LNG carrier


An LNG carrier is a tank ship designed for transporting liquefied natural gas.

Overview

The first oceangoing liquified natural gas tanker in the world was Methane Pioneer, which entered service in 1959 with a carrying capacity of 5,500 cubic metres. LNG carriers of increasing size have been built since then, leading to the fleet of today, where giant Q-Max LNG ships sail worldwide that can each carry up to.
A boom in U.S. natural gas production was enabled by hydraulic fracturing, creating large growth in natural gas production from 2010. The first U.S. LNG export facility was completed in 2016, with more following. The increasing supply of natural gas in the U.S. and export facilities expanded the demand for LNG carriers, to transport LNG around the world.
The 2022 Russian invasion of Ukraine dramatically increased the demand for LNG shipping worldwide. U.S. shipments to Europe more than doubled in 2022, to 2.7 trillion cubic feet.
As of 2023, there were 772 active LNG carriers in the world, however "this figure also includes floating storage units".

History

The first LNG carrier Methane Pioneer carrying, classed by Bureau Veritas, left the Calcasieu River on the Louisiana Gulf coast on 25 January 1959. Carrying the world's first ocean cargo of LNG, it sailed to the UK where the cargo was delivered. The success of the specially modified C1-M-AV1-type standard ship Normarti, renamed Methane Pioneer, caused the Gas Council and Conch International Methane Ltd. to order two purpose built LNG carriers to be constructed: Methane Princess and Methane Progress. The ships were fitted with Conch independent aluminum cargo tanks and entered the Algerian LNG trade in 1964. These ships had a capacity of.
In the late 1960s, opportunity arose to export LNG from Alaska to Japan, and in 1969 that trade with TEPCO and Tokyo Gas was initiated. Two ships, Polar Alaska and Arctic Tokyo, each with a capacity of, were built in Sweden. In the early 1970s, the US government encouraged US shipyards to build LNG carriers, and a total of 16 LNG ships were built. The late 1970s and early 1980s brought the prospect of Arctic LNG ships with a number of projects being studied.
With the increase in cargo capacity to approximately costing $250 million, new tank designs were developed, from Moss Rosenberg to Technigaz Mark III and Gaztransport No.96.
The size and capacity of LNG carriers has increased significantly, to. A vessel could cost $200 million.
Since 2005, Qatargas has pioneered the development of two new classes of LNG carriers, referred to as Q-Flex and Q-Max. Each ship has a cargo capacity of between and is equipped with a re-liquefaction plant.
Today we see interest for small scale LNG bunker carriers. Some need to stay below the life rafts of Cruise ships and Ropax vessels. Examples are the Damen LGC 3000 and the Seagas.
By 2005 a total of 203 vessels had been built, of which 193 were still in service. At the end of 2016, the global LNG shipping fleet consisted of 439 vessels. In 2017, an estimated 170 vessels are in use at any one time. At the end of 2018, the global fleet was approximately 550 vessels.
In 2021—2022, an LNG shipment from US to Europe could return a profit of $133—200 million. Shipping rates were $100,000 per day even for 5-year contracts, but can vary between $60,000—250,000.

New building

In 2021, 90 new LNG carriers were ordered. By 2022, high demand had shifted deliveries of new orders to 2027.
In November 2018, South Korean ship builders locked in 3 years worth of large-scale LNG carrier contracts - more than 50 orders - with a value of $9 billion. South Korean builders captured 78% of LNG-related ship building contracts in 2018, with 14% going to Japanese builders and 8% going to Chinese builders. The new contracts would boost the global LNG fleet by 10%. Of the global fleet, historically, about two-thirds of the ships have been built by South Koreans, 22% by Japanese, 7% by Chinese, and the rest built by a combination of France, Spain, and the United States. South Korea's success stems from innovation and price point; South Korean builders introduced the first ice-breaker type LNG vessels and South Korean builders have been successful in catering to increased customer preference for Q-max vessels over Moss type.
In 2018, South Korea's Hyundai Mipo Dockyard delivered the world's first LNG-fueled bulk carrier. It has the world's largest capacity at 50,000 dwt.
According to SIGTTO data, in 2019 there were 154 LNG carriers on order, and 584 operating LNG carriers.
In 2017, Daewoo Shipbuilding & Marine Engineering delivered the Christophe de Margerie, an icebreaking LNG tanker of 80,200 deadweight tons. Her capacity of is the consumption of Sweden for a month. She completed her first revenue voyage from Norway via the Northern Sea Route in the Arctic Ocean to South Korea. The shipyard has fourteen more on order.
In the case of small scale LNG carriers, the optimal size of a ship is determined by the project for which it is built, taking into consideration volume, destination and vessel characteristics.
List of small scale LNG carrier builders:
A typical LNG carrier has four to six tanks located along the center-line of the vessel. Surrounding the tanks is a combination of ballast tanks, cofferdams and voids; in effect, this gives the vessel a double-hull type design.
LNG carriers, like aircraft carriers, are among the most difficult vessels to build, taking as long as 30 months.
Inside each tank there are typically three submerged pumps. There are two main cargo pumps which are used in cargo discharge operations and a much smaller pump which is referred to as the spray pump. The spray pump is used for either pumping out liquid LNG to be used as fuel, or for cooling down cargo tanks. It can also be used for "stripping" out the last of the cargo in discharge operations. All of these pumps are contained within what is known as the pump tower which hangs from the top of the tank and runs the entire depth of the tank. The pump tower also contains the tank gauging system and the tank filling line, all of which are located near the bottom of the tank.
In membrane-type vessels there is also an empty pipe with a spring-loaded foot valve that can be opened by weight or pressure. This is the emergency pump tower. In the event both main cargo pumps fail the top can be removed from this pipe and an emergency cargo pump lowered down to the bottom of the pipe. The top is replaced on the column and then the pump is allowed to push down on the foot valve and open it. The cargo can then be pumped out.
All cargo pumps discharge into a common pipe which runs along the deck of the vessel; it branches off to either side of the vessel to the cargo manifolds, which are used for loading or discharging.
All cargo tank vapour spaces are linked via a vapour header which runs parallel to the cargo header. This also has connections to the sides of the ship next to the loading and discharging manifolds.

