Refrigeration – Processes – Circulating external gas
Patent
1985-05-21
1987-06-09
Capossela, Ronald C.
Refrigeration
Processes
Circulating external gas
62 36, 62 42, F25J 302
Patent
active
046718133
DESCRIPTION:
BRIEF SUMMARY
FIELD OF ART
This invention relates to a trouble-free nitrogen gas producing apparatus which can produce highly pure nitrogen gas at a low cost.
PRIOR ART
In the electronics industry, quite a large quantity of nitrogen gas is used and very high purity is now demanded to maintain and improve accuracy of parts.
Nitrogen gas has been produced so far by low temperature separation method by which air as the raw material is compressed with a compressor, then is put into an adsorption cylinder to eliminate CO.sub.2 gas and moisture content, then is cooled through heat exchange with refrigerant in a heat exchanger, then is turned into nitrogen gas product by low temperature separation in a rectifying column, and the nitrogen gas product is heated close to normal temperature through the said heat exchanger. In many cases, however, troubles result if the nitrogen gas is used as it is because of oxygen content included as impurity.
To remove oxygen as impurity, the following two methods are available.
One is to add a slight quantity of hydrogen to the nitrogen gas by using Pt catalyst and to turn the oxygen into water through reaction with the hydrogen in atmosphere of about 200.degree. C.
Another method is to put the oxygen in nitrogen gas in contact with Ni catalyst in atmosphere of about 200.degree. C. and to eliminate oxygen through reaction of Ni+1/20.sub.2 --NiO. By either method, however, the nitrogen gas must be heated to a high temperature and be put in contact with a catalyst. It isn't possible, therefore, to incorporate the apparatus into nitrogen gas producing apparatus of ultra-low temperature system.
A refining apparatus must be installed separately from the nitrogen gas producing apparatus, which makes the whole system larger.
Moreover, the first method requires a high level of skill for operation since the quantity of hydrogen must be controlled accurately. If the hydrogen added is not exactly in the quantity required for reaction with the oxygen impurity, the oxygen or the added hydrogen is still left as impurity.
By the second method, the cost of refining is increased by the H.sub.2 gas equipment for re-generation as it is necessary to regenerate NiO produced through reaction with the oxygen impurity (NiO+H.sub.2 --Ni+H.sub.2 O). It has been demanded, therefore, to solve these problems.
For the nitrogen gas producing apparatus of the conventional low temperature separation type, an expansion turbine is used for cooling the refrigerant of the heat exchanger to cool down the compressed air by heat exchange, and the turbine is driven by the pressure of the gas evaporated from the liquid air accumulated in the rectifying column (nitrogen of low boiling point is taken out as gas by low temperature separation and the residual air is accumulated as oxygen rich liquid air).
Follow-up operations of changing load (changes in taken out quantity of product nitrogen gas) is difficult since the turning speed of the expansion turbine is very fast (several tens of thousand per minute). It is, therefore, difficult to change the feeding quantity of liquid air to the expansion turbine exactly according to the changes in the quantity of taken-out product nitrogen gas so that the compressed air is cooled to a constant temperature at all times.
As the result, the purity of the product nitrogen gas differs and nitrogen gas of low purity is produced frequently.
The expansion turbine requires high precision in the mechanical structure because of high-speed revolution, the cost is high, and the intricated mechanism is subjected to frequent troubles.
Nitrogen gas producing apparatus of PSA system without any such expansion turbine, therefore, has been developed recently.
FIG. 1 shows the nitrogen gas producing apparatus of PSA system.
In the drawing, (1) is the air inlet, (2) is the air compressor, (3) is the after-cooler, (3a) is the cooling water supply channel, and (4) is the oil-water separator. (5) is the 1st adsorption tank, (6) is the 2nd adsorption tank, and V1, V2 are the air operated valves to feed the air compr
REFERENCES:
patent: 2664718 (1954-01-01), Rice
patent: 3404067 (1968-10-01), Rendos
patent: 3416323 (1968-12-01), Heinik
patent: 4133663 (1979-01-01), Skinner
patent: 4283212 (1981-08-01), Graham et al.
Capossela Ronald C.
Daidousanso Co. Ltd.
Miller Austin R.
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