dp03d

ExxonMobil Proprietary RESTRICTED ACCESS NOTICE DESIGN PRACTICES DUE TO THIRD PARTY PROPRIETARY INFORMATION This practice may contain third party information with confidentiality and use restrictions. EMRE's Law Department should be consulted prior to its release to any entity other than a 50% or more owned affiliate of Exxon Mobil Corporation who has an appropriate agreement (e.g. Standard Research Agreement, Upstream Cost Sharing Agreement) in place and their employees (this does not include in-house contractors, consultants, etc.) Any questions regarding Third Party Restricted Access should be directed to the appropriate contact in EMRE's Legal Department. A list of contacts can be found at: http:\\159.70.37.160\patents\assignresp91800.pdf To continue within this practice CLICK HERE ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 1 of 31 JET TRAYS DESIGN PRACTICES December, 2001 Changes shown by ➧ CONTENTS Section Page SCOPE ............................................................................................................................................................3 REFERENCES.................................................................................................................................................3 BACKGROUND...............................................................................................................................................3 DEFINITIONS ..................................................................................................................................................3 APPLICATION.................................................................................................................................................3 BASIC DESIGN CONSIDERATIONS..............................................................................................................4 TRAY SPACING......................................................................................................................................4 TOWER DIAMETER................................................................................................................................5 ULTIMATE CAPACITY............................................................................................................................5 NUMBER OF LIQUID PASSES...............................................................................................................5 DOWNCOMER SIZING...........................................................................................................................6 DOWNCOMER CLEARANCE .................................................................................................................6 DOWNCOMER SEALING .......................................................................................................................6 TRAY LAYOUT, TAB AREA, AND OUTLET WEIR HEIGHT ..................................................................7 TAB LAYOUT AND BLANKING...............................................................................................................7 WEEPING, DUMPING AND SPRAY REGIME OPERATION ..................................................................7 TRAY HYDRAULICS...............................................................................................................................7 OVERALL EFFICIENCY AND HEAT TRANSFER ..................................................................................7 START-UP CONSIDERATIONS .............................................................................................................8 DRAWING NOTES..................................................................................................................................8 DETAILED DESIGN PROCEDURE.................................................................................................................8 VAPOR AND LIQUID LOADINGS (STEP 1) ...........................................................................................8 TRIAL TRAY SPACING, SIZE AND LAYOUT (STEP 2) .........................................................................8 FINAL TRAY SPACING, SIZE AND LAYOUT (STEP 3) .........................................................................9 TRAY HYDRAULICS AND DOWNCOMER FILLING (STEP 4)...............................................................9 OVERALL EFFICIENCY (STEP 5) ..........................................................................................................9 BALANCED DESIGN (STEP 6).............................................................................................................10 TOWER CHECKLIST (STEP 7) ............................................................................................................10 NOMENCLATURE.........................................................................................................................................10 COMPUTER PROGRAMS ............................................................................................................................11 ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 2 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 CONTENTS (Cont) Section Page APPENDIX ....................................................................................................................................................12 JET TRAY CALCULATION FORM (CUSTOMARY).....................................................................................20 JET TRAY CALCULATION FORM (METRIC) ..............................................................................................26 TABLES Table 1 Jet Tray Design Principles (Metric Values Are In Parentheses).................................12 FIGURES Figure 1A Figure 1B Figure 2 Figure 3 Figure 4A Figure 4B Figure 5A Figure 5B Figure 6 Figure 7 KHL Factor For Jet Flood Equation (Customary Units) ...............................................14 KHL Factor For Jet Flood Equation (Metric Units) ......................................................14 Standard Surface Tension, σSTD (Same for Customary and Metric Units) ................15 Kσµ Factor For Jet Flood Equation (Same for Customary and Metric Units) .............15 Allowable Downcomer Filling For Jet Trays - All Systems (Customary Units)...........16 Allowable Downcomer Filling For Jet Trays - All Systems (Metric Units) ..................16 Overall Efficiency For Jet Trays In Hydrocarbon Service (Customary Units) .............17 Overall Efficiency For Jet Trays In Hydrocarbon Service (Metric Units).....................17 Pressure Balance For A Two-Pass Jet Tray (Same for Customary and Metric) ........18 Jet Tab Details ...........................................................................................................19 Revision Memo 12/01 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. