Steam and Water Analysis System (SWAS) – Corrosion Control in Boiler & Turbine
To monitor and control the purity of boiler feed water, Steam and water analysis system (SWAS) designed.
Steam and water analysis system (SWAS) is a system that is used to analyze and display critical information about steam or water in the power cycle. For any power plant running on steam, it is absolutely crucial to ensure about the purity of boiler feed water and steam during electricity generation; especially to steam equipment like steam turbine, superheater, boiler valves, condenser, steam boiler. A well-designed steam and water analysis system can help prevent damage of steam boiler, steam turbine, and other critical parameters in the steam. These parameters contain pH, silica, sodium, Conductivity, Dissolved Oxygen, Phosphate, and Chlorides etc. To keep the power plant operating and functioning with minimum corrosion, the power plant has fully integrated steam and water analysis system (SWAS).
To protect these types of equipment SWAS works into stages:-
1. Sample Extracting
2. Sample Transport
3. Sample Conditioning
4. Sample Analysis
1. Sample Extracting: In the sampling system, sample extraction probe is the first important component. The correct choice of sample extraction probe should never be overlooked as analysis of an extracted sample is going to represent the exact process condition. As the probe is directly attached to the process pipework, it may have to withstand severe conditions. For most applications, this sample probe is made up of stringent codes, which is an application to high-pressure and high-temperature pipework. It is used to measure the sample flow rate and sample extraction probe.
2. Sample Transport: The sample meets the least resistance is important while transporting the sample. To process the flow of sample joints and bends in the pipeline need to be minimal.
3. Sample Conditioning System: It is also known as sampling system and Wet Panel in some countries. In this stage, The sample coolers are used to cool the sample at the required temperature, then depressurized in pressure regulators and then transfer to various analyzer while the flow characteristics are kept constant through black pressure regulatory. While working with these systems, there is a lot of safety equipment provided in wet panels for operators safety.
There are few important components of sampling systems (WET RACK)
1. Sample Cooler: In the sampling system, sample coolers are CIOL-IN-SHELL type CONTRA-FLOW heat exchangers that play an important role in bringing down the temperature of the hot steam. The preferable sample cooler design should be a double helix. The coil should be in shell type to provide contra-flow heat exchange. Coil Materials are available such as Stainless steel AISI 316, Monal 400 & Inconel 625 and so on. It must meet ASME PTC 19.11 standard requirements.
2. High-Pressure Regulator:
Piston Type High-Pressure Regulations: These type of high-pressure regulators are used in primary conditioning where sample pressure is higher than 100 Kg/cm2.
3. Back Pressure Regulator (BRP): These type of regulators is used to avoid low flow conditions to analyzers in the events grab sample valve operations. In the absence of such a device, when the grab sample valve is opened the sample would flow to grab sample line. The combination of a pressure regulator and back pressure regulator in Steam and water analysis system provides very stable pressure and flow conditions, thereby ensuring reliable, accurate, and efficient analysis.
4. Sight Glass: This component is used to view the sample flow inside the sample line. The presence of cooling water is indicating through a rotating wheel and the side glass is made up of high-grade stainless steel.
5. Sample Filter: To ensure particle-free sample, sample filter is used. Using this any particle of size up to 40 microns can be filtered out. Forged stainless steel body and hexagonal cap are the two-part in sample filter which helps easy cleaning of a filter element.
6. Pressure Relief Valve: These components are fitted with sample cooler and protect sampler cooler in case the coil fails.
7. Hi-Temp Isolation Valve: This valve is used for most high pressure and temperature applications as it is easy to operate. It is designed with plug/seat geometry and stuffing box that allow these valves to operate for an extended period of time.
4. Sample Analysis System: A sample analysis system is also known as Analyser Panel, Dry Panel or Dry Rack in some countries. It is usually a free-standing enclosed panel containing transmitter electronics. The system mounted on panels. In this system stage, a sample is analyzed on the basis of pH, conductivity, chloride, dissolved oxygen, hydrazine, phosphate, silica, and sodium etc.
What Happen If You Don’t Have SWAS?
- Steam and Water Analysis system is mandatory in the thermal power plant as it keeps a constant watch on the problem associated with corrosion, dosing optimization, plant effluents, and boiler blowdown.
- In the thermal power plant, 50% of forced power plant shutdowns can be attributed to impurities. Steam and water analysis system is important to analyze the impurities in the turbine.
- SWAS is properly maintained in the power plant that runs at 95+PLF / PAF.
- People who have good knowledge, expertise and experience prefer on-line monitoring of all the necessary parameters involved in plant cycle chemistry.
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