Feedwater Monitoring via SWAS
Prosoft Engineering
Technical Compliance Specialist
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Primary Keyword: SWAS Panel
Secondary Keywords: SWAS Panel Maintenance, Online SWAS Panel, SWAS Panel India
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Introduction
Feedwater is one of the most important streams in a boiler and steam-water cycle. It carries treated water back toward the boiler or steam-generating equipment, making its chemical quality critical for controlling corrosion, deposition and contamination.
Feedwater chemistry can be affected by condensate contamination, make-up water quality, chemical dosing, deaerator performance, corrosion products and other process conditions. If contaminants enter the boiler through the feedwater system, they can become concentrated or transported through the steam-water cycle.
A properly engineered SWAS Panel (Steam and Water Analysis System) enables continuous monitoring of important feedwater chemistry parameters.
An Online SWAS Panel can integrate measurements such as conductivity, cation conductivity, pH, dissolved oxygen, sodium, silica and other parameters according to the plant's chemistry-control requirements.
For power plants, HRSG systems, captive power plants, cogeneration facilities and industrial boilers, reliable feedwater monitoring provides an important layer of protection for the complete steam-water cycle.
What Is Feedwater?
Feedwater is water supplied to a boiler, HRSG or steam-generating system for conversion into steam.
Depending on the plant configuration, feedwater may originate from:
Condensate
Condensate polishing systems
Demineralized water
Make-up water
Deaerator outlet
Feedwater treatment systems
Before entering the boiler, feedwater is normally treated and conditioned to control dissolved gases, ionic impurities and other contaminants.
The exact treatment and chemistry-control approach depends on:
Boiler design
Operating pressure
Materials
Cycle configuration
Water-treatment system
Chemistry program
OEM requirements
Why Is Feedwater Monitoring Important?
Feedwater is continuously introduced into the steam-generating system.
Therefore, poor feedwater quality can influence the entire cycle.
Potential consequences of inadequate feedwater chemistry include:
Corrosion
Deposition
Scaling
Boiler-tube damage
Steam contamination
Turbine deposition
Reduced heat-transfer efficiency
Increased chemical consumption
Reduced equipment reliability
Continuous monitoring helps operators identify changes early.
Role of a SWAS Panel in Feedwater Monitoring
A SWAS Panel provides the controlled sample-conditioning and analytical arrangement required to measure feedwater.
A typical sample path may be:
Feedwater Sample Point → Isolation Valve → Pressure Control → Sample Cooler → Temperature Measurement → Filtration → Flow Control → Analyzer → Drain/Return
Depending on the application, the system can include multiple analyzers.
The SWAS design should consider:
Feedwater pressure
Feedwater temperature
Sample flow
Required analytical parameters
Sample-line length
Cooling-water availability
Analyzer requirements
Plant chemistry philosophy
Typical Feedwater Sampling Points
Feedwater systems contain several potential monitoring locations.
1. Deaerator Outlet
Monitoring downstream of the deaerator can provide information about the chemistry of water entering the feedwater system.
Dissolved oxygen monitoring can be particularly relevant where required by the plant chemistry program.
2. Feedwater Pump Discharge
The feedwater pump discharge may provide a useful location for monitoring water quality before the water reaches the boiler or HRSG.
3. Economizer Inlet
In some applications, monitoring near the economizer inlet can provide information about the chemistry entering the boiler heat-recovery section.
4. Boiler Feedwater
A dedicated boiler feedwater sample point can be incorporated into the SWAS system according to the plant's chemistry-monitoring philosophy.
5. HRSG Feedwater
Combined-cycle plants may monitor feedwater associated with the HP, IP or LP circuits.
The actual sampling location should be selected based on the plant P&ID, representative sampling requirements and analyzer specifications.
Feedwater Parameters Commonly Monitored
The exact parameters depend on the plant design and chemistry program.
Typical measurements may include:
ParameterTypical PurposeConductivityGeneral ionic contamination monitoringCation ConductivitySensitive monitoring of certain ionic contaminantsDegassed Cation ConductivityHelps evaluate dissolved-gas contributionpHFeedwater chemistry controlDissolved OxygenCorrosion-control monitoringSodiumSensitive contamination monitoringSilicaMonitoring where silica transport/contamination is relevantTemperatureSample-condition monitoring
Other parameters can be added where required.
Conductivity Monitoring in Feedwater
Conductivity is a basic but valuable measurement for feedwater chemistry.
