Gas separation – Means within gas stream for conducting concentrate to collector
Patent
1991-08-13
1993-06-08
Chiesa, Richard L.
Gas separation
Means within gas stream for conducting concentrate to collector
55105, 55139, 323903, B03C 368
Patent
active
052175049
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for controlling, in an electrostatic precipitator unit with discharge electrodes and collecting electrodes between which dustladen gases are conducted for dust separation, the current pulse supplied to the discharge electrodes, in order to achieve maximum dust separation.
Usually, electrostatic precipitators are made up of a number of precipitator units arranged one after another, through which dustladen gases are successively conducted in order to be cleaned. Each of these electrostatic precipitator units has an inner chamber which is divided into a number of parallel gas passages by means of a number of vertical curtains of earthed steel plates arranged side by side to form the collecting electrodes of each unit. A number of vertical wires to which a negative voltage is connected are arranged in each gas passage to form the discharge electrodes of each unit. Due to corona discharges from the discharge electrodes, the gases are ionized in the electric field in the gas passages. The negative ions are attracted by the steel plates and, when moving towards these, collide with the dust particles in the gases, such that the particles are charged, whereupon they are separated from the gases when they are attracted by the nearest steel plate (collecting electrode), where they settle and form a growing layer of dust.
Generally, dust separation becomes more efficient as the voltage between the electrodes increases. The voltage should, however, not be too high, since that may cause flash-overs between the electrodes. Too high a current per unit area towards the collecting electrode may entail that the dust layer is charged faster than it is discharged towards said collecting electrode. Then, this charging of the dust layer entails sparking in the layer itself, so-called back-corona, and dust is thrown back into the gas. The risk of back-corona becomes greater as the resistivity of the dust increases.
To reduce the risk of back-corona, especially in separation of dust of high resistivity, and at the same time maintain such a current supply to the discharge electrodes that corona discharges occur therein, the discharge electrodes are now usually supplied with current pulses. Each precipitator unit has a separate, controllable current and/or voltage supplying circuit associated with control equipment, such that the current and/or voltage supplied to each unit can be separately controlled. Thus, the current supplied to the discharge electrodes of each unit is separately adjusted in such a manner that maximum dust separation is obtained. Today, such an adjustment is carried out entirely by hand in that the current pulse supply is adjusted and the alteration caused thereby of the degree of dust separation is controlled by measuring the opacity of the gases from the electrostatic precipitator. This adjustment is repeated until a lowest opacity value has been obtained. This method is, however, time-consuming and furthermore requires that the operator be specially trained and have great experience in electrostatic precipitators, since a considerable degree of "feeling" is needed to be able to decide which other parameters may possibly have influenced the opacity measuring during the setting operation. Furthermore, considerable adjustments have to be made for an efficient use of the opacity measurings.
SUMMARY AND OBJECTS OF THE PRESENT INVENTION
Therefore, the object of the present invention is to provide a simple current supply control method having none of the above disadvantages.
This object is achieved by a method where current pulses with a given pulse current are supplied to the discharge electrodes, that the pulse frequency is varried, that instantaneous values corresponding to one another, for the voltage between the discharge electrodes and the collecting electrodes are measured for a number of different pulse frequencies, and that the current pulse supply to the discharge electrodes is then set to the pulse frequency at which the greatest instantaneous value has been me
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ABB Flakt Aktiebolag
Chiesa Richard L.
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