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Introduction

Hydrazine monitoring has traditionally been associated with boiler and feedwater chemistry control in steam-generation and power-plant applications. Where hydrazine is used as an oxygen scavenger, monitoring its residual concentration can help operators maintain the desired chemical-treatment conditions and identify changes in feedwater chemistry.

An online hydrazine analyzer integrated into a properly engineered SWAS Panel provides continuous measurement without relying solely on periodic laboratory sampling.

However, reliable hydrazine measurement depends on more than the analyzer itself. Sample extraction, pressure reduction, cooling, flow control, sample-line materials, chemical conditioning, calibration, and maintenance all influence measurement performance.

This article explains the role of hydrazine monitoring in SWAS systems and the key considerations for integrating an online hydrazine analyzer into an Online SWAS Panel.

What Is Hydrazine Monitoring?

Hydrazine is a chemical that has been used in some boiler-water treatment programs primarily as an oxygen scavenger.

The objective of oxygen scavenging is to reduce dissolved oxygen and help limit corrosion in parts of the feedwater and steam-water cycle.

Where hydrazine treatment is used, monitoring can help determine whether the chemical-treatment system is operating within its intended range.

Typical monitoring locations may include:

• Feedwater

• Economizer inlet

• Boiler feedwater systems

• Deaerator-related streams

• Condensate systems

• Other chemistry-control points specified by the plant

The appropriate monitoring point depends on the plant chemistry program and operating conditions.

Why Monitor Hydrazine?

Hydrazine concentration can change due to:

• Chemical dosing variations

• Dissolved oxygen changes

• Feedwater chemistry changes

• Deaerator performance

• Chemical-treatment-system problems

• Process operating changes

Continuous measurement can provide faster information about these changes than periodic manual testing.

Hydrazine monitoring may therefore help operators:

• Verify chemical dosing

• Detect treatment deviations

• Monitor trends

• Support feedwater chemistry control

• Reduce dependence on manual sampling

The required hydrazine concentration should always be established according to the plant's chemistry program and applicable operating procedures.

Important Safety Consideration

Hydrazine is a hazardous chemical. It is toxic and requires appropriate controls for handling, storage, sampling, and waste management.

Therefore, a hydrazine monitoring system should be designed with appropriate:

• Chemical-handling procedures

• Personal protective equipment

• Sample containment

• Ventilation

• Waste handling

• Leak protection

• Safety procedures

The analyzer and SWAS system should be installed and operated according to applicable plant safety requirements and the chemical supplier's safety documentation.

Role of the SWAS Panel in Hydrazine Measurement

The SWAS Panel provides controlled sample conditions between the process stream and the online analyzer.

A simplified sample path may be:

Feedwater Sample → Isolation Valve → Pressure Reduction → Cooling → Flow Control → Hydrazine Analyzer → Drain

Depending on the application, the system may also include:

• Pressure gauges

• Temperature indicators

• Filters

• Sample flow indicators

• Calibration arrangements

• Chemical conditioning

• Sample distribution manifolds

• Drain and waste handling

The purpose of the SWAS system is to provide a representative and stable sample to the analyzer.

1. Select the Correct Sample Point

Sample-point selection is critical for hydrazine monitoring.

The sample should represent the process stream where hydrazine concentration is relevant to the plant's chemistry-control strategy.

Possible sample locations can include:

• Feedwater

• Deaerated feedwater

• Economizer inlet

• Condensate

• Other feedwater-related monitoring points

Before selecting a sample point, evaluate:

• Sample pressure

• Sample temperature

• Expected hydrazine concentration

• Dissolved oxygen concentration

• Sample flow

• Sample chemistry

• Distance from the panel

• Safety and accessibility

The plant's chemistry specialist should define the appropriate monitoring point.

2. Sample Pressure Reduction

Feedwater samples can be available at elevated pressure.

A pressure-reduction arrangement may therefore be required before the sample reaches the analyzer.

Typical components include:

• Isolation valve

• Pressure-reducing valve

• Needle valve

• Pressure gauge

• Back-pressure regulator where required

Pressure reduction should be controlled carefully to avoid:

• Flashing

• Bubble formation

• Flow instability

• Excessive pressure drop

• Changes in sample condition

The final sample pressure should remain within the analyzer manufacturer's specified range.

3. Sample Cooling

Hydrazine analyzer systems may require the process sample to be cooled before measurement.

