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300 Process Design of Separation Vessels

AbstractThis section provides information on the general process design of simple vessfor gas/liquid separation. Production separators are specifically addressed in Section 900.

The scope of this manual does not address the process design of chemical reaor columns employing trayed and packed internals. For information on these mcomplex functions, see the Column Sizing and Tray Layout Manual for Sieve and Bubble Cap Trays, available from the Technical Information Center, Chevron Research and Technology Company.

Contents Page

310 Introduction 300-3

320 Selection of Separator Type 300-3

330 Basic Sizing Information 300-4

331 Separation of Liquid Droplets from Vapor

332 Vapor Velocity in Mist Eliminators

333 Liquid Surge Volume

334 Separation of Liquid Phases

335 Coalescers

340 Design of Knockout Drums and Vertical Two Phase Separators 300-1

341 Design Gas and Liquid Rates

342 Diameter

343 Length

344 Demister Pad

345 Internals and Dimensions

350 Design of Horizontal Separators and Reflux Drums 300-13

Chevron Corporation 300-1 March 1990

300 Process Design of Separation Vessels Pressure Vessel Manual

6

351 Vapor Cross Section

352 Shell Length and Diameter

353 Water Separation from Hydrocarbon

354 Water Drawoff Leg

355 Details to Improve Separation

360 Design of High Pressure Vertical Three-phase Separators 300-1

361 Feed Inlet

362 Vapor Space

363 Liquid Surge

364 Liquid Phase Separation

370 Package Units 300-18

371 Knockout Drums

372 Filter-Separators

March 1990 300-2 Chevron Corporation

Pressure Vessel Manual 300 Process Design of Separation Vessels

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310 IntroductionThis section covers the process design of a vessel with a simple function: the stion of vapor from liquid or the separation of vapor and two liquid phases. The vessel may also serve the control function of providing residence time for one otwo liquids. Within the refinery, chemical plant, or gas processing plant, these vessels may be called knockout drums, accumulators, flash drums, vapor/liquidseparators, reflux drums, or three-phase separators. In the oil field, the term oil/gas/water separator may be used. These vessels are also found in fuel gas,steam, air (process, instrument, and utility), and relief systems. Note that prodution separators are specifically addressed in Section 900.

Although the design of separators is not standardized, designs for any of the abpurposes may be completed by procedures discussed in this section. Data sheare also included in the Standard Drawings and Forms section of this manual (Volume 2).

The following items are not included:

• Trial and error procedures for optimizing a design. This is best done with a computer program. See the References section of this manual for more information.

• Tabular material usually found in handbooks, such as areas of segments ofcircle, volumes of heads, etc.

• Design of Flare-System Knockout Drums. See the Instrumentation and Control Manual for Flare K.O. Drums.

Process design of pressure vessels used for other purposes (e.g., reactors andlation columns) are not covered here. To design columns for stagewise separatmass transfer (fractionators, absorbers, strippers, scrubbers) and to lay out traythe References section of this manual for more information.

320 Selection of Separator Type

Vertical SeparatorsThe vertical separator (Figure 300-5) accommodates a tangential inlet, which assists removal of entrained liquid from vapor. Knockout drums which protect compressors are a demanding service, and are usually vertical. The vertical serator takes less plot space than a horizontal separator, is not as susceptible to internal wave action, and is easier to clean.

Note Figures 300-5 and 300-6 are foldouts appearing at the end of this section

Horizontal SeparatorsThe horizontal separator (Figure 300-6) accommodates large liquid holdup voluand more easily provides large surface area for oil-water separation and for evotion of gas from liquid. The horizontal separator takes less vertical space than a



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vertical separator, which may be important for offshore installations (horizontal vessels are sometimes stacked). Also, piping may be cheaper.

330 Basic Sizing InformationSeparator design involves sizing the vessel to allow liquid to settle out and addiappropriate internal details such as mist eliminators. Vapor velocity must be reduced to prevent entrained liquid from going overhead with the vapor.

