IPE-TM-320 Fractionation
Guidelines for Sieve and Valve Tray Design
IPE-TM-320-15
1. Purpose
This procedure provides guidelines for Fractionating Column sieve and valve tray designs. Customer preferences or special considerations may preempt these guidelines. A related document is Tools Documentation "
2. Contents
1. Purpose 1
2. Contents 1
3. Definitions 2
3.1 Areas 2
3.2 Downcomer/Weir Configuration 3
3.3 Basic Cross Flow Tray Layouts 4
4. Choosing Sieve or Valve Trays 5
5. Barrel Factors 5
6. Diameter, Target Jet Flood and Swaging 5
7. System Limit 6
8. Downcomer Type 6
8.1 Minimum Downcomer Widths 6
9. Downcomer Clearance 7
10. Downcomer Liquid Velocity 7
11. Vapor Tunnels Through Downcomers 8
12. Downcomer Backup 8
13. Tray Spacing 9
14. Tray Thickness 10
15. Outlet Weir 10
15.1 Setting Weir Height 10
15.2 Swept Back Weirs 10
15.3 Notched Weirs 11
15.4 Liquid Head Over the Weir 11
16. Recessed Seal Pans and Inlet Weirs 11
17. Number of Flow Paths 11
18. Use of Three and Four Pass Trays 12
18.1 Tray Layouts 12
18.2 Five Pass Trays 13
19. Hole Diameter for Sieve Trays 13
20. Percent Hole Area for Sieve Trays 13
20.1 F-Factor 13
20.2 Punch Area 14
20.3 Calculating Hole Pitch 14
21. What If the Percent Hole Area Is Less Than 5%? 14
22. Tray Pressure Drop 15
23. Turndown 15
23.1 Weep Point 15
23.2 Dump Point 16
23.3 Tray Efficiency 16
23.4 Designing for Low Loadings in a Large Column 16
23.5 Critical Tray Pressure Drop 16
23.6 Valve Trays 16
24. Derating 17
25. Froth Initiator 17
Attachment 1 IPE-TM-320-15 19
3. Definitions
3.1 Areas
Column Area, AC
The area enclosed by column internal diameter.
Free Area, AF
The minimum area of the column available for vapor flow, or the column area minus the maximum area at the top of the downcomer or downcomers.
Bubbling Area, AB
The area of the column available for liquid/vapor contact, and is equal to column area minus sum of the downcomer and downcomer seal areas.
Downcomer Area, ADC
Top area is the maximum area at top of entry of downcomer. Bottom area is the minimum area at bottom of downcomer.
Downcomer Seal Area, ADS
Seal area is area below bottom of downcomer used to seal downcomer and distribute liquid to tray. For the illustration used, the seal area is equal to downcomer area.
Hole Area, AH
Total bubbling area open to vapor flow.
3.2 Downcomer/Weir Configuration
3.3 Basic Cross Flow Tray Layouts
4. Choosing Sieve or Valve Trays
Procedure Section 4 contains guidelines for choosing between sieve and valve trays.
5. Barrel Factors
The term "barrel factor" refers to either a feed barrel factor or a reboiler barrel factor. The feed barrel factor is defined as F/D2, where F is the feed rate in barrels per stream day (at 60F) and D is the bottom tray diameter in feet. The reboiler barrel factor is defined as Q/D2, where Q is the reboiler duty in 106 Btu/hour and D is the bottom tray diameter in feet.
Columns in similar service are expected to have similar barrel factors. Attachment 1 contains a table of barrel factors for many common columns. Each technology center maintains process checklists for each of their common processes. Typical column design values are included on these checklists. Use the information in General Reference document GR-14; “Quality Checklists” and the to located the checklist of interest.
6. Diameter, Target Jet Flood and Swaging
For a new column, select the diameter that satisfies the following criteria:
Procedure PCS-07; “Inflection Point Engineering Practice for Design Margins” section 7 provides the following limits
- Jet flood 82% (maximum)
- Percent Downcomer Velocity Limit (Inflection Point Engineering) 75% (maximum)
For revamp columns, limits are set by the probability of failure that is acceptable for a given job. However, a sense of confidence is possible provided the following criteria are satisfied.
- Jet flood 90% (maximum)
- Percent Downcomer Velocity Limit (Inflection Point Engineering) 90% (maximum)
A normal tray efficiency is expected up to a jet flood of 90%. Although a tray may handle loads from 90 to 100 percent of jet flood, there is a sacrifice in tray efficiency.
Frequently, two column sections have sufficiently different loads that two different diameters may be used. If the difference between the section diameters is at least 1.5 feet, or 20 percent, it is economical to swage the column. For many services, columns are not swaged so as to provide flexibility and future capacity. As an alternative to swaging, decrease the tray spacing. If swaging is chosen, the percent flood of the smaller section is expected to be less than that of the larger section.