A sample cooler should be selected according to:

• Maximum sample temperature

• Normal operating temperature

• Sample pressure

• Sample flow

• Cooling-water temperature

• Analyzer inlet-temperature requirement

The cooler should provide adequate performance during the plant's maximum operating conditions.

During commissioning, operators should verify the actual sample temperature at the analyzer inlet.

4. Maintain Stable Sample Flow

Stable sample flow is essential for reliable online measurement.

A typical sample-conditioning arrangement may include:

Sample Cooler → Flow-Control Valve → Flow Indicator → Hydrazine Analyzer

The analyzer manufacturer's specified flow range should be followed.

Low flow can result in:

• Slow response

• Poor sample replacement

• Measurement instability

Excessive flow can increase:

• Sample consumption

• Drain load

• Pressure fluctuations

A controlled and repeatable sample flow is therefore preferred.

5. Minimize Sample Transport Time

Hydrazine chemistry can be sensitive to sample conditions and residence time.

For this reason, the sample line between the extraction point and analyzer should generally be as short as practical.

Long sample lines can result in:

• Delayed response

• Chemical changes

• Increased residence time

• Greater contamination risk

• Difficulty maintaining sample conditions

The sample system should be engineered to minimize unnecessary dead volume.

6. Sample-Line Material Selection

Material selection is important in low-level water chemistry measurement.

Depending on the application, sample tubing may use materials such as:

• Stainless steel

• PTFE

• PFA

• Other compatible materials

The selection should be based on:

• Sample chemistry

• Temperature

• Pressure

• Analyzer requirements

• Plant standards

The objective is to minimize contamination, chemical interaction, and adsorption effects.

7. Hydrazine Analyzer Measurement Principle

The measurement principle depends on the analyzer technology.

Online hydrazine analyzers may use chemical, electrochemical, optical, or other analytical approaches depending on the manufacturer and model.

A typical analyzer system may:

1. Receive a conditioned sample.

2. Prepare or condition the sample.

3. Measure the hydrazine concentration.

4. Apply calibration data.

5. Display and transmit the concentration.

Before selecting an analyzer, the exact measurement principle and sample requirements should be reviewed carefully.

8. Chemical Conditioning

Some hydrazine measurement technologies may require chemical conditioning or reagents.

Where required, the system should provide:

• Reagent storage

• Reagent dosing

• Reagent tubing

• Controlled reaction conditions

• Reagent-level monitoring

• Waste handling

The chemical-conditioning system should be designed as an integral part of the analyzer installation rather than added as an afterthought.

9. Calibration of the Hydrazine Analyzer

Calibration is essential for maintaining reliable hydrazine measurement.

Depending on the analyzer, calibration may include:

• Zero calibration

• Single-point calibration

• Multi-point calibration

• Standard-solution verification

Calibration standards should be prepared and handled according to the analyzer manufacturer's recommendations.

Particular attention should be given to:

• Standard concentration

• Standard preparation

• Storage

• Expiry

• Contamination

• Calibration frequency

Calibration records should form part of the plant's analyzer maintenance documentation.

10. Interference and Sample Chemistry

Hydrazine measurement can be affected by the chemistry of the sample and the selected measurement technology.

Potential factors may include:

• Dissolved oxygen

• Oxidizing chemicals

• Temperature

• pH

• Other chemical species

• Sample residence time

The analyzer should therefore be selected based on the actual water chemistry rather than solely on the required measurement range.

Where necessary, the application should be reviewed by an analytical specialist before finalizing the SWAS configuration.

11. Drainage and Waste Handling

The SWAS Panel should provide a safe drainage arrangement.

If chemical reagents are used, the waste stream may contain sample and chemical residues.

The drainage system should prevent:

• Back pressure

• Flooding

• Cross-contamination

• Uncontrolled chemical discharge

Waste should be handled according to plant environmental, safety, and chemical-waste procedures.

12. DCS and SCADA Integration

A modern Online SWAS Panel can integrate the hydrazine analyzer with the plant automation system.

Depending on the analyzer, interfaces can include:

• 4–20 mA

• Digital outputs

• RS-485

• Modbus

• Ethernet

• Other industrial communication protocols

Typical signals include:

• Hydrazine concentration

• High hydrazine alarm

• Low hydrazine alarm

• Analyzer fault

• Calibration status

• Maintenance status

• Communication status

During commissioning, the complete signal path should be tested from the analyzer to the DCS, PLC, SCADA, or historian.

