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The Mitsubishi system which reduces SO₃ incorporates a gas to gas heat exchanger which is not new. But instead of providing gas reheat the heat is used in the condenser thereby increasing efficiency and recovering 2 MW in a 600 MW boiler as seen in hyperlink below.

Mitsubishi High Efficiency System
 

By placing the heat exchanger ahead of the precipitator and lowering the temperature below the acid dewpoint they cause SO₃ to condense on the flyash. In the case of a boiler with 10 ppm SO₃, there is a 90 percent reduction. Also there is very high particulate removal. The secret to corrosion prevention is maintenance of the correct flyash to SO₃ weight ratio as seen in hyperlink below.

MHI  High Efficiency System with correct flyash to SO₃ ratio
 

The cost after three years compares very favorably to either a WESP or alkali injection, as seen in hyperlink below.

Feasability study for 600 MW Boiler
 

Nine installations all have SO₃ stack concentrations of less than 1 ppm and particulate emissions as low as 0.002 gr/scf. Three of the units are more than 1,000 MW in size, as seen in hyperlink below.

MHI Experiences in Japan