New Generation Of ‘Green’ LNG Carriers

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  • IMO implements Energy Efficiency Design Index (EEDI) and the future Carbon Intensity Index (CII).
  • It will have a profound impact on how the next generation of LNG carriers are designed and equipped, driving investment in energy-saving devices.

A recent news article published in the Riviera states that Environmental pressures create new generation of ‘green’ LNG carriers.

IMO’s Energy Efficiency Design Index (EEDI)

Implementation of IMO’s Energy Efficiency Design Index (EEDI) and the future Carbon Intensity Index (CII) will have a profound impact on how the next generation of LNG carriers are designed and equipped, driving investment in energy-saving devices.

Two 174,000-m3 newbuild LNG carriers ordered by Capital Gas Ship Management Corp will each be equipped with two 1.9 MW Wärtsilä shaft generators to lower fuel consumption and yield efficiency gains.

While this might not seem earth-shattering, Capital Gas Ship Management Corp managing director Miltos Zisis says the decision to equip the ships with shaft generators was driven by a desire to continue to improve the shipowner’s fleet efficiency and reduce its environmental footprint. “The installation of advanced shaft-generator systems is one of the investments we are making in this direction,” he says.

In its other newbuildings in the series, Capital Gas Ship Management has incorporated air-lubrication systems, propeller boss cap fins and rudder bulbs to further increase energy efficiency and lower fuel consumption. Other LNG carrier owners are incorporating similar technologies.

Maran Gas Maritime’s newest LNG carrier

Maran Gas Maritime’s newest LNG carrier under construction at Samsung Heavy Industries (SHI) will be equipped with GE’s SeaGreen Power Take Off (PTO) system, incorporating GE’s latest medium voltage Advanced Permanent Magnet Machine (APMM).

The technology will help reduce Maran’s operating costs and the ship’s fuel consumption and greenhouse gas (GHG) emissions.

PTO is an effective way of incorporating GE’s hybrid electric ship technology where there is limited space, and it will provide electric power to the ship’s on-board network.

CO2 emitted per cargo-carrying capacity

CII is a measure of how efficiently a ship transports goods or passengers and is given in grams of CO2 emitted per cargo-carrying capacity and nautical mile.

Each LNG carrier will be assigned a reference CII level based on size and type. Starting in 2023, LNG carriers will have to reduce their CII by 5% as compared to 2019 reference levels. This will be followed by 7% in 2024, 9% in 2025 and 11% in 2026.

The reduction levels are compared with 2019 levels.

“Methane slip can be offset with current technologies and certain combustion systems”

Wärtsilä will supply four shaft-generator systems

Under an order received in August, Wärtsilä will supply four shaft-generator systems to provide PTO from the main engines for two LNG carriers.

By enabling PTO, the systems allow the main engine to generate electricity for onboard use, reducing fuel consumption, lowering emission levels, and improving both the vessels in line with EEDI and CII.

“We are committed to delivering products, systems, and solutions that contribute to the decarbonisation of the maritime sector,” says Wärtsilä Marine Power general manager sales Yiannis Christopoulos. “Our highly efficient shaft-generator systems utilise the latest technology to make a significant contribution to this ambition, while at the same time lowering operating costs for the customer.”

Nine-ship newbuilding programme

Under construction at South Korea’s Hyundai Heavy Industries (HHI), these LNG carriers are believed to be the last two vessels in a nine-ship newbuilding programme.

Amore Mio I and an unnamed sister ship will both fly the Marshall Islands flag and be among the first LNG carriers with MAN Energy Solutions’ new Otto-cycle, dual-fuel, low-pressure, two-stroke ME-GA engines.

Instrumental to the ME-GA engine’s early success has been its increased focus of methane-slip reduction through the use of MAN’s proprietary exhaust gas recirculation (EGR) solution. EGR is a NOemissions-reduction technique that enables IMO Tier III-compliance in diesel mode for the ME-GA.

Introduced in March 2021, the engines will not be sold without MAN’s EGR solution. Increasingly, shipowners are opting for low-pressure, Otto-cycle, dual-fuel, two-stroke engines in their LNG newbuildings. Of the 130 LNG carriers on order in 2020, 82 – or 63% – had WinGD X-DF Otto-cycle, dual-fuel propulsion.

“In shipping circles, we consider unburnt methane in ships’ engines to be a major concern and, of course, it is an important issue,” says Lloyd’s Register (LR) Global Gas segment manager Panayiotis Mitrou. “Engine designers and combustion experts are making great progress in reducing methane slip. Of course, we must not be complacent – the end objective is to eliminate methane slip entirely.”

Methane slip can be offset with current technologies

Mr Mitrou noted in a recent issue of Horizon that methane slip can be offset with current technologies and certain combustion systems. “Two‐stroke, high‐pressure, diesel‐technology engines, combined with power take‐off arrangements such as shaft generators, go a long way towards solving the problem. But other systems are under development that will tackle methane slip in existing engines, as well as other engine combustion arrangements,” he says.

LR is involved with various initiatives that would entirely eliminate methane emissions onboard ships.

“We are also working on a proposal for the funded development and full‐scale proof of concept of technology specifically tackling the shipboard methane issue,” says Mr Mitrou.

GTT has received an AiP for a ballast-free LNG bunker vessel (source: GTT)

Ballast-free ship design

Beyond GHG emissions, one of the biggest environmental compliance headaches for shipowners has been ballast water treatment. A new concept developed by France’s GTT offers a simple solution for LNG bunker vessel owners – a ballast-free ship.

The concept, called Shear-Water

The concept, called Shear-Water, has received approval-in-principle (AiP) from both the China Classification Society (CCS) and DNV. The LNG bunker ship incorporates a large bilge keel and a Flume anti-rolling tank supplied by German engineering firm Hoppe Marine. This Flume roll-damping tank is designed to operate at maximum efficiency when the vessel is empty, where rolling might be most severe. It can also be operated at design draft conditions with slightly less efficiency.

Most merchant vessels worldwide use ballast water to maintain stability and seaworthiness when the bunkers are empty or only partially loaded. However, this requires ballast water to be treated when discharged to avoid contamination of the environment and the release of invasive organisms.

This risk is eliminated in the new vessel

This risk is eliminated in the new vessel concept because the Flume tank is operated with fresh water, avoiding the ballast water treatment process. Additionally, a ballast-free ship offers advantages in terms of capex and opex, simplifying ship operation, reducing corrosion and extending service life.

The seakeeping behaviour of the Shear-Water design was extensively tested at the Hamburg Ship Model Basin, including different bilge keels and the operation of the ART in various load cases, sea-states and headings.

GTT said the results confirmed the efficiency of the installation, with a rate of roll reduction between 15% and 40% for full condition and 44% to 64% for empty condition.

Under a memorandum of understanding (MOU), GTT and CCS are further extending their co-operation on the application of membrane containment technology on a wide range of LNG vessel types, LNG-fuelled vessels and onshore applications. Plans call for joint development of designs for Chinese LNG inland waterway transportation, LNG carriers, LNG-fuelled vessels and onshore LNG storage tanks.

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Source: Riviera

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