331 Separation of Liquid Droplets from Vapor

Mass VelocityEntrained liquid droplets must settle out of the vapor stream as the vapor moveupward in a vertical separator or horizontally through the vapor space of a hori-zontal separator. The designer must keep vapor velocity sufficiently low by providing enough cross-sectional area. The area needed is found by using a cotion of maximum allowable mass velocity of the vapor stream. The following eqtion (plotted in Figure 300-1) is used for knockout drums which protect compressors. It is known to be satisfactory when used with other design detailspresented in later sections:

(Eq. 300-1)

where:Gc = Maximum allowable vapor mass velocity for a compressor

knockout drum, lb/hr/ft2

ρv = Vapor density, lb/ft3

ρl = Liquid density, lb/ft3

If the pressure is above 800 psig, the maximum allowable Gc is 90% of the value obtained from Equation 300-1.

Protection of a compressor is considered a critical service. For other services, uthe following:

Minimizing entrainment is especially important in the design of high-pressure serators for hydrocracking and residuum desulfurization plants. See Section 362 ffactors to be applied to Gc.

Gc 661 ρv ρ1 ρv–( )[ ]0.512=

Vapor to fuel gas G = 1.5 GcVapor to a distillation column G = 2.0 GcVapor to a condenser G = 2.5 Gc



apor ec-

er

Liquid ViscosityUse Equation 300-1 with caution for process applications where liquid viscosityexceeds 2.0 centistokes. Such systems may have a tendency to foam. Lower vvelocity (lower by a factor of two or three) or use of a mist eliminator may be efftive in breaking foam. Base the design on successful previous experience.

Capacity FactorA very minor change to the exponent in Equation 300-1 from 0.512 to 0.50 converts the equation to “capacity factor form,” allowing easy comparison to othsizing criteria of that form. (For example, see Equation 300-3 below.) The following equation is nearly equivalent to Equation 300-1.

Fig. 300-1 Allowable Mass Velocity for Compressor K.O. Drums at Pressures Below 800 psig

Notes:1. ρv = Actual vapor density, lb/ft3

ρL = Actual liquid density, lb/ft3

2. For pressure ≥ 800 psig, the allowable mass velocity is 90% of Gc from the above line.

3. For other services, the allowable mass velocity may be increased to:

4. Do not use where liquid viscosity exceeds 2.0 centistokes

5. Equation of a line is G = 661 [ρv(ρL - ρv)] 0.512 and is identical with 24 inch line on Drawing RD 46926-1.

• Vapor to fuel gas 1.5 Gc

• Vapor to distillation column 2.0 Gc

• Vapor to condenser 2.5 Gc



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(Eq. 300-2)

where:C = 0.188

Vc = Actual vapor velocity, ft/sec

332 Vapor Velocity in Mist EliminatorsMist eliminators, consisting either of knitted wire mesh pads (demisters) or corrgated sheet metal vanes, are often used in critical services to improve separatientrained liquid. Droplets that are too small to settle strike the wires or the vanecollecting to form larger drops. The larger drops run down the wires or vanes anfall from the bottom. Generally, the wire mesh type is preferred because of its bcollection efficiency for droplets in the 1 to 10 micron size range. A vane-type device usually has a higher vapor capacity and is more likely to resist plugging solids and viscous liquids.

A demister may be included in the design of a new separator on the basis of goexperience in similar service. A demister may be added to an existing separatoimprove removal of liquid from vapor, provided that it is known that poor separation is not the result of poor level control, plug flow, wave action, or some other factor.

For most applications, use a wire mesh demister, Yorkmesh Type 431 or equiva6 inches thick. Optimum superficial velocity (ignoring the space taken up by wiris given by:

(Eq. 300-3)

where:V = Optimum actual vapor velocity, ft/sec

Wire mesh demisters are reported to work well at velocities 30% to 110% of optimum; therefore, the design velocity is usually 75% of optimum (from Equati300-3). Note that this design velocity is still above Vc from Equation 300-2 (use of a demister does not influence the vessel diameter).

Vane-type mist eliminators are also sized with Equation 300-3 but with higher velocities usually allowed. For its product, York recommends a constant of 0.40place of 0.35) for upflow and 0.65 for horizontal flow. This factor appears adequate; however, the Company has little experience with vane-type mist elimtors in applications where their performance can be accurately determined.

