Water Detection in Mitsubishi Purifiers on Ships
Types of Water Detectors
The Water Detector Function (WD) of the Multi-Monitor in Mitsubishi fuel oil and lube oil purifiers is a device to prevent separated water from leaking into light liquid (purified oil). It is available in two types, i.e., pressure sensor type water detector and electrostatic capacity type water detector.
Operating Principle of Pressure Sensor Type Water Detector
The Water Detection system provided with a pressure sensor, which is called G-HIDENS system, is controlled on the automatic control panel via the Multi-Monitor of the purifier. The G-HIDENS system constantly monitors separated water being accumulated in the bowl by means of a pressure sensor installed in the circulation line and causes separated water to be discharged before it leaks into light liquid (purified oil).
In the clarifier operation, some of light liquid (purified oil) is returned to the feed liquid inlet via circulation line. The circulation line, which is provided with a back pressure valve, pressure sensor and pressure gauge, is maintained under a required level of back pressure by means of the back pressure valve, with the shut-off valve in the heavy liquid outlet line fully closed. The arrangement is shown in the figure above.
Upon arrival of separated water in the bowl at the top disc outside level, the circulation of light liquid is stopped with an instantaneous drop in circulation line pressure. Detecting this pressure change, the pressure sensor sends a signal to the control panel via the Multi-Monitor to tell that the predetermined quantity of separated water has been accumulated in the bowl and separated water is discharged, normally in the partial discharge mode. In some cases, total charge with sludge takes place, depending on time spent before detection of pressure drop. By this principle water is detected. Diagram below shows a condition when pressure falls due to arrival of water in the top disc periphery.
Electrostatic Capacity Type Water Detector
The electrostatic capacity type water detector relies on difference in dielectric constant between water and oil to determine the capacitance of oil, thereby detecting the water content of oil. This detector is installed in the light liquid connection line of the purifier and controlled on the automatic control panel. Figure below shows a capacitance type water detector connected to the purified oil outlet in a purifier.
In the clarifier operation, the detector monitors the water content of light liquid. When a rise of approximately 0.5% occurs in the water content, the detector recognizes it as “water in the bowl having arrived at predetermined level” and issues an output signal to the control panel. Water is discharged as a result.
Reference:
SAMGONG -MITSUBISHI SELFJECTOR Operation Manual