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ExxonMobil ProprietaryDRUMS Section Page

LIQUID-LIQUID AND VAPOR-LIQUID-LIQUIDSEPARATORS

V-B 1 of 23

DESIGN PRACTICES PROPRIETARY INFORMATION - For Authorized Company Use Only December, 2003

ExxonMobil Research and Engineering Company – Fairfax, VA

CONTENTSSection Page

Scope ................................................................................................................................................................ 3

References........................................................................................................................................................ 3DESIGN PRACTICES................................................................................................................................ 3ENVIRONMENTAL DESIGN PRACTICES................................................................................................ 3GLOBAL PRACTICES............................................................................................................................... 3OTHER REFERENCES............................................................................................................................. 3

DEFINITIONS..................................................................................................................................................... 4

APPLICATION ................................................................................................................................................... 4

BASIC DESIGN CONSIDERATIONS ................................................................................................................ 5INLET NOZZLES ....................................................................................................................................... 5LIQUID HOLDUP FOR PROCESS, CONTROL, AND SAFETY REQUIREMENTS................................... 5DROPLET SETTLING ............................................................................................................................... 5DROPLET SETTLING VELOCITY............................................................................................................. 5VAPOR SPACE ......................................................................................................................................... 6PREVENTION OF LIQUID REENTRAINMENT......................................................................................... 6SETTLING POTS....................................................................................................................................... 7SETTLING BAFFLES ................................................................................................................................ 7DUAL- MEDIA CRINKLE WIRE MESH SCREEN (DM-CWMS) ................................................................ 8DRAWING NOTES.................................................................................................................................... 8

DESIGN PROCEDURE...................................................................................................................................... 8DESIGN OF HORIZONTAL SETTLERS (WITH OR WITHOUT SETTLING BAFFLES)............................ 8DESIGN OF THREE COMPARTMENT HORIZONTAL SETTLERS.......................................................... 9

DESIGN CONSIDERATIONS FOR SELECTED SERVICES............................................................................. 9FEED SEPARATOR DRUMS FOR SOUR WATER STRIPPERS AND AMINE REGENERATORS ......... 9

SAMPLE PROBLEM ....................................................................................................................................... 10DESIGN BASIS ....................................................................................................................................... 10SOLUTION .............................................................................................................................................. 11

NOMENCLATURE........................................................................................................................................... 16

COMPUTER PROGRAMS............................................................................................................................... 16

APPENDIX ....................................................................................................................................................... 17

Changes shown by ➧

ExxonMobil ProprietarySection Page DRUMS

V-B 2 of 23 LIQUID-LIQUID AND VAPOR-LIQUID-LIQUIDSEPARATORS

December, 2003 PROPRIETARY INFORMATION - For Authorized Company Use Only DESIGN PRACTICES


Section Page

TABLE

Table 1 Settling Drum Design Criteria ........................................................................................................... 17

Table 2 Coalescence Media Application And Design Considerations ........................................................... 17

FIGURES

Figure 1 Typical Liquid-Liquid Settling Drum (1) ............................................................................................... 18

Figure 2 Drum With Horizontal Settling Baffles (Layout Of Typical Settling Baffle When Heavy Phase DropsLimit Settler Capacity)(1)(2) ................................................................................................................................. 19

Figure 3 Feed Drum For Sour Water Stripper Or Amine Regenerator(1)(2) ....................................................... 20

Figure 4 Horizontal Setting Drum With Two Stage Dm-Cwms Coalescence Media ....................................... 21

Figure 5 Sample Problem - Atmospheric Pipestill Distillate Drum ................................................................... 22

Revision Memo

12/03 Highlights of this revision are:

1. Added additional design guidelines for separators in vapor-liquid-liquid service.2. Revised required amine holdup time in the settling compartment of amine

regenerator feed drums.3. Revised the recommended difference in heights between oil and water overflow

baffles in Eq. (6).4. Added design considerations for alkylation settlers.5. Provided additional design guidelines for Figure 2.6. Corrected Figure 3 (Oil Overflow Baffle) and added note regarding location of vent

nozzle.



V-B 3 of 23



SCOPEThis subsection covers the design of both liquid-liquid and vapor-liquid-liquid separator drums (settlers). Guidelines are providedfor sizing horizontal gravity settlers including settlers for feed drums to sour water strippers and amine regenerators. Alsoincluded are design guidelines for sizing separator drum internals such as inlet distributors, settling baffles, anti-vortex baffles,and dual-media crinkle wire mesh screen. Design of vapor-liquid separators where only one liquid phase is present is covered inSection V-A.For liquid-liquid systems that form stable emulsions, special design criteria are needed. Special criteria are used for acid settlersin alkylation plants, as well as caustic and water wash drums in the reactor product stream of sulfuric acid alkylation units.Since hydrocarbons from gravity settlers may have entrainment levels as high as 200 ppm, insufficient water is removed ingravity settlers to meet distillate product quality specifications. Therefore, more effective drying equipment, such as sand filters,salt driers, or vacuum driers, may be required. Cartridge coalescers may be competitive for deentrainment when plot space islimited or throughput is low. ExxonMobil has experience with FACET International coalescers for water removal from alkylationC4 streams and Pall PhaseSep coalescers for caustic removal from cat naphtha streams. Separator design criteria for theremoval of oil from refinery wastewater are given in the ENVIRONMENTAL DESIGN PRACTICES, Section XIX, Water PollutionControl.When special considerations require that a settler be installed vertically, a SEPARATIONS SPECIALIST should be consulted forspecific recommendations.

REFERENCES

DESIGN PRACTICESSection V-A Vapor-Liquid SeparatorsSection XII InstrumentationSection XV Safety in Plant Design

ENVIRONMENTAL DESIGN PRACTICESSection XIX Water Pollution Control

GLOBAL PRACTICESGP 03-06-01 Piping for InstrumentsGP 05-01-01 Pressure VesselsGP 05-01-02 Additional Requirements for Special Criteria Pressure VesselsGP 05-02-01 Internals for Towers, Drums, and Fixed Bed ReactorsGP 15-05-01 Level Instruments

OTHER REFERENCES1. Ackerman, S., “Alkylation Reactor Products Treating Summary,” 96FPD4 80 (September 26, 1996).2. Baird, R. S. and R. J. Fiocco, “Guide for Applying Coalescing Media to Debottleneck Extractors, Liquid-Liquid Settlers and

Sand Filters,” ER&E Report EE.5E.93 (January 1993).3. Bustin, W. M., “Anti-Vortex Baffles,” ER&E Report EE.3R.54 (January 26, 1954).4. Canevari, G. P., Fiocco R. J., and Shrier A. L., “Liquid-Liquid Separations,” ER&E Report EE.10ER.66 (November 1, 1966).5. Fiocco, R. J., “Distillate Drying Handbook,” ER&E Report EE.96E.75 (December, 1975).6. Rouse, H., “Seven Exploratory Studies in Hydraulics,” Proc. ASCE 82. HY4 pp 1038 - 1 to 1038 - 34, (August, 1956).

➧ 7. EMRE Sulfuric Acid Alkylation Operating Manual, Section 4D - Settler, July 2001.





