SO₃ (Sulfur Trioxide)

In utility and industrial boilers, cement kilns and other fuel combustors, all sulfur in fuel is converted into sulfur oxides (either SO₂ or SO₃), with approximately 1-2% being SO₃. SO₃ contributes to the formation of condensable or fine particle emissions, known as particulates (PM).

The vanadium-based catalysts in SCRs cause the conversion of an additional 1-3% SO₂ into SO₃. Depending on the sulfur content of coal and type of SCR catalyst, SO₃ concentration varies between 10-120 ppm. High concentrations of SO₃ increase the dew point of acid in the flue gas. This leads to corrosion in the duct and increased temperatures out of the air pre-heater to avoid condensation of acid, which in turn decreases air pre-heater efficiency. Furthermore, SO₃ can form a recognizable blue plume which does not disperse easily and can generate public concerns.

The SOLVAir Approach

When used as a dry sorbent injected into a flue gas duct or baghouse, SOLVAir Select 200 quickly reacts with acid gases, forming a waste product that will not damage equipment. Its high surface area and small particle size make it very effective in the reaction.

Select 200 removes SO₃ at higher rates than lime and can be used at higher temperatures. SO₃ removal rates have been shown to be over 90%.

Select 200 can be injected almost anywhere in the process, from the boiler to just in front of a particulate collection device, at temperatures ranging from 275°F to 1500°F. The right choice for injection location depends on many factors specific to the site and our SOLVAir team would be happy to discuss treatment goals and what options have shown the most success.

Regulatory Environment

SO₃ is not currently regulated under the Clean Air Act but may be regulated under local standards or under regulations dealing with particulate (condensable) matter. With plants building more SCR and wet FGD systems, a byproduct will be an increase in SO₃ emissions year-round. This in turn may mandate the need for SO₃ reduction systems.

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SO₂  |  SO₃  |  HCl  |  Hg  |  Particulates