a plan for operating cost reduction and technology development of

Poster PO-28
A PLAN FOR OPERATING COST REDUCTION AND
TECHNOLOGY DEVELOPMENT OF LNG VAPORIZING SYSTEM
PLAN DE REDUCTION DES COUTS D’OPERATION ET DE
DEVELOPPEMENT DES TECHNOLOGIES POUR LE
SYSTEME DE VAPORISATION DU GNL
Ho-Yeon Kim
Jeong-Hwan Lee
Dong-Hyuk Kim
Young-Soon Baek
Kwang-Won Kim
Ki-Hwan Park
R&D Division, Korea Gas Corporation
Incheon, South Korea
[email protected]
ABSTRACT
This study was performed to establish an effective operating plan to reduce the
operating cost of LNG vaporizing system in Incheon R/T (Receiving Terminal), and to
develop a bench scale new type LNG vaporizer for lower seawater temperature.
To reduce the operating cost, we first analyzed the double train pump-seawater
pipeline network with the modified Linear Theory Method and the thermal performance
of ORVs (Open Rack Vaporizers) with the modified Wilson Plot Technique. From the
results, we estimated the unit cost of ORVs operation with the flow rate and the
temperature of seawater and were able to determine an effective operating mode of LNG
vaporizing system in Incheon R/T.
To develop new type vaporizer, we investigated two models: 1Body-1HX (Heat
eXchanger) with double tubes and 1Body-3HXs with single tubes, in applying an
intermediate fluid so as to overcome seawater icing of ORVs. In particular, the
intermediate fluids were investigated to apply freons or hydrocarbons. In the first year,
we performed basic analyses and fabricated a batch type vaporizer. In the second year, we
will create a bench scale vaporizer to modify and improve on the problems of the
characteristics of its structure and heat transfer, and then, will perform a final bench scale
vaporizer test for its performance verification. Also, we are planning to demonstrate its
realization for a real-scale system with scale-up parameters in conclusion.
Consequently, we have established an operating plan for the LNG vaporizing system
in Incheon R/T and driven the development of a new type vaporizer to positively resolve
the icing problem of ORVs in the winter season.
RESUME
Cette étude a été menée dans le but d’établir un plan d’opération efficace visant à
réduire les coûts d’opération du système de vaporisation du GNL (gaz naturel liquéfié) au
terminal de réception d’Incheon, et à développer un nouveau type de vaporiseur du GNL
à l’échelle du laboratoire pour les basses températures de l’eau de mer.
PO-28.1
SESSIONS
CONTENTS
Poster PO-28
Afin de réduire les coûts d’opération, nous avons tout d’abord analysé le réseau de
pipelines de pompage de l’eau de mer à train double, en utilisant la méthode dénommée,
et examiné la performance thermique des vaporiseurs dits à l’aide de la technique
d’analyse du transfert de chaleur dénommée. A partir des résultats obtenus, nous avons
estimé les coûts d’opération par unité des ORV avec le débit et la température de l’eau de
mer et avons pu déterminer le mode d’opération efficace du système de vaporisation du
GNL au terminal de réception d’Incheon.
Pour développer un nouveau type de vaporiseur, nous avons passé en revue deux
modèles d’échangeurs de chaleur que sont le modèle dit à tubes doubles et le modèle dit à
tubes uniques, en appliquant un fluide intermédiaire afin de surmonter le givrage de l’eau
de mer des ORVs. En particulier, les fluides intermédiaires ont été examinés pour une
application de fréons ou de hydrocarbures. Au cours de la première année, nous avons
effectué des analyses de base et fabriqué un vaporiseur de type discontinu. Au cours de la
deuxième année, nous mettrons au point un vaporiseur à l’échelle du laboratoire pour
modifier et améliorer les caractéristiques de sa structure et son transfert de chaleur, et,
ensuite, nous effectuerons un test final au banc d’essai pour vérifier sa performance. En
outre, nous envisageons de démontrer finalement sa réalisation à l’échelle réelle avec des
paramètres extrapolés.
