Section
4 System Design
4.1 General
4.1.1 Materials, components and equipment to be used in the construction of
regasification systems shall be suitable for the intended service conditions and
acceptable to LR. The materials, components and equipment shall also satisfy the
requirements of this Section.
4.1.3 The design, arrangements and selection of equipment shall be such as to
minimise the risk of fire and explosion from flammable products.
4.1.5 Any single failure of the regasification system shall not result in a
hazard that affects safety.
4.1.6 The regasification barge or offshore unit shall have adequate
capability for managing the boil-off gas generated by heat ingress through headers,
manifolds flexible hoses and loading arms during barge or offshore unit-to-ship
transfer operations.
4.1.7 The regasification system shall include provision to pre-cool the
product transfer piping system prior to barge or offshore unit-to-ship transfer
operations commencing.
4.2 Vaporisers
4.2.1 The requirements of these Rules apply to various types and designs of
vaporiser and process units, such as:
- Heat exchanger designs including:
- STV – Shell and tube heat exchanger type.
- PCHE – Printed circuit heat exchanger.
- AHHE – Air heated heat exchanger utilising forced
ventilation.
- CWHE – Coil wound heat exchanger.
- ORV – Open rack type utilising sea-water or a circulating
intermediate heated fluid.
- SCV – Submerged combustion type utilising the heat of
combustion of either oil or send-out gas.
4.2.3 The manufacture, installation and testing of vaporisers, including the
intermediate heat transfer vessels and pumping systems, shall be undertaken in
accordance with these.
4.2.4 All LNG high pressure pumps supplying vaporisers, which are capable of
developing a pressure exceeding the design pressure of the system into which they
are pumping, are to be provided with relief valves in closed circuit.
4.2.5 For STVs and ORVs, sea-water may be used as a primary heat source for
vaporisation. An intermediate heat transfer fluid may be proposed to reduce the
chance of freezing and effects of corrosion.
4.2.6 Where sea-water is used as the source of heat to vaporise the LNG, the
tubes shall be manufactured from a corrosion-resistant material, taking into
consideration the type and temperature of media conveyed. Where the ✠Lloyd’s
RGP+ Notation is to be assigned, suitable redundancy of the sea-water
circulation pump and LNG high pressure supply pumps shall be provided.
4.2.7 When an intermediate heat transfer fluid is used, and where the
✠Lloyd’s RGP+ Notation is to be assigned, dual compressors or circulating
pumps shall be provided. Where the heat transfer fluid goes through a phase change,
the applicable Sections of Pt 6, Ch 3 Refrigerated Cargo Installations shall be complied with.
4.2.8 Where potential risk of failure of a tube or passage could result in
gas entering the sea-water side:
- the sea-water side shall be designed to accept the full gas
pressure of the gas side;
- the sea-water side shall be protected with bursting discs or
relief valves in readily visible positions; the discharge from these
bursting discs or relief valves shall be taken to a suitable high-pressure
venting arrangement and the number and position of bursting discs or relief
valves shall be adequate to relieve the flow occurring due to failure of a
single tube.
4.2.9 If steam is used in a heat exchanger containing LNG, propane or other
flammable gas, the condensate shall not be passed directly back to the machinery
room. The steam-condensate shall be passed through a degassing tank located in a
gas-dangerous area. The vent outlet from the degassing tank shall be routed to a
safe location and be fitted with a flame screen. The degassing tank shall be fitted
with a gas detection and alarm system, see
Pt 11, Ch 13, 1.6 Gas detection.
4.2.10 If the barge or offshore unit is to operate in regions where
insufficient natural sources of heat are available for vaporisation, e.g. due to low
sea-water temperature, the design gas output conditions shall be maintained
utilising alternative means.
4.2.11 Where alternative means of heating the LNG are required, an independent
gas or oil supply system shall be provided to facilitate initial start-up.
