Gas separation: apparatus – Electric field separation apparatus – Including gas flow distribution means
Patent
1997-07-10
2000-06-06
Chiesa, Richard L.
Gas separation: apparatus
Electric field separation apparatus
Including gas flow distribution means
55DIG38, 96 88, 96 92, 96 97, 96 98, 110216, 110345, B03C 384
Patent
active
060713305
DESCRIPTION:
BRIEF SUMMARY
This application is the National Stage Application filed under 35 USC 371 of International Application No. PCT/JP96/02242 filed on Aug. 7, 1996.
TECHNICAL FIELD
The present invention relates to an electric dust collector also serving as an exhaust pipe lined with refractories.
BACKGROUND ART
Conventional electric dust collectors, used to remove dust from exhaust fumes and exhaust gas from smelting furnaces (steel converters, cupolas, etc.), heat treatment ovens (annealing ovens etc.), ceramics ovens (cement kilns etc.), incinerators, drying ovens, and heat engines, are arranged so that exhaust fumes or exhaust gas passes between many closely spaced dust collecting electrodes. This causes a heavy pressure loss. To prevent an electric dust collector from being exposed to high temperatures, a cooler or the like, also serving as a heat recovery heat exchanger or a gas neutralizer, is normally installed immediately upstream of the electric dust collector, thus increasing pressure loss. Due to pressure loss thus caused, only aeration is not sufficient to emit exhaust fumes or exhaust gas, and accordingly, an exhaust fan is essential for the emission. Because of their exposure to corrosive gas and heat, exhaust fans fail so frequently that they require laborious maintenance and inspection.
In addition, conventional electric dust collectors have the following problems: dust to fly off. electric resistance of more than 10.sup.12 .OMEGA..multidot.cm. less than 10.sup.4 .OMEGA..multidot.cm.
These problems reduce the rate of dust collection. To avoid the problems, conventional electric dust collectors require the following troublesome countermeasures:
It is an object of the present invention to provide an electric dust collector that needs no exhaust fan or special equipment dedicated to prevent dust from flying off.
DISCLOSURE OF THE INVENTION
An exhaust pipe (smokestack) according to the present invention, emitting into the air exhaust fumes from a burning chamber of an incinerator and so on, is made of steel sheeting and lined with refractories, since it is exposed to elevated temperatures due to exhaust fumes. The refractories are preferably castable refractories (refractive concrete composed mainly of SiO.sub.2 and Al.sub.2 O.sub.3) and the like.
The refractories are insulators at normal temperature, which conduct little electric current. During operation, the temperature at the surface of the refractories is around 800.degree. C., and that near heat-resistant anchors preventing the refractories from falling off reaches 400 to 500.degree. C. At such high temperatures, ordinary refractories lose their performance of electric insulation as an ordinary insulating material does. FIG. 1 shows the temperature dependence of a castable refractory.
Corona discharge requires high voltages. Since corona discharge involves a small current, however, the dust collecting electrode does not always need to be as conductive as metal. The electrode is only required to have enough conductivity to discharge collected dust.
According to the present invention, a discharge electrode is suspended at the center of an exhaust pipe, and a high DC voltage is applied between the discharge electrode and the external steel sheeting of the exhaust pipe (the steel sheeting and the discharge electrode have positive and negative polarity, respectively, as in general electric dust collectors).
The collector arranged as described above has a considerably long discharge gap both because the discharge electrode is at the center of the exhaust pipe (smokestack) and because the internal surface of the pipe is a dust collecting electrode. No literature describes in detail corona discharge occurring in such a long gap at high temperatures. Using a small dust collector with a short discharge gap, the inventors made sure that an electric current with two orders or more of magnitude larger flows in a gas at an atmospheric pressure and a temperature of 500 to 700.degree. C. than in a gas at normal temperature when the same voltage is applied. FIG. 2 s
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Matsubara Makoto
Watanabe Wataru
Chiesa Richard L.
Galaxy Yugen Kaisha
Snider Ronald R.
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