Prosoft/Automation
Prosoft/Automation
General5 Min Read · Published 2026-09-15

SWAS Panel for HRSG Applications

P

Prosoft Engineering

Technical Compliance Specialist

"A Heat Recovery Steam Generator (HRSG) recovers heat from hot exhaust gases, typically from a gas turbine, and uses this heat to generate steam. Depending on the design, an HRSG may contain economizers, evaporators, steam drums, superheaters, reheaters and multiple pressure levels."
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Introduction

A SWAS Panel for HRSG Applications is an important part of steam and water chemistry monitoring in combined cycle power plants, cogeneration facilities and industrial plants using Heat Recovery Steam Generators.

A Heat Recovery Steam Generator (HRSG) recovers heat from hot exhaust gases, typically from a gas turbine, and uses this heat to generate steam. Depending on the design, an HRSG may contain economizers, evaporators, steam drums, superheaters, reheaters and multiple pressure levels.

Because these components operate under demanding temperature and pressure conditions, maintaining appropriate water and steam chemistry is essential for protecting the HRSG and downstream steam turbine.

A properly engineered SWAS Panel (Steam and Water Analysis System) extracts representative samples from selected HRSG locations, conditions them to suitable analyzer inlet conditions and continuously monitors critical parameters such as conductivity, cation conductivity, pH, dissolved oxygen, silica and sodium.

What Is an HRSG?

An HRSG, or Heat Recovery Steam Generator, is a heat-recovery boiler used to convert waste heat into useful steam.

In a combined cycle power plant, the typical process is:

Gas Turbine → Hot Exhaust Gas → HRSG → Steam Generation → Steam Turbine → Condenser → Feedwater → HRSG

The HRSG may contain several heat-transfer sections, including:

  • Economizer

  • Evaporator

  • Steam drum

  • Superheater

  • Reheater

  • High-pressure section

  • Intermediate-pressure section

  • Low-pressure section

The actual configuration varies between plants.

Because different sections operate at different pressures and temperatures, sample points and SWAS requirements must be established from the specific HRSG design.

Why Is a SWAS Panel Important for HRSG Applications?

HRSG water-steam chemistry directly influences equipment reliability and operational performance.

Chemistry deviations can contribute to:

  • Corrosion

  • Deposits

  • Scaling

  • Heat-transfer deterioration

  • Tube damage

  • Steam contamination

  • Turbine deposits

  • Reduced equipment life

  • Increased maintenance

  • Unplanned outages

A SWAS Panel provides continuous information about selected chemistry parameters, allowing operators and chemistry personnel to identify abnormal trends more quickly.

Online measurement is particularly valuable because some contamination events can develop faster than periodic laboratory sampling can detect them.

Typical HRSG SWAS Monitoring Points

The actual sampling locations depend on HRSG design, pressure levels, cycle chemistry and the plant's monitoring philosophy.

Common locations can include:

Condensate

Condensate monitoring may help identify contamination entering the steam-water cycle.

Possible parameters include:

  • Conductivity

  • Cation conductivity

  • pH

  • Dissolved oxygen

  • Sodium

Feedwater

Feedwater chemistry is important for controlling corrosion and maintaining cycle chemistry.

Typical measurements may include:

  • pH

  • Conductivity

  • Cation conductivity

  • Dissolved oxygen

HP Drum Water

Where applicable, high-pressure drum-water monitoring can include:

  • Conductivity

  • pH

  • Silica

  • Phosphate where applicable

Main Steam

Steam purity is important for downstream steam-turbine protection.

Possible measurements include:

  • Silica

  • Sodium

  • Conductivity

  • Cation conductivity

Reheat Steam

Depending on the plant's chemistry-monitoring philosophy, selected reheat-steam streams may also be monitored.

