Coal-fired power plants depend on high-purity water and steam cycles to ensure efficient operation and minimize equipment degradation. The presence of trace-level anions, such as chloride, bromide, nitrate, phosphate, and sulfate, along with monovalent cations including sodium, Ammonium, and Potassium, can impact the performance and longevity of critical plant components.
Analyzing these ions in key systems, such as the condensate discharge pump, demineralization (demin) systems, and HRSG (Heat Recovery Steam Generator) steam drums is essential for maintaining water quality and ensuring overall operational reliability.
Chloride, bromide, nitrate, phosphate, and sulfate anions are critical to monitor due to their potential to cause corrosion, scaling, and fouling in boilers and turbine systems.
Chloride and sulfate can accelerate pitting and stress corrosion cracking in high-pressure environments, leading to costly repairs and downtime.
Phosphate, often added for pH control, must be carefully managed to prevent scaling or carryover into steam, which can damage turbine blades. Nitrate, though less common, may indicate contamination or degradation of water treatment processes, posing risks to system integrity.
Similarly, monovalent cations – sodium, Ammonium, and Potassium – are critical to monitor because they can form harmful deposits in boilers and turbines, reducing heat transfer efficiency and causing mechanical imbalances.
Ammonium, in particular, may be present due to water treatment processes or contamination, and its accumulation can alter pH levels, potentially exacerbating corrosion. Even at trace levels, these cations can indicate leaks in demin systems or other impurities, compromising water purity. Regular monitoring at the condensate discharge pump, demin systems, and drums ensures early detection of ionic contaminants, enabling timely corrective actions to maintain water chemistry within stringent operational limits.
Analysis and Importance of Monitoring Trace Anions and Cations
The membraPure IONUS Ion Chromatograph is employed to separate and quantify trace anions (chloride, bromide, nitrate, phosphate, sulfate) and cations (sodium, Ammonium, Potassium) in power plant water samples. The system uses anion-exchange chromatography with the memSep300HC column and a membraPure Suppressor2 to reduce background conductivity, enhancing the detection of low concentrations of anions via conductivity detection. For cations, cation-exchange chromatography is performed using the Repromer CAT column (Dr. Maisch), also with conductivity detection. Samples from HRSG drums, demin tanks, and condensate pump discharge are filtered (0.45 µm) and injected directly or diluted as needed to minimize matrix effects.
Monitoring these ions is essential for several reasons:
- Corrosion Control: Chloride, sulfate, and sodium can accelerate corrosion of boiler tubes, turbine blades, and other metal components, leading to pitting or stress corrosion cracking.
- Scaling Prevention: Phosphate and sulfate may contribute to scale formation on heat transfer surfaces, reducing thermal efficiency and increasing maintenance costs.
- System Integrity: Elevated levels of Ammonium or Potassium may indicate contamination or improper operation of demin systems, compromising water purity.
- Regulatory Compliance: Power plants must adhere to guidelines (ASME or EPRI standards) that specify allowable limits for ionic impurities to ensure safe and efficient operation.
- Operational Efficiency: Trace impurities can reduce steam quality, impacting turbine performance and overall plant efficiency.
Regular IC analysis enables early detection of ionic contaminants, allowing operators to take corrective actions such as adjusting chemical treatments or regenerating demin resins, thereby preventing equipment damage and optimizing plant performance.
In this application note, we examine the methodologies for determining trace-level anions and monovalent cations in coal-fired power plants. By implementing sensitive and reliable analytical techniques, operators can safeguard equipment, enhance efficiency, and ensure compliance with environmental and operational standards.
Inorganic Anions:
The anions of interest—chloride, bromide, nitrate, phosphate, and sulfate—are critical to monitor in coal-fired power plant water systems due to their potential to cause operational issues. Below is an overview of their origins, roles, and implications:
Chloride (Cl⁻):
- Origin: Chloride typically enters the system through raw water, coal combustion byproducts, or leaks in cooling water systems. It may also result from improper demin system operation or contamination from chemical treatments.
- Role/Implications: Chloride is highly corrosive, particularly in high-temperature and high-pressure environments like HRSG drums. Elevated chloride levels can cause pitting corrosion and stress corrosion cracking in stainless steel components, leading to equipment failure. Its presence often indicates contamination or inadequate demineralization.
