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.
4.1.2 Materials shall comply with the requirements of the Rules for the
Manufacture, Testing and Certification of Materials (hereinafter referred to as
the Rules for Materials) and Chapter 6 of the Rules for Ships for Liquefied Gases.
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
ship or barge shall have adequate capability for managing the boil-off
gas generated by heat ingress through headers, manifolds and loading
arms during ship-to-ship transfer operations.
4.1.7 The regasification
system shall include provision to pre-cool the product transfer piping
system prior to ship-to-ship transfer operations commencing.
4.2 Vaporisers
4.2.1 The requirements
of these Rules apply to various types of vaporiser, such as:
-
STV – Shell and tube heat-exchanger type.
-
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 the requirements of the Rules for Ships for Liquefied
Gases.
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
ofPt 6, Ch 3 Refrigerated Cargo Installations of the Rules for Ships
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 relief valves in readily visible positions; the
discharge from these relief valves shall be taken to a suitable high-pressure
venting arrangement and the number and position of 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 either propane or other gas, the condensate
shall not be passed directly back to the engine room. The 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 covered by the gas detection and alarm system, see
Ch 1, 4.3 Gas detection system.
4.2.10 If the LNG ship
is to operate in regions where insufficient natural sources of heat
are available for vaporisation, e.g. 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.
4.2.14 Commissioning
and testing of vaporisers shall be undertaken by the manufacturer
prior to units being installed on board.
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 the Rules
for Ships for Liquefied Gases, 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,
and 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 compartment, the air
flow from compartment purging or ventilation and stagnant areas, and
the manufacturer’s recommendations.
4.3.4 The gas detection
system serving the regasification system may be either independent
or combined with the gas detection system installed to allow compliance
with the Rules for Ships for Liquefied Gases.
4.3.5 The gas detection
is to be of the continuous monitoring type, capable of immediate response.
4.3.6 The gas detection
system serving the regasification system is otherwise to comply with
the construction and installation requirements of the Rules for Ships
for Liquefied Gases.
4.4 Emergency shutdown (ESD) system
4.4.1 An emergency shutdown
(ESD) system serving the regasification systems and equipment shall
be fitted and shall comply with the cause and effect matrix shown
in Table 1.4.1 ESD functional
arrangements, as applicable.
Table 1.4.1 ESD functional
arrangements
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|
Pumps
|
Compressor systems
|
Valves
|
Link
|
| Shutdown action
|
Cargo
pumps/ cargo booster pumps
|
Spray/
stripping pumps
|
Vapour
return compressors
|
Fuel gas
compressors
|
Reliquefaction plant, including condensate return pumps, if fitted
|
Gas
combustion unit
|
ESD
values Valves
|
Signal to
ship/ shore link***
|
| Initiation
|
| Emergency push buttons (See
Ch 1, 4.4 Emergency shutdown (ESD) system 4.4.2)
|
√
|
√
|
√
|
See Note 2
|
√
|
√
|
√
|
√
|
| Fire detection on deck or in
compressor house*
|
√
|
√
|
√
|
√
|
√
|
√
|
√
|
√
|
| High level in cargo tank
|
√
|
√
|
√
|
See Notes 1 and 2
|
See Notes 1 and 3
|
See Note 1
|
See Note 6
|
√
|
| Signal from ship/shore link
|
√
|
√
|
√
|
See Note 2
|
See Note 3
|
n/a
|
√
|
n/a
|
| Loss of motive power to ESD
valves**
|
√
|
√
|
√
|
See Note 2
|
See Note 3
|
n/a
|
√
|
√
|
| Main electric power failure
('blackout')
|
See Note 7
|
See Note 7
|
See Note 7
|
See Note 7
|
See Note 7
|
See Note 7
|
√
|
√
|
| Cargo tank level alarm override
(See Note 4)
|
See Note 4
|
See Notes 4 and 5
|
√
|
See Note 1
|
See Note 1
|
See Note 1
|
√
|
√
|
| 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
|
Note
1. These items of equipment can be
omitted from these specific automatic shutdown initiators provided the
compressor inlets are protected against cargo liquid ingress.
Note
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.
Note
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.
Note
4. An override of the overflow control
system may be used at sea to prevent false alarms or shutdowns. The
arrangements for the override system shall be such that inadvertent
operation is prevented. When level alarms are overridden, operation of
cargo pumps and the opening of manifold ESD valves shall be inhibited
and continuous visual indication shall be given at the relevant
control station(s) and the navigating bridge.
Note
5. Cargo spray or stripping pumps used to
supply forcing vaporiser may be excluded from the ESD system only when
operating in that mode.
Note
6. 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 each manifold 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.
