SONATRACH
NEW LNG TRAIN SKIKDA PROJECT
SKIKDA, ALGERIA
OPERATING MANUAL VOLUME 1, SECTION 6-1:
UNIT 15 DEFROST GAS & SEAL GAS
DOCUMENT NO: PP-AAA-PP1-117
KBR
JOB NO.: J6404
1 KM Issued for Implementation 17-Dec-12 MRC SPD
0 JDS Issued for Implementation 23-Nov-10 GRM BA AB
B JDS Issued for Client Approval 23-Sep-10 GRM BA -
A ACG Issued for Client Approval 04-Dec-09 VAS BA -
Rev. By Description Date KBR KBR CLIENT
Chkd App App
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
TABLE OF CONTENTS
1.0 INTRODUCTION ................................................................................................... 3
2.0 SYSTEM DESCRIPTION ...................................................................................... 4
3.0 OPERATIONS ...................................................................................................... 7
3.1 Normal Running................................................................................................................ 7
3.2 Typical Operating Parameters .......................................................................................... 7
3.3 Temporary Operation ....................................................................................................... 7
4.0 START-UP ............................................................................................................ 8
5.0 SHUTDOWN ......................................................................................................... 9
5.1 Normal Shutdown ............................................................................................................. 9
5.2 Process Upsets and Production Loss .............................................................................. 9
6.0 SAFETY/EMERGENCY SHUTDOWN ................................................................ 10
6.1 Safety Critical Shutdown Systems ................................................................................. 10
6.1.1 I-1500 - Liquefaction, Unit 15 ESD .............................................................................. 10
6.1.2 I-1515 - Boil Off Gas Header Vacuum Break .............................................................. 10
6.1.3 I-1580 - 15-ML01 Defrost Gas Heater Trip .................................................................. 10
6.1.4 I-1582 – Defrost Gas to Distribution Trip ..................................................................... 10
6.2 Pressure Safety Valve Summary ................................................................................... 11
6.3 Fire Protection Equipment .............................................................................................. 12
7.0 ATTACHMENTS ................................................................................................. 13
7.1 Attachment I: Equipment List ......................................................................................... 14
7.2 Attachment II: Utility Consumption ................................................................................ 15
Page 2 of 15 KBR
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
1.0 INTRODUCTION
This operating manual relates to the facilities indicated on Process Flow Diagram PR-15-PR-
32-004 and P&ID’s PR-15-SYPI-008 and PR-15-SYPI-008A.
Defrost Gas & Seal Gas System is primarily used during the start-up to provide warm, dry
feed gas to remove moisture from cryogenic equipment and piping. It is also used for drying
cryogenic pumps and other equipment after maintenance. During the normal operation, all
the connections from the defrost gas supply to the defrost gas headers remain closed.
This system has a thyristor controlled, electric Defrost Gas Heater, 15-ML01, which receives
feed gas from the Mercury Removal System. The warm feed gas is distributed through the
defrost gas headers to Unit 7, 15, 16, 20, 65 and 71.
Defrost gas is also used for the primary external backup Seal Gas System which provides
seal gas for the compressors in the liquefaction, refrigeration and storage units 15, 16, and
71. The compressors that use defrost gas as an external seal gas source, will use feed gas
as a secondary external seal gas source upon loss of defrost gas.
Page 3 of 15 KBR
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
Page 4 of 15 KBR
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
Page 5 of 15 KBR
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
2.0 SYSTEM DESCRIPTION
The dry feed gas from the Mercury Removal System is fed to the electric-powered Defrost
Gas Heater, 15-ML01, at 22°C. During the start up, the Defrost Gas Heater is set to warm
the feed gas to 60°C temperature (downstream of 15-PV-1117) but will vary depending on
phase of startup.
