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9/27/2012
Claude Liquefaction Process
Claude Liquefaction Process
• Support the throttle valve by an expander: – Gas expander: saturated or slightly superheated vapor – cooled and throttled to produce liquefaction (as in the Linde process) – unliquefied portion mixes with the expander exhaust and returns for recycle. Fig 9.7
Equations
Mass relations: m1= m2 + m15; m2= m3 = m4= m5; m5 = m6 + m11; m6 = m7 = m8; m8 = m9 + m10; m13= m10 + m12 = m14 = m15= m2
Natural gas, assumed here to be pure methane, is liquefied in a Claude process. Compression is to 60 bar and precooling is to 300 K. The expander and throttle exhaust to a pressure of 1 bar. Recycle methane at this pressure leaves the exchanger system at 295 K. Assume no heat leaks into the system from the surroundings, an expander efficiency of 75%, and an expander exhaust of saturated vapor. For a draw-off to the expander of 25% of the methane entering the exchanger system, what fraction of the methane is liquefied, and what is the temperature of the high-pressure steam entering the throttle valve? For superheated methane: H 4 1140.0
kJ kg
(at 300 K and 60 bar )
kJ kg
(at 295 K and 1 bar )
H15 1188.9
For saturated liquid: H 9 285.4 Claude process
Linde Process: x = 0
kJ kg
For saturated vapor: H12 796.9
(T sat 111.5 K and 1 bar )
kJ kJ , S12 9.521 (T sat 111.5 K and 1 bar ) kg kg K
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An energy balance on the right of the dashed vertical line: m 9 H 9 m 15H15 m 4 H 4 Wout
Claude Liquefaction Process
The expander operates adiabatically: Wout m 12 ( H12 H 5 ) z m 9 / m 4 12 / m 4 xm A mass balance: m 15 m 4 m 9
60 bar
60 bar H4= 1140
z 1 bar
60 bar
60 bar
xH12 H 5 H 4 H15 H 9 H15
H5 The equation defining expander efficiency: H H12 H 5 H S H12
1 bar 60 bar
1 bar
Guess T5 → H5, S5 → isentropic expansion → H’12 → H12 → check if satisfied?
H15=1188.9
1 bar
T5 253.6 K , H 5 1009.8
1 bar
1 bar H12 = 796.9 S12 = 9.521
z
kJ (at 60 bar ) kg
xH12 H 5 H 4 H15 0.25(796.9 1009.8) 1140.0 1188.9 0.113 H 9 H15 285.4 1188.9
H9 =289.4
11.3 % of the methane entering the exchanger system is liquefied!
An energy balance on the exchanger I: m 4 ( H 5 H 4 ) m 15 ( H15 H14 ) 0 A mass balance: m 15 m 4 m 9 H14
9 / m 4 zm
H5 H 4 1009.8 1140.0 kJ H15 1188.9 1042.1 1 z 1 0.113 kg T14 227.2 K
(at 60 bar )
An energy balance on the exchanger II: m 7 ( H 7 H 5 ) m 14 ( H14 H12 ) 0 A mass balance: m 7 m 4 m 12
14 m 4 m 9 m
1 z H14 H12 719.8 kJ H7 H5 1 x kg
x T7
T7 197.6 K
For the Linde system, x = 0: z
(at 60 bar )
xH12 H 5 H 4 H15 H 9 H15
z 0.0541
5.41 % of the methane entering the throttle valve emerges as liquid! kJ H 7 H 4 (1 z )H15 H10 769.2 kg T7 206.6 K (at 60 bar )
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