Control of Diesel Gaseous and Particulate Emissions with a Tube-Type Wet Electrostatic Precipitator

Abstract

In this study, experiments were performed with a benchscale tube-type wet electrostatic precipitator (wESPs) to investigate its effectiveness for the removal of mass-and number-based diesel particulate matter (DPM), hydrocarbons (HCs), carbon monoxide (CO), and oxides of nitrogen (NO x ) from diesel exhaust emissions. The concentration of ozone (O 3 ) present in the exhaust that underwent a nonthermal plasma treatment process inside the wESP was also measured. A nonroad diesel generator operating at varying load conditions was used as a stationary diesel emission source. The DPM mass analysis was conducted by means of isokinetic sampling and the DPM mass concentration was determined by a gravimetric method. An electrical low-pressure impactor (ELPI) was used to quantify the DPM number concentration. The HC compounds, n-alkanes, and polycyclic aromatic hydrocarbons (PAHs) were collected on a moisture-free quartz filter together with a PUF/XAD/PUF cartridge and extracted in dichloromethane with sonication. Gas chromatography (GC)/ mass spectroscopy (MS) was used to determine HC concentrations in the extracted solution. A calibrated gas combustion analyzer (Testo 350) and an O 3 analyzer were used for quantifying the inlet and outlet concentrations of CO and NO x (nitric oxide [NO] ϩ nitrogen dioxide [NO 2 ]), and O 3 in the diesel exhaust stream. The wESP was capable of removing approximately 67-86% of mass-and number-based DPM at a 100% exhaust volumetric flow rate generated from 0-to 75-kW engine loads. At 75-kW engine load, increasing gas residence time from approximately 0.1 to 0.4 sec led to a significant increase of DPM removal efficiency from approximately 67 to more than 90%. The removal of n-alkanes, 16 PAHs, and CO in the wESP ranged from 31 to 57% and 5 to 38%, respectively. The use of the wESP did not significantly affect NO x concentration in diesel exhaust. The O 3 concentration in diesel exhaust was measured to be less than 1 ppm. The main mechanisms responsible for the removal of these pollutants from diesel exhaust are discussed.