In-situ measurement and distribution of flue gas mercury for a utility PC boiler system

The in-situ instrumentation technique for measuring mercury and its speciation downstream a utility 100 MW pulverized coal (PC) fired boiler system was developed and conducted by the use of the Ontario hydro method (OHM) consistent with American standard test method together with the semi-continuous emissions monitoring (SCEM) system as well as a mobile laboratory for mercury monitoring. The mercury and its speciation concentrations including participate mercury at three locations of before air preheater, before electrostatic precipitator (ESP) and after ESP were measured using the OHM and SCEM methods under normal operation conditions of the boiler system as a result of firing a bituminous coal. The vapor-phase total mercury Hg (VT) concentration declined with the decrease of flue gas temperature because of mercury species transformation from oxidized mercury to particulate mercury as the flue gas moved downstream from the air preheater to the ESP and after the ESP. A good agreement for Hg⁰, Hg²⁺ and Hg (VT) was obtained between the two methods in the ash-free area. But in the dense particle-laden flue gas area, there appeared to be a big bias for mercury speciation owing to dust cake formed in the filter of OHM sampling probe. The particulate affinity to the flue gas mercury and the impacts of sampling condition to accuracy of measure were discussed.