HYDRAULIC BEHAVIOUR OF HIGLEIG-PORTSUDAN PIPELINE AT OPERATION AND SHUTDOWN CONDITIONS

Transcription

1 Journa of Engineering Science and echnoogy Vo. 9 No Schoo of Engineering ayor s Universiy HYRAULIC BEHAVIOUR OF HIGLEIG-PORSUAN PIPELINE A OPERAION AN SHUOWN CONIIONS MYSARA EISSA MOHYALINN Coege of Peroeum Engineering and echnoogy Sudan Universiy of Science and echnoogy Easern iem P. O. Box 73 Kharoum Sudan E-mai: mysara100@yahoo.com Absrac Experimena measuremens were carried ou o correae rheoogica properies of Nie bend wih emperaure wihin emperaure ranges a which Nie bend exhibis Newonian non-newonian and soidificaion behaviours. he deveoped correaions were used o describe he hydrauic condiions wihin each kiomere engh of he pipeine during operaion and he pressure difference required for resaring and fushing every kiomere engh of he pipeine afer specified shudown ime. Pressure osses wihin every kiomere engh of he pipeine a differen fow behaviours during he pipeine operaion have been sudied and anaysed. he required resaring pressure of every kiomere engh has aso been sudied aking ino consideraion he possibiiy of crude soidificaion. he pressure head ransverse beween every wo pump saions and he effec of fow rae on he pipeine overa pressure osses during operaing condiions were sudied. hese resus have been obained using numerica sofware deveoped by he auhor. Keywords: Nie bend Hydrauic Operaion Shudown. 1. Inroducion he hydrauic cacuaions of any pipeine ransporing crude oi highy depend on he rheoogica properies of he crude and he herma condiions of he pipeine. hese wo facors are ineraced as saed by Szias [1] any fuid fow hrough a pipeine creaes a paricuar amoun of hea which changes he origina hea condiion of he pipeine. he rae a which his hea is generaed depends on he rheoogica properies of he crude and i increases wih he viscosiy incremen. In fac his change in hea condiion wihin he pipeine resus in changing he viscosiy which in urns affecs he hydrauic condiions of he fuid. 463

2 464 Mysara E. Mohyadinn Nomencaures c Hea capaciy of he fuid J/kg. C Pipe diameer m f Fricion facor G Mass fow rae of he fuid kg/s hg Hydrauic gradien k Fuid consisency non-newonian behaviour K o Overa hea ransfer coefficien W/m. C L Pipeine engh m n Fow index non-newonian behaviour Re Reynods number Re M Reed and Merzner Reynods number for non-newonian fuids Re New Reynods number for Newonian fuids i Ine emperaure C o Surrounding emperaure C V Fuid veociy m/s Greek Symbos P f Pressure difference pressure oss due o fricion Pa P y Resaring pressure Pa µ Viscosiy Pa.s ρ f Fuid densiy kg/m 3 ρ 0 Fuid densiy a 0 C kg/m 3 τ y Yied sress Pa he Sudanese crude Nie bend which is produced from Higeig oi fied and ranspored hrough Higeig-PorSudan pipeine is a high wax conen crude oi wih high pour poin. I conains abou 5% w/w wax and is pour poins for differen heaing reamen emperaures wihou chemica addiives are in he range of 36 C~31.5 C. A a cerain emperaure above is pour poin Nie bend behaves as a high viscous pseudo pasic non-newonian fuid. Unike Newonian fuids whose rheoogica behavior is described by he inear Newon mode conaining a singe rheoogica parameer caed viscosiy and denoed µ pseudo pasic non-newonian fuids are described by he power aw mode which conains wo rheoogica parameers known as fuid consisency denoed as k and fow index denoed n []. ue o he non-ineariy of he reaionship beween he rheoogica properies of non-newonian fuids and emperaure hydrauic cacuaions of pipeines carrying non-newonian waxy crudes are very compex. As Nie bend exhibis non-newonian behavior wihin cerain emperaure range hydrauic cacuaions of Higeig-Porsudan pipeine shoud consider he emperaure dependency of a rheoogica properies wheher he crude exhibis Newonian or non-newonian behaviour. A very ow emperaures beow pour poin Nie bend may soidify and exhibi ge-ike behaviour a such condiions if he pipeine goes for panned or emergency shudown he resarabiiy coud no be achieved uness he avaiabe resaring pressure aows he rupure of he ge ike srucure. he force required o do so is known as yied sress and denoed as τ y. he yied sress is reaed o boh emperaure and shudown ime. Journa of Engineering Science and echnoogy Augus 014 Vo. 94

