DEMULSIFICATION &DESALINATION

8/13/2019 DEMULSIFICATION &DESALINATION

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DEMULSIFICATION

&DESALINATION

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In the reservoir, crude oil is in intimate contact with

formation water (connate) which is saline to varying degrees

and, oil and water have various other minor substances in

their composition which act as natural emulsifiers and fluid

flow conditions bring about thorough mixing and dispersal of

one phase in another i.e. forming EMULSIONS. Thus, the

problem of emulsion requires timely resolution by proper

method. Apart from dehydration, desalting and removal ofbasic sediment are to be attended to so as to make crude oil

marketable (water of 0.5% to 2% or less and salinity < 8 ptb)

depending on the sale price and contract specifications. Oil

must be demulsifiedas water causesrefining difficulties suchas corrosion, coke deposition, foaming, pipeline

transportation, tank corrosion, increased power

consumption and equipment wear and tear because of

increased viscosity and volumes with corresponding effects

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EMULSIONS

Emulsion - a mixture of two mutually immiscible liquids, one of

which is dispersed as droplets in the other & is stabilized by anemulsifying agent.

Dispersed dropletsare known as internal phase & liquid surroundingthem is theexternalorcontinuous phase.

Emulsifying agentseparates the dispersed droplets from continuousphase & continuous phase from the dispersed droplets.

In the oilfield, O&W are in 2 - phases and usually form a water-in-oilemulsion although occasionally the REVERSE or oil-in-wateremulsion will form.

Componentsofwater-in-oilemulsions:

Water -dispersed or internal phase

Oil -continuous or external phase

Emulsifying agent -stabilizes the dispersionThree components themselves will not form emulsion unless there is enough

agitation (disperse one liquid intoanother)

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Photomicrograph of normal emulsion Photomicrograph of emulsifying

agent surrounding a water droplet

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Photomicrograph of emulsifying agentpreventing two droplets from coalescing

Tight emulsion has small dispersed droplets which

have considerable resistance to settling & is usually

a stable emulsion

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Loose emulsion is less stable than a tight emulsion

because of the large dispersed droplets that tend to

settle easily.

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Chemical demulsifiers rupture the tough skin of film surrounding a

water droplet, thus allowing droplets to unite & settle.

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Stability of emulsion is dependant on degree of agitation, nature &

amount of emulsifying agent.

Stableemulsions may take weeks / months to separate if left

alone in tanks without treatment whereas unstable emulsions mayseparate relatively in no time into clean O &W phases.

Pure water & pure oil will never form an emulsion no matter how muchagitation is applied as these dislike each other intensely. Therefore, if

confinedin the same container, they will quickly find a state of existencewhich gives theleast contactor thesmallest interphase area.

A drop of water in a body of oil will take the shape which givesleast surfaceareasphere.Also, water drop will squeezeitself in astightlyas possibletoreduce itssize & therefore itssurfaceas much as possible.Measure of

such a drop shrinking force is calledSurfaceTension.Material at new surface which is in contact with gas (or air) or another

immiscible liquid as the case with O&W and this is known as interfacialtension

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The surface tension of water at 20 C is 73 dynes/cm whereas that of mostorganic liquids is about 28 dynes/cm & this varies from 20 to 30 dynes/cmfor crude oil & water. When oil & water are vigorously mixed, both typesof emulsions are formed, but primarily the minor phase tends to become

dispersed. Both type of emulsions tend to resolve and the surviving type(O/W or W/O) depend largely on the nature of stabilizer and the phaseratio.

Formation of emulsion involves creation of enormous areas of interphasewith attendant free energy supplied by agitation of pumps, friction in lineor pr. drop through valves.

Foe example, in half a gallon of oil a 1% emulsion consists of 0.0001 inches indiameter, these will be about 2 trillion of them & total area of interphasewill be about 400 sq. ft. which can gather considerable amount ofstabilizer or dust. In prime system of distilled water & pure HC (as Hexane)this free energy tends to subside and the drops collide to form free water.

When the drops meet & unite, larger drops thus formed have less surfacearea than the sum of surrounding surface areas of the smaller drops. So inkeeping with the desire of the water phase to find a state of existencegiving theleast surface area,drops will continue to unite until they havebecomeone large drop or body.

