| 摘要 |
PROBLEM TO BE SOLVED: To intermittently manufacture oxygen gas by providing a nitrogen circulating system for circulating the nitrogen whose amount is corresponding substantially to the half of the amount of liquefied nitrogen extracted from a device at the time of using oxygen. SOLUTION: Liquefied nitrogen is obtained through heat exchange between liquefied oxygen, running out into a condensing evaporator 15 at the bottom of a low-pressure tower, and nitrogen gas in the top part of a high-pressure tower 14 while the liquefied oxygen itself is evaporated to obtain oxygen gas and a part of the oxygen gas is extracted to obtain product oxygen gas through the cold heat exchanging unit 10b of a main heat exchanger 10 and the hot heat exchanging unit 10a of the same to increase the temperature of the same through heat exchange between material air at substantially a normal temperature. The nitrogen gas, led out into a flow passage 35 from the top of the low-pressure tower, is heated to the normal temperature through the cold heat exchanging unit 10b and the hot heat exchanging unit 10a, then, is conducted to the outside of the system through a flow passage 36. A part of the nitrogen gas, branched from the flow passage 36 into a flow passage 39, is introduced into a nitrogen compressor 40 to compress and pressurize it, then, is introduced from a flow passage 41 into the hot heat exchanging unit 10 and the cold heat exchanging unit 10b again to introduce it into the top of the high-pressure tower 14 after effecting heat exchange between feedback gas.
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