DEFINITIONSSettling Pot. A relatively small collection pot located on the bottom of a horizontal settling drum used to provide settling space tocollect the heavy liquid phase. When a relatively small amount of heavy liquid phase is present, a settling pot can be used toreduce the required drum size by eliminating the heavy phase layer in the bottom of the drum.Dual Media Crinkle Wire Mesh Screen (DM-CWMS). The primary mechanism for separation of immiscible liquid-liquid mixturesis gravity settling. Since settling velocity increases with liquid droplet diameter, separation can be significantly enhanced bypromoting the growth of droplets by coalescence. One method of promoting coalescence is by flowing droplet-containing liquidthrough a bed of solid media with high surface area, such as fine fibers, thin filaments, and small particles. DM-CWMS is a highsurface area, coalescing medium which is manufactured by co-knitting plastic filaments or glass fibers with metallic wire mesh.

APPLICATIONFor gravity settling of an immiscible liquid-liquid mixture to occur, two basic separation phenomenon must occur: (1) settling orrising of droplets from both liquid phases to the liquid-liquid interface level, and (2) coalescence of the droplets in the emulsionband at the interface between the two liquid phases. The design criteria in this subsection assume that coalescence of theemulsion band is rapid. If this assumption is not correct, contact a SEPARATIONS SPECIALIST.Rigorous gravity settler design requires information on feed drop size distribution. Since this information is usually not available,a simplified approach based on past experience is presented. Typical settlers designed with the criteria presented in thissubsection will have less than 200 ppm entrainment in each liquid product. This entrainment level is usually acceptable forproducts going to heat exchangers and fractionators since this concentration is smaller than the amount of second phase presentdue to solubility. If reduced entrainment levels are required, process specific data may be needed to establish the applicability ofgravity settling; perhaps a different separator device, such as a sand filter, may be needed.Whenever possible, one should avoid subjecting the settler feed to high shear stresses, such as those produced in pumps andpressure letdown systems. High shear stresses may generate small drops which will not separate in gravity settlers. A commonproblem in poorly operating gravity settlers is too high an inlet velocity.For settlers handling slow coalescing emulsions, separation of liquid droplets is not the controlling factor. In these settlers (suchas acid settlers in sulfuric acid alkylation plants), additional residence time and/or interface area may be required for coalescenceof the emulsion band at the interface. The use of settling baffles, DM-CWMS, or other coalescing devices may assist in theseseparations. Laboratory or plant data are typically required to guide these types of design since the liquid properties andpresence of surfactants or solids will affect separation rates.Settler designs for new services should be based on actual plant or laboratory data. A SEPARATIONS SPECIALIST should beconsulted on the type of data to be collected or regarding the basis for past designs.The following table gives experience limits for the design of liquid-liquid settlers. Designers should contact a SEPARATIONSSPECIALIST if the application is outside these experience limits.

LIQUID-LIQUID SETTLER DESIGN LIMITS

VARIABLE LOWER LIMIT UPPER LIMIT

Liquid Viscosity, cP (mPa�s) 0.05 (0.05) 10 (10)Liquid Density, lb/ft3 (kg/m3) 20 (320) 80 (1300)Density Difference, lb/ft3 (kg/m3) 6 (100) 62 (1000)Settling Baffle Spacing, in. (mm) 9 (225) -Interfacial Surface Tension, dyne/cm(mN/m)

10 (10) 50 (50)

Method of Droplet Generation - Mild mechanical mixing, such as extractors andorifice mixers or control valves with pressuredrops less than 20 psi (140 kPa)



V-B 5 of 23



BASIC DESIGN CONSIDERATIONS

INLET NOZZLES1. Separators Handling Liquids Only

For this service, the inlet nozzle should terminate in a tee distributor located at the normal interface (Figures 1 or 2). Thedistributor holes should be at least 0.5 in. (12.7 mm) in diameter and should point toward the near head of the drum. Asufficient number of holes should be provided to limit the liquid exit velocity to 1 ft/s (0.305 m/s) or less to avoid the formationof small droplets.If a bottom settling pot is provided, the bottom of the inlet distributor pipe should be elevated about 4 in. (100 mm) from thevessel bottom.

2. Separators Handling Liquids and Vapors➧ For this service, the inlet nozzle should be a slotted tee distributor located in the vapor space and designed for vapor-liquid

service as described in Section V-A (Vapor-Liquid Separators). For high vapor rate, non-fouling services (i.e., fractionatordistillate drums), a 6-inch thick, 5 lb/ft3 density (150 mm thick, 80 kg/m3 density) vertical CWMS should be provided betweeneach inlet nozzle and the 6 inch thick, 5 lb/ft3 density (150 mm, 80 kg/m3 density) horizontal CWMS. The vertical CWMSshould cover the entire drum cross-sectional area for vapor flow and should extend to the low interface level (LIL). The areafor vapor flow (in the drum and through the CWMS) should be sized for 125% of critical velocity at design gas flow rate. Forother critical services where high liquid-liquid separation efficiency is required, consult with a SEPARATIONS SPECIALIST.

LIQUID HOLDUP FOR PROCESS, CONTROL, AND SAFETY REQUIREMENTSDesign liquid holdup time is usually determined by process, control, or emergency requirements. Control and emergencyrequirements are covered in Sections XII, Instrumentation, and XV, Safety in Plant Design, respectively. Additional liquid holduprequirements for process reasons, such as caustic inventory for reasonable batch replacement intervals, need to be determinedprior to settler design.

DROPLET SETTLINGLiquid-liquid separation in horizontal gravity settlers is based on the assumptions that: (1) each phase is dispersed in the other,and (2) separation will occur if the holdup time of each phase is equal to or larger than the time required for the drops to rise orsettle to the interface.The holdup time required for separation in the light liquid phase is obtained by dividing the vertical distance between the top ofthe drum (or upper surface of the light liquid phase, if vapor is also present) and the interface level in question by the drop settlingvelocity of the heavy phase. Likewise, the time required for separation in the heavy liquid phase is obtained by dividing thevertical distance between the bottom of the drum and the interface in question by the drop settling (rising) velocity of the lightliquid phase. Drop settling velocity is calculated from Eq. (1a), (1b), or (1c) and the appropriate drop size from Table 1.

DROPLET SETTLING VELOCITYAlthough liquid-liquid settling is not a single-drop phenomenon, settling rate equations based on rigid spheres have provedsatisfactory for design purposes. The application of these equations, which are valid for vapor bubble diameters less than 0.0236in. (0.6 mm) and liquid droplet diameters less than 0.0394 in. (1.0 mm), depends on the Reynolds number of the bubbles ordrops. RANGE OF APPLICABLE REYNOLDS NUMBERS, Re

Stokes’ Law: VS = (C1) ��

�

�

��

�

�

µ∆Sd2

Re < 2 Eq. (1a)

Intermediate Law: VS = (C2) ��

�

�

��

�

�

µ

∆0.286

c0.429

0.7141.143

)(S )(S)( (d) Re ≥ 2 ≤ 500 Eq. (1b)

Newton’s Law: VS = (C3) 0.5

cSS d��

��

� ∆ Re > 500 Eq. (1c)





Re = (C4 ) µcS S Vd Eq. (2)

where: VS = Settling velocity of dispersed phase droplets or bubbles, in./min (mm/s)

C1 = Constant = 8.3x105 for Customary units (544 for Metric units)



C4 = Constant = 10.74 for Customary units (0.999 for Metric units)

d = Diameter of dispersed phase droplet or bubble, in. (mm)

∆S = Difference in specific gravities of continuous and dispersed phases (with respect to waterat 60°F), dimensionless (absolute value)

Sc = Specific gravity of continuous phase at conditions, dimensionless

µ = Viscosity of continuous phase at conditions, cP (mPa•s)

Note that for design purposes, VS is limited to a maximum value of 10 in./min (4.2 mm/s) to avoid situations where phenomenonsuch as turbulence could affect settling droplets. Also, since VS must be known before Re can be calculated to determine whichequation for VS applies, a trial-and-error calculation using an assumed value for VS is needed.

