6. gas gathering system
DESCRIPTION
lknlnkTRANSCRIPT
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GAS GATHERING SYSTEM
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Gas Gathering & TransportationGas Gathering & TransportationTransmisi gas kepada konsumen memerlukan 4 unit operasi: Gathering system Compression station Trunk line Distribution line
Pertimbangan ekonomi (terutama jarak jauh):1. Besarnya Q gas yang dikirim2. Panjang pipa3. Right of way (tempat diletakkannya pipa transmisi)4. Cross apa saja yang akan dipotong5. Maksimum elevasi6. Lokasi dan size compressor station7. Gas delivery (Q)8. Desain gathering systemPenekanan terutama pada: - well location
- right of way - Q yang dikehendaki - L - ΔP
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Tambahan bagi desain gas gathering system adalah distribusi gas ke konsumen yang menggunakan diameter kecil dan kompleks system.Desain engineer study terutama untuk pipe line jarak jauh dan tekanan tinggi.
Perhitungan yang dibuat terutama dalam hal:- penentuan diameter- gel strength- high pressure pompa- stimulation model untuk high pressure gas, diperlukan untuk mendapatkan maksimum efficiency
Reynold Number & Moody Friction FactorReynold Number & Moody Friction Factor
Pada flow gas system diperlukan energy di mana sebagian dari energy itu akan hilang (loss work).loss work = - friction loss internal loss
losser karena gesekandgn permukaan dinding pipa
Untuk laminar flow, loss work susah dicari secara teori, akan tetapi dengan pengalaman, actual losser dapat ditentukan.
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loss work = f (friction factor) dengan friction factor = f (Re)
di mana:fF = funning friction factorf = 4 fF Fig 7.1 (Chikoku)lw = mechanical energy to heat (lbf/lbm)gc = gravity conversion factorqv = flow velocity (ft/sec)D = pipe line diameter (ft)f = moody friction factorNRe= Reynold number
Practical purposes:
2L D 2
f
D 2 f )(
2F
2F
c
c
glw
gLlw
Dq
N
N
g
20Re
1488 Re
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di mana:q = gas flow rate (MSCFD)μ = gas viscosity (P,T) cpD = pipe diameter (in)ɣg = gas gravity ( air = 1)standard condition: 60oF, 14.73 psia
Relative Roughness (e/D)Relative Roughness (e/D)
Relative roughness tergantung dari:- Kekasaran pipa dan diameter pipa
Equation for Friction FactorEquation for Friction Factor
Ada 4 macam moody friction factor, tergantung pada Re.- Laminer zone: Re < 2000
- Critical zone: 2000 < Re < 40000.3Re
0.5 f
Fig 7.1
Fig 7.10
)()(
)()(
inDineor
ftDfteRR
Re
6464Ndu
f
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valid: 0.00001 < < 0.0001
- Transition zone: 4000 < Re <
- Turbulent zone: Re >
Pipe Line Flow EquationPipe Line Flow Equation
Weymouth: baik sekali untuk small diameter (dimulai D 15”)Panhandle & Modified Pan Handle untuk large diameter.
Weymouth Equation: Horizontal FlowQo Wo
isothermal gas flow horizontal line
D
16.12000
D 2log - 1.14
f1
16.12000
D 2log - 1.14
f1
Q Q
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Asumsi Weymouth:1. Perubahan energi kinetik = 02. Flow steady state3. Horizontal flow4. Panas (heat) tidak keluar terhadap gas atau sekitarnya5. Tidak ada kerja oleh gas, maka persamaan umumnya:
di mana:v = specific volumep = pressure (psia)f = moody fraction factor
= velocity (ft/sec)D = diameter pipa (ft)L = panjang pipa (ft)gc = conversion factor = 32.17
0 L (144) D 2g
f P v
0 lw P v
c
2
2sec lbfft lbm
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5.0522
21
9
522
21
52
22
12
92
59-
2
3
2
2
3
L f T zG D)PP(
PbTb3.23 h Q :atau
(5280L)G T z 2f 109444.1)12D)(PP53.29( h Q
