- Pressure Vessel Design Calculation Formula Excel
- Vessel Design Calculation Excel Spreadsheet
- Pressure Vessel Nozzle Design Calculation Excel
- Vessel Design Calculation Excel Spreadsheet
A Knockout drum with a misteliminator is common whenever a process requires entrained droplets to beseparated from a vapor stream. A simple knockout drum (no mist eliminator) willremove droplets larger than about 380 microns by gravity settling M. generallygravity settling removes more than 90% of the liquid entering the vessel.However the remaining droplets smaller than 380 microns can be a significantproblem for a downstream unit. A mist eliminator in the top of the knockoutdrum will remove the remaining droplets down to a diameter of 6 microns orless, depending on the type of mist eliminator. A knockout drum with misteliminator can achieve an overall efficiency of 99.99% liquid removal.
Knockout Drum Configurations
- 170Mpa for the given pressure vessel. Design So the design is safe from theoretical calculations. Dished end thickness calculations: Thickness required at the dished end t d =Pd/4σ h t d =3.5.3500/(4.170) = 18.01 in the calculation hoop stress σ h is taken as allowable limit of the material 170Mpa.
- FREE Tank Baffles Design Calculation By Daniel de la Torre tank, baffle, design This template contains a series of calculation sheets to assist you.
- The key design variable for entrainment separation vessels is a vapor load factor, first derived by souders and brown for predicting flooding in distillation columns (2). The derivation is based on the force balance calculation on a droplet falling through a vapor.
Knockout drums may be orientedvertically or horizontally. In both types, the mist eliminator may also beoriented vertically or horizontally. For a vertical mist eliminator (horizontalvapor flow), the drainage flow is cross-current, whereas for vertical upflowthe drainage flow is counter-current. Because cross-current flow results inless liquid holdup, a vertical mist eliminator can be operated at a highervapor loading without reentrainment (depending on the liquid load and on theheight).
Download encarta 2009 for windows 7. Design of Rectangular water tank excel sheet web share 2019-12-27T06:51:00-08:00 5.0 stars based on 35 reviews Design of Rectangular water tank xls Example of water tank design in excel sheeet. Water tank 1: Capacity: 80000 Litres Material. Jailbreak ipad ios 9.3 5.
A horizontal entrainmentseparation vessel can also be designed to operate as a droplet coalesce. Inthis case, the mist eliminator operates beyond the reentrainment load. Large,coalesced droplets blow off the down stream side of the mist eliminator and eithersettle by gravity or are collected by a vane type mist eliminator.
A preliminary analysis maysuggest that a horizontal knockout vessel may reduce cost. In the finalanalysis, however, many factors should be evaluated to arrive at the decisionbetween a horizontal versus a vertical vessel.
Design Load Factor
The key design variable forentrainment separation vessels is a vapor load factor, first derived by soudersand brown for predicting flooding in distillation columns (2). The derivationis based on the force balance calculation on a droplet falling through a vapor.
Fv1 = Vv *(ρV/(ρL-ρV))^.5
This vapor load factor is alsoreferred to as a K factor for purposes of determining the flux cross sectionarea of a mist eliminator or knockout drum. Typically, .3 to .35 ft/sec is usedas design K factor for entrainment separation vessel.
By expressing vapor loading interms of the Souders-Brown transformation, a design variable is created whichis largely independent of the system variable (molecular weight, density,pressure, temperature, viscosity, surface tension etc). this combined variablevapor load factor correlates buoyancy and differential inertial effects for awide range of liquid/vapor systems. A similar design variable, designated Fs isalso used for Liquid/Vapor systems. Fs accounts for vapor inertial effects butnot buoyancy effects or differential inertial effects.
Fs is defined as :
In hydrocarbon liquid/vaporsystems at a pressures higher than approximately 120 Psia, system load factorsless than 0.35 ft/sec should be used as the design basis. Droplet terminalvelocity departs significantly from Stoke's Law as the system approaches thecritical point. The main reason is that the interfacial tension decreases(approaches zero at the critical point ). Another reason is that the densitydifference (liquid-vapor) approaches zero.
