One of the big drivers of the utility industry's recovery has to be the estimated $15 billion engineered equipment market for flue gas desulfurization (FGD) systems. The Clean Air Interstate Rule (CAIR) has pushed utilities in 28 eastern states and the District of Columbia to retrofit many power plants with scrubbers over the next few years in order to reduce SO
2 emissions by an estimated 4.3 million tons by 2010, which is 45% lower than 2003 levels, according to the EPA. At full implementation, CAIR will reduce power plant SO
2 emissions in affected states to just 2.5 million tons—73% below 2003 emissions levels.
Scrubber system construction costs have come down from an average over $200/kW since the first FGD push in the mid-1990s to comply with the Clean Air Act Amendments of 1990. Purchase a system today, and the basic FGD system will have a sticker of around $150 to $200/kW, although special site requirements could drive that cost up, sometimes significantly. EPA studies related to CAIR implementation note that the market for FGD systems is on the order of 160,000 MW, requiring an investment of $25 billion. Many industry observers see those estimates as high, with real demand on the order to 80,000 to 90,000 MW. The differences seem to be related to the number of plants that will be retired rather than retrofitted.
Macroeconomic market issues are interesting, but they aren't very helpful when your plant is under the gun to install an FGD system. Once the decision is made to go ahead with one, it falls to plant engineers to select the right technology from a wide number of options that will match your particular fuel and plant configuration. Visit similar plants and talk to your colleagues. Read the technical literature. Quiz your consultants. In short, do your homework and pay attention to the design details.
Common materials problems
One particular problem reported by engineers during several FGD installations is how to correctly install and clean those stainless steel and nickel alloy components that carry the scrubber slurry and other system fluids. It seems like an inconsequential issue, but field experience has proven otherwise.
Stainless steels and nickel alloys usually are received in clean, uncontaminated condition, but during fabrication, contaminants such as dirt, oil and grease, and embedded iron can be deposited on the metal surface. Dirt can be easily removed by washing with a detergent followed by a water rinse. Oil and grease should be removed because they may contain sulfur, phosphorus, or other elements that could embrittle the alloys if they are subjected to the heat of welding. Degreasing solvents are used for removal of these contaminants.
During handling and fabrication, iron can be embedded in the metal surface. Embedded iron on the surface of the stainless steel can create initiation sites for pitting or crevice corrosion, with the corrosion continuing into the stainless steel beyond the initiation site. However, nickel alloys with over 8% molybdenum do not seem to be affected by embedded iron.
Heat tint has been found to lead to reduced corrosion resistance of stainless steels both in the heat-affected zone and the weld metal. On the other hand, numerous tests have shown that heat tint does not have any significant influence on the corrosion resistance of nickel alloys such as Alloy C-276.
Weld spatter and mechanical defects can also be focal points for pitting and crevice corrosion on both stainless steels and nickel alloys. They should be removed by light grinding with a flapper wheel, but care must be taken to ensure that where sheet linings or clad plate are concerned, grinding does not significantly reduce the thickness of the already-thin sections.
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