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Mastering Volatile Liquids Tank Level Measurement

S.R. Bhat (Technical Director, COMFIT)

Your approach to solve the level measurement issue in refrigerated tanks for volatile liquids is both intriguing and creative. Let's break down the concept and application:

1. Current Issues with Refrigerated Tank Level Measurement:

o Displacement and radar transmitters encounter issues like high cost, complicated calibration, difficult installations, and additional chamber requirements which not only add to the cost of installation but also increase the load on refrigeration system.

o Remote seal transmitters struggle at low temperatures, which can lead to frozen seals and their total failures.

2. Challenges with Traditional DP Transmitters:

o Installing DP transmitters at the bottom risks exposure to very low temperature fluids, leading to failure of the transmitters. This shall cause boiling in impulse lines resulting in vapours continuously getting replaced by fresh liquid from the tank and creating circulation with pulsating flow. This shall come in the way of measurements.

3. The Proposed Simplified Solution:

o By positioning the transmitter at the top of the tank, you avoid direct exposure to low-temperature liquids.

o Connecting the tank's top to the low-pressure side and the bottom to the high-pressure side of the transmitter. Provide no insulation on impulse lines. This can mitigate the risks associated with low-temperature liquids affecting the transmitters.

o Any low-temperature liquid entering the high-pressure side will vaporize immediately, which prevents the liquid from compromising the transmitter and ensures that only vapor is present in both impulse lines.

4. Advantages of the Proposed Solution:

o The impulse lines become self purging.

o Simplified calibration and maintenance due to more accessible positioning of the transmitter.

o No risk of transmitter malfunction due to low-temperature exposure.

o No heat loss in impulse lines in view of that getting filled by thermally non- conducting vapours at ambient temperatures.

Your idea to leverage the inherent properties of a volatile fluid and the concept of vapor pressure to simplify level measurement is clever. By ensuring only vapors occupy the impulse lines, you are using the volatility of the liquid in your favor, thereby potentially eliminating the problems you've identified with liquid presence in the impulse lines.

This is a successfully tried out solution for tanks storing liquid ethylene at - 120°C and ammonia tank at - 36°C.