Neumann, H

Perinic, G

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EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsHIGH CAPACITY HELIUM PURIFIER FOR 14 G/S AT 200 BARH. Neumann1, G. Perinic2The purifier comprises two independent purification lines. Each line is subdivided into three purificationstages which remove the impurities oil with coalescing filters and an active charcoal filled adsorber,moisture with a molecular sieve bed and oxygen and nitrogen by condensation in a phase separator andconsequent adsorption in a silicagel bed both at liquid nitrogen temperature. The purifier is designed fora throughput of 14 g/s at 200 bar in continuous operation. In non continuous operation, the purifier canbe run with a throughput of up to 28 g/s. The purified helium has an impurity content of less than1 ppm.1 Institut für Technische Physik, Forschungszentrum Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany2 LHC DivisionPresented at the Eighteenth International Cryogenic Engineering Conference (ICEC 18)21-25 February 2000, Bombay Mumbai, IndiaGeneva, Large Hadron Collider ProjectAdministrative SecretariatLHC DivisionCERNCH - 1211 Geneva 23SwitzerlandLHC Project Report 390Abstract26 July 2000HIGH CAPACITY HELIUM PURIFIER FOR 14 G/S AT 200 BARH. Neumann1 and G. Perinic21 Institut für Technische Physik, Forschungszentrum Karlsruhe, Postfach 3640,D-76021 Karlsruhe, Germany2 LHC Division, CERN, CH-1211 Genève 23, SwitzerlandThe purifier comprises two independent purification lines. Each line is subdividedinto three purification stages which remove the impurities oil with coalescing fil-ters and an active charcoal filled adsorber, moisture with a molecular sieve bedand oxygen and nitrogen by condensation in a phase seprator and consequent ad-sorption in a silicagel bed both at liquid nitrogen temperature. The purifier is d-signed for a throughput of 14g/s at 200bar in continuous operation. In non con-tinuous operation, the purifier can be run with a throughput of up to 28g/s. Thepurified helium has an impurity content of less than 1ppm.INTRODUCTIONThe 300W-1.8K-refrigerator described in [1] and the 2kW-4.4K-refrigerator described in [2,3,4] of theInstitute for Technical Physics (ITP) supply experiments of the ITP and several other Institutes of theResearch Centre Karlsruhe with more than 7000h of refrigeration and more than 200,000l of liquid he-lium per year. The cryogen helium is distributed and recovered via a widely branched transfer line sys-tem. For the liquefaction process the helium must fulfil very high purity standards. Due to the pollution ofthe helium introduced by the experiments (impurity: air), by the storage (impurity: air and moisture) andby the recovery compressors (impurity: oil) a high capacity and high quality purification system is essen-tial.In 1996 the old purification system built in 1969 has been replaced by a state-of-the-art fully automatically operated purification system. The paper presents the purifier layout and reports the experiencegained in the specification, manufacturing and commissioning process as well as the experience in threeyears operation.PLANT DESCRIPTIONThe new helium purifier consists of two identical and completely independent purification lines. Figure 1shows one line consisting of three purification stages.In the first stage oil impurities are removed in two steps. First two coalescing filters (vol. 0.5l) inseries extract oil droplets. Then the helium stream is led through an active charcoal filled adsorber (vol.56l) which removes remaining oil droplets and oil vapour.In the second stage moisture is extracted by the means of a molecular sieve bed (vol. 56l) and finallyin the third stage oxygen and nitrogen are removed. The third stage comprises two parts both at liquidnitrogen temperature, first a condensation stage which reduces the nitrogen and oxygen content down totheir respective vapour pressure and secondly a silicagel dsorption bed (six cylinders – each with 56l).Identical vessels have been chosen for the oil adsorber, the drier, the low temperature separator as well asthe low temperature adsorbers in order to reduce manufacturing costs.The purifier is designed for continuous operation with a throughput of 14g/s at 200bar which is en-sured by an alternating operation of the two purification lines. On the operational line, the low tempera-ture condensation stage will fill up with liquid nitrogen and liquid oxygen approximately every half hourin the worst case. It is therefore emptied automatically and online if a certain liquid level is reached. Fur-thermore, the first oil filter is automatically blown off every two hours to an oil sump. Both the drier stageand the low temperature adsorption stage are designed for an uptime of 12 hours which derives from thetime required to regenerate the loaded purifier line. The other