K. K. Dagde * and Y. T. Puyate **

Transcription

1 K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp Sx-lump netc mdellng f adabatc plug-flw rserreactr n an ndustral F unt K. K. Dagde * and Y. T. Puyate ** *( Department f hemcal/ Petrchemcal Engneerng, vers State Unversty f Scence and Technlgy, Prt Harcurt, Ngera,) **( Department f hemcal/ Petrchemcal Engneerng, vers State Unversty f Scence and Technlgy, Prt Harcurt, Ngera,) Abstract A sx-lump netc mdel s presented that descrbes the catalytc cracng reactns tang place n an ndustral rser-reactr. In ths scheme, s (prpane and prpylene gases) and s (butane and butylenes gases) cmpnents f lquefed petrleum gas are predcted ndependently, as well as gaslne, dry gas, and ce. The rser-reactr s mdelled as a plug-flw reactr peratng adabatcally. del-predcted yelds f gaslne, s, s, fuel gas, ce, and rser-reactr utlet-temperature, agree reasnably well wth plant data btaned frm an peratng ndustral rser-reactr. Senstvty analyss carred ut n the rser-reactr ndcates that nlet-temperature f gas-l (feed), catalystt-gas l rat, and ma flwrate f gas-l, are mprtant prce varables that affect the peratn f the rser-reactr. It s shwn that the mnmum catalyst-t-gas l rat requred fr maxmum cnversn f gas-l s. Smulatn results usng catalyst-t-gas l rat f 6.5, nlettemperature f gas-l f 55K, and ma flwrate f gas-l f 67.8 g/s, gve yelds f 5.8% gaslne, 6.% s,.68% s, 5.% fuel gas, 5.% ce, and 6.66% f uncnverted gas-l. Keywrds: ser-reactr; mdellng; catalytc cracng; lump; netcs. Intrductn rude l cntans hydrcarbns rangng frm lght gases and lquefed petrleum gas (LPG) t resdues blng abve 66K []. These prducts f varus blng pnts can be separated usng a dstllatn clumn. Hwever, dstllatn alne cannt prduce suffcent amunt f lghter fractns such as gaslne t meet publc demand. Thus, subsequent refnng prce nwn as flud catalytc cracng (F) s used and frms the heart f a mdern refnery rented twards maxmum gaslne prductn. Flud catalytc cracng, whch taes place n the presence f a catalyst, s a prce whereby heaver dstllates f crude l such as vacuum gas-l (VGO) and ther related heavy stcs are cnverted nt lghter prducts such as hgh ctane gaslne, lght cycle l, and gaseus prducts (LPG, fuel gas, etc.), as well as ce. The F prce cmprses manly tw reactrs: () a rser-reactr, where hgh mlecular weght hydrcarbns cme n cntact wth a catalyst and are craced nt lwer mlecular weght prducts wth smultaneus depstn f ce n the catalyst, and () a regeneratr-reactr, where the ce depsts n the catalyst are burnt-ff usng ar and the regenerated catalyst s returned t the rser-reactr t partly supply the heat requred fr the endthermc cracng reactns. The rser-reactr s prbably the mst mprtant equpment n a F plant because all cracng reactns and fuel frmatn ccur n ths reactr. A mathematcal mdel descrbng the peratns n a rser-reactr can be a valuable tl fr ptmzng the perfrmance f the rser-reactr n rder t btan hgher yeld f prducts. The frst prblem n the mdellng f F rser-reactr s selectn f the netcs scheme. One apprach that deals wth mult-cmpnent mxtures le gas-l whch cntans mre than, dfferent speces s the frmulatn f lumped netc schemes [,, ]. In a three-lump netc mdel, gas-l (.e. the feed, and taen as ne lump) s cnverted nt lght gases plus ce lump, and gaslne [5]. Subsequent studes n the lterature [6, 7, 8, 9] cnsdered the need t present ce and lght gases as separate lumps creatng a fur-lump netc mdel n whch gas-l s cnverted nt lght gases (-), ce, and gaslne; and a fve-lump netc mdel n whch gas-l s cnverted nt ce, gaslne, LPG (- ), and fuel gases (dry gases,.e. -). A majr ue that s cmmn wth the analyses presented n the lterature fr each f these netc mdels s that nly the netc parameters are determned but nt appled t smulate a functnal rser-reactr n an ndustral F unt. Obh et al. [] smulated an ndustral fludzedbed F rser-reactr usng a three-lump netc mdel, but the ce generated durng the cracng reactns culd nt be determned ndependently n the analyss. Snce the heat requred fr the cracng reactns s btaned partly by burnng-ff the ce depsted n the catalyst n the regeneratr, 557 P a g e

