: 6 : Advanced Binary Distillation Tarze variety oreo ee yee Gre used 3% can be analyzed by means of the MeCabe- vale or Lew approsches Open Steam Distillation Ged coat , Ka 7 104 contro = Top goction Hom empha 4 6 oO = oe Same a | Se eae mee ' wu | x,20.98 Vv jo coe heroes Lees) lee ion eee beet [int [eas ‘ yo gate aiag een mee Optimum feed stage ras a y=(W/V)x - (DV) x, Yes lame (tet. 1 Bottom OL | Pure water © Saturated Vopor x Saturated Liquid a Bottom Operating Line : Bottom Operating Line: The mass balances are V+B=L+s Vy + Bx, = Lx + Sy, (for methanol) Solve for y: y=(T/V)x + (S'V) y, - (BV) x, Simplifications: Since the steam is pure water vapor, y, = 0.0 (cont saturated, S = V and B = L (constant molal overflow). Then y=(D/V)x - (DV) x, 62AA ferrg- Same a ogn diff aerga rot 63 More ef ficten€ tuan_ Two Feeds ("9 “72 Fhex wlomn| teow \ RO tyres of Prodvet aren oL Two Seeol fine ¢ nprO72 Lu ES) L/0=10 Soturated Liquid ¢ p= lO13KPa Optimum Feeds 4> Join intertAre Linea 2 step PIF Verry imp To) A Ti toYBTS 1 Mad | 3 Tears. Proc axPartial Condenser ance envelope, (B) top operating line ial conde nser; (A) bala --7 8 Figure 4-20. Pa A When used? 3 When we recel diatillate (9 Vap. fort ~ top cperatin Aine an it r | ee tS inatead of Xp | | | Total Reboiler yobs 66a Ga Stage (ree - Product (2 OCS Gny £ ides iy One Side Stream é S calculation foal can be connidered > Gare a THe ative fee on negEnnio ing column — Feed Tae cuce CN FA — Feed gon threoud- max no of Atoges SO max purty — No peboilest — No stupr'rg = Top produch main attnactio rn Sect one — Bp of astt ea Bottom ol — Used When top producl mot rn — used to stant up column From to steady seeSteep P/F colomn ~ Geacl top HP cal Lat ie oe ONG ennich ing sectvon - FIFVVOSS _ No eomeleadent pecowty of fop product ct main need - — Gottom produ purty pA the — vAed Wher bottom product motive ele ec eas = Bottom OL abtt | es Top ob portizonta = Feed gos througls all Atager since Ahora a ot ers Ths more purct PELimiting conditions: Total Reflux Figure 4-25, Total reflux; (A) column, (B) McCabe-Thiele diagram Qe sed? Xuve 69. Minimum Reflux Ratio and Pinch Point : y vapor equilibrium line operating line rectifying section feed pinch feed pinch of a 4A \ stripping section \, profileXuve Xwve n | rn (Wen ae Mn (4-55) ‘Note that the minimum reflux ratio depends on xp, 2, and q and can depend on xg. The calculation of minimum reflux may be more complex when there are two feeds or a sidestream. This is explored in the homework problems. ‘The minimum reflux ratio is commonly used in specifying operating conditions. For example, we may specify the reflux ratio a5 L/D = 1.2(L/D) py». Minimum reflux would use the minimum amount of reflux iguid and hence the minimum amount of heat in the reboiler, but the maximum (infinite) number of stages and a maximum (infinite) diameter for a given separation. Obviously, the best operating conditions lies ‘somewhere between minimum and total reflux. As a rule of thumb, the optimum external reflux ratio is between 1.05 and 1.25 times (L/D)m,. (See Chapter 11 for more details.) A maximum L/V and hence a minimum boilup ratio V/B can also be defined. The pinch points will look the same as in Fi, -26A or 4-26B. Problem 4.C12 looks at this situation further. 2Minimum Reflux Ratror This 1A an exception Cure wer (Lk) min: -Esmin tun Alope of Top of = min Tun Top ob epwslibnivm Line a8 STR almost Fer apr No. of Alager @ce UT to reinkdin Pea Hran OnE So this situation rA not expect ed dof.Thu th a caleutation tem . WA «min «2. ref natio min OWA CAT URI Top ol, Bottom ob SS Seok tre a conve aa Sera intewot 4t0 Thin 4olps muol in calculation Pine ly PoindEfficiencies @ 3B New Uses for Old Columns n existing column for a problem it Why would we want to use a! wasn't designed for? First, it is usually cheape paid for than to buy a new one. Second, it is usually quicker to do minor m construction of a new column. Finally, for