Electrostatic desalters

Figure 2 Crude desalting (electrostatic desalting). A high-voltage electrostatic field acts to agglomerate dispersed oil droplets for water-oil separation after water wash desalting. (From Ref. 5.)...

Production of wet crude had been a growing fiald problem ir. Kuwait. Trie need to treat wet crude was felt for quite some time. Application of right technology and installation of proper desalting facilities were needed to solve this problem. Thus It was decided to Install electrostatic desalting plants progressively in Kuwait s oil fields. By the end of 1986, Ita plants, (6 conventional (AC] and 8 dual polarity (AC/DC)2 with a total capacity of over 790,000 STB/D of treated crude have been Installed. 

So far 14 plants of two stage electrostatic desalters have been installed. Figure 7 is a process flow diagram of a typical installation showing the main equipment. Each plant has been divided in two parallel trains of equal capacity and only one process train has been shown ir. Figure-7. The design data is listed in Table-I and the major plant components are Hated below ... 

The nested feed is then processed through two stare electrostatic desalters to remove water and salt to give a treated product witr a maximum of 0.11 hy volume of water and 5 FTP of salt. 

For a continued discussion of electrostatic desalters, see the section on production desalters later in this chapter. 

Figure 7.10 Illustration of a three-stage electrostatic desalting (emulsion breaking) system. From Grace [452]. Copyright 1992, American Chemical Society.

Electric desalting a continuous process to remove inorganic salts and other impurities from crude oil by settling out in an electrostatic field. 

Before distillation, crude oil salts and certain metals must be removed. The process of desalting is applied for this purpose. Desalting involves mixing the crude oil with water at a temperature of about 250°F (121.1°C) under enough pressure to prevent evaporation of both water and volatile crude oil components. The salts are dissolved and removed by the water. Oil/water emulsions often form which also contain salts. The emulsions can be broken by the use of high-voltage electrostatic coalescers or by the use of demulsifying chemicals. 

Field Desalting of Wet Crude in Kuwait by Chawla expands upon the principles describing electrostatic treating that are discussed in other papers in this section A specific oil-treating/desalting system is described. 

For comparison, assume that two methods of dehydration-desalting are present, one slightly more efficient than the other—for instance, one electrostatic and one mechanical coalescer. Further assume total net oil produced is 100,000 bopd, split evenly between the two methods. 

Electrostatic crude desalting systems are used in Kuwait. The system employs chemical demulsifiers, neat and an electrostatic field to dehydrate the crude. 

Due to various advantagss, electrostatic coalescing process has found wide applications and ras bcc. employed in Kuwait field desalting plants,... 

It is important to note that you should consider removing all free water before attempting to size the electrostatic water separation section. The dL factor calculated is only for this electrostatic section. You should therefore make a good estimate of how much water will pass into the electrostatic section and input this value in the Prod + Desalting Water, BPD input block. Inputting all of your production water will seriously err sizing results. Free water should be removed in free water knockout (KO) tanks or vessels upstream. True and needed electrostatic treater sizing may thereby be determined. 

Fig. 18.13. Electric desalting—CB I. Baker ProcessTechnology. Includes heater, mixing device, and electrostatic settler. (Source Hydrocarbon Processing, 2004 Refining Process Handbook, CD-ROM. Sept. 2004 Copyright 2002 by Gulf Publishing Co., all rights reserved.)...

The emulsion enters the desalter vessel where a high-voltage electrostatic field is applied. The electrostatic field causes the dispersed water droplets to coalesce, agglomerate, and settle to the lower portion of the vessel. The various contaminants from the crude oil concentrate in the water phase. The salts, minerals, and other water-soluble impurities are discharged from the settler to the effluent system. Clean, desalted hydrocarbon product flows from the top of the settler and is ready for the next processing step. 

The initial corrosion control system used in a crude unit is a desalter. Modern desalters separate oil and water electrostatically. The internals used to accomplish electrostatic separation are normally of a proprietary design. The vessel itself is usually carbon steel. The bottom is often cement lined to protect it from salt water corrosion. The payout on a desalter is difficult to establish. Desalters are normally used when the salt content of the crude exceeds 20 lb per 1,000 barrels (ptb). When high reliability of the unit is desired, crudes with salt contents of 8 to 10 ptb are desalted. When desalting is used, the target is 1 ptb or less. Fluctuations in salt content are particularly troublesome to the downstream equipment therefore, the desalter should be designed for the maximum anticipated salt content. 

Electrical Methods. The principle of electrostatic dehydration in emulsion breaking for both refinery desalting and oil-field production is essentially the same. The electric field produced disturbs the surface tension of each droplet, probably by causing polar molecules to reorient themselves. This reorientation weakens the film around each droplet because the polar... 

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