A New Steps Sequence Table to Improve the Performance of the Jam Petrochemical H 2 -PSA Industrial Plant

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1 The 14 th Natnal Chemcal Engneerng Congress (IChEC 01) Sharf Unversty of Technology, Tehran, Iran, October, 01 A New Steps Sequence Table to Improve the Performance of the Jam Petrochemcal H -PSA Industral Plant Ehsan Javad Shokroo*,1, Arash Farrokhzadeh, S.Ahmad Aboofazel 1, Mehd Farnae 1, Mohammad Shahcheragh 1 1 The N.S.F. Part Shm Knowledge Based Company, Shraz, Iran The Jam Petrochemcal Company, Jam, Iran *ehsan.javad@hotmal.com Abstract The Jam H -PSA ndustral plant was studed numercally by mathematcal modelng and numercal smulaton. The model ncludes balances n energy, mass and momentum and the coupled partal dfferental equatons are solved usng fully mplct fnte dfference scheme. The major dsadvantage of the steps sequence table of the Jam H -PSA plant s the exstence of a tmedelay between two purge (PG) steps. In addton, the tme of adsorpton (AD) step s not equal to PG step. The exstence of the tme-delay n PG step and not equally n tmes of the pressurzng (PR) and depressurzng (BD) steps can be nfluenced on the process performance (manly H recovery). In ths work, therefore, a steps sequence table s desgned n a way to take the same tme for AD and PG steps and also same tme for BD and PR steps. The two other characterstcs of the desgned sequence table are the contnuty of the PG step and purgng of a bed by two other beds effluent, n contrast to plant sequence table that two beds are regenerated by a bed effluent. Furthermore, the results of smulatons show that the H recovery s mproved wth the proposed steps sequence table n ths work. Keywords:Pressure Swng Adsorpton, Industral Plant, H Purfcaton, Numercal Smulaton, Zeolte 5A Research Hghlghts Numercal smulaton of a ndustral PSA unt. The desgnaton of the new steps sequence table for the Jam petrochemcal H -PSA plant. Study of the effect of steps sequence table on the performance of a ndustral PSA plant

2 A New Steps Sequence Table to Improve 1. Introducton PSA process s a wde operatng unt to separaton and purfcaton of gases that operates based on capablty of solds adsorpton and selectve separaton of gases. The mportant operatonal parameter n ths system s the pressure, and most ndustral unts operate at\or vcnty of the surroundng temperature. Today, the PSA process completely s known n a wde regon of the processes, and ths process was preferred n contrast to other conventonal separaton methods especally, for lower capacty and hgher purty. In ths work, the Jam H -PSA ndustral plant was studed by mathematcal modelng. Furthermore, a new steps sequence table s suggested for mprovng the performance of the plant.. Mathematcal Model In order to develop a mathematcal model for a PSA system the man assumptons that have been appled nclude: a) Gas behaves an deal gas, b) The flow pattern s descrbed by the axally dspersed plug-flow model, c) Adsorbng propertes throughout the tower would reman constant and unchanged, d) Radal gradent s to be neglgble, e) Equlbrum equatons for the components of feed (H, CH 4, CO) can be expressed by three-component Langmur-Freundlch sotherm, f) Mass transfer rate s expressed by a lnear drvng force equaton, g) Thermal equlbrum between gas and sold phases s assumed and h) Pressure drop along the bed s calculated by the Ergun s equaton. The model equatons for the bulk phase n the adsorpton bed are wrtten n Table 1. Table 1: Model equatons [1,]. C C ( C. u ) 1 ε q D.. L + + ρ 0 p = t z z ε t (1) C C ( C. u ) 1 N q D ε ρ t L z z p = ε = 1 t () T N T u T q h... (..,., ).. K + ε ρ c u T c c. ( H ) ( T T ) 0 l g p, g + + εt ρg p g + ρb p s ρ t B + w = z z z = 1 t RB, (3) Tw ρ. c. A = π R h ( T T ) ( ) ; w p, w w B, w π R h T B, o o w Tatm A = π w ( RB, o RB, ) t (4) P( t) = a. t + b. t+ c (5) dp 150 (1 ε ) (1 ε ) = a. µ. u + b. ρ. u. u ; a =. ; b = 1.75 dz 4R ε (6) Rpε p k qm,. B. P 4 q = ; s qm, = k1 + k. T; B = k3.exp( ) 1 + B j. P T (7) j j= 1 q 15D 0.5.( ) ; e 15 De = ω q ;..( 1. ) q ω = = C t Pr + B P (8) r c rc For the coupled PDEs problem, the well-known Danckwerts boundary condtons are appled [1,,3]. The adsorpton sotherm parameters and dffuson rate constant of H, CH 4 and CO over zeolte 5A s shown n Table. In Table 3 the characterstcs of adsorbent and adsorpton bed are ndcated. 3. Results and dscusson The plant operatng condtons data suppled by [4] can be found n Table 4. It was evdent from ths Table that the plant s a purfcaton process because the mpurtes n the feed flow

