FUEL CHEM^® SO₃ Mitigation Technology            (brochure)

The effects of sulfur trioxide (SO₃) formation are becoming increasingly problematic for power plants, particularly as the rate of deployment of Selective Catalytic Reduction (SCR) and flue gas desulfurization (FGD) systems (the latter known as “scrubbers”) accelerates in response to tightening environmental regulations. SO₃ can adversely affect a plant’s overall operating performance, impacting maintenance, efficiency and environmental status.

SO₃ is formed in the boiler by oxidation of sulfur dioxide (SO₂), which itself arises from the combustion of solid and liquid fuels containing sulfur. Additional SO₃ formation can also occur as SO₂ is oxidized across the SCR catalyst. The SO₃ can react with moisture in the flue gas to form sulfuric acid, which in turn will react with ammonia to form a sticky substance, ammonium bisulfate (ABS).

The amount of SO₃ generated, and its resulting impact, is plant specific, influenced by such variables as fuel characteristics, type of boiler and the oxidation level of a chosen SCR catalyst. In particular, as SCR-retrofitted power plants install scrubbers, operators will have the flexibility to utilize higher sulfur coals, which will only exacerbate SO₃ issues.

SO₃ and ABS formation can lead to numerous plant operating problems, including air pre-heater fouling and corrosion, SCR catalyst fouling and sulfuric acid aerosol emissions, the latter causing increased stack opacity and often offered to as “blue plume.” Scrubbers do not effectively remove SO₃ before exiting the plant as they are principally designed to capture SO₂.

Fuel Tech has developed an extremely effective, customized FUEL CHEM^® program to address these SO₃-related issues. Utilizing proprietary TIFI^™ Targeted In-Furnace Injection^™ technology, a magnesium hydroxide slurry is injected into the boiler in sufficient quantities to help control the deposition of sulfuric acid and ABS on the air pre-heater while otherwise limiting SO₃ formation across the SCR. In addition to SO₃-related benefits, a TIFI program provides a variety of other operating benefits, something that other SO₃ reduction technologies cannot offer.

The Company’s SO₃ mitigation technology is currently treating several large utility units with impressive results. For example, SO₃ reductions of 75% have been achieved. The impact of a TIFI program on reducing SO₃ and associated blue plume formation can be viewed in the "before and after" photos at the top of this web page.

Technical papers detailing the manner in which TIFI technology helps in the mitigation of SO₃ in coal- and oil-fired utility boilers are available in the Publication Library.

In addition to the direct benefits identified above, a TIFI program can also help counteract SO₃’s tendency to interfere with mercury (Hg) capture in those units burning higher sulfur coals and utilizing otherwise effective Hg capture technologies, such as activated carbon injection (ACI).

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