Changes in conductivity can indicate changes in ionic contamination.
Possible sources include:
Condensate contamination
Make-up water contamination
Chemical dosing
Treatment-system performance
Process leakage
Sample contamination
Continuous conductivity monitoring provides trend information and can help operators identify changes before they become significant.
Cation Conductivity Monitoring
Cation conductivity provides additional sensitivity to certain ionic contaminants.
The sample passes through a cation exchanger before reaching the conductivity cell.
A typical arrangement is:
Feedwater → Cooler → Flow Control → Cation Exchanger → Conductivity Cell
The condition of the cation resin is important.
If the resin becomes exhausted or contaminated, the measurement may no longer represent the intended analytical condition.
Cation resin should therefore be inspected and maintained according to the system design and manufacturer's recommendations.
Degassed Cation Conductivity
Dissolved carbon dioxide can contribute to conductivity after cation exchange.
A degassed cation conductivity system removes or reduces the influence of dissolved gases before the final conductivity measurement.
Comparing cation conductivity with degassed cation conductivity can provide additional diagnostic information.
However, plant chemistry conditions must be considered when interpreting the results.
pH Monitoring of Feedwater
pH control is an important component of many feedwater chemistry programs.
An online pH analyzer can provide continuous measurement and help identify changes in feedwater chemistry.
Reliable pH measurement requires attention to:
Sensor selection
Reference electrode condition
Temperature compensation
Sample flow
Calibration
Sample cleanliness
High-purity water can be challenging for pH measurement, so the analyzer and sample system should be specifically selected for the application.
Dissolved Oxygen Monitoring
Dissolved oxygen can play an important role in corrosion control.
A deaerator is commonly used in many boiler systems to reduce dissolved gases before feedwater enters the boiler.
Online dissolved oxygen monitoring can help evaluate the effectiveness of the chemistry-control system where DO measurement is part of the plant's monitoring strategy.
DO measurement is sensitive to air ingress.
Therefore, the sample system should minimize:
Leaks
Loose fittings
Air bubbles
Unnecessary dead legs
Excessive sample-line residence time
Sodium Monitoring
Sodium can be used as a sensitive indicator of certain contamination events.
Possible sources include:
Condenser leakage
Cooling-water ingress
Make-up water contamination
Treatment-system problems
Process contamination
Continuous sodium monitoring can provide early warning where low-level contamination detection is important.
Because sodium analyzers can be sensitive to sample contamination, sample-system cleanliness is essential.
Silica Monitoring
Silica can be included in feedwater monitoring where required by the plant chemistry program.
The importance of silica increases in applications where silica transport with steam and downstream deposition are concerns.
Online silica analysis can help operators monitor changes and investigate abnormal chemistry conditions.
Silica analyzer performance depends on:
Sample cleanliness
Sample flow
Temperature
Reagent condition
Calibration
Drainage
Sample Conditioning for Feedwater Monitoring
A feedwater sample may still require conditioning before it reaches an analyzer.
A typical conditioning arrangement can include:
Sample isolation valve
Pressure-reduction/control device
Sample cooler
Temperature sensor
Filter
Flowmeter
Flow-control valve
Analyzer manifold
Calibration connection
Drain or sample return
The objective is to provide a stable, representative and analyzer-compatible sample.
Pressure Reduction
Feedwater pressure can be high, particularly near the boiler feed pump discharge.
Analytical instruments generally require much lower and controlled pressure.
A pressure-control system may therefore be installed upstream of the analyzer.
The design should consider:
Maximum pressure
Normal pressure
Temperature
Flow
Pressure drop
Valve characteristics
Flashing risk
Analyzer requirements
There is no universal SWAS pressure setting.
The correct arrangement must be engineered according to actual plant conditions and analyzer specifications.
Feedwater Sample Cooling
Feedwater temperature may be too high for direct connection to many analytical instruments.
A sample cooler can reduce the temperature to the appropriate analyzer operating range.
Cooling performance depends on:
Sample temperature
Sample flow
Cooling-water temperature
Cooling-water flow
Heat-transfer area
Cooler material
Fouling
A simplified heat balance is:
Q = m × Cp × ΔT
Actual cooler sizing should be based on the complete process conditions and appropriate engineering calculations.
Sample Flow Control
Stable sample flow is important for reliable measurements.