3 The 14 th Natnal Chemcal Engneerng Congress (IChEC 01) Sharf Unversty of Technology, Tehran, Iran, October, 01 are less than 10 percent. In ths smulaton study, the feed components assumed to be H, CO and CH 4. Fgure 1 shows the H -PSA ndustral plant process. The current sequence table n the plant (a) together wth the peresented n ths work sequence table (b) are shown n fgure. As ndcated n fgure -a, the purge step s occurred at two tme sectons wth a delay as ID. In addton, the tme of adsorpton (AD) step s not equal to desorpton (PG 1 +PG ) step. Table : Equlbrum\Rate parameters and heat of adsorpton of H, CH 4 and CO on zeolte 5A. Parameter Component H CH 4 CO k (mol/gr),[5] k 10 3 (mol/gr.k),[5] k (1/atm),[5] k 4 (k),[5] k 5 (--),[5] k 6 (k),[5] Heat of adsorpton, - H (cal/mol),[6] Table 3: The characterstcs of adsorbent and adsorpton bed. Adsorbent, [5] Adsorpton bed Adsorbent Zeolte 5A Length, L (cm), [4] 339 Type Sphere Insde radus, R B, (cm), [4] 100 Average pellet radus, R p (cm) Outsde radus, R B,o (cm), [4] Partcle densty, ρ p (gr/cm 3 ) 1.16 Heat capacty of column, Cp w (cal/gr.k), [5] 0.1 Bulk densty, ρ B (gr/cm 3 ) Densty of column, ρ w (gr/cm 3 ), [5] 7.83 Heat capacty, Cp s (cal/gr.k) 0. Internal heat transfer coeffcent, h (cal/cm.k.s), [5] Partcle porosty, α 0.36 External heat transfer coeffcent, h o (cal/cm.k.s), [5] The tme of BD step (dump) also s not equal to PR step. The exstence of the tme-delay n PG step and not equally n tmes of the pressurzng (PR) and depressurzng (BD) steps can be nfluenced on the process performance (manly H recovery), so the peresented n ths work sequence table (fgure -b) s desgned n a way to take the same tme for AD and PG steps and also same tme for BD and PR steps. The two other characterstcs of the desgned sequence table are the contnuty of the PG step and purgng of a bed by two other beds effluent (PP), n contrast to plant sequence table that two beds are regenerated by a bed effluent. Furthermore, the total cycle tme of the desgned sequence table s equal to the tme of plant sequence table. The effect of the desgned sequence table, therefore, can be found n the numercal smulaton results. Fgure 3 llustrates smulated values for the pressure hstory durng a whole cycle wth the desgned sequence table. As ndcated n ths fgure, the total pressure s a constant value n AD, ID and PG steps and t changes as a nonlnear functon of tme n other steps. Fgure 4 depcts the cyclc partal concentraton of H for plant and desgned steps sequence table at the top of the bed. It s obvous from ths fgure that the H purty has an mnmum and maxmum quantty n the blow-down step because of depressurzed bed and the pressurzaton step as result of cleansed bed, respectvely. It was evdent also from ths fgure that the H purty s hgher correspond to desgned sequence table than the plant sequence table n all steps. In other word, t can be acheved the hgh pure H (as the current purty n the plant) wth usng hgher feed flow rates, whch s leadng cause of the ncreasng of H recovery. The process performance (H recovery), therefore, s mproved wth the desgned sequence table. H mole fracton at the base of the bed vs. PG step tme s shown n fgure 5. It can be seen from ths fgure that the declne rate of H wth PG step tme s lesser correspond to desgned sequence table than the plant sequence table. As expected, therefore, the adsorbent wll be regenerated farly well n PG step wth the

4 A New Steps Sequence Table to Improve desgned sequence table. Fgure 6 shows the H recovery as a functon of feed flow rate. Ths fgure also was announced that the desgned sequence table s well suted to hgher process performance (H recovery). There s a reason for ths, the equalty of the tme of AD and PG steps and also PR and BD steps wll be cause to decrease the tme of tal stream (PG & BD). Note that, gnorng the tme delay n PG step (ID) can be led to the decrease the PG step tme because of the PG step performs at once. Fgure 1: H -PSA ndustral plant process. Fgure : Steps sequence tables, a) used n the plant, b) presented n ths work. Fgure 3: The adsorpton bed pressure versus cycle tme. Fgure 4: Cyclc mole fracton of H at the top of the bed durng the whole cycle, the steps stuatons of the desgned sequence table are ndctaed

