Cryogenic Expanders Operating on LNG-FPSO Vessels

Hans E. Kimmel Executive Director

Research and Development Ebara International Corporation

Sparks, Nevada, USA hkimmel@ebaraintl.com

Hans E. Kimmel is Executive Director for Research and Development at Ebara International Corporation. He holds a Master Degree in Mechanical and Process Engineering and a PhD from Munich, Germany. His main contributions are primarily in the LNG technology.

Ebara Headquarter and Factory, Nevada, USA

EBARA International Corporation Cryodynamics Division

Company Profile

•Established in 1973 •Manufacturer of custom engineered liquefied gas pumps and expanders •Located in Sparks, Nevada, USA •Division of Ebara Corporation of Japan •5000 M2 factory with a modern, dedicated liquefied gas test facility • ISO 9001 Certified

Ebara LNG Test Facility in Nevada, USA

The liquefaction of Natural Gas requires a significant amount

of energy for the refrigeration process

Replacing the Joule-Thomson Valves

with Cryogenic LNG Expanders

reduce this amount of energy

Large 2.6 MW Cryogenic

LNG Expander for

Algeria, Skikda, at the Ebara Test Stand in Sparks,

Nevada, USA

Pressure reduction across the J-T valve

produces 10% undesirable vapour and only 90% of

the liquid LNG is delivered to the storage tank

Liquefaction Process without LNG Expander in Existing Plants with 100% Liquefaction Capacity.

Only 90% of LNG is produced.

Liquefaction Process with LNG Expander in Existing Plants with 100% Liquefaction Capacity. The LNG production increases from 90% to 95%

LNG Expander reduces the amount of undesirable LNG vapour from

10% to only 5%.

In existing plants 95% of the condensed LNG is delivered to the

storage tank

An additional 5%,

Cryogenic LNG Expanders have been in operation for

more than 16 years

LNG Expanders remove energy from the LNG stream by converting the pressure into electrical energy

decreasing the total power consumption

Floating vessels in recent years have almost the entire LNG technology chain, originally

developed and utilized on-shore, applied for the exploration and

exploitation of abundant off-shore natural gas wells.

FSRU

Floating Storage Regasification Units,

FPSO

Floating Production, Storage & Offloading Units,

FDPSO

Floating Drilling, Production, Storage & Offloading Units

are floating vessels used by the offshore industry for the drilling, processing, storage and transportation of

LNG

and for offloading the cargo in gaseous form at the destination.

Cryogenic LNG Expanders are part of every new land based liquefaction plant since 1996, and they are also part of the new off-shore LNG technology with its diverse floating units.

LNG Expanders are to be applied and utilized in the floating production, storage, offloading, regasification and reliquefaction of LNG, to increase the economical benefits of the entire system.

Ship movement is one of the most critical conditions for rotating equipment installed on floating units, particularly affecting the seating and the bearings

Rotating equipment with a vertical rotating shaft, like LNG pumps and expanders, is designed with a centre of gravity as low as possible to reduce the mechanical momentum generated by the ship movement.

Cross section of a land based LNG Expander. The LNG stream enters at the top and flows downward across the expander. The heavy generator mounted above the hydraulics puts the centre of gravity at a higher level.

Cross section of a floating LNG Expander. The LNG stream enters at the bottom and flows upward across the expander. The heavy generator is mounted below the hydraulics. The centre of gravity is at a lower level.

The ship movement, pitching and rolling, inflicts continuous side forces on the expander that can damage the rotating shaft and introduce stress to the shaft bearings. A specially designed seating and locking device is installed to secure the expander from this possible damage.

During off -shore operation, the expander rotor experiences gyroscopic forces. Acting on the rotating shaft bearings in radial direction, these gyroscopic forces are relatively small and depend on the rotating mass and speed.

Cryogenic expanders on floating units are used for refrigeration in the LNG liquefaction process and also for power recovery in the LNG regasification process.

The difference in temperature between the heat source and the heat sink are in the range of 170° Celsius, providing the preconditions for efficient power recovery.

Power Recovery

LNG regasification plants are large heat sinks and require large heat sources.

Power Recovery Cycle with Two-Phase Expansion

Net Generated Power = hNP

hNP = (h3 – h4) – (h2 – h1) Expander Power Pump Power

Schematic of the

Two-Phase Power Cycle

Compact Assembly of a pump and a

two-phase expander

The working fluid LPG is passed through two

separate heat exchangers and a single machine

which combines a pump and a two-phase expander

Advantages of the Compact Assembly ♦

The expander work output is larger than the pump work input and the difference in work is converted

by the generator into electrical energy ♦♦

The losses of a separate pump motor are eliminated

♦♦♦ The losses of the induction generator are recovered and used to heat the working fluid in addition to the

heat from sea water and other heat sources

Advantages continued ♦♦♦♦

Any leakage of the working fluid is within a closed loop and occurs only between pump and expander

♦♦♦♦♦ Any leakage of the working fluid is minimized due to equal pressure on both sides of the seal, and

small leakages are within a closed loop and occur only between pump, expander and generator.

♦♦♦♦♦♦ The axial thrust is minimized due to opposing

directions of the thrust forces, decreasing bearing friction and increasing bearing life.

Existing Field Proven Two-Phase Expanders

Cross section of

a Two-Phase LNG Expander

inside pressurized containment vessel with lower inlet and upper outlet nozzle

Metallic: Two-Phase Draft Tube Green: Jet Exducer Yellow: Turbine Runner Red: Nozzle Ring

Two-Phase hydraulic assembly

Two-Phase LNG Expander

at the Ebara Test Stand in Nevada, USA

Thank You for Your Attention