Advantages Of Filming Amines In Closed Circuit Water Systems

Benefits Of Filming Amines For Closed Circuit Water Systems

You may want to consider using film-forming amines (FFAs) for the treatment of your closed systems (LTHW and Chilled Water) as an alternative to other more traditional chemistries. Not only are there performance benefits and environmental advantages to using FFAs, but direct use costs can be reduced by up to 80%.

Introduced in the 1960s, film-forming amines were first used in steam boiler applications to protect condensate return lines from corrosion due to oxygen and carbon dioxide. Since then, advancements in technology have coincided with requirements in other application areas (such as modern multi-metal high-efficiency closed systems). This has led to the use of FFAs becoming much more widely accepted.

The Status Quo

Traditional chemical treatment programmes for closed systems are predominantly based on inorganic chemistry and comprise formulations based on nitrite, molybdate and/or synergistic blends of these two components.

Nitrite is relatively inexpensive, but it provides no protection to aluminium and can be susceptible to microbiological activity (depletion of inhibitor reserve by nitrite-reducing bacteria). It is relatively toxic and is subject to discharge regulations.

Molybdate is another type of anodic inhibitor based on the transition metal, molybdenum. These days, nitrite is typically blended with molybdate to overcome some of the above limitations. However, hybrid programmes still share some of the same concerns.

Mode of Action

Film-forming amines offer corrosion protection by adsorption onto the metal surface and forming a hydrophobic mono-molecular barrier between the water and the metal surface. FFAs are all-organic corrosion inhibitors which offer multi-metal protection through the creation of this physical protective barrier.

In addition to enhanced protection of mild steel, their affinity for surfaces of all metallurgies means that critical aluminium components are also protected. The film exhibits biocidal properties which may eliminate the requirement for supplementary biocide dosing. A surface-active biocide will serve to inhibit biofilm growth.

The Aluminium Conundrum

The Galvanic Series indicates that aluminium will always corrode preferentially to mild steel. The increased use of aluminium (in boilers and heat exchangers) presents the asset as the anode. Since corrosion always occurs at the anode, aluminium needs to be protected.

FFA molecules have an affinity for all metallurgy types and hence their use means that pH control for this amphoteric metal is less critical. The film-forming functionality of amines provides greater reassurance than the purely anodic inhibition offered by a standard molybdate/nitrite blend (and nitrite-only inhibitors offer no protection to aluminium at all).

Dosage & Cost

For closed systems, the dosage of FFAs is typically around one-tenth that of popular inorganic hybrid treatment programmes. Moreover, due to their mode-of-action, the dose-rate can (and for legacy systems should) start even lower than this. As such, the use-cost of amines is significantly lower than that of conventional chemistries.

Energy & Efficiency

Amines have a negligible effect on total dissolved solids, contributing very little additional solids to the recirculating water. Cleaner surfaces and leaner water will have a direct correlation with increased heat-transfer and reduced pumping costs.

HS&E Considerations

In addition to the technical and commercial benefits, lower dose-rates result in decreased usage (minimal chemical handling) and reduced inventory (optimal stock-holding) together with associated health & safety benefits. FFAs are non-toxic and readily biodegradable.

A Word About Micro

It is well-documented that nitrite-based inhibitors are depleted by nitrite-reducing bacteria (NRBs). Not only does this reduce the efficacy of mild steel corrosion inhibition, but the potential generation of ammonia (and resultant pH elevation) is detrimental to copper.

Film-forming amines have biocidal properties. In a well-maintained system, there may be no need to dose a separate (non-oxidising) biocide. Alternatively, where the use of a biocide is necessary, the required dose-rate will be lower in the presence of FFAs.

The growth of biofilm in heat exchangers can have a more significant effect on heat transfer than mineral scale. Studies show that just 20 microns of biofilm can reduce thermal efficiency by up to 30%. As such, any biocidal contribution from the protective film is beneficial.

Zero Liquid Discharge

This is the ultimate goal. Film-forming amines can be introduced on top of any existing chemical treatment programme. There is no need to drain the system. Elevated pH levels can be accommodated via their physical (film-forming) protection mechanism.

Filming amines have a strong affinity for metal surfaces and are agnostic to metallurgy. This is key for today’s high-efficiency multi-metal systems. Such affinity enables amines to penetrate existing corrosion deposits and general system debris.

This inherent clean-up capability of FFAs presents a viable alternative to system flushing when used in conjunction with side-stream filtration. In some cases, this can replace off-line cleaning and avoid the need to obtain a Discharge Consent from your sewerage provider.

This is a major benefit of cathodic inhibition. Under-dosing anodic inhibitors (e.g. nitrite) can be detrimental to the system. Whereas the reserve of amines can (and should) be gradually built-up in order to achieve the desired residual. This allows for controlled system clean-up.

Off-line Protection

Owing to the tenacity of the film formed, FFAs help to preserve critical assets during discontinuous operation, planned shutdowns and unexpected outages. In this scenario, the protective film remains and (on system refill) only the residual needs to be replenished.

Conclusion

The unique mode-of-action of FFAs results in performance gains at significantly lower concentrations when compared to traditional treatments. Their all-organic formulation has a minimal environmental impact. Lower use-rates serve to reduce chemical handling and inventory. This results in improved health & safety together with economic benefits.

Contact SMS Environmental's closed system department to discuss treatment options or read more on the range of closed system services which we offer.