As environmental regulations evolve, there is a growing need to improve the energy efficiency and reduce the emissions of LNG-fuelled ships. High-pressure MEGI engines, which have low methane slip and high power efficiency, are often selected for vessel main propulsion. However, with such high-pressure engines, finding a reliable, simple and cost-effective solution for boil-off gas management remains quite complex.

The fuel gas supply system of the MEGI engine requires a high-pressure compressor to manage boil-off gas of the LNG tank. Besides, ship-owners have preferred to install low-pressure compressors due to their lower cost. Thus, the boil-off gas can only be consumed by electrical generator, which limits the ability to manage the pressure of the LNG Tank.
 

The Recycool concept: a performant and cost effective BOG management solution


The RecycoolTM concept was developed by GTT. It allows to manage any excess boil off gas by recovering the cold energy available from the LNG vaporizer. Such cold power would otherwise be wasted into glycol or freshwater system.

The principle of the system consists in recovering the available cold energy in order to re-liquefy the excess boil-off which is not consumed by generators. Cold recovery is performed in two locations: in a Recondenser before the high-pressure pump and in a Pre-cooler located between the high-pressure pump and the high-pressure vaporizer.

 

RecycoolTM Key Features

Recycool


Compared to other existing recondenser solutions, RecycoolTM shows its advantage in terms of compactness and efficiency.

  • Simple architecture which consists in two heat exchangers (Recondenser and Pre-cooler) and a control valve
  • No rotating machine, only passive heat exchangers (Recondenser and Pre-cooler) and a control valve easily operable
  • Low CAPEX and OPEX
  • Improved vessel carbon footprint
  • Very High energy efficiency due to cold recovery process and system integration

NB1: Performance is independent of BOG temperature, since cold recovery is only performed on the LNG line – which allows to maintain high efficiency in a large working range

NB2: RecycoolTM high performance is increased from avoiding direct contact between the LNG stream and the BOG stream.

This concept has been already successfully tested on several LNG fueled container ships powered by a MEGI engine.