Cycle chemistry is an often overlooked, but critical, process in a power plant that helps provide and maintain the protective layer on equipment and surfaces. Monitoring your cycle chemistry starts with sample conditioning.
A well-designed sample conditioning and analysis system provides a sample representative of the process to the analyzers for good quality measurements. The key elements of a well designed conditioning system includes the control of sample flow, temperature, and pressure. By developing a well monitored cycle chemistry program, you will help maximize efficiency, protect equipment, and ensure operator and environmental safety.
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 can help provide the critical insights you need to monitor cycle chemistry, protect equipment and ensure safe operation.
Why Monitor Cycle Chemistry?
The main purpose of cycle chemistry is to help provide and maintain a protective layer on equipment surfaces to help you:
- Maximize heat transfer efficiency
- Reduce chemical cleanings
- Protect boiler and turbine life
- Minimize operational costs
- Ensure operator & environmental safety
quality information starts with quality samples
Monitoring cycle chemistry starts with sample conditioning. 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.”
Sample conditioning transports ultra-pure steam and water at elevated temperatures and pressures and controls the temperature, pressure and flow of these fluids to provide a reliable and representative sample suitable for analysis by the sampling system.
The validity of analysis data is only as good as the entire sampling and analysis process, from sample extraction to sample conditioning and analysis. An accurate data interpretation starts with conditioning the sample after extracting it from the process to prepare the sample for analysis.
Sample conditioning systems are the final stage to handle process samples, which are very important to ensure instruments or analyzers provide the critical data needed.
sample panel components
High Pressure Blowdowns – The best method for removing deposits in the sample lines and protecting coolers and conditioning equipment. From the point of extraction all the way through the panel, a high- pressure blowdown can purge any contaminants from the line.
Sample Coolers – These are the first step in temperature control so you can get accurate readings on high-temperature samples. There are two types of coolers to use in your sample panel:
- Primary Coolers – These take a lot of heat energy out of your sample, especially steam samples. They can help your sample approach temperatures within 5ºF (2.8 ºC) of the coolant water temperature.
- Secondary Coolers – These help you control the temperature of the sample to what is standard for chemistry measurements, removing variables that could be a source of error or uncertainty. They are recommended to control sample temperature to 77 °F +/-1 °F (25 °C +/-.5 °C).
Variable Pressure Reducing Element – A needle valve can help reduce pressure in samples less than 500 PSI, and a variable pressure reducing element can help reduce pressure in samples above 500 PSI. For example, the Sentry AutoVREL flow controller automates sample flow for frequent cycling or sliding pressures.
Magnetic Traps – These traps use high-strength magnets to isolate and remove corrosion products (such as magnetite particulates) from the sample stream to protect sample conditioning and analytical instruments from critical downtime and costly repairs. They’re equipped with a flush handle for purging trapped magnetite. Mag Traps are designed to not interfere with other sample constituents.
Filters – The last line of defense against magnetite before the sample enters the analyzer. They provide a 50-micron filtration rate and are equipped with a valve to blowdown trapped corrosion products.
Thermal Safety – It is important to provide thermal safety devices to protect operators, analyzers and sampling components from high temperature liquids. For example, the Sentry Thermal Shut-Off Valve (TSV) shuts down high-temperature samples in less than five seconds. It isolates the sample flow after pressure reduction and prevents high temperature samples from overwhelming the temperature control unit and frying analyzers.
Back Pressure Regulator/Relief Valve (BPRV) – To control flow, both EPRI and ASTM recommend a rod-in-tube pressure-reducing device and backpressure valve combination. A BPRV can assure constant pressure over a wide flow range to protect the system from over-pressurization. It also ensures constant flow to on-line analyzers for repeatable analysis results.
With these elements, you can plan and design a sampling system that controls velocity, pressure, temperature to accurately manage cycle chemistry, protect equipment and ensure safe operation.
Ready to learn more about sample conditioning? It's all in Sentry’s Webinar: Succeeding with Sample Conditioning.
