Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Patent
1998-01-07
1999-09-14
Kilner, Christopher B.
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
62906, 2611122, B01D 4700
Patent
active
059504544
DESCRIPTION:
BRIEF SUMMARY
Cloth packings or cloth-like packings with a low pressure drop and an ordered structure for use in mass transfer columns, and rectification using these packings.
The invention relates to packing elements for mass transfer columns and column internals formed therefrom, made of cloth material or cloth-like material, preferably of metal cloth, with an ordered structure and novel geometry for use in a mass transfer column with particularly low specific pressure drop, and to their use for the rectification of substance mixtures.
The workup of product mixtures by distillation generally affords the best results in the case of countercurrent distillation, also called rectification, ie. a distillation process in which the liquid flows downward as reflux and the vapor flows upward in the column. This results in enrichment of the more volatile components in the vapor and of the less volatile components in the liquid.
This mass and heat transport is intensified by elements fitted inside the column, such as column plates or packings, which ensure a sufficient contact time of the phases and a sufficiently large phase boundary area. However, these column internals, together with the reflux flowing downward result in a resistance to vapor flow in the column which is called the pressure drop. For a given column geometry, ie. diameter and column height, the pressure drop in a column depends not only on the nature and amount of the compounds to be rectified but also very strongly on the nature of the column internals.
Generally used for the fractionation of substance mixtures which require a high separation efficiency are rectification columns with internals made of metal cloth with an ordered structure. These cloth packings which are built up systematically in regular geometry and have defined areas for the countercurrent phases to pass through are distinguished from all other internals by the possibility of higher flow rates, a better separation effect and a lower specific pressure drop. They are therefore used in all vacuum rectifications in which, because of the temperature-sensitivity of the mixture to be separated, it is particularly important to limit the pressure drop in the column. Particularly suitable column packings are metal cloth packings of the BX and CY types supplied by Sulzer (cf. Sulzer company publication "Trennkolonnen fur Destillation und Absorption") and metal cloth packings with a similar effect supplied by other companies, eg. Montz-Pak type A3 from Montz GmbH and cloth-like packings such as the BSH types of Montz GmbH.
A diagrammatic representation of such columns is to be found, for example, on page 103 of the textbook "Thermische Trennverfahren" by Klaus Sattler, VCH Verlagsges.mbH, Weinheim (FRG), 1988. Concerning further details of the rectification of substance mixtures, we refer to this textbook by Klaus Sattler, pages 101-225, in particular 120-160 and 199-214.
The thermal stressability of many high-boiling mixtures is so low that, despite the use of the described metal cloth packings or cloth-like packings with an ordered structure and overhead pressures in the column of only 0.5 to 1 mbar, the pressure drop at the cloth packings which are required for the necessary separation efficiency would result in bottom temperatures which are above the decomposition range for the compounds to be separated.
It is an object of the present invention to develop novel cloth packings or cloth-like packings with an ordered structure which, with the same separation efficiency, show an even lower pressure drop than all column internals available hitherto, ie. cloth packings which permit even high-boiling air- and/or temperature-sensitive substance mixtures which require a high separation efficiency to be separated by distillation with good yields without using alternative costly distillation processes, such as high vacuum distillation or short-path distillation, and novel cloth packings which, owing to their low pressure drop, very generally permit low bottom temperatures and thus distillation under milder con
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Baldenius Kai-Uwe
Bockstiegel Bernhard
Burst Wolfram
Grafen Paul
Hartmann Horst
BASF - Aktiengesellschaft
Kilner Christopher B.
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