Make-Up Water

Make-up water quality may be monitored using:

  • Conductivity

  • pH

  • Silica

  • Sodium

Key Parameters Measured in HRSG SWAS

ParameterTypical HRSG ApplicationpHFeedwater and condensate chemistryConductivityGeneral ionic contamination monitoringCation ConductivityDetection of ionic contaminationDissolved OxygenCorrosion-control monitoringSilicaSteam-purity and deposit-risk monitoringSodiumContamination and steam-purity monitoringPhosphateDrum-water chemistry where applicableTemperatureSample-conditioning monitoringPressureSample-system monitoringFlowSample-system performance

Not every HRSG requires all of these parameters. The final analyzer selection should be based on the HRSG chemistry program, plant design and equipment/OEM requirements.

SWAS Sample Extraction from an HRSG

The SWAS system starts at the sample extraction point.

HRSG water and steam samples can be at elevated temperature and pressure. They therefore require a carefully designed extraction and conditioning system.

A typical sample path is:

HRSG Sample Point → Isolation Valve → Pressure Reduction → Sample Cooler → Temperature Measurement → Filtration → Flow Control → Analyzer → Drain

The sample system should provide:

  • Representative sampling

  • Safe isolation

  • Pressure reduction

  • Controlled cooling

  • Stable flow

  • Appropriate sample transport

  • Minimal contamination

  • Reliable drainage

A highly accurate analyzer cannot compensate for an improperly extracted or conditioned sample.

Pressure Reduction for HRSG Samples

HRSG sample points can operate at pressures significantly higher than the acceptable inlet conditions of online analyzers.

Pressure reduction is therefore a key SWAS design function.

Possible components include:

  • Pressure-reducing valves

  • Pressure regulators

  • Restrictors

  • Needle valves

  • Back-pressure regulators

The pressure-control system should be selected based on:

  • Process pressure

  • Process temperature

  • Sample flow

  • Analyzer inlet requirements

  • Sample chemistry

  • Required pressure stability

Improper pressure reduction may cause flashing, unstable flow, dissolved-gas loss and unreliable measurements.

Sample Cooling in HRSG SWAS

HRSG samples may be significantly hotter than the allowable operating temperature of online analyzers.

A sample cooler is therefore commonly installed to transfer heat from the process sample to cooling water or another suitable cooling medium.

Important design considerations include:

  • Maximum sample temperature

  • Sample pressure

  • Sample flow

  • Cooling-water temperature

  • Cooling-water flow

  • Required analyzer inlet temperature

  • Cooler material

  • Fouling conditions

  • Heat-transfer capacity

A basic heat-transfer relationship is:

Q = m × Cp × ΔT

Actual cooler sizing should be calculated from the specific process conditions and equipment requirements.

For SWAS Panel India installations, seasonal cooling-water conditions should also be considered during engineering.

Sample Flow Control

Stable sample flow is essential for reliable online analysis.

A typical HRSG SWAS system may include:

  • Flowmeter

  • Rotameter

  • Flow-control valve

  • Needle valve

  • Flow switch

  • Low-flow alarm

The correct flow depends on the analyzer manufacturer's requirements and the complete sample-conditioning arrangement.

There is no universal SWAS flow rate that applies to every HRSG analyzer.

Insufficient flow can cause:

  • Slow response

  • Sample stagnation

  • Unstable measurement

  • Excessive transport delay

  • Poor cooling performance

Excessive flow can result in:

  • Higher sample consumption

  • Increased drain load

  • Pressure instability

  • Unnecessary component loading

Online SWAS Panel for HRSG Monitoring

An Online SWAS Panel continuously measures selected steam and water chemistry parameters.

Depending on the HRSG application, the panel can integrate:

  • pH analyzer

  • Conductivity analyzer

  • Cation conductivity analyzer

  • Dissolved oxygen analyzer

  • Silica analyzer

  • Sodium analyzer

  • Phosphate analyzer

Online analysis can provide operators with:

  • Real-time measurements

  • Chemistry trends

  • High/low alarms

  • Analyzer diagnostics

  • Historical data

  • DCS/SCADA signals

The system can therefore become an important part of the plant's overall chemistry-monitoring and control strategy.

