LNG vessels – Introduction

LNG ships – Journey through time

Liquefied Natural Gas (LNG) ships are vessels designed to transport LNG from one location to another. Here’s an introduction to LNG ships based on past, present, and future developments:

1. Past: LNG shipping began in the mid-20th century when the first commercial LNG carrier was launched in 1959. These early vessels were small and had limited capacity, with most of them being used for domestic transportation in the United States. Over time, technological advancements led to the development of larger LNG carriers with greater efficiency and safety features.

2. Present: LNG shipping has become an important part of the global energy industry, with increasing demand for natural gas as a cleaner alternative to coal and oil. Today, there are over 500 LNG carriers in operation worldwide, transporting LNG from production sites to import terminals across the globe. Modern LNG ships are highly sophisticated vessels equipped with advanced technology to ensure safety and efficiency.

3. Future: The future of LNG shipping looks bright, with growing demand for natural gas expected to drive increased investment in the sector. The latest LNG ships are designed to be even more efficient and environmentally friendly, with the use of advanced propulsion systems and cleaner fuel options. In addition, the development of new technologies such as floating LNG terminals and small-scale LNG carriers is expected to further expand the industry in the coming years.

LNG carrier types

There are several types of LNG (liquefied natural gas) ships that are used to transport liquefied natural gas from one place to another. Here are some of the most common types:

1. Moss Tanker: This type of LNG ship is named after the Norwegian company Moss Rosenberg Verft, which developed it. Moss tankers have a spherical cargo tank made of aluminum alloy, which is supported by a cylindrical steel hull. They are often used for long-distance transport and are very efficient.

2. Membrane Tanker: Membrane tankers are designed to carry LNG in large, flexible membrane tanks that are made of a thin, stainless steel layer supported by insulation materials. They are more common than Moss tankers and are known for their high flexibility and low boil-off rates.

3. SPB (Self-Propelled Barge): SPBs are smaller LNG carriers that are designed for coastal and inland transport. They are usually used to transport LNG to locations that are not accessible by larger ships.

4. LPG Carrier Converted to LNG Carrier: Some LPG (liquefied petroleum gas) carriers have been converted to transport LNG. This is because LPG carriers are often similar in design to LNG carriers and can be retrofitted to carry LNG.

5. Small-Scale LNG Carrier: Small-scale LNG carriers are designed to transport smaller quantities of LNG, usually in the range of 1,000 to 30,000 cubic meters. They are often used for short-distance transport and for supplying LNG to remote areas.

6. Floating Storage and Regasification Unit (FSRU): FSRUs are not technically LNG carriers, but they are used to store LNG and convert it back into natural gas for distribution. FSRUs are typically stationed near shore and are connected to a pipeline network.

These are just some of the common types of LNG ships. There are other variations and designs that are used for different purposes, depending on the specific requirements of the LNG transport project.

LNG temperature and pressure control

LNG (liquefied natural gas) is a highly volatile and flammable substance that requires strict temperature and pressure control during transportation. Maintaining the cargo temperature and pressure is critical to ensure the safe and efficient transportation of LNG.

Temperature Control: LNG is transported at a temperature of around -162°C (-260°F), which requires specialized equipment and insulation to keep it at this temperature during transportation. LNG ships have onboard equipment, including cryogenic pumps, heat exchangers, and insulation, which are used to maintain the temperature of the cargo. The cargo tanks are also equipped with a temperature monitoring system that continuously monitors the temperature of the LNG to ensure that it remains within the required range.

Pressure Control: LNG is transported at a low pressure, typically around 0.25 bar (3.6 psi), which is much lower than the atmospheric pressure at sea level. The cargo tanks on LNG ships are designed to withstand the low pressure, and the pressure is maintained by controlling the boil-off gas (BOG) that is produced when LNG evaporates. BOG is typically compressed and used as fuel for the ship’s engines or returned to the cargo tanks as a vapor. To ensure that the pressure remains within the required range, the cargo tanks are equipped with pressure relief valves that release excess pressure when needed.

Overall, the maintenance of cargo temperature and pressure is critical for safe and efficient transportation of LNG, and LNG ships are designed with specialized equipment and systems to ensure that these parameters are carefully controlled.

Hazards of LNG Vessels with Regards to Flammability:

LNG is a highly flammable substance that can pose significant risks to people and the environment if it ignites. LNG is transported in its liquid state at extremely low temperatures, and when it is released from its containment, it rapidly expands and vaporizes into a gaseous state. In this gaseous state, LNG can easily ignite when it comes into contact with a source of ignition, such as sparks or flames.

To prevent LNG from igniting, safety measures are put in place throughout the LNG supply chain. At the production stage, safety systems are used to prevent over-pressurization, which can lead to leaks and spills. During transportation, LNG vessels are designed with safety features such as double-hull construction, high-pressure gas detection systems, and emergency shutdown systems. Additionally, LNG terminals have safety measures in place, such as fire suppression systems and vapor recovery systems, to prevent the release of LNG into the atmosphere.

In the event of an LNG leak or spill, it is essential to act quickly and safely to minimize the risk of ignition. First responders must take immediate action to contain the spill and prevent it from spreading. They must also establish a safe perimeter around the spill to prevent any ignition sources from coming into contact with the LNG. Additionally, emergency response teams must have the appropriate equipment and training to manage an LNG spill safely.

Hazards of LNG Vessels with Regards to Temperature:

LNG is transported at extremely low temperatures (-163°C), which can pose significant hazards to personnel and equipment. The extreme cold can cause burns and frostbite if LNG comes into contact with skin or eyes. It can also cause materials to become brittle and fracture, which can lead to equipment failure.

To prevent these hazards, LNG vessels are designed with specialized insulation and cryogenic tanks that are capable of withstanding the extreme temperatures. Additionally, safety protocols are put in place to minimize the risk of injury and damage to equipment. Personnel who work with LNG must be properly trained and equipped with personal protective equipment, such as cryogenic gloves and goggles, to prevent injury.

Hazards of LNG Vessels with Regards to Sloshing Effect:

During transportation, LNG can slosh around in the tanks, causing instability in the vessel. This can lead to capsizing or damage to the tanks, resulting in leaks and spills. The sloshing effect is caused by the movement of the LNG within the tanks due to the motion of the vessel. The amount of sloshing depends on several factors, including the size of the tank, the amount of LNG being transported, and the speed of the vessel.

To mitigate the hazards of the sloshing effect, LNG vessels are designed with specialized tanks that minimize the movement of LNG within the tank. The tanks may have baffles or other structures that prevent the LNG from sloshing. Additionally, LNG vessels are designed to maintain stability even in rough seas, and they may have specialized systems, such as ballast control systems, to maintain stability.

Overall, the hazards associated with LNG vessels are significant, but they can be mitigated through the use of specialized equipment, safety protocols, and effective training. The safe transportation of LNG is critical to ensuring that this valuable resource can be transported to where it is needed while minimizing the risks to people and the environment.