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 3 of 31 JET TRAYS DESIGN PRACTICES December, 2001 SCOPE This section covers the techniques for specifying the process design features of jet trays. Detailed mechanical design and tab arrangement are normally handled by the tray fabricator. A calculation form showing the step-by-step calculation procedure is given in the APPENDIX for both customary and metric units. Section III-A should also be consulted since it contains key definitions and figures that explain many of the basic concepts used when designing trays. For the design of tray-related tower internals, 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. REFERENCES Some of the following literature has been used in the preparation of this section. The rest is listed for convenient reference. GLOBAL PRACTICE GP 5-2-1 Internals for Towers and Drums OTHER LITERATURE O’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. BACKGROUND Jet trays have been used in the petroleum and chemical process industries since the early 1950’s. Because of their high vapor and liquid handling capacity and low cost, they replaced bubble cap trays in many services. Since the mid-1960’s, however, jet trays have been superseded by sieve trays and packing, which are more cost effective and have wider flexibility for most services. Nevertheless, jet trays are still important where very high liquid handling capacity is required, such as in the pumparound sections of various heavy hydrocarbon fractionators operating near atmospheric pressure. DEFINITIONS See Section III-A for an in-depth discussion of many of the basic concepts used when designing trays. NOMENCLATURE part of this section for the definition of specific terms. Also see the APPLICATION For most new distillation towers, sieve trays or packing are usually the best choice (see Section III-A). However, jet trays are recommended for heat transfer services, especially where high liquid loadings might require 3 or 4-pass sieve trays and hence complex transitions. For those cases, single or double-pass jet trays may be better. These services include pumparounds in atmospheric 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 this value 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 because of the downcomer area required. This narrow bubble area, in turn, can result in high localized vapor velocities, which may increase entrainment and cause premature flooding. In vacuum towers because of their inherently high pressure drop and poor efficiency due to the low liquid rates usually encountered in these units. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 4 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 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 may exist. VARIABLE Pressure, psia (kPa) Temperature, °F (°C) Diameter, ft (mm) 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) Tray Spacing, in. (mm) Open Area as % of Ab DC Clearance, in. (mm) DC inlet area as % of As Number of passes Outlet weir height, in. (mm) Tab size, in. (mm) Flow path length, in. (mm) 2.4 (2.4) 0.07 (0.07) 0.077 (1.2) 28 (450) 18 (460) 5% 1 (25) 6.8% 1 0 (0) 2 (50) ** 16 (410) * 72 (72) 1 (1) 2.3 (37) 62 (1000) 48 (1220) 30% 3.5 (90) LOWER LIMIT 15 (104) 65 (18) 7 (2100) UPPER LIMIT 100 (690) 800 (430) 46 (14,020) * 2 0 (0) 2 (50) 209 (5310) * * Jet trays should be designed so that the sum of the downcomer inlet area (Adi) and outlet area (Ado) is less than 45% of the superficial tower area (As). Remember that the tower diameter must be within the allowable range specified 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 since there is an increased fouling risk with small tabs. ** BASIC DESIGN CONSIDERATIONS The procedure outlined in this section for designing new towers involves calculating a trial diameter, tray spacing, and downcomer area, and then checking and revising (if necessary) this trial design for ultimate capacity, jet flooding and downcomer 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 the various types of tray limitations, see Section III-A. The equation numbers shown in the text correspond to their location on the JET TRAY CALCULATION FORM presented in the APPENDIX. TRAY SPACING The optimum combination of tray spacing and tower diameter is the one which minimizes total tower investment, subject to the condition 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 DESIGN PROCEDURE, as a function of tower diameter and service. No vapor capacity credit is allowed for tray spacings above 36 inches (900 mm) except for steam cracker primary fractionators. See also the discussion of downcomer filling under TRAY HYDRAULICS, and Table 1 in the APPENDIX. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 5 of 31 JET TRAYS DESIGN PRACTICES December, 2001 BASIC DESIGN CONSIDERATIONS (Cont) TOWER DIAMETER In addition to the criteria discussed below under DOWNCOMER SIZING, DOWNCOMER CLEARANCE and DOWNCOMER SEALING, the tower must provide enough cross-sectional area to avoid entrainment per the following jet flood equation. ù é ( VL / Ab ) actual ú ê × 100 ≤ 90% ê ( VL / Ab ) allowable ú û ë é VL ù = K HLK σµ ê ú ë Ab û allow where: VL (Customary or Metric) Eq. (3a5) = Vapor load, ft3/s (m3/s) = Bubble area, ft2 (m2) Ab 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 or 1B 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 primary fractionators should be designed using a special KHL factor. This factor is shown as Eq. (3a4) on the JET TRAY CALCULATION 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 be taken for tray spacings greater than 48 in.,(1220 mm). These two comments are specific to steam cracker primary fractionators 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 hydrocarbon towers. 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 CAPACITY Eq. (2c1) (below) gives the limiting vapor load for ultimate capacity. See the NOMENCLATURE section for the definition of the variables. The ratio of design vapor load, VL, to the vapor load for ultimate capacity VL(Ult) must be kept below 90%. If necessary, the tower diameter must be increased, even though Eq. (3a5) on jet flood has already been satisfied. However, the diameter calculated from Eq. (3a5) usually provides sufficient free area to satisfy the ultimate capacity limitation. é β ù é σL ù VL(Ult) = C1 A f ê ú úê ë 1 + β û ë ρL − ρV û é ρ − ρV ù where: β = 1.4 ê L ú ë ρV û 0.5 0.25 Eq. (2c1) C1= 0.62 for Customary units (0.378 for Metric units) NUMBER OF LIQUID PASSES Multiple-pass jet trays are less likely to be needed than is the case with other types of trays, because jet trays have an inherently high liquid handling capacity. This characteristic results from the horizontal component of the vapor velocity, as the vapor leaves the tab openings. This vapor jet action helps to propel the liquid across the tray. Therefore, when two-pass jet trays are required in a tower, it is because other types of trays in the adjacent sections of the tower are multiple-pass trays, not because single-pass jet trays would have been overloaded. When two-pass jet trays are used, no credit should be taken for extra vapor handling capacity. If the liquid rate exceeds 24 gpm/inch of diameter/pass (60 dm3/s/meter of diameter/pass) or if 3 or 4 pass jet trays are proposed, contact your FRACTIONATION SPECIALIST for advice. