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LNG World Shipping

LNG World Shipping

Next-generation carriers cut emissions for the long haul

Thu 06 Jun 2019 by John Snyder

Next-generation carriers cut emissions for the long haul
Energy Liberty was the first of four LNG carriers built with SPB cargo containment systems in 25 years

A pair of innovative LNG carriers will cut CO2 emissions by 40% on their route between the US Gulf Coast and Japan

Bushu Maru is one of the latest-generation LNG carriers built in Japan that aims to lower cargo-transportation costs for the long haul, increase cargo capacity and improve CO2 emissions by incorporating some key hullform and propulsion refinements.

Based on Sayaringo STaGE design from Japanese shipbuilder Mitsubishi Heavy Industries (MHI), Bushu Maru and its sister Nohshu Maru were delivered for a joint venture (JV) between JERA Co and NYK Line, destined to carry LNG cargoes from Freeport LNG, Quintana Island, Texas to Japan starting in 2020.

JERA was established in 2015 as an equal-share JV by TEPCO Fuel & Power, a unit of Tokyo Electric Power Co, and Chubu Electric Power Co. JERA has, along with Osaka Gas Trading & Export, LLC, BP Energy Company, Toshiba America LNG Corp, and SK E&S LNG, LLC,contracted under 20-year tolling agreements for 13.5 mta of LNG from Freeport LNG’s Trains 1-3 starting in 2020. Another 0.5 mta has been contracted to Trafigura Pte Ltd under a three-year sale and purchase agreement (SPA) commencing in 2020.

Design considerations 

A key consideration for the design of the vessels was the voyage between the US Gulf and East Coast and Japan. It’s about 10,000 nautical miles (18,500 km) through the expanded Panama Canal locks. The LNG carriers needed to be fuel efficient, to be able to operate in the North American Emissions Control Area, to fit through the Panama Canal, to have a low boil-off rate and to have expanded cargo capacity for improved economies of scale.

The Sayaringo STaGE design is the next evolutionary step from MHI’s earlier Sayaendo design. Like the carriers built to the Sayaendo design, one very noticeable design feature of Bushu Maru and Nohshu Maru is the distinctive continuous sheath that covers their four Moss-type cargo tanks. The word “Sayaringo” is a combination of the Japanese words “saya”, meaning “pod”, and “ringo”, meaning “apple.”

“Saya” refers to the cover, which was an adoption developed by MHI with support from Finland’s Aker Arctic Technology Inc. The cover has three key benefits.

First, the cover acts as a hull-reinforcement element, resulting in greater overall strength and a reduction in weight.

Second, the cover improves the aerodynamics of the vessel by substantially reducing longitudinal wind force that would be a drag on the ship’s propulsion, improving the ship’s fuel consumption.

Third, with the continuous tank cover, the cargo manifolds that connect with onshore LNG terminals during cargo loading/unloading are placed between No. 2 Tank and No. 3 Tank, and the cargo machinery room is arranged inside the tank cover between the No. 3 Tank and No. 4 Tank. The complex structures that support pipes, wires, and passageways placed over the cover are simpler than those of conventional tankers with semi-sphere tank covers, significantly enhancing maintainability.

Apple-shaped tanks

“Ringo” refers to the apple-shaped cargo tanks, which allow increased LNG cargo capacity compared with similar-sized carriers. The apple-shaped tanks consist of donut-shaped torus as well as semi-spheres and a cylinder. MHI modified the Moss-type tanks into an apple-like shape in order to increase the volumetric efficiency and maximise the cargo capacity without increasing the ship’s beam. This was a critical consideration in the ship’s design to allow it to pass through the newly expanded Panama Canal locks, which provide the shortest route between the US and Japan.

Each LNG carrier has an overall length of 297.5 m, beam of 48.9 m, depth of 27 m, draught of 11.5 m and capacity of 180,000 m3. Those dimensions translate into a highly versatile LNG carrier design that is able to operate to more than 100 LNG terminals worldwide while maximising cargo capacity.

