The steam and water analysis system ( SWAS ) is a system dedicated to steam or water analysis. In power plants, it is commonly used to analyze boiler and water vapor to ensure that water is used to produce clean electricity from impurities that can cause corrosion on any metal surface, such as in boilers and turbines.
Video Steam and water analysis system
Sistem analisis uap dan air (SWAS)
Corrosion and erosion are the main concerns in thermal power plants that operate with steam. Steam that reaches the turbine must be ultra-pure and therefore needs to be monitored for its quality. A well designed Steam and Water Analysis (SWAS) system can assist in monitoring vital parameters in steam. These parameters include pH, conductivity, silica, sodium, dissolved oxygen, phosphate and chloride. A properly designed SWAS should ensure that the sample represents to the point of analysis. To achieve this, it is important to pay attention to the following aspects of the sample:
- Extraction
- Carrying
- Conditioning
- Analysis
- Cleanliness
Sample extraction
To ensure that samples to be extracted for analysis represent the process conditions appropriately, it is important to select the correct sample extraction probe. The validity of the analysis depends heavily on a truly representative sample. Since the probe will be connected directly to the pipe process, it may have to withstand severe conditions. For most applications, the sample probe is made with the strict code that applies to high pressure high-temperature pipelines.
Choosing the right type of probe is a challenge. Its use depends on the parameters of the process flow to be measured, the required sample flow rate and the location of the sampling point (also called the 'tapping point'). An important aspect of the sample extraction probe design is that the vapor must enter the probe at the same rate as the steam that flows in the pipe from which the sample (can be either vapor or water) is extracted.
Transportation example
While transporting a sample, it is important that the sample meets the least resistance. Therefore the connections and bends in pipes need to be minimal.
Example conditioning system
Examples of conditioning systems in some countries are also called sampling systems , Wet Panel or Wet Racks . It is intended to store various components for sample conditioning. This may be an open shelf or enclosure with a corridor in between. The system contains sample conditioning equipment and sampling sinks. At this stage of the system, the sample is first cooled in the Sample Cooler, depressed in the Pressure Regulator and then fed to various analyzes while the flow characteristics are kept constant by using the Back Pressure Regulator.
The need to condition the sample exists, because the sensors used for online analysis can not handle water or steam samples at high temperature or pressure. To maintain the general reference of the analysis, the sample analysis should be carried out at 25 Â ° C. However, since the temperature compensation logic is available in most analyzes today, it is the practice to cool the sample to 25-40 Â ° C. with the help of a sample conditioning system which is well engineered and then feeds the conditioned sample to the analysis.
However, if the uncompensated sample is to be analyzed, it becomes important to cool the sample to 25 ° C/- 1 ° C. This can be achieved by two-stage cooling. In the first stage of cooling (also known as 'primary cooling'), the sample is cooled by using available cooling water. In most countries, cooling water is available in the range 30-32Ã, Â ° C. This cooling water can cool the sample up to 35 Â ° C (considering the approach temperature of 3 to 5 Â ° C). Coolant samples are used to achieve this. An example of a cooler is a heat exchanger specifically designed for a SWAS application. The preferred sample cooler for primary cooling is a double helix helix in a shell type design that provides a contraflow heat exchange.
The remaining cooling portion (ie from 35 to 25 ° C) is achieved by using cold water in the secondary cooling circuit. Cold water supply required from the factory or an independent chiller package may be considered for this purpose along with SWAS.
The sampling system may be either an open-frame free standing or a completely or partially closed design, depending on the user's choice, the environment that should be operated in & amp; criticality of operation.
Cooler example
In the sampling system, the sample cooler plays a major role in lowering the temperature of the hot vapor (or water) to a temperature acceptable by the on-line analyzer sensors. Some important design aspects of sample cooling are:
- Preferably the sample cooling design should be double helix, coil in the shell type, so it is designed to provide heat exchange counter flow. This makes the sample cooler, but very effective in terms of heat exchange.
- The sample rolls made of SS-316 stainless steel are suitable for normal cooling water conditions. However, if the chloride content in the cooling water is high (over 35 ppm), then other suitable coil materials such as Monel or Inconnel should be used depending on the quality of the cooling water.