VAPOR SPACEFor vapor-liquid-liquid services, see Section V-A (Vapor-Liquid Separators) for criteria on sizing the vapor space.

PREVENTION OF LIQUID REENTRAINMENTAnti-vortex baffles should be installed ahead of all liquid outlet nozzles to prevent reentrainment. The types used are subwaygrating baffles for bottom outlet nozzles, and square solid baffles for top liquid hydrocarbon outlet nozzles (Figure 1 and SectionV-A, Figure 11).Heavy Liquid Phase Outlet - Subway grating baffles are designed using criteria (Figure 11) in Section V-A; however, theminimum distance from the low interface level to the heavy liquid phase outlet nozzle is the larger of either 9 in. (230 mm) or thevalue calculated from Eq. (3):

=LIh 0.2

h

0.4h

1

Q C5

��

��

�−

ρ

ρ l

Eq. (3)

where: hLI = Minimum height from low interface level to outlet nozzle for heavy liquid phase, in.(mm)

C5 = Constant = 15 for Customary units (100 for Metric units)

Qh = Discharge rate of heavy phase, ft3/s (dm3/s)

�ρ = Density of light liquid phase at conditions, lb/ft3 (kg/m3)

ρh = Density of heavy liquid phase at conditions, lb/ft3 (kg/m3)

Light Liquid Phase Outlet - Design criteria for solid baffles used with light phase top outlet nozzles are given in Figure 1. Theminimum distance between the high interface level and the outlet nozzle is the larger of the two values calculated from Eqs. (4a)and (4b):



V-B 7 of 23



6CdHIh +=�

Eq. (4a)

=HIh ( )

( )0.25

0.25

0.5L7

hρ

ρ1d

C Q

��

�

�

��

�

�− �

�

Eq. (4b)

where: hHI = Minimum height from high interface level to outlet nozzle of light liquid phase, in. (mm)


C7 = Constant = 5.88 for Customary units (62.8 for Metric units)

QL = Discharge rate of light liquid phase, ft3/s (dm3/s)

�d = Diameter of outlet nozzle for light liquid phase, in. (mm)

Other terms are as defined for Eq. (3).

For vapor-liquid-liquid services, the light liquid phase is typically withdrawn through a bottom outlet nozzle with a straightextension (interior pipe extending up from the bottom nozzle) (Figure 5A). With these nozzles, subway grating anti-vortex baffles,designed according to criteria in Section V-A, should be used. The minimum distance the nozzle should extend above the highliquid-liquid interface level is the larger of 4 in. (100 mm) or the larger of the two values calculated from Eq. (4a) and Eq. (4b). Ifthe drum has a settling pot, the minimum extension above the bottom of the drum is 4 in. (100 mm).

SETTLING POTSWhen a relatively small amount of heavy liquid phase is present, it is often withdrawn through a settling pot on the bottom of thedrum. Settling pots permit a reduction in the drum size by eliminating the heavy phase layer on the bottom of the drum. Tosatisfy mechanical and economic considerations, settling pot diameters should not exceed the following:

Drum Diameter (D), in. (mm) Pot Diameter, max.D ≤ 40 (1000) D/2

40 (1000) < D < 60 (1500) 20 in. (500 mm)D ≥ 60 (1500) D/3

SETTLING BAFFLESHorizontal baffles may be used to reduce the distance which the drops must travel and thus reduce the required liquid holduptime for separation and subsequent drum size.In drums with settling baffles, the liquid holdup time between adjacent baffles (or shell and adjacent baffle) should be equal to orlarger than the time required for the drops to travel the vertical distance between the baffles (or shell and adjacent baffle). Thevertical spacing between adjacent baffles for a given drum size depends on the horizontal velocity of the phase in which thebaffles are to be installed, baffle length, and the drop settling velocity. Baffle spacing of 18 in. (450 mm) is required for access;however, spacings as low as 9 in. (230 mm) have been used for droplet settling. The calculation procedure is as follows:Step 1: Calculate the horizontal velocity of the liquid phase in which the settling baffles are to be installed. The horizontal

velocity is obtained by dividing the continuous phase volumetric flow rate by its vertical cross-sectional area for flow.This area is the area above the liquid-liquid interface when baffles are installed in the light liquid phase. This area is thearea below the interface for baffles installed in the heavy liquid phase.

Step 2: Calculate the settling velocity of the dispersed phase droplets, using Eq. (1a), (1b), or (1c) and the appropriate drop sizefrom Table 1.

Step 3: Calculate the maximum permissible vertical distance between adjacent baffles using Eq. (5):

h = C8 ��

��

�

hz

sb

VLVS Eq. (5)





where: h = Maximum permissible height between adjacent baffles, in. (mm)


VS = Settling velocity of dispersed phase droplets, in./min. (mm/s)

Vhz = Horizontal velocity of the liquid phase in which settling baffles are to be installed, in./min.(mm/s)

Lsb = Length of settling baffle, ft (m). This length is related to the drum size as shown inFigure 2.

Additional settling baffle design criteria are shown in Figure 2.

DUAL- MEDIA CRINKLE WIRE MESH SCREEN (DM-CWMS)DM-CWMS coalescence media can be used to increase drop size so that a greater portion of the drops will settle in the drum.DM-CWMS is not typically used in grassroots settlers since the research has not been done to prove that overall separator cost(capital and operating) would be reduced. However, it has been used for revamp applications as a means of increasing drumcapacity and improving separation efficiency. A single-stage design utilizing a horizontal DM-CWMS near the hydrocarbon outletis generally sufficient for most applications. For services where de-entrainment is critical, a two-stage configuration may bepreferred. Figure 4 shows a two-stage DM-CWMS liquid-liquid separator design.In a two-stage installation, the first DM-CWMS is installed vertically downstream of the feed inlet distributor; the majority of thedispersed droplets are coalesced in this stage. A second DM-CWMS pad is installed horizontally below the light phase outletnozzle to remove any entrainment. It should be positioned above the high interface level, but may be lowered to increase theflow area and reduce the liquid velocity, if necessary. The pad should not be placed below the drum centerline or the normalinterface level. A vertical baffle is required at the upstream edge of the DM-CWMS pad to prevent liquid bypass and an outletcollector is recommended for drums with diameters greater than 10 ft (3000 mm).Based on commercial experience with extractors, capacity increases up to 50% may be achieved at constant entrainment levelsafter installing coalescence media. In addition, coalescence media have successfully been applied at the Baton Rouge Refineryto reduce caustic entrainment from cat naphtha settlers. In this service, Baton Rouge experienced about a 70% reduction incaustic carryover at the same flow rates. Their original settlers had caustic carryover levels of 200-300 ppm; when coalescingelements were installed, the entrainment levels were reduced to 50-100 ppm. Baton Rouge later installed sand filters whichessentially eliminated the caustic entrainment.Table 2 gives application and design guidelines for liquid-liquid settlers utilizing DM-CWMS. Designers should contact aSEPARATIONS SPECIALIST if the application is outside these experience limits.