7. System Limit
In addition to the maximum capacity of a contacting device, the system limit is the maximum capacity for a given diameter that may be obtained regardless of the type of contacting device. This limit is reached when superficial vapor velocity shears the liquid into droplets that have a terminal velocity below the vapor velocity.
8. Downcomer Type
Downcomers serve three principle purposes:
- To collect the two phase mixture from the tray
- To disengage vapor from the liquid
- To uniformly distribute the clarified liquid to the tray below
Inflection Point Engineering normally designs straight chordal downcomers which is the simplest from a mechanical standpoint. A sloped downcomer has a bottom area that is less than the top area. The justification for this type of design is that as the vapor disengages from the downcomer liquid, the downcomer area can be reduced without an increase in the froth velocity. This extra area can be used for bubbling area. Other design variations on this type of downcomer include the use of a break or step. Refer to Section 3.2 for a diagram. Use of a sloped downcomer is to be considered if the top downcomer area is at least 15% of the column cross-sectional area. The bottom downcomer area is normally set at 50% of the top downcomer area.
8.1 Minimum Downcomer Widths
The minimum downcomer widths (at top) are as follows:
a. Side Downcomers
- For one and two pass trays use the larger of 5 inches (125 mm) or 8 percent of the column diameter. The 5 inch rule allows sufficient room for tray assembly. The 8 percent rule minimizes poor liquid flow profile across the tray due to flow constriction over a short outlet weir.
- For three and four pass trays use 10 percent of the column diameter. The 10 percent rule is similar to the 8 percent rule. Flow distribution problems are a bigger concern in three and four pass due to the lack of symmetry between the passes.
b. Center and Off-Center Downcomers
For center and off-center downcomers, the froth entering from each side can interfere with each other and cause a loss of tray capacity. Anti-jump baffles or wider downcomers can be used to alleviate this problem. Anti-jump baffles are vertical plates that are placed above center and off-center downcomers. For conventional valve or sieve trays, Inflection Point Engineering has normally not specified anti-jump baffles but has used a minimum non side downcomer width of 8 inches to avoid this type of interference. While this rule usually provides sufficient protection, the equation below needs to also be checked so as to avoid froth inlet interference on non side downcomers.
9. Downcomer Clearance
Set the downcomer clearance at a minimum of 1.5 inches (40 mm) for columns that operate at or above atmospheric pressure. In vacuum columns, the minimum downcomer clearance is generally 1.0 inches (25 mm). This lower clearance allows a lower outlet weir and gives a lower head on the tray and hence yields a lower tray pressure drop. In either case, increase the downcomer clearance, if needed, to give a velocity of less than 1.5 ft/s (0.457 m/s) under the downcomer.
10. Downcomer Liquid Velocity
The design downcomer liquid velocity needs to be low enough to allow any vapor bubbles that are swept into the downcomer to escape. The downcomer velocity is evaluated using the “Downcomer Velocity Limit (Inflection Point Engineering)” that is reported in Tray2. This is based on the old Koch Bulletin 960-1 correlation with the following two modifications.
- No credit is allowed for tray spacing larger than 24 inches.
- The second change is to the downcomer sizing curve located on Chart B in Koch Bulletin 960-1. A linear relationship is used for the allowable downcomer velocity as the delta vapor liquid density goes between 16 and 30.3 lb/ft3. For delta vapor liquid densities below 16 lb/ft3 and above 30.3 lb/ft3 the normal Chart B values are used.
On new designs, design the downcomers for 75% of the maximum velocity value. In the case of a sloped or stepped downcomer, use the Inflection Point Engineering correlation to set the top downcomer area. The bottom downcomer area is to be at least 50% of the top area.
The allowable downcomer velocity is a strong function of the activity on the bubbling area. For revamps, the downcomer velocity may be taken to 90% of the Inflection Point Engineering velocity limit provided that the jet flood is below 90%. Downcomer Velocity Limit (Inflection Point Engineering)values greater than 90% may be tolerable for revamps when the jet flood value is low, e.g. less than 70%. When reported, such as for sieve trays, the “Percent downcomer flood (FRI) should be used rather than Inflection Point Engineering limits on downcomer liquid velocity and downcomer backup.
11. Vapor Tunnels Through Downcomers
On two, three, and four pass trays, some vendors may specify vapor tunnels through the intermediate and/or center downcomers to equalize the pressure on all passes. However, Inflection Point Engineering does not recommend this practice because vapor tunnels block liquid flow down the downcomer.