Vc Cρ1 ρv–

ρv-----------------

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=

V 0.35ρ1 ρv–

ρv-----------------

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333 Liquid Surge VolumeUnless surge volume has been specified elsewhere, provide liquid volume betwthe maximum and minimum liquid levels to give the following residence times foeach product stream. This is for control purposes:

These volume requirements are additive. Thus, 100 gpm of reflux and 200 gpmnet product to storage would require 1400 gallons of surge.

For continuous water drawoff, size the water drawoff leg for a minimum of 10 minutes residence time. For manual, intermittent drawoff, size the leg to reqdrawoff no more than once per shift (usually 8 hours).

334 Separation of Liquid Phases

Terminal VelocitySizing of vessels for separation of liquid phases is based on a theoretical modeequations for terminal or free-settling velocity of a spherical particle in a fluid. Ain vapor-liquid separation, the point is to reduce the velocity of the bulk fluid enough to allow entrained droplets to settle. The general equation is:

(Eq. 300-4)

where:U = Particle settling velocity, ft/sec

g = Gravitational constant, 32.17 ft/sec2

Dp = Particle diameter, ft (see below)

ρp = Particle density, lb/ft3

ρ = Density of continuous phase, lb/ft3

C = Drag coefficient

Stream Time, Minutes

Distillation Column Reflux 6

Net Product to Storage 4

Net Product to Onplot Column or Heater

10

Net Product to Offplot Processing

20

U4 g Dp ρp ρ–( )

3 ρC( )------------------------------------0.5

=



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r

In the Stokes Law or “laminar flow” region (Reynolds number ≤ 2), the above equa-tion reduces to:

(Eq. 300-5)

where:µ = Viscosity of continuous phase, lb/ft • sec

Note

1 ft = 3.048 × 105 micron

1 cp = 6.72 × 10-4 lb/ft • sec.

The Reynolds number, Re, uses the particle (not the vessel) diameter:

(Eq. 300-6)

In the “intermediate flow” region (2 < Reynolds number ≤ 1000), use the following:

(Eq. 300-7)

Settling of liquid droplets within another liquid is usually within the laminar flow region. Assume laminar flow and use Equation 300-5. Compute U for a desiredp or Dp for a known U as required. Then use Equation 300-6 to compute Re; if it igreater than 2, use Equation 300-7. Reminder: this has nothing to do with movement of bulk phases within the vessel, which is assumed to be in plug flow.

Quality of SeparationMeasurement of droplet sizes (Dp) in industrial separators is impractical. We cannoverify the theoretical model; instead, we must rely on qualitative judgments. In general, when separators whose performance has been judged “good” are anawith the above terminal velocity correlations, it is found that the process conditiwould theoretically allow 100-micron drops to settle. Conditions which would allow only 300-micron and larger drops to settle correspond to “poor” separatio

Rather than using droplet-size calculations directly for a new design, use them,whenever possible, for comparing a new design with existing separators whoseperformances have been qualitatively judged. In the absence of data, design fosettling of 100-micron drops.

UgDp

2 ρp ρ–( )18µ---------------------------------=

ReDpUρ

µ---------------=

U1.81D

1.14 ρp ρ–( )0.71

µ0.43ρ0.29-----------------------------------------------------=



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Separating water from hydrocarbonSettling rates of 100-micron diameter water drops in hydrocarbon may be read directly from Figure 300-2. Hydrocarbon phase density and viscosity are at seprator operating temperature.

Fig. 300-2 Settling Rates of 100-Micron Diameter Water Drops in Hydrocarbons

Note:1. Settling rate calculated from:

a. Stokes’ law, where Re ≤ 2

b. Intermediate law, where Re ≥ 2

where:G = Gravitation constant

D = Diameter of water drop

ρ = Density units

µ = Viscocity

(In consistent units)

2. Curves show settling rate of 100-micron diam-eter water droplet with density of 62.4 lb/ft3. No vertical component of hydrocarbon velocity has been used.

