Presentation: A Better Alternative To SO₃ For Conditioning Electrostatic Precipitators

By Yougen Kong and Mike Wood, Solvay Chemicals Inc.

Many utilities use SO₃ to condition flue gas in order to improve the performance of the electrostatic precipitators (ESP). Per the recently proposed mercury (Hg) control regulations from EPA and state regulators, there will be tighter controls of mercury emissions from the stacks. SO₃ is known to inhibit mercury removal whether captured on fly ash or by using powdered activated carbon (PAC). Therefore, SO₃ should be removed in order to meet mercury regulations, but that may prove a challenge for those using SO3 to condition flue gases.

One solution to both problems is trona (Na₂CO₃.NaHCO₃.2H₂O). It can lower the resistivity of fly ash and aid in mercury capture by removing SO₃. It is well documented that increasing the sodium content in fly ash can lower its resistivity. Therefore, for the fly ash of high resistivity due to either low sulfur or sodium content of coal, adding trona will lower the resistivity of fly ash, and consequently improve the ESP performance. In addition, the added trona will remove SO₃ that would inhibit the mercury removal and cause visible blue plume. The trona addition system is simple and its capital cost is much lower than that of SO₃ production and injection system.

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