Aug-2020

Automated level measurement cuts desalter upsets (TIA)

The path from crude oil to high quality, usable products involves complex technical production and processing procedures in refineries, whereby several challenges have to be mastered, not only those of process measurement technology.

Sabrina Nees
Berthold Technologies GmbH & Co. KG

Article Summary

Before the crude oil passes through the various process steps, starting with distillation, it must be desalted. Therefore, desalting is the first stage treatment in a refinery, whereby the correct and efficient performance is essential to ensure smooth operation in all subsequent process steps.

With refiners trying to maximise their margins, they turn to the use of lower cost opportunity crudes. The increased use of such opportunity crudes can cause issues with the proper operation of the desalter and leads to the formation of greater emulsion layers inside the vessel. This emulsion robs the operator of valuable volume inside the vessel used to separate the oil and water. In turn, this decreases residence time inside the vessel, leading to increased carry-over of water, salts, and minerals. However, these can cause various issues downstream from tray damage, fouling of heat exchangers/furnaces, corrosion issues, and catalyst deactivation. In addition, large quantities of expensive chemicals are often added to prevent the excessive formation of emulsion. For these reasons, control of the emulsion layer is of great importance. With a reliable interface measurement, it is possible to react better and faster to the formation of the emulsion and thus to optimise the desalting process, which saves high consequential costs. Various technologies can be used for level and interface measurements on desalters. These include, for example, differential pressure, RF absorption probes, and radiation based density profile measurements.

Radiometric based multiphase level measurements are among the most reliable and durable measuring methods for an application under extreme conditions such as those prevailing in desalters. Berthold’s measurement solution EmulsionSENS consists of several detectors mounted on the vessel’s outside and multiple sources inserted into a dip pipe (see Figure 1). A shield mounted on the top of the dip pipe ensures safe handling and storage of the sources, not only during transportation but also during maintenance where entering the vessel is unavoidable. EmulsionSENS is available in two different arrangements and can therefore provide exactly the values needed. With the so-called aligned arrangement, you obtain very precise density information on each detector elevation. Using the so-called staggered arrangement provides not only the density values in the area between the detectors but also the position and thickness — in other words, the level values — of all the layers. In the desalter process, level monitoring is of great importance, especially in the area of the water outlet.

Refiners have experienced a decrease in the number of upsets in the desalters from two to six upsets per year to none in the two years in which they operate with a nuclear density profiling system. The main reason for this reduction of upsets is the ability to provide automatic control and a continuous adjustment of the water outlet valve to maintain proper control and minimise the risk of having salt, water, or mineral carry-over. Another advantage of level measurement is the monitoring of chemical usage, its optimisation, and the associated cost savings. In addition to reducing the number of upsets and the chemical savings, a refiner can greatly increase the reliability of downstream equipment of the desalters by severely limiting corrosion caused by salt carry-over and extending the catalyst life by increasing the efficiency of the desalter. All in all, the profitability of a refiner can be significantly increased.

This short case study originally appeared in PTQ's Technology In Action feature - Q3 2020 issue.

For more information: Sabrina.Nees@Berthold.com