Investigations On Increasing SO₂ Removal Efficiency From Flue Gas By OH, NH₂ Radicals In Pulsed Discharge Plasma Process

Pulse corona discharge induced plasma process for SO2 removal from flue gas is a novel technology being researched widely in many countries. The mechanism about desulphurization by corona discharge plasma is as follows: in pulsed discharge electric field, there are energetic electrons, which collide with gas molecules to produce active species such as kinds of radicals, and then SO2 molecules are oxygenated by these active species to produce SO3, H2SO4 and so on. When additive such as ammonia exists, sulphate will be the main finial product collected by precipitator. Because of the importance of radicals, increasing the number of the radicals is very useful for improving the SO2 removal efficiency. The paper aims at increasing the number of radicals produced by activating water vapor and NH3 in order to improve the SO2 removal efficiency by pulsed corona discharge processes. The main achievements and results are as follows:1. In order to optimize the conditions for activating water vapor and generate more OH radicals, at atmosphere, without any kind of inert gases added, OH radical is measured by optical emission spectroscopy in air corona discharge with water vapor. The influence of several factors on OH radical's generation has been studied by spectroscopy. The investigations show that different discharge modes affect the number of OH radicals generated: in positive pulsed corona discharge are generated the most OH radicals, as compared with positive DC corona discharge and negative DC corona discharge; and in negative DC corona discharge that is inferior to that in positive DC corona discharge. As a result, the number of OH radicals increases with the intensity of electric field and the density of water vapor molecules. And OH radicals generated in the process of corona discharge are mainly distributed in the range of 5mm near discharge nozzle-electrodes.2. Researches of optimizing the structure of discharge-electrode have been conducted. In our experiments it is demonstrated that thinner diameter of discharge-nozzle-electrode is more helpful to generate radicals. When the distance of nozzle-nozzle (sn) and the distance of nozzle-plate (S) are in accord with the equation: sn=0.5S+5. it is perfect for discharge-nozzle-electrode to activate gas molecules: When sn is bigger, the number of OH radicals increases unconspicuously; when sn is below the value, the number of OH radicals decreases with sn. When water vapor or NH3 are added into the reactor, the discharge current decreases to some extent, and the discharge current decreases several tens microampere whenthe volume of water vapor and NH3 lower by 10% and 2% respectively than that of flue gas.3. Several influence factors on SO2 removal from flue gas by activating water vapor have been studied. The experiments demonstrate that when water vapor is activated (water vapor being injected into the discharge gap by discharge-electrode). SO2 removal efficiency is obviously higher than that when water vapor is not activated (water vapor being added from the gas entrance of the reactor). The SO2 removal efficiency is higher with less diameter of discharge-nozzle-electrodes. Compared with the SO2 removal efficiency with 2mm inner-diameter discharge-nozzle-electrodes, the SO2 removal efficiency is higher by 3% than that with the 1mm inner-diameter discharge-nozzle-electrodes. The SO2 removal efficiency increases with input power and decreases with density of power. To some extent, the SO2 removal efficiency increases with the density of water vapor molecules.4. The experiments of several influence factors on SO2 removal efficiency from flue gas by activating NH3 have been conducted. The results show that SO2 removal efficiency is higher when NH3 is activated (NH3 being injected from discharge-nozzle-electrodes) than that when NH3 is not activated (NH3 being added from the gas entrance of the reactor). SO2 removal efficiency increases with the input power and decreases with the density of power. Higher initial co...