4.2.12 The regasification system may operate with a dual heat source with, for
example, a mixture of heat inputs from sea-water and a boiler.
4.2.13 Where aluminium alloy vertical tubes and horizontal headers are
constantly covered with sea-water, adequate protection against corrosion shall be
provided.
4.2.15 Water supply pumps shall be fitted with suitable inlet filters. It
shall be possible to remove and clean the filters whilst the regasification system
remains operational. Any regasification system-related sea-water inlet shall be
fitted with gratings and provision made to allow cleaning by low pressure steam or
compressed air.
4.2.16 A water treatment system shall be incorporated for use with submerged
combustion vaporisers to eliminate degradation of the tubes.
4.3 Gas detection system
4.3.1 In addition to the gas detection system fitted to allow compliance with
Pt 11, Ch 13 Instrumentation and Automation Systems, a permanently installed system of gas
detection and audible and visual alarms is to be fitted in:
- all enclosed spaces containing gas piping, liquid piping or
regasification equipment;
- other enclosed or semi-enclosed spaces where gas vapours may
accumulate;
- air-locks;
- secondary fluid expansion tanks;
- the condensate degassing tank.
4.3.2 Gas detection equipment is to be designed, installed and tested in
accordance with IEC 60079-29-1, an is to be suitable for the gases to be
detected.
4.3.3 The number and the positions of detection heads or sampling heads is to
be determined with due regard to the size and layout of the semi-enclosed space or
compartment and be in accordance with the equipment manufacturer’s recommendations.
Due regard is to be given to the air flow from compartment ventilation inlets and
outlets.
4.3.5 The gas detection is to be of the continuous monitoring type, capable of
immediate response.
4.4 Emergency shutdown (ESD) system
4.4.1 An emergency shutdown (ESD) system serving the regasification plant and
sub-systems and equipment shall be fitted and shall comply with the cause and effect
matrix shown in Table 20.4.1 ESD functional
arrangements as applicable.
4.4.2 The ESD system shall be activated by the manual and automatic inputs
listed in Table 20.4.1 ESD functional
arrangements. Any additional inputs shall only be included in
the ESD system if it can be shown that their inclusion does not reduce the integrity
and reliability of the system overall.
4.4.3 The ESD system shall return the regasification system to a safe static
condition, allowing remedial action to be taken. Due regard shall be given in the
design of the ESD system to avoid the generation of surge pressures within both the
liquid and vapour pipework.
4.4.4 The equipment to be shut down on ESD activation shall include manifold
valves during loading or discharge, and pumps and compressors associated with
transferring LNG and NG.
Table 20.4.1 ESD functional
arrangements
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Pumps
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Compressor
systems
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Valves
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Link
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| Shutdown action
Initiation
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Cargo pumps/cargo booster
pumps
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Spray/ stripping
pumps
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Vapour return
compressors
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Fuel gas compressors and
system
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Reliquefaction plant,
including condensate return pumps, if fitted
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Gas combustion
unit
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ESD valves
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Signal to barge or regas’
unit/shore link***
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| Emergency push buttons
(see
Pt 11, Ch 20, 4.4 Emergency shutdown (ESD) system 4.4.2)
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See Note 2
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| Fire detection on deck or
in compressor house*
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| High level in storage
tank
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See Notes 1 and 2
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See Notes 1 and 3
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See Note 1
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See Note 4
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| Signal from barge or regas’
unit/shore link
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See Note 2
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See Note 3
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n/a
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n/a
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| Loss of motive power to ESD
valves**
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See Note 2
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See Note 3
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n/a
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| Main electric power failure
('blackout')
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See Note 5
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See Note 5
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See Note 5
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See Note 5
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See Note 5
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See Note 5
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KEY
* Fusible plugs, electronic point temperature
monitoring or area fire detection may be used for this
purpose on deck
** Failure of hydraulic, electric or pneumatic
power for remotely operated ESD valve actuators
*** Signal need not indicate the event
initiating ESD
 Functional requirement
n/a Not applicable
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NOTES
1. These items of equipment can be omitted from
these specific automatic shutdown initiators provided the
compressor inlets are protected against cargo liquid
ingress.
