Page : 1 of 45
KLM Technology Technology Group
Rev: 01
Practical Engineering Engineering Guidelines Guidelines for Processing Processing Plant Solutions
www.klmtechgroup.com
Feb 2011
Author:
KLM Technology Group #03-12 Block Aronia, Riverria Condovilla, Taman Tampoi Utama Jalan Sri Perkasa 2 81200 Johor Bahru Malaysia
Distillation Tray Hydraulic
Rev 01 Aprilia Jaya Checked by:
(ENGINEERING DESIGN GUIDELINE)
Karl Kolmetz
TABLE OF CONTENT INTRODUCTION
4
Scope
4
Type of Tray Distillation
5
General Design Consideration Consideration
13
Tray Hydraulic Parameter
15
DEFINITION
29
NOMENCLATURE
32
THEORY OF THE DESIGN
34
(A). Tray Work
34
(B). Physical Properties
35
(i)
Density
35
(ii (ii)
Vis Viscosit osity y
36
(iii (iii))
Surf Surfac ace e Tens Tensio ion n
36
(C). Principal of Mass Transfer
36
(D). Tray Calculations
37
(i) (i)
The The Sele Select ctiion of Pass Pass Tray Tray
37
Page Page 2 of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
(ii)
Wee Weep Poin oint
38
(iii (iii))
Plat Plate e Pres Pressu sure re Drop Drop
39
(iv) (iv)
Down Downco come merr De Desi sign gn
45
(v) (v)
Entr Entrai ainm nmen entt (Jet (Jet Floo Floodi ding ng))
47
(vi) (vi)
Tray Tray Effi Effic cienc iency y
50
APPLICATION
54
REFEREENCE
59
CALCULATION SPREADSHEET SPREADSHEET Tray Hydraulic Design Spreadsheet.xls
60
LIST OF TABLE Table 1: The Detail of Cap Size and Weir Height
22
Table 2: R VW, KC, K O, ρVM Valve
42
LIST OF FIGURE Figure 1: Internal of Bubble Cap Tray
6
Figure 2: Sieve Tray
7
Figure 3: Dual Flow Tray
8
Figure 4: Valve Tray
9
Figure 5: Kind of Baffle Tray; (a) Shed Deck Tray, (b) Side to Side Tray, (c) Disk and Donuts Tray
11
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 3 of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
Figure 6: Typical Operating Region of Tray Column
16
Figure 7: Type of downcomer; (a) Sloped downcomer, (b) Straight
Downcomer, (c) Truncated downcomer, (d) Steparc downcomer
19
Figure 8: Tray Components
25
Figure 9: Two Pass Tray Components
26
Figure 10: Three Pass Tray Components
27
Figure 11: Four Pass Tray Components
28
Figure 12: Schematic Description of a Tray Section
35
Figure 13: Selection of Liquid Flow Arrangement
38
Figure 14: Weep Point Correlation
39
Figure 15: Orrifice Coefficient on Sieve Tray
44
Figure 16: Relation between Downcomer Area and Weir Length
45
Figure 17: Liquid Height in The Tray
47
Figure 18: Fair Coefficient
48
Figure 19: Entrainment Correlation
49
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 4 of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
INTRODUCTION Scope This design guideline covers the basic elements of tray hydraulics in sufficient detail to allow an engineer to design a trayed tower with the suitable size of tray spacing, weir height, holes, down-comer, and open area. These factors will influential flooding and weeping, and will effect the tray performance, capacity and efficiency. The design of trays depends on the density, the rate of vapor and liquid through the tray. tray. Each Each tray tray in a distil distillat lation ion column column is de desig signe ned d to promo promote te conta contact ct be betwe tween en the vapor and liquid on the stage, stage, so there is mass and heat transfer. Ideally, the vapor vapor and liquid leaving the stage are in equilibrium. Equilibrium is a function of the rate of mass and heat transfer between liquid and vapor in distillation and it has an effect on the efficiency of tray. To increase efficiency and capacity of tray, a system is needed which will cover the whole spectrum of tray applications. One of the keys to make good quality products and high purities is tray hydraulics. Parameters of tray hydraulics beside the geometry of the tray as it mention in first paragraph, are vapor-liquid loading, the allowable pressure drop on the tray and in the downcomer, flooding, turndown and weir loading. The design of tray hydraulics hydraulics may be influenced influenced by many factors, factors, includin including g process process requir requireme ement nts, s, econo economic mics s an and d safety safety.. In this this secti section, on, the there re are tab tables les tha thatt assis assistt in making these factored calculations from the various reference sources. Generally, path flow liquid on tray is divided into single pass, two pass, three pass, and four pass. In this guideline, these differences will be discussed in detail for the proper engineering design for vapor-liquid loading and down comer design. The theories used in this guideline are commonly used in industries such as Bennet, Van Winkle, Fair and Eduljee. Their application to tray hydraulic theory with examples will help the engineer understand tray hydraulics and be ready to perform the actual design of the trayed tower. Includ Included ed in this this gu guide idelin line e is an examp example le dat data a sheet sheet wh which ich is ge gene nera rally lly used in the industry and a calculation spreadsheet for the engineering design.
