Di am .
of
Sph er e
Dep t h of L i qu i d , m et er s
m et er s
0.5
0.5
0.065
–
1
0.262
0.524
–
2
0.654
2.094
4.189
–
4
1.440
5.236
16.755
33.510
–
6
2.225
8.378
29.322
83.776
113.097
–
8
3.011
11.519
41.888
134.041
226.194
268.082
–
10
3.796
14.661
54.454
184.307
339.292
469.144
523.598
–
12
4.581
17.802
67.021
234.572
452.389
670.206
837.757
904.778
14
5.367
20.944
79.587
284.837
565.486
871.268 1 151.916 1 357.167 1 436.754
16
6.152
24.086
92.153
335.103
678.583 1 072.329 1 466.075 1 809.556 2 052.505 2 144.66
18
6.938
27.227
104.720
385.368
791.681 1 273.391 1 780.234 2 261.945 2 668.257 2 948.91 3 053.63
20
7.723
30.369
117.286
435.634
904.778 1 474.453 2 094.393 2 714.334 3 284.009 3 753.15 4 071.50 4 188.79
25
9.687
38.223
148.702
561.297 1 187.521 1 977.107 2 879.791 3 845.306 4 823.388 5 763.77 6 616.19 7 330.38 8 181.22
30
11.650
46.077
180.118
686.961 1 470.264 2 479.762 3 665.188 4 976.279 6 362.767 7 774.39 9 160.88 10 471.97 13 089.96 14 137.16
35
13.614
53.931
211.534
812.625 1 753.007 2 982.416 4 450.586 6 107.251 7 902.146 9 785.01 11 705.56 13 613.56 17 988.69 21 205.73 22 449.28
40
15.577
61.785
242.950
938.288 2 035.750 3 485.071 5 235.983 7 238.223 9 441.525 11 795.62 14 250.25 16 755.15 22 907.43 28 274.31 32 070.40 33 510.29
45
17.541
69.639
274.366
1 063.952 2 318.493 3 987.725 6 021.381 8 369.196 10 980.904 13 806.24 16 794.94 19 896.74 27 816.16 35 342.89 41 691.52 46 076.65 47 712.90
50
19.504
77.493
305.781
1 189.615 2 601.237 4 490.379 6 806.778 9 500.168 12 520.283 15 816.86 19 339.63 23 038.33 32 724.90 42 411.47 51 312.64 58 643.01 63 617.20 65 449.79
T an k Wi d t h ,
m
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
1
2
4
6
8
10
12
14
16
18
20
25
30
35
40
45
50
–
–
–
–
–
–
–
–
–
T an k L en gt h , m
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
7.50
8.00
8.50
9.00
9.50
10.00
10.50
11.00
11.50
12.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
11.00
12.00
13.00
14.00
15.00
16.00
17.00
18.00
19.00
20.00
21.00
22.00
23.00
24.00
1.50
3.00
4.50
6.00
7.50
9.00
10.50
12.00
13.50
15.00
16.50
18.00
19.50
21.00
22.50
24.00
25.50
27.00
28.50
30.00
31.50
33.00
34.50
36.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
18.00
20.00
22.00
24.00
26.00
28.00
30.00
32.00
34.00
36.00
38.00
40.00
42.00
44.00
46.00
48.00
2.50
5.00
7.50
10.00
12.50
15.00
17.50
20.00
22.50
25.00
27.50
30.00
32.50
35.00
37.50
40.00
42.50
45.00
47.50
50.00
52.50
55.00
57.50
60.00
3.00
6.00
9.00
12.00
15.00
18.00
21.00
24.00
27.00
30.00
33.00
36.00
39.00
42.00
45.00
48.00
51.00
54.00
57.00
60.00
63.00
66.00
69.00
72.00
3.50
7.00
10.50
14.00
17.50
21.00
24.50
28.00
31.50
35.00
38.50
42.00
45.50
49.00
52.50
56.00
59.50
63.00
66.50
70.00
73.50
77.00
80.50
84.00
4.00
8.00
12.00
16.00
20.00
24.00
28.00
32.00
36.00
40.00
44.00
48.00
52.00
56.00
60.00
64.00
68.00
72.00
76.00
80.00
84.00
88.00
92.00
96.00
1 cu met er = 264.172 U .S. gal.
