Process for purifying raw-material gases by fractionation

A process for cleansing a raw material having a content of contaminants by fractionation, with which a raw material is split up into a stream of gas with a high purity and a stream of gas with a low purity, the contaminants having a higher boiling-point than the raw material, and at least one of the contaminants being an explosive substance, comprising:

• I. evaporating the raw material in a first evaporator to yield a raw-material gas, or making available a raw-material gas from a supply source,
• II. introducing the raw-material gas into a wash column in which a washing liquid for diminishing the content of contaminants trickles towards said gas,
• III. removing and partially condensing the raw-material gas purified in this way at the head of the wash column to form a condensate that is returned as washing liquid to the head of the wash column, and drawing off remaining raw-material gas from the wash column, the remaining raw-material gas having a lower content of contaminants than the raw-material gas yielded or made available in step I,
• IV. removing the washing liquid as a stream of liquid at the bottom of the wash column, the washing liquid having a higher content of contaminants than the washing liquid used in step II,
• V. introducing the washing liquid removed from the bottom of the wash column into the top of a second evaporator comprising a shell and horizontal tubes, wherein the washing liquid removed from the bottom of the wash column is introduced into the shell side of the second evaporator, enters a tube bundle in the second evaporator, and completely evaporates before reaching the bottom of the second evaporator to generate a vapour,
• VI. guiding the vapour and not yet evaporated washing liquid in co-current flow in the second evaporator, and
• VII. removing the vapour from the second evaporator as a stream of gas that exhibits a higher content of contaminants than the raw-material gas yielded or made available in step I.