Electrostatic heater-treaters

Some horizontal heater-treaters add an electrostatic grid in the coalescing section. Figure 1.25 illustrates a simplified schematic of a typical horizontal electrostatic treater. The flow path in an electrostatic heater-treater is basically the same as in a horizontal heater-treater, except that an electrostatic grid is included in the coalescing-settling section, which helps to promote coalescence of the water droplets. 

FIGURE 1.25. Simplified schematic of a horizontal electrostatic heater-treater. 

FIGURE 1.26. Electrical control system of an electrostatic heater-treater. 

Figure 1.28 shows one variation of the electrostatic heater-treater where the vessel only contains the coalescing section with the electrostatic grid. Units configured in this manner are called "oil dehydrators." They are capable of higher handling volumes and use separate... 

FIGURE 1.46. Typical vendor-supplied horizontal electrostatic heater-treater... 

An electrostatic heater-treater should be considered in fields with maximum salt content specifications imposed [10-30 lb per thousand barrels (PTB)], any time the BSStW must be reduced below 0.5%, and offshore facilities where space and/or heat is limited. 

Many combinations of hardware components are used in the dehvdration of crude streams. These range from flow tanks to sophisticated electrostatic ciehydratioiVdesalliug units, and include settlers, knockouts, splitters, heater-treaters and electrostatic dehvdrators. In a given situation, each ol these components may be patt ol an energy-optimized installation. The selection of a particular component depends on a nutnlx-r of parameters. 

Kf is 200 for heater-treater vessels and 170 for electrostatic vessels. Equation (4.1) is from Arnold and Thro [2],... 

The treater is the vessel that attempts to deliver pipeline-specification crude oil as its hydrocarbon product. Heater treaters typically aid in resolving emulsions by the addition of heat, the use of electrostatic grids, or the use of mechanical coalescing aids such as hay or baffle systems. 

Vertical treaters have a much lower volume-to-throughput ratio than gun barrels. As a result, more complete treatment is necessary in a shorter time. Solids control is as important as interface control, just as with the horizontal treater. Figure 5 illustrates a schematic of a vertical heater treater that also employs a dual-polarity electrostatic grid to effect more efficient coalescence and thereby better oil-water separation. 

Field experience tends to indicate that electrostatic treaters are effective at reducing water content in the crude to the 0.2-0.5% level. This makes them particularly attractive for oil desalting operations. However, for normal crude treating, where 0.5-1.0% BShorizontal heater-treater, neglecting any contribution from the electrostatic grids. By trial and error after installation, the electric grids may be able to allow treating to occur at lower temperatures. 

Gravitation A r, SEPARATORS, described in Parts I and 2 of this series, remove almost all of the water in produced fluids. However, contract specifications may call for almost complete water lemoval and it is sometimes necessary to include a heater or electrostatic treater unit as part of wellsite process equipment. 

There are two types of dehydration equipment that can make a 0.5% or less water cut. These are the electrostatic treater and the heater-... 

The electrostatic separator shown in Fig. 4.2 is normally placed in stream 6, shown in Fig. 4.1. A heater should be installed upstream of this electrostatic treater to control temperature. Here heating temperatures should normally range from 100 to 200°F for light crudes 22°API and above. For heavier crudes, use higher temperatures, such as 250°F for a 14°API crude oil. Some heavier crudes, below 14°API, may require temperatures up to 300°F for adequate electrostatic dehydration. This temperature is to achieve a gravity difference between the crude oil and water of 0.001 or more. The electric power required by these electrogrids is normally 0.05 to 0.10 kVA/ft2. The ft2 area is the horizontal cross-section area in the electric grid section of the electrostatic dehydrator. 

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