Emulsion desalting

The presence of these acids in crude oils and petroleum cuts causes problems for the refiner because they form stable emulsions with caustic solutions during desalting or in lubricating oil production very corrosive at high temperatures (350-400°C), they attack ordinary carbon steel, which necessitates the use of alloy piping materials. 

The amount of added water required for desalting may be minimized by adding a chemical emulsion breaker to the crude that is capable of displacing the surface-active components from the brine droplets. Quatemized carboxylic-sulfonic acid salts, shown in Figure 22-9, are useful for desalting [1791]. Preferably, the chemical emulsion breaker is used in combination with a delivery solvent, such as diethylene glycol monobutyl ether. 

P. R. Hart. Method of breaking reverse emulsions in a crude oil desalting system. Patent CA 2126889,1995. 

The selected biocatalyst is any of the already described alternatives based on R. rhodochrous bacteria ATCC No. 53968. Its concentration or proportion to the fossil fuel feedstock was neither reported nor claimed only a slight comment is made on the proportion between the crude oil and the biocatalytic aqueous solution, which states that it will not exceed one half the total incubation volumes. In addition, an additional amount of water, enough for desalting, is simultaneously added with the biocatalytic solution. The process is carried out by feeding the crude oil and water into a CSTR reaction vessel and stirred until an emulsion is formed. The mixture is incubated under stirring at temperature and pressure conditions, for a period of time adequate for both to occur, desalting and desulfurization. 

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. 

Desalter units generally will produce a dehydrated stream containing like amounts of BS W from each stage. Therefore, BS W can be considered pan through volume and the dilution water added is the amount of water to be recycled. The recycle pump, however, generally is oversized to com- >cnsate for difficult emulsion conditions and upsets in the system. 

Produced salt water, if it remains in the oil in sufficient quantities to require a dehydration-desalting facility, is carried in an emulsion state. The emulsion exists as a result of mechanical shearing of produced water and its dispersion into oil by turbulence. Once water is dispersed in droplets, many of them are combined with the various emulsifying agents produced in the crude and resist natural separation because of their size and envelopment by the emulsifying agents. 

Salt water is present in the crude in the form of emulsion. When the produced formation water is highly saline as is the case in Kuwait, then straight dehydration is not the solution and the crude is to be desalted as well. 

The water knockout tank is designed to separate all free water from the incoming field production oil. It generally uses a 30- to 60-min storage time. In many field cases, the free water is only 30 to 60% of the total water content in the oil. This is due to oil-water emulsions. The oil fed to the downstream dehydration tank (see Fig. 4.15) is treated with an emulsion breaker chemical that is injected into the feed line to the dehydrator tank. As much as 70% of the production may therefore be separated in the downstream dehydrator tank. The KO tank may also receive fresh water for desalting the crude oil through its feed line. 

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

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. 

IMULSIONS OF OIL AND WATER are one of many problems directly associated with the petroleum industry, in both oil-field production and refinery environments. Whether these emulsions are created inadvertently or are unavoidable, as in the oil-field production area, or are deliberately induced, as in refinery desalting operations, the economic necessity to eliminate emulsions or maximize oil-water separation is present. Furthermore, the economics of oil-water separation dictate the labor, resources, and monies dedicated to this issue. Before we describe the methods and economics of emulsion breaking at commercial facilities, we will restate several key concepts concerning emulsions and the petroleum industry. 

Oil-Water Interface Control. In any petroleum processing unit in which emulsions are resolved, an interface between oil and water must occur. The quality of this interface is directly related to the efficiency of demulsification in either a refinery desalter or an oil-field free-water knockout or treater. The sharper the transition between clean water and clean oil (or the tightness of the interface), the better the ability to control oil and water retention times and quality and operate the vessel. 

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... 

Bench-top testing will allow variation in chemical type and dosage, temperature, pressure, agitation, treatment time, electrical input (portable electric desalters only), and wash-water or diluent addition. Variations in temperature and pressure will not allow simulation of high pressures and temperatures. The bench-scale tests imply that a batch treatment of the emulsion is used to determine treating chemicals for a dynamic continuous treating system. Thus, results will have limitations even if the parameters of the test procedure are as accurate as possible. 

Desalting and drying processes are usually conducted in the industry at temperatures ranging from 50 tolOO°C. If a higher temperature is to be used, then the process must be carried out at a high pressure because of the need to keep the emulsion in the liquid phase. For this purpose, it is necessary to use separators with thicker walls. This leads to an increase in the price for the hardware. 

During electrical desalting, electricity is used to increase the rate of movement the water droplets with the solved salts as well as to accelerate the merging of small droplets to form bigger ones. These cause the separation of the droplets from the petroleum emulsion. 

Dissolvan Brands. [Hoechst AC] 0/ PO block polymers and/or oxyall lated resins emulsion breaker for w/o emulsions dehydration and desalting agents for crude oil. 

When crude oil enters a refinery, the first vessel in which it is treated is the desalter. Here it is mixed with water to remove any salts that may be present. In this process, an emulsion is formed, and it must be broken prior to further treatment. The majority of the emulsion is broken by an electric grid however, chemicals called emulsion breakers (organic salts) are also used to aid this process. 

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