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 5 of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
Types of Tray Distillation Column Distillation is the most widely used separation process in the chemical industries. It is normally used to separate a mixture of materials to obtain one or more desired products which is achieved by selection of conditions of temperature and pressure so that at least a vapor vapor an and d a liquid liquid phase phase coexis coexistt an and d a differ differen ence ce in relat relative ive conce concentr ntrati ation on of the the materials to be separated in the two phases is attained. Trays Trays are the most most commo commonly nly selec selected ted type type of disti distilla llatio tion n colum column. n. Traye Trayed d Co Colum lumns ns utilize a pressure and temperature differential to separate the products. For most tray columns, the weir holds a liquid level of each tray. The vapor must overcome this liquid head to move up the column. On the tray the vapor and liquid are contacted and then above the tray they are separated. Trayed column perform well in high liquid and vapor loading. At low flow parameters the capacity and efficiency of trays can be reduced. Tray have higher pressure drop than packing, and it may also have higher resistance to corrosion. corrosion. Some other items are to consider consider when to use trays in a tower. 1. 2. 3. 4.
Usually trays trays have downcomer capacity capacity problems in heavy heavy foaming service. service. Trays have have higher pressure pressure drop than than structured structured packing column column Trays Trays have a high resistan resistance ce to corrosion corrosion Entra Entrainm inmen entt is an issue issue with with trays trays.. Trays Trays usuall usually y ha have ve mo more re en entra trainm inmen entt tha than n packing. Excessive entrainment can lead to efficiency loss 5. Exces Excessiv sive e vapo vaporr an and d liquid liquid maldist maldistrib ribut ution ion can lead lead to a loss loss of effic efficien iency cy in a tray tower.
There are five major types of tray column; bubble cap tray, sieve deck tray, dual flow tray, valve tray and baffle tray. Bellow is discussed each type. A. Bubble Bubble Cap Cap Tray Tray The oldest widely used equilibrium-stage plate is the bubble cap tray. A bubble cap tray is perforated flat plate which has a riser (chimney) over the holes covered with a cap. They are usually equipped with slots to allow the passage of vapor to be mixed with the liquid flowing across the tray forming bubble where the mass transfer takes place. Each tray is provided with one or more downcomers which the liquid flowing across the tray is conducted to the tray below. A liquid head is maintained on the tray by a dam placed on outlet side of the tray near the downcomer, it called the outlet weir. Bubble cap tray is able to operate at low vapor and liquid rates (less than
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 6 of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
2 gpm per foot of average of flow width) because liquid and foam is trapped on the tray to a depth at least equal to the weir height. Bubble cap trays work well in high turndown applications because the orifices in the bubble caps are in the form of risers whose top opening is elevated significantly above the tray deck. The size of the cap tends to create hydraulic gradient across the deck and a high vapor side pressure drop. The cost of bubble cap tray is by far the highest.
