Radar Meets the Challenges of Liquefied Petroleum Gas Level Measurement

by | Aug 1, 2024 | Measurement Instrumentation | 0 comments

Thousands of radar level gauges are in service in LPG applications around the world.

Liquefied petroleum gas (LPG) produces lower greenhouse gas emissions than traditional solid fuels and is also comparatively easy to transport and store. For these reasons, demand is increasing globally. A well-established storage infrastructure is already in place. However, as I explained in an article in Tank Storage magazine, ‘Radar’s Solutions for LPG Storage’, the increased demand not only creates the need for greater storage capacity, but also makes it important to use existing capacity more efficiently. One way in which efficiency can be increased is through more accurate and reliable level measurement. The article states:

…Measuring the level of LPG within storage vessels – to support inventory management and overfill prevention – presents several challenges due to the nature of the gas and the pressurised tanks in which it is stored. Safety is of paramount concern as LPG is highly flammable, and tank gauging systems must adhere to strict safety standards to minimize the risk of spills, leaks and accidents.

Although LPG is stored in a liquid state under pressure, during certain conditions – such as rapid depressurization or temperature changes – it can vaporize, which can affect the apparent level in the tank. Pressurized LPG tanks can also have vapor spaces at the top, and the presence of vapor makes it challenging to obtain accurate level measurements. Tank gauging systems should therefore incorporate level measurement technology that can penetrate vapors and account for the presence of a vapor space. A further challenge is that LPG can foam when tanks are being filled, creating bubbles that can interfere with level measurement and lead to inaccurate readings.

The article explains that level measurement in LPG tanks has traditionally been performed using mechanical servo gauges. However, to ensure more accurate and reliable measurements, the modern approach involves integrating non-contacting radar devices – such as Emerson’s Rosemount™ 5900S Radar Level Gauge – into tank gauging systems. These devices use microwave signals – emitted towards the liquid surface and reflected back to the transmitter – to measure the level. The article continues:

In LPG applications, non-contacting radar level gauges have antennas specially designed to optimise accuracy by addressing the specific challenges posed by the properties of the product, including its dielectric constant, vapours, foam, temperature sensitivity, tank shape and signal reflections. To further optimise signal strength in LPG tanks, it is recommended that the radar signal is guided within a still-pipe. This results in a strong echo from the surface and provides highly accurate measurements. For peace of mind, the latest radar devices offer functionality that enables measurements to be verified in real time while the tank is in operation, via an inbuilt verification pin feature.

The Rosemount 5900S Radar Level Gauge from Emerson can be used for both tank gauging and separate OPS purposes, thereby requiring only one tank opening.

Because hydrocarbon vapor has a slightly larger effect on microwave propagation velocity than air, non-contacting radar devices need to compensate for this vapor effect in order to provide accurate measurements. The Rosemount 5900S Radar Level Gauge can calculate the vapor influence through online pressure measurement from an integrated pressure sensor, and information about the gas mixture. The level reading is then corrected automatically, ensuring that the measurement is accurate to ±1mm. 

Safety functions are critical in LPG applications, with an overfill prevention system (OPS) required to reduce safety risk. There is a widely-held belief that the tank gauging system and the OPS must incorporate different level measurement technologies – for example, radar level gauges and servo gauges. However, the article explains that this is a misconception, and is not a requirement of the International Electrotechnical Commission’s global functional safety standard IEC 61511. The standard in fact confirms that the same technology can be used for both the tank gauging system and the OPS.

When upgrading from mechanical devices to non-contacting radar level gauges, ease of installation should be a consideration. For example, if an existing LPG tank has only one opening available, the tank would need to be modified to enable two separate radar level gauges to be installed to support the tank gauging system and the OPS. Making this kind of modification may be cost-prohibitive, as it would involve the tank being taken out of service, thereby impacting throughput and profitability. The article states:

…This challenge is solved by the Rosemount 5900S 2-in-1 radar level gauge from Emerson, which consists of two separate and independent electrical units and a common antenna. This enables a single device to be used for both tank gauging and separate OPS purposes, therefore requiring only one tank opening and minimal or no modifications.

The article reveals that thousands of radar level gauges are in service in LPG applications around the world, and highlights a good example at an LPG terminal in Mexico. The terminal was operating with eight bullet-shaped LPG tanks, each with a storage capacity of 450,000 liters. This was proving insufficient to keep up with the growing demand for LPG, so the terminal operator decided to build a further 18 tanks. All 26 tanks were then included in an upgrade project to improve safety and operational efficiency. The article continues:

…As part of this upgrade, each of the 26 tanks was equipped with a Rosemount 5900S 2-in-1 radar level gauge with an LPG antenna specifically designed for the application. Each gauge was integrated with a Rosemount 2051 pressure transmitter to measure vapour space pressure. The new instrumentation set-up enables both level and pressure measurements to be obtained, along with providing overfill prevention, while using just one tank opening.

Rosemount TankMaster™ Inventory Management Software was integrated into the updated system to manage inventory calculations. Thanks to the additional storage tanks, upgraded tank gauging systems and improved inventory insight and control, the terminal now has increased capacity and improved efficiency and safety.

Visit here to learn more about Emerson’s LPG tank gauging solutions.

 

 

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