To comply with impending regulations on Hg emissions, coal-burning utilities need to evaluate the performance of various Hg control technologies, particularly SCR/ESP/FGD combinations and activated carbon injection (ACI). Unfortunately, the performance in field testing varies significantly with coal quality, and with the configuration and operation of units in the gas cleaning system. A multitude of factors have already been shown to affect Hg emissions, including coal-Cl, flyash LOI, the type of flyash collection system, whether an SCR or FGD is present, SO3 levels, and the ACI rate, sorbent type, and injection location.
NEA’s MercuRator™ is based on detailed reaction mechanisms for Hg oxidation and sorption in flue gas, with supporting mechanisms for Hg oxidation along SCR catalysts, halogen (Cl, Br) chemistry, and SO3 production and condensation. It predicts complete speciation from the furnace exit into the stack across every unit in a cleaning system. These results have already been validated with the reported speciation from over 200 field tests in commercial power plants. These capabilities position plant operators to (1) Optimize plant operating conditions and economics against Hg release goals; (2) Anticipate Hg emissions rates on the basis of coal properties and plant characteristics; (3) Manage Hg stack emissions in a reliable and cost-effective manner; and (4) Expedite the design of Hg control technologies by optimizing sorbent characteristics, ACI rate, halogenation agent injection conditions, and the operating conditions along a cleaning system.
Attempts to correlate Hg emissions with the primary operating factors in engineering regression models cannot predict the performance within useful quantitative tolerances, so companies currently face considerable uncertainties in their compliance planning activities for Hg control. Since 1998, NEA has been developing and validating reaction mechanisms to describe Hg transformations throughout coal-fired gas cleaning systems. Unlike simple engineering regression models which account only for statistical correlations of plant data, NEA’s reaction mechanisms use the distinctive fuel properties and operating conditions at each particular gas cleaning system within a company’s fleet of power stations. This unique attribute of NEA’s mechanistic approach accounts for the essential chemistry and transport phenomena that actually occur.
NEA’s reaction mechanisms have been consolidated into a user-friendly computer package called MercuRator™ . This package contains distinct mechanisms for in-flight Hg oxidation and sorption with any level of Cl and Br species; Hg oxidation along SCRs; Hg oxidation and sorption across fabric filters and ESPs; Hg removal with ACI; and Hg retention in wet, Ca-based FGD scrubbers. The configuration of units and operating conditions in the subject gas cleaning system determine the calculation sequence and operating conditions in NEA’s simulations.
We first calibrate the simulations with baseline Hg speciation data from the subject gas cleaning system, to circumvent gaps in the input specifications and to identify where Hg is oxidized and collected under current operating conditions. Then the simulations are expanded for injection of chlorine and bromine sources, such as CaBr2 and CaCl2; addition of SCRs and wet FGDs; and application of ACI with and without fabric filters. In each case study, the complete Hg speciation (Hg0, Hg2+, and Hg-Particulate) is predicted at the outlet of each control unit along the gas cleaning system, as the basis to accurately predict Hg emissions rates (lb Hg/TBtu) and stack concentrations.
Simulations based on MercuRator™ may be performed by NEA on a consulting basis or the package may be installed at a client’s company for in-house case studies. In either format, NEA is responsible for screening the input specifications for the subject gas cleaning system(s); calibrating the predictions for baseline operating conditions with Hg speciation data; and surveying target ranges for fuel quality and Hg control options. Contact NEA for more technical information and to arrange a price quotation.
The best summary overview is in the following book:
S. Niksa and B. Krishnakumar, “Predicting Hg emissions rates with device-level models and reaction mechanisms,” Ch. 27 in Mercury Emissions Control for Coal-Derived Gas Streams, Eds. E. Granite, Pennline, C. L. Senior, Wiley, 2012.
References on Hg oxidation and capture on carbon solids:
B. Krishnakumar and S. Niksa, “Predicting the impact of SO3 on mercury removal by carbon sorbents,” Proc. Int. Combust. Symp, 33, Combust. Institute, Pittsburgh, PA (2010).
B. Krishnakumar and S. Niksa, “Predicting SO3 levels along utility gas cleaning systems,” EPRI-DOE-EPA-A&WMA Combined Utility Air Pollution Control Symposium: The MEGA Symp., 2010, Baltimore, MD, Aug. 30 – Sep. 2.
B. Krishnakumar and S. Niksa, “Predicting Hg removals with ACI in utility gas cleaning systems,” EPRI-DOE-EPA-A&WMA Combined Utility Air Pollution Control Symposium: The MEGA Symp., 2010, Baltimore, MD, Aug. 30 – Sep. 2.
S. Niksa, B. Padak, B. Krishnakumar, and C. V. Naik, “Process chemistry of Br addition to utility flue gas for Hg emissions control,” Energy Fuels, 24(2):1020-29 (2010).
C. V. Naik, B. Krishnakumar, and S. Niksa, “Predicting Hg emissions from utility gas cleaning systems,” Fuel, 89:859-67 (2010).