En conséquence, nous avons établi un plan d’opération pour le système de
vaporisation du GNL au terminal de réception d’Incheon et conduit au développement
d’un nouvel type de vaporiseur pour résoudre les problèmes de givrage des ORVs en
hiver.
INTRODUCTION
KOGAS (Korea Gas Corporation) has been quickening the pace for productivity
elevation of LNG vaporizers as one of the operation goals in order to diversify its
business and intensify its competitive power in the domestic and foreign markets.
However, KOGAS has been faced with limited productivity elevation with the present
LNG vaporizers due to geographical location. In particular, the LNG vaporizers are core
facilities to produce NG from LNG of 16,650 ktons a year. In addition, KOGAS
experienced some difficulty with productivity due to the concentration of the gas demand
during the winter season, and moreover, the performance of ORVs is decreasing rapidly
from the lower temperature of seawater. For example, ORVs produce about 90 tons per
hour, that is, 50% of the rated capacity, at 3oC seawater. To meet the required supply,
KOGAS would need additional operation of SMVs (SubMerged combustion Vaporizers)
that are 6.5 times higher than the operating cost of ORVs.
As a result, KOGAS has embarked on establishing an effective operating plan of the
LNG vaporizing system and developing a new type vaporizer for lower seawater
temperature to technically resolve these problems. In part, we determined effective
operating modes of the LNG vaporizing system in Incheon R/T. Also, we are proceeding
to develop a bench scale vaporizer
NETWORK ANALYSIS
Incheon R/T has a vaporizing system that has 5 seawater pumps, 10 seawater heaters,
5 ORVs, and 8 SMVs in the first plant and 4 seawater pumps, 6 seawater heaters, 3
ORVs, and 10 SMVs in the second plant. Particularly, the operating costs of ORVs can
PO-28.2
SESSIONS
CONTENTS
i
∑K Q
ni
i
(75)
[51]
(74)
[48]
(73)
[49]
(72)
(71)
(70)
[46]
(69)
(27)
(29)
± ∑ h p = ∆H
SESSIONS
P1
(2)
P2
[2]
[1]
(1)
(24)
(26)
(28) [17]
(25)
[19]
[100] (131) [98]
(60)
[37]
(53)
(55)
[39]
(56)
[41]
(58)
(62) [43]
(31)
(46)
(49)
(45)
(50)
(3)
P3
[3]
(22)
(47)
(48)
(100)[68]
(104)
(105)
(106)
(107)
P4
(21)
(4)
[4]
(35)
(20)
(34)[21]
[27]
[29]
[33] [34]
(101)
(54)
[38]
(30) [16] (32)
(33) [15]
[28]
(23)
[20]
[32]
(57)
[40]
(103)
(61)
(80)
(81)
(59)
V1
(92)
[42]
[60]
[82]
(129) [69] (102)
(132)
(133)
[45]
(63)
(64)
[101]
H10
[44]
(65)
[61]
[102]
(66)
(67)
H9
[18]
(68)
[47]
(94)
[62]
(76)
[55]
(93)
[54]
(82)
[83] V2
(84)
(85)
(83)
[84] V3
[57]
(95)
(88)
[63]
[85]
[59]
[56]
(96)
[50]
(77)
V4
(89)
(86)
[64]
[86] V5
[58]
(87)
(91)
[65]
V6
(97)
[87]
(5)
P5
(19)
[14]
[5]
H2
(121)
[90]
H3
(122)
[91]
(123)
[92]
H4
[52]
H5
(124)
[93]
(111)
(125)
[94]
H6
(78)
(79)
[108]
[109]
H7
(126)
[95]
(127)
[96]
(135)
[97]
(18)
[30]
(17)
[31]
(6)
P6
[6]
(16)
[13]
(44)
(7)
(39)
(8)
[8]
(12)
(41)
P8
(13)
(38)
(40)[11]
[25]
P7
[7]
(14)
(36) [12]
(15)
[22] (37)
[26]
(43)
(120)
[23]
(128)
(9)
P9
(10)
[24]
(52)
(11)
[10]
(42)
[9]
(51)
(108)
[72]
(130)
[99]
(134)
[103]
[35]
H8
[36]
(109)
(139)
(140)
(112) (113) (114) (115) (116) (117) (118) (119)
[76]
[77]
[78]
[80]
[81]
[74]
[75]
[79]
[70]
H1
[71]
[53]
(110)
[73]
H11
i out
[66]
V7
(98)
[88]
(∑ Q )
[67]
(90)
V8
(136)
[104]
fi
(99)
[89]
(141)
[105]
(137)
[106]
[107]
(138)
i
[110]
(142)
(143)
(144)
N
H12
[111]
[112]
[113]
∑h
H13
H14
H15
H16
Poster PO-28
be determined from the operating costs of seawater pumps. To determine this, we must
have analyzed a double trained pump-seawater supply system of open circuit as shown in
Figure 1 with a modified Linear Theory Method [1].
