Modified on-line monitoring of total gaseous mercury in flue gases using Semtech Hg 2000 analyzer

The Semtech Hg 2000 analyzer continuously monitors the Hg0 content in flue gas. An on-line measurement method of total gaseous mercury in flue gas developed in our laboratory is described, which uses the absorption cell of the Semtech Hg Analyzer connected to a converter that is located in a furnace heated up to 650 degrees C. The converter can be heated up to 800 degrees C by both the furnace and an extra heating of a Ni-Cr alloy heating wire. Both the absorption cell and the converter are made of quartz. All gaseous Hg2+ species in flue gas are thermally reduced to Hg0 by the converter and detected by the Semtech Hg 2000 analyzer. The thermal reduction efficiencies of different conversion materials, which were filled in the converter, such as quartz chips, granular MgO, Ni and CoO powder, were tested using different flue gas conditions. Studies have shown that HCI is the major factor to inhibit the thermal reduction of Hg2+ to Hg0, and in the converter and the absorption cell Hg0 will react readily with HCl to form HgCl2. Both MgO and Ni could be used in the converter to absorb HCl in the flue gas, but Ni has better absorption efficiency. By using an original Semtech and a modified one, both Hg0 and total gaseous Hg contents in flue gas could be monitored simultaneously and continuously.