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Normaloilfield emulsions consist of an oil continuous or external phase,

and water dispersed or internal phase

Where high water cuts exist with low salt content & an emulsifying agentis present in the water phase, it is possible to formreverseemulsion with

water as continuous phase & oil droplets as internal phase. Also electrical

charges play strong role in stabilizing. These charges can be maintained in

waters of low conductivity or low salt content. As the salt content

increases, type of emulsion becomes less stable since the charges on oilparticles can bleed off & they can then more readily unite. With the

emulsifying agent in water, it tends to surround oil particles & trap them.

Inducedemulsions which are deliberately created for processing.

Dual (or complex) emulsions also form in low gravity, viscous crudes.

These contain water as external phase & have an internal water phase in

the dispersed oil.

Vast majority of oil treating systems deal with normal emulsions.

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Types of Emulsions+-------------------+-------------------------------+---------------------------+

Normal Induced Invert Dual

I (multiple)I Deliberately promoted, Oil in water systems single

as for encountered in including bothDesalting crude oil Refinery waste Disposal types

&

Effluents, invert muds

Real Pseudo

Stable, without Unstable prone to

separation in resolution, if given

stage separation adequate time or

or settlement by by simpler methods

gravity in storage. as centrifuging etc.

Multiphase flow leads to greater emulsification on account of intimate mixing

(G-O-W) and dispersion.

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EmulsifiersTo form an emulsion the system must have presence of water & oil, agitation and also

an emulsifying agentwhich has asurface activebehavior. Some of the elementshave preference for the oil, and others are more attracted to water. An emulsifiertends to be insoluble in one of the liquid phases whereby concentrating at theinterphase. It can act in one or more of the following manners:

Decreases the interfacial tensionof water droplet, thus causing smaller droplets toform which take longer to coalesce into larger droplets, which can settle quickly.

Forms a viscous coating on the dropletsthat keeps them from coalescing into largerdroplets when they collide.

Emulsifiers maybe polar molecules, which align themselves in such a manner as tocause an electrical charge on the surface of droplets. Since like charges repel, two

droplets must collide with sufficient force to overcome this repulsion beforecoalescence can occur.

Normally occurring surface active materials found in crude oil (asphaltines-generalterm applied to a large variety of high MW compositions containing sulpher,

nitrogen, oxygen & metals etc.) serve as emulsifiers. Paraffin's, resins, organicacids, metallic salts, colloidal silts & clay and asphaltenes arecommon emulsifiersin oilfields. Drilling muds & workover fluids are also sources of emulsifying agents(EA).

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Emulsifiers.contd.

Type and amount of EA has an immediate affect on emulsions

stability.

Temperature history of emulsions is equally important as it affects

the formationof paraffins & asphaltenes.

Speed of migrationof EA to the oil/water interphase and behavior in

terms of strength of interphase bond are important factors.

Emulsion treated soon after agitation or creation of paraffins &

asphaltenes can be less stable and easier to treat if the migration of

emulsifier is incomplete. Agedemulsion may be difficult to treat.

Normally lower the crude viscosity & lighter the crude the more

rapid is the aging process.

Therefore, early treatment may be a lesser factor in treating low

viscosity , highAPI gravity crudes.

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DEMULSIFIERSA demulsifier is effective in resolving emulsions through following four main

actions:

- Strong attraction to O-W interphase

- Flocculation

- Coalescence

- Solid wetting

Demulsifiers are similar in nature to emulsifiers and are surface activeagents with certain built in properties which make them effective in

disrupting the effect of EA. Action is all at water-oil interphase so it must

get there to do its job. Faster it gets there, better job it will do. Since the

emulsifier is fairly concentrated at the interphase and creates an

hindrance to demulsifier.Therefore a good demulsifier must have a good built-in ability tomigrate

quickly through the oil phase & compete against large odds for its place

at interphase.

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Once demulsifier reaches interphase, it proceeds to its major

action of flocculation. A good demulsifier, concentrated at

the surface of water droplet, has a strong attraction for

other droplets in same condition. By this mechanism , largebunches of drops are joined together. When magnified, they

take on appearance of bunches offish eggs.The oil takes on

abright appearancesince the smaller water droplets are no-

longer dispersed throughout the oil to diffuse light.