DRAWING NOTESIn addition to the usual notes on the design pressure and temperature and materials of construction, the following notes shouldbe considered for inclusion on the separator drum design specification drawing:1. GP 05-02-01 shall be followed.2. Manhead and vent nozzle shall be designed according to criteria given in GP 05-01-01.

DESIGN PROCEDURE

DESIGN OF HORIZONTAL SETTLERS (WITH OR WITHOUT SETTLING BAFFLES)The following procedure is recommended (see Figures 1 and 2):

Drum sizing calculations may be minimized by use of the following figures and tables in Section V-A (Vapor-LiquidSeparators):Table 2 and 2a, Area and Volume of Cylindrical Vessels.Table 5, Chord Lengths and Segment Areas vs. Chord Heights.

In addition, the PEGASYS Horizontal Drum Design and Rating and the PEGASYS Segments of Circle programs may be usedto facilitate design calculations.Step 1: Set the liquid holdup time based on the criteria given in “Basic Design Considerations,” under “Liquid Holdup for

Process, Control, and Safety Requirements.”Step 2: Estimate the minimum permissible distance between the low interface level (LIL) and the heavy phase outlet nozzle,

using criteria given below under “Prevention of Liquid Reentrainment.”



V-B 9 of 23



Step 3: Estimate the minimum permissible distance between the high interface level (HIL) and the light phase outlet nozzle,using criteria given below under “Prevention of Liquid Reentrainment.”

Step 4: If vapor is being separated, estimate the minimum permissible vapor space height using criteria given in Section V-A(Vapor-Liquid Separators).

Step 5: Assume a settler diameter and then calculate the settler length required to satisfy the liquid holdup time set in Step 1.Based on economic considerations, a length of 3 to 4 times the diameter is preferred.

Step 6: Check whether this settler satisfies the liquid-liquid separation criteria given previously under “Droplet Settling.” If thesettler size is not adequate, assume another diameter and repeat Steps 5 and 6 until a satisfactory design is obtained.Alternatively, settling baffles can be installed to reduce the holdup time required for separation (see Figure 2). Settlingbaffle design criteria are given previously under “Settling Baffles.”

DESIGN OF THREE COMPARTMENT HORIZONTAL SETTLERSThe following procedure is recommended:Step 1: Use the design criteria given in Figure 3 and in “Design Considerations for Selected Services,” under “Feed Separator

Drums for Sour Water Strippers and Amine Regenerators.”Step 2: Follow the applicable portions of Steps 4 through 6, above, for “Design of Horizontal Settlers (With or Without Settling

Baffles).”

DESIGN CONSIDERATIONS FOR SELECTED SERVICES

FEED SEPARATOR DRUMS FOR SOUR WATER STRIPPERS AND AMINE REGENERATORSTo minimize oil carryover into a sour water stripper or amine regenerator, three-compartment drums are typically used ahead ofthe tower. Design guidelines for these drums are given below and in Figure 3.Oil ConcentrationFor design purposes, assume that the oil concentration in the drum feed is 0.1 wt %.Water Holdup Time1. Sour Water Stripper Feed Drums

a. In refinery services, sixty to ninety minutes of water holdup time should be provided in the settling compartment.b. In chemical plant services, the water holdup time is the larger of either 10 minutes or the time calculated by dividing the

height of the settling compartment by the rising velocity of the oil drops. The oil drop rising velocity is calculated usingEq. (1a), (1b), or (1c) and the appropriate drop size from Table 1.

2. Amine Regenerator Feed Drums➧ The minimum amine holdup time in the settling compartment is the larger of either 20 minutes (per EMRE Gas Processes

Specialists) or the time calculated by dividing the vertical distance between the drum bottom and the oil/amine interface bythe rising velocity of the oil drops. Please note that minimum holdup time may vary depending on local and state coderequirements. Use Eq. (1a), (1b), or (1c) and Table 1.Baffle Height (see Figure 3)The heights of the oil and water overflow baffles are adjusted to maintain at least a 9 in. (230 mm) deep oil layer in thesettling compartment. The difference in heights between the oil and water overflow baffles is calculated by Eq. (6):

➧ ( )OWWBOB hhh =− ��

��

�−

wO

ρ

ρ1 + C9

0.67

c

WL

Q��

��

� [approximately 3 in. (75 mm) is typical] Eq. (6)

where: hOB = Vertical distance from the bottom of the drum to the top of the oil overflow baffle, in. (mm)

hWB = Vertical distance from the bottom of the drum to the top of the water (amine) overflowbaffle, in. (mm)

hOW = Vertical distance from the oil/water (amine) interface to the top of the oil overflow baffle,in. (mm) [9 in. (230 mm) minimum]

C9 = Constant = 0.09 for English units, (6.4 for Metric units)

QW = Throughput of sour water or amine solution, gpm, (dm3/s)

Lc = Chord length at the top of the water (amine) overflow baffle, ft (m)





ρo = Density (at conditions) of the heaviest hydrocarbon stream fed to the drum, lb/ft3, (kg/m3).

If the oil density is unknown, use 56 lb/ft3, (900 kg/m3).

ρw = Density of sour water or amine solution at conditions, lb/ft3, (kg/m3)

Eq (6), which is based on flow over a rectangular weir, accounts for the presence of oil and water in the settling compartment anda head of water above the top of the water overflow baffle.Velocity of Aqueous PhaseThe water (amine) velocity between the: (1) bottom of the oil compartment and the drum shell, and (2) the oil compartment andthe water (amine) overflow baffle should be limited to the smaller of 0.5 ft/s (0.15 m/s) or the value calculated using thedimensions given in Figure 3. This velocity restriction minimizes the pressure loss in the drum and subsequent reduction in oillayer thickness in the settling compartment.Vapor Flow AreaThe vapor flow area above the oil overflow baffle should be sized for 100%, or less, of critical velocity at normal gas flow rate.The minimum height of the vapor space is the larger of 12 in. (300 mm) or 20% of drum diameter. In addition, providing sufficientvolume for liquid holdup in the vapor space may avoid the need for sizing the pressure relief valve for liquid service. See SectionXV-C for special provisions regarding pressure relief valve sizing for a liquid overfill contingency.Surge Capacity1. For sour water drums, 15 minutes sour water surge capacity should be provided between the high and low water levels in the

water compartment. This is required to feed the stripper on flow control.2. For amine drums, at least 5 minutes amine surge capacity should be provided between the high and low levels in the amine

compartment.Settling PotsChemical plant amine regenerator feed drums are provided with settling pots for the removal of polymerization products (densehydrocarbons). The pot is located a minimum distance from the amine overflow baffle within the oil-water settling compartment.

➧ SULFURIC ACID ALKYLATION SETTLERSSettlers in sulfuric acid alkylation service are typically designed with settling baffles. These baffles typically have a thickness of 16gage and are sloped 5 degrees from horizontal. The baffles have lips on the top end. The standard baffle spacing is 1 inch (25mm). The baffles start 9 inches (230 mm) from the bottom and are installed in the lower 65-70% of the vessel diameter.