B. Sieve Sieve Tray Tray Sieve tray is perforated plate with holes punched into the plate and usually has holes 3/16 in to 1 in diameter. The standard size is 0.5 inch with the perforation punched downward. Vapor comes out from the holes to give a multi orifice effect. The vapor velocity keeps the liquid from flowing down through the holes (weeping). Vapor flow through the tray deck to contact the liquid is controlled by the number and size of the perforations. The punching direction affects the dry pressure drop, a smaller hole diameter result in lower pressure drop for the same open area. This due to the ratio of hole diameter to the tray thickness. The number and hole size are based on vapor flow up the tower. The liquid flow is transported down the tower by down-comers, a dam and overflow device on the side on the plate. A sieve tray has higher entrainment than valve valve tray at the same vapor vapor velocit velocity. y. This This is du due e to the spray of liquid liquid directe directed d upwards to the next tray. For efficient operation, the hole velocity must be sufficient to balance the head of liquid on the tray deck and thus prevent liquid from passing through the perforations to the tray below
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 7 of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
Sieve Sieve trays trays can be used used in almost almost all servi service ces. s. Sieve Sieve deck tray ha has s a minimu minimum m capacity approximately 70%. Their capacity and efficiency are at least as high as that that of othe otherr stan standa dard rd tray trays s used used comme commerc rcia ially lly.. Sieve Sieve tray trays s ma may y be used used in moderately fouling services, provided that large holes (3/4 to 1 in. [19 to 25 mm]) are used used.. Siev Sieve e tray trays s are are simpl simple e an and d ea easy sy to fabr fabric icat ate e an and d ther theref efor ore e rela relativ tivel ely y inexpensive. C. Dua Duall flow tray Dual flow tray is a sieve tray without a downcomer. Vapors move up to the tray above through the hole, while the liquid traveles down in the same hole that can resul resultt in mal-d mal-dist istrib ribut utio ion n an and d low effic efficien iency cy.. Dua Duall flow flow trays trays are are de desig signed ned with with enou en ough gh op open en area area on the the tray tray de deck ck to elim elimin inat ate e stag stagna nati tion on an and d prom promot ote e ba back ck missing that makes it suited to handle highly fouling services, slurries, and corrosive services. Dual flow trays are well suited also for the fractionation of polymerizable compounds and give more bubbling area, therefore have a greater capacity than other tray types. Dual flow tray is also the least expensive to make and easiest to install and maintain. Dual flow tray performs best in the operating region of 60 to 85 % of flood and increases the efficiency with vapor rate. The challenge of dual flow tray is mal-distribution in larger diameter towers. The top of a column will move in a typical storm as much as six inches. This movement will cause cause the hydra hydrauli ulic c load load to migrat migrate e in the colum column. n. If hydra hydrauli ulic c flow flow instab instabili ility ty is developed it propagates down the column. Improper feed, reflux or vapor distribution can also create mal-distribution problems, Dual flow tray have poor turndown ratio resulting from the rapid fall off in efficiency as the vapor vapor loadin loading g de decre crease ases. s. There Therefor fore e the op opera eratin ting g vapor vapor and liquid liquid rate rate ranges must be kept small. Two types of dual flow trays are available; standard deck and an d ripple rippled d de deck. ck. The The standa standard rd de deck ck ha has s a flat flat plate, plate, and the the ripple rippled d de deck ck ha has s sinusoidal sinusoidal waves
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 8 of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
D. Valve Tray Tray Valve Tray uses valve (moveable disc) which almost closes off completely at low vapor rate, thus minimize tray open area. When lifted, as vapor rate increases, the open area increases for vapor flow between the valve disc and the tray deck. Valves can be round or rectangular, with or without caging structured. Most types of valves, the opening may be varied by the vapor flow, so that the trays can operate over a wide range of flow rates with high separation efficiency and large flexibility. Because of their flexibility and price (slightly more expensive than sieve tray), valve trays are tending to replace bubble-cap trays. Valve tray has minimum capacity of approximately 60%. The dry pressure drop of valve tray is lower than bubble cap, because the valve does not need a chimney for the vapor and it depends on weight of valve.