:makainch D miles L Bila
D LG T z f2
PPPbTb
109444.129.53h) (Q
maka ,z dengan gIntegratin
0LP Tb
z Pb TQh Df101.9444 P
GPT z29.53
0DL
PD Tb 3000z Pb TQh 4
32.172f P
PG 29)zT 732.10( 144
GP 29zT 10.732
PMzRT lbm/ftv
D4
00.1z
pPb
TbT
3600Qh
ft1
secft
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di mana:Qh = gas flow rate (ft3/hr) @ PbTb = base temp (oR)Pb = base pressure (psia)P1 = inlet pressure (psia)P2 = outlet pressure (psia)D = inside diameter (inch)G = gas gravity (air = 1)T = average flow line temperature (oR)f = moody friction factorL = panjang pipe line (miles)
= gas deviation factorHal ini dapat ditulis sebagai berikut:z
2
5.0
5.25.02
22
15.0
D 2log - 1.14
1 turbulentf
factor ntransmisiof1
Dz T LG
)PP(f1
PbTb3.23 h Q
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22
21
32
31
21
P
P 21
21
21
21
5.031622
21
31
PPPP
32 Pm
:(Pm) pressuremean dalam z
PPv z
PPP z z
2zz z
P2
PP @ z
region) dalam P & (P z :mana di
z T LG D)PP(
PbTb 18.062 h Q
:menjadiakan disederhan tadiPersamaan D
0.032 f
D 0.48
D G Q 20 Re
2
1
Weymouth purpose
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Weymouth Equation: Non Horizontal Flow
2
23
2
3
2
3
2
3
2
3
32
2
3
H3
H2
3P
2P
2
1
22
1
PPP 1
PP
PPln
1PP 1y yln
05.1PP
:praktis Untuk
0y2 ... )1y(31 )1y(
21 )1y( y ln
H T z
0.01875G PPln
H T z )144(10.732
29G PP
:atau
H144zRTPG 29 P
T R zPG 29Sg
1449
HP
0L D c 29
fH c9
9P v
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(N.H) Dz L f T G
)PeP( PbTb 23.3Qh
l)(horizonta Dz L f T G)PP(
PbTb 23.3Qh
e PP
e PP
HT z
G01875.0PPln
Dz L f T G)PP(
PbTb 23.3Qh
BgG000529.0P
PG000529.0Bg
PHT z
G01875.0 PPP
HT z
G01875.0P
PP
5.05
22
s21
5.05
23
21
s/223
T z/H G01875.023
2
3
5.05
22
21
223
2
23
P2
P3 dianggap konstanP1
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Pan Handle Equation: Horizontal Flow
n321n
22
11
n
nSnSn
2
2S2S1
1
1S1
S
5.0522
s21
s.....sss sz T/HG 0.0375 s
z T/HG 0.0375 s
sL)1(ee.....
sL)1(ee
sL)1(e Le flow uniformNon
Ls
)1(e Le flow Uniform
elevationinlet -elevation outline H pipa panjang effective Le :mana di
Le z f T GD)Pe(P
PbTb 23.3Qh
Tb@Pb, day/ft rate flow gasz L T
PP
:mana di
DG1
PbTb 87.435Q
DQG 52 f1
35394.02
22
1
6182.24694.007881.1
1461.0
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Modified Pan Handle: Horizontal Flow
Clinedins Equation: Horizontal Flow
Dari dasar persamaan:
di mana:Q = volume flow rate (MCFD)Ppc= pseudo critical pressure (psia)D = pipe line internal diameter (inch)L = pipe line length (ft)Pr = pseudo reducer pressureT = average flow line temp (oR)G = gas gravitasiz = gas deviation factor @Tb, Pb
53.251.0
0.961
22
21
02.1
01961.05.0
DG z L TPP
PbTb 737Q
DQG 16.7
f1
5.051Pz
0
2Pz
0 f L T GD Pr
zPr Pr
zPr
PbPpc Tb zb 973.3Q
0lwPv
Pr zPr2P
0 Al (Katz- Kobayashi)
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GAS FLOW IN SERIES, PARALLEL, AND LOOPED PIPELINES
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7.4.1 Series Pipeline
Dengan Persamaan 7.48
Qh = 18,062 Tb (( p12-p22)D16/3 ) 0,5 ……..(7.48) Pb γg.T L Z
Karena p1 – p2 adalah konstan, Persamaan 7.48 dapat ditulis sebagai :Qh = K1 ( D16/3 ) 0,5 .........(7.70)
LAtau…
L = KD16/3 ……..(7.71) qh2
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L2,D2 L3,D3L1,D1
Dijadikan ….
Deq,Leq,Q=Q1=Q2=Q3Δp= Δp1+ Δp2 + Δp3
Series pipeline
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Jadi untuk memberikan kuantitas gas pada penurunan tekanan yang ada.Panjang berbanding lurus degan kenaikan diameter dengan power 16/3. Karena itu panjang ekivalen = DA-in,LA akan mempunyai penurunan tekanan yang sama dengan LB miles dalam DB.
