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ExxonMobil ProprietaryFRACTIONATING TOWERS Section Page

JET TRAYS III-D 1 of 31

DESIGN PRACTICES December, 2001


CONTENTSSection Page

SCOPE ............................................................................................................................................................3

REFERENCES.................................................................................................................................................3

BACKGROUND...............................................................................................................................................3

DEFINITIONS ..................................................................................................................................................3

APPLICATION.................................................................................................................................................3

BASIC DESIGN CONSIDERATIONS..............................................................................................................4TRAY SPACING......................................................................................................................................4TOWER DIAMETER................................................................................................................................5ULTIMATE CAPACITY............................................................................................................................5NUMBER OF LIQUID PASSES...............................................................................................................5DOWNCOMER SIZING...........................................................................................................................6DOWNCOMER CLEARANCE.................................................................................................................6DOWNCOMER SEALING .......................................................................................................................6TRAY LAYOUT, TAB AREA, AND OUTLET WEIR HEIGHT ..................................................................7TAB LAYOUT AND BLANKING...............................................................................................................7WEEPING, DUMPING AND SPRAY REGIME OPERATION..................................................................7TRAY HYDRAULICS...............................................................................................................................7OVERALL EFFICIENCY AND HEAT TRANSFER ..................................................................................7START-UP CONSIDERATIONS .............................................................................................................8DRAWING NOTES..................................................................................................................................8

DETAILED DESIGN PROCEDURE.................................................................................................................8VAPOR AND LIQUID LOADINGS (STEP 1) ...........................................................................................8TRIAL TRAY SPACING, SIZE AND LAYOUT (STEP 2) .........................................................................8FINAL TRAY SPACING, SIZE AND LAYOUT (STEP 3) .........................................................................9TRAY HYDRAULICS AND DOWNCOMER FILLING (STEP 4)...............................................................9OVERALL EFFICIENCY (STEP 5) ..........................................................................................................9BALANCED DESIGN (STEP 6).............................................................................................................10TOWER CHECKLIST (STEP 7) ............................................................................................................10

NOMENCLATURE.........................................................................................................................................10

COMPUTER PROGRAMS ............................................................................................................................11

Changes shown by ➧

ExxonMobil ProprietarySection Page FRACTIONATING TOWERS

III-D 2 of 31 JET TRAYSDecember, 2001 DESIGN PRACTICES


CONTENTS (Cont)Section Page

APPENDIX ....................................................................................................................................................12

JET TRAY CALCULATION FORM (CUSTOMARY).....................................................................................20

JET TRAY CALCULATION FORM (METRIC) ..............................................................................................26

TABLESTable 1 Jet Tray Design Principles (Metric Values Are In Parentheses).................................12

FIGURESFigure 1A KHL Factor For Jet Flood Equation (Customary Units) ...............................................14Figure 1B KHL Factor For Jet Flood Equation (Metric Units) ......................................................14Figure 2 Standard Surface Tension, σSTD (Same for Customary and Metric Units) ................15Figure 3 Kσµ Factor For Jet Flood Equation (Same for Customary and Metric Units) .............15Figure 4A Allowable Downcomer Filling For Jet Trays - All Systems (Customary Units)...........16Figure 4B Allowable Downcomer Filling For Jet Trays - All Systems (Metric Units) ..................16Figure 5A Overall Efficiency For Jet Trays In Hydrocarbon Service (Customary Units) .............17Figure 5B Overall Efficiency For Jet Trays In Hydrocarbon Service (Metric Units).....................17Figure 6 Pressure Balance For A Two-Pass Jet Tray (Same for Customary and Metric) ........18Figure 7 Jet Tab Details ...........................................................................................................19

Revision Memo12/01 Highlights of this revision are:

Specified a minimum tray deck thickness of 0.104 in. (2.8 mm).Included table of operating experience under APPLICATION.





SCOPEThis section covers the techniques for specifying the process design features of jet trays. Detailed mechanical design and tabarrangement are normally handled by the tray fabricator. A calculation form showing the step-by-step calculation procedure isgiven in the APPENDIX for both customary and metric units. Section III-A should also be consulted since it contains keydefinitions and figures that explain many of the basic concepts used when designing trays. For the design of tray-related towerinternals, such as nozzles, drawoff boxes and reboiler connections, refer to Section III-H. For jet trays in heat transfer service,the method given in Section III-F should be used to calculate the required number of trays.

REFERENCESSome of the following literature has been used in the preparation of this section. The rest is listed for convenient reference.

GLOBAL PRACTICEGP 5-2-1 Internals for Towers and Drums

OTHER LITERATUREO’Bara, J. T., Heat Transfer Coefficients for Jet Tray Pumparounds, ER&E Report No. EE.14ER.70, May 1, 1970.Colwell, C. J., New Direct Contact Heat Transfer Correlations for Towers, ER&E Report No. EE.98E.76, September, 1976.Niedzwiecki, J.L., Computer Program Update, Jet Tray Design Program #3019, CPEE-7, December, 1989.Pagendarm, S.M., PEGASYS Jet Tray Program Validation Cases, 97CET 073, May 20, 1997.

BACKGROUNDJet trays have been used in the petroleum and chemical process industries since the early 1950’s. Because of their high vaporand liquid handling capacity and low cost, they replaced bubble cap trays in many services. Since the mid-1960’s, however, jettrays have been superseded by sieve trays and packing, which are more cost effective and have wider flexibility for mostservices. Nevertheless, jet trays are still important where very high liquid handling capacity is required, such as in thepumparound sections of various heavy hydrocarbon fractionators operating near atmospheric pressure.

DEFINITIONSSee Section III-A for an in-depth discussion of many of the basic concepts used when designing trays. Also see theNOMENCLATURE part of this section for the definition of specific terms.

APPLICATIONFor most new distillation towers, sieve trays or packing are usually the best choice (see Section III-A). However, jet trays arerecommended for heat transfer services, especially where high liquid loadings might require 3 or 4-pass sieve trays and hencecomplex transitions. For those cases, single or double-pass jet trays may be better. These services include pumparounds inatmospheric pipestills; cat, coker and steam cracker primary fractionators; and visbreaker fractionators.Jet trays should not be used in the following cases:

• Where the liquid rate is below 4 gpm/inch of diameter per pass (10 dm3/s/m of diameter/pass). Liquid rates below thisvalue may result in spray regime operation with a consequent loss in tray efficiency.

• In towers less than 7 ft (2100 mm) in diameter. In these towers, the tray bubble area will become relatively small becauseof the downcomer area required. This narrow bubble area, in turn, can result in high localized vapor velocities, which mayincrease entrainment and cause premature flooding.

• In vacuum towers because of their inherently high pressure drop and poor efficiency due to the low liquid rates usuallyencountered in these units.




APPLICATION (Cont)➧ The table below, which is based on operating experience, lists the lower and upper operating limits for most jet tray designs. If

your case does not fall within these limits, contact your FRACTIONATION SPECIALIST to see what, if any, problems mayexist.

VARIABLE LOWER LIMIT UPPER LIMITPressure, psia (kPa) 15 (104) 100 (690)Temperature, °F (°C) 65 (18) 800 (430)Diameter, ft (mm) 7 (2100) 46 (14,020)Physical properties

surface tension, dyne/cm (mN/m)liquid viscosity, cP (mPa⋅s)vapor density, lb/ft3 (kg/m3)liquid density, lb/ft3 (kg/m3)

2.4 (2.4)0.07 (0.07)0.077 (1.2)

28 (450)

72 (72)1 (1)

2.3 (37)62 (1000)

Tray Spacing, in. (mm) 18 (460) 48 (1220)Open Area as % of Ab 5% 30%DC Clearance, in. (mm) 1 (25) 3.5 (90)DC inlet area as % of As 6.8% *Number of passes 1 2Outlet weir height, in. (mm) 0 (0) 0 (0)Tab size, in. (mm) 2 (50) ** 2 (50)

Flow path length, in. (mm) 16 (410) * 209 (5310) *

* Jet trays should be designed so that the sum of the downcomer inlet area (Adi) and outlet area (Ado) is less than45% of the superficial tower area (As). Remember that the tower diameter must be within the allowable rangespecified in the table.

** 1 in. (25 mm) jet tabs have been used in at least one service. This tab size is not recommended for designs sincethere is an increased fouling risk with small tabs.

BASIC DESIGN CONSIDERATIONSThe procedure outlined in this section for designing new towers involves calculating a trial diameter, tray spacing, anddowncomer area, and then checking and revising (if necessary) this trial design for ultimate capacity, jet flooding anddowncomer filling. This procedure results in a tray design which should not be subject to excessive entrainment, weeping,dumping or operation in the spray regime. The same criteria can be used for rating existing jet trays. For a discussion of thevarious types of tray limitations, see Section III-A. The equation numbers shown in the text correspond to their location on theJET TRAY CALCULATION FORM presented in the APPENDIX.

