LNG Steam Simulator Exercise


018. Run the Simulator to Change over to LNG Blow-off Gas Burning<

[Load Snapshot "Ex_018_Changing Over from DO to HFO_Burning"]

- Asssume scenario as described below [but check to confirm] and then follow the given procedures


Electrical Power:-

Shore Power:Off; Emergency Generator:Auto Stand-by; Turbo Generators:One on load and the other off; Diesel Generator:On Load

Deaerator:-

Full with guage glass reading between 60~70 mm

Both Boilers:-

Both Boiler Press - aboout 6 Mpa; Both boilers are running on HFO supply.

Condenser:-

Condenser Vacuum is Satisfactory and Cooling on

Distilled Water Tank (DWT) & Atmospheric Drain Tank (ADT):-

Both DWT & ADT about 60% full.

>> Procedure to burn Gas:-

Instructor LNG Tanks:
1 Open all 4 CArgo tank valves to the Vapour Main.
LD Compressors:
2 Open the Vapour Main to De-Mister valve.
3 Open LD 1 inlet and outlet valves.
4 Open LD 2 inlet and outlet valves.
5 Open Steam Heating to the gas Heater.
6 Start LD compressor 1
Note: The vanes are adjusted by a signal from the Fuel Gas (FG) Control Valve which is shut and so the LD compressor does not trip on HP outlet Pressure.
Main Distrib:
7 Close the ER Exhaust Fans breaker.
Gas Detection:
8 Start up the Vent Duct Fans 1 and 2.
9 Start up the Boiler Hood Fans 1 and 2.
FG Bnr Mgt:
10 Reset tne Master FG Valve - The "FG Extr. Fans" and "ER Extr. Fan MAster" FG V/V Trip Cause Lights extinguish.
11 Fuel Gas (LNG Boil off) can not be used until the gas lines are purged with Nitrogen.
12 There are 3 Purge sequences:
a) Main Line Purge
b) Stbd and Port Header Purge
c) Individiual Burner Purges
Purge Permissives:
13 Check - It can be seen that all these purge sequences are not available because the Main Nitrogen Valves are shut
FG Bnr Mgt:
14 Open the Nitrogen supply valve.
Purge Permissives:
15 Check - It can be seen thatall purge sequences are now available.
FG Bnr Mgt:
16 Main line Purge
17 Click MAIN LINE "N2 Purge" to initiate and run the Main Line Purge sequence.
18 The Main line purge sequence is as follows:
19 The Main line header vent valves will open automatically
20 A master gas valve trip due to N2 purge comes up as part of the purging sequence - this is normal.
21 The Main line purge valve will open automatically.
22 The Main line darkens to show the expulsion of the gas in the Main line.
23 Wait for the purge sequence to complete.
24 The purge is complete when the Main Line N2 purge light extinguishes.
25 Note: The Main Vents are left open at the end of the purge.
26 These will automatically shut when we introduce gas.
HDR/BNR Purge:
27 Click Stbd and Port "HDR/BNR N2 Purge" to initiate and run the HDR/BNR Purge sequence. This runs a purge sequence on the STBD Header (if required) followed by a purge on burners (if required.
28 Watch the Purge Sequence.
29 The Purge is complete when the HDR/BNR N2 Purge light extinguishes.
30 Close the Stbd Header Vent (Click HDR Vent "Close")
31 Close the Port Header Vent (Click HDR Vent "Close")
Stbd/Port Boiler:
32 Click FUEL GAS EMERG SHUT VALVE "Trip/Reset" to clear the HDR VENT V/V OPEN Trip
33 Click MASTER FUEL GAS VALVE "Trip /Reset" to clear the Trip.
FG Flow Ctrls:
34 Set to Manual and open to say 5% - do not set too high or the Master Gas Valve could trip on "BOG TEMP LL".
35 This can happen if we try to light up all gas burners simultaneously with a high gas flow - the steam header may not be quick enough to respond.
36 Also the LD Compressor vane angle is set by FG valve position and the LD compressor could Trip on HP outlet pressure.
FG BNR Operation:
37 Reset the MASTER FUEL GAS VALVE
38 Open the MASTER FUEL GAS VALVE
LD Compressor:
39 Check for HP OUT trip - reset if necessary
Stbd Light up:
40 Open the STBD FUEL GAS EMERGENCY SHUT V/V
41 Light up the STBD. Burner 1 - the burner light flashes green during the light up sequence
42 Wait for the burner to be lit (steady green)
43 Light up STBD Burner 2 - the burner light flashes green during the light up sequence
44 Wait for the burner to be lit (steady green)
Port Light up:
45 Open the PORT FUEL GAS EMERGENCY SHUT V/V
46 Light up the PORT Burner 1 - the burner light flashes green during the light up sequence
47 Wait for the burner to be lit (steady green)
48 Light up PORT Burner 2 - the burner light flashes green during the light up sequence
49 Wait for the burner to be lit (steady green)
NOTE: The FUEL MODE lights now indicate DUAL FUEL
FG Flow Ctrls:
50 Open up both the controllers to say 30%
Bnr Operation:
51 The FG control valves can be seen to open (to about say 30%) - note that the FO control valves close in reducing FO flow - a natural effect from the cascaded FO PID controllers.
52 This happens because the increased gas burn is tending to raise Boiler Drum Pressures
53 This results in the Plant Master( FO Controller) reducing its output to the Master Controllers (which are also FO controllers) and hence reducing the output of the Fuel and Air (FO Controllers)
BOG Ctrls:
54 Set to Auto and note the set point is now in kg/s (not %). Increase the set-point to say 0.5 kg/s (before the gas manifold pressure has a chance to fall and we loose the gas burners)
55 Note a manifold gas flow rate of about 0.5 kg/s corresponds to 0.25 kg/s per burner.
Instructor LNG Tanks:
56 Observe the gas flow rate is approximately 0.15%/day which is approximately the boil off required for zero pressure rise in the tanks

NOTE:

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