*Crude Distillation Unit (CDU) DOI: http://dx.doi.org/10.5772/intechopen.90394*

#### **Figure 3.**

*Some examples of devices for crude oil dewatering, degassing, and desalting. (a) Sump. (b) Separator. (c) Three-phases separator. (d) Hydrodynamic phase separator.*

Each of the above-mentioned apparatus has its own peculiarities and its own derivatives, according to the precise tasks to be accomplished:


• Field separator-electrostatic coagulator, horizontal apparatus of electrostatic coagulator. It contains the initial section of the chimney of the heating section for preheating.

are mainly operated as oil pre-treatment equipment: vertical, horizontal, and ball

The salts and minerals often present in the oil are mainly magnesium, calcium, and sodium chlorides with sodium chloride being the abundant type. These salts cause corrosion of equipment. For example, hydrogen chloride (HCl). Hydrogen chloride dissolves in the emulsion's water producing hydrochloric acid, an extremely corrosive acid. However, NaCl = Na<sup>+</sup> + Cl�. Water, though slight, but

Any remaining salts are neutralized by the injection of sodium hydroxide which

The electrical conductivity of oil emulsions is due to the ionic conductivity of oil,

reacts with the calcium and magnesium chloride to produce sodium chloride

**1.5 Description of dewatering of oil emulsions with electrostatic desalter**

the conductivity of dispersed water droplets in oil. Under certain conditions, droplets of emulsified water in oil form conductive structures in the form of "chains", located along the field lines [12, 22]. The electrical conductivity of the system in such cases increases sharply (hundreds and thousands of times) in comparison with the electrical conductivity of anhydrous oil. Electrical Conductivity of hydrocarbons (oil), the hydrocarbons have three types of conductivity regimes in

• The stable insulating regime, this regime is characterized by very high

resistance. In this state, conduction is related to traces of dissolved water in the

• The semiconductor, this regime is independent of the presence of water in the

• Conductor, relatively stable. The regime, however, it disappears by sufficient removal or reduction of the applied electric field and reappears when it is

because NaCl does not hydrolyze to the corrosive hydrogen chloride.

CaCl2 þ 2H2O ! Ca OH ð Þ<sup>2</sup> þ 2HCl (1) MgCl2 þ 2H2O ! Mg OH ð Þ<sup>2</sup> þ 2HCl (2)

CaCl2 þ 2NaOH ! Ca OH ð Þ<sup>2</sup> þ 2NaCl (3)

salt solution, there is a mixture of Na<sup>+</sup> cations and OH�, Cl�anions. Ions in the solution move randomly and constantly collide with each other [21]. But these collisions of Na<sup>+</sup> and OH� ions, H+ and Cl� ions do not lead to the formation of compounds, since NaOH is a strong base, and HCl is a strong acid. Since weak electrolytes are not formed when sodium chloride is dissolved in water, sodium chloride is not hydrolyzed. The concentration of H+ ions is equal to the concentration of OH� ions, so the color of the indicators does not change [13, 20]. All chemical compounds based on chlorine hydrolyze, except for NaCl, hydrolyze at

+OH�, thus, in the

dissociates into ions, and the equilibrium is established: H2O=H+

electrostatic desalter [1].

*Crude Distillation Unit (CDU)*

*DOI: http://dx.doi.org/10.5772/intechopen.90394*

**1.4 The salts in crude oil**

high temperature to hydrogen chloride:

general [23]:

**111**

hydrocarbon.

hydrocarbon.

restored to its initial value.

• Electromechanical separators-a horizontal device that is characterized by a combination of electrostatic grids, coalescing blocks, and the initial section of the chimney heating section for preheating.

The selection criterion of devices, it is recommended to consider the following parameters when choosing the equipment [8, 12, 18]:


In the separators, they usually separate gas is usually from the oil in two or three steps under slight pressure or dilution. The separators of the first stage simultaneously play the role of buffer reservoirs and are usually located on the deposit. The separators of the second and third stages are mostly on the territory of central collection and distribution points (the sites of pre-treatment and pumping of oil) [7, 17]. The vertical separators are more productive in comparison with horizontal ones, but also the vertical separators have a higher price. They are suitable for enterprises with high production capacities, as well as if the emulsion contains many solid particles [18]. The horizontal separators are the best option for processing small volumes of material, as well as liquids with a high content of dissolved gas. They are in the greatest demand, as they are quite productive and affordable. To achieve maximum efficiency when using horizontal oil and gas separators, the oil is mixed in the separation process; the temperature is increased, and the pressure is reduced. To increase the depth and improve the quality of separation in Russia, introducing hot drainage water before separation with a threephase separator is often used. Thus, they use heat, which increases the selection of gas, intensifies the process of demulsification of oil, improves the quality of spilled formation water, reduces investments, energy costs of processes, and significantly improves the conditions of Environmental protection. The three-phase separator can split oil, gas, and water at once. However, separators have limits. Even with a three-stage separation, complete separation of gas from oil is not achieved [8]. Besides, it should be noted that, despite the improvement in oil and gas separation techniques and technologies, field separators remain cumbersome and expensive devices [19]. Their operation is based on an inefficient gravitational principle and they are unproductive; the separators cease to function when the oil and gas mixture forms foam. The loss of energy contained in the flow of oil and gas, with a decrease in the pressure in the degassing in stages, leads to the need to use more pumping and compressor units for the collection and transportation of oil and gas through the pipeline [7, 8].

The final processes of dewatering and desalting are carried out at oil refineries with electrostatic desalter [20]. At the refinery, three types of electrostatic desalter are mainly operated as oil pre-treatment equipment: vertical, horizontal, and ball electrostatic desalter [1].