2 K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp. adequate predctn f the amunt f ce n the catalyst s mperatve durng netc mdellng f a rser-reactr. In rder t accunt fr ce frmatn n the catalyst, Obh et al. [] and Obh and Apa [] presented a fur-lump netc mdel t accunt fr the ce frmatn n the catalyst. But the weane f the fur-lump mdel s that the LPG and fuel gases are lumped tgether as lght gases, whch maes t mpble t cnsder ndvdual effects f LPG and fuel gases n the netc scheme. Ths dsadvantage f the fur-lump mdel was taen care f n a fve-lump netc mdel presented by Dagde et al. [], where gas-l s cnverted nt gaslne, LPG, dry gas, and ce. Hwever, the fve-lump scheme culd nt determne separately the s (prpane and prpylene gases) as well as s (butane and butylene gases) whch are lumped n the LPG. In ths wr, a sx-lump netc scheme fr an adabatc plug-flw rser-reactr s presented n whch gas-l s cnverted nt dry gas, ce, gaslne, s, and s. Such a netc scheme allws ndependent predctn f s and s whch have valuable dmestc and labratry applcatns, used as feedstc n the petrchemcal ndustry, and n cmprer and ar blwer desgn [].. The sx-lump netc mdel The sx-lmp netc mdel shwn n Fg. and prpsed by Ancheyta and Stel [] s used n ths study. The mdel aumes that gas-l () s cnverted t () gaslne (5+), () s (butane, I- butane and butene), () s (prpane and prpylene), (5) dry gas ( ), and (6) ce, as well as uncnverted VGO (decanted and lght cycle ls). The netcs f VGO cracng has been fund expermentally t fllw clsely a secnd-rder chemcal reactn [5], whle the cracng f gaslne and LPG ( s and s) fllw a frst-rder chemcal reactn [,, ]. Fg.. Schematc dagram f sx-lump netc scheme The fllwng rate equatns are frmulated fr the varus cmpnents f the sx-lump netc mdel shwn n Fg. : ( r ) ( y () 5 6) ( r ) [( ) y y ] () 5 6 ( r ) [( ) y y y ] () 5 ( r ) [ y y y y ] () 5 ( r ) [ y y y y ] (5) ( r ) ( y y ) (6) where j lumps t respect t lumps y Gas l () / are the rate cnstants fr the cracng f T lumps, wth j ; r ) (, are the reactn rates wth, wth,,, 5, 6; are the ma fractns f the varus dfferent lumps, and as the ma denstes f the T s the ttal ma densty f all the sx lumps; s the effectvene factr; and s the catalyst deactvatn functn. The deactvatn netc mdel f Weeman and Nace [5] s chsen n ths study because f ts smplcty and ppularty n F mdellng, where the decay f catalyst actvty due t ce depstn s represented by the catalyst deactvatn functn expreed n the frm exp d e (6) d t c (7) where s the catalyst decay ceffcent whch s related t the rser-temperature n the Arrhenus equatn exp E T (8) d d / Ga sl ne (5) s () s () 558 P a g e

3 K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp. t and c [5] t c s the catalyst resdence tme expreed as A L cat F (TO) d (9) where s the catalyst decay pre-expnental F netc factr, s the ma flwrate f gas-l, cat (TO) s the catalyst-t-gas l rat,. s the A ma densty f catalyst, s the cr-sectnal L area f the rser-reactr, s the heght f the rser-reactr, s the unversal gas cnstant, and T s the abslute temperature. Substtutng eq. (9) nt eq. (7) gves d A L exp cat F ( TO) () η The effectvene factr ( ) fr the catalytc cracng f vacuum gas-l s evaluated as [6]: tanh h h () h where s a mdfed Thele mdulus gven as h a ext ( n ) cat D eff n () α where n s the rder f reactn (equal t fr gasl cracng); ext s the catalyst-specfc external surface area; are the netc rate cnstants f the Deff respectve lumps; s the effectve dffusvty f gas-l thrugh the catalyst, and s the mlar cncentratn f the varus lumps. It s mprtant t nte that ext n eq. () can be L, defned usng the characterstc dmensn, Z f the Zelte crystallte (.e. catalyst partcle sze) snce all the cracng reactns tae place n the Zelte crystallte wth lttle nfluence frm the matrx f the catalyst [7]. Therefre, apprxmatng the crystallte gemetry t be a sphere, gves the catalyst-specfc external surface area as [] 6 ext LZ () α whch when substtuted nt eq. () yelds the fllwng expren fr gas-l: h LZ 6 cat ( 5 D 6 ) eff ( 5) where the subscrpt ndcates gas-l. It s expected