Corrosion in FGD Systems was Hot Topic on Thursday and Friday
There have been some substantial corrosion problems with FGD systems recently. The price of high nickel alloys such as C 276 rose out of sight five years ago. As a result, a number of systems were installed with the lower cost 2205. The problem is that while chloride levels may be acceptably low on the average there can be very low pH acids trapped in material built up on the plate surfaces. Crevice corrosion has also turned out to be unexpectedly high. As a segue into the session yesterday, the following web conversations were displayed.
davefitz (Mechanical) 2 Nov 07 8:38
We have built a series of FGD scrubbers for our coal-fired power plants. The scrubber mfr claims the 2205 components are suitable for slurry chloride content as high as 30,000 ppm. The blowdown system and wastewater bioreactor was then sized for a system chloride content of 20,000 ppm chlorides.
After 1 yr of operation, severe crevice corrosion at flanges and access hatches was evident; annual average Cl content was 16,000 ppm Chlorides with 5.5<pH<6.5, SO2 and O2 bubbling through the slurry.
Can anyone advise published corrosion curves for 2205 in a process solution similar to the above described process? As per the Corrosion Handbook (Outo Kumpu 9th ed pI:88 fig 1) 2205 is only suitable to 2000 ppm chlorides. Other utilities typically run to not greater than 8000 ppm chlorides.
It looks like our goose is well cooked.metengr (Materials) 2 Nov 07 15:59
davefitz;
Yes, it sounds like your FGD goose is cooked. We had contemplated a wet FGD for our two units and 2205 was proposed. Similar conditions to yours more or less, and I told the manufacturer no way. You need either a 6Mo or better material. Basis for the decision was as follows;
Special Metals, "Experience in Effective Application of Metallic Materials for Construction of FGD Systems", Shoemaker and Crum
"Corrosion Performance and Field Experience with Superduplex and Super Austenitic Stainless Steels in FGD Systems", Audouard, Verneau and Grockidavefitz (Mechanical) 4 Nov 07 14:02
Meteng.
another concern with these concrete absorber vessels is potential to corrode the CS rebar in the concrete. Initial concern is at access hatch frames, but general rebar corrosion may be a concern if chlorides can migrate by osmotic pressure thru concrete.
The first speaker addressed the problem by discussing the resin alternative. Ben R. Bogner, Market Specialist at AOC Resins LLC, chronicled experience with FRP Composites for the power industry. The thermal resistance, chemical resistance, cost and durability issues associated with FRP were discussed, along with three case histories of applications in the power industry. FRP is competitive with glass block as a liner for chimneys and is much less expensive than the high alloy steel alternatives.
Dr. Deba Maitra, Research & Technology at Special Metals Corporation, related the results of laboratory and field testing (at a power plant in Indiana which is experiencing corrosion of 2205) which showed that while the duplex steel was severely attacked by the environment, super-austenitic stainless steel and nickel-base alloy specimens were much more resistant. The super-austenitic stainless is about half the price of C 276 and has equivalent corrosion resistance. It is being used in a new scrubber system being built in North Dakota.
Devin Wachowiak, Applications Engineer at Rolled Alloys, listed the successes of AL-6XN and ZERON 100 in the FGD industry. These alloys have been used in FGD units for many years with many successful installations. There are installations in Europe as well as the U.S.
AL-6XN FGD Experience
Joe Vandiver, President of Cera-Corr Systems, explained that the company offers a choice as designers and constructors of monolithic, ceramic tile lined, reinforced concrete scrubber vessels (aka Stebbins Type), ceramic tile lining technology in concert and flakeglass reinforced laminate resin lining systems. The partners which include Universal Blastco, TAC and Blome, have experience with hundreds of scrubber systems. A new monolithic tile lined concrete vessel has lots of advantages including speed of construction (4ft/day vs. 1ft/day).
Don Kelley, Senior Scientist at Ashland Performance Materials, provided lots of examples to demonstrate that FRP made from Epoxy Vinyl Ester Resin compares favorably to acid brick-lined carbon steel, stainless steel and high alloy clad carbon steel for stack and duct applications. There has also been widespread use in scrubber vessel design. A new generation of resins provided clarity and therefore easy inspection. Derakane 510B-400 epoxy vinyl ester resin is good for 227°F and ideal for FGD. For constant operation to 275°F there is Hetron® FR998-35.
David McKissick of Hadek cited the low maintenance of the new chimney design that consists of a reinforced concrete shell with Pennguard lining applied directly to the concrete surface. The design is faster and less expensive to build as well as providing maintenance advantages.
The Bios, Abstracts and Photos for both days are linked below.