Prediction of Activated Carbon Injection Performance for Mercury Capture in a Full-Scale Coal-Fired Boiler

Abstract

Activated carbon injection (ACI) is an effective mercury control technology demonstrated in both short-term and long-term full-scale tests. The effectiveness of mercury capture by activated carbon depends on the mercury speciation, total mercury concentration, flue gas composition, method of capture, and activated carbon properties, such as pore size, type of carbon impregnation, and surface area, etc. It is also desired that an ACI system be designed to produce good mixing between the activated carbon and the flue gas. In recent years, General Electric Energy has conducted both short-term and long-term tests in large-scale coal-fired boilers for ACI mercury capture demonstration. The programs consisted of (1) combustion optimization to improve natural mercury capture by fly ash, (2) computational fluid dynamics (CFD) modeling of activated carbon injection to design ACI lances, (3) a short-term test to select the activated carbon type, and (4) a long-term test to evaluate the mercury capture performance. This paper presents the CFD modeling for an ACI demonstration in Sundance Station Unit 5. The CFD model developed describes the film mass transport, pore diffusion, and carbon surface adsorption and desorption phenomena for the prediction of the mercury capture rate. The model was applied to evaluate the lance design and to calculate the mercury capture rate. The test data were also presented for comparison with the model results.

Adsorption of Gaseous Mercury for Engineering Optimization: From Macrodynamics to Adsorption Kinetics and Thermodynamics

“…Adsorption, compared with catalytic conversion and liquid assimilation, is the most promising method for Hg 0 removal and recovery from a gaseous environment. − There are two main usages for the designed sorbents. One is activated carbon injection (ACI) technology, which has been widely studied and applied in the treatment of Hg 0 from coal-fired flue gas. , The injected activated carbon (AC) can be further separated by particulate control devices and become part of the fly ash . However, on one hand, the low mercury adsorption rate and capacity of AC would increase the operating costs, and on the other hand, the adsorbed mercury in AC would affect the quality of fly ash and cause the risk of mercury re-emission.…”

“…11,12 The injected activated carbon (AC) can be further separated by particulate control devices and become part of the fly ash. 13 However, on one hand, the low mercury adsorption rate and capacity of AC would increase the operating costs, and on the other hand, the adsorbed mercury in AC would affect the quality of fly ash and cause the risk of mercury re-emission. To deal with these, magnetic components can be introduced to achieve recyclability of spent sorbents.…”

Modeling and experimental studies of in-duct mercury capture by activated carbon injection in an entrained flow reactor

“…However, the models developed so far to predict sorbent injection for mercury capture are limited. Most existing models are based on the following fundamental theory to describe the process: three steps are assumed, and the steps include external film mass transfer, intraparticle diffusion and adsorption at activate sites [25][26][27][28][29][30][31][32]. Meserole et al [25] developed a theoretical model to predict mercury removal by sorbent injection.…”

“…Scala et al [28][29][30] combined the process of external mass transfer and intraparticle diffusion for predicting mercury capture in incinerator flue gas. Zhou et al [31] developed a CFD model to predict mercury capture rate and evaluate the lance design. The model described the external film mass transport, pore diffusion, surface adsorption and desorption process.…”

Radiative Forcing Associated with Particulate Carbon Emissions Resulting from the Use of Mercury Control Technology

“…Among the most mature technologies for controlling mercury emissions from CFPPs is the injection into the flue gas of powdered activated carbon (PAC) adsorbents that adsorb mercury while in suspension in the flue gas. Chemically treated PAC adsorbents have been shown to effectively reduce mercury emissions for most CFPP configurations and types of coal, both of which are important to overall reductions in mercury emissions. − A typical implementation of this control technology would entail the injection of PAC sorbent upstream of an electrostatic precipitator (ESP), a particulate matter (PM) control device widely use in CFPPs. However, the electrical resistivity of PAC (10 4 ohm-cm) is far below the accepted norms for optimal ESP removal efficiency (10 8 –10 12 ohm-cm , ).…”