Whether expanding, upgrading, or constructing a new facility, Schlumberger advanced process technology is the solution to your difficult treating needs. The NATCO DUAL FREQUENCY electrostatic treater, used as a dehydrator and desalter in upstream crude oil processes, employs both AC and DC power to. Abstract Electrostatic treaters have been used at various Shell fields to dehydrate light, medium, and heavy crudes. The performance and operating envelope of.
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Electrostatic Treater Operation are used for three-phase separation: Chemicals are usually injected into the emulsion upstream from the treater. Therefore, the treating process has already begun by the time the emulsion reaches the treater. Electrostatic treaters are used for three-phase separation: Electrostaatic enters the inlet section at the top of the unit and falls to the bottom of the vessel. It then travels upward across the firetubes and spills over a weir into the surge section.
From the surge section, emulsion flows through a spreader into the treating section where final separation of water and oil takes place.
Emulsion enters the treater, splashes over the U-shaped hood or downcomer and flows down-ward to the bottom of the vessel. Free gas is released as emulsion strikes the hood or down-comer and rises to the top of the inlet section.
Most free water in the emulsion quickly settles out and the remaining lighter liquids move upward through the water, which serves as a heated wash. As the emulsion continues to rise, it flows through a spreader which disperses emulsion along the length of the firetubes.
This action ensures maximum use of the firetubes for heating emulsion. Several things happen as emulsion moves upward across the firetubes. The firetubes heat the emulsion which aids in separation of oil and water.
Heated emulsion rises and spills over a weir out of the inlet section.
Emulsions and Electrostatic Treater Principles | SCIENCE PARK
Water, which has separated from the emulsion, settles to the bottom of the inlet section for removal. Gas, which has separated from the emulsion, rises to the top of the inlet section.
A gas equalizer pipe allows the gas from both sides of the baffle to be equalized, gathered, and removed from the vessel through the gas outlet. Some treaters have a heat exchanger installed on the inlet line. If used, incoming emulsion is preheated by the heat of outgoing oil. Therefore, the firetubes need to provide less heat.
The settling time for incoming oil is decreased, and the outgoing oil is cooled to a desirable storage temperature which minimizes vaporization and maintains a higher oil gravity. A major purpose of the surge section is to keep the treating section “fluid-packed. No clean oil leaves the treating section unless an equal amount of fluid enters the surge section. This is controlled by a float in the surge section which is mechanically linked to the oil dump valve.
NATCO DUAL POLARITY Electrostatic Treater
Inside the treating section, a flow spreader ensures uniform distribution of emulsion. It is in this section that final treating and settling takes place.
From the spreader emulsion rises upward toward the high-voltage, alternating-current, electrical grids. The lower grid is charged with 15, 20, volts of electricity while the upper grid is grounded.
Electrostatic treating begins below the treayer grid and is completed between the upper and lower grids where water droplets coalesce and settle out. As heated emulsion rises through the electrostatic field, water droplets are given an electrical charge, which causes them to become elongated and polarized.
Alternating current on the lower electrical grid GRIDS causes it to electrotsatic polarity trrater from positive to negative times per second or 60 cycles per second. This causes the water droplets to move around rapidly and collide with each other with enough force to break the thin film surrounding each droplet. The water droplets coalesce into larger droplets and settle to the bottom of the treating section for removal. Oil, which has separated from the water, rises to the top of the treating section.
A clean oil col-lection header skims off the clean oil for removal from the treater. The electrical system consists of a step-up transformer and two electrical grids electrodes.
Step-up transformers increase the incoming voltage to a higher level, e.
The two grids are suspended one above the other in the treating section. The upper grid is grounded to the vessel shell and is adjustable so that the electrostatic field can be regulated to meet varying coalescing requirements. The lower grid is not grounded and receives the electrical output from the transformer. Both grids are suspended from the top of the vessel shell by insulated hanger rods.
All components of the electrical system are designed for high voltage service. The transformer is the heart of the electrical system. Most electrostatic treaters have a reac-tance type transformer which has a reactor to protect the transformer from power surges and high voltage dispersion.
