How LNG Carriers (Gas Tankers) Work - Design Types, Loading & Discharge

Summary

This video explores LNG carriers, specialized ships for transporting liquefied natural gas. It covers the liquefaction process, ship layout, and key design types like Moss, Membrane, and SPB. The script delves into the loading procedure, including tank cooling, inert gas purging, and managing boiled-off gas (BOG) during voyages. It also mentions the reliquefaction process for unloading LNG and the use of a VPN for internet privacy.

Takeaways

• 🚢 LNG carriers are specialized ships designed for the long-distance transportation of liquefied natural gas.
• 🌡️ Natural gas is liquefied at -162°C (-260°F), which reduces its volume by approximately 600 times, a process known as liquefaction.
• 🔵 The liquefied natural gas (LNG) is not blue as depicted in animations; it is actually colorless.
• 🛳️ LNG carriers are large vessels, sometimes exceeding the length of an aircraft carrier.
• 🛡️ The industry primarily uses two design types for LNG carriers: Moss-type with spherical tanks, and Membrane-type with more rectangular-like tanks.
• 🛡️ All LNG carriers are required to have double hulls for added protection in case of collision, with water ballast tanks in between.
• 🔩 Moss-type tanks are independent, supported by a high tensile steel skirt, and feature a multi-layer barrier for containment and insulation.
• 🏗️ Membrane-type tanks are integrated into the ship's hull, offering better space utilization and efficiency in cargo capacity.
• 📐 The advanced but less popular SPB (Self-Supporting Prismatic Type B) design resembles oil tankers, with independent tanks inside the hull separated by bulkheads.
• 🌀 LNG loading involves a series of steps including purging with dry air, inert gas, and cold LNG vapor to ensure safety and prevent thermal stress.
• 🔄 During the voyage, boiled-off gas (BOG) is managed by using it as fuel or cooling it down with the help of a reliquefaction plant if necessary.

Q & A

What are LNG carriers and what are they used for?

LNG carriers, also known as liquefied natural gas carriers, are specialized ships designed to transport natural gas over long distances across the world in a liquefied state.

How is natural gas turned into LNG?

Natural gas is turned into LNG through a process called liquefaction, where the gas is cooled down to -162 °C (-260°F), reducing its volume by about 600 times.

What is the significance of the color representation of LNG in animations?

In reality, LNG has no color, unlike the blue representation often seen in animations, which is likely for visual distinction and not an accurate depiction of its appearance.

What are the two most popular design types of LNG carriers mentioned in the script?

The two most popular design types of LNG carriers mentioned are Moss-type and Membrane-type.

What is a double-hull design and why is it used in LNG carriers?

A double-hull design consists of an outer and an inner hull with space in between used for water ballast tanks. It is used in LNG carriers to protect the tanks and cargo inside in case of a collision.

How are the spherical tanks in Moss-type LNG carriers supported?

In Moss-type LNG carriers, the spherical tanks are independent and not part of the ship's hull. They are supported by a supporting skirt made of high tensile steel.

What is the primary barrier in LNG carrier tanks and what is it made of?

The primary barrier in LNG carrier tanks is made of aluminum alloy and serves as the main protective layer for the liquefied natural gas.

What is the advantage of the Membrane-type design over spherical tanks in terms of cargo capacity?

The Membrane-type design has a more rectangular-like tank that integrates directly into the ship's hull, resulting in better space utilization and more efficient fitting to the shape of the hull.

What is the purpose of the reliquefaction plant in an LNG carrier?

The reliquefaction plant is used to cool down and turn the boiled-off gas (BOG) back into a liquid state during the voyage, which can then be sent back to the cargo tank to prevent pressure build-up.

How is LNG loaded into the tanks of an LNG carrier?

LNG is loaded into the tanks using a filling line. Before loading, the tanks are purged of humid air with dry air, and then inert gas is replaced with warm LNG vapor to prepare the tanks for LNG loading.

What is BOG and how is it managed during an LNG carrier's voyage?

BOG stands for Boiled-off Gas, which is the gas that evaporates from the LNG due to external heat. It is managed by using it as a fuel source for the engine or by spraying cold LNG from the bottom of the tank to cool it down and prevent excessive pressure build-up.