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Poster PO-50
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REDUCING FLARING OF BOGS SHIPS BY INSTALLATION
OF AN LNG QUENCHING SYSTEM
Agus A. KhalikPT. Badak NGL Bontang
ABSTRACT
Badak LNG plant is located in Bontang, East Kalimantan, Indonesia. The facility
consists of eight LNG Trains with a total production capacity of 22.5 MTPA of LNG.
Badak has three LNG Loading Docks which is designed to provide a flexibility for
loading LNG ship at each of three Docks from any of two of the six Storage tanks.
During loading, LNG product from the LNG tanks is pumped to the ship through a pair of
the LNG transfer lines. Any return LNG vapor (Boil Off Gas) from the ship is flown tothe Marine flare or to the fuel gas system.
Badak experienced when cooling down an LNG ships tanks and ship LNG loading,
the warm BOG from the ship could not be recovered by the BOG Compressors and has to
be flared in order to control the ships tank pressure.
To reduce the gas flaring, Badak installed an LNG Quenching drum to cool the ships
BOG from Docks of -80oC or warmer to the required suction of the BOG Compressors of
-110oC. This effort resulted in reduction of ship BOG flaring approximately 212,500 Nm3
each ship and resulted in an increase in the Plant thermal efficiency of 0.21%.
The LNG quenching is vertical drum equipped with a section of structured packing.
Vapor from the dock enters the drum and flows upward through structured packing and
contact with LNG taken from Transfer lines. The LNG flow is controlled by gas exiting
the top of the drum. Any accumulated LNG in the drum is pumped back to the loading
line. By installing this facility, the ship BOG flaring during loading can be significantly
reduced and increased Plant thermal efficiency.
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INTRODUCTION
PT. Badak NGL operates the Liquid Natural Gas (LNG) plant located in Bontang,
East Kalimantan, Indonesia, which is owned by Pertamina (The Indonesian State Oil &
Gas firm). The facility consists of eight LNG Trains with a total production capacity of22.5 MTPA of LNG and 1.6 million m3of Hydrocarbon Condensate/year. The first two
Trains (A&B) were commissioned in July 1977 and the last, Train H, has been in
operation since November 1999.
PT. Badak has three LNG Loading docks which is designed to provide a flexibility for
loading LNG ship up to 145,000 m3at each of three Docks from any of two of the six
Storage tanks.
During cargo loading, LNG product from the LNG Storage tanks is pumped to the
LNG ship through a pair of the LNG transfer lines. LNG vapor (Boil-off gas or BOG)
generated from flashing or vaporized of LNG due to heat in leak on ships tank duringloading process is flown to shore through a BOG equalizing header line and to the fuel
gas system for fuel boiler through the BOG Compressors. Any unrecoverable LNG vapor
is routed to the Marine flare. Figure 1 shows the Schematic Process Flow Diagram of a
BOG system in PT. Badak.
One of the operational problems for the Storage and Loading area prior to 1983 was
the large amount of BOG has to be flared in Marine flare during any ship loading at Dock
#1 using single BOG Compressor, 24K-1, to recover the warm BOG from the ship and
LNG Storage tanks. This problem continued occurred even after installing two additional
BOG Compressors, 24K-1/8/9 in 1985.
Fuel Gas
System
for Boilers
LNG Process Train
Tank BOGProcess Off gas
LNG Storage Tanks LNG Ship
Feed Gas
Make-up
BOG Recovery
Compresoors
Figure 1: Schematic Process Flow Diagram of a BOG system
Marine
Flare
Feed Gas
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This paper is described the successful problem solving by installing LNG Quenching
drum, the amount of ship BOG flaring during loading can be significantly reduced and
results the increasing of the overall Plant Thermal Efficiency.
DISCUSSION
The large amount of BOG flaring in the past appeared due to inconsistency operating
condition for the BOG Compressors. The actual compressor operating conditioned
deviated from the design conditions. This led to a limit in compression capacity of the
BOG compressors due to warmer BOG conditions. In addition, there was less ships LNG
tank heel volume upon arrival at the Bontang loading terminal. The following is the
analysis to determine the possible causes of excess BOG flaring during LNG cargo
loading.
Compression Capacity of the BOG Compressor
In 1985, PT. Badak commenced operating three BOG Compressors 24K-1/8/9, torecover BOG liberated from the existing five LNG Storage tanks 24D-1/2/3/4/5 and Dock
#1 during cargo loading. The actual compression capacities of the BOG Compressors
shown in Table-1.
