Optimization of the dynamic response of electrostatic precipitator plates

Electrostatic precipitators are largely used to remove particles from exhaust gas flows in many kinds of industrial plants (and especially in power plants). Particles are made to precipitate on proper collecting plates, forming growing layers that are periodically removed by rapping. Conventional rapping is accomplished by single-shot hammer blows. This method is likely to conduct to large out-of-plane displacements of the plates (related to low frequency flexural modes) that seem to be counterproductive because they can cause excessive breaking up of the detached layer and consequently re-entrainment. This work presents new rapping techniques aiming to control (and reduce) the excitation of the low-frequency flexural modes of the plates. A twofold approach was considered, based on both the use of electromagnetic shakers (properly controlled) and on a patented multi-impact hammer. Interesting performances,at a very low cost, were attained by the multi-impact hammer which proved to be able to concentrate the excitation in the middle-high frequency band. Furthermore it allowed a considerable reduction of the peak force thus reducing the risk of `dynamic buckling' (often the cause of noticeable out-of-plane displacements). Extremely remarkable results were obtained with the use of an electromagnetic shaker applying sweep and multi-harmonic excitation to the plates (several force histories were tested).