In order to meet future requirements for raw gas treatment, concerning dust- and aerosol removal efficiencies, an integrated combination consisting of a wet electrostatic precipitator and a FGD (Flu Gas Desulphurisation) spray tower was designed to test its suitability for these requirements. The implementation of the wet electrostatic precipitator in the FGD-spray tower concept promises high removal efficiencies for dust and for acid mists, which are of course much higher than the removal efficiencies which can be achieved by the FGD spray tower itself. The corresponding demands on the wet electrostatic precipitator were high, because it has to be designed as a part of the FGD spray tower, therefore it must not have any influence on its efficiency or its design. As a consequence the wet electrostatic precipitator has to be operated at far higher flow velocities (4 –5 m/s) as it is usually operated (< 3 m/s) as a stand-alone unit, nevertheless removal efficiencies for dust and acid mists of 90% and higher have to be reached. In this respect it is also of the highest importance, that there is no negative impact on the plant availability, which could be caused by breaking of spraying electrodes by the reason of too high mechanical stress (oscillations) due to too high flow velocities. During 16 month of pilot operation the aspired removal efficiencies and the reliability concerning plant availability or absence of fouling was proven. Other main targets of this investigation were to figure out the removal efficiency for each particle class and its dependence on gas flow velocity and concentration. Additionally, a central question was, if clean gas emissions of ≤1 mg/Nm³ dry 6% O2 might be safely achieved. As the pilot plant is directly fed by raw gas from the boiler realistic testing conditions could be provided. The dust was taken from the last electrical field of the electrostatic precipitator of the power plant and was milled, classified and analysed, in order to define the input parameters for the wet ESP. Different dust concentrations were realised by the means of a pneumatic dust dosing system. Furthermore, acid mist could be dosed by the use of a sulphur burner which was equipped with an oxidation catalyst. This equipment allowed a wide operation range of raw gas flow, dust- and acid mists concentrations to be addressed during the tests.