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Frontiers in Energy

Front. Energy    2020, Vol. 14 Issue (3) : 452-462
Simulation of performance of intermediate fluid vaporizer under wide operation conditions
Bojie WANG1, Wen WANG1(), Chao QI1, Yiwu KUANG1, Jiawei XU2
1. Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Shanghai 200240, China
2. CNOOC Gas and Power Group, Beijing 100027, China
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The intermediate fluid vaporizer (IFV) is a typical vaporizer of liquefied natural gas (LNG), which in general consists of three shell-and-tube heat exchangers (an evaporator, a condenser, and a thermolator). LNG is heated by seawater and the intermediate fluid in these heat exchangers. A one-dimensional heat transfer model for IFV is established in this paper in order to investigate the influences of structure and operation parameters on the heat transfer performance. In the rated condition, it is suggested to reduce tube diameters appropriately to get a large total heat transfer coefficient and increase the tube number to ensure the sufficient heat transfer area. According to simulation results, although the IFV capacity is much larger than the simplified-IFV (SIFV) capacity, the mode of SIFV could be recommended in some low-load cases as well. In some cases at high loads exceeding the capacity of a single IFV, it is better to add an AAV or an SCV operating to the IFV than just to increase the mass flow rate of seawater in the IFV in LNG receiving terminals.

Keywords liquefied natural gas      intermediate fluid vapo-rizer      heat transfer performance      numerical simulation      extreme condition     
Corresponding Author(s): Wen WANG   
Online First Date: 03 July 2020    Issue Date: 14 September 2020
 Cite this article:   
Bojie WANG,Wen WANG,Chao QI, et al. Simulation of performance of intermediate fluid vaporizer under wide operation conditions[J]. Front. Energy, 2020, 14(3): 452-462.
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Bojie WANG
Chao QI
Jiawei XU
Fig.1  Structure of an IFV.
Fig.2  Schematic diagram of IFV.
Fig.3  Properties of methane with temperature at three different pressures.
Heat exchanger Zone Correlations Ref.
Evaporator Inside tube Nu=0.023Re0.8Pr0.3 [17]
Outside tube h=90 q0.67M 0.5Pr n( lgPr) 0.55 [18]
Condenser Inside tube Nu=0.0156Re0.82Pr0.5( ρwρb)0.3( c¯p cpb)n
n={0.4,for?Tb<T w<Tpc?and?for?1.2 Tpc<Tb<T w0.4+0.2(TwT pc1), for? Tb<Tpc<T w0.4+0.2(TwT pc1)[15( TbTpc 1)],for?Tpc<T b<1.2Tpc?and?Tb< Tw
c¯ p= TbTwdT/(Tw T b) =(h whb)/(T w Tb)
Outside tube h=0.79[ Gρl( ρl ρg)λ3r μlD (T po TW)]0.25?N eff1/6 [16,19]
Thermolator Inside tube Nu=0.023Re0.8Pr0.3 [17]
Outside tube Nu f={ 1.04Ref0.4Prf 0.36 (Prf/Prw)0.25,1<Re<5×1020.71 Re f0.5 Prf0.36( Pr f/ Pr w)0.25,5×102 <Re< 10 3 0.35( s1 s2)0.2 Ref0.6Prf0.36( Prf/ Prw)0.25, s1s22, 103<Re<2×1050.4 Re f0.6 Prf0.36 (Prf/Prw) 0.25,s1s 2>2, 103<Re<2×105 ?0.031 (s1s 2)0.2 Re f0.8 Prf0.36 (Prf/Prw) 0.25,2×105<Re<2×106 [20]
Tab.1  Heat transfer correlations of analysis model in heat exchangers
Item Evaporator Condenser Thermolator
Number of tubes 3000 881 3200
Length of each tube/m 9.0 18.0 3.6
Outside diameter of tube/mm 19.05 15.90 19.05
Thickness of tube wall/mm 1.2 1.6 1.8
Tab.2  Structure parameters of IFV
Fig.4  Elements in the discrete model for exchangers.
Fig.5  Logical diagram of the calculation program.
Fig.6  The temperature profiles in exchangers with different grids.
Case LNG mass flow rate/(t·h–1) LNG pressure/MPa
Case 1 175 6.3
Case 2 175 7.15
Case 3 175 × 1.05 6.3
Case 4 175 × 1.05 7.15
Tab.3  Operation parameters of LNG
TL1/K PL/MPa m˙ L/ (t·h1) TS1/K PS/Mpa m˙ S/ (t·h1)
113.15 6 180 281.15 0.2 8750
Tab.4  Parameters in typical operation status
Fig.7  The temperature profile in exchangers with different grids.
Fig.8  Influence of the tube diameter.
Fig.9  Average heat transfer coefficient at different tube diameters.
Fig.10  Influence of tube number.
Fig.11  Reynolds number along the channel at different tube numbers.
Fig.12  Heat transfer coefficient with different tube numbers.
Fig.13  Capacities of IFV and SIFV at different seawater inlet temperatures and mass flow rates.
Fig.14  Capacity of IFV variation with heat transfer area of thermolator.
Load/(t·h–1) T2/°C T3/°C Total heat exchange/MW Heat exchange in thermolator/kW Total pressure drop/kPa Pressure drop in thermolator/kPa
100 –0.40 6.46 19.84 566.88 71.89 31.21
90 0.59 6.79 17.92 379.32 58.01 25.18
80 1.49 7.01 15.98 283.77 45.96 19.87
70 2.31 7.12 14.03 254.24 35.29 15.22
60 3.11 7.34 12.06 218.43 25.23 11.80
Tab.5  Function of thermolator in operation
Fig.15  Temperature profile in an extreme condition.
Fig.16  Influence of seawater mass flow rate on outlet temperature of NG in a high-load condition.
T Temperature/K
P Pressure/MPa
m ˙ Mass flow rate/(kg·s–1)
ρ Density/(kg·m–3)
c Specific heat capacity/(kJ·kg–1·K–1)
λ Thermal conductivity/(W·m–1·K–1)
μ Dynamic viscosity/(Pa·s)
Re Reynolds number
Pr Prandtl number
Nu Nusselt number
G Gravitational acceleration/(m·s–2)
Q ˙ Heat flux/W
H Enthalpy/(J·kg–1)
α Heat transfer coefficient/(W·m–2·K–1)
A Area/m2
q Heat flux/(W·m–2)
r Heat of vaporization(J·kg–1)
cp Heat capacity/(J·kg–1·K)
cpb Average heat capacity/(J·kg–1·K)
M Mass flow rate/(kg·s–1)
n Constant
s1 Horizontal distance between neighboring tubes/m
s2 Vertical distance between neighboring tubes/m
D Diameter/m
S Seawater
po Propane
th Thermolator
ev Evaporator
con Condenser
in Based on the inside tube
out Based on the outside tube
w Based on the tube wall
p Constant pressure
l Based on saturated liquid
g Based on saturated vapor
f Based on fluid
b Average value
pc Pseudo-critical value
eff Effective
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