February 22, 2007

Utilities Report Cost Effective SO₃ Capture Solutions at the Hot Topic Hour Yesterday

The Hot Topic discussions on SO₃ on February 22 were dominated by the utilities. This illustrates that we are now in the solution stage and not back at problem solving.

Ed Bowes of Dominion presented impressive results from a demonstration of SO₃ reduction at the Dominion Chesterfield station. The combination of cooling the gas to close to 300°F and introduction of finely ground limestone prior to the air heater results in cost effective SO₃ reduction without major capital expense. Based on the demonstration results, Dominion will be incorporating this technology in upcoming full scale scrubber projects. Marsulex and Alstom Air Preheater are technology providers.

One utility who had researched the options said that their concern was plugging of the air heater. Ed said that while they have no long term experience, there was nothing in the demonstration to indicate that the relatively small amount of additional solids would cause problems. The power points are displayed in the FGD Decision Tree at

Doug Ritzenthaler of AEP provides a detailed analysis of a system approach to SO₃ reduction. While the use of trona injection has been a major tool in SO₃ capture, the whole system needs to be examined. The switch to a low SO₂ to SO₃ conversion catalyst paid for itself in reduced trona costs in a very short time frame.

Doug indicated that more needs to be learned about removal of SO₃ in the tray scrubber. One week it can be 70 percent and the next week it is 20 percent. The problem is not in measurement since the variations do not occur randomly. So if the reasons for the efficiency variation can be understood and harnessed, then it could be very cost effective.

AEP is now effectively reducing SO₃ with the system approach but is continuing to look for other opportunities to improve cost effectiveness. The location in the Decision Tree is:

Eric Van Rens of Mississippi Lime pointed out that lime is not only a cost effective way to reduce SO₃ but it has side benefits including corrosion reduction, enhanced mercury capture, and can reduce SO₂ reagent requirement. There are various grades and qualities of hydrated lime but the standard grade is effective. A listing of the advantages is displayed at

Jim Jarvis of URS provided new opportunities and insights on the use of sodium under the Codan patent. He pointed out that progress has been made to utilize less expensive reagents than SBS. In fact, a number of sodium compounds can be effectively used. This assures availability and cost minimization. Access the power points in the Decision Tree at

John Caine of Southern Environmental told participants that their 316 L wet precipitator with membrane collection plates now has two years of commercial operation with no corrosion of the casing. The reason is that the unit does not need makeup water. This eliminates the potential for chloride corrosion. The unit actually cools the saturated gas and is condensing water.

The conclusion is that use of the lower cost 316 L makes the WESP a very attractive option for SO₃ removal. Since the WESP also removes substantial quantities of mercury, it is even more cost effective as a multi-pollutant control device. His power points are in the following branch

Lime and Limestone Issues are the “Hot Topics” for March 1

Both lime and limestone are used for acid gas capture in power plants. The reagent represents a substantial percentage of the cost of SO₂ removal. Reagents also have new uses for capture of SO₃. Knowledge relative to the performance, availability and differences in the chemical, physical, mineral, and petrographical properties is important to the FGD operator. On Thursday, March 1, McIlvaine will conduct a “Hot Topic Hour” (or maybe two) on this subject. Here are the specific questions which will be addressed.

How does limestone quality affect efficiency and maintenance?  Specifically what differences in major and minor trace elements are important?  What about mineralogical differences (calcite, dolomite, clay minerals, quartz)?  What about petrographical differences (grain size, crystal size, porosity, interparticle cement)?

What is the trade off between particle size, power input and efficiency? What about regional grinding facilities? If high quality stone is going to be in short supply in the local area, doesn’t regional grinding make sense?

Will enough lime be available? What are the advantages and disadvantages of high magnesium lime? Can you contract long term at an attractive price? How can you increase the utilization?

What are the criteria to make wallboard quality gypsum? Will markets for other byproducts impact the decision between lime and limestone?

Who are the producers of lime and limestone and what areas do they serve?

What should you know about specific applications?

Limestone

CFB boilers

Limestone wet scrubbers

Lime

 Spray Drier SO₂ scrubber

 Circulating dry scrubber

 Wet lime scrubber

 SO₃ removal with lime injection

A brief discussion on the availability of lime and limestone for FGD internationally and the role of global producers will also be included. For more information or to register for this “Hot Topic Hour” session, click on

http://www.mcilvainecompany.com/brochures/FGDnetoppbroch/Default1.htm