From the Table-1 it is seen the compression capacity of the BOG compressors is very
sensitive to the suction temperature. In a constant flow operation, increasing the suction
temperature will decrease both discharge pressure and BOG recovery rate.
Table 1: Actual Compression Capacity of BOG Compressors 24K-1/8/9
Operating Conditions Compress. BOG Recovery Rates (Nm3
/h)Pressure (Psia) Number of BOG Compressor Running Description
Suction Discharge
Suct.Temp.
(oC) One Three
Rated /Design 15.2 80 -129 20,253 61,000
No Ship Loading 15.4 85 -140 20,735 62,000
During Ship Loading 15.4 71 -112 16,556 50,000
Effect of Ship Tank LNG Heel Volume on BOG Flaring During Loading Operation
Based on the LNG sales contract agreement, LNG ship calling at Bontang terminal
are divided into two categorized, Free on Board (FOB Trade) and Cost Insurance Freight(CIF Trade).
The FOB ships typically keep their tanks LNG heel volume at an appropriate ships
tank heel sufficient to cool the ship tanks to the desired loading temperature of -125oC or
colder upon arrival at the loading terminal. With this condition, LNG loading can be
performed without cooling down the ship tanks and directly for cargo loading. This only
requires 12.5 hours of loading time by using normally 4 loading pumps at the total
loading rate of about 10,000 m3/h.
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The CIF ships typically have ships tank LNG heels of less volume to allow higher
LNG discharging at the Buyer terminal. The reduced LNG heel volume results in a
warmer tank temperature of about -100oC upon arrival at the loading terminal. This
condition required to cool down of the ship tank to the desired starting loading
temperature of about -125oC or colder at ships equatorial tanks before starting the cargo
loading operation. At the normal cool down rate of -3oC/hour, the total loading time forthe CIF ships can be more than 20 hours, and the total BOG generation by the CIF ships
is more than FOB ships. Table 2 shows the affect of ship tank LNG heel volume to the
BOG flaring during loading operations for ship standard capacity of 125,000 m3of CIF
ship while Table-3 for FOB ship.
Table 2: BOG rates during CIF ship loading, including BOG from the LNG tanks
Boil Off Gas (BOG) Generated
CIF Ship
Ships
Tank Heel
(m3)
Vapor
Temp.
(oC) *)To Flare
(Nm
3
/h)
To Fuel
(Nm
3
/h)
Total
(Nm
3
/h)
Loading
Time
(Hours))
BOG Rate
(Nm3/hr)
Gemini 88 -102.8 483,000 1,061,000 1,544,000 24.9 62,000
Taurus 198 -113.9 397,000 830,000 1,227,000 20.2 61,000
Aquarius 281 -105.5 513,000 810,000 1,323,000 19.9 66,000
Average -107.4 465,000 21,7 63,000
Note : *) Temperature of ships tank condition at the arrival time in the Bontang loading terminal
From the Table 2 and Table 3 it can be seen that:
With a reduced volume of ships LNG tank heel volume on CIF ships, the total BOG
flaring during cargo loading was higher than FOB ships. Considerable BOG flaring occurred during loading of FOB ships, even though it has a
colder tank temperature (-135.1oC). This is due to heat leakage into the BOG line, which
may warm up the BOG by about 20oC before mixing with the BOG from the LNG tanks.
CIF ships require longer cargo loading time due to she need cool down LNG ships tanks
prior cargo loading, which is caused more BOG flaring.
Table 3: BOG rates during FOB ship loading, including BOG from LNG tanks
Boil Off Gas (BOG) Generated
FOB Ship
Heel
(m3)
Vapor
Temp.(oC) *) To Flare(Nm
3/h)
To Fuel(Nm
3/h)
Total(Nm
3/h)
Loading
Time(Hours)
BOG Rate
(Nm3/h)
Senshu Maru 862 -125.5 331,670 379,870 711,540 12.33 57,710
Banshu Maru 958 -138.4 289,860 552,920 842,780 12.62 66,780
Bishu Maru 584 -138.0 232,780 460,020 692,800 12.20 56,790
Bishu Maru 695 -138.6 277,960 503,330 781,250 12.28 63,620
Average -135.1 283,060 12.36 61,220
Note : *) Temperature of ships Ships tank condition at the arrival time in the Bontang loading
terminal
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The above analysis highlights that large BOG flaring in the past was mainly caused
by limited compression capacity due to warmer suction temperature conditions. As the
reduced LNG heel volume mode of operation on the CIF ships increases LNG delivery to
the buyer and to reduce BOG flaring during ship cargo loading operations, it was decided
to install a LNG quenching drum on the ship BOG return line.