Knockout Drum Design
A knockout drum (vertical orhorizontal) is typically sized for a system load factor of 0.3 to 0.35 ft/sec.However, because of the need for a mist eliminator support ring, and because ofroundup to the next standard vessel diameter, vertical knockout drums typicallyhave a design system load of 0.25 to 0.30 ft/sec. They typically operatebetween 0.20 and 0.35 ft/sec vapor load factor (3,4). If other constraints,such as space or cost, require a smaller vessel diameter, a design load factorof 0.45 ft/sec may be used; the result is a reduced margin of safety and an increased entrainment load on the misteliminator.
A vapor load factor of 0.2 to0.35 ft/sec is the optimum range for mist eliminators operating in verticalupflow. Consequently, a full diameter mist eliminator is usually appropriatefor a vertical knockout drum. However, if the knockout drum is sized accordingto a vapor load factor less than 0.2 ft/sec, the mist eliminator should besized for optimum efficiency. Consequently, a design other than the typicalfull diameter mist eliminator may be appropriate. For example, if the optimum mistpad diameter is significantly less than the vessel diameter, a sleeve mountingmay be appropriate. On the other hand, if the vessel diameter is too small toaccommodate the required mist eliminator area as a full diameter unit, the misteliminator may be oriented in the longitudinal axis.
For horizontal vessels, thediameter is based on the design factor of 0.35 ft/sec (as for verticalvessels).
However, because of liquidholdup, the cross sectional area for vapor flow causes an operating vapor loadfactor of 0.4 to 0.5 ft/sec for vertically installed mist eliminators. Thisvapor load corresponds to the optimum load for wire mesh pads in the horizontalflow. The design basis for the horizontal mist eliminator in a horizontalvessel should be K = 0.5 ft/sec (or less).
The height of a vertical knockoutdrum is constrained by a number of factors. The following design guidelines aretypical:
1.The top of a horizontal mist eliminator shouldbe at least one-half vessel diameter from the exit nozzle (top or sidemounted). This reduces the non-uniform flow through the pad caused by a radialpressure gradient.
2.The bottom of a mist eliminator should be atleast one vessel diameter from the centerline of the inlet nozzle (sidemounted). One-half vessel diameter is used in some cases (for light liquidloading) to satisfy space constraints. However, if the inlet fluid is aflashing liquid, one vessel diameter is essential for vapor/liquid disengaging.
3.The liquid level should be at least one-halfvessel diameter below the side inlet nozzle centerline in order to avoidinducing.
4.If the vessel is to provide a liquid surgevolume, the appropriate height increment will be required. For preliminarydesigns and cost estimates, the vessel aspect ratio (height/diameter) may be estimatedat 2.5 (for zero liquid holdup) or 3.0 (to allow for liquid holdup).
Knockout Drum OperatingFlexibility
Knockout drum turn-down andsurplus capacity (turn-up), result from the two-phase flow characteristics ofthe system. The process conditions for most knockout drum and mist eliminatorsapplication occur just below the typical pipe flow regime map. At a system loadfactor below approximately 0.5 ft/sec, the two- phase flow regime iscounter-current for the majority of the liquid. At a system load factor around1.0 ft/sec , the two phase flow regime becomes annular mist flow (for low tomoderate pressure systems). Between 0.5 and 1.0 ft/sec the entrainment loadincreases from a slight to 100% entrainment.
Entrainment load increasesconsiderably beyond a system load factor of 0.5 ft/sec. Therefore manydesigners would consider this value to be upper practical limit of vaporloading in a knockout drum. Since a knockout drum is designed on the basis of0.3 to 0.35 ft/sec system load factor, there is around 50% to 100% surpluscapacity.
Mist pad flooding typicallyoccurs around 0.5 to 0.7 ft/sec. Therefore, the practical maximum capacity ofthe mist pad/knockout drum combination is again approximately 0.5 ft/sec andthe surplus capacity is about 50%.
Pressure Vessel Design Calculation Formula Excel
Vessel Nozzles andInternals
A knockout drum typically has aside entry nozzle the vapor outlet is generally a top exit nozzle. The inletnozzle should be located one vessel diameter below the mist pad and one-halfvessel diameter above the normal liquid height. This configuration allows forthe maximum droplet separation by gravity as well as gas jet dispersion andflow distribution. Straightening vanes have been used to partially deflect theinlet jet, but no definitive conclusion have been reached concerning thebenefits of straightening vanes in entrainment separation vessels.