13. Alarm Configuration

Hydrazine alarm limits should be established by the plant's chemistry team.

Possible alarm functions include:

• High hydrazine

• Low hydrazine

• Analyzer fault

• Calibration failure

• Low sample flow

• Reagent low

• Communication failure

Alarm limits should be based on the specific treatment program, sample location, boiler chemistry, and plant operating procedures.

14. Multi-Parameter SWAS Integration

Hydrazine monitoring may be integrated with other feedwater and steam-cycle measurements.

A multi-parameter SWAS Panel India system could include:

ParameterMonitoring PurposeHydrazineOxygen-scavenger residual monitoring where applicableDissolved oxygenOxygen controlpHFeedwater chemistryConductivityGeneral water chemistryCation conductivityContamination monitoringSilicaSteam/water puritySodiumIonic contamination

The system should be designed so that each analyzer receives the sample conditions appropriate for its measurement technology.

15. Commissioning a Hydrazine Analyzer

A systematic commissioning procedure is recommended.

Step 1 – Mechanical inspection

Check:

• Sample tubing

• Valves

• Pressure-reduction devices

• Cooler

• Flow-control devices

• Analyzer connections

• Drain system

Step 2 – Leak testing

Check all sample and utility connections.

Step 3 – Flush the sample system

Flush the sample line according to the analyzer and SWAS commissioning procedure.

Step 4 – Establish sample conditions

Verify:

• Pressure

• Temperature

• Flow

Step 5 – Start the analyzer

Follow the manufacturer's startup instructions.

Step 6 – Check reagents or conditioning chemicals

Verify correct installation and suitability.

Step 7 – Calibrate

Perform the recommended calibration procedure.

Step 8 – Allow stabilization

Allow sufficient time for the analyzer and sample system to stabilize.

Step 9 – Test outputs

Verify:

• Analog output

• Digital signals

• Alarms

• Communication

Step 10 – Validate the result

Where appropriate, compare the online measurement against an independent laboratory or reference measurement.

SWAS Panel Maintenance for Hydrazine Monitoring

Regular SWAS Panel Maintenance should cover both the sample-conditioning equipment and analyzer.

Sample-system maintenance

Inspect:

• Sample flow

• Sample pressure

• Sample temperature

• Sample tubing

• Valves

• Cooler

• Filters

• Drainage

• Leaks

Analyzer maintenance

Check:

• Calibration

• Sensor or measurement cell

• Reagents

• Reagent tubing

• Pumps

• Optical/electrochemical components where applicable

• Diagnostic alarms

Safety maintenance

Because hydrazine is hazardous, also inspect:

• Chemical connections

• Reagent containers

• Waste lines

• Leak protection

• Ventilation

• Chemical labels

• Safety equipment

Maintenance personnel should follow the site's approved chemical-handling procedures.

Common Hydrazine Analyzer Problems

Unstable readings

Potential causes include:

• Variable sample flow

• Temperature fluctuations

• Air bubbles

• Sample contamination

• Analyzer calibration problems

• Chemical-conditioning problems

Unexpectedly high hydrazine reading

Possible causes include:

• Actual increase in chemical dosing

• Process chemistry change

• Calibration error

• Sample contamination

• Analyzer malfunction

The online measurement should be reviewed against process conditions and, where appropriate, a reference measurement.

Low or zero reading

Possible causes include:

• No sample flow

• Blocked sample line

• Low hydrazine concentration

• Calibration issue

• Analyzer fault

• Reagent/conditioning problem

Slow response

Potential causes include:

• Long sample line

• Low sample flow

• Excessive sample volume

• Sample-conditioning problems

• Analyzer stabilization time

Best Practices for Hydrazine Monitoring

1. Select a representative sample point

The monitoring location should be relevant to the plant's chemistry-control strategy.

2. Keep the sample path short

Minimize transport time and dead volume.

3. Control temperature

Use a properly sized sample cooler where required.

4. Maintain stable flow

Follow the analyzer's specified sample-flow requirements.

5. Minimize contamination

Use appropriate sample-line materials and clean installation practices.

6. Maintain calibration discipline

Use suitable standards and maintain calibration records.

7. Integrate safety into the design

Hydrazine handling requires appropriate containment, waste management, and personnel protection.

8. Maintain the complete SWAS system

Troubleshooting should consider the sample-conditioning system as well as the analyzer.