extraction stages have longer uptimes andare therefore maintained manually i.e. the second oil filter is checked at regular intervals and the activecharcoal of the oil adsorber is foreseen to be replaced after five years of operation.If necessary, either purifier line can also be run with a throughput of up to 28g/s by which, however,the uptime is reduced and hence the operation of the purifier becomes discontinuous.The regeneration of the operational purifier line is started by any one of the following five criterions:· dewpoint temperature at the drier outlet in excess of -67°C· nitrogen impurity at the centre of the last silicagel adsorption cylinder i  xcess of 10ppm· nitrogen impurity at the outlet of the purification line in excess of 10ppm· maximum uptime in excess of an operator defined time limit· manual triggering of the regeneration by the operatorFor the regeneration first the condensation stage is emptied and then the line is depressurised. The oilremoval stage and the drier are depressurised together to the helium recovery system (gasom ter). Thegas from the low temperature stage is analysed during depressurisation and directed to the helium recov-ery system as long as the oxygen content stays below 5%. Above 5% oxygen content this gas is fed intothe chimney. The oxygen content begins to rise at lower pressures due to the fact that the regeneration ofthe low temperature adsorbers is sta ted by the pressure decrease.After the depressurisation, the regeneration of the drier is achieved by heating up the adsorber bed to100°C while flushing it with dry nitrogen. In the low temperature stage first the dewar in which the ad-sorber cylinders are submerged is emptied recovering the liquid nitrogen to the buffer tank. Then the re-generation is carried out by warming up the adsorber cylinders externally by the means of a closed circuitheating loop until 200K are reached on the surface and in the centre of the adsorber cylinders. The regen-LN -tank2gasometercoalescingfiltersGN2GN2oilsumpadsorberwith active charcoaldrierH O-analysis2N -analysis2N -analysis2O -analysis2gasometerLN -dewar2silicagel adsorption bedcondensation stageF1stackimpure Heliumpure Heliumsymmetry linethe other purifying line consistsof the same purifying stages LN  for the parallelpurifying line2Figure 1Simplified process cheme of one purification lineeration is completed by an evacuation of the low temperature adsorbers together with the drier and a pres-surisation with pure helium.The purifier is equipped with an automatically process controll system (S5 115 U PLC fromSiemens) and a local operator panel. The purification, the change-over between the two lines as well asthe regeneration are controlled fully automatically, however, the operator can induce the various proc-esses manually on the local panel or from a remote supervisory syst m [5].COMMISSIONINGThe purifier manufactored by L´Air Liquide was delivered in mid 1996 almost completely assem-bled on one skid. On site only the liquid nitrogen buffer tank, the evacuation pumps, the interface con-nections and the control cubicle had to be mounted and the control and power cables to be installed andconnected.The commissioning showed very soon that the purification process worked very well and fulfilledthe specified requirements. However, it also became clear that the software required some improvement.In particular the loss of an important quantity of helium on one occasion which was due to an undiscov-ered faulty regeneration process configuration showed that a thorough analysis of the process logic inrespect of plant safety should have been carried out prior to the programming.Besides the software problems we also encountered a few hardware problems: The regenerationblowers had to be soundproofed in order to fulfil the severe regulations in the experimental hall. Allsafety valves had to be reset as the locking nuts of the adjustment screws had not been tightened correctlyby the manufacturer and the set pressure decreased due to the vibrations of the plant. Furthermore, it wasonly perceived during operation that the length of the capillary from the inside of the last low temperatureadsorber to the nitrogen trace analyser combined with the high operation pressure and the small flowthrough the analyser of 35l/h caused a time delay of the saturation signal of the adsorber of two hours.This problem was tackled by the installation of an 800l/h bypass of the analysers. In the process of solv-ing the time delay problem, an improved logic for the nitrogen trace analysers was found and imple-mented. It uses the analyser of the regenerating line as additional backup analyser for the operating linetaking samples at the outlet of the purifier.OPERATION EXPERIENCEAfter commissioning at the end of 1996 and the elimination of some technical faults during 1997 the puri-fier works