## 2 Materials and Method  
The experiments were conducted using a low-power boiler 1 that burned wood with a thermal power of 20 kW (Figure 1). The boiler has support 2 and the wood supply door 3. The boiler smoke outlet had an outer diameter of 125 mm. A connection tube (stainless steel tube) 4 (1.45 m long) between chimney 6 (stainless steel tube, PRESP) and boiler 3 has an access area 5 for measuring the smoke and gases after the boiler. The chimney has a height of 4.5 m, an inner diameter of 125 mm, and an outer diameter of 129 mm. Inside the chimney is a thin wire (discharge electrode, with a constant cross-section) 7 with a diameter of 0.75 mm, stretched on the central axis of the chimney through an electrical medium-voltage insulator 11 in the upper part of the chimney and an electrical medium-voltage insulator 13 in the lower part. The discharge electrode 7 is stretched, and there is a weight at the bottom. A metal conical cover is placed at the upper end of the chimney to prevent water from entering the chimney during rain. The chimney is supported by the support with legs 8, on which is an electromagnet 9 used for shaking, a collection device 10, a medium-voltage source 14 with conductor 15 supplying the discharge electrode 7 (negative polarity of the medium-voltage source), and conductor 16 (positive polarity of the medium-voltage source; it is also connected to the ground) that connects to the chimney 6 (the collection electrode). Chimney 6 is connected by two bridges, and metallic support 8 is connected by one bridge to an earth socket consisting of four electrodes inserted into the ground. The electric resistance is 3.5 \(\Omega\) (must be less than 4 \(\Omega\); measured with 8 PK-ST1520, Pro'sKit (Hsinchu, Taiwan)--device for measuring the earth socket with a resolution of 0.1 \(\Omega\)). PRESP can work in combination using two electrodes (one discharge electrode and another collection electrode, by applying a DC medium-voltage): a plasma reactor, with the possibility of reducing chemical compounds (CO, NOx), and an electrostatic precipitator to reduce the concentration of dust (PM) at the output of the chimney. During the operation of the PRESP, dirt is deposited on the medium-voltage electrical insulators. The electrical properties of medium-voltage electrical insulators are influenced by dust and gases resulting from combustion. To analyse the PRESP, it is compared with other CESP. Some characteristics of the domestic CESP connected to low-power boilers are as follows: radius of the collection tube r = 8 cm; active length of the precipitator L = 0.5 m; number of collection tubes n = 6; lateral surface for a tube S\({}_{\text{I}}\) = 0.19 m\({}^{2}\); total lateral surface: S\({}_{\text{It}}\) = 1.13 m\({}^{2}\); diameter of the discharge electrode with constant cross-section \(\Phi\)c = 1 mm; switching voltage source with medium voltage up to 30 kV, DC; and can be connected to a boiler with a maximum power of 50 kW [23]. The main features of the PRESP (Figure 1) connected to a 20 kW boiler are as follows:  
- Radius of the collection stainless steel tube: r = 62.5 mm (diameter D = 125 mm);  
- Active length of the precipitator: h = 4.5 m;  
- The number of collection tubes: n = 1;  
- Discharge electrode diameter (with a constant cross-section): \(\Phi\)c = 0.75 mm;  
- The maximum DC medium-voltage power supply (with short-circuit protection, max. 10 mA): U = 30 kV. The gas flow at the input of the domestic precipitator is Q = 40-65 m\({}^{3}\)/h (0.0111-0.018 m\({}^{3}\)/s) [5; 6; 9; 13; 23; 28]. The cross-section of the cylindrical precipitator is:  
\[S_{\text{t}}=\frac{\pi\cdot\text{D}^{2}}{4} \tag{1}\]  
Figure 1: Principle experimental scheme with a real PRESP connected to a low-power boiler. \(S_{t}\) = 0.012272 m\({}^{2}\). The average speed in the cross-section of the domestic precipitator can be computed as follows:  
\[v_{avg}=\frac{Q}{S_{t}} \tag{2}\]  
For Q = 40 m\({}^{3}\)/h, vavg = 0.904 m/s was obtained, and for Q = 65 m\({}^{3}\)/h, vavg = 1.469 m/s was obtained.