Safety Management System
1.
Safety
Feature Installations
A
centralized spill, fire and combustible gas alarm and control system will
provide input to an information management system. The primary purpose is to provide plant
operators with a central facility for monitoring the conditions of accidental
spill, fire and the release of combustible gas.
It will also provide the operators with the information and the means of
responding to emergencies involving these conditions.
The main
distributed control system, DCS console, is the physical operator/alarm and
control system interface and will be located in the central control room, which
is manned 24 hours a day. Various
lighted push buttons, digital read outs and annunciates provide the operator
with complete monitoring and control capabilities. The information management in the main DCS
console will display combustible gas concentrations, alarm locations, etc.
In the
event of total power failure, the LNG terminal will be shut down, the unloading
operation will be stopped and the boil-off gas will be routed to the LP and HP
vent system.
Color TV
monitors will be installed to allow a visual picture of the entire facility at
the central control room and gatehouse area.
Automatic
detection devices, manual alarms and audible and visual signaling devices will
be strategically located throughout the terminal. Hazard detection and alarm signaling devices
will report to the central control room and tie-in to the DCS.
Automatic
detection devices will include flame, fire and heat, smoke, low temperature and
combustible gas detectors. The hazard
detection system will be designed to minimize the time a spill, leak or fire
might go undetected by installing multiple and redundant different detectors
within the terminal to detect gas, fire, low temperatures and low and/or high
operating pressures outside normal operating levels. The detectors are located to provide warning
as quickly as possible. The detector
signals are continuously monitored by an online computer in the control room
that identifies a hazardous condition within the terminal to alarm and locate
the situation for operating personnel.
The
operators will be trained so that they are familiar with the fire prevention,
fire protection and fire fighting methods.
The
following safety and fire fighting features will be installed:
i. Deluge
systems will be installed on the tank roof.
ii. Spill-collection
system designed and located to deflect and prevent a pressurized LNG
spill. The LNG leak detection system is
typically designed to detect spills and to shutdown the plant less than two
minutes after a spill, and the LNG spill is able to be contained in the
drainage basin area. LNG spill sump will
be designed for removing water and keeping debris free.
iii. Install fixed
dry chemical fire suppression systems on the tank roof.
iv. Portable dry
chemical extinguishers will be installed on the tank roof platform.
v. Fixed high
expansion foam protect will be provided.
Foam generators will be blower type, with hydraulic turbine-driven fans,
producing a nominal 500:1 foam at an application rate of 120 m³/hour of
expanded foam per m² of contained LNG spill surface area.
vi. Hydrants
approximate 90 meters apart and firewater monitors approximate 60 meters apart
to be installed on the firewater main.
Isolation valves in the fire water main will be provided.
vii. Automatic
actuation for the firefight system will be automatic actuated by combustible
gas detectors and low temperature detectors installed near the entrance to the
LNG spill sump, and by means of voting UV/IR optical flame detectors.
The LP and HP vent system is designed to consider the
following:
- LNG tank
rollover and BOG from sudden drop in barometric pressure.
- The inner
tank-overfilling scenario is eliminated by safety instrumentation system by
tripping the unloading system.
The LNG terminal is designed for safe handling of vapor
discharges from the system, such as relief valves. During normal operation, there is no vent and
relief. Venting will be a rare event during
normal and unloading operations.
1.
Emergency
Shutdown (ESD) and Depressurization (EDP) System
The
isolation systems are located in different areas along with equipment with
fire, explosion and toxicity potential risks. An Emergency Shut Down (ESD) and
Emergency Depressurization (EDP) systems will be provided to protect plant
personnel, plant equipment and the environment in case of an emergency such as
fire, potential dangerous process upset or hydrocarbon leak. The ESD system will isolate the unit/system
where an incident is occurring from the adjacent units/system. The EDP system will reduce the hydrocarbon
inventory of the system and will decrease its pressure. Equipment and piping are divided into
sections called ESD zones, considering the plot plan and the process flow.
An emergency shutdown system (ESD) will be incorporated in
the design of the Terminal and provide the operators with the capability of
remotely shutting down the entire or selective portions of the Terminal.
There will be three major ESD modes for the Terminal:
i.
LNG unloading Isolation – The LNG unloading dock to
the LNG storage tanks.
The ESD
system will be installed on the LNG unloading lines to block in the unloading
lines in the case of an LNG leak, a sudden unplanned disconnect of the LNG
carrier, an external fire or any other emergency during unloading. It consists of quick shut-off valves at the
unloading dock. These valves are triggered
automatically by ship separation or high pressure or manually by an operator. The closure times of the valves are set to
prevent a liquid surge in the lines.
ii.
Send-out Shutdown – The LNG tanks through the
pipeline shutoff valves. Shut down the
Primary LNG pumps, send-out pumps and BOG compressors; Isolation of the
Terminal from the pipeline by closure ESD valves; Isolation of the high
pressure part of the Terminal by closure ESD valves at send-out pump suction,
primary pump discharge, compressor discharge, and depressurization of the
vaporizers.
iii.
