This
section describes briefly the facilities at the LNG terminal.
Jetty Structure
A jetty trestle structure, with a berth to
moor the carriers, will be of steel construction with a concrete deck, abutted
to a footing of rock. A typical steel trestle jetty is shown in Figure 1.1.
The pier, jetty head and ‘dolphins’ at the
berth, will have steel piles founded in the seabed
approximately 50m apart. On the jetty head, articulated piping (unloading arms)
will be installed to connect the carrier to the piping of the onshore Terminal. The unloading arms are designed
with an operating envelope that allows for prescribed carrier movement due to
environmental factors while the arms are connected.
Figure 1.1 Typical
Steel Trestle Jetty with Berthed Vessel
Three LNG storage tanks, each of capacity
up to 180,000 m3 will be built.
The tank design will be full containment,
with all tank connections made through the roof to maximize mechanical strength
and integrity. The double wall construction will comprise an inner wall of low
temperature steel and an outer wall of pre-stressed concrete. Full containment tanks
provide higher safety standards compared to single containment tanks in view of
the intrinsic robustness of the concrete outer structure.
The inner steel container will hold the
LNG at -162°C. Cryogenic steels will be used (such as 9% Ni),
which can withstand these very low temperatures. The outer concrete wall will
include a reinforced concrete bottom slab and roof. The wall will be designed
to withstand the cryogenic temperatures involved, ie
it will contain any leak from the inner tank. Insulation materials will be
applied to the space between the steel inner container and the outer concrete
tank to minimise the transfer of heat from the environment to the bulk
LNG. Boil-off gas from the LNG tank will
be compressed and fed into the sendout system (see Section
1.4).
Internal tank piping will be designed to
enable bottom or top filling without the need to install any connections
through the tank wall below the liquid level. Special attention will be given
to the instrumentation on the storage tanks. Alarm and shutdown devices will be
incorporated in the design to ensure safe tank operation. These alarms and
shutdown devices will be sequenced to conform to the requirements of the
operating philosophy and the safety failure mode analysis. Tanks will also be
provided with pressure relief safety valves with a set of pressure and vacuum
breaker relief valves.
Temperature and density measuring devices
along the height of the tank will be provided as a mean to help detect
stratification (formation of layers of LNG with different densities) and avoid
tank rollover. Automatic, continuous level measurement will be provided for the
storage tanks. A typical LNG storage tank is shown in Figure 1.2.
The tank design pressure will be 290 millibars (mbar), with all tanks intended to simultaneously
send out and receive LNG discharged by the LNG carrier. The LNG storage tanks
will be fitted with pressure-control valves (PCVs),
which will prevent excess vapour from accumulating in the tanks.
Figure 1.2 Typical
LNG Storage Tank
1.3
Boil-off Gas
(BOG) Handling System
Gas Compressors
Boil-off gases (BOGs)
produced during normal Terminal operations as a result of inevitable heat
transfer from the atmosphere to the storage tanks and piping as well as those
arising from ship unloading operations, will be sent to the BOG compressor and
re-condenser for condensing (liquefying) and re‑inclusion into the LNG
bulk product stream.
Vent System
The vent system is designed for emergency
venting. The vent will not be used under normal operations.
Because of the high pressures involved,
two stages of sendout pumps are required.
First Stage LNG Sendout
Pumps
Electrically driven high-capacity (first
stage) LNG sendout pumps will be installed in each
LNG storage tank. These pumps operate fully submerged in LNG and are located
within pump wells, allowing for easy pump removal, maintenance and installation.
The pump wells also serve as the discharge piping from the pumps and are
connected to the tank-top piping.
LNG from the in-tank pumps is routed
directly to the re-condenser. All boil-off vapours during normal sendout or during carrier unloading are routed to this drum, mixed with the LNG, and re-condensed
into the bulk LNG fluid. The re-condenser houses a packed bed of stainless‑steel
pall rings (or equivalent), which creates additional surface area for
vapour-liquid contact.