LNG QUENCHING DRUMS
Old LNG Quenching Drum, 24C-5
In 1987, PT. Badak designed a LNG Quenching Drum 24C-5 to recover BOG from
LNG ships loading at Dock #1. The design basis for the drum was to allow recovery of
the ship BOG at a conservative cargo loading rate at Dock #1. This design basis required
a drum size to recovery BOG up to 70,000 Nm3/hour at a temperature of -100oC or
colder.
Figure 2: Scheme of Old BOG Recovery System
PT
PT
19F-5
24PV-424
FUEL GAS SYSTEM( AS FUEL BOILERS)
19F-2
LNG TANK
24D-5
c/w
24K-1
16"
24K-9
c/w
c/w
16"
16"
36"
20"
20"
20"
20"
24"
24D-1
24D-4
24D-3
24D-2
20" 20"NC
24C-5
20"
24K-8
BOG QUENCHING
SHIPSRAIL
24PV-224
DOCK #1
BOG COMPRESSORS
The Quenching drum is horizontal equipped with a two stage LNG spray facilityinstalled in the inlet to the drum. The Quenching drum was located 700 m away from
Dock #1 to shore side and 200 m away from the BOG Compressors location as shown in
the Figure-2. It was decided to isolate the Quenching drum closer to the BOG
Compressors to maintain the cool suction temperature from the Quenching drum to the
Compressor suction. With an appreciate BOG temperature at the suction Compressor, it
would be possible to recover the BOG from the ship when the ship starts cargo loading
operations.
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The Quenching drum was designed to cool the ship BOG return from Dock #1 to -
110oC or colder. The BOG flows into the drum and then is sprayed with LNG taken from
any one of two LNG transfer line through two control valves. The cooled BOG
temperature is controlled below the warmest suction temperature of -100oC to avoid the
Compressor surge. A drain facility is provided including a Nitrogen connection to the
Marine flare, 19F-2 to drain any condensed LNG heavy components of the injected LNG.A high level alarm and BOG compressor shutdown was provided for Compressor
protection.
Table 4: BOG Flaring during Ship Cargo Loading for period of Jan.- Mar 1988
BOG Flaring (Nm3)No. Number of LNG Ship Loading
Total Each Ship
1. 15 ships (Jan. 1988) 3,826,700 255,180
2. 12 ships (Feb. 1988) 3,789,300 294,390
3. 11 ships (Mar. 1988) 2,126,500 193,320Average 247,630
The Quenching drum, 24C-5 was installed and put in service starting in April 1988.
The table-5 shows the BOG ship flaring was significantly reduced starting in May 1988
from 224477,,663300NNmm33 ttoo3355,,113300NNmm
33 The quantities of recovered BOG reduced the fuel gas
make-up from the feed gas system and resulted in an increase in the overall plant thermal
efficiency. Referring to the Table-3, the optimistic quantities of recovered BOG was
212,500 Nm3/ship in 1988 or reduced by 85.8%. This resulted in an increase in the
overall thermal efficiency of about 0.21%. Operational problem was experienced that the
LNG liquid collected in the bottom of the drum carried out to the suction BOGCompressor and was causing the Compressor tripped.
The old Quenching drum 24C-5 was taken out of service in August 1998 after the
new Quenching drum 24C-101 was placed in operation.
Table 5: BOG Flaring during Ship Loading After
Old Quenching Drum 24C-5 in Service
BOG Flaring (Nm3)
No. Number of LNG Ship LoadingTotal Each Ship
1. 13 ships (May 1988) 511,800 39,3702. 10 ships (Jun. 1988) 315,800 35,090
3. 14 ships (Jul. 1988) 433,200 30,940
Average 35,130
LNG Quenching Drum, 24C-101
Since the LNG Loading Dock #2 did not have a BOG recovery system, all BOG from
this dock flowed directly to the Marine Flare, 19F-21. This led PT. Badak to assign to
Dock #2 all FOB ships that have high LNG heels volume as an effort to minimize BOG
flaring during ship cargo loading operation.
