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Desalter interface control optimises crude processing (TIA)

To improve margins, refiners continuously look to optimise feedstock blends. Variability can bring significant operational challenges during the refining process that must be overcome.

Andrew Shaw and Neil Murch
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Article Summary
One critical need is the efficient removal of solids, salts, and water from crude feedstock. This has become increasingly difficult when processing certain opportunity crudes that can have all of these detrimental properties at high levels. It is essential that water washing of the crude is effective at removing these and that the oil can be efficiently separated prior to crude distillation.

Efficient separation requires the use of accurate and reliable interface control to manage its position and quality. An increasing number of refiners have deployed the Tracerco Profiler for desalter interface control.

This device provides an accurate measurement of the density distribution within a desalter, offering continuous high resolution imaging and control of each phase. This allows the most efficient operating conditions to be maintained as well as monitoring the effectiveness of chemical additive and mud washing.

With repeatable, accurate, and reliable real-time process measurements, the Profiler provides operators with interface confidence. If the interface can be controlled, it is feasible to raise the interface level closer to the coalescing electrostatic grid system, which in turn enhances separation of crude from water. By optimising separation to improve feedstock flexibility, upstream desalter mixing can be increased to maximise wash water contact, thus removing more undesirable materials.

Following a desalter improvement initiative, a European refiner said that the Profiler provided interesting information on the workings inside the desalter that was otherwise unseen. It allowed the refiner to see rises in the solid layer along with the effect of mud washing on this solid layer. The depth of the emulsion layer and its position within the desalter have been seen with significant changes on different feeds. It is used as another tool along with lab analysis to make optimisation decisions around the desalter. One unusual thing that the Profiler has shown is the emulsion layer of a higher density than the water layer found to be asphaltene stabilisation.

A North American refiner said that the accuracy and reliability of multiple real-time measurements gave the company the confidence to run levels closer to the grid, yielding higher efficiencies and throughputs, including the ability to process lower cost opportunity crudes. The refiner gained the ability to effectively process alternate feeds and increased throughput by 20 000 b/d.

By providing a high resolution measurement around the emulsion layer, the tendency to overdose chemicals is reduced. This enables refiners to reduce costs associated with chemical dosing, and enhance safety and associated environmental benefits.

This short case study originally appeared in PTQ's Technology In Action feature - Q3 2019 issue.

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