Closed SDBD-driven two-stage electrostatic precipitator

Abstract

Recently, the so-called two-stage electrostatic precipitators (ESPs) have again become an object of interest due to their usefulness in efficient collection of PM2.5 particles (of size < 2.5 μm) from polluted air. A two-stage ESP consists of two sections: an air ionisation and particle charging section (called a charging section) and a collecting section for precipitating the charged particles. The ESP has to be equipped with a means for forcing the polluted air to pass through both sections. Various forms of the corona discharges (DC, AC, pulsed) have been used for the air ionisation and particle charging in the first section, while the particle collecting section has usually been electrically supplied with a DC voltage of an amplitude insufficient for the corona discharge onset in this section. In this paper, we propose and present the use of the so-called surface dielectric barrier discharge (SDBD) in the form of an electrohydrodynamic (EHD) actuator as an alternative discharge source in the two-phase fluid (air + particles) of the two-stage ESP, instead of the commonly used corona discharge. Although different in terms of the electrical arrangement, discharge characteristics and morphology, the SDBD can play a similar role as the corona discharge plays in the two-stage ESPs. First, in the two-phase fluid (air + particle) of two-stage ESP the SDBD would be capable of generating bipolar (positive and negative) ions in air, which in turn would charge bipolarly the particles suspended in it. The bipolarly charged particles would agglomerate into larger charged particles, the collection of which is more efficient when subjected to the electrostatic force in the collecting section. Second, the SBDB would induce a unidirectional EHD flow in the two-phase fluid. The EHD flow can either enhance the primary flow of the two-phase fluid or act as a sole flow actuator (rather in relatively small ESPs). The suitability of SDBD for the two-stage ESP systems have been tested in the experiment performed by us using a laboratory-scale closed-volume SDBD-driven two-stage ESP. The experiment comprised measurements of the SDBD discharge characteristics, PTV (Particle Tracking Velocimetry) indirect detecting the production of bipolarly charged particles by the SDBD and then monitoring their trajectories in the collecting section of the SDBD-driven ESP, and qualitative and quantitative studies of the particle removal (or collection) efficiency of the closed SDBD-driven ESP. The PTV monitoring of the particle trajectories was aimed at visualization of the collecting section operation. The experimental results showed that the lab-scale SDBD-driven ESP has proved successful in collecting the particles suspended in air in a closed volume. However, it turned out that the presented lab-scale SDBD-driven ESP was not optimally designed. Despite this, it exhibited the particle removal efficiency similar to that of the single needle-to-plate negative DC corona one-stage ESP, considered as the basic unit for forming larger ESPs. After optimizing the design of lab-scale SDBD-driven ESP unit, we intend to study its performance in flow system, i.e. for the removal of particles from a particle-polluted air stream.