2. If the fuel gas compressor is used to return
cargo vapour to shore, it shall be included in the ESD
system only when operating in this mode.
3. If the reliquefaction plant compressors are
used for vapour return/shore line clearing, they shall be
included in the ESD system only when operating in that
mode.
4. A sensor operating independently of the high
liquid level alarm shall automatically actuate a shut-off
valve in a manner that will both avoid excessive liquid
pressure in the loading line and prevent the tank from
becoming liquid full. These sensors may be used to close
automatically the tank filling valve for the individual tank
where the sensors are installed, as an alternative to
closing the ESD valve provided at eachmanifold connection.
If this option is adopted, activation of the full ESD system
shall be initiated when the high-level sensors in all the
tanks to be loaded have been activated.
5. These items of equipment shall be designed
not to restart automatically upon recovery of main electric
power and without confirmation of safe conditions.
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4.4.6 The number and location of additional shutdown positions shall be
determined by the type, number, location and position of the regasification plant,
sub-systems and equipment.
4.5 Process shutdown (PSD) system
4.5.2 The activation of the PSD shall stop the supply of LNG to the LNG
suction drum, high pressure LNG pumps and gas discharge valve. Where the
installation comprises a number of separate regasification systems the PSD may be
system-specific as well as initiating a full shutdown. A PSD functional arrangement
matrix commensurate with that shown in Table 20.4.1 ESD functional
arrangements shall be provided.
4.5.3 Manual PSD points shall be arranged at each regasification system’s
control station and at locations as determined by the type, number, location and
position of the regasification systems and equipment. The process shutdown points
shall be clearly indicated.
4.5.4 Process shutdown valves in liquid piping shall close fully under all
service conditions within an acceptable duration of actuation. Due regard shall be
given in the design of the process shutdown system to avoid the generation of surge
pressures within drain pipelines and collect tanks. Information about the closing
time of the valves and their operating characteristics shall be available on board
and the closing time shall be verifiable and reproducible.
4.5.5 The closure time for the shutdown valve referred to in Pt 11, Ch 20, 5.4 Piping system testing and non-destructive examination shall be measured from the time of manual or automatic
initiation to final closure and is made up of a signal response time and a valve
closure time. Valve closure time shall be such as to avoid surge pressure in
pipelines.
4.6 Depressurisation and blowdown
system
4.6.1 In accordance with ISO 23251 or equivalent.
4.6.2 A depressurisation and blowdown system shall be provided for
depressurising high pressures liquid, vapour and gas systems. Each high pressure
system may contain; liquid pumps, gas compressors, vessels, heat exchangers and
pipework.
4.6.3 Where a liquid depressurisation system is provided, adequate provision
shall be made in the design and installation for the effects of back pressure after
the blowdown valve and the resulting volume of vapour flash gas due to the pressure
drop.
4.6.4 Manual and automatic activation of the depressurisation system shall be
provided.
4.6.5 Manual activation shall be possible from each regasification system’s
control station, at the send-out manifold, and from other locations as determined by
the type, number, location and position of the regasification systems and equipment.
The depressurisation and blowdown system activation points shall be clearly
indicated.
4.6.6 Automatic activation shall be part of the emergency shutdown
arrangements.
4.7 System and pressure vessel
protection
4.7.1 Each regasification system and associated pressure vessel is to be
fitted with a form of secondary protection. This may take the form of pressure
relief valves or alternatively an instrument-based system.
4.7.2 Pressure relief and venting system
- Each regasification unit shall be provided with safety
relief valves and venting arrangements which are to be separate from the
venting arrangements serving the LNG storage tanks. High pressure safety
relief valves, headers, knock-out pots, collection tanks, drain drums and
vent masts shall be located within the cargo deck area.
