Ⅳ. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 50 (2017)

Present status of the BigRIPS cryogenic plant
K. Kusaka,䠆1 M. Ohtake,䠆1 K. Yoshida,䠆1 M. Ohshima,䠆2 A. Mikami,䠆2 H. Hazama,䠆2 H. Miura,䠆2H. Shiraki,䠆2 H. Hirai,䠆2 M. Haneda,䠆2 R. Sasaki,䠆2 M. Nakayama䠆2 M. Noguchi,䠆3 and N. Suzuki䠆3Periodic maintenance of the oil-removal module in thehelium compressor unit is crucial to ensure the long-term
continuous operations of BigRIPS1). The oil-removal
module comprises a bulk oil separator (an oil vessel with ademister), three coalescer vessels, and two adsorbent
vessels (4SP and 5SP) that contain activated carbon andmolecular sieves. The periodic replacement of coalescer
filters and adsorbents ensure low oil contamination inhelium gas. We report our studies on oil contamination
performed over the past 9 years.
Each coalescer vessel contains four coalescer filters,
manufactured by Domnick Hunter,2) and all the filters werereplaced every 2 years since 2008. However, the filters usedfor 6 years were discontinued and replaced with thesuccessive product of Domnick Hunter in 2014. The drain
oil separated from the helium gas is sent to the compressor
via a drain line with solenoid valves, depending on the oillevel in the vessel. By measuring the operation interval of
the solenoid valves, the oil contamination level of thecoalescer vessels is evaluated.3)
Figure 1 shows an estimate of the oil contamination levelat the entrance of the third coalescer vessel as a function of
the coalescer filter operation time. The navy blue, green,and yellow diamonds represent the estimates for the2008-2009, 2010-2011, and 2012-2013 operations,
respectively. The coalescer filters used in those periods
were discontinued.2) The estimate for the 2014-2015
operation with the new coalescer filters is shown with pinkdiamonds. The oil contamination values measured using theoil check kit are also shown. The open triangles, squares,circles, and diamonds represent the results for the2008-2009, 2010-2011, 2012-2013, and 2014-2015
operations, respectively. Both estimates of the coilcontamination level are consistent with each other and theperformance efficiency of the new filter elements seems tobe similar to or better than that of the discontinued ones.
In addition to replacing the coalescer filters, we havereplaced the adsorbent in 4SP and 5SP to maintain theperformance of the oil-removal modules. The 4SP adsorbent
vessel contains activated carbon and molecular sieves, andthey are replaced with new ones every year. On the otherhand, the 5SP vessel contains activated carbon only, which
we replaced in 2009, 2011, 2013, and 2016. Used adsorbent
was sampled and sent to the adsorbent manufacturer fordegradation analysis. Sampled activated carbon was tested
and the following items were measured and reported: bulkdensity, loss on drying, and volatile matter content.
䠆1
䠆2
䠆3

RIKEN Nishina Center
Nippon Kucho Service Co., Ltd.
Mayekawa Mfg. Co., Ltd.

We show, as an example, results of the volatile matter
content, which we consider a good index of the amount ofoil adsorbed in activated carbon. Figure 2 shows the volatile
matter content of the activated carbon sampled from 4SP. In
each analysis, activated carbon was sampled from threedifferent parts of the adsorbent vessel. The results for thesample from the upper, middle, and lower part of the vessel
are indicated by blue, brown, and green bars, respectively.
The total operation time of each adsorbent is also indicated.
Before summer 2008 only two coalescer vessels wereused in the oil-removal module and the whole cryogenic
plant suffered from oil-contamination. The volatile matter
content of 8.7% indicates that the activated carbon wasbadly degraded. All the results except that for the sample
taken in 2008 are in the range of 2–3% and indicate thedegradation of the adsorbent in its early stage. This result
suggests that the three coalescer vessels work with
sufficient oil-separation efficiency.

Fig. 1. Oil contamination at the entrance of the third
coalescer vessel.

Fig. 2. Volatile matter content of the activated carbon
sampled from the 4SP adsorbent vessel.
References
1) K. Kusaka et al., RIKEN Accel. Prog. Rep. 43, 244 (2008).
2) http://www.parker.com/
3) K. Kusaka et al., RIKEN Accel. Prog. Rep. 41, 309 (2010).

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