TRAY SPACINGThe optimum combination of tray spacing and tower diameter is the one which minimizes total tower investment, subject to thecondition that tray spacing must be high enough to permit access for maintenance.Minimum tray spacings, which are based on maintenance considerations, are tabulated under DETAILED DESIGNPROCEDURE, as a function of tower diameter and service. No vapor capacity credit is allowed for tray spacings above 36inches (900 mm) except for steam cracker primary fractionators. See also the discussion of downcomer filling under TRAYHYDRAULICS, and Table 1 in the APPENDIX.





BASIC DESIGN CONSIDERATIONS (Cont)

TOWER DIAMETERIn addition to the criteria discussed below under DOWNCOMER SIZING, DOWNCOMER CLEARANCE and DOWNCOMERSEALING, the tower must provide enough cross-sectional area to avoid entrainment per the following jet flood equation.

( )( )

V / AV / A

100 90%L b actual

L b allowable

�

�

��

�

�

��

× ≤

VA

K KL

b allowHL

�

��

�

�� = σµ (Customary or Metric) Eq. (3a5)

where: VL = Vapor load, ft3/s (m3/s)

Ab = Bubble area, ft2 (m2)

KHL = Tray spacing - liquid rate factor, Figure 1A or 1B

Kσµ = Surface tension - viscosity factor, Figure 3

KHL, the tray spacing-liquid rate factor, has been developed from commercial data. It can be read directly from Figure 1A or1B or calculated from Eq. (3a2) or (3a3) found on the JET TRAY CALCULATION FORM.

Note: Because of the unique physical properties of the materials being handled, steam cracker primaryfractionators should be designed using a special KHL factor. This factor is shown as Eq. (3a4) on the JET TRAYCALCULATION FORM. In addition, for tray spacings between 36 and 48 in. (914-1220 mm) the KHL factor at 36 in.(914 mm) should be corrected upward by multiplying by (H/36)0.5 or (H/914)0.5 (metric). No capacity credit should betaken for tray spacings greater than 48 in.,(1220 mm). These two comments are specific to steam cracker primaryfractionators ONLY and are not applicable to other services.

The system property factor, Kσµ , is plotted on Figure 3. This correlation is based on data from a number of hydrocarbontowers.Since the jet flood Eq. (3a5) is empirical, capacity data for the type of tower being designed should be used whenever possible.This is especially true when revamping towers that are heavily loaded.

ULTIMATE CAPACITYEq. (2c1) (below) gives the limiting vapor load for ultimate capacity. See the NOMENCLATURE section for the definition of thevariables. The ratio of design vapor load, VL, to the vapor load for ultimate capacity VL(Ult) must be kept below 90%. Ifnecessary, the tower diameter must be increased, even though Eq. (3a5) on jet flood has already been satisfied. However, thediameter calculated from Eq. (3a5) usually provides sufficient free area to satisfy the ultimate capacity limitation.

V A1L(Ult) f

L

L V

0.25

=+

�

��

�

�� −�

��

�

��C1

ββ

σρ ρ

Eq. (2c1)

where: βρ ρ

ρ= 1.4 L V

V

0.5−�

��

�

��

C1= 0.62 for Customary units (0.378 for Metric units)

NUMBER OF LIQUID PASSESMultiple-pass jet trays are less likely to be needed than is the case with other types of trays, because jet trays have aninherently high liquid handling capacity. This characteristic results from the horizontal component of the vapor velocity, as thevapor leaves the tab openings. This vapor jet action helps to propel the liquid across the tray. Therefore, when two-pass jettrays are required in a tower, it is because other types of trays in the adjacent sections of the tower are multiple-pass trays, notbecause single-pass jet trays would have been overloaded. When two-pass jet trays are used, no credit should be taken forextra vapor handling capacity. If the liquid rate exceeds 24 gpm/inch of diameter/pass (60 dm3/s/meter of diameter/pass) or if 3or 4 pass jet trays are proposed, contact your FRACTIONATION SPECIALIST for advice.





DOWNCOMER SIZINGThe required downcomer inlet area is set by froth disengaging limitations. If insufficient area is provided, downcomer chokingmay back up froth onto the tray and cause premature flooding. The downcomer entrance velocity should be limited to amaximum of 0.35 ft/s (0.105 m/s), based on vapor-free liquid at operating conditions. For foaming or high-pressure systems(300 psig; 2070 kPa gauge or higher), this value should be reduced to 0.2 ft/s (0.06 m/s). For a straight downcomer, thesevalues automatically apply to the outlet as well. For the sloped or stepped downcomer, the outlet velocity should not exceed0.6 ft/s (0.18 m/s) for non-foaming systems and 0.4 ft/s (0.12 m/s) for foaming systems.To prevent choking of the downcomer inlet by the rapidly moving froth, an anti-jump baffle should be provided for center(inboard) downcomers. To insure good liquid distribution, the length of the downcomer apron must be at least 65% of the towerdiameter. This means that the downcomer outlet area (hence, the tray inlet area) must be at least 6.8% of the tower superficialarea, As. If the downcomer inlet area required to satisfy the velocity criteria exceeds 12% of As, then the outlet of a straightdowncomer would be oversized and a sloped or stepped downcomer should be considered. For revamps, consider specifyingmodified arc downcomers in order to maximize tray bubble area and vapor handling capacity. The above stated downcomerinlet velocities for straight downcomers must be satisfied with modified arc downcomers. The minimum rise criteria must alsobe satisfied. Center and off-center downcomers for 2 pass and multipass trays should maintain a minimum inlet width of 8 in.(200 mm). Sloped or stepped center (and off-center) downcomers should have a minimum outlet width of 6 in. (150 mm).At high liquid loadings, the required downcomer areas can become a large percentage of the tower area. Hence, there may notbe enough bubble area to provide a good tab layout. If the sum of the required downcomer inlet and outlet areas is greaterthan 45% of As, the tower diameter should be increased.See Section III-K for geometrical relationships of chords and circles to help calculate downcomer area, weir length, etc. Inaddition, the PEGASYS Geometry, Segments of Circles option can be used to determine geometric relationships.

DOWNCOMER CLEARANCEThe downcomer clearance is the vertical distance between the bottom edge of the downcomer apron and the tray deck. Thisclearance is based on a normal head loss (pressure drop) of 0.5 to 1.5 in. (13 to 38 mm) of hot liquid, according to thesubmerged weir formula [Eq. (4d1)] shown on the JET TRAY CALCULATION FORM. The clearance should be no smallerthan 1 in. (25 mm). In those cases where high liquid rates would require use of either a large downcomer clearance (over 3 in.[75 mm]) or a deep recessed inlet box, a shaped downcomer lip (see Section III-A) may be used instead. For a 2 in. (50 mm)shaped lip downcomer, the coefficient in the submerged weir formula [Eq. (4d1)] is reduced from 0.06 to 0.02 (customary); 160to 53 (metric). However, a shaped downcomer lip must not be used when either a recessed inlet box or an inlet weir has beenspecified. This is because the obstruction presented by the vertical face of the recessed inlet box, or by the inlet weir, wouldcause turbulence and defeat the purpose of the shaped downcomer lip.

DOWNCOMER SEALINGTo prevent some of the vapor from bypassing a tray by traveling up the downcomer, the downcomer must be sealed to within0.25 in. (6 mm) by the liquid on the tray below. Therefore, it is necessary to check the sum of the clear liquid height (hc) at theinlet to the tray and the head loss (hud), under the downcomer at the minimum liquid flow rate. This sum plus 0.25 in. (6 mm)should at least equal the downcomer clearance. If sealing is not obtained, consider one of the following steps to seal thedowncomer: adding an inlet weir, using a recessed inlet box, using a smaller clearance with a shaped lip, or decreasing thedowncomer clearance [down to a minimum of 1 in. (25 mm)]. The designer must check that the downcomer filling does notbecome excessive at design rates.The maximum depth for a recessed box is 6 in. (150 mm). However, recessed inlet boxes should be avoided at liquid ratesgreater than 11 gpm per inch of diameter per pass (28 dm3/s/m of diameter/pass). At such high liquid rates, the reversal indirection of flow under the bottom edge of the downcomer causes a high liquid buildup just downstream of the recessed box.This high inlet head, in turn, promotes dumping through the inlet rows of tabs. Under these conditions, a better solution is touse a shaped downcomer lip.The use of a shaped downcomer lip should be considered if a very wide range of liquid rates must be handled. The shapeddowncomer lip provides a lower head loss for a given clearance than does the standard sharp-edged downcomer. Asmentioned earlier, however, it should not be used if either a recessed box or an inlet weir has been specified.






