Features. Conference Report: NOx, SO3 in the spotlight at NETLNETL's 2006 Environmental Controls Conference

Power, Feb 2007 by Mann, Alfred N, Makovsky, Leo E, Inc, Management Services, Sarkus, Thomas A, Laboratory, National Energy Technology

The second paper was presented by Brad Adams, Marc Cremer, and Andrew Chiodo of REI; Craig Giesmann and Ken Stuckmeyer of Ameren; and John Boyle of Fuel Tech. The deep staging technology described in this paper makes extensive use of CFD, has been demonstrated on a commercial scale, and could prove capable of reducing NOface= Subscript; xface=-Subscript; levels to 0.15 lb/mmBtu at a much lower cost than using SCR.

face= Bold; The ABCs of SOface= Subscript; 3face=-Subscript; face=-Bold;

Bill Ellison gave the keynote address of the second ECC 2006 session, on SOface= Subscript; 3face=-Subscript; . He reviewed the high points of the 1998 NETL conference on sulfur trioxide as a way of showing progress since then.

Surprisingly, SOface= Subscript; 3face=-Subscript; emissions from power plants rival those from chemical plants. During combustion, sulfur in fossil fuels is converted to SOface= Subscript; 2face=-Subscript; , most of which is removed by flue gas desulfurization (FGD) before it reaches the stack. While SOface= Subscript; 2face=-Subscript; continues to be targeted for further reductions, SOface= Subscript; 3face=-Subscript; also has become a target for additional control.

Minor amounts of SOface= Subscript; 3face=-Subscript; are created by oxidation of SOface= Subscript; 2face=-Subscript; not only in the boiler but also downstream in the air heater and over the catalyst in the SCR reactor. If the SOface= Subscript; 3face=-Subscript; escapes, it can produce visible plumes and corrosive aerosol mists of sulfuric acid (Hface= Subscript; 2face=-Subscript; SOface= Subscript; 4face=-Subscript; ). FGD units cannot remove SOface= Subscript; 3face=-Subscript; as readily as they can SOface= Subscript; 2face=-Subscript; . Plants burning medium- or high-sulfur coal that are equipped with wet FGD systems are particularly prone to experiencing stack opacity problems due to emissions of sulfuric acid. Making the situation even worse are the corrosion and fouling of heat exchangers that the acid fosters.

face= Bold; Fouling inside, opacity outface=-Bold;

As Lewis Benson of Carmeuse North America Group and Bill Ellison explained in their paper and presentation, serious air preheater fouling by sticky, ABS-coated flyash can be prevented by efficient pre-removal of SOface= Subscript; 3face=-Subscript; , especially on high-sulfur units equipped with high-dust SCR systems. Depending on the composition of the coal being fired and the type and operation of the boiler, the average SOface= Subscript; 2face=-Subscript; -to-SOface= Subscript; 3face=-Subscript; conversion rate in the boiler can be as high as 1.5%. Measured overall SOface= Subscript; 3face=-Subscript; conversion rates across the SCR reactor may be as great as 4.5%, depending on the catalyst type and the reactor's operating temperature.

In several German power plants, sulfuric acid concentrations of 32 ppm have been measured downstream of a high-dust SCR system. Some of this gaseous acid condenses onto cold surfaces (