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 6 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 BASIC DESIGN CONSIDERATIONS (Cont) DOWNCOMER SIZING The required downcomer inlet area is set by froth disengaging limitations. If insufficient area is provided, downcomer choking may back up froth onto the tray and cause premature flooding. The downcomer entrance velocity should be limited to a maximum 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, these values automatically apply to the outlet as well. For the sloped or stepped downcomer, the outlet velocity should not exceed 0.6 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 tower diameter. This means that the downcomer outlet area (hence, the tray inlet area) must be at least 6.8% of the tower superficial area, As. If the downcomer inlet area required to satisfy the velocity criteria exceeds 12% of As, then the outlet of a straight downcomer would be oversized and a sloped or stepped downcomer should be considered. For revamps, consider specifying modified arc downcomers in order to maximize tray bubble area and vapor handling capacity. The above stated downcomer inlet velocities for straight downcomers must be satisfied with modified arc downcomers. The minimum rise criteria must also be 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 not be enough bubble area to provide a good tab layout. If the sum of the required downcomer inlet and outlet areas is greater than 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. In addition, the PEGASYS Geometry, Segments of Circles option can be used to determine geometric relationships. DOWNCOMER CLEARANCE The downcomer clearance is the vertical distance between the bottom edge of the downcomer apron and the tray deck. This clearance 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 the submerged weir formula [Eq. (4d1)] shown on the JET TRAY CALCULATION FORM. The clearance should be no smaller than 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); 160 to 53 (metric). However, a shaped downcomer lip must not be used when either a recessed inlet box or an inlet weir has been specified. This is because the obstruction presented by the vertical face of the recessed inlet box, or by the inlet weir, would cause turbulence and defeat the purpose of the shaped downcomer lip. DOWNCOMER SEALING To prevent some of the vapor from bypassing a tray by traveling up the downcomer, the downcomer must be sealed to within 0.25 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 the inlet 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 the downcomer: adding an inlet weir, using a recessed inlet box, using a smaller clearance with a shaped lip, or decreasing the downcomer clearance [down to a minimum of 1 in. (25 mm)]. The designer must check that the downcomer filling does not become 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 rates greater than 11 gpm per inch of diameter per pass (28 dm3/s/m of diameter/pass). At such high liquid rates, the reversal in direction 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 to use 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 shaped downcomer lip provides a lower head loss for a given clearance than does the standard sharp-edged downcomer. As mentioned earlier, however, it should not be used if either a recessed box or an inlet weir has been specified. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 7 of 31 JET TRAYS DESIGN PRACTICES December, 2001 BASIC DESIGN CONSIDERATIONS (Cont) TRAY LAYOUT, TAB AREA, AND OUTLET WEIR HEIGHT Important features of the tray layout are the bubble area Ab (Section III-A, Figure 12, Bubble Area Definitions) and the free area 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 nearest tab. 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 and heat 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 (75 to 150 mm) if permitted by the tray hydraulics. However, the tab area should not be less than 5% of the bubble area, Ab. The 2 in. (50 mm) nominal size tab should be used for all new jet tray designs. The tab area in ft2 (m2) can be calculated for revamps 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/water simulator indicate that an outlet weir has almost no effect on jet tray hydraulics. The liquid is lifted off the tray deck and thrown over the weir by the horizontally entering vapor (see Figure 6). Thus, the outlet weir does little to maintain liquid on the tray for holdup or downcomer sealing purposes. However, a term has been included in Eq. (4a1) on the JET TRAY CALCULATION FORM, to give a conservative value for downcomer filling calculations in the rare event an outlet weir has been provided. TAB LAYOUT AND BLANKING A detailed tab layout is not shown in ExxonMobil Design Specifications since this is handled by the vendor. The vendor will also 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)] and should be given a sketch similar to the one in Figure 6B, Section III-A (Typical Tray Layout) showing the general tray dimensions. It is sometimes necessary to blank tabs to maintain high efficiency in sections of towers where the vapor loadings change markedly. For new designs, the vendor should be told to preferentially blank tab rows downstream of the minor trusses since these rows tend to weep first. For revamps, the designer should also blank these rows first. The blanking should be placed on the underside of the tray deck. Do not blank more than half the tabs on a tray without consulting your FRACTIONATION SPECIALIST for assistance. WEEPING, DUMPING AND SPRAY REGIME OPERATION Spray regime operation should not occur if the liquid rate is kept above 4 gpm per inch of diameter per pass (10 dm3/s/m of diameter/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 HYDRAULICS The 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 tray hydraulics and downcomer filling of increasing dry tray pressure drop (decreasing tab area) can be calculated from Step 3b on the calculation form. Downcomer filling, as a percent of tray spacing, should not exceed the values given in Figure 4a or 4b as a function of pressure. 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 jumping across (choking) the inboard downcomer, with consequent premature flooding. (See Figure 6 of this section and Figure 14 of Section III-A.) OVERALL EFFICIENCY AND HEAT TRANSFER For 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 order to optimize tray efficiency. Under these conditions, the efficiency will be roughly 20 percentage points less than that of a sieve tray 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. Fe = Vo [ρv ] 0.5 A o / Ab (Customary or Metric) Eq. (3c1) ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 8 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 BASIC DESIGN CONSIDERATIONS (Cont) START-UP CONSIDERATIONS At very low vapor velocities (such as during start-up), jet trays normally dump, with the result that no liquid level is maintained on the tray. Hence, when revamping jet tray towers that contain thermosyphon reboilers, special provisions must be made so that 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 NOTES The 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 PROCEDURE The step-by-step procedure for designing a jet tray is given on the JET TRAY CALCULATION FORM (Customary or Metric) in the APPENDIX. Basically, the procedure involves assuming a trial design with the help of the principles given above, checking it 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 and application of the basic design considerations already discussed. The calculation step numbers and equation numbers referred to 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 a computer program like PRO/II. If minimum liquid and vapor loadings have not been specified, assume 70% of the design loadings. Vapor loadings to the tray in question along with liquid loadings from the tray should be used, since these are nearly always 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 sets the downcomer area(s) to be used for the first trial. However, tower diameter considerations further on in the design procedure may 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, a tray spacing of 24 in. (600 mm) or that shown below (whichever is larger) should be used. The values given below are the minimum, 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 and refineries may not permit smaller spacings. Downcomer filling requirements may dictate the use of a tray spacing larger than the 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 tray sections. Spacings up to 36 in. (900 mm) may be used to permit a higher superficial vapor velocity. