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The Agar Automatic Tank Dewatering System has responded with an excellent level of performance on the tank dewatering application at HHI - Kuwait on the "Crude Export Facilities at NTF, STF & MAA Project".
The Agar ID-201 oil/water interface detector is used as the Control Probe for dewatering the crude storage tanks and is located at the top of drain sump just below the tank floor. When clean water is detected, the water drain valve opens and remains open until a low concentration of oil is detected. Only clean, oil free water is discharged from the bottom of the sump.
An Alarm Probe is inserted lower into the sump, 50 cm below the Control Probe. This Alarm probe is meant to operate in a 100% clean water environment at all times. If there is an upset in the vessel or the water draw-off valve does not close properly, oily water will be detected at this lower elevation. The alarm probe then sends an alarm to the Control Room to close a secondary back-up drain valve.
As an added precaution, K.O.C. requires a second alarm probe outside of the tank. Refer to Figures 1 and 2.
No preventative maintenance is required on these probes because they continue to function even when coated with heavy oil or paraffin. Since they are located in the water draw-off sumps, there is no sludge or solids build-up to affect their performance.
There are several advantages to this unique control system:
- No oil is discharged with the waste water (less than 30ppm).
- The water quality is controlled in the sumps, below the floor of the tanks.
- The floor of the tanks are covered in oil (not water)…..eliminating any corrosion of the floor plates.
- Since there is a minimum amount of water in the tank, the risk of a Boil-over during a fire is eliminated.
See attached pictures and installation drawing.
The attached table shows the Site Acceptance Test results of four tanks achieving less than 15ppm oil discharge with the waste water and zero water at the tank bottom.
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