Procedure for Setting the Nitrogen System
The nitrogen generator is in automatic mode and the buffer tank pressurised.
a) Ensure that the manual isolating valves situated each side of the regulator control valves, both supply and exhaust for the headers are open:
Position Description Valve
Open Primary barrier header supply regulator inlet valve C568 Open Primary barrier header supply regulator outlet valve C567 Closed Cross-connection onto the secondary barrier header C577 Open Secondary barrier header supply regulator inlet valve C569 Open Secondary barrier header supply regulator outlet valve C565 Closed Header line isolating valves to the vacuum pumps C575 Open Primary barrier header exhaust regulator inlet valve C556 Open Primary barrier header exhaust regulator outlet valve C560 Open Secondary barrier header exhaust regulator inlet valve C557 Open Secondary barrier header exhaust regulator outlet valve C561 Closed Standby exhaust regulator cross-connecting valves C555 C554 b) Open the manual isolating valves to the primary and secondary
barriers spaces to each tank:
Position Description Valve
Open No.4 cargo tank secondary barrier N2 isolating valves C501 C500 Open No.4 cargo tank primary barrier N2 isolating valve C502 Open No.3 cargo tank secondary barrier N2 isolating valves C512 C510 Open No.3 cargo tank primary barrier N2 isolating valve C514 Open No.2 cargo tank secondary barrier N2 isolating valves C524 C522 Open No.2 cargo tank primary barrier N2 isolating valve C526 Open No.1 cargo tank secondary barrier N2 isolating valves C536 C534 Open No.4 cargo tank primary barrier N2 isolating valve C538 From the IAS display screen set up the primary and secondary barrier regulator valve header values for each system.
Section 5.2 - Page 2 of 4
Issue: 1 Heading - Page x of x Issue: 1
Illustration 5.2a Nitrogen Pressurisation and Control
PT PT PT
N2Buffer Tank C621
Regulating Valve for Inlet to Primary Insulation Space set at 0.4kPa Regulating Valve for Inlet to Secondary
Insulation Space set at 0.4kPa
Pressure Header
C577 C576 C575 C574
C579 C578
Cofferdam Tank 3 Tank 2
Tank 4 Regulating Valve for Exhaust
of Primary Insulation Space set at 0.9kPa abs Regulating Valve for Exhaust
of Secondary Insulation Space set at 0.7kPa
Section 5.2 - Page 3 of 4
Issue: 1
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c) Adjust the set point of the nitrogen supply regulating valves C566 to the primary header and C567 to the secondary header at 0.4kPa gauge and 0.2kPs gauge.
d) Adjust the set point of the nitrogen exhaust regulating valves C558, primary and C559, secondary at 0.6kPa and 0.4kPa gauge.
e) Open the manual isolating valves C621 and C619 on the insulation space pressurisation header and set the control valve C620 to 420kPa, to allow a supply of nitrogen to the headers from the nitrogen buffer tank in the engine room.
The system will automatically adjust the pressures in the primary and secondary barrier insulation spaces, exhausting if the pressure exceeds the exhaust valve set point and making it up if it falls below the supply valve set point. The pressurisation header control valve C620 can be adjusted to a higher value if the supply to the insulation spaces during the loading of the vessel is unable to allow for the greater demand as the primary and secondary barrier insulation spaces cool down.
CAUTION
The insulation spaces must at all times be protected against overpressure, which might otherwise result in membrane failure.