Characteristics of demulsifier to produce the joining of droplets

does not disrupt the continuity of the emulsifier filmbut just

adds to it. If the emulsifier has certain weeknesses, this

flocculation force may be sufficient to cause complete

resolution of emulsion.

However, in most cases further action is necessary for the

water droplets to unite & become large enough to settle out.

This action of uniting water droplets is called Coalescence.

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DEMULSIFIERS-------- contd.

Good demulsifier must not only be able to flocculate water

particles but also be able to disrupt films surrounding them & allowthem to unite. Such disruption removes the barriers or opens the doors.The strong natural desire for water to seek its kind is reestablished. Sincethe particles are all closer together because of flocculation, this dooropening process results in avery rapid growth of water drop size& waterseparation.

In most crude oils , solids such as iron sulphide, silt, clay, drillingmud, parrafin etc. complicate the demulsification process. They tend tocollect at interphase & contribute significantly to emulsion stability.Often such solids are primary stabilizing agents / materials & theirremoval is necessary to achieve satisfactory treatment.

For removal from interphase, these solids can be dispersed in theoil or they can be water wetted & removed with water. If, dispersed in

oil, emulsion may be treated, but the solids will still remain as acontaminant in oil. Therefore it is desirable to remove the solids withwater. Paraffins & organic solids are exception to this as these can berecovered in refining process.

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DEMULSIFIERS-------- contd.

Same type of action is used in either oil or water-wetting solids, only thechemical is different. In both cases, chemical has one end which is

strongly attracted to the solid & therefore forms a coating on it. Theother end has either a strong attraction for water or for oil &therefore will carry solid particles in that liquid.

It is very rare that a single chemical will produce all the actions of ademulsifier. Mostly two or more structures are blended to give thenecessary combination of actions.

Selection of demulsifier is made with process system in mind.As the field conditions change, the chemical requirements change.

Seasonal changes bring paraffin induced emulsion problems.Workovers contribute to solids content, which alters emulsionstability.

So, no matter how satisfactory a demulsifier is at one point of time, itcannot be assumed that it will stay over the life of field.

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DEHYDRATION OF CRUDE OILDehydration of the crude oil is necessary to bring it to the refinery

specifications.This is concerned with the reduction, removal, rupture, or counteraction

of the stabilizing films, coalescence of the droplets and gravityseparation of oil and water phases in a limited retention/residencetime e.q. 20 minutes or so.

According to Stokes law the velocity of settling drop of water is

proportional to cross sections area, difference in gravity of oil andwater and the viscosityof oil. Thus the most favorable conditionsexist when theoil has high API gravityandlow viscosity, and waterconsists oflarge, unstablized drops of salty water.

Using good production practice, the encroachment of water into theproducing formations may be delayed. The degree of emulsification

may be mitigated by good equipment maintenance whereby, to someextent, such water as is produced may be un-emulsified or freewater that will separate rapidly unassisted. Nonetheless a largeproportion of oil that is produced must be treated.

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DEHYDRATION OF CRUDE OIL..contd.

Means of treatment for dehydration of crude oil are:

Gravity separation Temperature effect (heat)

Chemical destabilization

Electrical treatment (electrostatic coalescers).

Gravity separation:

Most of the oil treating equipment rely on the gravity to separatewater droplets from oil continuous phase, because water dropletsare heavier than the volume of oil they displace. However gravityis resisted by a drag force caused by droplets downwardmovement through the oil. When the two forces are equal, aconstant velocity is reached, which can be computed from Stokes

law as :

1.78 x 10-6 ( S.G.) (dm)2Vt = -------------------------------

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Where Vt = downward velocity. of water droplet relative to the oil cont. phase,ft/s.

dm= diameter of water droplet, micron S.G.= difference in sp. gravity of oil & water. = dynamic viscosity of oil continuous phase, centipoises (cps)

From Stokeslaw it can be concluded that :

Larger the sizeof water droplet,larger the square of its diameterand thus, thegreaterits downward velocity. That is, the bigger the droplet size, the less time ittakes for the droplet to settle to the bottom of the vessel and thus it iseasier totreat oil.