quite well in continuous operation. The regeneration was usually started by the saturation ofthe low temperature adsorber. The other reasons for triggering the regeneration in the order of frequencywere a dew point temperature of the drier exceeding the limit and the manual triggering of the regenera-tion by the operators. Experience shows that triggering of the regeneration by the dewpoint t mperaturealarm which means a reduced uptime of the drier indicates an incomplete previous regeneration of thedrier. Triggering of the regeneration by the operator is mainly used just before a weekend to ensure thesupervision by the operators or to enable revision works on one line.Since the end of 1997 some new problems have emerged of which the most important ones shall bedescribed here.One particular problem are the l akages which have kept appearing on the numerous screwed joints.On the one hand leakages cause high helium losses at the pressure level of 200bar and on the other handthe resulting pressure loss in the stand-by purifier line has been found to cause a pressure wave goingalong with a very high flow rate upon putting the line into purifying mode. The high flow rate in the ad-sorber and the drier vessels do cause the whirl-up of the adsorbing material and hence the production ofdust. This dust is transported into the piping and causes in consequence the blockage of the downstreamfilters being the inlet filters of the gas analysers, whose blockage leads to an error of the impurity meas-urement. The blockage of the filter F1 (see Fig. 1) prevents a correct regeneration of the drier as the ad-sorber is no longer warmed up evenly and the desorbing moisture is not thoroughly extracted by the flushdry nitrogen gas. Water has been found in the piping underneath the drier and also in frozen form block-ing the heat exchanger of the low temperature stage. The blockage of the filter F1 has furthermore causeda repeated burn out of the regeneration heater of the drier as the heat is not carried off by the nitrogen.The problem of leakages has been tackled by replacing some of the screwed joints by welded joints. Fur-thermore, a little vessel has been installed underneath the drier which collects condensing water and lastbut not least the software has been modified to allow permanent pressurisation of the standby line fromthe operational line.Another important problem is the pollution of the analysers (multiple component detector WE3M-2by Linde). The gas to be analysed is stimulated to glow due to an alternating current discharge in themeasurement cell. The light intensity is proportional to the impurity content a d this intensity is assignedto a photo-current by sensors consisting of an interference filter and a photodiode. The sensors are locatedon the outside of a window of the measurement cell. Experience shows that impurities do create depositson the measurement cell window. Finally these deposits cause an incorrect measurement result of the gaspollution. An improvement of the analysers could be achieved by the installation of a light source withinthe measurement cell which is switched on at regular intervals while the alternating current discharge isswitched off. This light source could be used as a test signal for a windows check.CONCLUSIONSAfter installation and lengthy repair of initial technical faults the new helium purifier works reliable. Themain advantages of this new purifier in comparison with the older one are the fully automatically oper-ated purification system and consequently less demand of manpower. The main problems could be attrib-uted to leakages, obstruction of filters and pollution of the analysers. Future works concern the replace-ment of more screwed connections by welded connections to improve the tightness. Fur rmore, it isforeseen to improve the reliability of the nitrogen trace analysis by the implementation of a windowscheck. Finally the control system shall be completely integrated into the cryogenic network control sys-tem of the Forschungszentrum Karlsruhe described in [5].REFERENCES1. Frey, H. and Haefer, R.A. Tieftemperaturtechnologie (1981) ISBN 3-18-400503-8 2712. Spath, F., Heil, R., Lesser, J., Schimmer, H., Gray, A. and Wagner, U. A 2kW He Refrigerator for SC Magnet Tests Downto 3.3K Cryogenics (1992) 323. Spath, F., Heil, R., Lehmann, W., Lesser, J., Schimmer, H. and Weber, J. Performance Tests of a 2kW He Refrigerator forSC Magnet Tests Down to 3.3K Advances in Cryogenic Engineering (1994) 39 563-5704. Perinic, G. Experience in Four Years Operation of the 2kW He I-Refrigerator at FZK/Karlsruhe Advances in CryogenicEngineering (1998) 43 565-5695. Perinic, G. The Cryogenic Control Network at the Forschungszentrum Karlsruhe Proc. of the ICEC 17(1998) 855-858

High capacity Helium purifier for 14 g/s at 200 bar

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