The system may use:
Flowmeters
Rotameters
Needle valves
Flow-control valves
Pressure regulators
The required flow must be determined from the individual analyzer manufacturer's specification and the complete sample-conditioning design.
Too little flow can cause excessive transport delay and unstable measurements.
Excessive flow can increase water consumption and may affect the performance of the cooling and conditioning system.
Sample-Line Design for Feedwater
The sample line should be designed to provide a representative sample while minimizing delay and contamination.
Good design practices include:
Keep lines as short as practical
Minimize unnecessary bends
Avoid dead legs
Use appropriate materials
Prevent air ingress
Provide adequate drainage
Maintain stable flow
Provide accessibility for maintenance
Sample transport time can be estimated as:
Transport Time = Sample-Line Volume ÷ Sample Flow Rate
This becomes particularly important when rapid detection of chemistry changes is required.
Material of Construction
Material selection should be based on:
Feedwater chemistry
Pressure
Temperature
Corrosion resistance
Cleanliness
Analyzer requirements
Common materials may include:
SS 316/316L
SS 304/304L
PTFE
PFA
PVDF
For low-level measurements, the cleanliness and compatibility of wetted components can have a significant influence on measurement reliability.
Feedwater Monitoring in Thermal Power Plants
In thermal power plants, feedwater chemistry is closely connected to boiler and steam chemistry.
A SWAS system may monitor:
Condensate
Feedwater
Boiler water
Main steam
Reheat steam
Make-up water
Typical feedwater measurements may include:
Conductivity
Cation conductivity
pH
Dissolved oxygen
Sodium
Silica
The exact combination depends on the plant's chemistry program.
Feedwater Monitoring in Combined-Cycle Plants
Combined-cycle plants use HRSG systems to recover heat from gas-turbine exhaust and generate steam.
Feedwater monitoring can be associated with:
HP feedwater
IP feedwater
LP feedwater
Deaerator system
Condensate system
HRSG circuits
An integrated Online SWAS Panel can provide continuous measurements across multiple sample points.
Feedwater Monitoring in Captive Power Plants
Captive power plants in industries such as:
Steel
Cement
Sugar
Paper
Chemicals
Textiles
often operate their own boilers and steam systems.
Reliable feedwater monitoring can help support:
Boiler reliability
Chemistry control
Reduced corrosion risk
Reduced contamination
Improved operational stability
A suitably configured SWAS Panel India solution can be designed around the specific boiler and feedwater system.
Feedwater Monitoring in Industrial Boilers
Industrial boilers may have different chemistry requirements from large utility power plants.
The monitoring system should therefore be scaled according to:
Boiler pressure
Boiler capacity
Water-treatment system
Feedwater chemistry
Steam use
Material selection
Process requirements
A smaller industrial boiler may require fewer analytical parameters, while a high-pressure utility or HRSG system may require a broader chemistry-monitoring package.
PLC, HMI and DCS/SCADA Integration
A modern SWAS Panel can transmit feedwater chemistry information to the plant automation system.
Typical signals include:
Analyzer measurements
Sample temperature
Sample flow
Sample pressure
Analyzer status
Calibration status
Common fault
High/low alarms
Communication can be implemented using suitable interfaces such as:
4–20 mA
Digital signals
Modbus RTU
Modbus TCP
Ethernet
Other plant-approved protocols
The final architecture should be established during system engineering.
Feedwater Chemistry Alarm Management
Alarm configuration should cover both chemistry and sample-system conditions.
Chemistry alarms
Potential alarms include:
High conductivity
High cation conductivity
High sodium
High silica
High/low pH
High dissolved oxygen
Sample-system alarms
Examples include:
Low sample flow
High sample temperature
High sample pressure
Low cooling-water flow
Filter blockage
Analyzer alarms
Examples include:
Calibration failure
Sensor failure
Reagent low
Analyzer fault
Communication failure
Alarm limits should be established according to the plant chemistry program and applicable equipment requirements.
SWAS Panel Maintenance for Feedwater Monitoring
Reliable feedwater monitoring requires systematic SWAS Panel Maintenance.
Daily or Routine Checks
Operators can check:
Analyzer readings
Sample flow
Sample temperature
Cooling-water flow
Leakage
Drainage
Alarm status
Periodic Checks
Maintenance can include:
Filter inspection
Sensor inspection
Calibration
Valve inspection
Sample tubing inspection
Cooler inspection
Cation resin inspection
Reagent replacement where applicable
Planned Maintenance
Depending on the equipment and manufacturer's recommendations:
Detailed analyzer servicing
Sensor replacement
Calibration verification
Sample cooler inspection
Valve maintenance
Electrical inspection
PLC/HMI checks
DCS communication verification
Maintenance intervals should be established according to actual operating conditions and manufacturer recommendations.