12. Downcomer Backup
The material in the downcomer is a mixture of clear liquid and aerated froth. This material backs up to match the sums of the following items.
- Liquid head at the tray inlet
- Exit loss under the downcomer
- A total tray pressure drop
The liquid head at the tray inlet is frequently assumed to be equal to the sum of the weir height plus the calculated head over the outlet weir. This liquid head is not the same as the liquid head that is used to calculate tray pressure drop. Most tray pressure drop calculations use only a fraction of the weir height for the total tray pressure drop calculation.
Normally, this backup is not expressed as the height of the froth, but rather as the height of clear liquid that is needed for a hydraulic balance. This height is frequently expressed as a percent of tray spacing or tray spacing plus weir height.
Tray2 reports a “Downcomer backup as a % of Inflection Point Engineering maximum”, with this maximum being:
- 46% of tray spacing plus weir height if the gas density is less than 2.5 lb/ft3.
- 37% of tray spacing plus weir height if the gas density is more than 3.5 lb/ft3.
- A linear interpolation for gas densities between 2.5 and 3.5 lb/ft3.
section 10.8 contains guidelines for backup limit. For valve trays the following limits are normally used.
- 82% for new trays
- 90% for revamps
For sieve trays an FRI downcomer flood value is reported by Tray2. This value is considered to be more accurate than the backup method listed above. For sieve trays normally use the following maximums for the FRI downcomer flood value to avoid a downcomer backup problem. Meeting the Downcomer backup values is not required for these cases.
- 82% for new trays
- 90% for revamps
The FRI downcomer flood model (TR123) combines the effects of vapor entrainment (downcomer velocity) into the calculation of downcomer backup. Further, this model includes the effect that the bubbling area activity has on downcomer capacity. The higher the vapor velocity in the bubbling area, the lower the allowed velocity in the downcomer. This effect is so strong that most high pressure columns need to have low jet flood values to avoid a downcomer flood problem.
If downcomer backup is a problem, consider the following actions:
- Increase the number of passes.
- Increase the number of holes (watch for weeping).
- Increase the tray spacing.
13. Tray Spacing
Select tray spacing on the basis of both process and mechanical limitations. The majority of columns are at 24 inch (600 mm) tray spacing.
Excessive downcomer backup is the main process limitation for tray spacing. For most systems, increasing the tray spacing also increases the tray capacity. Due to this relationship, tray spacing is often varied to accomplish the following:
- Decrease costs by reducing the height of columns that have more than 60 trays.
- Avoid swaging a column by changing the tray spacing for various column sections. This typically does not include increasing tray spacing above 24 inches except for pumparound sections.
- Minimize column length/diameter ratio. Any column with top elevation over 130 feet and a length/diameter ratio over 15, or any column with a top elevation less than 130 feet and a length/diameter ratio over 20 may warrant special structural considerations. Typically, most modifications for large L/D ratios are not of great economic concern.
14. Tray Thickness
Inflection Point Engineering Standard Specification 3-18, Trays and Packing (Random and Structured), Section 3.1.a. lists minimum tray thicknesses. For carbon steel trays, use 10 gauge (0.134 inches). For alloy trays, use 14 gauge (0.074").
These thicknesses are the minimum values that provide acceptable tray life and structural strength. Generally, thicker trays are undesirable, as FRI studies have shown these trays perform with a slightly lower efficiency.
15. Outlet Weir
The outlet weir holds enough head on the tray to prevent vapor from entering the bottom of the downcomer. This prevents the loss of tray capacity due to blowing, which occurs when all the liquid is lifted off the tray floor. The disadvantage of increasing the weir height is that this increases the tray pressure drop and the tendency to weep.
15.1 Setting Weir Height
Generally, set the weir height via the desired seal (weir height minus the downcomer clearance). On atmospheric and pressurized columns, set the seal at 0.5 inches if the weir rate is less than 8 gpm/inch. If the weir rate is more than 8 gpm/inch, decrease the seal to 0.25 inches so as to minimize the downcomer backup. On rare occasions a zero or negative seal has been used; however, this practice is discouraged.
The importance of a low tray pressure drop occasionally results in the use of a zero seal in vacuum columns.
15.2 Swept Back Weirs
To reduce the weir rate or regulate the liquid distribution on three and four pass trays, some vendors may specify swept back weirs (see Section 3.2). Guidelines for the use on specification of swept back weirs are covered in Tools Documentation section 10.14 While it is rare for Inflection Point Engineering to specify swept back weirs, it is not a problem if a vendor wants to use them. Note that the area enclosed by the swept back weir and the downcomer is normally considered as downcomer area provided that it is less than 30% of the downcomer area it feeds.
