Assignment Of CII Rating To LNG Carriers
The "Carbon Intensity Indicator" (CII) is an operational performance indicator provided in MARPOL Annex VI in order to measure the carbon intensity of the ships, based on their annual fuel consumption, the distance travelled in the course of the year (expressed in nautical miles) and the time (hours) spent on voyages.
The Regulation 28 of MARPOL Annex VI requires that, on the basis of the annual fuel consumption data, the distance travelled in the course of the year and the time spent on voyages, after the end of the calendar year 2023 and after the end of each following calendar year, each ship of 5,000 gross tonnage and above to calculate the attained annual operational CII over a 12-month period from 1 January to 31 December for the preceding calendar year.
The attained annual operational CII of individual ships has to be calculated as the ratio of the total mass of CO2 emitted to the total transport work undertaken in a given calendar year1.
The total mass of CO2 is the sum of CO2 emissions (in grams) from all the fuel consumed on board a ship in a given calendar year. According to the Regulation 2.1.14 of MARPOL Annex VI, the fuel oil consumption data that has to be reported to the ship`s Administration should include the consumption data with regard to any fuel used for propulsion, including gas, distillate or residual fuels. Therefore, the LNG carriers using the boil-off gas as fuel should report the mass equivalent of the LNG volume consumed less the nitrogen mass content because the nitrogen does not contribute to CO2 emissions.
The total transport work is calculated as the product of the ship`s capacity and the distance travelled in nautical miles in a given calendar year. In the case of LNG carriers, the ship`s deadweight tonnage is used as the ship`s capacity and not the tanks` volumetric capacity.
The CII reference line values were calculated for each ship type based on the attained operational CII of individual ships of that type within specified DWT ranges in the year 2019.
For the LNG carriers, the CII reference line values were calculated based on the parameters specified for three DWT ranges:
- above 100,000 tons DWT;
- between 65,000 and 100,000 tons DWT;
- below 65,000 DWT2.
This was done without taking into consideration the difference between the propulsion systems installed on board the LNG carriers.
The world fleet of LNG carriers has 711 ships. Of these, there are 189 LNG carriers powered by conventional steam turbines, 17 LNG carriers powered by steam turbines with steam reheat technology, 8 LNG carriers powered by a hybrid propulsion system called "STaGE", 172 LNG carriers powered by the four-stroke dual or tri-fuel diesel electric engines, 48 LNG carriers powered by MAN B&W Diesel ME-C two-stroke low speed diesel engines and 277 LNG carriers powered by the two-stroke dual-fuel engines.
LNG Carriers Powered By Conventional Steam Turbines
The conventional steam turbines have a 30% propulsion efficiency. They were installed on board the LNG carriers build in the 1970s, 1980s, 1990s and early 2000s at a time when there was no other propulsion system available for this type of ships. They were designed not on fuel efficiency considerations but to use the boil-off gas generated by the LNG cargoes as fuel, taking into consideration a daily rate of boil-off gas of 0.15% based on the LNG tank insulation technology available at the time of the ship`s building.
The LNG industry demand for ships with larger capacity able to transport larger LNG volumes led to the introduction in 2006 of the four-stroke dual-fuel diesel electric engines and subsequently in 2007 of the two-stroke low speed diesel engines and in 2015 of the two-stroke dual-fuel engines.
The conventional steam turbines became the least efficient propulsion systems in the global LNG fleet. The LNG carriers powered by conventional steam turbines have the highest fuel consumption and generate the highest CO2 emissions per ton of all types of LNG carriers.
There are 189 conventional steam turbine LNG carriers currently in operation. Of these, there is one ship built in 1977 ("LNG Aquarius"), two ships built in 1989, 35 ships built in the 1990s, 146 ships built in the 2000s and 8 ships built between 2010 and 20143.
183 of the 189 conventional steam turbine LNG carriers have a deadweight between 66,000 and 90,000 tons.
The oldest ship "LNG Aquarius" built in 1977 has a deadweight of 72,622 tons.
In the case of the two LNG carriers built in 1989, "LNG Maleo" has a deadweight of 66,892 tons and "Northwest Sanderling" has a deadweight of 66,810 tons.