Common Feedwater SWAS Problems
High Conductivity
Possible causes include:
Actual contamination
Condensate contamination
Make-up water contamination
Chemical dosing
Treatment-system problems
Sample-system contamination
High Cation Conductivity
Investigate:
Ionic contamination
Condenser-related contamination
Cation resin condition
Sample-system cleanliness
Analyzer condition
High Dissolved Oxygen
Possible causes include:
Deaerator performance issues
Air ingress
Sample-line leakage
Poor sample conditioning
Sensor/calibration problems
High Sodium
Investigate:
Condenser leakage
Cooling-water ingress
Make-up water
Process contamination
Sample-system contamination
Analyzer/reagent condition
Unstable Readings
Check the complete sample path:
Sample pressure
Sample flow
Sample temperature
Air bubbles
Filter
Sensor
Calibration
Analyzer
Electrical connections
Feedwater SWAS Troubleshooting Sequence
A systematic approach can reduce unnecessary analyzer replacement.
Use the following sequence:
Process → Sample Point → Pressure → Cooling → Flow → Filtration → Sensor → Analyzer → Signal → DCS/SCADA
This separates process chemistry problems from sample-conditioning and instrumentation problems.
Dedicated vs Multiplexed Feedwater Monitoring
Dedicated Monitoring
Dedicated analyzers can continuously monitor individual sample streams.
Advantages
Continuous measurement
Fast response
Simple interpretation
No switching delay
Suitable for critical parameters
Multiplexed Monitoring
A multiplexed SWAS system can sequentially analyze several sample streams.
Advantages
Lower analyzer count
Centralized system
Potential capital-cost reduction
Useful where continuous measurement at every point is not required
However, multiplexed systems require careful management of:
Switching sequence
Flushing
Cross-contamination
Transport delay
Valve reliability
Dead volume
Relationship Between Feedwater and Condensate Monitoring
Feedwater and condensate monitoring should be viewed as interconnected parts of the steam-water cycle.
A simplified cycle is:
Boiler → Steam → Turbine/Process → Condenser → Condensate → Feedwater → Boiler
If condensate becomes contaminated, the contamination can potentially propagate into the feedwater system.
Monitoring both locations can therefore help identify where a chemistry problem may have originated.
Feedwater Monitoring and Deaerator Performance
The deaerator plays an important role in many boiler systems by reducing dissolved gases from feedwater.
Where dissolved oxygen monitoring is included, comparing measurements around the deaerator can provide useful information about system performance.
Other factors should also be considered, including:
Operating temperature
Pressure
Venting
Sample-system integrity
Oxygen scavenging/chemical treatment where applicable
The exact chemistry-control strategy varies by plant.
Feedwater SWAS Selection Checklist
Before selecting a system, collect:
Process Information
Feedwater source
Pressure
Temperature
Flow
Normal operating conditions
Maximum operating conditions
Sample-point location
Analytical Requirements
Conductivity
Cation conductivity
Degassed cation conductivity
pH
Dissolved oxygen
Sodium
Silica
Other required parameters
Sample Conditioning
Pressure reduction
Cooling
Filtration
Flow control
Drain/return
Calibration arrangement
Automation
PLC
HMI
DCS/SCADA
Communication protocol
Alarm requirements
Data logging
Mechanical Requirements
Panel material
Tubing material
Valve material
Cooler material
Pressure rating
Installation environment
Best Practices for Feedwater Monitoring via SWAS
For reliable operation:
Select a representative feedwater sample point.
Keep sample lines as short as practical.
Minimize dead legs and unnecessary fittings.
Use appropriate pressure reduction.
Design the cooler for actual process conditions.
Maintain stable sample flow.
Prevent air ingress.
Use suitable wetted materials.
Maintain filters and cation exchangers.
Calibrate analyzers according to manufacturer requirements.
Integrate alarms with the plant control system.
Compare online results with laboratory measurements where appropriate.
Maintain historical trends.
Keep critical spare parts available.
Follow a documented SWAS Panel Maintenance program.
