Measurement and Control of Mercury Emissions

Measurement

Mercury monitor and spike source

With new regulations in place for the control of vapor-phase mercury emissions, the ability to provide accurate measurement of flue gas concentrations of this toxic metal is crucial. Southern Research has developed a unique sampling system to quantify the concentrations of both elemental and oxidized mercury. The Southern Research system uses a unique non-catalytic, dry-gas conditioning system with a four-place switching box to provide simultaneous measurement of speciated mercury concentrations at two locations in a semi-continuous fashion. Mercury concentrations are measured with a Tekran Model 2537A analyzer. Samples are withdrawn from flue gas streams with inertial separation probes designed to eliminate passage of the mercury-laden flue gas through filter dust cakes. A unique continuous and quantifiable spiking capability is built into each probe to allow the injection of elemental mercury spikes in the sampled flue gas just after the probe inlet, without diluting the sampled stream. This ensures that the spiked mercury sample “sees” the same pathway as the actual flue gas sample. This unique spike and recovery system provides validation of the sampling system and an effective method for obtaining quantified uncertainties for each mercury species concentration measurement taken.

Control

QSIS^TM probe and gas conditioning system

Southern Research has experience and capabilities in evaluating the performance of a variety of mercury control options. Mercury control technologies that Southern Research has evaluated include injection of activated carbon and non-carbon-based sorbents and reagents upstream of electrostatic precipitators and fabric filters, and oxidizing agents and mercury capture in wet and dry FGD scrubbers. Southern Research also has extensive experience in quantifying the oxidation of mercury in SCR systems. Southern Research recently completed a four-year, EPRI-sponsored study to provide a better understanding of mercury chemistry in coal-fired boilers. These data along with the data obtained from several U.S. Department of Energy projects have been utilized in various modeling efforts. These results will aid in the development of techniques to promote mercury oxidation upstream of FGD scrubbing systems.

Based on the extensive research mentioned above, Southern Research has elucidated the mechanisms governing mercury oxidation and removal from coal-fired flue gas, with and without SCRs. Southern Research has developed models describing these mechanisms that can be used to predict mercury speciation and capture in coal-fired power plants. In these efforts, Southern Research has worked with universities and other research organizations to develop the most effective resources to help utilities make their most important mercury-control decisions.