| 摘要 |
Gas mixtures containing high concentrations (i.e. >1%) of condensible impurities are purified by cooling on heat exchange surfaces, pairs of such surfaces being operated alternately so that while one is being used to cool the gas mixture, deposited impurities are being re-evaporated from the other, e.g. by the passage of a scavenging gas or by reduction of pressure. Heat transfer is restricted in the region where the impurity content of the gas mixture is greatest by keeping the temperature difference between pairs of surfaces low, or by using an exchanger construction in which the surfaces are separated from each other by a gaseous medium which is continuously circulated through the apparatus. In a preferred embodiment (see Fig., not shown), gas from which condensibles are to be removed passes by line (8), heat exchangers (9, 10) and water separator (11) to cross-counterflow heat exchangers (12-15). Each comprises a plurality of tubes, of which half are supplied with the gas to be purified, and the other half with the scavenging gas in counterflow, and valve arrangements permitting the interchange of the gas supplies between the two sets. Gas is also supplied to the space between the tubes. The velocity of the scavenging gas decreases in counterflow to the gas being treated. A plurality of such exchangers are used in series in the removal of moisture, CO and CO2 from a high pressure H2 supply used in preparation of synthesis gas for NH3 production, the scavenging gas being an N2-CO mixture obtained by the subsequent final purification of the H2 by treatment with liquid N2 obtained from liquefaction of air. In another application, CO2 and H2S are removed from gas mixtures.
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