15.3 Notched Weirs
Weir rates of less than 0.5 gpm/inch may cause poor flow distribution across the tray. This makes the tray prone to blowing. In this event, specify a baffled weir. Each baffle on the weir is expected to be one-half the tray spacing in height and 2 to 6 inches wide. Select a total unbaffled length that gives 2 to 3 gpm/inch. Each unbaffled segment is expected to be at least 0.25 inches wide.
15.4 Liquid Head Over the Weir
The liquid head over the weir is often calculated using a version of the Francis Weir Equation. The Glitsch Bulletin 4900 uses the following equation:
How = 0.4 (GPM/Lwi)2/3
Where:
How = head over weir, inches of liquid
gpm = liquid rate, gal/min
Lwi = weir length, inches
A more complete discussion on the effect of weir rate is located in section 10.10.
16. Recessed Seal Pans and Inlet Weirs
Recessed seal pans and inlet weirs are two other methods vendors use to provide a liquid seal that prevents vapor from bypassing the tray and escaping up the downcomer. However, their tendency to act as trash collectors makes them undesirable. Scale and any loose hardware will collect in seal pans and behind inlet weirs. This may restrict the liquid flow from the downcomer. For this reason, Inflection Point Engineering Standard Specification 3-18, Trays and Packing (Random and Structured) prohibits using sumps for purposes other than drawoff. Some vendors use inlet weirs on feed trays in efforts to better distribute the feed liquid across the tray and to seal the feed line. While not encouraged, this practice is acceptable.
17. Number of Flow Paths
Section 3 above shows the basic layouts of one, two, three and four pass trays. Trays with fewer passes are simpler and less expensive than trays with more passes. This cost differential is small and hence does not normally influence the decision on the number of passes. As the column feed rate increases, the column diameter and weir length increase with the square root of the feed rate. Hence, the weir rate increases with capacity. This eventually causes a downcomer backup problem that must be fixed by increasing the tray spacing or by increasing the number of passes. With more passes, the weir length increases and there is a lower weir rate.
Additional passes also result in shorter flow path lengths. A shorter flow path length causes a lower efficiency. To provide a manway, for accessibility, the minimum flow path length is 16 inches (400 mm). The following table gives the minimum column diameter versus the number of flow paths that Tray2 uses and that the old Glitsch design manual uses.
Number of Flow Paths | Tray2 Minimum Diameter, ft | Glitsch Preferred minimum Diameter, ft |
|---|---|---|
| 1 2 3 4 | 2.5 4.5 8.5 12.0 | - 6.0 9.0 12.0 |
18. Use of Three and Four Pass Trays
Two special concerns surround the use of three and four pass trays. The first concern is that any feed (including reboiler vapor) onto or below these trays needs to be appropriately distributed between the passes. The second concern is how the intermediate downcomer liquid is split. Many customers and their contractors prohibit using three pass trays because of these concerns. While four pass trays have the same problem, customers frequently do not forbid the use of them. Inflection Point Engineering has designed many three and four pass trays, and their use has never caused any problems. Nevertheless, before designing a three or four pass tray, check the Basic Engineering Design Questionnaire (BEDQ) to see if the customer allows their use. Regardless of what the BEDQ says, inform the customer of any decision to use three pass trays early during the project work.
18.1 Tray Layouts
The methods for three and four pass tray layouts are equal flow path length and equal bubbling area. The majority of Inflection Point Engineering's trays are designed with an equal flow path length. Tray2 default layout in the design mode is equal flow path length with the following assumptions.
a. Three Pass Trays
- The side downcomer is sized for 31 percent of the tray liquid.
- The intermediate downcomer is sized for 69 percent of the tray liquid.
- b. Four Pass Trays
- The side downcomer is sized for 21 percent of the tray liquid.
- The center downcomer is sized for 58 percent of the tray liquid.
- The intermediate downcomer is sized for 50 percent of the tray liquid.
18.2 Five Pass Trays
Occasionally, a column could be designed with five or more tray passes. Tray2 does not accommodate this many tray passes, so hand calculations are necessary. Consider using a MD Tray on these columns.
19. Hole Diameter for Sieve Trays
For a given percent hole area, decreasing the hole diameter results in the following:
- A smaller tray pressure drop
- Greater tray capacity
- A greater tendency to weep
- An increased likelihood of fouling
Design all Inflection Point Engineering sieve trays with 0.5 inch (13 mm) holes unless the Technology Specialist has instructed otherwise. Inflection Point Engineering HF Alkylation Process Unit Isostrippers are an exception to the 0.5 inch hole size rule. Due to fouling concerns, design these trays with 0.75 inch (19mm) holes.