Us

gD2 ρH2O ρHC–

18µHC----------------------------------------------=

Us

1.81D1.14 ρH2O ρHC–

0.71

µHC0.43ρHC

0.29---------------------------------------------------------------------=



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341

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Separating hydrocarbon from waterAssume that a reflux drum operates at 100°F. The water leg should allow 100-micron oil droplets to “settle” upward. This will produce “good separation” of oil from water. If flow is laminar, we may substitute in Equation 300-5 and obtain the following equation (plotted in Figure 300-3) for allowable water velocin the leg:

(Eq. 300-8)

where:ρhc = Hydrocarbon density, lb/ft3

335 CoalescersA knitted wire mesh pad coalescer may be used to improve separation of waterfrom the hydrocarbon phase (Figures 300-4 and 300-7). Applications are basedexperience. The pad acts by the same mechanism as a demister (Section 332)Yorkmesh Type 421 or equal, 1-foot thick. The pad is usually oriented verticallyliquid flow is horizontal. Superficial hydrocarbon velocity should be 5 ft/min (0.083 ft/sec). In production separators, plate-type coalescers are used. They amore resistant to plugging than mesh pads.

Note Figures 300-7 and 300-8 are oversized foldouts at the end of this section

340 Design of Knockout Drums and Vertical Two Phase SeparatorsThe following design procedure is based on successful experience, plus some ratory studies which indicate the desirability of the several internal baffles. (SeeFigures 300-4 and 300-5.) Vendors may use other criteria with or without other proprietary internals. Less conservative designs should not be accepted unlessfactory performance has been demonstrated in a comparable application.

General design procedures are as follows, described in more detail in Sectionsthrough 345:

• Establish the design gas and liquid rates and densities.

• Determine required liquid surge volume.

• Set the diameter to provide an acceptable vapor velocity.

• If the liquid rate is appreciable, decide whether an inlet shroud ring will be used. If so, design the feed inlet and vapor space according to Sections 36362. If not, use Sections 342 and 345. The decision to use an inlet shroud usually based on past experience with similar separators.

• Set the shell length to provide adequate liquid surge volume.

U 4.19 104– ρhc 62.00–( )×=



ses.

• Size the demister pad, if required.

• Specify internals and dimensions.

341 Design Gas and Liquid RatesBase design conditions and rates on examination of all likely plant operating caProvide flexibility for extreme operating conditions. A separator must not limit plant operation. The design liquid rate should include “slugs” that may occur during startup or upset operation.

Fig. 300-3 Recommended Downward Velocity in Water Drawoff Legs

Notes:1. Recommended maximum velocity corresponds to the upward settling rate for a 100-micron diameter

hydrocarbon drop in a still water phase at 100°F.

2. Calculated using Stokes’ Law:

3. With water at 100°F, and 100-micron diameter drop:

Uft/sec = 4.19 × 10-4 (ρHC - 62)

U

gD2 ρHC ρH2O–

118µH2O----------------------------------------------=



ed by crit-

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342 DiameterSize the vessel so that vapor mass velocity is less than or equal to that computEquation 300-1. Derate if pressure is over 800 psig. Use a higher value for lessical services as detailed in Section 331.

343 LengthThe minimum dimensions in Figure 300-5 are based on the experience and labtory studies mentioned above. Use these dimensions or increase Dimension “Crequired for liquid residence time. If surge volume is unspecified, a minimum of3 minutes residence time should be provided within the controllable range. For compressor protection, a minimum of 5 minutes residence time, based on maximum expected liquid rate, should be provided between the high level alarm(LAH) and automatic shutdown (LSH) levels.

Fig. 300-4 Improved Separation in Horizontal Vessels



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If liquid residence time requirements result in an excessively long vessel, increathe diameter. In vertical vessels at moderate pressure, length/diameter ratios u3.0 or 4.0 are common.

The LSH (maximum liquid) level is just below the “donut” baffle ring. The minimum liquid level in a vessel with ellipsoidal heads is just above the tangentline; with hemispherical heads, the level may be down within the bottom head.

