24P114-P
Improving the start-up behavior of a gas separation membrane
for tritium removal system
トリチウム除去用気体分離膜の始動時分離特性の改善
Masahiro Tanaka1, Takahiko Sugiyama2
田中将裕1, 杉山貴彦2
1. National Institute for Fusion Science, Oroshi-cho, Toki, Gifu, 509-5292, Japan
2. Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
1. 核融合科学研究所 ヘリカル研究部 〒509-5292 岐阜県土岐市下石町322-6
2. 名古屋大学大学院 工学研究科 〒464-8601 名古屋市千種区不老町
A tritium removal system using gas separation membrane for dehumidification has been proposed anddeveloped. It is indicated the start-up transient phenomenon of gas separation performance. To improve thestart-up behavior, we focus on the application of PID control and keeping the polymer membrane in a drystate during shout-down period. As the results, the gas separation performance for dehumidification in thestart-up period was improved by keeping in a dry state in the apparatus during a shout down period. This
experimental result shows that the amount of water absorbed in polymer membrane play an important role
to suppress the start-up transient phenomenon.

1. Introduction
The most widely used atmospheric tritium
removal technique is oxidation of tritiatedhydrogen to water by catalytic oxidation reactors,
followed by adsorption process on a molecularsieve bed [1]. For the processing of a large
volume of air contained with tritium, tritium
removal system using a hollow-fiber-type
polyimide membrane has been developed anddemonstrated with the performance of tritium
recovery [2]. Since the polyimide material
absorbs water, a part of absorbed tritium isreleased at the start-up period when tritiatedwater is absorbed in the membrane.
To improve the start-up behavior of gas
separation membrane, we focus on the applicationof a standard proportional-integral-differential(PID) control technique and some preservation
methods after operation. In this paper, from aviewpoint of practical use, we discuss with thebehavior of the dew point at the start-up period incomparison with few methods.
2. Experimental apparatus
A schematic diagram of a gas separation
membrane apparatus is shown in Fig. 1. The
experimental apparatus consists of a compressor,
condensers, a membrane module, two mass flow
controllers, a pressure regulator, various sensors
and mass flow meter. A hollow fiber typepolyimide membrane module (UM-XC5, UBEindustry Ltd.) was used as membrane separator. The
shape of the membrane module is outer diameter of90 mm, and a length of 710 mm. The gas flow inthe membrane module was a counterflow type. The
experiments were operated at room temperature.
The feed flow rate was 6 Nm3/h. The gas pressure
was 0.8 MPa at the feed side of membrane moduleand atmospheric pressure at the permeated side. The
water vapor concentration in the feed gas was about
800 ppm. The pressure of permeated side wasalmost atmospheric pressure. A part of dried gas
was refluxed to the permeated side of the membranein order to control the dew point in the dried gas.
Then, the mass flow controller (FC2) wasautomatically controlled by PID control. The
maximum flow rate of FC2 was 3 Nm3/h. The dew
point in dried air was measured by an electrical
capacitance hygrometer (Moisture Image Series 1,GE sensing Co.). After the experimental operations,the apparatus was left to stand as it is, or was kept
at constant pressure of 100 Pa by a scroll pump.

Fig.1. A schematic diagram of membrane separator

3. Results and discussion
3.1 Effect of PID control in the start-up phase
Figure 2 shows the comparison of normal

-30with PID control

Feed flow rate: 6 Nm3/h
Feed Pressure: 0.8 MPa

15 hours

510Time [h]

15-60
-70

0200

400

600
800
Time (min)(b)

1000-801200-10Feed flow rate: 6 m3/h

15 hours

Target dew point

0-50

Dew point

13-70
20

Fig.2. Comparison of normal operation and PID
controlled operation at the start-up phase.

3.2 Effect of preserve condition after operation
Figure 3 shows the behavior of the start-up phasewithout PID control. The preserve conditions after
operation were atmospheric condition (0.1 MPa) orvacuum condition of 100 Pa. In the case ofatmospheric condition the permeated flow rateincreased at the start-up period. It would indicatethat the water content in the polyimide material
decreased with decreasing with the dew point. Thenthe permeated flow rate was kept at a constant flowrate when the dew point became to be less than-40oC. In the case of vacuum condition, the initial
dew point was less than -50oC even at the start-up
phase. Whereas the permeated flow rate was notchanged. It means that the polyimide material
becomes dry state. Therefore, the permeated flowrate is kept at constant even at the start-up period.
The time to target dew point was 8 hour. It took
longer time than the time in the case of applying
PID control as shown in Fig 2. However, the time
to reach the target dew point is of no importance,
but the total amount of released water fromapparatus should be minimized.
These experimental results are summarized inTable I in addition to the result of the combinationof PID control and vacuum condition in the shut
down period. The amount of released water atstart-up period was minimized by combining
vacuum condition and PID control. In this case,-30-4035 hours-20oPermeated flow

20-60-80

Purge flow rate: 1.2 m /hFeed Pressure: 0.8 MPa

Dew point ( C)

3-40-50-10Feed flow rate: 6 m3/h

Purge flow rate: 1.2 m /hFeed Pressure: 0.8 MPa

Permeated flow

2-20-30

ow/o PID control[Purge flow: 1.2 Nm3/h](a)-40-5018 hours

Dew point

Dew point ( C)-203

Permeated flow (NL/min)

Dew point [oC]-10although the time to low dew point took 8 hours,
the released water was reduced one-tenth ofcombination of atmospheric preserve anduncontrolled conditions. These results show that toimprove the start-up period is required not only thePID control but also the vacuum condition.

Permeated flow (NL/min)

operation and PID controlled operation at thestart-up phase. In this study, the target dew point
was determined at -70oC. The initial dew point
before the operation was more than -30oC. In thecase of normal operation without PID control, it
took 15 hours to reach the target dew point, when
the purge flow rate was set at 1.2 Nm3/h. Whereas,in the case of PID control operation, the time totarget dew point was reduced to 5 hours bycontrolling the purge flow rate. The application ofPID control on the membrane gas separation could
result in shorter the start-up period.

-60-7000200

400

600
800
Time (min)1000

1200-80

Fig.3. The behavior of the start-up phase without PID
control as compared with the preserve conditions:(a) atmospheric condition, (b) vacuum condition.
Table I. Summary of experimental results
Condition ina shut-down
periodPurge flow
Initial dew point[oC]
Time to dew pointof -70oC [hour]
Released water
vapor fromapparatus [mol]Atmosphericcondition

Vacuum condition
at 100 Pa

Constant:
1.2 Nm3/h[Uncontrol]

PID
control

Constant:
1.2 Nm3/h[Uncontrol]

PID
control

-23.1

-27.1

-45.7

-53

15

588

0.12

0.025

0.016

0.014

4. Summary
To improve the start-up behavior of the gas
separation membrane for dehumidification, wefocus on the application of PID control and keeping thepolymer membrane in a dry state during shout-down
period. It is found that the amount of water absorbed inpolymer membrane play an important role to suppress
the start-up transient phenomenon.
References[1] “Safe handling of tritium” Technical Reports Series
No. 324, IAEA, Vienna, (1991) 34.
[2] T. Hayashi, K. Okuno, T. Ishida, et al.,: Fusion Eng.
Des. 39-40 (1998) 901.