TRAY LAYOUT, TAB AREA, AND OUTLET WEIR HEIGHTImportant features of the tray layout are the bubble area Ab (Section III-A, Figure 12, Bubble Area Definitions) and the freearea Af (Section III-A, Figure 13, Free Area Definitions). These, in turn, depend on the liquid handling areas (downcomers)and waste area, Aw. The waste area, Aw, is defined as any unperforated area farther than 3 in. (75 mm) away from the nearesttab. Normally, there is no waste area on a jet tray, unless a very low tab area is required (part of the tray is left unperforated).The bubble area, Ab, and the vapor velocity Vo through the tabs have been shown to strongly influence plate efficiency andheat transfer. High velocities through the tabs and low ratios of tab area to bubble area lead to improved tray performance.This optimum can best be achieved if the tray is designed for a dry tray pressure drop (hed) between 3 and 6 in. of hot liquid (75to 150 mm) if permitted by the tray hydraulics. However, the tab area should not be less than 5% of the bubble area, Ab. The2 in. (50 mm) nominal size tab should be used for all new jet tray designs. The tab area in ft2 (m2) can be calculated forrevamps by multiplying the number of tabs by 0.0248 (0.0023). For tab details see Figure 7.Outlet weirs are not specified for new jet trays although they may exist on a few towers. Visual observations in an air/watersimulator indicate that an outlet weir has almost no effect on jet tray hydraulics. The liquid is lifted off the tray deck and thrownover the weir by the horizontally entering vapor (see Figure 6). Thus, the outlet weir does little to maintain liquid on the tray forholdup or downcomer sealing purposes. However, a term has been included in Eq. (4a1) on the JET TRAY CALCULATIONFORM, to give a conservative value for downcomer filling calculations in the rare event an outlet weir has been provided.

TAB LAYOUT AND BLANKINGA detailed tab layout is not shown in ExxonMobil Design Specifications since this is handled by the vendor. The vendor willalso set the number and location of major and minor trusses when the detailed mechanical design of the tray is performed.However, the vendor should be told the tab area required along with the open area per tab [0.0248 ft2/tab (0.0023 m2/tab)] andshould be given a sketch similar to the one in Figure 6B, Section III-A (Typical Tray Layout) showing the general traydimensions.It is sometimes necessary to blank tabs to maintain high efficiency in sections of towers where the vapor loadings changemarkedly. For new designs, the vendor should be told to preferentially blank tab rows downstream of the minor trusses sincethese rows tend to weep first. For revamps, the designer should also blank these rows first. The blanking should be placed onthe underside of the tray deck. Do not blank more than half the tabs on a tray without consulting your FRACTIONATIONSPECIALIST for assistance.

WEEPING, DUMPING AND SPRAY REGIME OPERATIONSpray regime operation should not occur if the liquid rate is kept above 4 gpm per inch of diameter per pass (10 dm3/s/m ofdiameter/pass) and the dry tray pressure drop is kept below 6 in. (150 mm) of hot liquid. To minimize weeping and dumping,the dry tray pressure drop at minimum vapor rates must equal or exceed 1.0 in. (25 mm) of hot liquid.

TRAY HYDRAULICSThe optimum dry tray pressure drop will generally fall in the range of 3 to 6 in. (75 to 150 mm) of hot liquid. The effect on trayhydraulics and downcomer filling of increasing dry tray pressure drop (decreasing tab area) can be calculated from Step 3b onthe calculation form.Downcomer filling, as a percent of tray spacing, should not exceed the values given in Figure 4a or 4b as a function ofpressure. Otherwise, the tray spacing and/or the tower diameter should be increased.If two-pass trays are used, anti-jump baffles must be provided on all inboard downcomers, to prevent liquid from jumpingacross (choking) the inboard downcomer, with consequent premature flooding. (See Figure 6 of this section and Figure 14 ofSection III-A.)

OVERALL EFFICIENCY AND HEAT TRANSFERFor most new designs, jet trays will only be used in the heat transfer sections of heavy hydrocarbon towers. For these cases,the number of trays should be determined by the methods in Section III-F.For revamps, the vapor-liquid mixing energy factor, Fe, given below should be equal or close to 70 (85 in metric units) in orderto optimize tray efficiency. Under these conditions, the efficiency will be roughly 20 percentage points less than that of a sievetray in the same service. Figures 5a and 5b give jet tray efficiencies as a function of Fe and the fluidity of the tray liquid.Whenever possible, however, past experience should be used as a guide for determining efficiency.

[ ]FVA / Aeo v

0.5

o b=

ρ(Customary or Metric) Eq. (3c1)





START-UP CONSIDERATIONSAt very low vapor velocities (such as during start-up), jet trays normally dump, with the result that no liquid level is maintainedon the tray. Hence, when revamping jet tray towers that contain thermosyphon reboilers, special provisions must be made sothat the reboiler will have liquid feed during start-up. This can be done by:• Providing a chimney tray as the drawoff tray (see Section III-H).• Installing a jumpover line from the tower bottoms drawoff line to the reboiler inlet. This jumpover must have a valve, so

that it can be closed when the reboiler is generating enough vapor to support the liquid on the drawoff tray.• For design of drawoffs and towers internals, see Section III-H.

➧ DRAWING NOTESThe following notes should be considered for inclusion on the tray drawing or specification.1. GP 5-2-1 shall be followed.2. The tab area per tray shall be ____. The jet tabs shall be constructed to the details shown in GP 5-2-1 with a tab area per

tab equal to 0.0248 ft2/tab (0.0023 m2/tab).3. A minimum tray deck thickness of 0.104 in. (2.8 mm) should be specified.4. Details of blanking pattern, if required (see TAB LAYOUT AND BLANKING).

DETAILED DESIGN PROCEDUREThe step-by-step procedure for designing a jet tray is given on the JET TRAY CALCULATION FORM (Customary or Metric) inthe APPENDIX. Basically, the procedure involves assuming a trial design with the help of the principles given above, checkingit against various potential operating limitations, and then modifying it as required to arrive at the optimum tray design.Deciding how to modify the trial design (changing diameter, spacing, downcomer size, etc.) will require judgment andapplication of the basic design considerations already discussed. The calculation step numbers and equation numbers referredto below are the same as those used on the calculation forms.

VAPOR AND LIQUID LOADINGS (STEP 1)This information is normally calculated as part of the heat and material balances for the tower and usually comes from acomputer program like PRO/II. If minimum liquid and vapor loadings have not been specified, assume 70% of the designloadings. Vapor loadings to the tray in question along with liquid loadings from the tray should be used, since these are nearlyalways the maximum values.

TRIAL TRAY SPACING, SIZE AND LAYOUT (STEP 2)Downcomer Areas. The velocity of the vapor-free liquid entering the downcomer should be limited to a maximum of 0.35 ft/s(0.105 m/s). For foaming or high pressure (greater than 300 psig; 2070 kPa gauge) systems, use 0.2 ft/s (0.06 m/s). This setsthe downcomer area(s) to be used for the first trial. However, tower diameter considerations further on in the design proceduremay require the downcomer area(s) to be increased.Tray Spacing. A low tray spacing [between 18 and 24 in. (450 and 600 mm)] is often the most economical. For the first trial, atray spacing of 24 in. (600 mm) or that shown below (whichever is larger) should be used. The values given below are theminimum, as determined by considerations of maintenance and depth of support beams. In special cases, smaller spacings[but not less than 18 in.; (450 mm)] can be used; but this makes maintenance very difficult and some chemical plants andrefineries may not permit smaller spacings. Downcomer filling requirements may dictate the use of a tray spacing larger thanthe minimum. Also, tray spacings of 27 to 36 in. (675-900 mm) are commonly used in pumparounds to provide extra capacity.This is done so that the pumparound section does not increase tower diameter over that required by adjacent sieve traysections. Spacings up to 36 in. (900 mm) may be used to permit a higher superficial vapor velocity.





DETAILED DESIGN PROCEDURE (Cont)

MINIMUM TRAY SPACING

CLEAN SERVICE FOULING SERVICE

TOWER DIAMETER, ft (mm) in. mm in. mmOver 7 to 7.5 (Over 2100 to 2250) 18* 450 21* 525Over 7.5 to 10 (Over 2250 to 3000) 18* 450 24 600Over 10 to 16.5 (Over 3000 to 5000) 21* 525 27 675Over 16.5 (Over 5000)** 24 600 30 750

* Minimum tray spacing with a manhead present is 24 in. (600 mm).** For towers larger than about 20 ft (6000 mm) in diameter, “lattice” type trusses should be used to facilitate

maintenance and promote good vapor distribution.Trial Tray Size. The trial diameter (Dtr) is calculated from the superficial area, As, which is determined by Eq. (2b5). At thispoint, Adi and Ado (Step 2a) should be checked to make sure that Ado ≥ 0.068 As. If Adi > 0.12 As, consider a sloped or steppeddowncomer. If the sum of Adi + Ado exceeds 45% of As, the tower diameter should be increased. If necessary, increase towerdiameter and correct KHL and Dtr. Also, Dtr should equal or exceed 7 ft (2100 mm) for new towers.Number of Liquid Passes. Jet trays will normally be single-pass, unless adjacent trays in the tower are multipass. However,the calculation form has been set up to handle multipass trays, if needed.Ultimate Capacity. The vapor load corresponding to ultimate capacity is calculated from Eq. (2c1). The ratio of design toultimate capacity vapor load must be kept below 90%.