Dual-media, crinkled wire mesh screens (DM-CWMS) have been installed in three ExxonMobil settlers and at two non-affiliatelocations to increase the capacity of a settler already containing settling baffles. All installations to date have been a hybrid ofDM-CWMS and settling baffles, thus not relying totally on screens. Based on this favorable experience, DM-CWMS shouldcontinue to be used in conjunction with baffles to provide incremental settling capacity. An actual installation of DM-CWMS mustconsider gaps between pads, spaces between rows, and space required for access. Because of reported fouling and loss of wiremetal, it is recommended that the DM-CWMS be replaced during each scheduled unit turnaround. The appropriate materials ofconstruction and a secure hold-down arrangement for the DM-CWMS must be provided in the design. A SEPARATIONSSPECIALIST should be consulted regarding sulfuric acid alkylation settler designs or revamps with DM-CWMS.

➧ HYDROFLUORIC ACID ALKYLATION SETTLERSSettlers in hydrofluoric (HF) acid alkylation service have been revamped with parallel plate pack internals. These proprietaryinternals provided by Vivendi Water Systems (USF Rossmark Waterbehandeling B.V.) in the Netherlands have been used tosuccessfully debottleneck two ExxonMobil settlers. The internals consist of perforated baffles immediately downstream of the inletdistributor, and a section of the sloped parallel plates downstream of the vertical baffles. The spacing between plates isapproximately 1 inch (25 mm). A SEPARATIONS SPECIALIST should be consulted regarding HF acid alkylation settler designsor revamps with parallel plate pack internals.

SAMPLE PROBLEM

DESIGN BASISThis is a separator drum in three-phase flow service (hydrocarbon vapor, hydrocarbon liquid, and water).Liquid Carryover - Since the overhead vapor from the drum is fed to a compressor, liquid carryover must be minimized (seeTable 1 of Section V-A).Holdup1. 10 minutes holdup between ELL (emergency liquid level) and HLL (high liquid level).



V-B 11 of 23



2. 2 minutes liquid holdup between HLL and LLL (low liquid level). The desired 15 minutes holdup for product feedingsubsequent process units will be provided in a downstream recontacting drum.

3. 2 minutes water holdup below LIL (low interface level).Feed Rates and Properties - The distillate drum feed depends on the crude oil fed to the atmospheric pipestill. For thisexample, it will be assumed that either stream A or B may be fed to the distillate drum. The flow rates and physical propertieslisted below are all at the drum operating conditions.

FEED A FEED B

PHYSICAL PROPERTY CUSTOMARY METRIC CUSTOMARY METRIC

Vapor flow rate, ft3/s (dm3/s) 31.5 892 - -

Vapor density, lb/ft3 (kg/m3) 0.27 4.33 - -Vapor viscosity, cP (mPa•s) 0.01 0.01 - -Hydrocarbon liquid flow rate, ft3/min (dm3/s) 245 116 295 139Hydrocarbon liquid density, lb/ft3 (kg/m3) 41.6 666 41.6 666Hydrocarbon liquid viscosity, cP (mPa•s) 0.319 0.319 0.319 0.319Hydrocarbon liquid surface tension, dynes/cm(mN/m)

20 20 20 20

Water flow rate, ft3/min (dm3/s) 20.87 9.85 20.87 9.85Water density, lb/ft3 (kg/m3) 61.86 991 61.86 991Water viscosity, cP (mPa•s) 0.612 0.612 0.612 0.612

SOLUTIONBased on design criteria in this subsection and in Section V-A, we will use a horizontal separator drum with a horizontal CWMS inthe vapor space. The drum vapor space and the CWMS should be sized for 100% of critical velocity at normal gas flow rate (see“Horizontal Separator Drums With and Without CWMS” in Section V-A). The procedure followed for this design is given below.See Figure 5A (Customary units) or Figure 5B (Metric units) of this Sample Problem for the final drum design.Minimum Permissible Distance Between LIL and Bottom of Drum - This distance, hLI, is the larger of 9 in. (230 mm) or thevalue calculated from Eq (3):

hLI = 12 in. (305 mm)

Since 12 in. (305 mm) > 9 in. (230 mm), hLI = 12 in. (305 mm)

Vertical Distance Between LIL and HIL (hLIL-HIL) - This distance is set at 14 in. (360 mm) for instrument requirements (seeSection XII-C, Level Measurement and Control).Horizontal Nozzle Extension - The hydrocarbon outlet nozzle exits through the bottom of the drum. The minimum permissibledistance hHI from the top of the hydrocarbon nozzle extension down to the HIL is the larger of 4 in. (100 mm) (vapor-liquid-liquidservice) or the value obtained from Eq. (4b), assuming d� = 10 in. (250 mm). The highest rate through the hydrocarbon outletnozzle is determined by Feed B.

hHI = 9.69 in. Call 10 in. (250 mm)

Minimum Permissible Distance Between LLL and Outlet Nozzle - This distance, hLL, is calculated from Eq. (13) of Section V-A:

hLL = 15.9 in. Call 16 in. (405 mm)

Drum Sizing - The estimate of the optimum drum size is a trial-and-error procedure. First, a drum diameter is assumed, andthen the drum length required to satisfy liquid holdup time is estimated and vapor disengaging heights are calculated. Then theadequacy of this drum size for liquid-liquid separation is checked. For a first trial, we will assume a 13 ft (4000 mm) diameterdrum. (This diameter turns out to be adequate, so no second trial is needed.)1. Vertical Heights and Vertical Cross-Sectional Areas

a. Vertical Height for Vapor Flow (hv) - The vertical cross-sectional area for vapor flow must satisfy the following criteria:maximum permissible vapor velocity is 100% of critical velocity and minimum permissible vertical height is the larger of20% of drum diameter or 12 in. (305 mm).Critical velocity is calculated from Eq. (1) of Section V-A:





Vc = 1.94 ft/s (0.593 m/s)

The vapor area, AV, required for this service is calculated by dividing the gas through-put by twice the critical velocity,since two inlet nozzles are used:

AV = 8.12 ft2 (0.752 m2)

The vertical height required to satisfy critical velocity criteria is calculated as follows:A

AV

drum = 0.0612

where Adrum is the drum vertical cross-sectional area and Av / Adrum = A* in Table 5 of Section V-A. The ratio of thevapor space height to drum diameter (R*) is:

R* = 0.112

But this ratio of 0.112 is less than the required 20% of drum diameter; therefore, the minimum vertical height for vaporflow is:

hv = (0.20) (13 ft) = 2.6 ft = 31.2 in. Call 31 in. (800 mm)

b. Vertical Area Between LLL and ELL (ALLL-ELL) - The vertical distance between the bottom of the drum and the LLL(hBtm-LLL) is:

hBtm-LLL = hLI + hLIL-HIL + hHI + hLL = 52 in. (1325 mm)

R* of Table 5 in Subsection A = 0.333;

A* of Table 5 is 0.292.

Therefore, the vertical cross-sectional area between the bottom of the drum and LLL (ABtm-LLL) is:ABtm-LLL = 0.292*Adrum = 38.8 ft2 (3.63 m2)

Since the minimum height for vapor flow is 31 in. (800 mm), the vertical cross-sectional area between ELL and the top ofthe drum (AELL-Top) is:

R* of Table 5 in Section V-A = 0.1987.

A* of Table 5 is 0.141.

