Viscotherm with Differential Pressure (DP) Transmitter:

• The viscotherm consists of a capillary tube connected to the discharge side of a gear pump driven by an electric motor.
• A DP transmitter measures the pressure difference in the capillary tube, which is directly proportional to the fuel oil's viscosity.
• The fuel oil passes through a heater controlled by a steam valve. The valve adjusts the steam flow to maintain the desired fuel viscosity.
• A controller compares the measured viscosity from the DP transmitter to the set point and sends a signal to regulate the steam valve.

Operation of Viscotherm:

• As fuel flows through the viscotherm, the gear pump diverts some of the fuel through the capillary tube.
• The DP transmitter measures the pressure difference across the capillary tube.
• The DP transmitter sends the viscosity data to the controller.
• The controller compares the measured viscosity to the set point value.
• If the viscosity deviates from the desired level, the controller adjusts the steam valve to increase or decrease the steam flow to the fuel heater.
• Adjusting the steam flow changes the fuel temperature, directly impacting viscosity to maintain optimal levels.

1. Forty-eight hours prior to entering the ECA, the low sulphur settling tank should be filled, the purifier started, and the service tank should be filled up and allow the purifier to continue running, and fuel should be circulated from the service to the settling tank. If the fuel is clean, there is no need to purify it, and it can directly fill the service tank.
2. Toolbox meetings should be conducted, informing the crew about the changeover along with the date and approximate time.
3. Using the FOBAS calculator, the exact time required for changeover can be calculated.
4. The bridge officers should be informed to give notice to the engine room 4-6 hours before entry to ECA.
5. Reduce the engine load to around 25 to 40% MCR during this process to ensure slow heat reduction. Max temperature change gradient of 2°C/min. The same can be controlled by the temperature controller on module by reducing gradient time. A slow temperature decrease is to prevent thermal shocking of the engine fuel system (fuel pump, fuel valves)
6. When the changeover is required to be carried out, close the steam heating valves to the heater. Wait until the viscosity rises to 18Cst. Also, close the steam tracing valve.
7. Make sure that the return line from the main engine is to the buffer tank and not return back to the service tank. This is to prevent cross-contamination.
8. When the viscosity is 18Cst or above, and the temperature of fuel oil has fallen below 90deg, slowly change over the three-way valve to take suction from the low sulphur tank.
9. The temperature will now gradually decrease until it reaches the temperature in the low sulphur service tank.
10. Now, the viscosity will start to decrease, and When the viscosity is reached below 8cst, open the valves to the cooler so that viscosity does not drop too much, as this will cause problems of lubrication to the fuel pumps.
11. Wait until all the fuel in the system is flushed with ultra-low sulphur fuel oil.
12. Gradually increase the engine load to 75% MCR and observe if the fuel pressure is constant.
13. Also, check the HFO service tank level is not increasing, which might be due to a leaking valve.
14. A suitable log entry should be made after the changeover operation.
15. Date and time of completion of fuel changeover
    1. Ship position - latitude and longitude, on completion of fuel changeover
    2. The volume of low sulphur fuel oil in each tank on completion of the changeover
    3. Tank identity
    4. Tank quantity
    5. Signature of a responsible officer.