Radiant energy – Radiant energy generation and sources
Patent
1991-06-27
1992-12-29
Berman, Jack I.
Radiant energy
Radiant energy generation and sources
2504923, 250424, 313420, H01J 3300
Patent
active
051754363
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an electron accelerator technique for producing electrons having an energy of 100 keV to 800 keV for use in industrial processes.
Typical industrial applications include electronic polymerization of coatings and filling materials onto the surface of or within a material web and radiation sterilization of packing materials and products. Recently the electron beam technique has become increasingly popular in the purification of flue gases from sulphur and nitrogen oxides.
There are usually two types of devices: devices emitting electrons from one point and devices producing a curtain-like electron beam, for instance, across a material web passed evenly through the device in the transverse direction. The purpose of nearly all such industrial applications is to apply an even electron beam or radiation dose to the surface of a moving material web or to provide a radiation dose as constant as possible over the cross-sectional area of a flue gas flow. A high vacuum prevails inside electron accelerators, the electrons being introduced in the devices through long and narrow windows of metal foil transversely positioned relative to the mass flow.
At present, there are only a few manufacturers in the world that supply devices producing a curtainlike electron beam. In all these devices, the narrow window of metal foil is disposed so as to be protected from the lines of force caused by the accelerating voltage and supported by a cooling grid. Being positioned on the path of travel of the electrons, the grid causes a dissipation which is always at least equal to the ratio of the surface area of the cooling supports and that of the window. In prior art devices, this dissipation varies from about 25 to 35%. In addition, acceleration of electrons from one opening to another across an accelerating voltage always causes the electrons to strike the edges of the window opening and the surface of the cooling and supporting ribs protruding from the window openings as seen from the inside, the resultant dissipations being of the order of 10 to 25%. The window itself causes a dissipation of at least 5 to 15%. If the windows are replaced with a small hole formed in the device for the emission of electrons and for the discharge of the air forced inside the vacuum space by means of high-efficiency pumps systems, the emitted electron beam is first very dense and has to be allowed to get more even in the air before use as all electron beam applications require an even dose per volume or area unit. It can be readily calculated that the power required in a flue gas application, for instance, for achieving a minimum dose at each point of the cross-sectional profile is thereby three times greater than in devices producing a curtainlike beam. At present, it is necessary to use high efficiencies in the hidden emission means when accelerating from opening to opening, which often consumes 5 to 10% of the total efficiency. The estimated performance of this acceleration technique is generally as low as 20 to 40%. For instance, the energy consumed in the purification of flue gases by this technique in large power plants amounts to several per cents of the electric power demand of the plant, wherefore an improved performance is an important factor in making the purchase of these devices more attractive.
The object of the invention is achieved by means of a method which is mainly characterized by what is disclosed in the claims.
The major advantages of the present invention are obtained particularly by the electron acceleration technique, in which the shaping of the electron paths is carried out first in connection with the low-energy acceleration while the electrons are efficiently passed through the windows in the proper high-energy acceleration. The performance of each individual device is also increased because several successive windows can be provided in the device, each window emitting a high-energy electron curtain.
In the following the method of the invention will be described in greater detail with reference to th
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Berman Jack I.
OY Tampella AB
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