344 Demister PadDemister pads are normally used only on compressor suction knockout drums.Velocity should be according to Equation 300-3.

345 Internals and DimensionsThe baffle ring above the feed inlet catches liquid that climbs the vessel wall. Itswidth is determined by Note 3 in Figure 300-5. The minimum value of Dimensio“B” is 3 feet 6 inches.

An approximately tangential entry according to Detail A is preferred, especially critical services. Detail B may be acceptable if a significant cost saving results. Where possible, review the construction and performance of separators in simiservice. Inlet piping should have relatively low velocity, typically 30 ft/sec, and aminimum of direction changes to reduce the formation of fine droplets.

The minimum recommended value of Dimension “E” is 2 feet 0 inches.

The donut baffle below the feed inlet prevents the vapor from disturbing and swirling the liquid surface. The gap at the wall allows liquid to drain continuousl

The minimum recommended value of Dimension “C” is 2 feet 0 inches.

350 Design of Horizontal Separators and Reflux DrumsThis section presents generally accepted methods for designing reflux and surgdrums. If water is present, it is usually present in small quantities and is collectea boot. See Figure 300-6. The focus here is primarily on process applications. Production separators are covered in Section 900, which also contains informaon personal computer software for sizing separators.

Briefly, the procedure is as follows, with each step described more fully in Secti351 through 355:

1. Establish design gas and liquid rates, densities, and liquid viscosity. Determthe required liquid surge volume(s). (See Section 341 for design objectives

2. Calculate the required cross section for vapor flow.

3. Specify the shell length and diameter to provide required vapor space plusrequired holdup volume for liquid.



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4. Check for adequate water separation. Adjust dimensions if necessary.

5. Size the water drawoff leg (if one is used).

351 Vapor Cross SectionThe cross-sectional area for longitudinal flow of vapor will be the largest of the following:

1. An area equal to 10% of the vessel cross section.

2. The area which results when the vertical height above the maximum liquid level (Dimension “D” minus Dimension “H” in Figure 300-6) is equal to 12 inches.

3. The area determined by applying Equation 300-1. (Derate or use a higher vof velocity for less critical service as discussed in Section 331.)

Note that in this case the vapor moves horizontally and the liquid droplets settleat right angles to the vapor flow. This would seem to be an advantage. Howeveis partially offset by turbulence and entrance/exit effects. If the vapor flow area ibe determined by Equation 300-1, some designers use 125% of the allowable Gc; others use Gc directly. The latter practice is recommended.

352 Shell Length and DiameterDetermine shell dimensions by trying various combinations of diameter, length,liquid depth. For any trial diameter, the maximum liquid level is known from the vapor cross-section calculation above. The minimum liquid level is at a height oone-eighth diameter from the bottom. (See Figure 300-6.)

The volume in between is hydrocarbon liquid surge. For each trial diameter, comthe required drum length. Include portions of the heads. Several combinations oflength and diameter will be found which satisfy the volume requirement. Use a length-to-diameter ratio (L/D) of at least 2.0. The distance from inlet to vapor oushould be at least 4 feet. It has been found that the cost of a horizontal vessel ogiven volume does not vary greatly as length-to-diameter ratio (L/D) varies from2 to 10. However, wave action is a concern in long vessels. Limiting the L/D ratito a maximum of 6.0 is recommended for horizontal vessels. For large vessels,tangent-tangent length of 20 feet is a convenient length.

353 Water Separation from HydrocarbonIf water separation is not a requirement, any of the vessel sizes meeting the suvolume and L/D requirements in Section 352 may be chosen. Otherwise, waterseparation must be checked. Using Equation 300-5 or 300-7 depending on the Reynolds number, compute the settling velocity for a 100-micron water droplet hydrocarbon. Hydrocarbon residence time (seconds) is surge volume divided bhydrocarbon flow rate. The settling distance is from maximum liquid level to



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minimum liquid level. If a 100-micron water droplet will fall through the settling distance within the hydrocarbon residence time, separation will be “good.”

