- The concentration of Sulphides in water depends on the sample pH.
- Between 0 and 6 the H2S is at the maximum concentration.
- Between 6 and 8.5 the H2S concentration decreases.
- Between 8.5 and 11 no H2S is present in the water.
- Above 11 S־־ concentration increases.
- Between 4 and 8.5 the HS־ increases.
- Between 8.5 and 11.5 the HS־ is at the maximum concentration.
- Above 11.5 the HS־ concentration decreases.
- At neutral pH (7) only H2S and HS־ are present.
The measurement principle is based on a variation of HENRY’s law :
the weight of any gas dissolved in a definite volume of liquid is proportional to the partial pressure the gas exerts above the liquid at a constant temperature.
The benefits of this technology can be summarised as follows:
The H2S sensor is immerged in the water. The sensor is equipped with a propriarity membrane. Due to the partial pressure effect, the membrane is only pervious to gases. No liquids, ions or solids can penetrate the sensing part.
The sensor contains a buffer solution with a redox catalyst and 3 electrodes. A defined polarization voltage is applied to the electrodes in order to give a well defined concentration ratio of the oxidized/reduced redox catalyst. The H2S reacts, first chemically in presence of the redox catalyst to form a reaction product. Then, the electrochemical oxidation of the reaction product takes place at the measuring electrode.
Due to the polarization voltage effect, the system can adjust the concentration ratio. The resulting current is proportional to the dissolved molecular amount of H2S present in the sample.
The pH pressure and temperature sensors are also immerged in
- Amines in water
- Water condensates
- Salty water
- Geothermal steams
- Other water applications
Henry’s Law. Detection of H2S / Sulphides using an electrochemical cell in relationship with pH and temperature.
Measuring ranges: 0.01-3 or 0.05-10 or 0.5-50 mg/l (to be stated). Other ranges, consult factory.
Range unit: Mg/l or PPM by weight (to be stated.)
Detection limit: 0.01 mg/l approx.
Response time: Less than 5s full scale (sample system excluded).
Resolution: 1μg/l (depending on the range.)
Linearity: ± 2% of the calibration full scale.
Reproducibility: ± 1% of the calibration full scale.
Accuracy: ± 2% of the instant value.
None for the following components (% vol):
- CO2 max 25.38 – H2 max 0.544 – CH4 max 5.78
- NH3 max 1000 PPM – CO max 92 PPM – CS2 max 5
- Organic solvents max 20 – Acetic acid max 1 mole/l – Salt – HCN
Yes for SO2 100 PPM equal 1 PPM H2S.
PH range: 0 – 8.5 (above on request)
Temperature: 0 – 30°C (above on request)
Pressure: 0 – 10 barg (above on request)
General purpose for WATERSULF™ 1000 and 5000 Ex II 2G / Eexd II CT 6 ATEX certified.
For –20°C up to +40°C for WATERSULF™ 3000 and 4000.
Distance between probe and electronics: 1500m