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MAGNETIC CAPTURE PROCESS IN A SUPERCONDUCTING HGMS
Y. Yanagisawa, T. Hasuda, J. Iwasaki
To cite this version:
Y. Yanagisawa, T. Hasuda, J. Iwasaki. MAGNETIC CAPTURE PROCESS IN A SUPER- CONDUCTING HGMS. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-771-C1-774.
�10.1051/jphyscol:19841157�. �jpa-00223630�
JOURNAL DE PHYSIQUE
Colloque C I , supplkment au no 1, Tome 45, janvier 1984 page C1-771
M A G N E T I C CAPTURE PROCESS I N A SUPERCONDUCTING HGMS
Y. Yanagisawa, T. Hasuda and J. Iwasaki
NationaZ Research I n s t i t u t e for PoZZution and Resources, M i t i , Japan
Rdsumb
-
Un sdparateur magnbtique supraconducteur B haut gradient a Etb dbveloppb, qui peut utiliser la mSme matrice que le ssparateur conven- tionnel existant dans ce laboratoire. L'avantage dconomique et l'appli- cabilitb technique du ssparateur supraconducteur ont dt6 demontrds dans le domaine du traitement des mingraux et de la ddsulfurisation du char- bon au Japon. Le processus de capture magndtique dans le sdparateur su- praconducteur pourrait prouver la capture significative de suspensions diamagnbtiques dans l'eau.Abstract - A superconducting HGMS system was developed which could share the matrix with the conventional one in this laboratory. The economic advantage and technical feasibility of superconducting HGMS were shown in the area of mineral processing and coal. desulfurization research in Japan. The magnetic capture process in superconducting HGMS could prove the significant capture of diamagnetics in water slurry.
In Eigh Gradient Magnetic Separation (HGMS) most of the magnets used are conventional electro-magnets and it is said that the operating cost is fairly high and unfavorable to energy saving, and that backwashing operation tends to be insufficient probably due to too fine wires and too dense packing of the matrix in waste water treatment in some steel plants. Superconducting HGMS has been recently paid attention, which could give a higher magnetic field or might release the matrix from too dense packing. Furthermore, superconducting HGMS of large size is said to be more economical than the conventional one in terms of both capital and operating costs /I/. However, there have been some practical problems with superconducting HGMS. One is backwashing operation, which seems to be mostly solved, at least in the laboratory or for pilot-scale projects, by the reciprocating canister system 121. Another problem is that there may be a mistrust or a mental barrier towards a new sophisticated technology / I / and an unfavorable view of the economic advantage of a superconducting magnet 131. In fact, superconducting technology has been studied little in the area of mineral and coal processing in Japan.
The authors have been working on the treatment of industrial slud s / 4 / and on the coal cleaning project by using a conventional HGMS ( SALA-HGMS 10-15-20 ) system for the past six years and they have noticed the great needs of higher magnetic field. Consequently a superconducting HGMS system has been developed, which are regarded as the first one in the area of mineral and coal processing in Japan. Experiments were carried out in order to obtain comparative
technical data with the conventional HGMS and also to give some concrete idea of superconductivity. The data were obtained in terms of the magnetic capture process suggested by the authors / 4 / for weakly magnetic particles as well as diamagnetics.
I - SUPERCONDUCTING HGMS
The specifications of the superconducting HGMS system were, from the experience, Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841157
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decided by considering the cost and cryogenic technology available at that time. The matrices used are of 40 mm in diameter and 150 mm high to be shared with the conventional one, which had a bore of 10 cm in diameter. The rated field was 8 T at 201 A and more than 90 percent uniform along 150 mm
in length. Stored energy was 1 1 . 1 kJ. The bore had a diameter of 45 mm and was maintained at room temperature.
Fig. I illustrates the superconducting HGMS system. For backwashing the time required to reduce the field from 8 T to 2 T was 3 minutes and also a simple rack-pinion device was developed to move manually the canister assembly out of the field of 2 T or less. Hence backwashing could be done quickly and safely without giving any disturbance to the
superconductivity. The magnet has never experienced
"quenching". For simplicity of the structure of the cryostat and of handling, helium was not recovered ( A compact
liquefier is said to have been developed for a linear motorcar
6
project ) . Since both HGMS systems were of laboratory-scale and had different bore diameters, it was rather difficult to directly compare their initial costs, but it seems that the installation cost for the superconducting one was much
smaller. If a compact liquefier was installed, the total cost might be similar to that of the conventional one. The
magnetic field profiles along the coil axis for both HGMS systems measured with a Hall Effect method indicate that the return frame keeper in the conventional one was very effective to minimize the leakage of the magnetic flux, while the coil in the superconducting one was made higher for the field uniformity, to allow much leakage of the flux.
It took at least 90 minutes and 100 Q of liquid nitrogen to cool down the magnet from room temperature to 77 K and 40 minutes and 50 R of liquid helium to 4.2 K. Once the magnet settled in superconductivity, the consumption rate of liquid helium was 1.14 &/hour at 0 T and 1.36 &/hour at 8 T, to make a 12-hour operation possible with one batch amount of liquid helium in the dewar. Power consumption was as low as 4 kW at 8 T, compared to 200 kW at 2 T for the conventional one.
Magnetic force FM exerted on a particle could be roughly expressed as follows 151:
FM = ~ ( ~ ~ - ~ m ) H . d H / d x = -(4/3) T T ~ ~ ( ~ ~ ~ ~ ~ ) H ~ M ~ / ~ where v: particle volume, xp,xm: magnetlc susceptibility of
particle and medium respect~vely, H: magnetic field, dH/dx:
field gradient, b: particle diameter, H,: applied field, Ma:
magnetization of matrix, a: wire diameter of matrix.