Bromide (Br⁻):
- Origin: Bromide is less common but may originate from raw water sources, especially in regions with brackish groundwater, or from coal ash residues. It can also be introduced through certain water treatment chemicals.
- Role/Implications: While bromide is less corrosive than chloride, its presence at elevated levels may indicate raw water intrusion or contamination. In some cases, bromide can form harmful disinfection byproducts if oxidants are used in water treatment, posing environmental concerns.
Nitrate (NO₃⁻):
- Origin: Nitrate typically enters via raw water or as a byproduct of ammonia oxidation in the system. It may also result from microbial activity in cooling water or environmental contamination.
- Role/Implications: Nitrate is less corrosive than chloride or sulfate but can contribute to corrosion under certain conditions, particularly in the presence of oxygen. Its presence may indicate external contamination or inefficiencies in water treatment processes, requiring further investigation.
Phosphate (PO₄³⁻):
- Origin: Phosphate is often intentionally added as a corrosion inhibitor or pH buffer in boiler water treatment programs. It may also enter through raw water or leaching from phosphate-based scale inhibitors.
- Role/Implications: When used correctly, phosphate helps prevent corrosion by forming protective films on metal surfaces. However, excessive phosphate can lead to scale formation (calcium phosphate) on heat transfer surfaces, reducing efficiency. Its presence in condensate or demin tanks may indicate carryover or improper dosing.
Sulfate (SO₄²⁻):
- Origin: Sulfate originates from raw water, coal combustion (sulfur oxides dissolving into water), or oxidation of sulfites used in oxygen scavenging. It can also result from leaks in cooling systems or improper demin performance.
- Role/Implications: Sulfate is highly corrosive and can form insoluble scales (calcium sulfate) that impair heat transfer. High sulfate levels in HRSG drums or condensate may indicate contamination or inadequate water treatment, posing risks to equipment longevity.
The presence of these anions, particularly at elevated levels, signals potential issues such as raw water intrusion, chemical carryover, or demin system failure. Regular IC monitoring ensures that these anions remain within acceptable limits (< 10 ppb for chloride and sulfate in high-purity systems per EPRI guidelines), protecting critical plant components.
Inorganic Cations
The cations of interest sodium, Ammonium, and Potassium are monitored to assess water purity and system performance. Their origins, roles, and implications are outlined below:
Sodium (Na⁺):
- Origin: Sodium is a common impurity in raw water and can enter through leaks, improper demin resin regeneration, or contamination from sodium-based chemicals (ex. sodium hydroxide used for pH control).
- Role/Implications: Sodium is highly undesirable in steam cycles as it can form corrosive sodium hydroxide in high-temperature environments, damaging boiler tubes and turbine blades. Its presence in demin tanks or condensate indicates demin system inefficiencies or contamination, necessitating immediate corrective action.
Ammonium (NH₄⁺):
- Origin: Ammonium is often intentionally added as ammonia or Ammonium hydroxide to control pH and minimize corrosion in the steam cycle. It may also result from decomposition of organic amines or microbial activity in raw water.
- Role/Implications: When used as a pH conditioner, Ammonium helps neutralize acidic conditions, protecting metal surfaces. However, excessive Ammonium in condensate or demin tanks may indicate carryover from dosing systems or contamination. It can also interfere with demin resin performance, reducing water purity.
Potassium (K⁺):
- Origin: Potassium is less common but may enter via raw water, coal ash, or Potassium-based treatment chemicals. It can also result from environmental contamination or leaks.
- Role/Implications: Like sodium, Potassium can contribute to corrosion by forming alkaline compounds in high-temperature environments. Its presence in HRSG drums or condensate often indicates external contamination or demin system failure, requiring investigation to prevent equipment damage.
Elevated levels of these cations, particularly sodium and Potassium, are red flags for water treatment system malfunctions or external contamination. Ammonium levels must be carefully controlled to balance corrosion protection with the risk of carryover. IC analysis with the Repromer CAT column provides the sensitivity needed to detect these cations at ppb levels, ensuring compliance with industry standards (ex. < 2 ppb for sodium in high-purity condensate).