Warm feed gas at 60°C is used as defrost gas which is necessary for drying certain
equipment such as the Main Cryogenic Heat Exchanger and cryogenic pumps and
compressors during the start up operations. Defrost gas is also used during the following:
• Pre-cool down
• Cool down
• Cold restart
• Warm up
The drying process ensures that the moisture content and heavy liquids are removed from
the equipment to prevent any freezing during normal operations. After the drying is
completed, all the defrost gas headers to the connected equipment remain shut during
normal operations. However, defrost gas to the Cold Flare KO Drums 65-MD02-A/02B,
Startup LNG/BUPRO Flash Drum 65-MD05, Cold/Heavy Liquid Drum 65-MD07, Common
Flare KO Drum 65-MD10 remains open because it is used to vaporize liquid in the drums.
Defrost Gas Heater, 15-ML01, supplies external seal gas to the compressors 15-MJ04, 16-
MJ01/02/03, and 71-MJ05-A/B/C. A continuous minimum flow passes through the heater to
the HP Fuel Gas KO and Mixing Drum, 15-MD05-A/B, to prevent the electric-powered
Defrost Gas Heater, 15-ML01, from overheating and tripping. If the Defrost Gas Heater
outlet reaches 100°C (taken from 15-TT-1118), the power supply will be cut off.
Page 6 of 15 KBR
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
3.0 OPERATIONS
3.1 Normal Running
The Defrost Gas Heater, 15-ML01, is electric powered and is a thyristor controlled system.
The heated defrost gas pressure is controlled by 15-PIC-1117 at 5.5 barg by throttling the
flow of defrost gas through 15-PV-1117.
Defrost and Seal Gas temperatures are controlled by 15-TIC-1119 which regulates the
heater’s thyristor power regulator. The seal gas supply operates at about 62 barg and about
80°C. After passing through the 15-PIC-1117, the pressure drops to about 5.4 to 8 barg
(depending on the desired setpoint selected) and the temperature drops to about 60°C for
the defrost gas portion of the header.
Shutdown valve 15-XV-1126 and interlock I-1582 are provided upstream of valve 15-PV-
1117. Temperature transmitter 15-TT-1116 provides input to interlock I-1582 which trips 15-
XV-1126 closed at 65°C and closes 15-PV-1117 to avoid sending Defrost gas to the header
above 65°C. If the downstream temperature is too high, the upstream temperature can be
lowered a few degrees so that both upstream and downstream temperatures are within an
acceptable range.
After completing the drying process for startup or maintenance, all the defrost header valves
must be in closed, except cold flare sparge gas supply and the continuous minimum flow to
the fuel gas system.
During the normal operations, Defrost Gas & Seal Gas System remains active providing seal
gas back up for the compressors 15-MJ04, 16-MJ01/02/03, , 71-MJ05-A/B/C.
3.2 Typical Operating Parameters
The following table contains typical operating variables for the Defrost Gas & Seal Gas
System.
Operating Variables for the Defrost Gas & Seal Gas System
Tag No. Description Typical Value Units
15-PIC-1117 Defrost Gas Header Pressure 5.4 to 8 barg
Controller
15-TIC-1119 Defrost Gas Temperature Controller 80 °C
15-TI-1123 Defrost Gas Temperature Indicator ~60 °C
3.3 Temporary Operation
Not-applicable.
Page 7 of 15 KBR
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
4.0 START-UP
This section outlines the steps necessary to place the Defrost Gas & Seal Gas System in
service. For the purpose of this section of the operating manual, it is assumed that the
following conditions exist: utilities are in service, feed gas is available, downstream units are
ready to receive the warm feed gas, electrical power is available and Defrost Gas & Seal
Gas system is purged and ready for start-up.
1. Confirm defrost gas header pressure controller 15-PIC-1117 is in manual and closed.
2. Confirm isolations valves to defrost and seal gas users are closed.
3. Slowly open the 4” isolation ball valve in line NG-15018-4” from the dry feed gas
upstream of the Feed Gas/HP Propane Cooler, 15-MC01, and pressurize the Defrost
Gas Heater, 15-ML01, and seal gas header.
