Mastering Film-Forming Amines: Continuous Dosing and Cycling Operation

Abstract 

With increasing demands for flexible plant operation, cycling conditions are becoming the norm rather than the exception. Film-forming amines (FFAs) are well-suited to this shift, offering protection not only during operation but also throughout unpredictable downtimes. This article explores the application of FFAs under cycling conditions, focusing on continuous dosing strategies, effects on system chemistry, and best practices for ensuring system reliability. Supported by case studies from combined cycle and biomass plants, this piece provides actionable insights for power plant chemists and operators managing dynamic operating regimes.

Introduction 

As power generation becomes increasingly flexible and decentralized, many plants are exposed to frequent starts and stops, partial load operation, and unpredictable downtimes. Traditional preservation techniques often fail under such conditions. Film-forming amines offer a unique advantage in these scenarios: by forming a protective monomolecular layer, they provide continuous protection across both operational and non-operational periods. This article investigates the role of FFAs in cycling operations, focusing on continuous dosing strategies, injection points, and monitoring methods.

Challenges of Cycling Operation 

Power plants operating under cycling regimes face multiple stressors: variable load, short startup windows, and increased corrosion risk during outages. Particularly vulnerable are areas of phase change, such as turbine blades, which undergo frequent wet-dry transitions. These conditions promote localized corrosion and erosion, especially when condensate impingement zones shift due to changing load profiles.

Furthermore, during shutdowns, stagnant conditions accelerate corrosion and lead to the mobilization of corrosion products. These oxides can circulate during the next start-up, increasing iron transport, blocking filters, and accelerating wear in sensitive components. Conventional preservation approaches—such as nitrogen blanketing, system draining, or air drying—require time, staff, and consistency, all of which are in short supply during daily or weekly load-following operations. As such, a more dynamic, inline method of protection is needed.

Continuous Dosing: Strategy and Rationale 

A key benefit of FFAs is their suitability for continuous, low-concentration dosing. Instead of toggling between operation and preservation, plant operators can maintain a stable protective baseline at all times. The FFA molecules adsorb to metal surfaces and reinforce protective layers, even in transitional phases.

When defining the concentration for continuous dosing, operators must consider the proportion of time spent in standby versus active production. Plants that remain offline for extended periods, such as seasonal biomass facilities, may benefit from slightly elevated concentrations. In contrast, plants that cycle frequently but with long operating blocks may achieve sufficient protection with lower residual concentrations. What matters is the consistency: the protective film builds and stabilizes best under stable chemical conditions.

Regular analysis of residual FFA levels in the system is necessary to verify dosing effectiveness. Concentrations are typically monitored in the condensate or feedwater section, and adjustments should be made to maintain a target range appropriate for system metallurgy and temperature.

Injection Points: Practical Considerations 

To achieve full distribution of the FFA product, injection points must be carefully selected. One commonly used location is the feedwater tank or deaerator, which allows for preheating and mixing of the product before it enters the main circuit. This ensures even dispersion and minimizes local over-concentration.

Alternatively, dosing can take place in the condensate line, upstream of the low-pressure preheaters. This position allows for earlier film formation on downstream piping and better protection of preheater surfaces, which are often subject to oxygen ingress and flow disruptions.

In plants equipped with air-cooled condensers (ACC), additional injection upstream of the ACC can be advantageous. ACCs are prone to corrosion during idle times, particularly in winter or humid climates. Targeted dosing in these areas helps protect large carbon steel surfaces that are otherwise difficult to preserve.

Each plant layout demands a system-specific assessment, considering flow patterns, metal types, temperature zones, and existing instrumentation. In dual-dosing setups, careful balancing between dosing points is needed to avoid over- or under-treatment of specific components.

Monitoring and System Response 

The introduction of FFAs in a system with established oxide layers may initially cause disturbances. The loosening or dissolution of loosely bound corrosion products can lead to elevated iron levels or fluctuations in cation conductivity. This transient behavior is part of the conditioning phase and usually stabilizes after a few days of continuous dosing.