Silica Monitoring in HRSG Applications

Silica is an important parameter in steam-cycle monitoring because it can be transported with steam under certain conditions and may contribute to deposits on turbine components.

An online silica analyzer can be installed on selected steam or water sample points.

A typical silica measurement arrangement may include:

Sample → Pressure Reduction → Cooling → Flow Control → Reagent System → Silica Analyzer → Drain

Depending on the analyzer design, the system may require:

  • Chemical reagents

  • Calibration solutions

  • Controlled sample flow

  • Temperature control

  • Regular maintenance

Analyzer-specific requirements should always be followed.

Sodium Monitoring in HRSG Applications

Sodium monitoring can provide useful information about certain contamination events in the steam-water cycle.

Depending on the chemistry program, sodium analyzers may be applied to:

  • Condensate

  • Feedwater

  • Main steam

  • Selected HRSG streams

Because sodium measurements can be sensitive to contamination, sample-system cleanliness is important.

Tubing, valves, fittings and other wetted components should be selected and maintained to minimize unintended contamination.

Dissolved Oxygen Monitoring

Dissolved oxygen monitoring can support corrosion-control programs in condensate and feedwater systems.

The sample system should minimize exposure to atmospheric oxygen.

Important considerations include:

  • Leak-free sample lines

  • Stable flow

  • Proper pressure

  • Appropriate temperature

  • Correct sensor installation

  • Proper calibration

Air bubbles or air ingress can produce misleading dissolved oxygen readings.

Conductivity and Cation Conductivity Monitoring

Conductivity provides an indication of ionic contamination in the water-steam cycle.

Cation conductivity can provide additional information about ionic impurities after the sample passes through an appropriate cation exchange arrangement.

These measurements may be used at selected HRSG locations such as:

  • Condensate

  • Feedwater

  • Steam

  • Other critical cycle streams

Stable temperature, flow and sensor condition are important for reliable results.

pH Monitoring in HRSG Systems

pH measurement can support control of feedwater and condensate chemistry.

Reliable pH measurement requires:

  • Suitable sample temperature

  • Stable flow

  • Proper sensor installation

  • Clean electrode

  • Correct calibration

  • Appropriate reference system

Because pH measurement can be sensitive to sample conditions, the complete sample system must be considered during SWAS design.

Phosphate Monitoring

Phosphate monitoring may be applicable where phosphate-based boiler-water treatment is used.

An online phosphate analyzer can provide continuous information about phosphate concentration in selected HRSG drum-water streams.

The system may include:

  • Sample conditioning

  • Reagent dosing

  • Chemical reaction

  • Optical measurement

  • Calibration

  • Drainage

The requirement for phosphate monitoring should be determined from the actual HRSG chemistry program rather than assuming that every HRSG uses phosphate treatment.

Dedicated vs Multiplexed HRSG SWAS

There are two common approaches to multi-point SWAS design.

Dedicated Analyzers

Each critical sample point has a dedicated analyzer.

Advantages

  • Continuous monitoring

  • Fast response

  • No switching delay

  • Reduced cross-contamination risk

  • Simple data interpretation

Limitations

  • Higher initial investment

  • More instruments

  • Larger panel

  • Increased maintenance requirements

Multiplexed Analysis

One analyzer can sequentially measure multiple sample streams.

Advantages

  • Fewer analyzers

  • Reduced initial cost

  • Compact system

  • Useful for selected non-critical measurements

Considerations

  • Valve sequencing

  • Sample switching time

  • Flushing

  • Cross-contamination

  • Transport delay

  • PLC programming

  • Analyzer stabilization time

Critical HRSG parameters should be evaluated carefully before choosing multiplexed measurement.

Sample Transport Time

The distance between the HRSG sample point and the SWAS Panel can affect measurement response.

A simplified relationship is:

Transport Time = Sample-Line Volume ÷ Sample Flow Rate

Long sample lines and low flow can significantly increase response time.