AELL-Top = 18.7 ft2 (1.78 m2)

The vertical cross-sectional area between LLL and ELL (ALLL-ELL) is:ALLL-ELL = Adrum - [ABtm-LLL + AELL-Top] = 75.2 ft2 (7.16 m2)

2. Holdup Requirementsa. Drum Length for 12 Minutes Holdup Between LLL and ELL

Ldrum = (Liquid Throughput) (Holdup Time)

ALLL ELL−

= 47.1 ft. Call 47 ft (14.0 m)

This results in a length/diameter ratio of 3.6 (3.5), which is satisfactory, since settlers are normally designed with alength/diameter ratio between 3:1 and 4:1.

b. Vertical Distance for 2 Minutes Holdup Between LLL and HLL (hLLL-HLL) - The vertical cross-sectional area requiredbetween LLL and HLL (ALLL-HLL) is:

ALLL-HLL = (Liquid Throughput) (Holdup Time)

DrumLength = 12.6 ft2 (1.19 m2)

The vertical cross-sectional area needed between the bottom of the drum and HLL (ABtm-HLL) is:ABtm-HLL = ABtm-LLL + ALLL-HLL = 51.4 ft2 (4.82 m2)

A* of Table 5 in Section V-A = 0.387;

R* of Table 5 is 0.411.



V-B 13 of 23



Therefore, the vertical height between the bottom of the drum and HLL (hBtm-HLL) is:hBtm-HLL = 0.411 D = 5.34 ft (1.63 m) = 64.1 in. Call 64 in. (1630 mm)

The vertical distance between LLL and HLL (hLLL-HLL) is:hLLL-HLL = hBtm-HLL - hBtm-LLL = 12 in. (305 mm)

This distance should be increased to 14 in. (360 mm) to accommodate a standard size external displacer levelcontroller (see Section XII-C, Level Measurement and Control).

Therefore, hLLL-HLL = 14 in. (360 mm)

c. Water Holdup Time Between LIL and the Drum Bottom - Using the ratio of hLI to D:R* = 0.0769

A* = 0.0354. Then the vertical cross-sectional area from the bottom of the drum to LIL (ABtm-LIL) is:ABtm-LIL = (A*) (Adrum) = 4.7 ft2 (0.45 m2)

The water holdup time (TW) is:

TW = (A )(L )Water Throughput

Btm LIL drum− = 10.6 min.

This holdup time exceeds the 2 minutes minimum holdup time set in the design basis, and is therefore adequate.d. Separation Rates - Separation rate estimates are based on the drop sizes given in Table 1, the properties of the two

liquid phases, and the settling rate equations.(1) Water from Hydrocarbon Liquid - Assuming that the Intermediate Settling Law applies for this system, the

separation velocity is calculated from Eq (1b):VS = 19.8 in./min. (8.6 mm/s)

Check adequacy of Intermediate Settling Law for this case:Re = 2.22

Since 2.0 < 2.22 < 500, the Intermediate Law applies.However, the maximum permissible settling velocity for drum design is 10 in./min. (4.2 mm/s).Therefore, VS = 10 in./min. (4.2 mm/s)

(2) Hydrocarbon Liquid from Water - Assuming that the Stokes’ Law applies for this system, the settling velocity iscalculated from Eq. (1a):

VS = 11.0 in./min. (4.9 mm/s)

Check adequacy of Stokes’ Settling Law for this case:

Re = 0.957

Since 0.957 < 2, Stokes’ Law applies.However, the maximum permissible separation velocity for design is 10 in./min. (4.2 mm/s).Therefore, VS = 10 in./min. (4.2 mm/s)

e. Holdup Time Between LIL and ELL Required for Water/Hydrocarbon Separation - The vertical distance betweenLIL and ELL (hLIL-ELL) is:

hLIL-ELL = D - (hv + hLI) = 113 in. (2890 mm)

Hydrocarbon holdup time (THC) required for separation of water drops is:

THC = hV

LIL ELL

S

− = 11.3 min.

f. Available Holdup Time Between LIL and ELL - The vertical height between the bottom of the drum and ELL is:hBtm-ELL = hLI + hLIL-ELL = 125 in. (3200 mm)

This is more than half the drum diameter. Therefore R* of Table 5 in Section V-A is:





(D - hBtm-ELL) / D = 0.1987;

A* of Table 5 is 0.141.Therefore, the vertical cross-sectional area between the bottom of the drum and ELL (ABtm-ELL), is:

ABtm-ELL = (1-A*) Adrum = 114 ft2 (10.8 m2)

The holdup time between LIL and ELL (TLIL-ELL) is:

TLIL-ELL = (A A )(L)

Hydrocarbon Liquid ThroughputBtm ELL Btm LIL− −−

= 17.4 min.

Therefore, the available holdup time is larger than that required for separation (17.4 vs. 11.3 minutes).This procedure was repeated to test the adequacy of the drum for separating water drops from hydrocarbon andhydrocarbon drops from water at various positions of the water/hydrocarbon and hydrocarbon/vapor interfaces. In allcases, the available holdup time was larger than the holdup time required for separation (see table below). Therefore,the assumed settler size is satisfactory for this service.

TEST OF ADEQUACY OF 13 FT (4.0 M) DIAMETER BY 47 FT (14.0 M) LONG HORIZONTALDRUM FOR WATER/HYDROCARBON LIQUID SEPARATION

AVAILABLE LIQUID LIQUID HOLDUP TIMECASES STUDIED HOLDUP TIME REQUIRED FOR SEPARATION TIME OF

(MINUTES) (MINUTES) SEPARATIONELL to LIL 17.4 11.3 Water Drops from

HydrocarbonHLL to LIL 7.4 5.6LLL to LIL 5.4 4.0ELL to HIL 15.8 9.9HLL to HIL 5.9 4.2LLL to HIL 3.9 2.6Drum Bottom to HIL 32.9 2.6 Hydrocarbon Drops

from WaterDrum Bottom to LIL 10.6 1.2 Hydrocarbon Drops

from Water

3. Inlet Nozzle Selection - Since the feed contains vapor, the inlet nozzle will be located above the liquid level. Either 90°elbows or slotted distributors should be used. One should try to use 90° elbows, since they are less expensive than slotteddistributor inlets.The maximum permissible gas velocity at the exit of 90° elbow inlets is calculated using Eq. (3c) of Section V-A, corrected forhorizontal drum application, and assuming f = 1.

VE = 26.3 ft/s (7.94 m/s)

If two 14 in. (350 mm) diameter 90° elbow inlets are used for this service, the gas velocity at the exit of the elbow of eachnozzle is calculated by dividing one-half the throughput by the pipe cross-sectional area.

V = 16.8 ft/s (5.29 m/s)

Since the calculated exit velocity of 16.8 ft/s (5.29 m/s) is less than the maximum permissible value of 26.3 ft/s (7.94 m/s),the assumed inlet nozzle design is acceptable.The bottom of the nozzles should be located at least 6 in. (150 mm) above the ELL. If short-radius elbows are used, thedistance from the top of the drum to the bottom of the 90° bend will be about 21 in. (530 mm) (see Table 4 of Section V-A).Therefore, the distance from the bottom of the inlet nozzle to the emergency liquid level will be 10 in. (250 mm), which islarger than the minimum permissible distance of 6 in. (150 mm) (see Section V-A under “Horizontal Separator Drums Withand Without CWMS”).