that dffusn f gas-l taes place n a USY Zelte, and the effectve dffusn ceffcent D eff f gas-l ( ) s gven by the Eryng equatn [8]. Deff Dp exp ED / T (6) Dp where s the pre-expnental factr fr E dffusn, and D s the actvatn energy fr dffusn. A value f D m p 9.58* s and E j D ml were used []... The rser-reactr mdel In the dervatn f the mathematcal mdel fr the rser-reactr, the fllwng aumptns are made: Axal dspersn n the rser-reactr s neglected. atalyst partcles have a unfrm sze n a gven dfferental element, and bth gas-l and gaslne have dentcal catalyst deactvatn functn, []. The rser wall s adabatc Feed vscsty and specfc heat capactes f all cmpnents are cnstant. Adsrptn and dspersn nsde the catalysts partcles are neglgble. Preure changes thrughut the rser heght are due t statc head f catalyst n the rser. e depstn n the catalyst des nt affect the flud flw. In each sectn f the rser-reactr, the catalyst and gas have the same temperature. The ce has the same specfc heat as the catalyst. The rser dynamcs s fast enugh t justfy plugflw characterstcs and a quas-steady state mdel. Instantaneus vaprzatn ccurs at the entrance f the rser-reactr [9]. racng reactns are cmpleted n the rserreactr,ce hence n reactn taes place n the strppng sectn. Applyng the cnservatn prncple t a cntrl A dl vlume ( ) f a plug-flw rser-reactr based n the abve aumptns, where dl s the dfferental heght f the reactr s cntrl vlume, gves the ma and energy balances as 559 P a g e

4 K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp. dy dy U ( r dt dl ) y L : y =,,, 5, 6 () ( 5 6) y (7) T Tref dy dy U ( r) dt dl We defne the fllwng dmensnle varables [( 5 6) y y ] (8) L Z (5) dy dy L U ( r) dt dl T (6) [( ) y y y ] (9) Tref 5 dy dy U ( r) dt dl [ y y y y ] () 5 dy5 dy5 U ( r5 ) dt dl [ y y y y ] () dy dy6 6 U ( r6) dt dl ( 6y 6y ) () dt A dl ( Fcat pcat F p) ( H) ( H) ( H ) y 5( H5) 6( H6) ( H ) ( H ) 5( H 5 y 6( H 6) y where ( H ) ( H ) y ( H ) y s the ma fractn f lump, 5 ) () s the average vd fractn n the rser-reactr, U s the rser superfcal velcty, cat s the ma flwrate f catalyst, pcat and p are the specfc heat capactes f catalyst and gas-l respectvely, and H j are the heat f reactn fr cracng lumps t j, and t s tme. Snce gas-l s the feed that s craced nt the varus prducts, the ma fractn f gas-l at the nlet ( L ) f the rser-reactr s unty, whle the ma fractns f the prducts at the nlet are equal t zer because n prduct s frmed at the nlet f the rser-reactr. Als, at the nlet f the rserreactr, the feed temperature s taen t be a T reference temperature ( ref ) equal t 8K []. These bundary cndtns at the nlet f the rserreactr are defned mathematcally as F where Z s the dmensnle heght f the rser-reactr, L s the varable heght f the rser-reactr, θ s the dmensnle rser temperature, and T s the rser temperature. Usng eqs. (5) and (6) n eqs. (7) (), and ntng that U F = A A gves dy A L dz F (7) ( ) y (8) 5 6 dy A L dz F y y ] [ (9) 5 6 dy A L dz F y y y ] [ () 5 dy A L dz F [ y y y y ] () 5 dy5 A L dz F [ y y y y ] () dy6 A L dz F d dz ( F cat L A pcat F ( y y ) () 6 6 p ) T ( ) ( ) H 5 H5 y ( H) ( H) 6( H6 ( ) 5( 5) H H y () ( H ) 6( H 6) y ( H) 5( H5) 5( 5) y H and the bundary cndtns () becme ref 56 P a g e

5 K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp. y LPG t Z : y y y y5 y6 (5) Dry gas ( 5 ) LPG t Dry gas where s the vlumetrc flw rate f gas-l. ( 5 ) atalyst Equatn (8) () were slved numercally decay ( usng a furth-rder unge-kutta algrthm d ) (Lee et al., usng the bundary cndtns (5). 