TOPIC 1: Gas Hydrates
46
©H
ERIOT
-W
ATT
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NIVERSITY B41OA December 2018 v3
So too, when working with gas hydrates, we can define
a similar distribution
coefficient, for hydrate forming compounds, between gas and hydrate phases
(on a water-free basis). The distribution coefficient
i
VS
K
,
between vapour and
solid for each compound is defined as:
i
i
i
VS
s
y
K
=
,
………………………………………
..
……
.(1.8)
Where,
i
y
is the mole fraction of component “
i
”
in the vapour phase on a
water-free basis.
i
s
is the mole fraction of the same component “
i
”
in the solid hydrate
phase on a water-free basis.
The distribution coefficient
VS
K
for methane is shown in Figure 23.
Figure 23:
VS
K
Values for Methane (Carson and Katz, 1942)
In a similar way Figures 24 to 30 (on the following pages)
provide the
distribution coefficients for some of the other more important components of
natural gases.
TOPIC 1: Gas Hydrates
50
©H
ERIOT
-W
ATT
U
NIVERSITY B41OA December 2018 v3
Figure 30:
VS
K
values for nitrogen (Jhaveri and Robinson, 1965)
The calculation is similar to dew point calculations, so that the hydrate point is
given by the condition
0
.
1
1
,
=
∑
=
n
i
i
VS
i
K
y
…………………………………
..
……
..(1.9)
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