= 219.9692 I mper ial gall ons
= 6.2898 bbls (42 U .S. gals)
–
l
pd
In h ibit or losses t o t h e h ydr oca r bon liqu id ph a se a r e mor e
difficu lt t o pr edict . Solu bilit y is a st r on g fu n ct ion of bot h t h e
wa t er ph a se a n d h ydr oca r bon ph a se composit ions. F ig. 20-66
pr esen t s exper imen t a l da t a 32,33,34 sh owin g solu bilit y of
m et h a n ol in a pa r a ffin ic h ydr oca r bon liqu id a s a fu n ct ion of
t em per a t u r e a n d met h a n ol con cen t r a t ion . Met h a n ol solu bilit y
in n a ph t h en ic h ydr oca r bon s is sligh t ly less t h a n pa r a ffin ic,
bu t solu bilit y in a r oma t ic h ydr oca r bon s may be fou r t o six
t imes h igh er t h a n in pa r a fins.
Solu bilit y of E G in t h e liqu id h ydr oca r bon ph a se is ext r em ely sm a ll. 29 A solu bilit y of 40 g/m 3 of NGL is oft en u sed
for design pu r poses. H owever, en t r a in m en t a n d ot h er ph ysica l losses m a y r esu lt in t ot a l losses sign ifica n t ly h igh er t h a n
t h is.
Example 20-10—2.83 (10 6) Sm 3/da y of n a t u r a l ga s leaves a n
offsh or e pla t for m a t 38°C a n d 8300 kPa (a bs). Th e ga s com es
on sh or e a t 4°C a n d 6200 kPa (a bs). Th e h ydr a t e t emper a t u r e
of t h e ga s is 18°C. Associa t ed con den sa t e pr odu ct ion is 56
m 3/St a n da r d m 3 (10 6 ). Th e con den sa t e h a s a den sit y of
778 kg/m 3 a n d a molecu la r ma ss of 140. Ca lcu la t e t h e a mou n t
of met h a n ol a n d 80 ma ss% E G in h ibit or r equ ir ed t o pr even t
h ydr a t e for m a t ion in t h e pipelin e.
S o lu t io n S t e p s :
Me t h a n o l
1. Ca lcu la t e t h e a mou n t of wa t er con den sed per da y
Tot a l met h a n ol in ject ion r a t e = 749 + 1310 + 56
= 2115 kg/da y
Met h a n ol left in t h e ga s ph a se ca n be r ecover ed by con den sa t ion wit h t h e r em a in in g wa t er in down st r ea m ch illin g pr ocesses. Likewise, t h e met h a n ol in t h e con den sa t e ph a se ca n be
r ecover ed by down st r ea m wa t er wa sh in g.
80 w t % E G
1. Ca lcu la t e r equ ir ed in h ibit or con cen t r a t ion fr om E q 20-6.
d = 14°C
mI =
In h ibit or losses r epr esen t a sign ifica n t oper a t in g cost a n d ca n
ca u se pr oblems in down st r ea m pr ocess u n it s. E fficien t in h ibit or sepa r a t ion sh ou ld be pr ovided.
ca n pr ovide sign ifica n t ben efit s compa r ed t o t h er modyn a mic
in h ibit or s in clu din g:
XI = 0.275, E q 20-7 (u se t h is va lu e in su bsequ en t ca lcu la t ion s)
3. Ca lcu la t e m a ss r a t e of in h ibit or solu t ion in wa t er ph a se
fr om E q. 20-8 (a ssu m e 100% m et h a n ol is in ject ed)
X R • m H 2O
(0.275) (1975)
mI =
=
= 749 kg/da y
XL − XR
(1 − 0.275)
4. E st ima t e va por iza t ion losses fr om F ig. 20-65.
@4°C a n d 6200 kP a (a bs),
kg/m 3
losses = 16.8 (10 -6 )
wt % MeOH
da ily losses = (16.8 x 10 -6 )(2.83 x 10 6)(27.5) =
1310 kg/da y
5. E st ima t e losses t o h ydr oca r bon liqu id ph a se fr om F ig.
20-66.
@4°C a n d 27.5 wt % MeOH, xMeOH ≈ 0.2 mol%
lb • mols of con den sa t e per da y –
56m 3
106 Sm 3
778k g
m3
(0 .28)(1975)
= 1063 k g/d ay
(0.8 − 0.28 )
Va por iza t ion a n d liqu id h ydr oca r bon losses a r e n egligible .