Greater the difference In density between water droplet and oil phase, thegreaterthedownward velocitymeaning, thelighter the crude, easier to treat oil.If crude gravity is 10o API and the fresh water, the settling velocity is zero, as

there is no gravity difference. Higher the temperature, lower the viscosity of oil and thus the greater

downward velocity, that is easierto treat oil at high temperature than at lowtemperature.

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COALESCENCE in treating oil system is time dependant. In dispersion of twoimmiscible liquids, immediate coalescence seldom occurs when two dropletscollide. If the droplet pair is exposed to turbulent pressure fluctuation, and thekinetic energy of adhesion between them, the contact will be broken beforecoalescence is completed.

Deep layer gravity settler experiments indicate that the time to grow a dropletsize due to coalescence can be estimated by the following equation:

dj - (do)j

t = --- X --------------

6 ks

where

do = initial droplet size

d = final droplet size = vol. Fraction of oil phaseks = empirical parameter for particular system

j = Empirical parameter always >3 and dependant on the probability thedroplets will bounce apart before coalescence occurs.

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When the energy of oscillations is very low so that bouncing of dropletsapproaches zero, j approaches 3. Assuming a value of 4, the min time required toobtain a desired particle diameter can be expressed :

d4 - (do)4t = --- X --------------

6 ks

Assuming, do is small relative to droplet size we wish to growby coalescence inour gravity settler, then the equation can be approximated :

d4t = --------------

2 ks

Following conclusions can be drawn :

Doublingof residence time increases the maximum size drop grown in a gravitysettler less than 19%. If the value of jis > 4thegrowth of the droplet diameterwill be evenslower.

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More dilute the dispersed phase, the greater the residence time needed to growparticle size. That is, coalescence occurs more rapidly in concentrateddispersions. That is the reason that oil is water washed by entering in thetreating vessel below the o/w interface in most treaters. Flocculation andcoalescence therefore occur most effectively at the interface zone between oil &water.

Temperature (heat) Effects: Heating of incoming oil/water stream for separating thephase is in use in oil Industry from earlier days. The addition of heat reduces theviscosity of the oil phase thereby allowing more settling velocities (StokesLaw).It also has the effect of dissolving the small crystals of paraffin and asphaltenesand thus neutralizing these effects as emulsifier. Treating temperatures, usually

range from 100o

to 160o

F. In treating the heavier crude the temperatures maybe as high as 300oF.

Heating causes a significant loss of lower boiling pointhydrocarbons (light ends).This results in shrinkageof the oil, orloss of volume. The molecules leaving theoil phase may be vented or compressed and sold with gas, even if they are soldwith gas, there will be probably a net loss of in revenue realized by converting

liquids volume Into gas volume. Figure approximately shows the amount ofshrinkage that may be expected.

Thus heating makes the crude oil recovered more heavier and thereby decreasing itsvalue.

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Dehydration of Crude Oil

..contd.

With the heating of oil, gas liberatedmay create problem in the treating

equipment if the equipment is not properly designed. In vertical heater-treater the gas rises through the coalescing section. If much gas isliberated, it can createturbulenceand disturbance toinhibit coalescence.Small gas bubbles have an attraction for surface active material andhence for the water droplets. The bubbles thus have a tendency to keepthe water droplets from settling and may even cause them, to carry overto oil outlet.

Horizontal heater-treaters tends to overcome this gas liberation problem bycoming to equilibrium in the heating section. Before introducing theemulsion to the settling-coalescing section. Some large crude processingsystems use a fluid packed, pumps-through system that keeps the crudewell above the bubble point. Top mounted degassing separators abovethe electrostatic coalescers have been used in some installations.

If properly done, heating an emulsion can greatly benefit water separationwithout much economic penalties.

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% loss by volume vs temperature API gravity loss vs temperature

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Relationship of sp. Gravity with temp. for three crude

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The demulsifier must also have an attraction for droplets

with a similar condition, which make large droplets tocluster together which under a microscope, appear like

bunches offish eggs. The oil will be onbrighter appearance

since drops are no longer present to scatter the light rays.

At this point the emulsifier film is still continuous. If the

emulsifier, is weak the flocculation force ma be enough to

call coalescence. This is not true in most cases and the

demulsifier mustneutralize the emulsifierand promote a

rupture of the droplet interface film. This is the opener

that causes coalescence. With the emulsion in flocculatedcondition thefilm ruptureresults in rapid growthof the

water drop size.