FINAL TRAY SPACING, SIZE AND LAYOUT (STEP 3)Tower Areas. Use the last value of Dtr calculated in Step 2(b) or 3(a) for the final tower diameter.Tab Details. For the first trial, the dry tray pressure drop, hed, is calculated from a value of the vapor velocity Vo, based on thetab area Ao calculated in Step 3(b). If this value of hed is acceptable (in the range of 3 to 6 in. [75 to 150 mm] of hot liquid),proceed directly to the next calculation step. However, if hed exceeds the recommended limit of 6 in. (150 mm) or if otherconsiderations (e.g., limited pressure drop across the tower) require a smaller value of hed, it will be necessary to recalculateVo, [Eq. (3b2)] and Ao, [Eq. (3b3)].The dry tray pressure drop should also be checked at minimum vapor rates to insure that excessive weeping is not a problem.To minimize weeping, hed(min) should be ≥ 1.0 in. (25 mm) of liquid at conditions. If it is not, reduce Ao and recalculate hed(min)and hed. If both criteria cannot be met simultaneously [6 in. maximum at design rate, 1 inch minimum at minimum rate (150mm and 25 mm respectively)] consult your FRACTIONATION SPECIALIST.Downcomers and Weirs. The length of the downcomer apron at the bottom of the downcomer should be checked to be surethat it is at least 65% of the final tower diameter. Consider a sloped or stepped downcomer if Adi > 0.12 As. In addition, fortwo-pass trays, the width of the inboard downcomer must be at least 8 in. (200 mm). Sloped or stepped center (and off-center)downcomers should have a minimum outlet width of 6 in. (150 mm). For tray geometry relationships, see Design Practice IIISection K.Mixing Energy. Check only when revamping existing distillation towers - ignore for pumparounds. If the mixing energy givesan undesirably low efficiency, hed should be increased (within the limitations discussed above) and the appropriate portions ofStep 3(b) recalculated. If there is no room for a higher hed in the design at this point, a moderate efficiency debit may have tobe accepted. (See Figure 5A or 5B).

TRAY HYDRAULICS AND DOWNCOMER FILLING (STEP 4)The sum of the clear liquid height (hc) at the inlet to the tray and the head loss under the downcomer (hud) plus 0.25 in. (6 mm)must be checked at the minimum liquid flow rates to ensure that it equals or exceeds the downcomer clearance, therebysealing the downcomer. If a seal is not obtained, consider the use of an inlet weir, a recessed inlet box, a smaller downcomerclearance, or a shaped downcomer lip. For tray geometry relationships, see Section III-K or use the PEGASYS Geometry,Segments of Circles option.If the criteria for downcomer filling as a percent of the tray spacing is exceeded, it will probably be necessary to increase thetray spacing, rather than make other adjustments to decrease tray pressure drop.

OVERALL EFFICIENCY (STEP 5)For new designs, jet trays are only recommended for heavy hydrocarbon heat transfer service. The number of trays in thisservice is set by heat transfer requirements (see Section III-F). If an old jet tray distillation tower is being revamped, then the




procedure given below can be used. However, past studies have shown that it is usually more cost effective to replace the jettrays with sieve trays or packing.

DETAILED DESIGN PROCEDURE (Cont)The overall efficiency (Figures 5a and 5b) and the required number of theoretical trays determine the minimum number ofactual trays. However, this correlation should be used for hydrocarbon distillation systems only. For non-hydrocarbonservices, the overall efficiency used should be based on past operating data, or your FRACTIONATION SPECIALIST should beconsulted for the proper efficiency.In deciding how many actual trays to specify for a given design, questions of design conservatism and flexibility must also beconsidered.

BALANCED DESIGN (STEP 6)Even when a new tray design or revamp meets all the above criteria, the designer should check to see if the design is as“balanced” as possible. That is, the “ideal” balanced design would have the jet flood velocity, the downcomer entrance velocityand downcomer filling all at approximately the same percentage of their respective limits (e.g. say 85% of the maximum jetflood, 85% of the allowable downcomer entrance velocity, and 85% of the allowable downcomer filling limits respectively). Thisprevents building a potential bottleneck into a tower and permits the unit to be pushed to its maximum by plant personnel. Thedesigner should consider running parametric PEGASYS computer cases to balance a design rather than carrying out severallengthy calculations by hand.

TOWER CHECKLIST (STEP 7)Table 7 of Section III-A [Tower Design Checklist (Trays)] contains a detailed tower checklist that should be reviewed for allnew designs as well as revamps.

NOMENCLATUREAb = Bubble area, ft2 (m2)Adi = Downcomer inlet area, ft2 (m2)Ado = Downcomer outlet area, ft2 (m2)Af = Average tower free area, ft2 (m2)

For multipass trays use the smallest value of Af. (See Figure 13, Design Practice III Section A, Free AreaDefinitions)

Ao = Tab area, ft2 (m2)As = Superficial (total) tower cross-sectional area, ft2 (m2)Aw = Waste area, ft2 (m2)c = Clearance between tray and downcomer apron at tray inlet, in. (mm)C1 = Constant used in Eq. (2c1)DT = Tower diameter, ft (mm)Dtr = Trial tower diameter, ft (mm)Eo = Overall Efficiency, %

Fe = Mixing energy factor = V ( )A / A

'o v0.5

o b

ρ Equation is the same for Customary and Metric but thenumerical values differ. See Figures 5A and 5B.

H = Tray spacing, in. (mm)hc = Clear liquid height on tray, in. (mm) of hot liquidhd = Downcomer filling, in. (mm) of hot liquidhed = Dry tray pressure drop, in. (mm) of hot liquidhi = Tray inlet head, in. (mm) of hot liquidht = Total tray pressure drop, in. (mm) of hot liquidhud = Head loss under downcomer, in. (mm) of hot liquidhwi = Inlet weir height, in. (mm)hwo = Outlet weir height, in. (mm)hwt = Wet tab pressure drop, in. (mm) of hot liquid





KHL = Tray spacing - liquid rate factor, dimensionless (see Figures 1A and 1B)Kσµ = Surface tension - viscosity factor, dimensionless (See Figure 3)

NOMENCLATURE (Cont)L′ = Liquid rate, gpm/inch of diameter/pass (dm3/s/m of diameter/pass)LL = Liquid load, ft3/s at conditionsLL(min) = Liquid load at minimum rate, ft3/s at conditionsLs = Liquid rate, gph/ft2 of tower cross-sectional area (dm3/s/m2/s)Ii = Inlet weir length, in. (mm)Io = Outlet weir length, in. (mm) (See Figure 12 in Section III-A, Bubble Area Definitions)Iud = Length of bottom edge of downcomer apron, in. (mm) (See Figure 12 in Section III-A, Bubble Area Definitions)Np = Number of liquid passesNT = Number of theoretical traysP = Pressure, psia (kPa abs)QL = Liquid rate, gpm (dm3/s) at conditionsqv = Volumetric vapor rate, ft3/s (m3/s)Vb = Vapor velocity based on tower bubble area, ft/s (m/s)Vdi = Downcomer inlet velocity, ft/s (m/s)Vdo = Downcomer outlet velocity, ft/s (m/s)

VL = Design vapor load = qvv

L v

0.5ρ

ρ ρ−�

��

�

�� at conditions, ft3/s (m3/s)

VL(Ult) = Ultimate capacity vapor load, dependent on system properties, ft3/s (m3/s) at conditionsVL(min) = Vapor load at minimum vapor rate (for flexibility calculations), ft3/s (m3/s) at conditionsVo = Vapor velocity through the tabs, ft/s (m/s)wL = Liquid rate, klb/hr (kg/s)wv = Vapor rate, klb/hr (kg/s)µL = Liquid viscosity at conditions, cP (mPa⋅s)ρL = Liquid density at conditions, lb/ft3 (kg/m3)ρv = Vapor density at conditions, lb/ft3 (kg/m3)σL = Liquid surface tension at conditions, dynes/cm (m N/m)σSTD = Standard surface tension, dynes/cm (mN/m) (see Figure 2)

COMPUTER PROGRAMSFor up-to-date information on available computer programs and how to use them, affiliate personnel should contact theirFRACTIONATION SPECIALIST. A site’s TECHNICAL COMPUTING CONTACT can also provide help on accessing availableprograms. The jet tray programs can be accessed through three sources.

AVAILABLE PROGRAMS

Source Program Name or Number Version Number

PEGASYS Fractionating Towers, Jet Trays 2.4

PRO/II Jet Tray Program 2.4

The Jet Tray programs utilize the design equations contained in this section, Table 1, and the equations on the JET TRAYCALCULATION FORM. They can be used for both designing new towers or trays, and rating existing trays. Existing traydesigns can be rated by specifying some or all of the tray hardware dimensions. The programs also include an option tocalculate jet tray heat transfer requirements for heavy hydrocarbon pumparounds (see Section III-F).




APPENDIX

TABLE 1JET TRAY DESIGN PRINCIPLES

(Metric Values are in Parentheses)

DESIGN FEATURE SUGGESTEDVALUES

ALLOWABLERANGE COMMENTS

1. Tray Spacing, in (mm) 24 to 36(600 to 900)

18 to 36 (460 to900) [up to 48

(1200) for steamcracker

fractionators]

It is generally economical to use minimum values, as limited bydowncomer filling or maintenance considerations. Use ofvariable spacings to accommodate loading changes from tray totray should be considered, to minimize tower height.

