Boots – shoes – and leggings
Patent
1994-05-09
1995-12-19
Cosimano, Edward R.
Boots, shoes, and leggings
323903, 364148, G05B 1302
Patent
active
054774640
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a method for controlling, in an electrostatic precipitator unit comprising discharge electrodes and collecting electrodes between which a varying high voltage is maintained, a pulsating direct current supplied to the electrodes.
The method is particularly suitable when the pulsating direct current is in the form of a pulse train which is synchronized with the frequency of the voltage from a main source and whose pulses are generated by supplying, by means of a phase angle controlled rectifier (thyristor), part of a half-wave of the mains voltage to the electrodes of the precipitator after step-up transformation, whereupon a plurality of periods of the main voltage may pass without current being supplied to the electrodes. Subsequently, part of a half-wave is again supplied, followed by a plurality of periods without current etc.
2) Description of Related Art
In many contexts, especially in flue gas cleaning, electrostatic precipitators are the most suitable dust collectors. Their design is robust and they are highly reliable. Moreover they are most efficient. Degrees of separation above 99.9% are not unusual. Since, when compared with fabric filters, their operating costs are low and the risk of damage and stoppage owing to functional disorders is considerably smaller, they are a natural choice in many cases.
The requirements of the authorities regarding the level of emissions from e.g. plants in which fossil fuels are combusted, are directed to the total amount of emissions. This means that functional troubles must be taken into consideration. When using electrostatic precipitators, the most frequent trouble is the cleaning of the filter involving rapping, which must be carried out to permit dust deposited on the collecting electrodes to be removed from the filter. In such filter cleaning, the emissions temporarily increase very strongly, if no specific measures are taken. One possible measure is disclosed in EP-162 826.
The total consumption of energy in the electrostatic precipitators in a large incineration plant may amount to several hundred kW. It has therefore become most important to reduce this consumption of energy as far as possible. This is especially important when dust of high resistivity is to be separated. In such cases, it is often necessary to work with extremely unfavorable operational parameters owing to the risk of electric breakdown in the dust layer which successively grows on the collecting electrodes. This leads to charges and dust being emitted from the collecting electrodes, so-called back corona.
In order to optimize the operation and reduce the energy consumption at the same time as the separation is improved, several methods for pulse feeding of the current to the filter have been suggested. Examples are to be found in U.S. Pat. Nos. 4,052,177 and 4,410,849. The former suggests the feeding of pulses in the order of microseconds, which means that the rectifiers become most expensive. The latter suggests pulses in the order of milliseconds, which may be achieved quite simply by selectively controlling ordinary thyristor rectifiers to which main frequency alternating current is supplied.
Independently of the selected technique, one tries of course to use it as efficiently and economically as possible. Above all, the emissions must be lower than the fixed limit values. Next, the costs thereof should be minimized.
The new techniques have resulted in an increasing number of control parameters and, consequently, an increasing complexity in the control systems. Unfortunately, this also means that the actual adjustment may be a major disturbance in the function of the separator. In the same way as the emissions increase during the rapping of the filter, the emissions will increase during the adjustment or during the checking of the control parameters as set.
If adjustment is effected manually by means of the reading on an opacimeter (tester for the optical density of smoke), this takes such a long t
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ABB Flakt AB
Cosimano Edward R.
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