O’Brien & Gere’s DI - Duct Injection Technologies™ encompasses four primary duct injection technologies, where specially selected sorbents are “injected” into the duct of a flue gas stream: 

• Trona / Sulfur Dioxide and Mercury Control – Dry sorbents, such as trona (natural sodium carbonate/sodium bicarbonate) are injected into the flue gas upstream of the baghouse or electrostatic precipitator to remove moderate levels of SO₂ (generally 50% to 75% level of control). This technology is normally used by smaller, older plants that were not required to install SO₂ scrubbers. O'Brien & Gere has also demonstrated that this technology can remove significant levels of mercury.
• Trona or Dry Lime Hydrate / Sulfur Trioxide Control – Larger power plants with existing SO₂ scrubbers often find that SO₃ passes through the scrubber, causing a blue or brown plume from the stack. The SO₃ also reacts with water or other compounds to cause costly duct corrosion and fouling issues. With this technology, O'Brien & Gere injects relatively low quantities of trona or dry lime hydrate to reduce sulfur trioxide levels and eliminate visual plume and corrosion issues.
• Activated Carbon / Mercury Control – This low capital and low operating cost technology can remove up to 95% of the mercury currently emitted. Flue gas injection of activated carbon-based or other specially developed sorbents is the new technology for mercury removal for coal-fired boilers.
• Dry Lime Hydrate or Trona / Hydrogen Chloride Control – Coal-fired boilers subject to the Industrial/ Commercial/ Institutional Boiler MACT Standard are often required to reduce hydrogen chloride emissions. By injecting dry lime hydrate or trona, this technology removes very high levels of this acid gas.  
  

• Economizer Inlet (If Temp < 800F)
  • Trona
• Air Heater Inlet (500 - 700F)
  • Trona
• Air Heater Outlet (~300F)
  • Trona & Hydrated Lime
  • Brominated/Activated Carbon
• ESP Outlet/Scrubber Inlet
  • Trona & Hydrated Lime 

Process Flow Diagram