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 9 of 31 JET TRAYS DESIGN PRACTICES December, 2001 DETAILED DESIGN PROCEDURE (Cont) MINIMUM TRAY SPACING CLEAN SERVICE TOWER DIAMETER, ft (mm) Over 7 to 7.5 Over 7.5 to 10 Over 10 to 16.5 Over 16.5 (Over 2100 to 2250) (Over 2250 to 3000) (Over 3000 to 5000) (Over 5000)** FOULING SERVICE in. 18* 18* 21* 24 mm 450 450 525 600 in. 21* 24 27 30 mm 525 600 675 750 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 this point, 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 stepped downcomer. If the sum of Adi + Ado exceeds 45% of As, the tower diameter should be increased. If necessary, increase tower diameter 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 to ultimate 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 the tab 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 other considerations (e.g., limited pressure drop across the tower) require a smaller value of hed, it will be necessary to recalculate Vo, [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 (150 mm 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 sure that it is at least 65% of the final tower diameter. Consider a sloped or stepped downcomer if Adi > 0.12 As. In addition, for two-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 III Section K. Mixing Energy. Check only when revamping existing distillation towers - ignore for pumparounds. If the mixing energy gives an undesirably low efficiency, hed should be increased (within the limitations discussed above) and the appropriate portions of Step 3(b) recalculated. If there is no room for a higher hed in the design at this point, a moderate efficiency debit may have to be 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, thereby sealing the downcomer. If a seal is not obtained, consider the use of an inlet weir, a recessed inlet box, a smaller downcomer clearance, 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 the tray 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 this service is set by heat transfer requirements (see Section III-F). If an old jet tray distillation tower is being revamped, then the ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 10 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 procedure given below can be used. However, past studies have shown that it is usually more cost effective to replace the jet trays 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 of actual trays. However, this correlation should be used for hydrocarbon distillation systems only. For non-hydrocarbon services, the overall efficiency used should be based on past operating data, or your FRACTIONATION SPECIALIST should be consulted for the proper efficiency. In deciding how many actual trays to specify for a given design, questions of design conservatism and flexibility must also be considered. 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 velocity and downcomer filling all at approximately the same percentage of their respective limits (e.g. say 85% of the maximum jet flood, 85% of the allowable downcomer entrance velocity, and 85% of the allowable downcomer filling limits respectively). This prevents building a potential bottleneck into a tower and permits the unit to be pushed to its maximum by plant personnel. The designer should consider running parametric PEGASYS computer cases to balance a design rather than carrying out several lengthy 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 all new designs as well as revamps. NOMENCLATURE Ab Adi Ado Af = = = = Bubble area, Downcomer inlet area, ft2 (m2) Downcomer outlet area, ft2 (m2) Average tower free area, ft2 (m2) For multipass trays use the smallest value of Af. (See Figure 13, Design Practice III Section A, Free Area Definitions) Tab area, ft2 (m2) Superficial (total) tower cross-sectional area, ft2 (m2) Waste area, ft2 (m2) Clearance between tray and downcomer apron at tray inlet, in. (mm) Constant used in Eq. (2c1) Tower diameter, ft (mm) Trial tower diameter, ft (mm) Overall Efficiency, % Mixing energy factor = ft2 (m2) Ao As Aw c C1 DT Dtr Eo Fe = = = = = = = = = Vo (ρv )0.5 ' A o / Ab Equation is the same for Customary and Metric but the numerical values differ. See Figures 5A and 5B. H hc hd hed hi ht hud hwi hwo hwt = = = = = = = = = = Tray spacing, in. (mm) Clear liquid height on tray, in. (mm) of hot liquid Downcomer filling, in. (mm) of hot liquid Dry tray pressure drop, in. (mm) of hot liquid Tray inlet head, in. (mm) of hot liquid Total tray pressure drop, in. (mm) of hot liquid Head loss under downcomer, in. (mm) of hot liquid Inlet weir height, in. (mm) Outlet weir height, in. (mm) Wet tab pressure drop, in. (mm) of hot liquid ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 11 of 31 JET TRAYS DESIGN PRACTICES December, 2001 KHL Kσµ = = Tray spacing - liquid rate factor, dimensionless (see Figures 1A and 1B) Surface tension - viscosity factor, dimensionless (See Figure 3) NOMENCLATURE (Cont) L′ = Liquid rate, gpm/inch of diameter/pass (dm3/s/m of diameter/pass) Liquid load, ft3/s at conditions Liquid load at minimum rate, ft3/s at conditions Liquid rate, gph/ft2 of tower cross-sectional area (dm3/s/m2/s) Inlet weir length, in. (mm) Outlet weir length, in. (mm) (See Figure 12 in Section III-A, Bubble Area Definitions) Length of bottom edge of downcomer apron, in. (mm) (See Figure 12 in Section III-A, Bubble Area Definitions) Number of liquid passes Number of theoretical trays Pressure, psia (kPa abs) Liquid rate, gpm (dm3/s) at conditions Volumetric vapor rate, ft3/s (m3/s) Vapor velocity based on tower bubble area, ft/s (m/s) Downcomer inlet velocity, ft/s (m/s) Downcomer outlet velocity, ft/s (m/s) é ρv ù Design vapor load = qv ê ú ë ρL − ρv û 0.5 LL = LL(min) = = Ls = Ii = Io Iud = Np NT P QL qv Vb Vdi Vdo VL = = = = = = = = = at conditions, ft3/s (m3/s) VL(Ult) = VL(min) = Vo = = wL = wv µL ρL ρv σL = = = = Ultimate capacity vapor load, dependent on system properties, ft3/s (m3/s) at conditions Vapor load at minimum vapor rate (for flexibility calculations), ft3/s (m3/s) at conditions Vapor velocity through the tabs, ft/s (m/s) Liquid rate, klb/hr (kg/s) Vapor rate, klb/hr (kg/s) Liquid viscosity at conditions, cP (mPa⋅s) Liquid density at conditions, lb/ft3 (kg/m3) Vapor density at conditions, lb/ft3 (kg/m3) Liquid surface tension at conditions, dynes/cm (m N/m) Standard surface tension, dynes/cm (mN/m) (see Figure 2) σSTD = COMPUTER PROGRAMS For up-to-date information on available computer programs and how to use them, affiliate personnel should contact their FRACTIONATION SPECIALIST. A site’s TECHNICAL COMPUTING CONTACT can also provide help on accessing available programs. The jet tray programs can be accessed through three sources. AVAILABLE PROGRAMS Source Program Name or Number Version Number PEGASYS PRO/II Fractionating Towers, Jet Trays Jet Tray Program 2.4 2.4 The Jet Tray programs utilize the design equations contained in this section, Table 1, and the equations on the JET TRAY CALCULATION FORM. They can be used for both designing new towers or trays, and rating existing trays. Existing tray designs can be rated by specifying some or all of the tray hardware dimensions. The programs also include an option to calculate jet tray heat transfer requirements for heavy hydrocarbon pumparounds (see Section III-F). ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 12 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 APPENDIX TABLE 1 JET TRAY DESIGN PRINCIPLES (Metric Values are in Parentheses) DESIGN FEATURE 1. Tray Spacing, in (mm) SUGGESTED VALUES 24 to 36 (600 to 900) ALLOWABLE RANGE 18 to 36 (460 to 900) [up to 48 (1200) for steam cracker fractionators] 7 (2100) to 46 (14,202) a) Liquid rate L′, gpm/in of diam/pass (dm3/s/m of diam/pass) — 4 to 24 (10 to 60) COMMENTS It is generally economical to use minimum values, as limited by downcomer filling or maintenance considerations. Use of variable spacings to accommodate loading changes from tray to tray should be considered, to minimize tower height. Jet trays should not be used for new towers with diameters less than 7 ft (2100 mm). If L’ is less than 4 gpm/in. of diameter/pass (10 dm3/s/m of diameter/pass), jet trays should not be used, because of the tendency for spray regime operation to occur. If L’ is greater than 24 gpm/in. of diameter/pass (60 dm3/s/m of diameter/pass) your FRACTIONATION SPECIALIST should be consulted. Set by Eq. (3a5). Design for 90% or less of the allowable vapor velocity. The liquid handling capacity of jet trays is not significantly affected by the number of passes. Use single-pass trays, unless adjacent trays in the tower are multiple-pass. Two-in. (50 mm) tabs are normally used. See Figure 7 for dimensions. In general, the lower the percent tab area, the higher the efficiency. A tray with 20% tab area gives good efficiency and flexibility without a capacity debit for a wide range of design liquid rates. Higher tab areas may be required at very high liquid rates to prevent excessive downcomer filling. Tab areas less than 5% are not recommended, because spray regime operation may occur. Bubble area should be maximized, for good contacting. Ratios of Ab/As less than 55% should not be used. In new designs, jet trays are only used in pumparound services where the number of trays is set by heat transfer requirements. When revamping existing jet trays in fractionation service, it is usually cost-effective to replace jet tray panels with sieve tray panels. Nevertheless, if the jet trays must be retained, the jet tray’s overall efficiency will be about 20 percentage points less than that of sieve or bubble cap trays at mixing energy functions (Fe) above 70 (85). This is true provided there is not a spray regime, flooding, or dumping limitation. For the efficiency at lower mixing energy values, see Figure 5A or 5B. Blanking is not generally required, unless the tower is being sized for future service at much higher rates. To maintain best efficiency, blank uniformly within the bubble area. Preferentially blank rows of tabs downstream of minor trusses, because these tabs are the most susceptible to dumping. See GP 5-2-1. 2. Tower Diameter, ft (mm) — b) Allowable vapor velocity Vb, ft/s (m/s) 3. Number of Liquid Passes — 1 See Comments 1 or 2 4. Tab Size and Layout a) Tab size, in. (mm) b) Tab area Ao, as percent of Ab — 2 (50) 12 to 25 — 2(50) 5 to 30 c) Bubble area Ab, as percent of As d) Overall efficiency 55 to 90 See Comments — See Comments e) Blanking — — ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 13 of 31 JET TRAYS DESIGN PRACTICES December, 2001 TABLE 1 JET TRAY DESIGN PRINCIPLES (Cont) (Metric Values are in Parentheses) DESIGN FEATURE 5. Downcomers and Weirs a) Allowable downcomer velocity, ft/s (m/s) SUGGESTED VALUES ALLOWABLE RANGE COMMENTS 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 and high-pressure systems. Downcomer outlet velocity should not exceed 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 exceeds 45% of As, the tower diameter should be increased. Chord length should be at least 65% of the tray diameter for good liquid distribution. Sloped downcomers can be used for high liquid rates, with maximum outlet velocity of 0.6 ft/s (0.18 m/s). Consider sloped downcomers if Adi > 0.12 As. Modified arc downcomers can be used with jet trays as long as the maximum downcomer inlet velocity and minimum rise criteria (10 in. [250mm] for jet trays) are satisfied. Whenever a two-pass tray is used, provide a 14 to 16 in. (350 to 400 mm) high anti-jump baffle, suspended lengthwise in the center of the inboard downcomer and extending the length of the downcomer, to prevent possible “choking” by froth entering the downcomer from opposite sides. See Figure 14, Design Practice III Section A, Figure 6 in this section, and GP 5-2-1. Set the clearance to give a head loss of approximately 1 in. (25 mm). Higher values can be used if necessary to assure sealing of the downcomer. If c > 3 in. (75 mm) (because of high liquid rates), consider use of a shaped downcomer lip to reduce the head loss. See Design Practice III Section A, Figure 11. Jet trays do not normally use outlet weirs. See the discussion under Basic Design Considerations. If, at minimum loadings, the sum of the clear liquid height on the tray and the head loss under the downcomer plus 0.25 in. (6 mm) does not exceed the downcomer clearance, reduce the downcomer clearance to the minimum of 1 in. (25 mm) (downcomer filling permitting) or add an inlet weir or recessed inlet box, in that order of preference. Do not use a recessed inlet box if L > 11 gpm/in of diameter/pass (28 dm3/s/m of diameter/pass). Maximum depth for a recessed box is 6 in. (150 mm). See Figures 4A and 4B of this section for the maximum percent downcomer filling as a function of system pressure. b) Type of downcomer Chordal See Comments c) Center and off-center (inboard) downcomer width and anti-jump baffles — 8 in. (200 mm) min.for inlet, 6 in. (150 mm) min. for outlet d) Clearance under downcomer (c), in. (mm) 1.5 (38 mm) 1 (25 mm) to 3.5 (90 mm) e) Outlet weir f) Downcomer seal — See Comments See Comments Inlet Weir or recessed Inlet Box g) Downcomer filling, % of tray spacing See Comments See Comments ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 14 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 FIGURE 1A KHL FACTOR FOR JET FLOOD EQUATION (CUSTOMARY UNITS) 0.55 36" 0.50 33" 30" 0.45 KHL 0.40 27" 24" Tray Spacing = 21" 0.35 DO NOT USE JET TRAY FOR L' < 4 0.30 0 4 8 KHL = 0.085H 0.5 KHL = 0.52(H/39.6)0.0252L' 12 L', gpm/inch of Diameter/Pass 16 20 24 DP3DF1A FIGURE 1B KHL FACTOR FOR JET FLOOD EQUATION (METRIC UNITS) 0.16 900 mm 0.15 0.14 0.13 0.12 KHL 0.11 0.10 0.09 0.08 0.07 0 10 20 30 40 50 60 DP3DF1B 800 mm 700 mm 600 mm Tray Spacing = 500 mm KHL = 0.00514H 0.5 DO NOT USE JET TRAYS FOR L' < 10 KHL = 0.158(H/1006)0.0101L' L', dm3/s Per Meter of Diameter/Pass ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 15 of 31 JET TRAYS DESIGN PRACTICES December, 2001 FIGURE 2 STANDARD SURFACE TENSION, σSTD (SAME FOR CUSTOMARY AND METRIC UNITS) 100 80 60 40 dyne/cm (mN/m) σ = 10a 0.244 µ L0.55 STD a = 1.68 - 20 STD, 10 8 6 4 σ 2 1 0.03 .05 .07 0.1 0.2 0.3 0.4 0.6 0.8 1 2 3 4 5 10 DP3DF2 Viscosity, cP or mPa•s FIGURE 3 Kσµ FACTOR FOR JET FLOOD EQUATION (SAME FOR CUSTOMARY AND METRIC UNITS) 2 1.5 K σµ 1 0.9 0.8 0.7 0.6 0.5 0.2 0.3 0.4 0.5 0.8 1 2 3 4 σ Actual/Standard Surface Tension Ratio, ( L/σSTD) K = σµ σL σSTD 0.317 for σL < 1.0 σSTD K = 1.0 for σµ σL ≥ 1.0 σSTD DP3DF3 ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 16 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 