Cycle chemistry management is the best way to help prevent, recognize and minimize potentially devastating water chemistry events in a facility. A well-planned and designed sampling system with the right instrumentation can help provide the critical insights you need to monitor cycle chemistry, protect equipment and ensure safe operation.
The elements of a SWAS
Effectively monitoring cycle chemistry in a power plant relies on the availability, accuracy and trustworthiness of analyzer data. Like most industrial monitoring systems, the quality of the data is governed by the entire SWAS. This system accesses the process at the point of measurement interest, then transports a representative amount of the process stream to the measurement tools (analyzers) safely and without changing the parameters of interest. It includes:
- Sample transport: Tubing and isolations valves
- Sample conditioning elements: Heat exchangers, pressure reduction valves and flow control elements
- Measurement tools: Online analyzers
Minimum key instrumentation
A steam-water cycle chemistry monitoring system that provides accurate and trustworthy critical insights starts with understanding the minimum key instrumentation required for the specific plant type, design and chemistry.
To ensure your plant has the proper minimum key instrumentation, it’s critical to consult relevant, up-to-date guidance published by the Electric Power Research Institute (EPRI), or a similar local organization, as well as the International Association for the Properties of Water and Steam (IAPWS) and corporate benchmarking.
As the EPRI CS-5164 standard says:
“The Primary objective of any sampling system is to transport and condition a sample without altering the characteristics of interest. The system parameters which need to be controlled are velocity, pressure and temperature.”
In addition, the IAPWS offers cycle chemistry guidelines on sample points and minimum levels of on-line chemical monitoring instrumentation for steam and water cycle chemistry control. According to IAPWS TGD2-09:
“Every plant should have a minimum level of instrumentation which can uniquely identify key parameters and drivers to each and every failure/damaged mechanism which can occur at that plant.”
The selection of measurement tools or analyzers is dependent on plant type, plant design and chemistry program. For example, the minimum key instrumentation recommended for a two-on-one combined cycle plant with all ferrous metallurgy and all volatile treatment (AVT) will differ from a traditional boiler unit with mixed metallurgy.
key measurement instrumentation
The main sample categories of interest in all steam power plants (except for nuclear and geothermal) include:
- Feed water
- Boiler Water
- Make-up water
Every plant should have instrumentation that provides reliable chemistry monitoring of locations and parameters around the cycle. A well-designed sample system helps keep cycle chemistry in control with accurate, timely data for corrective action.
- Conductivity after cation exchange (cation conductivity or CACE)
- Dissolved oxygen
- Degassed conductivity after cation exchange (DCC)
- Total Organic Carbon (TOC)*
*Plant and/or chemistry regime-specific.
Importance of cation exchange resin
According to the IAPWS TGD-09:
“The cation exchange resin removes ammonium, sodium and other cations, leaving an acidic solution of the anions. The conductivity of this solution is highly responsive to the presence of strong-acid anions because of the high equivalent conductivity of the hydrogen ion. Thus, conductivity after cation exchange is extremely effective for rapidly indicating the onset of cooling water ingress, particularly at seawater cooled sites, and for detecting contaminated make-up water.
The technique is most frequently applied to the monitoring of condensate, feedwater and condensed steam. It’s also applicable to the monitoring of boiler/evaporator water, provided the boiler/HRSG is operating with an AVT or a caustic dosing regime.”
Accurate and reliable swas sampling
Learn more about SWAS instrumentation in Sentry’s Webinar: Maximize Your SWAS Instrumentation.
- The ins and outs of steam and water analysis systems
- Key instrumentation and measurements within your SWAS
- pH and conductivity measurements
- Implications and considerations when upgrading instrumentation
Contact us at +1-262-567-7256, or complete our online contact form for more information.