Screw Compressors for Dual-fuel LNG Carrier

Kobe Steel, Ltd. said it has received an order to supply the first two screw compressors for use with marine dual fuel engines.

The compressors will be installed in an LNG carrier to be owned by a 50/50 joint venture between Mitsui O.S.K. Lines Co., Ltd. (or MOL) and Itochu Corporation for Uniper Global Commodities SE, a subsidiary of Uniper SE, Europe’s one of largest power and gas companies. Uniper Global Commodities will charter the new carrier for 20 years. Plans call for Kobe Steel to deliver the compressors in August 2017 to South Korea’s Daewoo Shipbuilding & Marine Engineering Co., Ltd., which is constructing the vessel.

The market size of nonstandard compressors for marine dual fuel engines is forecast to total over 20 billion yen for the coming five years, according to Kobe Steel. Kobe Steel aims to gain over 50 percent of the market by 2020.

Nonstandard compressors for marine dual fuel engines are generally used to compress vaporized LNG, namely boil-off gas (BOG), which is then sent to the engines. To date, marine dual fuel engines have been of the middle speed, four-stroke type and driven predominantly by low gas pressure, and the compressors for these engines have only been centrifugal compressors, which excel at low-pressure compression.

However, in recent years due to the need to save energy in ship operation and comply with stricter environmental regulations, dual fuel, low speed, two stroke engines that offer high efficiency with a 10-percent improvement in fuel consumption have entered the market. In the future, this type of engine will become the mainstream as its adoption is being considered for nearly all new vessels.
 
As marine dual fuel, low speed, two-stroke engines require relatively high gas pressure, centrifugal compressors are less efficient. These engines need to have their fuel gas (FG) pressure controlled within the allowable level of the load percentage of the engines. Screw compressors are highly suitable for these engines as they can keep pace with load fluctuations and operate most efficiently in the medium- to high-pressure range. Owing to this feature, screw compressors have been adopted for use with marine dual fuel engines for the first time.
 
Kobe Steel has received an additional order for one reciprocating compressor for BOG reliquefaction, which will be installed in the same vessel.
 
More than 100 LNG carriers have been constructed in the three years from 2013 to 2015. Although the shipbuilding boom has settled slightly due to the fall in raw material prices and the downturn in the world economy, demand remains high for LNG and the market for this clean fuel is expected to grow in the future.