many engineers solving the often knotty problems involved in adapting a column to a new separation is an interesting challenge. to modify a column that has already been odifications than to wait for The first thing to do when new chemicals are to be separated is clean the entire system and inspect it thoroughly. Is the system in good shape? If not, will minor maintenance and parts replacement put the carats D working order? If there are major structural problems s major corrosion, it will probably be cheape| long- term headache to buy new aTiGment, u Oo a ook simon calculations to determine how close the column will cone po mee ing the new separation specifications. Rarely will the Seearel ete cosine BG Problem. Difficulties can be with capacity. the separation required and problemsbraving Pseddo ey wave fnom morphree eqn =o7 Lvapon of §) Suppre ® EMV ~ ywe draw fue aaa meNF AUSSI 5 SP LES sill ’ : face = hae fs? & arth eee of ‘ ao #4 es y while doing StePPIY » J sage é€ ; : #8 Se E stra 07 parts * es Line got Orfer 9 ve wri fia, 4) Same fort Gol . 2) x AZ TE Sica PAO a ate EMV OR) om,’ Oly off Aile same TRIE jvst x ams az Aine quien fraction fae etaa LOX i @ Ke of Wel ES What can be done if the existing column cannot produce the SE ; desired product purities? e € as Find out whether the product specifications can be relaxed. A purity + Pfigecs% is much easier to obta) than 99.99%: " \2/ See if_a higher reflux ratio will do the separation: pepe er to 4 check if column vapor capacity and the reboller and condenser are in L/D affect only operating costs optimum feed \ h. If they are, changes large enoug) feed temperature. Thi \3¢ Change the stage optimum \aCwill a new feed sta stage is probably nonoptl specifications? SsO'7 Sup. Vapourt> 1 mole Ly vapour (ZA 4 mole nl Xe~ O05 xXp50'9 Reflux Sat hy £q data given St find No.of Stage 'f lolol reflux + Sleps 4) Draw ey cunve from tue dake Jiven 2) Draw TOP OL fennicave ofmmtotaamogUxglOlaales Jox Line | 3) stepping OSS Ail xefind CE) min Steps 1) Draw eq conve 2) Draw feed Line. Slope of feed Line = aus q-! ih ge Ae \ 1 ae es “Store = Ya point st Mine Para s (*e>%r)s 3) Join (Xe Xa) S int. of feedline 4 eq ure4 5 to get Bor WD Sain LX6-Xn) D int of Feed Mire G eg Dire! to Jet Tok 5) Find Alope of Tok We Know TOL parsed Haroug (po) g oleae cn arae He have L we sfind & from & vFind opt Seed pocot ion # Steg. bt (Emin ~ MO Ge (vap) | When Steps + 1) draw eq curve IR ceo ia a Cea ea cs ova | 8) baw feed Kink [ omvatt | Bol [ Voin feed line, ToL ink. 3 4 4) Draw i * " i 8 oo i f / + *% 4 7, G) axis #4 fine Yella OTS porch s fx R EN va To CO oR, (Rod Ling SY oT)| : b. mol/h of a 32 mol% The feed enters as a subcooled on the feed plate for every 4 denser and uses open = 0.75 and a bottoms e saturated p12. A distillation column is separating, 1000 ethanol, 68 mol% water mixture. liquid that will condense 1 mole of vapor moles of feed. The column has a partial con steam heating. We desire a distillate product Yo product x, = 0.10. CMO is valid. The steam used is pur water vapor. Data are in Table 2-1 and Figure 2-2. a. Find the minimum external reflux ratio. b. Use L/D = 2.0(L/D)min, and find the number of real stages and the real optimum feed location if the Murphree vapor efficiency is 2/3 for all stages. c. Find the steam flow rate used. 79 = 0.397 (tangent pinch) ; / (z) BiEL/VE) D)an (1-L/V |. ae 3 L/D ,, =1318, 1/v=—L/D_- | at - a si Be 1+L/D aoe | Top operating Line through y = x = yp = 0.75 4 Bottom through y=0, x=y, =0.1 and intersection feed and top operating lines 01 0, x=Yz Feed: L=L+F+.25F, q= d -25F, q=5/4, slope =q/ q~1 = timum feed is 3" from bottom. : ae condens es . feed is 3" from Need 9 real stages plus parti ‘rom figure slope of bottom operating line = L/V = 2.025 cia Since saturated steam and i ie CMO valid, B/S = Al lat cat eee er oo ah Sys +Fz=Bx, +Dy, 0 Solve 3 i ? Be qs. simultaneously. S = 760 Ibmoles/hr = 13,680 Ib stean/br. 80