The valve tray can used in condition where vapor rate change unpredictability over a given section of tower, a tower utilized in blocked operation at varying rate and feed compo composit sition ions, s, a fluctu fluctuat ation ions s in fee feed d rate, rate, an and d servic servicing ing of au auxil xiliar iary y eq equip uipmen mentt operating the entire unit at low rate.
E. Baffle Baffle Tray Baffle trays contain tower internals designed to cause the liquid to cascade down the tower in a series of curtains through which the vapor must pass as it rises through the tow tower er.. Baffle Baffle tray tray are genera generally lly used used in the de desup super erhe heati ating ng zone zone FCCU FCCU and Coker primary fractionators, Coker scrubbers and in other severely fouling services such as slurry strippers. Baffle tray has three type’s tray, there are Shed Decks, Side to Side Trays, Disk and Donuts Tray. a. Shed Shed Decks Decks Shed Deck trays are angle irons beam of various size from two to ten inches that are placed placed in rows across the column. column. The trays trays are rotated rotated 90°from 90° from tray to tray to distributed vapor-liquid. It has 50% open area and makes the efficiency very low. low. The fouling fouling po pote tenti ntial al of the the de deck cks s is almos almostt zero zero be becau cause se there there are no stag stagna nate te zone zones s an and d low low resi reside denc nce e time time.. The The effi effici cien ency cy of the the tray tray almo almost st These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 9 of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
matches the fouling potential, particularly if wide shed decks are utilized. Shed decks work well in fouling applications where their application is essentially for heat-transfer purposes. b. Side to Side Side Trays Trays Side to side tray is trays that allow the liquid to splash from side to side. The decks de cks can can be slope sloped. d. The The Vapor Vapor flowin flowing g upw upward ard throu through gh the curta curtain in of liqui liquid d leaving the tray above. Liquid fouling potential is low as with efficiency. c. Disk and Donuts Donuts Trays Trays Disk and donut trays are slightly sloped trays that allow the liquid to splash from inner circle ring to outer circle ring. Fouling potential of this tray is low along with the efficiency. efficiency. Standard Cross Flowing Trays Standard cross flow trays operate with the liquid flowing downwards through a column in a serpentine pattern while contacting the vapors that are flowing upward through the colum column. n. La Large rgerr diamet diameter er trays trays may be fitte fitted d with with multip multiple le do down wncom comer er to reduc reduce e the the liquid load across each active area section. This reduces the weir load and liquid head on the tray deck resulting in higher vapor capacity, lower pressure drop and improved operating turndown range. Once the liquid resistance becomes substantial, the liquid is normally split mechanically into multiple streams or passes. The number of passes to be used is specified through the hydraulic design of the tray. Tray fluid passes can be divided into single pass, two pass, three pass, and four pass. 1. Single Single pa pass ss In single pass, the liquid flow across the tray from the inlet to the outlet. The direction of the liquid on the trays one on the top of the other countercurrent. 2. Two pa pass ss Two pass pass trays trays are quite quite common common an and d ge gene neral rally ly don’t don’t po pose se signi signific fican antt de desig sign n chall challen enge ges s since since the flow flow pa paths ths an and d tray tray design designs s are symme symmetri tric. c. Two Two pa pass ss trays trays have got two different geometries. One tray is provided with side downcomers (panel
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 10 of of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
A) an and d the other other with with a centra centrall dow downc ncom omer er (pan (panel el B). Both ha have ve go gott flow flow pa path ths s perfectly symmetrical to the central axis. 3. Three Three pa pass ss Three pass trays are quite rare because of their inherent asymmetric design and diffic difficul ulty ty to ba balan lance. ce. This This tray tray is no nott symme symmetri trica cal. l. Thre Three e pa pass ss trays trays need need to be balanced to make sure that the Liquid over Vapor (L/V) ratio is constant for each pass. Three pass trays are discouraged and should be avoided whenever possible. They are very difficult to balance and introduce a feed or reflux but it has only one single design. 4. Four Four pa pass ss Four pass trays are much more common. Four pass trays has four different flow paths, two for the even and two for the odd trays, there is a need to balance the two different flow paths of the same trays.