3 Hydrauic Behaviour of Higeig-Porsudan Pipeine a Operaion and Shudown 465 In his paper experimena measuremens have been carried ou o describe he rheoogica behavior of Nie bend. Rheoogica modes of Nie bend were deveoped a emperaure ranges wihin which Nie bend exhibis Newonian non-newonian and soidified behaviours. hese modes were hen used o simuae pressure ransverse beween pump saions during he pipeine operaion under specified condiions. he modes aso are used o predic resaring pressure afer various shudown imes.. Research Mehodoogy he sudy of hydrauic behavior of Higieg-Porsudan pipeine has been achieved in wo seps: he firs sep: experimena measuremens In his sep sampes of Nie bend were subjec o shear using he viscomeer HAAKE V 150. ifferen heaing reamen emperaures and measuremen emperaures have been conroed using a waer bah. he heaing reamen emperaure is a emperaure o which he crude is heaed before he measuremen in order o rever he sampe o is origina properies o erase hisory effec whereas he measuremen emperaure is he emperaure a which a desired rheoogica propery is measured. In he pipeine arge scae he heaing emperaure simuaes he reamen emperaure of he ranspored crude whereas he measuremen emperaure simuaes he environmen surrounding emperaure he soi emperaure for buried pipeines. he second sep is numerica and compuaiona modeing his sep is achieved by empoying pubished mahemaica modes Appendix A o deveop a compuaiona oo. he modes used are discussed beow..1. Pressure difference Consider a horizona pipeine as iusraed in Fig. 1. he minimum pressure difference ha makes he fuid fow from he ine o he oue of he pipeine mus be greaer han he resisance force resuing from he fricion effec. So o evauae he fow efficiency of a pipeine ha equipped wih a specific energy generaion unis or o idenify he energy consumpion by fow he fricion pressure predicion is an essenia. Fig. 1. irecion of Fow and Fricion in a Pipe Segmen. he fricion pressure can be cacuaed using he foowing equaion [3]: ρlv P f = f 1 d Journa of Engineering Science and echnoogy Augus 014 Vo. 94

4 466 Mysara E. Mohyadinn In case of non-isoherma ransporaion boh ρ and f in Eq. 1 are emperaure-dependen. ifferen modes are used o describe he emperaure dependency of densiy. he mode used in his sudy considers he crude densiy a 0 o C as a reference densiy o obain he densiy a any emperaure [3]: ρ = ρ ρ he fricion facor f for differen fow regimes aminar or urbuen changes wih emperaure mainy due o emperaure effecs on rheoogica parameers wihin which crude behaves as Newonian or non-newonian fuid. A equaions ha used o cacuae he fricion facor f depend on he reaionship f = f Re where Re is he Newonian Reynods number or non-newonian Reed and Mezner Reynods number which can be obained from he foowing equaions: ρ v Re New = 3 µ Re M = 8 n 1 n n v ρ 3n + 1 k 4n ue o he variaion in rheoogica properies aong he pipeine differen poins aong he pipeine have differen Reynods numbers; accordingy assuming a consan fow rae fricion facor is obviousy varied wihin Newonian and non- Newonian ranges of emperaure. Laminar and urbuen regimes have aso been considered and Kemowski equaions were empoyed for fricion facor cacuaion when crude foow urbuen regime due o high fow veociy [4]. 4.. Hydrauic cacuaions of Higieg-Porsudan pipeine during operaion condiion he oa norma-force-curve sope of nose-cyinder-boaai body is deermined by he summaion of he norma-force-curve sopes of he nose wih he effec of cyindrica par and aferbody. Considering he pressure-emperaure dependency Eq. 1 has been appied o obain he pressure difference for each kiomeer engh variaion aong he pipeine. he hydrauic gradien beween wo poins can be cacuaed from he foowing equaion: hg P1 h1 + ρg L L = where P h and L are pressure eevaion and disance difference respecivey beween poin 1 and. abe 1 shows he eevaion of every pump saion aong Higeig-Porsudan pipeine and he disance beween he pipeine ine and every pump saion. 5 Journa of Engineering Science and echnoogy Augus 014 Vo. 94