989). Estmatn f netc parameters The rser-reactr mdel equatns cntan unnwn netc parameters such as the reactn rate cnstants ( ) fr the varus reactn paths, j and the catalyst deactvatn functn ( ). These cnstants have t be determned befre equatns (8)-() can be ntegrated. The netc parameters fr the cracng reactns based n the sx-lump netc mdel are presented n Table. Table. Estmated netc parameters fr cracng reactns n the rser-reactr [5] eactn path Gas-l t gaslne ( ) Gas-l t LPG ( ) Gas-l t LPG ( ) Gas-l t dry gas ( 5 ) Gas l t ce ( 6 ) Gaslne t LPG ( ) Gaslne t LPG ( ) Gaslne t Dry gas ( 5 ) Gaslne t ce ( 6 ) LPG t LPG ( ) Preexpnen tal cnstant (s ) Actvat n energy (J/m l) Hea t f reac tn (J/ g) Stch metr c ceffc ent V j The reactn rate cnstants are functns f temperature generally gven by the Arrhenus relatn (Levenspel, 999) E j exp T where the prme ndcates values f (6) j predcted by eq. (6), K are the pre-expnental netc cnstants fr the respectve lumps, and E are the actvatn energes f the dfferent lumps. The rate cnstants ( ), and the stchmetrc ceffcents j ( V j ) f the varus lumps are expreed as (Dagde, 9) Vg V V,, Vg (7) g V (8) V (9) 5 Vd 5, Vd d () 6 Vc 6, Vc () c g Vg, Vg () V g V 5 gd 5 V 6 gc 6 V 5 V d 5,,, g Vg () g Vgd () d g Vgc (5) c, V (6), V d (7) d 56 P a g e

6 K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp. 5 V the physcal prpertes f the reactng speces, d 5 Vd (8) and catalyst are presented n Table 6. s the mlecular weght f gasl, g where d s the mlecular weght f gaslne, s the mlecular weght f LPG ( ), the mlecular weght f LPG ( ), c s the mlecular weght f ce, d s the mlecular weght f dry gas, V g s the stchmetrc rat f gas-l t gaslne, V s the stchmetrc rat f gas-l t, V s the stchmetrc rat f gas-l t, V d s the stchmetrc rat f gas-l t dry gas, V c s the stchmetrc rat f gas-l t ce, V s the stchmetrc rat f gaslne t, g V g s the stchmetrc rat f gaslne t, V gd s the stchmetrc rat f gaslne t dry gas, V gc s the stchmetrc rat f gaslne t ce, V s the stchmetrc rat f t, s the stchmetrc V d rat f t dry gas, and V d s s the stchmetrc rat f t dry gas. Table shws the average mlecular weghts f the sx lumps used n the study. Table. Average mlecular weghts f the sx lumps [, ] Lump Average mlecular weght (g/ml) Gas l 86 * Gaslne g 7.8** LPG ( ) LPG ( ) 9.** 7.** Dry gas d 8. ** e c **. Prpertes f feed and prducts, and dmensns f sme cmpnents f F unt The prpertes f feed and prducts f the sx-lump catalytc cracng prce, and the dmensns f sme cmpnents f F unt, are presented n Tables and respectvely. The feedstc cmpstn s gven n Table 5, whle Table. Prpertes f feed and prducts f F [] mpnent API mpst Flw rate (g/s) Gravty n, (wt. %) Gas-l feed Fuel gas LPG LPG Gaslne Lght cycle l Bttms e Table. Dmensns f sme cmpnents f F unt [] Parameter Value (m) eactr heght.9 eactr dameter.9 yclne heght. yclne dameter.5 Dsengager heght.9 Table 5. Feedstc cmpstn [] Hydrcarbn % a Paraffns 5. Naphthenes 6. Armatcs 8.5 Table 6. Physcal prpertes f reactng speces and catalyst [] Parameter Value Vapur densty, g/m 9.5 Lqud densty, g/m 9.8 Specfc heat f gas, J/g K. Specfc heat f lqud, J/g.67 K Heat f vapurzatn, J/g 56 Bul densty f catalyst, 975 g/m Partcle sze f catalyst, m 6 75 Specfc heat capacty f. catalyst, J/g K a flwrate f catalyst 7975 frm the rser t regeneratr, g/hr 56 P a g e

7 a Fractn f Gas-l, Gaslne, and e a Fractn f LPG, LPG and Fuel Gases Fractnal yeld f Gaslne and e Fractnal yeld f LPG, LPG and Fuel Gases K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp. 5. esults and Dscun Table 7 shws the cmparsn between plant data and mdel-predctns f the catalytc cracng f gas-l based n the sx-lump netc scheme, ndcatng that the mdel-predctns cmpare reasnably well wth the plant data. Table 7. mparsn between mdelpredctns and plant data f F rser-reactr Parameter Plant data delpredctn Ga-l (wt.%) Gaslne (wt.%) LPG (wt.%).7.68 LPG (wt.%) Fuel Gases (wt.%) e (wt.%) ser utlettemperature, K Fgure shws the varatns f ma fractn f gas-l and the varus prducts f the catalytc cracng prce wth the dmensnle heght f the rser-reactr, ndcatng that the ma fractn f gas-l decreases as the heght f the rser-reactr ncreases, whle the ma fractns f gaslne, LPG, fuel gas, and ce, ncrease as the rser-heght ncreases. As gas-l enters the rserreactr, t s craced nt the varus prducts as t s cnveyed up the reactr n cntact wth the catalyst. LPG Fractn LPG Fractn Fuel Gases Gas-Ol Gaslne e Dmensnle Heght f ser - eactr Fg.. Varatns f ma fractn f gas-l and prducts f catalytc cracng wth dmensnle heght f rser-reactr The rate f cracng f gas-l and the cntact tme f gas-l and catalyst, ncrease as the heght f the rser-reactr