Accurate and easy monitoring of steam purity can help minimize the occurrence and degree of carryover and thus guarantee a trouble free operation. Depending upon the level of steam purity desired, two methods of monitoring for solids entrainment are available.
- Sodium ion analyzer
- Low level conductivity monitors
Sodium ion analysis use an ion selective probe, similar to a pH probe, to measure the level of sodium ion in the condensed steam. This method is extremely accurate for levels of sodium as low as 0.1 ppb. Because of this low level accuracy, the instrument is most valuable where only “slight” carryover is a problem such as in a steam turbine system. “Slight” or “minimal” carryover is defined as less than 1 ppm sodium.
The drawbacks to the use of this instrument are:
- High initial cost
- Fixed ranges of monitoring
- 0 to 1 ppm Na
- 1 to 10 ppm Na
- 10 to 100 ppm Na
- Slow response
- Frequent maintenance
These instruments have gained popularity primarily in high pressure applications and are used for low level monitoring of steam purity. Steam monitoring for carryover in more conventional steam systems may or may not involve the use of the more sophisticated sodium analyzer. If monitoring for gross carryover, the use of simple low level conductivity testing is sufficient. With low level conductivity monitoring, a baseline conductivity is established and considered the operational norm against which excursions are compared.
The advantages are:
- Low cost
- Fast response
- Wide monitoring ranges
- Low maintenance
Low level conductivity monitoring allows the establishment of a technique which assures the customer of safe, pure steam without the associated hassles of maintaining a sensitive sodium analyzer. Continuous conductivity monitoring of condensate streams is relatively inexpensive and can alarm before major carryover upset conditions occur.