In older plants, inlet deflectorbaffles were installed in some knockout drums. The idea was to direct the inletjet downward and thus to improve the effectiveness of separation. Such aconfiguration causes a large pressure drop and in many cases interferes withentrainment separation because of breaking coalesced droplets into smallerones. There is no evidence that an inlet deflector improves performance.
If side exit nozzles are used, aspecial arrangement is required to avoid non-uniform flow in the misteliminator.The centerline of a side exit nozzle should be one-half pad diameterabove the mist pad. Alternatively an upward directed elbow internal nozzle fora side exit can be used to promote uniform flow in the mist pad.
Nozzle sizes correspond to theadjoining pipe size. In the preliminary design of the vessel, the nozzle sizecan be estimated by a 'quick estimate' method.
A horizontal entrainmentseparation vessel can also be designed to operate as a droplet coalesce. Inthis case, the mist eliminator operates beyond the reentrainment load. Large,coalesced droplets blow off the down stream side of the mist eliminator and eithersettle by gravity or are collected by a vane type mist eliminator.
A preliminary analysis maysuggest that a horizontal knockout vessel may reduce cost. In the finalanalysis, however, many factors should be evaluated to arrive at the decisionbetween a horizontal versus a vertical vessel.
Design Load Factor
The key design variable forentrainment separation vessels is a vapor load factor, first derived by soudersand brown for predicting flooding in distillation columns (2). The derivationis based on the force balance calculation on a droplet falling through a vapor.
Fv1 = Vv *(ρV/(ρL-ρV))^.5
This vapor load factor is alsoreferred to as a K factor for purposes of determining the flux cross sectionarea of a mist eliminator or knockout drum. Typically, .3 to .35 ft/sec is usedas design K factor for entrainment separation vessel.
By expressing vapor loading interms of the Souders-Brown transformation, a design variable is created whichis largely independent of the system variable (molecular weight, density,pressure, temperature, viscosity, surface tension etc). this combined variablevapor load factor correlates buoyancy and differential inertial effects for awide range of liquid/vapor systems. A similar design variable, designated Fs isalso used for Liquid/Vapor systems. Fs accounts for vapor inertial effects butnot buoyancy effects or differential inertial effects.
Fs is defined as :
In hydrocarbon liquid/vaporsystems at a pressures higher than approximately 120 Psia, system load factorsless than 0.35 ft/sec should be used as the design basis. Droplet terminalvelocity departs significantly from Stoke's Law as the system approaches thecritical point. The main reason is that the interfacial tension decreases(approaches zero at the critical point ). Another reason is that the densitydifference (liquid-vapor) approaches zero.
Knockout Drum Design
A knockout drum (vertical orhorizontal) is typically sized for a system load factor of 0.3 to 0.35 ft/sec.However, because of the need for a mist eliminator support ring, and because ofroundup to the next standard vessel diameter, vertical knockout drums typicallyhave a design system load of 0.25 to 0.30 ft/sec. They typically operatebetween 0.20 and 0.35 ft/sec vapor load factor (3,4). If other constraints,such as space or cost, require a smaller vessel diameter, a design load factorof 0.45 ft/sec may be used; the result is a reduced margin of safety and an increased entrainment load on the misteliminator.
A vapor load factor of 0.2 to0.35 ft/sec is the optimum range for mist eliminators operating in verticalupflow. Consequently, a full diameter mist eliminator is usually appropriatefor a vertical knockout drum. However, if the knockout drum is sized accordingto a vapor load factor less than 0.2 ft/sec, the mist eliminator should besized for optimum efficiency. Consequently, a design other than the typicalfull diameter mist eliminator may be appropriate. For example, if the optimum mistpad diameter is significantly less than the vessel diameter, a sleeve mountingmay be appropriate. On the other hand, if the vessel diameter is too small toaccommodate the required mist eliminator area as a full diameter unit, the misteliminator may be oriented in the longitudinal axis.