2. Tower Diameter, ft (mm) — 7 (2100) to 46(14,202)

Jet trays should not be used for new towers with diameters lessthan 7 ft (2100 mm).

a) Liquid rate L′, gpm/in ofdiam/pass (dm3/s/m ofdiam/pass)

— 4 to 24 (10 to 60) If L’ is less than 4 gpm/in. of diameter/pass (10 dm3/s/m ofdiameter/pass), jet trays should not be used, because of thetendency for spray regime operation to occur. If L’ is greaterthan 24 gpm/in. of diameter/pass (60 dm3/s/m of diameter/pass)your FRACTIONATION SPECIALIST should be consulted.

b) Allowable vapor velocityVb, ft/s (m/s)

— See Comments Set by Eq. (3a5). Design for 90% or less of the allowable vaporvelocity.

3. Number of Liquid Passes 1 1 or 2 The liquid handling capacity of jet trays is not significantlyaffected by the number of passes. Use single-pass trays,unless adjacent trays in the tower are multiple-pass.

4. Tab Size and Layout — —a) Tab size, in. (mm) 2 (50) 2(50) Two-in. (50 mm) tabs are normally used. See Figure 7 for

dimensions.

b) Tab area Ao, as percentof Ab

12 to 25 5 to 30 In general, the lower the percent tab area, the higher theefficiency. A tray with 20% tab area gives good efficiency andflexibility without a capacity debit for a wide range of designliquid rates. Higher tab areas may be required at very highliquid rates to prevent excessive downcomer filling. Tab areasless than 5% are not recommended, because spray regimeoperation may occur.

c) Bubble area Ab, aspercent of As

55 to 90 — Bubble area should be maximized, for good contacting. Ratiosof Ab/As less than 55% should not be used.

d) Overall efficiency See Comments See Comments In new designs, jet trays are only used in pumparound serviceswhere the number of trays is set by heat transfer requirements.When revamping existing jet trays in fractionation service, it isusually cost-effective to replace jet tray panels with sieve traypanels. Nevertheless, if the jet trays must be retained, the jettray’s overall efficiency will be about 20 percentage points lessthan that of sieve or bubble cap trays at mixing energy functions(Fe) above 70 (85). This is true provided there is not a sprayregime, flooding, or dumping limitation. For the efficiency atlower mixing energy values, see Figure 5A or 5B.

e) Blanking — — Blanking is not generally required, unless the tower is beingsized for future service at much higher rates. To maintain bestefficiency, blank uniformly within the bubble area. Preferentiallyblank rows of tabs downstream of minor trusses, because thesetabs are the most susceptible to dumping. See GP 5-2-1.





TABLE 1JET TRAY DESIGN PRINCIPLES (Cont)

(Metric Values are in Parentheses)

DESIGN FEATURE SUGGESTEDVALUES

ALLOWABLERANGE COMMENTS

5. Downcomers and Weirsa) Allowable downcomer

velocity, ft/s (m/s)0.35

(0.105)See Comments Downcomer inlet velocity should not exceed 0.35 ft/s (0.105 m/s)

for non-foaming systems or 0.2 ft/s (0.06 m/s) for foaming andhigh-pressure systems. Downcomer outlet velocity should notexceed 0.6 ft/s (0.18 m/s) for non-foaming systems and 0.4 ft/s(0.12 m/s) for foaming systems. If the sum of Adi + Ado exceeds45% of As, the tower diameter should be increased.

b) Type of downcomer Chordal See Comments Chord length should be at least 65% of the tray diameter for goodliquid distribution. Sloped downcomers can be used for highliquid rates, with maximum outlet velocity of 0.6 ft/s (0.18 m/s).Consider sloped downcomers if Adi > 0.12 As. Modified arcdowncomers can be used with jet trays as long as the maximumdowncomer inlet velocity and minimum rise criteria (10 in.[250mm] for jet trays) are satisfied.

c) Center and off-center(inboard) downcomer widthand anti-jump baffles

— 8 in. (200 mm)min.for inlet, 6in. (150 mm)min. for outlet

Whenever a two-pass tray is used, provide a 14 to 16 in. (350 to400 mm) high anti-jump baffle, suspended lengthwise in thecenter of the inboard downcomer and extending the length of thedowncomer, to prevent possible “choking” by froth entering thedowncomer from opposite sides. See Figure 14, DesignPractice III Section A, Figure 6 in this section, and GP 5-2-1.

d) Clearance underdowncomer (c), in. (mm)

1.5(38 mm)

1 (25 mm) to3.5 (90 mm)

Set the clearance to give a head loss of approximately 1 in.(25 mm). Higher values can be used if necessary to assuresealing of the downcomer. If c > 3 in. (75 mm) (because of highliquid rates), consider use of a shaped downcomer lip to reducethe head loss. See Design Practice III Section A, Figure 11.

e) Outlet weir — See Comments Jet trays do not normally use outlet weirs. See the discussionunder Basic Design Considerations.

f) Downcomer seal See Comments Inlet Weir orrecessed Inlet

Box

If, at minimum loadings, the sum of the clear liquid height on thetray and the head loss under the downcomer plus 0.25 in. (6 mm)does not exceed the downcomer clearance, reduce thedowncomer clearance to the minimum of 1 in. (25 mm)(downcomer filling permitting) or add an inlet weir or recessedinlet box, in that order of preference. Do not use a recessed inletbox if L > 11 gpm/in of diameter/pass (28 dm3/s/m ofdiameter/pass). Maximum depth for a recessed box is 6 in.(150 mm).

g) Downcomer filling, % of trayspacing

See Comments See Comments See Figures 4A and 4B of this section for the maximum percentdowncomer filling as a function of system pressure.




FIGURE 1AKHL FACTOR FOR JET FLOOD EQUATION

(CUSTOMARY UNITS)0.55

0.50

0.45

0.40

KHL

0.35

0.3024201612840

36"

33"

30"

27"

24"

Tray Spacing = 21"

KHL = 0.085H 0.5

KHL = 0.52(H/39.6)0.0252L'

L', gpm/inch of Diameter/Pass

DO NOT USE JETTRAY FOR L' < 4

DP3DF1A

FIGURE 1BKHL FACTOR FOR JET FLOOD EQUATION

(METRIC UNITS)

Tray Spacing = 500 mm

900 mm

800 mm

700 mm

600 mm

DO NOT USEJET TRAYSFOR L' < 10

L', dm3/s Per Meter of Diameter/Pass

6050403020100

0.16

0.15

0.14

0.13

0.12

0.11

0.10

0.09

0.08

0.07

KHL

KHL = 0.00514H 0.5

KHL = 0.158(H/1006)0.0101L'

DP3DF1B





FIGURE 2STANDARD SURFACE TENSION, σσσσSTD

(SAME FOR CUSTOMARY AND METRIC UNITS)

Viscosity, cP or mPa•s

0.03 .05 1054321.07 0.1 0.2 0.3 0.4 0.6 0.8

10080

60

40

20

108

6

4

2

1

σ STD = 10a

σ ST

D, d

yne/

cm (m

N/m

)

a = 1.68 - 0.2440.55µL

DP3DF2

FIGURE 3Kσµ FACTOR FOR JET FLOOD EQUATION

(SAME FOR CUSTOMARY AND METRIC UNITS)

0.6

0.5

0.7

0.80.9

1

1.5

2

K σµ

0.2 0.3 0.4 0.5 0.8 1 2 3 4

Actual/Standard Surface Tension Ratio, (σL/σSTD)

σSTDσSTD σSTD< 1.0

0.317forKσµ = Kσµ = 1.0 for

σL σLσL ≥ 1.0DP3DF3




FIGURE 4AALLOWABLE DOWNCOMER FILLING FOR JET TRAYS - ALL SYSTEMS

(CUSTOMARY UNITS)

Tower Pressure, psia

Allo

wab

le %

Dow

ncom

er F

illing

400350300250200150100500

60

55

50

45

40

35

30

Where:DCF = Allowable % Downcomer Filling p = Tower Pressure, psia

DCF = 50 for p ≤ 90 psia = 50 -0.0545 (P-90) for p>90 and ≤ 365 psia = 35 for p>365 psia

DP3DF4A

FIGURE 4BALLOWABLE DOWNCOMER FILLING FOR JET TRAYS - ALL SYSTEMS

(METRIC UNITS)

Tower Pressure, kPa300025002000150010005000

60

55

50

45

40

35

30

Allo

wab

le %

Dow

ncom

er F

illing

Where:DCF = Allowable % Downcomer Filling p = Tower Pressure, kPa

DCF = 50 for p ≤ 600 kPa = 50 - 0.0079 (P - 600) for p>600 and ≤ 2500 kPa = 35 for p>2500 kPa

DP3DF4B





FIGURE 5AOVERALL EFFICIENCY FOR JET TRAYS IN HYDROCARBON SERVICE

(CUSTOMARY UNITS)

