Medium Purity Condensate Monitoring - Emerson · Medium Purity Condensate Monitoring Background...
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Application Note Power Medium Purity Condensate Monitoring Background Process In high pressure boilers, it is necessary to monitor the return condensate before it goes back to the boiler to ensure that it is not contaminated beyond acceptable limits. In smaller boilers, the return condensate can have a fairly high dissolved solids concentration, which can be measured with a standard conductivity meter. In the case of large boilers, such as those used to generate electricity, the allowable level of solids is in the low parts-per- million range. The conductivity caused by the dissolved solids is often masked by the larger conductivities of water treatment chemicals that have been added to protect the boiler. In a case like this, the Larson Lane Condensate Monitor Model CH16D is used to separate the conductivity caused by the dissolved solids from the conductivity caused by the water treatment chemicals. In high purity boilers, the Total Dissolved Solids (TDS) level of the water ought to be limited to a maximum of 1 to 2 ppm and sometimes less than 0.1 ppm. In order to do this, it is necessary to start with deionized water, which will have a conductivity in the range of 0.055–0.1 μS/cm (μS/cm). Various water treatment chemicals are then added to the deionized water to prevent deposits from forming, to regulate the pH, and in other ways to improve boiler life and performance. When the water is boiled, most of the solids remain in the boiler with a few of them being carried over into the steam. In time, some steam will be lost and require make-up water to be added. This will eventually cause a build-up of undesirable dissolved solids in the water such as chlorides or sulfates, gases such as carbon dioxide or oxygen, and other harmful materials. A simple conductivity measurement of this water would measure the total conductivity of the “good stuff,” such as the water treatment chemicals, and the “bad stuff,” such as the chlorides, sulfates, etc. In a smaller boiler, the total conductivity could be between 1 and 20 μS/cm (or in some plants even higher), and it will be necessary to detect contamination in the order of 0.1 to 2 ppm, which would add 0.2 to 5 μS/cm. This is not a very sensitive technique. One of the simplest methods of detecting small amounts of contamination in return condensate is through the use of a cation conductivity measurement. In this type of measurement, the condensate must first be cooled to under 122 °F (50 °C) – preferably under 86 °F (30 °C) to prolong resin life. The sample pressure must be reduced to under 5 psi in most systems before the condensate enters the cation column. When the water passes through the cation resin bed, the resin exchanges any positive ions in the solution for hydrogen ions. If a salt, such as NaCl, passes through the resin, the Na + ion is held in the bed, and an H + ion is released. In so doing, 1 ppm of NaCl salt (which has a conductivity of approximately 2.2 μS/cm) is converted to 1 ppm of HCl acid (which has a conductivity of approximately 11.7 μS/cm). In a like manner, other salts are converted to their corresponding acids, which have 3 to 6 times the conductivity of the corresponding salt. This is shown in Figure 1. Chemicals that are alkaline in nature, including most water treatment chemicals, also have their positive ion portion bound in the resin column with a corresponding release of hydrogen ion. Thus, a chemical such as ammonia (which would be NH 4 OH in water), which has a conductivity of approximately 6.6 μS/cm for 1 ppm, has the NH 4 + ion bound up in the resin bed and an H+ ion released making HOH, or water, with no added conductivity. In this way, most water treatment chemicals become bound in the column and release water, reducing the conductivity contributed by these chemicals to close to zero. Chemicals that are acidic, such as H 2 CO 3 (which is formed when CO 2 dissolves in water), pass through the resin unchanged. When the return condensate passes through the cation column, the conductivity of the “bad stuff,” such as an acid, would be unchanged, while that of dissolved salts would increase 3 to 6 times. The conductivity of the “good stuff,” such as water treatment chemicals, will generally decrease to near zero. Thus, the cation conductivity coming out of the resin column is caused by the undesirable materials in the water. In this type of a system, we could detect as little as 10–20 ppb of dissolved solids in condensate that has a total conductivity of 5 μS/cm.
Transcript of Medium Purity Condensate Monitoring - Emerson · Medium Purity Condensate Monitoring Background...
Application Note Power
Medium Purity Condensate Monitoring
Background
Process
In high pressure boilers, it is necessary to monitor the return condensate before it goes back to the boiler to ensure that it is not contaminated beyond acceptable limits. In smaller boilers, the return condensate can have a fairly high dissolved solids concentration, which can be measured with a standard conductivity meter. In the case of large boilers, such as those used to generate electricity, the allowable level of solids is in the low parts-per-million range. The conductivity caused by the dissolved solids is often masked by the larger conductivities of water treatment chemicals that have been added to protect the boiler. In a case like this, the Larson Lane Condensate Monitor Model CH16D is used to separate the conductivity caused by the dissolved solids from the conductivity caused by the water treatment chemicals.
In high purity boilers, the Total Dissolved Solids (TDS) level of the water ought to be limited to a maximum of 1 to 2 ppm and sometimes less than 0.1 ppm. In order to do this, it is necessary to start with deionized water, which will have a conductivity in the range of 0.055–0.1 μS/cm (μS/cm). Various water treatment chemicals are then added to the deionized water to prevent deposits from forming, to regulate the pH, and in other ways to improve boiler life and performance.
