en.Wedoany.com Reported - The goal of flue gas treatment is not to move pollutants from stacks into wastewater, solid waste or secondary aerosols. Mature Flue Gas Desulfurization and Denitrification Technology must also address FGD wastewater, gypsum, ammonia slip, spent catalysts and by-product salts.
Wet FGD produces wastewater that may contain suspended solids, chloride, sulfate, heavy metals, fluoride and refractory substances. EPA’s 2024 final rule for steam electric power generating effluent guidelines established more stringent discharge standards for three wastewater streams generated at coal-fired power plants: FGD wastewater, bottom ash transport water and combustion residual leachate. This shows that FGD wastewater has become an important compliance issue for coal plants, not a side concern.
FGD gypsum is also critical. Gypsum quality is affected by fuel sulfur, desulfurization operation, fly ash contamination, chloride and impurities. If stable, it can be reused in building materials or cement set control. If impurities are high or market demand is weak, it becomes a storage burden. Semi-dry and dry FGD by-products also require clear disposal or utilization pathways.
The main secondary issue in denitrification is ammonia slip. Excess ammonia injection, poor flow distribution or declining catalyst activity can increase ammonia slip. It wastes reagent and may react with SO₃ to form ammonium bisulfate, causing air preheater fouling, duct deposits and fine particle formation. Spent SCR catalysts containing vanadium, tungsten and titanium require regeneration or proper disposal.
Flue gas projects should calculate wastewater, solid waste and secondary gas emissions from the design stage. Wet FGD must define wastewater treatment and gypsum use. SCR must include ammonia slip control, ammonia injection optimization and catalyst life management. Semi-dry FGD must calculate by-product ash volume and disposal routes. Reliable flue gas treatment is not only outlet compliance; it is avoiding new environmental burdens across the whole system.
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