Check the various trial sets of drum dimensions found in Section 352. For conssurge volume, settling distance decreases and separation improves as L/D incrIncrease L/D until water separation becomes satisfactory or until the maximum of 6.0 is reached. In the latter case, increase vessel size at constant L/D. Hydrocarbon liquid surge will be in excess of the requirement.

Water will collect along the bottom of the vessel before running into the boot. Thhydrocarbon liquid outlet is therefore raised above the bottom in order to avoid drawing water. The clearance is 2 to 6 inches depending on the volume of wateexpected.

354 Water Drawoff LegThe water surge volume in the drawoff leg is found from criteria in Section 333.This is the volume between maximum and minimum levels shown in Figure 300The rate at which 100-micron oil droplets will move upward is found from Equation 300-8 (or 300-7). Size the diameter of the drawoff leg so that the watevelocity downward is less than the oil droplet velocity upward.

355 Details to Improve SeparationA horizontal separator is not often used ahead of a compressor because of thebility of entrained liquid in the vapor. The situation can be improved by use of ademister pad over the vapor outlet. The pad cross-sectional area is found by Equation 300-3. The pad is supported in a housing of either round or rectangulacross section as shown in Figure 300-4.

Difficult hydrocarbon-water separation may be helped by a wire mesh coalescepad. The pad is located as close as possible to the inlet end of the separator. SFigure 300-4. The pad extends up to the maximum liquid level. Vane-type padsmay be used in production separators.

The water rate may be so large, or the upward settling rate of oil droplets so slothat a water boot of impractical diameter would be required. In this case, water holdup time and hydrocarbon-water interface area are provided by holding watevolume within the main compartment of the separator. See Figure 300-4. The hcarbon outlet is raised to a point 2 to 6 inches above the highest hydrocarbon-winterface level.

If the primary concern is to provide interface area and water holdup time for seption of oil droplets, then a transverse weir may be used to assure that water volwithin the main compartment is maintained. Drain holes are provided in the weiempty the water at shutdown. The water-hydrocarbon interface is controlled in tboot as before. Since the water behind the weir is not controllable, it does not sas surge volume.



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If increased water surge volume must be provided, then one controller maintainthe hydrocarbon-water interface within the vessel and another controller handlethe hydrocarbon level. A water boot is not required.

360 Design of High Pressure Vertical Three-phase SeparatorsThis section discusses the results of using separators in high-pressure hydroprcessing plants. See Figures 300-7 and 300-8. There is a considerable cost inceto minimize the size of these vessels. The design procedure is an iterative procperformed by the Hydroprocessing Division, Chevron Research and TechnologCompany, using a proprietary computer program. Contact them for assistance.

361 Feed InletFeed may enter tangentially as shown in Figure 300-7 (expensive in a thick-walvessel) or straight in with a right-angle turn (Figure 300-8). Feed pipe entry throthe head, not shown, is another alternative; feed is released into the vessel at tsame point as in the other designs. A shroud ring with a sloped ramp baffle is uto direct liquid to the wall. Radial width of the space within the shroud is 0.1 timvessel diameter. (Note that the cross-sectional area for vapor flow upward is reduced to 64% of its value elsewhere in the vapor space; this is taken into accby use of the derating factors in Section 362.) The inlet nozzle diameter is sizevelocity of 30 ft/sec. Height of the shroud ring is twice the inlet nozzle diameter.

362 Vapor SpaceAllowable mass velocity, based on the full cross section of the vessel (not the circular space inside the shroud) is Gc from Equation 300-1, multiplied by a derating factor. That factor is 0.5 for hot separators in residuum desulfurizer andvacuum residuum desulfurizer plants, 0.7 for other high pressure separators in hydroprocessing plants, and 0.9 for other separators and knockout drums at presures above 800 psig. Vessel diameter, Dimension “D” in Figure 300-7, is at leathat which corresponds to the allowable mass velocity just determined. The diaeter may be larger if liquid surge requirements would require an L/D ratio greatethan 3.

The head is hemispherical. The vapor outlet nozzle is in the head. The demisteused, is mounted on a baffle ring at the tangent line. The width of the ring (crossectional area left for vapor flow through the demister) is determined by Equatio300-3. The baffle ring is at least 2 feet 0 inches above the shroud. If there is nodemister, then an outlet baffle is placed on the centerline as in Figure 300-8.