When the water is boiled, most of the solids remain in the boiler with a few of them being carried over into the steam. In time, some steam will be lost and require make-up water to be added. This will eventually cause a build-up of undesirable dissolved solids in the water such as chlorides or sulfates, gases such as carbon dioxide or oxygen, and other harmful materials.
A simple conductivity measurement of this water would measure the total conductivity of the “good stuff,” such as the water treatment chemicals, and the “bad stuff,” such as the chlorides, sulfates, etc. In a smaller boiler, the total conductivity could be between 1 and 20 μS/cm (or in some plants even higher), and it will be necessary to detect contamination in the order of 0.1 to 2 ppm, which would add 0.2 to 5 μS/cm. This is not a very sensitive technique.
One of the simplest methods of detecting small amounts of contamination in return condensate is through the use of a cation conductivity measurement. In this type of measurement, the condensate must first be cooled to under 122 °F (50 °C) – preferably under 86 °F (30 °C) to prolong resin life. The sample pressure must be reduced to under 5 psi in most systems before the condensate enters the cation column.
When the water passes through the cation resin bed, the resin exchanges any positive ions in the solution for hydrogen ions. If a salt, such as NaCl, passes through the resin, the Na+ ion is held in the bed, and an H+ ion is released. In so doing, 1 ppm of NaCl salt (which has a conductivity of approximately 2.2 μS/cm) is converted to 1 ppm of HCl acid (which has a conductivity of approximately 11.7 μS/cm). In a like manner, other salts are converted to their corresponding acids, which have 3 to 6 times the conductivity of the corresponding salt. This is shown in Figure 1.
Chemicals that are alkaline in nature, including most water treatment chemicals, also have their positive ion portion bound in the resin column with a corresponding release of hydrogen ion. Thus, a chemical such as ammonia (which would be NH4OH in water), which has a conductivity of approximately 6.6 μS/cm for 1 ppm, has the NH4
+ ion bound up in the resin bed and an H+ ion released making HOH, or water, with no added conductivity. In this way, most water treatment chemicals become bound in the column and release water, reducing the conductivity contributed by these chemicals to close to zero.
Chemicals that are acidic, such as H2CO3 (which is formed when CO2 dissolves in water), pass through the resin unchanged.
When the return condensate passes through the cation column, the conductivity of the “bad stuff,” such as an acid, would be unchanged, while that of dissolved salts would increase 3 to 6 times. The conductivity of the “good stuff,” such as water treatment chemicals, will generally decrease to near zero. Thus, the cation conductivity coming out of the resin column is caused by the undesirable materials in the water. In this type of a system, we could detect as little as 10–20 ppb of dissolved solids in condensate that has a total conductivity of 5 μS/cm.
Power
1056 Dual Input Intelligent Analyzer
Figure 1
� Multi-parameter – single or dual input � Easy to install with modular boards,
removable connectors, easy to wire power, sensors, and outputs.
� Intuitive menus screens with advanced diagnostics and help screens save maintenance time.
� Exclusive Quick Start screens appear and the instrument auto-recognizes each measurement board and prompts the user for immediate deployment
Inlet
Outlet (drain)
To make this measurement, the customer will need to reduce the return condensate to a maximum of 122 °F (50 °C) and 5 psi. The cation column would be the Model CH16D, with standard resin, or the Model CH16DE, which has a resin that changes color to indicate when it needs replacement.
An Endurance™ 404 conductivity flow cell with a1056 cation conductivity analyzer is used to measure the outlet of the column. Since this water is coming from a cation column, it is acidic and requires an instrument with a temperature compensator designed to track ultrapure cation water. In some cases, the customer may also want to measure the condensate water before it goes into the column, which will give an indication of the condition of the cation column and the water treatment system. In this case, an additional 404 flow cell and a1056 dual input conductivity analyzer would be used because this analyzer offers the flexibility of one analyzer to measure two cell inputs.
INLETNeutral SaltsNa++ Cl- 2.2 μS/ppm2Na++ Cl- 2.1μS/ppm
AlkalineNH4+ OH- 6.6 μS/ppm(Ammonia in Water)
Acid2H+ + CO3
-2 5μS/ppm(Carbon Dioxide in Water)
OutletChanges to AcidH+ + Cl- 11.7 μS/ppm2H+ + SO4
-2
8.8 μS/ppm
Changes to WaterH++ OH- 0 μS/ppm
Remains Unchanged2H++ CO3
-2 5 μS/ppm
Flow Meter
H+
H+H+
H+
H+
H+H+
H+ H+
H+
H+H+
H+H+
H+H+
H+H+
CationColumn
Flow Valve
Conductivity Cell
Instrumentation
404 Flow-ThroughContacting Conductivity Sensor
� Small hold-up volume to ensure fast response to changing conductivity.
� PVC construction capable up to 60 °C (two required).
� 316SST construction up to 100 °C (two required).
� Housing protects sample from air contamination.
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Power
Notes
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LIQ-ANO-Power-Purity-Condensate-Monitoring
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