PowerGen Past Research
CAER is focusing on the three areas of stationary emissions control. They are: arsenic poisoning of SCR catalysts, SO3 mitigation, and mercury mitigation through wet flue gas desulfurization. With the implementation of the 2005 Clean Air Interstate Rules (CAIR) and Clean Air Mercury Rules (CAMR)], SCR catalyst management (e.g. catalyst poisoning), wet stack blue plume (sulfuric gases) and mercury mitigation are urgent issues to utilities.
Arsenic Poisoning of SCR Catalysts
Arsenic, a heavy metal naturally occurring in coal, is a highly deleterious substance. This metal can be released to the flue gas through coal combustion, and poison the catalyst for selective catalytic reduction (SCR). The research at CAER focuses on the effectiveness of fixed-bed limestone implementation on arsenic reduction in coal combustion flue gas.
Sulfuric acid (SO3) is a precursor to acid aerosol/condensable emissions, and can cause plant operation problems like air-heater plugging and fouling, back-end corrosion, and plume opacity. Studies indicate that a bluish smoke can be observed if SO3 concentrations are over 2ppmv in the stack exhaust stream. These issues will be exacerbated with the widespread retrofitting of selective catalytic reduction (SCR) for NOx control on coal-fired plants, as SCR catalysts are known to further oxidize a portion of the flue gas.
Theoretically, SO3 is easily dissolved/absorbed into water. So whatever SO3 formed on the furnace and across the SCR bed should be captured in the wet flue gas desulfurization device (WFGD). However, in reality, it does not. In fact, only about 50% of the SO3 entering the scrubber is removed in the scrubber. The remaining SO3/ H2SO4 in the range of 10 to 20 ppmv in the flue gas stream emits from the stack, which is far above the visible plume concentration, especially when SCR is in-service. This study will develop a two-stage chemical-free technology coupled with WFGD for SO3 mitigation.
- Investigation of a Novel Approach to Control Blue Plume from the Wet Flue Gas Desulfurization (WFGD) Process - CAER Project Factsheet Summary
Mercury Re-emission from Wet Flue Gas Desulfurization (WFGD)
In addition to SO2 control, wet scrubbing could potentially provide a reliable and cost-effective gaseous phase mercury control. The most important factor influencing mercury control emissions by wet scrubbers is mercury speciation in the flue gas. Gaseous-phase mercury can appear as elemental mercury (Hg0) or as oxidized mercury (Hg2+). Hg0 is nearly insoluble in water, whereas Hg2+ is exceedingly soluble. Aqueous-based control technologies such as WFGD systems should be effective in controlling Hg2+ emissions. However, during work aimed at enhancing the mercury-removal performance of wet FGD systems, investigators discovered that under some circumstances, oxidized mercury initially captured in a wet FGD system can be re-emitted in elemental form. It will be worthwhile to conduct further detailed studies on a slip-stream WFGD apparatus under real coal-combustion conditions.
In this project mercury speciation and gas-phase mercury absorption through WFGD uses a portable slip-stream unit to pull flue gas from a utility boiler, and pours existing recirculating slurry into the testing device. We are investigating conditions such as spiked ash, gas and slurry compositions; and simulated FGD operation conditions such as L/G, and various chemical additives, as well as injection approaches. This project primarily focuses on elemental mercury remission across WFGD with/without SCR in existing conventional boiler systems. The impact of SCR on fly ash characterization is also being investigated.
- Investigation on Mercury Re-emission from WFGD - CAER Project Factsheet Summary
Contact: Kunlei Liu
After coal is mined, it is cleaned and prepared for burning. This removes impurities in order to boost the heat content of the coal and improve power plant efficiency. Removing impurities also reduces maintenance costs at the power plant and extends the plant's operating life. Another reason for coal preparation is to reduce potential air pollutants, especially sulfur dioxide.
The CAER has a long and respected research history in coal cleaning and preparation. Among the efforts that have been examined are:
- solving problems associated with coal slurry impoundments;
- liberating and removing mineral matter and related sulfur from coal prior to combustion;
- recovering, reducing moisture and thickening fine coal from impoundments for its safe disposal.