PCI-697: DISTILLATION CONTROL. Department of Chemical Engineering KFUPM

Transcription

1 PCI-697: DISTILLATION CONTROL Department of Chemcal Engneerng KFUPM Topc: Dtllaton Prncple and Dynamc Dr. Houam Bnou

2 Objectve of dtllaton control Operate n Safe, Stable Manner Operate Wthn Equpment Contrant Produce Product at Dered Qualte Mnmze Propagaton of Dturbance to Downtream Unt Mnmze Energy Conumpton 2

3 Operatng wndow Steam Condenate Capacty Lmt Floodng Bolup Rate, V Contour of Contant Separaton Veel Preure Lmt Column Preure, pa 3

4 Key apect n dtllaton control Preure Control Materal and Energy Balance Control Product Qualty Control Product Qualty Meaurement Control Technque and Stratege 4

5 Ma and Energy Balance Control L Materal Balance Control Feed R F SP QC D L Reflux rato affect both cutpont and fractonaton Feed R SP QC F D L QC SP F cutpont and fractonaton are clearly eparated SP QR F L QC F SP Energy Balance Control SP Q R F B 5

6 Type of Dtllaton Column Batch and Contnuou Column Type of Contnuou Column bnary mult-component mult-product extractve azeotropc Type of column nternal trayed packed 6

7 Non Ideal VLE behavor 7

8 Lmt of Dtllaton by Azeotrope Vapor Mole Fracton of Ethanol Ethanol / Water Sytem Lqud Mole Fracton of Ethanol Dtllaton range retrcted by the azeotropc pont. Bnary azeotropc mxture, uch a ethanol/water and IPA/water, can be eparated nto ther pure component by dtllaton by the addton of a thrd component, o called the entraner, whch form a ternary azeotrope wth a lower bolng pont than any bnary azeotrope Sl

9 Separaton of Azeotropc Mxture Add the Thrd Component Azeotropc Dtllaton: Volatle Addton Extractve Dtllaton: Non-volatle Addton Shft the Azeotropc Pont by Changng Preure 9

10 Azeotropc dtllaton Azeotropc v. Extractve Dtllaton By formng a ternary heterogeneou azeotrope lower than any other bnary azeotropc temperature, nearly pure ethanol can be obtaned a a bottom product n an azeotropc dtllaton column. Ethanol obtaned a a bottom product from an azeotropc dtllaton column ung an entraner uch a benzene or normal pentane. Extractve dtllaton By addng a olvent whch excluvely famlar wth a wanted component n a feed mxture, a dered component can be obtaned n an extractve dtllaton column overhead. Ethanol obtaned a a top product from an extractve dtllaton wth ethylene glycol olvent. 10

11 Azeotropc v. Extractve Dtllaton RECYCLE UPPER PHASE LOWER PHASE SOLVENT PURE ETHANOL FEED FEED PURE ETHANOL Azeotropc Dtllaton Extractve Dtllaton 11

12 Preure-Swng Dtllaton 12

13 Dtllaton Column 13

14 Reboler There are a number of degn of reboler. Ther degn prncple can be regarded a that of heatexchanger that are requred to tranfer enough energy to brng the lqud at the bottom of the column to bolng pont. 14

15 Reboler 15

16 Reboler 16

17 Reboler 17

18 Reboler Tube bundle 18

19 Condener & Reflux Drum The vapor move up the column, and a t ext the top of the unt, t cooled by a condener. The condened lqud tored n a holdng veel known a the reflux drum. Some of th lqud recycled back to the top of the column and th called the reflux. The condened lqud that removed from the ytem known a the dtllate. 19

20 Condener & Reflux Drum 20

21 Tray 21

22 Random Packng 22

23 Structured Packng 23

24 Vapour Flow Condton Advere vapor flow condton can caue : Foamng Dumpng/Weepng Entranment Floodng 24

25 Vapor Flow Condton Foamng Foamng refer to the expanon of lqud due to paage of vapor or ga. Although t provde hgh nterfacal lqud-vapor contact, exceve foamng often lead to lqud buldup on tray. In ome cae, foamng may be o bad that the foam mxe wth lqud on the tray above. Whether foamng wll occur depend prmarly on phycal properte of the lqud mxture, but ometme due to tray degn and condton. Whatever the caue, eparaton effcency alway reduced. 25