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 11 of of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
General Design Consideration Consideration A tray tray hydra hydrauli ulic c de desig sign n is no norma rmally lly divide divided d into into two main main steps steps,, a proce process ss de desig sign n followed by a mechanical design. The purpose of the process design is to calculate the jet jet flood flood,, en entra trainm inmen entt limits limits,, pres pressu sure re drop, drop, dow downco ncomer mer backu backup, p, do downc wncom omer er inlet inlet veloc velocity ity,, weir weir loadin loadings, gs, do down wnco comer mer reside residence nce time, time, wee weepin ping g an and d effic efficien iency cy.. On the other hand, the mechanical design focuses on the tray design. In designing tray there are many factor have to be considered for the suitability of the hydraulic such as the safety, environmental requirements, tray performance, economics of the design and other parameters, which may constrain the work. Tray Tray tow tower ers s may be used used for many many vapor vapor liquid liquid conta contact cting ing operat operation ions. s. A proce process ss engineer can use the following guideline in making preliminary selection on whether use tray column for particular application. 1. The The op oper erat atio ion n invo involv lves es liqu liquid id that that cont contai ains ns disp disper erse sed d soli solids ds.. Tray Tray are are mo more re accessible and convenient for cleaning 2. Trays Trays have a high resistanc resistance e to corrosion corrosion 3. Tray can be designed to handle handle wide range range of liquid rates rates without flooding. flooding. 4. Inte Inters rsta tage ge cool coolin ing g can can be inst instal alle led d on the the tray trays s to remo remove ve he heat ats s of reac reacti tion on or solution. 5. Trays Trays are preferr preferred ed if side streams streams are to be produced produced like refinery refinery crude distillati distillation on column. 6. When large temperature temperature changes changes are involved, as in distillation distillation operations. operations. 7. There There is a lack of experien experience ce in the service service 8. Vessel wall needs needs periodic periodic inspection inspection 9. There There are multipl multiple e liquid liquid phases phases 10.There are many internal transitions There There are five five type types s of tray trays s tha thatt ha have ve ea each ch ad advan vantag tages es an and d disad disadvan vantag tages es.. The The principal for selection type of tray which used consider to their cost, capacity, operating range, efficiency and pressure drop. Here the principal when select type of tray. 1. Cost: Cost: Sieve tray and dual flow tray are relatively relatively inexpe inexpensive nsive,, valve valve trays are slightly slightly more expensive than sieve tray, and bubble cap is the most expensive. The relative cost depend on the material construction used, for the mild steel the ratios of bubble cap, valve and sieve are 3 : 1.5 : 1.
