Back to Index

LNG ( liquefied natural gas Processes)
The Kryopak EXP® liquefied natural gas (LNG) Process
Advantages and benefits of Kryopak’s EXP® process:
Compressor/expander efficiencies are reaching more than 85%
LNG Terminals
Phillips Optimized Cascade
Single Mixed refrigerant Prico Dual Mixed Refrigerant The Liquefin Axens process
 
 Single Flow Mixed Refrigerant 
Mixed Fluid Cascade (MFC)
C3MR APCl 

LNG History
CHINA GAS seeks great leap forward
LNG Plants Add Capacity  CONVERSION TABLES EXCEL
LNG Plants
LNG News.htm
LNG Busses
Introduction to Kryopak
lng CalStart
The Kryopak EXP® liquefied natural gas (LNG) Process

Other major commercial LNG processes usually design for base load (large scale) LNG plant by employing complicated processes and equipment to reduce operation energy consumption.
For small scale LNG plant, like remote gas liquefaction, it is neither economic nor practical to use major commercial processes. This is due to their complicated processes, limited flexibility for feed gas flow rate, and process gas composition fluctuating.

Please observe the Q/T diagram of a typical gas liquefaction process, especially three zones noted in the process of the gas being liquefied (See Below).

Q/T Diagram of Typical Gas Liquefaction

A pre-cooling zone is followed by a liquefaction zone and completed by a sub-cooling zone.
All of these zones are characterized by having different curve slopes (specific heats) along the process.
The Q/T curve shape is different for different gas compositions; in other words, the cooling, liquefaction and sub-cooling zones are in different temperature and cooling duty zones for different gas compositions.

Mixed Refrigerant cycles designs try to closely approach the cooling curve of the gas being liquefied. They use special mixes of multi-component refrigerants trying to match cooling curves at different zones/stages of the liquefaction process to achieve high refrigeration efficiency and reduce energy consumption.
When gas composition is away from the design gas, the Q/T curve shifts, but refrigeration does not because it is fixed by premixed refrigerants.
Temperature approaches are not achieved as designed and therefore refrigeration efficiency deviates.

Kryopak’s EXP® process employs refrigeration generated by a single semi-closed isentropic expansion of gases.
Composition of refrigerant gas is the same as the vapor generated from final product flash (See Below). By this means no mechanical refrigeration is used in the system as seen in the mixed refrigerant processes.
Kryopak EXP® simplifies the gas liquefaction process accordingly. By recycling the gas, the slope of the Q/T curves are accordingly changed per the cooling input at the different zones by the recycling refrigerant gas.
The Kryopak EXP® gas liquefaction process obtains profiles close to the gas refrigerant used, thus minimizing deviations due to gas composition fluctuations.

The amount of flow used in the recycles, feed gas, and refrigerant pressure levels alter the shape of the Q/T curves, which are part of the design parameters used in achieving an optimum design. The control system recognizes these fluctuations and automatically changes as required for optimum system performance.


Simplified Kryopak EXP® Process Diagram

Simplified Kryopak EXP® Q/T Composition Curves

In the Kryopak EXP® process, work and refrigeration are extracted from the expansion process. The refrigeration is used to aid the liquefaction process and work extracted is utilized to partially recompress the refrigerant gas.

Thermodynamically speaking, this expansion cycle is as efficient as the most advanced mixed refrigerant cycles. Today, compressor/expander efficiencies are reaching more than 85%. This represents an emerging opportunity to assist gas liquefiers using this technology in the LNG business.

Using this design philosophy, the Kryopak EXP® process is able to achieve a mid level specific refrigeration energy consumption of 0.20 - 0.23 hp/lb LNG (13.5 – 15.5 kW/ton-day LNG) compared to the reported design energy consumption of 0.18-0.25 hp/lb LNG (12.2 – 16.8 kW/ton-day LNG) for existing MR LNG processes.
One of our typical designs with 150,000 Nm3/day (125 tons /day LNG) has a total refrigeration energy consumption of only 2,550 kW.

Advantages and benefits of Kryopak’s EXP® process:

Extremely simple compared with the MR processes
Adaptable to different quality of feed gas without changing plant efficiency, as the refrigeration cycle works with the purpose of producing refrigeration to satisfy the refrigeration demand imposed by the LNG requirements
The refrigerant is always in gas phase, which eliminates the requirement of refrigerant inventory and separators for their handling, with the correspondent impact in the safety on the facility, and therefore simplifies the construction of the cold box exchanger also.
There is no need for premixing of refrigerant
All of the equipment employed by the Kryopak EXP® process are standard conventional oil and gas field processing equipment using no new or unproved technology. 

As evaluated by Project Technical Liaison & Associates (PTL), one of the world's leading LNG facility evaluation firms:
“The Kryopak EXP® process has the advantage of using a simple cooling system with a relatively small number of pieces of equipment operating at cryogenic temperatures and a fast approach to equilibrium upon warm start-up. The simplicity of the design and the self equilibrating nature of the process provide straightforward operation. The process is not very sensitive to reasonable changes in feed gas composition (as evidenced by the three cases examined)… The equipment required in the plant is standard and is readily available from various vendors…”

Kryopak EXP ® LNG Process Applications…

Remote gas recovery, peakshaving, small scale, base load.
1.0 MMscfd to 11 MMscfd (2x104 Nm3/day to 30x104 Nm3/day) reciprocating compressor without heat recovery, specific energy consumption of 0.22-0.23 hp/lb LNG depending on design air temperature, full skid plant.
15 MMscfd to 200 MMscfd (40x104 Nm3/day to 5x106 Nm3/day) centrifugal compressor with heat recovery, specific energy consumption of 0.20 hp/lb LNG, partially skid plant. 
The C3MR APCl process
Phillips Optimized Cascade Process
Single Mixed refrigerant Prico Process
Dual Mixed Refrigerant Process
The Liquefin Axens process
Single Flow Mixed Refrigerant Cycle
Mixed Fluid Cascade (MFC) Process