This system was being modeled with 712 pipes, 681 junctions, and 31 loops. To solve
it, the continuity equation on the junctions gives
− (∑ Q i )in = C
(1)
where C is the external flow at the junction. Qi is the volumetric flow into or out of the
junction. Energy equations on real loops becomes
=0
(2)
Figure 1. Schematic of the double train pump-seawater supply system
where hfi is the head loss of the pipe in the real loop. Also, energy equations on pseudo
loops are as follows
(3)
where Ki is the Hazen-Williams coefficient, hp is the head produced by the pump, and ∆H
is the head difference between two reservoirs. Of particular note, the heads of pumps as
shown in Figure 2 are expressed as
PO-28.3
CONTENTS
Poster PO-28
h p = AQ2 + BQ + H o
(4)
where A, B, and Ho are constants for a given pump. Eq. (4) is replaced with a linear
equation by a transformation equation [2] which is followed by
G =Q+
B
2A
(5)
70
70
1st plant
2nd plant
60
60
Head(m)
50
50
40
40
30
30
20
2
1st plant: hP = -0.709Q -3.007Q+62.2
2
2nd plant: hP = -0.648Q -5.040Q+64.0
20
10
10
0
0
0
1
1
2
2
3
3
4
4
5
5
6
6
Flowrates(cms)
Figure 2. Characteristic curves of pumps in each plant
The system is simultaneously solved from the preceding governing equations to
determine the flow rates of the pipes. From the results, we found the mean static
pressures of pumps and the end junctions of ORVs with the use of the following
equations
HP =
∑H
P
N pump
, H orv =
∑H
orv
(6)
N orv
With Eq. (6), we can determine the new external flow rates at the end junctions of each
ORV. The equation becomes
Qj = Qj +
H orv, j
∑H
× λ∆Q
(7)
orv , j
where λ is the weight factor to accelerate the convergence rate. The stop condition of the
calculation is when the norm of external flow rates is less than tolerance level, and
otherwise, is calculated repetitively. From the above calculation, we can find the
operating cost of pumps and calculate the unit cost of seawater to be provided.
HEAT TRANSFER ANALYSIS
The thermal characteristics of ORVs are very complex due to the spread of icing
growth or other unknown factors. Thus, we made our approach with two assumptions:
PO-28.4
SESSIONS
CONTENTS
Poster PO-28
ORVs are operated under no icing conditions and any boiling in star-finned tubes has not
occurred. Also, we could apply the modified Wilson plot technique [3] with the operation
data of ORVs.
The total resistance for ORV can be expressed as
1
1
1
=
+
+ RW
UA h t A t h s A s
(8)
where t and s denote the LNG side and the seawater side, respectively, and Rw is the
resistance of the tube wall. Generally, the convective coefficients can be obtained from
Nu numbers of the LNG side and seawater side. The Nu number of seawater gives
Nu S = C S Re Sd PrS0.4
(9)
where Cs, Res, and Prs denote the constant, Reynolds number, and Prandtl number,
respectively. The Reynolds number of the seawater side can be found with the flow
model on falling film by Bird [4]. The Res becomes
Re S =
4Γ
δ 3 ρg
, Γ=
µ
3υ
(10)
where µ, ν, δ, ρ, and g are viscosity, kinematic viscosity, flow thickness, density, and
gravity, respectively. The Nu number of the LNG side also is expressed as
Nu t = C t Re at Prt0.4
(11)
The wall resistance for a tube can be calculated from
RW =
ln(D o / D i )
2πkL
(12)
where Do, Di, k, and L denote outer diameter, inner diameter, thermal conductivity, and
tube length, respectively.
