11-6-08

NO_x Catalyst Suppliers are improving their Hg Oxidation and SO₃ Minimization

NO_x catalyst performance on mercury and SO₃ was the subject addressed by five experts yesterday in the McIlvaine Hot Topic Hour. Speakers were

Steve Guglielmo, Hitachi

Mark Ehrnschwender, Evonik

Mike Cooper, SCR-Tech

John Cochran, CERAM

Ken Jeffers, Argillon

Steve updated participants on the latest performance data on TRAC™, which maintains NO_x removal while oxidizing mercury and reducing the conversion of SO₂ to SO₃. TRAC was applied on a 640 MW unit and replaced one of three catalyst layers. Mercury capture in the downstream scrubber increased from 30 to 70 percent.

TRAC™ can be used with both PRB and Eastern bituminous coal-fired boilers
Less than 0.25 percent SO₂/SO₃ oxidation rate per layer for Eastern bituminous
Sorbent injection for SO₃ mitigation can be reduced
Ninety-five percent of Hg oxidation can be achieved at airheater outlet to avoid activated carbon injection for Eastern bituminous coal and PRB with minimal or no halogen injection
Catalyst volume can be reduced by using TRAC.

Mark championed the holistic approach which emphasizes guarantees based on end of life performance rather than initial.

The Evonik Process has demonstrated the ability to modify the formulation of the original catalyst for SO₂ to SO₃ conversion reduction.
The NO_x deactivation over time will reduce the effectiveness of the mercury reaction due to a reduction in catalyst potential.
The capture of mercury is not just tied to the SCR. The wet FGD system and the flopping of the mercury state from elemental to oxidized back to elemental are critical to mercury capture.
The mercury and SO₃ measurement equipment is not accurate enough to measure slight variations, making guarantees hard to prove or disprove.
Any guarantees would need to be tied to “end of life” and not at the beginning of the catalyst operation and also include all layers that are in service.

Mike explained that

The SO₂ oxidation reaction primarily occurs over same reaction site as NO_x reduction but…
- Higher “activation energy” makes it harder for the catalyst
- Kinetic control vs. mass transfer control means it occurs more in the catalyst micro & meso pore structure.
Re-impregnation provides opportunities to favor mass-transfer (DeNO_x) over kinetic (SO₂ oxidation) reactions by control of V₂O₅ distribution and dispersion.
Mercury oxidation rates over various types of catalyst can be effectively studied using micro-reactors.
Preliminary studies indicate that mercury oxidation rates over regenerated honeycomb catalyst are same or better over new, but much more work is required!

John reported that 85 percent mercury removal is being achieved in a Midwest utility using Ceram catalyst. At the same time NO_x removal is 92 percent with a 2 ppm slip and SO₂ to SO₃ oxidation is less than 0.5 percent.

Ken described the Johnson Matthey synergy with Argillon and the extensive testing of mercury oxidation in the European MERCURY CAP program as well as the performance of 200 MW of low temperature mercury oxidation catalyst at Lower Colorado River Authority.

Bios, photos and abstracts are included in the following link.

Bios, Photos and Abstracts - Hot Topic Hour November 6, 2008

The following individual power points can be viewed in the NO_x Decision Tree.

Stephen Guglielmo - Hitachi

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