LNG (Liquefied Natural Gas) tank gauging systems require highly accurate and reliable devices to ensure proper measurement of tank levels, temperature, and density due to the sensitive and volatile nature of LNG. Here are the key gauging devices commonly used in LNG tank gauging systems:
1. Radar Level Gauges
- Description: These non-contact radar gauges use microwave pulses to measure the liquid level by detecting the time delay between emission and reflection of the radar signal.
- Types:
- Guided Wave Radar: Uses a probe to guide the radar waves, offering higher accuracy in LNG tanks.
- Non-Contact Radar: Measures the level by emitting waves from the top of the tank.
- Advantages:
- High precision and reliability, even under extreme temperature and pressure conditions.
- Suitable for large tanks and capable of measuring in cryogenic environments.
2. Servo Tank Gauges
- Description: Servo gauges use a displacer that is lowered into the tank and suspended in the liquid. The system measures the force required to keep the displacer balanced, which corresponds to the liquid level.
- Advantages:
- High accuracy in measuring both level and density.
- Can be combined with other devices for additional measurements like temperature.
3. Float and Tape Gauges
- Description: These traditional gauges use a float that rests on the surface of the LNG and is connected to a tape or wire. The position of the float is used to determine the level.
- Advantages:
- Simple, reliable, and low maintenance.
- Accurate for basic level measurement in less complex environments.
- Limitations:
- May not be as accurate or suitable for highly dynamic or critical LNG systems.
4. Capacitance Level Gauges
- Description: These gauges measure the change in capacitance between two conductive plates or probes as the LNG level changes.
- Advantages:
- Accurate in measuring both level and liquid density.
- Suitable for cryogenic environments like LNG tanks.
- Limitations: Susceptible to changes in liquid composition and vapor phase, requiring compensation.
5. Temperature Sensors
- Description: LNG tank gauging systems require temperature measurements at various levels within the tank. Resistance Temperature Detectors (RTDs) or thermocouples are often used.
- Advantages:
- Accurate monitoring of LNG temperature, which is critical for density and volume calculations.
- Provides compensation for thermal stratification within the tank.
6. Pressure Sensors
- Description: These sensors measure the vapor pressure in the tank and the pressure at different levels within the liquid to help determine the level and density of LNG.
- Advantages:
- Essential for calculating the mass of LNG in the tank.
- Can also detect abnormal pressure changes to prevent potential safety hazards.
7. Density Profiling Sensors
- Description: These sensors measure the density of LNG at various heights within the tank. Combined with level measurement, it provides accurate mass and volume calculations.
8. Tank Management Software
- Description: Modern LNG tank gauging systems often integrate with advanced software that collects data from various sensors (level, temperature, density, etc.) and processes it to provide real-time information on tank contents.
- Advantages:
- Provides complete inventory management.
- Enables remote monitoring and alerts for abnormal conditions.
9. Hybrid Gauging Systems
- Description: These systems combine different gauging technologies like radar, servo, and capacitance gauges to improve accuracy, redundancy, and reliability in LNG tank measurement.
- Advantages:
- More reliable in complex LNG tank environments.
- Can measure multiple parameters (level, temperature, density) simultaneously.
10. Mass Flow Meters (Coriolis Meters)
- Description: These meters measure the mass flow rate of LNG as it enters or leaves the tank, providing crucial data for custody transfer applications.
- Advantages:
- Highly accurate mass flow measurement.
- Often used in tandem with level gauges for real-time inventory management.
These devices, often integrated into a comprehensive tank gauging system, help ensure the safe and efficient management of LNG storage and transport by providing real-time, accurate data on liquid levels, temperatures, and densities.