Wednesday, July 1, 2020

ODME

A step by step guide of how to operate ODME and principle of its operation

How does ODME do it
ODME controls the operation of two valves
  1. Valve to slop tank.
  2. Valve to overboard tank.
These two valve will never be open or close together. If one is open, the other will be in close position.

The formula for Instantaneous rate of discharge is
Now if ODME need to measure IRD, it surely need values for oil content in PPM and Flow rate.
  • Speed connection is usually given either from log or GPS.
  • All these values are fed to the computing unit of the ODME. 
  • Computing unit does all the mathematical calculations to get the required values. 
  • Most of the times you will find the computing unit in Cargo control room.
Flow rate
  • ODME computing unit gets the flow rate from flow meter. 
  • A small sample line goes from the main line, pass through the flow meter and goes back to the main line. 
  • Flow meter calculates the flow in m3/Hr and gives this value to the computing unit through a signal cable.
Measuring PPM
  • Measuring cell is the component that measures the amount of oil (in ppm) in the water. Measuring cell is located in a cabinet called “Analysing unit”. Most of the times you will find “Analysing unit” in the pump room.
  • The measuring principle relies upon the fact that different liquids have different light scattering characterstics. Based on the light scattering pattern of oil, measuring cell determines the oil content.
  • The sample water is passed through a quartz glass tube. And the oil content is determined by passing this sample water in different detectors in series.
  • But to measure PPM in a water sample, a sample from the discharge water need to pass through the measuring cell. This job is done by a sample pump.
  • Sample pump draws the sample from the discharge line before the discharge valves. This sample is sent to the measuring cell (in analysing unit) for measuring the oil content and then sent back into the same discharge line.
  • To clean the measuring cell, ODME runs cleaning cycle in pre-defined interval during its operation. The cleaning cycle involves flushing the cell with fresh water.

If the ODME has provision for detergent injection, the required amount of detergent will be injected during the cleaning cycle
We need to make sure that the detergent tanks is not empty and we use maker recommended detergent only.
Operation of ODME
  • Allow minimum 36 hours settling time
  • We will wash the tanks and collect the slops in slop tank. But before we can start pumping out oily water through ODME, we need to allow a minimum of 36 hours settling time. This settling time ensures that the oil has separated completely from the water.
  • We may argue that if our discharge is limited to 30L/NM, then what difference does it make with settling time ? But the fact is that even when we can use the ODME to discharge oily water, we must ensure that the oil is minimum in the water

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