Suez University Faculty Of Petroleum & Mining Engineering TYPES AND AND DESIGN OF THE THE TOWERS TRAYS Student/ Mohamed Salah abou El_hamed
Dr Mostafa
Department/ Petroleum Refining Year/ Fourth Scope types and design of the towers trays
Mohamed salah
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This design guideline covers the basic elements of tray hydraulics in sucient 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 inuential ooding and weeping, .and will eect the tray performance, capacity and eciency
The design of trays depends on the density, the rate of vapor and li!uid through the tray. "ach tray in a distillation column is designed to promote contact between the vapor and li!uid on the stage, so there is mass and heat transfer. #deally, .the vapor and li!uid leaving the stage are in e!uilibrium "!uilibrium is a function of the rate of mass and heat transfer between li!uid and vapor in distillation and it has an eect on .the eciency of tray To increase eciency and capacity of tray, a system is needed which will cover the whole spectrum of tray applications. $ne of the %eys to ma%e good !uality products and high purities is tray hydraulics. &arameters of tray hydraulics beside the geometry of the tray as it mention in 'rst paragraph, are vapor-li!uid loading, the allowable pressure drop on the tray and in the downcomer, ooding, turndown and weir .loading The design of tray hydraulics may be inuenced by many factors, including process re!uirements, economics and safety.
types and design of the towers trays
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#n this section, there are tables that assist in ma%ing these .factored calculations from the various reference sources Generally, path ow liquid on tray is divided into single pass, two pass, three pass, and four pass. In this guideline, these dierences will be discussed in detail for the proper engineering design for vaporliquid loading and down co!er .design The theories used in this guideline are commonly used in industries such as )ennet,*an +in%le, air and "dulee. Their application to tray hydraulic theory with eamples will help the engineer understand tray hydraulics and be ready to perform .the actual design of the trayed tower #ncluded in this guideline is an eample data sheet which is generally used in the industry and a calculation spreadsheet for .the engineering design In order for good separation "or fractionation# to occur in distillation colu!n, the vapors !ust have good contact with the .liquid on each tray +hen the large bubble is bro%en into several smaller bubbles, the smaller bubbles epose more surface area for .vapor li!uid contact
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Type Tray Distil latio Colu
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types and design of the towers trays
Mohamed salah
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0istillation is the most widely used separation process in the chemical industries. #t is normally used to separate a miture 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 and a li!uid phase coeist and a dierence in relative concentration of the materials to be .separated in the two phases is attained Trays are the most commonly selected type of distillation column. Trayed olumns utilize a pressure and temperature dierential to separate the products. or most tray columns, the weir holds a li!uid level of each tray. The vapor must overcome this li!uid head to move up the column. $n the tray the vapor and li!uid are contacted and then above the tray they are separated. Trayed column perform well in high li!uid and vapor loading. 2t low ow parameters the capacity and eciency of .trays can be reduced Tray have higher pressure drop than pac%ing, and it may also .have higher resistance tocorrosion .3ome other items are to consider when to use trays in a tower 4sually trays have downcomer capacity problems in heavy .1 .foaming service Trays have higher pressure drop than structured pac%ing .( column Trays have a high resistance to corrosion ./ "ntrainment is an issue with trays. Trays usually have more .5 entrainment than pac%ing. "cessive entrainment can lead to .eciency loss
types and design of the towers trays
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"cessive vapor and li!uid maldistribution can lead to a loss .6 .of eciency in a tray tower
In order for good separation "or fractionation# to occur in distillation colu!n, the vapors !ust have good contact with the .liquid on each tray $hen the large bubble is bro%en into several s!aller bubbles, the s!aller bubbles e&pose !ore surface area for .vapor liquid contact
' h e r e a r e f i v e ! a ( o r t ypes of tray colu!n) bubble cap tray, sieve dec% tray, dual ow .tray, valve tray and ba*e tray. +ellow is discussed each type types and design of the towers trays
