Method and apparatus for pre-heating LNG boil-off gas to ambient temperature prior to compression in a reliquefaction system

A technology for reliquefaction and boil-off gas is applied in the field of equipment used to preheat LNG boil-off gas to normal temperature before compression in a reliquefaction system, which can solve problems such as reducing equipment performance.

Active Publication Date: 2009-06-03
WARTSILA OIL & GAS SYST
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  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Employing recondensed BOG to provide this cooling also degrades equipment performance measured in terms of energy per unit of reliquefied BOG returned to the storage tank

Method used

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  • Method and apparatus for pre-heating LNG boil-off gas to ambient temperature prior to compression in a reliquefaction system

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Experimental program
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Embodiment Construction

[0015] The present invention will now be described with reference to Figure 1, which shows the novel features of an LNG RS with normal temperature BOG compression.

[0016] The figure schematically shows the shipping compartment 74, which holds a certain amount of LNG72. The BOG evaporated from the LNG enters the pipe 1 connected to the first heat exchanger H10. In this heat exchanger, as described later, BOG is heated to near normal temperature. After this preheating, BOG enters the first-stage BOG compressor C11 via pipe 2. The BOG compressor is shown as three-stage centrifugal compressors C11, C12, C13 connected to each other via pipes 3-7 through intercoolers H11, H12, and aftercoolers H13 as shown in the figure, but other compressor types are also applicable . The preheating ensures that the heat generated by the compression can be dissipated through the cooling water in the intercoolers H11, H12 and the aftercooler H13.

[0017] The pressurized BOG is then provided through p...

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Abstract

The present invention provides a method and an apparatus of pre-heating LNG boil-off gas (BOG) stream (1) flowing from a reservoir (74) in a reliquefaction system, prior to compression (C11, C12, C13). The method comprises heat exchanging the BOG stream in a first heat exchanger (H10), against a second coolant stream (59) having a higher temperature than the BOG stream (1), where the second coolant stream (59) is obtained by selectively splitting a first coolant stream (56) into said second coolant stream (59) and a third coolant stream (57), said third coolant stream being flowed into a first coolant passage in a reliquefaction system cold box (H20), whereby the BOG has reached near-ambient temperatures prior to compression and the low temperature duty from the BOG is substantially preserved within the reliquefaction system, and thermal stresses in the cold box (H20) are reduced. Prior to the compression step, the BOG is pre-heated to substantially ambient temperatures, by heat exchanging (H10) the BOG with said coolant, said coolant prior to the heat exchange having a higher temperature than the BOG.

Description

Technical field [0001] The present invention relates to the field of reliquefying boil-off gas from liquefied natural gas (LNG). More specifically, the present invention relates to a method and apparatus for preheating an LNG boil-off gas (BOG) stream flowing from a reservoir in a reliquefaction system before compression. Background technique [0002] The new generation of LNG ships was established with the introduction of the LNG Reliquefaction System (LNG RS). Previously, basically all LNG ships were driven by steam turbines fueled by boil-off gas (BOG) that evaporates from the cargo during transportation. In the period when the total amount of BOG is insufficient to meet the entire energy demand, it is necessary to provide further LNG to the boiler through a forced distiller. [0003] The new generation LNG RS is able to collect, cool and reliquefy all BOG and therefore maintain the entire cargo volume during the entire full-load and full-cabin voyage. It can be propelled by a...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): F25J1/00F17C13/00F25J1/02
CPCF25J1/0025F25J1/0204F25J1/0288F25J1/005F25J2290/62F25J1/0072F25J1/0267F25J2220/62F25J2230/30F25J1/0265F17C13/00F25J1/00F25J1/02
Inventor B·豪克达尔
Owner WARTSILA OIL & GAS SYST
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