Page 23 - 2022 - Q4 - Minerva in Focus

Attending the gas trials of Minerva Amorgos

Mrs Foteini Volaki had attended the Gas The gassing up and cooling down of the ambient temperature to prevent the forma-
Trials of Minerva Gas' newly built Minerva remaining three tanks was conducted after tion of dry ice by the CO2 contained in the
Amorgos at SHI in South Korea and pre- unberthing the LNG Terminal for three days inert gas and condensation of the water. Cold
sents her experiences. in total. During the cooling down of one cargo Natural Gas was taken from all tanks and
tank, a certain amount of BOG is generated. returned to their bottom in Warm Natural
As per SIGTTO, the term ‘Gas Trials’ encompass- This BOG was used to gas up the next cargo Gas form, at approximately +80oC, produced
es those tests undertaken when a quantity of tank before its cooling down. This sequential by HD compressors and warm-up heaters.
LNG is taken onboard for testing shipboard operation resulted in no natural gas being In that way, the introduced hot gas caused
machinery at the design temperature. Gas vented into the atmosphere since all gas was the evaporation of the unpumpable LNG. The
Trials are carried out prior to the vessel en- consumed gradually by the consumers and warm-up operation was continued until the
tering service to confirm the correct function, oxidized by the GCU. secondary barrier’s temperature indicated at
integrity, and capacity of the complete cargo During the Gas Trials, the Gas Management least +5 °C.
system, including containment, insulation, car- System (GMS) of the main propulsion engines, Then, the tank inerting was carried out. In
go handling equipment, pipelines, valves, and the diesel generator engines, and the gas this process, warm natural gas exits from the
the equipment handling the boil-off-gas. combustion unit, including cargo handling top of each tank and is displaced by nitrogen
The procedure adhered to for Minerva Amorgos equipment, such as low-duty compressors introduced at the bottom through the liquid
diverged from the methods followed for her and forcing vaporizers, was also confirmed. filling line as heavier gas. The procedure’s
two sister vessels (Minerva Kalymnos & Min- After completing the Self Checks, Safety Tests purpose is to avoid having an air/NG mixture
erva Chios), with the main difference being the were carried out, including the Gas and Pilot within the flammable range. Hence the tar-
gassing up, cooling down, and loading of only Trip Tests, and changeovers were conducted on get is a hydrocarbon content of cargo tank
one tank alongside the Terminal. both M/Es and DGs. Subsequently, the cargo ≤ 2% in volume. All associated cargo piping
The Gas Trials began with the tanks and barri- tank pressure control was achieved using the and equipment are filled with N2 by flow
ers already inerted with GN2 to prevent a flam- BOG as fuel on MEs and DGs and with GCU and establishment during this operation.
mable atmosphere, followed by the gassing-up sub-cooler use. Tank aeration was the last step, concluding
process after berthing at the Terminal, where During the cargo pump tests, each cargo tank the vessel’s Gas Trials scheme. Dry air was
the GN2 at Tank No.4 was displaced by intro- was stripped of cargo to the minimum level, introduced at the top of the tanks through
ducing warm natural gas. Basically, at this stage, and LNG was gathered again in the No.4 the vapor line, and nitrogen was discharged
LNG is supplied by the Terminal to the vessel’s cargo tank. The vessel returned to the Ter- from the bottom through the filling line and
LNG vaporiser through the spray line. The pro- minal, and the remaining LNG was unloaded, the liquid header to the No.1 vent mast. Once
duced warm natural gas enters the tank via the reaching the unpumpable level as far as the O2 content is raised to 20% in volume,
vapor line, while the GN2, as a heavier gas, is practicable. Before cargo tank inerting and entering cargo tanks is permitted for inspec-
vented through vent mast No.1. On completion aeration, the cargo tank was warmed up to tions, cleaning, or repairs.
of gassing up the No.4 cargo tank, it is then
cooled down before loading to a temperature
of -130oC. The purpose of cooling down is to
lower the temperature of the tank walls, pump
tower, and insulation at a controlled rate, there-
by reducing thermal stresses and the volume of
boil-off gas generated during the early stages
of loading. Approximately 4,400 m3 of cargo
was loaded at Tank No.4, and the generated
BOG was returned with free flow to shore.

by Foteini Volaki
Terminal Compatibility Officer Photo 1: GCU Safety Test Photo 2: Interior of Mark III Flex + after aeration
Minerva Gas Inc.

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