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Vacuum Recovery Phase in a Chromatographic System
for Removal of 85Kr from Xenon
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Scale Up The current system needs to be scaled
up to handle the large amount of xenon that must
be purified. First, the column mass will be
increased by a factor of ten. The geometry of
the column will also be changed. This will allow
xenon to be fed into the column at a faster rate.
The xenon condenser will also be redesigned.
It was discovered running in the current regime
that the condenser has limited condensing power
as it fills. Xenon was not condensing in the
condenser but was instead returning to the
column. This produced a loss of xenon. The
condenser must also be able to hold the entire
mass of xenon which the current condenser cannot
do. The LUX gas storage system will be used to
condense the purified xenon. Finally, the
recovery cycle will be operated at low pressure.
This will increase the volume flow rate and
decrease the propagation time of xenon through
the column. The mass scale up and condenser
redesign will be explored at a later time because
the vacuum recovery was studied first.
Results Operating the recovery phase at low
pressure will increase the volume flow rate of
the carrier gas in the adsorber. Figure 3 shows
that the volume flow rate is also related to the
mass flow of the carrier gas. Higher mass flows
lead to lower volume flows because the vacuum
pump keeping the pressure in the column low
cannot maintain low pressure at high mass flow.
Fig 3. The volume flow rate as a function of
mass flow. At higher mass flows the vacuum pump
was unable to maintain low pressure in the
column, so the volume flow rate was affected.
Fig 2. The schematic of the CWRU krypton
purification system. The lines in red are new
additions for recovery at low pressure. The
flow path for purification is shown as a heavy
blue, and direction of flow is counterclockwise.
Operating the recovery phase at low pressure does
act to reduce t. As Figure 4 shows, a factor of
two reduction in pressure decreases t by that
same factor.
Fig 4. Mass spectrometer measurement of the
output of the charcoal column during the recovery
phase at atmospheric pressure and at half an
atmosphere. The recovery time at half the
pressure takes half as long.
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Vacuum Recovery Inserting a vacuum pump
immediately after the column allows the recovery
cycle to operate at lower pressure. The lower
pressure serves to increase the volume flow rate
of the carrier gas while maintaining the mass
flow rate. Decreasing the pressure by a factor
of ten will increase the volume flow rate by the
same factor and effectively decrease the
propagation time by ten as well. The volume
flow rate is related to the mass flow rate by the
pressure, but in this system the relationship is
not linear. As the mass flow rate is increased,
the vacuum pump cannot maintain the desired
pressure. The volume flow rate is maximized at
lower mass flow rates. Figure 3 shows that the
volume flow rate is higher for slower mass flow
rates in the system. This suggests that the
column should be operated with mass flow between
10 and 20 slpm.
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Conclusions It has been demonstrated that the
xenon purification system can operate at 10 torr
during the recovery phase. This will increase
the volume flow rate and drastically reduce t.
The optimal pressure and mass flow regime has yet
to be determined experimentally. Increasing the
volume flow rate by a significant factor is the
first step in scaling up the system. Next, the
column will be investigated, and its mass and
geometry will change. Then the condenser will be
redesigned to accommodate the increased
purification rate. Finally, the system will be
fully automated.