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A better picture inside the desalter

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Hydrocarbon Engineering,


Ask any refinery operator where the bottleneck is in their process, and chances are, they will tell you it is in the desalter. Incoming crude oil – especially heavy crude – moves through a desalter before making its way through the rest of an oil and gas refinery. This first step can be time-consuming, and it is made worse by using unreliable measurements to control the process.

Refineries have traditionally used capacitance probes, displacers, and even guided wave radars to try and track the interface between hydrocarbon, emulsion, and water inside the desalter. All of these technologies, however, fall short. Changing the densities and fluid dynamics of incoming crude oil and improper sensor calibrations all lead to measurement errors.

To overcome these challenges and improve efficiency, more oil and gas refineries are turning to radiometric technology like VEGA's Multi-point Density Array (MDA) system for a more reliable and accurate 'look' at what is happening inside these large vessels.

Multi-point Density Array: How it works

The MDA system provides continuous density data at individual measurement points on a vessel. Multiple sources and detectors are installed at fixed locations on a desalter, and each measurement is specific to a horizontal plane of elevation. This gives operators a real-time density profile of the contents inside.

An accurate density profile provides a reliable measurement that allows operators to differentiate between water, hydrocarbons, and if applicable, an emulsion layer. A detailed picture enables operators to make advanced control decisions for better process efficiency. This can save money with more effective chemical usage and prevent process upsets due to a rising water level, growing emulsion layer, or other potential setbacks.

VEGA's MDA system uses low-activity Cesium sources, sensitive density detectors, and longer process paths up to 26 in. to minimise the influence of any buildup. These density measurements can be inputted directly into a distributed control system (DCS) to visualise interface, level, and density control without requiring a separate computer for processing and averaging algorithms.

Getting the MDA up and running takes a simple calibration, requiring two data points. The first data point is collected when the separator vessel is empty, and the second is collected when the vessel is filled with a fluid of a known density, which can be either water or some type of hydrocarbon. Once calibration is complete, operators can expect reliable, repeatable measurements for years to come without the need for additional recalibrations.

Low-maintenance solution keeps the desalter running

Each detector in the MDA system is mounted externally, so they have no direct contact with the process, eliminating the possibility for corrosion or detector damage due to temperature. This eliminates most ongoing maintenance and repair costs. Plus, refineries no longer need to purchase a cooling system or use exotic materials capable of withstanding any harsh or difficult process conditions.

In the rare instance a detector requires maintenance, there is no need for a process shutdown. The externally mounted detectors are easily accessible, and with multiple independent measurement points, a single offline detector only means the loss of one of those measurements. The rest of the system continues operating.

The MDA's design ensures each detector does not influence another's accuracy, and the system can continue to provide highly reliable measurements. Taken together, the MDA's features create an easily managed, reliable system that delivers real results for refineries around the world.

Desalter efficiency clears the bottleneck

In North American refineries alone, VEGA has installed more than 200 MDA systems. At any refinery, optimising operations begins at the desalter where better control has several benefits, all of which lead to lower costs, increased throughput, and shorter resonance times.

Long resonance times in the desalter slows down the entire process. To combat this, operators add expensive chemicals to help facilitate the separation of hydrocarbons from water. Using too many chemicals is not only expensive, but it also affects downstream processes when those same chemicals must be removed. VEGA's MDA system gives operators a real-time look at the separation process, so they can optimise chemical usage.

As hydrocarbons and water separate in the vessel, the water at the bottom must be siphoned off. Using a density measurement, operators have a better understanding of the water level and can take immediate action when water level rises too high. Conversely, operators can confidently remove the water without fear of siphoning away any of the valuable hydrocarbons.

Taking immediate action is just as important when refineries are separating heavy crude and the emulsion layer expands faster than expected. Those moments can be the difference between continued operation and process-crippling grid shortages.

Receiving a consistent interface measurement using the MDA is both faster and more reliable than taking regular samples. That is because VEGA's solution makes it easier to distinguish between the water, oil, and emulsion layers inside the separator.

VEGA's Multi-point Density Array delivers independent measurements to create a density profile that allows refinery operators to exercise real-time control over the product level inside separators. This unparalleled control is helping preserve the life of equipment and improve production in refineries all over North America.

Read the article online at: https://www.hydrocarbonengineering.com/refining/04032020/a-better-picture-inside-the-desalter/

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