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To solve the operational problems with the old Quenching drum 24C-5, it was
decided in 1997, as part of the LNG Train G expansion project scope, PT. Badak
commenced to construct a larger New LNG Quenching drum 24C-101 in anticipation of
increased LNG cargoes operating eight LNG Trains. A process scheme was developed to
recover BOG during simultaneous loading at Dock #1 and any one of the other two docks
(Dock #2 or Dock #3). The design basis of the drum is to recover BOG at theconservative loading case of simultaneously start loading from two docks. This design
basis required a drum size to receive BOG at 125,000 Nm3/h, at a temperature of -115oC.
Figure 3: New LNG Quenching Drum, 24C-101
LT932
PSV
1001
A
PSV
1001
B
LE
931
LCH
H
931
900
300
150
150
2" 300#
32"MM
24"MM
4"
3"
2" 300#
2" 300#
API-FLG
26"
3" 300#
3" 300#
VENT
3"300# 24"
3"LO
3"
24LNG5029-3"-PD1B-C140
24LNG5020-3"-PD1B-C140
24LNG5028-3"-PD1B-C140
24LNG5030-4"-
PD1B-C140
3"
4"
N/PNC
3"NC
24C-101 C
C
24LNG5014-3"-PD1B-C140
24G-101
LIQUID DISTRIBUTOR
STRUCTURED PACKING
FROM LOADING DOCKS
TO BOG COMPRESSOR
The New Quenching drum, 24C-101 is vertical drum equipped with a section of
structured packing and two liquid drain pumps, 24G-101A/B. As shown in the Figure-4,
the drum is located close to the existing ones. BOG from the loading docks enters the
new Quenching drum and flows upward through a section of structured packing andcontacts with sprayed LNG taken from LNG Transfer line #1 of Dock #1. The LNG flow
is controlled by the temperature of gas exiting the top of the Quenching drum using a
temperature controller valve, 24TV-1002, set at -140oC. The structured packing is
provided to maximized contact between the vapor and the sprayed LNG. Any excess LNG
leakage through the packing is pumped by drain pump 24G-101 back to the transfer line
for Dock #1. The new Quenching drum 24C-101 was installed and put in service started
in August 1998.
The Table 6 shows that by operating the new Quenching drum 24C-101, PT. Badak
could successfully reduce BOG flaring by 226,280 Nm3/ship during loading, with various
cases of simultaneously ship loading at Dock #3 and any one of other two docks, Dock #2or Dock #3.
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Table 6 : BOG Flaring during Ship Loading
After Quenching Drum 24C-101 in Service
BOG Flaring (Nm3)
Period Number of LNG Ship LoadingTotal Each Ship
Oct .1998 24 ships 613,320 22,850Nov. 1998 28 ships 486,340 20,330
Dec. 1998 28 ships 584,440 20,870
Average 21,350
Referring to the Table 6 shows that by operating the new Quenching drum 24C-101,
PT. Badak could successfully reduced BOG flaring by 226,280 Nm3/ship or reduced by
91.4%. during loading, with various cases of simultaneously ship loading at Dock #1 and
any one of other two docks, Dock #2 or Dock #3. This resulted in an increase in the
overall thermal efficiency of about 0.214%.
Figure 4: Scheme of New BOG Recovery System
PT
PT
LC
PT
PT
PT
19F-36
FROM SHIP TANKS
DOCK #2
SHIPS RAIL
19F-21
19F-5
24PV-424
RETURN TO LNGTRANFER LINE #2
LNG TANK
24D-6
NCFUEL GAS SYSTEM( AS FUEL BOILER)
26"
26"
SHIPS RAIL
FROM LNG TANKS
DOCK #3
24PV-22419F-2
LNGQUENCE FROM LNG
TRANFER LINE #1
LNG TANK
24D-5
c/w
24K-16
24"
c/w
24K-1
16"
c/w
c/w
16"
16"
36"
20"
20"
20"
20"
24"
24D-1
24D-4
24D-3
24D-2
20" 20"NC
24C-5
20"
24C-101
24G-101A
CONCLUSIONS
The above analysis demonstrated that the larger BOG flaring in the past was mainly
caused by limited compression capacity of the existing BOG compressors due to warmer
suction temperature
With installation of both LNG Quenching drums, 24C-5 and 24C-101, PT. Badak was
successfully in reduce the BOG flaring from ship by 212,500 Nm3/ship (86.5%) and
226,280 Nm3/ ship (91.4%) respectively.
By installing this facility, the ships BOG flaring during cargo loading can be significantlyreduced and increased the overall Plant thermal efficiency of 0.21% .