ncreases. Hence, the ma fractn f gas-l decreases frm an ntal value f unty ( = ) at the nlet f the rser-reactr t a mnmum value at the utlet f the reactr, whle the ma fractn f ndvdual prduct ncreases frm an ntal value f zer frm the nlet f the rser-reactr t a maxmum value at the utlet f the reactr. The dependence f the yeld f the varus prducts f the catalytc cracng prce n the fractnal cnversn f gas-l s shwn n Fg., ndcatng that the fractnal yeld f each prduct ncreases as the fractnal cnversn f gas-l ncreases Gaslne e LPG Fractn L P G F ractn F uel G ases Fractnal nversn f Gas-l Fg.. Dependence f yeld f prducts f catalytc cracng n fractnal cnversn f gasl Ths s a result f the cracng f gas-l t frm the varus prducts whse yelds ncrease as the cnversn f gas-l ncreases. Fgure shws the temperature prgren alng the rser-reactr, where the temperature nsde the reactr decreases frm an nlet value f abut 8K t abut 66K at the ext f the reactr. Snce the endthermc cracng reactns tae place alng the rser-reactr, and the rate f cracng ncreases wth the heght f the reactr, the heat absrbed by the cracng reactns als ncreases wth the heght f the rser-reactr whle the temperature n the rser-reactr decreases as the heght f the reactr ncreases as btaned n Fg P a g e

8 ser - eactr Temperature (K) a Fractn K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp Gas-Ol Gaslne LPG Fractn LPG Fractn Fuel Gases e Dmensnle Heght f ser - eactr Fg.. Steady-state temperature prfle alng the rser-reactr Hwever, the temperature at any pnt alng the rser-reactr des nt change wth tme whch means that the rser-reactr perates at steady-state. 5.. Senstvty Analyss A smulatn mdel can be used t ptmze plant perfrmance by chsng the ptmal set f peratng cndtns such as temperature, preure, flwrate, etc. In ths wr, the effects f nlet-temperature f gas-l, catalyst-t-gas l rat, and ma flwrate f gas-l, n the yeld f prducts and utlet-temperature f the rser-reactr are nvestgated. Fgure 5 shws the effect f nlettemperature f gas-l n the ma fractns f gasl and prducts f the catalytc cracng prce, ndcatng that the ma fractns f gas-l and prducts f the catalytc cracng prce are practcally ndependent f the nlet-temperature f gas-l untl 9K, beynd whch, the ma fractns f the prducts decrease sharply whle the ma fractn f gas-l ncreases tremendusly. Inspectn f Fgs.,, and 5 reveals that the lnear sectn f the prfle fr gas-l n Fg. 5 crrespnds t the mnmum ma fractn f gasl, whle the lnear part f the prfles (Fg. 5) fr the varus prducts f the cracng prce crrespnds t the maxmum ma fractn f the respectve prducts. Ths suggests that ne r mre f the smulated peratng cndtns f the rserreactr (e.g. catalyst-t-gas l rat f 6.5, gas-l ma flwrate f 67.8 g/s; nlet-temperature f gasl f 55K) gve(s) maxmum cnversn f gas-l wth crrespndng maxmum yeld f prducts Inlet Temperature f Gas-l (K) Fg. 5. Varatns f ma fractn f gas-l and prducts f catalytc cracng wth nlet-temperature When the cnversn f gas-l s maxmum, the rate f cracng f gas-l and the quantty f heat absrbed by the endthermc cracng reactns are als maxmum, s that any ncrease n the nlet-temperature f gas-l up t 9K des affect the maxmum cnversn f gasl. Beynd gas-l nlet-temperature f 9K, the catalyst becmes deactvated and the rate f cracng decreases greatly, s that the quantty (and ma fractn) f uncraced gas-l n the rserreactr ncreases whle the yeld (and ma fractn) f the prducts decreases accrdngly as btaned n Fg. 5. Thus, hgh nlet-temperature f gas-l up t 9K and abve d nt favur the catalytc cracng prce as t can cause permanent catalyst deactvatn and cnsequent reductn n the cnversn f gas-l and yeld f prducts. Fgure 6 shws the effect f nlettemperature f gas-l n the utlet-temperature f the rser-reactr, ndcatng that the utlettemperature f the rser-reactr ncreases nearly prprtnately as the nlet-temperature f gas-l ncreases up t 9K; thereafter, the utlettemperature f the rser-reactr rses sharply as the nlet-temperature f gas-l ncreases. The nearly prprtnate ncrease n the rser utlet-temperature as the nlet-temperature f gas-l ncreases up t 9K s cnsstent wth Fg. 5. Snce the rate f cracng f gas-l s maxmum at the smulated peratng cndtns as explaned n the precedng sectn fr Fg. 5, t means the quantty f heat absrbed by the endthermc cracng reactns s als maxmum and mre heat cannt be absrbed by the cracng reactns. 56 P a g e

