Abstract: The overall effective volume of a horizontal gas flow electrostatic precipitator is divided into at least four electrostatic field units arranged in stages, there being at least upper and lower vertically aligned stages, the precipitator having a dust exit bunker which receives dust collected in each of the upper and lower stages. Below the collector electrodes of the upper stage are collection pockets which communicate with the dust exit bunker through downwardly extending dust passages located in the lower stage. These passages are internal passages within hollow collector electrodes of the lower stage. The electrostatic field units are, independently of one another, each connected to a respective separate controllable power supply means so that it is possible to generate, in each respective stage, a separate controllable high voltage.