Modeling Mercury Removal by Sorbent Injection

Abstract

Sorbents for removing mercury from flue gases of coal-fired power plants are presently being evaluated due to potential regulation of mercury emissions under Title III of the 1990 Clean Air Act Amendments. Laboratory tests have been conducted to evaluate the adsorption characteristics of potential sorbents and the effects of flue gas constituents on these characteristics. This paper presents a theoretical model that combines the adsorption characteristics measured in the lab with mass transfer considerations to predict mercury removal by the duct injection process in actual flue gas streams. The model was used to determine the effect of various sorbent properties on mercury removal when injecting a powdered sorbent upstream of either an electrostatic precipitator (ESP) or fabric filter. Mercury removal is expected to differ between these configurations since the mass transfer conditions are different in an ESP and fabric filter. The model was used to determine when mercury removal is limited by mass transfer and when it is limited by sorbent capacity. This information defines conditions when removal can be improved by reducing particle size or increasing sorbent capacity. In both cases, removal can be increased by injecting more sorbent.

Modeling Sorbent Injection for Mercury Control in Baghouse Filters: I—Model Development and Sensitivity Analysis

“…Meserole et al 4 extended the model of Chen and co-workers 1,2 to account for the additional Hg removal that is encountered as a result of the extended contact time between the sorbent particle and Hg on the fabric filter. Mercury removal in the duct was assumed to be external mass transfer-limited and the model did not incorporate any terms to account for intraparticle diffusion.…”

Coal Cleaning Versus the Reduction of Mercury and other Trace Elements’ Emissions from Coal Combustion Processes

“…Therefore, studies into simpler methods to be used as major and supporting technologies of mercury emissions reduction are necessary. It has to be emphasised that according to the data provided by EMEP (European Monitoring and Evaluation Programme), the annual emission of mercury into the air from the territory of Poland reached ca 20 Mg [2], which accounted for approximately 10% of mercury emissions in Europe [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Currently, mercury emission from anthropogenic sources amounts to 14.6 Mg/a [5].…”

Assessing Sorbents for Mercury Control in Coal-Combustion Flue Gas

“…The results presented here often are compared to model predictions. The EPRI theoretical model 14 incorporates physical adsorption characteristics and mass transfer processes. The constants in the model are determined from fixed-bed breakthrough data measured in the laboratory.…”

“…Significant progress has been made in understanding how these processes work and in developing models and test equipment to evaluate these technologies. [11][12][13][14] Based on these developments, EPRI and its test team have developed a program to help utilities evaluate Hg emissions and control options for their power-producing units. The objective of the program is to measure flue gas Hg concentration and speciation and removal effectiveness of existing air pollution control equipment at selected power plants, and to assess potential options with corresponding feasibility and projected costs to further reduce stack Hg emissions.…”