The present invention relates to an electrostatic precipitator, more particularly, an electrostatic precipitator having a novel construction and capable of collecting dust particles having extremely high specific resistance as well.
Electrostatic precipitators, hereinafter called E.P., of prior-art construction have the disadvantage in that when dust particles have a resistivity of higher than 10.sup.11 .OMEGA.-cm, they cannot function owing to the back ionization taking place. Further disadvantages of the prior EP are as follows:
1. When the resistivity of dust particles is higher than 10.sup.11 .OMEGA.-cm, back ionization takes place in the layer of dust particles accumulated on the dust-collecting electrodes, causing the dust-collecting efficiency to decrease substantially so that it cannot function with practical efficiency. Two main reasons thereof are as follows: (a) The back ionization taking place in the layer of accumulated dust causes frequent spark discharges and as a result, the E.P. can no longer operate unless the applied voltage is made very low, giving rise to a substantial decrease of dust-collecting efficiency; (b) When the resistivity of the dust layer becomes higher further, the back ionization taking place in the layer of accumulated dust causes a large corona-discharge current to flow even at a low applied voltage. As a result, a large quantity of positive ions are generated from the layer of accumulated dust and a fairly large number of the negatively charged dust particles are changed over to positive charges by them. These positively charged dust particles are attracted toward the discharge electrodes, but since a strong electric wind is being discharged from the discharge electrodes, these positively charged dust particles are mostly not absorbed by the discharge electrodes, and almost all are re-charged to negative charges and move back to the dust-collecting electrodes, where these negatively charged dust particles are again re-charged to positive by the positive ions generated by the back ionization. In this manner, these dust particles move back and forth between the respective dust-collecting and discharge electrodes, eventually going out from the stack without being collected. PA1 2. The electric field generated between the discharge electrodes and dust-collecting electrodes is non-uniform throughout the E.P. from the inlet to the outlet, particularly in the vicinity of the discharge electrodes, where, strong electric winds are generated due to corona discharges, thereby producing eddy current winds in the dust-collecting space. As a result, the gas flow containing dust particles produces turbulent flow, greatly reducing the dust-collecting efficiency. Therefore, to enhance the dust-collecting efficiency, it is necessary to decrease the gas flow velocity and also to make the flow passage longer. As a result, it has heretofore been unavoidable that the E.P. become large in size. PA1 3. Since the prior art E.P. must be large in size for the reason mentioned above, a larger space is necessary for the installation thereof, and the costs of such prior art E.P. manufacture and installation are unavoidably expensive. PA1 4. Since dust particles are collected in electric fields, the layer of accumulated dust becomes non-uniform in thickness, and the undulating surfaces of the dust layer causes spark discharges to occur frequently. PA1 5. Since the electric field is non-uniform, unnecessarily excessive corona discharges take place, consuming a substantial amount of unnecessary electric power. PA1 6. Upon hammering the discharge electrodes, they are subjected to vigorous mechanical vibrations, therefore, the material fatigue due to the mechanical vibrations causes the discharge electrodes to break. PA1 7. The fine dust particles released by rapping of the dust-collecting electrodes are liable to be reentrained in the gas flow due to the electric wind.
An object of the present invention is to provide a novel E.P. device, which is free from the above-described disadvantages of the prior-art E.P. and moreover is more advantageous in various other respects.