Proper mud washing is a best practice

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Solids and grease that settle at the bottom of a desalter vessel can build up to form a mud or a sludge. It occupies space, which decreases the residence time for oil droplets to separate from water (Figure 1).

If not addressed, solids can plug off draws in the effluent water header, which can lead to increased currents and straight line velocities inside the desalter and pull the oil/water interface into the effluent water headed for the wastewater treatment plant.

fig 1 3 Proper mud washing is a best practice

Mud washing is an excellent way to ensure residence time is not reduced. The practice allows a desalter to fully perform its function – remove water, salt and solids from the oil leaving for the crude unit and oil-free water leaving for the wastewater treatment plant to remove contaminants.

Most desalters include mud wash headers with a brine recycle system. Water is pumped out of a desalter and back in through nozzles, which acts as a power wash on the desalter’s bottom surface.

The key questions are the frequency of mud washing and whether the source of water for the mud wash is fresh or effluent.

Periodic and continuous mud washing each have their pros and cons. The use of fresh water, effluent, and even steam, which provides additional heat and can assist in oil dispersion, also have their positives and negatives. However, good observation, sampling and testing will ensure that a refinery benefits from mud washing (Table 2).

fig 1 4 Proper mud washing is a best practice

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