4. Line up minimum flow from the heater to the HP Fuel Gas KO and Mixing Drum, 15-
MD05-A/B, through PG-15350-2”.
5. Put heater temperature controller 15-TIC-1119 on automatic at a set point of 80ºC.
This temperature will vary depending on the phase of MCHE cool down. Refer to the
APCI cooldown procedure for the MCHE.
6. Put defrost gas pressure controller 15-PIC-1117 on automatic at a set point of 5.5 barg.
7. Place the thyristor heater control Local / Remote hand switch 15-HS-1136 to Remote.
8. Place power switch 15-HS-1121 to the ‘ON’ position to start the heater.
9. Line up seal gas to seal gas users.
10. Line up defrost gas to users as needed.
11. Adjust 15-TIC-1119 as needed to satisfy temperatures for the seal gas supply and
defrost gas header.
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NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
5.0 SHUTDOWN
5.1 Normal Shutdown
The following steps are based on a planned shutdown of the Defrost Gas & Seal Gas
System.
1. Communicate with operating personnel in all units that use the Defrost Gas and Seal
Gas to ensure that they know that the supply to them will be stopped and that they
accept it. The Cold Flare and Common/Existing Flare Systems will not have Defrost
Gas to vaporize liquids in the Cold Flare KO Drums 65-MD02-A/02B, Startup
LNG/BUPRO Flash Drum 65-MD05, Cold/Heavy Liquid Drum 65-MD07, and Common
Flare KO Drum 65-MD10.
2. Isolate defrost gas and seal gas from users.
3. Place the Defrost Gas Heater, 15-ML01, thyristor heater control Local / Remote
handswitch, 15-HS-1136, to Local.
4. Place power switch 15-HS-1121 to the ‘off’ position to shutdown the heater.
5. Discontinue minimum flow through heater to the HP Fuel Gas KO and Mixing Drum, 15-
MD05-A/B, and isolate heater feed.
5.2 Process Upsets and Production Loss
In the event of a change in conditions or trips, the process may become upset and possibly
require shutdown. In an emergency requiring a shutdown of the Defrost Gas & Seal Gas
System, the system should be shut down as outlined above. Below are possible causes for
upset and actions to be taken.
1. Loss of Electrical Power
Loss of electrical power will shutdown the Defrost Gas Heater, 15-ML01, and will cause a
decrease in the temperature of Defrost & Seal Gas system and could affect any defrost
activities, or interrupt the external seal gas supply to the compressors.
2. Loss of Instrument Air
Loss of instrument air will cause control valves to fail to their safe position. Consequences of
the loss of instrument air for the major control and isolation valves are given below:
• 15-ESDV-1185, 15-ESDV-1196, 15-XV-1126 and 15-PV-1117 will fail close.
• 15-XV-1186 will fail open.
Seal gas will continue to be supplied by feed gas from 01-IC03.
3. Loss of Feed Gas
On loss of dry feed gas from the Mercury Removal System, moist feed gas from 01-IC03 will
be used as seal gas. Defrost gas operations must be suspended to avoid moist gas from
flowing to low temperature sections.
On total loss of feed gas, the Defrost Gas & Seal Gas System will be shutdown.
Page 9 of 15 KBR
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
6.0 SAFETY/EMERGENCY SHUTDOWN
6.1 Safety Critical Shutdown Systems
6.1.1 I-1500 - Liquefaction, Unit 15 ESD
The Liquefaction Unit ESD Interlock I-1500 is activated by the Plant ESD Interlock I-0000.
The Liquefaction Unit ESD Interlock I-1500 takes action in Scrub Column System by closing
feed gas to Feed Gas/HP Propane Cooler, 15-MC01, valve 15-ESDV-1196; closing Scrub
Column, 15-MD01, overheads to MCHE valve 15-ESDV-1277; closing Scrub Column Reflux
Drum, 15-MD02, overheads to MCHE valve 15-ESDV-1143; tripping Scrub Column Bottoms.
