TPG 4140 Natural Gas
December 15, 2014
Professor Jon Steinar Gudmundsson
PROBLEM 1 (15 %)
(a) Drying and removal of sour gases are standard operations in the processing of natural gas. Which of these is carried out first and why?
(b) An expander and a Joule-Thomson valve are used to cool natural gas. Which of these two methods gives lower temperature and why?
(c) What are amines used for in the processing of natural gas and what is the main chemical amines are based on?
(d) What is meant by dew point and what two dew points are considered most important for the transport of natural gas?
PROBLEM 2 (15 %)
(a) Make a simple sketch that illustrates the drying of natural gas using TEG.
(b) Make a simple sketch of the cross-section of a large-diameter subsea pipeline carrying natural gas from Norway to the Continent or the United Kingdom. Show the main elements/components and name these.
(c) Make a sketch showing the main components of a natural gas combined cycle power plant.
(d) Make a simple sketch illustrating surge control.
(e) What process does the figure below illustrate?
1

PROBLEM 3 (15 %)
The reservoir performance of a natural gas reservoir is shown below.
(a) What is the original gas in place?
(b) What are the reserves, assuming a typical recovery percent?
G
[GSm
3
] p
R
[bara] p
R
/z
[bara]
0
5.7
11.3
22.6
45.3
275
254
236
199
126
296
277
260
222
140
PROBLEM 4 (20 %)
(a) What three countries are the largest traditional suppliers of natural gas to
Europe (EU)?
(b) What is meant by a take-or-pay contract?
(c) Derive the equation q s .
c .
 q

 p p s .
c .

 
T s .
c .

T  
1 z
(d) In terms of o.e. (oil equivalent), is more oil or natural gas exported from Norway?
(e) What is meant by R/P ratio?
(f) Have the proved natural gas reserves in the world increased or decreased the last 10 years and the last 20 years? OK to answer with yes and/or no.
(g) Have CO
2
emissions in the United States increased or decreased in recent years?
(h) What is meant by 40 MJ/Sm
3
and what does the number represent in Norwegian energy statistics?
(i) What is the approximate pressure and temperature in the tanks of LNG carriers (ships)?
(j) What physical effect is included in the Haaland-equation and not in the Blasiusequation?
2

PROBLEM 5 (20 %)
(a) Non-associated gas must be sent from a platform to an onshore facility for further processing. Hence, the gas is to be compressed from 2 bara and 15 ºC to 32 bara in a two-stage compressor with intermediate cooling. Consider that the pressure ratio in each stage is 4 and the temperature at the inlet of the second stage is 15 ºC. Calculate the total compressor power consumption assuming adiabatic compression with 80 % efficiency in each stage. Will the power consumption be larger or smaller in a single stage compression?
(b) Calculations indicate that the non-associated natural gas will form natural gas hydrate if the dehydration process in the platform does not perform as expected (dew point water specification is not reached). Assuming that the gas after compression flows in a
6 inch ID subsea pipeline to the onshore process facility, which is located at 1 km distance from the platform, calculate the temperature drop in the pipeline. Will natural gas hydrate form in the bulk flow of the pipeline if the dehydration process fails?
Consider that the seawater temperature is 5 ºC, the overall heat transfer coefficient 2
W/m
2
.K and the natural gas hydrate will form in presence of small amounts of condensed water when the bulk fluid is cooled below 20 ºC.
Mass rate gas m = 360 kg/h
Relative density γ (gravity) of gas 0.70
Heat capacity at constant pressure C p
= 2.3 kJ/kg.K
Heat capacity at constant volume C v
= 2.0 kJ/kg.K
Assume that the heat capacities remain constant in both problems and that the temperature at the pipeline inlet is the same as the outlet temperature of the second stage compression.
3

PROBLEM 6 (15 %)
(a) What natural gas product has a density of 450 kg/m
3
and contains 600 m
3
of natural gas at standard conditions?
(b) What do the two curves in the figure below show and what does the point where the curves cross each other represent?
(c) What is meant by skin in a natural gas production well?
(d) Different compressor types are considered suitable for different compression duties.
For which of the following duties are axial, centrifugal and reciprocating compressors considered most suitable:
(i) Large to medium flow, high pressure
(ii) Large flow, low pressure
(iii) Medium to low flow, high pressure.
(e) The concentration of carbon monoxide (CO) and nitrous oxides (NO x
) in the exhaust from natural gas turbines change with (depends on) temperature. Make a simple sketch showing qualitatively these changes (concentrations against temperature).
4

EQUATIONS pV = z n RT
R = 8.314 kJ/kmol.K
= 8314.34 J/kmol.K
 


 gas
 air

 s .
c .



M gas
M air


M air = 28.97 [kg/kmol]
T s .
c .

15

C (in Norway, 60 º F in USA) p s.c.
= 1 atm (Norway and USA)
0 °C = 273.15 K q s .
c .
 q

 p s p
.
c .

