REDUCING FLARING OF BOG S SHIPS BY INSTALLATION OF AN LNG QUENCHING SYSTEM

Transcription

1 REDUCING FLARING OF BOG S SHIPS BY INSTALLATION OF AN LNG QUENCHING SYSTEM Agus A. Khalik. 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 to the Marine flare or to the fuel gas system. Badak experienced when cooling down an LNG ship s 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 ship s tank pressure. To reduce the gas flaring, Badak installed an LNG Quenching drum to cool the ship s BOG from Docks of -80 o C or warmer to the required suction of the BOG Compressors of -110 o C. This effort resulted in reduction of ship BOG flaring approximately 212,500 Nm 3 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. PO-50.1

2 INTRODUCTION. 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 of 22.5 MTPA of LNG and 1.6 million m 3 of 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 Badak has three LNG Loading docks which is designed to provide a flexibility for loading LNG ship up to 145,000 m 3 at 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 ship s tank during loading 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. Badak. Feed Gas Make-up Fuel Gas System for Boilers BOG Recovery Compresoors Marine Flare Process Off gas Tank BOG LNG Process Train Feed Gas LNG Storage Tanks LNG Ship Figure 1: Schematic Process Flow Diagram of a BOG system 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 PO-50.2

3 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 ship s 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,. Badak commenced operating three BOG Compressors 24K-1/8/9, to recover 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 Description Pressure (Psia) Suct.Temp. Number of BOG Compressor Running Suction Discharge ( o C) One Three Rated /Design ,253 61,000 No Ship Loading ,735 62,000 During Ship Loading ,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 tank s LNG heel volume at an appropriate ship s tank heel sufficient to cool the ship tanks to the desired loading temperature of -125 o C 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 m 3 /h. PO-50.3

4 The CIF ships typically have ship s 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 -100 o C upon arrival at the loading terminal. This condition required to cool down of the ship tank to the desired starting loading temperature of about -125 o C or colder at ship s equatorial tanks before starting the cargo loading operation. At the normal cool down rate of -3 o C/hour, the total loading time for the 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 m 3 of CIF ship while Table-3 for FOB ship. Table 2: BOG rates during CIF ship loading, including BOG from the LNG tanks CIF Ship Ship s Tank Heel (m 3 ) Vapor Temp. ( o C) *) Boil Off Gas (BOG) Generated To Flare To Fuel Loading Time (Hours) BOG Rate (Nm 3 /hr) Gemini ,000 1,061,000 1,544, ,000 Taurus , ,000 1,227, ,000 Aquarius , ,000 1,323, ,000 Average ,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 ship s 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 ( o C). This is due to heat leakage into the BOG line, which may warm up the BOG by about 20 o C before mixing with the BOG from the LNG tanks. CIF ships require longer cargo loading time due to she need cool down LNG ship s tanks prior cargo loading, which is caused more BOG flaring. Table 3: BOG rates during FOB ship loading, including BOG from LNG tanks FOB Ship Heel (m 3 ) Vapor Temp. ( o C) *) Boil Off Gas (BOG) Generated To Flare To Fuel Loading Time (Hours) BOG Rate Senshu Maru , , , ,710 Banshu Maru , , , ,780 Bishu Maru , , , ,790 Bishu Maru , , , ,620 Average , ,220 Note : *) Temperature of ships Ships tank condition at the arrival time in the Bontang loading terminal PO-50.4

5 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,. 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 Nm 3 /hour at a temperature of -100 o C or colder. Figure 2: Scheme of Old BOG Recovery System 24D-1 BOG COMPRESSORS 36" 24D-2 24D-3 24K-8 24" 24D-4 24K-9 NC 24K-1 24C-5 BOG QUENCHING SHIP S RAIL FUEL GAS SYSTEM ( AS FUEL BOILERS ) LNG TANK 24D-5 DOCK #1 24PV F-5 24PV F-2 The Quenching drum is horizontal equipped with a two stage LNG spray facility installed 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. PO-50.5

6 The Quenching drum was designed to cool the ship BOG return from Dock #1 to o C 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 -100 o C 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 No. Number of LNG Ship Loading BOG Flaring (Nm 3 ) Each Ship ships (Jan. 1988) 3,826, , ships (Feb. 1988) 3,789, , ships (Mar. 1988) 2,126, ,320 Average 247,630 The Quenching drum, 24C-5 was installed and put in service starting in April The table-5 shows the BOG ship flaring was significantly reduced starting in May 1988 from 247,630 Nm 3 to 35,130 Nm 3 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 Nm 3 /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 BOG Compressor 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 No. Number of LNG Ship Loading BOG Flaring (Nm 3 ) Each Ship ships (May 1988) 511,800 39, ships (Jun. 1988) 315,800 35, ships (Jul. 1988) 433,200 30,940 LNG Quenching Drum, 24C-101 Average 35,130 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. 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. PO-50.6

7 LCH H 931 PSV 1001 B PSV 1001 A C Poster PO-50 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,. 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 the conservative loading case of simultaneously start loading from two docks. This design basis required a drum size to receive BOG at 125,000 Nm 3 /h, at a temperature of -115 o C. Figure 3: New LNG Quenching Drum, 24C-101 3" NC 24LNG5030-4"- PD1B-C140 4" NC N/P 3" 24LNG5020-3"-PD1B-C140 24LNG5029-3"-PD1B-C140 3" LO VENT TO BOG COMPRESSOR 3" 24LNG5028-3"-PD1B-C140 3" 300# 24" 3" 300# 24"M M 3" 300# 24LNG5014-3"-PD1B-C140 LIQUID DISTRIBUTOR STRUCTURED PACKING 32"M M 24C-101 C 26" LT 932 FROM LOADING DOCKS API-FLG 2" 300# LE 931 2" 300# " 300# 3" 4" 24G-101 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 and contacts 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 -140 o C. 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 The Table 6 shows that by operating the new Quenching drum 24C-101,. Badak could successfully reduce BOG flaring by 226,280 Nm 3 /ship during loading, with various cases of simultaneously ship loading at Dock #3 and any one of other two docks, Dock #2 or Dock #3. PO-50.7

8 Table 6 : BOG Flaring during Ship Loading After Quenching Drum 24C-101 in Service Period Number of LNG Ship Loading BOG Flaring (Nm 3 ) Each Ship Oct ships 613,320 22,850 Nov ships 486,340 20,330 Dec ships 584,440 20,870 Average 21,350 Referring to the Table 6 shows that by operating the new Quenching drum 24C-101,. Badak could successfully reduced BOG flaring by 226,280 Nm 3 /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 24D-1 36" 24D-2 24D-3 24" 24D-4 NC 24K-1 24" 24C-5 24K-16 LNG TANK 24D-5 24C-101 LNG QUENCE FROM LNG TRANFER LINE #1 FUEL GAS SYSTEM ( AS FUEL BOILER ) LNG TANK 24D-6 NC LC 24PV F-2 RETURN TO LNG TRANFER LINE #2 24G-101A SHIP S RAIL 24PV " 19F-5 26" FROM LNG TANK S DOCK #3 19F-21 SHIP S RAIL FROM SHIP TANK S DOCK #2 19F-36 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,. Badak was successfully in reduce the BOG flaring from ship by 212,500 Nm 3 /ship (86.5%) and 226,280 Nm3/ ship (91.4%) respectively. By installing this facility, the ships BOG flaring during cargo loading can be significantly reduced and increased the overall Plant thermal efficiency of 0.21%. PO-50.8