How cargo pumps handle ice conditions

Operations under harsh environmental conditions such as ice and severe sub-zero temperatures pose a challenge for ship operators. Depending on the purpose and the location, additional requirements are necessary to ensure a safe and effective operation. Such requirements cover vessel construction and machinery (also called ‘winterised’ vessels), and appropriately trained ship operators. Under these already challenging conditions, the electrically-driven cargo deep-well pump system should provide efficient and reliable discharging operations.

The MarFlex electrically driven deep-well pump, with its electric motor, is installed on open deck without the need of insulation of the external pump parts, electric motor and cables, despite the extremely low outside temperature. The electric motor is protected by standstill heating when the pump is switched off, which only consumes a minimal amount of power.

“In a cold environment, cargo heating with deck mounted heaters is the most efficient solution”

The design of the pump ensures easy operation because the lubrication oil of the long shaft does not require to be circulated, as an increased viscosity due to low temperatures does not affect the lubrication. The on-deck installation is simple and enables easy access in case of maintenance. The system is always ready for immediate use because there is no heating of substantial quantities of hydraulic oil required, and it does not have to be preheated before the discharging of the cargo (oil/chemicals) begins. This ensures significant energy saving. By protecting the motors and pump parts with a PVC canvas cover, with a cold resistance down to -50°C, de-icing before discharging is not required.

To keep the cargo well pumpable, heating is usually done by means of in-tank heating coils or deck mounted heaters. In a cold environment, cargo heating with deck mounted heaters is the most efficient solution. The entire cargo is pumped from the tank through the deck heater, where it is evenly warmed by the heating elements, and then recirculated to the tank. In both cases, the electrically driven deep-well pump can be used to keep the cargo warm at a steady pace, due to the VSD system. The system offers the opportunity to operate two pumps on a reduced rate through one frequency converter. With the correct system configuration, all pumps together can be used for recirculation of the cargo, without the need of using one frequency converter per pump. In addition, MarFlex deep-well pumps can, at various levels, be fitted with cargo temperature sensors for cargo temperature monitoring.

Where a tanker is designed for icebreaking activities, both the construction of the vessel and the equipment on board must be adapted due to the heavy forces that are placed on the construction and the equipment. MarFlex will carry out extensive stress calculations (stress analysis) and will, in collaboration with the shipyard, advise on the appropriate tank supports for the deep-well pumps to ensure the required strength.

MarFlex has supplied deep-well pump systems for some arctic tankers operating around Sabetta, in Russia. These vessels are thoroughly winterised for operations in ambient temperatures down to -50°C. MarFlex has had the pump equipment, including the electric motors, tested at -60°C, both in standby mode and running condition.