LNG Systems for Offshore Applications

Introduction

Due to large reserves and because it is a relatively clean fuel, Natural Gas has become one of the most important sources of energy in the world.

At the same time, the presence of oil associated gas and "stranded" gas in locations remote from existing infrastructure is a headache to Governments and the Oil and Gas Industry. Economic and environmentally sound development of many of these resources is difficult, particularly for the offshore fields. The result is 150 billion standard cubic meter of natural gas being flared annually in the world.

For offshore oil fields with gas co-production in the order of 50 – 300 MMSCFD most offshore operators have been restricted to gas reinjection in order to reduce or eliminate gas flaring.

Aragon, a company in the Sevan Marine Group, has developed concepts and liquefaction systems for offshore LNG production in the order of 0.3 – 2.5 mta LNG (approx. 50 – 300 MMSCFD gas). Aragon’s systems now offer an alternative to reinjection or flaring, with a potential to become the technology of choice for offshore applications for many years.

Offloading of FLNG production unit

Applications

  • Gas from stranded gas fields
  • Associated gas from new or exsisting oil producers
  • Converted ship or a new hull, a cylindrical shaped hull or barge
  • Generic or tailor-made
  • Mid-size liquefaction plant for 0.3 - 4.8 mtpa LNG
  • Feed gas up to 19 Mill Sm3/day

Technologies

There are fundamental differences between onshore process plant facilities and the offshore environments. An offshore LNG production plant will obviously have quite different technology selection criteria than onshore facilities. Process efficiencies will always be an important selection criterion because poor efficiency may reduce product yield, increased utility systems and refrigeration compressor capacity.

In the offshore environment other aspects are also of high importance:

  • Process plant compactness, low weight, and inherent process safety
  • Limited space and availability for maintenance, and limited accommodation capacity are other parameters that must be considered
  • Process robustness and the sensitivity to variable feed gas and process conditions must be taken into consideration
  • Significantly higher start and stop frequency is likely, and simple and safe start and shutdown must be ensured
  • Number of operators and their required education and training must be considered


For the above reasons it is usually concluded that offshore medium size LNG plants should be based on gas expander technologies, e.g. single or dual nitrogen expander cycles.

 


Aragon’s patent pending Optimised Expander Cycle offers improvements to the conventional nitrogen expander cycle:

  • The cycle offers up to 50% higher process efficiency than a conventional single nitrogen expander, but with the same low complexity and equipment count.
  • In more advanced configurations, specific power consumption as low as 0.40 kWh/kg LNG may be obtained. (high seawater temperature in a tropical environment)
  • Uses well-proven equipment only
  • Superior to Mixed Refrigerant Cycles when it comes to simplicity and operation
  • High inherent safety
  • Simple to start, operate and shut down
  • Simple refrigerant generation
  • Robust for changing feed gas composition
  • Insensitive to ship motions

 

 

Floating concepts

LNG FPSO / Generic LNG FPSO LNG and Oil FPSO
  • For associated gas fields 
  • For small stranded gas fields 
  • Can receive gas from new or existing oil FPSO (separate hull), or from gas wells 
  • Medium size, 0.3 – 4.8 mtpa LNG 
  • 1 – 4 LNG trains 
  • LM2500 or LM6000, or equivalent drivers 
  • Simple fluid inlet separation (optional)
  • LPG fractionation and stabilisation (optional)
  • Gas treatment & conditioning 
  • Liquefaction 
  • LNG storage & offloading
  • For oil fields with associated gas 
  • One hull for oil and LNG 
  • Medium size, 0.3 – 4.8 mtpa LNG 
  • LM2500 or LM6000, or equivalent drivers 
  • 1 – 4 LNG trains 
  • Oil separation 
  • Water treatment 
  • Gas treatment & conditioning 
  • Liquefaction 
  • Oil storage & offloading 
  • LNG storage & offloading



"Flex LNGP1" - Generic LNG FPSO topside by Kanfa Aragon (Picture with courtesy of Samsung Heavy Industries, Ltd.)

Kanfa Aragon AS - Fantoftveien 42 - 5072 Bergen - Norway - Tel: 0047 901 45 757 - kut@aragon.no
 sitemap
Admin