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 12 of of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
2. Cap Capac acity ity:: The The diame diameter ter of the the colum column n requir required ed for a given given flow flow rate rates s either either the capacity. The highest capacity is the sieve follow with dual flow, valve and bubble cap. 3. Operat Operating ing range range:: Bubbl Bubble e cap ha have ve a po posit sitive ive liqui liquid d seal seal there therefor fore e can op opera erate te effi efficie cient ntly ly at very very low low vapo vaporr rate rates. s. Siev Sieve e tray tray relie relies s on the the flow flow of vapo vaporr through the holes to hold the liquid on the tray and cannot operate at very low vapo vaporr rates rates.. But, But, with with good good de desig sign, n, sieve sieve tray tray can be de desig signe ned d to give give a satisfactory operating range, typically, from 50 to 120% of design capacity. Valve tray is intended to give greater flexibility than sieve tray. 4. Efficien Efficiency: cy: The Murphree Murphree efficiency efficiency of all types types of trays trays are almost almost the same when operating over their design flow range. 5. Press Pressure ure drop: drop: Pressu Pressure re drop drop de depe pend nd on the de deta tailil de desig sign n of the tray. tray. Genera Generally lly,, sieve trays give the lowest pressure drop followed by valves and the highest is bubble cap. The service conditions should be consideration as well because the tray hydraulic is designed to accommodate all combinations of loading situations such as heat and mass transfer, density and rate of vapor and liquid, equilibrium phase, pressure, temperature and other other momen moments ts tha thatt may occur occur simult simultane aneou ously sly and the they y are used to resu result lt the the efficiency of tray. The first step to tray distillation column is determining the rate of vapor and liquid from density of vapor and fluid, it will influence to tray spacing, weir height, open area, and pressure drop. drop. In general, the steps to tray hydraulic hydraulic designed are summarized summarized into the follows. 1. Calc Calcul ulat ate e the the ma maxi ximu mum m an and d mini minimu mum m vap vapor an and d liq liquid uid flow flow rate rates s for for the the turndown ratio required. 2. Select Select a trial trial plate plate spacin spacing g 3. Estimate Estimate the the column column diamete diameterr 4. Decide Decide the liquid liquid flow arrang arrangeme ement nt 5. Make a trial plate lay out: downcomer downcomer area, area, active area, area, hole area, area, hole size, weir height 6. Che Check ck the the weeping weeping rate 7. Che Check ck the plate plate press pressure ure drop drop 8. Che Check ck downcom downcomer er backup backup These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 13 of of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
9. Recalculate Recalculate the percentage percentage flooding based based on chosen column diameter. diameter. 10.Check entrainment 11.. Predic 11 Predictin ting g the eff effici icien ency cy:: po point int eff effici icien ency cy,, Mu Murph rphree ree effic efficien iency cy an and d overa overallll efficiency. 12.Optimize design to find smallest diameter and plate spacing acceptable (lowest cost). The theoretical explanation and sample calculations of each step above are discussed in detail in later sections.
Tray Hydraulic Parameter The plate structure must be designed to support the hydraulic loads on the plate during opera operatio tion n an and d the loads loads impose imposed d du durin ring g cons constru tructi ction on and ma maint inten enan ance. ce. The ba basic sic requirements of a tray are that should: 1. Provide good vapor-liquid contact 2. provide sufficient sufficient liquid holdup holdup for good good mass transfer transfer (high efficiency) efficiency) 3. ha have ve suffi sufficie cient nt area area and spacing spacing to keep keep the en entra trainm inmen entt an and d pressu pressure re drop drop within acceptable limits 4. have sufficie sufficient nt downcomer downcomer area area for the liquid to flow freely from tray to tray The range of operation of the installed trays governs the maximum and minimum vapor and liquid loads. loads. The The maximu maximum m po poss ssibl ible e loadi loading ng of vapo vaporr an and d liquid liquid is impor importan tantt to determine diameter column and tray hydraulic parameter such as pressure drop. Figure 7 is a typical operating region for tray. When the vapor loading is raise at constant liquid loading, the entrainment (jet flooding) is reached. The liquid content in the column is increases as well as the pressure drop over the total height of the column. Otherwise, when the liquid loading is raise at constant vapor load the downcomer flooding can be achieved. The downcomer is not able to handle the high loading and therefore the liquid content and the pressure drop of the column increase. For both the vapor and liquid loading, lower and upper limits exist. Hydraulic mechanism should be control these limits. The operating area of a column should be chosen by carefully considering these limitations. The operation area is located under the jet flood line. In this area a wide surface area of the phases is present for the mass transfer and the best mixing of the phases exist.
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 14 of of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
For both the vapor and liquid loading, lower and upper limits exist. Hydraulic mechanism should control these limits.
