A model is proposed to predict the weathering of LNG stored in containment tanks
. It dispenses
with a standard approximation
where
the
temperature of the
generated vapour within the tank is
assumed to be the same
as that of
the stored LNG. Instead
, it treats the heat influx from the
surroundings into the vapour and liquid phases
separately
and allows for the heat transfer between
the two phases.
The model
was validated only by comparing with the compositional data, as no
reliable measurements of vapour temperature are available.
The simulation
results
indicate that the temperature of the vapour phase will be higher than that of
the
LNG,
by approximately 8
0
C over a period of one year, providing the heat transfer from the
vapour is by conduction only;
thus supporting circumstantial industrial findings.
The effect on the
Boil-
off Gas (BOG)
is considerable and the results indicate that the BOG rate will decrease
by
as
much as 25% for particular scenarios. This has important consequence
s for weathering models
used
in industry
, which currently assume isothermal conditions within the containment tanks
.
In the initial stages of weathering
, the nitrogen content of
LNG will have a marked effect on
the rate
of
BOG generation. The lowest BOG rate is observed when the LNG contains approximately 1.4-
1.5% of nitrogen.