3.61M

BOG

1. TRAINING

INTRODUCTION TO BOG
TRAINING
14:08

2.

Boil Off Gas
Boil Off Gas is generated by
Flashing of LNG R/D into LNG tanks
Introduction of Hot Gas into the tank
Operations of LNG pumps in the Tanks
Heat in-leak to lines and tanks
Long or short LNG circulation
Return of warm vapour from ship
14:08

3. Usage of BOG

BOG is compressed and sent to the fuel gas system for operation of gas
turbines and other users.
Hot gas supply to LNG tanks
Excess gas can be recompressed back to NG feed gas to LNG trains.
14:08

4. Handling BOG

Holding Mode
Loading Mode
BOG from the LNG storage tanks is
routed to the end flash compressor
which compresses the gas and sent
it to HP fuel gas.
As more BOG is generated during
ship loading, the BOG compressor
is put in service in addition to the
end flash compressor
Excess FG can be recompressed back to the NG feed gas.
14:08

5.

Fuel Gas System
14:08

6. FG System

14:08

7. BOG Process

Suction Drum
Controls suction temperature to compressor between –110 to -125oC
• 34 TIC 351 -LNG from loading lines for quenching to maintain comp
suction temp. at –110oC
• Recycle valve opens if suction temp is too low ( -125oC)
Maintains a liquid level for pump soaking/operation
• LICA 342 taking LNG from loading lines
• P3404A/B returns excess LNG to loading lines
14:08

8. P3404 A/B

LNG return pumps
Pump cooldown and filling using small line
from suction line to pump casing drain
Cooldwon rate monitored
Pump filling /soaking ( min 5 hrs)
Suction and discharge valves open
Priming line closed when pots are full
Bypass NRV open on stdby pump to
maintain at operating temp. Closed when
pump in service
Cable Junction box continuous N2 purging
Only one pump in service at one time due
to only one fixed min flow line shared by
both pumps.
14:08

9. Pump Cable Seals

Cable seal purge arrangement
N2 supply locked open
Adjustible flow valve on inlet line
Pressure alarm
RO on outlet / vent line
Note
High press alarm may be due to
excess N2 supply pressure or
due to gas leaks from pump gas
test at the vent line to determine
which case
14:08

10. Review Questions

1.
How is BOG generated, handled and used?
2.
BOG temperature ranges and reasons for different temp.
3.
Purpose and method of maintaining K3401 suction temperature
4.
Why a level is required at V3401 and how the level is maintained
5.
Why P3404A/B cannot run in parallel and what control is in place
to prevent this.
6.
Pump cooldown and soaking method
7.
Pump line up on standby and in service
8.
Cable seal purge – purpose and line up
14:08

11. BOG compressors Graphic view

14:08

12. BOG compressor train

14:08

13. BOG train machines

Electrical motor
Motor purge
Siemens,
LP compressor
Siemens
5 stages centrifugal , barrel type
IGV
HP compressor
Siemens
5 stages centrifugal horizontal split
14:08

14. LP Compressor

14:08

15. HP Compressor

14:08

16. Vibration Monitoring

14:08

17. Machine Lubrication

Lubrication oil – bearings and gears
•Temperature – controlled by TC valve
•Tank heaters, coolers and by pass flow
•Pressure - controlled by PC valve
•Flows – controlled by ROs
( monitor the return flow in each SG)
Power failure –LO pumps not available.
Oil from OH tank lubricate the machine while they run down to stop.
Seal heating oil – prevent seal cease due to cold process
Emergency pump for heating oil
14:08

18. Lube Oil System

14:08

19.

Machine Lubrications
14:08

20. Bearings

14:08

21. Lube oil pumps

14:08

22. Gear pumps

Discharge valve always full open before start pump and during operations.
RV on discharge must be always lined up.
14:08

23. Lube Oil Accumulator

14:08

24. Oil Accumulator Function

Prevents compressor from tripping
When the LO pump trips
Oil pressure will drop slightly before the standby pump has time to bring up the
normal pressure
This dip in pressure could cause compressor trip ( even for split second)
The Oil accumulator is always line up and charged to cushion this pressure dip
and prevent a trip.
However the N2 bladder must be always healthy in order to have accumulator
power.
N2 bladder check is required as a recurring duty
14:08

25. N2 Accumulator Check

Inform panel operator
Start the standby LO pump
Close main valve to N2 Accumulator
Open N2 accumulator drain valve to tank
Watch pressure gauge on top of accumulator
It should drop and settle out at about 2 barg
Wait 5 mins to make sure pressure is constant.
Closed drain valve
Crack cpen main valve to slowly fill the accumulator with oil.
When pressure is same as header pressure, open fully the main valve
Stop the standby pump
14:08

26. LO Overhead Tank

No emergency LO pump for K3401 machines
An overhead tank is provided for this purpose
The OH tank is constantly filled and overflowed back to the main tank to maintain
the oil at working temperature. A NRV on the main line allows the oil to flow
downwards only. The bypass valve of the RO is used only for initial filling.
The rate of oil flow is controlled by LO pressure and the RO in the fill line.
Operator monitor the overflow through the sight glass
When power failure occurs, compressors and LO pumps stop. Oil from OH tank
drains down via the outlet pipe to the bearings of the machines, then to the main
tank.
The volume of oil is sufficient for the machines to come to a complete stop.
14:08

27. LO OH Tank and Valves

14:08

28. Duplex LO Filters

14:08

29. Filter change-over

1
Fill and pressurise the spare filter
Open the vent valve from the spare filter
Open the pressurising valve
Watch the oil flow is continuous in the SG on the vent line
Close the vent valve when filter is filled
2
Swing over smoothly using 6-way valve lever
Close equalising valve
Vent the isolated filter
Drained and prepared for change out.
14:08