20. Percent Hole Area for Sieve Trays
The percent hole area is defined as the hole area expressed as a percent of the bubbling area. The normal range of this variable is 5 to 15 percent. As the hole area increases, the percent jet flood and tray pressure drop will decrease, but the tendency for weeping will increase. Determine the optimum number of holes by balancing the need to limit downcomer backup versus the need to limit the tendency to weep.
20.1 F-Factor
Initially set the number of holes based on the hole F-Factor, defined as follows:
Hole F-Factor = (hole velocity) (ρV)0.5
Hole velocity = ft/s
ρV = vapor density, lb/ft3
ρL = liquid density, lb/ft3
Use the following rule for setting the hole F-Factor:
Hole F-Factor = 2.8 (ρL - ρV)0.5
Decreasing the hold F-factor by up to 20% may be advantageous in high pressure columns. This may better locate the design between the onset of weeping and downcomer backup flooding. The F-Factor for the maximum design vapor load normally ranges from 12 to 20.
20.2 Punch Area
The punch area is the bubbling area minus the obstructed area. Estimate the punch area by subtracting 20% of the whole tower area from the bubbling area.
20.3 Calculating Hole Pitch
The arrangement of holes may be triangular, square, or rectangular pitch. However, normally triangular pitch is used.
The hole pitch is expected to be in the range of 1 to 2 inches for 0.5 inch holes. For circular valves, the valve density is normally valves/ft2. This is a pitch of 3 to 6 inches. Use the following equations to convert the hole area, hole diameter, and punch area into hole pitch:
Pitch Type Pitch AH/AP N/AP N/AH
Triangular
Square
DH = Hole Diameter, inches
AH = Hole Area, ft2
AP = Punch Area, ft2
P = Pitch, inches
N = Number of Holes
21. What If the Percent Hole Area Is Less Than 5%?
For a sieve tray, a hole area of less than 5% of the bubbling area raises concerns that tray efficiency will be reduced. Mainly, vapor and liquid are not mixed as well when holes are spaced too widely. The two most common reasons for having a low percent hole area are:
- Column diameter is significantly larger than necessary. This first cause may result from the decision not to swage the upper section of a column. The resultant excess bubbling area may cause the percent hole area to drop below 5%. One possible solution is over sizing the downcomers to decrease the bubbling area.
- Relatively large downcomer area. For columns that require the downcomers to be a very high percent of the column cross-sectional area, the minimum flow path length may result in more bubbling area than is needed. This second cause is often seen in sidecut strippers or steam strippers where the V/L is relatively small. Low tray efficiency is often expected in these columns. A hole area as low as 3% is acceptable.
If the percent hole area is too small, punch the deck using the minimum desired percent hole area. Use blanking strips to limit the total number of holes. Begin with an inlet and outlet quieting zone of 4 to 5 inches.
22. Tray Pressure Drop
Assume that the tray pressure drop is the sum of the dry tray pressure drop, plus the hydrostatic head of froth on the tray. Some correlations adjust the dry tray pressure drop to account for the presence of liquid.
The hydrostatic head is assumed to have two components—the head of froth behind the weir and the head of froth over the weir. The head of froth behind the weir is normally a fraction of the weir height (e.g., 0.4). Use a variation of the Francis Weir Equation to calculate the head over the weir.
Design a tray so it is positioned between weeping and downcomer backup problems. Do not design the tray to meet a certain pressure drop. Given these facts, the following are some general guidelines as to what is typical for an actual tray:
- Most tray pressure drops are in the range of 0.09 to 0.12 psi per tray. For most process specifications use a pressure drop of 0.12 psi per tray.
- In vacuum service, use a tray pressure drop of 0.05 psi if a low pressure drop is critical.
- In columns with high density liquid, e.g., aromatic columns, an appropriate tray pressure drop may be as high as 0.15 psi per tray.
23. Turndown
The criteria used to judge turndown makes reference to weep point and dump point.
23.1 Weep Point
Weep point is the condition for a given tray where liquid starts to pass through the holes. It has been demonstrated that satisfactory operation may be obtained with some amount of weeping. A theoretical approach to tray efficiency indicates 20 percent liquid weepage causes a 10 percent loss in tray efficiency if uniform tray weepage assumed. For design loads, operation is expected to be above the weep point.
23.2 Dump Point
Dump point is the condition for the same tray where all the liquid goes through the holes. For turndown conditions, operation is expected to be well above the dump point.
23.3 Tray Efficiency
If tray efficiency is maintained at low vapor and liquid rates, holding a constant V/L ratio will cause a saving in utilities during turndown.
If tray efficiency is a problem during turndown, increase the reboiler and condenser duties to obtain the desired split. Normally there is much more concern with increasing the capacity of commercial trays rather than weepage at low throughput. A design that incorporates a low hole area to minimize weepage may be tight if additional throughput is desired.
