de Glossar

Oil trace measurement

The most widespread application of the Sigrist fluorescence instrument is the detection of traces of hydrocarbons in water.

In the laboratory, hydrocarbon determination is carried out by infrared absorption measurement. Because the water itself absorbs the infrared radiation, the hydrocarbons have to be extracted first with a solvent (carbon tetrachloride or a freon). This sample preparation (mixing, separation, drying) excludes continuous measurement and makes it very costly to operate such analyzers in industrial applications. A simple substitute solution now in use is turbidity measurement. Although it does detect tiny suspended oil droplets, it also reacts to other turbidity substances and fails to detect dissolved hydrocarbons.

For these reasons, the measurement of fluorescence has been adopted as direct detection method. It picks up the fluorescing substances regardless of their form (dissolved, emulsified, etc.) specifically and without requiring the use of reagents.

The most important industrial applications are:

  • oil extraction. The extracted crude oil is mixed with water, which must be separated from the oil and then cleaned before being discharged to the environment. The tolerable residual oil content of the water is monitored by means of fluorescence measurement.
  • oil tankers. Because the ballast water is badly contaminated with oil, it has to be treated either on board or ashore before being returned to the sea. Here too, continuous fluorescence instruments check the water's residual oil content.
  • heat exchangers. In production processes in the petrochemical industry, large numbers of heat exchangers are used for heating and cooling with steam or water. Leaks in these exchangers cause contamination of the water or condensate, which can have costly and dangerous consequences.
  • wastewater. Industrial wastewater effluents may not be polluted with hydrocarbons. Fluorescence instruments monitor the officially prescribed limits continuously. The following sketch illustrates sampletaking from the wastewater drain.

Sampletaking from a wastewater drain

 

  • potable water. Spring water and surface water used for drinking water supplies can be contaminated with hydrocarbons as a result of accidents or leaks in fuel oil tanks. Continuous oil trace detection ensures clean drinking water.
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