Section 5.2 - Page 4 of 4
5.3.2 Cofferdam Heating and Control 5.3.3 Hull Ventilation
Illustrations
5.3.1a Glycol Water Heater 5.3.2a Cofferdam Heating System
Issue: 1 Heading - Page x of x
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Issue: 1
TI TI TT
TS TS TS TS
PT PI TI
TT
PI PI PS
PI TT
Illustration 5.3.1a Glycol Water Heater Key
Glycol Glycol (Standby) Desuperheated Steam Air
Condensate Fresh Water Electrical Signal Air Eliminator Glycol Expansion Tank
1m3 LG
LS Glycol Reserve Tank
6m3 LG
Gauze Diaphragm (Located in Safe
Area)
Gauze Diaphragm
Filling Connection
Mixing Tank 0.2m3 Fresh Water
Supply
Compressed Air
To Drain
From Electric Motor Room (Usual Load)
To Electric Motor Room (Usual Load)
TI TS TT
TIC
TI
Glycol Water Heater No.1 (High Load) Steam Supply
Steam Drain
PT PI TI
TT
PI PI PS
PI TT From Electric
Motor Room (Standby Load)
To Electric Motor Room (Standby Load)
TI TS TT
TIC
TI
Glycol Water Heater No.2 (High Load) Steam Supply
To Drain Steam Drain
S040
S041 Electrical Glycol
Water Heater (Normal Load) Glycol Water
Circulating Pump No.1 32m3/h at 30mth
Glycol Water Circulating Pump No.2
32m3/h at 30mth Glycol Water
Pneumatic Pump
Cargo Electrical Room
A
AA
Section 5.3.1 - Page 1 of 2
Issue: 1
5.3 COFFERDAM HEATING SYSTEM
5.3.1 GLYCOL WATER HEATERSteam Glycol Heaters
Maker: Gefico Enterprise
No. of sets: 2
Type: Straight tube
Glycol flow: 32m3/h Inlet temperature: 75°C Outlet temperature: 90°C Heating steam: 7 bar(a) Transfer thermal energy: 400kW
Capacity: 24,665kg/h glycol water
Electric Glycol Heater
Maker: Termoelectrica Vila S.A.
No. of sets: 1
Type: Continuous Glycol flow: 32m3/h Outlet temperature: 90°C
Capacity: 24,665kg/h glycol water Heating elements: 90kW (3x 30kW)
Glycol Water Pump
Make: Bombas Azcue. S.A.
No. of sets: 2
Type: Horizontal centrifugal pump Capacity: 32m3/h at 30mth
The glycol water heating system is located in the cargo motor room and serves the purpose of heating glycol water which is pumped around the cofferdam system to maintain the temperature inside those spaces at approximately +5°C.
As requested by the I.G.C. Code this system is ‘fully redundant’, where every part of the system is doubled by a standby unit, from the source of heat, two boilers, to the heat exchangers and heating coils.
The liquid dome space, which is an enclosed space, is also provided with this heating system which is normally operational during cargo operations.
Each cofferdam is fitted with two sets of heating coils, one set fixed on the aft bulkhead and the other on the forward bulkhead. Each set of coils is designed for 100% capacity at design conditions.
Each liquid dome is fitted with two sets of heating coils fixed on the casing wall. Each set of coils is designed for 100% capacity at design conditions.
The system is comprised of:
• Two glycol water centrifugal circulating pumps which are rated at 32m3/h
• Two 100% steam heaters (high load demand) with steam demand regulating valve
• A single 90kW electric heater (normal load demand)
• A glycol expansion tank of 1,000 litres capacity
• A glycol storage tank of 6,000 litres capacity
• A glycol mixing tank of 200 litres
• One pneumatically operated expansion tank topping up pump
The glycol high loading steam heaters are heated from the low pressure steam generator supply range, with the condensate drains passing back to the engine room via the contaminated steam drains system.
The electric glycol heater which is used for the normal heating demand is fitted with a range of heater banks, three each of 30kW.
