Simultaneous removal of Hg/NO/SO2 by ozone generated from flue gas by using irradiation of 190 nm vacuum ultra violet (VUV).

Environmentally Friendly Techniques

• Simultaneous removal of Hg/NO/SO2 by ozone generated from flue gas by using irradiation of 190 nm vacuum ultra violet (VUV).

Background ＆ Objectives

In pulverized coal combustion, the volatility of mercury and its compounds are emitted during combustion. In general, emissions of mercury from coal combustion sources are approximately 20–50% elemental mercury (Hg0) and 50–80% divalent mercury (HgII), which may be predominantly HgCl2. HgII is water-soluble and may be removed from the flue gas by wet FGDs and dry deposition close to combustion sources, while Hg0 is diffused in atmosphere because Hg0 has a high vapor pressure and low water-solubility. To reduce mercury levels in the environment and human exposure, control techniques are desired. The main objective of this work is to investigate the influence of ozone injection on mercury removal efficiency to establish effective measures for mercury control. The 190 nm VUV was employed to generate ozone. It is a unique methodology to generate ozone without byproducts such as NOx and N2O, hence flue gases from coal combustors can use as a raw material of ozone. 　In current experiment, model gas mixtures (Hg0/O2/N2 system, Hg0/O2/NO/N2 system, and Hg0/O2/NO/SO2/N2 system) were used at room temperature. The model gas was oxidized by ozone before treatments by the wet scrubber. Elemental mercury was converted to HgO by reaction with ozone at room temperature, and 99% Hg0 removal was attained from the model gas by the wet scrubber. Simultaneously, removal of NO and SO2 was examined as a multipollutant control technology. A part of NO in the model gas was converted to NO2 by reaction with ozone, and about 50% NO removal was obtained. When diluted calcium hydroxide was used as the solvent of the wet scrubber, removal efficiency of Hg0, NO, and SO2 were significantly increased.

Hg removal is an important issue for coal users.	190nm VUV reactor for ozone generation.
Mercury analyzer for Hg0 and HgII	Hg0 removal by ozone injection at room temperature.