9 a Fractn ser - eactr Outlet Temperature (K) ser - eactr Outlet Temperature (K) K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp. Fg. 7. Varatns f ma fractn f gas-l and prducts f catalytc cracng wth catalyst-t-gas l rat Inlet Temperature f Gas-l (K) Fg. 6. Varatn f rser-reactr utlettemperature wth nlet-temperature f gas-l Therefre, any ncrease n the nlettemperature f gas-l results n a crrespndng ncrease n the rser-temperature whch s manfested n the utlet-temperature f the rserreactr as shwn n Fg. 6 up t gas-l nlettemperature f 9K. Beynd nlet-temperature f gas-l f 9K, the catalyst becmes deactvated and the rate f cracng f gas-l decreases s that the quantty f uncraced gas-l n the rser-reactr ncreases as explaned abve. It s the extra heat n the ncreased quantty f uncraced gas-l caused by the reduced rate f the cracng reactns that shts up the rser-temperature and/r utlettemperature f the rser-reactr fr nlet-temperature f gas-l greater than 9K as btaned n Fg. 6. Fgure 7 shws the effect f catalyst-t-gas l rat (TO) n the ma fractns f gas-l and the prducts f the catalytc cracng prce. The ma fractn f gas-l decreases slghtly t a mnmum value as the TO ncreases frm t, and then remans apprxmately cnstant at the mnmum value fr TO. The slght decrease n the ma fractn f gas-l fr TO s a result f ts cnversn t prducts, wth the rate f cnversn f gas-l ncreasng as TO ncreases frm t Gas-Ol LPG Fractn Fuel Gases Gaslne LPG Fractn e 5 5 atalyst-t-gas l at (TO) Accrdngly, the ma fractn f all the prducts ncreases slghtly t a maxmum value as the TO ncreases frm t ; thereafter, the ma fractn f each prduct remans cnstant at the maxmum value fr TO. Increasng the TO means ncreasng the ma flwrate f catalyst enterng the reactr wth respect t the ma flwrate f gas-l. Wth mre catalyst avalable n the rser-reactr, the number f actve stes f catalyst fr the cracng reactns als ncreases resultng n ncreased cnversn f gas-l t prducts, but the catalyst spends le tme n the rser-reactr at hgh TO than at lw TO. Thus, a mnmum value f TO s recmmended fr maxmum cnversn f gas-l, and the value f TO = 6.5 used n the present smulatns s cnsstent wth Fg. 7 whch als cnfrms the results n Fg. 5. Fgure 8 shws the effect f catalyst-t-gas l rat n the utlet-temperature f the rserreactr, ndcatng that the utlet-temperature f the rser-reactr decreases slghtly frm abut 668K t a mnmum value f 66K as the TO ncreases frm t ; thereafter, the rser-reactr utlettemperature remans practcally cnstant at the mnmum value fr TO atalyst-t-gas l at (TO) Fg. 8. Varatn f rser-reactr utlettemperature wth catalyst-t-gas l rat The slght decrease n rser-reactr utlettemperature fr TO s due t the heat absrbed by the endthermc cracng reactns f gas-l and s cnsstent wth Fg. 7 fr the same range f TO. Fr TO, the rate f cracng f gas-l s maxmum and remans cnstant at the maxmum value. Wth maxmum rate f cracng f gas-l, the quantty f heat absrbed by the 565 P a g e

10 ser - eactr Outlet Temperature (K) a Fractn K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp. endthermc cracng reactns s als maxmum, resultng n a cnstant utlet temperature f the rser-reactr fr TO as btaned n Fg. 8. Fgure 9 shws the effect f ma flwrate f gas-l n ts ma fractn and ma fractn f prducts f the catalytc cracng prce., ndcatng that the ma fractn f gaslne ncreases t a maxmum value f abut.6 crrespndng t ma flwrate f gas-l f abut 5 g/s; thereafter, the ma fractn f gaslne decreases as the ma flwrate f gas-l ncreases Gas-Ol Gaslne LPG Fractn LPG Fractn Fuel Gases e gaslne and ther prducts) as the ma flwrate f gas-l ncreases, ndcates that the verall rate f the endthermc catalytc cracng reactns decreases as the ma flwrate f gas-l ncreases s that the quantty (and ma fractn) f uncraced gas-l n the rser-reactr ncreases as the ma flwrate f gas-l ncreases as btaned