These transformers are oil-immersed and meet all reasonable electrical safety requirements. A circuit breaker, located between the power source and the transformer, protects the transformer from electrical power failures.
A fused disconnect at the power source is recommended for maximum safety. Oil level in the treating section is maintained by the oil dump valve, which is operated by a float in the surge section. When emulsion rises above a pre-set level in the surge section, the float rises with the emulsion and causes the dump valve to open, which allows oil to leave the vessel.
When the emulsion returns to the pre-set level, the dump valve closes and allows oil to accumulate in the treating section. Free water and treated water levels in the treater are maintained by water dump valves. As with the oil dump valve, water dump valves open to remove water when the interfaces rise above pre-set levels and close when the interfaces return to pre-set levels.
Both water dump valves operate by means of Interface level controllers which use gas or compressed air to open and close the dump valves.
This is achieved by the level controller diverting gas or compressed air to the diaphragm of the dump valve. Gas or compressed air pressure offsets the spring tension holding the diaphragm in the closed position. This action lifts the diaphragm and allows water to flow through the dump valve.
When the interface returns to its pre-set level, the level controller vents the gas or compressed air and allows the diaphragm to seat, closing the dump valve.
Some electrostatic treaters are designed to allow water in the inlet section to join water in the treating seciion before being removed from the treater. This arrangement utilizes one dump valve and level controller to maintain water ievels in the treater.
Mechanically operated oil dump valves and gas-operated water dump valves have been discussed in this manual. Other types of oil and water dump valves may be used on electrostatic treaters. Operating temperature is important and will vary from lease to lease. The lowest possible temperature to adequately treat the emulsion should be used. In warmer climates, heating may be necessary only in colder months. When heating is required, lower temperatures can be used in electrostatic treaters than in conventional heater treaters.
If fluid temper-ature gets below this level, the grids will not have the proper treating effect on the emulsion.
The relation of chemicals to temperature is an important factor to be considered. Usually less chemical is required to treat a warm emulsion.
However, elctrostatic savings in chemical with higher temperatures may be offset by the loss of revenue caused by gravity and volume losses in the oil and increased fuel costs.
Temperature controls or thermostats are an important part of any emulsion treater. If they fail to function properly, the burners could remain trater or on all the time. If they remain off, treatfr emulsion may cool so that it does not completely break up. If the burners remain on, the treater may overheat and be damaged, the lighter ends of the oil may be cooked off changing gravity, and oil volume will be decreased resulting in lost revenue. Firetubes should be inspected at periodic intervals.
Since most emulsions being treated contain a certain amount of sludge and solids, the firetubes should be checked for corrosion, rust and accumulation of scale.
The burner flame should aim straight down the center of the firetube. If it hits the firetube directly, a hot spot will form and premature firetube failure will occur. The burner should come on and burn steadily for a long period of time rather than blasting on and off. A yellow flame with just enough air to keep from forming soot is best. Electrostatic treaters operate under working pressures of 5 to 50 psi. The maximum electrostayic pressure for a treater can be found on the manufacturer’s information plate attached to the treater.
The type of valves and controls used varies depending on the treater construction. Electrosatic, water, and gas discharge lines must be equipped with controls. Since electrostatic treaters operate under pressure, they should be equipped with pressure relief electrsotatic that have enough capacity to protect the treater if pressure increases.
Gas leaving at the top of the treater is controlled by a gas back-pressure valve which controls the pressure in the treater. The inlet and surge sections are held at a slightly higher pressure than the treating section. When there is not enough entrained gas in the incoming fluid to treate necessary pressure, a make-up gas line is usually connected to the gas equalizer. There are several reasons why a higher pressure is maintained in the first two sections. Recommended steps for safely lighting a gas-fired electrostatic treater.
For smooth operation, the following maintenance checks should be performed as indicated:. Water levels treatee pre-set.
When the water level changes, these checks can be done to restore it to the pre-set condition:.