OCTOBER 1, 2013 — To reduce fuel consumption during slow steaming, a 318,000 dwt Maersk Tankers VLCC has been retrofitted with Variable Turbine Inlet system (VTI) turbochargers.

Cross-section view of VTI turbocharger

According to Mitsubishi Heavy Industries Marine Machinery & Engine Co., Ltd. (MHI-MME), the retrofit saw fuel consumption improve 1.6 – 3.2% in the load range of 10 to 50% MCR, with an "attractively short" pay-back period.

The retrofit was carried out on the VLCC Maersk Ingrid during her first drydocking in May 2013.

Maersk Ingrid's main engine is a Wärtsilä 7RTA82T with two Mitsubishi MET71MA turbochargers that were manufactured by Hyundai Heavy Industries, under license.

VTI is a system developed by MHI-MME for the MET turbocharger series. The gas inlet passage is equipped with an on-off valve which changes turbine capacity in two stages by admitting the exhaust gas into two separated concentric segments of the nozzle ring. When the vessel is in slow steaming mode, scavenging air pressure of main engine is increased by closing the on-off valve which thus decreases fuel consumption rate and CO2 emission.

MHI-MME has delivered more than 10 VTI systems for newbuilding projects. However, the Maersk Ingrid is the first in-service vessel to be retrofitted with the system.

VTI system installed in Maersk Ingrid

MHI-MME supplied the gas inlet inner casing with VTI system for the vessel. The retrofit work was completed in four days.

NOx emission was measured at sea trial after retrofit, and confirmed to comply with IMO Tier 2 regulations.

"Moreover," says MHI-MME, "we confirmed the expected fuel consumption reduction effect at the Low-load operation without sacrificing the performance in the high-load range."

Mr. Vaibhav Chavate, who led this first retrofit project for the shipowner, concluded that the fuel consumption reduction was 1.6 – 3.2% in the load range of 10 to 50% MCR and the pay-back period is attractively short. The application of VTI to further vessels with MET turbochargers is now under consideration by A.P. Moller.

MHI-MME says that the VTI Turbocharger is not only a suitable system for slow steaming, but its simple structure results in high reliability while achieving low costs and easy maintenance. In addition,it says, the VTI system is easy to retrofit on conventional MET turbochargers by just adding a nozzle and an on-off value to the exhaust gas inlet area.