5 Hydrauic Behaviour of Higeig-Porsudan Pipeine a Operaion and Shudown 467 abe 1. Sudan Pipeine Pumps Saions Locaions and Eevaions. Saion No. isance km Eevaion m PS# 1 in Higig PS# PS# PS# PS# PS# ermina in por Sudan Hydrauic cacuaions of Higieg-Porsudan pipeine during shudown condiion Resaring pressure is cacuaed considering a fow behaviours Newonian non-newonian and soidificaion of he crude. he resaring pressure for he soidificaion-absen condiion is simpy prediced using Eq. 1 considering he emperaure disribuion a any ime afer shudown and negecing he ransien pressure resuing from he acousic wave propagaion. If he pipeine is shudown for ong period of ime he emperaure of crude may drop o beow he crude soidificaion emperaure. In his case addiiona pressure is required o exceed he yied sress before crude fows smoohy. For soidified pipeines he resaring pressure which is equivaen o he yied pressure pus he fricion pressure srongy increases wih shudown ime due o he emperaure drop. he yied pressure is reaed o he yied sress by he foowing equaion: 4τ y Py = 6 3. Resus and iscussion 3.1. Experimena resus he soidificaion poin of he crude was found o be 9 C when he crude was preheaed o 60 C. he soidificaion emperaure is considered as an approximaed vaue used o disinguish beween he Newonian and non- Newonian ranges of emperaure. If he emperaure is 1 C above he soidificaion poin he crude is assumed o be Newonian. he heaing emperaure is a simuaed vaue of he pipeine ine emperaure. Using his vaue he experimens resu in he foowing rheoogica equaions µ = k = 6 10 e 8 n = Journa of Engineering Science and echnoogy Augus 014 Vo. 94

6 468 Mysara E. Mohyadinn Equaions 7 8 and 9 describe he emperaure dependency of viscosiy for Newonian fow fuid consisency and fow index for non-newonian fuid. hese equaions are uiized o describe he hydrauic condiions aong he pipeine Beow he soidificaion emperaure he crude yied sress is found o be reaed o emperaure as foows: τ y = Equaion 10 is used o predic resaring pressure of he pipeine afer various shudown imes by inroducing he yied sress o Eq. 6. Wiiams [5] have obained a inear reaionship beween he waxy crude yied sress and he ime. heir reaionship was emphasized by Fig. which is obained from experimena measuremens carried ou by he auhor. he ony difference beween he wo resus is ha shorer sanding imes have been chosen in he presen measuremens. Fig.. he Reaionship beween Yied Srengh and Sanding ime. 3.. Numerica resus Operaion condiions Figures 3a and b show exampes of emperaure disribuion aong he pipeine. his disribuion is a fow rae of 0.33 m 3 /s equivaen o bb/day ine emperaure 60 C and soi emperaure 3 C and 43 C respecivey. Experimena resus indicae ha he abnorma emperaure he emperaure beow which he crude fow changes from Newonian fow o non-newonian fow of Nie bend is 40 C. Figure 3a shows ha he abnorma emperaure is reached a he disance 600 km whie Fig. 3b shows ha he emperaure is higher han he abnorma emperaure hroughou he pipeine engh because soi emperaure is higher he abnorma emperaure. Journa of Engineering Science and echnoogy Augus 014 Vo. 94

7 Hydrauic Behaviour of Higeig-Porsudan Pipeine a Operaion and Shudown 469 emperaure emperaure C isance km a Soi emperaure 3 C. b Soi emperaure 43 C. Fig. 3. emperaure isribuions aong Higeig-Porsudan Pipeine Ine emperaure 60 C and Fow Rae 0.33 m 3 /s. he pressure emperaure dependence is iusraed in Figs. 4a and b in which he disribuion of every kiomeer pressure difference pressure oss is obained. he boundary beween Newonian and non-newonian behavior is iusraed in Fig. 4a whie Fig. 4b indicaes ha he crude behaves as Newonian fuid hroughou he pipeine engh. Figure 4a shows a sudden increase of pressure oss afer more han 500 km. his sudden increase of pressure oss is due o emperaure decinaion a his poin o he abnorma emperaure as indicaed Fig. 3. In oher words from he pipeine ine o he sudden eevaion poin he crude behaves as Newonian whereas afer he sudden eevaion poin i behaves as non-newonian isance km Pressure oss kpa/km isance km a Soi emperaure 3 C. Pressure oss/km kpa/km isance km b Soi emperaure 43 C. Fig km Pressure Losses isribuion aong Higeig-Porsudan Pipeine Ine emperaure 60 C and Fow Rae 0.33 m 3 /s. Pressure ransverse beween every wo pump saions is normay iusraed by a sraigh ine wih sope equas o he hydrauic gradiens beween hese saions. he pressure difference is he fricion pressure of he pipeine segmen ha joins hese wo saions. Figures 5 and 6 iusrae he pressure head ransverse beween every wo pump saions using he same inpu daa ha resu in Figs. 3 and 4 respecivey. In Fig. 5 non-newonian fow appeared afer 350 km Newonian fow as iusraed in Fig. 3 whereas here is no non-newonian fow in Fig. 6. he Journa of Engineering Science and echnoogy Augus 014 Vo. 94

