offshore LNG

 


 

Liquefaction of natural gas to LNG in floating module is the only available option for remote offshore gas reservoirs. Aero-derivative gas turbine driven centrifugal compressors -- because of compact, light-weight, simple and reliable design -- are the best and optimum selection for offshore LNG units. Presented concepts and details in this article allow substantial reduction in total cost of ownership, better production flexibility and reliability of offshore refrigeration centrifugal compressor trains.

Brayton backing cycle to increase efficiency by half

An externally heated Brayton cycle turbine might be used to generate power from heat recovered from the exhaust of a conventional internally fired Brayton gas turbine. However the Brayton turbine is very sensitive to ambient conditions and to the turbine inlet temperature, which in this application is dependent on the exhaust temperature of the primary turbine. These factors limit its use as a backing device, and this article received little support.

Surge in practice

The operating range of centrifugal or axial compressors is limited by an instability range commonly called 'Surge' which occurs during low flow or high head conditions and can result in extensive damage. In compressor surge, the energy of flow reversal is accompanied by a loud explosive noise and excessive vibration. Resulting flow reversal and pressure pulsation from surge can cause extensive damage to the compressor system through induced forces such as thrust reversal, radial and axial excitation of the rotor, etc. 

Dry gas seal, problems

Common dry gas seal failures are discussed below along with their causes and remedies. This is from a case study by Rajmal Majhi and Riccardo Schiappacasse of GE Oil & Gas Global Services Engineering presented at the first Middle East Turbomachinery Symposium (Feb. 14-16) in Qatar.

 

* Inadequate fuel gas pressure during start up

Turbomachinery Fundamentals

Recuperators have been used by a number of manufacturers to increase their gas turbine's efficiency. The recuperator is a heat exchanger that utilizes the gas turbine's hot exhaust air to pre-heat the combustion air. If done properly, theoretical efficiency improvements up to 20% are possible over a wide operating range. This advanced cycle is often applied to small to mid-size electrical power generation gas turbines (30 kW to 6 MW) so that they can compete with reciprocating engines on efficiency. 

 

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