SO₂ (Sulfur Dioxide)

In utility boilers, industrial boilers, cement kilns and other fuel combustors, sulfur in fuel is converted into sulfur oxides (SO₂, SO₃) during combustion. Typically, over 98% of sulfur oxides in the boiler flue gas is SO₂, with the remainder being SO₃. SO₂ and SO₃ contribute to acid rain but there are differences in how these compounds are regulated and treated.

The SOLVAir Approach

For smaller boilers in the utility sector and for the vast majority of industrial boilers, it is too expensive to treat SO₂ with wet scrubbers which typically use lime. For these boilers Dry Sorbent Injection is often the most economical choice. There are two primary sorbents used in this application, SOLVAir Select 200 trona and SOLVAir Select 300 sodium bicarbonate. These compounds are injected dry into the duct through a series of injection lances that disperse the material throughout the duct.

The trona Select 200 product has been milled to a size that represents a good compromise between reactivity in the duct which depends on small particles and ease of handling which is helped by larger particles. Select 200 can be milled for increased performance but it is not required. The sodium bicarbonate Select 300 is more reactive, treats to higher removals but requires milling with either a pin mill or for optimum performance, an air classifying hammer mill.

Which product is right for you? We recommend trona for baghouse applications where removal of up to 70% SO₂ is required and ESP applications for removal up to 50%. Sodium bicarbonate can remove over 90% SO₂ in baghouse applications and 70% in ESP applications.

Regulatory Environment

After a brief vacation in 2008, CAIR is back. On March 10, 2005, the EPA issued the Clean Air Interstate Rule (CAIR), which permanently caps emissions of SO₂ and NO_x in 28 eastern states and the District of Columbia. When fully implemented, CAIR will reduce SO₂ emission levels in these states by over 70% below 2003 levels, and NO_x emissions by over 60% below 2003 levels. In 2010, CAIR will reduce SO₂ emissions by 5.4 million tons, or 57%, from 2003 levels in these states.

Future Trends

It is expected that similar SO₂ emissions reduction regulations will be enacted for the remaining western states and emission levels will continue to become more restrictive.

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SO₃  |  HCl  |  Hg  |  Particulates