The full version of this information can be found in the January 2020 of Hydrocarbon Engineering.
A well-designed steam and water sampling system can give you the critical insights you need to monitor steam and condensate quality, cycle chemistry (power production) and identify potential problems in your Hydrocarbon plant.
Hydrocarbon processes require large amounts of energy, much of which is supplied by steam from on-site boilers, co-generation facilities, and local utilities designed to supply excess steam to neighboring facilities.
The efficiency of these processes relies on optimizing heat transfer in processing plants and controlling the inputs to steam production, such as returned condensate and makeup water, and the quality of the steam in processing equipment like heat exchangers.
steam and condensate chemistry
Cycle chemistry monitors and protects any equipment directly involved with condensate, feed water and other aspects of the steam/water cycle, such as boilers, turbines, heating systems and piping. Cycle chemistry monitoring systems help plants maintain steam and water chemistry within operating limits to prevent potentially catastrophic equipment failures.
A well-planned and designed sampling system can help provide the critical insights you need to monitor cycle chemistry.
In co-generation and utility plants, chemistry in the entire steam-water cycle is closely monitored to ensure steam quality and to prevent and control corrosion in the system. Most plants typically monitor chemistry parameters such as:
- Cation conductivity
- Total Organic Carbon (TOC)
Other parameters can be monitored as well. These will be dependent on system design, metallurgy, water characteristics and boiler chemistry.
In the past, many of these measurements were taken through the analysis of grab samples sampling points at the pressure reduction valve and sample cooler. But the quality of these measurements was often not representative of the entire process.
Accurate and repeatable analysis
The validity of your analysis data is only as good as the entire sampling and analysis process.
With today’s analyzer technology, you can implement online chemistry parameter measurements that automate the data collection process and remove sample collection and analysis bias.
Make sure your sample is representative. Having a high confidence in your analysis data starts with a high-quality sample that is representative of the process. In the steam-water circuit, that means the sample is flowing and unaltered by the sampling process.
Measure the right characteristics. The objective is to remove an amount of the sample from the process and move it to conditioning and analysis without unintentionally altering the characteristics that you’re measuring.
In the case of steam and water sampling, we want to measure all characteristics, including:
- Ionic species
- Dissolved species
These measurements indicate the real-time state of the cycle chemistry to help you identify contaminants and control chemical addition.
Extract the sample. Proper sampling begins with extracting the sample from the process correctly:
- Select a sample point that allows flow without altering its characteristics.
- Use non-reactive sample tubing that allows turbulent flow and proper sample velocity. Most sampling systems use a flow rate of about 1200 cc/min and 1/4 or 3/8 inch tubing.
- Minimize the length of tubing run from point of extraction to the sample conditioning equipment to ensure a representative sample.
Condition the sample. Sample conditioning consists of controlling three main sample variables:
- Velocity - Maintaining sample integrity requires a velocity that ensures equilibrium.
- Temperature - The temperature of the sample must be reduced to a temperature that the analysis instruments can tolerate, ideally 25°C (77°F). This requires two-stage cooling and a controlled, chilled water supply.
- Pressure - The sample pressure must be reduced from process levels to a safe and usable level for the analyzers, typically about 20 psig (1.4 bar).
Select chemistry parameter instruments. There are a wide range of online chemistry parameter instruments that can measure properly conditioned samples, including transmitter-based instruments suitable for operation in hazardous areas. Selecting the right equipment is based on the parameters you’re measuring to give insight into cycle chemistry effectiveness and identify abnormal conditions.
Need help designing your sampling system or selecting the right equipment for your plant? Contact us.