During SWAS engineering, consider:

  • Sample-line length

  • Internal tubing diameter

  • Flow rate

  • Pressure

  • Sample temperature

  • Analyzer response time

This is particularly important for alarms and contamination events where rapid detection is required.

SWAS Panel PLC and HMI

A PLC/HMI system can provide centralized monitoring and control of the HRSG SWAS.

The PLC can monitor:

  • Sample flow

  • Sample temperature

  • Sample pressure

  • Cooling-water status

  • Analyzer status

  • Valve positions

  • Calibration status

  • Alarm conditions

  • Communication status

The HMI can display:

  • Real-time analyzer readings

  • Trends

  • Alarms

  • Analyzer status

  • Sample-system status

  • Maintenance information

  • Multiplexing sequence

DCS/SCADA Integration

HRSG SWAS systems can be integrated into the plant DCS or SCADA system.

Depending on project requirements, communication can be through:

  • 4–20 mA signals

  • Digital signals

  • Modbus RTU

  • Modbus TCP

  • Ethernet

  • OPC-based interfaces

  • Other approved communication protocols

Typical DCS signals include:

  • Analyzer value

  • High alarm

  • Low alarm

  • Analyzer fault

  • Sample-flow status

  • Sample-temperature alarm

  • Calibration status

  • Maintenance status

  • Communication failure

Proper signal scaling, tag mapping and alarm verification should be completed during commissioning.

SWAS Alarm Configuration for HRSG

A well-designed SWAS system should monitor both chemistry and equipment conditions.

Chemistry alarms

  • High conductivity

  • High cation conductivity

  • High silica

  • High sodium

  • High dissolved oxygen

  • High/low pH

  • High phosphate where applicable

Sample-system alarms

  • Low sample flow

  • High sample temperature

  • High sample pressure

  • Cooling-water failure

  • Filter blockage

Analyzer alarms

  • Sensor failure

  • Calibration failure

  • Reagent low

  • Analyzer fault

  • Communication failure

Alarm setpoints should be established according to the plant chemistry program, operating philosophy and applicable equipment requirements.

SWAS Panel Maintenance for HRSG Applications

SWAS Panel Maintenance should address the entire system, not only the online analyzers.

Daily Inspection

Check:

  • Sample flow

  • Sample pressure

  • Sample temperature

  • Leakage

  • Analyzer status

  • Alarms

  • Drainage

Weekly Inspection

Inspect:

  • Sample tubing

  • Valves

  • Flowmeters

  • Filters

  • Cooler

  • Electrical connections

  • Analyzer condition

Periodic Maintenance

Depending on the system:

  • Clean filters

  • Inspect sample lines

  • Clean sensors

  • Verify calibration

  • Check flow-control devices

  • Inspect reagent systems

  • Verify alarm operation

  • Review analyzer trends

Planned Annual Maintenance

Depending on manufacturer recommendations:

  • Sensor replacement

  • Analyzer servicing

  • Reagent-system servicing

  • Valve maintenance

  • Cooler inspection

  • Tubing replacement

  • PLC/HMI backup

  • DCS communication testing

  • Critical-spares review

Maintenance intervals should be based on manufacturer recommendations, operating hours and actual sample conditions.

Common HRSG SWAS Problems

1. Low Sample Flow

Possible causes:

  • Blocked filter

  • Blocked sample tubing

  • Valve partially closed

  • Pressure regulator problem

  • Flow-control problem

2. High Sample Temperature

Possible causes:

  • Insufficient cooling-water flow

  • Cooler fouling

  • High cooling-water temperature

  • Incorrect sample flow

  • Inadequate cooler capacity

3. Unstable Readings

Possible causes:

  • Air bubbles

  • Variable sample flow

  • Sensor fouling

  • Poor calibration

  • Sample contamination

  • Electrical interference

4. High Conductivity

Possible causes may include:

  • Cycle contamination

  • Condenser leakage

  • Chemical contamination

  • Sample-system contamination

5. High Silica or Sodium

Possible causes may include:

  • Make-up water contamination

  • Condenser leakage

  • Water-treatment problems

  • Steam carryover

  • Other cycle contamination

The actual process cause should be confirmed using supporting chemistry measurements and plant operating information.