23.4 Designing for Low Loadings in a Large Column
This difficult problem may arise if the design requires a range of loadings for initial and future operations. In this case, supply the hole area for the future and install blanking strips for initial operation. Install the blanking strips perpendicular to liquid flow. Equally divide the blanked area between the front and tail end of flow path.
23.5 Critical Tray Pressure Drop
For operations in which tray pressure drop is critical (e.g., vacuum columns), the turndown is normally very poor. Do not expect a design for low turndown.
23.6 Valve Trays
If the minimum design Vload is less than 50 percent of the maximum design Vload, or if turndown is a serious concern, specify the use of valve trays because the turndown is better than that of sieve trays. If valve trays are specified, Inflection Point Engineering Standard Specification 3-18, Trays and Packing (Random and Structured), requires the vendor to use two different valve thicknesses at least three gauge numbers apart, so as to provide a good turndown. Procedure section 4, has additional justification for the use of valve trays.
24. Derating
Vapor density and foaming are two frequently discussed derating factors. All correlations used in Tray2 have vapor density adjustments within the correlations. Tray2 allows for a user input for a foam derating factor.
Use a derating factor for foaming on systems where foaming is a reasonable possibility. The column is then derated as follows:
| Actual % Flood | = | (Calculated % Flood) / (Derating Factor) |
|---|---|---|
| Actual % Downcomer Velocity Limit | = | (% Downcomer Velocity Limit) / (Derating Factor) |
| Actual % Downcomer Flood (FRI) | = | % Downcomer Flood (FRI) / (Derating Factor) |
The presence of surfactants usually causes foam. Particulate matter, temperature, and pressure affect the degree and stability of foam. Foam derating factors are only derived through experience. Some common systems are as follows:
| SYSTEM | DERATING FACTOR |
|---|---|
| BF3, Freon | 0.90 |
| FCC Gas Con Primary Absorber | 0.75 |
| FCC Sponge Absorber | 0.75 |
| FCC MC Kero/LCO Section | 0.9 |
| FCC MC LCO PA | 0.9 |
| FCC MC Kero/LCO Sidecut Stripper | 0.9 |
| FCC Gas Con Stripper | 0.85 |
| Amine Regenerator | 0.85 |
| Amine Absorber | 0.70 |
| MEK | 0.60 |
| Caustic Regenerators | 0.15 |
| Waste Water Stripper | 0.65 |
| Cold Caustic/Gas Contacting | 0.70 |
25. Froth Initiator
A froth initiator is a device that creates intimate vapor-liquid contact at inlet of the tray flow path. This additional contact decreases or eliminates inlet side weeping, improves the flow path hydraulics, and makes more froth that increases mass transfer. D. B. Carson and K. D. Uitti of Inflection Point Engineering invented this device in an attempt to improve performance on a 20 foot diameter vacuum column that used valve trays.
Consider froth initiators for all columns with a high weep possibility.
A styrene finishing column is an example of the type of column that may make good use of a froth initiator.
A Inflection Point Engineering slotted sieve tray is the preferred alternative to using froth initiator.
Figure 1
Revision
Indication