Overall Shutdown – From the ship-unloading area
through the pipeline shutoff valves, with activation of modes 1 and 2 above
The following Shutdown functions will be provided:
- Block in of the LNG loading arms
- Block in of the LNG vapor return arm
- Block in at shore line all unloading lines
- Block in of LNG lines to LNG storage tanks
- Shut down return gas
- Shut down LP LNG send-out pumps in the LNG
tanks
- Block in send-out valves to BOG condenser
- Shut down BOG compressors
- Shut down HP LNG booster pumps
- Block in LNG to vaporizers
- Block in the outlet of the vaporizers
- Emergency depressurizing the vaporizer
units
Detector types will include:
- Fire/Flame detectors
- Gas detectors
- Low temperature detectors
- High-level shutdowns on the LNG storage
tanks’ High-pressure shutdowns
- Low flow shutdowns
- Smoke detectors (for Buildings)
- Heat detectors
- Camera surveillance of the facility
- Manual ESD activation stations
2.
Instrumentation,
Control and Tank Level Measurement
The control
system of the plant is performed by a Distributed Control System (DCS).
The major
process control loops described below are shown in the Process Flow Diagrams.
The
control system for the Terminal will be designed for fail-safe operation. The control valves will be designed to move
to a “fail safe” position, fully opened or closed, depending on the service.
The LNG
flow unloaded from the ship is measured by flow recorders in both unloading
lines.
The LNG
flow from the in-tank LNG send-out pumps is controlled by kickback into the LNG
storage tank. The LNG level in the BOG
condenser is used to control the LNG feed flow rate to the BOG condenser. The send-out flow to each LNG vaporizer uses
a flow controller that is reset by the vaporizer outlet gas temperature.
Each LNG vaporizer has an independent control system. The seawater flow is adjusted by a butterfly
valve. The gas outlet temperature of
each vaporizer is also controlled. The
LNG flow is controlled by a flow control valve, which is overridden by low-low
flow of seawater or low temperature at the vaporizer outlet.
The proper
pressure control of the LNG storage tanks is of utmost importance both in terms
of safeguarding the mechanical integrity of the LNG storage tanks and the
overall safety of the terminal. The tank
pressure is primarily controlled by using the gage pressure in the boil-off
vapor header to load or unload the reciprocating boil-off gas compressor. If the LNG storage tank pressure falls to
below the minimum allowable operating limit, natural gas would then be fed from
the vacuum breaker header to increase the pressure. The final level of protection against low or
vacuum pressure levels is provided by vacuum breaker relief valves, which would
allow ambient air into the LNG storage tanks to prevent collapse if the
pressure were to drop below -5 mbarg vacuum (the typical negative design
pressure).
A pressure
controller that relieves excess vapor to the low-pressure vent at high tank
vapor header pressures provides the primary tank overpressure protection. A secondary level of tank overpressure
protection is provided by the tank relief valves which discharge directly to
the atmosphere.
For LNG
tank level measurement, an automatic, multi-sensor probe assembly, a tank top
entry electronic control module, continuous level and density measurement with
temperature and pressure monitoring will be provided. These measurements are achieved by means of a
control unit and an electro-mechanical drive mechanism, which operates as a
unit to position a multi-sensor probe assembly suspended within the LNG storage
tank. The probe is moved vertically by
the drive mechanism in response to commands generated by the control unit. Both automatic and manual control of the
probe assembly is incorporated into the system design. All system components, which are located
inside the tank, can be completely removed from the tank for inspection and/or
maintenance at any time. The system has a probe enclosure assembly with viewing
glass, which allows for probe to be removed from tank for maintenance. Solid-state level sensors detect liquid and
vapor interface. This system will also
effectively detect any LNG layering so that preventative measures can be taken.
Enraf and Scientific Instruments (SII), for example, manufacture such
instrument packages for the LNG tanks.
An additional microprocess-based Servo Tank
Gauge is provided to measure the level with accuracies to +/-0.04” and a
solid-state based temperature gauging system is provided with accuracies up to
0.1 °C.
The volume
of LNG delivered for any given shipment will be able to be checked by
calculation based on measurement of level, temperature and pressure in the LNG
tanks.
3.
LNG Spill / Storm Water Containment
The LNG Terminal shall be curbed for containment of LNG
spills and storm water. Catch basins
shall be located strategically on the LNG Terminal to collect LNG spills and
storm water and shall gravity flow to a Storm water / LNG Spill Sump via a
collection header. Open collection pan
shall be provided under equipment where there is a possibility of a large LNG
leak, and will be routed to the collection header.
LNG leak detection will be provided by:
a. Gas
detectors
b. Low
temperature detectors
The detection system will be designed to detect spills and
to shut down the plant within two minutes after a spill occurs.
All
the detection systems are connected to ESD and activate alarms on the operators’
console placed in the Main Control Room, Field Control Room, and Jetty Control
Room.
High expansion foam system will be provided to control LNG
fires and vapor dispersion of LNG spills.
Foam will be discharged to cover the impoundment area to a depth of 0.6
meter within 2 minutes.
The LNG spill sump will serve the following purposes:
a. Vaporization
reduction
b. Thermal
radiation reduction
c. Efficient
application area for high expansion foam
In the event of a large LNG spill, it will be collected in
the sump. Low temperature alarm will
activate high expansion foam.