HRSG SWAS Troubleshooting Sequence

A structured troubleshooting approach can prevent unnecessary analyzer replacement.

Use the following sequence:

Process → Sample → Conditioning → Sensor → Analyzer → Signal → DCS/SCADA

For example, if a silica analyzer shows an unexpected increase, engineers should first verify whether the process chemistry has actually changed. They should then check sample flow, pressure, temperature, sample cleanliness, analyzer condition and finally the transmitted signal.

Material of Construction

Material selection for an HRSG SWAS Panel should consider:

  • Sample chemistry

  • Temperature

  • Pressure

  • Corrosion resistance

  • Cleanliness

  • Mechanical requirements

  • Analyzer requirements

Potential materials include:

  • SS 316/316L

  • SS 304/304L

  • PTFE

  • PFA

  • PVDF

  • PVC

  • Polypropylene

Different materials may be appropriate for different components.

SWAS Panel Design Considerations for India

For SWAS Panel India projects, site-specific environmental conditions should be considered.

Important factors include:

  • High summer ambient temperature

  • Cooling-water temperature

  • Humidity

  • Dust

  • Electrical supply

  • Instrument-air availability

  • Cooling-water quality

  • Drainage

  • Sample-line length

  • Maintenance accessibility

  • Spare-parts availability

  • Indoor/outdoor installation

  • Area classification

The system should be engineered around actual site conditions and not simply based on a generic standard panel.

HRSG SWAS Commissioning

Before commissioning, engineers should verify the following.

Mechanical

  • Correct sample connections

  • Correct valve orientation

  • No leakage

  • Correct MOC

  • Proper drainage

Sample Conditioning

  • Correct pressure

  • Correct temperature

  • Stable flow

  • Adequate cooling

  • No flashing

  • No air ingress

Analyzers

  • Correct installation

  • Calibration

  • Configuration

  • Stable measurement

  • Alarm verification

Automation

  • PLC I/O

  • HMI

  • Power supply

  • Earthing

  • Communication

DCS/SCADA

  • Tag mapping

  • Signal scaling

  • Alarm status

  • Communication

  • Trend verification

A commissioning report should record initial readings, sample conditions and analyzer status.

How to Select a SWAS Panel for HRSG Applications

Before specifying a system, collect:

HRSG Information

  • HRSG manufacturer

  • HRSG configuration

  • Number of pressure levels

  • Sample points

  • Operating pressure

  • Operating temperature

  • Steam conditions

Sample Information

  • Sample chemistry

  • Sample flow

  • Sample-line distance

  • Cooling-water conditions

  • Drainage arrangement

Analytical Requirements

  • Parameters

  • Measuring ranges

  • Required accuracy

  • Response requirements

  • Analyzer technology

Automation Requirements

  • PLC

  • HMI

  • DCS

  • SCADA

  • Communication protocols

  • Alarm philosophy

  • Data logging

Mechanical Requirements

  • Panel/enclosure type

  • MOC

  • Indoor/outdoor installation

  • Environmental conditions

  • Area classification

Benefits of an Online SWAS Panel for HRSG

A properly designed Online SWAS Panel can provide:

  • Continuous HRSG chemistry monitoring

  • Early contamination detection

  • Improved cycle chemistry control

  • Better protection of HRSG components

  • Improved steam-purity monitoring

  • Turbine protection

  • Corrosion-risk monitoring

  • Scaling-risk monitoring

  • Faster response to abnormal conditions

  • Historical trend analysis

  • DCS/SCADA integration

  • Improved maintenance planning

Why Choose Prosoft Automation for HRSG SWAS Solutions?

