It is generally accepted that a minimum economic level for LNG import/export project is in the neighbourhood of one million tons per annum. Since a first small scale LNG plant was developed in the U.S.A., about sixty of such plants have been built in the world. These small plants are all for peak shaving purposes and not for base load plants. Drastic changes of the energy situation in the past few years have so far influenced the basis of evaluating the value of energy from political and economical stand points. Further careful study of a total system involving liquefaction, storage and transportation will bring about a possibility that the erection of a small base load plant, not regarded as economical prior to the advent of the energy crisis, will become economical and viable. The application of a mobile plant will become further advantageous in solving construction problems arising from unknown local conditions, and its mobility will be useful for the utilization of small gas sources which are rather short-lived. The utilization of a mobile plant for a small scale LNG project will not only contribute greatly to a producing country but also meet the ever-increasing need of a clean pollution-free energy in a consuming country.
Developments of multifilamentary (MF) superconducting compound wires have gained much interest for their high transition temperature Tc, upper critical field Hc2, critical current density Jc and good stability. In these few years, A-15 crystal-type compounds Nb3Sn and V3Ga have been fabricated into MF wires for practical use by the so-called composite process. In this process, a composite of the Cu-Sn alloy matrix and Nb cores or that of the Cu-Ga alloy matrix and V cores is fabricated into a thin wire and then heat treated. The MF Nb3Sn and V3Ga wires show the highest over-all Jc, in the present available superconductors, for the field range from 50 to 120kOe and from 120 to 170kOe, respectively. In the pulsed current excitation, critical current of the MF V3Ga coil does not decrease up to exciting speeds of over 200kOe/sec while that of the MF Nb-Ti wire coil decreases rapidly at an exciting speed of about 20kOe/sec. The MF Nb3Sn conductors with large current-carrying capacities for nuclear fusion magnet are being developed. Besides A-15 crystal type compound, C-15 type Laves phase compound V2(Hf, Zr) have been also fabricated into a MF wire by the composite process in which a composite of the V sheath and Hf-66%Zr alloy cores is fabricated and then heat treated. This material shows nearly the same H-Jc characteristics as Nb3Sn and has much better mechanical properties than A-15 crystal-type compounds. The MF compound wires shall be widely used for winding homogeneous and stable high-field magnets which are useful for NMR research and, in larger scale, for synchrotron accelerator, fusion reactor, energy storage and electrical rotating machines.
In order to meet the recent demand for large scale helium compressors, we have undertaken the development of a scerw compressor of the oil injection type. As a first step in this project, a screw compressor with a capacity of appox. 120Nm3/hr has been constructed and tested. The compressor consists of a compression unit and an oil separation unit. The construction is characterized by a tandem type design, two stages of which are connected hermetically on both sides of the motor. By injection of a considerable amount of oil in the compression process, the following performance characteristics are obtained; a high compression ratio as a single stage and the lowering of discharge gas temperature in contrast to oil free type compressors. Since our screw compressor is of the oil injection type, the reliability of the refrigerator/liquefier system strongly depends on the removal of the oil from the discharge gas. This problem has been solved by the development a special oil separation unit. In a 100hr operational period of the compressor combined with a refrigerator/liquefier, no reduction in the liquefaction rate has been recognized. Results confirm the feasibility of this type of compressor and suggest a direction for further development of large scale screw compressors of the oil injection type.