If the LNG side correlation and the wall resistance are known, the following
expression can be used to calculate the seawater side parameters Cs and d.
ln(1 / y S ) = ln(C S ) + d ln(Re S )
(13)
where ys is expressed as
⎡ 1
⎤
1
0.4
yS = ⎢
− RW −
⎥ (Pr) Ak / D S
a
0.4
C t [(Re) (Pr) Ak / D] t ⎦
⎣ UA
[
]
(14)
where A is the area of heat transfer. From Eq. (13), the seawater side graph should
therefore yield a straight line. The slope and intercept can then be used to calculate d and
Cs, respectively.
PO-28.5
SESSIONS
CONTENTS
Poster PO-28
If the seawater side correlation and the wall resistance are known, the following
expression can be used to determine the LNG side correlation
ln(1 / y t ) = ln(C t ) + a ln(Re t )
(15)
where yt can be written as
⎡ 1
⎤
1
0.4
yt = ⎢
− RW −
⎥ (Pr) Ak / D t
d
0.4
C S (Re) (Pr) Ak / D S ⎦
⎣ UA
[
] [
]
(16)
The above equation should therefore yield a straight line that can be used to calculate
both a and Ct.
Assuming that both the seawater side and LNG side resistances are know, the tube
wall resistance can be calculated from
1
1
1
=
+
+ RW
UA h t A t h S A S
(17)
The above equation should result in a straight line with a slope equal to unity and an
intercept equal to wall resistance value. From the calculations, a, d, Ct, and Cs were
converged at 1.0325, 0.806, 0.0018, and 0.000489, respectively. Also, Rw was converged
at 4.20e-5 K/kW.
NEW TYPE VAPORIZER
To develop a new type vaporizer, we investigated with two models: 1Body-1HX with
double tubes and 1Body-3HX with single tubes. We found that 1Body-1HX was not
suitable to directly apply it to the field due to more required power and more difficult
manufacturing, and so, we determined 1Body-3HX as the new type vaporizer model.
Also, we surveyed hydrocarbons and freons to find a good intermediate fluid. From table
1, we were able to discover that propane is an excellent fluid to be applied to the new
type vaporizer, and especially, the spread of icing of propane never occurred under the
operation condition of LNG because its icing point is lower by about 20K. Lastly,
propane is very easy to purchase for commercial use and is priced lower than any other
fluid. As such, propane was chosen as the intermediate fluid.
We performed basic analyses to manufacture a batch-type vaporizer. The LNG side is
divided by three zones, which are the liquid phase flow, two phase flow, and gas phase
flow zones. The liquid phase and gas phase flow are analyzed by using a Dittus-Boelter’s
equation for turbulent flow [5]. The two phase flow zones are also estimated with Shah
correlation [6] and Kandlikar’s correlation [7]. The propane side is separated by two
zones, which are the condensation and pool boiling zones. The pool boiling zone is
considered with Rohsenow’s model [8] and the condensation zone is from the single tube
model [9]. From the above calculation results, we were able to design a batch-type
vaporizer, and subsequently, we are in the process of manufacturing an apparatus which
has two cooling heat exchangers, two test sections, and three supply tanks for LNG, LN2,
and water. These will be used to precisely find the coefficient of heat transfer on the
inside and outside of the tube at a later time.
PO-28.6
SESSIONS
CONTENTS
Poster PO-28
Table 1. Thermodynamic characteristics of targeted fluids
Item
Boiling point [K]
Icing point [K]
Critical temperature [K]
Latent heat [kJ/kg]
Specific volume [m3/kg]
Propane
230.9
83.2
367.4
423.9
0.4153
Ethane
184.7
101.2
305.4
488.6
0.4837
R-12
243.4
115.0
384.7
167.2
0.1607
R-22
232.4
113.2
369.2
234.1
0.2126
RESULTS AND DISCUSSION
We learned that the unit cost of ORVs operation is ₩ 110.8/m3 at 5oC seawater, and
3
o
3
₩120.3/m at 3 C seawater, with constant 8,000m /hr of seawater from the network
analysis on the pump seawater supply system and the heat transfer analysis on the ORVs.