8 470 Mysara E. Mohyadinn eevaion of every pump saion has been indicaed by wriing he saion number a is specified ocaion on he pipeine profie. Fig. 5. Pressure ransverse beween Pump Saions of Higeig-Porsudan Pipeine Ine emperaure 60 C Soi emperaure 3 C Fow Rae 0.33 m 3 /s. Fig. 6. Pressure ransverse beween Pump Saions of Higeig-Porsudan Pipeine Ine emperaure 60 C Soi emperaure 4 C Fow Rae 0.33 m 3 /s. Effec of fow rae on overa pressure difference pressure oss he effecs of fow rae on he overa pressure difference for Nie bend fow were obained for differen soi emperaures as shown in abe. he abe shows ha for mass fow raes of more han 300 kg/s pressure osses highy increase so very high fow raes are no recommended. If increasing fow rae is a mus measures shoud be aken o decrease pressure osses. his can be achieved by heaing he crude or injecing fow modifiers o decrease viscosiy and hence decrease pressure osses. Journa of Engineering Science and echnoogy Augus 014 Vo. 94

9 Hydrauic Behaviour of Higeig-Porsudan Pipeine a Operaion and Shudown 471 abe. he Overa Pressure ifference Variaion wih Mass Fow Rae a ifferen Soi emperaures. Soi emperaure o C Mass Fow Rae kg/s he pipeine overa pressure drop kpa Shudown condiions Figures 7 o 1 show he emperaure and resaring pressure difference disribuion aong he pipeine every 1 hrs afer shudown. Newonian non- Newonian and soidified enghs of he pipeine have been indicaed by differen coored ines. A soi emperaure of 4 C which is greay higher he soidificaion poin he crude is exhibis Newonian fow no maer how ong he fow is sopped and hence i is easy o resar he pipeine. A soi emperaure 3 C he crude iniiay exhibis Newonian fow a earier shudown imes wihin near disances from he pipeine ine. For onger shudown imes he disance wihin which he crude exhibis Newonian fow becomes shorer uni reach he ime when he crude exhibis non-newonian for a he engh of he pipeine and hence resaring pressure increases. A soi emperaure 7 C which is ower han he soidificaion emperaure he crude wi exhibi non-newonian fow few hours afer he shudown and hen soidify. In his case very high resaring pressure is required which may exceed he pump saions capabiiy. Fig. 7. ransien emperaure isribuion aong he Pipeine every 1 Hours afer Shudown. Ine emperaure 60 C Soi emperaure 4 C Fow Rae 0.33 m 3 /s. Journa of Engineering Science and echnoogy Augus 014 Vo. 94

10 47 Mysara E. Mohyadinn Fig. 8. ransien emperaure isribuion aong he Pipeine every 1 Hours afer Shudown. Ine emperaure 60 C Soi emperaure 3 C Fow Rae 0.33 m 3 /s. Fig. 9. ransien emperaure isribuion aong he Pipeine every 1 Hours afer Shudown. Ine emperaure 60 C Soi emperaure 7 C Fow Rae 0.33 m 3 /s. Fig km ransien Resaring Pressure isribuion aong he Pipeine every 1 Hours afer Shudown. Ine emperaure 60 C Soi emperaure 4 C Fow Rae 0.33 m 3 /s. Journa of Engineering Science and echnoogy Augus 014 Vo. 94