FIGURE 4A ALLOWABLE DOWNCOMER FILLING FOR JET TRAYS - ALL SYSTEMS (CUSTOMARY UNITS) 60 DCF = 50 for p ≤ 90 psia = 50 -0.0545 (P-90) for p>90 and ≤ 365 psia = 35 for p>365 psia Where: DCF = Allowable % Downcomer Filling p = Tower Pressure, psia 55 Allowable % Downcomer Filling 50 45 40 35 30 0 50 100 150 200 250 300 350 400 DP3DF4A Tower Pressure, psia FIGURE 4B ALLOWABLE DOWNCOMER FILLING FOR JET TRAYS - ALL SYSTEMS (METRIC UNITS) 60 DCF = 50 for p ≤ 600 kPa = 50 - 0.0079 (P - 600) for p>600 and≤ 2500 kPa = 35 for p>2500 kPa Where: DCF = Allowable % Downcomer Filling p = Tower Pressure, kPa 55 Allowable % Downcomer Filling 50 45 40 35 30 0 500 1000 1500 Tower Pressure, kPa 2000 2500 3000 DP3DF4B ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 17 of 31 JET TRAYS DESIGN PRACTICES December, 2001 FIGURE 5A OVERALL EFFICIENCY FOR JET TRAYS IN HYDROCARBON SERVICE (CUSTOMARY UNITS) 120 110 100 90 Overall Efficiency, Eo, % 80 40 70 60 50 40 30 20 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 DP3DF5A 1) For non-hydrocarbon services, consult your FRACTIONATION SPECIALIST 2) Fe ≥70 provides maximum jet tray efficiency 50 Fe≥70 30 25 Eo = 35.4 (FLUIDITY)0.47 - 10(1 + 10x0.958 e ) F Average Fluidity of Liquid on Tray (1/µL), cP-1 FIGURE 5B OVERALL EFFICIENCY FOR JET TRAYS IN HYDROCARBON SERVICE (METRIC UNITS) 120 110 100 90 Overall Efficiency, Eo, % 60 80 50 70 40 60 50 40 30 20 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Average Fluidity of Liquid on Tray (1/µL), (mPa⋅s)-1 Eo = 35.4 (FLUIDITY)0.47 - 10(1+10x0.965 e ) F 1) For non-hydrocarbon services, consult your FRACTIONATION SPECIALIST 2) Fe ≥85 provides maximum jet tray efficiency Fe≥85 30 DP3DF5B ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 18 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 FIGURE 6 PRESSURE BALANCE FOR A TWO-PASS JET TRAY (SAME FOR CUSTOMARY AND METRIC) IDEALIZED OPERATION (Assumed for Calculation Purposes) Anti-Jump Baffle h*t hd hud h*i h*wt h*t = from calculation form ht h*ud hc hwt h*t = from calculation form hd hud h*i h*wt h*c hi h*i assumed* = h*c h*c Froth ACTUAL OPERATION h*d * Clear Liquid Vapor Pressure Balance for Center (Inboard) Downcomer Filling: ρL ρL - ρv + hi + 1, in + 25,mm (Customary) (Metric) h*d = (h*t + h*ud) Pressure Balance for Side (Outboard) Downcomer Filling: hd = (ht + hud) ρL ρL - ρv + h*i + 1, in + 25,mm (Customary) (Metric) 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. DP3DF6 ExxonMobil Research and Engineering Company – Fairfax, VA Disengaging Choking ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 19 of 31 JET TRAYS DESIGN PRACTICES December, 2001 ➧ A FIGURE 7 JET TAB DETAILS Tray Plate B B Tab C L C B E F D Tangent Point Plan B-B DP3Df07 SECTION THROUGH TAB CENTERLINE TABLE OF DIMENSIONS inches Dimension A B C D E F 2 (Nominal) 2 1 2 11/16 0.104 (minimum) Tolerance — + 1/8, – 0 ± 1/64 ± 3/32 ± 1/32 –0 Dimension 51 50 25 50 17.5 2.8 (minimum) millimeters Tolerance — + 3, – 0 ± 0.5 ± 2.5 ± 0.8 –0 ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 20 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 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 Vapor rate, wv, klb/hr Vapor rate, qv = 1000 w v , ft3/s 3600 ρv 0.5 _______________ _______________ ρv wv Eq. (1a1) qv _______________ _______________ _______________ é ρv ù VL = qv ê ú ρL − ρ v û ë Eq. (1a2) VL _______________ _______________ Minimum vapor rate, wv(min), klb/hr Density at minimum rates, ρv( min), Minimum vapor rate, qv(min) qv(min) = 1000 w v(min) 3600 ρv(min) 0.5 lbs/ft3 _______________ _______________ Eq. (1a3) qv(min) _______________ é ù ρv (min) VL(min) = qv(min) ê ú ê ρL(min) − ρv(min) ú ë û (b) Liquid from the tray Eq. (1a4) VL(min) _______________ Temperature, oF Viscosity, µL, cP Surface Tension, σL, dynes/cm Density, ρL, lb/ft3 Liquid rate, wL, klb/hr Liquid rate, L = L _______________ µL σL ρL wL , ft3/s Eq. (1b1) LL Eq. (1b2) QL _______________ _______________ _______________ _______________ _______________ _______________ _______________ _______________ 1000 wL 3600 ρL Liquid rate, QL = LL(448.9), gpm Minimum liquid rate, wL(min), klb/hr Density at minimum rates, ρL(min), lb/ft3 Minimum liquid rate, LL(min) = 1000 wL(min) 3600 ρL(min) , ft3/s Eq. (1b3) LL(min) Eq. (1b4) QL(min) _______________ _______________ Minimum liquid rate, QL(min) = LL(min) (448.9), gpm ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 21 of 31 JET TRAYS DESIGN PRACTICES December, 2001 JET TRAY CALCULATION FORM (CUSTOMARY) (Cont) Tray number(s) _______ _______ Inboard* Outboard 2. Trial Tray Spacing, Size and Layout (a) Downcomer Areas Adi = LL/0.35, ft2 (For revamps, make sure Vdi ≤ 0.35 ft/s) Set such that (LL/0.6) ≤ Ado ≤ (LL/0.35), Ado, (See Design Practice III Section A, Figure 12, Bubble Area Definitions) ft2. ft2 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 Size VL [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 Kσµ from Figure 3 or from: é σ ù Kσµ = ê L ú ë σ STD û 0.317 Eq. (2a1) Adi Eq. (2a2) Ado _______________ _______________ _______________ Eq. (2b1) σSTD Kσµ Eq. (2b2) _______________ _______________ for σL < 1.0 σ STD OR Kσµ = 1.0 for σL ≥ 1.0 σ STD VL 0.06 K σµ (H)0.5 Eq. (2b3) Tray spacing, H, inches (first trial, use 24 inches) Trial As = H Eq. (2b4) As Eq. (2b5) Dtr _______________ _______________ _______________ Dtr = 1.128 (As)0.5, ft 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 Capacity Average free area, Af, ft2 (See Figure 13, Design Practice III Section A, Free Area Definitions) Af ù é β ù é σL VL(Ult) = 0.62 Af ê ú ú ê ë 1 + β û ë ρL − ρv û é ρ − ρv ù Where: β = 1.4 ê L ú ë ρv û 0.5 0.25 _______ _______ Eq. (2c1) VL(Ult) _______ _______ 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. _______________ ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 22 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 JET TRAY CALCULATION FORM (CUSTOMARY) (Cont) Tray number(s) _______ _______ Inboard* Outboard 3. Final Tray Spacing, Size and Layout (a) Tower Diameter and Areas Np = Number of liquid passes L’, GPM/inch of diameter/pass = KHL from Figure 1A or from: KHL = 0.085 [H]0.5 or é H ù KHL = 0.52 ê ú ë 39.6 û 0.0252 L' Np _______________ _______________ _______________ (12 D tr ) (Np ) QL Eq. (3a1) L′ KHL Eq. (3a2) Eq. (3a3) (Use lower value of KHL from Eq. (3a2) or (3a3) or determine appropriate KHL equation from L’ and boundary line shown on Figure 1A.) ------------------------------------------------------------------------------------------------------------------------------------------------------------------------KHL for Steam Cracker Primary Fractionators only é H ù KHL = 0.553 ê ú ë 68.6 û 0.28 +L S /4500 Eq. (3a4) _______________ Where: LS = 60 QL AS For tray spacings > 36 in. multiply the KHL factor at 36 in. by [H/36]0.5. Take no credit for spacings > 48 in. