Liquefied Natural Gas (LNG) and Its Equipment

Liquefied Natural Gas (LNG)

Introduction

Liquefied Natural Gas (LNG), predominantly composed of methane (CH₄) with some ethane (C₂H₆), is cooled to liquid form to enable easy and safe non-pressurised storage or transport. At standard conditions, LNG occupies approximately 1/600th of the volume of natural gas in its gaseous state.
Today, LNG has become a key player in the global energy market, providing a cleaner alternative to coal and oil for power generation and industrial applications. The growth of LNG has been further fueled by geopolitical shifts, particularly the increase in natural gas production from shale fields in North America.

Properties and Hazards Liquefied Natural Gas is odourless, colourless, non-toxic, and non-corrosive. Its hazards include flammability after vaporisation, freezing, and asphyxiation. The liquefaction process involves removing components like dust, acid gases, helium, water, and heavy hydrocarbons to prevent downstream issues. The gas is condensed into a liquid at about −162 °C (−260 °F) and transported at around 25 kPa (4 psi), roughly 1.25 times atmospheric pressure.

Composition and Processing Extracted natural gas contains methane, ethane, propane (C₃H₈), butane (C₄H₁₀), and CO₂. Removing acidic elements like hydrogen sulphide (H₂S) and carbon dioxide (CO₂) is essential to prevent equipment damage. The gas stream is separated into liquefied petroleum fractions (butane and propane) and lighter methane and ethane fractions, which are then liquefied for LNG production.

Historical Context In the 20th century, natural gas was often flared in regions without viable pipelines as no storage or transport method existed. Technological cryogenic storage and transportation advancements have commercialised natural gas, creating a global market.

Energy Content and Density LNG’s heating value varies based on its source and liquefaction process, typically around 50 MJ/kg (higher heating value) or 45 MJ/kg (lower heating value). The density of LNG is approximately 0.41 to 0.5 kg/litre. Its volumetric energy density is about 2.4 times that of compressed natural gas (CNG), comparable to propane and ethanol, but only 60% of diesel and 70% of gasoline.

Applications and Equipment LNG’s use as fuel is significant in the industry. It affects vehicle range, with LNG providing a higher range than CNG but lower than diesel.

A block flow diagram usually shows the flow of the LNG production process from raw natural gas input to liquefaction and storage. It arranges the blocks sequentially. The big block depicts each primary process—separation, liquefaction, and storage—while the connecting lines between these blocks illustrate the flow of materials and energy. Smaller blocks linked to the main process flow could show other tools and safety precautions.

1. LNG Pump Skid: Transfers LNG from storage tanks to transport vehicles or other storage systems.
2. LNG Cryogenic Tanks:  Store LNG at very low temperatures to keep it liquid. The purpose of these tanks is to keep the LNG at a very low temperature, preventing it from vaporizing back into gas. They are usually double-walled and insulated to minimize heat ingress.
3. Cryogenic Liquid Semi-trailers: Transport LNG long distances while maintaining its cryogenic state.LNG is being transported over land using cryogenic semi-trailers. The insulated tanks in these trailers help preserve the LNG in its cryogenic form.
4. LNG Storage Tanks for Permanent Stations: These are fixed storage solutions for LNG at fueling stations or industrial sites.
5. LNG Vehicle Gas Supply Systems: These are installed in vehicles to store and manage LNG as fuel.
6. LNG Transport Containers: Safely and efficiently transport LNG.
7. LNG Dispensers: Dispense LNG into vehicles at fueling stations.
8. LNG Vaporizers: Convert LNG back into its gaseous form for various applications.Once it reaches its destination, LNG may be converted back to natural gas for industrial, domestic, or power-generating purposes. Regasification heats the LNG to convert it from liquid to gas. Raising the temperature to typical ambient levels causes LNG vaporizers—heat exchangers—to turn LNG back into gas.
9. LNG Fueling Stations: Complete systems for refuelling vehicles with LNG.
10. LNG Bunkering Equipment: Transfer LNG to ships.
11. LNG Loading Arms: Transfer LNG between tanks, trucks, or ships.
12. LNG Pressure Regulators: Control the pressure of LNG within a system.
13. LNG Transfer Hoses: Safely transfer LNG between containers or systems.
14. LNG Compressors: Compress natural gas into LNG for storage and transport.
15. LNG Heat Exchangers: Cool natural gas to its liquid state during liquefaction.
16. LNG Boil-Off Gas Compressors: Manage and compress gas that boils off from LNG during storage.
17. LNG Tank Level Gauges: Measure the level of LNG in storage tanks.
18. LNG Safety Valves: Prevent overpressure and ensure safe operation of LNG systems.
19. LNG Leak Detectors: Detect LNG leaks to prevent accidents.
20. LNG Emergency Shut Down (ESD) Systems: Quickly shut down LNG operations in an emergency.
21. LNG Pipeline Systems: Safely transport LNG over long distances.
22. LNG Flare Systems: Safely burn off excess gas in LNG facilities.
23. LNG Insulation Materials: Insulate tanks and pipelines to maintain the cryogenic temperature of LNG.
24. LNG Process Control Systems: Monitor and control the processes involved in LNG production, storage, and transport.
25. LNG Sampling Systems: Take samples of LNG for quality control and analysis.

These pieces of equipment are critical for the safe and efficient handling, storage, transport, and use of LNG in various applications.

LNG quality affects equipment performance. Although guidelines for fuel composition exist, few standards are in place. LNG is primarily methane, with smaller amounts of ethane, propane, butanes, and nitrogen. The design of the liquefaction plant and transportation time influence LNG quality, typically described by energy content, combustion characteristics, and impurity levels.

Conclusion The development of LNG technology has transformed natural gas into a viable global energy source, offering diverse applications and benefits in energy density, storage, and transportation.