Note
7. 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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4.4.2 The ESD system
shall be activated by the manual and automatic inputs listed in Table 1.4.1 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 the 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
cargo in either liquid or gaseous state.
4.4.5 The emergency shutdown
system associated with the regasification system shall be designed,
manufactured and tested in accordance with the principles stated in
Ch 5, 5.6 of the Rules for Ships for Liquefied Gases.
4.4.6 The number and
location of additional shutdown positions shall be determined by the
type, number, location and position of the regasification 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 full shutdown. A PSD functional arrangement
matrix commensurate with that shown in Table 1.4.1 ESD functional
arrangements shall be provided.
4.5.3 Manual PSD points
shall be arranged at the regasification system 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 visible.
4.5.4 Process shutdown
valves in liquid piping shall close fully under all service conditions
within 30 seconds of actuation. 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
of 30 seconds for the shutdown valve referred to in Ch 1, 4.5 Process shutdown (PSD) system 4.5.4 shall be measured from the time of manual or automatic
initiation to final closure. This is called the total shutdown time
and is made up of a signal response time and a valve closure time.
The valve closure time shall be such as to avoid surge pressure in
pipelines. Valves shall close smoothly.
4.6 Depressurisation and blowdown system
4.6.1 A depressurisation
and blowdown system shall be provided for depressurising the high
pressure liquid and gas pumps, vessels and pipework.
4.6.2 Where a liquid
depressurisation system is provided, adequate provision shall be made
in the design and installation for the effects of back pressure in
the system and vapour flash-off when the pressures of liquids in the
blowdown system are reduced.
4.6.3 Manual and automatic
activation of the depressurisation system shall be provided.
4.6.4 Manual activation
shall be possible from the regasification 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.
4.6.5 Automatic activation
shall be part of the emergency shutdown arrangements.
4.7 Pressure relief and venting system
4.7.1 Each regasification
unit shall be provided with dedicated high pressure safety relief
valves and venting arrangements. The arrangements shall be independent
from the venting arrangements serving the cargo tanks. High pressure
safety relief valves, headers, knock-out/drain drum and vent masts
shall be located within the cargo deck area.
4.7.2 High pressure safety
relief valves and venting arrangements for liquid and gas phases shall
be provided for each regasification system. The safety relief valve
support arrangements shall withstand the loads imposed by discharges.
4.7.3 Where multiple
regasification systems are installed, the design of pressure safety
relief and venting arrangements shall consider the maximum combined
release rate.
4.7.4 The gaseous phase
safety relief valves shall be led to the dedicated high pressure vent
mast for the regasification system required by Ch 1, 4.7 Pressure relief and venting system 4.7.1. The high pressure vent mast shall be sized to handle the
maximum regasification capacity and to ensure safe dispersal of the
gas.
4.7.5 The liquid phase
safety relief valves shall be led to a knock-out/drain drum having
adequate capacity for the maximum LNG inflow anticipated within the
design of the regasification unit. The knock-out drum shall be fitted
with a level switch to stop all high pressure LNG pumps. Any LNG from
the vent knock-out drum shall be safely drained or be allowed to boil
off and vapour to be returned to the ship’s vapour header.
4.7.6 LNG suction and
LNG knock-out/drain drums shall be fitted with pressure safety relief
valves in accordance with the Rules for Ships for Liquefied Gases.
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 Chapter 11 of the Rules for Ships for Liquefied Gases.
4.8.2 The water spray deluge system and dry chemical powder system installed on
board the ship shall be capable of providing coverage for the areas defined in Chapter 11 of the Rules for Ships for Liquefied Gases and
the regasification system simultaneously.
4.8.3 The ship’s
water spray deluge system shall be designed to cover the regasification
equipment, ship-to-ship LNG loading arms and 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 Ch 1, 2 Submission of plans and documentation.
4.8.5 Fire protection
arrangements shall be such as to prevent possible jet fires propagating
from the regasification unit to the adjacent cargo tank areas. Proposed
arrangements shall be evaluated in the risk based studies in Ch 1, 3 Risk based analysis.
4.9 Location and arrangement of equipment
4.9.1 The location of
the regasification unit shall be considered part of the cargo area
as defined in Ch 1,1.3.6 of the Rules for Ships for Liquefied Gases.
The regasification unit and all its associated equipment shall be
located as far as is reasonably possible from the 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 Chapter 3 of the Rules for Ships for Liquefied Gases.
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
Ch 1, 3 Risk based analysis), and shall be
acceptable to LR.
4.9.5 The ship structure
shall be protected from possible cryogenic spills at the regasification
unit and suction drum in way of fittings, fixtures and demountable
joints except in those locations where the structure material can
withstand cryogenic temperatures.
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