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Liquefaction by Cooling
Liquefaction by Cooling
This method is satisfactory if the liquefaction process does not
require
very low temperatures. Example butane, propane, Examples of
theseare the hydrocarbons butane and propane, which can both exist
as
liquids at room temperature if they are contained at elevated
pressures.
Mixtures of hydrocarbons can also be obtained as liquids and
these
include liquefied petroleum gas (LPG) and liquefied natural gas
(LNG).
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c Dr. M. Zahurul Haq (BUET) Thermodynamics Relations M E 6101
(2011) 17 / 22
Liquefaction by Cooling
Liquefaction by Expansion
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1 Compress isentropically to 2, where P2 > Pc2 As T2 > Ta,
cool it to Tausing ambient sources, and further cool
to T3 using available cold sources.
3 Expand isentropically form 3 to 4 liquid formation.c
Dr. M. Zahurul Haq (BUET) Thermodynamics Relations ME 6101
(2011) 18 / 22
Liquefaction by Cooling
Gas Expansion & Joule-Thomson coefficient
The temperature behaviour of a fluid during a throttling process
is
described by Joule-Thomson coefficient, JT.
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JTTP
h
= ve : temperature increase
0 : temperature same+ve : temperature drop
c Dr. M. Zahurul Haq (BUET) Thermodynamics Relations M E 6101
(2011) 19 / 22
Liquefaction by Cooling
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A cooling effect cannot be achieved by throttling unless the
fluid is
below its maximum inversion temperature
. For hydrogen its valueis -68oC and hydrogen must be cooled
below this temperature if
further cooling is to be achieved.c
Dr. M. Zahurul Haq (BUET) Thermodynamics Relations ME 6101
(2011) 20 / 22
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Liquefaction by Cooling
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P= RTvb
av2
=
JT=
1CP RT
P+
a
v2(vb)
2av3 v
Maximum inversion temperature= 6.75Tc
Minimum inversion temperature= 0.75Tc
If air is compressed to a pressure of 200 bar and a temperature
of
52o C, after the throttling to 1 bar it will be cooled to 23o C.
In case of
helium, throttling from the came condition will result in 64o
C.c
Dr. M. Zahurul Haq (BUET) Thermodynamics Relations M E 6101
(2011) 21 / 22
Liquefaction by Cooling
Simplified Linde Liquefaction Plant
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Two performance parameters:
Yield, z: mass of liquid produced per unit mass of gas
compressed.
Sp. work required, wz: work per unit mas of liquid produced.
z= y
m =
h7 h2
h7 h5wz=
Win
zc
Dr. M. Zahurul Haq (BUET) Thermodynamics Relations ME 6101
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