Operating Conditions of the Method
Anions
| IC System | IONUS Ion Chromatograph |
| Column | memSep300HC (4 mm x 250 mm) |
| Eluent | 2.5 mM Sodium Carbonate / 0.05 mM Thiocyanate |
| Suppressor | membraPure IC Suppressor² |
| Sample | Filtration (0.45 µm), Dilution as applicable, 1:15 |
| Injection | 400 µL |
| Water Source | Aquinity² P10 Analytical (0.055 µS/cm, Type I) |
Cations
| IC System | IONUS Ion Chromatograph |
| Column | Repromer Cat, 7 µm, (4 mm x 250 mm) (Dr. Maisch) |
| Eluent | 3.5 mM Methane sulfonic Acid |
| Sample | Filtration (0.45 µm), Dilution as applicable, 1:15 |
| Injection | 400 µL |
| Water Source | Aquinity² P10 Analytical (0.055 µS/cm, Type I) |
Standards and Sample Preparation
Anion standards with concentrations are as follows:
| Analyte | Concentration |
| Chloride | 103 ppb |
| Nitrite | 103 ppb |
| Bromide | 102 ppb |
| Nitrate | 102 ppb |
| Phosphate | 202 ppb |
| Sulfate | 209 ppb |
The cation standard with concentrations are as follows:
| Analyte | Concentration |
| Sodium | 96 ppb |
| Ammonium | 188 ppb |
| Potassium | 95 ppb |
The samples were obtained from a Coal-Fired Power Plant as follows:
| Sample # Assigned | Description |
| 01 | HRSG1 HP Drum |
| 02 | HRSG1 IP Drum |
| 03 | HRSG1 LP Drum |
| 04 | HRSG2 HP Drum |
| 05 | HRSG2 IP Drum |
| 06 | HRSG2 LP Drum |
| 07 | Demin Tank 1 |
| 08 | Demin Tank 2 |
| 09 | Condensate Discharge Pump |
The samples (HP = High Pressure; LP = Low Pressure; IP = Intermediate Pressure) were assigned an internal laboratory tracking number upon arrival at our facility. The samples were filtered through a 0.45 µm syringe filter.
Most samples were analyzed without dilution, however, as applicable, several were diluted in ultra-high purity deionized water from the Aquinity² P10 water purification system, filtered through a 0.45 µm IC filter into a 2 mL vial with a septa cap. All standards, samples, and final quality control checks were loaded into the membraPure autosampler for analysis. The results were evaluated and calculated by the software Clarity, DataApex.
The Results
Please see the full result of the sample analysis in the Table 1 below. All results are reported in ppb. The corresponding chromatograms can be found in the appendix. Figure 2 shows the standard used with all possible components for comparison. Figure 3 shows the results from the three samples with regard to HRSG1. As the chromatography curves for HRSG2 are similar, these data are not shown. Figure 4 summarises the results from the analysis of the two demin unit tanks. Figure 5 shows the chromatogram of the sample taken from the condensate of the discharge pump.
The following figures show the results of the cation analyses in the same order as the anions. Only sodium, Ammonium and Potassium were of interest for this project.
Conclusion
The membraPure IONUS Ion Chromatograph, equipped with the memSep300HC column and membraPure Suppressor2 for anions and the Repromer CAT column for cations, offers a robust and sensitive solution for monitoring trace anions (chloride, bromide, nitrate, phosphate, sulfate) and cations (sodium, Ammonium, Potassium) in coal-fired power plant HRSG drums, demin tanks, and condensate pump discharge. By providing rapid and accurate quantification of these ionic impurities, the IONUS system enables power plant operators to detect contamination, prevent corrosion and scaling, and maintain compliance with industry standards. Regular IC analysis is a critical tool for ensuring water and steam purity, protecting valuable equipment, and optimizing plant efficiency. This method is particularly valuable for its ability to handle complex aqueous matrices with minimal sample preparation, making it an essential component of modern power plant water chemistry programs.
The membraPure IONUS IC Advantage
Accurately measuring trace anions and trace cations in a coal-fired power plant is crucial for proper operations and equipment maintenance. The membraPure IONUS Ion Chromatograph stands out as the ideal solution for this demanding application.
