18 Water / Wastewater
FILM FORMING AMINES AND THEIR APPLICATIONS IN THE POWER PLANT INDUSTRY
Introduction Use of Film Forming Amines (FFA) or Film Forming Amine Product (FFAP) is a growing trend in the power industry for maintenance of boiler systems. Case study literature suggests FFAPs offer protection from corrosion, reduce corrosion product transport, provide smooth heat transfer surfaces, and protect equipment during shutdown or layups. FFAPs can be used with or replace conventional corrosion inhibitor treatment regimes. FFAPs are used in various kinds of steam- generating power plants including conventional fossil, combined cycle, nuclear, and biomass power plants. They are also applied to different components of the steam cycle including the boiler feedwater, generator, and condensate return lines. As water treatment chemical vendors continue to expand their product offerings, FFAP formulations are being customized to suit the individual power plant’s operational conditions.
FFA Benefi ts
FFA technology has been shown to offer better heat transfer rates across steel tube surfaces than traditional phosphate-based corrosion inhibitor programs. Case studies in the literature also document improved bubble evaporation and the formation of smooth and homogeneous magnetite layers. FFAs will adsorb to the protective metal oxide layer and provide an extra barrier between it and the water or steam. Additionally, it has been shown that FFAPs remove loosely bound deposits within the boiler system resulting in cleaner surfaces overall. Together, these performance improvements can lead to reductions in operating costs.
FFAP Properties
FFAPs have a strong surface affi nity for metals, forming an impermeable layer which prevents corrosive agents from contacting the surface. This binding behavior can be attributed to the chemical structures of FFAs, which are long carbon chains with an amine at one end. The amine “head” attaches to a metallic surface while the “tail” forms a protective hydrophobic fi lm layer.
Octadecylamine (ODA) is an example of the simplest FFA molecule and is constructed from a straight chain of 18 carbons. ODA was the primary FFA in use over 40 years ago when it was fi rst introduced. More complex FFAPs were introduced to the marketplace as ODA operational challenges began to be better understood. These newer FFA compounds contain various functional groups such as primary or secondary amines which branch off from the FFA backbone. They may be referred to as polyamines or fatty amines. As use of FFAs has grown, many chemical vendors have created their own proprietary FFAPs which are formulated with other amines as well as neutralizing and emulsifi er agents.
FFAPs are usually touted as a greener alternative than conventional boiler treatment chemicals such as hydrazine. Since FFAs are relatively non-toxic, extensive personal protective equipment (PPE) is not required when working with these products.
FFA Pitfalls
While FFA treatment programs offer many benefi ts, some drawbacks are possible. A primary concern is the formation of FFA degradation products which are largely carbon dioxide and organic acids that form after extended exposure to high heat. These degradation products can lower the pH of condensed steam and increase Conductivity After Cation Exchange (CACE) unless compensated for by other water treatment methods. Another major concern is optimizing for the appropriate dosage. Overdosing offers no additional protection and runs the risk of creating micelles or “gunk balls” that can clog pipes and reduce effi ciency. Supplier product and site-specifi c dosage rate recommendations should be followed.
Preparations Before Switching to an FFA Program
It is important to establish baseline readings of key steam cycle performance indices before changing the treatment regimen. Without these reference points, plant personnel will not have the ability to validate quantitatively whether the addition of an FFA/ FFAP has provided any benefi t. Some of these key parameters include total iron and/or copper, feedwater pH, oxygen, and CACE. Also, inspecting interior surfaces for loose deposits and sludge on high pressure (HP) evaporators or conventional boiler waterwalls is recommended before starting a course of FFA/FFAP. If the deposits are not removed, under deposit corrosion may occur.
IET JANUARY / FEBRUARY 2022
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