S. Niksa and Y. Hou, “Identifying the best options for Hg control with MercuRator™: Low-rank fuels, halogenation agents, and sorbent injection,” Paper No. 58, EPRI-DOE-EPA-A&WMA Combined Utility Air Pollution Control Symposium: The MEGA Symp., 2008, Baltimore, MD, Aug. 25-28, EPRI.
S. Niksa and N. Fujiwara, “Estimating Hg emissions from coal-fired power stations in China,” Fuel, 88(1):214-17 (2008).
S. Niksa, C. V. Naik, M. S. Berry, and L. Monroe, “Enhanced Hg oxidation with Br addition at Plant Miller,” Fuel Process. Technol, 90:1372-77 (2009).
B. Krishnakumar, C. V. Naik, and S. Niksa, “Predicting Mercury Emissions Rates From Utility Gas Cleaning Systems with SCR/ESP/Wet FGD Combinations or Activated Carbon Injection,” EPRI-DOE-EPA-A&WMA Combined Utility Air Pollution Control Symposium: The MEGA Symp., Paper No. 91, 2006, Baltimore, MD, Aug. 28- 31, EPRI.
S. Niksa and N. Fujiwara, “Predicting extents of mercury oxidation in coal-derived flue gas,” J. AWMA, 55: 930-39 (2005).
S. Niksa and N. Fujiwara, “Predicting Complete Hg Speciation Along Coal-Fired Utility Exhaust Systems,” EPRI-DOE-EPA-A&WMA Combined Utility Air Pollution Control Symposium: The MEGA Symp., Paper No. 45, 2004, Washington, DC, Aug. 29- Sep. 1, EPRI.
S. Niksa and N. Fujiwara, “Predicting Mercury Speciation in Coal-Derived Flue Gases,” EPRI-DOE-EPA-A&WMA Combined Utility Air Pollution Control Symposium: The MEGA Symp. 2003, EPRI.
N. Fujiwara, Y. Fujita, K. Tomura, H. Moritomi, T. Tuji, and S. Takasu, S. Niksa, “Mercury transformations in the exhausts from laboratory coal flames,” Fuel, 81(16):2045-52 (2002).
S. Niksa, N. Fujiwara, Y. Fujita, K. Tomura, H. Moritomi, T. Tuji, and S. Takasu, “A mechanism for Hg oxidation in coal-derived exhausts,” J. AWMA, 52(8):894-901 (2002).
S. Niksa, J. J. Helble, and N. Fujiwara, “Interpreting Laboratory Test Data on Homogeneous Mercury Oxidation in Coal-Derived Exhausts,” Proc. U. S. EPA-DOE-EPRI combined Power Plant Air Pollutant Control Symp.: The Mega Symp. And AWMA Specialty Conf. on Mercury Emissions: Fate, Effects, and Control, Chicago, IL, Aug. 21-23, 2001.
S. Niksa, J. J. Helble, and N. Fujiwara, “Kinetic Modeling of Homogeneous Mercury Oxidation: the importance of NO and H2O in predicting oxidation in coal-derived systems,” Environ. Sci. Technol., 35, 3701-3706 (2001).
References on Hg oxidation along SCRs:
S. Niksa, B. Krishnakumar, F. Ghoreishi, and C. Tyree, “Analytical management of SCR catalyst lifetimes and multipollutant performance,” EPRI-DOE-EPA-A&WMA Combined Utility Air Pollution Control Symposium: The MEGA Symp., 2012, Baltimore, MD, Aug. 20 – 23.
B. Krishnakumar, S. Niksa, and A. Freeman Sibley, “Predicting the multipollutant performance of full-scale SCR systems with bromine addition,” Int. Conf. on Air Quality VIII, UND EERC, Arlington, VA, Oct. 2011.
S. Niksa and A. Freeman Sibley, “Relating catalyst properties to the multipollutant performance of full-scale SCR systems,” EPRI-DOE-EPA-A&WMA Combined Utility Air Pollution Control Symposium: The MEGA Symp., 2010, Baltimore, MD, Aug. 30 – Sep. 2.
S. Niksa and A. Freeman Sibley, “Predicting the multipollutant performance of utility SCR systems,” Ind. Eng. Chem. Res., 49, 6332-41 (2010).
S. Niksa, D. P. Bour, T. A. Burnett, and N. B. Handagama, “Use predictive techniques to guide your mercury compliance strategy,” POWER, 151(8):60-66 (2007).
S. Niksa and N. Fujiwara, “A predictive mechanism for mercury oxidation on SCR catalysts under coal-derived flue gas,” J. AWMA, 56: 1866-75 (2005).
References on Hg chemistry in FGDs:
B. Krishnakumar and S. Niksa, “Interpreting the re-emission of elemental mercury during wet FGD scrubbing,” Int. Conf. on Air Quality VIII, UND EERC, Arlington, VA, Oct. 2011.
S. Niksa and N. Fujiwara, “The Impact of Wet FGD Scrubbing On Hg Emissions From Coal-Fired Power Stations,” J. AWMA, 55:970-77 (2005).