363 Liquid SurgeSurge volume for hydrocarbon is the space between the high liquid level (HLL) the “donut” baffle ring and the low liquid level (LLL) at the horizontal baffle whicsupports the coalescer. Surge volume for water is the space between the high i



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oil

face level (see “Interface Levels” in Section 364 below) and the bottom of the coalescer pad.

364 Liquid Phase Separation

Flow of LiquidsOil and water flow downward to the left of the horizontal baffle in Figure 300-7. Bulk oil passes through the coalescer pad; water droplets are coalesced and sefrom the oil in the oil drawoff compartment to the right of the coalescer pad. Bulwater flows downward to the left of the coalescer pad and collects in the bottomhead below the oil-water interface.

Interface LevelsThe high interface level (HIL on Figure 300-7) is determined by the maximum velocity allowed for oil flow through the coalescer pad (see the next paragraph)The normal interface level, NIL, is Dimension “J” (usually 1 foot) below the HIL and Dimension “I” (usually 6 inches) above the lower edge of the pad. The low interface level, LIL, is 6 inches below the bottom tangent line, below the pad. Thinterface might have to be held at the LIL if the coalescer became plugged.

Coalescer Pad AreaThe pad is not necessarily located on the vessel centerline. Pad width (not thickness) will be equal to or less than the vessel diameter. If the interface were at thHIL, bulk oil would flow only through that portion of the pad between the HIL anthe horizontal baffle at the top of the pad. The HIL is placed to make the oil velocity through that cross section equal to 5 ft/min per Section 335. The total pheight is the height just determined plus the sum of Dimensions “I” and “J.”

Elevation of Horizontal BaffleDimension “C,” height of the baffle above the bottom tangent line, is the total paheight plus any additional height left for flow of oil if the coalescer should plug (usually zero but up to 1 foot). The minimum recommended value of Dimension“C” is 3 feet 0 inches.

Separation of Water Droplets from OilPlacement of the pad in the horizontal direction is shown by Dimension “G” in Figure 300-7. The oil holdup volume for separation of water droplets is boundedthe horizontal baffle supporting the pad, the NIL, the vessel wall, and the left (upstream) face of the pad. Oil residence time is the holdup volume divided by flowrate. Settling distance is from baffle to NIL. As in Section 353, use Equation300-5 or 300-7 to estimate the water droplet size which will move through the settling distance during the oil residence time. Apply the quality of separation criteria in Section 334.



the t hich

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tor pa-sed

Separation of Oil from WaterCompute the bulk water velocity through the horizontal cross-sectional area to left of the coalescer pad. An oil droplet must have an upward settling velocity aleast equal to the downward bulk water velocity. Compute the oil droplet size wwill settle upward through the water.

370 Package Units

371 Knockout DrumsGas streams are commonly contacted with amine solutions or other solvents foremoval of hydrogen sulfide. Separation of liquid hydrocarbon from the gas aheof the H2S absorber, to minimize foaming, is considered a more demanding serthan compressor protection. The Company has used Porta-Test Recycling Septors as knockout drums for this purpose, and achieved satisfactory results.

372 Filter-SeparatorsA filter-separator may be used in a gas processing plant, after a primary separaor a knockout drum, as the final cleanup ahead of amine treatment. The filter-serator removes fine solid particles as well as liquid droplets. The Company has uthe following with satisfactory results:

• Peco Series 75H horizontal filter-separator, sold by Perry Equipment Corporation

• Model HFS horizontal filter-separator, Peerless Manufacturing Company



March 1990

Pressure Vessel Manual

Chevron Corporation 300-19

Fig. 300-5 Vertical Two-Phase Separator Data Sheet


March 1990

Fig. 3


00-6 Horizontal Separator Data Sheet


March 1990



Fig. 300-7 Vertical, High Pressure Three-Phase Separator Data Sheet


March 1990



Fig. 300-8 Vertical Three-Phase Separator Data Sheet