Gas Processes Handbook - 95

2019 GAS PROCESSES HANDBOOK
PROCESS CATEGORIES

COMPANY INDEX

LNG

AP-N™ Nitrogen Recycle LNG Process

Boiloff/react gas to flow-by/fuel
Aftercooler

Application: Liquefaction of natural gas for peakshaving, product distribution or
floating production storage and offloading (FPSO) applications.
Description: Natural gas is pretreated to remove water (H2O) and carbon dioxide
(CO2). A fraction of the pretreated natural gas is used to regenerate the CO2 /H2O
removal system. The remaining gas is cooled, and the heavier hydrocarbons (HC)
are removed in a knockout drum or multistage separation device. The resulting vapor
product is then condensed to produce LNG. Boiloff gas (BOG) from the LNG storage
and the collected heavier HCs are warmed in the exchangers and mixed with the
CO2/H2O-laden regeneration gas. The resulting gas stream is then returned to the
feed gas supply or to a low-pressure fuel system.
Cooling is provided by a nitrogen (N2) recycle refrigeration system, which
utilizes an N2 recycle compressor, an N2 compander and a cold box that houses the
liquefaction heat exchangers. N2 is compressed in the N2 recycle compressor and
cooled in an aftercooler. A compander incorporates a compression stage and an
expansion stage on a single shaft. N2 dropping from high to low pressure across
the expander wheel provides refrigeration and generates rotational force, which is
absorbed by the compressor wheel providing a portion of the total N2 compression
required. A portion of the N2 stream is expanded in the compander, providing part
of the refrigeration requirement. The remaining N2 is expanded with an expansion
valve and provides the rest of the refrigeration required for liquefaction.
There are many variations in the specific configuration of the N2 refrigeration
cycle (pressures, number of expanders, expander arrangements, etc.). The
configuration is driven by the need to develop the most cost-effective solution
for the plant size, final refrigeration temperature required and project-specific
economic evaluation criteria.
Economics: N2 recycle plants typically offer a lower capital solution for small-plant
applications and provide an attractive liquefication process option for applications
where HC refrigerants may be undesirable.

N2
compressor

Aftercooler
N2
compander

Feed gas

H2O/CO2
removal
BOG
compressor
Liquefaction
exchangers

Heavy HC
knockout drum
LIC

LNG
storage

Reference: Bronfenbrenner, J. C. and W. R. Miller, "On a smaller scale," LNG Industry,
Winter 2008.
Licensor: Air Products and Chemicals Inc.
Website: www.airproducts.com/LNG
Contact: info@airproducts.com

Installations: Three units in operation in peakshaving applications. Six N2 recycle
units in operation for LNG subcooling. Floating LNG applications include Petronas'
FLNG Satu, 1.2-MMtpy capacity, first cargo April 2017; and Petronas' FLNG Dua,
1.5-MMtpy capacity, commissioning expected in 2020.

Copyright © 2019 Gulf Energy Information. All rights reserved.
https://www.hydrocarbonprocessing.com/ http://www.airproducts.com/LNG
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