Monitoring processes with radiometric measurements (TIA)

Reliable measurement solutions for refineries as well as for petrochemical industries are not a matter of course.

Sabrina Nees
Berthold Technologies

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Article Summary

The prevailing conditions are anything but ideal and thus pose great challenges for every measurement. Radiometric measurements for such demanding industrial processes have been around for several decades. In the meantime, they are an important mainstay in performing the most difficult and critical level and density measurements or even as limit switches. Thereby, the measurement is based on a simple yet sophisticated concept – the principle of attenuation. The gamma radiation emitted by a radioactive source penetrates the vessel and its contents and is then detected by the detector arranged opposite. Depending on the density of the penetrated matter, the radiation is attenuated. This attenuation in combination with an appropriate calibration, makes it possible to determine the density or even the level of the vessel contents. Often monitoring of only one layer is not sufficient. Due to separation processes in refineries and chemical plants, for example caused by different densities or chemical compositions, several layers can make level measurement more difficult, especially if the levels of each individual phase are of interest. Measurements of more than two phases or of interfaces that are not clearly defined, for instance in separator vessels, require a more complex solution. Such a multiphase level measurement system, like Berthold’s EmulsionSENS, consists of several density measurements installed on different heights with detectors mounted on the vessel outside and sources inserted into a closed dip pipe inside the vessel to create a density profile of the vessel contents. Using sophisticated algorithms, EmulsionSENS can not only output the measured density values but can also determine the filling levels of each individual layer.

The use of radioactivity implies certain expenses, such as official permits, hence measurements based on radiation are usually the very last option used for level, level switch, or density measurements. However, with the appropriate precautions and compliance with a few regulations, this non-contacting and non-intrusive technology offers advantages. Berthold’s detectors are equipped with a patented method which allows for reliable compensation of temperature influences and ageing effects, leading to outstanding measuring performance over many years. The high sensitivity of the detectors is one reason for the need for low source activities and associated low dose rates or radiation exposure. Used components are not exposed to harsh process conditions and thus aggressive atmospheres, high temperatures, or high pressure is no problem, and there is no risk of hazardous material leaks.

Using the laws of physics and statistics as well as sophisticated software, nuclear based measurements are successful and reproducible. The advantages of the system extend throughout its lifetime: starting with the simple installation, which can also be easily retrofitted to existing tanks, through smooth handling and wear- and maintenance-free operation, to long, reliable, and safe use in combination with a one-time calibration. In addition to these advantages, the operating costs themselves are low. Additionally, thousands of dollars can be saved each year in reduced downtime and equipment and maintenance costs.

The fact that nuclear measurement gauges have no moving parts or components inside vessels that could need replacement, makes them a solution for accurate and repeatable measurements in rugged and hostile process environments. But even the most robust measurement has its challenges; for radiation based measurements this is interference radiation, especially in industrial complexes. Interference radiation is caused by non-destructive testing, which means typically weld or vessel integrity inspections and are basically performed on a daily schedule. Such interferences can cause a significant increase in the count rate detected and therefore a misinterpretation of the supposedly measured level. Since neither the timing nor the impact of interference radiation is predictable, radiometric measurements require a reliable solution for dealing with such events. With the features X-Ray interference protection (XIP) and radiation interference discrimination (RID) available, continuous process flows can be ensured, unplanned shutdowns avoided, and thus real added value is provided when using radiometry, even during the presence of interference radiation.

Companies including Exxon Mobil, Shell, Conoco Phillips, and Lukoil have been using radiometric measurements for several years or decades and benefit from the positive outcomes. Users repeatedly report on the reliability of the systems and the resulting reduced failures. A refinery, for example, was averaging two upsets a year caused by the desalter. After installing a radiometric measurement system, there were no upsets over a period greater than three years. Fewer upsets also mean less corrosion and fouling. Another frequently mentioned advantage is the reduction of chemical consumption due to better control. As an example, an average daily consumption of demulsifier agent at 250 litres costs around $20000. Reducing chemicals by only 5% results in daily cost savings of around $1000.

This short case study originally appeared in PTQ's Technology In Action feature - Q1 2021 issue.

For more information: Sabrina.Nees@Berthold.com

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