Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Patent
1994-12-14
1997-03-25
Capossela, Ronald C.
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
62906, 62924, F25J 300
Patent
active
056133740
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for separating air at low temperature in which purified and cooled air is passed into a distillation system comprising at least one rectification column and therein is subjected to rectification in a counter-current material exchange between a vapor and a liquid phase, wherein the material exchange in at least one section of at least one rectification column is effected by a packing, as well as an air separation installation for carrying out the process.
For some time a start has been made in low temperature technology, in particular in the separation of air, to employ packings which hitherto have been employed mainly for other separation purposes. The expression "packing" in this context includes both structured packings as well as random packings (randomly, packed packing bodies).
For example, from EP-A-O 321 163 it is known to employ at least in a section of the low pressure column of a dual-stage air separator a packing. In this context it is proposed to employ packings known from other fields of distillation, because; so it is claimed; the special properties of the packing: are immaterial. Conventionally such, for example structured packings, have a specific surface area, (i.e. surface area available for the material exchange in relation to the overall volume of the packing) of 125 to 700 m.sup.2 /m.sup.3. The employment of packings of higher density in industrial air separators has so far not been known. EP-A-O 467 395, in which in a broad sense a range between 250 and 1000 m.sup.2 /m.sup.3 is mentioned, is limited in the concrete examples to specific surface areas of not more than 700 m.sup.2 /m.sup.3.
Due to the pressure drop being lower as compared to columns equipped exclusively with conventional rectification trays, the process for a given set of products specifications can be operated at lower input pressure. However, the thereby attained reduced energy costs are counteracted by increased costs for the manufacture of the rectification column.
Accordingly, it is an object of the present invention to provide, a process and an apparatus of the aforesaid type which is economically particularly favorable, in particular in view of relatively low installation costs.
This object is attained in that the material exchange is effected in at least one partial region of at least one rectification column by a packing having a specific surface area of at least 1000 m.sup.2 /m.sup.3.
Due to the input and withdrawal of different fractions, different sections of an air separation column generally are subject to different loadings, i.e. different throughput rates of vapor and liquid. If, in particular in sections of a rectification column for an air separation process subject to relatively low loading, a packing is employed, it was found within the scope of the invention, that due to the employment of a packing having a very high specific surface area the height of the corresponding column sections filled with packings will be considerably lower. Compared with the processes known according to the state of the art, a lower overall height of the column for a given material exchange effect results and combined therewith correspondingly lower installation costs. This applies of course to an increased extent to a rectification column wherein in all packed sections employ packing of at least 1000 m.sup.2 /m.sup.3.
From earlier measurements in the range of specific surface areas up to about 500 m.sup.2 /m.sup.3 one would, however, have expected that the hydraulic properties of a very dense packing would clearly deteriorate, that in particular the pressure loss per theoretical plate would increase appreciably with increasing packing densities and also that the column diameter required for a pre-set gas load would increase. Because of the well founded expectation that this inter-relationship would continue at higher absolute specific surface areas, such denser packings, because of the foreseeable economic disadvantages when employed in industrial air separators, ware not taken into consi
REFERENCES:
patent: 5237823 (1993-08-01), Cheung
Moll Anton
Rohde Wilhelm
Capossela Ronald C.
Linde Aktiengesellschaft
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