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A. Bubble Cap Tray The oldest widely used e!uilibrium-stage plate is the bubble cap tray. 2 bubble cap tray is perforated at plate which has a riser 7chimney8 over the holes covered with a cap. They are usually e!uipped with slots to allow the passage of vapor to be mied with the li!uid owing across the tray forming bubble where the mass transfer ta%es place. "ach tray is provided with one or more downcomers which the li!uid owing across the tray is conducted to the tray below. 2 li!uid head is maintained on the tray by a dam placed on outlet side of the tray near the downcomer, it called the outlet weir. )ubble cap tray is able to operate at low vapor and li!uid rates 7less than ( gpm per foot of average of ow width8 because li!uid and foam is trapped on the tray to a depth at least e!ual to the weir .height )ubble cap trays wor% well in high turndown applications because the ori'ces in the bubble caps are in the form of risers .whose top opening is elevated signi'cantly above the tray dec% The size of the cap tends to create hydraulic gradient across the dec% and a high vapor side pressure drop. The cost of .bubble cap tray is by far the highest
types and design of the towers trays
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B. Sieve Tray 3ieve tray is perforated plate with holes punched into the plate and usually has holes /:19 in to 1 in diameter. The standard size is ;.6 inch with the perforation punched downward. *apor comes out from the holes to give a multi ori'ce eect. The vapor velocity %eeps the li!uid from owing do through the holes 7weeping8. *apor ow through the tray dec% to contact the li!uid is controlled by the number and size .of the perforations The punching direction aects 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 thic%ness. The number and hole size are based on vapor ow up the tower. The li!uid ow is transported down the tower by down-comers, a dam and overow device on the side on the .plate 2 sieve tray has higher entrainment than valve tray at the same vapor velocity. This is due to the spray of li!uid directed upwards to the net tray. or ecient operation, the hole velocity must be sucient to balance the head of li!uid on the tray dec% and thus prevent li!uid from passing through the perforations to the tray 3ieve trays can be used in almost all .services types and design of the towers trays
Mohamed salah
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3ieve dec% tray has a minimum capacity approximately 70%. Their capacity and eciency are at least as high as that of other standard trays used commercially. 3ieve trays may be used in moderately fouling services, provided that large holes 7/:5 to 1 in. =1> to (6 mm?8 are used. Sieve trays are simple and easy to fabricate and therefore relatively inexpensive .
C. Dual o! tray 0ual ow tray is a sieve tray without a downcomer. *apors move up to the tray above through the hole, while the li!uid traveles down in the same hole that can result in mal-distribution and low eciency. 0ual ow trays are designed with enough open area on the tray dec% to eliminate stagnation and promote bac% missing that ma%es it suited to handle highly fouling services, slurries, and corrosive services. 0ual ow 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. 0ual ow tray is also the least epensive to ma%e and easiest to install and maintain. 0ual ow tray performs best in the operating region of 9; to @6 A of ood and increases the eciency with vapor rate. The challenge of dual ow tray is mal-distribution in larger diameter towers. The top of a column will move in a typical storm as much as si inches. This movement will cause the hydraulic load to types and design of the towers trays
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migrate in the column. #f hydraulic ow instability is developed it propagates down the column. #mproper feed, reu or vapor distribution can also create mal-distribution problems, 0ual ow tray have poor turndown ratio resulting from the rapid fall o in eciency as the vapor loading decreases. Therefore the operating vapor and li!uid rate ranges must be %ept small. Two types of dual ow trays are availableB standard dec%and rippled dec%. The standard dec% has a at plate, and the rippled dec% has sinusoidal waves.
D.
"alve Tray *alve Tray uses valve 7moveable disc8 which almost closes o completely at low vapor rate, thus minimize tray open area. +hen lifted, as vapor rate increases, the open area increases for vapor ow between the valve disc and the tray dec%. *alves can be round or rectangular, with or without caging structured. Most types of valves, the opening may be varied by the vapor ow, so that the trays can operate over a wide range of ow rates with high separation eciency and large eibility. )ecause of their eibility and price 7slightly more epensive than sieve tray8, valve trays are tending to replace bubble-cap trays. *alve tray has minimum capacity of approimately 9;A. 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. types and design of the towers trays
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The valve tray can used in condition where vapor rate change unpredictability over a given section of tower, a tower utilized in bloc%ed operation at varying rate and feed compositions, a uctuations in feed rate, and servicing of auiliary e!uipment operating the entire unit at low rate.
types and design of the towers trays
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Comparsion of Common Tray Types
types and design of the towers trays
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Summary the Geo!etry and ayout of -o!!on 'ray 'ypes at Dierent perating ressures
types and design of the towers trays
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