Of the 35 LNG carriers built in the 1990s, two ships have a deadweight of 35,760 tons, one ship has a deadweight of 48,817 tons, 32 ships have a deadweight between 71,000 and 77,000 tons.
Of the 146 LNG carriers built in the 2000s, one ship has a deadweight of 34,800 tons, two ships have a deadweight of 39,483 tons, 143 ships have a deadweight between 73,000 and 82,000 tons.
The 8 ships built between 2010 and 2014 have a deadweight between 79,000 and 90,000 tons.
LNG Carriers Powered By Steam Turbines With Steam Reheat Technology
The steam turbines with steam reheat technology have a 35% propulsion efficiency.
The steam reheat technology improves the thermal efficiency of the steam turbine propulsion system with approximately 15% compared to the conventional steam turbine plants. The improvements in the efficiency of the steam turbines brought by the steam reheat technology had as effect a lower fuel consumption than that of the conventional steam turbine plants.
In the case of Sayaendo class LNG carriers built by Mitsubishi Heavy Industries between 2014 and 2018, the continuous steel cover over the cargo tanks that reduces the wind pressure from the front, along with the lighter hull structure and the steam reheat technology contribute to a 20% reduction in the fuel consumption and to a proportional CO2 emission reduction compared to the conventional steam turbine LNG carriers built in the 2000s.
There are 17 LNG carriers powered by steam turbines with steam reheat technology:
- 5 LNG carriers with a deadweight between 83,000 and 87,257 tons, built by Kawasaki Heavy Industries between 2011 and 2018;
- 8 LNG carriers with a deadweight between 80,000 and 86,497 tons, built by Mitsubishi Heavy Industries as Sayaendo class between 2014 and 2018;
- 4 LNG carriers with a deadweight between 84,291 and 84,333 tons, built by Hyundai Heavy Industries between 2017 and 2018.
LNG Carriers Powered By STaGE Hybrid Propulsion System
STaGE propulsion system has an approximately 40% propulsion efficiency.
There are 8 LNG carriers with STaGE hybrid propulsion system built between 2018 and 2019 by Mitsubishi Heavy Industries. They have a deadweight between 87,494 and 97,955 tons.
LNG Carriers Powered By The Four-Stroke, Dual Or Tri-Fuel Diesel Electric Engines
LNG carriers powered by the four-stroke, dual or tri-fuel diesel electric engines have a propulsion efficiency ranging from 40 to 45%.
There are 172 LNG carriers powered by four-stroke, dual or tri-fuel diesel electric engines, including 13 Icebreakers, built between 2006 and 2024. Of these, there are three small-scale ships with a deadweight between 16,250 and 31,712 tons and 169 conventional size ships with a deadweight between 72,800 and 99,000 tons.
LNG Carriers Powered By The Low Speed Two-Stroke Diesel Engines
There are 48 LNG carriers powered by low speed two-stroke diesel engines:
- 13 Q-Max LNG carriers powered by MAN B&W Diesel 7S70ME-C electronically controlled low speed two-stroke diesel engines running on heavy fuel oil in conjunction with reliquefaction plants. Ten of the thirteen ships have a deadweight of 130,000 tons. The other three ships have a deadweight of 155,000 tons. They were built between 2008 and 2010.
- 31 Q-Flex LNG carriers powered by MAN B&W Diesel 6S70ME-C electronically controlled low speed two-stroke diesel engines running on heavy fuel oil in conjunction with reliquefaction plants.
They have a deadweight between 104,000 and 122,000 tons. They were built between 2007 and 2010.
- 4 Conventional size LNG carriers powered by MAN B&W Diesel 6S70ME-C8 electronically controlled low speed two-stroke diesel engines running on heavy fuel oil in conjunction with reliquefaction plants. They have a deadweight between 96,193 and 96,355 tons. They were built between 2015 and 2016.
MAN B&W Diesel electronically controlled low speed two-stroke diesel engines have a propulsion efficiency of approximately 50% but the power consumption by the reliquefaction plant reduces their efficiency.
LNG Carriers Powered By The Two-Stroke Dual-Fuel Engines
There are 277 LNG carriers powered by the two-stroke dual-fuel engines.