The Liquefaction Unit ESD Interlock I-1500 takes action in the Defrost Gas & Seal Gas
System by tripping Boil Off Gas Header Vacuum Break interlock I-1515 and Defrost Gas
Heater Trip interlock I-1580.
6.1.2 I-1515 - Boil Off Gas Header Vacuum Break
The Boil Off Gas Header Vacuum Break Interlock I-1515 opens wet feed gas valve to supply
secondary source of gas for vacuum relief, purge gas, or backup seal gas on low dry gas
pressure from 15-PAL-1184 or Liquefaction Unit ESD Interlock I-1500. The interlock opens
the wet gas to recycle gas header valve 15-XV-1186, and closes the dry gas valve 15-
ESDV-1185.
The reset hand switch 15-HS-1184 opens 15-ESDV-1185 and closes 15-XV-1186, the
recycle gas pressure returns to normal operating.
6.1.3 I-1580 - 15-ML01 Defrost Gas Heater Trip
Defrost Gas Heater, 15-ML01, Trip Interlock I-1580 trips the Defrost Gas Heater, 15-ML01,
on Hi-Hi defrost gas temperature by heater trip signal 15-XY-1255 or Liquefaction Unit ESD
Interlock I-1500.
6.1.4 I-1582 – Defrost Gas to Distribution Trip
Defrost Gas to Distribution Trip Interlock I-1582 trips 15-XV-1126 closed on Hi-Hi Defrost
Gas Temperature, 15-TAHH-1116 and also closes 15-PV-1117.
Page 10 of 15 KBR
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
6.2 Pressure Safety Valve Summary
The Defrost Gas & Seal Gas System Pressure Relief Valve Summary contains a listing of all
the pressure relief valves associated with this system.
Defrost Gas & Seal Gas System Pressure Relief Valve Summary
Set Pressure
Valve Number Description/Location (barg)
15-PRV-1116 15-ML01 Defrost Gas Heater Effluent/Relief to 75
Cold Flare Header
15-PRV-1194 Defrost Gas Distribution Header/Relief to Cold 10
Flare Header
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NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
6.3 Fire Protection Equipment
The Defrost Gas & Seal Gas System Fire Protection Equipment Summary is included in
below listing of Liquefaction Unit Fire Protection Equipment
Defrost Gas & Seal Gas System Fire Protection Equipment Summary
Description Quantity
Refrigeration Cooling Area
63-SP-005 Fire Blanket 2
63-SP-008 Fire Water Monitor (Grade) 5
63-SP-010 Live Hose Reel 3
63-SP-011 Hydrant Cabinet 4-Way 2
63-SP-024 Firewater Monitor Mounted on Four Way Hydrant 2
63-SP-050 Fire Water Monitor (Elevated) 3
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NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
7.0 ATTACHMENTS
The following attachments are included in this section of the Operating Manual:
7.1 Attachment I: Equipment List
7.2 Attachment II: Utility Consumption
Page 13 of 15 KBR
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
7.1 Attachment I: Equipment List
The following is a list of equipment associated with the Defrost Gas & Seal Gas System.
Defrost Gas & Seal Gas System Equipment List
Design Design
Equipment Pressure Temp
No. Description (barg) (ºC)
15-ML01 Defrost Gas Heater 75 110/-15
Page 14 of 15 KBR
NEW LNG TRAIN SKIKDA PROJECT DOCUMENT NO.
SKIKDA, ALGERIA PP-AAA-PP1-117
OPERATING MANUAL VOLUME I, SECTION 6-1: REVISION 1
DEFROST GAS & SEAL GAS 17 DECEMBER 2012
7.2 Attachment II: Utility Consumption
Following are the equipment associated with the Defrost Gas & Seal Gas System and their
expected consumption.
Defrost Gas & Seal Gas System
Available
Electrical
Load
Equipment No. Description (kW)
15-ML01 Defrost Gas Heater 1570
Page 15 of 15 KBR