5 The 14 th Natnal Chemcal Engneerng Congress (IChEC 01) Sharf Unversty of Technology, Tehran, Iran, October, 01 Fgure 5:H mole fracton at the base of the bed Vs. PG step tme, a) result wth the plant sequence table, b) result wth the desgned sequence table. Fgure 6: H recovery as a functon of feed flow rate. Table 4: Industral H -PSA operatng condton [4]. Composton, Mol (%) Feed Product Tal H N 0.01 Balance 0.0 CO ppm 1.00 CO 10 ppm Balance 0.00 CH Balance C H 6 10 ppm Balance 0.00 C H 4 10 ppm Balance 0.00 Unt Recovery (%) Pressure (bar) Temperature ( c) Flow Rate (N.m 3 /h) Conclusons A new steps sequence table s desgned for mprovng the performance of the Jam petrochemcal H -PSA plant. The steps sequence table s desgned n a way to take the same tme for adsorpton (AD) and purge (PG) steps and also same tme for blow-down (BD) and pressurzaton (PR) steps. In addton, two other advantages of the desgned sequence table are the contnuty of the PG step and purgng of a bed by two other beds effluent, n contrast to plant sequence table that two beds are regenerated by a bed effluent. Fnally, the results of smulatons show that the proposed steps sequence table n ths work takes precedence over the sequence table n-use n the Jam petrochemcal co. 5. Acknowledgment The authors gratefully acknowledge the Jam petrochemcal co. for agreement wth ths research. Nomenclature A w wall cross-sectonal area (cm ) PP provdng purge step AD adsorpton step Pr reduced pressure, (---) B L-F parameter (atm -1 ) PG purge step BD blow down step PR pressurzaton step cp g gas heat capactes (cal/g.k) q amount adsorbed (mol/g) cp s pellet heat capactes (cal/g.k) q* equlbrum amount adsorbed (mol/g) cp w wall heat capactes (cal/g.k) q m saturated amount adsorbed (mol/g) D L axal dsperson coeffcent (cm /s) R gas constant (cal/mol.k) ED equalzaton to depressurzaton step R p radus of the pellet (cm) EP equalzaton to pressurzaton step R B nsde outsde radus of the bed (cm) h nternal heat-transfer coeffcent (cal/cm.k.s) R Bo outsde outsde radus of the bed (cm) h o external heat-transfer coeffcent (cal/cm.k.s) t tme (s) H average heat of adsorpton (cal/mol) T gas phase temperature (k)

6 A New Steps Sequence Table to Improve ID dle step T atm temperature of the atmosphere (K) k parameter for the LDF model T w wall temperature (K) K L axal thermal conductvty (cal/cm.s.k) u ntersttal velocty (cm/s) L bed length (cm) y mole fracton of speces n gas phase P total pressure (atm) Z axal dstance (cm) Greek Letters Subscrpts α partcle porosty B bed ε vodage of the adsorbent bed component ε t total vod fracton p pellet ρ g gas densty (g/cm 3 ) g gas phase ρ p pellet densty (g/cm 3 ) s sold ρ B bulk densty (g/cm 3 ) w wall ρ w wall densty (g/cm 3 ) References [1] Mofarah, M.; Javad Shokroo, E.,"Numercal Smulaton of a Pressure Swng Adsorpton for Ar Separaton", 7 th Internatonal Chemcal Engneerng Conference & Exhbton, Ksh, Iran, 011. [] Javad Shokroo, E.; Mofarah, M.,"Study of Ntrogen Producton from Ar Usng Pressure Swng Adsorpton", The 3 rd Conference of Separaton Scence and Engneerng, Zahedan, Iran, 01. [3] Jee, J. G.; Park, H. J. ; Haam, S. J. ; Lee, C. H.,"Effects of Nonsobarc and Isobarc Steps on O Presure Swng Adsorpton for an Aerator", Ind. Eng. Chem. Res., 41, 4383, 00. [4] Natonal Petrochemcal Co., Jam Petrochemcal Co., H -PSA Plant. [5] Yang, J.; Lee, C-H,"Separaton of Hydrogen Mxtures by a Two-Bed Pressure Swng Adsorpton Process Usng Zeolte 5A", Ind. Eng. Chem. Res., 36, , [6] Yang, J.; Park, M-W., Chang, J-W., Ko, S-M., Lee, C-H,"Effect of Pressure Drop n a PSA Process", Korean J. of Chem. Eng., (15), 11-16,