The largest LNG carrier with two-stroke dual-fuel engines currently in operation is the Q-Max LNG carrier, "Rasheeda" with a deadweight of 130,208 tons. When it was originally built in 2010, "Rasheeda" had two MAN B&W Diesel 7S70ME-C electronically controlled low speed two-stroke diesel engines running on heavy fuel oil in conjunction with a reliquefaction plant.
Those engines were converted in 2015 into ME-GI engines (M-type, Electronically Controlled, Gas Injection engines). These engines were the first two-stroke dual-fuel engines installed on board an LNG carrier.
ME-GI engines are high-pressure dual-fuel engines designed by MAN B&W for LNG carriers to comply with the IMO NOx Tier II emission limits4. They have a 50% propulsion efficiency.
MAN B&W has developed another engine based on ME-GI, the M-type, Electronically Controlled, Gas Admission (ME-GA) engine. The first LNG carriers equipped with ME-GA engine were built in 2023.
The other type of two-stroke dual-fuel engines are X-DF series built by Winterthur Gas & Diesel (WinGD). The first LNG carrier with X-DF engines, "SK Audace" was built in 2017.
The first generation of X-DF engines had a 47% propulsion efficiency.
In 2020, Winterthur Gas & Diesel introduced the second-generation of X-DF engines.
MAN B&W`s ME-GA engines and WinGD`s second-generation of X-DF engines are currently the most efficient engines in the global LNG fleet. They have the lowest fuel consumption and the lowest emission levels of CO2 than all other engines currently used in LNG shipping.
Besides the Q-Max LNG carrier, "Rasheeda", among the LNG carriers with two-stroke dual-fuel engines, there are 6 LNG carriers with a transport capacity of 200,000 cbm and a deadweight between 105,602 and 107,817 tons, 261 conventional size LNG carriers with a transport capacity between 170,000 and 180,000 cbm and a deadweight between 90,000 and 96,000 tons, one conventional size LNG carrier, "Seri Cempaka" with a transport capacity of 150,200 cbm and a deadweight of 84,311 tons, five mid-scale size LNG carriers with a deadweight between 42,000 and 45,462 tons and three small-scale size LNG carriers with a deadweight between 17,000 and 18,433 tons.
The two-stroke dual-fuel engines have become the predominant propulsion system in the LNG fleet, particularly in the case of ships with a transport capacity between 170,000 and 180,000 cbm, the size range where the two-stroke dual-fuel engines are considered to be the most efficient. They set a CII reference line value too low not only for the steam turbine LNG carriers but also for LNG carriers with dual or tri-fuel diesel electric engines, which are within the 65,000 and 100,000 tons DWT range. As a result, most of the LNG carriers powered by steam turbines are unable to achieve the operational carbon intensity rating A, B or C.
In order to avoid a premature phasing out of 183 LNG carriers (steam turbine LNG carriers within the 65,000 and 100,000 tons DWT range), INTERTANKO proposed the introduction of a CII averaging mechanism that would enable the LNG carrier operators to calculate a CII for their entire fleet by averaging "D" and "E" ratings of the steam turbine LNG carriers with the ratings of the modern LNG carriers powered by two-stroke dual-fuel engines5.
by Vlad Cioarec, International Trade Consultant
This article has been published in Commoditylaw`s Gas Trade Review Edition No. 4.
Endnotes:
1. See Resolution MEPC.352 (78) – "2022 Guidelines on Operational Carbon Intensity Indicators and the Calculation Methods (CII Guidelines, G1)"
2. See Resolution MEPC.353 (78) – "2022 Guidelines On The Reference Lines For Use With Operational Carbon Intensity Indicators (CII Reference Lines Guidelines, G2)"
3. LNG carrier "Pacific Arcadia" was the last LNG carrier built with conventional steam turbines.
4. ME-GI engines are fitted with NOx emission control technologies, the exhaust gas recirculation (EGR) and the selective catalytic reduction (SCR), to comply with the NOx Tier III emission limits not only when operating in gas mode but also when operating in fuel oil mode.
5. See IMO document MEPC 79/7/1 – "The need for urgent mitigations to address the challenges of GHG short-term measures when applied to steam driven LNG ships" submitted by INTERTANKO at the 79th session of the Marine Environment Protection Committee.