Dynamic measurement of mercury adsorption and oxidation on activated carbon in simulated cement kiln flue gas

Mercury emissions from cement plants are being regulated by environmental agencies in most countries. Both dynamic mercury emissions in cement kiln systems and removal of mercury by sorbent injection require continuous mercury emission monitoring. Dry converters for total mercury measurements are still under development and are investigated in this work.

A commercial red brass converter was tested at 180°C and it was found that the red brass chips work in nitrogen atmosphere only, but do not work properly under simulated cement kiln flue gas conditions. Test of the red brass converter using only elemental mercury shows that when HCl is present with either SO2 or NOx the mercury measurement after the converter is unstable and lower than the elemental mercury inlet level.

The conclusion is that red brass chips cannot fully reduce oxidized mercury to elemental mercury when simulated cement kiln gas is applied. A sodium sulfite-based converter material was prepared by dry impregnation of sodium sulfite and calcium sulfate powders on zeolite pellets using water glass as binder.

The sulfite converter works well at 500°C with less than 10ppmv HCl in the simulated cement kiln flue gas. The 95% response time of the sulfite converter is short and typically within 2min. Dynamic mercury adsorption and oxidation tests on commercial activated carbons Darco Hg and HOK standard were performed at 150°C using simulated cement kiln gas and a fixed bed reactor system.

It is shown that the converter and analyzer system is capable of following the transient mercury outlet concentration in a satisfactory way. Suggestions for practical applications of the sulfite converter in both lab and cement plants are presented.