OPERADORES NO ACOTADOS
Lema 6.3. Si T es esencialmente autoadjunto, entonces T tiene una ´unica ex- ex-tensi´ on autoadjunta 9
494 405
493
492
491
062 CL042F0
487 483 485
020
010
030
040
XH5321G
Key
Degassing Line Into Main Cargo Pump Cable Penetration
Dry Air Inert Gas 1
2
1
2
To Engine Room
To Insulation Spaces
Dry Air from Engine Room
LD Compressor No. 1 (Inboard)
Dual Purpose Heaters
Main Vaporiser Demister
Forcing Vaporiser HD Compressor No. 1
(Inboard)
HD Compressor No. 2 (Outboard)
LD Compressor No. 2 (Outboard)
Vent Gas Heater
1 2
1 2
Jettison
Tank 1
Tank 4
Tank 2
Tank 3
Liquid Dome
Vapour Dome
Liquid Dome
Vapour Dome
Liquid Dome
Vapour Dome
Liquid Dome
Vapour Dome
4.3.6 Aerating Introduction
Prior to entry into the cargo tanks the inert gas must be replaced with air.
With the Inert Gas and Dry-Air System (see 2.6) in Dry-Air production mode, the cargo tanks are purged with dry air until a reading of 20% oxygen by volume is reached.
Operation
The Inert Gas and Dry-Air System produces dry air with a dew point of -55°C to -65°C.
The dry air enters the cargo tanks via the vapour header, to the individual vapour domes.
The inert gas/dry-air mixture is exhausted from the bottom of the tanks to the atmosphere at No. 2 mast riser via the tank loading pipes, the liquid header, and removable bend CL/042FO.
During aerating the pressure in the tanks must be kept low to maximise a piston effect.
The operation is complete when all the tanks have a 20%
oxygen value and a methane content of less than 0.2% by volume (or whatever is required by the relevant authorities) and a dew point below -40°C.
Before entry test for traces of noxious gases (carbon dioxide less than 0.5% by volume, and carbon monoxide less than 50ppm) which may have been constituents of the inert gas. In addition take appropriate precautions as given in the Tanker Safety Guide and other relevant publications.
The pressure in the tanks is adjusted to 1020 mbars a.
Aeration carried out at sea as a continuation of gas freeing will take approximately 20 hours
! WARNING
Take precautions to avoid concentrations of inert gas or nitrogen in confined spaces which could be hazardous to personnel. Before entering any such areas, test for sufficient oxygen > 20% and for traces of noxious gases: CO2< 0.5% and CO < 50 ppm.
The operating procedure is as follows: (see figure 4.3.6a)
• Prepare the inert gas plant for use in the dry air mode.
• Install the spool piece CL.042FO for venting the
mixture inert gas / dry air from the LNG header.
• At the vent mast No. 2, open the valves 062; 483, 485.
Adjust the set point of 487 at 20 mbars above atmospheric pressure.
• Open the filling valves 040, 030, 020, 010 on each tank.
• Open the vapour valves 494, 493, 492, 491 on each tank.
• On the dry air/inert gas discharge line, open the isolating valve XH/5321G located before the two non return valves. Change the spectacle blank over into the open position, which is located after the non return valves on A deck forward of the accommodation block port side.
• Start the dry air generator.
• Open the valves 460, 405 to supply dry air to the vapour header.
• Observe the tank pressures and insulation space pressures, to ensure that the tank pressures are higher than the space pressures by 10mbar.g at all times.
• Approximately once an hour, take samples from the filling pipe test connections to test the discharge from the bottom of the tanks for oxygen content.
• When the oxygen content reaches 20%, isolate and shut in the tank.
• When all the tanks are completed and all piping has been aired out, raise the pressure to 100mbar g in each tank and shut the filling and vapour valves on each tank. Restore the tank pressure controls and valves to vent from the vapour header.
• During the time that dry air from the inert gas plant is supplied to the tanks, use the dry air to flush out inert gas from vaporisers, compressors, gas heaters, crossover’s, pump risers and emergency pump wells.
Piping containing significant amounts of inert gas should be flushed out. Smaller piping may be left filled with inert gas or nitrogen.
! CAUTION
During the time a tank is opened for inspection, dry air will be permanently blown through the filling line to prevent the entry of humidity from the ambient air.
4.3 Out of Service Operations - Page 11 Issue: 1
Cargo Systems and Operating Manual LNG LERICI
Fire in Cargo Area and Use of Dry Powder Operate ESDS to stop cargo operations.
Sound ships fire alarm.
Start water spray pumps.
Stop vent fans and secure crew quarters zone.
If vessel is in port the fire fighting gear (pressurised fire main) will already be arranged on deck.
Fire parties should be dressed in fire suits with B.A.
Using a fine water spray curtain, ensure that the source of fuel (gas/liquid) to the fire is isolated.
Dry powder either through hand held hoses or fixed monitors is the most effective fire fighting medium.
Firefighting Procedures
Although the flash point of LNG is -175°C, the rapid vapourisation of any exposed LNG prevents any ignition of the liquid itself and an LNG fire is thus a cold vapour fire.