- High pressure safety relief valves and venting arrangements
for liquid and gas shall be provided for each regasification system. The
safety relief valve support arrangements shall be suitable to withstand the
loads imposed by relief valve opening.
- Where multiple regasification systems are installed, the
design of pressure safety relief and venting arrangements shall consider the
maximum combined release rate.
- The gaseous phase safety relief valves shall be led to a
dedicated high pressure vent mast for the regasification system required by
(a). The high pressure vent mast shall be sized to handle the maximum
regasification capacity and to ensure safe dispersal of the gas.
- The liquid phase safety relief valves shall be led to a
knock-out pot, collection tank or drain drum having adequate capacity for
the maximum LNG inflow anticipated within the design of the regasification
unit. The collection vessel shall be fitted with a level switch to stop all
high pressure LNG pumps. Any LNG from the collection vessel shall be safely
drained back to the LNG storage tanks or be allowed to boil off and vapour
to be returned to the barge or offshore unit’s vapour header.
- LNG collection vessels shall be fitted with pressure safety
relief valves in accordance with Pt 11, Ch 5 Process Pressure Vessels and Liquids, Vapour and Pressure Piping Systems and Offshore Arrangements.
- Pressure safety relief valves and venting arrangements and
locations shall comply with Pt 11, Ch 8 Vent Systems for Cargo Containment .
4.7.3 Instrument-based system
- Instrument-based systems, in compliance with ISO 10418, may be
used for both primary and secondary protection provided it is implemented in
accordance with IEC 61511-1.
4.8 Fire protection and fire
extinction
4.8.1 The regasification system shall be protected with both a water spray
deluge system plus a dry chemical powder system and a fire detection system. The
systems shall meet the requirements of Pt 11, Ch 11 Fire Prevention and Extinction .
4.8.2 The water spray deluge system and dry chemical powder system installed
on board the barge or offshore unit shall be capable of providing coverage for the
areas defined in Pt 11, Ch 11 Fire Prevention and Extinction and the regasification system simultaneously.
4.8.3 The barge or offshore unit’s water spray deluge system shall be
designed to cover the regasification equipment, barge or offshore unit-to-ship LNG
flexible hoses or loading arms and gas export manifold.
4.8.4 Protection from fire and heat shall be provided as necessary for the
safe escape of personnel in case of an emergency. Details shall be submitted for
appraisal as indicated in Pt 11, Ch 20, 2.1 General 2.1.1.
4.8.5 Fire protection arrangements shall be such as to prevent possible jet
fires propagating from the regasification unit to the adjacent LNG storage tank
areas. Proposed arrangements shall be evaluated in the risk based studies in Pt 11, Ch 20, 3.2 System safety risk assessment.
4.9 Location and arrangement of
equipment
4.9.1 The location of the regasification unit and its sub-systems containing
LNG and NG shall be considered part of the cargo area. The regasification units and
all their associated equipment shall be located as far as is reasonably possible
from accommodation spaces.
4.9.2 The regasification system machinery may be located on the open deck or
in cargo pump and cargo compressor rooms. Arrangements of such spaces shall be in
accordance with the requirements of Pt 11, Ch 3 Ship Arrangements.
4.9.3 When the regasification units are located on open deck they shall be
placed in a sheltered location protected from green water.
4.9.4 The locations of the system arrangements, including vaporisers, high
pressure pumps, suction drums, heaters, liquid pumps and ancillary piping systems,
shall be defined and evaluated in the system safety risk assessment, see Section
Pt 11, Ch 20, 3.2 System safety risk assessment, and shall be acceptable to LR.
4.9.5 The deck plating and sub-structure of the barge or offshore unit shall
be protected from possible cryogenic spills associated with the regasification unit
and suction drum in way of fittings, fixtures and demountable joints. No protection
will be required in locations where the deck and sub-structure material can
withstand cryogenic temperatures.
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