DEFINITIONS Active Active Area Area (or Bubbl Bubble e Ar Area ea)) - the the de deck ck are area of the the tray tray wh whic ich h ma may y eith eithe er be perforated or fitted with valves or bubble caps and is the area available for vapor/liquid contacting Blowing Blowing Flood Flood - occur occurs s at low liquid liquid rates rates at wh which ich the tray tray op oper erate ates s in the spray spray regime resulting in massive entrainment of liquid to the tray above to the extent that the tray deck is essentially blown dry. Calming zones - unperforated strips of plate at the inlet and outlet sides of the plate Downcomer - a vertical channel that connects a tray with the next tray below which carries froth and creates residence time which helps the vapor disengage from the froth. Downcomer Area - is the area available for the transport of liquid from one tray to the next tray below. Downcomer Back-up Flood - occurs when the head of liquid in the downcomer backs up onto the tray deck. The head of clear liquid in the downcomer is a balance of the pressure drop across the tray plus the head loss through the downcomer clearance. However an aeration factor must be applied to estimate the actual height of aerated liquid in the downcomer Downcomer Clearance - is the space below the downcomer apron allowing liquid to flow flow from from the the do down wnco come merr to the the tray tray de deck ck be belo low. w. This This mu must st be size sized d to prov provid ide e a balance between the minimum head loss required for good liquid distribution across the tray deck and avoiding excessive downcomer back-up. Downcomer clear liquid - the measure of the amount of liquid in the downcomer. Downcomer FloodFlood - occurs at high liquid loads when the downcomers are too small to allow effective effective vapor vapor disenga disengageme gement nt (either (either because because the downward downward velocity velocity or "inlet "inlet veloc velocity ity"" of the liquid liquid is too high high or else else insuff insuffici icien entt resid residen ence ce time) time) caus causing ing vapor vapor
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 15 of of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
entrainm entra inmen entt to the tray tray be below low.. The resul resultin ting g increa increased sed ae aera ratio tion n of the liquid liquid in the the downcomer may also cause premature downcomer back-up flood. Downcomer froth backup - the amount of froth in the downcomer which is a function of the the press pressure ure drop across across the tray deck the froth froth level level on the the tray tray itself itself an and d any frictional losses in the downcomer and its clearance. Downcome Downcomerr vel velocity ocity - the ma max ximu imum clear lear liq liquid veloc locity ity into into the the top top of the the downcomer. Entrainment Entrainment Limit - is reached when the velocity of vapor through the tray open area is high enough to project liquid droplets to the tray above. Flow Flow Path Length Length - is the span of tray deck between the downcomer inlet and the outlet weir and is the shortest path that the liquid takes in crossing the active area from one downcomer to the next. This has a big influence on tray efficiency, particularly in small columns as well as trays with large or multiple downcomers. Head of clear liquid - a function of weir height and weir length (as well as liquid and vapo vaporr rate rates s an and d ph phys ysic ical al prop proper erti ties es)) an and d so pres pressu sure re drop drop ma may y be redu reduce ced d by increasing the number of flow paths in high liquid rate services. Jet Flood - is the criteria used to predict the point at which massive liquid carryover will occur due to the height of spray on the tray deck exceeding the available tray space. It is normal practice to limit tray design to a maximum of 80% of jet flood to allow a safety margin on tower control, possible discrepancies of VLE data and also the limitations of the flooding correlation used. Number of Flow Paths - Larger diameter trays may be fitted with multiple downcomers to reduce the liquid load across each active area section. This reduces the weir load and liquid head on the tray deck resulting in higher vapor capacity, lower pressure drop and improved operating turndown range. Open Area (or Hole Area) - is the aggregate area available for vapor passage through the tray deck via perforations or valve and bubble cap slots. This is a critical factor in the tray operating range since high vapor velocity through the open area (hole velocity) will induce heavy liquid entrainment (as well as high pressure drop), but low hole velocity may allow liquid to "weep" or even "dump" through the tray deck to the tray below. The