Ignition of a flammable mixture of natural gas vapour requires a spark of similar ignition energy as would ignite other hydrocarbon vapours. The auto-ignition temperature of methane in air (595°C) is higher than other hydrocarbons.
Electrostatic ignition on LNG is not a hazard during normal operations. This is because the permanent, positive pressure in LNG tanks maintained by gas boil-off prevents air entering these spaces to form flammable mixtures in tanks or lines.
Burning of LNG vapours produces a similar flame size and heat radiation to other hydrocarbon fires, but little smoke is produced.
From a firefighting viewpoint LNG/cold vapour fires have the characteristics of both liquid and gaseous hydrocarbon fires.
The procedure for fighting these fires is:
a) Isolate the source of leak, stop loading/discharging, shut all manifold valves.
b) Sound the alarm.
c) Provide protection for adjacent equipment and for firefighters.
powder. Do not agitate the surface of any pool of LNG.
e) Remain on guard against possible re-ignition.
The exact procedure will depend upon the nature of the incident.
Firefighting
The following firefighting media can be used
Water
Water should not be used to extinguish LNG fires.
A water spray or fog should be used to protect personnel and to cool areas adjacent to the fire.
Care is necessary to avoid water running off any adjacent structure and aggravating burning LNG, or splashing into spill trays which may contain LNG, thus causing them to overflow onto unprotected steelwork.
Foam
Foam adequately applied to a depth of between 1 and 2m, will largely suppress the radiation from the flame to the liquid below, thereby reducing the vaporisation rate and rate of burning. The difficulty arises in trying to contain the foam mat covering, due to the lack of structures acting as containment areas and the effects of wind dispersing the foam.
High expansion foam has been used successfully on LNG pool fires. If a stable foam is used, it has been found that if is freezes at the interface, the rate of vaporisation is reduced. If, on the other hand, the foam breaks down into the liquid beneath, the vaporisation rate may increase. In general, unless the foam can be contained, foam fixed installations are not fitted to LNG ships for liquified gas firefighting.
Smothering Systems
CO2 and nitrogen smothering systems are only effective when injected into enclosed spaces, or spaces that can be isolated by the closing of doors, flaps and hatch covers.
The process by which these gases fight fires, is by displacing oxygen to a level which will not support combustion. It is therefore not considered practical for fighting fires on the open cargo deck.
The extinguishing power of dry chemical powder depends on the chemical reaction of the small particles when exposed to flame. They are flame inhibiting agents and have been widely proved in LNG fire tests.
Various types of powder are marketed, potassium based powders are more effective than sodium based or multi-purpose powders, but not all are foam compatible. All powders are liable to compact when subject to humid conditions or vibration, so filling and maintenance instructions should be carefully observed.
The maximum possible rate of application of dry powder is desirable. As many high velocity jets as possible should be brought to bear at once, preferably in a down wind direction. Jets should be aimed with the objective of reducing boil-off rate by sweeping over whole fire area and on no account must the surface of LNG pool be agitated. Possible re-ignition must be guarded against.
Fire in the Cargo Compressor Motor Room
The cargo compressor and motor rooms are protected by a fixed CO2smothering system consisting of 18 cylinders, each with a capacity of 60 litres. They are arranged in 2 banks that are housed in the CO2 bottle store, which is located aft of the motor room. The compressor room requires all 18 of the CO2cylinders, while the motor room requires 9 of the 18 CO2cylinders.
Injection of CO2is carried out from designated compressor and motor room control box stations, located in the CO2 bottles store. Operating instructions are contained inside the control box stations. Opening the control box station door trips the ventilation fans.
Ventilation of Hazardous Spaces
No tank, cofferdam or other enclosed space may be entered until it has been thoroughly ventilated. The atmosphere must be tested for hydrocarbons and oxygen and a safe entry certificate issued by a responsible officer.
The compressor house and motor room fans must be running at all times.
Ballast tanks and cofferdams must be ventilated and atmospheres tested, and safe entry permits issued by responsible officer prior to entry.
Safety trolley to be standing by point of entry.
Personnel entering must be kitted out with cap lamp and battery, cyalume light stick, VHF transceiver and personal oxygen analyser.
Rollover
• The rollover phenomenon is characterised by a sudden rapid generation of vapour. This problem arises because LNG is a multi-component mixture whose boiling point increases as its density increases.
It mainly occurs in the land storage tanks when an heavier, warmer liquid is added to the bottom of a tank containing a lighter liquid. The energy transmitted into the tanks contents though the walls is partially used to vapourise the lighter layer and to warm-up the heavier layer. When its density approaches that of the lighter layer, it suddenly rises and, without the confining effect of the colder layer, rapid boiling and mixing occur. If exhaust devices and vents have insufficient capacity to handle the vapour so generated, tank failure may result.
• Rollover is not expected to occur on ship since the motions in open sea serve to mix the cargo.
4.4 Emergency Operations and Procedures - Page 1 Issue: 1
4.4.1a Cargo Discharging Without Gas Return From Shore Issue: 1