14131211109876543210

1) For non-hydrocarbon services, consult your FRACTIONATION SPECIALIST2) Fe ≥70 provides maximum jet tray efficiency

25

30

40

50

Fe≥70

120

110

100

90

80

70

60

50

40

30

20

10

0

Ove

rall

Effic

ienc

y, E

o, %

Eo = 35.4 (FLUIDITY)0.47 - 10(1 + 10x0.958 )

DP3DF5A

Fe

Average Fluidity of Liquid on Tray (1/µL), cP-1

FIGURE 5BOVERALL EFFICIENCY FOR JET TRAYS IN HYDROCARBON SERVICE

(METRIC UNITS)

1) For non-hydrocarbon services, consult your FRACTIONATION SPECIALIST2) Fe ≥85 provides maximum jet tray efficiency

120

110

100

90

80

70

60

50

40

30

20

10

0

Ove

rall

Effic

ienc

y, E

o, %

14131211109876543210

Eo = 35.4 (FLUIDITY)0.47 - 10(1+10x0.965 )

30

40

50

60

Fe≥85

DP3DF5B

Fe

Average Fluidity of Liquid on Tray (1/µL), (mPa⋅s)-1




FIGURE 6PRESSURE BALANCE FOR A TWO-PASS JET TRAY

(SAME FOR CUSTOMARY AND METRIC)

*

Vapor

Clear Liquid

Cho

king

Dis

enga

ging

Froth

Anti-Jump Baffle

ACTUAL OPERATIONIDEALIZED OPERATION(Assumed for Calculation Purposes)

hd

hd

h*t = from calculation form

hud

hud

hwt

ht

hc

h*i

h*i h*c

h*c

h*t

h*wt

h*wt

h*d

hi

h*ud

h*i assumed* = h*c

Notes:1. Terms with asterisks (*) refer to center (inboard) downcomer, those without asterisks refer to side (outboard) downcomer.2. With slight modification, the pressure balance equation for side (outboard) downcomer filling applies also for single pass trays.3. For meanings of symbols, see NOMENCLATURE.

Pressure Balance for Center (Inboard) Downcomer Filling:

hd = (ht + hud) + h*i + 1, in (Customary) + 25,mm (Metric)

+ hi + 1, in (Customary) + 25,mm (Metric)

ρL

ρL - ρv

ρL - ρv

ρLh*d = (h*t + h*ud)

DP3DF6

h*t = from calculation form

Pressure Balance for Side (Outboard) Downcomer Filling:





➧ FIGURE 7JET TAB DETAILS

DP3Df07

Tab CLB

B

D

E

TrayPlate

SECTION THROUGH TAB CENTERLINETangent Point

Plan B-B

A

C

BF

TABLE OF DIMENSIONS

inches millimetersDimension Tolerance Dimension Tolerance

A 2 (Nominal) — 51 —B 2 + 1/8, – 0 50 + 3, – 0C 1 ± 1/64 25 ± 0.5D 2 ± 3/32 50 ± 2.5E 11/16 ± 1/32 17.5 ± 0.8F 0.104 (minimum) – 0 2.8 (minimum) – 0




JET TRAY CALCULATION FORM (CUSTOMARY)Location & Project __________________________________________________ Date_______________________________Tower Number _____________________________________________________ By ________________________________Service ___________________________________________________________

Tower Section (Top, Bottom, etc.) _______________Tray Number(s) Covered by this Design _______________Design Based on Tray Number _______________

1. Vapor and Liquid Loadings at Conditions(a) Vapor to the tray

Temperature, oF _______________Pressure, psia _______________Density, ρv, lb/ft3 ρv _______________Vapor rate, wv, klb/hr wv _______________

Vapor rate, q 1000 w3600 v

v

v=

ρ, ft3/s Eq. (1a1) qv _______________

0.5

vL qV ��

��

�

ρ−ρρ=

vL

v Eq. (1a2) VL _______________

Minimum vapor rate, wv(min), klb/hr _______________Density at minimum rates, ρv( min), lbs/ft3 _______________Minimum vapor rate, qv(min) _______________

qv(min) =1000 w3600

v(min)

v(min)ρEq. (1a3) qv(min) _______________

0.5

v(min)(min)L

(min)vv(min)L(min)

qV��

�

��

�

ρ−ρρ

= Eq. (1a4) VL(min) _______________

(b) Liquid from the trayTemperature, oF _______________Viscosity, µL, cP µL _______________Surface Tension, σL, dynes/cm σL _______________Density, ρL, lb/ft3 ρL _______________Liquid rate, wL, klb/hr wL _______________

Liquid rate, L 1000 w 3600 L

L

L=

ρ, ft3/s Eq. (1b1) LL _______________

Liquid rate, QL = LL(448.9), gpm Eq. (1b2) QL _______________Minimum liquid rate, wL(min), klb/hr _______________Density at minimum rates, ρL(min), lb/ft3 _______________

Minimum liquid rate, L1000 w3600L(min)

L(min)= L(min)ρ

, ft3/s Eq. (1b3) LL(min) _______________

Minimum liquid rate, QL(min) = LL(min) (448.9), gpm Eq. (1b4) QL(min) _______________





JET TRAY CALCULATION FORM (CUSTOMARY) (Cont)Tray number(s) _______ _______

Inboard* Outboard2. Trial Tray Spacing, Size and Layout

(a) Downcomer AreasAdi = LL/0.35, ft2 (For revamps, make sure Vdi ≤ 0.35 ft/s) Eq. (2a1) Adi _______________Ado, ft2. Set such that (LL/0.6) ≤ Ado ≤ (LL/0.35), ft2 Eq. (2a2) Ado _______________(See Design Practice III Section A, Figure 12, Bubble Area Definitions)If Adi > 0.12 As, consider a sloped or stepped downcomer.Minimum Ado or Adi = 0.068 As.For foaming or high-pressure systems, use Adi = LL/0.2

(b) Trial Tray SizeVL [from Eq. (1a2)] _______________Surface tension, σL (Step 1b)Standard surface tension, σSTD, from Figure 2 or from: σSTD = 10a where a = 1.68 – 0.244/µL 0.55 Eq. (2b1) σSTD _______________Kσµ from Figure 3 or from: Kσµ _______________

Kσµ =σ

σσ

σL

STD

L

STD for < 1.0

�

��

�

��

0.317

Eq. (2b2)

OR

Kσµ = 1.0 for L

STD

σσ

≥ 1.0 Eq. (2b3)

Tray spacing, H, inches (first trial, use 24 inches) H _______________

Trial As = V0.06 K H

L

σµ( )0.5 Eq. (2b4) As _______________

Dtr = 1.128 (As)0.5, ft Eq. (2b5) Dtr _______________Check Adi and Ado. Both must be > 6.8% of As. If necessary,correct As and Dtr.Minimum diameter for new towers is 7 ft.

(c) Ultimate CapacityAverage free area, Af, ft2 (See Figure 13, Design Practice III Section A, Free Area Definitions)

Af _______ _______

VL(Ult) = 0.62 Af 0.25

vL

L

1 �

�

��

�

ρ−ρσ

��

��

�

β+β Eq. (2c1) VL(Ult) _______ _______

Where: 0.5

v

vL1.4 ��

��

�

ρρ−ρ=β

Design vapor load, VL [from Eq. (1a2)]VL/VL(Ult), as %; must be ≤ 90% _______________If necessary, adjust tower diameter and repeat appropriate portions of Steps 2(a) and 2(b)

* For 2-pass trays.





Inboard* Outboard3. Final Tray Spacing, Size and Layout

(a) Tower Diameter and AreasNp = Number of liquid passes Np _______________

L’, GPM/inch of diameter/pass = ( ) ( )

Q12 D N

L

tr pEq. (3a1) L′ _______________

KHL from Figure 1A or from: KHL _______________KHL = 0.085 [H]0.5 Eq. (3a2)

or

KHL = 0.52 H39.6

0.0252 L'�

��

�

�� Eq. (3a3)

(Use lower value of KHL from Eq. (3a2) or (3a3) or determineappropriate KHL equation from L’ and boundary line shown onFigure 1A.)

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------KHL for Steam Cracker Primary Fractionators only

KHL = 0.553 H68.6

0.28 LS /4500�

��

�

��

+Eq. (3a4) _______________

Where: LS = 60 QA

L

S

For tray spacings > 36 in. multiply the KHL factor at36 in. by [H/36]0.5. Take no credit for spacings > 48 in.

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------Kσµ from Step 2b _______________Ab = As – Adi – Ado – Aw (if any), ft2 Ab _______________

VA

L

b allow

�

��

�

�� = KHL Kσµ Eq. (3a5) _______________

VA

L

b actual

�

��

�

�� = V

AL

b (from Eq. (1a2)) Eq. (3a6) _______________

Ratio of actual/allowable, VL/Ab, as %, must be ≤ 90%. AdjustDtr or H and repeat calculations from Step 2(c) until desiredratio is obtained. Also, check Adi and Ado as % of As.Final tower diameter, DT, ft DT _______________Final tray spacing, H, in. H _______________Superficial area, As, ft2 As _______________Estimated waste area, Aw (if any), ft2 Aw _______ _______Bubble area, Ab, ft2 (Figure 12, Design Practice III Section A) Ab _______ _______Free area, Af, ft2 (Figure 13, Design Practice III Section A) Af _______________

* For 2-pass trays.






