An online analyser detects these corrosive substances in concentrations lower than 5 ppb and helps prevent corrosion.
The risk of corrosion in power plants by chlorides (Cl-) and sulphates (SO42-), even at low ppb concentrations, is high. Continuous monitoring is therefore of the utmost importance to avoid corrosion in the boiler, steam generator, turbine or other vital components. Until recently, samples could only be analysed in the laboratory. The results are not always reliable owing to frequent contamination when sampling.
Online analysis of chlorides and sulphates is becoming increasingly important
In the current energy landscape, thermal power stations are increasingly being shut down and restarted in order to be able to meet the strongly fluctuating energy demand. Repeated heating and cooling of the installation only increases the risk of corrosion. This makes online measurement of chlorides and sulphates even more important.
Tried everything, but nothing works
Given the importance of online chloride and sulphate determination, various techniques have been tried. An obvious first choice is to rely on the results of the DDC (Degassed Cation Conductivity) measurements that are available anyway. The limit for Cl- and SO42- is 2 to 5 ppb (parts per billion). Even in pure water, these amounts give too little an increase in conductivity. Furthermore a conductivity measurement, even in DCC, is not selective.
An inexpensive and relatively simple technique is to use ion-selective electrodes (especially for chloride). Here too the very low measuring range plays a part. In the low ppb range, the accuracy and stability are insufficient for realising a reliable measurement.
Hence ion chromatography. Although this is a tired and tested technique that has already proven its worth on a laboratory scale, it does not seem obvious to make the technology suitable for an industrial online analysis for power plants. After all, with an online analyser you have to pay a lot of attention to minimal maintenance and ‘serviceability’.
What you need is: MCE, Microfluidic Capillary Electrophoresis
With its 3000CS, Mettler Toledo Thornton has recently developed an analyser that is compact, reliable and requires little maintenance. The analyser is based on MCE. The principle is based on the mobility of charged particles (ions) in an electric field with large voltage differences.
Briefly explained, the device works as follows: a sample, mixed with an internal standard, is ‘pulled’ by a voltage difference through a capillary, whereby the different ions are separated and separately detected by a precision conductivity sensor.
In addition to the continuous analysis, it is possible to analyse samples manually. For example from a few less critical places. Optionally, a ‘sequencer’ can also be used to automatically analyse a few measurement points one after the other. A full analysis cycle takes 15-30 minutes. The lab can’t follow that fast!
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