4. CWMS Design (from Section V-A) - The CWMS area is based on 100% of critical velocity:



V-B 15 of 23



CWMS area = 31.5

1.94 = 16.2 ft2 (1.50 m2)

Use a 6 in. (150 mm) thick, 5 lb/ft3 (80 kg/m3) CWMS. The minimum permissible distance between ELL and the bottomof the CWMS (hCWMS-ELL) is one foot (300 mm). The available distance from the top of the CWMS to the vapor outletnozzle (ho) is:

ho = hv - (hCWMS-ELL + CWMS thickness) = 13 in. (330 mm)

Assuming a square CWMS, the length of each side is:

LCWMS = 16.2 = 4.02 ft (1.225 m) = 48.3 in. Call 48 in. (1225 mm)

Assuming a gas outlet nozzle diameter do of 24 in. (600 mm), the minimum permissible distance from the CWMS top tothe gas outlet nozzle is calculated from Eq. (12a) of Section V-A:

ho = 12 in. (305 mm)

Since the available distance is larger than the minimum permissible distance [13 in. (330 mm) vs. 12 in. (305 mm)], flowmaldistribution will not be a problem and the outlet design is acceptable.

5. Design of Anti-Vortex Baffles (from Section V-A)a. Water Outlet Nozzle - Square tiers of subway grating should be used. The length of the side of each grating should be

24 in. (600 mm), which is four times the outlet nozzle diameter. The bottoms of the lowest, intermediate, and topgratings should be located at 2 (50), 5 (125), and 8 (200) in. (mm) above the water outlet nozzle, respectively.Remaining design criteria are given in Figure 11 of Section V-A.

b. Hydrocarbon Outlet Nozzle - Square tiers of subway grating should be used. The length of the side of each gratingshould be 40 inches (1000 mm) for a 10 in. (250 mm) diameter hydrocarbon nozzle. The bottoms of the lowest,intermediate, and top gratings should be located at 2 (50), 8 (200), and 14 (350) in. (mm) above the hydrocarbon outletnozzle, respectively.





NOMENCLATUREAdrum = Vertical cross-sectional area of horizontal drum, ft2 (m2).AV = Cross-sectional area for vapor flow, ft2 (m2).D = Drum diameter, ft (m).d = Diameter of dispersed phase droplet or bubble, in. (mm).

dl = Diameter of outlet nozzle for light liquid phase, in. (mm).

do = Diameter of outlet nozzle, in. (mm).h = Maximum permissible height between two adjacent baffles, in. (mm).hHI = Minimum height from high interface level to outlet nozzle of light liquid phase, in. (mm).hLI = Minimum height from low interface level to outlet nozzle for heavy liquid phase, in. (mm).hLL = Minimum height from bottom of drum to bottom light hydrocarbon outlet nozzle, in. (mm).hOB = Vertical distance from bottom of drum to top of oil overflow baffle, in. (mm) (see Figure 3).hOW = Vertical distance from oil/water interface to top of oil overflow baffle, in. (mm) (see Figure 3).hWB = Vertical distance from bottom of drum to top of water or amine overflow baffle, in. (mm) (see Figure 3).ho = Height between top of CWMS and vapor outlet nozzle, in. (mm).hv = Chord height of segment for vapor flow, ft (m).LCWMS = Length of long side of rectangular CWMS, ft (m).Lc = Chord length at top of water (or amine) overflow baffle, ft (m).Ldrum = Length of drum, ft (m).Lsb = Length of settling baffle, ft (m).Q = Liquid discharge rate, ft3/s (dm3/s).QW = Throughput of sour water or amine solution, gpm (dm3/s).Qh = Discharge rate of heavy phase, ft3/s (dm3/s).Re = Reynolds number of drop or bubble, dimensionless [Eq (2)].∆S = Difference in specific gravities of continuous and dispersed phases (with respect to water at 60°F),

dimensionless (absolute value).Sc = Specific gravity of continuous phase at conditions, dimensionless.THC = Holdup time of hydrocarbon phase, min.TW = Holdup time of water phase, min.V = Velocity, ft/s (m/s).VE = Maximum mixture velocity at the exit of the inlet nozzle, such that entrainment will not occur at the liquid

surface, ft/s (m/s).Vc = Critical velocity, ft/s (m/s).Vhz = Horizontal velocity of the liquid phase in which settling baffles are to be installed, in./min (mm/s).VS = Separation velocity of dispersed phase droplets, in./min (mm/s).

ρl = Density of light liquid phase at conditions, lb/ft3 (kg/m3).

ρh = Density of heavy liquid phase at conditions, lb/ft3 (kg/m3).ρO = Density of heavy oil phase at conditions, lb/ft3 (kg/m3).ρw = Density of sour water or amine solution at conditions, lb/ft3 (kg/m3).µ = Viscosity of continuous phase at conditions, cP (mPa•s, equivalent to cP).

COMPUTER PROGRAMSThe design of horizontal settlers can be facilitated by the use of the PEGASYS Horizontal Drum and Segments of Circleprograms. These PEGASYS programs utilize the design equations contained in this subsection and the geometry correlationscontained in Table 5 in Section V-A. The Horizontal Drum Program can be used for both designing new vapor-liquid-liquidsettlers and rating existing settlers.



V-B 17 of 23



APPENDIX

Table 1Settling Drum Design Criteria

Drop Size for Drum DesignDrop Size, inches (mm)

Light Liquid Phase Density Heavy Liquid Phase (Both Phases)53 lb/ft3 (850 kg/m3) and lower Water, Caustic, or Amine 0.005 (0.13)

Higher than 53 lb/ft3 (850 kg/m3) Water, Caustic, or Amine 0.0035 (0.089)Liquid Holdup Considerations1. Settling requirements of individual phases.2. Minimum instrument dimensions as given in Section XII-C.3. Holdup requirements for controlling process. For normal circumstances, the holdup between high and low interface

levels should be 2 minutes on product to storage or 15 minutes on product feeding subsequent process equipment.Refer to Section XII-C for additional considerations.

4. Inventory requirements for startup, shutdown, makeup, etc.

Table 2Coalescence Media Application And Design Considerations

DESIGNCONSIDERATION

VALUESSUGGESTED

ALLOWABLERANGE

COMMENTS

Velocity 10 gpm/ft2(0.7 cm/s)

10-15 gpm/ft2(0.7-1.0 cm/s)

DM-CWMS is generally not required for liquid velocities below 10 gpm/ft2 (0.7cm/s). Maximum liquid velocity is dependent on the service. SEPARATIONSSPECIALISTS may be consulted for guidance.

DM-CWMSThickness

18 in.(450 mm)

12-24 in.(300-600 mm)

A thickness of 18 in. (450 mm) is recommended for most applications. Athicker pad may be considered when entrainment removal is critical or for liquidvelocities greater than 15 gpm/ft2 (1.0 cm/s).

CWMS Density 10 lb/ft3(160 kg/m3)

9-15 lb/ft3(144-240 kg/m3)

Performance is similar for DM-CWMS densities in the allowable range at liquidvelocities less than 15 gpm/ft2 (1.0 cm/s). For critical services with liquidvelocities greater than 15 gpm/ft2, a density of 15 lb/ft3 (240 kg/m3) may beconsidered. Densities below 9 lb/ft3 (144 kg/m3) are not recommended.

Droplet Size Liquid de-entrainment is dependent on the initial drop size distribution. DM-CWMS is highly effective for removing droplets of the size typically generatedby extractors, orifice mixers, and other mild mechanical contacting equipment(e.g., greater than 20-40 µm).

Pressure Drop Pressure drop is typically less than 1 in. H2O/ft (0.8 kPa/m) of DM-CWMS.Fouling Service Standard DM-CWMS design is normally not recommended for solids-containing

streams unless a prefilter is provided. The use of gapped DM-CWMS orrandom packing can be used in potentially fouling services without a solidsprefilter; the location of pressure relief valves may be an issue.