| Attachment 1 IPE-TM-320-15 Barrel Factors | Attachment 1 IPE-TM-320-15 Barrel Factors | Attachment 1 IPE-TM-320-15 Barrel Factors | Attachment 1 IPE-TM-320-15 Barrel Factors | Attachment 1 IPE-TM-320-15 Barrel Factors | Attachment 1 IPE-TM-320-15 Barrel Factors | Attachment 1 IPE-TM-320-15 Barrel Factors | Attachment 1 IPE-TM-320-15 Barrel Factors | Attachment 1 IPE-TM-320-15 Barrel Factors | Attachment 1 IPE-TM-320-15 Barrel Factors | Attachment 1 IPE-TM-320-15 Barrel Factors |
|---|---|---|---|---|---|---|---|---|---|---|
No. Trays | Tray Spacing Inches | Receiver Temp. F | Receiver Temp. F | Receiver Pressure psig | F/D2 | R/F | Q/D2 | Tray Eff. | Comments | |
| Crude Distillation Unit | ||||||||||
| Crude Preflash Column | 30 | 24 | 100 | 100 | 5-20 | 150 | -- | -- | Maxwell | On lift |
| Crude Column | 45-55 | 24 | 100-120 | 100-120 | 5-10 | 150 | -- | -- | Maxwell | On lift (75% Fld) |
| Vacuum Column | -- | Packing | -- | -- | -- | 50 | -- | -- | Maxwell | On lift |
| Sidecut Stripper | ||||||||||
| Steam Stripped | 5-7 | 24 | -- | -- | -- | 350 | -- | -- | 50% | 10 lbs stm/bbl prod (50% Fld) |
| Reboiled | 5-7 | 24 | -- | -- | -- | 225 | -- | -- | 50% | |
| Stabilizer | 30 | 24 | 100-120 | 100-120 | 120-150 | 225 | 0.75 | -- | ||
| Naphtha Splitter | 30 | 24 | 100-120 | 100-120 | 5-20 | 200 | 0.5-0.65 | -- | 75% | |
| Visbreaking | ||||||||||
| Flash Fractionation | 16-20 | 300-500 | -- | |||||||
| Resid. Stripper | -- | 275-325 | -- | |||||||
| FCC | ||||||||||
| Main Column | 24-30 | 160 | Raw Oil Feed | |||||||
| Unicracking | ||||||||||
| Product Fractionator | 38-44 | 24-30 | Bubble point | Bubble point | 5 | 130* | R/D 1.0 min. | * | ||
| Sidecut Strippers | ||||||||||
| Steam | 6 | 24 | 450 | - | 50% | Strip 15 vol% (min) | ||||
| Reboiled | 10 | 24 | 400 | - | 60% | Strip 25 vol% (min) | ||||
| Stripper Debutanizer (not first) | 30 40 | 24 24 | 100-110 100-110 | 100-110 100-110 | 100-150 125 | 500 200 | R/D 1.0 min 0.75 | - 0.35 | 50% below feed tray 70% above feed tray 75% | |
| Naphtha Splitter Deethanizer Depropanizer | 30 30 30 | 24 24 24 | Bubble Point 100 100 | Bubble Point 100 100 | 15-20 220-250 250-300 | 200 150 - | 0.5 R/D 0.5 0.5 | 0.35 - - | 75% 80% 75% | |
| Unionfining | ||||||||||
| Naphtha Splitter | 30 | 24 | Bubble Point | Bubble Point | 10-25 | 05.-1.0 | 80% | |||
| NHT Stripper (Reboiled) | 25 | 24 | 100-130 | 100-130 | 125-150 | 250 | 0.3 | 70% | 20 Stripping Trays | |
| Stripper (Steam Stripped) | 30 | 24 | 100-130 | 100-130 | 100-150 | 500 | R/D 1.0 min | 50% below feed tray 70% above feed tray | AGO/VGO 25 F Water DP Margin | |
| O2 Stripper | 15 | 24 | 100 | 100 | 120 | 400-500 | 0.15 | 0.39 | ||
| Flashpoint Fractionator | 20 | 24 | 200 | 0.15 | For AGO (Reboiled) | |||||
| Flashpoint Fractionator | 20 | 24 | 500 | 0.15 | For VGO (Feed Heater) | |||||
| Recycle Gas Scrubber | 9 | 24 | 33 | 70% foam derating factor | ||||||
| Unsaturated Gas Plant | ||||||||||
| Primary Absorber | 30-40 | 24 | 100 | 100 | 200-250 | 600 | l/v=1.5 | 33% | On rich oil | |
| Sponge Absorber | 35 ft | Packing | 125 | 125 | 200-250 | 400-480 | l/v=0.4 | Trays - 25% #2 RSR-5’ HETP | On rich oil | |
| Stripper | 30-36 | 24 | 100 | 100 | 200-250 | 550 | d/f=0.26 | 0.42 | 50% | |
| Debutanizer | 30-40 | 24 | 100-120 | 100-120 | 150-170 | 300 | 0.75 | 0.41 | 75% | |
| Saturated Gas Plant | ||||||||||
| LPG Deethanizer | 30-36 | 30 | 100 | 400-500 | 400-500 | 100 | 1.5 | C2 75%, H2S 50%, H20 50% | ||