- The built-in "safety" safety valve on the side of the cooling shell is a must, thus preventing shell explosions in the event of sample roll failure.
- The sample cooling design must meet the ASME standard requirements of PTC 19.11.
Pressure reduction
After the sample is cooled, the sample pressure must be reduced to meet the needs of the sensor receiving this sample. Typically, sensors such as pH, conductivity, silica, sodium, and hydrazine require low pressure samples for healthy operation.
Pressure-type barrier-in-tube pressure is the most effective pressure reduction method. As per the latest technology, variable pressure shaft reducer in tubes with heat-retention and safety valve devices (VRTS) is considered to be the most reliable and secure device. Variable Rod in Tube System (VRTS) is the system itself that handles some important aspects of sample conditioning. Pressure reducer in the VRTS is rated for high temperatures up to 550 Deg C and high pressure. No need to filter before VRTS, due to on-line cleaning, without using any tool. For maintenance, no need to turn off. Cleaning can be done only by turning the knob for 20 turns and re-applying pressure. During high temperature cut-offs, operators can collect samples through separate ports. It is an energy-efficient device because it operates without external electrical power. There is built-in security for the operator, because the safety valve is installed with the system.
Sample analysis system
A sample analysis system in some countries is also called Panel Analyzer , Dry Panel or Dry Rack . Usually closed panels free standing. This system contains electronic transmitters, usually mounted on the panel. At this stage of the system, samples are analyzed at pH, conductivity, silica, phosphate, chloride, dissolved oxygen, hydrazine, sodium etc.
Type of conductivity measurement
Three types of conductivity measurements are usually performed:
- Specific Conductivity,
- Conductivity of cations and
- Conductivity cation de-gassed.
There is a difference between these three types of measurements.
- The specific conductivity gives the overall conductivity value of the sample and is the most common measurement
- Conductivity of a cation is a measurement of conductivity after Column Cation. In the Cation Column, H resin replaces the positive ions of all the solutes in solution. When this happens, the desired chemical (and alkaline or basic) chemicals are converted to H2O, that is water. (eg NH4OH H () gives NH4 and H2O). Dirt is nothing but salt with different properties. These are converted into respective acids (eg NaCl H () giving HCl and CL-). Thus the effect of chemical treatment masking on the conductivity value is eliminated, while the conversion of salt to the corresponding acid has an effect of increasing the corresponding conductivity value to about 3 times its original value. Thus, in essence, the cation conductivity acts as a conductivity amplifier due to impurities and conductivity eliminators due to the treatment chemicals.
- Conductivity de-gassed is the best conductivity measurement. Here we remove the effects of soluble gas masking, especially CO2, on conductivity measurements. In the De-Gassed conductivity system, there is reboil space to heat the sample, so that the dissolved gas is released and then there is a cooling mechanism, where the hot liquid is cooled again. The conductivity measured after this process is indeed 'real' conductivity value due to 'dissolved' impurities after removing dissolved gases.
Silica problem
When it comes to the safety and efficiency of steam turbines and boilers in power plants, silica is one of the most important factors to be monitored. The deposition of various impurities on turbine blades has been identified as one of the most common problems. Various deposit compounds on the turbine blades. Of all these compounds, silica precipitate (SiO 2) can occur at lower operating pressures as well. Therefore silica precipitation is very common in turbines rather than other types of deposits. Silica is usually stored in the medium pressure and low pressure parts of the turbine. This precipitate is difficult to remove, disturbs the geometry of the turbine blades and ultimately produces vibrations that cause imbalance and loss of output from the turbine.
Another important area of ​​concern as far as the precipitation of silica is concerned is the boiler tube. The silica scale is one of the most difficult scales to eliminate. Due to its low thermal conductivity, a very thin silica deposit can reduce heat transfer significantly, reduce efficiency, lead to hot spots and eventually break.
Because of all these problems, it is important to monitor the silica level by using an on-line silica analysis that can measure the silica level to ppb level (parts per billion).
Maps Steam and water analysis system
See also
- Boiler (power plant)
- Supercritical Steam Generator
References
Source of the article : Wikipedia
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