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Dehydration of Crude Oil..contd.Demulsifiers neutralizing the emulsifier depend upon the type of

emulsifiers. Iron sulfides, clays and drilling mud can be water wetcausing them to leave te interface and be diffused into the water

droplet. Paraffinsand asphaltenes could be dissolved or altered to maketan films less viscous so that they will flow out of easily on collision orcould be made oil wet so that they will be dispersed in the oil.

It would be unusual if one chemical structure could produce all fourdesirable actions. A blend of compounds is therefore used to achieve the

right balance of activity.

The demulsifier selection should be made considering the process system. Ifthe treating process is a settling tank, a relative slow acting compoundcan be applied with good results. If the process is achem-electric processwhere some of theflocculation and coalescing actionin achieved by anelectric field, then there is need for quick acting compound, but not onethat must complete the droplet building action.

Selectionofdemulsifier is always made depending upon field conditionsand this mayvary over the life of field.

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Dehydration of Crude Oil .contd.

Electrical Treatment (Electrostatic Coalesces) :

Coalescing and collision of the small water drop dispersed in the crude can be accomplished by

subjecting the water-in-oil emulsion to a high voltage electric field which induces dipoleattraction

between them. After coalescence, separation of phases are due to gravity.

When a nonconductive (oil) containing a dispersed conductive big (water) is subjected to an

electrostatic field, the conductive particles or droplets are caused to combine by one of three

physical phenomena.

* Thedroplets become polarized and tend to align themselves with the lines of electric force.In doing so the +ve and ve poles of the droplets are brought adjacent to each other.

Electrical detraction brings the droplets together and causes then to coalesce.

Droplets are attracted to an electrode due to an induced charge. In an AC field due to inertia

small droplets vibrate over a larger distance than larger droplets promoting coalescence. In

DC field, the droplets intend to collect on the electrodes forming larger and larger drops

until they fall by gravity. Theelectric field tends to distortand thusweaken the emulsifying film.

Whatever the actual mechanism, the electric field causes the droplets to move about rapidly in

random directions, which increase the chances of collision with proper velocity, coalescence

occurs.

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Dehydration of Crude Oil

..contd.The attraction between water droplets in an electric field is given by:

Ks 2 (dm)6F = -------------------- (with S dm)

S4

Where,

F = Attraction force between droplets

Ks = Constant for system = Voltage gradientdm = Diameter of droplets

S = Distance between droplets

This indicates that thegreater the voltage gradientthegreater the forcescausing coalescence. However, experimental data shows that at somegradient the water droplets can be pulled apart and a strong emulsioncan be developed. For this reason electrostatic treaters are normallyequipped with mechanism for adjusting the gradient of the field.

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Photos clipped from a movie sequence in an electric feasibility test cell

to determine an emulsionssusceptibility to break up in an electric field

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Photos start with a tight emulsion & proceed to breakup at lower end.

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INDIRECT LINE / BATH HEATER

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Schematic Diagram - Indirect Line Heater

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INDIRECT BATH HEATER

Applications :

To heat natural gas to a temperature sufficient to prevent hydrate

formation when line p. & t. are reduced. Installed on the flow line upstream of the pressure reducing choke on

low temperature separation units

Used upstream of conventional stage separation hook-ups.

May be installed upstream of short cycle hydrocarbon recovery units tomaintain constant inlet gas temperatures.

May be used upstream of glycol dehydration units.Basic partsof the indirect heater are:

flow coil, firebox and shell

The heater is normally ahorizontal vessel (Shell)mounted onsteel saddlesor skids.

Water is used to transfer heat from the firebox to the flow coil. Theheatingtubeis mounted in thelower segmentof the vessel and the coil in theupper portion (Figure).

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Coil tube size ranges from 1 to 6 inch pipe,depending on heater size. The tube bundleusually is arranged so that it may be divided into

two or more separate coils in case it is desired toflow more than one gas/oil stream through thesame heater.

Pipe or plate is used for the fabrication of

theheating tube. The heat transfer rate variesfrom about9, 000 to 15, 000 Btu/ft2 of heatingtube surface. The stack furnishes the draftnecessary to full combustion products throughthe heating tube. The stack diameter and length

is best determined by experiment to give thehighest efficiency for a particular heating tubedesign.