Real-time monitoring tools, such as online analyzers, help track FFA concentrations and adjust dosing rates. These devices are particularly helpful in plants with varying load levels, where manual sampling may not capture rapid chemistry shifts. Nonetheless, routine laboratory testing remains essential. During the implementation phase, daily manual measurements are recommended to verify online results and detect anomalies.

Operators must also distinguish between FFA-related effects and other contributors to conductivity. For example, FFAs can break down into CO₂, temporarily increasing conductivity without indicating contamination. In such cases, degassed conductivity monitoring (D-CACE) can help isolate the contribution of volatile organics from true salt-based conductivity changes.

Impact on Condensate Polishing Units 

When mixed-bed condensate polishing units are in use, the interaction with FFAs must be carefully considered. FFAs can adsorb to resin surfaces or accumulate in certain layers, affecting exchange dynamics. In some cases, operators have observed flotation phenomena, where organic loading caused resin bed disruption.

To address this, several strategies have been implemented: operating CPUs at elevated temperatures improves resin kinetics and reduces accumulation, while warm or hot regeneration cycles support thorough removal of organic residues. Caustic backwash steps may also aid in restoring bed performance, provided the chemical compatibility with the resin is ensured.

Before introducing FFAs into systems with CPUs, compatibility testing is highly recommended. This can include pilot studies or resin samples analyzed after short exposure periods. Where issues are anticipated, dosing locations can be modified to limit resin exposure or bypass CPUs during peak loading phases.

Decomposition and Thermal Effects 

Under normal operating temperatures, FFAs are stable and maintain their protective function. However, at elevated metal temperatures—typically above 400°C—thermal decomposition begins. This leads to the formation of gaseous by-products such as carbon dioxide and methane, which may influence conductivity and gas-phase analysis.

The decomposition behavior is formulation-dependent. Some FFAs degrade more rapidly than others, and their breakdown can release small organic acids that affect system chemistry. To quantify these effects, system operators should conduct baseline measurements of CACE and total organic carbon (TOC), both before and after FFA implementation.

In plants equipped with D-CACE systems, operators can better distinguish between increases in conductivity due to FFA degradation versus those from actual salt contamination. These analytical capabilities improve dosing precision and minimize overreactions to normal decomposition signatures.

Case Studies 

Combined Cycle Plant (Germany) A combined cycle power plant operating in a two-on-one configuration experienced repeated issues with high iron transport during daily starts. The iron contributed to rapid fouling of condensate filters and increased clogging during start-up. After implementing continuous FFA dosing at the condensate pump discharge, iron levels dropped by over 70% within three weeks. The plant reported smoother start-ups and eliminated the need for additional nitrogen blanketing.

Biomass Plant (Sweden) A biomass facility designed for seasonal, peak load operation faced difficulties preserving its feedwater tank and turbine lines during extended downtimes. A continuous FFA concentration of 0.3 ppm was maintained throughout the heating season. Subsequent inspections showed a shift from red oxide films to dark, compact magnetite layers. Water repellency improved, and turbine blade surfaces showed significantly less scale formation compared to previous years.

Conclusion 

The transition to flexible, cycling operation has changed the expectations for water-steam chemistry. Film-forming amines offer a solution tailored to this environment: continuous, low-level dosing that protects both active and idle plant components.

To be successful, application of FFAs under cycling conditions requires more than simply adding product to the system. Operators must consider injection timing, location, system dynamics, and analytical response. With appropriate setup and monitoring, FFAs can stabilize chemistry, reduce component wear, and minimize the operational burden of traditional preservation techniques.

As demonstrated in both fossil and biomass plants, this strategy is not theoretical—it is already improving performance in real-world scenarios. Film-forming amines are no longer niche products for preservation alone; they are becoming a central element of modern power plant water treatment.

Author Bio 

Ronny Wagner is the Managing Director at REICON Wärmetechnik und Wasserchemie Leipzig GmbH. As an experienced water treatment professional, he specializes in the application of film-forming amines in water-steam cycles, as well as in closed cooling and heating systems. With over 15 years of experience in the preservation of nuclear, fossil, and industrial power plants, he has played a pivotal role in advancing industry best practices. As an active member of vgbe and the IAPWS Power Cycle Chemistry (PCC) group, he has co-authored several international standards for the safe and effective application of film-forming amines in power plant chemistry.