n Fg. 9. (It s wrthy f nte frm Fg. 9 that althugh the rate f cracng f gas-l t gaslne ncreases t sme extent as the ma flwrate f gas-l ncreases, the rates f all the ther cracng reactns n the sx-lump netc mdel (Fg. ) decrease as the ma flwrate f gas-l ncreases; ths justfes the decrease n the verall rate f the endthermc cracng reactns as the ma flwrate f gas-l ncreases). Fgure shws the effect f ma flwrate f gas-l n the rser-reactr utlettemperature, ndcatng that the rser-reactr utlettemperature ncreases as the ma flwrate f gasl ncreases a Flwrate f Gas-l (Kg/s) Fg. 9. Varatn f ma fractn f gas-l and prducts f catalytc cracng wth ma flwrate f gas-l The ma fractn f gas-l ncreases nearly lnearly as ts ma flwrate ncreases, whle the ma fractns f the ther prducts (except gaslne) decrease as the ma flwrate f gas-l ncreases. We nte that TO = 6.5 was used n Fgs. ; therefre, ncreasng the ma flwrate f nly gas-l whle that f the catalyst remans cnstant, means decreasng the TO wth the effect that the cntact tme f gas-l and catalyst decreases. Thus, as the ma flwrate f gas-l ncreases, the cntact tme f gas-l and catalyst decreases, and the rate f the endthermc cracng reactns and yeld f prducts als decrease, whch s nt fully satsfed by nly gaslne (see Fg. 9). The ntal ncrease n the ma fractn f gaslne as the ma flwrate f gas-l ncreases may partly be attrbuted t () a balance between the reduced cntact tme f catalyst and gas-l, and the ncreased quantty f gas-l enterng the rserreactr per unt tme, s that the rate f cracng f gas-l ncreases, and () the effect f zelte catalyst mst ften used n F whch exhbts the unque prperty f selectvely enhancng the yeld f gaslne. Beynd ma flwrate f gas-l f 5 g/s, the cntact tme f gas-l and catalyst becmes t shrt t sustan effcent cracng f gas-l, s the ma fractn f gaslne decreases. On the ther hand, the cntnuus ncrease n the ma fractn f gas-l (despte ts cnversn t a Flwrate f Gas-l (Kg/s) Fg.. Varatn f rser-reactr utlettemperature wth ma flwrate f gas-l It may be neceary t ndcate that the ttal quantty f heat n the rser-reactr s suppled partly by the regenerated catalyst frm the regeneratr and partly by the gas-l enterng the rser-reactr. Snce gas-l enters the rser-reactr at a cnstant temperature, bth the quantty f heat generated by nly gas-l n the rser-reactr and the ttal quantty f heat n the reactr ncrease as the ma flwrate f gas-l ncreases. Gven that the verall rate f the endthermc cracng reactns tang place n the rser-reactr decreases as the ma flwrate f gas-l ncreases, the ttal quantty f heat absrbed by catalytc cracng reactns als decreases as the ma flwrate f gas-l ncreases, such that the rser-temperature and/r utlettemperature f the rser-reactr ncreases as the ma flwrate f gas-l ncreases as btaned n Fg P a g e

11 K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp. 6. nclusn A sx-lump netc scheme whch descrbes the catalytc cracng reactns tang place n an adabatc plug-flw rserreactr has been presented. The advantage f the sx-lump netc mdel s that t allws ndependent predctns f s and s. It s shwn that catalyst-t-gas l rat, nlettemperature f gas-l, and ma flwrate f gas-l, have sgnfcant effects n the peratn f the rserreactr, and a mnmum catalyst-t-gas l rat f s requred fr maxmum cnversn f gas-l. Smulatn results presented n the study usng catalyst-t-gas l rat f 6.5, nlet-temperature f gas-l f 55K, and ma flwrate f gas-l f 67.8 g/s, gve yelds f 5.8% gaslne, 6.% s,.68% s, 5.% fuel gas, 5.% ce, and 6.66% f uncnverted gas-l. L z characterstc dmensn f Zelte crystallte used n eq. (), m mlecular weght f lump used n eqs. (7)-(8), g/ml r - rate f cracng speces, s unversal gas cnstant, J/ml K t tme, s T abslute temperature, K T reference temperature, K T V ref temperature f rser-reactr, K j defned n eqs. (7)-(8). y ma fractn f cmpnent dmensnle heght f rser-reactr. Z stchmetrc rat f lump t lump j Nmenclature A cr-sectnal area f the rser-reactr, m mlar cncentratn f lump, ml/m p specfc heat capacty f the catalyst n the cat rser-reactr, J/g K p specfc heat capacty f gas-l n the rser-reactr, J/g K TO catalyst-t-gas