For horizontal vessels, thediameter is based on the design factor of 0.35 ft/sec (as for verticalvessels).
However, because of liquidholdup, the cross sectional area for vapor flow causes an operating vapor loadfactor of 0.4 to 0.5 ft/sec for vertically installed mist eliminators. Thisvapor load corresponds to the optimum load for wire mesh pads in the horizontalflow. The design basis for the horizontal mist eliminator in a horizontalvessel should be K = 0.5 ft/sec (or less).
The height of a vertical knockoutdrum is constrained by a number of factors. The following design guidelines aretypical:
1.The top of a horizontal mist eliminator shouldbe at least one-half vessel diameter from the exit nozzle (top or sidemounted). This reduces the non-uniform flow through the pad caused by a radialpressure gradient.
2.The bottom of a mist eliminator should be atleast one vessel diameter from the centerline of the inlet nozzle (sidemounted). One-half vessel diameter is used in some cases (for light liquidloading) to satisfy space constraints. However, if the inlet fluid is aflashing liquid, one vessel diameter is essential for vapor/liquid disengaging.
3.The liquid level should be at least one-halfvessel diameter below the side inlet nozzle centerline in order to avoidinducing.
4.If the vessel is to provide a liquid surgevolume, the appropriate height increment will be required. For preliminarydesigns and cost estimates, the vessel aspect ratio (height/diameter) may be estimatedat 2.5 (for zero liquid holdup) or 3.0 (to allow for liquid holdup).
Knockout Drum OperatingFlexibility
Knockout drum turn-down andsurplus capacity (turn-up), result from the two-phase flow characteristics ofthe system. The process conditions for most knockout drum and mist eliminatorsapplication occur just below the typical pipe flow regime map. At a system loadfactor below approximately 0.5 ft/sec, the two- phase flow regime iscounter-current for the majority of the liquid. At a system load factor around1.0 ft/sec , the two phase flow regime becomes annular mist flow (for low tomoderate pressure systems). Between 0.5 and 1.0 ft/sec the entrainment loadincreases from a slight to 100% entrainment.
Entrainment load increasesconsiderably beyond a system load factor of 0.5 ft/sec. Therefore manydesigners would consider this value to be upper practical limit of vaporloading in a knockout drum. Since a knockout drum is designed on the basis of0.3 to 0.35 ft/sec system load factor, there is around 50% to 100% surpluscapacity.
Mist pad flooding typicallyoccurs around 0.5 to 0.7 ft/sec. Therefore, the practical maximum capacity ofthe mist pad/knockout drum combination is again approximately 0.5 ft/sec andthe surplus capacity is about 50%.
Pressure Vessel Design Calculation Formula Excel
Vessel Nozzles andInternals
A knockout drum typically has aside entry nozzle the vapor outlet is generally a top exit nozzle. The inletnozzle should be located one vessel diameter below the mist pad and one-halfvessel diameter above the normal liquid height. This configuration allows forthe maximum droplet separation by gravity as well as gas jet dispersion andflow distribution. Straightening vanes have been used to partially deflect theinlet jet, but no definitive conclusion have been reached concerning thebenefits of straightening vanes in entrainment separation vessels.
In older plants, inlet deflectorbaffles were installed in some knockout drums. The idea was to direct the inletjet downward and thus to improve the effectiveness of separation. Such aconfiguration causes a large pressure drop and in many cases interferes withentrainment separation because of breaking coalesced droplets into smallerones. There is no evidence that an inlet deflector improves performance.
If side exit nozzles are used, aspecial arrangement is required to avoid non-uniform flow in the misteliminator.The centerline of a side exit nozzle should be one-half pad diameterabove the mist pad. Alternatively an upward directed elbow internal nozzle fora side exit can be used to promote uniform flow in the mist pad.
Nozzle sizes correspond to theadjoining pipe size. In the preliminary design of the vessel, the nozzle sizecan be estimated by a 'quick estimate' method.
The vessel manway may allowvessel entry below or above the mist eliminator. A manway location below themist eliminator is typical. It should be located at 90 degrees from the inletjet.
A vortex breaker in the bottom ofthe vessel prevents potential pump suction problems if a pump is used to removecollected liquids.
