Obstacles in the Development of Mercury Continuous Emissions MonitorsProceedings of the 20 20th th Annual International Pittsburgh Coal Conference

摘要

There has been great progress in the development of mercury continuous emissions monitors(CEMs) over the past thirty years.Pending regulation of coal-fired elec electric utiliti tric utilities for mercuryes emissions is a driver for continued progress in this area.Most of the continuous emissions monitorsfor mercury in flue gas or fuel gas (syngas) are based upon ultraviolet (UV) spectroscopy.Elementalmercury can absorb and emit 253.7-nm radiation,and this is the underlying mechanism for atomicabsorption spectrometry (AAS),atomic fluorescence spectrometry (AFS),and inductively coupledplasma atomic emission spectrometry (ICP-AES)-based CEMs.A major obstacle in the measurement of mercury is the occurrence of undesire undesiredphotochemical reactions.These deleterious reactions are the quenching and sensitized oxidationsof mercury.Use of the Zeeman effect in order to account for absorption of 253.7- nm radiation bysulfur dioxide present in flue gas will not correct for the sensitized oxidation of mercury.Gold trapsand sensors are often used in an attempt to avoid quenching and sensitized oxidation of mercury,butare themselves subject to poisoning by flue gas or syngas constituents.The chemical reactions of mercury in solution,on surfaces surfaces,and in th ,the gas-phase pose ae significant challenge in the measurement of mercury.Loss of mercury from dilute solutions can bea significant problem for CEMs.Loss or oxidation of gas phase mercury via adsorption or catalysison solid surfaces is another significant challenge in the measurement of tra trace levels of ce mercury.Contamination is a concern in the determination of trace levels of mercury.The inexpensive lightsource used in many spectrop spectrophotometers introduces a small uncertainty in the determination ofhotometers