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With impending regulation of mercury from coal-fired power plants, it is important to concentrate efforts on the most mature retrofit control technologies. Injection of powdered activated carbon (PAC) has been deemed the most mature technology, but has until recently only been demonstrated in bench- and pilot-scale experiments. This paper presents some of the results from a field evaluation program of sorbent injection upstream of existing particulate control devices (PCDs). An important component of the field demonstration program is to characterize the fly ash that results from injection of PAC upstream of a baghouse or electrostatic precipitator (ESP). Leaching analyses were performed on fly ash collected during two different field demonstrations; one fly ash was derived from bituminous coal and the other from a subbituminous coal. Several widely accepted leaching methods were used in order to assess the stability of the ash by-product in landfill situations; other ash characterization tests were also used in the study. Little or no detectable Hg was leached as a result of the various leaching protocols. The subbituminous ash conformed to the ASTM C-618 standard for Class C fly ash, but did not pass the Foam Index Test that is also required for sale of this ash for use in concrete formulation.

One of the challenges facing both regulators and the regulated community in dealing with air toxic emissions and their control, is the need to accurately measure and characterize these emissions. The current technology for measuring metallic components in emission streams requires manual sample extraction, recovery and preservation of the sample, and finally analysis of the sample using laboratory instrumentation. While these techniques are capable of analyzing trace concentrations of metals with adequate accuracy and precision, they all have numerous drawbacks due to their complexity and the fact that they do not provide real-time data. This paper describes two programs that ADA Technologies has undertaken to develop measurement technology for toxic metals in combustion flue gas. These research programs are directed at overcoming limitations of the current state-of-the-art measurement systems in order to meet the needs for accurate and reliable monitoring of toxic metal emissions from stationary sources. Both programs focus on the development of instrumentation for the detection and quantization of trace levels of air toxic metals in combustion gas environments. The instruments are being designed to function as continuous, real-time, on-line analyzers that can serve as parts of a feedback process to control air toxic metals emissions.

As part of a larger investigation on freeze-thaw durability of masonry segmental retaining wall (SRW) units, specimens of various geometries were extensively evaluated for their resonant frequency prior to freeze-thaw exposure. These pretest trials were conducted to assess the applicability of the impact resonance method on these specimens, to identify factors affecting test result interpretation, and to obtain initial values for future comparison with values after freeze-thaw cycling. The importance of correctly identifying resonant frequencies corresponding to different modes of vibration of the specimen is highlighted, and methods to achieve this in the laboratory are discussed. The effects of specimen moisture content variations, temperature, and sampling parameters on resonant frequency are also presented.