In particular, at 3oC seawater, the unit cost was ₩143.0/m3 when the flow rate of
seawater was 10,000m3/hr, and was ₩153.9/m3 when it was 5,000m3/hr. These results
revealed that an increase of seawater for ORVs created a rise in the operating cost of
ORVs, and also, that the temperature of seawater has a huge effect on the rise of the
operating cost of ORVs, as shown in Figure 3.
Figure 3. Unit operating costs of NG production on ORV with flow rate of seawater
Consequently, the decrease of the flow rate within limited ranges of seawater
temperature reduces the unit operating costs of ORVs. But in the case of below 1.5oC
seawater, the costs indicated a rapid decrease due to much greater reduction of NG yields.
This is because the spread of ice at the tube surface of ORVs largely increases the thermal
resistance of ORVs.
PO-28.7
SESSIONS
CONTENTS
Poster PO-28
Accordingly, we determined the flow rate of supply seawater, which is fixed at
8,000m3/hr, to be below its 1.5oC, and the operation of seawater heater is definitely not
appropriate, anytime. We were able to determine that the operation of SMVs must
vaporize the remainder, which ORVs could not do, targeting the total LNG in the winter
season. Also, we were able to establish more effective operation modes on the LNG
vaporizing system, in part.
CONCLUSIONS
The LNG vaporizing system is the main factor in determining KOGAS’s productivity
in its R/Ts. At the present time, it has improved from effective operation modes and
changes in the operation conditions such as the flow rate of seawater, in part. But this
cannot fundamentally resolve the problem which ORVs vaporizing the lower amounts of
LNG below 5oC seawater. Thus, the development of a new type vaporizer is necessary
and required.
Consequently, KOGAS will be quickening the pace for productivity elevation of LNG
vaporizers as one of the operation goals in order to diversify its business and intensify its
competitive power in the domestic and foreign markets.
ACKNOWLEDGMENTS
This research was supported by KOGAS. We would like to thank financial aid, and
especially acknowledge the continuing guidance and encouragement of coworkers in the
R&D Division of KOGAS.
REFERENCES CITED
[1] D.J. Wood and C.O.A. Charles, 1972, Hydraulic network analysis usig linear theory,
J. of the Hydraulics Division, Proceedings of the American Society of Civil
Engineers, Vol. 98, No. HY7, pp. 1157-1170.
[2] R.W. Jeppson, Analysis of flow in pipe networks, 1977, Ann Arbor Science.
[3] H.F. Khartabil, R.N. Christensen, and D.E. Richards, 1988, A modified Wilson plot
technique for determining heat transfer correlations, 2nd U.K. National Conference on
Heat Transfer, September.
[4] R.B. Bird, W.E. Stewart, and E. N. Lightfoot, Transport Phenomena, 1960, John
Wiley & Sons.
[5] F.W. Dittus and L.M.K. Boelter, 1930, University of California Publications on
Engineering, Vol. 2, pp. 443, Berkeley.
[6] M.M. Shah, 1976, A new correlation for heat transfer during boiling flow throught
pipes, ASHRAE Trans., Vol. 82, part 2, pp. 66-86.
[7] S.G. Kandlikar, 1989, A general correlation for saturated two-phase flow boiling heat
transfer inside horizontal and vertical tubes, J. Heat Transfer, Vol. 112, pp. 219-228.
[8] W.M. Rohsenow, 1962, A method of correlating heat transfer data for surface boiling
of liquids, Trans. ASME, Vol. 84, pp. 969.
[9] V.P. Carey, Liquid-vapor phase-change phenomena, 1992, Hemisphere Publishing
Corporation.
PO-28.8
SESSIONS
CONTENTS