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Wärtsilä has announced that it is to supply the main engines for two environmentally sustainable tugs being built for CNOOC Energy Technology & Services Limited (CETS), a subsidiary of the state-owned China National Offshore Oil Corp. (CNOOC).

The vessels are the first in a planned series to be fuelled by liquefied natural gas (LNG), and will be the first tugs in China ever to be operated on gas. The contract was signed in the beginning of July 2012 and the order is included in the third quarter 2012 order book.

The strategy of CNOOC is aimed at achieving more clean energy in its operations. According to Wärtsilä, the low emission levels made possible by its dual-fuel engine technology is particularly beneficial for vessels operating close to population centres, as tugs frequently are, while the high fuel efficiency enables lower operating costs.

The 6500 bhp tugs will operate along China's coastline, and will be fuelled from the company's own bunkering terminals.

"We are delighted to be co-operating with CNOOC in supplying the main engines for these gas fuelled tugs. It is a landmark project that is very much in line with the marine sector's key targets of achieving greater sustainability with better fuel efficiency. We endorse CNOOC's strategic move towards cleaner energy and the use of LNG as a marine fuel, which is precisely in line with Wärtsilä's own strategy," said Aaron Bresnahan, Vice President Wärtsilä Ship Power Specials.

The vessels will each be powered by two 6-cylinder Wärtsilä 34DF in line dual-fuel engines. Delivery is scheduled at the beginning of 2013, and the first of the tugs is expected to be delivered in June 2013.

Wärtsilä dual-fuel (DF) engines

Wärtsilä's advanced dual-fuel technology was first launched in the early 1990s for use in land-based power plant applications. The first marine installation came a decade later. The technology enables the engine to be operated on either natural gas, light fuel oil (LFO), or heavy fuel oil (HFO), and switching between fuels can take place seamlessly during operation, without loss of power or speed. Wärtsilä DF engines are designed to have the same output regardless of the fuel used.

The fitting of Wärtsilä DF engines onboard the first LNG Carriers in 2006 set a trend in the industry. Since that introduction, 65 percent of all new LNG Carriers have been fitted with Wärtsilä dual-fuel engines.

When operating in gas mode, the nitrogen oxide (NOx) emissions are at least 85 percent below those specified in the current IMO regulations, and CO2 emissions are some 25 percent less than those of a conventional marine engine running on diesel fuel. Additionally, the sulphur oxide (SOx) and particle emissions are negligible at almost zero percent.

Wärtsilä has recently achieved the notable milestone of supplying dual-fuel propulsion engines to 100 Liquefied Natural Gas (LNG) Carrier vessels. As of end May, Wärtsilä has sold some 720 DF engines, and has accumulated more than 5 million running hours of experience with this technology.