Benefits of an Online SWAS Panel for Feedwater
A properly designed Online SWAS Panel can provide:
Continuous feedwater chemistry monitoring
Early contamination detection
Better boiler chemistry control
Improved corrosion-risk management
Reduced dependence on manual sampling
Continuous trend information
Automated alarms
DCS/SCADA integration
Faster troubleshooting
Improved maintenance planning
Better steam-cycle reliability
Why Choose Prosoft Automation for Feedwater SWAS?
Prosoft Automation provides application-oriented SWAS solutions for steam and water chemistry monitoring.
Our approach considers the complete measurement chain:
Sample Extraction → Pressure Reduction → Cooling → Conditioning → Flow Control → Online Analysis → PLC/HMI → DCS/SCADA
This approach is important because the performance of a water chemistry analyzer depends heavily on the quality and stability of the sample supplied to it.
Prosoft solutions can be configured for:
Feedwater monitoring
Condensate monitoring
Boiler-water monitoring
Saturated-steam monitoring
Superheated-steam monitoring
HRSG applications
Thermal power plants
Captive power plants
Cogeneration plants
Industrial boilers
Process industries
Frequently Asked Questions
What is feedwater monitoring via SWAS?
Feedwater monitoring via SWAS is the continuous analysis of boiler or HRSG feedwater to monitor important chemical parameters and identify contamination or chemistry changes.
Which parameters are commonly monitored in feedwater?
Conductivity, cation conductivity, pH and dissolved oxygen are commonly considered. Sodium, silica and degassed cation conductivity may also be included depending on the plant chemistry program.
Why is dissolved oxygen monitored in feedwater?
Dissolved oxygen can contribute to corrosion mechanisms. Where DO monitoring is part of the plant chemistry strategy, online measurement can help evaluate and control oxygen levels.
Why is conductivity important in feedwater?
Conductivity provides an indication of dissolved ionic contamination and can help identify changes in feedwater quality.
Can sodium be measured continuously in feedwater?
Yes. An online sodium analyzer can be incorporated into a SWAS system where sensitive contamination monitoring is required.
Is a sample cooler necessary for feedwater monitoring?
It depends on the actual feedwater temperature and the analyzer's allowable sample-temperature range. Where the sample is too hot, a properly designed sample cooler is required.
How often should a feedwater SWAS system be maintained?
Maintenance frequency depends on the analyzer technology, sample quality, plant conditions and manufacturer recommendations. Routine inspection, calibration, sensor checks, filter maintenance and sample-system inspection are important.
Can a feedwater SWAS Panel be connected to DCS?
Yes. A suitably engineered SWAS Panel can transmit analytical values, alarms and system status to the plant DCS/SCADA system.
What causes unstable feedwater analyzer readings?
Potential causes include fluctuating sample flow, temperature changes, air bubbles, sample contamination, sensor condition, calibration problems and analyzer faults. The complete sample path should be checked before replacing the analyzer.
What information is required to design a feedwater SWAS Panel?
Important information includes sample location, pressure, temperature, flow, required analytical parameters, sample-line length, cooling-water availability, drainage/return arrangement, automation requirements and analyzer specifications.
Conclusion
Feedwater is a critical part of every boiler and steam-water cycle. Maintaining its chemical quality helps control contamination and supports the reliable operation of boilers, HRSGs, turbines, condensers and associated equipment.
A properly engineered SWAS Panel provides the sampling, pressure control, cooling, filtration, flow control and online analysis required for continuous feedwater chemistry monitoring.
Conductivity, cation conductivity, pH, dissolved oxygen, sodium, silica and other parameters can be selected according to the plant's chemistry-control requirements.
The reliability of an Online SWAS Panel depends on the complete sample-conditioning system as well as the analyzer. Representative sampling, suitable sample-line design, stable flow and temperature, appropriate materials, proper calibration and planned SWAS Panel Maintenance are essential.
Feedwater monitoring should therefore be considered together with condensate, boiler-water and steam monitoring as part of an integrated steam and water chemistry strategy.
Prosoft Automation can support application-specific SWAS Panel solutions for feedwater, condensate, boiler water and steam monitoring in power generation and industrial process applications.
Talk to Our Application Specialist
Share your feedwater sample point, pressure, temperature, required parameters and plant application with Prosoft Automation.
Our application team can help evaluate the sampling arrangement and recommend a suitable SWAS configuration for your requirements.
Talk to our application specialist for a free site-application consultation.