26 Vapor Flow Condton Floodng Floodng brought about by exceve vapor flow, caung lqud to be entraned n the vapor up the column. The ncreaed preure from exceve vapor alo back up the lqud n the downcomer, caung an ncreae n lqud holdup on the plate above. Dependng on the degree of floodng, the maxmum capacty of the column may be everely reduced. Floodng detected by harp ncreae n column dfferental preure and gnfcant decreae n eparaton effcency. 26

27 Vapor Flow Condton Entranment Entranment refer to the lqud carred by vapor up to the tray above and agan caued by hgh vapor flow rate. It detrmental becaue tray effcency reduced: lower volatle materal carred to a plate holdng lqud of hgher volatlty. It could alo contamnate hgh purty dtllate. Exceve entranment can lead to floodng. 27

28 Vapor Flow Condton Weepng/Dumpng Th phenomenon caued by low vapor flow. The preure exerted by the vapor nuffcent to hold up the lqud on the tray. Therefore, lqud tart to leak through perforaton. Exceve weepng wll lead to dumpng. That the lqud on all tray wll crah (dump) through to the bae of the column (va a domno effect) and the column wll have to be re-tarted. Weepng ndcated by a harp preure drop n the column and reduced eparaton effcency. 28

29 Column Dameter Mot of the above factor that affect column operaton due to vapor flow condton: ether exceve or too low. Vapor flow velocty dependent on column dameter. Weepng determne the mnmum vapor flow requred whle floodng determne the maxmum vapor flow allowed, hence column capacty. Thu, f the column dameter not zed properly, the column wll not perform well. Not only wll operatonal problem occur, the dered eparaton dute may not be acheved. 29

30 Column Dameter 30

31 Defnton of a tage n a proce L n,x n L out,x out V out,y out V n,y n A ngle tage a devce or a ubunt of the proce, where two (or more) phae of a dfferent compoton come n contact wth each other, exchange and leave wth new compoton - Ma balance Overall Component L + V = L + V n n n n n out n out out L x + V y = L x + V out out y out - Energy balance L n,h n V out,h out Q L h + V h + Q = L h + V n n n n out out out h out L out,h out V n,h n 31

32 Dtllaton Dynamc MESH M=Ma E=Equlbrum S=ummaton H=Enthalpy 32

33 Dtllaton Dynamc Perforated plate Plate - 1 L -1 Plate V Preure P Temperature T Downcomer Clear Lqud Froath Plate + 1 V +1 Vapor tream L V +2 L +1 Plate

34 Dtllaton Dynamc Ma and Energy Balance Plate k - 1 V k y k L k 1 x k-1 Plate k V k+1 y k+1 L k x k Plate k

35 Dtllaton Dynamc Ma and Energy Balance A tray (k) 35

36 Dtllaton Dynamc Ma and Energy Balance Plate k - 1 V k L k 1 F, x F, h F Plate k y k x k-1 V k+1 y k+1 L k x k Plate k

37 Dtllaton Dynamc Ma and Energy Balance Feed tray (k=f) 37

38 Dtllaton Dynamc Ma and Energy Balance V 2, y 2 V 1 L 1, x D D, x D condener 38

39 Dtllaton Dynamc Ma and Energy Balance Reflux drum (k=1) 39

40 Dtllaton Dynamc Ma and Energy Balance V k y k L k 1 x k-1 B x k reboler k = n 40

41 Dtllaton Dynamc Ma and Energy Balance Reboler (k=n) 41

42 Dtllaton Dynamc (Equaton of State) The Soave-Redlch-Kwong Equaton of State P = RT a ( V b) ( V ( V + b) ) Z 3 Z 2 + Z ( 2 A B B ) A B = 0 Z. Nar and H. Bnou, "Applcaton of the Soave-Redlch-Kwong Equaton of State Ung Mathematca," Journal of Chemcal Engneerng of Japan, 40(6), 2007 pp Note that the Peng-Robnon EOS can alo be ued Z. Nar and H. Bnou, Applcaton of the Peng-Robnon Equaton of State ung Matlab, Chemcal Engneerng Educaton, Sprng ue

43 Dtllaton Dynamc 43 Equlbrum relaton C to 1 for = = v l K φ φ ( ) ( ) + = v v v v v Z B Z B B A A B A B Z B B Z ln 2 ln 1 exp φ C 1 or wth = = x K y SRK EOS

