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Use of an Eductor/Ejector to Pressurize Boiloff/Flash Gas from an LNG Plant

IP.com Disclosure Number: IPCOM000239410D
Publication Date: 2014-Nov-05
Document File: 2 page(s) / 18K

Publishing Venue

The IP.com Prior Art Database

Abstract

Eductors (or ejectors) are a low cost way to pressurize a fluid stream. This publication describes the application of one to LNG. Specifically, an eductor is used to pressurize a boil off gas (BOG) stream from an LNG tank. To provide the necessary energy, a small high pressure natural gas stream is used. The eductor pressurizes the BOG stream in order to overcome the pressure drop that results from warming it stream to near ambient temperature.

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Use of an Eductor/Ejector to Pressurize Boiloff/Flash Gas from an LNG Plant

Referring to Figure 1, natural gas feed stream 100 is divided into two portions, 101 and 136. Major portion 101 is cooled and liquefied in one or more heat exchangers (102,106,110) to form an LNG stream (112) which is sent to a tank (128). Refrigeration to cool and liquefy the feed is provided by a refrigerant (not shown) which can be a mixed refrigerant, a series of pure refrigerants or any other LNG refrigeration methods that are well known in the art. From the tank (128) an LNG stream (196) and a vapor stream (129) are produced, the vapor stream resulting from flash into the tank and boiloff from heatleak. The minor portion of the feed stream (136) may be cooled in an exchanger (131). All or a portion of the feed stream may be used in a mixing ejector (138) to pressurize the boiloff/flash stream (129). The combined stream is warmed in exchanger (131) before being compressed (130) and either recycled to feed as shown (126) or used as fuel in the LNG plant or sent to another natural gas pipeline. A common purpose of the ejector is to pressurize the boiloff/flash stream so that it is above atmospheric pressure entering the compressor (131).

In this example the ejector feed stream (136) is taken from the plant feed, however it may be taken from any location as the feed is being cooled and liquefied (104,108,112). The ejector feed stream may also be taken from the fuel gas system or mixed...