In case that Emergency Situation should be generated at LNG Carrier or LNG all working(loading and unloading) must be automatically stopped. At this time, Stop or Shut- Down the main equipment related operation and transfer the ESD status signal to meet the emergency. Above mentioned functions will be done automatically, this is ESDS for LNG Carrier. There are various emergency case, but first of all we define the major case like Fire, Unsafe status of Cargo Tank, Manual Shut-Down etc.
In the event of fire, certain off limit condition or other emergency condition, the entire cargo system, low & high duty compressors and master fuel gas valve to the main boiler may be shut down by single initiation. And there are three emergency shutdown interface connections made to the shore facility, is electrical, optical and pneumatic. In port, the optical link and pneumatic systems will inform the shore of any ship’s emergency shutdown actuation and will stop the loading or discharge pumps and close the shore liquid valve.
Air Control Board
The Air control board is one part of the whole ESDS to monitor and detect the pneumatic air pressure and eventually control the emergency shutdown system of LNG Carriers.
Air of 7~9 barg is supplied to the Air Control Board and one transmitter are provided to detect the air pressure and send out the pressure value to ESD main controller for automatic control the Pneumatic system pressure using electro-pneumatic solenoid valve.
If the control air pressure for the Air Control Board is lower than normally supplied air then pressure switch detect the pressure value and send the electrical signal to main controller.
3-way test cock are provided to test the functionality of the pressure gauge and pressure transmitter individually.
This pneumatic air control system onboard ship is linked to the pneumatic air line of the terminal to initiate the ESD system by setting the ESD pressure to the required value of each terminal.
Pneumatic Link Box
The Pneumatic Link transmitter box is used to set the operating air pressure of the ESDS onboard ship to the required value of each terminal.
There are only one Pressure transmitter and 3-way test cock in this box but it can be measured any LNG terminal set point flexible
Air Release Solenoid valve
Air releasing solenoid valve is open that means de-energized , when ESD occurs from ESD main controller.
Automatic shutdowns occurs when any of the following conditions
-Cargo vapor main line header pressure falls to within 0.3 kPa of atmospheric pressure.
-Cargo vapor main line header pressure & primary insulation space pressurization main line equal pressure.
-Pressure difference between each cargo tank pressure & primary insulation space pressure becomes 0.5 kPa
-Each cargo tank pressure falls to the primary insulation space pressure.
-Any cargo tank level extremely high (99% volume)
-Automatic shutdown for electric fail.
-Automatic shutdown by hydraulic oil pressure low.
-Shutdown signal from the terminal.
-Automatic shutdown by pneumatic pressure low in ship/shore connection.
-Automatic shutdown by control air pressure low.
GMB has proposed new concept of pneumatic system for Emergency Shutdown System, The new concept of air control board adopts just one pressure transmitter instead of three pressure switches that enables to control the air pressure as pre-defined set value through PLC and air control valve.
As a result, the system becomes much simple and the overall board size can be reduced drastically so that the maintenance and operation become easier than previous concept.
Moreover, this new concept enables the pneumatic ESD link as entirely worldwide compatible system. In other words, the three (3) pressure switches are replace by one pressure transmitter and the required setting values are selected by just pushing the +/- buttons on the monitor or other similar device located in CCR.
Against old concept of ESDS, new concept system can be simplified by using just one smart pressure transmitter and the logic can be much simple.
The pneumatic link pressure (downstream of electro-pneumatic regulator) is automatically controlled to follow given set point that is pre-determined through CCR by operator.
The air supply solenoid valve is energized to open during normal operations and get closed when an ESD condition is detected. If the pressurized air in the pneumatic link is released by any ESD signal, the pressure transmitter of the pneumatic link pressure transmitter box detects the ESD condition.
ESD condition happens as in the previous configuration as well.
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