Recent advances in mercury removal technology at the National Energy Technology Laboratory

Abstract

The in-house research effort on mercury studies at the National Energy Technology Laboratory is an integrated, multi-task approach, including experimentation at both the laboratory-scale and the pilot-scale, as well as a numerical modeling effort to aid in interpretation of pilot-scale results. In the laboratory-scale work, novel sorbents and techniques for the removal of mercury from flue gas are being investigated using a small packed-bed reactor. The reactor system is used to screen novel sorbents for their capability to remove mercury from gas streams. The capacities of these novel sorbents are determined as a function of gas composition and temperature and are compared to results with commercially available activated carbons. In the pilot-scale work, an existing pilot unit has been characterized with respect to the distribution and fate of hazardous air pollutants in flue gas, with an emphasis on mercury. The pilot unit is a 500-lb/h (227-kg/h) pulverized coal-fired (PCFC) combustion system that includes a furnace, air preheater, spray dryer, ductwork and a pulse-jet fabric filter. The investigations with this unit have entailed evaluation of various activated carbons and novel sorbents, as well as comparisons of various sampling techniques for the determination of total and speciated forms of mercury. The impact of various parameters (temperature, sorbent-to-mercury ratio, baghouse pressure drop) on the removal of mercury has been investigated. Additionally, a slipstream allows for the investigation of sorbent injection in a fly ash-free flue gas over a wide range of operating conditions, including residence time. A summary of the results for mercury measurement and control from the 500-lb/h (227-kg/h) PCFC combustion system will be presented, as well as the evaluation of methods for measurement of in-duct removals using the slipstream. Finally, a discussion of the numerical modeling effort will be given.