Unit 051 (Refrigrant System)
MR Circuit, The purpose of the MR circuit is to cool and liquefy the feed gas in unit 041
Main Cryogenic Heat Exchanger (MCHE) with maintaining the temperature at -132 oC on
the warm bundle by controlled JT valve (051-PV-2740) and cold bundle ends at -156 oC
(holding mode) or -165oC (loading mode) by controlled JT valve (051-PFV-2940) on the
MCHE.
The MR refrigeration to liquefy the feed gas is supplied by a mixture of nitrogen,
methane, ethane and propane. Methane, ethane and propane make-up requirements
are supplied from the light-end fractionation unit, while the nitrogen make-up is
supplied from utility.
The propane refrigeration system utilizes propane evaporating at three pressure levels
to supply refrigeration to cooling process at the feed circuit, the MR circuit and the
Fractionation Unit. Each level of chilling is provided by a successive flash to a lower
pressure level. As the pressure is reduced, the propane boils at colder temperature. The
propane make-up requirements are supplied from De-C3 overhead vapor and Bulet
(074-D-1002).
To produce LNG, a refrigerant with a certain temperature is needed as a cooling medium
and a liquefaction of sweet gas from Scrub column in MCHE, by maintaining the
temperature approach on the warm and cold bundle ends on the MCHE. therearefore, to
support these process are provided refrigrant by two major systems: the Propane
Refrigeration System and the Mixed Refrigerant Refrigeration (MR) System.
Propane Refrigeration System
The propane refrigeration system utilizes propane evaporating at three pressure levels to
supply refrigeration to the feed gas circuit, the MR circuit and the fractionation unit. Each
level of chilling is provided by a successive flash to a lower pressure level. There level of
propane pressure is low pressure (0.25 kg/cm2, -36 0C), medium pressure (2.18 kg/cm2, -
12 0C) and high pressure (5.18 kg/cm2, 8.5 0C). Propane from the discharge of 051-C-
1001 (C3 refrigerant compressor) is desuperheated by fan on-off control to avoid
condensation in 051-E-1001, so it can be used as anti surge gas returned back to
compressor suction through anti surge pipeline Then, propane is condensed in 051-E-
1002 C3 condenser. The condensed propane is collected in propane accumulator (051-D-
1004), in the C3 accumulator there is a reclaimer, which functions to condense the C3
that has not been liquefied, using the liquid c3 output of the accumulator then trouted to
lower the temperature of the C3 so that it can be used as a cooling media at reclaimer
column. The propane liquid from 051-D-1004 C3 accumulator is transferred through
propane subcooler (051-E-1003) before supplied to each compressor suction drum. Then
propane introduced to propane compressor (GTC 1). Propane vapor make-up during
normal operation comes from depropanizer column overhead 041-T-1004. Propane liquid
can be supplied from 074-D-1002A/B propane refrigerant storage tank to 051-D-1004 C3
accumulator during start-up.
Mixed Refrigerant Refrigeration (MR) System
The refrigeration to liquefy the feed gas is supplied by a mixture of nitrogen (10 %),
methane (43%), ethane (41 %) and propane(6 %), known as mixed refrigerant (MR).
Methane, ethane and propane make-up requirements are supplied from the light-end
fractionation unit, while the nitrogen make-up is supplied from nitrogen header Unit 066.
MR vapor from Suction Drum ( Pres. 2 Kg/cm2) will compres by 051-C-1002 then the
temperature will reduced by LP MR Compressor after cooler 051-E-1004, then compresed
up to High pressure at the 051-C-1003 HP MR Compressor then MR from 051-C-1003 HP
MR Compressor is cooled by ambient air in the 051-E-1005 HP MR Compressor After
Cooler and then is further cooled and partially condensed in 051-E-1006, 051-E-1007 and
051-E-1008 MR/C3 Chillers. The partially condensed mixed refrigerant from the 051-E-
1008 is phase separated in the 051-D-1007 HP MR Separator.The vapor from 051-D-1007
HP MR Separator is condensed and subcooled in the 041-E-1001 Main Cryogenic Heat
Exchanger (MCHE) in Unit 041 Gas Liquefaction/Fractionation. It exits at the cold bundle
end of 041-E-1001 MCHE and is reduced in pressure across the ‘cold’ Joule-Thomson (JT)
valve PCV-2490. After this ‘cold’ JT valve, the low pressure and cryogenic temperature MR
stream is distributed by the distributor at the top of the cold bundle in 041-E-1001. The
liquid from 051-D-1007 HP MR Separator is subcooled in the warm bundle of 041-E-1001
MCHE. This liquid is reduced in pressure by ‘warm’ JT valve PV-2470. The JT valve outlet
stream is sent to the 041-E-1001 MCHE shell side. This stream mixes inside 041-E-1001
MCHE with the low pressure mixed refrigerant from the cold bundle. there are installed
distributors at the top of the warm bundle of 041-E-1001 MCHE assure the even
distribution of vapor and liquid over the warm bundle. The low pressure mixed
refrigerant is totally vaporized and superheated in the warm bundle of 041-E-1001 MCHE