Inboard* Outboard(b) Tab Details

Tab area, Ao (first trial use 15% of Ab; minimum tab area is 5% of Ab) Ao _______________

Tab velocity, Vo = qA

v

o [from Eq (1a1)], ft/s Vo _______________

Dry tray pressure drop, hed, in. of hot liquid

hed = 1.73 Vo2 ρρ

v

LEq. (3b1) hed _______________

If hed exceeds 6 in. of hot liquid, set hed = 6 andrecalculate Vo, ft/s.

Vo = 0.76 h ed L

v

ρρ

�

��

�

��

0.5

Eq. (3b2) Vo _______________

Ao = qV

v

o[from Eq. (1a1)], ft2 Eq. (3b3) Ao _______________

hed(min), inches - calculate hed at minimum rates. Value shouldexceed 1 in. of hot liquid to avoid weeping. If it does not,decrease Ao and recalculate hed(min) and hed to be sureboth are within acceptable range.

(c) Mixing Energy(Check only when revamping existing distillation towers - ignorefor pumparounds)

Fe = [ ]V A / A

o v

o b

0.5ρEq. (3c1) Fe _______________

Check efficiency (Figure 5A) at this value of Fe. If efficiency istoo low, increase hed (but not above 6 in.) and recalculateVo, Ao, and Fe.

(d) Downcomers and WeirsFinal downcomer inlet area, Adi, ft2 Adi _______ _______Final downcomer outlet area, Ado, ft2 Ado _______ _______Outlet weir height, hwo, in.** hwo _______ _______Outlet weir length, lo, in.** lo _______ _______Inlet weir height, hwi, in. (if any) hwi _______ _______Inlet weir length, li, in. (if any) li _______ _______Length of bottom edge of downcomer, lud, in. lud _______ _______

* For 2-pass trays. ** If outlet weir is present. Outlet weirs are NOT specified for new jet tray designs.





Inboard* Outboard4. Tray Hydraulics

(a) Clear Liquid Height, hched [from Step 3b, Eq. (3b1)] _______________L’ [from Step 3a, Eq. (3a1)] _______________

hc = 0.08 **h0.5L 2.6 + AAh 6.0 wo

2/32

b

oed +′

��

�

�

��

�

�

��

��

�Eq. (4a1) hc _______ _______

(b) Wet Tab Pressure Drop, hwthwt = 0.63 (hed)0.85 Eq. (4b1) hwt _______________

(c) Total Tray Pressure Drop, htht = hc + hwt + 1.0 Eq. (4c1) ht _______ _______

orht = hed, whichever is greater Eq. (4c2) _______ _______

(d) Head Loss Under Downcomer, hud

hud = 0.06 Qc l N

L

ud p

2�

��

�

��

Eq. (4d1) hud _______ ______

Assume c = 1.5 in. for first trial. If hud> > 1.0, increase c untilhud ≈ 1.0 in.Note: For shaped downcomers, use coefficient of 0.02 in Eq. (4d1) instead of 0.06.

(e) Inlet head, hiFor tray without an inlet weir or recessed inlet box, hi = hc. hi _______ _______For tray with inlet weir (no recessed inlet box)

hi = 0.5 wi

2/3

ip

L hl NQ +

��

�

��

�Eq. (4e1) hi _______ _______

For tray with recessed inlet box (no inlet weir or shaped lip).

hi = 0.08 3/22

b

oed L1.1

AA36h ′

��

�

�

��

�

�+�

�

��

�Eq. (4e2) hi _______ _______

or

hi = 0.5 QN l

L

p ud

2/3�

�

��

�

�

��

Eq. (4e3) hi _______ _______

whichever is greater.(f) Downcomer Sealing (Check only if a recessed inlet box is not used.)

hi at minimum loadings, in. Recalculate Eq. (4e1) for minimum rates. hi _______ _______hud at minimum loadings, in. Recalculate Eq. (4d1) for minimum rates. hud _______ _______hi + hud at minimum loadings, in. _______ _______If (hi + hud + 0.25 in.) < c, the downcomer will not be sealed at minimum loadings.See Basic Design Considerations for recommended method of obtaining a downcomer seal.







Inboard* Outboard(g) Downcomer Filling, hd

Note: With 2-pass trays, for inboard hd use hi on outboard trayand vice versa. (See Figure 6.) For a tray with a recessed inletbox or an inlet weir, multiply hud by 2.0.

( )h = h h h 1.0 ind t udL V

i+−

�

��

�

�� + + Lρ

ρ ρ. Eq. (4g1) hud _______ _______

hd as % of tray spacing %hd _______ _______Allowable hd as % of tray spacing: See Figure 4A. _______ _______If a higher tray spacing is needed, adjust H and repeat Steps3(a) and 4(g).If tower diameter is also adjusted (i.e., to optimize design % ofallowable VL/Ab), also check Adi and Ado as a % of As. Repeatall calculations from Step 2(c).

(h) Downcomer Velocity[If final downcomer area is different than Step 2(a)]

Vdi =LA

L

diEq. (4h1) Vdi _______ _______

Vdi must be equal or less than 0.35 ft/s. Also see Table 1, item 5a.

Vdo = LA

L

doEq. (4h2) Vdo _______ _______

Vdo must be equal or less than 0.6 ft/s. Also see Table 1, item 5a.5. Overall Efficiency (Check Only for Distillation Tower Revamps)

Number of theoretical trays required, NT NT ______________Eo = Overall efficiency, % [Figure 5A and Step (3c1)] Eo ______________Number of actual trays specified (NT/Eo) ______________See Section III-F to determine number of actual trays inpumparound sections.

6. Balanced DesignReview paragraph in text entitled Balanced Design(Step 6) to ensure that final tray design is as“balanced” as possible.

7. Tower ChecklistSee Table 7 in Section III-A for Tower Design Checklist (Trays).

* For 2-pass trays.




JET TRAY CALCULATION FORM (METRIC)

Location & Project __________________________________________________ Date_______________________________Tower Number _____________________________________________________ By ________________________________Service _____________________________________________________________

Tower Section (Top, Bottom, etc.) _______________Tray Number(s) Covered by this Design _______________Design Based on Tray Number _______________

1. Vapor and Liquid Loadings at Conditions(a) Vapor to the tray

Temperature, oC _______________Pressure, kPa _______________Density, ρv, kg/m3 ρv _______________Vapor rate, wv, kg/s wv _______________

Vapor rate, q wv

v

v=

ρ, m3/s Eq. (1a1) qv _______________

V qL vv

0.5

=−

�

��

�

��

ρρ ρL v

Eq. (1a2) VL _______________

Minimum vapor rate, wv(min), kg/s _______________Density at minimum rates, ρv(min) , kg/m3 _______________

Minimum vapor rate, qv(min) _______________

q w v(min)

v(min)

v(min)=

ρEq. (1a3) qv(min) _______________

0.5

v(min)L(min)

v(min)v(minL(min) )qV

��

�

��

�

ρ−ρρ

= Eq. (1a4) VL(min) _______________

(b) Liquid from the trayTemperature, oC _______________Viscosity, µL, m Pa•s µL _______________Surface Tension, σL, mN/m σL _______________Density, ρL, kg/m3 ρL _______________Liquid rate, wL, kg/s wL _______________

Liquid rate, Q 1000 w L

L

L=

ρ, dm3/s Eq. (1b1) QL _______________

Minimum liquid rate, wL(min), kg/s _______________Density at minimum rates, ρL(min), kg/m3 _______________

Minimum liquid rate, Q1000 w

L(min)L(min)

L(min)=

ρ, dm3/s Eq. (1b2) QL(min) _______________





JET TRAY CALCULATION FORM (METRIC) (Cont)Tray number(s) _______ _______

Inboard* Outboard2. Trial Tray Spacing, Size and Layout

(a) Downcomer Areas

( ) ( )A Q1000 0.105di

L= , m2(for revamps, make sure Vdi ≤ 0.105 m/s) Eq. (2a1) Adi _______________

Ado, m2. Set such that Eq. (2a2) Ado _______________

( ) ( ) ( ) ( )Q

1000 0.18A Q

1000 0.105 L

doL≤ ≤

(See Design Practice III Section A, Figure 12)If Adi > 0.12 As, consider a sloped or stepped downcomer.Minimum Ado or Adi = 0.068 As.For foaming or high-pressure systems, use

( ) ( )A Q1000 0.06di

L= , m2

(b) Trial Tray SizeVL [from Eq. (1a2)]

_______________Surface tension, σL (Step 1b)

_______________Standard surface tension, σSTD, from Figure 2 or from:σSTD = 10a where a = 1.68 – 0.244/µL 0.55 Eq. (2b1) σSTD _______________Kσµ from Figure 3 or from: Kσµ _______________

Kσµ = σσ

σσ

L

STD

0.317L

STD for < 1.0

�

��

�

�� Eq. (2b2)

OR

Kσµ = 1.0 for L

STD

σσ

≥ 1.0 Eq. (2b3)

Tray spacing, H, (first trial, use 600 mm) H _______________

Trial As = 278V K (H)

L0.5

σµ, m2 Eq. (2b4) As _______________

Dtr = 1130 (As)0.5, mm Eq. (2b5) Dtr _______________Check Adi and Ado. Both must be ≥ 6.8% of As. If necessary,correct As and Dtr.Minimum diameter for new towers is 2100 mm.