Selecting a Hydrazine Analyzer for a SWAS Panel

Before selecting an analyzer, evaluate:

Selection ParameterImportanceMeasurement rangeHighDetection capabilityHighSample temperatureHighSample pressureHighSample flowHighMeasurement response timeMedium/HighMeasurement principleHighReagent requirementsMedium/HighCalibration methodHighMaintenance requirementsHighDCS/SCADA interfaceHighAlarm functionsMedium/HighSpare-parts availabilityHighLocal technical supportHighChemical safety requirementsVery HighTotal cost of ownershipHigh

For a SWAS Panel India project, availability of local technical support, spare parts, calibration assistance, and operator training should also be considered.

Hydrazine Monitoring Versus Dissolved Oxygen Monitoring

Hydrazine and dissolved oxygen provide different information about feedwater chemistry.

ParameterPrimary InformationHydrazineResidual oxygen-scavenger concentration where hydrazine treatment is usedDissolved OxygenActual dissolved oxygen concentration

Monitoring both parameters can provide a more complete picture of the effectiveness of an oxygen-control strategy where applicable.

However, the exact monitoring philosophy should be established by the plant chemistry team.

Benefits of Online Hydrazine Monitoring

An online hydrazine analyzer integrated into a SWAS system can provide:

• Continuous monitoring

• Faster detection of treatment changes

• Reduced dependence on manual sampling

• Better visibility of chemical-treatment performance

• Trend monitoring

• Integration with DCS/SCADA

• Improved process control

• Better documentation of chemistry conditions

These benefits are particularly valuable where feedwater chemistry needs close and continuous monitoring.

Hydrazine Monitoring in Modern Online SWAS Panels

A modern SWAS installation can integrate hydrazine measurement with automated sample conditioning and centralized plant monitoring.

A typical arrangement is:

Feedwater Sample

↓

Sample Isolation

↓

Pressure Reduction

↓

Sample Cooling

↓

Flow Control

↓

Hydrazine Analyzer

↓

Drain / Waste Handling

↓

DCS / SCADA / Historian

Additional analyzers can be integrated through a multi-stream sample-conditioning system.

Frequently Asked Questions

Why is hydrazine monitored in a SWAS system?

Where hydrazine is used as part of a boiler-water treatment program, monitoring its residual concentration can help operators assess chemical-treatment conditions and identify changes in the feedwater system.

Is hydrazine still used in every modern power plant?

No. Treatment chemistry varies by plant design and operating philosophy. Some facilities use alternative oxygen-control strategies. Hydrazine monitoring is therefore application-specific.

Is hydrazine hazardous?

Yes. Hydrazine requires appropriate handling, containment, personal protection, ventilation, and waste-management procedures. The applicable safety documentation and plant procedures should always be followed.

Can a hydrazine analyzer be installed on an existing SWAS Panel?

Potentially, provided the existing system can provide the required sample pressure, temperature, flow, materials compatibility, drainage, and analyzer installation conditions.

Can hydrazine and dissolved oxygen analyzers be installed together?

Yes. They can provide complementary information about oxygen-control chemistry where hydrazine treatment is used.

How often should a hydrazine analyzer be calibrated?

The appropriate calibration frequency depends on analyzer technology, operating conditions, required accuracy, and manufacturer recommendations.

What causes unstable hydrazine measurements?

Common causes include unstable sample flow, temperature changes, contamination, air bubbles, calibration problems, chemical-conditioning problems, and analyzer faults.

Conclusion

Hydrazine monitoring can provide valuable information for steam-cycle and feedwater chemistry control where hydrazine is part of the plant's treatment program.

A properly engineered SWAS Panel ensures that the online analyzer receives a representative sample under controlled pressure, temperature, and flow conditions. Sample-line design, material selection, calibration, chemical conditioning, drainage, safety, and preventive maintenance all contribute to reliable measurement.

For long-term performance, the hydrazine analyzer should be treated as part of the complete sample-conditioning and water-chemistry monitoring system rather than as an isolated instrument.

Prosoft Automation can support customers with engineered SWAS Panel solutions, online water chemistry analyzers, sample-conditioning systems, multi-parameter SWAS systems, analyzer integration, commissioning, and SWAS Panel Maintenance support.

Download our product catalogue to review Prosoft Automation's SWAS and online water-analysis solutions and discuss the appropriate configuration for your application.