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INDIRECT BATH HEATER..contd.

Fuel gasfor the burner is usually obtained from a 1,000 psi orlower pressure source. Pressure reducing regulators of 1 inchpipe size and 1, 000 psi maximum inlet pressure are good in most

cases, and are less expensive than a pilot operated reducingregulator.

Two reducing regulators are used in series when fuel gassupply pressure exceeds 200 psi. One regulator will reduce thepressure to about 100-150 psi and the second regulator willprovide fuel gas to burner at operating pressure. The burnerpressuremay be setas low as 5 psiwhen the temperature controlvalve is in the full open position and at higher pressuresdepending on the particular design.

Temperature controller is located downstream from thereducing regulators andcontrols thevolume of gasto the burner.

Normally, 1900

F is the maximum temperature recommended forthe water bath.

Proper selection of the water bath temperature will preventover-heating of the gas stream andreduceoperating expense.

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The burner is so positioned that the productsof combustion are effective on the entirelength of the heating tube. The raw gas isfirst mixed with air prior to entering theburner. This primary air (intake is through

flame arrester) furnishes a large percentage

of the total air required for completecombustion. Additional air required issupplied by the secondary air adjustment.With proper size burner orifice and supply

gas pressure, the flame should be blue orblue-orange in color. Also, the flame shouldbe on, or nearly on, the burner tip.

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Pilot is located near the burner. To insure the pilot a

continuous supply of gas, its source is located upstream from the

temperature controller.Fuel gas straineris placed upstream fromthe temperature controller and pilot supply connections. This

preventsforeign particles from clogging orifices or lodging on the

seat of the temperature controller. Liquids are also collected in

the lower portion.

Shell is designed to operate at atmospheric pressure.

Dimensions of the shell are held to a minimum thus reducing both

the quantity of heating medium required and heat loss to the

atmosphere. Cover plates for the coil and heating tube are sealed

tight to the shell to prevent leakage of the heat transfer medium.

The fill cap serves as a liquid expansion chamber in addition to

providing a surface for condensation of water vapor.

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Submerged or long nose choked (Figure) may be used onthe inlet to the indirect heater coil. Its function is toincrease the temperature differencebetween the gasand water, and thus a large mean temperaturedifference can be used in calculations. Since thechoke is immersed in the hot water bath at the pointof pressure reduction, the heated choke body and coilprevent hydrate formation.

In order for thewater bathheat to reachthe gas in thetube bundle, it mustpenetrate several resistances toheat flow: the water film on the exterior surface ofthe flow pipe; the pipe wall and the inside gas film.

These resistances depend on many factors: specific

heat, density, viscosity, temperature of the gas andwater, flow rates of the gas, tube wall thickness andconditions of the tube surface.

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The indirect heater should be

inspected periodically to insure maximumperformance. Scale on the heating tube and coilbundle lowers the heat transfer rate and should beremoved. The water bath must cover all of the coilsand its level is easily inspected through the fillconnections. If liquid collects in the fuel supply gasline, it is advisable to use a liquid trap upstream fromthe reducing regulator to avoid burner and pilotmalfunctions.

Water for the heating medium should be as pure aspossible and free of dirt, sand or other foreignmaterial. Proper burner adjustment saves valuablefuel.

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L N Ch k U d i I di t H t


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Long Nose Choke Used in Indirect Heater

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Vertical Treater (Schematic)44


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TREATING EQUIPMENTThe most commonly used single well lease treaters is thevertical treater as shown. Flow enters the top of the

treater into a gas separation section. Care must beexercised to size this section so that it has adequatedimensions to separate the gas from the inlet flow. If thetreater is located downstream of a separator, thischamber can be very small. The gas separation section

should have aninlet diverterandamist extractor.The liquids flow through adown comerto the base of thetreater, which serves as a free-water knockout section. Ifthe treater is located down-stream of a free-waterknockout, the bottom section can be very small. If the

total wellstream is to be treated this section should besized for 3 to 5 minutes retention timefor both the oil andthe water to allow the free water to settle out. Thisminimizes the amount of fuel gas needed to heat theliquid stream rising through the heating section.

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The end of the down comer should be slightly below the oil

water interface to water washthe oil being treated. This

will assist in the coalescence of water droplets in the oil.

