391-Methanol Operations / 748
Met
h
anol
Op
erations
BOS-PRD-07.900609
pump. The Nitrogen aims to replace the methanol during the offloading. When discharging, watch the
nitrogen inlet pressure constantly, on the pressure gauge on methanol tank vent pipe.
Pumping rate is usually around 120 m3/h with 4 bars of pressure in the hose. The by-pass valve on the
discharge line may be used to set the offloading pressure. The delivery capacity to be regulated by adjusting
the hydraulic flow.
T
h
e
d
is
ch
arge rate is to
b
e 80% o
f
t
h
e N2 s
upp
ly rate
Start slow rate with pressure at 2 bars. Then increase to 80 m3/h with a pressure of 3 bars at ship manifold
Cargo tank to be maintained at positive pressure throughout the offloading
In case of ship’s nitrogen plant failure, even if receiver is able to supply N2, operation is cancelled until the
ship has recovered her N2 station.
Make sure pressure valves are not stucked in open position, this would result in waste of nitrogen.
When a methanol discharge pump breaks down, use the other methanol discharge pump as an emergency
pump.
Methanol tank’s oxygen level must be regularly checked during the offloading, and must remain under 8%. If
any doubt, increase the nitrogen pressure in the methanol tank by reducing the discharging rate, until the
pressure valve releases and check oxygen level at PV valve.
In case of a pressure drop to less than 0 bar would occur in a methanol tank, it becomes an emergency
situation as oxygen is subject to enter and mix with methanol. Stop immediately the transfer to recover
positive pressure.
When the offloading is completed, disconnect the discharge hose, and close the purge valves, after purging
discharge line with nitrogen.
The padding line valves are kept open, the regulator will hold a nitrogen over pressure in the tank. The
pressure will be approx. 0,15 bar.
Methanol
gas measurements to be carried out regularly.
4
.2.
6 C
o
m
p
letion o
f
o
p
eration
- C
leaning
When the last offloading operation has been completed, the ship
shall
be flushed as per following procedure
and the last flushing, at least,
shall
be done with FW.
Fill the Methanol tanks with water to about 50%, using the loading /discharge line.
Discharge the water overboard by means of Methanol pump. Continue the water filling / discharging
operation until the flammable vapour concentration in the Methanol tanks is below 30% of lower flammable
limit (LEL), before gas freeing at deck level (through open manholes) is permitted (SOLAS Ch.II-2 Pt.D
Reg.59.2). The methanol tanks have to be pressurless before the manhole to the tank is opened.
The cofferdams
shall
remain filled with nitrogen until the methanol tanks are gas-freed.
The access trunk vent / drain valve
shall
be closed before opening the manhole into methanol
tank.
Ventilation of methanol tanks can be done by filling of water into the tank.
Before next filling of methanol into the tank, discharge the water out of the tank, clean and dry the tank
properly.
The discharge of the polluted water overboard
shall
be done as per MARPOL Annex II Reg.5.4. The
discharge of Chemical Product into the sea is prohibited unless the following condtions are satisfied:
Version 04. Original date: 22/06/2012. Version date: 31/12/2014. Valid version only on QMS site. Uncontrolled document when printed.
Procedure prepared by: BOS Head of Operations. Approved by: BOS Head of Operations. Validated by: BOS Quality Representative.
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