Prosoft Automation can develop application-oriented SWAS Panel solutions for:

  • Combined cycle power plants

  • HRSG systems

  • Cogeneration plants

  • Industrial steam systems

  • Captive power plants

  • Process industries with waste-heat boilers

A typical solution can incorporate:

  • Sample extraction

  • Pressure reduction

  • Sample cooling

  • Flow control

  • Filtration

  • pH analysis

  • Conductivity analysis

  • Cation conductivity

  • Dissolved oxygen

  • Silica

  • Sodium

  • Phosphate where required

  • PLC/HMI

  • DCS/SCADA integration

  • Alarm monitoring

  • Data logging

Each system should be engineered according to actual HRSG process conditions, chemistry requirements and customer specifications.

HRSG SWAS Panel Selection Checklist

Before ordering a SWAS Panel, confirm:

  • HRSG configuration

  • Number of pressure levels

  • Number of sample points

  • Sample pressure

  • Sample temperature

  • Sample flow

  • Sample chemistry

  • Required analytical parameters

  • Analyzer measuring ranges

  • Pressure-reduction arrangement

  • Sample cooler requirements

  • Cooling-water availability

  • Flow-control arrangement

  • Filtration

  • Material of construction

  • Dedicated or multiplexed system

  • PLC/HMI

  • DCS/SCADA interface

  • Alarm requirements

  • Data logging

  • Calibration arrangement

  • Drainage

  • Spare parts

  • Maintenance access

  • Environmental conditions

  • Area classification

Frequently Asked Questions

What is a SWAS Panel used for in an HRSG?

A SWAS Panel safely extracts and conditions water and steam samples from an HRSG and continuously measures selected chemistry parameters.

Which parameters are commonly monitored?

Common parameters include pH, conductivity, cation conductivity, dissolved oxygen, silica and sodium. Phosphate may also be monitored where applicable.

Why is sample conditioning important?

HRSG samples can be at high temperature and pressure. Pressure reduction, cooling and flow control are necessary to deliver a suitable sample to the analyzer.

Is an Online SWAS Panel necessary for every HRSG?

The exact requirement depends on the plant's chemistry program, HRSG design, monitoring philosophy and project specifications.

Why is silica monitored in HRSG systems?

Silica monitoring can support steam-purity control because silica can be transported with steam under certain conditions and may contribute to deposits on turbine components.

Why is sodium monitored?

Sodium can be a useful indicator of certain contamination events and may be monitored in selected condensate, feedwater or steam streams.

Can one analyzer monitor several HRSG sample points?

Yes. Multiplexed SWAS systems can sequentially connect an analyzer to multiple sample streams. However, switching time, flushing, cross-contamination and response time must be considered.

How often should SWAS Panel Maintenance be performed?

Maintenance frequency depends on analyzer technology, sample quality, operating conditions and manufacturer recommendations. Regular inspections should be combined with planned preventive maintenance.

Can an HRSG SWAS Panel be connected to DCS?

Yes. A SWAS system can be designed to communicate with the plant DCS or SCADA through suitable analog, digital or communication interfaces.

Can Prosoft Automation supply HRSG SWAS systems in India?

Yes. Prosoft Automation can provide application-oriented SWAS Panel India solutions for HRSG and combined cycle applications based on actual process and analytical requirements.

Conclusion

A SWAS Panel for HRSG Applications provides continuous monitoring of critical steam and water chemistry parameters and supports reliable operation of HRSGs and downstream steam-cycle equipment.

The effectiveness of the system depends on proper sample extraction, pressure reduction, cooling, flow control, filtration, analyzer selection, calibration and automation. Sample-system design is just as important as analyzer accuracy.

Regular SWAS Panel Maintenance should cover the complete sample-conditioning system as well as the analytical instruments.

A correctly engineered Online SWAS Panel can help plant operators identify contamination, chemistry deviations and abnormal operating conditions at an early stage, supporting improved reliability and equipment protection.

Need Help Selecting an HRSG SWAS Panel?

Every HRSG has different sample conditions, pressure levels, temperature ranges and chemistry-monitoring requirements.

Talk to our application specialist to discuss your HRSG sample points, required parameters and SWAS configuration.

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