
21
of the power supply
10
. The AC voltage of 3300 V is obtained by stepping down an extra high tension voltage of 66000 V with a step-down transformer installed in a plant or the like. A harmonic suppression filter circuit
22
is connected to the input side of the power supply
10
to suppress the high-order harmonics formed by subsequent AC/DC converting. Since the fundamental frequency of the filter circuit
22
is 50 Hz or 60 Hz, the filter circuit
22
is required to be quite large in order that the third, fifth, and higher-order harmonics of the fundamental frequency should be suppressed so as not to affect the commercial AC power supply.
Circuit breakers
23
are disposed on the power supply lines and can break the circuit instantaneously in response to the signal from a controller
25
. An induction voltage regulator (IVR)
24
is disposed in the downstream side of the circuit breakers
23
. The IVR varies the AC output voltage by changing a flux linkage in accordance with an axial rotation driven by a motor, thus providing a kind of variable-voltage mechanisms. The output voltage is adjusted in the IVR
24
as follows: The DC output voltage Vo applied to the accelerating tube
13
is detected by a voltage detector
29
, and the motor is rotated so as to keep the DC output voltage Vo detected by the voltage detector
29
constant. If an overcurrent is detected by a current detector
26
disposed in the downstream side of the IVR
24
, then the circuit breakers
23
are opened by the controller
25
. Thus, the protection from the overcurrent in the power supply
10
is achieved.
A step-up transformer
27
is connected to the downstream side of the IVR
24
, and rectifying devices
28
are connected to the output of the step-up transformer
27
. Each of the rectifying devices
28
produces a DC voltage of about 20 kV. The output DC voltage Vo of about 800 kV can be obtained as a whole by connecting these rectifying devices
28
in series. The DC output voltage Vo is divided by voltage dividing resistances
30
connected to the accelerating electrodes in the accelerating tube
13
. The divided DC output voltages are applied to the accelerating electrodes for accelerating the electrons. On the other hand, a filament
31
for generating thermoelectrons is provided in the accelerating tube
13
. An alternating current is supplied from an AC power supply
32
to the filament
31
to heat the filament
31
for thereby emitting the thermoelectrons therefrom. The thermoelectrons emitted from the filament
31
in the accelerating tube
13
are accelerated by the accelerating electrodes in the accelerating tube
13
, passes through the irradiation window
15
, and is emitted from the accelerating tube
13
to the outside as a high-energy electron beam E.
Such a conventional power supply for an electron beam irradiation apparatus has the following problems.
First, since the IVR is employed for adjusting the DC output voltage Vo, it is necessary that the motor is controlled to be rotated so as to keep the output voltage Vo constant against the variations of the input voltage of the commercial AC power supply. However, the rotational speed of the motor is too slow to follow an abrupt variation of the input voltage or the load. Therefore, the abrupt variation of the input voltage varies the output voltage Vo to thus weaken the lens effect of the accelerating tube, thus scattering the electron beam and causing an obstacle to the irradiation of the electron beam.
Secondly, when a DC power supply of a high voltage is used as a power supply, a local electric discharge or a short-circuit tends to occur between electrodes in the accelerating tube or near the rectifying devices. If such a local electric discharge occurs, an overcurrent flows in the circuit to break the rectifying elements such as diodes. Once the rectifying elements are broken, it is difficult to repair or replace the broken elements because they are immersed in insulating oil of a high-pressure tank and protected thereby, thus requiring high cost and a lot of time for restoring. Therefore, as soon as an overcurrent flows in the circuit, it is necessary to open the circuit breakers
23
and to stop applying a high DC voltage for thereby prote
Kiga Masahiro
Nakamura Atsushi
Yosioka Takesi
Ebara Corporation
Lee John R.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Vanore David A.
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