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REDUCING FLARING OF BOGS SHIPS BY INSTALLATION

OF AN LNG QUENCHING SYSTEM

Agus A. KhalikPT. Badak NGL Bontang

khalik@badaklng.co.id

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% .