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Parasti l lat ion Process for New TowersFor new construction, we assume a scenario ofperforming a given separation a t specifiedconditions. Using th e Parast i l lat ion process,tower height ca n be reduced by 20-25%, but theinstalled cost about 1.6 N Parasti l lat ion processstages will be 12 to 14% rrore. on purely econanicgrourrls, one must carpare th e savings due to a20-25% reduction in tower height to th e cost of12-14% rrore for tower intervals.On average, we expect the trade-off to be sane-lNhat in favor of th e Parasti l lat ion process. Insane cases of very high incremental cost fo rincreased tower height, e.g . , offshore, a i r -transportable packaged units, or envirorrrentalconstraints, then th e Parasti l lat ion process willbe strongly favored. Also, it i s strongly favoredin the case of low liquid loading where half-passtrays would be required fo r dis t i l la t ion .Parasti l lat ion Process Best for RevampSSeveral reasons may exist for revamping a di s t i l -lat ion colUllU1:

(a) save energy(b) Improve separation(c) Increase capacityIn a l l cases, the parast i l lat ion process shouldbe evaluated as a candidate. Because rroretheoretical stages ca n be obtained, it wil l improveseparation and/or reduce energy cOnstlll'ption. Incases of low liquid loading, there i s nearly alwayssignif icant increase in capacity.Studying th e nurrber of existing colUllU1S in variousservices shows tha t a large number are candidatesfo r retrofi t t ing to us e the Parasti l lat ionprocess. Table 1 shavs th e resul ts for a nurrberof geograrhical areas arourrl th e world in variousirrlustry segments. Alrrost 10,000 colUllU15 inNorth America, Western Europe and Japan arecandidates for Parasti l lat ion process re trof i t .

TABLE 1. Existing Retrofi t candidateTowers for the parast i l lat ion ProcessNorth Western IndustryAmerica Europe Japan Total

REFININ:; 2500 1200 450 4150GAS PRCX:ESSIN:; 1000 1000OLEFINS 230 260 100 590PErRCCHEMICALS 1500 1600 750 3850GOO 'TOTAL 5230 3060 1300 9590Parasti l lat ion Process - Design and UseEach pa i r of Parasti l lat ion stages ca n be viewedas two half-tray sections separated by a dividingplate; the downstream half i s lowered a ha l f trayspacing below th e upstream half . Because vaporr ising fran one tray traverses a fu l l tray spacing

before reaching the tray above, there i sof capacity due to je t or entraimlent f lapproach when carpared to conventional t rhydraulics. In tenus of pure liquid downflood, there i s a reduction of tray spacione-half of th e conventional spacing.In order to take full advantage of th e po ent ialimprovement when using th e Parast i l lat ion recessski l l i s required to insure th e correct t oftray is used. The optimum selection will eliminate downa:rner l iquid flooding as a poss' i l i ty .Using one-, two- or four-pass arrangement , th edesigner can uti l ize available weir 1 perhalf t ray , equivalent to a minimum of 0. 3 timescolumn diameter to a maximum of 1.8 times colUllU1diameter. As there i s no loss of C01UllU1 ea, antherefore no constraint in th e selection f downa:rner size, th e design ca n always ensure tentrairrrent flood governs th e capacity l ' ' t .The us e of one-, two- or four-pass Paras l lat ionstages allows th is process to be subst i tu fo rconventional dis t i l la t ion in nearly a l l seswhere single-pass trays were formerly , an d irrost cases where two-pass conventional t r ys wereused, on a minimun 21-24 inch tray spac' Theri s no loss of capacity, but a rrost signif cant gain fractionation in every case due to th e increasin theoretical stages. I t i s not suitabl forcertain applications, such as pumparourrl ectionsof crude colUllU15, where liquid load i s en . elythe predaninant factor. I t i s of rrost va ue wherthe rhase loadings are reasonably balan , orwhen th e vapor phase load governs th e de s gn .The rrost significant design consideration for theParast i l lat ion process i s that a ll of th e timetested hydraulic calculation techniques 1 ng usedfo r dis t i l la t ion tray design are equally pplicabto Parastillation tray design.TESTS OF THE PARASTILIATION PRCCESSTotal reflux tes ts of Parasti l lat ion pr ss vs.t radi t ional dis t i l la t ion were conducted a th eUniversity of Manchester Inst i tute of Sci ce andTechnology (UMIST) and have been reported indetail (1). Tests were conducted in a 2- t . diarreter column with three t radi t ional dis t i lat ionsieve trays an d six Parar;tillation ProceS siEvetrays of similar design. Spacing between t rayswas 24 in . in each case. Average resul ts fran thtes ts are given in Table 2 where it can seenthat th e Parast i l lat ion process produced ch rrorseparation than dis t i l la t ion .