The IONUS stands out for its exceptional precision, setting a new benchmark in anion analysis.
At the core of its performance is an advanced eluent delivery system that ensures a consistent flow of eluent, an essential factor for achieving reliable separation of various anions.
Complementing this is precise temperature control, which keeps the column at a stable temperature, enabling optimal peak resolution for accurate identification and quantification.
Additionally, the instrument’s accurate sample injection mechanism delivers a consistent sample volume with every run, minimizing errors and enhancing reproducibility. Finally, the advanced detector cell offers outstanding signal stability, ensuring dependable and consistent detection of anions throughout the analytical process.
Optimized Separations: The IONUS goes beyond precision with its:
- Next-Generation IC Suppressor: This innovative technology significantly enhances the separation of anions commonly found in amine solutions. The suppressor improves the analysis of Chloride, Nitrite, Bromide, Nitrate, Phosphate, and Sulfate in the various power plant waters.
- Proven Analytical Column: The robust and reliable column ensures efficient separation and long-lasting performance for trace level Ion Analysis.
By combining exceptional precision with optimized separations, the membraPure IONUS empowers you with the confidence to make informed decisions about plant operations and matinenance requirements.
Benefits of Utilizing the IONUS Ion Chromatograph for this Application
The membraPure IONUS Ion Chromatograph is best suited for the application of measuring trace anions and cations in various power plant waters because of the following:
- Performance: The precision delivery of the eluent, the stable temperature of the column temperature, the accurate delivery of the sample into the system, and the stability of the detector cell all contribute to the quality analysis of the low level anions. With the introduction of our new IC Suppressor and the utilization of a rugged, proven, analytical column, the separation is optimal for this application on the IONUS.
- Reliability: Measuring trace anions in various power plant waters is critical to the proper operations and matinenance oft he power plant. The instrument selected needs to perform when needed without issue. The IONUS is the proven performer as it automatically rinses and equilibrates itself prior to the first injection, assuring the analysis is reliable from the start.
- Easy to Use: The IONUS will be installed by a qualified engineer. Once operational, the analysis will be as simple as Filter, Dilute, Load, and Go. Many labs are manned by technicians, not degreed chemists. Therefore, the more simple and reliable the operation, the faster qualified data can be produced. It really is just that simple.
- ROI: Yes, companies want an instrument that delivers optimal return on their investment, and the IONUS is the choice Ion Chromatograph to deliver, not just the best result, but the best ROI! The German-made, German-produced IONUS will be working and producing quality data long after others are being replaced.
Appendix
Table 1: Results of the different samples (all results are reported in ppb)
| Cl | NO2 | Br | NO3 | PO4 | SO4 | Na | NH4 | K | |
| 01 | 51 | nd | 4 | nd | 10 | 12 | 22 | 842 | nd |
| 02 | 5 | nd | 2 | Nd | nd | 3 | 13 | 657 | nd |
| 03 | 723 | nd | 3 | 3 | nd | 86 | 309 | 826 | 14 |
| 04 | 12 | nd | 5 | 3 | nd | 8 | 8 | 1244 | nd |
| 05 | 5 | nd | 3 | 3 | 25 | nd | 12 | 785 | nd |
| 06 | 1085 | nd | 3 | 3 | nd | 123 | 444 | 908 | 20 |
| 07 | 5517 | nd | nd | 14 | nd | 543 | 2280 | 64 | 260 |
| 08 | 7 | nd | nd | nd | nd | nd | 16 | 1 | 2 |
| 09 | 5184 | nd | 3 | 12 | nd | 434 | 2073 | 138 | 167 |
| QC | 103 | 104 | 93 | 103 | 197 | 201 | 90 | 184 | 95 |
| QC Value | 103 | 102 | 102 | 102 | 202 | 209 | 96 | 188 | 95 |
Notes: nd = Non-Detect
Chromatograms: Anions
Chromatograms: Cations
Below are representative chromatograms for the cations analyzed. We were only interested in the Sodium, Ammonium, and Potassium. We detected a late eluting peak, but did not attempt to identify or quantitate it.
