These guidelines describe loading, heating and discharging molasses based on experience. They are to be regarded as general guidelines only.
Molasses is a very high viscous product (a non-Newtonian fluid).The ability to pump this product depends on a number of factors:
Loading
1. Before loading, carry out a purge routine, to verify absence of any leakage.
2. Before loading, fill the cofferdam with fresh water [± 5–10 ltr.], to prevent crystallization of molasses in case of seal leakage.
3. Carefully start loading via drop line only (if possible) Avoid free fall of molasses through the tank hatch. Free fall may cause the molasses to entrap air bubbles (aeration), thus increasing fermentation tendency. Fermentation gases may not escape the cargo and cause serious problems during discharge.
Heating
1. Keep the cargo temperature at ± 35 – 38 °C during voyage to maintain an adequate pumping condition of the cargo.
2. Avoid a too high cargo temperature to prevent possible increase of a fermentation process.
3. Check the temperature rise over the cargo heaters (if installed) regularly. Maximum temperature increase over cargo heaters during heating operation is 10 °C. This is the most important checkpoint to avoid crystallization and blockage of the cargo heater. Increase the pump capacity in case of a too high increase of temperature until an acceptable increase of temperature is achieved. Be aware that operating the pump at a too high speed for a long period of time increases the risk of crystallization of molasses in the pump’s shaft seal area
4. Maximum recommended temperature of the heating medium is 110 °C.Do not expose the heating medium directly to the cargo pump, cargo pump discharge line or stripping line, this may cause crystallization of molasses and damage the seal arrangement. Maximum allowed temperature in the cargo pump is 110 °C.
5. Run the cargo pump at a reduced speed that matches molasses flow behavior. Monitor the electric motor amperes carefully.
6. During normal heating operation the pressure drop over the cargo heater should not exceed 3 bar.
Discharge
1. Increase the cargo temperature to the recommended temperature for discharge. Maximum discharge temperature is 40 °C.
2. Stop the heating operation as follows:
- close the steam valve upstream the cargo heater.
- stop the pump after 10 – 15 minutes.
- close the cargo valve upstream the cargo heater.
- drain the cargo in the heater back to the tank.
3. Avoid to many pipe bends and pressure loss in the discharge line. Use a discharge hose as big as possible.
4. Use booster pumps if a high discharge head is required due to shore arrangement and location of shore tank and/or ship.
5. Run the cargo pump at reduced speed and monitor the electric motor amperes. A change in absorbed electrical power is a possible indication of cavitation and a signal to reduce the speed of the pump.
6. Reduce the pump’s speed more at a cargo tank level of approximately ¼ to prevent foaming and possibility of cavitation.
7. To decrease the foam quantity in the molasses during the last part of discharging several methods have been tried:
- adding of chemicals (non-toxic).
- re-circulation through the drop line.
- adding of steam through tank hatch or Butterworth opening.
- adding of air into molasses through tank hatch in order to stop fermenting process.
8. Purge the cofferdam on all cargo pumps after completion of the discharge.
Always follow charter’s instructions if more restricted then above.
Exposure of molasses to higher temperatures than given above may cause crystallizing with blocked cargo heater as result. Therefore we recommend the highest precaution and attention to the heating operation and guidelines provided.
As stated at the beginning, molasses is complicated cargo and information given above is to be regarded as guideline only.
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