44 Lght hydrocarbon mxture DePreter chart (1953) 44

45 Thermodynamc data for mxture: Smplfed model Raoult law (Ideal oluton/deal ga): p = x P Dalton law (Ideal ga): p = y P p the partal preure of component K-value for deal ga/deal oluton ytem: K P = / P Relatve volatlty for deal ga/deal oluton ytem: K / K = P / j P j V L T, P Antone equaton: ln P = A T B + C 45

46 Thermodynamc calculaton ung K-value Bubble pont Procedure: a) Select T b) K (T) c) calculate: K x >1 K x d) f T too hgh e) Adjutng T g) Fnal compoton can be corrected ung y = Kx K x 46

47 Dtllaton Dynamc Enthalpy departure from deal behavor 2 ( RT ) ( RT ) 2 1 Z + B d H D = RT ( Z 1) + Log T A A RT B Z dt P P P SRK EOS 47

48 Lqud and vapor phae enthalpe deal cae 48 ) ( ) ( ), ( 2, 2,1 1 ref L P ref L P L T T C x T T C x T x h + = [ ] [ ] ) ( ) ( ), ( 2, 2 2,1 1 1 ref V P ref V P V T T C x T T C y T y H = λ λ

49 Dtllaton Dynamc column dameter d her heght Downcomer hw perforated area actve area Aa Lqud arrvng from plate above 49

50 Dtllaton Dynamc d 50

51 Dtllaton Dynamc Franc Wer Formula Hydrodynamc conderaton 51

52 Dtllaton Dynamc Summaton rule 52

53 5% potve tep n the reflux rato at t=10 mn 3.40 reflux rato R= R= tme 53

54 Dynamc repone of dtllate mole fracton (potve tep n the reflux rato at t=100 mnute) (mult-component dtllaton 27 plate column ; ethane/propane/n-c4and n-c5 mxture) Nar, Z. and H. Bnou, Rgorou dtllaton dynamc mulaton ung a computer algebra, Computer Applcaton n Engneerng Educaton, DOI: /cae.20385,

55 Dynamc repone of dtllate mole fracton (potve/negatve tep n the reflux rato at t=100 mnute) (bnary dtllaton of benzene-toluene mxture) Bnou, H., E. Al-Mutar and N. Faqr, Study of the eparaton of mple bnary and ternary mxture of aromatc compound, Computer Applcaton n Engneerng Educaton, DOI: /cae.20533,

56 Dynamc repone of dtllate mole fracton (potve/negatve tep n the rebol rato at t=100 mnute) (bnary dtllaton of benzene-toluene mxture) Bnou, H., E. Al-Mutar and N. Faqr, Study of the eparaton of mple bnary and ternary mxture of aromatc compound, Computer Applcaton n Engneerng Educaton, DOI: /cae.20533,

57 Challenge for control Bnary dtllaton of benzene-toluene mxture Dual product control of a bnary dtllaton column, ung reflux and rebol rato a manpulated varable, dffcult becaue the two control loop nteract. For example, f dtllate purty need to be adjuted, the reflux rato ncreaed, whch affect n a negatve way the bottom purty. Thu, the rebol rato manpulated by the bottom control loop, whch ncreae the overhead vapor flow rate and affect the top control loop. 57

58 58 Frt-order tranfer functon wth dead tme, obtaned ung Mathematca, are gven below: Tranfer functon (bnary dtllaton of benzene-toluene mxture) e G + = ) ( e G + = ) ( e G + = ) ( e G + = ) ( e G d + = ) ( e G d + = ) ( [ ] ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( x G G S R G G G G x x f d d b d + = where the nput-output model :

59 Wood and Berry deved a non-nteractng control (here we ue SIMULINK) R. K. Wood and M. W. Berry, Termnal compoton control of a bnary dtllaton column, Chem Eng Sc 28 (1973),

60 Wood and Berry deved a non-nteractng control (both bottom and dtllate purty n controlled) 0.98 dtllate dtllate compoton tme bottom compoton bottom tme Bnou, H., E. Al-Mutar and N. Faqr, Study of the eparaton of mple bnary and ternary mxture of aromatc compound, Computer Applcaton n Engneerng Educaton, DOI: /cae.20533,