L’A= DA 16/3
LB (
DB )
L’A= LB DA 116/3
DBOleh karena itu series line menghasilkan panjang ekivalen total :
LAeq= LA + L’A = LA + LB DA 16/3
DB ………(7.73)
Volume laju alir qh gas akan menghasilkan dr harga p1, p2, Yg, T and z, dapat dihitung dengan persamaan 7.48 dengan DA LAeq,tetapi , dr persamaan 7.70 laju alir berbanding lurus dengan (1/L)0,5. Jadi perubahan persen (%) dari volume laju alir adalah :
Δqh=((1/LAeq)0,5 – (1/L)0,5) …..(7.74)
(1/ L )0,5
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Panjang ekivalen dan diameter dapat di gambarkan :
L1 = L2 DA 16/3
DB….(7.75)
AtauD1 = D2 DA 3/16
DB….(7.76)
Menggunakan persamaan Weymouth dengan faktor friksi :
L1 = L2 f2 D1 16/3
f1 D2 ….(7.77)Atau :
D1 = D2 f2 L1 16/3
f1 L2 ….(7.78)
Dengan menggunakan LA miles untuk bagian A, persamaan.7.48 adalah :
qAPb ( Yg T )0,5 = constant = p12 – p22 = p12 – p22 18.062Tb ( DA 16/3 ) LA z B LA z A
Atau..( p12 – p22 ) LA z A = ( p12 – p22 ) LA z B ….(7.79)
Dengan cara trial dan error menggunakan P2 sebagao variabel, dengan asumsi :
za = zb = zp1 + zp2 2
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Persamaan7.75 dapat diperpanjang menjadi 3 pipa atau lebih dalam series :
Qt = q1 = q2 = q3
Total penurunan tekanan adalah jumlah dari penurunan tekanan:
Δpt = Δp1 + Δp2 + Δp3
Atau…
(p12 – p42) = YgzTqt2Pb2Le
(18.062 )2 Tb2 D16/3
= YgzTPb2 (q12 L1) + (q22 L2) + (q32 L3 )
(18.062)2 Tb2 ( D116/3) (D216/3) (D36/3) Sehingga :
Le = L1 + L2 + L3
D16/3 D116/3 D216/3 D316/3 …..(7.80)
Menggunakan persamaan Weymouth yang mengandung f,
fLe = f1L1 + f2L2 + f3L3 + ……. + fnLn
D5 D15 D25 D35 Dn5 .....(7.81)
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7.4.2 Parallel Pipelines
Menggunakan persamaan Weymouth, ( tanpa f ),
Qh = constant ( D16/3 ) = constant ( D8/3 ) …..(7.82)
Perbandingan produksi baru dengan yang lama adalah :
qt = qA + qB = ( 1 + qB ) = ( 1 + ( DA )8/3 )
qA qA qA ( DA ) …..(7.83)
Persen (%) peningkatan dalam kapasitas :
% peningkatan qh = qB x 100 = 100 ( DB )8/3
qA ( DA ) …..(7.84)
5.03/165.03/165.03/165.022
5.03/1622
33
22
11)21(062.18
)21(062.18
LD
LD
LDpp
PbTb
YgTz
LeDpp
PbTb
YgTzqt
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QT= ( Q3+Q4 ) = Q1 =Q2
ΔP3 = ΔP4
Dijadikan :
Paralled Series
qt p1 p2 qtDA = 4 in
Db = 6 in
D1,L1,q1
D2,L2,q2
D3,L3,q3
qtP1 P2 qt
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5.03/165.03/165.03/165.03/16
33
22
111
LD
LD
LD
LeD
5.055.055.055.055.05
........
3.3
2.2
1.1
.
Lnfn
DnLfD
LfD
LfD
LefD
Sehingga :
Jika persamaan Weymouth, yang terdapat faktor friksi (f), persamaannya menjadi :
7.4.3 Looped Pipelines
Berdasarkan aliran paralel didalam loop, menggunakan persamaan Weymouth (tanpa f) :5.03/16
tan
LDtconsqh
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D3,L3,Q3
D1,L1 D2L2Q2 D4L4
Q1 Q4
QT= ( Q2+ Q3 ) = Q1 = Q4
Looped Series
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Dari persamaan sebelumnya :
2/1
3/8
2/1
3/8
2/1
3/8
)'('
LBDB
LADA
ABLABD
2
2/13/82/13/8 1'
1'
1'
LBABDDB
LAABDDA
ABL
Penyelesaian persamaan diatas menggunakan panjang ekivalen dari hasil segmen loop :
D’AB dipilih dari diameter yang sama selain segme loop,
D’AB = DC = DA
Persamaan disederhanakan menjadi :2
2/13/82/1 111'
LBDCDB
LA
ABL
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Kemudian, jika panjang aliran paralel sama, LA = LB persamaan menjadi :
2
3/82/1
11
1'
DCDB
LA
ABL
Perbandingan aliran setelah looping maka laju alir awal adalah :
1'
100100%
'5.0
5.0
LLo
qoqoqqhinincrease
LLo
qoq
Dimana : :qo = Laju alir awal sebelum loopingq = Laju rate setelah loopingLo = Panjang awal pipaL’ = Panjang Ekivalen pipa setelah looping = L’AB + LC