Table 2. UMIST Totalrrol %

D ~ s t ~ l l a t l . o n Location (3 Trays)Reflux 70.8Bottan Downa:rner 10.8Reboiler 2. 5

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t1=asured bottom.downcx::Iller and reboiler liquidcx:rnpositions were used to calculate Ev of thereboiler in each case. With these values set ,E'mv for disti l lat ion and Parasti l lat ion processwere calculated. Also an apparent Emv fo rParasti l lat ion process was calculated. This wasdone using a tradit ional disti l lat ion simulationfor three stages above th e reboiler and gettingFmv corresponding to th e Parasti l lat ion processtes t results , Table 3. Reboiler efficiencies areessentially th e same in each case. Apparent Emvfor Parasti l lat ion process i s 78% vs. an actualE'mv of 62% for disti l lat ion. Parasti l lat ionprocess gave a 26% increase of theoretical stages.

Table 3. Murphree vapor efficienciescalculated fran UMIST tes ts .Itan Disti l lat ion Parasti l lat ionEv (Reboi1er) 67.3% 67.9%Fmv (Trays) 61.7% 68.9%Apparent 78.2%*Apparent Fmv i s that required of three d i s t i l -lat ion trays to give th e separation produced bysix Parasti l lat ion process trays.Part of th e enhancerrent o::mes fran a higher Fm.1,69% for Parasti l lat ion process as canpared to 62%fo r disti l lat ion. I t i s higher for tw:::J reasons.First , since wier heights and loadings were aboutth e same on each tes t , th e liquid depth in Para-sti l lat ion process was greater than in d i s t i l -lation. This is a design difference and i s notan inherent benefit of Parasti11ation process.Secorrl, l iquid always flONS in th e same directionon a given side of th e co1tmU1. in Parasti l lat ionprocess, i. e . , Parasti11ation process approachesLewis Case II as previously mentioned.l'obst of th e enhancanent i s due to th e inherentParasti l lat ion process advantage which resultsfran th e mechanical arranganent for contactingvapor and l iquid. In sumnary, increased Murphreevapor efficiency accounts for th e rrove fran 61.7%to 68.9% and th e Parasti l lat ion process rraterialbalance effects account for th e renain::ler to getan over a l l efficiency of 78.2% for the Parasti1-1ation process as canpared to 61.7% for dis t i l la-t ion.Parasti l lat ion Process in Crnmercial OperationsThe f i r s t ccmrercial instal lat ion of th e Parasti1-1ation was done in Eng1arrl in a co1tmU1. whereconventional seive trays above th e feed werereplaced with Parasti l lat ion trays, ro t existingPall rings were l e f t in th e section !:;e1CM th e feed.The operation of this co1tmU1. (Co1tmU1. #1) metdesign expectations for increased purit ies andincreased capacity an d resulted in a sat isf iedclient.

Two rrore ccmnercia1 installat ions were started upin England in la te 1985; both are operating asexpected with CXIllp1ete cl ient satisfaction. Wehave obtained cl ient pennission to publish scaledt es t results fran one co1tmU1. and general mechanicaldetai ls about another.One co1unn (Co1tmU1. #2) in which 28 Parast i l lat iontrays were installed on 21 inch spacings was 3. 5feet in diameter and 32 feet high. This was a newco1unn so no canparison with previous operations i spossible. The co1unn i s perfonning as expectedwith cx:mp1ete cl ient satisfaction.Another co1unn (Co1unn #3) in which 32 Parasti1-1ation trays (arrl one conventional seive tray a tth e feed) were installed on 27 inch spacings was 3feet in diameter and 50 feet high. Results fransamples taken during normal operations are shownin Table 4.

Table 4. Parasti l lat ion Results a tOperating Conditions (Co1unn #3)Reflux ratio = 0.37

weight FractionCCI\JX?nentA 0.75 0.99883 0.00294B 0.25 0.00117 0.99706

A reflux rat io of 0.37 i s nCM required to performessentially the same separation tha t was beingperfonned with conventional disti l lat ion a t areflux rat io of 0.63. Ccrrp.1ter simulation resultsshCM that , whereas conventional dis t i l la t ionprovided 7 to 8 theoret ical stages of separation,th e Parasti l lat ion process gives 10 to 11 theo-retical stages in th e same column height.Detailed operating resul ts fo r this column areavailable on a confidential basis to partiesapproved by th e cl ient .OONCLUSIONThe Parasti l lat ion process ha s been thoroughlytested in laboratory arrl ccmnercial operations,and nCM i s ready for general use in cases whereapplicable.References(1) Canfield, F.B., Chemical Engineering Progress,p. 58 , v. 60 , February 1984.(2) Jenkins, A.E.O., U.S. Patent 4,496,430, U.K.Patent 2,093,712 an d numerous foreign patents.(3) Jenkins, A.E.O., U.S. Patent 4,582,569.(4) Anon., Chemical Week, p. 30 , OctOOer 19 , 1983.(5) Lewis, J r . , W.K., IE: , p. 399, v. 38 , 1936.

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