Tangential entry nozzles havebeen used on knockout vessels, but the swirling action of the gas can interferewith the operation of the mist eliminator. The insertion type unit may be usedwith a tangential inlet.
Selecting MistEliminators
The term 'mist eliminator' isused to denote two basic types: the fiber-bed (or candle) type, and the mistpad (or mesh) type. The fiber-bed is typically a set of cylindrical units whichoperates at a lower gas flux (lower system load factor) than the mist pad type.The mist pad type may be constructed from knitted wire mesh, woven wire mesh,or corrugated parallel plates. The typical mist pad is an eight inch thick disk(6 inch mesh thickness plus two inches for grids) which mounts in the bore of avessel such as a distillation column or entrainment separation vessel. Typicalmesh thickness varies from 4 inches to 12 inches depending upon the efficiencyrequired.
Mist pads are manufactured in anarray of unit designs to satisfy a variety of criteria such as maximumefficiency, pressure drop constraints, non fouling, or corrosion.
Vane Mist Eliminators
The Vane type mist pad is alsocalled a parallel plate type or a 'chevron' type. Vane mist eliminatorstypically operate at higher vapor load factors than wire mesh types because ofless susceptibility to flooding. A design K factor of 0.45 ft/sec is typicalfor vertical upflow (0.65 ft/sec for horizontal flow).
Vane mist eliminators are alsoless susceptible to fouling than wire mesh types. Higher flow rate of drainageliquid prevents adherence of solid particles to the surface of the plates.
The efficiency of vane misteliminator is less than that of wire mesh because of lower surface area perunit volume (specific surface area). However for many chemical processes theefficiency is adequate to control entrainment.
Vane Units may be used inconjunction with wire mesh pad such as for a coalescing knockout drum describedearlier, in which the vane unit is installed downstream of the wire mesh pad.The opposite configuration (vane unit upstream of the wire mesh pad) may beused in a fouling service. The vane unit removes the solid particulates (andlarger droplets), whereas the wire mesh unit removes the small droplets.
In general, vane mist pads shouldbe selected when high liquid rates or high particulate loading are expected.TEX-MESH Technical bulletin 104 discusses design and selection guidelines forvane mist eliminators.
Mist EliminatorsOperating Envelope
The operating envelopes of theentrainment separation vessel and the mist eliminator should be matched tooptimize efficiency and cost.
Since a mist eliminator functionsprimarily by inertial impaction, higher vapor velocity corresponds to higherefficiency. Increasing liquid load can induce flooding. Flooding can interferewith entrainment removal even after the upset subsides and flow returns tonormal. Eventually, the flood will drain away and the pad will operateproperly. Figure 2A shows the operating envelope of a TEX-MESH TM-1109 misteliminator in terms of pressure drop versus system load factor. Below the floodpoint the mist eliminator operates along the curves representing a particularentrainment rate. Once the flood point is reached the pressure drop is notquite unique function of vapor rate and liquid rate. Furthermore, there is ahysteresis effect when vapor or liquid rate is reduced. This hysteresis isbelieved to be caused by the meta-stable holdup volume in the mist pad matrix.
Figure 2B depicts the efficiencyversus droplet size for a TEX-MESH TM-1109 mist eliminator at the design loadfactor of 0.35 ft/sec. At a vapor load greater than the design point, thecut-point diameter decreases. Likewise for decreased vapor load, the cut-pointdroplet size increases. Below about 0.1 ft/sec system load factor, inertialimpaction diminishes considerably.
Consequently, the efficiency ofdroplet capture also decreases. For example, the curve in figure 2B has a D99cut-point of 5.5 microns (99%efficiency at 5.5 microns for 0.35 ft/sec vaporload factor). For a vapor load factor of 0.5 ft/sec the D99 cut-point shifts to4.7 micron. For a vapor load factor of 0.1 ft/sec the D99 cut-point shifts to10.5 microns.
Blanking to adjustoperating range
Because mist eliminators have afairly narrow operating range for efficient droplet removal, blanking platesare sometimes used to increase the flux through an existing mist pad. Oftensegmental blanking plates at the sides of a full diameter square misteliminator provide operating conditions in the optimum range. For maximumeffectiveness blanking plates may be placed opposite one another on both sidesof the pad.
