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The VF-AFE: optimises engine speed, reduces specific fuel consumption

The VF-AFE: optimises engine speed, reduces specific fuel consumption



New fuel saving system for vessels

GE’s technology upgrade enables ship owners gain a plethora of savings in fuel consumption, emissions and maintenance costs

June 2013

A new power and propulsion system that reduces fuel consumption by controlling engine speed on platform support vessels has been unveiled by GE’s Power Conversion business.

The Variable Frequency Active Front-End power and propulsion system, or VF-AFE, enables ship owners using conventional power system components to lower engine speeds when feasible, cut fuel consumption, and reduce emissions and maintenance requirements.

“We are increasing efficiency of existing technology for the benefit of our customers,” says Paul English marine leader of GE Power Conversion. The VF-AFE system allows the use of conventional power system components (main switchboard drives, etc), so learning how to operate it is relatively easy, and operators require minimal training.

“Today, when you operate a conventional engine, its speed is always constant, whatever the load,” English says. “So when the load is reduced, you are using more energy than you need, because the pistons continue to run at an unnecessarily high speed. This lowers your efficiency. The VF-AFE enables you to recover that lost efficiency.”

When a support vessel is operating in dynamic positioning (DP) mode, the load on the engines is reduced, just to counter the effect of wind and waves, but all engines are kept running in order to provide redundancy. This means that, if the power from one engine is lost, power is still available from the others to keep the vessel in position. This arrangement while effective is not the most efficient. With VF-AFE, all the engines remain connected, but their speed can be cut when the load is reduced.

“We have made a calculation based on specific operating conditions, assuming a fuel price of $900 per tonne,” says English. “We estimate that, with the engines loaded at 50 per cent of rated load for a full year on a ship with 8 MW of installed power operating for 300 days a year, 24 hours a day, the fuel savings could be up to $300,000 per year.”

The active front end drives more than just the engine. Auxiliaries onboard the vessel still require a fixed frequency, so extra equipment will be needed to convert the variable frequency from the VF-AFE into a fixed frequency. This requires an additional investment by the customer but, even so, GE estimates that the return on the total investment is achieved in less than a year.

“This solution is unique to GE,” says English. “We have looked at what can be done with existing technology that customers are using and have engineered a way to make this existing technology, that a customer is comfortable with, more efficient.”

The VF-AFE uses a version of GE Power Conversion’s MV 3000 low voltage drive that has been modified to make it more compact.




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