The oil and emulsion rises over the heater fire-

tubes to a coalescing section where sufficient retention

time is provided to allow the small water particles in the oil

continuous phase to coalesce and settle to the bottom.

Treated oil flows out the oil outlet. Any gas, flashed

from the oil due to heating, flows through the equalizing

line to the gas space above. Oil level is maintained by

pneumatic or level operated dump valves. Oil-waterinterface is controlled by an interface controller.


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HEATER TREATER (Chem. Electrostatic)

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HEATER TREATER


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Heater treater is a horizontal vessel employing a vertical flow pattern.Methods of heating, chemical action, electrical coalescence, waterwashing of oil & settling for demulsficationare used. Movements offluids are controlled by differential pressure combined with statichead.

Parts/components of heater treater are:

Inlet degassing section

Heating section

Differential oil control chamber Coalescing section (Electrical chamber)

Inlet Degassing Section: Oil mixed with demulsifierenters the heatertreater through degassing section, above the fire tubes. Free gas is

liberated from the flow stream & equalized across the entiredegassing & heater areas of the treater. The degassing section isseparated from heating section by baffles. The fluid travelsdownwards from the degassing area and enters the heating sectionunder the fire tubes through multiple orifice distribution.

..contd.

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Heating Section Thi ti i t f fi t b b t


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Heating Section: This section consists of a fire tube bentat 180. The constant level in maintained by weir height.Oil enters this section from bottom of degassing section &passes through heater at bottom and washing action takes

place & free water & solids fall out of oil stream. Thewater level in this section is controlled by a weighted,displacement type interface control valve. The oil andentrained water flow upwards from the distributorsaround the fire tubes, where the required temperature is

reached. The increase in temp. of oil releases someadditional gas. The heat released gas then joins the freegas from the inlet section and is discharged from thetreater through a gas pressure control valve.

Burners are designed for maximum heat output with

minimum fuel consumption & maintenance requiring littleadjustments. Pilots are fixed type & require noadjustments. Fuel gas supply is to be properly adjusted &regulated which is free of liquids & solid particles.

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( h l i )


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* Differential Oil Control Chamber:

The heated fluid transfers from the heating section over the fixed weir into adifferential oil control chamber, which contains a liquid level control float. The

fluid travels downwards to near the bottom of oil control chamber where theopening of the coalescing section distributors are located.

* Coalescing Section (Electrical Chamber): Heater treater uses a high voltagepotential on the electrodes for coalescing of water droplets in the final phase ofprocessing. The electrodes are suspended on the insulated hanger from theupper portion of vessel. The Ground electrode is furnished with solid steelhangers to ensure grounding with the steel of the treater.

Anexternally mounted,oil immersed high voltage transformer is furnished toprovide the power to electrodes. The transformer uses 240 volts in primary &supplied about 16500 volts in secondary. The high voltage secondary isconnected to charged electrode through a specially designed high voltageentrance busing for insulation. Secondary is also connected to voltmeter &external pilot indicating lamp. The oil & entrainedwater enter the coalescingsection from the differential control chamber through multiple, full length

distributors. As the oil & entrained water come into contact with electrical fieldin the grid area, final coalescing of water takes place.

The water falls back to the water area at the bottom and the clean oil continuesto rise to the top, where it enters a collector and is discharged through the cleanoil outlet control valve.

........contd.

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CHECKS FOR HEATER TREATERS: Burners

Valves & controls and sight glasses

Safety valve

Fire Tube

TROUBLE SHOOTING OF HEATER TREATERS: Pilot light going off

Oil treatment not proper

Pressure in heater treater not remaining constant and going down

Main burner going off without attaining required temp.

Temp. of heating chamber is low

Temp. of heating chamber is high

Pressure inside the chamber shoots up and safety valve starts blowing

Bulb of the electrical chamber does not glow

Level of oil is not maintained

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Desalination of crude oil

Desaltingimproves the efficiencyof refinery operations withoutfrequent shut down & corrosion problems, contaminations ofcatalysts & products, besides a number of other benefits in a dayto day handling and oil processing in refinery.

