September 21, 2006

FGD Wastewater Hot Topic Hour

Forty people including major utilities and A/Es participated in the 80 minute discussion of FGD wastewater while viewing the relevant branches of the FGD Decision Tree. The utilities on the line were generally in the process of planning FGD systems and wanted to know what was available to help them meet wastewater discharge limits.

This is a relatively new challenge for the industry. Paul Chu of EPRI indicated that his organization would be supporting research and analysis regarding removal of soluble metals from the wastewater specifically, as well as a broad range of contaminants. He invited those companies with potential solutions to contact him (see our Networking Directory for his contact information).

Bill Ellison of Ellison Consultants was asked to cover alternatives. He pointed out that if you install a dry CFB unit you can mix contaminated wastewater from various power plant sources with the gypsum/flyash combination resulting in a fixed non-leachable product. As a result the FGD system has a positive impact on wastewater quality. He also pointed out that the natural oxidation wet lime systems also result in encapsulating the toxic materials in the fixed disposable sludge product. Therefore it may be worthwhile to consider this option before proceeding with a wet limestone system.

Suppliers of systems talked at length from actual experience. So there was a comfort level that heavy metals can be reduced to meet even stringent limits. In the past there has been the perception that the use of dibasic acid would result in increased wastewater treatment costs. But now if you are using biological agents to capture the heavy metal, the organic acid actually becomes a food source for the microbes.

A number of the schemes show lime as the neutralizing agent with additional chemicals for heavy metal capture. There is as much as 500,000 tons/yr of hydrochloric, hydrofluoric and other acids which would be captured if all the plants had wet FGD. This would require a lot of lime. The fact that a number of lime and magnesium producers were participating in the discussions was undoubtedly due to this potential.

There were also some suppliers of corrosion resistant materials participating. The wastewater design is critical to materials selection. If there is a high bleed of wastewater, then chloride levels are low. A tight system can result in 20,000 ppm of chlorides or even higher in the recirculating loop. Some designers are beginning to ask whether it makes sense to build scrubbers of C 276 to handle the high chlorides and then remove them downstream. Is there some way to combine the new needs for heavy metal removal and biological treatment with a means of keeping chlorides lower in the recirculating scrubber loop?

A wealth of information was presented by supplier companies. Here are summaries of their presentations as they appear in our FGD Decision Tree. If you are a subscriber to the tracking or Air Quality Decisions then you can hyperlink directly from this Alert to their power point material. Also we will be posting the entire audio/visual recording to our services in the next several weeks.

Continuing Decision Process For: Products

Zenon's ABMet^® (Advanced Biological Metals) removal system is a technology for the removal of metals and inorganics from FGD wastewater. The ABMet^® process uses naturally occurring microbes to treat wastewater. Zenon says that the ABMet^® removal results cannot be matched by physical/chemical processes.      

Selenate and selenite are reduced to insoluble elemental selenium. Nitrates are reduced to N₂. Cr, Ni, Cd, Cu, Zn, Hg and other metals are also removed with efficiencies greater than 99 percent. The technology has been demonstrated on 12 different wastewaters and as of 9/2006 orders are being processed for four full scale systems.

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/McIlvaine 060920.pdf

Continuing Decision Process For: Products

Siemens Water Technologies (U.S. Filter) has five full scale FGD wastewater treatment systems in design stage, with more systems pending. They include some projects utilizing the selenium removal systems of GE/Zenon. Systems use chemical and physical treatment to remove suspended solids, heavy metals, BOD, and nitrogen. They also adjust pH and temperature. Siemens can supply equipment and turnkey systems. It also offers build, own, operate and maintain (BOOM) and project financing.

Advice to owners is that copied designs don’t work. Work closely with an experienced provider to value engineer the design. Pay particular attention to selection of mechanical equipment, instrumentation and materials of construction. Build in a safety margin to allow for variance between actual and predicted wastewater quality.

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/Siemens - FGD Solutions Sep06.ppt

Continuing Decision Process For: Products

TMT 15® is being used in both the scrubber slurry and wastewater treatment for mercury removal. At higher pH it also effectively precipitates Cu, Zn, Ni, Cd and other heavy metals. TMT works in the presence of complexes whereas neutralization fails. Estimated usage in wastewater treatment is 2-10 ml TMT/ton of coal. It can also be used to prevent mercury re-emission in the scrubber but this requires 10-50 ml TMT/ton of coal.

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/TMT Hot Topic Presentation.pdf

Continuing Decision Process For: Products

Fifty to eighty percent selenium removal is achieved with Nalmet. Nalco also provides a variety of solutions relative to FGD operation and maintenance. In one case sludge dewatering in centrifuges was greatly improved. In another a dual polymer program resulted in 90% reduction in thickener effluent turbidity and improved gypsum quality. Chemical feed automation in one plant reduced polymer usage by 40%.

Nalco CaSO₄ scale control treatment greatly reduced cleaning of six scrubber modules in one plant when introduced in the scrubber recycle line. A plant with an NPDEAS discharge violation for mercury levels 2-3 times allowable utilized Nalmet to meet compliance for three years. Over 50 FGD processes use Nalco programs.

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/Optimized Nalco FGD Capabilities- Hot Topics.ppt

Continuing Decision Process For: Products

Emerson has a new pH meter (PERpH-X) which performs better in scrubber slurries. A coal-fired power plant with an FGD system is now using the new 3400HTVP. In a scrubber slurry application the previous pH sensor lasted less than eight weeks. The new sensor is still working well after 12 weeks.