With regard to pollution control and electrical discharges in gases,the most popular techniques used to be electrostatic precipitation and ozone generation.Both of them have a history of over a century.In an electrical discharge,electrons,ions,and radicals can be generated.Over the past 20 years,streamer corona plasma techniques have been widely considered to be very suitable for large volume gas cleaning.We recently proposed a novel four stage plasma-assisted flue gas cleaning system for multi-pollutants emission control.It mainly consists of bi-polar dry plasma pre-oxidation and pre-charging,dry electrostatic precipitation(ESP),NH3 based flue gas desulfurization(FGD)and wet plasma oxidation and precipitation.The first stage consists of a bi-polar pre-oxidation reactor.The flue gas is divided into two parts,one is processed with positive streamer corona discharge,and another one is with negative corona.Two main functions of the stage is NO oxidation and bi-polar corona induced fine particle agglomeration.The so-called AC/DC energization technique is used for positive streamer corona discharge.Negative corona discharge is produced with a three-phase transformer rectifier.For typical Chinese coal-fired power plants with a dust concentration of up to 20-30g/m3 and under 120-140℃,achievable electric fields with the techniques are about 3kV/cm for positive and negative corona discharges.With regard to fine particle grade collection efficiency of the ESP,experiments have demonstrated that more than 98%collection efficiency can be achieved by integrating the bi-polar pre-oxidation.In order to achieve an high fine particle collection efficiency,the ESP is designed according to our proposed criteria of EaEpS>720(kV/cm)2(m2/m3/s),where S,Ea and Ep are specific collection area,average and peak electric fields,respectively.Our industrial applications with up to 300MW coal-fired generators showed that when the fields and the collection area match the criteria the ESP outlet dust concentration is usually less than 30mg/m3.The FGD could consist of two parts.A dry stage is usually placed in front of the FGD to concentrate(NH4)2SO4.Conventional FGD techniques could be used for such integration.The last stage is a wet AC/DC plasma reactor.Its two main functions are fine aerosol collection,NO2 scrubbing and aqueous by-products oxidation to convert S(Ⅳ)ions to S(Ⅵ)ions.The energy consumption for S(Ⅳ)to S(Ⅵ)conversion is around 20-25Wh/mol.With regard to costs of these systems,today a non-thermal plasma system can be utilized at a similar cost of the ESP,but with functions of achieving particle collection and inducing chemical reactions.