Utilization of Water Utility Lime Sludge for Flue Gas Desulfurization in Coal-Fired Power Plants: Part II. Lime Sludge Characterization and Mercury Re-emission

Abstract

The feasibility of utilizing lime sludge in the flue gas desulfurization process of coal-fired power plants was evaluated through laboratory-scale studies. Eight lime sludge samples, collected from various water treatment plants, and a high-purity limestone sample were extensively characterized and tested for their ability to capture SO from a simulated flue gas, while investigating the mercury reemission profiles during the scrubbing process. The reactivity of lime sludge samples for acid neutralization was significantly higher than the reactivity of the tested limestone sample. At doses less than that of the limestone sample, the lime sludge materials reduced the SO concentration from 2,000 to <0.5 ppm. The residual lime, higher surface area, and more accessible pores in lime sludge samples were the major factors contributing to their higher reactivity. Concentrations of several elements including B, Mg, Mn, Fe, Cu, Zn, As, Sr, and Ba in some of the tested lime sludge samples were considerably higher than those elements in the limestone. However, no significant leaching of these elements into the scrubber solutions was observed. To investigate mercury reemission during the scrubbing process, ionic mercury was introduced into the simulated slurry and mercury reemission was monitored continuously. Results showed that compared with the limestone sample, the lime sludge samples tested had lower or similar cumulative mercury reemissions. However, different lime sludge samples showed different emission profiles. No conclusive correlation between the composition or trace element content of lime sludge samples and their mercury reemission could be identified. This result was likely due to the oxidative condition of the scrubbing process, which prohibited the reducing species from transforming the ionic mercury into elemental mercury.

Evaluation of Modified Activated Carbons for Mercury Reemission Control During Neutralization of a Simulated Wastewater from the Direct Contact Cooler of a Pressurized Oxy-Combustion Process

“…A high-purity limestone powder (described elsewhere 21 ) was obtained from a local coal-fired power plant and used as the base source for the neutralization. In some preliminary experiments, CaCO 3 was used instead of the limestone powder.…”

Utilization of Water Utility Lime Sludge for Flue Gas Desulfurization in Coal-Fired Power Plants: Part III. Testing at a Higher Scale and Assessment of Selected Potential Operational Issues

“…Synthetic gypsum samples (identified as "SL4 gypsum" and "SL5 gypsum") were prepared from lime sludge samples through reaction with H 2 SO 4 , according to a method described in our previous work. 3 A high-purity limestone sample used in the FGD process and a gypsum sample (FGD by-product) were collected from a local power plant and identified as "limestone" and "gypsum" in this work. More details on these samples, including their characterization data, can be found in Part II of this work.…”

“…More details on these samples, including their characterization data, can be found in Part II of this work. 3 2.2. Laboratory Testing with a Simulated Flue Gas.…”

“…2 In Part II of this work, the feasibility of lime sludge utilization in the flue gas desulfurization (FGD) process was evaluated by conducting laboratory-scale tests with a simulated flue gas at a flow rate of 0.5 L/min (LPM). 3 Eight lime sludge samples and a baseline limestone sample were evaluated for their performance capability to remove SO 2 from a simulated flue gas, while monitoring Hg re-emission from the scrubber. These results confirmed the high performance of different tested lime sludge samples for SO 2 capture.…”

“…Furthermore, replacing limestone with lime sludge did not increase Hg reemission or cause additional issues for leaching undesirable elements into the scrubber slurry. 3 Testing at higher scales is needed to further demonstrate the performance of lime sludge for FGD application. Furthermore, potential operational issues should be addressed before lime sludge utilization is considered for large-scale implementation.…”