MaterialsSelection

Stainless steel wire and polypropylene filament are the most common materialsof construction. A diameter of 0.011 in. (0.3 mm) is typically specified. EitherKYNAR, HALAR, or Polytetrafluorethylene (PTFE) may be used in place ofpolypropylene for operating temperatures above 140°F (60°C). Contact yourMATERIALS SPECIALIST for the design material selection based on fluidproperties, operating temperatures, and steam out temperatures.





Figure 1Typical Liquid-Liquid Settling Drum (1)

InletDistributor (4)

SECTION AA

DP5BF1

Min.(2)

Provides sufficient time to allowlight phase to settle from heavyphase

Heavy PhaseOutlet Anti-Vortex

Baffles (3)

Ldrum = 3 to 4 D

Normal Interface Level

SolidBaffle

Light PhaseOutlet

Min.(2)

Min.(2) Mixture

Inlet

Provides sufficient holdup timeto allow heavy phase to settlefrom light phase

A

D

B

A

B

d�

d�

2 d�

2 d�

d�

0.5 d�

0.5 d�

SECTION BB

Notes:➧ (1) If the settler does not contain a vapor space, one gage glass and one level controller should be used. It should extend

between the low level alarm and the emergency level. Additional information on gage glasses is given in GP 03-06-01 andGP 15-05-01. Level instruments should be located at the outlet end of the drum. Settlers containing a vapor space haveadditional features and requirements not shown in this figure. If the settler contains vapor space, two gage glasses andtwo level controllers should be used: one should be located between the heavy and the light liquid phases and the otherbetween the light liquid phase and the vapor space.

(2) Minimum distance considering reinforcement and fabrication requirements given in GP 05-01-01 and GP 05-01-02.(3) Anti-vortex baffle design is based on criteria given in Design Procedures under “Prevention of Liquid Reentrainment.”(4) Inlet distributor shall be a tee distributor with a hole velocity of 1 ft/s (0.305 m/s) or less and minimum hole size of 0.5 in.

(13 mm).



V-B 19 of 23



Figure 2Drum With Horizontal Settling Baffles

(Layout Of Typical Settling Baffle When Heavy Phase Drops Limit Settler Capacity)(1)(2)

Settling Baffles

Settling BaffleInlet Nozzle

0.25 Ldrum

1 in. (25 mm)

1 in. (25 mm)

Ldrum = 3 to 4 D

2 in. (50 mm)

Heavy PhaseOutlet

SECTION AA

Anti-VortexBaffles

Min.(4)

Light PhaseOutlet

Min.(4)Alternate Inlet Nozzle

Entry Port

Min. = 18 in. (450 mm)

Min. = 18 in. (450 mm)

Min. = 18 in. (450 mm)Interface

Level

2 in. (50 mm) Lip (1)(2)4D4

D

D

A A

DP5BF2

Notes:(1) When light phase drops limit settler capacity, a 2 in. (50 mm) lip should be placed on the underside of each baffle at the

outlet end of the drum.➧ (2) When heavy phase drops limit settler capacity, a 2 in. (50 mm) lip should be placed on the topside of each baffle at the

outlet end of the drum.(3) If the settler does not contain a vapor space, a gage glass and one level controller should be used. It should extend

between the low level alarm and the emergency level. Additional information on gage glasses is given in GP 03-06-01 andGP 15-05-01. Level instruments should be located at the outlet end of the drum. Settlers containing a vapor space haveadditional features and requirements not shown in this figure. If the settler contains a vapor space, two gage glasses andtwo level controllers should be used: one should be located between the heavy and the light liquid phases and the otherbetween the light liquid phase and the vapor space.

(4) Minimum distance considering reinforcement and fabrication requirements given in GP 05-01-01 and GP 05-01-02.➧ (5) Settling baffles may be sloped 2 to 5° toward vessel shell to facilitate drainage.





Figure 3Feed Drum For Sour Water Stripper Or Amine Regenerator(1)(2)

Oil Outlet Nozzle

Oil Overflow Baffle

SECTION AAOIL COMPARTMENT

6 in. (150 mm)

D8 (Min.)

[or 12 in. (300 mm) Min.]D12

hOB

3 D to 4 D

1.5 to 2.5 D

Oil Outlet NozzleDrain

Water

4 in. (100 mm) hOB

Oil Overflow Baffle

Settling Compartment

OilCompartment

(6)

Oil

2 ft. (600 mm)

Vapor SpaceSplash Baffle (5)

[or 6 in. (150 mm) Min.]12D

D

A

A

hOW

ImpingementBaffle

D

6 in. (150mm) Min.

Min. (4)

Min. (4)Inlet Nozzle

D D12to 32 (Min.)

Min. (4)

WaterCompartment

Anti-VortexBaffles

WaterOutlet Nozzle

Water (or Amine)Overflow Baffle

hWB

Vent and BalanceLine (3) (7)

DP5BF3

Notes:(1) A manhead should be located at each end of the drum. Level instruments should be provided in the three compartments.(2) Baffles must be leveled and the tolerance on baffle height is ± 1/8 in. (3 mm).(3) See GP 05-01-01.(4) Minimum distance considering reinforcement and fabrication requirements given in GP 05-01-01 and GP 05-01-02.(5) The splash baffle should extend from wall to wall.(6) Provide anti-vortex baffles directly above the oil outlet nozzle, adjacent to the drum wall. Baffle design should be based on

criteria in Section V-A.➧ (7) Vent nozzle should be located directly over the oil compartment.



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Figure 4Horizontal Setting Drum With Two Stage Dm-Cwms Coalescence Media

Inlet Nozzle

Support Rings

Vertical Baffle

Interface

Heavy Phase Outlet

Light PhaseOutlet

Min.

D/4Anti-Vortex

Baffles

D/2

18 in.(450 mm)

Typical

D

18 in. (450 mm)Typical

DP5BF4





Figure 5Sample Problem - Atmospheric Pipestill Distillate Drum

(Customary Units)

Inlet Nozzle (1) Inlet Nozzle (1)Vent (2)Vapor Outlet

Nozzle

14 in. 24 in.

13 in.

48 in.

10 in.

10 in.

6 in.

14 in.

14 in.

26 in.

12 in.

ELL

HLL

LILHIL

LLL

47 ft.

23 ft. 6 in.Min.

2 ft. 7 in.

4 ft. 11 in.

13 ft. 0 in.

HydrocarbonOutlet Nozzle

WaterOutlet Nozzle

Anti-VortexBaffles

DP5BFA

Notes:(1) Short radius elbows should be used for this service.(2) Provide one manhead at end opposite to vent nozzle. Manhead and vent should be designed according to criteria given in

GP 05-01-01.



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FIGURE 5BSample Problem - Atmospheric Pipestill Distillate Drum (Metric Units)

Inlet Nozzle (1) Inlet Nozzle (1)Vent (2)Vapor Outlet

Nozzle

350

350

14000

7000

600

250

1225

250

150Anti-Vortex

Baffles

WaterOutlet Nozzle

HydrocarbonOutlet Nozzle

Min.

ELL

HLLLLL

HILLIL

4000

800

1515

360

655

360310

DP5BFB

Notes:(1) Short radius elbows should be used for this service.(2) Provide one manhead at end of drum opposite to vent nozzle. Manhead and vent should be designed according to criteria

given in GP 05-01-01.(3) All dimensions are in mm.

dp05b

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