Digox 602 dac

DAC measurement has become an important basic parameter in the water-steam cycle; especially in the combined cycle of a peaking power plant. DAC measurement is recommended as standard in feed water and steam. Thanks to the DAC measurement, it measures the conductivity value without the influence of CO2, which significantly reduces the start-up time of the power plant. For power plant operators, this is not only an environmental benefit, but also an economic one.

Acid Conductivity

In a cation filter, H + from the exchanged cations are combined with OH- from the alkalizing agent to water. The remaining conductivity is determined by autoprotolysis of pure water plus impurities in the form of anions, i.e. CO3 2-.
For steam turbine operation, the acid conductivity must not exceed the threshold of 0.2 μS / cm.

The causes of increased conductivity can be the following:

• dirty piping system, high corrosion conditions
• cooling water leakage into the condenser
• air leakage into the atmosphere with the impact of CO2
• organic substances in the boiler feed water - the impact of CO2 after heating 

Degassed Cation Conductivity

For the shortest possible start-up phase, the conductive acid must be measured without affecting the conductivity caused by the dissolution of CO2. The threshold value for turbine operation is thus reached faster. Dissolved CO2 increases conductivity but does not damage the turbine.

Therefore, it is necessary to remove carbonic acid from the sample and measure the conductivity again (degassed acid conductivity). On the one hand, the start-up phase can be significantly shortened, on the other hand, organic matter and the ingress of atmospheric air can be monitored.

With Digox 602 dac, you have a universal measuring device available for this type of task. In the compact design, you have the first double conductivity measurement, including a cation filter, automatic deaeration and pH calculation according to VGB-S006, then the detachable operation of the degassing unit with conductivity measurement before and after degassing. Depending on the efficiency, degassing can be calculated at 100%.