Anyde-hydradationmethod has one serious limitation that it canreduce the water content only to a certain extent(acceptable torefinery 0.1 to 1%). This however, leaves the problem of saltcontent of crude oil. With very little exceptions, thesalt in crudeoil exists as the total of that salt which is in solution in theremnant brinestill associated with the oil either in some sort orgeneral dispersion or in droplets highly stabilized by theemulsifying agents present.

That is, the principal salt content of any oil sample of given volume isthe amount of total salt in solution within the brine which remainsdispersed in that oil volume.

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Desalination of crude oilcontd.

For this reason total salt contentof oil is a function notonly of salt water remaining in oil but also of

concentration of salt in that water. The water-solublemineral salts are contained in water from most of theoilfields of the world. Saltsare predominantlychlorides ofsodium, calcium & their salinity varies usually in the rangeof 20,000 to 1,30,000 ppm equivalent of sodium chloride.The quantitative unit of salt measurement is usuallypoundsof chlorides per 1000 bbl of oil (ptb).

Even if1% waterremains in dehydrated oil, with salinityof20, 000 ppmof Nacl,70 pounds of saltwill be containedin each1000 bblof that clean oil.

Any quantity above 10-17 lbs per 1000 bbls (p.t.b) is usuallyconsidered ascausing problemsin refinery processing.

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.contd.

Thus there is a further need of

dehydration of DESALTING which is

simply considered as asecond stepof

dehydration in oilfield. Desalting,

which follows the initial dehydration

consists of:

Adding dilution (or fresh) water to

the crude oil which is usually 5 to 7 %

of flow rate of crude

Thorough mixing of dilution water

with the crude to dilute saline water

through tee which shears dilution

water into droplets & disperses it

thoroughly in the crude oil

Emulsion treatment (withoutageing)or second stage dehydration

to separate the crude oil & brine

phases

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CAPSULE ( l i & i )


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CAPSULE (emulsions & its treatment)

Components of water-in-oil emulsions:

- water

- oil- emulsifying agent

Conditions to form stable emulsion:

- two immiscible liquids

- agitation

What the emulsifier does:

- reduces surface tension- forms physical barrier

- suspends water droplets

What affects emulsion stability:

- Oil viscosity

- Agitation

- Time- Strength of emulsifying agent

Actions of demulsifier:

- strong attraction to oil-water interface

- flocculation

- coalescence

- solids wetting

Types of treating vessels:

- settling tank

- gun barrel

- vertical treater

- horizontal treater

- chemelectric treater

Treating requires combination of:

- chemical addition

- agitation

- heat

- heat

- electricity

- settling

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DEHYDRATION OF CRUDE OIL (S mmar )


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DEHYDRATION OF CRUDE OIL (Summary) Why Necessary:

- refinery specifications

- reduction, removal, rupture or counteraction of stabilizing films

- coalescence of droplets & gravity separation

- keeping retention time approximately of 20 minutes

Most Favorable Conditions:

- oil has high API

- low viscosity

- water of large unstabilized drops of salty water

Adopting:

- good production practices

- delay water encroachment

Treatment:- gravity separation

- coalescence

- temperature (heat ) effect

- chemical destabilization

- electrical treatment (i.e. electric coalescence) 57


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Demulsification & Desalting (Digest)

Stability of Emulsion: Drop size

Type of emulsifying agent

Water content

Viscosity

Presence of solids

Existance of electrical charges in water molecule

Surface tension & interfacial tension

Film strength

Densityrelative density

Ageing

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Demulsification & Desalting (Digest)


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Demulsification & Desalting (Digest) contd.

Commonly used:

Washing & providing continuous phase water wash to reduce salinity

Settling in tank to provide low velocity & increase residence time to allow free waterto separate

Mechanical treating by using centrifugal forces or other means to separate O, G & W.

Heating to:

Reduce oil viscosity which enhances coalescence

Cause thermal expansion of droplets which rupture film & help coalescence

Aid dispersion of emulsifying agent into oil phase Create thermal current for water movement & collision

Chemical Treating:

Demulsifier weakens emulsifier envelope on water droplet

Reduce interfacial tension

Increase molecular attraction of emulsifier & enhances separation

Electrical Treating: Water molecule forming a dipole is basis of electrostatic coalescence

Causes coalescence of smaller to larger droplets

Allows faster settling of drops

Date post:	04-Jun-2018
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DEMULSIFICATION &DESALINATION

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