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 16 of of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
influe influenc nce e of op open en area area on pressu pressure re drop drop also also impac impacts ts on the liquid liquid ba backck-up up in the the downcomer Operating area - the range of vapor and liquid rates over which the plate will operate satisfactorily (the stable operating range). Outlet Weir Height - The outlet weir is used to maintain a head of liquid on the tray deck as well as to ensure a positive vapor seal to the bottom of the downcomer. Tray Pressur Pressure e Drop - may also also be a limiti limiting ng crite criterio rion n pa part rticu icular larly ly in low press pressur ure e services. The operating tray pressure drop is the sum of the dry pressure drop caused by the resistance to vapor flow through the tray open area and the head of clear liquid on the tray deck. Tray Spacing - is the vertical distance between adjacent tray decks. This effects both the height of spray that may be generated on the tray deck before liquid carryover and also the allowable head of liquid in the downcomers. Turndown ratio - the ratio of the highest to the lowest flow rates System limit (ultimate capacity) - the maximum available capacity for vapor flow in a given column diameter with a known liquid rate and physical properties. The ratio of design vapor load to the vapor load for ultimate capacity. Vapor Vapor hand handlin ling g ca capa paci city ty of a tray tray - propo proporti rtion onal al to the active active area area (i.e. (i.e. inver inverse sely ly proportional to the approach to Jet Flood) Weeping - occurs when the velocity of the vapor through the tray open area is too low to prevent liquid from leaking through the open area thus by-passing contact area to the tray tray be below low.. Mo Most st valve valve and sieve sieve trays trays will will we weep ep in no norma rmall operat operation ion.. Weeping Weeping is considered excessive when it is sufficient to cause loss of efficiency - usually 10 to 20%. Weep point - the lower limit of the operating range occurs when liquid leakage through the plate holes becomes excessive. Weir loading – a measure of the amount of liquid going over the outlet weir.
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 17 of of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
NOMENCLATURE a Aa Aap Ac Ad Ah Co dh EMV EO EOG Hv hap hc hbc hd hdc hf how hr ht hw KG KL Lm Lw Lwd M NG NL P QL R Rvw T tG
Interfacial area, m 2 Active area, m 2 The clearance area under downcomer, m 2 Column Area, m 2 Downcomer area, m 2 Hole area, m 2 Orifice coefficient coefficient Hole diameter, mm Murphree efficiency Overall efficiency Point efficiency Valve thickness (mm) The clearance area under the downcomer, m 2 Clear liquid head, mm Downcomer backup , mm Dry drop, mm Downcomer headloss, mm Froth height, mm Height of liquid crest over weir, mm Residual head drop, mm Total pressure drop, mm Weir height, mm Vapor phase mass transfer coefficient , mm/s Liquid phase mass transfer coefficient, mm/s Liquid rate, kmole/s Liquid flow rate, kg/s Liquid flow rate in downcomer, kg/s Molecular weight, kg/kmol Vapor phase mass transfer Liquid phase mass transfer Absolute pressure, N/m 2 or Pa Liquid rate, m 3 /s Universal gas constant, JK -1mol-1 Ratio of valve weight with legs to valve weight without legs Absolute temperature, K Vapor residence time, s
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
Page Page 18 of of 45
KLM Technology Group Distillation Distillation Tray Hydraulic Practical Engineering Engineering Guidelines Guidelines for Processing Plant Solutions
tL tr ua ud uh uf uvh OBP uvh CBP Vm Vw Xn
(ENGINEERING (ENGINEERING DESIGN GUIDELINES) GUIDELINES)
Rev: 01
Feb 2011
Liquid residence time, s Downcomer residence time, s Vapor velocity through active area Downcomer velocity, m/s Vapor velocity through hole area, m/s Flooding velocity, m/s Vapor hole velocity in opened balance point, m/s Vapor hole velocity in closed balance point, m/s Vapor rate, kmole/s Vapor flow rate, kg/s
Greek Letters Ψ σ
ρ
µ Φ
Entrainment Entrainment fractionating fractionating Surface tension, dyne/cm Density, kg/m 3 Viscosity, cP Froth density
Superscript L V
liquid phase vapor phase
These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. cases. They were designed designed for engineers engineers to do preliminary preliminary designs designs and process process specificatio specification n sheets. sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document document is entrusted entrusted to the recipient recipient personally, personally, but the copyright copyright remains remains with us. It must not be copied, copied, reproduced or in any way communicated or made accessible to third parties without our written consent.