• Sign ifica n t ly lower in h ibit or con cen t r a t ion s a n d t h er efor e dosa ge r a t es. Con cen t r a t ion s r a n t e fr om 0.1 t o 1.0
ma ss per cen t polymer in t h e fr ee wa t er ph a se, wh er ea s
a lcoh ols ca n be a s h igh a s 50%
• Lower in h ibit or loss ca u sed by eva por a t ion , pa r t icu la r ly
compa r ed t o m et h a n ol
• Redu ced ca pit a l expen ses t h r ou gh decr ea sed ch emia l
st or a ge a n d in ject ion r a t e r equ ir em en t s; a n d n o n eed for
r egen er a t ion beca u se t h e ch emica ls a r e n ot cu r r en t ly r ecover ed. Th ese a r e especia lly a ppr opr ia t e for offsh or e
wh er e weigh t a n d spa ce a r e cr it ica l t o cost s
• Redu ced oper a t in g expen ses in ma n y ca ses t h r ou gh decr ea sed ch emica l con su mpt ion a n d deliver y fr equ en cy
• In cr ea sed pr odu ct ion r a t es, wh er e in h ibit or in ject ion ca pa cit y or flowlin e ca pa cit y is limit ed
• Lower t oxicit y
∆W = 698 mg/Sm 3
Wa t er con den sed = (2.83 x 10 6 )(6 9 8 ) =
1 9 7 5 (1 0 6 ) m g/d a y = 1 9 7 5 k g/d a y
2. Ca lcu la t e r equ ir ed met h a n ol in h ibit or con cen t r a t ion
fr om E q 20-5 a n d 20-7 (wit h F ig. 20-59).
d = 14°C
M = 32
Solvin g for XI ,
XI = 0.255, E q 20-5
2.83 x 10 6 Sm 3
da y
M = 62
Solvin g for XI , XI = 0.28
2. Ca lcu la t e ma ss r a t e of in h ibit or in wa t er ph a se fr om E q.
20-8.
L ow D o s a g e H y d r a t e I n h ib it o r s (L DH Is ) — LDHIs
Win = 850 mg /Sm 3
Win = 152
___________
mg/Sm 3_
fr om F ig. 20-4,
kg met h a n ol = (1.76)(32) = 56 kg/da y
1 k g • m ol
140 kg
= 881 kg • mol/da y
kg • mol met h a n ol = (881)(0.002) = 1.76 kg • mols/da y
Kin e t ic H y d r a t e I n h ib it o r s — KHIs wer e design ed t o
in h ibit h ydr a t e for m a t ion in flowlin es, pipelin es, a n d down h ole equ ipmen t oper a t in g wit h in h ydr a t e-for min g con dit ion s
su ch a s su bsea a n d cold-wea t h er en vir on men t s. Th eir u n iqu e
ch em ica l st r u ct u r e sign ifica n t ly r edu ces t h e r a t e of n u clea t ion
a n d h ydr a t e gr owt h du r in g con dit ion s t h er modyn a mica lly fa vor a ble for h ydr a t e for ma t ion , wit h ou t a lt er in g t h e t h er modyn a mic h ydr a t e for ma t ion con dit ion s (i.e., t em per a t u r e a n d
pr essu r e). Th is mech a n ism differ s fr om m et h a n ol or glycol,
wh ich depr ess t h e t h er m odyn a m ic h ydr a t e for m a t ion t emper a t u r e so t h a t a flowlin e oper a t es ou t side h ydr a t e-for min g
con dit ion s.
KH Is C o m p a r e d t o Me t h a n o l o r Gly c o ls — KHIs
in h ibit h ydr a t e for ma t ion a t a con cen t r a t ion r a n ge of 0.1–1.0
ma ss per cen t polym er in t h e fr ee wa t er ph a se. At t h e ma ximu m r ecom men ded dosa ge, t h e cu r r en t in h ibit ion ca pa bilit ies
a r e –2°C of su bcoolin g in a ga s syst em a n d –7°C in a n oil syst em wit h effor t s con t in u in g t o expa n d t h e r egion of effect iven ess. For r ela t ive compa r ison , met h a n ol or glycol t ypica lly
20-21
et a l
P
T
v
u
h
s
P
T
vf
vg
uf
u fg
u fg
h fg
h fg
hg
sf
sfg
sg