l rat D eff effectve dffusvty f gas-l thrugh the catalyst, m /s D p pre-expnental factr fr dffusn used n eq. (6), m /s E D actvatn energy fr dffusn used n eq. (6), J/ml F ma flwrate f gas-l, g/s F cat ma flwrate f catalyst, g/s h mdfed Thele mdulus used n eq. (). h mdfed Thele mdulus fr gas-l used n eq. (5). d catalysts decay ceffcent used n eq. (8), - s catalyst decay pre-expnental netc d - factr used n eq. (8), s ntrnsc rate cnstants f speces, m /g j ml s r m 6 /g ml s pre-expnental (r Arrhenus) factr ml s L used n eq. (6), m /g ml s r m 6 /g heght f rser-reactr, m Gree Letters ext catalyst-specfc external surface area used n eq. (), m - average vd fractn n the rser-reactr ma densty f gas-l, g/m ma densty f catalyst, g/m cat ma densty f lump, g/m T ttal ma densty f all lumps defned after eq. (6), g/m H j heat f reactn fr cracng lump t j, J/ml catalyst deactvatn functn. dmensnle temperature f rser-reactr vlumetrc flwrate f gas-l used n eq. (7), m /s effectvene factr eferences [] Wlsn, J. W. Flud atalytc racng Technlgy and Operatn, Penn Well Bs, Lndn (997). [] Ahar J. S., A. Farsh and K. Frsat, A athematcal delng f the ser eactr n Industral F Unt. Petrleum and al, 5(), 5 (8). [] Xu, O, S. U. Hng Ye,. U. Sheng Jng and. H. U. Jan, 7-Lump Knetc del fr esdual Ol atalytc racng. J. Zhejang Unv. Sc. A, 7(), 9 9 (6). [] Al-Sabaw,., J. A. Atas, and H. I. de Lasa, Knetc delng f atalytc racng f Gas-Ol Feedstcs: eactn 567 P a g e

12 K. K. Dagde, Y. T. Puyate / Internatnal Jurnal f Engneerng esearch and Applcatns (IJEA) ISSN: Vl., Iue 6, Nvember- December, pp. and Dffusn Phenmena. Ind. Eng. hem. es., 5, (6). [5] Weeman, V. W. and D.. Nace, Knetcs f atalytc racng Selectvty n Fxed, vng, and Flud Bed eactrs. AIhE J., 6(), 97- (97). [6] Lee, L. S., V. W. hen and T. N. Huang, Fur-Lump Knetc del fr atalytc racng Prce. anad. J. hem. Eng., 67, 65 6 (989). [7] Wang, L. Y., B. L. Yang and Z. W. Wang, Lumps and Knetcs fr Secndary eactns n atalytcally raced Gaslne. hem. Eng. J., 9( ), 9 (5). [8] Ancheyta-Juarez, J., L. F. Isunza, E. A. drguez and J... ayrga, A Strategy fr Knetc Parameter Estmatn n the Flud atalytc racng Prce. Amer. hem. Sc., 6(), (997). [9] Hagelberg, P., I. Els, J. Hltunen, K. Lpanene, V.. Nem, J. Attama and A.O.I. Krause, Knetc f atalytc racng wth Shrt ntact Tmes. Appl. atalyss A,, 7-8(). [] Obh, E. O., J. G. Apa and K. K. Dagde, Applcatn f the Three-Lump Knetc del fr the atalytc racng f Gas- Ol n a Fludzed Bed eactr. Inter. J. Sc. & Technl., (&), 9-5 (5). [] Obh, E. O., J. G. Apa, K. K. Dagde and D. O. Njbuenwu, Applcatn f the Fur-Lump Knetc del fr the Smulatn f a Fludzed Bed eactr fr atalytc racng f Gas-Ol. J. Eng., 6(), 7 (6). [] Obh, E. O. and J. G. Apa, dellng f a Flud atalytc (F) ser eactr: The Fur-Lump del. J. delng, Desgn and gt. Eng. Sys., (), 9 5 (). [] Dagde, K. K., J. G. Apa, Y. T. Puyate and E. O. Obh, Fve-Lump Knetc del fr Flud atalytc racng f Gas-Ol n a Fludzed Bed eactr. J. Ngeran Sc. hem. Engrs., (&), 9 (8). [] Ancheyta, J. and. Stel, Knetc dellng f Vacuum Gas-Ol atalytc racng. J. excan hem. Sc., 6(), 8 (). [5] Dagde, K. K. Develpment f del Equatns fr the Smulatn f Flud atalytc racng eactrs, Ph.D. Thess, Department f hemcal/petrchemcal Engneerng, vers State Unversty f Scence and Technlgy, Prt Harcurt (9). [6] Levenspel, O. hemcal eactn Engneerng, rd Ed., Jhn Wley and Sns, New Yr (999), pp [7] Tnett, G., J. A., Atas and H. I. de Lasa, F atalysts wth Dfferent Zelte rytallte Szes: Actvty, Structural Prpertes, and eactvty. Appl. atalyss A,, 9-5 (). [8] uthven, D.. Prncples f Adsrptn and Adsrptn Prcees, Jhn Wlley, New Yr (98). [9] Al, H., S. han and J. P. rru, delng and ntrl f a ser Type Flud atalytc racng (F) Unt. Trans. Inst. hem. Engrs., 75, (997). [] NPH. New Prt Harcurt efnery mpany: Tranng Prject Specfc fr Senr Staff, Area, Prce Descrptn, mernt (987). [] en, J., H. X. Weng and F. Y. Lu, Study n mpstn and Structure f Heavy Ol. Petrleum Prceng, (9), 56 6 (99). [] Pext, F.. and J. L. eders, eactn n ult-ndexed ntnuus xtures: atalytc racng f Petrleum Fractns. AIhE J., 7(), (). 568 P a g e