Typical cargo cycle

A typical cargo cycle starts with the tanks in a "gas free" condition, meaning the tanks are full of air, which allows maintenance on the tank and pumps. Cargo cannot be loaded directly into the tank, as the presence of oxygen would create an explosive atmospheric condition within the tank, and the rapid temperature change caused by loading LNG at could damage the tanks.
First, the tank must be 'inerted' to eliminate the risk of explosion. An inert gas plant burns diesel in air to produce a mixture of gases. This is blown into the tanks until the oxygen level is below 4%.
Next, the vessel goes into port to "gas-up" and "cool-down", as one still cannot load directly into the tank: The CO2 will freeze and damage the pumps and the cold shock could damage the tank's pump column.
LNG is brought onto the vessel and taken along the spray line to the main vaporiser, which boils off the liquid into gas. This is then warmed up to roughly in the gas heaters and then blown into the tanks to displace the "inert gas". This continues until all the CO2 is removed from the tanks. Initially, the IG is vented to atmosphere. Once the hydrocarbon content reaches 5% the inert gas is redirected to shore via a pipeline and manifold connection by the HD compressors. The shore terminal then burns this vapour to avoid the dangers of having large amounts of hydrocarbons present which may explode.
Now the vessel is gassed up and warm. The tanks are still at ambient temperature and are full of methane.
The next stage is cool-down. LNG is sprayed into the tanks via spray heads, which vaporises and starts to cool the tank. The excess gas is again blown ashore to be re-liquified or burned at a flare stack. Once the tanks reach about the tanks are ready to bulk load.
Bulk loading starts and liquid LNG is pumped from the storage tanks ashore into the vessel tanks. Displaced gas is blown ashore by the HD compressors. Loading continues until typically 98.5% full is reached.
The vessel can now proceed to the discharge port. During passage various boil-off management strategies can be used. Boil-off gas can be burned in boilers to provide propulsion, or it can be re-liquefied and returned to the cargo tanks, depending on the design of the vessel.
Once in the discharge port, the cargo is pumped ashore using the cargo pumps. As the tank empties, the vapour space is filled by either gas from ashore or by vaporising some cargo in the cargo vaporiser. Either the vessel can be pumped out as far as possible, with the last being pumped out with spray pumps, or some cargo can be retained on board as a "heel".
This must be done gradually otherwise the tanks will be cold shocked if loaded directly into warm tanks. Cool-down can take roughly 20 hours on a Moss vessel, so carrying a heel allows cool-down to be done before the vessel reaches port giving a significant time saving.
If all the cargo is pumped ashore, then on the ballast passage the tanks will warm up to ambient temperature, returning the vessel to a gassed up and warm state. The vessel can then be cooled again for loading.
If the vessel is to return to a gas free state, the tanks must be warmed up by using the gas heaters to circulate warm gas. Once the tanks are warmed up, the inert gas plant is used to remove the methane from the tanks. Once the tanks are methane free, the inert gas plant is switched to dry air production, which is used to remove all the inert gas from the tanks until they have a safe working atmosphere.
Transportation of natural gas both in the form of LNG and by pipeline causes greenhouse gas emissions, but in different ways. With pipelines, most of the emissions stem from the production of steel pipe; with LNG most of the emissions stem from liquefaction. For both pipelines and LNG, propulsion causes additional emissions.