 
T s .
c .

T  
1 z
  pM zRT
WI

GCV

 p
  p g
  p a
  p f g = gravity (hydrostatic), a = acceleration, f = wall friction
 p g
  g h for liquid
𝑇
𝑅
= 𝑇 + 𝑑𝑇 ℎ 𝑑ℎ p g
 p o exp
 
 z gM
R T
L

 for gas
 p f
 f
2
L
 u
2 d d A
2
M f m
2 z R T
 p
2

2
 p
1
2  f d ln

 p
2
2 p
1
2



L

0
5 p

V
RT
 b
 a
V ( V
 b ) p

V
RT
 b

V ( V a
 b )
 b ( V
 b ) p
1 v
1 k  p
2 v
2 k
W

2

1 vdp
P ideal
 m
M
P real

P ideal

RT
1

 k k

1







 p
2 p
1

 k

1 k

1




T
2
T
1


 p
2 p
1

 k

1 k k

C
C p v p

2
 p
1 p
3

0 .
5
 p

Aq

Bq
2 dp
T
2

 u
   u
2 dx k

T


T
1

T
 exp



U m

C p d
L



T

K
M

1 x mass
 x mass



T
 
72 ln( 1
 x mole
)
CostB

CostA


Cap .
B
Cap .
A


0 .
65 q

 k

2
 rh

 dp dr
F ( p )


 p
 z

 q s .
c .
 p s .
c .
T
 kh
 z
T s .
c .


 ln


 p
2  p
2 w

R r e r w



3
4
 s q

C
 p
R
2  p
2 wf
 n p
 z p i z i

 1

G
G i





Re

 ud
 f

0 .
316
Re
0 .
25
1 f
 
1 .
8 n log 






6 .
9
Re n
 k
3 .
75 d n = 1 for liquid & n = 3 for gas q m

C

1
1
 
4

4 d
2
2
 p

1
1 .
11 n



P

P
0
 c
G w
G
( G

G
0
)
 c
F w
F
( F

F
0
) u g , max


175

1



0 .
43
6

CONVERSION FACTORS
Traditional units
LENGTH mile (mi) yard (yd) foot (ft) inch (in)
VOLUME
US-gallon (gal)
UK-gallon (gal)
API barrel (bbl) kubikkfot (cf)
MASS pound (lbm)
US-ton (ton)
UK-ton (ton, tonne)
TEMPERATURE
Rankin (R)
Celciusgrader (C)
Fahrenheit (F)
ENERGY, WORK kalori (cal) erg
British Termal Unit (BTU)
Kilowattime (kWh)
POWER hestekraft (elektrisk) (hk, hp) hestekraft (hydraulisk)
FORCE dyn (dyn) kilopond, eller kilogramkraft (kp/kgf) poundforce (lbf)
PRESSURE bar (bar) pound per square inch (psi) atmosfære (atm) mm kvikksølv (torr)
VISCOSITY poise (p) centipoise (cp) lbf/(ft 2 /s)
DENSITY
API-gravity (API) g/cm 3 lbm/US-gal lbm/UK-gal lbm/ft 3
VOLUME FLOW liter pr. sek. (l/s) fat pr. dag (bbl/d) kubikkfot pr. dag (cf/d)
US-gallon pr. minutt (gal/min)
#: Exact value
SI-equivalents
M
1609.344 m #
0.9144 m #
0.3048 m #
0.0254 m # m3
0.00378541 m 3
0.00454609 m 3
0.158987 m 3
0.0283167 m 3 kg
0.45359 kg
907.185 kg
1016.05 kg
Kelvin: K
5/9 K #
K = C + 273
C = (F-32) ∙ 5/9
Joule: J
4.184 J #
10E-7 J
1055.06 J
3600 kJ
Watt: W
746 W #
746.043 W
Newton: N
10E-5 N #
9.80665 N
4.44822 N
Pascal: Pa
10 5 Pa
6894.76 Pa
1.01325 bar #
133.322 Pa
Pa.s
10E-1 Pa.s #
10E-3 Pa.s #
4.78803 Pa.s kg/m 3 kg/m 3 = (141.5)(1000)/(131.5 + API)
1000 kg/m 3 #
119.826 kg/m 3
99.7763 kg/m 3
16.0185 kg/m 3 m 3 /s
10E-3 m 3 /s
1.8401E-6 m 3 /s
3.2774E-7 m 3 /s
6.30903E-5 m 3 /s
Useful info.
3 ft = 1 yd
12 in = 1 ft
1 bbl = 42 US gal
1 bbl ~ 5.62 cf
R = F + 460
J = Nm
W = J/s
N = kg m/s 2 dyn = g cm/s 2
Pa = N/m 2
1 bar ~ 14.5 psi
1 atm ~ 14.7 psi
1 atm ~ 1.01 bar
Pa.s = kg/s.m poise = dyn/cm 2 s
7