Ingangsdatum: 04-07-1983
4.1
Though flue gas systems differ in detail certain basic principles
remain the same.
These are:
.1 starting up the inert gas plant;
.2
shutting down the inert gas plant;
.3 safety
checks when the inert gas plant is shut down.
In all cases the manufacturer's detailed instructions
should be followed.
4.2Start-up procedures should be as follows:
.1 Ensure boiler is producing flue gas with an oxygen content of
5 per cent by volume or less (for existing ships 8 per cent by volume
or, wherever practicable, less).
.2 Ensure that
power is available for all control, alarm and automatic shut-down
operations.
.3 Ensure that the quantity of
water required by the scrubber and deck water seal is being maintained
satisfactorily by the pumps selected for this duty.
.4 Test operation of the alarm and shutdown features of the
system dependent upon the throughput of water in the scrubber and deck
seal.
.5 Check that the gas-freeing fresh air
inlet valves where fitted are shut and the blanks in position are
secure.
.6 Shut off the air to any air sealing
arrangements for the flue gas isolating valve.
.7 Open the flue gas isolating valve.
.8 Open the selected blower suction valve. Ensure that the
other blower suction and discharge valves are shut unless it is intended
to use both blowers simultaneously.
.9 Start
the blower.
.10 Test blower "failure" alarm.
.11 Open the blower discharge valve.
.12 Open the recirculating valve to enable
plant to stabilize.
.13 Open the flue gas
regulating valve.
.14 Check that oxygen content
is 5 per cent by volume or less, (for existing ships 8 per cent by
volume or, wherever practicable, less) then close the vent to atmosphere
between the gas pressure regulating valve and the deck isolating valve.
Note: Some oxygen
analyzers require as much as two hours to stabilize before accurate
readings can be obtained.
.15
The inert gas system is now ready to deliver gas to the cargo tanks.
4.3Shut-down procedures should be as follows:
.1 When all tank atmospheres have been checked
for an oxygen level of not more than 8 per cent and the required in-tank
pressure has been obtained, shut the deck isolating/non-return valve.
.2 Open vent to atmosphere between the gas
pressure regulating valve and the deck isolating/non-return valve.
.3 Shut the gas pressure regulating valve.
.4 Shut down the inert gas blower.
.5 Close the blower suction and discharge
valve. Check that the drains are clear. Open the water washing system on
the blower while it is still rotating with the power supply of the
driving motor turned off, unless otherwise recommended by the
manufacturer. Shut down the water washing plant after a suitable period.
.6 Close the flue gas isolating valve and
open the air sealing system.
.7 Keep the full
water supply on the scrubber tower in accordance with the manufacturer's
recommendation.
.8 Ensure that the water supply
to the deck water seal is running satisfactorily, that an adequate water
seal is retained and that the alarm arrangements for it are in order.
4.4 Safety checks when
inert gas plant is shut down should be as follows:
.1 The water supply and water
level in the deck seal should be ascertained at regular intervals, at
least once per day depending on weather conditions.
.2 Check the water level in water loops installed in
pipework for gas, water or pressure transducers, to prevent the backflow
of hydrocarbon gases into gas safe spaces.
.3
In cold weather, ensure that the arrangements to prevent the freezing of
sealing water in the deck seals, pressure vacuum breakers etc. are in
order.
.4 Before the pressure in the inerted
cargo tanks drops to 100 millimetres they should be re-pressurized with
inert gas.
4.5Possible failures of inert gas system and actions to be taken
include:
.1 High oxygen content which
may be caused or indicated by the following conditions:
.1.1 poor combustion control at the boiler, especially
under low load conditions;
.1.2 drawing air
down the uptake when boiler gas output is less than the inert gas blower
demand, especially under low load conditions;
.1.3 air leaks between the inert gas blower and the boiler
uptake;
.1.4 faulty operation or calibration of
the oxygen analyzer;
.1.5 inert gas plant
operating in the recirculation mode, or
.1.6
entry of air into the inert gas main through the pressure vacuum valves,
mast risers etc. due to maloperation.
.2 If the inert gas plant is delivering inert gas with an
oxygen content of more than 5 per cent, the fault should be traced and
repaired. Reg. 62.19.5 requires, however, that all cargo tank operations
shall be suspended if the oxygen content exceeds 8 per cent unless the
quality of the gas is improved.
.3 Inability to maintain positive pressure during cargo
discharge or deballasting operations which may be caused by:
.3.1 inadvertent closure of the inert gas
valves;
.3.2 faulty operation of the automatic
pressure control system;
.3.3 inadequate blower
pressure; or
.3.4 a cargo discharge rate in
excess of the blower output.
.4 The cargo discharge or deballasting should be stopped or
reduced depending on whether or not the positive pressure in the tanks
can be maintained while the fault is rectified.