crude oil desalting

   When crude oil is recovered it contains salts, sand, water and small contents of metals such as copper, nickel, and vanadium. Crude oil often contains water, inorganic salts, suspended solids, and water-soluble trace metals. As a first step in the refining process, to reduce corrosion, plugging, and fouling of equipment and to prevent poisoning the catalysts in processing units, these contaminants must be removed by desalting (dehydration).

  The desalting of crude oil is a process that does not have a high profile, but is vital to the operation of the modern petroleum refinery. Desolaters provide more protection to costly refinery equipment than any other single piece of process hardware. The salts that are most frequently present in crude oil are calcium, sodium and magnesium chlorides. If these compounds are not removed from the oil several problems arise in the refining process. The high temperatures that occur downstream in the process could cause water hydrolysis, which in turn allows the formation of corrosive hydrochloric acid. Sand, silts and salt cause deposits and foul heat exchangers. The need to supply heat to vaporize water reduces crude pre-heat capacity. Sodium, arsenic and other metals can poison catalysts. By removing the suspended solids, they are not carried into the burner and eventually flue gas, where they would cause problems with environmental compliance such as flue gas opacity norms 

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Factors affecting crude oil desalting :

The objective of oil desalting is to remove water-soluble salts and the entrained water, which normally contains dissolved salts. Formation water flows with crude in two types: free and emulsified. The free water is not intimately mixed in the crude and is found in larger drops scattered throughout the oil phase. This kind of water is easy to remove by gravity oil-water separators, surge tanks (wet tanks), and desalting vessels. On the other hand, emulsified waters are intimately mixed and found scattered in tiny drops in the oil phase. This kind is hard to remove by simple settling devices, so further treatment such as chemical injection, freshwater dilution, mixing, heating, and electricity are required. The addition of diluent water, heating, and applying electricity can enhance gravity separation.

Factors affecting desalting performance are:

Types of pumps

      A pump is a device used to transport fluids, such as liquid (pump) , gases (compressor) or slurries . A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps.Their names describe the method for moving a fluid.

Types

• Positive displacement pump

MORE     A positive displacement pump moves a fluid by trapping a fixed amount of it then forcing (displacing) that trapped volume into the discharge pipe.

Some positive displacement pumps work using an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. The volume is constant given each cycle of operation. positive displacement pumps are in hydraulic systems to a pressure up to 34500 bar.

Positive displacement pump behavior and safety