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School of Civil, Environmental & Chemical Engineering

PROC 2080

Process Thermodynamics

Lecture 5

Flow Processes Liquefaction Processes

Lecturer: Dr Greg Griffin

Liquefaction Processes

Liquefaction is the process of converting materials that are gases at ambient temperature and atmospheric pressure to liquids

Common liquefied gases are: LPG used as fuel LNG for shipment of natural gas fuel over long

distances Oxygen for metallurgical and mineral processes Nitrogen common coolant Hydrogen rocket fuel Helium superconductors

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Liquefaction Processes

To cool gases can use: heat exchanger at constant pressure. expansion process from which work is obtained. a throttling process

Liquefaction Processes

Inversion curves: Gases will only cool on expansion when within the

inversion curves.

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The Linde liquefaction process Depends solely on throttling expansion:

Compression cooling to ambient temperature (even further by refrigeration) throttling and liquefaction.

The Linde liquefaction processExample 1:Dry methane is supplied by a compressor and pre-cooling system to the cooler of a Linde liquid-methane system (see previous figure) at 60 bar and 300 K. The low-pressure methane leaves the cooler at a temperature 5 K lower than the temperature of the incoming high-pressure methane. The separator operates at 1 bar, and the product is saturated liquid at this pressure. What is the fraction of gas entering the cooler that is liquefied? What is the temperature of the stream entering the throttling valve?

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The Linde liquefaction processSo z = m9/m4 = (H4 H15)/ (H9 H15)

The Claude liquefaction process Part of the high pressure gas is diverted and passes through an

expander Cooled gas is mixed with unliquefied, saturated gas from separator

and used to cool the gases entering the throttling valve.

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The Claude liquefaction processExample 2:Dry methane is supplied by a compressor and pre-cooling system to the cooler of a Claude liquid-methane system (see previous figure) at 60 bar and 300 K. The recycle stream (stream 15) leaving the heat exchanger is at 295 K. The high-pressure gas is cooled to 250 K in the first heat exchanger (i.e. stream 5 is at 250 K) and 25% of this flow is diverted to the expander which operates at 70% efficiency. The separator operates at 1 bar, and the product is saturated liquid at this pressure. What is the fraction of gas entering in stream 4 that is liquefied? What is the temperature of stream 7?

The Claude liquefaction processx = m12/m4

z = m9/m4 = (x(H12 H11)+(H4 H15))/ (H9 H15)

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14 April: mid-semester test Start time Venue: 80.06.005. Writing starts at

12:45 a.m. if your surname starts with the letters A-I. Writing starts at 2:45 if your surname starts with the letters J- Z. There are no lecture or tutorial on the day.

Duration - 90 minutes Run under exam conditions. Test is open book - Students may use any

printed matter No text-storing calculators Test covers the material performed in weeks 1

4 only.

11 April: mid-semester test Examples of mid-semester tests and solutions

can be found on blackboard Do not rely solely on previous mid-semester

tests ensure you understand the tutorials and examples given in weeks 1 4.

Test paper provides all data you should not need to seek data from text books.

However, test will not provide formulas.