| Refrig. Deethanizer | 36 | 30 | 30 | 335 | 335 | 200 | 0.4 | |||
| Debutanizer | 30-40 | 24 | 100-145 | 150 | 150 | 260-350 | 0.50-1.00 | 0.37 | 75% | |
| C3/C4 Splitter | 40-55 | 24 | 100-130 | 220-260 | 220-260 | 180 | 1.3 | 0.32 | 80% | |
| Platforming | ||||||||||
| Depropanizer | 30 | 24 | 200 | 0.50 | ||||||
| Debutanizer | 30 | 24 | 100-120 | 150-250 | 150-250 | 340 | 0.3-0.50 | 0.40 | 75% | |
| Depentanizer | 36 | 24 | 125 | 125 | 250 | 0.55 | 0.44 | 75% | ||
| Deethanizer (Debut.Liquid) | 40 | 30 | 250 | 0.55 | 0.21 | C2 75% | ||||
| Ref. Splitter | 50 | 24 | 130-150 | 1.0 | 1.0 | 100-150 | 0.5-0.55 | 0.35-0.45 | 75% | |
| Recovery Plus | 30% | |||||||||
| Detal | ||||||||||
| Isostripper | 70 | 24 | 100 | 140 | 140 | -- | -- | |||
| Depropanizer | 36 | 150 | 1.5 | |||||||
| HF Stripper | 20 | 24 | 100 | 200 | 200 | 250 | -- | V/L=0.35 | ||
| Sulfolane | ||||||||||
| Stripper | 30-36 | 24 | 120 | 1.0 | 1.0 | 400-600 | -- | |||
| Recovery Column | 30-34 | 30 abv fd 24 blw fd | 100 | 220 mm Hg | 220 mm Hg | 250-450 | -- | Also 40-65 Extract/D2 | ||
| Aromatic Fractionation | ||||||||||
| Benzene | 60 | 24 | 160 | 1.0 | 1.0 | 180-220 | 0.8-1.1 | 0.30 | 80% | IR Below Sidecut |
| Toluene | 60 | 24 | 235 | 1.0 | 1.0 | 105-125 | 1.1-1.3 | 0.30 | 80% | Low pressure |
| Toluene | 70-75 | 24 | 335 | 45 | 45 | 120-130 | 1.2-1.4 | 0.32 | 80% | Pressurized for reboiling |
| Xylene | 60 | 24 | 310 | 1.0 | 1.0 | 60-90 | 1.2-1.8 | 80% | Low pressure | |
| Xylene Splitter | 180-220 | 18 | 440-460 | 80-100 | 80-100 | 50-80 | 8 - 9 | 80% | High Recovery (85/90) | |
| Xylene Splitter | 140-200 | 18 | 440-460 | 80-100 | 80-100 | 60-80 | 1.5-2.8 | 0.45-0.50 | 80% | Low Recovery (10/30) |
| O-Xylene Rerun | 80-90 | 18 | 265-275 | 1.0 | 1.0 | 80-100 | 1.5-2.5 | 0.30 | 80% | 98-99.5 Purity |
| Xylene Rerun | 90-120 | 18 | 440-460 | 80-100 | 80-100 | 60-90 | 1.5-2.8 | 0.35-0.40 | 80% | High Pressure |
| Xylene Rerun | 100-140 | 14-18 | 440-460 | 80-100 | 80-100 | 65-100 | 1.5-2.8 | 0.40-0.45 | 70% | MD Trays |
| Amine Unit | ||||||||||
| Amine Regenerator | 50% | |||||||||
| Penex Unit | ||||||||||
| Deiso Pentanizer | 80-100 | 121 | 22 | 22 | 1.8-2.5 | 75% | nC5 Sidedraw | |||
| Parex | ||||||||||
| Extract | 50 | 24 | 250 | 1.0 | 1.0 | 165 | 0.65 | 0.30 | 80 | |
| Raffinate | 70 | 24 | 250 | 1.0 | 1.0 | 160 | 0.75 | 0.35 | 80 | IR Below Sidecut |
| Raffinate | 90 | 14-18 | 250 | 1.0 | 1.0 | 185 | 0.75 | 0.40 | 62 | MD trays |
| Finishing | 60 | 24 | 150 | 1.0 | 1.0 | 110 | 1.0-1.2 | 0.30 | 80 | |
| Detergent Alky | ||||||||||
| Paraffin | 36 | 30-24 | 200 | 30-45 mm Hg | 30-45 mm Hg | Top 32 Bottom 120 | 0.75 | Top 0.032 Bott. 0.12 | 75 | |
| Pacol PreFrac | ||||||||||
| Stripper | 55 | 24 | 190 | 1.0 | 1.0 | 103 | .45 | 0.29 | Cool Receiver to condense water | |
| Rerun | 65 | 24 | 400 | 1.0 | 1.0 | 118 | 0.9 | 0.28 | ||
| Propylene Unit | ||||||||||
| C3 Splitter | 180 | 14 | 80 | 160-190 | 160-190 | 33-57 | 14.5 | 0.55-0.62 | 80% | MD trays heat pumped |
| Q-Max | ||||||||||
| Cumene/DIPB Alpha ~ 3.7 | 50% | |||||||||
| Tatoray | ||||||||||
| Stripper | 44 | 24 | 104 | 120 | 120 | 200 | 0.4-0.8 | 0.35 | 70 | |
| Isomar | ||||||||||
| Deheptanizer | 25-40 | 24 | 104-130 | 40-100 | 40-100 | 0.25-0.80 | 0.25-0.33 | 70 | ||
| Sour Water Stripper | 40 | |||||||||
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