11 Hydrauic Behaviour of Higeig-Porsudan Pipeine a Operaion and Shudown 473 Fig km ransien Resaring Pressure isribuion aong he Pipeine every 1 Hours afer Shudown. Ine emperaure 60 C Soi emperaure 3 C Fow Rae 0.33 m 3 /s. Fig km ransien Resaring Pressure isribuion aong he Pipeine every 1 Hours afer Shudown. Ine emperaure 60 C Soi emperaure 7 C Fow Rae 0.33 m 3 /s. 4. Concusions Combining he experimena work wih he deveoped compuaiona oo he foowing remarks can be concuded: Nie bend exhibis differen rheoogica behaviours a differen ranges of emperaure. I is recommended o operae he pipeine a high emperaures a which crude is expeced o exhibi Newonian fow o reduce fricion osses and hence save pumping energy. Journa of Engineering Science and echnoogy Augus 014 Vo. 94

12 474 Mysara E. Mohyadinn he rheoogica properies of Nie bend are markedy emperaure-dependan. his fac shoud be considered for predicion of hydrauic behavior of Higeig- Porsudan pipeine during operaion and shudown condiions. he soidificaion emperaure of Nie bend was found o be 9 C. A emperaures beow his vaue he crude is expeced o form a ge-ike srucure ha hinders resaring of he pipeine. epending on fow and herma characerisics Nie bend may exhibis differen behaviours wihin differen segmens. he far disance from he ine he more possibiiy o exhibi non-newonian fow and hence he more pumping pressure is required o fush a uni engh. A he wors condiion he crude may be geed a emperaures ower han is soidified poin. I is imporan o resar he pipeine as quicky as possibe when i goes for panned or emergency shudown o avoid pressure decrease beow he soidified poin. References 1. Szias A.P Producion and ranspor of oi and gas. nd Ed. Par B. Esevier Science Pubisher.. Wasp E.J.; Kenny J.P.; and Ghandi R.L Soid-iquid fow surry pipeine ransporaion. rans ech Pubn. 3. Xiaoheng Y.; and Gouzhong Z Oi pipeine design and conro. universiy of peroeum China press Bansa R.K A exbook of fuid mechanics and hydrauic machines. Laxmi Pubicaions P Ld New ehi. 5. Wiiams.M.; Hsu J.J.C.; and Paerson H.L Sysem deveoped o predic waxy crude s breakaway yied sress. Oi and Gas Journa 94 51; Appendix A Mahemaica modes in operaion condiion emperaure a engh L from he ine can be obained from Eq. A-1 k + π i 0exp A Gc = o he cacuaed emperaure is hen used o cacuae he densiy and viscosiy a he engh. he densiy is cacuaed from Eq. A- beow whereas he viscosiy is cacuaed from he formuaed viscosiy-emperaure equaion. ρ = ρ ρ 0 A- 0 0 he fow behavior is idenified wheher i is Newonian or non-newonian by comparing he emperaure wih he pour poin. Consequeny he fricion facor is cacuaed from he foowing equaions for aminar or urbuence regimes. Journa of Engineering Science and echnoogy Augus 014 Vo. 94

13 Hydrauic Behaviour of Higeig-Porsudan Pipeine a Operaion and Shudown 475 Newonian fow fricion facor cacuaion ρ 1v Re New = A-3 µ - Laminar regime 64 f = A-4 Re New - urbuen regime < Re New Re New f = A Re New Re New Non-Newonian fow fricion facor cacuaion Re M = 8 n n n 1 - Laminar regime v ρ A-6 3n + 1 k 4n f 16 = Re A-7 MR Criica Reed and Mezner Reynods number: 6464n Re = A-8 MRC n + n - urbuen regime + n 1+ n m = 0.314n n φ = exp n E = exp3.57n φ f = E Re.3 m MR / ReMR 4. A-9 Fricion facor is reaed o he coefficien facor of fow by his equaion: f i = 4 f A-10 Journa of Engineering Science and echnoogy Augus 014 Vo. 94

14 476 Mysara E. Mohyadinn Journa of Engineering Science and echnoogy Augus 014 Vo. 94 Fricion pressure 1 LV f P i f = ρ A-11 Mahemaica modes in shudown condiions he foowing equaions are used for shudown cacuaions. In addiion o he disance a parameers are funcions in ime. emperaure disribuion + = b Gc k o ine π exp A-1 where s s o o c c k b ρ ρ = Resaring Pressure: - Newonian crude Resaring Re v New µ ρ = A-13 Re 64 f i = A-14 - Non-Newonian crude resaring Re 1 k n n v n n n MR + = ρ A-15 Re 64 f i = A-16 - Geed crude Resaring p y y 4000 τ = A-17