(c) Ultimate CapacityAverage free area, Af, m2 (See Figure 13, Design Practice III Section A) Af _______ _______

VL(Ult) = 0.378 Af 0.25

vL

L

1 ��

��

�

ρ−ρσ

��

��

�

β+β Eq. (2c1) VL(Ult) _______ _______

* For 2-pass trays.





Inboard* Outboard

where: βρ ρ

ρ=

−�

��

�

��1.4 L v

v

0.5

Design vapor load, VL [from Eq. (1a2)] _______________VL/VL(Ult), as %; must be ≤ 90% _______________If necessary, adjust tower diameter and repeat appropriateportions of Steps 2(a) and 2(b)

3. Final Tray Spacing, Size and Layout(a) Tower Diameter and Areas

Np = Number of liquid passes Np _______________

L’, dm3/s/m of diameter/pass = ( ) ( )1000 Q D N

L

tr pEq. (3a1) L’ _______________

KHL from Figure 1B or from: KHL _______________KHL = 0.00514 [H]0.5 Eq. (3a2)

or

KHL = 0.158 H

1006

0.0101L'�

��

�

�� Eq. (3a3)

(Use lower value of KHL from Eq. (3a2) or (3a3) or determineappropriate KHL equation from L’ and boundary line shown onFigure 1B.)-------------------------------------------------------------------------------------------------------------------------------------------------------------

KHL for Steam Cracker Primary Fractionators only

KHL = 0.169 H1743

0.28 LS /50.9�

��

�

��

+Eq. (3a4) _______________

Where: LS = QA

L

s

For tray spacings > 914 mm, multiply the KHL factor at914 mm by [H/914]0.5. Take no credit for spacings > 1220 mm.

-------------------------------------------------------------------------------------------------------------------------------------------------------------Kσµ from Step 2b _______________Ab = As – Adi – Ado – Aw (if any), m2 Ab _______________

VA

L

b allow

�

��

�

�� = KHL Kσµ Eq. (3a5) _______________

VA

L

b actual

�

��

�

�� =

VLAb

[from Eq. (1a2)] Eq. (3a6) _______________

Ratio of actual/allowable, VL/Ab, as %, must be ≤ 90%. AdjustDtr or H and repeat calculations from Step 2(c) until desiredratio is obtained. Also, check Adi and Ado as % of As.

* For 2-pass trays.






Inboard* OutboardFinal tower diameter, DT, mm. DT _______________Final tray spacing, H, mm H _______________Superficial area, As, m2 As _______________Estimated waste area, Aw (if any), m2 _______ _______Bubble area, Ab, m2 (Figure 12, Design Practice III Section A) Ab _______ _______Free area, Af, m2 (Figure 13, Design Practice III Section A) Af _______ _______

(b) Tab DetailsTab area, Ao (first trial use 15% of Ab; minimum tab area is 5% of Ab) Ao _______________

Tab velocity, Vo = qA

v

o [from Eq. (1a1)], m/s Vo _______________

Dry tray pressure drop, hed, mm of hot liquid

hed = 473 Vo2 ρρ

v

LEq. (3b1) hed _______________

If hed exceeds 150 mm of hot liquid, set hed = 150 andrecalculate Vo, m/s.

Vo = 0.046 hed L

v

0 5 .ρ

ρ�

��

�

�� Eq. (3b2) Vo _______________

Ao = qV

v

o [from Eq. (1a1)], m2 Eq. (3b3) Ao _______________

hed(min), mm - calculate hed at minimum rates. Value shouldexceed 25 mm of hot liquid to avoid weeping. If it does not, hed (min) _______________decrease Ao and recalculate hed(min) and hed to be sure both are acceptable.

(c) Mixing Energy(Check only when revamping existing distillation towers - ignorefor pumparounds)

Fe = [ ]V A / A

o v

o b

0.5ρEq. (3c1) Fe _______________

Check efficiency (Figure 5b) at this value of Fe. If efficiency is too low,increase hed (but not above 150 mm) and recalculate Vo, Ao, and Fe.

(d) Downcomers and WeirsFinal downcomer inlet area, Adi, m2 Adi _______ _______Final downcomer outlet area, Ado, m2 Ado _______ _______Outlet weir height, hwo, mm** hwo _______ _______Outlet weir length, lo, mm** lo _______ _______Inlet weir height, hwi, mm (if any) hwi _______ _______Inlet weir length, li, mm (if any) li _______ _______Length of bottom edge of downcomer, lud, mm lud _______ _______

* For 2-pass trays. ** If outlet weir is present. Outlet weirs are NOT specified for new tray designs.





Inboard* Outboard4. Tray Hydraulics

(a) Clear Liquid Height, hched [from Step 3b, Eq. (3b1)] _______________L’ [from Step 3a, Eq. (3a1)] _______________

2.9 + AAh 0.263h

2

b

oedc �

�

�

�

��

�

�

��

��

�= L′2/3 + 0.5 hwo ** Eq. (4a1) hc _______ _______

(b) Wet Tab Pressure Drop, hwthwt = 1.02 (hed)0.85 Eq. (4b1) hwt _______________

(c) Total Tray Pressure Drop, htht = hc + hwt + 25 Eq. (4c1) ht _______ _______ orht = hed, whichever is greater Eq. (4c2) _______ _______

(d) Head Loss Under Downcomer, hud

hud = 160 1000 Qc l N

L

ud p

2�

��

�

��

Eq. (4d1) hud _______ _______

Assume c = 38 mm for first trial. If hud >> 25, increase c untilhud ≈ 25 mmNote: For shaped downcomers, use coefficient of 53 in Eq. (4d1) instead of 160.

(e) Inlet Head, hiFor tray without an inlet weir or recessed inlet box, hi = hc. hi _______ _______For tray with inlet weir (no recessed inlet box),

hi = 6.93 1000 QN l

L

p i

2/3�

��

�

��

+ hwi Eq. (4e1) hi _______ _______

For tray with recessed inlet box (no inlet weir or shaped lip),

hi = ��

�

�

��

�

�+�

�

��

�1.2

AAh 1.6

2

b

oed L′2/3 Eq. (4e2) hi _______ _______

or

hi = 6.93 1000 QN l

L

p ud

2/3�

��

�

��

Eq. (4e3) hi _______ _______

whichever is greater.(f) Downcomer Sealing (Check only if a recessed inlet box is not used.)

hi at minimum loadings, mm. Recalculate Eq. (4e1) for minimum rates. _______ _______hud at minimum loadings, mm. Recalculate Eq. (4d1) for minimum rates. _______ _______







Inboard* Outboardhi + hud at minimum loadings, mm. _______ _______If (hi + hud + 6 mm) < c, the downcomer will not be sealed atminimum loadings. See Basic Design Considerations forrecommended method of obtaining a downcomer seal.

(g) Downcomer Filling, hdNote: With 2-pass trays, for inboard hd use hi on outboard trayand vice versa. (See Figure 6.) For a tray with a recessed inletbox or an inlet weir, multiply hud by 2.0.

hd = (ht + hud) L

L v

ρρ ρ−�

��

�

�� + hi + 25 mm Eq. (4g1) hd _______ _______

hd as % of tray spacing %hd _______ _______Allowable hd as % of tray spacing: See Figure 4b. _______ _______If a higher tray spacing is needed, adjust H and repeat Steps3(a) and 4(g).If tower diameter is also adjusted (i.e., to optimize design % ofallowable VL/Ab), also check Adi and Ado as a % of As. Repeatall calculations from Step 2(c).

(h) Downcomer Velocity[If final downcomer area is different than Step 2(a)]

V Q1000 Adi

L

di= , m/s Eq. (4h1) Vdi _______ _______

Vdi must be equal or less than 0.105 m/s. Also see Table 1, item 5a.

V Q1000 Ado

L

do= , m/s Eq. (4h2) Vdo _______ _______

Vdo must be equal or less than 0.18 m/s. Also see Table 1, item 5a.5. Overall Efficiency (Check Only for Distillation Tower Revamps)

Number of theoretical trays required, NT NT _______________Eo = Overall efficiency, % [Figure 5B and Step (3c1)] Eo _______________Number of actual trays specified (NT/Eo) _______________See Section III-F to determine number of actual trays in pumparound sections.

6. Balanced DesignReview paragraph in text entitled Balanced Design(Step 6) to ensure that final tray design is as“balanced” as possible.

7. Tower ChecklistSee Table 7 in Section III-A for Tower Design Checklist.

* For 2-pass trays.

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