Second Stage
LNG Sendout
Pumps
LNG from the re-condenser on level control
is directed to the second stage sendout pumps. The
second stage sendout pumps are high‑pressure
pumps, delivering LNG to the LNG Vaporisers (see Section 1.5) at a pressure of 75 to 80 bar (which could be increased to 100 bar).
Stored LNG will need to be re-gasified in order for it to be conveyed along the gas
transportation pipework. This will be accomplished
via LNG Vaporisers, which will either utilise piped seawater (in open-rack
vaporisers) or hot combustion gases (in submerged combustion vaporisers) to
raise the temperature of the LNG to ambient temperature, thereby causing it to
re‑gasify.
·
Open Rack Vaporisers. In open-rack vaporisers (ORVs) seawater flows over aluminium heat exchange panels that contain tubes through which the LNG flows. The
seawater falls over the panels to a trough below and is then discharged back to
the sea. A typical vaporiser used for LNG Terminals is shown in Figure 1.3.
·
Submerged Combustion Vaporisers. Submerged Combustion Vaporisers (SCVs) involve burning off a small amount of gas and using
the heat of combustion to maintain the temperature of a water bath. The cold
LNG passes through coils within the bath and gets vaporised.
Figure 1.3 Typical Open Rack Vaporiser
The gas leaving the LNG Vaporiser will be
routed to the sendout gas pipework.
Fire water
A closed-loop fire water system will be
provided to protect the LNG Terminal equipment, utilities, storage and
unloading areas. The system will include main pumps and a standby mobile pump,
along with hydrants and monitors. Fire water will also be provided to protect
the berth.
Security
Security will be designed to prevent
unauthorised access and to ensure the safety and integrity of the facilities.
The site will be provided with a perimeter fence.
1.8
Utilities and
Ancillary Facilities
Nitrogen
Nitrogen in the gaseous form will be
required at the LNG Terminal for purging of equipment during maintenance as
well as during start-up. A facility for onsite nitrogen generation through PSA process or air
separation unit will be provided. Details will be finalised during detailed design.
Power
For the Soko
site, onsite power generation by gas turbines will be provided in addition to subsea power cables.
Water
Service and drinking water tanks will be
required. Maximum 80m3/hr service water will be required for startup or shutdown operation. Seawater will be used for general washdown
purposes.
Sewerage
Sewage will be treated onsite in a packaged
plant compliant with relevant local regulations.
Communications
Arrangements will be made for provision of
telephone and emergency communications.
Fuel and Materials Storage
Diesel will be stored on-site in a
permanent fuel tank. Diesel will
serve as fuel for the emergency generator. Diesel will be transported to site
by barges.
Plant and Instrument Air
Atmospheric air will be compressed by
centrifugal compressors (each driven by electric motors) and dried for use as
both plant and instrument air.
Plant Buildings
The following permanent buildings will be
provided on site for the operational phase:
·
administration
building;
·
control
room;
·
workshop
and store room; and
·
gatehouse.
Site access will be
provided by boat. Emergency access by helicopters will also be provided.
Detailed process
flow diagram of the LNG terminal is shown in Figure 1.4, with details of the process streams indicated.
Figure 1.4 Detailed
Process Flow Diagram for Soko LNG Terminal
Upon
completion of all control systems testing, the units will be purged of oxygen
using nitrogen as the displacement gas. Various Terminal units will then be
checked for pressure leaks by pressurising and depressurising over an
approximate three-day period. The Terminal will then begin cooldown
operations using LNG. In this process, a small continuous flow of LNG will
accumulate in the tanks displacing the inert nitrogen to the atmosphere via a
vent. The cooldown will continue with LNG being
introduced gradually to the piping and other equipment.
2.2.1
Overview
The facilities that comprise the LNG
Terminal are described above. Operation of the Terminal facilities will
include the following significant process operations:
·
LNG
carrier approach, berthing and departure;
·
LNG
unloading from carriers at the marine facility and transfer to shore;
·
LNG
storage in onshore storage tanks;
·
Re-gasification
of the LNG to natural gas in LNG vaporisers; and
·
Final
sendout of natural gas via a pipework.