Mist Pad Mounting
A mist pad is mounted in sectionswhich are sized to pass through the manway. The sections are supported by asupport ring (typically 2' X ¼')
The sections are fastened bytie-wires, 'j' bolts, or hold-down bars. The sections are also tie wiredtogether. The grids on a wire mist pad not only maintain the integrity of themesh, but also provide support up to maximum span of about six feet. For plasticgrids, the span should be reduced to about four feet. Support beams across thevessel are used to support longer spans of mist pad sections. In some cases,grids may be constructed from heavy-duty metal bars to span more than six feet.
Dual support rings (above andbelow) are sometimes used for mounting mist eliminators. In this case, one ofthe rings has a removable segment for mounting and demounting the pad.
Vane mist pads do not need gridsbecause the corrugated plates and tie bolts provide structural rigidity.However, support beams are still required to support spans longer than sixfeet. Dual support rings, held-down bars, or 'J' bolts may be used to securethe sections.
If the knockout is appreciablylarger than the correct diameter for a mist pad, it is often more costeffective to install the optimum diameter pad than to blank a full diameterpad. One approach is to install a vertical sleeve for mounting the misteliminator. Another approach is to mount a 'can' on top of a wide support ring.
TEX-MESH Technical bulletin 103provides additional details on the installation of mist eliminators.
Operating Problems
If specified properly, a mist padgenerally operates effectively and is essentially an inconspicuous component ina process. However, problems are generally a result of fouling (plugging of themist pad by solid particles). At start-up, if the process equipment upstream ofthe mist pad is not flushed adequately, the mist pad is likely to collect dirt,scale, and other debris.
Furthermore, after the plant hasoperated for some time, solids can eventually plug the mist eliminator.
Mist pads are efficientcollectors of solids as well as liquids. If the solids are likely to reach themist eliminator, a continuous or intermittent wash system above the padestablishes counter-current wash flow throughout the pad. Spraying from underthe pad establishes heavy liquid loading at the bottom and a 'dry' condition atthe top of the pad. It is critical to limit the total liquid loading (washliquid plus entrainment) to about 1.0 gpm/ft2. If higher liquid loading isunavoidable, then a corresponding decrease in vapor loading is required toavoid flooding.
Vane mist pads seldom failbecause of fouling. Solids either pass through or are washed off by the coalescedliquid.
Relief Panels have been installedin the mist pads, but they often cause problems. When a mist pad becomesplugged, either the excess pressure drop indicates the problem, or tie wires orother mechanical supports fail, causing an upset in the process. A fouled padis difficult to clean, but it is sometimes done.
Non-Uniform flow in a mist padcan cause a local re-entrainment or local inefficiency.
If fouling is not present,non-uniform flow is caused by improper placements of nozzles, baffles orblanking plates.
Since wire mesh mist eliminatorstypically are constructed from stainless steel wire 0.006 to 0.011 inch indiameter, if corrosion failure is a problem, it will become obviousimmediately. Correct material selection is essential.
Other EntrainmentSeparators
A cyclone separator can be usedto collect entrainment, but the efficiency decreases with increasing diameter.Consequently, at the scale of process plant equipment, the cost and efficiencyoften are not competitive compared to a knockout drum with a mist eliminator.
Sometimes, a mist eliminatorknockout drum is used downstream of cyclone separator to improve the efficiencyof entrainment separation.
Electrostatic precipitators areoften used to remove small droplets as well as particulates. They are much morecostly than knockout drum mist eliminators and significantly increase risk ofexplosion with combustible materials. For these reasons, a mist eliminator isoften used upstream of an electrostatic precipitator.
Conclusion
Vessel Design Calculation Excel Spreadsheet
The purpose of an entrainmentseparator is to maximize the detrimental effect of entrained liquid in a vaporstream. Very often, a knockout drum with a mist eliminator is the most costeffective method for entrainment control. Properly designed, the unit willprovide trouble-free performance for many years.
Pressure Vessel Nozzle Design Calculation Excel
Download: Design of Gravity Deacanter
Vessel Design Calculation Excel Spreadsheet
Tagged as : Piping Design
