Chemical & Process Technology

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In gas processing and LNG production industry, heavy hydrocarbon (C5+) is removed from natural gas. One of the common way being used is cool natural gas to cryogenic temperature (-40 to -60 degC) so that C1 to C4 remain in gas phase while C5+ is knocked out as liquid phase. This is normally known as Condensate Recovery. Some natural gas is cooled to lower temperature (-70 to -90 degC) to remove C3+ and produce C3 for propylene related product. This is normally known as Propane Recovery. Similarly, the natural gas is cooled to temperature around -90 to -110 degC to remove C2+ and produce C2 for ethylene related product. This is normally known as Ethane Recovery. In LNG production, after the C2+ is removed from natural gas, it is further cooled to about -160 degC to separate inert gas (N2) and storage LNG at -160degC.

There are three important process to bring the natural gas temperature down to cryogenic temperature region :

• Mechanical Refrigeration (force cooling)
• Joule-Thompson (JT) valve pressure reduction
• Gas expansion with Turbo expander

Mechanical Refrigeration
The common refrigeration loop used are propane, ethane, methane, nitrogen, etc. These components are found in natural gas and it is normally extracted, purified and make-up to any losses in the refrigeration loop. As pure component is having contant heat of vaporization at particular pressure level, it would to low efficiency and high capex refrigeration system. Mixture of above component are used. Read more about refrigeration...

Joule Thompson (JT) valve
As fluid is forced through a valve with pressure reduction while minimising heat losses to surrounding, the fluid will experience isenthalpic process (constant enthalpy) and lead to temperature drop at low pressure level. This is a throttling process common called Joule-Thomson (JT) process and the valve used is JT valve. This phenomena is known as JT effect.
Mojority of gases are respecting JT rules except hydrogen, helium, neon , etc. Read more about JT...

Expansion Turbine
High pressure gas is allowed to flow through turboexpander or turbo-expander or expansion turbine (centrifugal or axial), works is produced and used to drive another equipment. This type of expansion process is an isentropic process (constant entropy) which could lead to very low temperature. Read more about Expansion Turbine...

Cryogenic Chilling Technique Video Clip
Following is a video clip presented the three processes to achieve cryogenic chilling.