2.2.2
LNG Carrier Approach
In the final segment of the approach
fairway, tugboats will assist in controlling the heading and speed of the
carrier while entering into and manoeuvring within the turning circle as well
as for the final approach towards the jetty.
The tugboats will continue to assist until the mooring operation has
been completed. The number and bollard pull of tugboats for such operations
will be based on the findings of a simulation study for the safe manoeuvring of
the LNG carrier.
LNG will be pumped from the storage tanks
of the LNG carriers, through unloading arms on the jetty, to the storage tanks
onshore via insulated unloading lines.
It will take approximately 18 hrs to
unload an LNG carrier. During cargo discharge the vapour pressure in the LNGC
cargo tanks will be maintained by returning vapour from the shore. With this
balanced system, under normal circumstances, no hydrocarbons will be released
to the atmosphere from ship or shore. Unloading rates vary between 12,000 and 14,000 m3 per hour depending on the size of the carrier.
Before disconnecting the unloading arms,
remaining liquid will be drained and the arms purged with nitrogen. The onshore liquid pipework will be left full
and a minor circulation maintained to hold the temperature at approximately -162ºC.
This is required to avoid thermal cycling of the piping.
Ballasting operations (i.e. taking on
seawater to compensate for the unloaded mass of LNG) will be concurrent with
the LNG unloading. Under normal circumstances, the LNG carrier will leave the berth
approximately 24 hours after arrival. This includes allowances for the
pre-cooling operations, arrival cargo measurements, unloading
operations, cargo measurements on completion of discharge and nitrogen
displacement of unloading arms prior to disconnection.
To reduce the potential for LNG spillage,
the carrier and shore Emergency Shut Down (ESD) systems will be interlinked
such that an unusual event on either will automatically activate a transfer
system shutdown (ESD I) and in a severe case will also disconnect the unloading
arms (ESD II). An ESD I test will be completed before the start of unloading
operations. In the event of an ESD II unloading arm disconnection, LNG spillage
would be very small due to the activation of isolation valves on either side of
the Emergency Release coupler.
Before and during LNG transfer operations,
a safety zone of approximately 250m around the LNG carrier will be maintained.
2.2.4
Onshore Modes of Operation
The LNG Terminal will operate in two main
modes of operation:
·
Unloading Mode – The unloading
mode is the period when an LNG carrier is moored to the jetty and is connected via the
unloading arms and the jetty piping to the onshore storage tank. The pumps on
the LNG carrier will transfer the LNG in both the unloading and the
re-circulation lines to the onshore storage tanks. At the end of unloading,
pressurised nitrogen gas will be used to purge the arms of LNG before
disconnecting;
·
Holding Mode – The holding mode
is the period when no unloading takes place. During the holding mode, cryogenic
conditions will be maintained in the unloading line by circulating LNG to the
jetty head and back to the onshore storage tanks or the sendout
system via a dedicated
re-circulation line.
During both of these modes of operation, sendout of LNG to the vaporisers and gas pipeline will
continue.
Utilities required during the operation of
the Terminal facilities are summarised in Table
2.1.
Table 2.1 Utilities
Material |
Use |
Handling and Transport |
Storage quantity |
Diesel |
Operation (for emergency generator) |
Barge |
20 m3
|
Liquified
nitrogen |
Maintenance (purging) |
Drum to be
filled via barge every 2 weeks |
25 m3 |
Hydrochloric
acid 30% HCl |
Maintenance; neutralise using caustic and flush
to ocean |
Aboveground
storage on a skid |
200 L |
Caustic
soda 10% NaOH |
To neutralize the acid from maintenance of the
electro-chlorination units |
Drum |
2 m3 |
Raw
water |
Fire fighting and for service |
Pump |
1,500 m3 |
Seawater
|
Vaporisers |
Pump |
|
Electricity
|
|
132 kV
or 111 kV |
|