Hybrid propulsion plant

Like the Sayaendo design, Sayaringo STaGE incorporates a hybrid propulsion plant using steam turbines and gas engines. The hybrid propulsion plant consists of an ultra-steam turbine (UST) plant on the port side and a combination of a dual-fuel diesel engine (DFE) and a propulsion electric motor (PEM), a DFE-PEM plant, on the starboard side. The DFE can operate on both gas and oil.

The exhaust-gas and jacket waste heat from the DFE are recovered and used to heat the feedwater to the UST plant, improving overall fuel efficiency.

In the UST plant, the heated feedwater flows to the boiler to generate steam to be used to drive the turbine. The electricity generated by the DFE drives the PEM. Ordinarily, a huge amount of waste heat from the DFE is dumped into the exhaust-gas and jacket cooling water. But the STaGE plant uses the waste heat to heat the boiler feedwater, enhancing the plant’s total efficiency.

The waste heat from the DFE is also recycled to generate auxiliary steam as well as the drive steam for the main turbine, also enhancing total efficiency. Instead of a turbine generator used in conventional steam turbine plants, the power generator of the DFE plant supplies power to the ship, resulting in a simpler plant configuration and higher efficiency.

The STaGE plant itself emits an estimated 20% less CO2 than conventional turbine plants.

Twin-skeg design

Bushu Maru and Noshu Maru also incorporate a twin-skeg hullform, which combined with the lower wind resistance offered by the continuous tank cover design, improves manoeuvrability as compared with single-shaft LNG carriers with conventional tanks, according to Japan Marine Science Inc.

MHI reports that the Sayaringo STaGE design as a whole emits about 40% less CO2 per cargo unit than conventional LNG carriers. It estimates the STaGE power plant and hullform improvement with the enlarged twin-skeg each reduce CO2 emissions by 20% per cargo unit, and that the continuous cover adds another 3 to 4% reduction due to its lower wind resistance.


Pioneering pair of LNG carriers to serve Cove Point LNG

Mitsui OSK Lines, Ltd (MOL) christened two LNG carriers that are some of the first large newbuilds of their type to be fitted with self-supporting prismatic IMO Type B (SPB) cargo-containment tanks in 25 years.

Built by Japan United Marine (JMU), Energy Universe and Energy Innovator were christened to serve the trade route between Dominion Energy’s Cove Point LNG in Maryland and Tokyo Gas Co, Ltd under a 20-year agreement. In May 2018, Tokyo Gas began receiving its first shipments of LNG from the Cove Point LNG project at Negishi LNG Terminal.

According to the US Department of Energy, Cove Point was one of four US LNG terminals that exported a total of 483 cargoes in 2018, a jump from 262 export cargoes in 2017.

Energy Universe flies the Panamanian flag and is 100% owned and managed by MOL.

Energy Innovator flies the Japanese flag and is 90% owned by MOL and 10% by Tokyo LNG Tanker Co, Ltd.

Each vessel has an overall length of 300 m, beam of 48.9 m and depth of 11.5 m, a capacity of 165,000 m3 and a tri-fuel diesel-electric (TFDE) propulsion system. Each LNG carrier will have a service speed of 19.5 knots.

Developed by IHI back in the 1980s, the SPB tank-containment system is subdivided into four spaces by a centreline, liquid-tight bulkhead and a transverse swash bulkhead. This subdivision, with the stiffened plate structure of both the shell and the internal supporting elements, strengthens the SPB system to obviate the risk of cargo sloshing damage at all fill levels.

The prismatic shape of the SPB tanks also makes them space-efficient. They can be constructed to accommodate specific hull lines to optimise the space available.

Back in 2017, JMU delivered the first vessel in the series, Energy Liberty. While a floating storage and regasification unit (FSRU) for Exmar was fitted with an SPB containment system, Energy Liberty was the first LNG carrier built with the system since Polar Eagle in 1993.

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