Therefore it is expected that in superconducting HGMS very fine or very weakly magnetic particles could be captured and that even diamagnetics could be caught 161.
Fig. 1
Superconducting HGMS system
1 : magnet 2: helium dewar 3: nitrogen dewar 4: pole piece 5: matrix 6: cryostat 7: stand 8: rack-pinion 9: power lead 10: feed tank I1 - EXPERIMENTAL
Experiments were conducted in the superconducting HGMS system by using quartz, cassiterite, hematite, pyrite particles and two samples of Japanese coal products suspended in slurry with deionized water to keep them dispersed. The data were obtained in terms of the magnetic capture process suggested by the authors 141, which describes the processes of initial capture, build-up of mags and breakthrough. In this system flow rate was 2 R/min at highest and much attention was paid to prevent suspended solids in slurry from sedimentation.
When a constant-head tank with a recirculating pump was used, only coal samples were found disintegrated during experiments. Hence a feed tank with adequate
agitation was installed with a sufficient head and as closely as possible to the feed inlet, to minimize a horizontal part of the feed pipe.
Particle size distributions and magnetic susceptibility of the samples tested were given in Table 1.
Table 1 Some properties of the samples tested Sample Size ~istribution(%) Susceptibility,
volume (cgsxl o - ~ ) quartz*
---
100 100 100 -1.264cassiterite 100 61 31 -2.019 hematite* 100 100 99 256.0
pyrite 100 78 47 -
Yotsuyama coal 100 70 37 0.258 Miike 2U**coal 100 39 18 -
water -
- -
-0.720*Same samples in the reference 141, **2nd Upper Seam
The matrix used was medium expanded metal with wire diameter of 400 pm and packing density of 5 percent in the canister ( the matrix weight was 180 g ) . I11
-
RESULTS AND DISCUSSIONSThe magnetic capture process of quartz particles was shown in Fig. 2, where Y was the percentage of slurry density of passing fraction against that of feed and W was the cumulative weight of the sample fed so far, corresponding to processing time. The figure indicates that undoubtedly diamagnetic quartz particles in water were captured in this superconducting HGMS system to a small amount, and that the magnetic capture became increased as the flow velocity smaller and as the field higher beyond 2 T.
Those of cassiterite, pyrite and hematite were obtained and it was also shown that diamagnetic cassiterite particles in water slurry were much captured at 8 T, compared to at 2 T or 0 T, and that for paramagnetic pyrite or hematite particles more amount was captured at 8 T than at 2 T, which prove the higher capturing ability of superconducting HGMS than conventional HGMS. All of these data could be used when modelling of the magnetic capture process was required to predict the comprehensive performance of a HGMS system /4,7/.
Those of the coals were also obtained to testify the coal desulfurization in the superconducting HGMS. Each passing fraction was analysed for total sulfur with a LECO SC 132 sulfur determinator. Total sulfur content of Yotsuyama coal was 3.87 percent, of which pyrite sulfur was estimated approximately at 1 4 percent. For Miike coal total sulfur was 3.77 percent of which pyrite sulfur 31 percent. The yield Y into nonmags vs sulfur removal Z in cumulative forms were plotted in Fig. 3. From the curves in the figure operating conditions necessary for obtaining a desired product as nonmags could be found. For example if the sulfur removal by 30 percent is needed with the yield of 5 0 percent, a field of 8 T, a flow velocity of 1.5 cm/s and a feed weight of coal in one cycle of 45 g should be selected in this system. It demonstrates how effectively the data of magnetic capture process can be used. As to Yotsuyama coal sulfur rejection was found to be 4 percent at highest.
IV - CONCLUSIONS
A superconducting HGMS system was developed, where the matrix could be shared with the conventional one in this laboratory. The economic advantage and
technical feasibility of the superconducting system were ascertained in this study. The magnetic capture process obtained in this system could indicate that diamagnetics were captured more as the field became higher than 2 T. It is also expected that superconducting HGMS could be one of the techniques which
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meet the severe requirement for coal desulfurization in Japan, despite the complicated properties of coal and minerals in it, their liberation problems etc. are to be elucidated.
The authors are grateful to Emeritus Prof. T. Imaizumi, the University of Tokyo, for his kind advice to improve the manuscript. Special thanks are due to Mr Y. Nakayama, Mr I. Takano and Mr T. Toyoda, Tokyo Shibaura Electric Co.
for their sincere help and useful discussions.
References
1) Gerber R., IEEE Trans. Magn. Maa-18(3) (May 1982) 81 2-81 6.
2) Riley P.W. & Hocking D., IEEE Trans. Magn. Man-17(6) (Nov 1981) 3299-3301.
3 ) Marston P.G., 5th Int. Conf. Magn. Technl. Rome (Apr 1975).
4) Yanagisawa Y. et al, IEEE Trans. Magn. Maa-17(6) (Nov 1981) 3317-3319.
5) Hasuda T. et al, J. MMIJ 97(1125) (Nov 1981) 1181-1186.
6) Friedlaender F.G. et al, IEEE Trans. Magn.
an-lb5(6)
(Nov 1979) 1526-1528.7) Gerber R. et al, IEEE Trans. Magn. Mag-18(6) (Nov 1982) 1671-1673.
Fig. 2 Magnetic capture process of quartz in superconducting HGMS with flow velocity uo(cm/s) and field Ho(T) as parameters. Slurry density was about 4 %.
8 0' 4
Fig. 3
,
A&.
Sulfur removal Z and sulfur
content S were plotted
- -
against yield Y into nonmags S in cumulative forms for " 4 0 - Pliike Coal.
N
20-
0
0 20 40 60 80 100
Y
( % I
-
2 ' $Y,
I I I I 0