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------Kσµ from Step 2b _______________ 2 Ab = As – Adi – Ado – Aw (if any), ft Ab _______________ é VL ù = KHL Kσµ ê ú ë Ab û allow é VL ù V = L (from Eq. (1a2)) ê ú Ab û actual Ab ë Eq. (3a5) _______________ Eq. (3a6) _______________ Ratio of actual/allowable, VL/Ab, as %, must be ≤ 90%. Adjust Dtr or H and repeat calculations from Step 2(c) until desired ratio is obtained. Also, check Adi and Ado as % of As. Final tower diameter, DT, ft Final tray spacing, H, in. Superficial area, As, ft2 Estimated waste area, Aw (if any), ft2 Bubble area, Ab, ft2 (Figure 12, Design Practice III Section A) Free area, Af, ft2 (Figure 13, Design Practice III Section A) * For 2-pass trays. DT H As Aw Ab Af _______________ _______________ _______________ _______ _______ _______ _______ _______________ ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 23 of 31 JET TRAYS DESIGN PRACTICES December, 2001 JET TRAY CALCULATION FORM (CUSTOMARY) (Cont) Tray number(s) _______ _______ Inboard* Outboard (b) Tab Details Tab area, Ao (first trial use 15% of Ab; minimum tab area is 5% of Ab) Tab velocity, Vo = qv [from Eq (1a1)], ft/s Ao Ao Vo _______________ _______________ Dry tray pressure drop, hed, in. of hot liquid hed = 1.73 Vo2 ρv ρL Eq. (3b1) hed _______________ If hed exceeds 6 in. of hot liquid, set hed = 6 and recalculate Vo, ft/s. éh ρ ù Vo = 0.76 ê ed L ú ë ρv û 0.5 Eq. (3b2) Vo Eq. (3b3) Ao _______________ Ao = qv [from Eq. (1a1)], ft2 Vo _______________ hed(min), inches - calculate hed at minimum rates. Value should exceed 1 in. of hot liquid to avoid weeping. If it does not, decrease Ao and recalculate hed(min) and hed to be sure both are within acceptable range. (c) Mixing Energy (Check only when revamping existing distillation towers - ignore for pumparounds) Fe = Vo [ρv ] A o / Ab 0.5 Eq. (3c1) Fe _______________ Check efficiency (Figure 5A) at this value of Fe. If efficiency is too low, increase hed (but not above 6 in.) and recalculate Vo, Ao, and Fe. (d) Downcomers and Weirs Final downcomer inlet area, Adi, ft2 Final downcomer outlet area, Ado, ft2 Outlet weir height, hwo, in.** Outlet weir length, lo, in.** Inlet weir height, hwi, in. (if any) Inlet weir length, li, in. (if any) Length of bottom edge of downcomer, lud, in. * For 2-pass trays. Adi Ado hwo lo hwi li lud _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ ** If outlet weir is present. Outlet weirs are NOT specified for new jet tray designs. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 24 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 JET TRAY CALCULATION FORM (CUSTOMARY) (Cont) Tray number(s) _______ _______ Inboard* Outboard 4. Tray Hydraulics (a) Clear Liquid Height, hc hed [from Step 3b, Eq. (3b1)] L’ [from Step 3a, Eq. (3a1)] 2 ù é éA ù hc = 0.08 ê6.0 hed ê o ú + 2.6 ú L′ 2/3 + 0.5 h wo * * ú ê ë Ab û û ë _______________ _______________ Eq. (4a1) hc _______ _______ (b) Wet Tab Pressure Drop, hwt hwt = 0.63 (hed)0.85 (c) Total Tray Pressure Drop, ht ht = hc + hwt + 1.0 Eq. (4b1) hwt Eq. (4c1) ht Eq. (4c2) _______________ _______ _______ _______ _______ or ht = hed, whichever is greater (d) Head Loss Under Downcomer, hud é QL hud = 0.06 ê ê c lud Np ë ù ú ú û 2 Eq. (4d1) hud _______ ______ Assume c = 1.5 in. for first trial. If hud> > 1.0, increase c until hud ≈ 1.0 in. Note: For shaped downcomers, use coefficient of 0.02 in Eq. (4d1) instead of 0.06. (e) Inlet head, hi For tray without an inlet weir or recessed inlet box, hi = hc. For tray with inlet weir (no recessed inlet box) hi _______ _______ é Q ù hi = 0.5 ê L ú ê Np l i ú ë û 2/3 + hwi Eq. (4e1) hi _______ _______ For tray with recessed inlet box (no inlet weir or shaped lip). 2 ù é éA ù hi = 0.08 ê36hed ê o ú + 1.1ú L′ 2 / 3 ú ê ë Ab û û ë Eq. (4e2) hi _______ _______ or é Q ù hi = 0.5 ê L ú ê ú ë Np lud û (f) 2/3 Eq. (4e3) hi _______ _______ whichever is greater. Downcomer Sealing (Check only if a recessed inlet box is not used.) hi at minimum loadings, in. Recalculate Eq. (4e1) for minimum rates. hud at minimum loadings, in. Recalculate Eq. (4d1) for minimum rates. hi 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. * For 2-pass trays. ** If outlet weir is present. Outlet weirs are NOT specified for new jet tray designs. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 25 of 31 JET TRAYS DESIGN PRACTICES December, 2001 JET TRAY CALCULATION FORM (CUSTOMARY) (Cont) Tray number(s) _______ _______ Inboard* Outboard (g) Downcomer Filling, hd Note: With 2-pass trays, for inboard hd use hi on outboard tray and vice versa. (See Figure 6.) For a tray with a recessed inlet box or an inlet weir, multiply hud by 2.0. é ρL ù hd = (ht + hud ) ê ú + h + 1.0 in. ρL − ρV û i ë Eq. (4g1) hud _______ _______ _______ _______ _______ _______ hd as % of tray spacing Allowable hd as % of tray spacing: See Figure 4A. If a higher tray spacing is needed, adjust H and repeat Steps 3(a) and 4(g). If tower diameter is also adjusted (i.e., to optimize design % of allowable VL/Ab), also check Adi and Ado as a % of As. Repeat all calculations from Step 2(c). (h) Downcomer Velocity [If final downcomer area is different than Step 2(a)] Vdi = LL A di LL A do %hd Eq. (4h1) Vdi _______ _______ Vdi must be equal or less than 0.35 ft/s. Also see Table 1, item 5a. Vdo = Eq. (4h2) Vdo _______ _______ 5. Vdo must be equal or less than 0.6 ft/s. Also see Table 1, item 5a. Overall Efficiency (Check Only for Distillation Tower Revamps) Number of theoretical trays required, NT Eo = Overall efficiency, % [Figure 5A and Step (3c1)] Number of actual trays specified (NT/Eo) See Section III-F to determine number of actual trays in NT Eo ______________ ______________ ______________ 6. pumparound sections. Balanced Design Review paragraph in text entitled Balanced Design (Step 6) to ensure that final tray design is as “balanced” as possible. Tower Checklist See Table 7 in Section III-A for Tower Design Checklist (Trays). 7. * For 2-pass trays. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 26 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 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 Vapor rate, wv, kg/s Vapor rate, qv = wv , m3/s ρv 0.5 _______________ _______________ ρv wv Eq. (1a1) qv _______________ _______________ _______________ é ρv ù VL = qv ê ú ρL − ρv û ë Eq. (1a2) VL _______________ _______________ _______________ _______________ Minimum vapor rate, wv(min), kg/s Density at minimum rates, ρv(min) , kg/m3 Minimum vapor rate, qv(min) qv(min) = w v(min) ρv(min) 0.5 Eq. (1a3) qv(min) _______________ VL(min) é ù ρv(min) = qv(min ) ê ú ρL(min) − ρv(min) ú ê ë û Eq. (1a4) VL(min) _______________ (b) Liquid from the tray Temperature, oC Viscosity, µL, m Pa•s Surface Tension, σL, mN/m Density, ρL, Liquid rate, wL, kg/s kg/m3 Liquid rate, QL = 1000 wL , dm3/s ρL µL σL ρL wL Eq. (1b1) QL _______________ _______________ _______________ _______________ _______________ _______________ _______________ _______________ , dm3/s Eq. (1b2) QL(min) Minimum liquid rate, wL(min), kg/s Density at minimum rates, ρL(min), kg/m3 Minimum liquid rate, QL(min) = 1000 wL(min) ρL(min) _______________ ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 27 of 31 JET TRAYS DESIGN PRACTICES December, 2001 JET TRAY CALCULATION FORM (METRIC) (Cont) Tray number(s) _______ _______ Inboard* Outboard 2. Trial Tray Spacing, Size and Layout (a) Downcomer Areas (for revamps, make sure Vdi ≤ 0.105 m/s) QL A di = , m2 (1000) ( 0.105) Eq. (2a1) Adi _______________ Ado, m2. Set such that Eq. (2a2) Ado _______________ (1000) ( 0.18) QL ≤ A do ≤ (1000) ( 0.105) QL (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 di = (1000) ( 0.06) QL , m2 (b) Trial Tray Size VL [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 Kσµ from Figure 3 or from: é σ ù Kσµ = ê L ú ë σ STD û 0.317 Eq. (2b1) σSTD Kσµ Eq. (2b2) _______________ _______________ for σL < 1.0 σ STD OR Kσµ = 1.0 for σL ≥ 1.0 σ STD Eq. (2b3) Tray spacing, H, (first trial, use 600 mm) Trial As = 278VL K σµ (H)0.5 , m2 H Eq. (2b4) As Eq. (2b5) Dtr _______________ _______________ _______________ Dtr = 1130 (As)0.5, mm 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 Capacity Average free area, Af, m2 (See Figure 13, Design Practice III Section A) ù é β ù é σL VL(Ult) = 0.378 Af ê ú ú ê 1 + β û ë ρL − ρv û ë 0.25 Af _______ _______ Eq. (2c1) VL(Ult) _______ _______ * For 2-pass trays. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 28 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 JET TRAY CALCULATION FORM (METRIC) (Cont) Tray number(s) _______ _______ Inboard* Outboard é ρ − ρv ù where: β = 1.4 ê L ú ë ρv û 0.5 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) Final Tray Spacing, Size and Layout (a) Tower Diameter and Areas Np = Number of liquid passes L’, dm3/s/m of diameter/pass = KHL from Figure 1B or from: KHL = 0.00514 [H]0.5 or é H ù 0.0101L' KHL = 0.158 ê ú ë 1006 û _______________ _______________ 3. Np _______________ _______________ _______________ ( D tr ) (Np ) 1000 QL Eq. (3a1) L’ KHL Eq. (3a2) Eq. (3a3) (Use lower value of KHL from Eq. (3a2) or (3a3) or determine appropriate KHL equation from L’ and boundary line shown on Figure 1B.) ------------------------------------------------------------------------------------------------------------------------------------------------------------KHL for Steam Cracker Primary Fractionators only é H ù KHL = 0.169 ê ú ë 1743 û 0.28 + L S /50.9 Eq. (3a4) _______________ Where: LS = QL As For tray spacings > 914 mm, multiply the KHL factor at 914 mm by [H/914]0.5. Take no credit for spacings > 1220 mm. ------------------------------------------------------------------------------------------------------------------------------------------------------------_______________ Kσµ from Step 2b Ab _______________ Ab = As – Adi – Ado – Aw (if any), m2 é VL ù = KHL Kσµ ê ú ë Ab û allow VL é VL ù = [from Eq. (1a2)] ê ú ë Ab û actual A b Eq. (3a5) _______________ Eq. (3a6) _______________ Ratio of actual/allowable, VL/Ab, as %, must be ≤ 90%. Adjust Dtr or H and repeat calculations from Step 2(c) until desired ratio is obtained. Also, check Adi and Ado as % of As. * For 2-pass trays. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 29 of 31 JET TRAYS DESIGN PRACTICES December, 2001 JET TRAY CALCULATION FORM (METRIC) (Cont) Tray number(s) _______ _______ Inboard* Outboard DT _______________ H _______________ As _______________ _______ _______ Ab _______ _______ Af _______ _______ Ao Vo _______________ _______________ Final tower diameter, DT, mm. Final tray spacing, H, mm Superficial area, As, m2 Estimated waste area, Aw (if any), m2 Bubble area, Ab, m2 (Figure 12, Design Practice III Section A) Free area, Af, m2 (Figure 13, Design Practice III Section A) (b) Tab Details Tab area, Ao (first trial use 15% of Ab; minimum tab area is 5% of Ab) q Tab velocity, Vo = v [from Eq. (1a1)], m/s Ao Dry tray pressure drop, hed, mm of hot liquid hed = 473 Vo2 ρv ρL Eq. (3b1) hed _______________ If hed exceeds 150 mm of hot liquid, set hed = 150 and recalculate Vo, m/s. éh ρ ù Vo = 0.046 ê ed L ú ë ρv û 0.5 Eq. (3b2) Vo Eq. (3b3) Ao _______________ Ao = qv [from Eq. (1a1)], m2 Vo _______________ hed(min), mm - calculate hed at minimum rates. Value should exceed 25 mm of hot liquid to avoid weeping. If it does not, decrease Ao and recalculate hed(min) and hed to be sure both are acceptable. (c) Mixing Energy (Check only when revamping existing distillation towers - ignore for pumparounds) Fe = Vo [ρv ] A o / Ab 0.5 hed (min) _______________ Eq. (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 Weirs Final downcomer inlet area, Adi, m2 Final downcomer outlet area, Ado, m2 Outlet weir height, hwo, mm** Outlet weir length, lo, mm** Inlet weir height, hwi, mm (if any) Inlet weir length, li, mm (if any) Length of bottom edge of downcomer, lud, mm * For 2-pass trays. Adi Ado hwo lo hwi li lud _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ ** If outlet weir is present. Outlet weirs are NOT specified for new tray designs. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary Section III-D Page 30 of 31 FRACTIONATING TOWERS JET TRAYS DESIGN PRACTICES December, 2001 JET TRAY CALCULATION FORM (METRIC) (Cont) Tray number(s) _______ _______ Inboard* Outboard 4. Tray Hydraulics (a) Clear Liquid Height, hc hed [from Step 3b, Eq. (3b1)] L’ [from Step 3a, Eq. (3a1)] 2 ù é éA ù hc = ê0.263 hed ê o ú + 2.9 ú L′2/3 + 0.5 hwo ** ú ê ë Ab û û ë _______________ _______________ Eq. (4a1) hc _______ _______ (b) Wet Tab Pressure Drop, hwt hwt = 1.02 (hed)0.85 (c) Total Tray Pressure Drop, ht ht = hc + hwt + 25 Eq. (4b1) hwt Eq. (4c1) ht Eq. (4c2) _______________ _______ _______ _______ _______ or ht = hed, whichever is greater (d) Head Loss Under Downcomer, hud é 1000 QL ù hud = 160 ê ú ê ú ë c lud Np û 2 Eq. (4d1) hud _______ _______ Assume c = 38 mm for first trial. If hud >> 25, increase c until hud ≈ 25 mm Note: For shaped downcomers, use coefficient of 53 in Eq. (4d1) instead of 160. (e) Inlet Head, hi For tray without an inlet weir or recessed inlet box, hi = hc. For tray with inlet weir (no recessed inlet box), hi _______ _______ é1000 QL ù hi = 6.93 ê ú ê Np l i ú û ë 2/3 + hwi Eq. (4e1) hi _______ _______ For tray with recessed inlet box (no inlet weir or shaped lip), 2 ù é éA ù hi = ê1.6 hed ê o ú + 1.2ú L′2/3 ú ê ë Ab û û ë Eq. (4e2) hi _______ _______ or é 1000 QL ù hi = 6.93 ê ú ê Np lud ú ë û 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. * For 2-pass trays. _______ _______ _______ _______ ** If outlet weir is present. Outlet weirs are NOT specified for new jet tray designs. ExxonMobil Research and Engineering Company – Fairfax, VA ExxonMobil Proprietary FRACTIONATING TOWERS Section III-D Page 31 of 31 JET TRAYS DESIGN PRACTICES December, 2001 JET TRAY CALCULATION FORM (METRIC) (Cont) Tray number(s) _______ _______ Inboard* Outboard _______ _______ hi + hud at minimum loadings, mm. If (hi + hud + 6 mm) < c, the downcomer will not be sealed at minimum loadings. See Basic Design Considerations for recommended method of obtaining a downcomer seal. (g) Downcomer Filling, hd Note: With 2-pass trays, for inboard hd use hi on outboard tray and vice versa. (See Figure 6.) For a tray with a recessed inlet box or an inlet weir, multiply hud by 2.0. é ρL ù hd = (ht + hud) ê ú + hi + 25 mm ρL − ρv û ë Eq. (4g1) hd _______ _______ _______ _______ _______ _______ hd as % of tray spacing Allowable hd as % of tray spacing: See Figure 4b. If a higher tray spacing is needed, adjust H and repeat Steps 3(a) and 4(g). If tower diameter is also adjusted (i.e., to optimize design % of allowable VL/Ab), also check Adi and Ado as a % of As. Repeat all calculations from Step 2(c). (h) Downcomer Velocity [If final downcomer area is different than Step 2(a)] Vdi = QL , m/s 1000 A di QL , m/s 1000 A do %hd Eq. (4h1) Vdi _______ _______ Vdi must be equal or less than 0.105 m/s. Also see Table 1, item 5a. Vdo = Eq. (4h2) Vdo _______ _______ 5. Vdo must be equal or less than 0.18 m/s. Also see Table 1, item 5a. Overall Efficiency (Check Only for Distillation Tower Revamps) Number of theoretical trays required, NT Eo = Overall efficiency, % [Figure 5B and Step (3c1)] Number of actual trays specified (NT/Eo) See Section III-F to determine number of actual trays in pumparound sections. Balanced Design Review paragraph in text entitled Balanced Design (Step 6) to ensure that final tray design is as “balanced” as possible. Tower Checklist See Table 7 in Section III-A for Tower Design Checklist. NT Eo _______________ _______________ _______________ 6. 7. * For 2-pass trays. ExxonMobil Research and Engineering Company – Fairfax, VA