Alarms
Tag Description Low High
5720
TT2003 No.1 heater outlet temperature 55°C 90°C TT2005 No.2 heater outlet temperature 55°C 92°C TT2004 No.1 heater control temperature 35°C 92°C TT2007 No.2 heater control temperature 42°C 95°C TT2002 Standby coil return header 10°C TT2001 Main coil return header
PT2008 No.1 heater inlet pressure 1.5 bar 4.0 bar PT2004 No.2 heater inlet pressure 2.0 bar 4.0 bar
Section 5.3.1 - Page 2 of 2
Issue: 1 Heading - Page x of x
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Issue: 1
Illustration 5.3.2a Cofferdam Heating System
Key
Glycol Glycol (Standby) Electrical Signal Air Eliminator
No.5 Cofferdam No.4 Cofferdam No.3 Cofferdam No.2 Cofferdam No.1 Cofferdam
TT TT
TC
TT TT TT
A A
TC TC TC TC TC
A A
A A
A A
A A
A
Tank 4 Liquid Dome Tank 3 Liquid Dome Tank 2 Liquid Dome Tank 1 Liquid Dome
TT TC
A A
TT TC
A A
TT TC
A A
A
Main Supply Line Standby Supply Line
Standby Return Line Main Return Line To/From Cargo Electrical Room
TT
Section 5.3.2 - Page 1 of 4
Issue: 1
5.3.2 COFFERDAM HEATING AND CONTROL
The cofferdam heating system is a semi sealed system where the glycol/water mixture is contained within the system. Expansion in the system is allowed for by a 1,000 litre expansion tank.
The level in the system is maintained by glycol from the reserve header tank being mixed with fresh water in the 200 litre mixing tank to the required glycol to water ratio of 45%. When the system is required to be topped up, this mixture is fed to the expansion tank by a pneumatic pump.
The temperature inside the cofferdam is affected by the temperature of the ballast spaces, the outside air temperature and the cooling effect from the cargo tanks. The purpose of this system is to ensure that the cofferdam is kept at 5°C when the cargo tanks are in a cold condition. During ballast voyages the heating coils are not normally in use.
Each cofferdam is heated by two independent systems, one is in service while the other is on standby.
The maximum heating condition is determined by the following extreme operating conditions:
• External air temperature: -18°C
• Sea water temperature: 0°C
The heating requirements for the individual cofferdams and tank casings are as follows, the length of the heating coils for the main and standby systems are also indicated:
• No.1 cofferdam 56.815W - heating coil length of 344m x 2
• No.2 cofferdam 86.241W - heating coil length of 522m x 2
• No.3 cofferdam 86.241W - heating coil length of 522m x 2
• No.4 cofferdam 86.241W - heating coil length of 522m x 2
• No.5 cofferdam 44.859W - heating coil length of 272m x 2
• No.1 tank casing 2,943.5W - heating coil length of 15m x 2
• No.2 tank casing 2,943.5W - heating coil length of 15m x 2
• No.3 tank casing 2,943.5W - heating coil length of 15m x 2
• No.4 tank casing 2,943.5W - heating coil length of 15m x 2
Any failure of the cofferdam heating system with cargo on board must be treated as serious and repairs must be made immediately. In the case of suspected leaks, regular soundings of the cofferdams will indicate into which space glycol water is leaking. Each cofferdam is fitted with temperature sensors on each forward and aft bulkhead which will also give an early indication of a heating tube failure.
Any accumulation of water in the cofferdam areas can be pumped out using the pneumatically operated water drain pumps, which are located in each of the cofferdam spaces.
System Operation
There are two independent glycol circulation systems, classified as main and standby. Each system discharges to its respective coils in the cofferdams via dedicated steam heaters, although they share a common electric heater and expansion tank via a series of crossover valves. The electric heater is used during normal load conditions and the steam heaters are used for high load conditions.
The flow of the glycol/water mixture to each set of heating coils is through a three-way and throttling valve on the inlet side to the heating coils. The standby circulation system can be put into service immediately in the event of a failure of the main circulation system. Additionally, in the event of failure of either pump or cofferdam heating coils, it is also possible to cross-connect the systems via a series of crossover valves on the suction and discharge sides of the pumps and on the discharge side of the heaters.
The automatic temperature control to each circuit is controlled by steam regulating valves on each steam heater and by the automatic switching in/out of the heating banks on the electric heater, controlling the temperature as required.
A temperature element at the top of each cofferdam sends a signal to its respective three-way temperature flow control regulating valve both on the main and standby system. The three-way control valve will regulate the glycol flow either into the bank of coils or via the bypass line and thereby maintain the cofferdam space at the required temperature of 5°C.
The automatic flow control to each cofferdam and liquid dome is achieved by means of a three-way valve on each header. Throttling valves on each header return line are set after conducting trials and should not be adjusted unless in a problematic situation.