Adequate Provision of Tank Auxiliaries

In the absence of precision instruments, a decrease in BOR with time, below the normal boil-off, could be the first sign of stratification in a tank, and possibly be the only indication available towards deciding to commence a mixing operation. 

High precision instruments are required to detect density, temperature, and composition changes of the order of 1 %, while location of the liquid-liquid interface requires multi-point measuring heads, or a vertically traversing head, all measuring to 0.1 % precision. This level of precision is a challenge. Measurement of temperature to 0.1 % can be achieved in the laboratory, but considerable effort is required to meet this level of precision under industrial conditions. The precision of normal industrial thermometers is in the range of 1-2 %. 

The measurement of density with in-situ instruments to the required precision of 0.1 % is difficult to achieve—the advent of cold electronics should help [4]. 

Measurement of composition by liquid withdrawal through a capillary tube, followed by total evaporation and gas phase analysis, is extremely time consuming and expensive for any continuous monitoring programme to be maintained. Furthermore the accuracy will be plagued by the Marangoni film flows. 

The interface may be detectable using ultrasonic or electromagnetic (optical, radio, etc.) waves. It is therefore possible that a cryogenic sonar/radar system, using low temperature electronics, could be devised to detect stratification. 

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